Microstructural changes of a thermally aged stainless steel submerged arc weld overlay cladding of nuclear reactor pressure vessels

NASA Astrophysics Data System (ADS)

Takeuchi, T.; Kameda, J.; Nagai, Y.; Toyama, T.; Matsukawa, Y.; Nishiyama, Y.; Onizawa, K.

2012-06-01

The effect of thermal aging on microstructural changes in stainless steel submerged arc weld-overlay cladding of reactor pressure vessels was investigated using atom probe tomography (APT). In as-received materials subjected to post-welding heat treatments (PWHTs), with a subsequent furnace cooling, a slight fluctuation of the Cr concentration was observed due to spinodal decomposition in the δ-ferrite phase but not in the austenitic phase. Thermal aging at 400 °C for 10,000 h caused not only an increase in the amplitude of spinodal decomposition but also the precipitation of G phases with composition ratios of Ni:Si:Mn = 16:7:6 in the δ-ferrite phase. The degree of the spinodal decomposition in the submerged arc weld sample was similar to that in the electroslag weld one reported previously. We also observed a carbide on the γ-austenite and δ-ferrite interface. There were no Cr depleted zones around the carbide.

Spinodal decomposition regions of InxGa1-xSbyAszN1-y-z, InxGa1-xSbyPzN1-y-z and InxGa1-xAsyPzN1-y-z alloys

NASA Astrophysics Data System (ADS)

Elyukhin, Vyacheslav A.

2017-07-01

Considerable interest in highly mismatched semiconductor alloys as materials for device applications has recently been shown. However, the spinodal instability can be a serious obstacle to their use. Here, the spinodal decomposition regions of dilute nitride InxGa1-xSbyAszN1-y-z, InxGa1-xSbyPzN1-y-z and InxGa1-xAsyPzN1-y-z quinary alloys lattice matched to III-V compounds are studied from 0 °C to 1000 °C. The alloys contain six types of chemical bonds corresponding to the constituent compounds, and rearrangement of atoms changes the bonds between them. Therefore, a size and location of the spinodal decomposition regions depend on the enthalpies of constituent compounds, internal strain energy, coherency strain energy and entropy. Among the considered alloys, InxGa1-xSbyAszN1-y-z lattice matched to InAs, InxGa1-xSbyPzN1-y-z lattice matched to GaP and InP and InxGa1-xAsyPzN1-y-z lattice matched to GaAs and InP are most suitable for device applications.

A parallel domain decomposition-based implicit method for the Cahn–Hilliard–Cook phase-field equation in 3D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Xiang; Yang, Chao; State Key Laboratory of Computer Science, Chinese Academy of Sciences, Beijing 100190

2015-03-15

We present a numerical algorithm for simulating the spinodal decomposition described by the three dimensional Cahn–Hilliard–Cook (CHC) equation, which is a fourth-order stochastic partial differential equation with a noise term. The equation is discretized in space and time based on a fully implicit, cell-centered finite difference scheme, with an adaptive time-stepping strategy designed to accelerate the progress to equilibrium. At each time step, a parallel Newton–Krylov–Schwarz algorithm is used to solve the nonlinear system. We discuss various numerical and computational challenges associated with the method. The numerical scheme is validated by a comparison with an explicit scheme of high accuracymore » (and unreasonably high cost). We present steady state solutions of the CHC equation in two and three dimensions. The effect of the thermal fluctuation on the spinodal decomposition process is studied. We show that the existence of the thermal fluctuation accelerates the spinodal decomposition process and that the final steady morphology is sensitive to the stochastic noise. We also show the evolution of the energies and statistical moments. In terms of the parallel performance, it is found that the implicit domain decomposition approach scales well on supercomputers with a large number of processors.« less

Flash nano-precipitation of polymer blends: a role for fluid flow?

NASA Astrophysics Data System (ADS)

Grundy, Lorena; Mason, Lachlan; Chergui, Jalel; Juric, Damir; Craster, Richard V.; Lee, Victoria; Prudhomme, Robert; Priestley, Rodney; Matar, Omar K.

2017-11-01

Porous structures can be formed by the controlled precipitation of polymer blends; ranging from porous matrices, with applications in membrane filtration, to porous nano-particles, with applications in catalysis, targeted drug delivery and emulsion stabilisation. Under a diffusive exchange of solvent for non-solvent, prevailing conditions favour the decomposition of polymer blends into multiple phases. Interestingly, dynamic structures can be `trapped' via vitrification prior to thermodynamic equilibrium. A promising mechanism for large-scale polymer processing is flash nano-precipitation (FNP). FNP particle formation has recently been modelled using spinodal decomposition theory, however the influence of fluid flow on structure formation is yet to be clarified. In this study, we couple a Navier-Stokes equation to a Cahn-Hilliard model of spinodal decomposition. The framework is implemented using Code BLUE, a massively scalable fluid dynamics solver, and applied to flows within confined impinging jet mixers. The present method is valid for a wide range of mixing timescales spanning FNP and conventional immersion precipitation processes. Results aid in the fabrication of nano-scale polymer particles with tuneable internal porosities. EPSRC, UK, MEMPHIS program Grant (EP/K003976/1), RAEng Research Chair (OKM), PETRONAS.

Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal

NASA Astrophysics Data System (ADS)

Hosseini, Vahid A.; Thuvander, Mattias; Wessman, Sten; Karlsson, Leif

2018-07-01

Low-temperature phase separations (T < 500 °C), resulting in changes in mechanical and corrosion properties, of super duplex stainless steel (SDSS) base and weld metals were investigated for short heat treatment times (0.5 to 600 minutes). A novel heat treatment technique, where a stationary arc produces a steady state temperature gradient for selected times, was employed to fabricate functionally graded materials. Three different initial material conditions including 2507 SDSS, remelted 2507 SDSS, and 2509 SDSS weld metal were investigated. Selective etching of ferrite significantly decreased in regions heat treated at 435 °C to 480 °C already after 3 minutes due to rapid phase separations. Atom probe tomography results revealed spinodal decomposition of ferrite and precipitation of Cu particles. Microhardness mapping showed that as-welded microstructure and/or higher Ni content accelerated decomposition. The arc heat treatment technique combined with microhardness mapping and electrolytical etching was found to be a successful approach to evaluate kinetics of low-temperature phase separations in SDSS, particularly at its earlier stages. A time-temperature transformation diagram was proposed showing the kinetics of 475 °C-embrittlement in 2507 SDSS.

Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal

NASA Astrophysics Data System (ADS)

Hosseini, Vahid A.; Thuvander, Mattias; Wessman, Sten; Karlsson, Leif

2018-04-01

Low-temperature phase separations (T < 500 °C), resulting in changes in mechanical and corrosion properties, of super duplex stainless steel (SDSS) base and weld metals were investigated for short heat treatment times (0.5 to 600 minutes). A novel heat treatment technique, where a stationary arc produces a steady state temperature gradient for selected times, was employed to fabricate functionally graded materials. Three different initial material conditions including 2507 SDSS, remelted 2507 SDSS, and 2509 SDSS weld metal were investigated. Selective etching of ferrite significantly decreased in regions heat treated at 435 °C to 480 °C already after 3 minutes due to rapid phase separations. Atom probe tomography results revealed spinodal decomposition of ferrite and precipitation of Cu particles. Microhardness mapping showed that as-welded microstructure and/or higher Ni content accelerated decomposition. The arc heat treatment technique combined with microhardness mapping and electrolytical etching was found to be a successful approach to evaluate kinetics of low-temperature phase separations in SDSS, particularly at its earlier stages. A time-temperature transformation diagram was proposed showing the kinetics of 475 °C-embrittlement in 2507 SDSS.

Spinodal decomposition in amorphous metal-silicate thin films: Phase diagram analysis and interface effects on kinetics

NASA Astrophysics Data System (ADS)

Kim, H.; McIntyre, P. C.

2002-11-01

Among several metal silicate candidates for high permittivity gate dielectric applications, the mixing thermodynamics of the ZrO2-SiO2 system were analyzed, based on previously published experimental phase diagrams. The driving force for spinodal decomposition was investigated in an amorphous silicate that was treated as a supercooled liquid solution. A subregular model was used for the excess free energy of mixing of the liquid, and measured invariant points were adopted for the calculations. The resulting simulated ZrO2-SiO2 phase diagram matched the experimental results reasonably well and indicated that a driving force exists for amorphous Zr-silicate compositions between approx40 mol % and approx90 mol % SiO2 to decompose into a ZrO2-rich phase (approx20 mol % SiO2) and SiO2-rich phase (>98 mol % SiO2) through diffusional phase separation at a temperature of 900 degC. These predictions are consistent with recent experimental reports of phase separation in amorphous Zr-silicate thin films. Other metal-silicate systems were also investigated and composition ranges for phase separation in amorphous Hf, La, and Y silicates were identified from the published bulk phase diagrams. The kinetics of one-dimensional spinodal decomposition normal to the plane of the film were simulated for an initially homogeneous Zr-silicate dielectric layer. We examined the effects that local stresses and the capillary driving force for component segregation to the interface have on the rate of spinodal decomposition in amorphous metal-silicate thin films.

Two-dimensional spinodal interface in one-step grown graphene-molybdenum carbide heterostructures

NASA Astrophysics Data System (ADS)

Qiao, Jia-Bin; Gong, Yue; Liu, Haiwen; Shi, Jin-An; Gu, Lin; He, Lin

2018-05-01

Heterostructures made by stacking different materials on top of each other are expected to exhibit unusual properties and new phenomena. Interface of the heterostructures plays a vital role in determining their properties. Here, we report the observation of a two-dimensional (2D) spinodal interface in graphene-molybdenum carbide (α -M o2C ) heterostructures, which arises from spinodal decomposition occurring at the heterointerface, by using scanning tunneling microscopy. Our experiment demonstrates that the 2D spinodal interface modulates graphene into whispering gallery resonant networks filled with quasibound states of massless Dirac fermions. Moreover, below the superconducting transition temperature of the underlying α -M o2C , the 2D spinodal interface behaves as disorders, resulting in the breakdown of the proximity-induced superconductivity in graphene. Our result sheds light on tuning properties of heterostructures based on interface engineering.

Comparison of vapor formation of water at the solid/water interface to colloidal solutions using optically excited gold nanostructures.

PubMed

Baral, Susil; Green, Andrew J; Livshits, Maksim Y; Govorov, Alexander O; Richardson, Hugh H

2014-02-25

The phase transformation properties of liquid water to vapor is characterized by optical excitation of the lithographically fabricated single gold nanowrenches and contrasted to the phase transformation properties of gold nanoparticles located and optically excited in a bulk solution system [two and three dimensions]. The 532 nm continuous wave excitation of a single gold nanowrench results in superheating of the water to the spinodal decomposition temperature of 580 ± 20 K with bubble formation below the spinodal decomposition temperature being a rare event. Between the spinodal decomposition temperature and the boiling point liquid water is trapped into a metastable state because a barrier to vapor nucleation exists that must be overcome before the thermodynamically stable state is realized. The phase transformation for an optically heated single gold nanowrench is different from the phase transformation of optically excited colloidal gold nanoparticles solution where collective heating effects dominates and leads to the boiling of the solution exactly at the boiling point. In the solution case, the optically excited ensemble of nanoparticles collectively raises the ambient temperature of water to the boiling point where liquid is converted into vapor. The striking difference in the boiling properties of the single gold nanowrench and the nanoparticle solution system can be explained in terms of the vapor-nucleation mechanism, the volume of the overheated liquid, and the collective heating effect. The interpretation of the observed regimes of heating and vaporization is consistent with our theoretical modeling. In particular, we explain with our theory why the boiling with the collective heating in a solution requires 3 orders of magnitude less intensity compared to the case of optically driven single nanowrench.

Structural Evolution Following Spinodal Decomposition of the Pseudoternary Compound (Pb0.3Sn0.1Ge0.6)Te

NASA Astrophysics Data System (ADS)

Dado, Boaz; Gelbstein, Yaniv; Mogilansky, Dimitri; Ezersky, Vladimir; Dariel, Moshe P.

2010-09-01

Pseudoternary (Ge,Sn,Pb)Te compounds display favorable thermoelectric properties. Spinodal decomposition in the quasiternary (Ge,Sn,Pb)Te system is at the origin of a wide solubility gap at low Sn concentrations. The structural evolution of the spinodal decomposition was investigated as a function of aging time at 500°C, using x-ray diffraction, electron microscopy, and scanning electron microscopy. The evolution of the structure at 500°C consists initially of a short diffusion-controlled demixing stage into Pb- and Ge-rich coherent areas, with compositions corresponding to the inflection points of the free-energy curve. The Pb-rich areas adopt configurations associated with the directions of the soft elastic moduli of the cubic compound. Both the Pb- and Ge-rich areas are supersaturated and undergo in a second stage a nucleation and growth process and give rise to a biphased structure with equilibrium compositions corresponding to the boundaries of the miscibility gap. The resulting Pb-rich areas display a relatively stable microstructure suggesting the presence of long-range interactions between the Pb-rich precipitates in the Ge-rich matrix.

Low-Temperature Aging of Delta-Ferrite in 316L SS Welds; Changes in Mechanical Properties and Etching Properties

NASA Astrophysics Data System (ADS)

Abe, Hiroshi; Shimizu, Keita; Watanabe, Yutaka

Thermal aging embrittlement of LWR components made of stainless cast (e.g. CF-8 and CF-8M) is a potential degradation issue, and careful attention has been paid on it. Although welds of austenitic stainless steels (SSs) have γ-δ duplex microstructure, which is similar to that of the stainless cast, examination on thermal aging characteristics of the SS welds is very limited. In order to evaluate thermal aging behavior of weld metal of austenitic stainless steel, the 316L SS weld metal has been prepared and changes in mechanical properties and in etching properties at isothermal aging at 335°C have been investigated. The hardness of the ferrite phase has increased with aging, while the hardness of austenite phase has stayed same. It has been suggested that spinodal decomposition has occurred in δ-ferrite by the 335°C aging. The etching rates of δ-ferrite at immersion test in 5wt% hydrochloric acid solution have been also investigated using an AFM technique. The etching rate of ferrite phase has decreased consistently with the increase in hardness of ferrite phase. It has been thought that this characteristic is also caused by spinodal decomposition of ferrite into chromium-rich (α') and iron-rich (α).

Spinodal Decomposition for the Cahn-Hilliard Equation in Higher Dimensions.Part I: Probability and Wavelength Estimate

NASA Astrophysics Data System (ADS)

Maier-Paape, Stanislaus; Wanner, Thomas

This paper is the first in a series of two papers addressing the phenomenon of spinodal decomposition for the Cahn-Hilliard equation where , is a bounded domain with sufficiently smooth boundary, and f is cubic-like, for example f(u) =u-u3. We will present the main ideas of our approach and explain in what way our method differs from known results in one space dimension due to Grant [26]. Furthermore, we derive certain probability and wavelength estimates. The probability estimate is needed to understand why in a neighborhood of a homogeneous equilibrium u0≡μ of the Cahn-Hilliard equation, with mass μ in the spinodal region, a strongly unstable manifold has dominating effects. This is demonstrated for the linearized equation, but will be essential for the nonlinear setting in the second paper [37] as well. Moreover, we introduce the notion of a characteristic wavelength for the strongly unstable directions.

Spinodal Decomposition for theCahn-Hilliard Equation in Higher Dimensions:Nonlinear Dynamics

NASA Astrophysics Data System (ADS)

Maier-Paape, Stanislaus; Wanner, Thomas

This paper addresses the phenomenon of spinodal decomposition for the Cahn-Hilliard equation where Ω⊂n, n∈{1,2,3 }, is a bounded domain with sufficiently smooth boundary, and f is cubic-like, for example f(u) =u-u3. Based on the results of [26] the nonlinear Cahn-Hilliard equation will be discussed. This equation generates a nonlinear semiflow in certain affine subspaces of H2(Ω). In a neighborhood Uɛ with size proportional to ɛn around the constant solution , where μ lies in the spinodal region, we observe the following behavior. Within a local inertial manifold containing there exists a finite-dimensional invariant manifold which dominates the behavior of all solutions starting with initial conditions from a small ball around with probability almost 1. The dimension of is proportional to ɛ-n and the elements of exhibit a common geometric quantity which is strongly related to a characteristic wavelength proportional to ɛ.

High temperature phase decomposition in Ti{sub x}Zr{sub y}Al{sub z}N

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lind, Hans; Pilemalm, Robert; Rogström, Lina

2014-12-15

Through a combination of theoretical and experimental observations we study the high temperature decomposition behavior of c-(Ti{sub x}Zr{sub y}Al{sub z}N) alloys. We show that for most concentrations the high formation energy of (ZrAl)N causes a strong tendency for spinodal decomposition between ZrN and AlN while other decompositions tendencies are suppressed. In addition we observe that entropic effects due to configurational disorder favor a formation of a stable Zr-rich (TiZr)N phase with increasing temperature. Our calculations also predict that at high temperatures a Zr rich (TiZrAl)N disordered phase should become more resistant against the spinodal decomposition despite its high and positivemore » formation energy due to the specific topology of the free energy surface at the relevant concentrations. Our experimental observations confirm this prediction by showing strong tendency towards decomposition in a Zr-poor sample while a Zr-rich alloy shows a greatly reduced decomposition rate, which is mostly attributable to binodal decomposition processes. This result highlights the importance of considering the second derivative of the free energy, in addition to its absolute value in predicting decomposition trends of thermodynamically unstable alloys.« less

Spinodal decomposition of the gamma-phase upon quenching in the Ti-Al-Nb ternary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rios, Orlando; Ebrahimi, Fereshteh

2010-01-01

The {gamma}-TiAl with L1{sub 0} crystal structure shows extensive solubility for Nb at elevated temperatures. Recently (Rios et al., Acta materialia 2009; 57:6243), we have demonstrated that the high-Nb {gamma}-TiAl phase becomes unstable upon rapid cooling into a nano-scale two-phase microstructure. In this paper, using detailed compositional and microstructural analyses, we have demonstrated that this phase goes through a spinodal decomposition that results in the compositionally distinct phases identified as a lower-Nb {gamma}-phase and the h-phase, which is rich in Nb and forms by the ordering of this element in the {gamma}-phase.

Stabilizing the body centered cubic crystal in titanium alloys by a nano-scale concentration modulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, H. L.; Shah, S. A. A.; Hao, Y. L.

It is well-known that the body centered cubic (bcc) crystal in titanium alloys reaches its stability limit as the electron-to-atom (e/a) ratio of the alloy drops down to ~4.24. This critical value, however, is much higher than that of a multifunctional bcc type alloy (e/a = 4.15). Here we demonstrate that a nano-scale concentration modulation created by spinodal decomposition is what stabilizes the bcc crystal of the alloy. Aided by such a nano-scale concentration heterogeneity, unexpected properties from its chemically homogeneous counterpart are obtained. This provides a new strategy to design functional titanium alloys by tuning the spinodal decomposition.

Gradient and size effects on spinodal and miscibility gaps

NASA Astrophysics Data System (ADS)

Tsagrakis, Ioannis; Aifantis, Elias C.

2018-05-01

A thermodynamically consistent model of strain gradient elastodiffusion is developed. Its formulation is based on the enhancement of a robust theory of gradient elasticity, known as GRADELA, to account for a Cahn-Hilliard type of diffusion. Linear stability analysis is employed to determine the influence of concentration and strain gradients on the spinodal decomposition. For finite domains, spherically symmetric conditions are considered, and size effects on spinodal and miscibility gaps are discussed. The theoretical predictions are in agreement with the experimental trends, i.e., both gaps shrink as the grain diameter decreases and they are completely eliminated for crystals smaller than a critical size.

Optically transparent, mechanically durable, nanostructured superhydrophobic surfaces enabled by spinodally phase-separated glass thin films

NASA Astrophysics Data System (ADS)

Aytug, Tolga; Simpson, John T.; Lupini, Andrew R.; Trejo, Rosa M.; Jellison, Gerald E.; Ivanov, Ilia N.; Pennycook, Stephen J.; Hillesheim, Daniel A.; Winter, Kyle O.; Christen, David K.; Hunter, Scott R.; Haynes, J. Allen

2013-08-01

We describe the formation and properties of atomically bonded, optical quality, nanostructured thin glass film coatings on glass plates, utilizing phase separation by spinodal decomposition in a sodium borosilicate glass system. Following deposition via magnetron sputtering, thermal processing and differential etching, these coatings are structurally superhydrophilic (i.e., display anti-fogging functionality) and demonstrate robust mechanical properties and superior abrasion resistance. After appropriate chemical surface modification, the surfaces display a stable, non-wetting Cassie-Baxter state and exhibit exceptional superhydrophobic performance, with water droplet contact angles as large as 172°. As an added benefit, in both superhydrophobic and superhydrophilic states these nanostructured surfaces can block ultraviolet radiation and can be engineered to be anti-reflective with broadband and omnidirectional transparency. Thus, the present approach could be tailored toward distinct coatings for numerous markets, such as residential windows, windshields, specialty optics, goggles, electronic and photovoltaic cover glasses, and optical components used throughout the US military.

Optically transparent, mechanically durable, nanostructured superhydrophobic surfaces enabled by spinodally phase-separated glass thin films.

PubMed

Aytug, Tolga; Simpson, John T; Lupini, Andrew R; Trejo, Rosa M; Jellison, Gerald E; Ivanov, Ilia N; Pennycook, Stephen J; Hillesheim, Daniel A; Winter, Kyle O; Christen, David K; Hunter, Scott R; Haynes, J Allen

2013-08-09

We describe the formation and properties of atomically bonded, optical quality, nanostructured thin glass film coatings on glass plates, utilizing phase separation by spinodal decomposition in a sodium borosilicate glass system. Following deposition via magnetron sputtering, thermal processing and differential etching, these coatings are structurally superhydrophilic (i.e., display anti-fogging functionality) and demonstrate robust mechanical properties and superior abrasion resistance. After appropriate chemical surface modification, the surfaces display a stable, non-wetting Cassie-Baxter state and exhibit exceptional superhydrophobic performance, with water droplet contact angles as large as 172°. As an added benefit, in both superhydrophobic and superhydrophilic states these nanostructured surfaces can block ultraviolet radiation and can be engineered to be anti-reflective with broadband and omnidirectional transparency. Thus, the present approach could be tailored toward distinct coatings for numerous markets, such as residential windows, windshields, specialty optics, goggles, electronic and photovoltaic cover glasses, and optical components used throughout the US military.

Phase-field modeling of diffusional phase behaviors of solid surfaces: A case study of phase-separating Li XFePO 4 electrode particles

DOE PAGES

Heo, Tae Wook; Chen, Long-Qing; Wood, Brandon C.

2015-04-08

In this paper, we present a comprehensive phase-field model for simulating diffusion-mediated kinetic phase behaviors near the surface of a solid particle. The model incorporates elastic inhomogeneity and anisotropy, diffusion mobility anisotropy, interfacial energy anisotropy, and Cahn–Hilliard diffusion kinetics. The free energy density function is formulated based on the regular solution model taking into account the possible solute-surface interaction near the surface. The coherency strain energy is computed using the Fourier-spectral iterative-perturbation method due to the strong elastic inhomogeneity with a zero surface traction boundary condition. Employing a phase-separating Li XFePO 4 electrode particle for Li-ion batteries as a modelmore » system, we perform parametric three-dimensional computer simulations. The model permits the observation of surface phase behaviors that are different from the bulk counterpart. For instance, it reproduces the theoretically well-established surface modes of spinodal decomposition of an unstable solid solution: the surface mode of coherent spinodal decomposition and the surface-directed spinodal decomposition mode. We systematically investigate the influences of major factors on the kinetic surface phase behaviors during the diffusional process. Finally, our simulation study provides insights for tailoring the internal phase microstructure of a particle by controlling the surface phase morphology.« less

Aging Degradation of Austenitic Stainless Steel Weld Probed by Electrochemical Method and Impact Toughness Evaluation

NASA Astrophysics Data System (ADS)

Singh, Raghuvir; Das, Goutam; Mahato, B.; Singh, P. K.

2017-03-01

The present study discriminates the spinodal decomposition and G-phase precipitation in stainless steel welds by double loop electrochemical potentio-kinetic reactivation method and correlates it with the degradation in toughness property. The welds produced with different heat inputs were aged up to 10,000 hours at 673 K to 723 K (400 to 450 °C) and evaluated subsequently for the degree of sensitization (DOS) and impact toughness. The DOS values obtained were attributed to the spinodal decomposition and precipitation of G-phase. Study shows that the DOS correlates well with the impact toughness of the 304LN weld. Prolonged aging at 673 K and 723 K (400 °C and 450 °C) increased the DOS values while the impact toughness was decreased. The weld fabricated at 1 kJ/mm of heat input, produced higher DOS, compared to that at 3 kJ/mm. The geometrical location along the weld is shown to influence the DOS; higher values were obtained at the root than at the topside of the weld. Vermicular and columnar microstructure, in addition to the spinodal decomposition and G-phase precipitation, observed in the root side of the weld appear risky for the impact toughness.

Unconditionally energy stable time stepping scheme for Cahn–Morral equation: Application to multi-component spinodal decomposition and optimal space tiling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tavakoli, Rouhollah, E-mail: rtavakoli@sharif.ir

An unconditionally energy stable time stepping scheme is introduced to solve Cahn–Morral-like equations in the present study. It is constructed based on the combination of David Eyre's time stepping scheme and Schur complement approach. Although the presented method is general and independent of the choice of homogeneous free energy density function term, logarithmic and polynomial energy functions are specifically considered in this paper. The method is applied to study the spinodal decomposition in multi-component systems and optimal space tiling problems. A penalization strategy is developed, in the case of later problem, to avoid trivial solutions. Extensive numerical experiments demonstrate themore » success and performance of the presented method. According to the numerical results, the method is convergent and energy stable, independent of the choice of time stepsize. Its MATLAB implementation is included in the appendix for the numerical evaluation of algorithm and reproduction of the presented results. -- Highlights: •Extension of Eyre's convex–concave splitting scheme to multiphase systems. •Efficient solution of spinodal decomposition in multi-component systems. •Efficient solution of least perimeter periodic space partitioning problem. •Developing a penalization strategy to avoid trivial solutions. •Presentation of MATLAB implementation of the introduced algorithm.« less

Jammed Limit of Bijel Structure Formation

DOE PAGES

Welch, P. M.; Lee, M. N.; Parra-Vasquez, A. N. G.; ...

2017-11-02

Over the past decade, methods to control microstructure in heterogeneous mixtures by arresting spinodal decomposition via the addition of colloidal particles have led to an entirely new class of bicontinuous materials known as bijels. We present a new model for the development of these materials that yields to both numerical and analytical evaluation. This model reveals that a single dimensionless parameter that captures both chemical and environmental variables dictates the dynamics and ultimate structure formed in bijels. We also demonstrate that this parameter must fall within a fixed range in order for jamming to occur during spinodal decomposition, as wellmore » as show that known experimental trends for the characteristic domain sizes and time scales for formation are recovered by this model.« less

United States Air Force Summer Faculty Research Program (1987). Program Technical Report. Volume 2.

DTIC Science & Technology

1987-12-01

the area of statistical inference, distribution theory and stochastic * •processes. I have taught courses in random processes and sample % j .functions...controlled phase separation of isotropic, binary mixtures, the theory of spinodal decomposition has been developed by Cahn and Hilliard.5 ,6 This theory is...peak and its initial rate of growth at a given temperature are predicted by the spinodal theory . The angle of maximum intensity is then determined by

Localized instabilities and spinodal decomposition in driven systems in the presence of elasticity

NASA Astrophysics Data System (ADS)

Meca, Esteban; Münch, Andreas; Wagner, Barbara

2018-01-01

We study numerically and analytically the instabilities associated with phase separation in a solid layer on which an external material flux is imposed. The first instability is localized within a boundary layer at the exposed free surface by a process akin to spinodal decomposition. In the limiting static case, when there is no material flux, the coherent spinodal decomposition is recovered. In the present problem, stability analysis of the time-dependent and nonuniform base states as well as numerical simulations of the full governing equations are used to establish the dependence of the wavelength and onset of the instability on parameter settings and its transient nature as the patterns eventually coarsen into a flat moving front. The second instability is related to the Mullins-Sekerka instability in the presence of elasticity and arises at the moving front between the two phases when the flux is reversed. Stability analyses of the full model and the corresponding sharp-interface model are carried out and compared. Our results demonstrate how interface and bulk instabilities can be analyzed within the same framework which allows us to identify and distinguish each of them clearly. The relevance for a detailed understanding of both instabilities and their interconnections in a realistic setting is demonstrated for a system of equations modeling the lithiation and delithiation processes within the context of lithium ion batteries.

Small Angle Neutron Scattering Study in Multi-Component Polymer Systems: Spinodal Decomposition and Beyond

NASA Astrophysics Data System (ADS)

Han, Charles

Institute for Advanced Study, Shenzhen University, Shenzhen, China In memory of Professor John Kohn at this symposium, a time resolved SANS study for the early stage of spinodal decomposition kinetics of deuterated polycarbonate/poly(methylmethacrylate) blend will be reviewed which gives a clear proof of the Cahn-Hillard-Cook theory. This early stage of spinodal decomposition kinetics has been observed starting from the dimension (q-l) comparable to the single chain radius of gyration, Rg\\ , for a binary polymer mixture. The results provide an unequivocal quantitative measure of the virtual structure factor, S (q, ∞); the relationship of qm and qc through rate of growth, Cahn-plot analysis, and singularity in S (q, ∞); the growth of fluctuation of qRg <1 and intra-chain relaxation of qRg >1. More recent study of using mixed suspensions of polystyrene microspheres and poly(N-isopropylacrylamide) microgels as a molecular model system which has a long range repulsive interaction potential and a short range attractive potential, will also be discussed. In this model system, dynamic gelation, transition to soft glass state and cross-over to hard glass state will be demonstrated and compared with available theories for glass transition in structural materials. Acknowledgements go to: Polymers Division, and NCNR of NIST, and to ICCAS, Beijing, China. Also to my colleagues: M. Motowoka, H. Jinnai, T. Hashimoto, G.C. Yuan and H. Cheng.

Formation of metastable phases by spinodal decomposition

PubMed Central

Alert, Ricard; Tierno, Pietro; Casademunt, Jaume

2016-01-01

Metastable phases may be spontaneously formed from other metastable phases through nucleation. Here we demonstrate the spontaneous formation of a metastable phase from an unstable equilibrium by spinodal decomposition, which leads to a transient coexistence of stable and metastable phases. This phenomenon is generic within the recently introduced scenario of the landscape-inversion phase transitions, which we experimentally realize as a structural transition in a colloidal crystal. This transition exhibits a rich repertoire of new phase-ordering phenomena, including the coexistence of two equilibrium phases connected by two physically different interfaces. In addition, this scenario enables the control of sizes and lifetimes of metastable domains. Our findings open a new setting that broadens the fundamental understanding of phase-ordering kinetics, and yield new prospects of applications in materials science. PMID:27713406

Mechanical model for filament buckling and growth by phase ordering.

PubMed

Rey, Alejandro D; Abukhdeir, Nasser M

2008-02-05

A mechanical model of open filament shape and growth driven by phase ordering is formulated. For a given phase-ordering driving force, the model output is the filament shape evolution and the filament end-point kinematics. The linearized model for the slope of the filament is the Cahn-Hilliard model of spinodal decomposition, where the buckling corresponds to concentration fluctuations. Two modes are predicted: (i) sequential growth and buckling and (ii) simultaneous buckling and growth. The relation among the maximum buckling rate, filament tension, and matrix viscosity is given. These results contribute to ongoing work in smectic A filament buckling.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

PubMed Central

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; Peng, Haowei; Deml, Ann M.; Matthews, Bethany E.; Schelhas, Laura T.; Toney, Michael F.; Gordon, Roy G.; Tumas, William; Perkins, John D.; Ginley, David S.; Gorman, Brian P.; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-01-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region. PMID:28630928

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the criticalmore » composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Furthermore, thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.« less

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys.

PubMed

Holder, Aaron M; Siol, Sebastian; Ndione, Paul F; Peng, Haowei; Deml, Ann M; Matthews, Bethany E; Schelhas, Laura T; Toney, Michael F; Gordon, Roy G; Tumas, William; Perkins, John D; Ginley, David S; Gorman, Brian P; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-06-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

DOE PAGES

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; ...

2017-06-07

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the criticalmore » composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Furthermore, thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.« less

Compositional partitioning during the spinodal decomposition in Cu-Ni-Sn alloy

NASA Astrophysics Data System (ADS)

Basak, C. B.; Poswal, A. K.

2018-05-01

Spinodal decomposition in Cu-9.4at%Ni-3.1at%Sn alloy was elucidated with the new insight from the experimental EXAFS analysis supported by ab initio total energy calculations suggesting the strong influence of the first near-neighbour atoms. Enthalpy of mixing was calculated for all crystallographically unique first near-neighbour configurations and finally an average positive enthalpy of mixing of 1604 J/mol was obtained. Combination of ab initio results, XRD and EXAFS analysis indicate that one of the daughter phase becomes rich in Ni and Sn than the other phase; in contrary to the earlier proposition that Cu/Ni ratio remains constant in both daughter phases. It is also shown that the present thermodynamic description requires further refinement to extend the miscibility gap towards lower Ni content in Cu-Ni-Sn system.

Irradiation response of delta ferrite in as-cast and thermally aged cast stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhangbo; Lo, Wei-Yang; Chen, Yiren

To enable the life extension of Light Water Reactors (LWRs) beyond 60 years, it is critical to gain adequate knowledge for making conclusive predictions to assure the integrity of duplex stainless steel reactor components, e.g. primary pressure boundary and reactor vessel internal. Microstructural changes in the ferrite of thermally aged, neutron irradiated only, and neutron irradiated after being thermally aged cast austenitic stainless steels (CASS) were investigated using atom probe tomography. The thermal aging was performed at 400 °C for 10,000 h and the irradiation was conducted in the Halden reactor at ~315 °C to 0.08 dpa (5.6 × 10more » 19 n/cm 2 E > 1 MeV). Low dose neutron irradiation at a dose rate of 5 × 10 -9 dpa/s was found to induce spinod,al decomposition in the ferrite of as-cast microstructure, and further to enhance the spinodal decomposition in the thermally aged cast alloys. Regarding the G-phase precipitates, the neutron irradiation dramatically increases the precipitate size, and alters the composition of the precipitates with increased, Mn, Ni, Si and Mo and reduced Fe and Cr contents. Lastly, The results have shown that low dose neutron irradiation can further accelerate the degradation of ferrite in a duplex stainless steel at the LWR relevant condition.« less

Irradiation response of delta ferrite in as-cast and thermally aged cast stainless steel

DOE PAGES

Li, Zhangbo; Lo, Wei-Yang; Chen, Yiren; ...

2015-08-08

To enable the life extension of Light Water Reactors (LWRs) beyond 60 years, it is critical to gain adequate knowledge for making conclusive predictions to assure the integrity of duplex stainless steel reactor components, e.g. primary pressure boundary and reactor vessel internal. Microstructural changes in the ferrite of thermally aged, neutron irradiated only, and neutron irradiated after being thermally aged cast austenitic stainless steels (CASS) were investigated using atom probe tomography. The thermal aging was performed at 400 °C for 10,000 h and the irradiation was conducted in the Halden reactor at ~315 °C to 0.08 dpa (5.6 × 10more » 19 n/cm 2 E > 1 MeV). Low dose neutron irradiation at a dose rate of 5 × 10 -9 dpa/s was found to induce spinod,al decomposition in the ferrite of as-cast microstructure, and further to enhance the spinodal decomposition in the thermally aged cast alloys. Regarding the G-phase precipitates, the neutron irradiation dramatically increases the precipitate size, and alters the composition of the precipitates with increased, Mn, Ni, Si and Mo and reduced Fe and Cr contents. Lastly, The results have shown that low dose neutron irradiation can further accelerate the degradation of ferrite in a duplex stainless steel at the LWR relevant condition.« less

Phase segregation in multiphase turbulent channel flow

NASA Astrophysics Data System (ADS)

Bianco, Federico; Soldati, Alfredo

2014-11-01

The phase segregation of a rapidly quenched mixture (namely spinodal decomposition) is numerically investigated. A phase field approach is considered. Direct numerical simulation of the coupled Navier-Stokes and Cahn-Hilliard equations is performed with spectral accuracy and focus has been put on domain growth scaling laws, in a wide range of regimes. The numerical method has been first validated against well known results of literature, then spinodal decomposition in a turbulent bounded flow (channel flow) has been considered. As for homogeneous isotropic case, turbulent fluctuations suppress the segregation process when surface tension at the interfaces is relatively low (namely low Weber number regimes). For these regimes, segregated domains size reaches a statistically steady state due to mixing and break-up phenomena. In contrast with homogenous and isotropic turbulence, the presence of mean shear, leads to a typical domain size that show a wall-distance dependence. Finally, preliminary results on the effects to the drag forces at the wall, due to phase segregation, have been discussed. Regione FVG, program PAR-FSC.

Size effects of solvent molecules on the phase behavior and effective interaction of colloidal systems with the bridging attraction.

PubMed

Chen, Jie; Wang, Xuewu; Kline, Steven R; Liu, Yun

2016-11-16

There has been much recent research interest towards understanding the phase behavior of colloidal systems interacting with a bridging attraction, where the small solvent particles and large solute colloidal particles can be reversibly associated with each other. These systems show interesting phase behavior compared to the more widely studied depletion attraction systems. Here, we use Baxter's two-component sticky hard sphere model with a Percus-Yevick closure to solve the Ornstein-Zernike equation and study the size effect on colloidal systems with bridging attractions. The spinodal decomposition regions, percolation transition boundaries and binodal regions are systematically investigated as a function of the relative size of the small solvent and large solute particles as well as the attraction strength between the small and large particles. In the phase space determined by the concentrations of small and large particles, the spinodal and binodal regions form isolated islands. The locations and shapes of the spinodal and binodal regions sensitively depend on the relative size of the small and large particles and the attraction strength between them. The percolation region shrinks by decreasing the size ratio, while the binodal region slightly expands with the decrease of the size ratio. Our results are very important in understanding the phase behavior for a bridging attraction colloidal system, a model system that provides insight into oppositely charged colloidal systems, protein phase behavior, and colloidal gelation mechanisms.

Spinodal assisted growing dynamics of critical nucleus in polymer blends

NASA Astrophysics Data System (ADS)

Zhang, Xinghua; Qi, Shuanhu; Yan, Dadong

2012-11-01

In metastable polymer blends, nonclassical critical nucleus is not a drop of stable phase in core wrapped with a sharp interface, but a diffuse structure depending on the metastability. Thus, forming a critical nucleus does not mean the birth of a new phase. In the present work, the nonclassical growing dynamics of the critical nucleus is addressed in the metastable polymer blends by incorporating self-consistent field theory and external potential dynamics theory, which leads to an intuitionistic description for the scattering experiments. The results suggest that the growth of nonclassical critical nucleus is controlled by the spinodal-decomposition which happens in the region surrounding the nucleus. This leads to forming the shell structures around the nucleus.

Sponge-like Si-SiO2 nanocomposite—Morphology studies of spinodally decomposed silicon-rich oxide

NASA Astrophysics Data System (ADS)

Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.; Mikolajick, T.

2013-09-01

Sponge-like Si nanostructures embedded in SiO2 were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.

High T c layered ferrielectric crystals by coherent spinodal decomposition

DOE PAGES

Susner, Michael A.; Belianinov, Alex; Borisevich, Albina Y.; ...

2015-11-13

Research in the rapidly-developing field of 2D-electronic materials has thus far been focused on metallic and semiconducting materials. However, complementary dielectric materials such as non-linear dielectrics are needed to enable realistic device architectures. Candidate materials require tunable dielectric properties and pathways for heterostructure assembly. Here we report on a family of cation-deficient transition metal thiophosphates whose unique chemistry makes them a viable prospect for these applications. In these materials, naturally occurring ferrielectric heterostructures composed of centrosymmetric In 4/3P 2S 6 and ferrielectrically-active CuInP 2S 6 are realized by controllable chemical phase separation in van-der-Waals bonded single crystals. CuInP 2S 6more » by itself is a layered ferrielectric with Tc just over room-temperature which rapidly decreases with homogenous doping. Surprisingly, in our composite materials, the ferrielectric Tc of the polar CuInP 2S 6 phase increases. This effect is enabled by unique spinodal decomposition that retains the overall van-der-Waals layered morphology of the crystal, but chemically separates CuInP 2S 6 and In 4/3P 2S 6 within each layer. The average spatial periodicity of the distinct chemical phases can be finely controlled by altering the composition and/or synthesis conditions. One intriguing prospect for such layered spinodal alloys is large volume synthesis of 2D in-plane heterostructures with periodically alternating polar and non-polar phases.« less

Phase Transformations of an Fe-0.85 C-17.9 Mn-7.1 Al Austenitic Steel After Quenching and Annealing

NASA Astrophysics Data System (ADS)

Cheng, Wei-Chun

2014-09-01

Low-density Mn-Al steels could potentially be substitutes for commercial Ni-Cr stainless steels. However, the development of the Mn-Al stainless steels requires knowledge of the phase transformations that occur during the steel making processes. Phase transformations of an Fe-0.85 C-17.9 Mn-7.1 Al (wt.%) austenitic steel, which include spinodal decomposition, precipitation transformations, and cellular transformations, have been studied after quenching and annealing. The results show that spinodal decomposition occurs prior to the precipitation transformation in the steel after quenching and annealing at temperatures below 1023 K and that coherent fine particles of L12-type carbide precipitate homogeneously in the austenite. The cellular transformation occurs during the transformation of high-temperature austenite into lamellae of austenite, ferrite, and kappa carbide at temperatures below 1048 K. During annealing at temperatures below 923 K, the austenite decomposes into lamellar austenite, ferrite, κ-carbide, and M23C6 carbide grains for another cellular transformation. Last, when annealing at temperatures below 873 K, lamellae of ferrite and κ-carbide appear in the austenite.

Effects of Thermal Aging on Material Properties, Stress Corrosion Cracking, and Fracture Toughness of AISI 316L Weld Metal

NASA Astrophysics Data System (ADS)

Lucas, Timothy; Forsström, Antti; Saukkonen, Tapio; Ballinger, Ronald; Hänninen, Hannu

2016-08-01

Thermal aging and consequent embrittlement of materials are ongoing issues in cast stainless steels, as well as duplex, and high-Cr ferritic stainless steels. Spinodal decomposition is largely responsible for the well-known "748 K (475 °C) embrittlement" that results in drastic reductions in ductility and toughness in these materials. This process is also operative in welds of either cast or wrought stainless steels where δ-ferrite is present. While the embrittlement can occur after several hundred hours of aging at 748 K (475 °C), the process is also operative at lower temperatures, at the 561 K (288 °C) operating temperature of a boiling water reactor (BWR), for example, where ductility reductions have been observed after several tens of thousands of hours of exposure. An experimental program was carried out in order to understand how spinodal decomposition may affect changes in material properties in Type 316L BWR piping weld metals. The study included material characterization, nanoindentation hardness, double-loop electrochemical potentiokinetic reactivation (DL-EPR), Charpy-V, tensile, SCC crack growth, and in situ fracture toughness testing as a function of δ-ferrite content, aging time, and temperature. SCC crack growth rates of Type 316L stainless steel weld metal under simulated BWR conditions showed an approximate 2 times increase in crack growth rate over that of the unaged as-welded material. In situ fracture toughness measurements indicate that environmental exposure can result in a reduction of toughness by up to 40 pct over the corresponding at-temperature air-tested values. Material characterization results suggest that spinodal decomposition is responsible for the degradation of material properties measured in air, and that degradation of the in situ properties may be a result of hydrogen absorbed during exposure to the high-temperature water environment.

On spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Lin; Guo, Wei; Poplawsky, J. D.

Here, alnico is a prime example of a finely tuned nanostructure whose magnetic properties are intimately connected to magnetic annealing (MA) during spinodal transformation and subsequent lower temperature annealing (draw) cycles. Using a combination of transmission electron microscopy and atom probe tomography, we show how these critical processing steps affect the local composition and nanostructure evolution with impact on magnetic properties. The nearly 2-fold increase of intrinsic coercivity (H ci) during the draw cycle is not adequately explained by chemical refinement of the spinodal phases. Instead, increased Fe-Co phase (α 1) isolation, development of Cu-rich spheres/rods/blades and additional α 1more » rod precipitation that occurs during the MA and draw, likely play a key role in Hci enhancement. Chemical ordering of the Al-Ni-phase (α 2) and formation of Ni-rich (α 3) may also contribute. Unraveling of the subtle effect of these nano-scaled features is crucial to understanding on how to improve shape anisotropy in alnico magnets.« less

On spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study

DOE PAGES

Zhou, Lin; Guo, Wei; Poplawsky, J. D.; ...

2018-04-26

Here, alnico is a prime example of a finely tuned nanostructure whose magnetic properties are intimately connected to magnetic annealing (MA) during spinodal transformation and subsequent lower temperature annealing (draw) cycles. Using a combination of transmission electron microscopy and atom probe tomography, we show how these critical processing steps affect the local composition and nanostructure evolution with impact on magnetic properties. The nearly 2-fold increase of intrinsic coercivity (H ci) during the draw cycle is not adequately explained by chemical refinement of the spinodal phases. Instead, increased Fe-Co phase (α 1) isolation, development of Cu-rich spheres/rods/blades and additional α 1more » rod precipitation that occurs during the MA and draw, likely play a key role in Hci enhancement. Chemical ordering of the Al-Ni-phase (α 2) and formation of Ni-rich (α 3) may also contribute. Unraveling of the subtle effect of these nano-scaled features is crucial to understanding on how to improve shape anisotropy in alnico magnets.« less

Temperature driven evolution of thermal, electrical, and optical properties of Ti-Al-N coatings.

PubMed

Rachbauer, Richard; Gengler, Jamie J; Voevodin, Andrey A; Resch, Katharina; Mayrhofer, Paul H

2012-03-01

Monolithic single phase cubic (c) Ti 1- x Al x N thin films are used in various industrial applications due to their high thermal stability, which beneficially effects lifetime and performance of cutting and milling tools, but also find increasing utilization in electronic and optical devices. The present study elucidates the temperature-driven evolution of heat conductivity, electrical resistivity and optical reflectance from room temperature up to 1400 °C and links them to structural and chemical changes in Ti 1- x Al x N coatings. It is shown that various decomposition phenomena, involving recovery and spinodal decomposition (known to account for the age hardening phenomenon in c-Ti 1- x Al x N), as well as the cubic to wurtzite phase transformation of spinodally formed AlN-enriched domains, effectively increase the thermal conductivity of the coatings from ∼3.8 W m -1  K -1 by a factor of three, while the electrical resistivity is reduced by one order of magnitude. A change in the coating color from metallic grey after deposition to reddish-golden after annealing to 1400 °C is related to the film structure and discussed in terms of film reflectivity.

Reconciliation of Cahn-Hilliard predictions for spinodal decomposition lengthscales in polymer blends

NASA Astrophysics Data System (ADS)

Cabral, Joao

Spinodal decomposition (SD) of partially miscible polymer blends can yield well-defined nanostructures with prescribed lengthscales and connectivity, and applications ranging from membranes and scaffolds to photovoltaics. Cahn-Hilliard-Cook (CHC) theory estimates the initial, dominant SD wavenumber to be qm =√{G''/4 k } , where G'' is the second derivative of the free energy of mixing with respect to concentration and k is a structural parameter which can be computed from the segment lengths and volumes of monomer units. Tuning G'', with quench depth into the two phase region, for instance, should thus provide a facile and precise means for designing polymeric bicontinuous structures. The fulfillment of this potential rests on the thermodynamics of available polymer systems, coarsening kinetics, as well as engineering constraints. We extensively review experimental measurements of G'' in both one- and two-phase blend systems, and critically examine the accuracy of this fundamental prediction against achievements over the past 4 decades of polymer blend demixing. Despite widespread misconceptions in detecting and describing SD, we find the CHC relation to be remarkably accurate and conclude with design considerations and limitations for polymer nanostructures via SD, reflecting on John Cahn's contributions to the field.

Arrest scenarios in concentrated protein solutions - from hard sphere glasses to arrested spinodal decomposition

NASA Astrophysics Data System (ADS)

Stradner, Anna; Bucciarelli, Saskia; Casal, Lucia; Foffi, Giuseppe; Thurston, George; Farago, Bela; Schurtenberger, Peter

2014-03-01

The occurrence of an arrest transition in concentrated colloid suspensions and its dependence on the interaction potential is a hot topic in soft matter. Such arrest transitions can also occur in concentrated protein solutions, as they exist e.g. in biological cells or are increasingly used in pharmaceutical formulations. Here we demonstrate the applicability of concepts from colloid science to understand the dynamics of concentrated protein solutions. In this presentation we report a combination of 3D light scattering, small-angle X-ray scattering and neutron spin echo measurements to study the structural properties as well as the collective and self diffusion of proteins in highly concentrated solutions on the relevant length and time scales. We demonstrate that various arrest scenarios indeed exist for different globular proteins. The proteins chosen are different bovine lens crystallins. We report examples of hard and attractive glass transitions and arrested spinodal decomposition directly linked to the effective pair potentials determined in static scattering experiments for the different proteins. We discuss these different arrest scenarios in view of possible applications of dense protein solutions as well as in view of their possible relevance for living systems.

Spatially modulated structural colour in bird feathers.

PubMed

Parnell, Andrew J; Washington, Adam L; Mykhaylyk, Oleksandr O; Hill, Christopher J; Bianco, Antonino; Burg, Stephanie L; Dennison, Andrew J C; Snape, Mary; Cadby, Ashley J; Smith, Andrew; Prevost, Sylvain; Whittaker, David M; Jones, Richard A L; Fairclough, J Patrick A; Parker, Andrew R

2015-12-21

Eurasian Jay (Garrulus glandarius) feathers display periodic variations in the reflected colour from white through light blue, dark blue and black. We find the structures responsible for the colour are continuous in their size and spatially controlled by the degree of spinodal phase separation in the corresponding region of the feather barb. Blue structures have a well-defined broadband ultra-violet (UV) to blue wavelength distribution; the corresponding nanostructure has characteristic spinodal morphology with a lengthscale of order 150 nm. White regions have a larger 200 nm nanostructure, consistent with a spinodal process that has coarsened further, yielding broader wavelength white reflectance. Our analysis shows that nanostructure in single bird feather barbs can be varied continuously by controlling the time the keratin network is allowed to phase separate before mobility in the system is arrested. Dynamic scaling analysis of the single barb scattering data implies that the phase separation arrest mechanism is rapid and also distinct from the spinodal phase separation mechanism i.e. it is not gelation or intermolecular re-association. Any growing lengthscale using this spinodal phase separation approach must first traverse the UV and blue wavelength regions, growing the structure by coarsening, resulting in a broad distribution of domain sizes.

Spatially modulated structural colour in bird feathers

PubMed Central

Parnell, Andrew J.; Washington, Adam L.; Mykhaylyk, Oleksandr O.; Hill, Christopher J.; Bianco, Antonino; Burg, Stephanie L.; Dennison, Andrew J. C.; Snape, Mary; Cadby, Ashley J.; Smith, Andrew; Prevost, Sylvain; Whittaker, David M.; Jones, Richard A. L.; Fairclough, J. Patrick. A.; Parker, Andrew R.

2015-01-01

Eurasian Jay (Garrulus glandarius) feathers display periodic variations in the reflected colour from white through light blue, dark blue and black. We find the structures responsible for the colour are continuous in their size and spatially controlled by the degree of spinodal phase separation in the corresponding region of the feather barb. Blue structures have a well-defined broadband ultra-violet (UV) to blue wavelength distribution; the corresponding nanostructure has characteristic spinodal morphology with a lengthscale of order 150 nm. White regions have a larger 200 nm nanostructure, consistent with a spinodal process that has coarsened further, yielding broader wavelength white reflectance. Our analysis shows that nanostructure in single bird feather barbs can be varied continuously by controlling the time the keratin network is allowed to phase separate before mobility in the system is arrested. Dynamic scaling analysis of the single barb scattering data implies that the phase separation arrest mechanism is rapid and also distinct from the spinodal phase separation mechanism i.e. it is not gelation or intermolecular re-association. Any growing lengthscale using this spinodal phase separation approach must first traverse the UV and blue wavelength regions, growing the structure by coarsening, resulting in a broad distribution of domain sizes. PMID:26686280

Dynamics of polymerization induced phase separation in reactive polymer blends

NASA Astrophysics Data System (ADS)

Lee, Jaehyung

Mechanisms and dynamics of phase decomposition following polymerization induced phase separation (PIPS) of reactive polymer blends have been investigated experimentally and theoretically. The phenomenon of PIPS is a non-equilibrium and non-linear dynamic process. The mechanism of PIPS has been thought to be a nucleation and growth (NG) type originally, however, newer results indicate spinodal decomposition (SD). In PIPS, the coexistence curve generally passes through the reaction temperature at off-critical compositions, thus phase separation has to be initiated first in the metastable region where nucleation occurs. When the system farther drifts from the metastable to unstable region, the NG structure transforms to the SD bicontinuous morphology. The crossover behavior of PIPS may be called nucleation initiated spinodal decomposition (NISD). The formation of newer domains between the existing ones is responsible for the early stage of PIPS. Since PIPS is non- equilibrium kinetic process, it would not be surprising to discern either or both structures. The phase separation dynamics of DGEBA/CTBN mixtures having various kinds of curing agents from low reactivity to high reactivity and various amount of curing agents were examined at various reaction temperatures. The phase separation behavior was monitored by a quantity of scattered light intensity experimentally and by a quantity of collective structure factor numerically. Prior to the study of phase separation dynamics, a preliminary investigation on the isothermal cure behavior of the mixtures were executed in order to determine reaction kinetics parameters. The cure behavior followed the overall second order reaction kinetics. Next, based on the knowledge obtained from the phase separation dynamics study of DGEBA/CTBN mixtures, the phase separation dynamics of various composition of DGEBA/R45EPI mixtures having MDA as a curing agent were investigated. The phase separation behavior was quite dependent upon the composition variation. R45EPI itself can react with itself or with DGEBA without curing, therefore three-component system was considered in this mixture. For the numerical studies of this three- component mixture, a system that is composed of a reactive component-1 that is miscible with its growing molecules and another reactive component-2 that is not miscible with its growing molecules was considered with crosslinking reaction kinetics of the each component.

Dynamics of phase separation of binary fluids

NASA Technical Reports Server (NTRS)

Ma, Wen-Jong; Maritan, Amos; Banavar, Jayanth R.; Koplik, Joel

1992-01-01

The results of molecular-dynamics studies of surface-tension-dominated spinodal decomposition of initially well-mixed binary fluids in the absence and presence of gravity are presented. The growth exponent for the domain size and the decay exponent of the potential energy of interaction between the two species with time are found to be 0.6 +/- 0.1, inconsistent with scaling arguments based on dimensional analysis.

DRoplet and hAdron generator for nuclear collisions: An update

NASA Astrophysics Data System (ADS)

Tomášik, Boris

2016-10-01

The Monte Carlo generator DRAGON simulates hadron production in ultrarelativistic nuclear collisions. The underlying theoretical description is provided by the blast-wave model. DRAGON includes second-order angular anisotropy in transverse shape and the amplitude of the transverse expansion velocity. It also allows to simulate hadron production from a fragmented fireball, e.g. as resulting from spinodal decomposition happening at the first-order phase transition.

Temperature driven evolution of thermal, electrical, and optical properties of Ti–Al–N coatings

PubMed Central

Rachbauer, Richard; Gengler, Jamie J.; Voevodin, Andrey A.; Resch, Katharina; Mayrhofer, Paul H.

2012-01-01

Monolithic single phase cubic (c) Ti1−xAlxN thin films are used in various industrial applications due to their high thermal stability, which beneficially effects lifetime and performance of cutting and milling tools, but also find increasing utilization in electronic and optical devices. The present study elucidates the temperature-driven evolution of heat conductivity, electrical resistivity and optical reflectance from room temperature up to 1400 °C and links them to structural and chemical changes in Ti1−xAlxN coatings. It is shown that various decomposition phenomena, involving recovery and spinodal decomposition (known to account for the age hardening phenomenon in c-Ti1−xAlxN), as well as the cubic to wurtzite phase transformation of spinodally formed AlN-enriched domains, effectively increase the thermal conductivity of the coatings from ∼3.8 W m−1 K−1 by a factor of three, while the electrical resistivity is reduced by one order of magnitude. A change in the coating color from metallic grey after deposition to reddish-golden after annealing to 1400 °C is related to the film structure and discussed in terms of film reflectivity. PMID:23482424

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Wei; Sneed, Brian T.; Zhou, Lin

Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology andmore » volume fractions of Fe–Co-rich and Νi–Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2–4 nm Fe-rich α 1 phases that are nucleated in the Ni-rich α 2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. Lastly, we discuss the complementary benefits and challenges associated with correlative STEM-EDS and APT.« less

Intergranular Corrosion Behavior of 304LN Stainless Steel Heat Treated at 623 K (350 °C)

NASA Astrophysics Data System (ADS)

Singh, Raghuvir; Kumar, Mukesh; Ghosh, Mainak; Das, Gautam; Singh, P. K.; Chattoraj, I.

2013-01-01

Low temperature sensitization of 304LN stainless steel from the two pipes, differing slightly in chemical composition, has been investigated; specimens were aged at 623 K (350 °C) for 20,000 hours and evaluated for intergranular corrosion and degree of sensitization. The base and heat-affected zone (HAZ) of the 304LN-1 appear resistant to sensitization, while 304LN-2 revealed a "dual" type microstructure at the transverse section and HAZ. The microstructure at 5.0-mm distance from the fusion line indicates qualitatively less sensitization as compared to that at 2.0 mm. The 304LN-2 base alloy shows overall lower degree of sensitization values as compared to the 304LN-1. A similar trend of degree of sensitization was observed in the HAZ where it was higher in the 304LN-1 as compared to the 304LN-2. The weld zone of both the stainless steels suffered from cracking during ASTM A262 practice E, while the parent metals and HAZs did not show such fissures. A mottled image within the ferrite lamella showed spinodal decomposition. The practice E test and transmission electron microscopy results indicate that the interdendritic regions may suffer from failure due to carbide precipitation and due to the evolution of brittle phase from spinodal decomposition.

Phase transformation in SiOx/SiO₂ multilayers for optoelectronics and microelectronics applications.

PubMed

Roussel, M; Talbot, E; Pratibha Nalini, R; Gourbilleau, F; Pareige, P

2013-09-01

Due to the quantum confinement, silicon nanoclusters (Si-ncs) embedded in a dielectric matrix are of prime interest for new optoelectronics and microelectronics applications. In this context, SiO(x)/SiO₂ multilayers have been prepared by magnetron sputtering and subsequently annealed to induce phase separation and Si clusters growth. The aim of this paper is to study phase separation processes and formation of nanoclusters in SiO(x)/SiO₂ multilayers by atom probe tomography. Influences of the silicon supersaturation, annealing temperature and SiO(x) and SiO₂ layer thicknesses on the final microstructure have been investigated. It is shown that supersaturation directly determines phase separation regime between nucleation/classical growth and spinodal decomposition. Annealing temperature controls size of the particles and interface with the surrounding matrix. Layer thicknesses directly control Si-nc shapes from spherical to spinodal-like structures. Copyright © 2012 Elsevier B.V. All rights reserved.

Computational nano-material design of exotic luminescent materials based upon europium doped gallium nitrides

NASA Astrophysics Data System (ADS)

Masago, Akira; Fukushima, Tetsuya; Sato, Kazunori; Katayama-Yoshida, Hiroshi

2015-03-01

Eu-doped GaN has attracted much attention, because the red light luminescence ability provides us with expectations to realize monolithic full-color LEDs, which work on seamless conditions such as substrates, electrodes, and operating bias voltages. Toward implementation of multifunctional activity into the luminescent materials using the spinodal nano-structures, we investigate atomic configurations and magnetic structures of the GaN crystal codoped with Eu, Mg, Si, O, and/or the vacancies using the density functional method (DFT) calculations. Our calculations show that the impurity clusterized distributions are energetically favorable more than the homogeneous distribution. Moreover, analyses of the formation energy and binding energy suggest that the clusterized distributions are spontaneously formed by the nano-spinodal decomposition. Though the host matrix has no magnetic moments, the cluster has finite magnetic moments, where Zener's p-f exchange interaction works between the Eu f-state and the nearby N p-states.

Mechanisms of radiation-induced segregation in CrFeCoNi-based single-phase concentrated solid solution alloys

DOE PAGES

He, Mo-Rigen; Wang, Shuai; Shi, Shi; ...

2016-12-31

Single-phase concentrated solid solution alloys have attracted wide interest due to their superior mechanical properties and enhanced radiation tolerance, which make them promising candidates for the structural applications in next-generation nuclear reactors. However, little has been understood about the intrinsic stability of their as-synthesized, high-entropy configurations against radiation damage. In this paper, we report the element segregation in CrFeCoNi, CrFeCoNiMn, and CrFeCoNiPd equiatomic alloys when subjected to 1250 kV electron irradiations at 400 °C up to a damage level of 1 displacement per atom. Cr/Fe/Mn/Pd can deplete and Co/Ni can accumulate at radiation-induced dislocation loops, while the actively segregating elementsmore » are alloy-specific. Moreover, electron-irradiated matrix of CrFeCoNiMn and CrFeCoNiPd shows L1 0 (NiMn)-type ordering decomposition and <001>-oriented spinodal decomposition between Co/Ni and Pd, respectively. Finally, these findings are rationalized based on the atomic size difference and enthalpy of mixing between the alloying elements, and identify a new important requirement to the design of radiation-tolerant alloys through modification of the composition.« less

Decomposition pathways in age hardening of Ti-Al-N films

NASA Astrophysics Data System (ADS)

Rachbauer, R.; Massl, S.; Stergar, E.; Holec, D.; Kiener, D.; Keckes, J.; Patscheider, J.; Stiefel, M.; Leitner, H.; Mayrhofer, P. H.

2011-07-01

The ability to increase the thermal stability of protective coatings under work load gives rise to scientific and industrial interest in age hardening of complex nitride coating systems such as ceramic-like Ti1-xAlxN. However, the decomposition pathway of these systems from single-phase cubic to the thermodynamically stable binary nitrides (cubic TiN and wurtzite AlN), which are essential for age hardening, are not yet fully understood. In particular, the role of decomposition kinetics still requires more detailed investigation. In the present work, the combined effect of annealing time and temperature upon the nano-structural development of Ti0.46Al0.54N thin films is studied, with a thermal exposure of either 1 min or 120 min in 100 °C steps from 500 °C to 1400 °C. The impact of chemical changes at the atomic scale on the development of micro-strain and mechanical properties is studied by post-annealing investigations using X-ray diffraction, nanoindentation, 3D-atom probe tomography and high-resolution transmission electron microscopy. The results clearly demonstrate that the spinodal decomposition process, triggering the increase of micro-strain and hardness, although taking place throughout the entire volume, is enhanced at high diffusivity paths such as grain or column boundaries and followed within the grains. Ab initio calculations further show that the early stages of wurtzite AlN precipitation are connected with increased strain formation, which is in excellent agreement with experimental observations.

Multiple Nonstoichiometric Phases with Discrete Composition Ranges in the CaAu5−CaAu4Bi−BiAu2 System. A Case Study of the Chemistry of Spinodal Decomposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Qisheng; Corbett, John D.

2010-04-01

Synthetic explorations in the CaAu{sub 5}-CaAu{sub 4}Bi-BiAu{sub 2} system at 400 C reveal five separate solid solution regions that show three distinct substitution patterns in the CaAu{sub 5} parent: (I) CaAu{sub 4}(Au{sub 1-m}Bi{sub m}) with 0 {le} m {le} 0.15(1), (II) 0.33(1) {le} m {le} 0.64(1), (III) 0.85(4) {le} m {le} 0.90(2); (IV) (Ca{sub 1-r}Au{sub r})Au{sub 4}(Bi{sub 1-s}Au{sub s}) with 0 {le} r {le} 0.39(1) and 0 {le} s {le} 0.12(2); (V) (Ca{sub 1-p-q}Au{sub p}Bi{sub q})Au{sub 4}Bi with 0.09(2) {le} p {le} 0.13(1) and 0.31(2) {le} q {le} 0.72(4). Single crystal X-ray studies establish that all of these phase regionsmore » have common cubic symmetry F{sub 4}3m and that their structures (MgCu{sub 4}Sn-type, an ordered derivative of MgCu{sub 2}) all feature three-dimensional networks of Au{sub 4} tetrahedra, in which the truncated tetrahedra are centered and capped by Ca/Au, Au/Bi, or Ca/Au/Bi mixtures to give 16-atom Friauf polyhedra. TB-LMTO-ASA and -COHP calculations also reveal that direct interactions between Ca-Au and Ca-Bi pairs of atoms are relatively weak and that the Bi-Au interactions in the unstable ideal CaAu{sub 4}Bi are antibonding in character at E{sub F} but that their bonding is optimized at {+-}1 e. Compositions between the five nonstoichiometric phases appear to undergo spinodal decompositions. The last phenomenon has been confirmed by HRTEM, STEM-HAADF, EPMA, and XRD studies of the nominal composition CaAu{sub 4.25}Bi{sub 0.75}. Its DTA analyses suggest that the phases resulting from spinodal decomposition have nearly the same melting point ({approx}807 C), as expected, and that they are interconvertible through peritectic reactions at {approx}717 C.« less

Effect of Secondary Phase Precipitation on the Corrosion Behavior of Duplex Stainless Steels.

PubMed

Chan, Kai Wang; Tjong, Sie Chin

2014-07-22

Duplex stainless steels (DSSs) with austenitic and ferritic phases have been increasingly used for many industrial applications due to their good mechanical properties and corrosion resistance in acidic, caustic and marine environments. However, DSSs are susceptible to intergranular, pitting and stress corrosion in corrosive environments due to the formation of secondary phases. Such phases are induced in DSSs during the fabrication, improper heat treatment, welding process and prolonged exposure to high temperatures during their service lives. These include the precipitation of sigma and chi phases at 700-900 °C and spinodal decomposition of ferritic grains into Cr-rich and Cr-poor phases at 350-550 °C, respectively. This article gives the state-of the-art review on the microstructural evolution of secondary phase formation and their effects on the corrosion behavior of DSSs.

Microscale Heat Transfer Enhancement using Spinodal Decomposition of Binary Liquid Mixtures: A Collaborative Modeling/Experimental Approach

DTIC Science & Technology

2013-09-01

heat transfer coefficients due to the high heat of vapor- ization. Many authors ([ Mudawar (2001)], [ Mudawar and Bowers (1999)] and [Kandlikar (2005...Letters, 95, (2005), 1. [Rosales and Meneveau (2006)] C. Rosales and C. Meneveau. Physics of Fluids, 18, (2006), 075104. [ Mudawar and Bowers (1999)] I... Mudawar and M.B. Bowers, Ultra-high crit- ical heat flux (CHF) for subcooled water flow boiling-I: CHF data and parametric effects for small

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Woo-Young; Seol, Jae-Bok, E-mail: jb-seol@postech.ac.kr; Kwak, Chan-Min

The compositional distribution of In atoms in InGaN/GaN multiple quantum wells is considered as one of the candidates for carrier localization center, which enhances the efficiency of the light-emitting diodes. However, two challenging issues exist in this research area. First, an inhomogeneous In distribution is initially formed by spinodal decomposition during device fabrication as revealed by transmission electron microscopy. Second, electron-beam irradiation during microscopy causes the compositional inhomogeneity of In to appear as a damage contrast. Here, a systematic approach was proposed in this study: Electron-beam with current density ranging from 0 to 20.9 A/cm{sup 2} was initially exposed to themore » surface regions during microscopy. Then, the electron-beam irradiated regions at the tip surface were further removed, and finally, atom probe tomography was performed to run the samples without beam-induced damage and to evaluate the existence of local inhomegenity of In atoms. We proved that after eliminating the electron-beam induced damage regions, no evidence of In clustering was observed in the blue-emitting InGaN/GaN devices. In addition, it is concluded that the electron-beam induced localization of In atoms is a surface-related phenomenon, and hence spinodal decomposition, which is typically responsible for such In clustering, is negligible for biaxially strained blue-emitting InGaN/GaN devices.« less

Correlative Energy-Dispersive X-Ray Spectroscopic Tomography and Atom Probe Tomography of the Phase Separation in an Alnico 8 Alloy.

PubMed

Guo, Wei; Sneed, Brian T; Zhou, Lin; Tang, Wei; Kramer, Matthew J; Cullen, David A; Poplawsky, Jonathan D

2016-12-01

Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology and volume fractions of Fe-Co-rich and Νi-Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2-4 nm Fe-rich α 1 phases that are nucleated in the Ni-rich α 2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. The complementary benefits and challenges associated with correlative STEM-EDS and APT are discussed.

Correlative Energy-Dispersive X-Ray Spectroscopic Tomography and Atom Probe Tomography of the Phase Separation in an Alnico 8 Alloy

DOE PAGES

Guo, Wei; Sneed, Brian T.; Zhou, Lin; ...

2016-12-21

Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology andmore » volume fractions of Fe–Co-rich and Νi–Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2–4 nm Fe-rich α 1 phases that are nucleated in the Ni-rich α 2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. Lastly, we discuss the complementary benefits and challenges associated with correlative STEM-EDS and APT.« less

Formation and Evolution of Target Patterns in Cahn-Hilliard Flows: An Extension of the Flux Expulsion Studies in MHD

NASA Astrophysics Data System (ADS)

Fan, Xiang; P H Diamond Collaboration; Luis Chacon Collaboration

2017-10-01

Spinodal decomposition is a second order phase transition for a binary liquid mixture to evolve from a miscible phase (e.g., water + alcohol) to two co-existing phases (e.g., water + oil). The Cahn-Hilliard model for spinodal decomposition is analogous to 2D MHD. We study the evolution of the concentration field in a single eddy in the 2D Cahn-Hilliard system to better understand scalar mixing processes in that system. This study extends investigations of the classic studies of flux expulsion in 2D MHD and homogenization of potential vorticity in 2D fluids. Simulation results show that there are three stages in the evolution: (A) formation of a ``jelly roll'' pattern, for which the concentration field is constant along spirals; (B) a change in isoconcentration contour topology; and (C) formation of a target pattern, for which the isoconcentration contours follow concentric annuli. In the final target pattern stage, the isoconcentration bands align with stream lines. The results indicate that the target pattern is a metastable state. Band merger process continues on a time scale exponentially long relative to the eddy turnover time. The band merger process resembles step merger in drift-ZF staircases. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Award Number DE-FG02-04ER54738.

The Power of Materials Science Tools for Gaining Insights into Organic Semiconductors

NASA Astrophysics Data System (ADS)

Treat, Neil D.; Westacott, Paul; Stingelin, Natalie

2015-07-01

The structure of organic semiconductors can be complex because features from the molecular level (such as molecular conformation) to the micrometer scale (such as the volume fraction and composition of phases, phase distribution, and domain size) contribute to the definition of the optoelectronic landscape of the final architectures and, hence, to device performance. As a consequence, a detailed understanding of how to manipulate molecular ordering, e.g., through knowledge of relevant phase transitions, of the solidification process, of relevant solidification mechanisms, and of kinetic factors, is required to induce the desired optoelectronic response. In this review, we discuss relevant structural features of single-component and multicomponent systems; provide a case study of the multifaceted structure that polymer:fullerene systems can adopt; and highlight relevant solidification mechanisms such as nucleation and growth, liquid-liquid phase separation, and spinodal decomposition. In addition, cocrystal formation, solid solutions, and eutectic systems are treated and their relevance within the optoelectronic area emphasized.

748 K (475 °C) Embrittlement of Duplex Stainless Steel: Effect on Microstructure and Fracture Behavior

NASA Astrophysics Data System (ADS)

Örnek, Cem; Burke, M. G.; Hashimoto, T.; Engelberg, D. L.

2017-04-01

22Cr-5Ni duplex stainless steel (DSS) was aged at 748 K (475 °C) and the microstructure development correlated to changes in mechanical properties and fracture behavior. Tensile testing of aged microstructures confirmed the occurrence of 748 K (475 °C) embrittlement, which was accompanied by an increase of strength and hardness and loss of toughness. Aging caused spinodal decomposition of the ferrite phase, consisting of Cr-enriched α″ and Fe-rich α' and the formation of a large number of R-phase precipitates, with sizes between 50 and 400 nm. Fracture surface analyses revealed a gradual change of the fracture mode from ductile to brittle delamination fracture, associated with slip incompatibility between ferrite and austenite. Ferrite became highly brittle after 255 hours of aging, mainly due to the presence of precipitates, while austenite was ductile and accommodated most plastic strain. The fracture mechanism as a function of 748 K (475 °C) embrittlement is discussed in light of microstructure development.

Thermoelectric Properties of Self Assembled TiO2/SnO2 Nanocomposites

NASA Technical Reports Server (NTRS)

Dynys, Fred; Sayir, Ali; Sehirlioglu, Alp

2008-01-01

Recent advances in improving efficiency of thermoelectric materials are linked to nanotechnology. Thermodynamically driven spinodal decomposition was utilized to synthesize bulk nanocomposites. TiO2/SnO2 system exhibits a large spinodal region, ranging from 15 to 85 mole % TiO2. The phase separated microstructures are stable up to 1400 C. Semiconducting TiO2/SnO2 powders were synthesized by solid state reaction between TiO2 and SnO2. High density samples were fabricated by pressureless sintering. Self assemble nanocomposites were achieved by annealing at 1000 to 1350 C. X-ray diffraction reveal phase separation of (Ti(x)Sn(1-x))O2 type phases. The TiO2/SnO2 nanocomposites exhibit n-type behavior; a power factor of 70 W/mK2 at 1000 C has been achieved with penta-valent doping. Seebeck, thermal conductivity, electrical resistivity and microstructure will be discussed in relation to composition and doping.

Thermoelectric Properties of Self Assemble TiO2/SnO2 Nanocomposites

NASA Technical Reports Server (NTRS)

Dynys, Fred; Sayir, Ali; Sehirlioglu, Alp

2008-01-01

Recent advances in improving efficiency of thermoelectric materials are linked to nanotechnology. Thermodynamically driven spinodal decomposition was utilized to synthesize bulk nanocomposites. TiO2/SnO2 system exhibits a large spinodal region, ranging from 15 to 85 mole % TiO2. The phase separated microstructures are stable up to 1400 C. Semiconducting TiO2/SnO2 powders were synthesized by solid state reaction between TiO2 and SnO2. High density samples were fabricated by pressureless sintering. Self assemble nanocomposites were achieved by annealing at 1000 to 1350 C. X-ray diffraction reveal phase separation of (Ti(x)Sn(1-x))O2 type phases. The TiO2/SnO2 nanocomposites exhibit n-type behavior; a power factor of 70 (mu)W/m sq K at 1000 C has been achieved with penta-valent doping. Seebeck, thermal conductivity, electrical resistivity and microstructure will be discussed in relation to composition and doping.

Microcanonical model for interface formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rucklidge, A.; Zaleski, S.

1988-04-01

We describe a new cellular automaton model which allows us to simulate separation of phases. The model is an extension of existing cellular automata for the Ising model, such as Q2R. It conserves particle number and presents the qualitative features of spinodal decomposition. The dynamics is deterministic and does not require random number generators. The spins exchange energy with small local reservoirs or demons. The rate of relaxation to equilibrium is investigated, and the results are compared to the Lifshitz-Slyozov theory.

Spatial and directional control of self-assembled wrinkle patterns by UV light absorption

NASA Astrophysics Data System (ADS)

Kortz, C.; Oesterschulze, E.

2017-12-01

Wrinkle formation on surfaces is a phenomenon that is observed in layered systems with a compressed elastic thin capping layer residing on a viscoelastic film. So far, the properties of the viscoelastic material could only be changed replacing it by another material. Here, we propose to use a photosensitive material whose viscoelastic properties, Young's modulus, and glass transition temperature can easily be adjusted by the absorption of UV light. Employing UV lithography masks during the exposure, we gain additionally spatial and directional control of the self-assembled wrinkle pattern formation that relies on a spinodal decomposition process. Inspired by the results on surface wrinkling and its dependence on the intrinsic stress, we also derive a method to avoid wrinkling locally by tailoring the mechanical stress distribution in the layered system choosing UV masks with convex patterns. This is of particular interest in technical applications where the buckling of surfaces is undesirable.

Effect of Secondary Phase Precipitation on the Corrosion Behavior of Duplex Stainless Steels

PubMed Central

Chan, Kai Wang; Tjong, Sie Chin

2014-01-01

Duplex stainless steels (DSSs) with austenitic and ferritic phases have been increasingly used for many industrial applications due to their good mechanical properties and corrosion resistance in acidic, caustic and marine environments. However, DSSs are susceptible to intergranular, pitting and stress corrosion in corrosive environments due to the formation of secondary phases. Such phases are induced in DSSs during the fabrication, improper heat treatment, welding process and prolonged exposure to high temperatures during their service lives. These include the precipitation of sigma and chi phases at 700–900 °C and spinodal decomposition of ferritic grains into Cr-rich and Cr-poor phases at 350–550 °C, respectively. This article gives the state-of the-art review on the microstructural evolution of secondary phase formation and their effects on the corrosion behavior of DSSs. PMID:28788129

Topology-generating interfacial pattern formation during liquid metal dealloying

DOE PAGES

Geslin, Pierre -Antoine; McCue, Ian; Gaskey, Bernard; ...

2015-11-19

Liquid metal dealloying has emerged as a novel technique to produce topologically complex nanoporous and nanocomposite structures with ultra-high interfacial area and other unique properties relevant for diverse material applications. This process is empirically known to require the selective dissolution of one element of a multicomponent solid alloy into a liquid metal to obtain desirable structures. However, how structures form is not known. Here we demonstrate, using mesoscale phase-field modelling and experiments, that nano/microstructural pattern formation during dealloying results from the interplay of (i) interfacial spinodal decomposition, forming compositional domain structures enriched in the immiscible element, and (ii) diffusion-coupled growthmore » of the enriched solid phase and the liquid phase into the alloy. We highlight how those two basic mechanisms interact to yield a rich variety of topologically disconnected and connected structures. Furthermore, we deduce scaling laws governing microstructural length scales and dealloying kinetics.« less

The BCC/B2 morphologies in Al xNiCoFeCr high-entropy alloys

DOE PAGES

Ma, Yue; Jiang, Beibei; Li, Chunling; ...

2017-02-15

Here, the present work primarily investigates the morphological evolution of the body-centered-cubic (BCC)/B2 phases in Al xNiCoFeCr high-entropy alloys (HEAs) with increasing Al content. It is found that the BCC/B2 coherent morphology is closely related to the lattice misfit between these two phases, which is sensitive to Al. There are two types of microscopic BCC/B2 morphologies in this HEA series: one is the weave-like morphology induced by the spinodal decomposition, and the other is the microstructure of a spherical disordered BCC precipitation on the ordered B2 matrix that appears in HEAs with a much higher Al content. The mechanical properties,more » including the compressive yielding strength and microhardness of the Al xNiCoFeCr HEAs, are also discussed in light of the concept of the valence electron concentration (VEC).« less

Topology-generating interfacial pattern formation during liquid metal dealloying.

PubMed

Geslin, Pierre-Antoine; McCue, Ian; Gaskey, Bernard; Erlebacher, Jonah; Karma, Alain

2015-11-19

Liquid metal dealloying has emerged as a novel technique to produce topologically complex nanoporous and nanocomposite structures with ultra-high interfacial area and other unique properties relevant for diverse material applications. This process is empirically known to require the selective dissolution of one element of a multicomponent solid alloy into a liquid metal to obtain desirable structures. However, how structures form is not known. Here we demonstrate, using mesoscale phase-field modelling and experiments, that nano/microstructural pattern formation during dealloying results from the interplay of (i) interfacial spinodal decomposition, forming compositional domain structures enriched in the immiscible element, and (ii) diffusion-coupled growth of the enriched solid phase and the liquid phase into the alloy. We highlight how those two basic mechanisms interact to yield a rich variety of topologically disconnected and connected structures. Moreover, we deduce scaling laws governing microstructural length scales and dealloying kinetics.

Low-Temperature Aging Characteristics of Type 316L Stainless Steel Welds: Dependence on Solidification Mode

NASA Astrophysics Data System (ADS)

Abe, Hiroshi; Watanabe, Yutaka

2008-06-01

Thermal aging embrittlement of light water reactor (LWR) components made of stainless steel cast has been recognized as a potential degradation issue, and careful attention has been paid to it. Although welds of austenitic stainless steels have γ-δ duplex microstructure, which is similar to that of the stainless steel cast, examination of the thermal aging characteristics of the stainless steel welds is very limited. In this investigation, two types of type 316L stainless steel weld metal with different solidification modes were prepared using two kinds of filler metals having tailored Ni equivalent and Cr equivalent. Differences between the two weld metals in the morphology of microstructure, in the composition of δ-ferrite, and in hardening behaviors with isothermal aging at 335 °C have been investigated. The hardness of the ferrite phase has increased with aging time, while the hardness of austenite phase has stayed the same. The mottled aspect has been observed in δ-ferrite of aged samples by transmission electron microscopy (TEM) observation. These characteristics suggest that spinodal decomposition has occurred in δ-ferrite by aging at 335 °C. The age-hardening rate of δ-ferrite was faster for the primary austenite solidification mode (AF mode) sample than the primary ferrite solidification mode (FA mode) sample in the initial stage of the aging up to 2000 hours. It has been suggested that the solidification mode can affect the kinetics of spinodal decomposition.

Stabilization of X–Au–X complexes on the Au(111) surface: A theoretical investigation and comparison of X = S, Cl, CH 3S, and SiH 3S

DOE PAGES

Lee, Jiyoung; Boschen, Jeffery S.; Windus, Theresa L.; ...

2017-01-27

Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology andmore » volume fractions of Fe–Co-rich and Νi–Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2–4 nm Fe-rich α 1 phases that are nucleated in the Ni-rich α 2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. The complementary benefits and challenges associated with correlative STEM-EDS and APT are discussed.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tucker, J. D.; Miller, M. K.; Young, G. A.

Duplex stainless steels are desirable for use in power generation systems due to their attractive combination of strength, corrosion resistance, and cost. However, thermal embrittlement at intermediate homologous temperatures of ~887°F (475°C) and below, via spinodal decomposition, limits upper service temperatures for many applications. New lean grade duplex alloys have improved thermal stability over standard grades and potentially increase the upper service temperature or the lifetime at a given temperature for this class of material. The present work compares the thermal stability of lean grade, alloy 2003 to standard grade, alloy 2205, through a series of isothermal agings between 500°Fmore » (260°C) and 900°F (482°C) for times between 1 and 10,000 hours. Aged samples were characterized by changes in microhardness and impact toughness. Additionally, atom probe tomography was performed to illustrate the evolution of the α-α' phase separation in both alloys at select conditions. Atom probe tomography confirmed that phase separation occurs via spinodal decomposition for both alloys and identified the formation of Ni-Cu-Si-Mn-P clusters in alloy 2205 that may contribute to embrittlement of this alloy. The impact toughness model predictions for upper service temperature show that alloy 2003 can be considered for use in 550°F applications for 80 year service lifetimes based on a Charpy V-notch criteria of 35 ft-lbs at 70°F. Alloy 2205 should be limited to 500°F applications.« less

Mechanical property degradation and microstructural evolution of cast austenitic stainless steels under short-term thermal aging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lach, Timothy G.; Byun, Thak Sang; Leonard, Keith J.

Mechanical testing and microstructural characterization were performed on short-term thermally aged cast austenitic stainless steels (CASS) to understand the severity and mechanisms of thermal-aging degradation experienced during extended operation of light water reactor (LWR) coolant systems. Four CASS materials – CF3, CF3M, CF8, and CF8M – were thermally aged for 1500 hours at 290 °C, 330 °C, 360 °C, and 400 °C. All four alloys experienced insignificant change in strength and ductility properties but a significant reduction in absorbed impact energy. The primary microstructural and compositional changes during thermal aging were spinodal decomposition of the δ-ferrite into α/ α`, precipitationmore » of G-phase in the δ-ferrite, segregation of solute to the austenite/ ferrite interphase boundary, and growth of M23C6 carbides on the austenite/ferrite interphase boundary. These changes were shown to be highly dependent on chemical composition, particularly the concentration of C and Mo, and aging temperature. A comprehensive model is being developed to correlate the microstructural evolution with mechanical behavior and simulation for predictive evaluations of LWR coolant system components.« less

A New Approach to Kinetics of Spinodal Decomposition in the Linear Regime.

DTIC Science & Technology

1980-08-28

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The solubility of hydrogen and deuterium in alloyed, unalloyed and impure plutonium metal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richmond, Scott; Bridgewater, Jon S; Ward, John W

2010-01-01

Hydrogen is exothermically absorbed in many transition metals, all rare earths and the actinides. The hydrogen gas adsorbs, dissociates and diffuses into these metals as atomic hydrogen. Absorbed hydrogen is generally detrimental to Pu, altering its properties and greatly enhancing corrosion. Measuring the heat of solution of hydrogen in Pu and its alloys provides significant insight into the thermodynamics driving these changes. Hydrogen is present in all Pu metal unless great care is taken to avoid it. Heats of solution and formation are provided along with evidence for spinodal decomposition.

A high-resolution analytical scanning transmission electron microscopy study of the early stages of spinodal decomposition in binary Fe–Cr

DOE Office of Scientific and Technical Information (OSTI.GOV)

Westraadt, J.E., E-mail: johan.westraadt@nmmu.ac.za; Olivier, E.J.; Neethling, J.H.

2015-11-15

Spinodal decomposition (SD) is an important phenomenon in materials science and engineering. For example, it is considered to be responsible for the 475 °C embrittlement of stainless steels comprising the bcc (ferrite) or bct (martensite) phases. Structural characterization of the evolving minute nano-scale concentration fluctuations during SD in the Fe–Cr system is, however, a notable challenge, and has mainly been considered accessible via atom probe tomography (APT) and small-angle neutron scattering. The standard tool for nanostructure characterization, viz. transmission electron microscopy (TEM), has only been successfully applied to late stages of SD when embrittlement is already severe. However, we heremore » demonstrate that the structural evolution in the early stages of SD in binary Fe–Cr, and alloys based on the binary, are accessible via analytical scanning TEM. An Fe–36 wt% Cr alloy aged at 500 °C for 1, 10 and 100 h is investigated using an aberration-corrected microscope and it is found that highly coherent and interconnected Cr-rich regions develop. The wavelength of decomposition is rather insensitive to the sample thickness and it is quantified to 2, 3 and 6 nm after ageing for 1, 10 and 100 h, which is in reasonable agreement with prior APT analysis. The concentration amplitude is more sensitive to the sample thickness and acquisition parameters but the TEM analysis is in good agreement with APT analysis for the longest ageing time. These findings open up for combinatorial TEM studies where both local crystallography and chemistry is required. - Highlights: • STEM-EELS analysis was successfully applied to resolve early stage SD in Fe–Cr. • Compositional wavelength measured with STEM-EELS compares well to previous ATP studies. • Compositional amplitude measured with STEM-EELS is a function of experimental parameters. • STEM-EELS allows for combinatorial studies of SD using complementary techniques.« less

Assessment of thermal embrittlement in duplex stainless steels 2003 and 2205 for nuclear power applications

DOE PAGES

Tucker, J. D.; Miller, M. K.; Young, G. A.

2015-04-01

Duplex stainless steels are desirable for use in power generation systems due to their attractive combination of strength, corrosion resistance, and cost. However, thermal embrittlement at intermediate homologous temperatures of ~887°F (475°C) and below, via spinodal decomposition, limits upper service temperatures for many applications. New lean grade duplex alloys have improved thermal stability over standard grades and potentially increase the upper service temperature or the lifetime at a given temperature for this class of material. The present work compares the thermal stability of lean grade, alloy 2003 to standard grade, alloy 2205, through a series of isothermal agings between 500°Fmore » (260°C) and 900°F (482°C) for times between 1 and 10,000 hours. Aged samples were characterized by changes in microhardness and impact toughness. Additionally, atom probe tomography was performed to illustrate the evolution of the α-α' phase separation in both alloys at select conditions. Atom probe tomography confirmed that phase separation occurs via spinodal decomposition for both alloys and identified the formation of Ni-Cu-Si-Mn-P clusters in alloy 2205 that may contribute to embrittlement of this alloy. The impact toughness model predictions for upper service temperature show that alloy 2003 can be considered for use in 550°F applications for 80 year service lifetimes based on a Charpy V-notch criteria of 35 ft-lbs at 70°F. Alloy 2205 should be limited to 500°F applications.« less

Random scalar fields and hyperuniformity

NASA Astrophysics Data System (ADS)

Ma, Zheng; Torquato, Salvatore

2017-06-01

Disordered many-particle hyperuniform systems are exotic amorphous states of matter that lie between crystals and liquids. Hyperuniform systems have attracted recent attention because they are endowed with novel transport and optical properties. Recently, the hyperuniformity concept has been generalized to characterize two-phase media, scalar fields, and random vector fields. In this paper, we devise methods to explicitly construct hyperuniform scalar fields. Specifically, we analyze spatial patterns generated from Gaussian random fields, which have been used to model the microwave background radiation and heterogeneous materials, the Cahn-Hilliard equation for spinodal decomposition, and Swift-Hohenberg equations that have been used to model emergent pattern formation, including Rayleigh-Bénard convection. We show that the Gaussian random scalar fields can be constructed to be hyperuniform. We also numerically study the time evolution of spinodal decomposition patterns and demonstrate that they are hyperuniform in the scaling regime. Moreover, we find that labyrinth-like patterns generated by the Swift-Hohenberg equation are effectively hyperuniform. We show that thresholding (level-cutting) a hyperuniform Gaussian random field to produce a two-phase random medium tends to destroy the hyperuniformity of the progenitor scalar field. We then propose guidelines to achieve effectively hyperuniform two-phase media derived from thresholded non-Gaussian fields. Our investigation paves the way for new research directions to characterize the large-structure spatial patterns that arise in physics, chemistry, biology, and ecology. Moreover, our theoretical results are expected to guide experimentalists to synthesize new classes of hyperuniform materials with novel physical properties via coarsening processes and using state-of-the-art techniques, such as stereolithography and 3D printing.

Dynamic light scattering study on phase separation of a protein-water mixture: Application on cold cataract development in the ocular lens

NASA Astrophysics Data System (ADS)

Petta, V.; Pharmakakis, N.; Papatheodorou, G. N.; Yannopoulos, S. N.

2008-06-01

We present a detailed dynamic light scattering study of the phase separation in the ocular lens emerging during cold cataract development. Cold cataract is a phase separation effect that proceeds via spinodal decomposition of the lens cytoplasm with cooling. The intensity autocorrelation functions of the lens protein content are analyzed with the aid of two methods, providing information on the populations and dynamics of the scattering elements associated with cold cataract. It is found that the temperature dependence of many measurable parameters changes appreciably at the characteristic temperature ˜16±1°C which is associated with the onset of cold cataract. By extending the temperature range of this work to previously inaccessible regimes, i.e., well below the phase separation or coexistence curve at Tcc , we have been able to accurately determine the temperature dependence of the collective and self-diffusion coefficients of proteins near the spinodal. The analysis showed that the dynamics of proteins bears some resemblance to the dynamics of structural glasses, where the apparent activation energy for particle diffusion increases below Tcc , indicating a highly cooperative motion. Application of ideas developed for studying the critical dynamics of binary protein-solvent mixtures, as well as the use of a modified Arrhenius equation, enabled us to estimate the spinodal temperature Tsp of the lens nucleus. The applicability of dynamic light scattering as a noninvasive, early-diagnostic tool for ocular diseases is also demonstrated in light of the findings of the present paper.

Effect of Substrate Wetting on the Morphology and Dynamics of Phase Separating Multi-Component Mixture

NASA Astrophysics Data System (ADS)

Goyal, Abheeti; Toschi, Federico; van der Schoot, Paul

2017-11-01

We study the morphological evolution and dynamics of phase separation of multi-component mixture in thin film constrained by a substrate. Specifically, we have explored the surface-directed spinodal decomposition of multicomponent mixture numerically by Free Energy Lattice Boltzmann (LB) simulations. The distinguishing feature of this model over the Shan-Chen (SC) model is that we have explicit and independent control over the free energy functional and EoS of the system. This vastly expands the ambit of physical systems that can be realistically simulated by LB simulations. We investigate the effect of composition, film thickness and substrate wetting on the phase morphology and the mechanism of growth in the vicinity of the substrate. The phase morphology and averaged size in the vicinity of the substrate fluctuate greatly due to the wetting of the substrate in both the parallel and perpendicular directions. Additionally, we also describe how the model presented here can be extended to include an arbitrary number of fluid components.

Solid-liquid and liquid-solid transitions in metal nanoparticles.

PubMed

Hou, M

2017-02-22

The melting and solidification temperatures of nanosystems may differ by several hundred Kelvin. To understand the origin of this difference, transitions in small metallic nanoparticles on the atomic scale were analyzed using molecular dynamics (MD). Palladium was used as a case study, which was then extended to a range of other elemental metals. It was argued that in realistic environments, such as gases at low pressure (of the order of 1 mbar), heat transfers allow the microcanonical thermal equilibrium evolution of the nanoparticles between successive collisions with gas atoms. This is shown to have no significant influence on the mechanism of melting, whereas in an isolated nanoparticle, solidification triggers a huge and rapid increase in temperature. A simple relationship between the melting and solidification temperatures was found, indicating that the magnitude of the latent heat of melting governs undercooling. Whereas melting occurs via heterogeneous nucleation, solidification displays characteristics of spinodal decomposition. Consistently, the melting temperature scales with the surface-to-volume ratio, whereas the solidification temperature displays no significant dependence on the particle size.

Vitrification and gelation in sticky spheres

NASA Astrophysics Data System (ADS)

Royall, C. Patrick; Williams, Stephen R.; Tanaka, Hajime

2018-01-01

Glasses and gels are the two dynamically arrested, disordered states of matter. Despite their importance, their similarities and differences remain elusive, especially at high density, where until now it has been impossible to distinguish them. We identify dynamical and structural signatures which distinguish the gel and glass transitions in a colloidal model system of hard and "sticky" spheres. It has been suggested that "spinodal" gelation is initiated by gas-liquid viscoelastic phase separation to a bicontinuous network and the resulting densification leads to vitrification of the colloid-rich phase, but whether this phase has sufficient density for arrest is unclear [M. A. Miller and D. Frenkel, Phys. Rev. Lett. 90, 135702 (2003) and P. J. Lu et al., Nature 435, 499-504 (2008)]. Moreover alternative mechanisms for arrest involving percolation have been proposed [A. P. R. Eberle et al., Phys. Rev. Lett. 106, 105704 (2011)]. Here we resolve these outstanding questions, beginning by determining the phase diagram. This, along with demonstrating that percolation plays no role in controlling the dynamics of our system, enables us to confirm spinodal decomposition as the mechanism for gelation. We are then able to show that gels can be formed even at much higher densities than previously supposed, at least to a volume fraction of ϕ = 0.59. Far from being networks, these gels apparently resemble glasses but are still clearly distinguished by the "discontinuous" nature of the transition and the resulting rapid solidification, which leads to the formation of inhomogeneous (with small voids) and far-from-equilibrium local structures. This is markedly different from the glass transition, whose continuous nature leads to the formation of homogeneous and locally equilibrated structures. We further reveal that the onset of the attractive glass transition in the form of a supercooled liquid is in fact interrupted by gelation. Our findings provide a general thermodynamic, dynamic, and structural basis upon which we can distinguish gelation from vitrification.

Using the Binary Phase-Field Crystal Model to Describe Non-Classical Nucleation Pathways in Gold Nanoparticles

NASA Astrophysics Data System (ADS)

Smith, Nathan; Provatas, Nikolas

Recent experimental work has shown that gold nanoparticles can precipitate from an aqueous solution through a non-classical, multi-step nucleation process. This multi-step process begins with spinodal decomposition into solute-rich and solute-poor liquid domains followed by nucleation from within the solute-rich domains. We present a binary phase-field crystal theory that shows the same phenomology and examine various cross-over regimes in the growth and coarsening of liquid and solid domains. We'd like to the thank Canada Research Chairs (CRC) program for funding this work.

Coherent and incoherent phase stabilities of thermoelectric rocksalt IV-VI semiconductor alloys

NASA Astrophysics Data System (ADS)

Doak, Jeff W.; Wolverton, C.

2012-10-01

Nanostructures formed by phase separation improve the thermoelectric figure of merit in lead chalcogenide semiconductor alloys, with coherent nanostructures giving larger improvements than incoherent nanostructures. However, large coherency strains in these alloys drastically alter the thermodynamics of phase stability. Incoherent phase stability can be easily inferred from an equilibrium phase diagram, but coherent phase stability is more difficult to assess experimentally. Therefore, we use density functional theory calculations to investigate the coherent and incoherent phase stability of the IV-VI rocksalt semiconductor alloy systems Pb(S,Te), Pb(Te,Se), Pb(Se,S), (Pb,Sn)Te, (Sn,Ge)Te, and (Ge,Pb)Te. Here we use the term coherent to indicate that there is a common and unbroken lattice between the phases under consideration, and we use the term incoherent to indicate that the lattices of coexisting phases are unconstrained and allowed to take on equilibrium volumes. We find that the thermodynamic ground state of all of the IV-VI pseudobinary systems studied is incoherent phase separation. We also find that the coherency strain energy, previously neglected in studies of these IV-VI alloys, is lowest along [111] (in contrast to most fcc metals) and is a large fraction of the thermodynamic driving force for incoherent phase separation in all systems. The driving force for coherent phase separation is significantly reduced, and we find that coherent nanostructures can only form at low temperatures where kinetics may prohibit their precipitation. Furthermore, by calculating the energies of ordered structures for these systems we find that the coherent phase stability of most IV-VI systems favors ordering over spinodal decomposition. Our results suggest that experimental reports of spinodal decomposition in the IV-VI rocksalt alloys should be re-examined.

Coherency strain engineered decomposition of unstable multilayer alloys for improved thermal stability

NASA Astrophysics Data System (ADS)

Forsén, R.; Ghafoor, N.; Odén, M.

2013-12-01

A concept to improve hardness and thermal stability of unstable multilayer alloys is presented based on control of the coherency strain such that the driving force for decomposition is favorably altered. Cathodic arc evaporated cubic TiCrAlN/Ti1-xCrxN multilayer coatings are used as demonstrators. Upon annealing, the coatings undergo spinodal decomposition into nanometer-sized coherent Ti- and Al-rich cubic domains which is affected by the coherency strain. In addition, the growth of the domains is restricted by the surrounding TiCrN layer compared to a non-layered TiCrAlN coating which together results in an improved thermal stability of the cubic structure. A significant hardness increase is seen during decomposition for the case with high coherency strain while a low coherency strain results in a hardness decrease for high annealing temperatures. The metal diffusion paths during the domain coarsening are affected by strain which in turn is controlled by the Cr-content (x) in the Ti1-xCrxN layers. For x = 0 the diffusion occurs both parallel and perpendicular to the growth direction but for x > =0.9 the diffusion occurs predominantly parallel to the growth direction. Altogether this study shows a structural tool to alter and fine-tune high temperature properties of multicomponent materials.

Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing

PubMed Central

Li, Ning; Perea, José Darío; Kassar, Thaer; Richter, Moses; Heumueller, Thomas; Matt, Gebhard J.; Hou, Yi; Güldal, Nusret S.; Chen, Haiwei; Chen, Shi; Langner, Stefan; Berlinghof, Marvin; Unruh, Tobias; Brabec, Christoph J.

2017-01-01

The performance of organic solar cells is determined by the delicate, meticulously optimized bulk-heterojunction microstructure, which consists of finely mixed and relatively separated donor/acceptor regions. Here we demonstrate an abnormal strong burn-in degradation in highly efficient polymer solar cells caused by spinodal demixing of the donor and acceptor phases, which dramatically reduces charge generation and can be attributed to the inherently low miscibility of both materials. Even though the microstructure can be kinetically tuned for achieving high-performance, the inherently low miscibility of donor and acceptor leads to spontaneous phase separation in the solid state, even at room temperature and in the dark. A theoretical calculation of the molecular parameters and construction of the spinodal phase diagrams highlight molecular incompatibilities between the donor and acceptor as a dominant mechanism for burn-in degradation, which is to date the major short-time loss reducing the performance and stability of organic solar cells. PMID:28224984

Path-integral simulation of ice Ih: The effect of pressure

NASA Astrophysics Data System (ADS)

Herrero, Carlos P.; Ramírez, Rafael

2011-12-01

The effect of pressure on structural and thermodynamic properties of ice Ih has been studied by means of path-integral molecular dynamics simulations at temperatures between 50 and 300 K. Interatomic interactions were modeled by using the effective q-TIP4P/F potential for flexible water. Positive (compression) and negative (tension) pressures have been considered, which allowed us to approach the limits for the mechanical stability of this solid water phase. We have studied the pressure dependence of the crystal volume, bulk modulus, interatomic distances, atomic delocalization, and kinetic energy. The spinodal point at both negative and positive pressures is derived from the vanishing of the bulk modulus. For P<0, the spinodal pressure changes from -1.38 to - 0.73 GPa in the range from 50 to 300 K. At positive pressure the spinodal is associated with ice amorphization, and at low temperatures it is found to be between 1.1 and 1.3 GPa. Quantum nuclear effects cause a reduction of the metastability region of ice Ih.

DE-NE0000724 - Research Performance Final Report - Investigation of Thermal Aging Effects on the Evolution of Microstructure and Mechanical Properties of Cast Duplex Stainless Steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ankem, Sreeramamurthy; Perea, Daniel E.; Kolli, R. Prakash

This report details the research activities carried out under DOE-NEUP award number DE-NE0000724 concerning the evolution of structural and mechanical properties during thermal aging of CF–3 and CF–8 cast duplex stainless steels (CDSS). The overall objective of this project was to use state-of-the-art characterization techniques to elucidate trends and phenomena in the mechanical and structural evolution of cast duplex stainless steels (CDSS) during thermal aging. These steels are commonly used as structural materials in commercial light water nuclear power plants, undergoing aging for decades in operation as cooling water pipes, pump casings, valve bodies, etc. During extended exposure to thesemore » conditions, CDSS are known to undergo a change in mechanical properties resulting in a loss of ductility, i.e. embrittlement. While it is generally accepted that structural changes within the ferrite phase, such as decomposition into iron (Fe)-rich and chromium (Cr)-rich domains, lead to the bulk embrittlement of the steels, many questions remain as to the mechanisms of embrittlement at multiple length scales. This work is intended to shed insight into the atomic level composition changes, associated kinetic mechanisms, and effects of changing phase structure on micro- and nano-scale deformation that lead to loss of impact toughness and tensile ductility in these steels. In general, this project provides a route to answer some of these major questions using techniques such as 3-dimensional (3-D) atom probe tomography (APT) and real-microstructure finite element method (FEM) modeling, which were not readily available when these steels were originally selected for service in light water reactors. Mechanical properties evaluated by Charpy V-notch impact testing (CVN), tensile testing, and microhardness and nanohardness measurements were obtained for each condition and compared with the initial baseline properties to view trends in deformation behavior during aging. Concurrent analysis of the microstructure and nanostructure by atom probe tomography (APT) and transmission electron microscopy (TEM) provide mechanistic insight into the kinetic and mechanical behavior occurring on the nano-scale. The presence and morphology of the ferrite, austenite, and carbide phases have been characterized, and formation of new phases during aging, including spinodal decomposition products (α- and α'-ferrite) and G-phase, have been observed. The mechanical and structural characterization have been used to create accurate FEM models based on the real micro- and nano-structures of the systems. These models provide new insight into the local deformation behavior of these steels and the effects of each individual phase (including ferrite, austenite, carbides, and spinodal decomposition products) on the evolving bulk mechanical behavior of the system. The project was divided into three major tasks: 1. Initial Microstructure and Mechanical Property Survey and Initiate Heat Treatment; 2. Microstructural Characterization and Mechanical Property Testing During Aging; and 3. Microstructure-based Finite Element Modeling. Each of these tasks was successfully executed, resulting in reliable data and analysis that add to the overall body of work on the CDSS materials. Baseline properties and aging trends in mechanical data confirm prior observations and add new insights into the mechanical behavior of the steels. Structural characterization on multiple length scales provides new information on phase changes occurring during aging and sheds light on the kinetic processes occurring at the atomic scale. Furthermore, a combination of mechanical testing and microstructural characterization techniques was utilized to design FEM models of local deformation behavior of the ferrite and austenite phases, providing valuable new information regarding the effects of each of the microstructural components on the hardening and embrittlement processes. The data and analysis presented in this report and the publication associated with this project (§V) increase the understanding of aging and deformation in CF–3 and CF–8 steels. These results provide valuable information that can be utilized to aid in making informed decisions regarding the ongoing use of these steels in commercial nuclear infrastructure.« less

Unconditionally stable, second-order accurate schemes for solid state phase transformations driven by mechano-chemical spinodal decomposition

DOE PAGES

Sagiyama, Koki; Rudraraju, Shiva; Garikipati, Krishna

2016-09-13

Here, we consider solid state phase transformations that are caused by free energy densities with domains of non-convexity in strain-composition space; we refer to the non-convex domains as mechano-chemical spinodals. The non-convexity with respect to composition and strain causes segregation into phases with different crystal structures. We work on an existing model that couples the classical Cahn-Hilliard model with Toupin’s theory of gradient elasticity at finite strains. Both systems are represented by fourth-order, nonlinear, partial differential equations. The goal of this work is to develop unconditionally stable, second-order accurate time-integration schemes, motivated by the need to carry out large scalemore » computations of dynamically evolving microstructures in three dimensions. We also introduce reduced formulations naturally derived from these proposed schemes for faster computations that are still second-order accurate. Although our method is developed and analyzed here for a specific class of mechano-chemical problems, one can readily apply the same method to develop unconditionally stable, second-order accurate schemes for any problems for which free energy density functions are multivariate polynomials of solution components and component gradients. Apart from an analysis and construction of methods, we present a suite of numerical results that demonstrate the schemes in action.« less

Giant-Magnetoresistance(GMR) Siegel KEY FIRST Experimental Discovery Decade-Earlier PRE-``Fert"-``Gruenberg" in Nuc"el"ar ``Super"alloys: Science?;``SEANCE!!!; Ethics?; SHMETHICS!!!

NASA Astrophysics Data System (ADS)

Hoffman, R.; Siegel, E.

2010-03-01

(So MIScalled) ``Fert"-``Grunberg"[PRL(1988;1989)] GMR 2007 physics Nobel/Wolf/Japan-Prizes VS. decade-earlier(1973-1977) KEY FIRST Siegel at:Westin"kl"ouse/PSEG/IAEA/ABB[google:``Martin Ebner"(94-04) in financial media]/Vattenfall/Wallenbergs/nuc"el"ar-DoE Labs[at flickr.com, search on ``Giant- Magnotoresistance''; find: Intl.Conf.Mag.Alloys & Oxides(ICMAO), Haifa(Aug./1977); J.Mag.Mag.Mtls,(JMMM)7,312(1978)``unavailable: not yet scanned''/modified(last R(H) GMR Figs(7;8) deleted!!!) on JMMM/Reed-Elsevier website until 7/29/08 conveniently one- half-year after last (Nobel)award(12/2007); conveniently effectively deleted!!!; google: ``If Leaks Could Kill''; many APS/MRS Mtgs(1970s)<<<1988/1989] decade-earlier GMR: (1978)<<< (1988); 1988-1978 =10 years = one full decadeprecedence!!!] first experimental discovery in (so MIScalled) ``super''alloys [182/82, Hastelloy-X, 600, 690(!!!), Stainless-Steels: ANY/ALL!!!] generic endemic Wigner's[JAP,17,857(1946)]- disease/Ostwald-ripening/spinodal-decomposition/overageing- embrittlement/ thermo-mechanical-INstability!

Dewetting of thin polymer films: an X-ray scattering study

NASA Astrophysics Data System (ADS)

Müller-Buschbaum, P.; Stamm, M.

1998-06-01

The surface morphology of different dewetting states of thin polymer films (polystyrene) on top of silicon substrates was investigated. With diffuse X-ray scattering in the region of total external reflection a high in-plane resolution was achieved. We observe a new nano-dewetting structure which coexists with the well known mesoscopic dewetting structures of holes, cellular pattern and drops. This nano-dewetting structure consists of small dimples with a diameter in the nanometer range. It results from the dewetting of a remaining ultra-thin polymer layer and can be explained with theoretical predictions of spinodal decomposition. The experimental results of the scattering study are confirmed with scanning-force microscopy measurements.

Simulation of alnico coercivity

DOE PAGES

Ke, Liqin; Skomski, Ralph; Hoffmann, Todd D.; ...

2017-07-10

Micromagnetic simulations of alnico show substantial deviations from Stoner-Wohlfarth behavior due to the unique size and spatial distribution of the rod-like Fe-Co phase formed during spinodal decomposition in an external magnetic field. Furthemore, the maximum coercivity is limited by single-rod effects, especially deviations from ellipsoidal shape, and by interactions between the rods. In both the exchange interaction between connected rods and magnetostatic we consider the interaction between rods, and the results of our calculations show good agreement with recent experiments. Unlike systems dominated by magnetocrystalline anisotropy, coercivity in alnico is highly dependent on size, shape, and geometric distribution of themore » Fe-Co phase, all factors that can be tuned with appropriate chemistry and thermal-magnetic annealing.« less

Phase stability in thermally-aged CASS CF8 under heavy ion irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Meimei; Miller, Michael K.; Chen, Wei-Ying

2015-07-01

The stability of the microstructure of a cast austenitic stainless steel (CASS), before and after heavy ion irradiation, was investigated by atom probe tomography (APT). A CF8 ferrite–austenite duplex alloy was thermally aged at 400 °C for 10,000 h. After this treatment, APT revealed nanometer-sized G-phase precipitates and Fe-rich α and Cr-enriched α' phase separated regions in the ferrite. The thermally-aged CF8 specimen was irradiated with 1 MeV Kr ions to a fluence of 1.88 × 10 19 ions/m 2 at 400 °C. After irradiation, APT analysis revealed a strong spatial/dose dependence of the G-phase precipitates and the α–α' spinodalmore » decomposition in the ferrite. For the G-phase precipitates, the number density increased and the mean size decreased with increasing dose, and the particle size distribution changed considerably under irradiation. The inverse coarsening process can be described by recoil resolution. The amplitude of the α–α' spinodal decomposition in the ferrite was apparently reduced after heavy ion irradiation.« less

On the fine structure of meteoritical taenite/tetrataenite and its interpretation

NASA Astrophysics Data System (ADS)

Albertsen, J. F.; Nielsen, H. P.; Buchwald, V. F.

1983-04-01

TEM, electron microprobe, and Moessbauer spectroscopy are used in investigating taenite fields from several meteorites. A delicate pattern of antiphase domains is revealed in the tetrataenite, as is the presence of low-Ni taenite at the antiphase boundaries in what was hitherto believed to be pure tetrataenite. The observations suggest that the 'cloudy taenite' (cloudy zone II) was formed by a magnetically induced spinodal decomposition of the metastable taenite during slow cooling below 400 C. It is thought likely that decompositin occurs when the Curie temperature of the alloy changes rapidly with composition, as it does in f.c.c. iron-nickel alloys containing approximately 28-43 percent Ni (wt pct). The large contribution to Gibbs free energy from magnetic ordering leads to inflections in the Gibbs free energy curve, making the alloy unstable with regard to decomposition, in this case into a magnetically and atomically ordered Ni-rich alloy plus a magnetically and atomically disordered Ni-poor alloy. The model accounts well for the structure and composition of the two phases in the cloudy taenite.

A theoretical investigation of mixing thermodynamics, age-hardening potential, and electronic structure of ternary M11–xM2xB2 alloys with AlB2 type structure

PubMed Central

Alling, B.; Högberg, H.; Armiento, R.; Rosen, J.; Hultman, L.

2015-01-01

Transition metal diborides are ceramic materials with potential applications as hard protective thin films and electrical contact materials. We investigate the possibility to obtain age hardening through isostructural clustering, including spinodal decomposition, or ordering-induced precipitation in ternary diboride alloys. By means of first-principles mixing thermodynamics calculations, 45 ternary M11–xM2xB2 alloys comprising MiB2 (Mi = Mg, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta) with AlB2 type structure are studied. In particular Al1–xTixB2 is found to be of interest for coherent isostructural decomposition with a strong driving force for phase separation, while having almost concentration independent a and c lattice parameters. The results are explained by revealing the nature of the electronic structure in these alloys, and in particular, the origin of the pseudogap at EF in TiB2, ZrB2, and HfB2. PMID:25970763

FRAUD/SABOTAGE Killing Nuclear-Reactors Need Modeling!!!: "Super"alloys GENERIC ENDEMIC Wigner's-Disease/.../IN-stability: Ethics? SHMETHICS!!!

NASA Astrophysics Data System (ADS)

Asphahani, Aziz; Siegel, Sidney; Siegel, Edward

2010-03-01

Carbides solid-state chemistry domination of old/new nuclear- reactors/spent-fuel-casks/refineries/jet/missile/rocket-engines in austenitic/FCC Ni/Fe-based(so miscalled)``super"alloys(182/82; Hastelloy-X,600,304/304L-SSs,...,690!!!) GENERIC ENDEMIC EXTANT detrimental(synonyms): Wigner's-diseas(WD)[J.Appl.Phys.17,857 (1946)]/Ostwald-ripening/spinodal-decomposition/overageing- embrittlement/thermal-leading-to-mechanical(TLTM)-INstability: Mayo[Google:``If Leaks Could Kill"; at flickr.com search on ``Giant-Magnotoresistance"; find: Siegel[J.Mag.Mag.Mtls.7,312 (1978)]<<<``Fert"-"Gruenberg"(1988/89)2007-physics Nobel/Wolf/ Japan-prizes]necessitating NRC-inspections of 40+25 = 65 Westin- ``KLouse PWRs(12/2006)]-Lai[Met.Trans.AIME,9A,827(1978)]-Sabol- Stickler[Phys.Stat.Sol.(1970)]-Ashpahani[Intl.Conf. H in Metals, Paris(1977]-Russell[Prog.Mtls.Sci.(1983)]-Pollard[last UCS rept. (9/1995)]-Lofaro[BNL/DOE/NRC Repts.]-Pringle[Nuclear-Power:From Physics to Politics(1979)]-Hoffman[animatedsoftware.com], what DOE/NRC MISlabels as ``butt-welds" ``stress-corrosion cracking" endpoint's ROOT-CAUSE ULTIMATE-ORIGIN is WD overageing-embritt- lement caused brittle-fracture cracking from early/ongoing AEC/ DOE-n"u"tional-la"v"atories sabotage!!!

FRAUD/SABOTAGE Killing Nuclear-Reactors Need Modeling!!!: ``Super'' alloys GENERIC ENDEMIC Wigner's-Disease/.../IN-stability: Ethics? SHMETHICS!!!

NASA Astrophysics Data System (ADS)

O'Grady, Joseph; Bument, Arlden; Siegel, Edward

2011-03-01

Carbides solid-state chemistry domination of old/new nuclear-reactors/spent-fuel-casks/refineries/jet/missile/rocket-engines is austenitic/FCC Ni/Fe-based (so miscalled)"super"alloys(182/82;Hastelloy-X,600,304/304L-SSs,...690!!!) GENERIC ENDEMIC EXTANT detrimental(synonyms): Wigner's-disease(WD) [J.Appl.Phys.17,857 (46)]/Ostwald-ripening/spinodal-decomposition/overageing-embrittlement/thermal-leading-to-mechanical(TLTM)-INstability: Mayo[Google: fLeaksCouldKill > ; - Siegel [ J . Mag . Mag . Mtls . 7 , 312 (78) = atflickr . comsearchonGiant - Magnotoresistance [Fert" [PRL(1988)]-"Gruenberg"[PRL(1989)] 2007-Nobel]necessitating NRC inspections on 40+25=65 Westin"KL"ouse PWRs(12/2006)]-Lai [Met.Trans.AIME, 9A,827(78)]-Sabol-Stickler[Phys.Stat.Sol.(70)]-Ashpahani[ Intl.Conf. Hydrogen in Metals, Paris(1977]-Russell [Prog.Mtls.Sci.(1983)]-Pollard [last UCS rept.(9/1995)]-Lofaro [BNL/DOE/NRC Repts.]-Pringle [ Nuclear-Power:From Physics to Politics(1979)]-Hoffman [animatedsoftware.com], what DOE/NRC MISlabels as "butt-welds" "stress-corrosion cracking" endpoint's ROOT-CAUSE ULTIMATE-ORIGIN is WD overageing-embrittlement caused brittle-fracture cracking from early/ongoing AEC/DOE-n"u"tional-la"v"atories sabotage!!!

Spinodals with Disorder: From Avalanches in Random Magnets to Glassy Dynamics

NASA Astrophysics Data System (ADS)

Nandi, Saroj Kumar; Biroli, Giulio; Tarjus, Gilles

2016-04-01

We revisit the phenomenon of spinodals in the presence of quenched disorder and develop a complete theory for it. We focus on the spinodal of an Ising model in a quenched random field (RFIM), which has applications in many areas from materials to social science. By working at zero temperature in the quasistatically driven RFIM, thermal fluctuations are eliminated and one can give a rigorous content to the notion of spinodal. We show that the latter is due to the depinning and the subsequent expansion of rare droplets. We work out the associated critical behavior, which, in any finite dimension, is very different from the mean-field one: the characteristic length diverges exponentially and the thermodynamic quantities display very mild nonanalyticities much like in a Griffith phenomenon. From the recently established connection between the spinodal of the RFIM and glassy dynamics, our results also allow us to conclusively assess the physical content and the status of the dynamical transition predicted by the mean-field theory of glass-forming liquids.

Temperature dependence of the magneto-controllable first-order phase transition in dilute magnetic fluids

NASA Astrophysics Data System (ADS)

Ivanov, A. S.

2017-11-01

Experimental study was carried out to investigate the influence of particle size distribution function on the temperature dependent magneto-controllable first-order phase transition of the "gas-liquid" type in magnetic fluids. The study resolves one crisis situation in ferrohydrodynamic experiment made by several research groups in the 1980-1990s. It is shown that due to polydispersity magnetic fluids exhibit phase diagrams which are divided into three regions by vaporus and liquidus curves. Granulometric data states the primary role of the width of the particle size distribution function in the process of spinodal decomposition. New modified Langevin parameter is introduced for unification of liquidus curves of different ferrofluids despite the significant difference between the curves (one order of magnitude) in (H, T) coordinates.

Hydrodynamic fluctuations, nonequilibrium equations of state, and the shift of the spinodal line in polymer solutions under flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Criado-Sancho, M.; Casas-Vazquez, J.; Jou, D.

1997-08-01

In the literature, the shift of the spinodal line of polymer solutions under flow is attributed either to an actual shift of the spinodal due to a nonequilibrium modification of the equation of state for the chemical potential, or to an apparent shift due to an increase of hydrodynamic fluctuations owing to the flow. Here we see that both approaches are compatible and that both effects add up. {copyright} {ital 1997} {ital The American Physical Society}

Mechanically modulated dewetting by atomic force microscope for micro- and nano- droplet array fabrication.

PubMed

Wang, Feifei; Li, Pan; Wang, Dong; Li, Longhai; Xie, Shuangxi; Liu, Lianqing; Wang, Yuechao; Li, Wen Jung

2014-10-06

Organizing a material into well-defined patterns during the dewetting process provides an attractive micro-/nano-fabrication method without using a conventional lithographic process, and hence, offers potential applications in organic electronics, optics systems, and memory devices. We report here how the mechanical modification of polymer surface by an Atomic Force Microscope (AFM) can be used to guide thin film dewetting evolution and break the intrinsic spatial correlation of spontaneous instability. An AFM is used to implement the mechanical modification of progressively narrow grids to investigate the influence of pattern size on the modulation of ultrathin polystyrene films dewetting evolution. For films with different initial thicknesses, when grid size is close to or below the characteristic wavelength of instability, the spinodal dewetting is suppressed, and film rupture is restricted to the cutting trench. We will show in this paper it is possible to generate only one droplet per gridded area on a thin film subsequent to nucleation dominated dewetting on a non-patterned substrate. Furthermore, when the grid periodicity exceeds the spinodal length, the number of droplets in predefined areas gradually approaches that associated with unconfined dewetting.

Mechanically Modulated Dewetting by Atomic Force Microscope for Micro- and Nano- Droplet Array Fabrication

PubMed Central

Wang, Feifei; Li, Pan; Wang, Dong; Li, Longhai; Xie, Shuangxi; Liu, Lianqing; Wang, Yuechao; Li, Wen Jung

2014-01-01

Organizing a material into well-defined patterns during the dewetting process provides an attractive micro-/nano-fabrication method without using a conventional lithographic process, and hence, offers potential applications in organic electronics, optics systems, and memory devices. We report here how the mechanical modification of polymer surface by an Atomic Force Microscope (AFM) can be used to guide thin film dewetting evolution and break the intrinsic spatial correlation of spontaneous instability. An AFM is used to implement the mechanical modification of progressively narrow grids to investigate the influence of pattern size on the modulation of ultrathin polystyrene films dewetting evolution. For films with different initial thicknesses, when grid size is close to or below the characteristic wavelength of instability, the spinodal dewetting is suppressed, and film rupture is restricted to the cutting trench. We will show in this paper it is possible to generate only one droplet per gridded area on a thin film subsequent to nucleation dominated dewetting on a non-patterned substrate. Furthermore, when the grid periodicity exceeds the spinodal length, the number of droplets in predefined areas gradually approaches that associated with unconfined dewetting. PMID:25283744

Mechanisms for Non-Linear Optical Behaviour in Molecular Fluids

NASA Astrophysics Data System (ADS)

McEwan, Kenneth J.

Available from UMI in association with The British Library. Requires signed TDF. This thesis describes a study of the non-linear optical mechanisms that allow high power laser radiation to interact and change the optical properties of fluid based media. Attention is focused on understanding the finite time-scale of the microscopic response and its influence on the experimental observation. Two classes of material are studied: liquid crystalline fluids in their isotropic phase and suspensions of particles capable of absorbing the laser radiation. In the former case a quantitative description of the optical transients seen in two experiments, degenerate four wave mixing and "z-scan" (self-focusing), is obtained. This description is based upon an analysis of refractive index changes associated with laser-induced molecular reorientation and with thermal effects, for molecules that absorb the laser radiation. Material parameters for a large range of nematogens are obtained by applying this description to experimental data. In the absorbing colloidal suspensions a novel mechanism for degenerate four wave mixing is identified and studied. The experimental results are suggestive of a mechanism in which vapour bubbles nucleate explosively around the colloidal particles and drive a coherent sound -wave excitation of the fluid. Theoretical studies confirm that rapid bubble nucleation is possible by a process of spinodal decomposition under the experimental conditions and it is shown that this mechanism can be expected to give rise to transient behaviour of the type observed. Finally laser-induced refractive index changes in a colloidal suspension in a solid matrix are studied. The dynamics of the formation of refractive index gratings is examined and correlated with microscopically observed structural changes in the matrix. ftn*Funded by DRA, Electronics Division (formerly RSRE).

Phase stability in thermally-aged CASS CF8 under heavy ion irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Meimei; Miller, Michael K.; Chen, Wei-Ying

2015-07-01

The stability of the microstructure of a cast austenitic stainless steel (CASS), before and after heavy ion irradiation, was investigated by atom probe tomography (APT). A CF8 ferrite-austenite duplex alloy was thermally aged at 400 degrees C for 10,000 h. After this treatment, APT revealed nanometer-sized G-phase precipitates and Fe-rich alpha and Cr-enriched alpha' phase separated regions in the ferrite. The thermally-aged CF8 specimen was irradiated with 1 MeV Kr ions to a fluence of 1.88 x 10(19) ions/m(2) at 400 degrees C. After irradiation, APT analysis revealed a strong spatial/dose dependence of the G-phase precipitates and the alpha-alpha' spinodalmore » decomposition in the ferrite. For the G-phase precipitates, the number density increased and the mean size decreased with increasing dose, and the particle size distribution changed considerably under irradiation. The inverse coarsening process can be described by recoil resolution. The amplitude of the alpha-alpha' spinodal decomposition in the ferrite was apparently reduced after heavy ion irradiation. (C) 2015 Elsevier B.V. All rights reserved« less

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

DOE PAGES

Santodonato, Louis J.; Zhang, Yang; Feygenson, Mikhail; ...

2015-01-20

The alloy-design strategy of combining multiple elements in near-equimolar ratios has shown great potential for producing exceptional engineering materials, often known as “high-entropy alloys”. Understanding the elemental distribution, and, thus, the evolution of the configurational entropy during solidification, is undertaken in the present study using the Al 1.3CoCrCuFeNi model alloy. Here we show that even when the material undergoes elemental segregation, precipitation, chemical ordering, and spinodal decomposition, a significant amount of disorder remains, due to the distributions of multiple elements in the major phases. In addition, the results suggest that the high-entropy-alloy-design strategy may be applied to a wide rangemore » of complex materials, and should not be limited to the goal of creating single-phase solid solutions.« less

The effects of phase transformation on the structure and mechanical properties of TiSiCN nanocomposite coatings deposited by PECVD method

NASA Astrophysics Data System (ADS)

Abedi, Mohammad; Abdollah-zadeh, Amir; Bestetti, Massimiliano; Vicenzo, Antonello; Serafini, Andrea; Movassagh-Alanagh, Farid

2018-06-01

In the present study, the effects of phase transformations on the structure and mechanical properties of TiSiCN coatings were investigated. TiSiCN nanocomposite coatings were deposited on AISI H13 hot-work tool steel by a pulsed direct current plasma-enhanced chemical vapor deposition process at 350 or 500 °C, using TiCl4 and SiCl4 as the precursors of Ti and Si, respectively, in a CH4/N2/H2/Ar plasma as the source of carbon and nitrogen and reducing environment. Some samples deposited at 350 °C were subsequently annealed at 500 °C under Ar atmosphere. Super hard self-lubricant TiSiCN coatings, having nanocomposite structure consisting of TiCN nanocrystals and amorphous carbon particles embedded in an amorphous SiCNx matrix, formed through spinodal decomposition in the specimens deposited or annealed at 500 °C. In addition, it was revealed that either uncomplete or relatively coarse phase segregation of titanium compounds was achieved during deposition at 350 °C and 500 °C, respectively. On the contrary, by deposition at 350 °C followed by annealing at 500 °C, a finer structure was obtained with a sensible improvement of the mechanical properties of coatings. Accordingly, the main finding of this work is that significant enhancement in key properties of TiSiCN coatings, such as hardness, adhesion and friction coefficient, can be obtained by deposition at low temperature and subsequent annealing at higher temperature, thanks to the formation of a fine grained nanocomposite structure.

Theory and experimental evidence of phonon domains and their roles in pre-martensitic phenomena

NASA Astrophysics Data System (ADS)

Jin, Yongmei M.; Wang, Yu U.; Ren, Yang

2015-12-01

Pre-martensitic phenomena, also called martensite precursor effects, have been known for decades while yet remain outstanding issues. This paper addresses pre-martensitic phenomena from new theoretical and experimental perspectives. A statistical mechanics-based Grüneisen-type phonon theory is developed. On the basis of deformation-dependent incompletely softened low-energy phonons, the theory predicts a lattice instability and pre-martensitic transition into elastic-phonon domains via 'phonon spinodal decomposition.' The phase transition lifts phonon degeneracy in cubic crystal and has a nature of phonon pseudo-Jahn-Teller lattice instability. The theory and notion of phonon domains consistently explain the ubiquitous pre-martensitic anomalies as natural consequences of incomplete phonon softening. The phonon domains are characterised by broken dynamic symmetry of lattice vibrations and deform through internal phonon relaxation in response to stress (a particular case of Le Chatelier's principle), leading to previously unexplored new domain phenomenon. Experimental evidence of phonon domains is obtained by in situ three-dimensional phonon diffuse scattering and Bragg reflection using high-energy synchrotron X-ray single-crystal diffraction, which observes exotic domain phenomenon fundamentally different from usual ferroelastic domain switching phenomenon. In light of the theory and experimental evidence of phonon domains and their roles in pre-martensitic phenomena, currently existing alternative opinions on martensitic precursor phenomena are revisited.

Soft matter: rubber and networks

NASA Astrophysics Data System (ADS)

McKenna, Gregory B.

2018-06-01

Rubber networks are important and form the basis for materials with properties ranging from rubber tires to super absorbents and contact lenses. The development of the entropy ideas of rubber deformation thermodynamics provides a powerful framework from which to understand and to use these materials. In addition, swelling of the rubber in the presence of small molecule liquids or solvents leads to materials that are very soft and ‘gel’ like in nature. The review covers the thermodynamics of polymer networks and gels from the perspective of the thermodynamics and mechanics of the strain energy density function. Important relationships are presented and experimental results show that the continuum ideas contained in the phenomenological thermodynamics are valid, but that the molecular bases for some of them remain to be fully elucidated. This is particularly so in the case of the entropic gels or swollen networks. The review is concluded with some perspectives on other networks, ranging from entropic polymer networks such as thermoplastic elastomers to physical gels in which cross-link points are formed by glassy or crystalline domains. A discussion is provided for other physical gels in which the network forms a spinodal-like decomposition, both in thermoplastic polymers that form a glassy network upon phase separation and for colloidal gels that seem to have a similar behavior.

Thermal Aging Phenomena in Cast Duplex Stainless Steels

DOE PAGES

Byun, T. S.; Yang, Y.; Overman, N. R.; ...

2015-11-12

We used cast stainless steels (CASSs)for the large components of light water reactor (LWR) power plants such as primary coolant piping and pump casing. The thermal embrittlement of CASS components is one of the most serious concerns related to the extended-term operation of nuclear power plants. Many past researches have concluded that the formation of Cr-rich alpha-phase by Spinodal decomposition of delta-ferrite phase is the primary mechanism for the thermal embrittlement. Cracking mechanism in the thermally-embrittled duplex stainless steels consists of the formation of cleavage at ferrite and its propagation via separation of ferrite-austenite interphase. This article intends to providemore » an introductory overview on the thermal aging phenomena in LWR-relevant conditions. Firstly, the thermal aging effect on toughness is discussed in terms of the cause of embrittlement and influential parameters. Moreover, an approximate analysis of thermal reaction using Arrhenius equation was carried out to scope the aging temperatures for the accelerated aging experiments to simulate the 60 and 80 years of services. Further, an equilibrium precipitation calculation was performed for model CASS alloys using the CALPHAD program, and the results are used to describe the precipitation behaviors in duplex stainless steels. Our results are also to be used to guide an on-going research aiming to provide knowledge-based conclusive prediction for the integrity of the CASS components of LWR power plants during the service life extended up to and beyond 60 years.« less

Thermal Aging Phenomena in Cast Duplex Stainless Steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Byun, T. S.; Yang, Y.; Overman, N. R.

Cast stainless steels (CASSs) have been extensively used for the large components of light water reactor (LWR) power plants such as primary coolant piping and pump casing. The thermal embrittlement of CASS components is one of the most serious concerns related to the extended-term operation of nuclear power plants. Many past researches have concluded that the formation of Cr–rich α'-phase by Spinodal decomposition of δ-ferrite phase is the primary mechanism for the thermal embrittlement. Cracking mechanism in the thermally-embrittled duplex stainless steels consists of the formation of cleavage at ferrite and its propagation via separation of ferrite-austenite interphase. This articlemore » intends to provide an introductory overview on the thermal aging phenomena in LWR relevant conditions. Firstly, the thermal aging effect on toughness is discussed in terms of the cause of embrittlement and influential parameters. An approximate analysis of thermal reaction using Arrhenius equation was carried out to scope the aging temperatures for the accelerated aging experiments to simulate the 60 and 80 years of services. Further, equilibrium precipitation calculation was performed for model CASS alloys using the CALPHAD program and the results are used to describe the precipitation behaviors in duplex stainless steels. These results are also to be used to guide an on-going research aiming to provide knowledge-based conclusive prediction for the integrity of the CASS components of LWR power plants during the service life extended up to and beyond 60 years.« less

A phase-plane analysis of localized frictional waves

NASA Astrophysics Data System (ADS)

Putelat, T.; Dawes, J. H. P.; Champneys, A. R.

2017-07-01

Sliding frictional interfaces at a range of length scales are observed to generate travelling waves; these are considered relevant, for example, to both earthquake ground surface movements and the performance of mechanical brakes and dampers. We propose an explanation of the origins of these waves through the study of an idealized mechanical model: a thin elastic plate subject to uniform shear stress held in frictional contact with a rigid flat surface. We construct a nonlinear wave equation for the deformation of the plate, and couple it to a spinodal rate-and-state friction law which leads to a mathematically well-posed problem that is capable of capturing many effects not accessible in a Coulomb friction model. Our model sustains a rich variety of solutions, including periodic stick-slip wave trains, isolated slip and stick pulses, and detachment and attachment fronts. Analytical and numerical bifurcation analysis is used to show how these states are organized in a two-parameter state diagram. We discuss briefly the possible physical interpretation of each of these states, and remark also that our spinodal friction law, though more complicated than other classical rate-and-state laws, is required in order to capture the full richness of wave types.

A phase-plane analysis of localized frictional waves

PubMed Central

Dawes, J. H. P.; Champneys, A. R.

2017-01-01

Sliding frictional interfaces at a range of length scales are observed to generate travelling waves; these are considered relevant, for example, to both earthquake ground surface movements and the performance of mechanical brakes and dampers. We propose an explanation of the origins of these waves through the study of an idealized mechanical model: a thin elastic plate subject to uniform shear stress held in frictional contact with a rigid flat surface. We construct a nonlinear wave equation for the deformation of the plate, and couple it to a spinodal rate-and-state friction law which leads to a mathematically well-posed problem that is capable of capturing many effects not accessible in a Coulomb friction model. Our model sustains a rich variety of solutions, including periodic stick–slip wave trains, isolated slip and stick pulses, and detachment and attachment fronts. Analytical and numerical bifurcation analysis is used to show how these states are organized in a two-parameter state diagram. We discuss briefly the possible physical interpretation of each of these states, and remark also that our spinodal friction law, though more complicated than other classical rate-and-state laws, is required in order to capture the full richness of wave types. PMID:28804255

A phase-plane analysis of localized frictional waves.

PubMed

Putelat, T; Dawes, J H P; Champneys, A R

2017-07-01

Sliding frictional interfaces at a range of length scales are observed to generate travelling waves; these are considered relevant, for example, to both earthquake ground surface movements and the performance of mechanical brakes and dampers. We propose an explanation of the origins of these waves through the study of an idealized mechanical model: a thin elastic plate subject to uniform shear stress held in frictional contact with a rigid flat surface. We construct a nonlinear wave equation for the deformation of the plate, and couple it to a spinodal rate-and-state friction law which leads to a mathematically well-posed problem that is capable of capturing many effects not accessible in a Coulomb friction model. Our model sustains a rich variety of solutions, including periodic stick-slip wave trains, isolated slip and stick pulses, and detachment and attachment fronts. Analytical and numerical bifurcation analysis is used to show how these states are organized in a two-parameter state diagram. We discuss briefly the possible physical interpretation of each of these states, and remark also that our spinodal friction law, though more complicated than other classical rate-and-state laws, is required in order to capture the full richness of wave types.

LB3D: A parallel implementation of the Lattice-Boltzmann method for simulation of interacting amphiphilic fluids

NASA Astrophysics Data System (ADS)

Schmieschek, S.; Shamardin, L.; Frijters, S.; Krüger, T.; Schiller, U. D.; Harting, J.; Coveney, P. V.

2017-08-01

We introduce the lattice-Boltzmann code LB3D, version 7.1. Building on a parallel program and supporting tools which have enabled research utilising high performance computing resources for nearly two decades, LB3D version 7 provides a subset of the research code functionality as an open source project. Here, we describe the theoretical basis of the algorithm as well as computational aspects of the implementation. The software package is validated against simulations of meso-phases resulting from self-assembly in ternary fluid mixtures comprising immiscible and amphiphilic components such as water-oil-surfactant systems. The impact of the surfactant species on the dynamics of spinodal decomposition are tested and quantitative measurement of the permeability of a body centred cubic (BCC) model porous medium for a simple binary mixture is described. Single-core performance and scaling behaviour of the code are reported for simulations on current supercomputer architectures.

Theory of Metastable State Relaxation in a Gravitational Field for Non-Critical Binary Systems with Non-Conserved Order Parameter

NASA Technical Reports Server (NTRS)

Izmailov, Alexander F.; Myerson, Allan S.

1993-01-01

A new mathematical ansatz is developed for solution of the time-dependent Ginzburg-Landau nonlinear partial differential equation describing metastable state relaxation in binary (solute+solvent) non-critical solutions with non-conserved scalar order parameter in presence of a gravitational field. It has been demonstrated analytically that in such systems metastability initiates heterogeneous solute redistribution which results in the formation of a non-equilibrium singly-periodic spatial solute structure in the new solute-rich phase. The critical radius of nucleation and the induction time in these systems are gravity-dependent. It has also been proved that metastable state relaxation in vertical columns of supersaturated non-critical binary solutions leads to formation of the solute concentration gradient. Analytical expression for this concentration gradient is found and analysed. It is concluded that gravity can initiate phase separation (nucleation or spinodal decomposition).

New type of nonglossy image-receiving sheet

NASA Astrophysics Data System (ADS)

Aono, Toshiaki; Shibata, Takeshi; Nakamura, Yoshisada

1990-07-01

We have developed a new type of non-glossy surface of an image receiving sheet for a photothermographic color hardcopy system. There is a basic conflict in realizing uniform dye transfer with use of a receiving sheet having a matted surface, because when the degree of roughness exceeds a certain extent, uneven dye transfer readily takes place. It: has been solved by use of "microscopic" phase separation of a certain water-soluble polymer blend which constitutes the surface layer of the image receiving sheet. One of the preferable polymer blends for our purpose proved to be a ternary system, consisting of sodium salt of polymethacrylic acid (PMAA-Na), ammonium salt of polyacrylic acid (PAA-NH4) and water. Phase separation, which proceeded during the evaporation of water from the coated mixture, turned out to be of a spinodal decomposition type and thus capable of stably providing a desirable non-glossy surface.

Structure and magnetic properties of Alnico ribbons

NASA Astrophysics Data System (ADS)

Zhang, Ce; Li, Ying; Han, Xu-Hao; Du, Shuai-long; Sun, Ji-bing; Zhang, Ying

2018-04-01

Al-Ni-Co alloy has been widely applied in various industrial fields due to its excellent thermal and magnetic stability. In this paper, new Al-Ni-Co ribbons are prepared by simple processes combining melt-spinning with annealing, and their phase transition, microstructure and magnetic properties are studied. The results show that after as-spun ribbons are annealed, the grain size of ribbons increases from 1.1 ± 0.3 μm to 4.8 ± 0.8 μm, but still much smaller than that of the bulk Al-Ni-Co alloy manufactured by traditional technologies. In addition, some rod-like Al70Co20Ni10-type, Al9Co2-type and Fe2Nb-type phases are precipitated at grain boundaries; simultaneously, the distinct spinodal decomposition microstructure with periodic ingredient variation is thoroughly formed in all grains by the reaction of α → α1 + α2. Furthermore, the α1 and α2 distribute alternately like a maze, the Fe-Co-rich α1 phase holds 35.9-47.3 vol%, while the Al-Ni-rich α2 phase occupies the rest. Finally, the coercivity of annealed ribbons can reach to 485.3 ± 76.6 Oe. If the annealed ribbons are further aged at 560 °C, their Hc even increases to 738.1 ± 81.0 Oe. The coercivity mechanism is discussed by the combination of microstructure and domain structure.

Principles of Considering the Effect of the Limited Volume of a System on Its Thermodynamic State

NASA Astrophysics Data System (ADS)

Tovbin, Yu. K.

2018-01-01

The features of a system with a finite volume that affect its thermodynamic state are considered in comparison to describing small bodies in macroscopic phases. Equations for unary and pair distribution functions are obtained using difference derivatives of a discrete statistical sum. The structure of the equation for the free energy of a system consisting of an ensemble of volume-limited regions with different sizes and a full set of equations describing a macroscopic polydisperse system are discussed. It is found that the equations can be applied to molecular adsorption on small faces of microcrystals, to bound and isolated pores of a polydisperse material, and to describe the spinodal decomposition of a fluid in brief periods of time and high supersaturations of the bulk phase when each local region functions the same on average. It is shown that as the size of a system diminishes, corrections must be introduced for the finiteness of the system volume and fluctuations of the unary and pair distribution functions.

Effect of finite particle number sampling on baryon number fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steinheimer, Jan; Koch, Volker

The effects of finite particle number sampling on the net baryon number cumulants, extracted from fluid dynamical simulations, are studied. The commonly used finite particle number sampling procedure introduces an additional Poissonian (or multinomial if global baryon number conservation is enforced) contribution which increases the extracted moments of the baryon number distribution. If this procedure is applied to a fluctuating fluid dynamics framework, one severely overestimates the actual cumulants. We show that the sampling of so-called test particles suppresses the additional contribution to the moments by at least one power of the number of test particles. We demonstrate this methodmore » in a numerical fluid dynamics simulation that includes the effects of spinodal decomposition due to a first-order phase transition. Furthermore, in the limit where antibaryons can be ignored, we derive analytic formulas which capture exactly the effect of particle sampling on the baryon number cumulants. These formulas may be used to test the various numerical particle sampling algorithms.« less

Preventing Thin Film Dewetting via Graphene Capping.

PubMed

Cao, Peigen; Bai, Peter; Omrani, Arash A; Xiao, Yihan; Meaker, Kacey L; Tsai, Hsin-Zon; Yan, Aiming; Jung, Han Sae; Khajeh, Ramin; Rodgers, Griffin F; Kim, Youngkyou; Aikawa, Andrew S; Kolaczkowski, Mattew A; Liu, Yi; Zettl, Alex; Xu, Ke; Crommie, Michael F; Xu, Ting

2017-09-01

A monolayer 2D capping layer with high Young's modulus is shown to be able to effectively suppress the dewetting of underlying thin films of small organic semiconductor molecule, polymer, and polycrystalline metal, respectively. To verify the universality of this capping layer approach, the dewetting experiments are performed for single-layer graphene transferred onto polystyrene (PS), semiconducting thienoazacoronene (EH-TAC), gold, and also MoS 2 on PS. Thermodynamic modeling indicates that the exceptionally high Young's modulus and surface conformity of 2D capping layers such as graphene and MoS 2 substantially suppress surface fluctuations and thus dewetting. As long as the uncovered area is smaller than the fluctuation wavelength of the thin film in a dewetting process via spinodal decomposition, the dewetting should be suppressed. The 2D monolayer-capping approach opens up exciting new possibilities to enhance the thermal stability and expands the processing parameters for thin film materials without significantly altering their physical properties. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of finite particle number sampling on baryon number fluctuations

DOE PAGES

Steinheimer, Jan; Koch, Volker

2017-09-28

The effects of finite particle number sampling on the net baryon number cumulants, extracted from fluid dynamical simulations, are studied. The commonly used finite particle number sampling procedure introduces an additional Poissonian (or multinomial if global baryon number conservation is enforced) contribution which increases the extracted moments of the baryon number distribution. If this procedure is applied to a fluctuating fluid dynamics framework, one severely overestimates the actual cumulants. We show that the sampling of so-called test particles suppresses the additional contribution to the moments by at least one power of the number of test particles. We demonstrate this methodmore » in a numerical fluid dynamics simulation that includes the effects of spinodal decomposition due to a first-order phase transition. Furthermore, in the limit where antibaryons can be ignored, we derive analytic formulas which capture exactly the effect of particle sampling on the baryon number cumulants. These formulas may be used to test the various numerical particle sampling algorithms.« less

Spontaneous symmetry breaking and phase coexistence in two-color networks

NASA Astrophysics Data System (ADS)

Avetisov, V.; Gorsky, A.; Nechaev, S.; Valba, O.

2016-01-01

We consider an equilibrium ensemble of large Erdős-Renyi topological random networks with fixed vertex degree and two types of vertices, black and white, prepared randomly with the bond connection probability p . The network energy is a sum of all unicolor triples (either black or white), weighted with chemical potential of triples μ . Minimizing the system energy, we see for some positive μ the formation of two predominantly unicolor clusters, linked by a string of Nb w black-white bonds. We have demonstrated that the system exhibits critical behavior manifested in the emergence of a wide plateau on the Nb w(μ ) curve, which is relevant to a spinodal decomposition in first-order phase transitions. In terms of a string theory, the plateau formation can be interpreted as an entanglement between baby universes in two-dimensional gravity. We conjecture that the observed classical phenomenon can be considered as a toy model for the chiral condensate formation in quantum chromodynamics.

Nanostructure and giant magnetoresistive properties of granular systems.

PubMed

Kooi, B J; Vystavel, T; De Hosson, J T

2001-03-01

This article aims to make a connection between the microstructures of various nanostructured alloys and giant magnetoresistive (GMR) properties. The GMR behavior of nanoclusters embedded in a nonmagnetic matrix differs considerably from an alloy with the content of a magnetic phase above the percolation threshold; that is to say, an increase of GMR effect upon going from 300 to 10 K for the former and a decrease of the GMR effect for the latter. The following materials systems were examined with high-resolution transmission electron microscopy and magnetoelectrical resistance measurements: magnetic Co and CoFe nanoclusters in a Au matrix, NiFe clusters in a Cu matrix, and NiFe/Cu spinodal decomposition waves with interconnection of the magnetic phase. After annealing (> or = 300 degrees C), Co particles in Au become semi- or incoherent, whereas under other conditions and in all other systems, the interfaces remain coherent. This state of coherency at the interface between magnetic particles and a nonmagnetic matrix turned out to have a detectable influence on the GMR behavior.

Bicontinuous structured liquids with sub-micrometre domains using nanoparticle surfactants

DOE PAGES

Huang, Caili; Forth, Joe; Wang, Weiyu; ...

2017-09-25

Bicontinuous jammed emulsions (or bijels) are tortuous, interconnected structures of two immiscible liquids, kinetically trapped by colloidal particles that are irreversibly bound to the oil–water interface. A wealth of applications has been proposed for bijels in catalysis, energy storage and molecular encapsulation, but large domain sizes (on the order of 5 µm or larger) and difficulty in fabrication pose major barriers to their use. In this paper, we show that bijels with sub-micrometre domains can be formed via homogenization, rather than spinodal decomposition. We achieve this by using nanoparticle surfactants: polymers and nanoparticles of complementary functionality (for example, ion-pairing) thatmore » bind to one another at the oil–water interface. This allows the stabilization of the bijel far from the demixing point of the liquids, with interfacial tensions on the order of 20 mN m -1. Finally, furthermore, our strategy is extremely versatile, as solvent, nanoparticle and ligand can all be varied.« less

Bicontinuous structured liquids with sub-micrometre domains using nanoparticle surfactants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Caili; Forth, Joe; Wang, Weiyu

Bicontinuous jammed emulsions (or bijels) are tortuous, interconnected structures of two immiscible liquids, kinetically trapped by colloidal particles that are irreversibly bound to the oil–water interface. A wealth of applications has been proposed for bijels in catalysis, energy storage and molecular encapsulation, but large domain sizes (on the order of 5 µm or larger) and difficulty in fabrication pose major barriers to their use. In this paper, we show that bijels with sub-micrometre domains can be formed via homogenization, rather than spinodal decomposition. We achieve this by using nanoparticle surfactants: polymers and nanoparticles of complementary functionality (for example, ion-pairing) thatmore » bind to one another at the oil–water interface. This allows the stabilization of the bijel far from the demixing point of the liquids, with interfacial tensions on the order of 20 mN m -1. Finally, furthermore, our strategy is extremely versatile, as solvent, nanoparticle and ligand can all be varied.« less

Spontaneous symmetry breaking and phase coexistence in two-color networks.

PubMed

Avetisov, V; Gorsky, A; Nechaev, S; Valba, O

2016-01-01

We consider an equilibrium ensemble of large Erdős-Renyi topological random networks with fixed vertex degree and two types of vertices, black and white, prepared randomly with the bond connection probability p. The network energy is a sum of all unicolor triples (either black or white), weighted with chemical potential of triples μ. Minimizing the system energy, we see for some positive μ the formation of two predominantly unicolor clusters, linked by a string of N_{bw} black-white bonds. We have demonstrated that the system exhibits critical behavior manifested in the emergence of a wide plateau on the N_{bw}(μ) curve, which is relevant to a spinodal decomposition in first-order phase transitions. In terms of a string theory, the plateau formation can be interpreted as an entanglement between baby universes in two-dimensional gravity. We conjecture that the observed classical phenomenon can be considered as a toy model for the chiral condensate formation in quantum chromodynamics.

Separation processes during binary monotectic alloy production

NASA Technical Reports Server (NTRS)

Frazier, D. O.; Facemire, B. R.; Kaukler, W. F.; Witherow, W. K.; Fanning, U.

1984-01-01

Observation of microgravity solidification processes indicates that outside of sedimentation, at least two other important effects can separate the phases: critical-point wetting and spreading; and thermal migration of second-phase droplets due to interfacial tension gradients. It is difficult to study these surface tension effects while in a unit gravity field. In order to investigate the processes occurring over a temperature range, i.e., between a consolute point and the monotectic temperature, it is necessary to use a low-gravity environment. The MSFC drop tube (and tower), the ballistic trajectory KC-135 airplane, and the Space Shuttle are ideal facilities to aid formation and testing of hypotheses. Much of the early work in this area focuses on transparent materials so that process dynamics may be studied by optical techniques such as photography for viewing macro-processes; holography for studying diffusional growth; spinodal decomposition and coalescence; ellipsometry for surface wetting and spreading effects; and interferometry and spectroscopy for small-scale spatial resolution of concentration profiles.

Phase separation like dynamics during Myxococcus xanthus fruiting body formation

NASA Astrophysics Data System (ADS)

Liu, Guannan; Thutupalli, Shashi; Wigbers, Manon; Shaevitz, Joshua

2015-03-01

Collective motion exists in many living organisms as an advantageous strategy to help the entire group with predation, forage, and survival. However, the principles of self-organization underlying such collective motions remain unclear. During various developmental stages of the soil-dwelling bacterium, Myxococcus xanthus, different types of collective motions are observed. In particular, when starved, M. xanthus cells eventually aggregate together to form 3-dimensional structures (fruiting bodies), inside which cells sporulate in response to the stress. We study the fruiting body formation process as an out of equilibrium phase separation process. As local cell density increases, the dynamics of the aggregation M. xanthus cells switch from a spatio-temporally random process, resembling nucleation and growth, to an emergent pattern formation process similar to a spinodal decomposition. By employing high-resolution microscopy and a video analysis system, we are able to track the motion of single cells within motile collective groups, while separately tuning local cell density, cell velocity and reversal frequency, probing the multi-dimensional phase space of M. xanthus development.

Enhanced Hydrate Nucleation Near the Limit of Stability.

PubMed

Jimenez-Angeles, Felipe; Firoozabadi, Abbas

2015-03-30

Clathrate hydrates are crystalline structures composed of small guest molecules trapped into cages formed by hydrogen-bonded water molecules. In hydrate nucleation, water and the guest molecules may stay in a metastable fluid mixture for a long period. Metastability is broken if the concentration of the guest is above certain limit. We perform molecular dynamics (MD) simulations of supersaturated water-propane solutions close to the limit of stability. We show that hydrate nucleation can be very fast in a very narrow range of composition at moderate temperatures. Propane density fluctuations near the fluid-fluid demixing are coupled with crystallization producing en- hanced nucleation rates. This is the first report of propane-hydrate nucleation by MD simulations. We observe motifs of the crystalline structure II in line with experiments and new hydrate cages not reported in the literature. Our study relates nucleation to the fluid-fluid spinodal decomposition and demonstration that the enhanced nucleation phenomenon is more general than short range attractive interactions as suggested in nucleation of proteins.

Dynamic density functional theory with hydrodynamic interactions: theoretical development and application in the study of phase separation in gas-liquid systems.

PubMed

Kikkinides, E S; Monson, P A

2015-03-07

Building on recent developments in dynamic density functional theory, we have developed a version of the theory that includes hydrodynamic interactions. This is achieved by combining the continuity and momentum equations eliminating velocity fields, so the resulting model equation contains only terms related to the fluid density and its time and spatial derivatives. The new model satisfies simultaneously continuity and momentum equations under the assumptions of constant dynamic or kinematic viscosity and small velocities and/or density gradients. We present applications of the theory to spinodal decomposition of subcritical temperatures for one-dimensional and three-dimensional density perturbations for both a van der Waals fluid and for a lattice gas model in mean field theory. In the latter case, the theory provides a hydrodynamic extension to the recently studied dynamic mean field theory. We find that the theory correctly describes the transition from diffusive phase separation at short times to hydrodynamic behaviour at long times.

Dynamic density functional theory with hydrodynamic interactions: Theoretical development and application in the study of phase separation in gas-liquid systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kikkinides, E. S.; Monson, P. A.

Building on recent developments in dynamic density functional theory, we have developed a version of the theory that includes hydrodynamic interactions. This is achieved by combining the continuity and momentum equations eliminating velocity fields, so the resulting model equation contains only terms related to the fluid density and its time and spatial derivatives. The new model satisfies simultaneously continuity and momentum equations under the assumptions of constant dynamic or kinematic viscosity and small velocities and/or density gradients. We present applications of the theory to spinodal decomposition of subcritical temperatures for one-dimensional and three-dimensional density perturbations for both a van dermore » Waals fluid and for a lattice gas model in mean field theory. In the latter case, the theory provides a hydrodynamic extension to the recently studied dynamic mean field theory. We find that the theory correctly describes the transition from diffusive phase separation at short times to hydrodynamic behaviour at long times.« less

Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal K xFe 2-ySe 2

DOE PAGES

Liu, Yong; Xing, Qingfeng; Straszheim, Warren E.; ...

2016-02-11

Here, we report how the superconducting phase forms in pseudo-single-crystal K xFe 2-ySe 2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition.more » It should be emphasized that the phase separation in pseudo-single-crystal K xFe 2-ySe 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less

Kinetics of sub-spinodal dewetting of thin films of thickness dependent viscosity.

PubMed

Kotni, Tirumala Rao; Khanna, Rajesh; Sarkar, Jayati

2017-05-04

An alternative explanation of the time varying and very low growth exponents in dewetting of polymer films like polystyrene films is presented based on non-linear simulations. The kinetics of these films is explored within the framework of experimentally observed thickness dependent viscosity. These films exhibit sub-spinodal dewetting via formation of satellite holes in between primary dewetted holes under favorable conditions of excess intermolecular forces and film thicknesses. We find that conditions responsible for sub-spinodal dewetting concurrently lead to remarkable changes in the kinetics of dewetting of even primary holes. For example, the radius of the hole grows in time with a power-law growth exponent sequence of [Formula: see text], in contrast to the usual  ∼4/5. This is due to the cumulative effect of reduced rim mobility due to thickness dependent viscosity and hindrance created by satellite holes.

FNAS modify matric and transparent experiments

NASA Technical Reports Server (NTRS)

Smith, Guy A.; Kosten, Sue E.; Workman, Gary L.

1992-01-01

Monotectic alloy materials are created by rapid melt/rapid solidification processing on the NASA KC-135. Separation of the uniform liquid into two liquids may occur by either of two processes; spinodal decomposition or nucleation followed by growth. In the first case, the liquid is unstable to composition waves, which form and grow, giving liquids of two different compositions. In the latter process discrete particles of the second liquid phase form via thermal fluctuations and then grow by diffusion. The two processes are very different, with the determining process being dictated by temperature, composition, and thermodynamic characteristics of the alloy. The first two quantities are process variables, while the third is determined by electronic interactions between the atoms in the alloy. In either case the initial alloy decomposition is followed by coarsening, resulting in growth of the particle size at nearly constant volume fraction. In particular, reduced gravity experiments on monotectic solutions have shown a number of interesting results in the KC-135. Monotectic solutions exhibit a miscibility gap in the liquid state, and consequently, gravity driven forces can dominate the solidification parameters at 1 g. In reduced gravity however, the distribution of the phases is different, resulting in new and interesting microstructures. The Rapid Melt/Rapid Quench Furnace allows one to melt a sample and resolidify it in one parabola of the KC-135's flight path, thus eliminating any accumulative influence of multiple parabolas to affect the microstructure of the material.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Altabet, Y. Elia; Debenedetti, Pablo G., E-mail: pdebene@princeton.edu; Stillinger, Frank H.

In particle systems with cohesive interactions, the pressure-density relationship of the mechanically stable inherent structures sampled along a liquid isotherm (i.e., the equation of state of an energy landscape) will display a minimum at the Sastry density ρ{sub S}. The tensile limit at ρ{sub S} is due to cavitation that occurs upon energy minimization, and previous characterizations of this behavior suggested that ρ{sub S} is a spinodal-like limit that separates all homogeneous and fractured inherent structures. Here, we revisit the phenomenology of Sastry behavior and find that it is subject to considerable finite-size effects, and the development of the inherentmore » structure equation of state with system size is consistent with the finite-size rounding of an athermal phase transition. What appears to be a continuous spinodal-like point at finite system sizes becomes discontinuous in the thermodynamic limit, indicating behavior akin to a phase transition. We also study cavitation in glassy packings subjected to athermal expansion. Many individual expansion trajectories averaged together produce a smooth equation of state, which we find also exhibits features of finite-size rounding, and the examples studied in this work give rise to a larger limiting tension than for the corresponding landscape equation of state.« less

Self organized striping in ultra thin polymer films near melt: An investigation using Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Singh, Satya Pal

2018-05-01

This paper work presents the results of Monte Carlo simulation performed for ultra thin short chained polymer films near melt, under strong confinement. Thin polymer films get ruptured when annealed above their glass transition temperatures. The pattern formations are generally explained on the basis of spinodal mechanism, if the thickness of the film is of the order of few tens of nanometers i.e. <100 nm. In this case, the film seems to tear apart in strips. The free end segments of the chains are more dynamic and coalescence into one another. This process seems to dominate over the spinodal waves resulting into a different type of dynamics. Polymer chains with 30 monomers are taken. 160, 200 and 240 chains are taken for three different cases of the studies. The three cases correspond to three different thickness of the films with 8, 10 and 12 layers of chains along direction perpendicular to the confining substrates. The bottom surface has affinity to monomers, whereas the upper surface has hard wall interaction with the monomers. Different time micrographs of the films are plotted along with density distributions of the monomers to explore the process.

On spinodal points and Lee-Yang edge singularities

NASA Astrophysics Data System (ADS)

An, X.; Mesterházy, D.; Stephanov, M. A.

2018-03-01

We address a number of outstanding questions associated with the analytic properties of the universal equation of state of the φ4 theory, which describes the critical behavior of the Ising model and ubiquitous critical points of the liquid–gas type. We focus on the relation between spinodal points that limit the domain of metastability for temperatures below the critical temperature, i.e. T < Tc , and Lee-Yang edge singularities that restrict the domain of analyticity around the point of zero magnetic field H for T > Tc . The extended analyticity conjecture (due to Fonseca and Zamolodchikov) posits that, for T < Tc , the Lee-Yang edge singularities are the closest singularities to the real H axis. This has interesting implications, in particular, that the spinodal singularities must lie off the real H axis for d < 4 , in contrast to the commonly known result of the mean-field approximation. We find that the parametric representation of the Ising equation of state obtained in the \\renewcommandε{\\varepsilon} \

Phase transition dynamics for hot nuclei

NASA Astrophysics Data System (ADS)

Borderie, B.; Le Neindre, N.; Rivet, M. F.; Désesquelles, P.; Bonnet, E.; Bougault, R.; Chbihi, A.; Dell'Aquila, D.; Fable, Q.; Frankland, J. D.; Galichet, E.; Gruyer, D.; Guinet, D.; La Commara, M.; Lombardo, I.; Lopez, O.; Manduci, L.; Napolitani, P.; Pârlog, M.; Rosato, E.; Roy, R.; St-Onge, P.; Verde, G.; Vient, E.; Vigilante, M.; Wieleczko, J. P.; Indra Collaboration

2018-07-01

An abnormal production of events with almost equal-sized fragments was theoretically proposed as a signature of spinodal instabilities responsible for nuclear multifragmentation in the Fermi energy domain. On the other hand finite size effects are predicted to strongly reduce this abnormal production. High statistics quasifusion hot nuclei produced in central collisions between Xe and Sn isotopes at 32 and 45 A MeV incident energies have been used to definitively establish, through the experimental measurement of charge correlations, the presence of spinodal instabilities. N/Z influence was also studied.

Sizes of lipid domains: What do we know from artificial lipid membranes? What are the possible shared features with membrane rafts in cells?

PubMed

Rosetti, Carla M; Mangiarotti, Agustín; Wilke, Natalia

2017-05-01

In model lipid membranes with phase coexistence, domain sizes distribute in a very wide range, from the nanometer (reported in vesicles and supported films) to the micrometer (observed in many model membranes). Domain growth by coalescence and Ostwald ripening is slow (minutes to hours), the domain size being correlated with the size of the capture region. Domain sizes thus strongly depend on the number of domains which, in the case of a nucleation process, depends on the oversaturation of the system, on line tension and on the perturbation rate in relation to the membrane dynamics. Here, an overview is given of the factors that affect nucleation or spinodal decomposition and domain growth, and their influence on the distribution of domain sizes in different model membranes is discussed. The parameters analyzed respond to very general physical rules, and we therefore propose a similar behavior for the rafts in the plasma membrane of cells, but with obstructed mobility and with a continuously changing environment. Copyright © 2017 Elsevier B.V. All rights reserved.

The effect of spontaneous curvature on a two-phase vesicle

PubMed Central

Cox, Geoffrey; Lowengrub, John

2015-01-01

Vesicles are membrane-bound structures commonly known for their roles in cellular transport and the shape of a vesicle is determined by its surrounding membrane (lipid bilayer). When the membrane is composed of different lipids, it is natural for the lipids of similar molecular structure to migrate towards one another (via spinodal decomposition), creating a multi-phase vesicle. In this article, we consider a two-phase vesicle model which is driven by nature’s propensity to maintain a minimal state of elastic energy. The model assumes a continuum limit, thereby treating the membrane as a closed three-dimensional surface. The main purpose of this study is to reveal the complexity of the Helfrich two-phase vesicle model with non-zero spontaneous curvature and provide further evidence to support the relevance of spontaneous curvature as a modelling parameter. In this paper, we illustrate the complexity of the Helfrich two-phase model by providing multiple examples of undocumented solutions and energy hysteresis. We also investigate the influence of spontaneous curvature on morphological effects and membrane phenomena such as budding and fusion. PMID:26097287

Ising-like patterns of spatial synchrony in population biology

NASA Astrophysics Data System (ADS)

Noble, Andrew; Hastings, Alan; Machta, Jon

2014-03-01

Systems of coupled dynamical oscillators can undergo a phase transition between synchronous and asynchronous phases. In the case of coupled map lattices, the spontaneous symmetry breaking of a temporal-phase order parameter is known to exhibit Ising-like critical behavior. Here, we investigate a noisy coupled map motivated by the study of spatial synchrony in ecological populations far from the extinction threshold. Ising-like patterns of criticality, as well as spinodal decomposition and homogeneous nucleation, emerge from the nonlinear interactions of environmental fluctuations in habitat quality, local density-dependence in reproduction, and dispersal. In the mean-field limit, the correspondence to the Ising model is exact: the fixed points of our dynamical system are given by the equation of state for Weiss mean-field theory under an appropriate mapping of parameters. We have strong evidence that a quantitative correspondence persists, both near and far from the critical point, in the presence of fluctuations. Our results provide a formal connection between equilibrium statistical physics and population biology. This work is supported by the National Science Foundation under Grant No. 1344187.

Morphological Simulation of Phase Separation Coupled Oscillation Shear and Varying Temperature Fields

NASA Astrophysics Data System (ADS)

Wang, Heping; Li, Xiaoguang; Lin, Kejun; Geng, Xingguo

2018-05-01

This paper explores the effect of the shear frequency and Prandtl number ( Pr) on the procedure and pattern formation of phase separation in symmetric and asymmetric systems. For the symmetric system, the periodic shear significantly prolongs the spinodal decomposition stage and enlarges the separated domain in domain growth stage. By adjusting the Pr and shear frequency, the number and orientation of separated steady layer structures can be controlled during domain stretch stage. The numerical results indicate that the increase in Pr and decrease in the shear frequency can significantly increase in the layer number of the lamellar structure, which relates to the decrease in domain size. Furthermore, the lamellar orientation parallel to the shear direction is altered into that perpendicular to the shear direction by further increasing the shear frequency, and also similar results for larger systems. For asymmetric system, the quantitative analysis shows that the decrease in the shear frequency enlarges the size of separated minority phases. These numerical results provide guidance for setting the optimum condition for the phase separation under periodic shear and slow cooling.

Direct comparison of Fe-Cr unmixing characterization by atom probe tomography and small angle scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Couturier, Laurent, E-mail: laurent.couturier55@ho

The fine microstructure obtained by unmixing of a solid solution either by classical precipitation or spinodal decomposition is often characterized either by small angle scattering or atom probe tomography. This article shows that a common data analysis framework can be used to analyze data obtained from these two techniques. An example of the application of this common analysis is given for characterization of the unmixing of the Fe-Cr matrix of a 15-5 PH stainless steel during long-term ageing at 350 °C and 400 °C. A direct comparison of the Cr composition fluctuations amplitudes and characteristic lengths obtained with both techniquesmore » is made showing a quantitative agreement for the fluctuation amplitudes. The origin of the discrepancy remaining for the characteristic lengths is discussed. - Highlights: •Common analysis framework for atom probe tomography and small angle scattering •Comparison of same microstructural characteristics obtained using both techniques •Good correlation of Cr composition fluctuations amplitudes from both techniques •Good correlation of Cr composition fluctuations amplitudes with classic V parameter.« less

Atomic Layer Deposition of Bismuth Vanadates for Solar Energy Materials.

PubMed

Stefik, Morgan

2016-07-07

The fabrication of porous nanocomposites is key to the advancement of energy conversion and storage devices that interface with electrolytes. Bismuth vanadate, BiVO4 , is a promising oxide for solar water splitting where the controlled fabrication of BiVO4 layers within porous, conducting scaffolds has remained a challenge. Here, the atomic layer deposition of bismuth vanadates is reported from BiPh3 , vanadium(V) oxytriisopropoxide, and water. The resulting films have tunable stoichiometry and may be crystallized to form the photoactive scheelite structure of BiVO4 . A selective etching process was used with vanadium-rich depositions to enable the synthesis of phase-pure BiVO4 after spinodal decomposition. BiVO4 thin films were measured for photoelectrochemical performance under AM 1.5 illumination. The average photocurrents were 1.17 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode using a hole-scavenging sulfite electrolyte. The capability to deposit conformal bismuth vanadates will enable a new generation of nanocomposite architectures for solar water splitting. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self Organization in Compensated Semiconductors

NASA Astrophysics Data System (ADS)

Berezin, Alexander A.

2004-03-01

In partially compensated semiconductor (PCS) Fermi level is pinned to donor sub-band. Due to positional randomness and almost isoenergetic hoppings, donor-spanned electronic subsystem in PCS forms fluid-like highly mobile collective state. This makes PCS playground for pattern formation, self-organization, complexity emergence, electronic neural networks, and perhaps even for origins of life, bioevolution and consciousness. Through effects of impact and/or Auger ionization of donor sites, whole PCS may collapse (spinodal decomposition) into microblocks potentially capable of replication and protobiological activity (DNA analogue). Electronic screening effects may act in RNA fashion by introducing additional length scale(s) to system. Spontaneous quantum computing on charged/neutral sites becomes potential generator of informationally loaded microstructures akin to "Carl Sagan Effect" (hidden messages in Pi in his "Contact") or informational self-organization of "Library of Babel" of J.L. Borges. Even general relativity effects at Planck scale (R.Penrose) may affect the dynamics through (e.g.) isotopic variations of atomic mass and local density (A.A.Berezin, 1992). Thus, PCS can serve as toy model (experimental and computational) at interface of physics and life sciences.

Plant Identity Influences Decomposition through More Than One Mechanism

PubMed Central

McLaren, Jennie R.; Turkington, Roy

2011-01-01

Plant litter decomposition is a critical ecosystem process representing a major pathway for carbon flux, but little is known about how it is affected by changes in plant composition and diversity. Single plant functional groups (graminoids, legumes, non-leguminous forbs) were removed from a grassland in northern Canada to examine the impacts of functional group identity on decomposition. Removals were conducted within two different environmental contexts (fertilization and fungicide application) to examine the context-dependency of these identity effects. We examined two different mechanisms by which the loss of plant functional groups may impact decomposition: effects of the living plant community on the decomposition microenvironment, and changes in the species composition of the decomposing litter, as well as the interaction between these mechanisms. We show that the identity of the plant functional group removed affects decomposition through both mechanisms. Removal of both graminoids and forbs slowed decomposition through changes in the decomposition microenvironment. We found non-additive effects of litter mixing, with both the direction and identity of the functional group responsible depending on year; in 2004 graminoids positively influenced decomposition whereas in 2006 forbs negatively influenced decomposition rate. Although these two mechanisms act independently, their effects may be additive if both mechanisms are considered simultaneously. It is essential to understand the variety of mechanisms through which even a single ecosystem property is affected if we are to predict the future consequences of biodiversity loss. PMID:21858210

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yong; Xing, Qingfeng; Straszheim, Warren E.

Here, we report how the superconducting phase forms in pseudo-single-crystal K xFe 2-ySe 2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition.more » It should be emphasized that the phase separation in pseudo-single-crystal K xFe 2-ySe 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less

How does low temperature coupled with different pressures affect initiation mechanisms and subsequent decompositions in nitramine explosive HMX?

PubMed

Wu, Qiong; Xiong, Guolin; Zhu, Weihua; Xiao, Heming

2015-09-21

We have performed ab initio molecular dynamics simulations to study coupling effects of temperature (534-873 K) and pressure (1-20 GPa) on the initiation mechanisms and subsequent chemical decompositions of nitramine explosive 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). A new initiation decomposition mechanism of HMX was found to be the unimolecular C-H bond breaking, and this mechanism was independent of the coupling effects of different temperatures and pressures. The formed hydrogen radicals could promote subsequent decompositions of HMX. Subsequent decompositions were very sensitive to the pressure at low temperatures (534 and 608 K), while the temperature became the foremost factor that affected the decomposition at a high temperature (873 K) instead of the pressure. Our study may provide a new insight into understanding the coupling effects of the temperature and pressure on the initiation decomposition mechanisms of nitramine explosives.

Inertial effects in three-dimensional spinodal decomposition of a symmetric binary fluid mixture: a lattice Boltzmann study

NASA Astrophysics Data System (ADS)

Kendon, Vivien M.; Cates, Michael E.; Pagonabarraga, Ignacio; Desplat, J.-C.; Bladon, Peter

2001-08-01

The late-stage demixing following spinodal decomposition of a three-dimensional symmetric binary fluid mixture is studied numerically, using a thermodynamically consistent lattice Boltzmann method. We combine results from simulations with different numerical parameters to obtain an unprecedented range of length and time scales when expressed in reduced physical units. (These are the length and time units derived from fluid density, viscosity, and interfacial tension.) Using eight large (2563) runs, the resulting composite graph of reduced domain size l against reduced time t covers 1 [less, similar] l [less, similar] 105, 10 [less, similar] t [less, similar] 108. Our data are consistent with the dynamical scaling hypothesis that l(t) is a universal scaling curve. We give the first detailed statistical analysis of fluid motion, rather than just domain evolution, in simulations of this kind, and introduce scaling plots for several quantities derived from the fluid velocity and velocity gradient fields. Using the conventional definition of Reynolds number for this problem, Re[phi] = ldl/dt, we attain values approaching 350. At Re[phi] [greater, similar] 100 (which requires t [greater, similar] 106) we find clear evidence of Furukawa's inertial scaling (l [similar] t2/3), although the crossover from the viscous regime (l [similar] t) is both broad and late (102 [less, similar] t [less, similar] 106). Though it cannot be ruled out, we find no indication that Re[phi] is self-limiting (l [similar] t1/2) at late times, as recently proposed by Grant & Elder. Detailed study of the velocity fields confirms that, for our most inertial runs, the RMS ratio of nonlinear to viscous terms in the Navier Stokes equation, R2, is of order 10, with the fluid mixture showing incipient turbulent characteristics. However, we cannot go far enough into the inertial regime to obtain a clear length separation of domain size, Taylor microscale, and Kolmogorov scale, as would be needed to test a recent ‘extended’ scaling theory of Kendon (in which R2 is self-limiting but Re[phi] not). Obtaining our results has required careful steering of several numerical control parameters so as to maintain adequate algorithmic stability, efficiency and isotropy, while eliminating unwanted residual diffusion. (We argue that the latter affects some studies in the literature which report l [similar] t2/3 for t [less, similar] 104.) We analyse the various sources of error and find them just within acceptable levels (a few percent each) in most of our datasets. To bring these under significantly better control, or to go much further into the inertial regime, would require much larger computational resources and/or a breakthrough in algorithm design.

A cavitation transition in the energy landscape of simple cohesive liquids and glasses

NASA Astrophysics Data System (ADS)

Altabet, Y. Elia; Stillinger, Frank H.; Debenedetti, Pablo G.

2016-12-01

In particle systems with cohesive interactions, the pressure-density relationship of the mechanically stable inherent structures sampled along a liquid isotherm (i.e., the equation of state of an energy landscape) will display a minimum at the Sastry density ρS. The tensile limit at ρS is due to cavitation that occurs upon energy minimization, and previous characterizations of this behavior suggested that ρS is a spinodal-like limit that separates all homogeneous and fractured inherent structures. Here, we revisit the phenomenology of Sastry behavior and find that it is subject to considerable finite-size effects, and the development of the inherent structure equation of state with system size is consistent with the finite-size rounding of an athermal phase transition. What appears to be a continuous spinodal-like point at finite system sizes becomes discontinuous in the thermodynamic limit, indicating behavior akin to a phase transition. We also study cavitation in glassy packings subjected to athermal expansion. Many individual expansion trajectories averaged together produce a smooth equation of state, which we find also exhibits features of finite-size rounding, and the examples studied in this work give rise to a larger limiting tension than for the corresponding landscape equation of state.

Self-assembled structural color in nature

NASA Astrophysics Data System (ADS)

Parnell, Andrew

The vibrancy and variety of structural color found in nature has long been well-known; what has only recently been discovered is the sophistication of the physics that underlies these effects. In the talk I will discuss some of our recent studies of the structures responsible for color in bird feathers and beetle elytra, based on structural characterization using small angle x-ray scattering, x-ray tomography and optical modeling. These have enabled us to study a large number of structural color exhibiting materials and look for trends in the structures nature uses to provide these optical effects. In terms of creating the optical structure responsible for the color of the Eurasian Jay feathers (Garrulus glandarius) the nanostructure is produced by a phase-separation process that is arrested at a late stage; mastery of the color is achieved by control over the duration of this phase-separation process. Our analysis shows that nanostructure in single bird feather barbs can be varied continuously by controlling the time the keratin network is allowed to phase separate before mobility in the system is arrested. Dynamic scaling analysis of the single barb scattering data implies that the phase separation arrest mechanism is rapid and also distinct from the spinodal phase separation mechanism i.e. it is not gelation or intermolecular re-association. Any growing lengthscale using this spinodal phase separation approach must first traverse the UV and blue wavelength regions, growing the structure by coarsening, resulting in a broad distribution of domain sizes. AJP acknowledges financial support via the APS/DPOLY exchange lectureship 2017.

[Critical phenomena, phase equilibria, and the temperature and structural optimum of homeostasis, as revealed by a model system water-biopolymer-electrolyte].

PubMed

Rozhkov, S P

2005-01-01

Equations of spinodal and two quasispinodals corresponding to critical and supercritical phase transitions leading to a rise of different dynamic structures of solution in the phase diagram of a model system water-biopolymer-electrolyte were obtained. The section of the phase diagram was considered where there exists the probability of quasi-equilibrium monomer-cluster and the principle of water-ion homeostasis is realized. Based on these results, a possible mechanism of origination of unspecific adaptation reactions of a biomolecular system at the stage of chemical evolution was suggested.

Multi-Phase Field Models and Microstructural Evolution with Applications in Fuel Cell Technology

NASA Astrophysics Data System (ADS)

Davis, Ryan Scott

The solid oxide fuel cell (SOFC) has shown tremendous potential as an efficient energy conversion device that may be instrumental in the transition to renewable resources. However, commercialization is hindered by many degradation mechanisms that plague long term stability. In this dissertation, computation methods are used to explore the relationship between the microstructure of the fuel cell anode and performance critical metrics. The phase field method and standard modeling procedures are introduced using a classic model of spinodal decomposition. This is further developed into a complete, multi-phase modeling framework designed for the complex microstructural evolution of SOFC anode systems. High-temperature coarsening of the metallic phase in the state-of-the-art SOFC cermet anode is investigated using our phase field model. A systematic study into the effects of interface properties on microstructural evolution is accomplished by altering the contact angle between constituent phases. It is found that metrics of catalytic activity and conductivity display undesirable minima near the contact angle of conventional SOFC materials. These results suggest that tailoring the interface properties of the constituent phases could lead to a significant increase in the performance and lifetime of SOFCs. Supported-metal catalyst systems are investigated in the first detailed study of their long-term stability and application to SOFC anode design. Porous support structures are numerically sintered to mimic specific fabrication techniques, and these structures are then infiltrated with a nanoscale catalyst phase ranging from 2% to 21% loading. Initially, these systems exhibit enhanced potential for catalytic activity relative to conventional cells. However, extended evolution results in severe degradation, and we show that Ostwald ripening and particle migration are key kinetic processes. Strong geometric heterogeneity in the support structure via a novel approach to nanopore formation is proposed as a potential solution for catalyst stabilization.

Modification of linear prepolymers to tailor heterogeneous network formation through photo-initiated Polymerization-Induced Phase Separation

PubMed Central

Szczepanski, Caroline R.; Stansbury, Jeffrey W.

2015-01-01

Polymerization-induced phase separation (PIPS) was studied in ambient photopolymerizations of triethylene glycol dimethacrylate (TEGDMA) modified by poly(methyl methacrylate) (PMMA). The molecular weight of PMMA and the rate of network formation (through incident UV-irradiation) were varied to influence both the promotion of phase separation through increases in overall free energy, as well as the extent to which phase development occurs during polymerization through diffusion prior to network gelation. The overall free energy of the polymerizing system increases with PMMA molecular weight, such that PIPS is promoted thermodynamically at low loading levels (5 wt%) of a higher molecular weight PMMA (120 kDa), while a higher loading level (20 wt%) is needed to induce PIPS with lower PMMA molecular weight (11 kDa), and phase separation was not promoted at any loading level tested of the lowest molecular weight PMMA (1 kDa). Due to these differences in overall free energy, systems modified by PMMA (11 kDa) underwent phase separation via Nucleation and Growth, and systems modified by PMMA (120 kDa), followed the Spinodal Decomposition mechanism. Despite differences in phase structure, all materials form a continuous phase rich in TEGDMA homopolymer. At high irradiation intensity (Io=20mW/cm2), the rate of network formation prohibited significant phase separation, even when thermodynamically preferred. A staged curing approach, which utilizes low intensity irradiation (Io=300µW/cm2) for the first ~50% of reaction to allow phase separation via diffusion, followed by a high intensity flood-cure to achieve a high degree of conversion, was employed to form phase-separated networks with reduced polymerization stress yet equivalent final conversion and modulus. PMID:26190865

FRAUD/SABOTAGE Killing Nuclear-Reactors!!! ``Super"alloys GENERIC ENDEMIC Wigner's-Disease IN-stability!!!

NASA Astrophysics Data System (ADS)

Asphahani, Aziz; Siegel, Sidney; Siegel, Edward

2010-03-01

Siegel [[J.Mag.Mag.Mtls.7,312(78); PSS(a)11,45(72); Semis.& Insuls.5(79)] (at: ORNL, ANS, Westin``KL"ouse, PSEG, IAEA, ABB) warning of old/new nuclear-reactors/spent-fuel-casks/refineries/ jet/missile/rocket-engines austenitic/FCC Ni/Fe-based (so MIS- called)``super"alloys(182/82;Hastelloy-X; 600;304/304L-SSs; 690 !!!) GENERIC ENDEMIC EXTANT detrimental(synonyms): Wigner's- diseas(WD)[J.Appl.Phys.17,857(46)]; Ostwald-ripening; spinodal- decomposition; overageing-embrittlement; thermomechanical- INstability: Mayo[Google: ``If Leaks Could Kill"; at flickr.com search on ``Giant-Magnotoresistance"; find: [Siegel<<<``Fert"(88) 2007-Nobel/Wolf/Japan-prizes]necessitating NRC inspections on 40+25=65 Westin``KL"ouse PWRs(12/06)]; Lai[Met.Trans.AIME,9A,827 (78)]-Sabol-Stickler[PSS(70)]; Ashpahani[Intl.Conf. H in Metals (77)]; Russell[Prog. Mtls.Sci.(83)]; Pollard[last UCS rept. (9/95)]; Lofaro[BNL/DOE/NRC Repts.]; Pringle[Nuclear-Power:From Physics to Politics(79)]; Hoffman[animatedsoftware.com],...what DOE/NRC MISlabels as ``butt-welds" ``stress-corrosion cracking" endpoint's ROOT-CAUSE ULTIMATE-ORIGIN is WD overageing-embrit- tlement caused brittle-fracture cracking from early/ongoing AEC/DOE-n``u''tional-la``v''atories sabotage!!!

Structuring of Fluid Adlayers upon Ongoing Unimolecular Adsorption

NASA Astrophysics Data System (ADS)

Schaefer, C.

2018-01-01

Fluids with spatial density variations of single or mixed molecules play a key role in biophysics, soft matter, and materials science. The fluid structures usually form via spinodal decomposition or nucleation following an instantaneous destabilization of the initially disordered fluid. However, in practice, an instantaneous quench is often not viable, and the rate of destabilization may be gradual rather than instantaneous. In this work we show that the commonly used phenomenological descriptions of fluid structuring are inadequate under these conditions. We come to that conclusion in the context of surface catalysis, where we employ kinetic Monte Carlo simulations to describe the unimolecular adsorption of gaseous molecules onto a metal surface. The adsorbates diffuse at the surface and, as a consequence of lateral interactions and due to an ongoing increase of the surface coverage, phase separate into coexisting low- and high-density regions. The typical size of these regions turns out to depend much more strongly on the rate of adsorption than predicted from recently reported phenomenological models. We discuss how this finding contributes to the fundamental understanding of the crossover from liquid-liquid to liquid-solid demixing of solution-cast polymer blends.

The effect of microstructural evolution on hardening behavior of type 17-4PH stainless steel in long-term aging at 350 deg. C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Jun; Zou Hong; Li Cong

2006-12-15

The effect of microstructural evolution on hardening behavior of 17-4PH stainless steel in long-term aging at 350 deg. C was studied by X-ray diffraction and transmission electron microscopy. The results showed that there is the matrix of lath martensite and nanometer-sized particles of {epsilon}-Cu precipitated from the matrix after the alloy is solution treated and tempered. When the alloy was aged 350 deg. C for 9 months, {alpha}-{alpha}' spinodal decomposition occurred along the grain boundaries and caused an increase in hardness which compensated for the weakening effect due to ripening of the {epsilon}-copper precipitates. Upon further aging to 12 months,more » the Cr-rich {alpha}'-phase and M{sub 23}C{sub 6} precipitated, both of which strengthened the alloy considerably and led to enhanced hardening despite the continued softening by overaging of the {epsilon}-copper precipitates. With the aging time extended to 15 months, substantial reversed austenite transformed and precipitation of the intermetallic G-phase occurred near the {epsilon}-Cu precipitates in the matrix. The abundant amount of reversed austenite that transformed led to rapid softening.« less

Unparticle-Higgs field mixing: Mikheyev-Smirnov-Wolfenstein resonances, seesaw mechanism, and spinodal instabilities

NASA Astrophysics Data System (ADS)

Boyanovsky, D.; Holman, R.; Hutasoit, Jimmy A.

2009-04-01

Motivated by slow-roll inflationary cosmology we study a scalar unparticle weakly coupled to a Higgs field in the broken symmetry phase. The mixing between the unparticle and the Higgs field results in a seesaw type matrix and the mixing angles feature a Mikheyev-Smirnov-Wolfenstein (MSW) effect as a consequence of the unparticle field being noncanonical. We find two (MSW) resonances for small and large spacelike momenta. The unparticlelike mode features a nearly flat potential with spinodal instabilities and a large expectation value. An effective potential for the unparticlelike field is generated from the Higgs potential, but with couplings suppressed by a large power of the small seesaw ratio. The dispersion relation for the Higgs-like mode features an imaginary part even at “tree level” as a consequence of the fact that the unparticle field describes a multiparticle continuum. Mixed unparticle-Higgs propagators reveal the possibility of oscillations, albeit with short coherence lengths. The results are generalized to the case in which the unparticle features a mass gap, in which case a low energy MSW resonance may occur for lightlike momenta depending on the scales. Unparticle-Higgs mixing leads to an effective unparticle potential of the new-inflation form. Slow-roll variables are suppressed by seesaw ratios and the anomalous dimensions and favor a red spectrum of scalar perturbations consistent with cosmic microwave background data.

Ab initio Kinetics and Thermal Decomposition Mechanism of Mononitrobiuret and 1,5-Dinitrobiuret

DTIC Science & Technology

2016-03-14

Journal Article 3. DATES COVERED (From - To) Feb 2015-May 2015 4. TITLE AND SUBTITLE Ab initio Kinetics and Thermal Decomposition Mechanism of 5a...tetrazole-free, nitrogen-rich, energetic compounds. For the first time, the thermal decomposition mechanisms of MNB and DNB have been investigated...potential energy surfaces for thermal decomposition of MNB and DNB were characterized at the RCCSD(T)/cc-pV∞Z//M06-2X/aug- cc-pVTZ level of theory

In situ creation of reactive polymer nanoparticles and resulting polymer layers formed at the interfaces of liquid crystals (Conference Presentation)

NASA Astrophysics Data System (ADS)

Kang, Shin-Woong; Kundu, Sudarshan; Park, Heung-Shik; Oh, Keun Chan; Lyu, Jae Jin

2017-02-01

We report the in situ creation of reactive polymer nanoparticles and resulting polymer networks formed at the interfaces of liquid crystals. It is known that polymerization-induced phase separation proceeds in two distinct regimes depending on the concentration of monomer. For a high monomer concentration, phase separation occurs mainly through the spinodal decomposition process, consequently resulting in interpenetrating polymer networks. For a dilute system, however, the phase separation mainly proceeds and completes in the binodal decomposition regime. The system resembles the aggregation process of colloidal particle. In this case, the reaction kinetics is limited by the reaction between in situ created polymer aggregates and hence the network morphologies are greatly influenced by the diffusion of reactive polymer particles. The thin polymer layers localized at the surface of substrate are inevitably observed and can be comprehended by the interfacial adsorption and further cross-linking reaction of reactive polymer aggregates at the interface. This process provides a direct perception on understanding polymer stabilized liquid crystals accomplished by the interfacial polymer layer. The detailed study has been performed for an extremely dilute condition (below 0.5 wt%) by employing systematic experimental approaches. Creation and growth of polymer nanoparticles have been measured by particle size analyzer. The interfacial localization of polymer aggregates and resulting interfacial layer formation with a tens of nanometer scale have been exploited at various interfaces such as liquid-solid, liquid-liquid, and liquid-gas interfaces. The resulting interfacial layers have been characterized by using fuorescent confocal microscope and field emission scanning electron microscope. The detailed processes of the polymer stabilized vertically aligned liquid crystals will be discussed in support of the reported study.

Effects of defects on thermal decomposition of HMX via ReaxFF molecular dynamics simulations.

PubMed

Zhou, Ting-Ting; Huang, Feng-Lei

2011-01-20

Effects of molecular vacancies on the decomposition mechanisms and reaction dynamics of condensed-phase β-HMX at various temperatures were studied using ReaxFF molecular dynamics simulations. Results show that three primary initial decomposition mechanisms, namely, N-NO(2) bond dissociation, HONO elimination, and concerted ring fission, exist at both high and lower temperatures. The contribution of the three mechanisms to the initial decomposition of HMX is influenced by molecular vacancies, and the effects vary with temperature. At high temperature (2500 K), molecular vacancies remarkably promote N-N bond cleavage and concerted ring breaking but hinder HONO formation. N-N bond dissociation and HONO elimination are two primary competing reaction mechanisms, and the former is dominant in the initial decomposition. Concerted ring breaking of condensed-phase HMX is not favored at high temperature. At lower temperature (1500 K), the most preferential initial decomposition pathway is N-N bond dissociation followed by the formation of NO(3) (O migration), although all three mechanisms are promoted by molecular vacancies. The promotion effect on concerted ring breaking is considerable at lower temperature. Products resulting from concerted ring breaking appear in the defective system but not in the perfect crystal. The mechanism of HONO elimination is less important at lower temperature. We also estimated the reaction rate constant and activation barriers of initial decomposition with different vacancy concentrations. Molecular vacancies accelerate the decomposition of condensed-phase HMX by increasing the reaction rate constant and reducing activation barriers.

Effect of Copper Oxide, Titanium Dioxide, and Lithium Fluoride on the Thermal Behavior and Decomposition Kinetics of Ammonium Nitrate

NASA Astrophysics Data System (ADS)

Vargeese, Anuj A.; Mija, S. J.; Muralidharan, Krishnamurthi

2014-07-01

Ammonium nitrate (AN) is crystallized along with copper oxide, titanium dioxide, and lithium fluoride. Thermal kinetic constants for the decomposition reaction of the samples were calculated by model-free (Friedman's differential and Vyzovkins nonlinear integral) and model-fitting (Coats-Redfern) methods. To determine the decomposition mechanisms, 12 solid-state mechanisms were tested using the Coats-Redfern method. The results of the Coats-Redfern method show that the decomposition mechanism for all samples is the contracting cylinder mechanism. The phase behavior of the obtained samples was evaluated by differential scanning calorimetry (DSC), and structural properties were determined by X-ray powder diffraction (XRPD). The results indicate that copper oxide modifies the phase transition behavior and can catalyze AN decomposition, whereas LiF inhibits AN decomposition, and TiO2 shows no influence on the rate of decomposition. Possible explanations for these results are discussed. Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Energetic Materials to view the free supplemental file.

Physical limit of stability in supercooled D2O and D2O+H2O mixtures

NASA Astrophysics Data System (ADS)

Kiselev, S. B.; Ely, J. F.

2003-01-01

The fluctuation theory of homogeneous nucleation was applied for calculating the physical boundary of metastable states, the kinetic spinodal, in supercooled D2O and D2O+H2O mixtures. The kinetic spinodal in our approach is completely determined by the surface tension and equation of state of the supercooled liquid. We developed a crossover equation of state for supercooled D2O, which predicts a second critical point of low density water-high density water equilibrium, CP2, and represents all available experimental data in supercooled D2O within experimental accuracy. Using Turnbull's expression for the surface tension we calculated with the crossover equation of state for supercooled D2O the kinetic spinodal, TKS, which lies below the homogeneous nucleation temperature, TH. We show that CP2 always lies inside in the so-called "nonthermodynamic habitat" and physically does not exist. However, the concept of a second "virtual" critical point is physical and very useful. Using this concept we have extended this approach to supercooled D2O+H2O mixtures. As an example, we consider here an equimolar D2O+H2O mixture in normal and supercooled states at atmospheric pressure, P=0.1 MPa.

Novel self-organization mechanism in ultrathin liquid films: theory and experiment.

PubMed

Trice, Justin; Favazza, Christopher; Thomas, Dennis; Garcia, Hernando; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

2008-07-04

When an ultrathin metal film of thickness h (<20 nm) is melted by a nanosecond pulsed laser, the film temperature is a nonmonotonic function of h and achieves its maximum at a certain thickness h*. This is a consequence of the h and time dependence of energy absorption and heat flow. Linear stability analysis and nonlinear dynamical simulations that incorporate such intrinsic interfacial thermal gradients predict a characteristic pattern length scale Lambda that decreases for h>h*, in contrast to the classical spinodal dewetting behavior where Lambda increases monotonically as h2. These predictions agree well with experimental observations for Co and Fe films on SiO2.

The roles of the binodal curve and the spinodal curve in expansions from the supercritical state with flashing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knuth, Eldon L.; Miller, David R.; Even, Uzi

2014-12-09

Data extracted from time-of-flight (TOF) measurements made on steady-state He free jets at Göttingen already in 1986 and for pulsed Ne free jets investigated recently at Tel Aviv have been added to an earlier plot of terminal condensed-phase mass fraction x{sub 2∞} as a function of the dimensionless scaling parameter Γ. Γ characterizes the source (fluid species, temperature, pressure and throat diameter); values of x{sub 2∞} are extracted from TOF measurements using conservation of energy in the free-jet expansion. For nozzles consisting of an orifice in a thin plate; the extracted data yield 22 data points which are correlated satisfactorilymore » by a single curve. The Ne free jets were expanded from a conical nozzle with a 20° half angle; the three extracted data points stand together but apart from the aforementioned curve, indicating that the presence of the conical wall influences significantly the expansion and hence the condensation. The 22 data points for the expansions via an orifice consist of 15 measurements with expansions from the gas-phase side of the binodal curve which crossed the binodal curve downstream from the sonic point and 7 measurements with expansions of the gas-phase product of the flashing which occurred after an expansion from the liquid-phase side of the binodal curve crossed the binodal curve upstream from the sonic point. The association of these 22 points with a single curve supports the alternating-phase model for flows with flashing upstream from the sonic point proposed earlier. In order to assess the role of the spinodal curve in such expansions, the spinodal curves for He and Ne were computed using general multi-parameter Helmholtz-free-energy equation-of-state formulations. Then, for the several sets of source-chamber conditions used in the free-jet measurements, thermodynamic states at key locations in the free-jet expansions (binodal curve, sonic point and spinodal curve) were evaluated, with the expansion presumed to be metastable from the binodal curve to the spinodal curve. TOF distributions with more than two peaks (interpreted earlier as superimposed alternating-state TOF distributions) indicated flashing of the metastable flow downstream from the binodal curve but upstream from the sonic point. This relatively early flashing is due apparently to destabilizing interactions with the walls of the source. If the expansion crosses the binodal curve downstream from the nozzle, the metastable fluid does not interact with surfaces and flashing might be delayed until the expansion reaches the spinodal curve. It is concluded that, if the expansion crosses the binodal curve before reaching the sonic point, the resulting metastable fluid downstream from the binodal curve interacts with the adjacent surfaces and flashes into liquid and vapor phases which expand alternately through the nozzle; the two associated alternating TOF distributions are superposed by the chopping process so that the result has the appearance of a single distribution with three peaks.« less

Decomposition mechanism of chromite in sulfuric acid-dichromic acid solution

NASA Astrophysics Data System (ADS)

Zhao, Qing; Liu, Cheng-jun; Li, Bao-kuan; Jiang, Mao-fa

2017-12-01

The sulfuric acid leaching process is regarded as a promising, cleaner method to prepare trivalent chromium products from chromite; however, the decomposition mechanism of the ore is poorly understood. In this work, binary spinels of Mg-Al, Mg-Fe, and Mg-Cr in the powdered and lump states were synthesized and used as raw materials to investigate the decomposition mechanism of chromite in sulfuric acid-dichromic acid solution. The leaching yields of metallic elements and the changes in morphology of the spinel were studied. The experimental results showed that the three spinels were stable in sulfuric acid solution and that dichromic acid had little influence on the decomposition behavior of the Mg-Al spinel and Mg-Fe spinel because Mg2+, Al3+, and Fe3+ in spinels cannot be oxidized by Cr6+. However, in the case of the Mg-Cr spinel, dichromic acid substantially promoted the decomposition efficiency and functioned as a catalyst. The decomposition mechanism of chromite in sulfuric acid-dichromic acid solution was illustrated on the basis of the findings of this study.

An ab initio molecular dynamics study of thermal decomposition of 3,6-di(azido)-1,2,4,5-tetrazine.

PubMed

Wu, Qiong; Zhu, Weihua; Xiao, Heming

2014-10-21

Ab initio molecular dynamics simulations were performed to study the thermal decomposition of isolated and crystal 3,6-di(azido)-1,2,4,5-tetrazine (DiAT). During unimolecular decomposition, the three different initiation mechanisms were observed to be N-N2 cleavage, ring opening, and isomerization, respectively. The preferential initial decomposition step is the homolysis of the N-N2 bond in the azido group. The release mechanisms of nitrogen gas are found to be very different in the early and later decomposition stages of crystal DiAT. In the early decomposition, DiAT decomposes very fast and drastically without forming any stable long-chains or heterocyclic clusters, and most of the nitrogen gases are released through rapid rupture of nitrogen-nitrogen and carbon-nitrogen bonds. But in the later decomposition stage, the release of nitrogen gas is inhibited due to low mobility, long distance from each other, and strong carbon-nitrogen bonds. To overcome the obstacles, the nitrogen gases are released through slow formation and disintegration of polycyclic networks. Our simulations suggest a new decomposition mechanism for the organic polyazido initial explosive at the atomistic level.

A density functional theory study of the decomposition mechanism of nitroglycerin.

PubMed

Pei, Liguan; Dong, Kehai; Tang, Yanhui; Zhang, Bo; Yu, Chang; Li, Wenzuo

2017-08-21

The detailed decomposition mechanism of nitroglycerin (NG) in the gas phase was studied by examining reaction pathways using density functional theory (DFT) and canonical variational transition state theory combined with a small-curvature tunneling correction (CVT/SCT). The mechanism of NG autocatalytic decomposition was investigated at the B3LYP/6-31G(d,p) level of theory. Five possible decomposition pathways involving NG were identified and the rate constants for the pathways at temperatures ranging from 200 to 1000 K were calculated using CVT/SCT. There was found to be a lower energy barrier to the β-H abstraction reaction than to the α-H abstraction reaction during the initial step in the autocatalytic decomposition of NG. The decomposition pathways for CHOCOCHONO 2 (a product obtained following the abstraction of three H atoms from NG by NO 2 ) include O-NO 2 cleavage or isomer production, meaning that the autocatalytic decomposition of NG has two reaction pathways, both of which are exothermic. The rate constants for these two reaction pathways are greater than the rate constants for the three pathways corresponding to unimolecular NG decomposition. The overall process of NG decomposition can be divided into two stages based on the NO 2 concentration, which affects the decomposition products and reactions. In the first stage, the reaction pathway corresponding to O-NO 2 cleavage is the main pathway, but the rates of the two autocatalytic decomposition pathways increase with increasing NO 2 concentration. However, when a threshold NO 2 concentration is reached, the NG decomposition process enters its second stage, with the two pathways for NG autocatalytic decomposition becoming the main and secondary reaction pathways.

New mechanism for autocatalytic decomposition of H2CO3 in the vapor phase.

PubMed

Ghoshal, Sourav; Hazra, Montu K

2014-04-03

In this article, we present high level ab initio calculations investigating the energetics of a new autocatalytic decomposition mechanism for carbonic acid (H2CO3) in the vapor phase. The calculation have been performed at the MP2 level of theory in conjunction with aug-cc-pVDZ, aug-cc-pVTZ, and 6-311++G(3df,3pd) basis sets as well as at the CCSD(T)/aug-cc-pVTZ level. The present study suggests that this new decomposition mechanism is effectively a near-barrierless process at room temperature and makes vapor phase of H2CO3 unstable even in the absence of water molecules. Our calculation at the MP2/aug-cc-pVTZ level predicts that the effective barrier, defined as the difference between the zero-point vibrational energy (ZPE) corrected energy of the transition state and the total energy of the isolated starting reactants in terms of bimolecular encounters, is nearly zero for the autocatalytic decomposition mechanism. The results at the CCSD(T)/aug-cc-pVTZ level of calculations suggest that the effective barrier, as defined above, is sensitive to some extent to the levels of calculations used, nevertheless, we find that the effective barrier height predicted at the CCSD(T)/aug-cc-pVTZ level is very small or in other words the autocatalytic decomposition mechanism presented in this work is a near-barrierless process as mentioned above. Thus, we suggest that this new autocatalytic decomposition mechanism has to be considered as the primary mechanism for the decomposition of carbonic acid, especially at its source, where the vapor phase concentration of H2CO3 molecules reaches its highest levels.

A characterization of the two-step reaction mechanism of phenol decomposition by a Fenton reaction

NASA Astrophysics Data System (ADS)

Valdés, Cristian; Alzate-Morales, Jans; Osorio, Edison; Villaseñor, Jorge; Navarro-Retamal, Carlos

2015-11-01

Phenol is one of the worst contaminants at date, and its degradation has been a crucial task over years. Here, the decomposition process of phenol, in a Fenton reaction, is described. Using scavengers, it was observed that decomposition of phenol was mainly influenced by production of hydroxyl radicals. Experimental and theoretical activation energies (Ea) for phenol oxidation intermediates were calculated. According to these Ea, phenol decomposition is a two-step reaction mechanism mediated predominantly by hydroxyl radicals, producing a decomposition yield order given as hydroquinone > catechol > resorcinol. Furthermore, traces of reaction derived acids were detected by HPLC and GS-MS.

Nanoclusters first: a hierarchical phase transformation in a novel Mg alloy

NASA Astrophysics Data System (ADS)

Okuda, Hiroshi; Yamasaki, Michiaki; Kawamura, Yoshihito; Tabuchi, Masao; Kimizuka, Hajime

2015-09-01

The Mg-Y-Zn ternary alloy system contains a series of novel structures known as long-period stacking ordered (LPSO) structures. The formation process and its key concept from a viewpoint of phase transition are not yet clear. The current study reveals that the phase transformation process is not a traditional spinodal decomposition or structural transformation but, rather a novel hierarchical phase transformation. In this transformation, clustering occurs first, and the spatial rearrangement of the clusters induce a secondary phase transformation that eventually lead to two-dimensional ordering of the clusters. The formation process was examined using in situ synchrotron radiation small-angle X-ray scattering (SAXS). Rapid quenching from liquid alloy into thin ribbons yielded strongly supersaturated amorphous samples. The samples were heated at a constant rate of 10 K/min. and the scattering patterns were acquired. The SAXS analysis indicated that small clusters grew to sizes of 0.2 nm after they crystallized. The clusters distributed randomly in space grew and eventually transformed into a microstructure with two well-defined cluster-cluster distances, one for the segregation periodicity of LPSO and the other for the in-plane ordering in segregated layer. This transformation into the LPSO structure concomitantly introduces the periodical stacking fault required for the 18R structures.

Two-dimensional Turbulence in Symmetric Binary-Fluid Mixtures: Coarsening Arrest by the Inverse Cascade

NASA Astrophysics Data System (ADS)

Perlekar, Prasad; Pal, Nairita; Pandit, Rahul

2017-03-01

We study two-dimensional (2D) binary-fluid turbulence by carrying out an extensive direct numerical simulation (DNS) of the forced, statistically steady turbulence in the coupled Cahn-Hilliard and Navier-Stokes equations. In the absence of any coupling, we choose parameters that lead (a) to spinodal decomposition and domain growth, which is characterized by the spatiotemporal evolution of the Cahn-Hilliard order parameter ϕ, and (b) the formation of an inverse-energy-cascade regime in the energy spectrum E(k), in which energy cascades towards wave numbers k that are smaller than the energy-injection scale kin j in the turbulent fluid. We show that the Cahn-Hilliard-Navier-Stokes coupling leads to an arrest of phase separation at a length scale Lc, which we evaluate from S(k), the spectrum of the fluctuations of ϕ. We demonstrate that (a) Lc ~ LH, the Hinze scale that follows from balancing inertial and interfacial-tension forces, and (b) Lc is independent, within error bars, of the diffusivity D. We elucidate how this coupling modifies E(k) by blocking the inverse energy cascade at a wavenumber kc, which we show is ≃2π/Lc. We compare our work with earlier studies of this problem.

Two-dimensional Turbulence in Symmetric Binary-Fluid Mixtures: Coarsening Arrest by the Inverse Cascade.

PubMed

Perlekar, Prasad; Pal, Nairita; Pandit, Rahul

2017-03-21

We study two-dimensional (2D) binary-fluid turbulence by carrying out an extensive direct numerical simulation (DNS) of the forced, statistically steady turbulence in the coupled Cahn-Hilliard and Navier-Stokes equations. In the absence of any coupling, we choose parameters that lead (a) to spinodal decomposition and domain growth, which is characterized by the spatiotemporal evolution of the Cahn-Hilliard order parameter ϕ, and (b) the formation of an inverse-energy-cascade regime in the energy spectrum E(k), in which energy cascades towards wave numbers k that are smaller than the energy-injection scale kin j in the turbulent fluid. We show that the Cahn-Hilliard-Navier-Stokes coupling leads to an arrest of phase separation at a length scale Lc, which we evaluate from S(k), the spectrum of the fluctuations of ϕ. We demonstrate that (a) Lc ~ LH, the Hinze scale that follows from balancing inertial and interfacial-tension forces, and (b) Lc is independent, within error bars, of the diffusivity D. We elucidate how this coupling modifies E(k) by blocking the inverse energy cascade at a wavenumber kc, which we show is ≃2π/Lc. We compare our work with earlier studies of this problem.

Role of PO4 tetrahedron in LiFePO4 and FePO4 system.

PubMed

Zeng, Yuewu

2015-06-01

Using high resolution transmission electron microscopy with image simulation and Fourier analysis, the Li1- x FePO4 (x < 0.01), Li1- x FePO4 (x ∼ 0.5), and FePO4 particles, prepared by charging or discharging the 053048 electrochemical cells (thickness: 5 mm, width: 30 mm, height: 48 mm) and dismantled inside an Ar-filled dry box, were investigated. The high resolution images reveal: (1) the solid solution of Li1- x FePO4 (x < 0.01) contains some missing Li ions leading PO4 group distorted around M1 tunnel of the unit cell; (2) the texture of the particles of Li1- x FePO4 (x ∼0.5) has homogeneously distributed compositional domains of LiFePO4 and FePO4 resulting from spinodal decomposition which promote Li ion easily getting into the particle due to uphill diffusion, (3) the particles of FePO4 formed in charging have heavily distorted lattice and contain some isolated LiFePO4 , (4) interface between LiFePO4 and FePO4 and between amorphous and crystal region provides the lattice distortion of small polarons. © 2015 Wiley Periodicals, Inc.

Kinetics and Equilibrium of Age-Induced Precipitation in Cu-4 At. Pct Ti Binary Alloy

NASA Astrophysics Data System (ADS)

Semboshi, Satoshi; Amano, Shintaro; Fu, Jie; Iwase, Akihiro; Takasugi, Takayuki

2017-03-01

Transformation kinetics and phase equilibrium of metastable and stable precipitates in age-hardenable Cu-4 at. pct Ti binary alloy have been investigated by monitoring the microstructural evolution during isothermal aging at temperatures between 693 K (420 °C) and 973 K (700 °C). The microstructure of the supersaturated solid solution evolves in four stages: compositional modulation due to spinodal decomposition, continuous precipitation of the needle-shaped metastable β'-Cu4Ti with a tetragonal structure, discontinuous precipitation of cellular components containing stable β-Cu4Ti lamellae with an orthorhombic structure, and eventually precipitation saturation at equilibrium. In specimens aged below 923 K (650 °C), the stable β-Cu4Ti phase is produced only due to the cellular reaction, whereas it can be also directly obtained from the intergranular needle-shaped β'-Cu4Ti precipitates in specimens aged at 973 K (700 °C). The precipitation kinetics and phase equilibrium observed for the specimens aged between 693 K (420 °C) and 973 K (700 °C) were characterized in accordance with a time-temperature-transformation (TTT) diagram and a Cu-Ti partial phase diagram, which were utilized to determine the alloy microstructure, strength, and electrical conductivity.

Suppression of turbulent energy cascade due to phase separation in homogenous binary mixture fluid

NASA Astrophysics Data System (ADS)

Takagi, Youhei; Okamoto, Sachiya

2015-11-01

When a multi-component fluid mixture becomes themophysically unstable state by quenching from well-melting condition, phase separation due to spinodal decomposition occurs, and a self-organized structure is formed. During phase separation, free energy is consumed for the structure formation. In our previous report, the phase separation in homogenous turbulence was numerically simulated and the coarsening process of phase separation was discussed. In this study, we extended our numerical model to a high Schmidt number fluid corresponding to actual polymer solution. The governing equations were continuity, Navier-Stokes, and Chan-Hiliard equations as same as our previous report. The flow filed was an isotropic homogenous turbulence, and the dimensionless parameters in the Chan-Hilliard equation were estimated based on the thermophysical condition of binary mixture. From the numerical results, it was found that turbulent energy cascade was drastically suppressed in the inertial subrange by phase separation for the high Schmidt number flow. By using the identification of turbulent and phase separation structure, we discussed the relation between total energy balance and the structures formation processes. This study is financially supported by the Grand-in-Aid for Young Scientists (B) (No. T26820045) from the Ministry of Education, Cul-ture, Sports, Science and Technology of Japan.

Low-temperature spin dynamics of Mn-rich Mn(Ga)As nanoclusters embedded in a GaAs matrix

NASA Astrophysics Data System (ADS)

Wang, Weizhu; Deng, Jiajun; Lu, Jun; Sun, Baoquan; Zhao, Jianhua

2008-03-01

Recently, the composite systems of Mn-rich Mn(Ga)As nanoclusters embedded in GaAs matrices have received an increasing attention due to the large magneto-optical and magneto-resistance effects at room temperature which could be applied to spin-electronic devices. In this work, we report the low-temperature spin dynamic behaviours including memory effects and slow magnetic relaxation of such composite systems. The systems can be formed by in situ postgrowth annealing of (Ga,Mn)As films at 650 ^oC for 10 min because of spinodal decomposition. High-resolution TEM images show zincblende Mn-rich Mn(Ga)As nanoclusters with a diameter in the range of 10-20 nm embedded in a GaAs matrix. From zero-field cooled and field cooled measurements, we can observe a clear bifurcation of the two curves demonstrating the existence of the spin-glass-like phase below the blocking temperature in the systems with high Mn concentration. Memory effects and slow magnetic relaxation, the typical characteristics of spin-glass-like phases, are also detected, and the hierarchical model is confirmed to be in accordance with such low-temperature behaviours. On the other hand, for samples with low Mn content, ferromagnetic order remains up to 360K.

Collapse kinetics of vibrated granular chains

NASA Astrophysics Data System (ADS)

Jeng, Pei-Ren; Chen, Kuan Hua; Hwang, Gwo-jen; Lien, Chenhsin; To, Kiwing; Chou, Y. C.

2011-12-01

The kinetics of the collapse of the coil state into condensed states is studied with vibrated granular chain composed of N metal beads partially immersed in water. The radius of gyration of the chain, Rg is measured. For short chains (N < 140), disk-like condensed state is formed and Rg decreases with time such that the function ΔRg2 (≡ Rg2 - Rg2(∞)) = A e-t/τ, where the relaxation time τ follows a power-law dependence on the chain length N with an exponent γ = 1.9 ± 0.2. For the chains with length N ≥ 300, rod-like clusters are observed during the initial stage of collapse and Rg2 = Rg2(0) - Btβ, with β = 0.6 ± 0.1. In the coarsening stage, the exponential dependence of ΔRg2 on time still holds, however, the relaxation time τ fluctuates and has no simple dependence on N. Furthermore, the time dependence of the averaged radius of gyration of the individual clusters, Rg,cl can be described by the theory of Lifshitz and Slyozov. A peak in the structure function of long chains is observed in the initial stage of the collapse transition. The collapse transition in the bead chains is a first order phase transition. However, features of the spinodal decomposition are also observed.

Two-dimensional Turbulence in Symmetric Binary-Fluid Mixtures: Coarsening Arrest by the Inverse Cascade

PubMed Central

Perlekar, Prasad; Pal, Nairita; Pandit, Rahul

2017-01-01

We study two-dimensional (2D) binary-fluid turbulence by carrying out an extensive direct numerical simulation (DNS) of the forced, statistically steady turbulence in the coupled Cahn-Hilliard and Navier-Stokes equations. In the absence of any coupling, we choose parameters that lead (a) to spinodal decomposition and domain growth, which is characterized by the spatiotemporal evolution of the Cahn-Hilliard order parameter ϕ, and (b) the formation of an inverse-energy-cascade regime in the energy spectrum E(k), in which energy cascades towards wave numbers k that are smaller than the energy-injection scale kin j in the turbulent fluid. We show that the Cahn-Hilliard-Navier-Stokes coupling leads to an arrest of phase separation at a length scale Lc, which we evaluate from S(k), the spectrum of the fluctuations of ϕ. We demonstrate that (a) Lc ~ LH, the Hinze scale that follows from balancing inertial and interfacial-tension forces, and (b) Lc is independent, within error bars, of the diffusivity D. We elucidate how this coupling modifies E(k) by blocking the inverse energy cascade at a wavenumber kc, which we show is ≃2π/Lc. We compare our work with earlier studies of this problem. PMID:28322219

Microstructural evolution in a 17-4 PH stainless steel after aging at 400 C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murayama, M.; Hono, K.; Katayama, Y.

1999-02-01

The microstructure of 17-4 PH stainless steel at various stages of heat treatment, i.e., after solution heat treatment, tempering at 580 C, and long-term aging at 400 C, have been studied by atom probe field ion microscopy (APFIM) and transmission electron microscopy (TEM). The solution-treated specimen consists largely of martensite with a small fraction of {delta}-ferrite. No precipitates are present in the martensite phase, while spherical fcc-Cu particles are present in the {delta}-ferrite. No precipitates are present in the martensite phase, while spherical fcc-Cu particles are present in the {delta}-ferrite. After tempering for 4 hours as 580 C, coherent Cumore » particles precipitate in the martensite phase. At this stage, the Cr concentration in the martensite phase is still uniform. After 5000 hours aging at 400 C, the martensite spinodaly decomposes into Fe-rich {alpha} and Cr-enriched {alpha}{prime}. In addition, fine particles of the G-phase (structure type D8{sub a}, space group Fm{bar 3}m) enriched in Si, Ni, and Mn have been found in intimate contact with the Cu precipitates. Following spinodal decomposition of the martensite phase, G-phase precipitation occurs after long-term aging.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siol, Sebastian; Holder, Aaron; Ortiz, Brenden R.

Here, the controlled decomposition of metastable alloys is an attractive route to form nanostructured thermoelectric materials with reduced thermal conductivity. The ternary SnTe–MnTe and SnTe–SnSe heterostructural alloys have been demonstrated as promising materials for thermoelectric applications. In this work, the quaternary Sn 1–yMnyTe 1–xSe x phase space serves as a relevant model system to explore how a combination of computational and combinatorial-growth methods can be used to study equilibrium and non-equilibrium solubility limits. Results from first principle calculations indicate low equilibrium solubility for x,y < 0.05 that are in good agreement with results obtained from bulk equilibrium synthesis experiments andmore » predict significantly higher spinodal limits. An experimental screening using sputtered combinatorial thin film sample libraries showed a remarkable increase in non-equilibrium solubility for x,y > 0.2. These theoretical and experimental results were used to guide the bulk synthesis of metastable alloys. The ability to reproduce the non-equilibrium solubility levels in bulk materials indicates that such theoretical calculations and combinatorial growth can inform bulk synthetic routes. Further, the large difference between equilibrium and non-equilibrium solubility limits in Sn 1–yMn yTe 1–xSe x indicates these metastable alloys are attractive in terms of nano-precipitate formation for potential thermoelectric applications.« less

Theoretical study of the decomposition mechanism of environmentally friendly insulating medium C3F7CN in the presence of H2O in a discharge

NASA Astrophysics Data System (ADS)

Zhang, Xiaoxing; Li, Yi; Xiao, Song; Tian, Shuangshuang; Deng, Zaitao; Tang, Ju

2017-08-01

C3F7CN has been the focus of the alternative gas research field over the past two years because of its excellent insulation properties and environmental characteristics. Experimental studies on its insulation performance have made many achievements. However, few studies on the formation mechanism of the decomposition components exist. A discussion of the decomposition characteristics of insulating media will provide guidance for scientific experimental research and the work that must be completed before further engineering application. In this study, the decomposition mechanism of C3F7CN in the presence of trace H2O under discharge was calculated based on the density functional theory and transition state theory. The reaction heat, Gibbs free energy, and activation energy of different decomposition pathways were investigated. The ionization parameters and toxicity of C3F7CN and various decomposition products were analyzed from the molecular structure perspective. The formation mechanism of the C3F7CN discharge decomposition components and the influence of trace water were evaluated. This paper confirms that C3F7CN has excellent decomposition characteristics, which provide theoretical support for later experiments and related engineering applications. However, the existence of trace water has a negative impact on C3F7CN’s insulation performance. Thus, strict trace water content standards should be developed to ensure dielectric insulation and the safety of maintenance personnel.

Method for producing microchannels in drawn material

DOEpatents

D'urso, Brian R [Clinton, TN; Simpson, John T [Clinton, TN

2009-12-29

A microchannel glass article includes a glass body having a porous, spinodal nanostructure and defining at least one microchannel extending from a surface of the article substantially through the article.

Viscosity effects on the thermal decomposition of bis(perfluoro-2-N-propoxypropionyl) peroxide in dense carbon dioxide and fluorinated solvents.

PubMed

Bunyard, W C; Kadla, J F; DeYoung, J; DeSimone, J M

2001-08-01

The thermal decomposition of the free-radical initiator bis(perfluoro-2-N-propoxyprionyl) peroxide (BPPP) was studied in dense carbon dioxide and a series of fluorinated solvents. For the fluorinated solvents, the observed first-order decomposition rate constants, k(obs), increased with decreasing solvent viscosity, suggesting a single-bond decomposition mechanism. The k(obs) values are comparatively larger in dense carbon dioxide and similar to the "zero-viscosity" rate constants extrapolated from the decomposition kinetics in the fluorinated solvents. The decomposition activation parameters demonstrate a compensation behavior of the activation enthalpy with the activation entropy upon change in solvent viscosity. Comparison of the change in activation parameter values upon change in solvent viscosity for BPPP with two additional initiators, acetyl peroxide (AP) and trifluoroacetyl peroxide (TFAP), further suggests that carbon dioxide exerts a very minimal influence on the decomposition mechanism of these initiators through solvent-cage effects.

Theoretical studies of the decomposition mechanisms of 1,2,4-butanetriol trinitrate.

PubMed

Pei, Liguan; Dong, Kehai; Tang, Yanhui; Zhang, Bo; Yu, Chang; Li, Wenzuo

2017-12-06

Density functional theory (DFT) and canonical variational transition-state theory combined with a small-curvature tunneling correction (CVT/SCT) were used to explore the decomposition mechanisms of 1,2,4-butanetriol trinitrate (BTTN) in detail. The results showed that the γ-H abstraction reaction is the initial pathway for autocatalytic BTTN decomposition. The three possible hydrogen atom abstraction reactions are all exothermic. The rate constants for autocatalytic BTTN decomposition are 3 to 10 40 times greater than the rate constants for the two unimolecular decomposition reactions (O-NO 2 cleavage and HONO elimination). The process of BTTN decomposition can be divided into two stages according to whether the NO 2 concentration is above a threshold value. HONO elimination is the main reaction channel during the first stage because autocatalytic decomposition requires NO 2 and the concentration of NO 2 is initially low. As the reaction proceeds, the concentration of NO 2 gradually increases; when it exceeds the threshold value, the second stage begins, with autocatalytic decomposition becoming the main reaction channel.

Nitrosonium-Catalyzed Decomposition of S-Nitrosothiols in Solution

PubMed Central

Zhao, Yi-Lei; McCarren, Patrick R.; Houk, K. N.; Choi, Bo Yoon; Toone, Eric J.

2008-01-01

The decomposition of S-nitrosothiols (RSNO) in solution under oxidative conditions is significantly faster than can be accounted for by homolysis of the S-N bond. Here we propose a cationic chain mechanism in which nitrosylation of nitrosothiol produces a nitrosylated cation that, in turn, reacts with a second nitrosothiol to produce disulfide and the NO dimer. Nitrosylated dimer acts as a source of nitrosonium for nitrosothiol nitrosylation, completing the catalytic cycle. The mechanism accounts for several unexplained facets of nitrosothiol chemistry in solution, including the observation that the decomposition of an RSNO is accelerated by O2, mixtures of O2 and NO, and other oxidants, that decomposition is inhibited by thiols and other antioxidants, that decomposition is dependent on sulfur substitution, and that decomposition often shows non-integral kinetic orders. PMID:16076198

Interactions of Hydrazine and Blowby Gases

NASA Technical Reports Server (NTRS)

Meagher, Nancy E.

2003-01-01

The interactions between hydrazine and blowby gases from pyrovalves was explored in this research project. Investigating the decomposition chemistry of hydrazine through detailed chemical kinetic modeling is a project started last summer while participating in the Summer Faculty Fellowship program. During the 1999-2000 academic year, the chemical kinetic mechanism for hydrazine decomposition developed while a SFF at NASA's White Sands Test Facility was further revised and validated against the limited experimental data in the literature. This mechanism was then used in assessing the effects of blowby gas species on hydrazine decomposition. The combustion products introduced into the fuel line by pyrovalve actuation consist primarily of hydrogen gas. Hydrogen is also a product of the decomposition of hydrazine. Additional gaseous chemical species are introduced into the fuel, as well as metals and metal salts that deposit onto the walls of the fuel line. The deposition process is undoubtedly very rapid, and exothermic. Therefore, the major focus of this summer's work was examining the effects of hydrogen presence on hydrazine decomposition, with some representative calculations including the remaining gaseous species found to exist in blowby gases. Since hydrogen is a product of hydrazine decomposition, all reactions necessary to evaluate its effect on hydrazine decomposition chemistry were in the original mechanism developed. However, the mechanism needed to be considerably expanded to include the reactions of the other gaseous blowby species with hydrazine, all the intermediate species formed in its decomposition, and each other. The expanded mechanism consists of 70 species interacting via a network of 452 reactions. Calculations with molecular hydrogen introduced into hydrazine gas in an inert bath gas indicate that H2 presence as an initial reactant in substantial amounts can dramatically impact the decomposition process for hydrazine. The other gaseous blowby species (CO, CO2, H2O, CH4, O2, and N2) were found to have little effect compared to the inclusion of hydrogen itself as an initial reagent. This result is undoubtedly due, in part, to the fact that the blowby gas used in these calculations consisted of 94.6% H2. A more rigorous examination of the behavior of the full detailed mechanism under a variety of conditions was not performed.

Dynamics of a discrete chain of bi-stable elements: A biomimetic shock absorbing mechanism

NASA Astrophysics Data System (ADS)

Cohen, T.; Givli, S.

2014-03-01

A biomimetic shock absorbing mechanism, inspired by the bi-stable elongation behavior of the giant protein titin, is examined. A bi-stable element, composed of three mass particles with monotonous interaction forces, is suggested to facilitate an internal degree of freedom of finite mass which contributes significantly to dissipation upon unlocking of an internal link. An essential feature of the suggested element is that it undergoes reversible rapture and therefore retrieves its initial configuration once unloaded. The quasistatic and dynamic behaviors are investigated showing similarity to the common tri-linear bi-stable response, with two steady phases separated by a spinodal region. The dynamic behavior of a chain of elements is also examined, for several loading scenarios, showing that the suggested mechanism serves as an efficient shock absorber in a sub-critical dampening environment, as compared with a simple mass on spring system. Propagation of shock waves and refraction waves in an element chain is observed and the effect of natural imperfections is considered.

Study on US/O3 mechanism in p-chlorophenol decomposition

PubMed Central

Xu, Xian-wen; Xu, Xin-hua; Shi, Hui-xiang; Wang, Da-hui

2005-01-01

Study on the effects of sonolysis, ozonolysis and US/O3 system on the decomposition of p-chlorophenol in aqueous solutions indicated that in the cases of US/O3 system, individual ozonolysis and sonolysis, the decomposition rate of p-chlorophenol reached 78.78%, 56.20%, 2.79% after a 16-min reaction while its CODcr (chemical oxygen demand) removal rate was 97.02%, 62.17%, 3.67% after a 120-min reaction. The decomposition reaction of p-chlorophenol follows pseudo-first-order kinetics. The enhancement factors of p-chlorophenol and its CODcr under US/O3 system reached 63% and 237% respectively. The main intermediates during the decomposition include catechol, hydroquinone, p-benzoquinone, phenol, fumaric acid, maleic acid, oxalic acid and formic acid. The decomposition mechanism of p-chlorophenol was also discussed. PMID:15909343

Nitrosonium-catalyzed decomposition of s-nitrosothiols in solution: a theoretical and experimental study.

PubMed

Zhao, Yi-Lei; McCarren, Patrick R; Houk, K N; Choi, Bo Yoon; Toone, Eric J

2005-08-10

The decomposition of S-nitrosothiols (RSNO) in solution under oxidative conditions is significantly faster than can be accounted for by homolysis of the S-N bond. Here we propose a cationic chain mechanism in which nitrosation of nitrosothiol produces a nitrosated cation that, in turn, reacts with a second nitrosothiol to produce nitrosated disulfide and the NO dimer. The nitrosated disulfide acts as a source of nitrosonium for nitrosothiol nitrosation, completing the catalytic cycle. The mechanism accounts for several unexplained facets of nitrosothiol chemistry in solution, including the observation that the decomposition of an RSNO is accelerated by O(2), mixtures of O(2) and NO, and other oxidants, that decomposition is inhibited by thiols and other antioxidants, that decomposition is dependent on sulfur substitution, and that decomposition often shows nonintegral kinetic orders.

Density-dependent liquid nitromethane decomposition: molecular dynamics simulations based on ReaxFF.

PubMed

Rom, Naomi; Zybin, Sergey V; van Duin, Adri C T; Goddard, William A; Zeiri, Yehuda; Katz, Gil; Kosloff, Ronnie

2011-09-15

The decomposition mechanism of hot liquid nitromethane at various compressions was studied using reactive force field (ReaxFF) molecular dynamics simulations. A competition between two different initial thermal decomposition schemes is observed, depending on compression. At low densities, unimolecular C-N bond cleavage is the dominant route, producing CH(3) and NO(2) fragments. As density and pressure rise approaching the Chapman-Jouget detonation conditions (∼30% compression, >2500 K) the dominant mechanism switches to the formation of the CH(3)NO fragment via H-transfer and/or N-O bond rupture. The change in the decomposition mechanism of hot liquid NM leads to a different kinetic and energetic behavior, as well as products distribution. The calculated density dependence of the enthalpy change correlates with the change in initial decomposition reaction mechanism. It can be used as a convenient and useful global parameter for the detection of reaction dynamics. Atomic averaged local diffusion coefficients are shown to be sensitive to the reactions dynamics, and can be used to distinguish between time periods where chemical reactions occur and diffusion-dominated, nonreactive time periods. © 2011 American Chemical Society

Thermal Decomposition Mechanism of CL-20 at Different Temperatures by ReaxFF Reactive Molecular Dynamics Simulations.

PubMed

Wang, Fuping; Chen, Lang; Geng, Deshen; Wu, Junying; Lu, Jianying; Wang, Chen

2018-04-26

Hexanitrohexaazaisowurtzitane (CL-20) has a high detonation velocity and pressure, but its sensitivity is also high, which somewhat limits its applications. Therefore, it is important to understand the mechanism and characteristics of thermal decomposition of CL-20. In this study, a ε-CL-20 supercell was constructed and ReaxFF-lg reactive molecular dynamics simulations were performed to investigate thermal decomposition of ε-CL-20 at various temperatures (2000, 2500, 2750, 3000, 3250, and 3500 K). The mechanism of thermal decomposition of CL-20 was analyzed from the aspects of potential energy evolution, the primary reactions, and the intermediate and final product species. The effect of temperature on thermal decomposition of CL-20 is also discussed. The initial reaction path of thermal decomposition of CL-20 is N-NO 2 cleavage to form NO 2 , followed by C-N cleavage, leading to the destruction of the cage structure. A small number of clusters appear in the early reactions and disappear at the end of the reactions. The initial reaction path of CL-20 decomposition is the same at different temperatures. However, as the temperature increases, the decomposition rate of CL-20 increases and the cage structure is destroyed earlier. The temperature greatly affects the rate constants of H 2 O and N 2 , but it has little effect on the rate constants of CO 2 and H 2 .

Dynamics in the Decompositions Approach to Quantum Mechanics

NASA Astrophysics Data System (ADS)

Harding, John

2017-12-01

In Harding (Trans. Amer. Math. Soc. 348(5), 1839-1862 1996) it was shown that the direct product decompositions of any non-empty set, group, vector space, and topological space X form an orthomodular poset Fact X. This is the basis for a line of study in foundational quantum mechanics replacing Hilbert spaces with other types of structures. Here we develop dynamics and an abstract version of a time independent Schrödinger's equation in the setting of decompositions by considering representations of the group of real numbers in the automorphism group of the orthomodular poset Fact X of decompositions.

Thermal Decomposition Behavior of Hydroxytyrosol (HT) in Nitrogen Atmosphere Based on TG-FTIR Methods.

PubMed

Tu, Jun-Ling; Yuan, Jiao-Jiao

2018-02-13

The thermal decomposition behavior of olive hydroxytyrosol (HT) was first studied using thermogravimetry (TG). Cracked chemical bond and evolved gas analysis during the thermal decomposition process of HT were also investigated using thermogravimetry coupled with infrared spectroscopy (TG-FTIR). Thermogravimetry-Differential thermogravimetry (TG-DTG) curves revealed that the thermal decomposition of HT began at 262.8 °C and ended at 409.7 °C with a main mass loss. It was demonstrated that a high heating rate (over 20 K·min -1 ) restrained the thermal decomposition of HT, resulting in an obvious thermal hysteresis. Furthermore, a thermal decomposition kinetics investigation of HT indicated that the non-isothermal decomposition mechanism was one-dimensional diffusion (D1), integral form g ( x ) = x ², and differential form f ( x ) = 1/(2 x ). The four combined approaches were employed to calculate the activation energy ( E = 128.50 kJ·mol -1 ) and Arrhenius preexponential factor (ln A = 24.39 min -1 ). In addition, a tentative mechanism of HT thermal decomposition was further developed. The results provide a theoretical reference for the potential thermal stability of HT.

Phase separation in thermal systems: A lattice Boltzmann study and morphological characterization

NASA Astrophysics Data System (ADS)

Gan, Yanbiao; Xu, Aiguo; Zhang, Guangcai; Li, Yingjun; Li, Hua

2011-10-01

We investigate thermal and isothermal symmetric liquid-vapor separations via a fast Fourier transform thermal lattice Boltzmann (FFT-TLB) model. Structure factor, domain size, and Minkowski functionals are employed to characterize the density and velocity fields, as well as to understand the configurations and the kinetic processes. Compared with the isothermal phase separation, the freedom in temperature prolongs the spinodal decomposition (SD) stage and induces different rheological and morphological behaviors in the thermal system. After the transient procedure, both the thermal and isothermal separations show power-law scalings in domain growth, while the exponent for thermal system is lower than that for isothermal system. With respect to the density field, the isothermal system presents more likely bicontinuous configurations with narrower interfaces, while the thermal system presents more likely configurations with scattered bubbles. Heat creation, conduction, and lower interfacial stresses are the main reasons for the differences in thermal system. Different from the isothermal case, the release of latent heat causes the changing of local temperature, which results in new local mechanical balance. When the Prandtl number becomes smaller, the system approaches thermodynamical equilibrium much more quickly. The increasing of mean temperature makes the interfacial stress lower in the following way: σ=σ0[(Tc-T)/(Tc-T0)]3/2, where Tc is the critical temperature and σ0 is the interfacial stress at a reference temperature T0, which is the main reason for the prolonged SD stage and the lower growth exponent in the thermal case. Besides thermodynamics, we probe how the local viscosities influence the morphology of the phase separating system. We find that, for both the isothermal and thermal cases, the growth exponents and local flow velocities are inversely proportional to the corresponding viscosities. Compared with the isothermal case, the local flow velocity depends not only on viscosity but also on temperature.

Inhomogeneities and superconductivity in poly-phase Fe-Se-Te systems

NASA Astrophysics Data System (ADS)

Hartwig, S.; Schäfer, N.; Schulze, M.; Landsgesell, S.; Abou-Ras, D.; Blum, Ch. G. F.; Wurmehl, S.; Sokolowski, A.; Büchner, B.; Prokeš, K.

2018-02-01

The impact of synthesis conditions, post-preparation heating procedure, aging and influence of pressure on the superconducting properties of FeSe0.4Te0.6 crystals is reported. Two FeSe0.4Te0.6 single crystals were used in the study, prepared from stoichiometric melt but cooled down with very different cooling rates, and investigated using magnetic bulk and electrical-resistivity methods. The fast-cooled crystal contains large inclusions of Fe3Se2.1Te1.8 and exhibits bulk superconductivity in its as-prepared state, while the other is homogeneous and shows only traces of superconductivity. AC susceptibility measurements under hydrostatic pressure show that the superconducting transition temperature of the inhomogeneous crystal increases from 12.3 K at ambient pressure to Tsc = 17.9 K at 9 kbar. On the other hand, neither pressure nor mechanically-induced stress is sufficient to induce superconductivity in the homogeneous crystal. However, an additional heat treatment at 673 K followed by fast cooling down and/or long-term aging at ambient conditions leads to the appearance of bulk superconductivity also in the latter sample. This sample remains homogeneous on a scale down to few μm but shows an additional magnetic phase transition around 130 K suggesting that it must be inhomogeneous. For comparison also Fe3Se2.1Te1.8 polycrystals have been prepared and their magnetic properties have been studied. It appears that this phase is not superconducting by itself. It is concluded that nano-scale inhomogeneities that appear in the FeSexTe1-x system due to a spinodal decomposition in the solid state are necessary for bulk superconductivity, possibly due to minor changes in the crystal structure and microstructure. Macroscopic inclusions quenched by fast cooling from high temperatures lead obviously to strain and hence variations in the lattice constants, an effect that is further supported by application of pressure/stress.

Effect of Isomorphous Substitution on the Thermal Decomposition Mechanism of Hydrotalcites

PubMed Central

Crosby, Sergio; Tran, Doanh; Cocke, David; Duraia, El-Shazly M.; Beall, Gary W.

2014-01-01

Hydrotalcites have many important applications in catalysis, wastewater treatment, gene delivery and polymer stabilization, all depending on preparation history and treatment scenarios. In catalysis and polymer stabilization, thermal decomposition is of great importance. Hydrotalcites form easily with atmospheric carbon dioxide and often interfere with the study of other anion containing systems, particularly if formed at room temperature. The dehydroxylation and decomposition of carbonate occurs simultaneously, making it difficult to distinguish the dehydroxylation mechanisms directly. To date, the majority of work on understanding the decomposition mechanism has utilized hydrotalcite precipitated at room temperature. In this study, evolved gas analysis combined with thermal analysis has been used to show that CO2 contamination is problematic in materials being formed at RT that are poorly crystalline. This has led to some dispute as to the nature of the dehydroxylation mechanism. In this paper, data for the thermal decomposition of the chloride form of hydrotalcite are reported. In addition, carbonate-free hydrotalcites have been synthesized with different charge densities and at different growth temperatures. This combination of parameters has allowed a better understanding of the mechanism of dehydroxylation and the role that isomorphous substitution plays in these mechanisms to be delineated. In addition, the effect of anion type on thermal stability is also reported. A stepwise dehydroxylation model is proposed that is mediated by the level of aluminum substitution. PMID:28788231

Invar alloys: information from the study of iron meteorites.

NASA Astrophysics Data System (ADS)

Goldstein, J. I.; Williams, D. B.; Zhang, J.; Clarke, R.

The iron meteorites were slow cooled (<108years) in their asteroidal bodies and are useful as indicators of the phase transformations which occur in Fe-Ni alloys. In the invar composition range, the iron meteorites contain a cloudy zone structure composed of an ordered tetrataenite phase and a surrounding honeycomb phase either of gamma or alpha phase. This structure is the result of a spinodal reaction below 350°C. The Santa Catharina iron meteorite has the typical invar composition of 36 wt% Ni and its structure is entirely cloudy zone although some of the honeycomb phase has been oxidized by terrestrial corrosion. Invar alloys would contain such a cloudy zone structure if more time was available for cooling. A higher temperature spinodal in the Fe-Ni phase diagram may be operative in invar alloys but has not been observed in the structure of the iron meteorites.

xEMD procedures as a data - Assisted filtering method

NASA Astrophysics Data System (ADS)

Machrowska, Anna; Jonak, Józef

2018-01-01

The article presents the possibility of using Empirical Mode Decomposition (EMD), Ensemble Empirical Mode Decomposition (EEMD), Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) and Improved Complete Ensemble Empirical Mode Decomposition (ICEEMD) algorithms for mechanical system condition monitoring applications. There were presented the results of the xEMD procedures used for vibration signals of system in different states of wear.

Decomposition Mechanism and Decomposition Promoting Factors of Waste Hard Metal for Zinc Decomposition Process (ZDP)

NASA Astrophysics Data System (ADS)

Pee, J. H.; Kim, Y. J.; Kim, J. Y.; Seong, N. E.; Cho, W. S.; Kim, K. J.

2011-10-01

Decomposition promoting factors and decomposition mechanism in the zinc decomposition process of waste hard metals which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility amount was suppressed and zinc steam pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP. Reaction was done for 2 hrs at 650 °C, which 100 % decomposed the waste hard metals that were over 30 mm thick. As for the separation-decomposition of waste hard metals, zinc melted alloy formed a liquid composed of a mixture of γ-β1 phase from the cobalt binder layer (reaction interface). The volume of reacted zone was expanded and the waste hard metal layer was decomposed-separated horizontally from the hard metal. Zinc used in the ZDP process was almost completely removed-collected by decantation and volatilization-collection process at 1000 °C. The small amount of zinc remaining in the tungsten carbide-cobalt powder which was completely decomposed was fully removed by using phosphate solution which had a slow cobalt dissolution speed.

Effect of the Hartmann number on phase separation controlled by magnetic field for binary mixture system with large component ratio

NASA Astrophysics Data System (ADS)

Heping, Wang; Xiaoguang, Li; Duyang, Zang; Rui, Hu; Xingguo, Geng

2017-11-01

This paper presents an exploration for phase separation in a magnetic field using a coupled lattice Boltzmann method (LBM) with magnetohydrodynamics (MHD). The left vertical wall was kept at a constant magnetic field. Simulations were conducted by the strong magnetic field to enhance phase separation and increase the size of separated phases. The focus was on the effect of magnetic intensity by defining the Hartmann number (Ha) on the phase separation properties. The numerical investigation was carried out for different governing parameters, namely Ha and the component ratio of the mixed liquid. The effective morphological evolutions of phase separation in different magnetic fields were demonstrated. The patterns showed that the slant elliptical phases were created by increasing Ha, due to the formation and increase of magnetic torque and force. The dataset was rearranged for growth kinetics of magnetic phase separation in a plot by spherically averaged structure factor and the ratio of separated phases and total system. The results indicate that the increase in Ha can increase the average size of separated phases and accelerate the spinodal decomposition and domain growth stages. Specially for the larger component ratio of mixed phases, the separation degree was also significantly improved by increasing magnetic intensity. These numerical results provide guidance for setting the optimum condition for the phase separation induced by magnetic field.

Fabrication of electrically bistable organic semiconducting/ferroelectric blend films by temperature controlled spin coating.

PubMed

Hu, Jinghang; Zhang, Jianchi; Fu, Zongyuan; Weng, Junhui; Chen, Weibo; Ding, Shijin; Jiang, Yulong; Zhu, Guodong

2015-03-25

Organic semiconducting/ferroelectric blend films attracted much attention due to their electrical bistability and rectification properties and thereof the potential in resistive memory devices. During film deposition from the blend solution, spinodal decomposition induced phase separation, resulting in discrete semiconducting phase whose electrical property could be modulated by the continuous ferroelectric phase. However, blend films processed by common spin coating method showed extremely rough surfaces, even comparable to the film thickness, which caused large electrical leakage and thus compromised the resistive switching performance. To improve film roughness and thus increase the productivity of these resistive devices, we developed temperature controlled spin coating technique to carefully adjust the phase separation process. Here we reported our experimental results from the blend films of ferroelectric poly(vinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) and semiconducting poly(3-hexylthiophene) (P3HT). We conducted a series of experiments at various deposition temperatures ranging from 20 to 90 °C. The resulting films were characterized by AFM, SEM, and VPFM to determine their structure and roughness. Film roughness first decreased and then increased with the increase of deposition temperature. Electrical performance was also characterized and obviously improved insulating property was obtained from the films deposited between 50 and 70 °C. By temperature control during film deposition, it is convenient to efficiently fabricate ferroelectric/semiconducting blend films with good electrical bistability.

Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows

NASA Astrophysics Data System (ADS)

Liang, Hong; Xu, Jiangrong; Chen, Jiangxing; Wang, Huili; Chai, Zhenhua; Shi, Baochang

2018-03-01

In this paper, we present a simple and accurate lattice Boltzmann (LB) model for immiscible two-phase flows, which is able to deal with large density contrasts. This model utilizes two LB equations, one of which is used to solve the conservative Allen-Cahn equation, and the other is adopted to solve the incompressible Navier-Stokes equations. A forcing distribution function is elaborately designed in the LB equation for the Navier-Stokes equations, which make it much simpler than the existing LB models. In addition, the proposed model can achieve superior numerical accuracy compared with previous Allen-Cahn type of LB models. Several benchmark two-phase problems, including static droplet, layered Poiseuille flow, and spinodal decomposition are simulated to validate the present LB model. It is found that the present model can achieve relatively small spurious velocity in the LB community, and the obtained numerical results also show good agreement with the analytical solutions or some available results. Lastly, we use the present model to investigate the droplet impact on a thin liquid film with a large density ratio of 1000 and the Reynolds number ranging from 20 to 500. The fascinating phenomena of droplet splashing is successfully reproduced by the present model and the numerically predicted spreading radius exhibits to obey the power law reported in the literature.

Self-Organization of Polymer Brush Layers in a Poor Solvent

NASA Astrophysics Data System (ADS)

Karim, A.; Tsukruk, V. V.; Douglas, J. F.; Satija, S. K.; Fetters, L. J.; Reneker, D. H.; Foster, M. D.

1995-10-01

Synthesis of densely grafted polymer brushes from good solvent polymer solutions is difficult when the surface interaction is only weakly attractive because of the strong steric repulsion between the polymer chains. To circumvent this difficulty we graft polymer layers in a poor solvent to exploit attractive polymer-polymer interactions which largely nullify the repulsive steric interactions. This simple strategy gives rise to densely grafted and homogeneous polymer brush layers. Model end-grafted polystyrene chains (M_w = 105,000) are prepared in the poor solvent cyclohexane (9.5 °C) where the chains are chemically attached to the surface utilizing a trichlorosilane end-group. Polished silicon wafers were then exposed to the reactive polymer solutions for a series of “induction times” tau_I and the evolving layer was characterized by X-ray reflectivity and atomic force microscopy. Distinct morphologies were found depending on tau_I. For short tau_I, corresponding to a grafting density less than 5 mg/m^2, the grafted layer forms an inhomogeneous island-like structure. At intermediate tau_I, where the coverage becomes percolating, a surface pattern develops which appears similar to spinodal decomposition in bulk solution. Finally, after sufficiently long tau_I, a dense and nearly homogeneous layer with a sharp interface is formed which does not exhibit surface pattern formation. The stages of brush growth are discussed qualitatively in terms of a random deposition model.

Unraveling the physical meaning of the Jaffe-Manohar decomposition of the nucleon spin

NASA Astrophysics Data System (ADS)

Wakamatsu, M.

2016-09-01

A general consensus now is that there are two physically inequivalent complete decompositions of the nucleon spin, i.e. the decomposition of the canonical type and that of mechanical type. The well-known Jaffe-Manohar decomposition is of the former type. Unfortunately, there is a wide-spread misbelief that this decomposition matches the partonic picture, which states that motion of quarks in the nucleon is approximately free. In the present monograph, we reveal that this understanding is not necessarily correct and that the Jaffe-Manohar decomposition is not such a decomposition, which natively reflects the intrinsic (or static) orbital angular momentum structure of the nucleon.

In situ spectroscopic studies on vapor phase catalytic decomposition of dimethyl oxalate.

PubMed

Hegde, Shweta; Tharpa, Kalsang; Akuri, Satyanarayana Reddy; K, Rakesh; Kumar, Ajay; Deshpande, Raj; Nair, Sreejit A

2017-03-15

Dimethyl Oxalate (DMO) has recently gained prominence as a valuable intermediate for the production of compounds of commercial importance. The stability of DMO is poor and hence this can result in the decomposition of DMO under reaction conditions. The mechanism of DMO decomposition is however not reported and more so on catalytic surfaces. Insights into the mechanism of decomposition would help in designing catalysts for its effective molecular transformation. It is well known that DMO is sensitive to moisture, which can also be a factor contributing to its decomposition. The present work reports the results of decomposition of DMO on various catalytic materials. The materials studied consist of acidic (γ-Al 2 O 3 ), basic (MgO), weakly acidic (ZnAl 2 O 4 ) and neutral surfaces such as α-Al 2 O 3 and mesoporous precipitated SiO 2 . Infrared spectroscopy is used to identify the nature of adsorption of the molecule on the various surfaces. The spectroscopy study is done at a temperature of 200 °C, which is the onset of gas phase decomposition of DMO. The results indicate that the stability of DMO is lower than the corresponding acid, i.e. oxalic acid. It is also one of the products of decomposition. Spectroscopic data suggest that DMO decomposition is related to surface acidity and the extent of decomposition depends on the number of surface hydroxyl groups. Decomposition was also observed on α-Al 2 O 3 , which was attributed to the residual surface hydroxyl groups. DMO decomposition to oxalic acid was not observed on the basic surface (MgO).

Causal mechanisms of soil organic matter decomposition: Deconstructing salinity and flooding impacts in coastal wetlands

USGS Publications Warehouse

Stagg, Camille L.; Schoolmaster, Donald; Krauss, Ken W.; Cormier, Nicole; Conner, William H.

2017-01-01

Coastal wetlands significantly contribute to global carbon storage potential. Sea-level rise and other climate change-induced disturbances threaten coastal wetland sustainability and carbon storage capacity. It is critical that we understand the mechanisms controlling wetland carbon loss so that we can predict and manage these resources in anticipation of climate change. However, our current understanding of the mechanisms that control soil organic matter decomposition, in particular the impacts of elevated salinity, are limited, and literature reports are contradictory. In an attempt to improve our understanding of these complex processes, we measured root and rhizome decomposition and developed a causal model to identify and quantify the mechanisms that influence soil organic matter decomposition in coastal wetlands that are impacted by sea-level rise. We identified three causal pathways: 1) a direct pathway representing the effects of flooding on soil moisture, 2) a direct pathway representing the effects of salinity on decomposer microbial communities and soil biogeochemistry, and 3) an indirect pathway representing the effects of salinity on litter quality through changes in plant community composition over time. We used this model to test the effects of alternate scenarios on the response of tidal freshwater forested wetlands and oligohaline marshes to short- and long-term climate-induced disturbances of flooding and salinity. In tidal freshwater forested wetlands, the model predicted less decomposition in response to drought, hurricane salinity pulsing, and long-term sea-level rise. In contrast, in the oligohaline marsh, the model predicted no change in response to sea-level rise, and increased decomposition following a drought or a hurricane salinity pulse. Our results show that it is critical to consider the temporal scale of disturbance and the magnitude of exposure when assessing the effects of salinity intrusion on carbon mineralization in coastal wetlands. Here we identify three causal mechanisms that can reconcile disparities between long-term and short-term salinity impacts on organic matter decomposition.

Causal mechanisms of soil organic matter decomposition: deconstructing salinity and flooding impacts in coastal wetlands.

PubMed

Stagg, Camille L; Schoolmaster, Donald R; Krauss, Ken W; Cormier, Nicole; Conner, William H

2017-08-01

Coastal wetlands significantly contribute to global carbon storage potential. Sea-level rise and other climate-change-induced disturbances threaten coastal wetland sustainability and carbon storage capacity. It is critical that we understand the mechanisms controlling wetland carbon loss so that we can predict and manage these resources in anticipation of climate change. However, our current understanding of the mechanisms that control soil organic matter decomposition, in particular the impacts of elevated salinity, are limited, and literature reports are contradictory. In an attempt to improve our understanding of these complex processes, we measured root and rhizome decomposition and developed a causal model to identify and quantify the mechanisms that influence soil organic matter decomposition in coastal wetlands that are impacted by sea-level rise. We identified three causal pathways: (1) a direct pathway representing the effects of flooding on soil moisture, (2) a direct pathway representing the effects of salinity on decomposer microbial communities and soil biogeochemistry, and (3) an indirect pathway representing the effects of salinity on litter quality through changes in plant community composition over time. We used this model to test the effects of alternate scenarios on the response of tidal freshwater forested wetlands and oligohaline marshes to short- and long-term climate-induced disturbances of flooding and salinity. In tidal freshwater forested wetlands, the model predicted less decomposition in response to drought, hurricane salinity pulsing, and long-term sea-level rise. In contrast, in the oligohaline marsh, the model predicted no change in response to drought and sea-level rise, and increased decomposition following a hurricane salinity pulse. Our results show that it is critical to consider the temporal scale of disturbance and the magnitude of exposure when assessing the effects of salinity intrusion on carbon mineralization in coastal wetlands. Here, we identify three causal mechanisms that can reconcile disparities between long-term and short-term salinity impacts on organic matter decomposition. © 2017 by the Ecological Society of America.

Analysis of Decomposition for Structure I Methane Hydrate by Molecular Dynamics Simulation

NASA Astrophysics Data System (ADS)

Wei, Na; Sun, Wan-Tong; Meng, Ying-Feng; Liu, An-Qi; Zhou, Shou-Wei; Guo, Ping; Fu, Qiang; Lv, Xin

2018-05-01

Under multi-nodes of temperatures and pressures, microscopic decomposition mechanisms of structure I methane hydrate in contact with bulk water molecules have been studied through LAMMPS software by molecular dynamics simulation. Simulation system consists of 482 methane molecules in hydrate and 3027 randomly distributed bulk water molecules. Through analyses of simulation results, decomposition number of hydrate cages, density of methane molecules, radial distribution function for oxygen atoms, mean square displacement and coefficient of diffusion of methane molecules have been studied. A significant result shows that structure I methane hydrate decomposes from hydrate-bulk water interface to hydrate interior. As temperature rises and pressure drops, the stabilization of hydrate will weaken, decomposition extent will go deep, and mean square displacement and coefficient of diffusion of methane molecules will increase. The studies can provide important meanings for the microscopic decomposition mechanisms analyses of methane hydrate.

[Progress in Raman spectroscopic measurement of methane hydrate].

PubMed

Xu, Feng; Zhu, Li-hua; Wu, Qiang; Xu, Long-jun

2009-09-01

Complex thermodynamics and kinetics problems are involved in the methane hydrate formation and decomposition, and these problems are crucial to understanding the mechanisms of hydrate formation and hydrate decomposition. However, it was difficult to accurately obtain such information due to the difficulty of measurement since methane hydrate is only stable under low temperature and high pressure condition, and until recent years, methane hydrate has been measured in situ using Raman spectroscopy. Raman spectroscopy, a non-destructive and non-invasive technique, is used to study vibrational modes of molecules. Studies of methane hydrate using Raman spectroscopy have been developed over the last decade. The Raman spectra of CH4 in vapor phase and in hydrate phase are presented in this paper. The progress in the research on methane hydrate formation thermodynamics, formation kinetics, decomposition kinetics and decomposition mechanism based on Raman spectroscopic measurements in the laboratory and deep sea are reviewed. Formation thermodynamic studies, including in situ observation of formation condition of methane hydrate, analysis of structure, and determination of hydrate cage occupancy and hydration numbers by using Raman spectroscopy, are emphasized. In the aspect of formation kinetics, research on variation in hydrate cage amount and methane concentration in water during the growth of hydrate using Raman spectroscopy is also introduced. For the methane hydrate decomposition, the investigation associated with decomposition mechanism, the mutative law of cage occupancy ratio and the formulation of decomposition rate in porous media are described. The important aspects for future hydrate research based on Raman spectroscopy are discussed.

Initial mechanisms for the unimolecular decomposition of electronically excited bisfuroxan based energetic materials.

PubMed

Yuan, Bing; Bernstein, Elliot R

2017-01-07

Unimolecular decomposition of energetic molecules, 3,3'-diamino-4,4'-bisfuroxan (labeled as A) and 4,4'-diamino-3,3'-bisfuroxan (labeled as B), has been explored via 226/236 nm single photon laser excitation/decomposition. These two energetic molecules, subsequent to UV excitation, create NO as an initial decomposition product at the nanosecond excitation energies (5.0-5.5 eV) with warm vibrational temperature (1170 ± 50 K for A, 1400 ± 50 K for B) and cold rotational temperature (<55 K). Initial decomposition mechanisms for these two electronically excited, isolated molecules are explored at the complete active space self-consistent field (CASSCF(12,12)/6-31G(d)) level with and without MP2 correction. Potential energy surface calculations illustrate that conical intersections play an essential role in the calculated decomposition mechanisms. Based on experimental observations and theoretical calculations, NO product is released through opening of the furoxan ring: ring opening can occur either on the S 1 excited or S 0 ground electronic state. The reaction path with the lowest energetic barrier is that for which the furoxan ring opens on the S 1 state via the breaking of the N1-O1 bond. Subsequently, the molecule moves to the ground S 0 state through related ring-opening conical intersections, and an NO product is formed on the ground state surface with little rotational excitation at the last NO dissociation step. For the ground state ring opening decomposition mechanism, the N-O bond and C-N bond break together in order to generate dissociated NO. With the MP2 correction for the CASSCF(12,12) surface, the potential energies of molecules with dissociated NO product are in the range from 2.04 to 3.14 eV, close to the theoretical result for the density functional theory (B3LYP) and MP2 methods. The CASMP2(12,12) corrected approach is essential in order to obtain a reasonable potential energy surface that corresponds to the observed decomposition behavior of these molecules. Apparently, highly excited states are essential for an accurate representation of the kinetics and dynamics of excited state decomposition of both of these bisfuroxan energetic molecules. The experimental vibrational temperatures of NO products of A and B are about 800-1000 K lower than previously studied energetic molecules with NO as a decomposition product.

Two-structure thermodynamics for the TIP4P/2005 model of water covering supercooled and deeply stretched regions.

PubMed

Biddle, John W; Singh, Rakesh S; Sparano, Evan M; Ricci, Francesco; González, Miguel A; Valeriani, Chantal; Abascal, José L F; Debenedetti, Pablo G; Anisimov, Mikhail A; Caupin, Frédéric

2017-01-21

One of the most promising frameworks for understanding the anomalies of cold and supercooled water postulates the existence of two competing, interconvertible local structures. If the non-ideality in the Gibbs energy of mixing overcomes the ideal entropy of mixing of these two structures, a liquid-liquid phase transition, terminated at a liquid-liquid critical point, is predicted. Various versions of the "two-structure equation of state" (TSEOS) based on this concept have shown remarkable agreement with both experimental data for metastable, deeply supercooled water and simulations of molecular water models. However, existing TSEOSs were not designed to describe the negative pressure region and do not account for the stability limit of the liquid state with respect to the vapor. While experimental data on supercooled water at negative pressures may shed additional light on the source of the anomalies of water, such data are very limited. To fill this gap, we have analyzed simulation results for TIP4P/2005, one of the most accurate classical water models available. We have used recently published simulation data, and performed additional simulations, over a broad range of positive and negative pressures, from ambient temperature to deeply supercooled conditions. We show that, by explicitly incorporating the liquid-vapor spinodal into a TSEOS, we are able to match the simulation data for TIP4P/2005 with remarkable accuracy. In particular, this equation of state quantitatively reproduces the lines of extrema in density, isothermal compressibility, and isobaric heat capacity. Contrary to an explanation of the thermodynamic anomalies of water based on a "retracing spinodal," the liquid-vapor spinodal in the present TSEOS continues monotonically to lower pressures upon cooling, influencing but not giving rise to density extrema and other thermodynamic anomalies.

Supersaturated Electrolyte Solutions: Theory and Experiment

NASA Technical Reports Server (NTRS)

Izmailov, Alexander F.; Myerson, Allan S.; Na, Han-Soo

1995-01-01

Highly supersaturated electrolyte solutions can be prepared and studied employing an electrodynamic levitator trap (ELT) technique. The ELT technique involves containerless suspension of a microdroplet thus eliminating dust, dirt, and container walls which normally cause heterogeneous nucleation. This allows very high supersaturations to be achieved. A theoretical study of the experimental results obtained for the water activity in microdroplets of various electrolyte solutions is based on the development of the Cahn-Hilliard formalism for electrolyte solutions. In the approach suggested the metastable state for electrolyte solutions is described in terms of the conserved order parameter omega(r,t) associated with fluctuations of the mean solute concentration n(sub 0). Parameters of the corresponding Ginzburg-Landau free energy functional which defines the dynamics of metastable state relaxation are determined and expressed through the experimentally measured quantities. A correspondence of 96-99 % between theory and experiment for all solutions studied was achieved and allowed the determination of an analytical expression for the spinodal concentration n(sub spin), and its calculation for various electrolyte solutions at 298 K. The assumption that subcritical solute clusters consist of the electrically neutral Bjerrum pairs has allowed both analytical and numerical investigation of the number-size N(sub c) of nucleation monomers (aggregates of the Bjerrum pairs) which are elementary units of the solute critical clusters. This has also allowed estimations for the surface tension Alpha, and equilibrium bulk energy Beta per solute molecule in the nucleation monomers. The dependence of these properties on the temperature T and on the solute concentration n(sub 0) through the entire metastable zone (from saturation concentration n(sub sat) to spinodal n(sub spin) is examined. It has been demonstrated that there are the following asymptotics: N(sub c), = I at spinodal concentration and N(sub c) = infinity at saturation.

Experimental and DFT simulation study of a novel felodipine cocrystal: Characterization, dissolving properties and thermal decomposition kinetics.

PubMed

Yang, Caiqin; Guo, Wei; Lin, Yulong; Lin, Qianqian; Wang, Jiaojiao; Wang, Jing; Zeng, Yanli

2018-05-30

In this study, a new cocrystal of felodipine (Fel) and glutaric acid (Glu) with a high dissolution rate was developed using the solvent ultrasonic method. The prepared cocrystal was characterized using X-ray powder diffraction, differential scanning calorimetry, thermogravimetric (TG) analysis, and infrared (IR) spectroscopy. To provide basic information about the optimization of pharmaceutical preparations of Fel-based cocrystals, this work investigated the thermal decomposition kinetics of the Fel-Glu cocrystal through non-isothermal thermogravimetry. Density functional theory (DFT) simulations were also performed on the Fel monomer and the trimolecular cocrystal compound for exploring the mechanisms underlying hydrogen bonding formation and thermal decomposition. Combined results of IR spectroscopy and DFT simulation verified that the Fel-Glu cocrystal formed via the NH⋯OC and CO⋯HO hydrogen bonds between Fel and Glu at the ratio of 1:2. The TG/derivative TG curves indicated that the thermal decomposition of the Fel-Glu cocrystal underwent a two-step process. The apparent activation energy (E a ) and pre-exponential factor (A) of the thermal decomposition for the first stage were 84.90 kJ mol -1 and 7.03 × 10 7  min -1 , respectively. The mechanism underlying thermal decomposition possibly involved nucleation and growth, with the integral mechanism function G(α) of α 3/2 . DFT calculation revealed that the hydrogen bonding between Fel and Glu weakened the terminal methoxyl, methyl, and ethyl groups in the Fel molecule. As a result, these groups were lost along with the Glu molecule in the first thermal decomposition. In conclusion, the formed cocrystal exhibited different thermal decomposition kinetics and showed different E a , A, and shelf life from the intact active pharmaceutical ingredient. Copyright © 2018 Elsevier B.V. All rights reserved.

Molecular dynamics simulations of methane hydrate decomposition.

PubMed

Myshakin, Evgeniy M; Jiang, Hao; Warzinski, Robert P; Jordan, Kenneth D

2009-03-12

Molecular dynamics simulations have been carried out to study decomposition of methane hydrate at different cage occupancies. The decomposition rate is found to depend sensitively on the hydration number. The rate of the destruction of the cages displays Arrhenius behavior, consistent with an activated mechanism. During the simulations, reversible formation of partial water cages around methane molecules in the liquid was observed at the interface at temperatures above the computed hydrate decomposition temperature.

Mechanism of thermal decomposition of K2FeO4 and BaFeO4: A review

NASA Astrophysics Data System (ADS)

Sharma, Virender K.; Machala, Libor

2016-12-01

This paper presents thermal decomposition of potassium ferrate(VI) (K2FeO4) and barium ferrate(VI) (BaFeO4) in air and nitrogen atmosphere. Mössbauer spectroscopy and nuclear forward scattering (NFS) synchrotron radiation approaches are reviewed to advance understanding of electron-transfer processes involved in reduction of ferrate(VI) to Fe(III) phases. Direct evidences of Fe V and Fe IV as intermediate iron species using the applied techniques are given. Thermal decomposition of K2FeO4 involved Fe V, Fe IV, and K3FeO3 as intermediate species while BaFeO3 (i.e. Fe IV) was the only intermediate species during the decomposition of BaFeO4. Nature of ferrite species, formed as final Fe(III) species, of thermal decomposition of K2FeO4 and BaFeO4 under different conditions are evaluated. Steps of the mechanisms of thermal decomposition of ferrate(VI), which reasonably explained experimental observations of applied approaches in conjunction with thermal and surface techniques, are summarized.

Spectroscopic and Computational Investigation of Room-Temperature Decomposition of a Chemical Warfare Agent Simulant on Polycrystalline Cupric Oxide

DOE PAGES

Trotochaud, Lena; Tsyshevsky, Roman; Holdren, Scott; ...

2017-08-21

Certain organophosphorus molecules are infamous due to their use as highly toxic nerve agents. The filtration materials currently in common use for protection against chemical warfare agents were designed before organophosphorus compounds were used as chemical weapons. A better understanding of the surface chemistry between simulant molecules and the individual filtration-material components is a critical precursor to the development of more effective materials for filtration, destruction, decontamination, and/or sensing of nerve agents. Here, we report on the surface adsorption and reactions of a sarin simulant molecule, dimethyl methylphosphonate (DMMP), with cupric oxide surfaces. In situ ambient pressure X-ray photoelectron andmore » infrared spectroscopies are coupled with density functional calculations to propose mechanisms for DMMP decomposition on CuO. We find extensive room temperature decomposition of DMMP on CuO, with the majority of decomposition fragments bound to the CuO surface. We observe breaking of PO-CH3, P-OCH3, and P-CH3bonds at room temperature. On the basis of these results, we identify specific DMMP decomposition mechanisms not seen on other metal oxides. Participation of lattice oxygen in the decomposition mechanism leads to significant changes in chemical and electronic surface environment, which are manifest in the spectroscopic and computational data. This study establishes a computational baseline for the study of highly toxic organophosphorous compounds on metal oxide surfaces.« less

Spectroscopic and Computational Investigation of Room-Temperature Decomposition of a Chemical Warfare Agent Simulant on Polycrystalline Cupric Oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trotochaud, Lena; Tsyshevsky, Roman; Holdren, Scott

Certain organophosphorus molecules are infamous due to their use as highly toxic nerve agents. The filtration materials currently in common use for protection against chemical warfare agents were designed before organophosphorus compounds were used as chemical weapons. A better understanding of the surface chemistry between simulant molecules and the individual filtration-material components is a critical precursor to the development of more effective materials for filtration, destruction, decontamination, and/or sensing of nerve agents. Here, we report on the surface adsorption and reactions of a sarin simulant molecule, dimethyl methylphosphonate (DMMP), with cupric oxide surfaces. In situ ambient pressure X-ray photoelectron andmore » infrared spectroscopies are coupled with density functional calculations to propose mechanisms for DMMP decomposition on CuO. We find extensive room temperature decomposition of DMMP on CuO, with the majority of decomposition fragments bound to the CuO surface. We observe breaking of PO-CH3, P-OCH3, and P-CH3bonds at room temperature. On the basis of these results, we identify specific DMMP decomposition mechanisms not seen on other metal oxides. Participation of lattice oxygen in the decomposition mechanism leads to significant changes in chemical and electronic surface environment, which are manifest in the spectroscopic and computational data. This study establishes a computational baseline for the study of highly toxic organophosphorous compounds on metal oxide surfaces.« less

Theoretical evidence of the observed kinetic order dependence on temperature during the N(2)O decomposition over Fe-ZSM-5.

PubMed

Guesmi, Hazar; Berthomieu, Dorothee; Bromley, Bryan; Coq, Bernard; Kiwi-Minsker, Lioubov

2010-03-28

The characterization of Fe/ZSM5 zeolite materials, the nature of Fe-sites active in N(2)O direct decomposition, as well as the rate limiting step are still a matter of debate. The mechanism of N(2)O decomposition on the binuclear oxo-hydroxo bridged extraframework iron core site [Fe(II)(mu-O)(mu-OH)Fe(II)](+) inside the ZSM-5 zeolite has been studied by combining theoretical and experimental approaches. The overall calculated path of N(2)O decomposition involves the oxidation of binuclear Fe(II) core sites by N(2)O (atomic alpha-oxygen formation) and the recombination of two surface alpha-oxygen atoms leading to the formation of molecular oxygen. Rate parameters computed using standard statistical mechanics and transition state theory reveal that elementary catalytic steps involved into N(2)O decomposition are strongly dependent on the temperature. This theoretical result was compared to the experimentally observed steady state kinetics of the N(2)O decomposition and temperature-programmed desorption (TPD) experiments. A switch of the reaction order with respect to N(2)O pressure from zero to one occurs at around 800 K suggesting a change of the rate determining step from the alpha-oxygen recombination to alpha-oxygen formation. The TPD results on the molecular oxygen desorption confirmed the mechanism proposed.

Photodegradation at day, microbial decomposition at night - decomposition in arid lands

NASA Astrophysics Data System (ADS)

Gliksman, Daniel; Gruenzweig, Jose

2014-05-01

Our current knowledge of decomposition in dry seasons and its role in carbon turnover is fragmentary. So far, decomposition during dry seasons was mostly attributed to abiotic mechanisms, mainly photochemical and thermal degradation, while the contribution of microorganisms to the decay process was excluded. We asked whether microbial decomposition occurs during the dry season and explored its interaction with photochemical degradation under Mediterranean climate. We conducted a litter bag experiment with local plant litter and manipulated litter exposure to radiation using radiation filters. We found notable rates of CO2 fluxes from litter which were related to microbial activity mainly during night-time throughout the dry season. This activity was correlated with litter moisture content and high levels of air humidity and dew. Day-time CO2 fluxes were related to solar radiation, and radiation manipulation suggested photodegradation as the underlying mechanism. In addition, a decline in microbial activity was followed by a reduction in photodegradation-related CO2 fluxes. The levels of microbial decomposition and photodegradation in the dry season were likely the factors influencing carbon mineralization during the subsequent wet season. This study showed that microbial decomposition can be a dominant contributor to CO2 emissions and mass loss in the dry season and it suggests a regulating effect of microbial activity on photodegradation. Microbial decomposition is an important contributor to the dry season decomposition and impacts the annual litter turn-over rates in dry regions. Global warming may lead to reduced moisture availability and dew deposition, which may greatly influence not only microbial decomposition of plant litter, but also photodegradation.

Influence of gamma-irradiation on the non-isothermal decomposition of calcium-gadolinium oxalate

NASA Astrophysics Data System (ADS)

Moharana, S. C.; Praharaj, J.; Bhatta, D.

Thermal decomposition of co-precipitated unirradiated and irradiated Ca-Gd oxalate has been studied by adopting differential thermal analysis (DTA) and thermogravimetric (TG) techniques. The reaction occurs through two stages corresponding to the decomposition of gadolinium oxalate (Gd-Ox) followed by that of calcium oxalate (Ca-Ox). The kinetic parameters for both the stages are calculated by using solid state reaction models and Coats-Redfern's equation. The co-precipitation as well as irradiation alter the DTA peak temperatures and the kinetic parameters of Ca-Ox. The decomposition of Gd-Ox follows the two dimensional Contracting area (R-2) mechanism, while that of Ca-Ox follows the Avrami-Erofeev (A(2)) mechanism (n =2), which are also exhibited by the co-precipitated and irradiated samples. Co-precipitation decreases the energy of activation and the pre-exponential factor of the individual components but the reverse phenomenon takes place upon irradiation of the co-precipitate. The mechanisms underlying the phenomena are explored.

Nano or micro? A mechanism on thermal decomposition of ammonium perchlorate catalyzed by cobalt oxalate.

PubMed

Zou, Min; Jiang, Xiaohong; Lu, Lude; Wang, Xin

2012-07-30

Micrometer-sized cobalt oxalates with different morphologies have been prepared in the presence of surfactants. The effect of catalysts morphology on the thermal decomposition of ammonium perchlorate (AP) was evaluated by differential thermal analysis (DSC). Remarkably, contrary to the well-accepted concepts, no direct relationship between the morphologies of catalysts and their activities has been observed. Based on the structural and morphological variation of the catalysts during the reaction, a catalytic mechanism on thermal decomposition of ammonium perchlorate catalyzed by cobalt oxalate is proposed. We believe that it is the "self-crushing and self-distributed" occurred within the reaction that really works for the improvement of the overall catalytic activities. In this process, both catalysts and reactants have been crashed and distributed uniformly in an automatic way. This work provides an in-depth insight into the thermal decomposition mechanism of AP as catalyzed by oxalates. Copyright © 2012 Elsevier B.V. All rights reserved.

Development of Novel Decontamination and Inerting Techniques for Explosives Contaminated Facilities. Phase 1. Identification and Evaluation of Novel Decontamination Concepts. Volume 1

DTIC Science & Technology

1983-07-01

the decomposition reaction (Leider, 1981; Kageyama, 1973; Wolfrom, 1956), 2) Hydrolysis of linkages between glucose units (Urbanski, 1964), 3... dehydration ), 2) Acceleration period (to 50 percent decomposition ), 3) First order reaction rate period. The products of thermal decomposition of...simple mechanism to clean an entire building at once. o Depending on the contaminant, thermal decomposition and or hydrolysis may occur. o May be

Determination of the thermal stability of perfluoropolyalkyl ethers by tensimetry

NASA Technical Reports Server (NTRS)

Helmick, Larry A.; Jones, William R., Jr.

1992-01-01

The thermal decomposition temperatures of several perfluoropolyalkyl ether fluids were determined with a computerized tensimeter. In general, the decomposition temperatures of the commercial fluids were all similar and significantly higher than those for noncommercial fluids. Correlation of the decomposition temperatures with the molecular structures of the primary components of the commercial fluids revealed that the stability of the fluids was not affected by carbon chain length, branching, or adjacent difluoroformal groups. Instead, stability was limited by the presence of small quantities of thermally unstable material and/or chlorine-containing material arising from the use of chlorine containing solvents during synthesis. Finally, correlation of decomposition temperatures with molecular weights for two fluids supports a chain cleavage reaction mechanism for one and an unzipping reaction mechanism for the other.

Explosive decomposition of hydrazine by rapid compression of a gas volume

NASA Technical Reports Server (NTRS)

Bunker, R. L.; Baker, D. L.; Lee, J. H. S.

1991-01-01

In the present investigation of the initiation mechanism and the explosion mode of hydrazine decomposition, a 20 cm-long column of liquid hydrazine was accelerated into a column of gaseous nitrogen, from which it was separated by a thin Teflon diaphragm, in a close-ended cylindrical chamber. Video data obtained reveal the formation of a froth generated by the acceleration of hydrazine into nitrogen at the liquid hydrazine-gaseous nitrogen interface. The explosive hydrazine decomposition had as its initiation mechanism the formation of a froth at a critical temperature; the explosion mode of hydrazine is a confined thermal runaway reaction.

Resolving Some Paradoxes in the Thermal Decomposition Mechanism of Acetaldehyde

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sivaramakrishnan, Raghu; Michael, Joe V.; Harding, Lawrence B.

2015-07-16

The mechanism for the thermal decomposition of acetaldehyde has been revisited with an analysis of literature kinetics experiments using theoretical kinetics. The present modeling study was motivated by recent observations, with very sensitive diagnostics, of some unexpected products in high temperature micro-tubular reactor experiments on the thermal decomposition of CH3CHO and its deuterated analogs, CH3CDO, CD3CHO, and CD3CDO. The observations of these products prompted the authors of these studies to suggest that the enol tautomer, CH2CHOH (vinyl alcohol), is a primary intermediate in the thermal decomposition of acetaldehyde. The present modeling efforts on acetaldehyde decomposition incorporate a master equation re-analysismore » of the CH3CHO potential energy surface (PES). The lowest energy process on this PES is an isomerization of CH3CHO to CH2CHOH. However, the subsequent product channels for CH2CHOH are substantially higher in energy, and the only unimolecular process that can be thermally accessed is a re-isomerization to CH3CHO. The incorporation of these new theoretical kinetics predictions into models for selected literature experiments on CH3CHO thermal decomposition confirms our earlier experiment and theory based conclusions that the dominant decomposition process in CH3CHO at high temperatures is C-C bond fission with a minor contribution (~10-20%) from the roaming mechanism to form CH4 and CO. The present modeling efforts also incorporate a master-equation analysis of the H + CH2CHOH potential energy surface. This bimolecular reaction is the primary mechanism for removal of CH2CHOH, which can accumulate to minor amounts at high temperatures, T > 1000 K, in most lab-scale experiments that use large initial concentrations of CH3CHO. Our modeling efforts indicate that the observation of ketene, water and acetylene in the recent micro-tubular experiments are primarily due to bimolecular reactions of CH3CHO and CH2CHOH with H-atoms, and have no bearing on the unimolecular decomposition mechanism of CH3CHO. The present simulations also indicate that experiments using these micro-tubular reactors when interpreted with the aid of high-level theoretical calculations and kinetics modeling can offer insights into the chemistry of elusive intermediates in high temperature pyrolysis of organic molecules.« less

Molecular Mechanisms in the shock induced decomposition of FOX-7

NASA Astrophysics Data System (ADS)

Mishra, Ankit; Tiwari, Subodh C.; Nakano, Aiichiro; Vashishta, Priya; Kalia, Rajiv; CACS Team

Experimental and first principle computational studies on FOX 7 have either involved a very small system consisting of a few atoms or they did not take into account the decomposition mechanisms under extreme conditions of temperature and pressure. We have performed a large-scale reactive MD simulation using ReaxFF-lg force field to study the shock decomposition of FOX 7. The chemical composition of the principal decomposition products correlates well with experimental observations. Furthermore, we observed that the production of N2 and H2O was inter molecular in nature and was through different chemical pathways. Moreover, the production of CO and CO2 was delayed due to production of large stable C,O atoms cluster. These critical insights into the initial processes involved in the shock induced decomposition of FOX-7 will greatly help in understanding the factors playing an important role in the insensitiveness of this high energy material. This research is supported by AFOSR Award No. FA9550-16-1-0042.

Initial decomposition mechanism for the energy release from electronically excited energetic materials: FOX-7 (1,1-diamino-2,2-dinitroethene, C{sub 2}H{sub 4}N{sub 4}O{sub 4})

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Bing; Yu, Zijun; Bernstein, Elliot R., E-mail: erb@lamar.Colostate.edu

Decomposition of the energetic material FOX-7 (1,1-diamino-2,2-dinitroethylene, C{sub 2}H{sub 4}N{sub 4}O{sub 4}) is investigated both theoretically and experimentally. The NO molecule is observed as an initial decomposition product subsequent to electronic excitation. The observed NO product is rotationally cold (<35 K) and vibrationally hot (2800 K). The initial decomposition mechanism is explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) level illustrate that conical intersections play an essential role in the decomposition mechanism. Electronically excited S{sub 2} FOX-7 can radiationlessly relax to lower electronic states through (S{sub 2}/S{sub 1}){sub CI} and (S{submore » 1}/S{sub 0}){sub CI} conical intersections and undergo a nitro-nitrite isomerization to generate NO product on the S{sub 0} state. The theoretically predicted mechanism is consistent with the experimental results. As FOX-7 decomposes on the ground electronic state, thus, the vibrational energy of the NO product from FOX-7 is high. The observed rotational energy distribution for NO is consistent with the final transition state structure on the S{sub 0} state. Ground state FOX-7 decomposition agrees with previous work: the nitro-nitrite isomerization has the lowest average energy barrier, the C–NH{sub 2} bond cleavage is unlikely under the given excitation conditions, and HONO formation on the ground state surface is energy accessible but not the main process.« less

Towards a thermodynamics of active matter.

PubMed

Takatori, S C; Brady, J F

2015-03-01

Self-propulsion allows living systems to display self-organization and unusual phase behavior. Unlike passive systems in thermal equilibrium, active matter systems are not constrained by conventional thermodynamic laws. A question arises, however, as to what extent, if any, can concepts from classical thermodynamics be applied to nonequilibrium systems like active matter. Here we use the new swim pressure perspective to develop a simple theory for predicting phase separation in active matter. Using purely mechanical arguments we generate a phase diagram with a spinodal and critical point, and define a nonequilibrium chemical potential to interpret the "binodal." We provide a generalization of thermodynamic concepts like the free energy and temperature for nonequilibrium active systems. Our theory agrees with existing simulation data both qualitatively and quantitatively and may provide a framework for understanding and predicting the behavior of nonequilibrium active systems.

NDMA formation by chloramination of ranitidine: kinetics and mechanism.

PubMed

Roux, Julien Le; Gallard, Hervé; Croué, Jean-Philippe; Papot, Sébastien; Deborde, Marie

2012-10-16

The kinetics of decomposition of the pharmaceutical ranitidine (a major precursor of NDMA) during chloramination was investigated and some decomposition byproducts were identified by using high performance liquid chromatography coupled with mass spectrometry (HPLC-MS). The reaction between monochloramine and ranitidine followed second order kinetics and was acid-catalyzed. Decomposition of ranitidine formed different byproducts depending on the applied monochloramine concentration. Most identified products were chlorinated and hydroxylated analogues of ranitidine. In excess of monochloramine, nucleophilic substitution between ranitidine and monochloramine led to byproducts that are critical intermediates involved in the formation of NDMA, for example, a carbocation formed from the decomposition of the methylfuran moiety of ranitidine. A complete mechanism is proposed to explain the high formation yield of NDMA from chloramination of ranitidine. These results are of great importance to understand the formation of NDMA by chloramination of tertiary amines.

Importance of Force Decomposition for Local Stress Calculations in Biomembrane Molecular Simulations.

PubMed

Vanegas, Juan M; Torres-Sánchez, Alejandro; Arroyo, Marino

2014-02-11

Local stress fields are routinely computed from molecular dynamics trajectories to understand the structure and mechanical properties of lipid bilayers. These calculations can be systematically understood with the Irving-Kirkwood-Noll theory. In identifying the stress tensor, a crucial step is the decomposition of the forces on the particles into pairwise contributions. However, such a decomposition is not unique in general, leading to an ambiguity in the definition of the stress tensor, particularly for multibody potentials. Furthermore, a theoretical treatment of constraints in local stress calculations has been lacking. Here, we present a new implementation of local stress calculations that systematically treats constraints and considers a privileged decomposition, the central force decomposition, that leads to a symmetric stress tensor by construction. We focus on biomembranes, although the methodology presented here is widely applicable. Our results show that some unphysical behavior obtained with previous implementations (e.g. nonconstant normal stress profiles along an isotropic bilayer in equilibrium) is a consequence of an improper treatment of constraints. Furthermore, other valid force decompositions produce significantly different stress profiles, particularly in the presence of dihedral potentials. Our methodology reveals the striking effect of unsaturations on the bilayer mechanics, missed by previous stress calculation implementations.

An ab initio molecular orbital study of the mechanism for the gas-phase water-mediated decomposition and the formation of hydrates of peroxyacetyl nitrate (PAN).

PubMed

Li, Yumin; Francisco, Joseph S

2005-08-31

There is uncertainty in the mechanism for the hydrolysis of peroxyacetyl nitrate (PAN), and experimental attempts to detect products of the direct reaction have been unsuccessful. Ab initio calculations are used to examine the energetics of water-mediated decomposition of gas-phase PAN into acetic acid and peroxynitric acid. On the basis of ab initio calculations, an alternative reaction mechanism for the decomposition of PAN is proposed. The calculations indicate that the barrier for one water addition to PAN is large. However, including additional water molecules reveals a substantially lower energy route. The calculations suggest that the formation of PAN hydrate complexes are energetically favorable and stable. Additional waters are increasingly efficient at stabilizing hydrated PAN.

The implications of microbial and substrate limitation for the fates of carbon in different organic soil horizon types of boreal forest ecosystems: a mechanistically based model analysis

USGS Publications Warehouse

He, Y.; Zhuang, Q.; Harden, Jennifer W.; McGuire, A. David; Fan, Z.; Liu, Y.; Wickland, Kimberly P.

2014-01-01

The large amount of soil carbon in boreal forest ecosystems has the potential to influence the climate system if released in large quantities in response to warming. Thus, there is a need to better understand and represent the environmental sensitivity of soil carbon decomposition. Most soil carbon decomposition models rely on empirical relationships omitting key biogeochemical mechanisms and their response to climate change is highly uncertain. In this study, we developed a multi-layer microbial explicit soil decomposition model framework for boreal forest ecosystems. A thorough sensitivity analysis was conducted to identify dominating biogeochemical processes and to highlight structural limitations. Our results indicate that substrate availability (limited by soil water diffusion and substrate quality) is likely to be a major constraint on soil decomposition in the fibrous horizon (40–60% of soil organic carbon (SOC) pool size variation), while energy limited microbial activity in the amorphous horizon exerts a predominant control on soil decomposition (>70% of SOC pool size variation). Elevated temperature alleviated the energy constraint of microbial activity most notably in amorphous soils, whereas moisture only exhibited a marginal effect on dissolved substrate supply and microbial activity. Our study highlights the different decomposition properties and underlying mechanisms of soil dynamics between fibrous and amorphous soil horizons. Soil decomposition models should consider explicitly representing different boreal soil horizons and soil–microbial interactions to better characterize biogeochemical processes in boreal forest ecosystems. A more comprehensive representation of critical biogeochemical mechanisms of soil moisture effects may be required to improve the performance of the soil model we analyzed in this study.

Solubility limits in quaternary SnTe-based alloys [Metastability and solubility limits in quaternary SnTe-based alloys guided by combinatorial sputtering

DOE PAGES

Siol, Sebastian; Holder, Aaron; Ortiz, Brenden R.; ...

2017-05-09

Here, the controlled decomposition of metastable alloys is an attractive route to form nanostructured thermoelectric materials with reduced thermal conductivity. The ternary SnTe–MnTe and SnTe–SnSe heterostructural alloys have been demonstrated as promising materials for thermoelectric applications. In this work, the quaternary Sn 1–yMnyTe 1–xSe x phase space serves as a relevant model system to explore how a combination of computational and combinatorial-growth methods can be used to study equilibrium and non-equilibrium solubility limits. Results from first principle calculations indicate low equilibrium solubility for x,y < 0.05 that are in good agreement with results obtained from bulk equilibrium synthesis experiments andmore » predict significantly higher spinodal limits. An experimental screening using sputtered combinatorial thin film sample libraries showed a remarkable increase in non-equilibrium solubility for x,y > 0.2. These theoretical and experimental results were used to guide the bulk synthesis of metastable alloys. The ability to reproduce the non-equilibrium solubility levels in bulk materials indicates that such theoretical calculations and combinatorial growth can inform bulk synthetic routes. Further, the large difference between equilibrium and non-equilibrium solubility limits in Sn 1–yMn yTe 1–xSe x indicates these metastable alloys are attractive in terms of nano-precipitate formation for potential thermoelectric applications.« less

Adiabatic burst evaporation from bicontinuous nanoporous membranes

PubMed Central

Ichilmann, Sachar; Rücker, Kerstin; Haase, Markus; Enke, Dirk

2015-01-01

Evaporation of volatile liquids from nanoporous media with bicontinuous morphology and pore diameters of a few 10 nm is an ubiquitous process. For example, such drying processes occur during syntheses of nanoporous materials by sol–gel chemistry or by spinodal decomposition in the presence of solvents as well as during solution impregnation of nanoporous hosts with functional guests. It is commonly assumed that drying is endothermic and driven by non-equilibrium partial pressures of the evaporating species in the gas phase. We show that nearly half of the liquid evaporates in an adiabatic mode involving burst-like liquid-to-gas conversions. During single adiabatic burst evaporation events liquid volumes of up to 107 μm3 are converted to gas. The adiabatic liquid-to-gas conversions occur if air invasion fronts get unstable because of the built-up of high capillary pressures. Adiabatic evaporation bursts propagate avalanche-like through the nanopore systems until the air invasion fronts have reached new stable configurations. Adiabatic cavitation bursts thus compete with Haines jumps involving air invasion front relaxation by local liquid flow without enhanced mass transport out of the nanoporous medium and prevail if the mean pore diameter is in the range of a few 10 nm. The results reported here may help optimize membrane preparation via solvent-based approaches, solution-loading of nanopore systems with guest materials as well as routine use of nanoporous membranes with bicontinuous morphology and may contribute to better understanding of adsorption/desorption processes in nanoporous media. PMID:25926406

Active Brownian agents with concentration-dependent chemotactic sensitivity.

PubMed

Meyer, Marcel; Schimansky-Geier, Lutz; Romanczuk, Pawel

2014-02-01

We study a biologically motivated model of overdamped, autochemotactic Brownian agents with concentration-dependent chemotactic sensitivity. The agents in our model move stochastically and produce a chemical ligand at their current position. The ligand concentration obeys a reaction-diffusion equation and acts as a chemoattractant for the agents, which bias their motion towards higher concentrations of the dynamically altered chemical field. We explore the impact of concentration-dependent response to chemoattractant gradients on large-scale pattern formation, by deriving a coarse-grained macroscopic description of the individual-based model, and compare the conditions for emergence of inhomogeneous solutions for different variants of the chemotactic sensitivity. We focus primarily on the so-called receptor-law sensitivity, which models a nonlinear decrease of chemotactic sensitivity with increasing ligand concentration. Our results reveal qualitative differences between the receptor law, the constant chemotactic response, and the so-called log law, with respect to stability of the homogeneous solution, as well as the emergence of different patterns (labyrinthine structures, clusters, and bubbles) via spinodal decomposition or nucleation. We discuss two limiting cases, where the model can be reduced to the dynamics of single species: (I) the agent density governed by a density-dependent effective diffusion coefficient and (II) the ligand field with an effective bistable, time-dependent reaction rate. In the end, we turn to single clusters of agents, studying domain growth and determining mean characteristics of the stationary inhomogeneous state. Analytical results are confirmed and extended by large-scale GPU simulations of the individual based model.

Properties of solid solutions, doped film, and nanocomposite structures based on zinc oxide

NASA Astrophysics Data System (ADS)

Lashkarev, G. V.; Shtepliuk, I. I.; Ievtushenko, A. I.; Khyzhun, O. Y.; Kartuzov, V. V.; Ovsiannikova, L. I.; Karpyna, V. A.; Myroniuk, D. V.; Khomyak, V. V.; Tkach, V. N.; Timofeeva, I. I.; Popovich, V. I.; Dranchuk, N. V.; Khranovskyy, V. D.; Demydiuk, P. V.

2015-02-01

A study of the properties of materials based on the wide bandgap zinc oxide semiconductor, which are promising for application in optoelectronics, photovoltaics and nanoplasmonics. The structural and optical properties of solid solution Zn1-xCdxO films with different cadmium content, are studied. The samples are grown using magnetron sputtering on sapphire backing. Low-temperature photoluminescence spectra revealed emission peaks associated with radiative recombination processes in those areas of the film that have varying amounts of cadmium. X-ray phase analysis showed the presence of a cadmium oxide cubic phase in these films. Theoretical studies of the solid solution thermodynamic properties allowed for a qualitative interpretation of the observed experimental phenomena. It is established that the growth of the homogeneous solid solution film is possible only at high temperatures, whereas regions of inhomogeneous composition can be narrowed through elastic deformation, caused by the mismatch of the film-backing lattice constants. The driving forces of the spinodal decomposition of the Zn1-xCdxO system are identified. Fullerene-like clusters of Znn-xCdxOn are used to calculate the bandgap and the cohesive energy of ZnCdO solid solutions. The properties of transparent conductive ZnO films, doped with Group III donor impurities (Al, Ga, In), are examined. It is shown that oxygen vacancies are responsible for the hole trap centers in the zinc oxide photoconductivity process. We also examine the photoluminescence properties of metal-ZnO nanocomposite structures, caused by surface plasmons.

Wetting in a phase separating polymer blend film: quench depth dependence

PubMed

Geoghegan; Ermer; Jungst; Krausch; Brenn

2000-07-01

We have used 3He nuclear reaction analysis to measure the growth of the wetting layer as a function of immiscibility (quench depth) in blends of deuterated polystyrene and poly(alpha-methylstyrene) undergoing surface-directed spinodal decomposition. We are able to identify three different laws for the surface layer growth with time t. For the deepest quenches, the forces driving phase separation dominate (high thermal noise) and the surface layer grows with a t(1/3) coarsening behavior. For shallower quenches, a logarithmic behavior is observed, indicative of a low noise system. The crossover from logarithmic growth to t(1/3) behavior is close to where a wetting transition should occur. We also discuss the possibility of a "plating transition" extending complete wetting to deeper quenches by comparing the surface field with thermal noise. For the shallowest quench, a critical blend exhibits a t(1/2) behavior. We believe this surface layer growth is driven by the curvature of domains at the surface and shows how the wetting layer forms in the absence of thermal noise. This suggestion is reinforced by a slower growth at later times, indicating that the surface domains have coalesced. Atomic force microscopy measurements in each of the different regimes further support the above. The surface in the region of t(1/3) growth is initially somewhat rougher than that in the regime of logarithmic growth, indicating the existence of droplets at the surface.

Benchmark problems for numerical implementations of phase field models

DOE PAGES

Jokisaari, A. M.; Voorhees, P. W.; Guyer, J. E.; ...

2016-10-01

Here, we present the first set of benchmark problems for phase field models that are being developed by the Center for Hierarchical Materials Design (CHiMaD) and the National Institute of Standards and Technology (NIST). While many scientific research areas use a limited set of well-established software, the growing phase field community continues to develop a wide variety of codes and lacks benchmark problems to consistently evaluate the numerical performance of new implementations. Phase field modeling has become significantly more popular as computational power has increased and is now becoming mainstream, driving the need for benchmark problems to validate and verifymore » new implementations. We follow the example set by the micromagnetics community to develop an evolving set of benchmark problems that test the usability, computational resources, numerical capabilities and physical scope of phase field simulation codes. In this paper, we propose two benchmark problems that cover the physics of solute diffusion and growth and coarsening of a second phase via a simple spinodal decomposition model and a more complex Ostwald ripening model. We demonstrate the utility of benchmark problems by comparing the results of simulations performed with two different adaptive time stepping techniques, and we discuss the needs of future benchmark problems. The development of benchmark problems will enable the results of quantitative phase field models to be confidently incorporated into integrated computational materials science and engineering (ICME), an important goal of the Materials Genome Initiative.« less

Self-assembly of amorphous biophotonic nanostructures by phase separation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dufresne, Eric R.; Noh, Heeso; Saranathan, Vinodkumar

2009-04-23

Some of the most vivid colors in the animal kingdom are created not by pigments, but by wavelength-selective scattering of light from nanostructures. Here we investigate quasi-ordered nanostructures of avian feather barbs which produce vivid non-iridescent colors. These {beta}-keratin and air nanostructures are found in two basic morphologies: tortuous channels and amorphous packings of spheres. Each class of nanostructure is isotropic and has a pronounced characteristic length scale of variation in composition. These local structural correlations lead to strong backscattering over a narrow range of optical frequencies and little variation with angle of incidence. Such optical properties play important rolesmore » in social and sexual communication. To be effective, birds need to precisely control the development of these nanoscale structures, yet little is known about how they grow. We hypothesize that multiple lineages of birds have convergently evolved to exploit phase separation and kinetic arrest to self-assemble spongy color-producing nanostructures in feather barbs. Observed avian nanostructures are strikingly similar to those self-assembled during the phase separation of fluid mixtures; the channel and sphere morphologies are characteristic of phase separation by spinodal decomposition and nucleation and growth, respectively. These unstable structures are locked-in by the kinetic arrest of the {beta}-keratin matrix, likely through the entanglement or cross-linking of supermolecular {beta}-keratin fibers. Using the power of self-assembly, birds can robustly realize a diverse range of nanoscopic morphologies with relatively small physical and chemical changes during feather development.« less

Does increasing pressure always accelerate the condensed material decay initiated through bimolecular reactions? A case of the thermal decomposition of TKX-50 at high pressures.

PubMed

Lu, Zhipeng; Zeng, Qun; Xue, Xianggui; Zhang, Zengming; Nie, Fude; Zhang, Chaoyang

2017-08-30

Performances and behaviors under high temperature-high pressure conditions are fundamentals for many materials. We study in the present work the pressure effect on the thermal decomposition of a new energetic ionic salt (EIS), TKX-50, by confining samples in a diamond anvil cell, using Raman spectroscopy measurements and ab initio simulations. As a result, we find a quadratic increase in decomposition temperature (T d ) of TKX-50 with increasing pressure (P) (T d = 6.28P 2 + 12.94P + 493.33, T d and P in K and GPa, respectively, and R 2 = 0.995) and the decomposition under various pressures initiated by an intermolecular H-transfer reaction (a bimolecular reaction). Surprisingly, this finding is contrary to a general observation about the pressure effect on the decomposition of common energetic materials (EMs) composed of neutral molecules: increasing pressure will impede the decomposition if it starts from a bimolecular reaction. Our results also demonstrate that increasing pressure impedes the H-transfer via the enhanced long-range electrostatic repulsion of H +δ H +δ of neighboring NH 3 OH + , with blue shifts of the intermolecular H-bonds. And the subsequent decomposition of the H-transferred intermediates is also suppressed, because the decomposition proceeds from a bimolecular reaction to a unimolecular one, which is generally prevented by compression. These two factors are the basic root for which the decomposition retarded with increasing pressure of TKX-50. Therefore, our finding breaks through the previously proposed concept that, for the condensed materials, increasing pressure will accelerate the thermal decomposition initiated by bimolecular reactions, and reveals a distinct mechanism of the pressure effect on thermal decomposition. That is to say, increasing pressure does not always promote the condensed material decay initiated through bimolecular reactions. Moreover, such a mechanism may be feasible to other EISs due to the similar intermolecular interactions.

Double Bounce Component in Cross-Polarimetric SAR from a New Scattering Target Decomposition

NASA Astrophysics Data System (ADS)

Hong, Sang-Hoon; Wdowinski, Shimon

2013-08-01

Common vegetation scattering theories assume that the Synthetic Aperture Radar (SAR) cross-polarization (cross-pol) signal represents solely volume scattering. We found this assumption incorrect based on SAR phase measurements acquired over the south Florida Everglades wetlands indicating that the cross-pol radar signal often samples the water surface beneath the vegetation. Based on these new observations, we propose that the cross-pol measurement consists of both volume scattering and double bounce components. The simplest multi-bounce scattering mechanism that generates cross-pol signal occurs by rotated dihedrals. Thus, we use the rotated dihedral mechanism with probability density function to revise some of the vegetation scattering theories and develop a three- component decomposition algorithm with single bounce, double bounce from both co-pol and cross-pol, and volume scattering components. We applied the new decomposition analysis to both urban and rural environments using Radarsat-2 quad-pol datasets. The decomposition of the San Francisco's urban area shows higher double bounce scattering and reduced volume scattering compared to other common three-component decomposition. The decomposition of the rural Everglades area shows that the relations between volume and cross-pol double bounce depend on the vegetation density. The new decomposition can be useful to better understand vegetation scattering behavior over the various surfaces and the estimation of above ground biomass using SAR observations.

Rupture mechanism of liquid crystal thin films realized by large-scale molecular simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Trung D; Carrillo, Jan-Michael Y; Brown, W Michael

2014-01-01

The ability of liquid crystal (LC) molecules to respond to changes in their environment makes them an interesting candidate for thin film applications, particularly in bio-sensing, bio-mimicking devices, and optics. Yet the understanding of the (in)stability of this family of thin films has been limited by the inherent challenges encountered by experiment and continuum models. Using unprecedented largescale molecular dynamics (MD) simulations, we address the rupture origin of LC thin films wetting a solid substrate at length scales similar to those in experiment. Our simulations show the key signatures of spinodal instability in isotropic and nematic films on top ofmore » thermal nucleation, and importantly, for the first time, evidence of a common rupture mechanism independent of initial thickness and LC orientational ordering. We further demonstrate that the primary driving force for rupture is closely related to the tendency of the LC mesogens to recover their local environment in the bulk state. Our study not only provides new insights into the rupture mechanism of liquid crystal films, but also sets the stage for future investigations of thin film systems using peta-scale molecular dynamics simulations.« less

Determination of the thermal stability of perfluoroalkylethers

NASA Technical Reports Server (NTRS)

Helmick, Larry S.; Jones, William R., Jr.

1990-01-01

The thermal decomposition temperatures of several commercial and custom synthesized perfluoroalkylether fluids were determined with a computerized tensimeter. In general, the decomposition temperatures of the commercial fluids were all similar and significantly higher than those for custom synthesized fluids. Correlation of the decomposition temperatures with the molecular structures of the primary components of the commercial fluids revealed that the stability of the fluids is not affected by intrinsic factors such as carbon chain length, branching, or cumulated difluoroformal groups. Instead, correlation with extrinsic factors revealed that the stability may be limited by the presence of small quantities of thermally unstable material and/or chlorine-containing material arising from the use of chlorine-containing solvents during synthesis. Finally, correlation of decomposition temperatures with molecular weights for Demnum and Krytox fluids supports a chain cleavage reaction mechanism for Demnum fluids and an unzipping reaction mechanism for Krytox fluids.

The correlation between elongation at break and thermal decomposition of aged EPDM cable polymer

NASA Astrophysics Data System (ADS)

Šarac, T.; Devaux, J.; Quiévy, N.; Gusarov, A.; Konstantinović, M. J.

2017-03-01

The effect of simultaneous thermal and gamma irradiation ageing on the mechanical and physicochemical properties of industrial EPDM was investigated. Accelerated ageing, covering a wide range of dose rates, doses and temperatures, was preformed in stagnant air on EPDM polymer samples extracted from the cables in use in the Belgian nuclear power plants. The mechanical properties, ultimate tensile stress and elongation at break, are found to exhibit the strong dependence on the dose, ageing temperature and dose rate. The thermal decomposition of aged polymer is observed to be the dose dependent when thermogravimetry test is performed under air atmosphere. No dose dependence is observed when thermal decomposition is performed under nitrogen atmosphere. The thermal decomposition rates are found to fully mimic the reduction of elongation at break for all dose rates and ageing temperatures. This effect is argued to be the result of thermal and radiation mediated oxidation degradation process.

Metal-porphyrin: a potential catalyst for direct decomposition of N(2)O by theoretical reaction mechanism investigation.

PubMed

Maitarad, Phornphimon; Namuangruk, Supawadee; Zhang, Dengsong; Shi, Liyi; Li, Hongrui; Huang, Lei; Boekfa, Bundet; Ehara, Masahiro

2014-06-17

The adsorption of nitrous oxide (N2O) on metal-porphyrins (metal: Ti, Cr, Fe, Co, Ni, Cu, or Zn) has been theoretically investigated using density functional theory with the M06L functional to explore their use as potential catalysts for the direct decomposition of N2O. Among these metal-porphyrins, Ti-porphyrin is the most active for N2O adsorption in the triplet ground state with the strongest adsorption energy (-13.32 kcal/mol). Ti-porphyrin was then assessed for the direct decomposition of N2O. For the overall reaction mechanism of three N2O molecules on Ti-porphyrin, two plausible catalytic cycles are proposed. Cycle 1 involves the consecutive decomposition of the first two N2O molecules, while cycle 2 is the decomposition of the third N2O molecule. For cycle 1, the activation energies of the first and second N2O decompositions are computed to be 3.77 and 49.99 kcal/mol, respectively. The activation energy for the third N2O decomposition in cycle 2 is 47.79 kcal/mol, which is slightly lower than that of the second activation energy of the first cycle. O2 molecules are released in cycles 1 and 2 as the products of the reaction, which requires endothermic energies of 102.96 and 3.63 kcal/mol, respectively. Therefore, the O2 desorption is mainly released in catalytic cycle 2 of a TiO3-porphyrin intermediate catalyst. In conclusion, regarding the O2 desorption step for the direct decomposition of N2O, the findings would be very useful to guide the search for potential N2O decomposition catalysts in new directions.

Singularity-free interpretation of the thermodynamics of supercooled water

NASA Astrophysics Data System (ADS)

Sastry, Srikanth; Debenedetti, Pablo G.; Sciortino, Francesco; Stanley, H. E.

1996-06-01

The pronounced increases in isothermal compressibility, isobaric heat capacity, and in the magnitude of the thermal expansion coefficient of liquid water upon supercooling have been interpreted either in terms of a continuous, retracing spinodal curve bounding the superheated, stretched, and supercooled states of liquid water, or in terms of a metastable, low-temperature critical point. Common to these two scenarios is the existence of singularities associated with diverging density fluctuations at low temperature. We show that the increase in compressibility upon lowering the temperature of a liquid that expands on cooling, like water, is not contingent on any singular behavior, but rather is a thermodynamic necessity. We perform a thermodynamic analysis for an anomalous liquid (i.e., one that expands when cooled) in the absence of a retracing spinodal and show that one may in general expect a locus of compressibility extrema in the anomalous regime. Our analysis suggests that the simplest interpretation of the behavior of supercooled water consistent with experimental observations is free of singularities. We then develop a waterlike lattice model that exhibits no singular behavior, while capturing qualitative aspects of the thermodynamics of water.

Nitrations Conference Held at Menlo Park, California on 27-29 July 1983.

DTIC Science & Technology

1983-09-01

MECHANISM OF HOMOGENEOUS GAS-PHASE DECOMPOSITION OF NITROTOLUENES" D. F. McMillen, C. W. Larson, and D. M. Golden...NITROAROMATICS. THE MECHANISM OF HOMOGENEOUS GAS-PHASE DECOMPOSITION OF NITROTOLUENES" i 6:00 Wine Tasting 7:00 Banquet, International Dining Room THURSDAY, JULY...which undergo hydrolysis or oxidations in strong acid solutions can he easily nitrated. Aryl nitriles, which could not be dinitrated without

An optimized ensemble local mean decomposition method for fault detection of mechanical components

NASA Astrophysics Data System (ADS)

Zhang, Chao; Li, Zhixiong; Hu, Chao; Chen, Shuai; Wang, Jianguo; Zhang, Xiaogang

2017-03-01

Mechanical transmission systems have been widely adopted in most of industrial applications, and issues related to the maintenance of these systems have attracted considerable attention in the past few decades. The recently developed ensemble local mean decomposition (ELMD) method shows satisfactory performance in fault detection of mechanical components for preventing catastrophic failures and reducing maintenance costs. However, the performance of ELMD often heavily depends on proper selection of its model parameters. To this end, this paper proposes an optimized ensemble local mean decomposition (OELMD) method to determinate an optimum set of ELMD parameters for vibration signal analysis. In OELMD, an error index termed the relative root-mean-square error (Relative RMSE) is used to evaluate the decomposition performance of ELMD with a certain amplitude of the added white noise. Once a maximum Relative RMSE, corresponding to an optimal noise amplitude, is determined, OELMD then identifies optimal noise bandwidth and ensemble number based on the Relative RMSE and signal-to-noise ratio (SNR), respectively. Thus, all three critical parameters of ELMD (i.e. noise amplitude and bandwidth, and ensemble number) are optimized by OELMD. The effectiveness of OELMD was evaluated using experimental vibration signals measured from three different mechanical components (i.e. the rolling bearing, gear and diesel engine) under faulty operation conditions.

Dominant modal decomposition method

NASA Astrophysics Data System (ADS)

Dombovari, Zoltan

2017-03-01

The paper deals with the automatic decomposition of experimental frequency response functions (FRF's) of mechanical structures. The decomposition of FRF's is based on the Green function representation of free vibratory systems. After the determination of the impulse dynamic subspace, the system matrix is formulated and the poles are calculated directly. By means of the corresponding eigenvectors, the contribution of each element of the impulse dynamic subspace is determined and the sufficient decomposition of the corresponding FRF is carried out. With the presented dominant modal decomposition (DMD) method, the mode shapes, the modal participation vectors and the modal scaling factors are identified using the decomposed FRF's. Analytical example is presented along with experimental case studies taken from machine tool industry.

Decomposition of standing litter in arid grasslands: Interactions between sunlight, non-rainfall moisture, microbes, and plant traits

NASA Astrophysics Data System (ADS)

Logan, J. R. V.; Jacobson, P. J.; Jacobson, K. M.; Evans, S.

2017-12-01

Although arid lands make up 40% of the Earth's land surface, we still lack a strong understanding of carbon cycling and plant decomposition in these systems. One reason for this is that field studies typically only focus on decomposition at or below the ground surface even though standing dead litter (material that has not yet fallen to the ground) accounts for more than 50% of total necromass in many of these systems. While recent work has begun to recognize the important and unique aspects of standing litter decomposition, few studies have investigated specific mechanisms controlling rates of mass loss. We hypothesized that initial photodegradation of the outer plant cuticle of standing litter is an important determinant of litter decomposition because this process increases moisture absorption and subsequent opportunities for biological decomposition. Our preliminary results offer support for this hypothesis. We found that standing grass stems with their cuticles artificially removed had greater water absorbance and more than 400% greater mass loss over a 6-month period relative to controls with intact cuticles. Additionally, spectroscopic measurements of cuticle integrity showed damage to the litter surface after a period of extended photodegradation, allowing increased moisture uptake during simulated fog/dew events. These findings are especially important in the context of recent work by us and others showing that non-rainfall moisture (fog, dew, and water vapor) plays a much larger role in arid land decomposition than previously thought. Improving our understanding of the mechanisms driving decomposition of standing litter will enable us to develop a more predictive understanding of carbon storage in arid lands.

Observations and implications of liquid–liquid phase separation at high relative humidities in secondary organic material produced by α-pinene ozonolysis without inorganic salts

DOE PAGES

Renbaum-Wolff, Lindsay; Song, Mijung; Marcolli, Claudia; ...

2016-07-01

Particles consisting of secondary organic material (SOM) are abundant in the atmosphere. In order to predict the role of these particles in climate, visibility and atmospheric chemistry, information on particle phase state (i.e., single liquid, two liquids and solid) is needed. Our paper focuses on the phase state of SOM particles free of inorganic salts produced by the ozonolysis of α-pinene. Phase transitions were investigated in the laboratory using optical microscopy and theoretically using a thermodynamic model at 290 K and for relative humidities ranging from < 0.5 to 100%. In the laboratory studies, a single phase was observed frommore » 0 to 95% relative humidity (RH) while two liquid phases were observed above 95% RH. For increasing RH, the mechanism of liquid–liquid phase separation (LLPS) was spinodal decomposition. The RH range over which two liquid phases were observed did not depend on the direction of RH change. In the modeling studies, the SOM took up very little water and was a single organic-rich phase at low RH values. At high RH, the SOM underwent LLPS to form an organic-rich phase and a water-rich phase, consistent with the laboratory studies. The presence of LLPS at high RH values can have consequences for the cloud condensation nuclei (CCN) activity of SOM particles. In the simulated Köhler curves for SOM particles, two local maxima were observed. Depending on the composition of the SOM, the first or second maximum can determine the critical supersaturation for activation. Recently researchers have observed inconsistencies between measured CCN properties of SOM particles and hygroscopic growth measured below water saturation (i.e., hygroscopic parameters measured below water saturation were inconsistent with hygroscopic parameters measured above water saturation). Furthermore, the work presented here illustrates that such inconsistencies are expected for systems with LLPS when the water uptake at subsaturated conditions represents the hygroscopicity of an organic-rich phase while the barrier for CCN activation can be determined by the second maximum in the Köhler curve when the particles are water rich.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Renbaum-Wolff, Lindsay; Song, Mijung; Marcolli, Claudia

Particles consisting of secondary organic material (SOM) are abundant in the atmosphere. In order to predict the role of these particles in climate, visibility and atmospheric chemistry, information on particle phase state (i.e., single liquid, two liquids and solid) is needed. Our paper focuses on the phase state of SOM particles free of inorganic salts produced by the ozonolysis of α-pinene. Phase transitions were investigated in the laboratory using optical microscopy and theoretically using a thermodynamic model at 290 K and for relative humidities ranging from < 0.5 to 100%. In the laboratory studies, a single phase was observed frommore » 0 to 95% relative humidity (RH) while two liquid phases were observed above 95% RH. For increasing RH, the mechanism of liquid–liquid phase separation (LLPS) was spinodal decomposition. The RH range over which two liquid phases were observed did not depend on the direction of RH change. In the modeling studies, the SOM took up very little water and was a single organic-rich phase at low RH values. At high RH, the SOM underwent LLPS to form an organic-rich phase and a water-rich phase, consistent with the laboratory studies. The presence of LLPS at high RH values can have consequences for the cloud condensation nuclei (CCN) activity of SOM particles. In the simulated Köhler curves for SOM particles, two local maxima were observed. Depending on the composition of the SOM, the first or second maximum can determine the critical supersaturation for activation. Recently researchers have observed inconsistencies between measured CCN properties of SOM particles and hygroscopic growth measured below water saturation (i.e., hygroscopic parameters measured below water saturation were inconsistent with hygroscopic parameters measured above water saturation). Furthermore, the work presented here illustrates that such inconsistencies are expected for systems with LLPS when the water uptake at subsaturated conditions represents the hygroscopicity of an organic-rich phase while the barrier for CCN activation can be determined by the second maximum in the Köhler curve when the particles are water rich.« less

Control and characterization of textured, hydrophobic ionomer surfaces

NASA Astrophysics Data System (ADS)

Wang, Xueyuan

Polymer thin films are of increasing interest in many industrial and technological applications. Superhydrophobic, self-cleaning surfaces have attracted a lot of attention for their application in self-cleaning, anti-sticking coatings, stain resistance, or anti-contamination surfaces in diverse technologies, including medical, transportation, textiles, electronics and paints. This thesis focuses on the preparation of nanometer to micrometer-size particle textured surfaces which are desirable for super water repellency. Textured surfaces consisting of nanometer to micrometer-sized lightly sulfonated polystyrene ionomer (SPS) particles were prepared by rapid evaporation of the solvent from a dilute polymer solution cast onto silica. The effect of the solvent used to spin coat the film, the molecular weight of the ionomer, and the rate of solvent evaporation were investigated. The nano-particle or micron-particle textured ionomer surfaces were prepared by either spin coating or solution casting ionomer solutions at controlled evaporation rates. The surface morphologies were consistent with a spinodal decomposition mechanism where the surface first existed as a percolated-like structure and then ripened into droplets if molecular mobility was retained for sufficient time. The SPS particles or particle aggregates were robust and resisted deformation even after annealing at 120°C for one week. The water contact angles on as-prepared surfaces were relatively low, ~ 90° since the polar groups in ionomer reduce the surface hydrophobicity. After chemical vapor deposition of 1H,1H,2H,2H-perfluorooctyltrichlorosilane, the surface contact angles increased to ~ 109° on smooth surfaces and ~140° on the textured surfaces. Water droplets stuck to these surfaces even when tilted 90 degrees. Superhydrophobic surfaces were prepared by spraying coating ionomer solutions and Chemical Vapor Deposition (CVD) of 1H,1H,2H,2H-perfluorooctyltrichlorosilane onto textured surfaces. The surfaces after CVD of silane exhibited water contact angle of 152° and the water droplet stuck to the surfaces without falling even when tilted upside down. This kind of sticky superhydrophobic surface would have potential applications in no-loss transport of liquid, and cleaning robots.

Thermal Decomposition Mechanism of Butyraldehyde

NASA Astrophysics Data System (ADS)

Hatten, Courtney D.; Warner, Brian; Wright, Emily; Kaskey, Kevin; McCunn, Laura R.

2013-06-01

The thermal decomposition of butyraldehyde, CH_3CH_2CH_2C(O)H, has been studied in a resistively heated SiC tubular reactor. Products of pyrolysis were identified via matrix-isolation FTIR spectroscopy and photoionization mass spectrometry in separate experiments. Carbon monoxide, ethene, acetylene, water and ethylketene were among the products detected. To unravel the mechanism of decomposition, pyrolysis of a partially deuterated sample of butyraldehyde was studied. Also, the concentration of butyraldehyde in the carrier gas was varied in experiments to determine the presence of bimolecular reactions. The results of these experiments can be compared to the dissociation pathways observed in similar aldehydes and are relevant to the processing of biomass, foods, and tobacco.

Resonance-Based Sparse Signal Decomposition and its Application in Mechanical Fault Diagnosis: A Review.

PubMed

Huang, Wentao; Sun, Hongjian; Wang, Weijie

2017-06-03

Mechanical equipment is the heart of industry. For this reason, mechanical fault diagnosis has drawn considerable attention. In terms of the rich information hidden in fault vibration signals, the processing and analysis techniques of vibration signals have become a crucial research issue in the field of mechanical fault diagnosis. Based on the theory of sparse decomposition, Selesnick proposed a novel nonlinear signal processing method: resonance-based sparse signal decomposition (RSSD). Since being put forward, RSSD has become widely recognized, and many RSSD-based methods have been developed to guide mechanical fault diagnosis. This paper attempts to summarize and review the theoretical developments and application advances of RSSD in mechanical fault diagnosis, and to provide a more comprehensive reference for those interested in RSSD and mechanical fault diagnosis. Followed by a brief introduction of RSSD's theoretical foundation, based on different optimization directions, applications of RSSD in mechanical fault diagnosis are categorized into five aspects: original RSSD, parameter optimized RSSD, subband optimized RSSD, integrated optimized RSSD, and RSSD combined with other methods. On this basis, outstanding issues in current RSSD study are also pointed out, as well as corresponding instructional solutions. We hope this review will provide an insightful reference for researchers and readers who are interested in RSSD and mechanical fault diagnosis.

Resonance-Based Sparse Signal Decomposition and Its Application in Mechanical Fault Diagnosis: A Review

PubMed Central

Huang, Wentao; Sun, Hongjian; Wang, Weijie

2017-01-01

Mechanical equipment is the heart of industry. For this reason, mechanical fault diagnosis has drawn considerable attention. In terms of the rich information hidden in fault vibration signals, the processing and analysis techniques of vibration signals have become a crucial research issue in the field of mechanical fault diagnosis. Based on the theory of sparse decomposition, Selesnick proposed a novel nonlinear signal processing method: resonance-based sparse signal decomposition (RSSD). Since being put forward, RSSD has become widely recognized, and many RSSD-based methods have been developed to guide mechanical fault diagnosis. This paper attempts to summarize and review the theoretical developments and application advances of RSSD in mechanical fault diagnosis, and to provide a more comprehensive reference for those interested in RSSD and mechanical fault diagnosis. Followed by a brief introduction of RSSD’s theoretical foundation, based on different optimization directions, applications of RSSD in mechanical fault diagnosis are categorized into five aspects: original RSSD, parameter optimized RSSD, subband optimized RSSD, integrated optimized RSSD, and RSSD combined with other methods. On this basis, outstanding issues in current RSSD study are also pointed out, as well as corresponding instructional solutions. We hope this review will provide an insightful reference for researchers and readers who are interested in RSSD and mechanical fault diagnosis. PMID:28587198

The decomposition of fine and coarse roots: their global patterns and controlling factors

PubMed Central

Zhang, Xinyue; Wang, Wei

2015-01-01

Fine root decomposition represents a large carbon (C) cost to plants, and serves as a potential soil C source, as well as a substantial proportion of net primary productivity. Coarse roots differ markedly from fine roots in morphology, nutrient concentrations, functions, and decomposition mechanisms. Still poorly understood is whether a consistent global pattern exists between the decomposition of fine (<2 mm root diameter) and coarse (≥2 mm) roots. A comprehensive terrestrial root decomposition dataset, including 530 observations from 71 sampling sites, was thus used to compare global patterns of decomposition of fine and coarse roots. Fine roots decomposed significantly faster than coarse roots in middle latitude areas, but their decomposition in low latitude regions was not significantly different from that of coarse roots. Coarse root decomposition showed more dependence on climate, especially mean annual temperature (MAT), than did fine roots. Initial litter lignin content was the most important predictor of fine root decomposition, while lignin to nitrogen ratios, MAT, and mean annual precipitation were the most important predictors of coarse root decomposition. Our study emphasizes the necessity of separating fine roots and coarse roots when predicting the response of belowground C release to future climate changes. PMID:25942391

Skating on a Film of Air: Drops Impacting on a Surface

NASA Astrophysics Data System (ADS)

Kolinski, John M.; Rubinstein, Shmuel M.; Mandre, Shreyas; Brenner, Michael P.; Weitz, David A.; Mahadevan, L.

2012-02-01

The commonly accepted description of drops impacting on a surface typically ignores the essential role of the air that is trapped between the impacting drop and the surface. Here we describe a new imaging modality that is sensitive to the behavior right at the surface. We show that a very thin film of air, only a few tens of nanometers thick, remains trapped between the falling drop and the surface as the drop spreads. The thin film of air serves to lubricate the drop enabling the fluid to skate on the air film laterally outward at surprisingly high velocities, consistent with theoretical predictions. Eventually this thin film of air breaks down as the fluid wets the surface via a spinodal-like mechanism. Our results show that the dynamics of impacting drops are much more complex than previously thought, with a rich array of unexpected phenomena that require rethinking classic paradigms.

Modeling of UV laser-induced patterning of ultrathin Co films on bulk SiO2: verification of short- and long-range ordering mechanisms

NASA Astrophysics Data System (ADS)

Trice, Justin; Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, R.

2006-03-01

Irradiating ultrathin Co films (1 to 10 nm) by a short-pulsed UV laser leads to pattern formation with both short- and long-range order (SRO, LRO). Single beam irradiation produces SRO, while two-beam interference irradiation produces a quasi-2D arrangement of nanoparticles with LRO and SRO. The pattern formation primarily occurs in the molten phase. An estimate of the thermal behavior of the film/substrate composite following a laser pulse is presented. The thermal behavior includes the lifetime of the liquid phase and the thermal gradient during interference heating. Based on this evidence, the SRO is attributed to spinodal dewetting of the film while surface tension gradients induced by the laser interference pattern appear to influence LRO [1]. [1] C.Favazza, J.Trice, H.Krishna, R.Sureshkumar, and R.Kalyanaraman, unpublished.

Calvin Mukarakate | NREL

Science.gov Websites

for the Symposium on Thermal and Catalytic Sciences for Biofuels and Biobased Products. He is also a ;Unimolecular Thermal Decomposition of Dimethoxybenzenes," Journal of Chemical Physics (2014) "Real ," Green Chemistry (2014) "Biomass Pyrolysis: Thermal Decomposition Mechanisms of Furfural and

Perfluoropolyalkylether decomposition on catalytic aluminas

NASA Technical Reports Server (NTRS)

Morales, Wilfredo

1994-01-01

The decomposition of Fomblin Z25, a commercial perfluoropolyalkylether liquid lubricant, was studied using the Penn State Micro-oxidation Test, and a thermal gravimetric/differential scanning calorimetry unit. The micro-oxidation test was conducted using 440C stainless steel and pure iron metal catalyst specimens, whereas the thermal gravimetric/differential scanning calorimetry tests were conducted using catalytic alumina pellets. Analysis of the thermal data, high pressure liquid chromatography data, and x-ray photoelectron spectroscopy data support evidence that there are two different decomposition mechanisms for Fomblin Z25, and that reductive sites on the catalytic surfaces are responsible for the decomposition of Fomblin Z25.

Phase transitions in core-collapse supernova matter at sub-saturation densities

NASA Astrophysics Data System (ADS)

Pais, Helena; Newton, William G.; Stone, Jirina R.

2014-12-01

Phase transitions in hot, dense matter in the collapsing cores of massive stars have an important impact on the core-collapse supernova mechanism as they absorb heat, disrupt homology, and so weaken the developing shock. We perform a three-dimensional, finite temperature Skyrme-Hartree-Fock (SHF) study of inhomogeneous nuclear matter to determine the critical density and temperature for the phase transition between the pasta phase and homogeneous matter and its properties. We employ four different parametrizations of the Skyrme nuclear energy-density functional, SkM*, SLy4, NRAPR, and SQMC700, which span a range of saturation-density symmetry energy behaviors constrained by a variety of nuclear experimental probes. For each of these interactions we calculate free energy, pressure, entropy, and chemical potentials in the range of particle number densities where the nuclear pasta phases are expected to exist, 0.02-0.12 fm-3, temperatures 2-8 MeV, and a proton fraction of 0.3. We find unambiguous evidence for a first-order phase transition to uniform matter, unsoftened by the presence of the pasta phases. No conclusive signs of a first-order phase transition between the pasta phases is observed, and it is argued that the thermodynamic quantities vary continuously right up to the first-order phase transition to uniform matter. We compare our results with thermodynamic spinodals calculated using the same Skyrme parametrizations, finding that the effect of short-range Coulomb correlations and quantum shell effects included in our model leads to the pasta phases existing at densities up to 0.01 fm-3 above the spinodal boundaries, thus increasing the transition density to uniform matter by the same amount. The transition density is otherwise shown to be insensitive to the symmetry energy at saturation density within the range constrained by the concordance of a variety of experimental constraints, and can be taken to be a well determined quantity.

Kinetics of gas phase formic acid decomposition on platinum single crystal and polycrystalline surfaces

NASA Astrophysics Data System (ADS)

Detwiler, Michael D.; Milligan, Cory A.; Zemlyanov, Dmitry Y.; Delgass, W. Nicholas; Ribeiro, Fabio H.

2016-06-01

Formic acid dehydrogenation turnover rates (TORs) were measured on Pt(111), Pt(100), and polycrystalline Pt foil surfaces at a total pressure of 800 Torr between 413 and 513 K in a batch reactor connected to an ultra-high vacuum (UHV) system. The TORs, apparent activation energies, and reaction orders are not sensitive to the structure of the Pt surface, within the precision of the measurements. CO introduced into the batch reactor depressed the formic acid dehydrogenation TOR and increased the reaction's apparent activation energies on Pt(111) and Pt(100), consistent with behavior predicted by the Temkin equation. Two reaction mechanisms were explored which explain the formic acid decomposition mechanism on Pt, both of which include dissociative adsorption of formic acid, rate limiting formate decomposition, and quasi-equilibrated hydrogen recombination and CO adsorption. No evidence was found that catalytic supports used in previous studies altered the reaction kinetics or mechanism.

Tautomerism and thermal decomposition of tetrazole: high-level ab initio study.

PubMed

Kiselev, Vitaly G; Cheblakov, Pavel B; Gritsan, Nina P

2011-03-10

The mutual interconversion and decomposition reactions of four tetrazole isomers (1H-TZ, 2H-TZ, 5H-TZ, and an N-heterocyclic carbene 14H) have been studied theoretically using the W1 high-level procedure. Computations allowed resolution of the existing discrepancies in the mechanism and key intermediates of TZ thermolysis. The tautomeric equilibria between 1H-TZ, 2H-TZ, and 14H turned out to play a very important role in the mechanism of thermal decomposition. Although the barriers of monomolecular tautomeric transformations were found to be high (∼50-70 kcal/mol), the concerted double H atom transfer reactions in the H-bonded complexes of TZ tautomers have profoundly lower barriers (∼18-28 kcal/mol). These reactions lead to fast interconversion between 1H-TZ, 2H-TZ, and 14H. The carbene 14H has never been considered before; however, it was predicted to be a key intermediate in the mechanism of thermal decomposition of TZ. For all species considered, the unimolecular reactions of N(2) elimination were predicted to dominate over the elimination of hydrazoic acid. In agreement with existing experimental data, the effective activation energy of thermolysis was calculated to be 36.2 kcal/mol.

Kinetics and mechanism of solid decompositions — From basic discoveries by atomic absorption spectrometry and quadrupole mass spectroscopy to thorough thermogravimetric analysis

NASA Astrophysics Data System (ADS)

L'vov, Boris V.

2008-02-01

This paper sums up the evolution of thermochemical approach to the interpretation of solid decompositions for the past 25 years. This period includes two stages related to decomposition studies by different techniques: by ET AAS and QMS in 1981-2001 and by TG in 2002-2007. As a result of ET AAS and QMS investigations, the method for determination of absolute rates of solid decompositions was developed and the mechanism of decompositions through the congruent dissociative vaporization was discovered. On this basis, in the period from 1997 to 2001, the decomposition mechanisms of several classes of reactants were interpreted and some unusual effects observed in TA were explained. However, the thermochemical approach has not received any support by other TA researchers. One of the potential reasons of this distrust was the unreliability of the E values measured by the traditional Arrhenius plot method. The theoretical analysis and comparison of metrological features of different methods used in the determinations of thermochemical quantities permitted to conclude that in comparison with the Arrhenius plot and second-law methods, the third-law method is to be very much preferred. However, this method cannot be used in the kinetic studies by the Arrhenius approach because its use suggests the measuring of the equilibrium pressures of decomposition products. On the contrary, the method of absolute rates is ideally suitable for this purpose. As a result of much higher precision of the third-law method, some quantitative conclusions that follow from the theory were confirmed, and several new effects, which were invisible in the framework of the Arrhenius approach, have been revealed. In spite of great progress reached in the development of reliable methodology, based on the third-law method, the thermochemical approach remains unclaimed as before.

Thermochemistry, Tautomerism, and Thermal Decomposition of 1,5-Diaminotetrazole: A High-Level ab Initio Study.

PubMed

Shakhova, Margarita V; Muravyev, Nikita V; Gritsan, Nina P; Kiselev, Vitaly G

2018-04-19

Thermochemistry, kinetics, and mechanism of thermal decomposition of 1,5-diaminotetrazole (DAT), a widely used "building block" of nitrogen-rich energetic compounds, were studied theoretically at a high and reliable level of theory (viz., using the explicitly correlated CCSD(T)-F12/aug-cc-pVTZ procedure). Quantum chemical calculations provided detailed insight into the thermolysis mechanism of DAT missing in the existing literature. Moreover, several contradictory assumptions on the mechanism and key intermediates of thermolysis were resolved. The unimolecular primary decomposition reactions of the seven isomers of DAT were studied in the gas phase and in the melt using a simplified model of the latter. The two-step reaction of N 2 elimination from the diamino tautomer was found to be the primary decomposition process of DAT in the gas phase and melt. The effective Arrhenius parameters of this process were calculated to be E a = 43.4 kcal mol -1 and log( A/s -1 ) = 15.2 in a good agreement with the experimental values. Contrary to the existing literature data, all other decomposition channels of DAT isomers turned out to be kinetically unimportant. Apart from this, a new primary decomposition channel yielding N 2 , cyanamide, and 1,1-diazene was found for some H-bonded dimers of DAT. We also determined a reliable and mutually consistent set of thermochemical values for DAT (Δ f H solid 0 = 74.5 ± 1.5 kcal·mol -1 ) by combining theoretically calculated (W1 multilevel procedure along with an isodesmic reaction) gas phase enthalpy of formation (Δ f H gas 0 = 100.7 ± 1.0 kcal·mol -1 ) and experimentally measured sublimation enthalpy (Δ sub H 0 = 26.2 ± 0.5 kcal·mol -1 ).

Decomposition of amino diazeniumdiolates (NONOates): molecular mechanisms.

PubMed

Shaikh, Nizamuddin; Valiev, Marat; Lymar, Sergei V

2014-12-01

Although diazeniumdiolates (X[N(O)NO](-)) are extensively used in biochemical, physiological, and pharmacological studies due to their ability to release NO and/or its congeneric nitroxyl, the mechanisms of these processes remain obscure. In this work, we used a combination of spectroscopic, kinetic, and computational techniques to arrive at a quantitatively consistent molecular mechanism for decomposition of amino diazeniumdiolates (amino NONOates: R2N[N(O)NO](-), where R=N(C2H5)2 (1), N(C3H4NH2)2 (2), or N(C2H4NH2)2 (3)). Decomposition of these NONOates is triggered by protonation of their [NN(O)NO](-) group with the apparent pKa and decomposition rate constants of 4.6 and 1 s(-1) for 1; 3.5 and 0.083 s(-1) for 2; and 3.8 and 0.0033 s(-1) for 3. Although protonation occurs mainly on the O atoms of the functional group, only the minor R2N(H)N(O)NO tautomer (population ~10(-7), for 1) undergoes the NN heterolytic bond cleavage (kd~10(7) s(-1) for 1) leading to amine and NO. Decompositions of protonated amino NONOates are strongly temperature-dependent; activation enthalpies are 20.4 and 19.4 kcal/mol for 1 and 2, respectively, which includes contributions from both the tautomerization and bond cleavage. The bond cleavage rates exhibit exceptional sensitivity to the nature of R substituents which strongly modulate activation entropy. At pH<2, decompositions of all three NONOates that have been investigated are subject to additional acid catalysis that occurs through di-protonation of the [NN(O)NO](-) group. Copyright © 2014 Elsevier Inc. All rights reserved.

Decomposition of amino diazeniumdiolates (NONOates): Molecular mechanisms

DOE PAGES

Shaikh, Nizamuddin; Valiev, Marat; Lymar, Sergei V.

2014-08-23

Although diazeniumdiolates (X[N(O)NO] -) are extensively used in biochemical, physiological, and pharmacological studies due to their ability to release NO and/or its congeneric nitroxyl, the mechanisms of these processes remain obscure. In this work, we used a combination of spectroscopic, kinetic, and computational techniques to arrive at a quantitatively consistent molecular mechanism for decomposition of amino diazeniumdiolates (amino NONOates: R 2N[N(O)NO] -, where R = —N(C 2H 5) 2(1), —N(C 3H 4NH 2) 2(2), or —N(C 2H 4NH 2) 2(3)). Decomposition of these NONOates is triggered by protonation of their [NN(O)NO] - group with the apparent pKa and decomposition ratemore » constants of 4.6 and 1 s -1 for 1; 3.5 and 0.083 s -1 for 2; and 3.8 and 0.0033 s -1 for 3. Although protonation occurs mainly on the O atoms of the functional group, only the minor R 2N(H)N(O)NO tautomer (population ~ 10 -7, for 1) undergoes the N—N heterolytic bond cleavage (k d ~ 107 s -1 for 1) leading to amine and NO. Decompositions of protonated amino NONOates are strongly temperature-dependent; activation enthalpies are 20.4 and 19.4 kcal/mol for 1 and 2, respectively, which includes contributions from both the tautomerization and bond cleavage. Thus, the bond cleavage rates exhibit exceptional sensitivity to the nature of R substituents which strongly modulate activation entropy. At pH < 2, decompositions of all three NONOates that have been investigated are subject to additional acid catalysis that occurs through di-protonation of the [NN(O)NO] - group.« less

Pyrolysis and Matrix-Isolation FTIR of Acetoin

NASA Astrophysics Data System (ADS)

Cole, Sarah; Ellis, Martha; Sowards, John; McCunn, Laura R.

2017-06-01

Acetoin, CH_3C(O)CH(OH)CH_3, is an additive used in foods and cigarettes as well as a common component of biomass pyrolysate during the production of biofuels, yet little is known about its thermal decomposition mechanism. In order to identify thermal decomposition products of acetoin, a gas-phase mixture of approximately 0.3% acetoin in argon was subject to pyrolysis in a resistively heated SiC microtubular reactor at 1100-1500 K. Matrix-isolation FTIR spectroscopy was used to identify pyrolysis products. Many products were observed in analysis of the spectra, including acetylene, propyne, ethylene, and vinyl alcohol. These results provide clues to the overall mechanism of thermal decomposition and are important for predicting emissions from many industrial and residential processes.

Excited electronic state decomposition mechanisms and dynamics of nitramine energetic materials and model systems

NASA Astrophysics Data System (ADS)

Greenfield, Margo

Energetic materials play an important role in aeronautics, the weapon industry, and the propellant industry due to their broad applications as explosives and fuels. RDX (1,3,5-trinitrohexahydro-s-triazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) are compounds which contain high energy density. Although RDX and HMX have been studied extensively over the past several decades a complete understanding of their decomposition mechanisms and dynamics is unknown. Time of flight mass spectroscopy (TOFMS) UV photodissociation (ns) experiments of gas phase RDX, HMX, and CL-20 generate the NO molecule as the initial decomposition product. Four different vibronic transitions of the initial decomposition product, the NO molecule, are observed: A2Sigma(upsilon'=0)←X 2pi(upsilon"=0,1,2,3). Simulations of the rovibronic intensities for the A←X transitions demonstrate that NO dissociated from RDX, HMX, and CL-20 is rotationally cold (˜20 K) and vibrationally hot (˜1800 K). Conversely, experiments on the five model systems (nitromethane, dimethylnitramine (DMNA), nitropyrrolidine, nitropiperidine and dinitropiperazine) produce rotationally hot and vibrationally cold spectra. Laser induced fluorescence (LIF) experiments are performed to rule out the possible decomposition product OH, generated along with NO, perhaps from the suggested HONO elimination mechanism. The OH radical is not observed in the fluorescence experiments, indicating the HONO decomposition intermediate is not an important pathway for the excited electronic state decomposition of cyclic nitramines. The NO molecule is also employed to measure the dynamics of the excited state decomposition. A 226 nm, 180 fs light pulse is utilized to photodissociate the gas phase systems. Stable ion states of DMNA and nitropyrrolidine are observed while the energetic materials and remaining model systems present the NO molecule as the only observed product. Pump-probe transients of the resonant A←X (0-0) transition of the NO molecule show a constant signal indicating these materials decompose faster than the time duration of the 226 nm laser light. Calculational results together with the experimental results indicate the energetic materials decompose through an internal conversion to very highly excited (˜5 eV of vibrational energy) vibrational states of their ground electronic state, while the model systems follow an excited electronic state decomposition pathway.

Time-resolved spectroscopic measurements of shock-wave induced decomposition in cyclotrimethylene trinitramine (RDX) crystals: anisotropic response.

PubMed

Dang, Nhan C; Dreger, Zbigniew A; Gupta, Yogendra M; Hooks, Daniel E

2010-11-04

Plate impact experiments on the (210), (100), and (111) planes were performed to examine the role of crystalline anisotropy on the shock-induced decomposition of cyclotrimethylenetrinitramine (RDX) crystals. Time-resolved emission spectroscopy was used to probe the decomposition of single crystals shocked to peak stresses ranging between 7 and 20 GPa. Emission produced by decomposition intermediates was analyzed in terms of induction time to emission, emission intensity, and the emission spectra shapes as a function of stress and time. Utilizing these features, we found that the shock-induced decomposition of RDX crystals exhibits considerable anisotropy. Crystals shocked on the (210) and (100) planes were more sensitive to decomposition than crystals shocked on the (111) plane. The possible sources of the observed anisotropy are discussed with regard to the inelastic deformation mechanisms of shocked RDX. Our results suggest that, despite the anisotropy observed for shock initiation, decomposition pathways for all three orientations are similar.

Ozone decomposition

PubMed Central

Batakliev, Todor; Georgiev, Vladimir; Anachkov, Metody; Rakovsky, Slavcho

2014-01-01

Catalytic ozone decomposition is of great significance because ozone is a toxic substance commonly found or generated in human environments (aircraft cabins, offices with photocopiers, laser printers, sterilizers). Considerable work has been done on ozone decomposition reported in the literature. This review provides a comprehensive summary of the literature, concentrating on analysis of the physico-chemical properties, synthesis and catalytic decomposition of ozone. This is supplemented by a review on kinetics and catalyst characterization which ties together the previously reported results. Noble metals and oxides of transition metals have been found to be the most active substances for ozone decomposition. The high price of precious metals stimulated the use of metal oxide catalysts and particularly the catalysts based on manganese oxide. It has been determined that the kinetics of ozone decomposition is of first order importance. A mechanism of the reaction of catalytic ozone decomposition is discussed, based on detailed spectroscopic investigations of the catalytic surface, showing the existence of peroxide and superoxide surface intermediates. PMID:26109880

Thermal Decomposition Mechanisms of Alkylimidazolium Ionic Liquids with CN-containing Anions

DTIC Science & Technology

2014-11-01

anion calculated at the M06/6-31+G(d,p) level of theory and using the generic ionic liquid (GIL) model to simulate the condensed phase methyl...decomposition mechanisms of alkylimidazolium ionic liquids with CN-containing anions 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d...perform, display, or disclose the work. 14. ABSTRACT Due to the unusually high heats of vaporization of room-temperature ionic liquids (RTILs

Changes in bacterial and eukaryotic communities during sewage decomposition in Mississippi River water

EPA Science Inventory

Microbial decay processes are one of the mechanisms whereby sewage contamination is reduced in the environment. This decomposition process involves a highly complex array of bacterial and eukaryotic communities from both sewage and ambient waters. However, relatively little is kn...

Azole energetic materials: Initial mechanisms for the energy release from electronical excited nitropyrazoles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Bing; Yu, Zijun; Bernstein, Elliot R., E-mail: erb@lamar.Colostate.edu

2014-01-21

Decomposition of energetic material 3,4-dinitropyrazole (DNP) and two model molecules 4-nitropyrazole and 1-nitropyrazole is investigated both theoretically and experimentally. The initial decomposition mechanisms for these three nitropyrazoles are explored with complete active space self-consistent field (CASSCF) level. The NO molecule is observed as an initial decomposition product from all three materials subsequent to UV excitation. Observed NO products are rotationally cold (<50 K) for all three systems. The vibrational temperature of the NO product from DNP is (3850 ± 50) K, 1350 K hotter than that of the two model species. Potential energy surface calculations at the CASSCF(12,8)/6-31+G(d) level illustratemore » that conical intersections plays an essential role in the decomposition mechanism. Electronically excited S{sub 2} nitropyraozles can nonradiatively relax to lower electronic states through (S{sub 2}/S{sub 1}){sub CI} and (S{sub 1}/S{sub 0}){sub CI} conical intersection and undergo a nitro-nitrite isomerization to generate NO product either in the S{sub 1} state or S{sub 0} state. In model systems, NO is generated in the S{sub 1} state, while in the energetic material DNP, NO is produced on the ground state surface, as the S{sub 1} decomposition pathway is energetically unavailable. The theoretically predicted mechanism is consistent with the experimental results, as DNP decomposes in a lower electronic state than do the model systems and thus the vibrational energy in the NO product from DNP should be hotter than from the model systems. The observed rotational energy distributions for NO are consistent with the final structures of the respective transition states for each molecule.« less

Molecular mechanism of metal-independent decomposition of lipid hydroperoxide 13-HPODE by halogenated quinoid carcinogens.

PubMed

Qin, Hao; Huang, Chun-Hua; Mao, Li; Xia, Hai-Ying; Kalyanaraman, Balaraman; Shao, Jie; Shan, Guo-Qiang; Zhu, Ben-Zhan

2013-10-01

Halogenated quinones are a class of carcinogenic intermediates and newly identified chlorination disinfection by-products in drinking water. 13-Hydroperoxy-9,11-octadecadienoic acid (13-HPODE) is the most extensively studied endogenous lipid hydroperoxide. Although it is well known that the decomposition of 13-HPODE can be catalyzed by transition metal ions, it is not clear whether halogenated quinones could enhance its decomposition independent of metal ions and, if so, what the unique characteristics and similarities are. Here we show that 2,5-dichloro-1,4-benzoquinone (DCBQ) could markedly enhance the decomposition of 13-HPODE and formation of reactive lipid alkyl radicals such as pentyl and 7-carboxyheptyl radicals, and the genotoxic 4-hydroxy-2-nonenal (HNE), through the complementary application of ESR spin trapping, HPLC-MS, and GC-MS methods. Interestingly, two chloroquinone-lipid alkoxyl conjugates were also detected and identified from the reaction between DCBQ and 13-HPODE. Analogous results were observed with other halogenated quinones. This represents the first report that halogenated quinoid carcinogens can enhance the decomposition of the endogenous lipid hydroperoxide 13-HPODE and formation of reactive lipid alkyl radicals and genotoxic HNE via a novel metal-independent nucleophilic substitution coupled with homolytic decomposition mechanism, which may partly explain their potential genotoxicity and carcinogenicity. Copyright © 2013 Elsevier Inc. All rights reserved.

Ab initio kinetics and thermal decomposition mechanism of mononitrobiuret and 1,5-dinitrobiuret

NASA Astrophysics Data System (ADS)

Sun, Hongyan; Vaghjiani, Ghanshyam L.

2015-05-01

Mononitrobiuret (MNB) and 1,5-dinitrobiuret (DNB) are tetrazole-free, nitrogen-rich, energetic compounds. For the first time, a comprehensive ab initio kinetics study on the thermal decomposition mechanisms of MNB and DNB is reported here. In particular, the intramolecular interactions of amine H-atom with electronegative nitro O-atom and carbonyl O-atom have been analyzed for biuret, MNB, and DNB at the M06-2X/aug-cc-pVTZ level of theory. The results show that the MNB and DNB molecules are stabilized through six-member-ring moieties via intramolecular H-bonding with interatomic distances between 1.8 and 2.0 Å, due to electrostatic as well as polarization and dispersion interactions. Furthermore, it was found that the stable molecules in the solid state have the smallest dipole moment amongst all the conformers in the nitrobiuret series of compounds, thus revealing a simple way for evaluating reactivity of fuel conformers. The potential energy surface for thermal decomposition of MNB was characterized by spin restricted coupled cluster theory at the RCCSD(T)/cc-pV∞ Z//M06-2X/aug-cc-pVTZ level. It was found that the thermal decomposition of MNB is initiated by the elimination of HNCO and HNN(O)OH intermediates. Intramolecular transfer of a H-atom, respectively, from the terminal NH2 group to the adjacent carbonyl O-atom via a six-member-ring transition state eliminates HNCO with an energy barrier of 35 kcal/mol and from the central NH group to the adjacent nitro O-atom eliminates HNN(O)OH with an energy barrier of 34 kcal/mol. Elimination of HNN(O)OH is also the primary process involved in the thermal decomposition of DNB, which processes C2v symmetry. The rate coefficients for the primary decomposition channels for MNB and DNB were quantified as functions of temperature and pressure. In addition, the thermal decomposition of HNN(O)OH was analyzed via Rice-Ramsperger-Kassel-Marcus/multi-well master equation simulations, the results of which reveal the formation of (NO2 + H2O) to be the major decomposition path. Furthermore, we provide fundamental interpretations for the experimental results of Klapötke et al. [Combust. Flame 139, 358-366 (2004)] regarding the thermal stability of MNB and DNB, and their decomposition products. Notably, a fundamental understanding of fuel stability, decomposition mechanism, and key reactions leading to ignition is essential in the design and manipulation of molecular systems for the development of new energetic materials for advanced propulsion applications.

Ab Initio Kinetics and Thermal Decomposition Mechanism of Mononitrobiuret and 1,5- Dinitrobiuret

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Hongyan; Vaghjiani, Ghanshyam G.

2015-05-26

Mononitrobiuret (MNB) and 1,5-dinitrobiuret (DNB) are tetrazole-free, nitrogen-rich, energetic compounds. For the first time, a comprehensive ab initio kinetics study on the thermal decomposition mechanisms of MNB and DNB is reported here. In particular, the intramolecular interactions of amine H-atom with electronegative nitro O-atom and carbonyl O-atom have been analyzed for biuret, MNB, and DNB at the M06-2X/aug-cc-pVTZ level of theory. The results show that the MNB and DNB molecules are stabilized through six-member-ring moieties via intramolecular H-bonding with interatomic distances between 1.8 and 2.0 Å, due to electrostatic as well as polarization and dispersion interactions. Furthermore, it was foundmore » that the stable molecules in the solid state have the smallest dipole moment amongst all the conformers in the nitrobiuret series of compounds, thus revealing a simple way for evaluating reactivity of fuel conformers. The potential energy surface for thermal decomposition of MNB was characterized by spin restricted coupled cluster theory at the RCCSD(T)/cc-pV∞ Z//M06-2X/aug-cc-pVTZ level. It was found that the thermal decomposition of MNB is initiated by the elimination of HNCO and HNN(O)OH intermediates. Intramolecular transfer of a H-atom, respectively, from the terminal NH2 group to the adjacent carbonyl O-atom via a six-member-ring transition state eliminates HNCO with an energy barrier of 35 kcal/mol and from the central NH group to the adjacent nitro O-atom eliminates HNN(O)OH with an energy barrier of 34 kcal/mol. Elimination of HNN(O)OH is also the primary process involved in the thermal decomposition of DNB, which processes C2v symmetry. The rate coefficients for the primary decomposition channels for MNB and DNB were quantified as functions of temperature and pressure. In addition, the thermal decomposition of HNN(O)OH was analyzed via Rice–Ramsperger–Kassel–Marcus/multi-well master equation simulations, the results of which reveal the formation of (NO2 + H2O) to be the major decomposition path. Furthermore, we provide fundamental interpretations for the experimental results of Klapötke et al. [Combust. Flame 139, 358–366 (2004)] regarding the thermal stability of MNB and DNB, and their decomposition products. Notably, a fundamental understanding of fuel stability, decomposition mechanism, and key reactions leading to ignition is essential in the design and manipulation of molecular systems for the development of new energetic materials for advanced propulsion applications.« less

Ab initio kinetics and thermal decomposition mechanism of mononitrobiuret and 1,5-dinitrobiuret.

PubMed

Sun, Hongyan; Vaghjiani, Ghanshyam L

2015-05-28

Mononitrobiuret (MNB) and 1,5-dinitrobiuret (DNB) are tetrazole-free, nitrogen-rich, energetic compounds. For the first time, a comprehensive ab initio kinetics study on the thermal decomposition mechanisms of MNB and DNB is reported here. In particular, the intramolecular interactions of amine H-atom with electronegative nitro O-atom and carbonyl O-atom have been analyzed for biuret, MNB, and DNB at the M06-2X/aug-cc-pVTZ level of theory. The results show that the MNB and DNB molecules are stabilized through six-member-ring moieties via intramolecular H-bonding with interatomic distances between 1.8 and 2.0 Å, due to electrostatic as well as polarization and dispersion interactions. Furthermore, it was found that the stable molecules in the solid state have the smallest dipole moment amongst all the conformers in the nitrobiuret series of compounds, thus revealing a simple way for evaluating reactivity of fuel conformers. The potential energy surface for thermal decomposition of MNB was characterized by spin restricted coupled cluster theory at the RCCSD(T)/cc-pV∞ Z//M06-2X/aug-cc-pVTZ level. It was found that the thermal decomposition of MNB is initiated by the elimination of HNCO and HNN(O)OH intermediates. Intramolecular transfer of a H-atom, respectively, from the terminal NH2 group to the adjacent carbonyl O-atom via a six-member-ring transition state eliminates HNCO with an energy barrier of 35 kcal/mol and from the central NH group to the adjacent nitro O-atom eliminates HNN(O)OH with an energy barrier of 34 kcal/mol. Elimination of HNN(O)OH is also the primary process involved in the thermal decomposition of DNB, which processes C2v symmetry. The rate coefficients for the primary decomposition channels for MNB and DNB were quantified as functions of temperature and pressure. In addition, the thermal decomposition of HNN(O)OH was analyzed via Rice-Ramsperger-Kassel-Marcus/multi-well master equation simulations, the results of which reveal the formation of (NO2 + H2O) to be the major decomposition path. Furthermore, we provide fundamental interpretations for the experimental results of Klapötke et al. [Combust. Flame 139, 358-366 (2004)] regarding the thermal stability of MNB and DNB, and their decomposition products. Notably, a fundamental understanding of fuel stability, decomposition mechanism, and key reactions leading to ignition is essential in the design and manipulation of molecular systems for the development of new energetic materials for advanced propulsion applications.

Development of rate expressions for the thermal decomposition of RDX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erickson, K.L.; Behrens, R. Jr.; Bulusu, S.

Decomposition and combustion of energetic materials involve processes in both condensed and gas phases. Development of reliable models for design, performance, stability, and hazard analyses requires detailed understanding of the mechanisms for both the initial condensed phase decomposition of the energetic material and the subsequent reaction of the decomposition species to form the ultimate reaction products. Those mechanisms must be described in terms of constitutive rate expressions that can be incorporated into mathematical models. The thermal decomposition of RDX has been studied by Behrens and Bulusu using Simultaneous Thermogravimetric Modulated Beam Mass Spectrometry (STMBMS). Their work provides a basis formore » developing some of the constitutive rate expressions that are needed in models for design, performance, stability and hazard analyses involving RDX. Behrens and Bulusu have identified four primary reaction pathways that control the liquid-phase decomposition of RDX at temperatures between 200 and 215{degrees}C, and one that controls solid-phase decomposition at temperatures below 200{degrees}C. Two of the liquid-phase pathways appear to be first order in RDX. Arrhenius parameters for the first-order rate constants were evaluated from data reported by Behrens and Bulusu. Reaction rates extrapolated to temperatures between 370 and 450{degrees}C are in good agreement with global reaction rates observed by Trott et al. using high-speed photography and laser-heated thin-film samples. Furthermore, the STMBMS results of Behrens and Bulusu appear to be consistent with condensed-phase infrared results reported by Trott et al. and Erickson et al.« less

Development of rate expressions for the thermal decomposition of RDX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erickson, K.L.; Behrens, R. Jr.; Bulusu, S.

Decomposition and combustion of energetic materials involve processes in both condensed and gas phases. Development of reliable models for design, performance, stability, and hazard analyses requires detailed understanding of the mechanisms for both the initial condensed phase decomposition of the energetic material and the subsequent reaction of the decomposition species to form the ultimate reaction products. Those mechanisms must be described in terms of constitutive rate expressions that can be incorporated into mathematical models. The thermal decomposition of RDX has been studied by Behrens and Bulusu using Simultaneous Thermogravimetric Modulated Beam Mass Spectrometry (STMBMS). Their work provides a basis formore » developing some of the constitutive rate expressions that are needed in models for design, performance, stability and hazard analyses involving RDX. Behrens and Bulusu have identified four primary reaction pathways that control the liquid-phase decomposition of RDX at temperatures between 200 and 215[degrees]C, and one that controls solid-phase decomposition at temperatures below 200[degrees]C. Two of the liquid-phase pathways appear to be first order in RDX. Arrhenius parameters for the first-order rate constants were evaluated from data reported by Behrens and Bulusu. Reaction rates extrapolated to temperatures between 370 and 450[degrees]C are in good agreement with global reaction rates observed by Trott et al. using high-speed photography and laser-heated thin-film samples. Furthermore, the STMBMS results of Behrens and Bulusu appear to be consistent with condensed-phase infrared results reported by Trott et al. and Erickson et al.« less

In situ chemical oxidation of contaminated groundwater by persulfate: decomposition by Fe(III)- and Mn(IV)-containing oxides and aquifer materials.

PubMed

Liu, Haizhou; Bruton, Thomas A; Doyle, Fiona M; Sedlak, David L

2014-09-02

Persulfate (S2O8(2-)) is being used increasingly for in situ chemical oxidation (ISCO) of organic contaminants in groundwater, despite an incomplete understanding of the mechanism through which it is converted into reactive species. In particular, the decomposition of persulfate by naturally occurring mineral surfaces has not been studied in detail. To gain insight into the reaction rates and mechanism of persulfate decomposition in the subsurface, and to identify possible approaches for improving its efficacy, the decomposition of persulfate was investigated in the presence of pure metal oxides, clays, and representative aquifer solids collected from field sites in the presence and absence of benzene. Under conditions typical of groundwater, Fe(III)- and Mn(IV)-oxides catalytically converted persulfate into sulfate radical (SO4(•-)) and hydroxyl radical (HO(•)) over time scales of several weeks at rates that were 2-20 times faster than those observed in metal-free systems. Amorphous ferrihydrite was the most reactive iron mineral with respect to persulfate decomposition, with reaction rates proportional to solid mass and surface area. As a result of radical chain reactions, the rate of persulfate decomposition increased by as much as 100 times when benzene concentrations exceeded 0.1 mM. Due to its relatively slow rate of decomposition in the subsurface, it can be advantageous to inject persulfate into groundwater, allowing it to migrate to zones of low hydraulic conductivity where clays, metal oxides, and contaminants will accelerate its conversion into reactive oxidants.

In Situ Chemical Oxidation of Contaminated Groundwater by Persulfate: Decomposition by Fe(III)- and Mn(IV)-Containing Oxides and Aquifer Materials

PubMed Central

2015-01-01

Persulfate (S2O82–) is being used increasingly for in situ chemical oxidation (ISCO) of organic contaminants in groundwater, despite an incomplete understanding of the mechanism through which it is converted into reactive species. In particular, the decomposition of persulfate by naturally occurring mineral surfaces has not been studied in detail. To gain insight into the reaction rates and mechanism of persulfate decomposition in the subsurface, and to identify possible approaches for improving its efficacy, the decomposition of persulfate was investigated in the presence of pure metal oxides, clays, and representative aquifer solids collected from field sites in the presence and absence of benzene. Under conditions typical of groundwater, Fe(III)- and Mn(IV)-oxides catalytically converted persulfate into sulfate radical (SO4•–) and hydroxyl radical (HO•) over time scales of several weeks at rates that were 2–20 times faster than those observed in metal-free systems. Amorphous ferrihydrite was the most reactive iron mineral with respect to persulfate decomposition, with reaction rates proportional to solid mass and surface area. As a result of radical chain reactions, the rate of persulfate decomposition increased by as much as 100 times when benzene concentrations exceeded 0.1 mM. Due to its relatively slow rate of decomposition in the subsurface, it can be advantageous to inject persulfate into groundwater, allowing it to migrate to zones of low hydraulic conductivity where clays, metal oxides, and contaminants will accelerate its conversion into reactive oxidants. PMID:25133603

Thermal decomposition of pyrazole to vinylcarbene + N 2: A first principles/RRKM study

NASA Astrophysics Data System (ADS)

da Silva, Gabriel

2009-05-01

Thermal decomposition of pyrazole, a five-membered nitrogen-containing heterocycle, has been studied using ab initio G3X theory and RRKM rate theory. The decomposition mechanism involves an intramolecular hydrogen shift to 3 H-pyrazole, followed by ring opening to 3-diazo-1-propene and dissociation to vinylcarbene (CH 2CHCH) + N 2. At 1 atm the calculated rate equation k [s -1] = 1.26 × 10 50T-10.699e -41200/T is obtained, which agrees with the results of flash vacuum pyrolysis experiments. The pyrazole decomposition product vinylcarbene is expected to rearrange to propyne, making pyrazole decomposition essentially thermoneutral. It is hypothesized that at high concentrations vinylcarbene could undergo a self-reaction to 1,3- and 1,4-cyclohexadiene.

Au particle formation on the electron beam induced membrane

NASA Astrophysics Data System (ADS)

Choi, Seong Soo; Park, Myoung Jin; Han, Chul Hee; Oh, Sae-Joong; Kim, Sung-In; Park, Nam Kyou; Park, Doo-Jae; Choi, Soo Bong; Kim, Yong-Sang

2017-02-01

Recently the single molecules such as protein and deoxyribonucleic acid (DNA) have been successfully characterized by using a portable solidstate nanopore (MinION) with an electrical detection technique. However, there have been several reports about the high error rates of the fabricated nanopore device, possibly due to an electrical double layer formed inside the pore channel. The current DNA sequencing technology utilized is based on the optical detection method. In order to utilize the current optical detection technique, we will present the formation of the Au nano-pore with Au particle under the various electron beam irradiations. In order to provide the diffusion of Au atoms, a 2 keV electron beam irradiation has been performed During electron beam irradiations by using field emission scanning electron microscopy (FESEM), Au and C atoms would diffuse together and form the binary mixture membrane. Initially, the Au atoms diffused in the membrane are smaller than 1 nm, below the detection limit of the transmission electron microscopy (TEM), so that we are unable to observe the Au atoms in the formed membrane. However, after several months later, the Au atoms became larger and larger with expense of the smaller particles: Ostwald ripening. Furthermore, we also observe the Au crystalline lattice structure on the binary Au-C membrane. The formed Au crystalline lattice structures were constantly changing during electron beam imaging process due to Spinodal decomposition; the unstable thermodynamic system of Au-C binary membrane. The fabricated Au nanopore with an Au nanoparticle can be utilized as a single molecule nanobio sensor.

Uphill diffusion in multicomponent mixtures.

PubMed

Krishna, Rajamani

2015-05-21

Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations.

Persistent dopants and phase segregation in organolead mixed-halide perovskites

DOE PAGES

Rosales, Bryan A.; Men, Long; Cady, Sarah D.; ...

2016-07-25

Organolead mixed-halide perovskites such as CH 3NH 3PbX 3–aX' a (X, X' = I, Br, Cl) are interesting semiconductors because of their low cost, high photovoltaic power conversion efficiencies, enhanced moisture stability, and band gap tunability. Using a combination of optical absorption spectroscopy, powder X-ray diffraction (XRD), and, for the first time, 207Pb solid state nuclear magnetic resonance (ssNMR), we probe the extent of alloying and phase segregation in these materials. Because 207Pb ssNMR chemical shifts are highly sensitive to local coordination and electronic structure, and vary linearly with halogen electronegativity and band gap, this technique can provide the truemore » chemical speciation and composition of organolead mixed-halide perovskites. We specifically investigate samples made by three different preparative methods: solution phase synthesis, thermal annealing, and solid phase synthesis. 207Pb ssNMR reveals that nonstoichiometric dopants and semicrystalline phases are prevalent in samples made by solution phase synthesis. We show that these nanodomains are persistent after thermal annealing up to 200 °C. Further, a novel solid phase synthesis that starts from the parent, single-halide perovskites can suppress phase segregation but not the formation of dopants. Our observations are consistent with the presence of miscibility gaps and spontaneous spinodal decomposition of the mixed-halide perovskites at room temperature. This underscores how strongly different synthetic procedures impact the nanostructuring and composition of organolead halide perovskites. In conclusion, better optoelectronic properties and improved device stability and performance may be achieved through careful manipulation of the different phases and nanodomains present in these materials.« less

Persistent dopants and phase segregation in organolead mixed-halide perovskites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosales, Bryan A.; Men, Long; Cady, Sarah D.

Organolead mixed-halide perovskites such as CH 3NH 3PbX 3–aX' a (X, X' = I, Br, Cl) are interesting semiconductors because of their low cost, high photovoltaic power conversion efficiencies, enhanced moisture stability, and band gap tunability. Using a combination of optical absorption spectroscopy, powder X-ray diffraction (XRD), and, for the first time, 207Pb solid state nuclear magnetic resonance (ssNMR), we probe the extent of alloying and phase segregation in these materials. Because 207Pb ssNMR chemical shifts are highly sensitive to local coordination and electronic structure, and vary linearly with halogen electronegativity and band gap, this technique can provide the truemore » chemical speciation and composition of organolead mixed-halide perovskites. We specifically investigate samples made by three different preparative methods: solution phase synthesis, thermal annealing, and solid phase synthesis. 207Pb ssNMR reveals that nonstoichiometric dopants and semicrystalline phases are prevalent in samples made by solution phase synthesis. We show that these nanodomains are persistent after thermal annealing up to 200 °C. Further, a novel solid phase synthesis that starts from the parent, single-halide perovskites can suppress phase segregation but not the formation of dopants. Our observations are consistent with the presence of miscibility gaps and spontaneous spinodal decomposition of the mixed-halide perovskites at room temperature. This underscores how strongly different synthetic procedures impact the nanostructuring and composition of organolead halide perovskites. In conclusion, better optoelectronic properties and improved device stability and performance may be achieved through careful manipulation of the different phases and nanodomains present in these materials.« less

Phase separation, crystallization and polyamorphism in the Y2O3 Al2O3 system

NASA Astrophysics Data System (ADS)

Skinner, Lawrie B.; Barnes, Adrian C.; Salmon, Philip S.; Crichton, Wilson A.

2008-05-01

A detailed study of glass formation from aerodynamically levitated liquids in the (Y2O3)x(Al2O3)1-x system for the composition range 0.21<=x<=0.41 was undertaken by using pyrometric, optical imaging and x-ray diffraction methods. Homogeneous and clear single-phase glasses were produced over the composition range 0.27 \\lesssim x \\lesssim 0.33 . For Y2O3-rich compositions (0.33 \\lesssim x \\le 0.375 ), cloudy materials were produced which contain inclusions of crystalline yttrium aluminium garnet (YAG) of diameter up to 40 µm in a glassy matrix. For Y2O3-poor compositions around x = 0.24, cloudy materials were also produced, but it was not possible to deduce whether this resulted from (i) sub-micron inclusions of a nano-crystalline or glassy material in a glassy matrix or (ii) a glass formed by spinodal decomposition. For x = 0.21, however, the sample cloudiness results from crystallization into at least two phases comprising yttrium aluminium perovskite and alumina. The associated pyrometric cooling curve shows slow recalescence events with a continuous and slow evolution of excess heat which contrasts with the sharp recalescence events observed for the crystallization of YAG at compositions near x = 0.375. The materials that are the most likely candidates for demonstrating homogeneous nucleation of a second liquid phase occur around x = 0.25, which corresponds to the limit for formation of a continuous random network of corner-shared AlO4 tetrahedra.

Laser Ignition of Nitramine Composite Propellants and Crack Propagation and Branching in Burning Solid Propellants

DTIC Science & Technology

1987-10-01

34 Proceedings of the 16th JANNAF Com- bustion Meeting, Sept. 1979, Vol. II, pp. 13-34. 44. Schroeder , M. A., " Critical Analysis of Nitramine Decomposition...34 Proceedings of the 19th JANNAF Combustion Meeting, Oct. 1982. 47. Schroeder , M. A., " Critical Analysis of Nitramine Decomposition Data: Ac- tivation...the surface of the propellant. This is consis- tent with the decomposition mechanism considered by Boggs[48] and Schroeder [43J. They concluded that the

Heterogeneous nucleation on rough surfaces: Generalized Gibbs' approach.

PubMed

Abyzov, Alexander S; Schmelzer, Jürn W P; Davydov, Leonid N

2017-12-07

Heterogeneous nucleation (condensation) of liquid droplets from vapor (gas) on a defective solid surface is considered. The vapor is described by the van der Waals equation of state. The dependence of nucleating droplet parameters on droplet size is accounted for within the generalized Gibbs approach. As a surface defect, a conic void is taken. This choice allows us to simplify the analysis and at the same time to follow the main aspects of the influence of the surface roughness on the nucleation process. Similar to condensation on ideal planar surfaces, the contact angle and catalytic factor for heterogeneous nucleation on a rough surface depend on the degree of vapor overcooling. In the case of droplet formation on a hydrophilic surface of a conic void, the nucleation rate considerably increases in comparison with the condensation on a planar interface. In fact, the presence of a defect on the hydrophilic surface leads to a considerable shift of the spinodal towards lower supersaturation in comparison with heterogeneous nucleation on a planar interface. With the decrease in the void cone angle, the heterogeneous spinodal approaches the binodal, and the region of metastability is diminished at the expense of the instability region.

Gauge-invariant effective potential: Equilibrium and nonequilibrium aspects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyanovsky, D.; Brahm, D.; Holman, R.

1996-07-01

We propose a gauge-invariant formulation of the effective potential in terms of a gauge-invariant order parameter, for the Abelian Higgs model. The one-loop contribution at zero and finite temperature is computed explicitly, and the leading terms in the high temperature expansion are obtained. The result is contrasted with the effective potential obtained in several covariant gauge-fixing schemes, and the gauge-invariant quantities that can be reliably extracted from these are identified. It is pointed out that the gauge-invariant effective potential in the one-loop approximation is complex for {ital all} {ital values} of the order parameter between the maximum and the minimummore » of the tree level potential, both at zero and nonzero temperatures. The imaginary part is related to long-wavelength instabilities towards phase separation. We study the real-time dynamics of initial states in the spinodal region, and relate the imaginary part of the effective potential to the growth rate of equal-time gauge-invariant correlation functions in these states. We conjecture that the spinodal instabilities may play a role in nonequilibrium processes {ital inside} the nucleating bubbles if the transition is first order. {copyright} {ital 1996 The American Physical Society.}« less

Pathways from disordered to ordered nanostructures from defect guided dewetting of ultrathin bilayers.

PubMed

Hens, Abhiram; Mondal, Kartick; Biswas, Gautam; Bandyopadhyay, Dipankar

2016-03-01

Transitions from spinodal to pattern-guided dewetting of a bilayer of ultrathin films (<10nm) confined between a pair of patterned surfaces have been explored employing molecular dynamic (MD) simulations. The physical or chemical defects of different sizes and shapes are decorated on the confining substrates by either removal or addition of multiple layers of similar or dissimilar atoms. The simulations are performed to identify the transition from spinodal pathway to the heterogeneous nucleation route, with the variation in the size of the substrate patterns. The MD simulations reveal the limits beyond which the defects can guide the dewetting to generate ordered patterns of nanoscopic size and periodicity. Comparing the results obtained from the MD simulations with the more widely employed continuum dynamics approach highlights the importance of the MD approach in quantitatively analyzing the dynamics of the dewetting of ultrathin films. The study demonstrates that the pattern-guided dewetting of confined bilayers can lead to ordered holes, droplets, and stripes with size and periodicity less than 10nm, which are yet to be realized experimentally and can be of significance for a number of future applications. Copyright © 2015 Elsevier Inc. All rights reserved.

Kinetics of Polydomain Ordering at Second-Order Phase Transitions (by the Example of the AuCu3 Alloy)

NASA Astrophysics Data System (ADS)

Feldman, E. P.; Stefanovich, L. I.; Gumennyk, K. V.

2008-08-01

Kinetics of polydomain spinodal ordering is studied in alloys of AuCu3 type. We introduce four non-conserved long-range order parameters whose sum, however, is conserved and, using the statistical approach, follow the temporal evolution of their random spatial distribution after a rapid temperature quench. A system of nonlinear differential equations for correlators of second and third order is derived. Asymptotical analysis of this system allows to investigate the scaling regime, which develops on the late stages of evolution and to extract additional information concerning the rate of decrease of the specific volume of disordered regions and the rate of decrease of the average thickness of antiphase boundaries. Comparison of these results to experimental data is given. The quench below the spinodal and the onset of long-range order may be separated by the incubation time, whose origin is different from that in first-order phase transitions. Numerical integration of equations for correlators shows also, that it is possible to prepare a sample in such a way that its further evolution will go with formation of transient kinetically slowed polydomain structures different from the final L12 structure.

Thermodynamic and Dynamic Aspects of Ice Nucleation

NASA Technical Reports Server (NTRS)

Barahona, Donifan

2018-01-01

It is known that ice nucleating particles (INP) immersed within supercooled droplets promote the formation of ice. Common theoretical models used to represent this process assume that the immersed particle lowers the work of ice nucleation without significantly affecting the dynamics of water in the vicinity of the particle. This is contrary to evidence showing that immersed surfaces significantly affect the viscosity and diffusivity of vicinal water. To study how this may affect ice formation this work introduces a model linking the ice nucleation rate to the modification of the dynamics and thermodynamics of vicinal water by immersed particles. It is shown that INP that significantly reduce the work of ice nucleation also pose strong limitations to the growth of the nascent ice germs. This leads to the onset of a new ice nucleation regime, called spinodal ice nucleation, where the dynamics of ice germ growth instead of the ice germ size determines the nucleation rate. Nucleation in this regime is characterized by an enhanced sensitivity to particle area and cooling rate. Comparison of the predicted ice nucleation rate against experimental measurements for a diverse set of species relevant to cloud formation suggests that spinodal ice nucleation may be common in nature.

Instability in bacterial populations and the curvature tensor

NASA Astrophysics Data System (ADS)

Melgarejo, Augusto; Langoni, Laura; Ruscitti, Claudia

2016-09-01

In the geometry associated with equilibrium thermodynamics the scalar curvature Rs is a measure of the volume of correlation, and therefore the singularities of Rs indicates the system instabilities. We explore the use of a similar approach to study instabilities in non-equilibrium systems and we choose as a test example, a colony of bacteria. In this regard we follow the proposal made by Obata et al. of using the curvature tensor for studying system instabilities. Bacterial colonies are often found in nature in concentrated biofilms, or other colony types, which can grow into spectacular patterns visible under the microscope. For instance, it is known that a decrease of bacterial motility with density can promote separation into bulk phases of two coexisting densities; this is opposed to the logistic law for birth and death that allows only a single uniform density to be stable. Although this homogeneous configuration is stable in the absence of bacterial interactions, without logistic growth, a density-dependent swim speed v(ρ) leads to phase separation via a spinodal instability. Thus we relate the singularities in the curvature tensor R to the spinodal instability, that is the appearance of regions of different densities of bacteria.

An effective hierarchical model for the biomolecular covalent bond: an approach integrating artificial chemistry and an actual terrestrial life system.

PubMed

Oohashi, Tsutomu; Ueno, Osamu; Maekawa, Tadao; Kawai, Norie; Nishina, Emi; Honda, Manabu

2009-01-01

Under the AChem paradigm and the programmed self-decomposition (PSD) model, we propose a hierarchical model for the biomolecular covalent bond (HBCB model). This model assumes that terrestrial organisms arrange their biomolecules in a hierarchical structure according to the energy strength of their covalent bonds. It also assumes that they have evolutionarily selected the PSD mechanism of turning biological polymers (BPs) into biological monomers (BMs) as an efficient biomolecular recycling strategy We have examined the validity and effectiveness of the HBCB model by coordinating two complementary approaches: biological experiments using existent terrestrial life, and simulation experiments using an AChem system. Biological experiments have shown that terrestrial life possesses a PSD mechanism as an endergonic, genetically regulated process and that hydrolysis, which decomposes a BP into BMs, is one of the main processes of such a mechanism. In simulation experiments, we compared different virtual self-decomposition processes. The virtual species in which the self-decomposition process mainly involved covalent bond cleavage from a BP to BMs showed evolutionary superiority over other species in which the self-decomposition process involved cleavage from BP to classes lower than BM. These converging findings strongly support the existence of PSD and the validity and effectiveness of the HBCB model.

Theoretical study on the mechanism of the reaction of FOX-7 with OH and NO2 radicals: bimolecular reactions with low barrier during the decomposition of FOX-7

NASA Astrophysics Data System (ADS)

Zhang, Ji-Dong; Zhang, Li-Li

2017-12-01

The decomposition of 1,1-diamino-2,2-dinitroethene (FOX-7) attracts great interests, while the studies on bimolecular reactions during the decomposition of FOX-7 are scarce. This study for the first time investigated the bimolecular reactions of OH and NO2 radicals, which are pyrolysis products of ammonium perchlorate (an efficient oxidant usually used in solid propellant), with FOX-7 by computational chemistry methods. The molecular geometries and energies were calculated using the (U)B3LYP/6-31++G(d,p) method. The rate constants of the reactions were calculated by canonical variational transition state theory. We found three mechanisms (H-abstraction, OH addition to C and N atom) for the reaction of OH + FOX-7 and two mechanisms (O abstraction and H abstraction) for the reaction of NO2 + FOX-7. OH radical can abstract H atom or add to C atom of FOX-7 with barriers near to zero, which means OH radical can effectively degrade FOX-7. The O abstraction channel of the reaction of NO2 + FOX-7 results in the formation of NO3 radical, which has never been detected experimentally during the decomposition of FOX-7.

Anaerobic decomposition of humic substances by Clostridium from the deep subsurface

PubMed Central

Ueno, Akio; Shimizu, Satoru; Tamamura, Shuji; Okuyama, Hidetoshi; Naganuma, Takeshi; Kaneko, Katsuhiko

2016-01-01

Decomposition of humic substances (HSs) is a slow and cryptic but non-negligible component of carbon cycling in sediments. Aerobic decomposition of HSs by microorganisms in the surface environment has been well documented; however, the mechanism of anaerobic microbial decomposition of HSs is not completely understood. Moreover, no microorganisms capable of anaerobic decomposition of HSs have been isolated. Here, we report the anaerobic decomposition of humic acids (HAs) by the anaerobic bacterium Clostridium sp. HSAI-1 isolated from the deep terrestrial subsurface. The use of 14C-labelled polycatechol as an HA analogue demonstrated that the bacterium decomposed this substance up to 7.4% over 14 days. The decomposition of commercial and natural HAs by the bacterium yielded lower molecular mass fractions, as determined using high-performance size-exclusion chromatography. Fourier transform infrared spectroscopy revealed the removal of carboxyl groups and polysaccharide-related substances, as well as the generation of aliphatic components, amide and aromatic groups. Therefore, our results suggest that Clostridium sp. HSAI-1 anaerobically decomposes and transforms HSs. This study improves our understanding of the anaerobic decomposition of HSs in the hidden carbon cycling in the Earth’s subsurface. PMID:26743007

Experimental and modeling study on decomposition kinetics of methane hydrates in different media.

PubMed

Liang, Minyan; Chen, Guangjin; Sun, Changyu; Yan, Lijun; Liu, Jiang; Ma, Qinglan

2005-10-13

The decomposition kinetic behaviors of methane hydrates formed in 5 cm3 porous wet activated carbon were studied experimentally in a closed system in the temperature range of 275.8-264.4 K. The decomposition rates of methane hydrates formed from 5 cm3 of pure free water and an aqueous solution of 650 g x m(-3) sodium dodecyl sulfate (SDS) were also measured for comparison. The decomposition rates of methane hydrates in seven different cases were compared. The results showed that the methane hydrates dissociate more rapidly in porous activated carbon than in free systems. A mathematical model was developed for describing the decomposition kinetic behavior of methane hydrates below ice point based on an ice-shielding mechanism in which a porous ice layer was assumed to be formed during the decomposition of hydrate, and the diffusion of methane molecules through it was assumed to be one of the control steps. The parameters of the model were determined by correlating the decomposition rate data, and the activation energies were further determined with respect to three different media. The model was found to well describe the decomposition kinetic behavior of methane hydrate in different media.

Modeling Oil Shale Pyrolysis: High-Temperature Unimolecular Decomposition Pathways for Thiophene.

PubMed

Vasiliou, AnGayle K; Hu, Hui; Cowell, Thomas W; Whitman, Jared C; Porterfield, Jessica; Parish, Carol A

2017-10-12

The thermal decomposition mechanism of thiophene has been investigated both experimentally and theoretically. Thermal decomposition experiments were done using a 1 mm × 3 cm pulsed silicon carbide microtubular reactor, C 4 H 4 S + Δ → Products. Unlike previous studies these experiments were able to identify the initial thiophene decomposition products. Thiophene was entrained in either Ar, Ne, or He carrier gas, passed through a heated (300-1700 K) SiC microtubular reactor (roughly ≤100 μs residence time), and exited into a vacuum chamber. The resultant molecular beam was probed by photoionization mass spectroscopy and IR spectroscopy. The pyrolysis mechanisms of thiophene were also investigated with the CBS-QB3 method using UB3LYP/6-311++G(2d,p) optimized geometries. In particular, these electronic structure methods were used to explore pathways for the formation of elemental sulfur as well as for the formation of H 2 S and 1,3-butadiyne. Thiophene was found to undergo unimolecular decomposition by five pathways: C 4 H 4 S → (1) S═C═CH 2 + HCCH, (2) CS + HCCCH 3 , (3) HCS + HCCCH 2 , (4) H 2 S + HCC-CCH, and (5) S + HCC-CH═CH 2 . The experimental and theoretical findings are in excellent agreement.

Temperature sensitivity and enzymatic mechanisms of soil organic matter decomposition along an altitudinal gradient on Mount Kilimanjaro

NASA Astrophysics Data System (ADS)

Blagodatskaya, Evgenia; Blagodatsky, Sergey; Khomyakov, Nikita; Myachina, Olga; Kuzyakov, Yakov

2016-02-01

Short-term acceleration of soil organic matter decomposition by increasing temperature conflicts with the thermal adaptation observed in long-term studies. Here we used the altitudinal gradient on Mt. Kilimanjaro to demonstrate the mechanisms of thermal adaptation of extra- and intracellular enzymes that hydrolyze cellulose, chitin and phytate and oxidize monomers (14C-glucose) in warm- and cold-climate soils. We revealed that no response of decomposition rate to temperature occurs because of a cancelling effect consisting in an increase in half-saturation constants (Km), which counteracts the increase in maximal reaction rates (Vmax with temperature). We used the parameters of enzyme kinetics to predict thresholds of substrate concentration (Scrit) below which decomposition rates will be insensitive to global warming. Increasing values of Scrit, and hence stronger canceling effects with increasing altitude on Mt. Kilimanjaro, explained the thermal adaptation of polymer decomposition. The reduction of the temperature sensitivity of Vmax along the altitudinal gradient contributed to thermal adaptation of both polymer and monomer degradation. Extrapolating the altitudinal gradient to the large-scale latitudinal gradient, these results show that the soils of cold climates with stronger and more frequent temperature variation are less sensitive to global warming than soils adapted to high temperatures.

Roots Stimulate Expression of Decomposition Transcripts in the Soil Microbiome

NASA Astrophysics Data System (ADS)

Nuccio, E. E.; Karaoz, U.; Zhou, J.; Brodie, E.; Firestone, M.; Pett-Ridge, J.

2016-12-01

The soil surrounding plant roots, the rhizosphere, has long been recognized as a zone of great functional importance in terrestrial ecosystems. Rhizosphere microorganisms can affect the breakdown of plant tissues and root litter, and can accelerate the decomposition of detrital plant biomass, which is a process commonly described as "priming." However, the molecular mechanisms underlying rhizosphere C cycling are poorly understood, and the carbohydrate and lignolytic gene transcripts mediating the decomposition of root litter in soil are largely unidentified. We hypothesized that root exudates stimulate the expression of enzymes that are involved in decomposition of macromolecular C compounds. To assess how the abundance and diversity of decomposition enzymes differs in the rhizosphere relative to the surrounding bulk soil, we sequenced the community gene expression (metatranscriptomes) and single cell genomes of rhizosphere and bulk soil associated with wild oat (Avena fatua) over time (3, 6, 12, and 22 days). To isolate roots of a defined age in a mature plant, we used microcosms with a transparent experimental sidecar to track roots as they grew. Our results showed that a large number of C decomposition enzymes were more highly expressed in the rhizosphere compared to bulk soil, and that overall, transcripts tended to be elevated in younger roots than older roots. Genes relevant to aromatic C breakdown (nitroreductase, 4-hydroxybenzoate degradation, pectin methylesterase) and organic N cycling (ammonification) were elevated in the rhizosphere. This work identifies the potential molecular mechanisms that underpin priming in rhizosphere soil.

A Deep Insight into the Details of the Interisomerization and Decomposition Mechanism of o-Quinolyl and o-Isoquinolyl Radicals. Quantum Chemical Calculations and Computer Modeling.

PubMed

Dubnikova, Faina; Tamburu, Carmen; Lifshitz, Assa

2016-09-29

The isomerization of o-quinolyl ↔ o-isoquinolyl radicals and their thermal decomposition were studied by quantum chemical methods, where potential energy surfaces of the reaction channels and their kinetics rate parameters were determined. A detailed kinetics scheme containing 40 elementary steps was constructed. Computer simulations were carried out to determine the isomerization mechanism and the distribution of reaction products in the decomposition. The calculated mole percent of the stable products was compared to the experimental values that were obtained in this laboratory in the past, using the single pulse shock tube. The agreement between the experimental and the calculated mole percents was very good. A map of the figures containing the mole percent's of eight stable products of the decomposition plotted vs T are presented. The fast isomerization of o-quinolyl → o-isoquinolyl radicals via the intermediate indene imine radical and the attainment of fast equilibrium between these two radicals is the reason for the identical product distribution regardless whether the reactant radical is o-quinolyl or o-isoquinolyl. Three of the main decomposition products of o-quinolyl radical, are those containing the benzene ring, namely, phenyl, benzonitrile, and phenylacetylene radicals. They undergo further decomposition mainly at high temperatures via two types of reactions: (1) Opening of the benzene ring in the radicals, followed by splitting into fragments. (2) Dissociative attachment of benzonitrile and phenyl acetylene by hydrogen atoms to form hydrogen cyanide and acetylene.

Metagenomic analysis of antibiotic resistance genes (ARGs) during refuse decomposition.

PubMed

Liu, Xi; Yang, Shu; Wang, Yangqing; Zhao, He-Ping; Song, Liyan

2018-04-12

Landfill is important reservoirs of residual antibiotics and antibiotic resistance genes (ARGs), but the mechanism of landfill application influence on antibiotic resistance remains unclear. Although refuse decomposition plays a crucial role in landfill stabilization, its impact on the antibiotic resistance has not been well characterized. To better understand the impact, we studied the dynamics of ARGs and the bacterial community composition during refuse decomposition in a bench-scale bioreactor after long term operation (265d) based on metagenomics analysis. The total abundances of ARGs increased from 431.0ppm in the initial aerobic phase (AP) to 643.9ppm in the later methanogenic phase (MP) during refuse decomposition, suggesting that application of landfill for municipal solid waste (MSW) treatment may elevate the level of ARGs. A shift from drug-specific (bacitracin, tetracycline and sulfonamide) resistance to multidrug resistance was observed during the refuse decomposition and was driven by a shift of potential bacteria hosts. The elevated abundance of Pseudomonas mainly contributed to the increasing abundance of multidrug ARGs (mexF and mexW). Accordingly, the percentage of ARGs encoding an efflux pump increased during refuse decomposition, suggesting that potential bacteria hosts developed this mechanism to adapt to the carbon and energy shortage when biodegradable substances were depleted. Overall, our findings indicate that the use of landfill for MSW treatment increased antibiotic resistance, and demonstrate the need for a comprehensive investigation of antibiotic resistance in landfill. Copyright © 2018. Published by Elsevier B.V.

Ab initio investigation of the thermal decomposition of n-butylcyclohexane.

PubMed

Ali, Mohamad Akbar; Dillstrom, V Tyler; Lai, Jason Y W; Violi, Angela

2014-02-13

Environmental and energy security concerns have motivated an increased focus on developing clean, efficient combustors, which increasingly relies on insight into the combustion chemistry of fuels. In particular, naphthenes (cycloalkanes and alkylcycloalkanes) are important chemical components of distillate fuels, such as diesel and jet fuels. As such, there is a growing interest in describing napthene reactivity with kinetic mechanisms. Use of these mechanisms in predictive combustion models aids in the development of combustors. This study focuses on the pyrolysis of n-butylcyclohexane (n-BCH), an important representative of naphthenes in jet fuels. Seven different unimolecular decomposition pathways of C-C bond fission were explored utilizing ab initio/DFT methods. Accurate reaction energies were computed using the high-level quantum composite G3B3 method. Variational transition state theory, Rice-Ramsperger-Kassel-Marcus/master equation simulations provided temperature- and pressure-dependent rate constants. Implementation of these pathways into an existing chemical kinetic mechanism improved the prediction of experimental OH radical and H2O speciation in shock tube oxidation. Simulations of this combustion showed a change in the expected decomposition chemistry of n-BCH, predicting increased production of cyclic alkyl radicals instead of straight-chain alkenes. The most prominent reaction pathway for the decomposition of n-BCH is n-BCH = C3H7 + C7H13. The results of this study provide insight into the combustion of n-BCH and will aid in the future development of naphthene kinetic mechanisms.

Gas-liquid nucleation at large metastability: unusual features and a new formalism

NASA Astrophysics Data System (ADS)

Santra, Mantu; Singh, Rakesh S.; Bagchi, Biman

2011-03-01

Nucleation at large metastability is still largely an unsolved problem, even though it is a problem of tremendous current interest, with wide-ranging practical value, from atmospheric research to materials science. It is now well accepted that the classical nucleation theory (CNT) fails to provide a qualitative picture and gives incorrect quantitative values for such quantities as activation-free energy barrier and supersaturation dependence of nucleation rate, especially at large metastability. In this paper, we present an alternative formalism to treat nucleation at large supersaturation by introducing an extended set of order parameters in terms of the kth largest liquid-like clusters, where k = 1 is the largest cluster in the system, k = 2 is the second largest cluster and so on. At low supersaturation, the size of the largest liquid-like cluster acts as a suitable order parameter. At large supersaturation, the free energy barrier for the largest liquid-like cluster disappears. We identify this supersaturation as the one at the onset of kinetic spinodal. The kinetic spinodal is system-size-dependent. Beyond kinetic spinodal many clusters grow simultaneously and competitively and hence the nucleation and growth become collective. In order to describe collective growth, we need to consider the full set of order parameters. We derive an analytic expression for the free energy of formation of the kth largest cluster. The expression predicts that, at large metastability (beyond kinetic spinodal), the barrier of growth for several largest liquid-like clusters disappears, and all these clusters grow simultaneously. The approach to the critical size occurs by barrierless diffusion in the cluster size space. The expression for the rate of barrier crossing predicts weaker supersaturation dependence than what is predicted by CNT at large metastability. Such a crossover behavior has indeed been observed in recent experiments (but eluded an explanation till now). In order to understand the large numerical discrepancy between simulation predictions and experimental results, we carried out a study of the dependence on the range of intermolecular interactions of both the surface tension of an equilibrium planar gas-liquid interface and the free energy barrier of nucleation. Both are found to depend significantly on the range of interaction for the Lennard-Jones potential, both in two and three dimensions. The value of surface tension and also the free energy difference between the gas and the liquid phase increase significantly and converge only when the range of interaction is extended beyond 6-7 molecular diameters. We find, with the full range of interaction potential, that the surface tension shows only a weak dependence on supersaturation, so the reason for the breakdown of CNT (with simulated values of surface tension and free energy gap) cannot be attributed to the supersaturation dependence of surface tension. This remains an unsettled issue at present because of the use of the value of surface tension obtained at coexistence.

Pursuing reliable thermal analysis techniques for energetic materials: decomposition kinetics and thermal stability of dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50).

PubMed

Muravyev, Nikita V; Monogarov, Konstantin A; Asachenko, Andrey F; Nechaev, Mikhail S; Ananyev, Ivan V; Fomenkov, Igor V; Kiselev, Vitaly G; Pivkina, Alla N

2016-12-21

Thermal decomposition of a novel promising high-performance explosive dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) was studied using a number of thermal analysis techniques (thermogravimetry, differential scanning calorimetry, and accelerating rate calorimetry, ARC). To obtain more comprehensive insight into the kinetics and mechanism of TKX-50 decomposition, a variety of complementary thermoanalytical experiments were performed under various conditions. Non-isothermal and isothermal kinetics were obtained at both atmospheric and low (up to 0.3 Torr) pressures. The gas products of thermolysis were detected in situ using IR spectroscopy, and the structure of solid-state decomposition products was determined by X-ray diffraction and scanning electron microscopy. Diammonium 5,5'-bistetrazole-1,1'-diolate (ABTOX) was directly identified to be the most important intermediate of the decomposition process. The important role of bistetrazole diol (BTO) in the mechanism of TKX-50 decomposition was also rationalized by thermolysis experiments with mixtures of TKX-50 and BTO. Several widely used thermoanalytical data processing techniques (Kissinger, isoconversional, formal kinetic approaches, etc.) were independently benchmarked against the ARC data, which are more germane to the real storage and application conditions of energetic materials. Our study revealed that none of the Arrhenius parameters reported before can properly describe the complex two-stage decomposition process of TKX-50. In contrast, we showed the superior performance of the isoconversional methods combined with isothermal measurements, which yielded the most reliable kinetic parameters of TKX-50 thermolysis. In contrast with the existing reports, the thermal stability of TKX-50 was determined in the ARC experiments to be lower than that of hexogen, but close to that of hexanitrohexaazaisowurtzitane (CL-20).

A review of plutonium oxalate decomposition reactions and effects of decomposition temperature on the surface area of the plutonium dioxide product

NASA Astrophysics Data System (ADS)

Orr, R. M.; Sims, H. E.; Taylor, R. J.

2015-10-01

Plutonium (IV) and (III) ions in nitric acid solution readily form insoluble precipitates with oxalic acid. The plutonium oxalates are then easily thermally decomposed to form plutonium dioxide powder. This simple process forms the basis of current industrial conversion or 'finishing' processes that are used in commercial scale reprocessing plants. It is also widely used in analytical or laboratory scale operations and for waste residues treatment. However, the mechanisms of the thermal decompositions in both air and inert atmospheres have been the subject of various studies over several decades. The nature of intermediate phases is of fundamental interest whilst understanding the evolution of gases at different temperatures is relevant to process control. The thermal decomposition is also used to control a number of powder properties of the PuO2 product that are important to either long term storage or mixed oxide fuel manufacturing. These properties are the surface area, residual carbon impurities and adsorbed volatile species whereas the morphology and particle size distribution are functions of the precipitation process. Available data and experience regarding the thermal and radiation-induced decompositions of plutonium oxalate to oxide are reviewed. The mechanisms of the thermal decompositions are considered with a particular focus on the likely redox chemistry involved. Also, whilst it is well known that the surface area is dependent on calcination temperature, there is a wide variation in the published data and so new correlations have been derived. Better understanding of plutonium (III) and (IV) oxalate decompositions will assist the development of more proliferation resistant actinide co-conversion processes that are needed for advanced reprocessing in future closed nuclear fuel cycles.

Acid and alkali effects on the decomposition of HMX molecule: a computational study.

PubMed

Zhang, Chaoyang; Li, Yuzhen; Xiong, Ying; Wang, Xiaolin; Zhou, Mingfei

2011-11-03

The stored and wasted explosives are usually in an acid or alkali environment, leading to the importance of exploring the acid and alkali effects on the decomposition mechanism of explosives. The acid and alkali effects on the decomposition of HMX molecule in gaseous state and in aqueous solution at 298 K are studied using quantum chemistry and molecular force field calculations. The results show that both H(+) and OH(-) make the decomposition in gaseous state energetically favorable. However, the effect of H(+) is much different from that of OH(-) in aqueous solution: OH(-) can accelerate the decomposition but H(+) cannot. The difference is mainly caused by the large aqueous solvation energy difference between H(+) and OH(-). The results confirm that the dissociation of HMX is energetically favored only in the base solutions, in good agreement with previous HMX base hydrolysis experimental observations. The different acid and alkali effects on the HMX decomposition are dominated by the large aqueous solvation energy difference between H(+) and OH(-).

Photodegradation Pathways in Arid Ecosystems

NASA Astrophysics Data System (ADS)

King, J. Y.; Lin, Y.; Adair, E. C.; Brandt, L.; Carbone, M. S.

2013-12-01

Recent interest in improving our understanding of decomposition patterns in arid and semi-arid ecosystems and under potentially drier future conditions has led to a flurry of research related to abiotic degradation processes. Oxidation of organic matter by solar radiation (photodegradation) is one abiotic degradation process that contributes significantly to litter decomposition rates. Our meta-analysis results show that increasing solar radiation exposure corresponds to an average increase of 23% in litter mass loss rate with large variation among studies associated primarily with environmental and litter chemistry characteristics. Laboratory studies demonstrate that photodegradation results in CO2 emissions. Indirect estimates suggest that photodegradation could account for as much as 60% of ecosystem CO2 emissions from dry ecosystems, but these CO2 fluxes have not been measured in intact ecosystems. The current data suggest that photodegradation is important, not only for understanding decomposition patterns, but also for modeling organic matter turnover and ecosystem C cycling. However, the mechanisms by which photodegradation operates, along with their environmental and litter chemistry controls, are still poorly understood. Photodegradation can directly influence decomposition rates and ecosystem CO2 flux via photochemical mineralization. It can also indirectly influence biotic decomposition rates by facilitating microbial degradation through breakdown of more recalcitrant compounds into simpler substrates or by suppressing microbial activity directly. All of these pathways influence the decomposition process, but the relative importance of each is uncertain. Furthermore, a specific suite of controls regulates each of these pathways (e.g., environmental conditions such as temperature and relative humidity; physical environment such as canopy architecture and contact with soil; and litter chemistry characteristics such as lignin and cellulose content), and these controls have not yet been identified or quantified. To advance our understanding of photodegradation and its role in decomposition and in ecosystem C cycling, we must characterize its mechanisms and their associated controls and incorporate this understanding into biogeochemical models. Our objective is to summarize the current state of understanding of photodegradation and discuss some paths forward to address remaining critical gaps in knowledge about its mechanisms and influence on ecosystem C balance.

The relative importance of decomposition and transport mechanisms in accounting for C profiles

NASA Astrophysics Data System (ADS)

Guenet, B.; Eglin, T.; Vasilyeva, N.; Peylin, P.; Ciais, P.; Chenu, C.

2012-10-01

Soil is the major terrestrial reservoirs of carbon, and a substantial part of this carbon is stored in deep layers, typically deeper than 50 cm below the surface. Several studies underlined the quantitative importance of this deep Soil Organic Carbon (SOC) pool and models are needed to better understand this stock and its evolution under climate and land-uses changes. In this study, we test and compare 3 simple theoretical models of vertical transport for SOC against SOC profiles measurements from a long-term bare fallow experiment carried out by the Central-Chernozem State Natural Biosphere Reserve named after V.V. Alekhin, in the Kursk Region of Russia. The transport schemes tested are diffusion, advection or both diffusion and advection. They are coupled to two different formulations of soil carbon decomposition kinetics. The first formulation is a first order kinetics widely used in global SOC decomposition models; the second one links SOC decomposition rate to the amount of fresh organic matter, representing a "priming effect". Field data are from a set of three bare fallow plots where soil received no input during the past 20, 26 and 58 yr respectively. Parameters of the models were optimized using a Bayesian method. The best results are obtained when SOC decomposition is assumed to be controlled by fresh organic matter. In comparison to the first-order kinetic model, the "priming" model reduces the underestimation of SOC decomposition in the top layers and the over estimation in the deep layers. We also observe that the transport scheme that improved the fit with the data depends on the soil carbon mineralization formulation chosen. When soil carbon decomposition is modelled to depend on the fresh organic matter amount, the transport mechanisms which improves best the fit to the SOC profile data is the model representing both advection and diffusion. Interestingly, the older the bare fallow is, the lesser the need for diffusion is. This suggests that stabilized carbon may not be transported within the profile by the same mechanisms than more labile carbon.

Ab initio kinetics and thermal decomposition mechanism of mononitrobiuret and 1,5-dinitrobiuret

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Hongyan, E-mail: hongyan.sun1@gmail.com, E-mail: ghanshyam.vaghjiani@us.af.mil; Vaghjiani, Ghanshyam L., E-mail: hongyan.sun1@gmail.com, E-mail: ghanshyam.vaghjiani@us.af.mil

2015-05-28

Mononitrobiuret (MNB) and 1,5-dinitrobiuret (DNB) are tetrazole-free, nitrogen-rich, energetic compounds. For the first time, a comprehensive ab initio kinetics study on the thermal decomposition mechanisms of MNB and DNB is reported here. In particular, the intramolecular interactions of amine H-atom with electronegative nitro O-atom and carbonyl O-atom have been analyzed for biuret, MNB, and DNB at the M06-2X/aug-cc-pVTZ level of theory. The results show that the MNB and DNB molecules are stabilized through six-member-ring moieties via intramolecular H-bonding with interatomic distances between 1.8 and 2.0 Å, due to electrostatic as well as polarization and dispersion interactions. Furthermore, it was foundmore » that the stable molecules in the solid state have the smallest dipole moment amongst all the conformers in the nitrobiuret series of compounds, thus revealing a simple way for evaluating reactivity of fuel conformers. The potential energy surface for thermal decomposition of MNB was characterized by spin restricted coupled cluster theory at the RCCSD(T)/cc-pV∞ Z//M06-2X/aug-cc-pVTZ level. It was found that the thermal decomposition of MNB is initiated by the elimination of HNCO and HNN(O)OH intermediates. Intramolecular transfer of a H-atom, respectively, from the terminal NH{sub 2} group to the adjacent carbonyl O-atom via a six-member-ring transition state eliminates HNCO with an energy barrier of 35 kcal/mol and from the central NH group to the adjacent nitro O-atom eliminates HNN(O)OH with an energy barrier of 34 kcal/mol. Elimination of HNN(O)OH is also the primary process involved in the thermal decomposition of DNB, which processes C{sub 2v} symmetry. The rate coefficients for the primary decomposition channels for MNB and DNB were quantified as functions of temperature and pressure. In addition, the thermal decomposition of HNN(O)OH was analyzed via Rice–Ramsperger–Kassel–Marcus/multi-well master equation simulations, the results of which reveal the formation of (NO{sub 2} + H{sub 2}O) to be the major decomposition path. Furthermore, we provide fundamental interpretations for the experimental results of Klapötke et al. [Combust. Flame 139, 358–366 (2004)] regarding the thermal stability of MNB and DNB, and their decomposition products. Notably, a fundamental understanding of fuel stability, decomposition mechanism, and key reactions leading to ignition is essential in the design and manipulation of molecular systems for the development of new energetic materials for advanced propulsion applications.« less

Deformation twinning induced decomposition of lamellar LPSO structure and its re-precipitation in an Mg-Zn-Y alloy

NASA Astrophysics Data System (ADS)

Shao, X. H.; Zheng, S. J.; Chen, D.; Jin, Q. Q.; Peng, Z. Z.; Ma, X. L.

2016-07-01

The high hardness or yield strength of an alloy is known to benefit from the presence of small-scale precipitation, whose hardening effect is extensively applied in various engineering materials. Stability of the precipitates is of critical importance in maintaining the high performance of a material under mechanical loading. The long period stacking ordered (LPSO) structures play an important role in tuning the mechanical properties of an Mg-alloy. Here, we report deformation twinning induces decomposition of lamellar LPSO structures and their re-precipitation in an Mg-Zn-Y alloy. Using atomic resolution scanning transmission electron microscopy (STEM), we directly illustrate that the misfit dislocations at the interface between the lamellar LPSO structure and the deformation twin is corresponding to the decomposition and re-precipitation of LPSO structure, owing to dislocation effects on redistribution of Zn/Y atoms. This finding demonstrates that deformation twinning could destabilize complex precipitates. An occurrence of decomposition and re-precipitation, leading to a variant spatial distribution of the precipitates under plastic loading, may significantly affect the precipitation strengthening.

Deformation twinning induced decomposition of lamellar LPSO structure and its re-precipitation in an Mg-Zn-Y alloy

PubMed Central

Shao, X. H.; Zheng, S. J.; Chen, D.; Jin, Q. Q.; Peng, Z. Z.; Ma, X. L.

2016-01-01

The high hardness or yield strength of an alloy is known to benefit from the presence of small-scale precipitation, whose hardening effect is extensively applied in various engineering materials. Stability of the precipitates is of critical importance in maintaining the high performance of a material under mechanical loading. The long period stacking ordered (LPSO) structures play an important role in tuning the mechanical properties of an Mg-alloy. Here, we report deformation twinning induces decomposition of lamellar LPSO structures and their re-precipitation in an Mg-Zn-Y alloy. Using atomic resolution scanning transmission electron microscopy (STEM), we directly illustrate that the misfit dislocations at the interface between the lamellar LPSO structure and the deformation twin is corresponding to the decomposition and re-precipitation of LPSO structure, owing to dislocation effects on redistribution of Zn/Y atoms. This finding demonstrates that deformation twinning could destabilize complex precipitates. An occurrence of decomposition and re-precipitation, leading to a variant spatial distribution of the precipitates under plastic loading, may significantly affect the precipitation strengthening. PMID:27435638

In Situ Probes of Capture and Decomposition of Chemical Warfare Agent Simulants by Zr-Based Metal Organic Frameworks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plonka, Anna M.; Wang, Qi; Gordon, Wesley O.

Recently, Zr-based metal organic frameworks (MOFs) were shown to be among the fastest catalysts of nerve-agent hydrolysis in solution. Here, we report a detailed study of the adsorption and decomposition of a nerve-agent simulant, dimethyl methylphosphonate (DMMP), on UiO-66, UiO-67, MOF-808, and NU-1000 using synchrotron-based X-ray powder diffraction, X-ray absorption, and infrared spectroscopy, which reveals key aspects of the reaction mechanism. The diffraction measurements indicate that all four MOFs adsorb DMMP (introduced at atmospheric pressures through a flow of helium or air) within the pore space. In addition, the combination of X-ray absorption and infrared spectra suggests direct coordination ofmore » DMMP to the Zr6 cores of all MOFs, which ultimately leads to decomposition to phosphonate products. Our experimental probes into the mechanism of adsorption and decomposition of chemical warfare agent simulants on Zr-based MOFs open new opportunities in rational design of new and superior decontamination materials.« less

In Situ Probes of Capture and Decomposition of Chemical Warfare Agent Simulants by Zr-Based Metal Organic Frameworks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plonka, Anna M.; Wang, Qi; Gordon, Wesley O.

Zr-based metal organic frameworks (MOFs) have been recently shown to be among the fastest catalysts of nerve-agent hydrolysis in solution. We report a detailed study of the adsorption and decomposition of a nerve-agent simulant, dimethyl methylphosphonate (DMMP), on UiO-66, UiO-67, MOF-808, and NU-1000 using synchrotron-based X-ray powder diffraction, X-ray absorption, and infrared spectroscopy, which reveals key aspects of the reaction mechanism. The diffraction measurements indicate that all four MOFs adsorb DMMP (introduced at atmospheric pressures through a flow of helium or air) within the pore space. In addition, the combination of X-ray absorption and infrared spectra suggests direct coordination ofmore » DMMP to the Zr6 cores of all MOFs, which ultimately leads to decomposition to phosphonate products. These experimental probes into the mechanism of adsorption and decomposition of chemical warfare agent simulants on Zr-based MOFs open new opportunities in rational design of new and superior decontamination materials.« less

In Situ Probes of Capture and Decomposition of Chemical Warfare Agent Simulants by Zr-Based Metal Organic Frameworks

DOE PAGES

Plonka, Anna M.; Wang, Qi; Gordon, Wesley O.; ...

2016-12-30

Recently, Zr-based metal organic frameworks (MOFs) were shown to be among the fastest catalysts of nerve-agent hydrolysis in solution. Here, we report a detailed study of the adsorption and decomposition of a nerve-agent simulant, dimethyl methylphosphonate (DMMP), on UiO-66, UiO-67, MOF-808, and NU-1000 using synchrotron-based X-ray powder diffraction, X-ray absorption, and infrared spectroscopy, which reveals key aspects of the reaction mechanism. The diffraction measurements indicate that all four MOFs adsorb DMMP (introduced at atmospheric pressures through a flow of helium or air) within the pore space. In addition, the combination of X-ray absorption and infrared spectra suggests direct coordination ofmore » DMMP to the Zr6 cores of all MOFs, which ultimately leads to decomposition to phosphonate products. Our experimental probes into the mechanism of adsorption and decomposition of chemical warfare agent simulants on Zr-based MOFs open new opportunities in rational design of new and superior decontamination materials.« less

Mechanism of the Thermal Decomposition of Ethanethiol and Dimethylsulfide

NASA Astrophysics Data System (ADS)

Melhado, William Francis; Whitman, Jared Connor; Kong, Jessica; Anderson, Daniel Easton; Vasiliou, AnGayle (AJ)

2016-06-01

Combustion of organosulfur contaminants in petroleum-based fuels and biofuels produces sulfur oxides (SO_x). These pollutants are highly regulated by the EPA because they have been linked to poor respiratory health and negative environmental impacts. Therefore much effort has been made to remove sulfur compounds in petroleum-based fuels and biofuels. Currently desulfurization methods used in the fuel industry are costly and inefficient. Research of the thermal decomposition mechanisms of organosulfur species can be implemented via engineering simulations to modify existing refining technologies to design more efficient sulfur removal processes. We have used a resistively-heated SiC tubular reactor to study the thermal decomposition of ethanethiol (CH_3CH_2SH) and dimethylsulfide (CH_3SCH_3). The decomposition products are identified by two independent techniques: 118.2 nm VUV photoionization mass spectroscopy and infrared spectroscopy. The thermal cracking products for CH_3CH_2SH are CH_2CH_2, SH, and H_2S and the thermal cracking products from CH_3SCH_3 are CH_3S, CH_2S, and CH_3.

The neural basis of novelty and appropriateness in processing of creative chunk decomposition.

PubMed

Huang, Furong; Fan, Jin; Luo, Jing

2015-06-01

Novelty and appropriateness have been recognized as the fundamental features of creative thinking. However, the brain mechanisms underlying these features remain largely unknown. In this study, we used event-related functional magnetic resonance imaging (fMRI) to dissociate these mechanisms in a revised creative chunk decomposition task in which participants were required to perform different types of chunk decomposition that systematically varied in novelty and appropriateness. We found that novelty processing involved functional areas for procedural memory (caudate), mental rewarding (substantia nigra, SN), and visual-spatial processing, whereas appropriateness processing was mediated by areas for declarative memory (hippocampus), emotional arousal (amygdala), and orthography recognition. These results indicate that non-declarative and declarative memory systems may jointly contribute to the two fundamental features of creative thinking. Copyright © 2015 Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Núñez-Coavas, H.

As cast Cu{sub 90}Co{sub 10} ribbons rapidly solidified by twin-roller melt spinning, exhibit special microstructure features. This processing method provides scenarios where a different phase selection takes place; coherent Co precipitates form directly from solidification, with neither a spinodal-like composition oscillation nor a discontinuously precipitated laminar phase. Samples are processed at tangential wheel speeds of 10 m/s (V10), 15 m/s (V15), 20 m/s (V20) and 30 m/s (V30). Microstructures resulting from this single step process are characterized and the hysteresis properties and the magnetoresistance effects evaluated. Samples V30 have a quite uniform density of coherent precipitates, with a narrow sizemore » distribution around 4 nm. On contrary, non-uniform precipitate distributions are found in samples cooled at lower rates; zones with a high density of coherent Co-rich precipitates are found forming colonies. These colonies are consistent with the extended compositional fluctuations occurring during very early stages in the cooling process. Samples may exhibit wide (V10) and even bimodal (V15) size distributions. Only samples V30 behave close to the ideal superparamagnetism. Samples V20 present relatively large coercivity and relative remanence and behave as an interacting superparamagnet, while the hysteresis loops of ribbons cooled at lower rates exhibit a ferromagnetic contribution in addition to the superparamagnetic-like one. This ferromagnetic component arises from blocked precipitates, larger than the upper bound size for superparamagnetic behavior at 300 K (12 nm). Room temperature magnetoresistance values associated to granular scattering units decrease as the mean precipitate size increases, but they remain below 2%, which is lower than that measured in samples annealed after rapid solidification, indicating that in this latter case contributions from the spinodally segregated matrix take place in addition to that of Co granules. - Highlights: •Microstructures of twin-rolled Cu{sub 90}Cu{sub 10} alloys are for the first time characterized. •Coherent Co-rich precipitates distribute forming dense colonies inside the grains. •No coexisting multilayer-like structures (spinodal or laminar phases) are detected. •Magnetic hysteresis arises from inter-particle interaction in these dense colonies. •Magnetoresistance level in these purely granular systems is low (1.6% at 300 K).« less

Processing of alnico permanent magnets by advanced directional solidification methods

DOE PAGES

Zou, Min; Johnson, Francis; Zhang, Wanming; ...

2016-07-05

Advanced directional solidification methods have been used to produce large (>15 cm length) castings of Alnico permanent magnets with highly oriented columnar microstructures. In combination with subsequent thermomagnetic and draw thermal treatment, this method was used to enable the high coercivity, high-Titanium Alnico composition of 39% Co, 29.5% Fe, 14% Ni, 7.5% Ti, 7% Al, 3% Cu (wt%) to have an intrinsic coercivity (H ci) of 2.0 kOe, a remanence (B r) of 10.2 kG, and an energy product (BH) max of 10.9 MGOe. These properties compare favorably to typical properties for the commercial Alnico 9. Directional solidification of highermore » Ti compositions yielded anisotropic columnar grained microstructures if high heat extraction rates through the mold surface of at least 200 kW/m 2 were attained. This was achieved through the use of a thin walled (5 mm thick) high thermal conductivity SiC shell mold extracted from a molten Sn bath at a withdrawal rate of at least 200 mm/h. However, higher Ti compositions did not result in further increases in magnet performance. Images of the microstructures collected by scanning electron microscopy (SEM) reveal a majority α phase with inclusions of secondary αγ phase. Transmission electron microscopy (TEM) reveals that the α phase has a spinodally decomposed microstructure of FeCo-rich needles in a NiAl-rich matrix. In the 7.5% Ti composition the diameter distribution of the FeCo needles was bimodal with the majority having diameters of approximately 50 nm with a small fraction having diameters of approximately 10 nm. The needles formed a mosaic pattern and were elongated along one <001> crystal direction (parallel to the field used during magnetic annealing). Cu precipitates were observed between the needles. Regions of abnormal spinodal morphology appeared to correlate with secondary phase precipitates. The presence of these abnormalities did not prevent the material from displaying superior magnetic properties in the 7.5% Ti composition. As a result, higher Ti compositions did not display the preferred spinodal microstructure, explaining their inferior magnetic properties.« less

The mechanism of the photochemical oxidation of water to oxygen with silver chloride colloids

NASA Astrophysics Data System (ADS)

Chandrasekaran, K.; Thomas, J. K.

1983-05-01

Photoexcitation of silver chloride colloids in the presence of excess silver ions, leads to the decomposition of water. Hydroxyl radicals were found to be intermediates in the decomposition process. Irradiation leads to hydroxyl radicals, which recombine to give hydrogen peroxide, on the colloidal particle surface. Subsequent decomposition of H 2O 2 to give O 2 is catalyzed by silver ions. Addition of alcohols such as methanol and isopropanol reduce the oxygen yield, as they react with OH radicals and reduce the H 2O 2 yield.

Three phase crystallography and solute distribution analysis during residual austenite decomposition in tempered nanocrystalline bainitic steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caballero, F.G.; Yen, Hung-Wei; Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006

2014-02-15

Interphase carbide precipitation due to austenite decomposition was investigated by high resolution transmission electron microscopy and atom probe tomography in tempered nanostructured bainitic steels. Results showed that cementite (θ) forms by a paraequilibrium transformation mechanism at the bainitic ferrite–austenite interface with a simultaneous three phase crystallographic orientation relationship. - Highlights: • Interphase carbide precipitation due to austenite decomposition • Tempered nanostructured bainitic steels • High resolution transmission electron microscopy and atom probe tomography • Paraequilibrium θ with three phase crystallographic orientation relationship.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Ning; Shen, Tielong; Kurtz, Richard

The properties of nano-scale interstitial dislocation loops under the coupling effect of stress and temperature are studied using atomistic simulation methods and experiments. The decomposition of a loop by the emission of smaller loops is identified as one of the major mechanisms to release the localized stress induced by the coupling effect, which is validated by the TEM observations. The classical conservation law of Burgers vector cannot be applied during such decomposition process. The dislocation network is formed from the decomposed loops, which may initiate the irradiation creep much earlier than expected through the mechanism of climb-controlled glide of dislocations.

Identifying the Thermal Decomposition Mechanism of Guaiacol on Pt(111): An Integrated X-ray Photoelectron Spectroscopy and Density Functional Theory Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hensley, Alyssa J.; Wockel, Claudia; Gleichweit, Christoph

Using a concerted effort from both experiment and theory, we determine the thermal decomposition mechanism for guaiacol on Pt(111), a reaction of interest in the area of bio-oil upgrading. This work serves as a demonstration of the power of combining in situ temperature-programmed X-ray photoelectron spectroscopy cos (TPXPS) and density functional theory (DFT) to elucidate complex reaction mechanisms occurring on heterogeneous surfaces. At low temperature (230 K), guaiacol was found to chemisorb with the aromatic ring parallel to the Pt(111) surface with five distinct carbon species and three oxygen species. As the temperature was increased, TPXPS showed several significant changesmore » to the surface species. The increase in the species associated with the decomposition of the functional groups of guaiacol is followed by their subsequent disappearance and an increase in the nonaromatic carbon signal. On the basis of an energetic analysis of the various mechanisms using DFT, along with the comparison of the experimentally and theoretically derived core-level binding energies, we determined that guaiacol's decomposition mechanism occurs via the dehydrogenation of both the methyl and hydroxyl functional groups, followed by demethylation of the CH2 or CH group to form 1,2-benzoquinone. Further heating to above 375 K likely breaks the aromatic ring and results in the rapid formation and desorption of CO, accounting for the disappearance of the 0 is signal above 450 K These results show that a knowledgeable application of TPXPS and DFT can result in the quantitative identification of surface species during complex reactions, providing insight useful for the design of future heterogeneous surfaces.« less

Catalytic effects of inorganic acids on the decomposition of ammonium nitrate.

PubMed

Sun, Jinhua; Sun, Zhanhui; Wang, Qingsong; Ding, Hui; Wang, Tong; Jiang, Chuansheng

2005-12-09

In order to evaluate the catalytic effects of inorganic acids on the decomposition of ammonium nitrate (AN), the heat releases of decomposition or reaction of pure AN and its mixtures with inorganic acids were analyzed by a heat flux calorimeter C80. Through the experiments, the different reaction mechanisms of AN and its mixtures were analyzed. The chemical reaction kinetic parameters such as reaction order, activation energy and frequency factor were calculated with the C80 experimental results for different samples. Based on these parameters and the thermal runaway models (Semenov and Frank-Kamenestkii model), the self-accelerating decomposition temperatures (SADTs) of AN and its mixtures were calculated and compared. The results show that the mixtures of AN with acid are more unsteady than pure AN. The AN decomposition reaction is catalyzed by acid. The calculated SADTs of AN mixtures with acid are much lower than that of pure AN.

Thermal decomposition of gaseous ammonium nitrate at low pressure: kinetic modeling of product formation and heterogeneous decomposition of nitric acid.

PubMed

Park, J; Lin, M C

2009-12-03

The thermal decomposition of ammonium nitrate, NH(4)NO(3) (AN), in the gas phase has been studied at 423-56 K by pyrolysis/mass spectrometry under low-pressure conditions using a Saalfeld reactor coated with boric acid. The sublimation of NH(4)NO(3) at 423 K was proposed to produce equal amounts of NH(3) and HNO(3), followed by the decomposition reaction of HNO(3), HNO(3) + M --> OH + NO(2) + M (where M = third-body and reactor surface). The absolute yields of N(2), N(2)O, H(2)O, and NH(3), which can be unambiguously measured and quantitatively calibrated under a constant pressure at 5-6.2 torr He are kinetically modeled using the detailed [H,N,O]-mechanism established earlier for the simulation of NH(3)-NO(2) (Park, J.; Lin, M. C. Technologies and Combustion for a Clean Environment. Proc. 4th Int. Conf. 1997, 34-1, 1-5) and ADN decomposition reactions (Park, J.; Chakraborty, D.; Lin, M. C. Proc. Combust. Inst. 1998, 27, 2351-2357). Since the homogeneous decomposition reaction of HNO(3) itself was found to be too slow to account for the consumption of reactants and the formation of products, we also introduced the heterogeneous decomposition of HNO(3) in our kinetic modeling. The heterogeneous decomposition rate of HNO(3), HNO(3) + (B(2)O(3)/SiO(2)) --> OH + NO(2) + (B(2)O(3)/SiO(2)), was determined by varying its rate to match the modeled result to the measured concentrations of NH(3) and H(2)O; the rate could be represented by k(2b) = 7.91 x 10(7) exp(-12 600/T) s(-1), which appears to be consistent with those reported by Johnston and co-workers (Johnston, H. S.; Foering, L.; Tao, Y.-S.; Messerly, G. H. J. Am. Chem. Soc. 1951, 73, 2319-2321) for HNO(3) decomposition on glass reactors at higher temperatures. Notably, the concentration profiles of all species measured could be satisfactorily predicted by the existing [H,N,O]-mechanism with the heterogeneous initiation process.

Thermal Decomposition of Gaseous Ammonium Nitrate at Low Pressure: Kinetic Modeling of Product Formation and Heterogeneous Decomposition of Nitric Acid

NASA Astrophysics Data System (ADS)

Park, J.; Lin, M. C.

2009-10-01

The thermal decomposition of ammonium nitrate, NH4NO3 (AN), in the gas phase has been studied at 423-56 K by pyrolysis/mass spectrometry under low-pressure conditions using a Saalfeld reactor coated with boric acid. The sublimation of NH4NO3 at 423 K was proposed to produce equal amounts of NH3 and HNO3, followed by the decomposition reaction of HNO3, HNO3 + M → OH + NO2 + M (where M = third-body and reactor surface). The absolute yields of N2, N2O, H2O, and NH3, which can be unambiguously measured and quantitatively calibrated under a constant pressure at 5-6.2 torr He are kinetically modeled using the detailed [H,N,O]-mechanism established earlier for the simulation of NH3-NO2 (Park, J.; Lin, M. C. Technologies and Combustion for a Clean Environment. Proc. 4th Int. Conf. 1997, 34-1, 1-5) and ADN decomposition reactions (Park, J.; Chakraborty, D.; Lin, M. C. Proc. Combust. Inst. 1998, 27, 2351-2357). Since the homogeneous decomposition reaction of HNO3 itself was found to be too slow to account for the consumption of reactants and the formation of products, we also introduced the heterogeneous decomposition of HNO3 in our kinetic modeling. The heterogeneous decomposition rate of HNO3, HNO3 + (B2O3/SiO2) → OH + NO2 + (B2O3/SiO2), was determined by varying its rate to match the modeled result to the measured concentrations of NH3 and H2O; the rate could be represented by k2b = 7.91 × 107 exp(-12 600/T) s-1, which appears to be consistent with those reported by Johnston and co-workers (Johnston, H. S.; Foering, L.; Tao, Y.-S.; Messerly, G. H. J. Am. Chem. Soc. 1951, 73, 2319-2321) for HNO3 decomposition on glass reactors at higher temperatures. Notably, the concentration profiles of all species measured could be satisfactorily predicted by the existing [H,N,O]-mechanism with the heterogeneous initiation process.

MEG masked priming evidence for form-based decomposition of irregular verbs

PubMed Central

Fruchter, Joseph; Stockall, Linnaea; Marantz, Alec

2013-01-01

To what extent does morphological structure play a role in early processing of visually presented English past tense verbs? Previous masked priming studies have demonstrated effects of obligatory form-based decomposition for genuinely affixed words (teacher-TEACH) and pseudo-affixed words (corner-CORN), but not for orthographic controls (brothel-BROTH). Additionally, MEG single word reading studies have demonstrated that the transition probability from stem to affix (in genuinely affixed words) modulates an early evoked response known as the M170; parallel findings have been shown for the transition probability from stem to pseudo-affix (in pseudo-affixed words). Here, utilizing the M170 as a neural index of visual form-based morphological decomposition, we ask whether the M170 demonstrates masked morphological priming effects for irregular past tense verbs (following a previous study which obtained behavioral masked priming effects for irregulars). Dual mechanism theories of the English past tense predict a rule-based decomposition for regulars but not for irregulars, while certain single mechanism theories predict rule-based decomposition even for irregulars. MEG data was recorded for 16 subjects performing a visual masked priming lexical decision task. Using a functional region of interest (fROI) defined on the basis of repetition priming and regular morphological priming effects within the left fusiform and inferior temporal regions, we found that activity in this fROI was modulated by the masked priming manipulation for irregular verbs, during the time window of the M170. We also found effects of the scores generated by the learning model of Albright and Hayes (2003) on the degree of priming for irregular verbs. The results favor a single mechanism account of the English past tense, in which even irregulars are decomposed into stems and affixes prior to lexical access, as opposed to a dual mechanism model, in which irregulars are recognized as whole forms. PMID:24319420

Differences in the sensitivity of fungi and bacteria to season and invertebrates affect leaf litter decomposition in a Mediterranean stream.

PubMed

Mora-Gómez, Juanita; Elosegi, Arturo; Duarte, Sofia; Cássio, Fernanda; Pascoal, Cláudia; Romaní, Anna M

2016-08-01

Microorganisms are key drivers of leaf litter decomposition; however, the mechanisms underlying the dynamics of different microbial groups are poorly understood. We investigated the effects of seasonal variation and invertebrates on fungal and bacterial dynamics, and on leaf litter decomposition. We followed the decomposition of Populus nigra litter in a Mediterranean stream through an annual cycle, using fine and coarse mesh bags. Irrespective of the season, microbial decomposition followed two stages. Initially, bacterial contribution to total microbial biomass was higher compared to later stages, and it was related to disaccharide and lignin degradation; in a later stage, bacteria were less important and were associated with hemicellulose and cellulose degradation, while fungi were related to lignin decomposition. The relevance of microbial groups in decomposition differed among seasons: fungi were more important in spring, whereas in summer, water quality changes seemed to favour bacteria and slowed down lignin and hemicellulose degradation. Invertebrates influenced litter-associated microbial assemblages (especially bacteria), stimulated enzyme efficiencies and reduced fungal biomass. We conclude that bacterial and fungal assemblages play distinctive roles in microbial decomposition and differ in their sensitivity to environmental changes, ultimately affecting litter decomposition, which might be particularly relevant in highly seasonal ecosystems, such as intermittent streams. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Measurement of the energy dependence of X-ray-induced decomposition of potassium chlorate.

PubMed

Pravica, Michael; Bai, Ligang; Sneed, Daniel; Park, Changyong

2013-03-21

We report the first measurements of the X-ray induced decomposition of KClO3 as a function of energy in two experiments. KClO3 was pressurized to 3.5 GPa and irradiated with monochromatic synchrotron X-rays ranging in energy from 15 to 35 keV in 5 keV increments. A systematic increase in the decomposition rate as the energy was decreased was observed, which agrees with the 1/E(3) trend for the photoelectric process, except at the lowest energy studied. A second experiment was performed to access lower energies (10 and 12 keV) using a beryllium gasket; suggesting an apparent resonance near 15 keV or 0.83 Ǻ maximizing the chemical decomposition rate. A third experiment was performed using KIO3 to ascertain the anionic dependence of the decomposition rate, which was observed to be far slower than in KClO3, suggesting that the O-O distance is the critical factor in chemical reactions. These results will be important for more efficiently initiating chemical decomposition in materials using selected X-ray wavelengths that maximize decomposition to aid useful hard X-ray-induced chemistry and contribute understanding of the mechanism of X-ray-induced decomposition of the chlorates.

Lignin decomposition is sustained under fluctuating redox conditions in humid tropical forest soils

Treesearch

Steven J. Hall; Whendee L. Silver; Vitaliy I. Timokhin; Kenneth E. Hammel

2015-01-01

Lignin mineralization represents a critical flux in the terrestrial carbon (C) cycle, yet little is known about mechanisms and environmental factors controlling lignin breakdown in mineral soils. Hypoxia is thought to suppress lignin decomposition, yet potential effects of oxygen (O2) variability in surface soils have not been explored. Here, we...

Thermal decomposition of FC(O)OCH3 and FC(O)OCH2CH3.

PubMed

Berasategui, M; Argüello, G A; Burgos Paci, M A

2018-05-09

The thermal decomposition of methyl and ethyl formates has been extensively studied due to their importance in the oxidation of several fuels, pesticidal properties and their presence in interstellar space. We hitherto present the study of the thermal decomposition of methyl and ethyl fluoroformates, which could help in the elucidation of the reaction mechanisms. The reaction mechanisms were studied using FTIR spectroscopy in the temperature range of 453-733 K in the presence of different pressures of N2 as bath gas. For FC(O)OCH3 two different channels were observed; the unimolecular decomposition which is favored at higher temperatures and has a rate constant kFC(O)OCH3 = (5.3 ± 0.5) × 1015 exp[-(246 ± 10 kJ mol-1/RT)] (in units of s-1) and a bimolecular channel with a rate constant kFC(O)OCH3 = (1.6 ± 0.5) × 1011 exp[-(148 ± 10 kJ mol-1/RT)] (in units of s-1 (mol L)-1). However for ethyl formate, only direct elimination of CO2, HF and ethylene operates. The rate constants of the homogeneous first-order process fit the Arrhenius equation kFC(O)OCH2CH3 = (2.06 ± 0.09) × 1013 exp[-(169 ± 6 kJ mol-1/RT)] (in units of s-1). The difference between the mechanisms of the two fluoroformates relies on the stabilization of a six-centered transition state that only exists for ethyl formate. First principles calculations for the different channels were carried out to understand the dynamics of the decomposition.

Initial mechanisms for the decomposition of electronically excited energetic materials: 1,5′-BT, 5,5′-BT, and AzTT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Bing; Yu, Zijun; Bernstein, Elliot R., E-mail: erb@lamar.Colostate.edu

2015-03-28

Decomposition of nitrogen-rich energetic materials 1,5′-BT, 5,5′-BT, and AzTT (1,5′-Bistetrazole, 5,5′-Bistetrazole, and 5-(5-azido-(1 or 4)H-1,2,4-triazol-3-yl)tetrazole, respectively), following electronic state excitation, is investigated both experimentally and theoretically. The N{sub 2} molecule is observed as an initial decomposition product from the three materials, subsequent to UV excitation, with a cold rotational temperature (<30 K). Initial decomposition mechanisms for these three electronically excited materials are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) level illustrate that conical intersections play an essential role in the decomposition mechanism. Electronically excited S{sub 1} molecules can non-adiabatically relaxmore » to their ground electronic states through (S{sub 1}/S{sub 0}){sub CI} conical intersections. 1,5′-BT and 5,5′-BT materials have several (S{sub 1}/S{sub 0}){sub CI} conical intersections between S{sub 1} and S{sub 0} states, related to different tetrazole ring opening positions, all of which lead to N{sub 2} product formation. The N{sub 2} product for AzTT is formed primarily by N–N bond rupture of the –N{sub 3} group. The observed rotational energy distributions for the N{sub 2} products are consistent with the final structures of the respective transition states for each molecule on its S{sub 0} potential energy surface. The theoretically derived vibrational temperature of the N{sub 2} product is high, which is similar to that found for energetic salts and molecules studied previously.« less

Effects of copolymer composition, film thickness, and solvent vapor annealing time on dewetting of ultrathin block copolymer films.

PubMed

Huang, Changchun; Wen, Gangyao; Li, Jingdan; Wu, Tao; Wang, Lina; Xue, Feifei; Li, Hongfei; Shi, Tongfei

2016-09-15

Effects of copolymer composition, film thickness, and solvent vapor annealing time on dewetting of spin-coated polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films (<20nm thick) were mainly investigated by atomic force microscopy. Surface chemical analysis of the ultrathin films annealed for different times were performed using X-ray photoelectron spectroscopy and contact angle measurement. With the annealing of acetone vapor, dewetting of the films with different thicknesses occur via the spinodal dewetting and the nucleation and growth mechanisms, respectively. The PS-b-PMMA films rupture into droplets which first coalesce into large ones to reduce the surface free energy. Then the large droplets rupture into small ones to increase the contact area between PMMA blocks and acetone molecules resulting from ultimate migration of PMMA blocks to droplet surface, which is a novel dewetting process observed in spin-coated films for the first time. Copyright © 2016 Elsevier Inc. All rights reserved.

Novel mechanisms for self-assembled pattern formation in nanoscopic metal films

NASA Astrophysics Data System (ADS)

Kalyanaraman, R.; Trice, J.; Favazza, C.; Thomas, D.; Sureshkumar, R.

2007-03-01

Classical hydrodynamic theory of dewetting of spinodally unstable thin films (Vrij, Disc. farad. Soc. 1966) predicts a monotonic increase in patterning length scales with increasing film thickness. We verified this effect for nanoscopic Co metal films following melting by ns laser pulses for thickness regime h<=hc˜8,m (Favazza et al. Nanotechnology, 2006). However, a dramatic change is observed beyond this thickness hc, with length scales decreasing with increasing h. This novel behavior arises from strong thickness dependence of heating by ultrafast laser light resulting in thermocapillary effects, whose magnitude and sign are thickness dependent. We modified the classical theory, according to which the instability occurs when the stabilizing capillary force is overcome by destabilizing attractive long-range interactions, to include thermocapillary effects. The modified theory accurately predicts the experimentally observed trend. This result suggests that a variety of new length scales can be accessed by robust self-assembly via dewetting of metal films under ultrafast light.

The origins of microstructure in phase inversion coatings or membranes: Snapshots of the transient from time-sectioning cryo-SEM

NASA Astrophysics Data System (ADS)

Prakash, Sai Sivasankaran

2001-11-01

Time-sectioning cryogenic scanning electron microscopy (cryo-SEM) is a unique method of visualizing how the microstructure of liquid coatings evolves during processing. Time-sectioning means rapidly freezing (nearly) identical specimens at successively later stages of the process; doing this requires that coating and drying be well controlled in the dry phase inversion process, and solvents exchange likewise in the wet phase inversion process. With control, frozen specimens are fractured, etched by limited sublimation, sputter-coated, and imaged at temperatures of ca -175°C. The coatings examined were of cellulose acetate, of high and low molecular weights, and polysulfone in mixed solvents and nonsolvents: acetone and water with cellulose acetate undergoing dry phase inversion; and tetrahydrofuran, dimethylacetamide, ethanol with polysulfone undergoing dry-wet phase inversion. All coatings, cast on silicon substrates, were initially homogeneous. The initial compositions of the high and low molecular weight cellulose acetate ternary solutions were "off-critical" and "near-critical", respectively, connoting their proximities to the critical or plait point of the phase diagram. The initial composition of the polysulfone quaternary solution was located near the binodal of the pseudo-ternary phase diagram. It appeared that as the higher molecular weight cellulose acetate coating dries, it nucleates and grows polymer-poor droplets that coalesce into a bicontinuous structure underlying a thin, dense skin. Bicontinuity of structure was verified by stereomicroscopy of the dry sample. The lower molecular weight cellulose acetate coating phase-separates, seemingly spinodally, directly into a bicontinuous structure whose polymer-rich network, stressed by frustrated in-plane shrinkage, ruptures far beneath the skin in some locales to form macrovoids. When, after partial drying, the polysulfone coating was immersed in a bath of water, a nonsolvent, it appeared to swell in thickness as it phase-separates. A dense skin, thinner than a micron, appeared to overlie a two-phase substructure that is punctuated with pear-shaped macrovoids. At early immersion times, this substructure is visibly bicontinuous or open-celled near the bath-side, and dispersion-like (droplets dispersed in a polymeric matrix) or closed-celled near the substrate-side. Moreover, in the bicontinuous regions, length-scales of the individual phases seem to increase across the coating thickness from the bath-side to the substrate-side. After prolonged immersion, the substructure, excluding the macrovoids, is entirely bicontinuous. The bicontinuity presumably results from a combination of spinodal decomposition and nucleation and growth plus coalescence. Quite strikingly, macrovoids are present exclusively in regions where phases are bicontinuous, and are absent where droplets are dispersed in the polymeric matrix. Evidence suggests that macrovoids result from an instability caused by a progressive rupture of polymer-rich links deeper and deeper beneath the skin, aggravated by stress localization in the rupturing network and a buildup of pressure in the polymer-poor phase (the pore space), as suspected by Grobe and Meyer in 1959.

Characterization of a High Strength, Refractory High Entropy Alloy, AlMo0.5NbTa0.5TiZr

NASA Astrophysics Data System (ADS)

Jensen, Jacob

High entropy alloys (HEAs) are a relatively new class of materials that have garnered significant interest over the last decade due to their intriguing balance of properties including high strength, toughness, and corrosion resistance. In contrast to conventional alloy systems, HEAs are based on four or more principal elements with near equimolar concentrations and tend to have simple microstructures due to the preferential formation of solid solution phases. HEAs appear to offer new pathways to lightweighting in structural applications, new alloys for elevated temperature components, and new magnetic materials, but more thorough characterization studies are needed to assess the viability of the recently developed multicomponent materials. One such HEA, AlMo0.5NbTa0.5TiZr, was selected to be the basis for this characterization study in part due to its strength at elevated temperatures (sigma0.2 = 1600 MPa at T = 800 °C) and low density compared with commercially available Ni-based superalloys. The refractory element containing HEA composition was developed in order to balance the high temperature strength of the refractory elements with the desirable properties achieved by the high entropy alloying design approach for potential use in aerospace thermal protection and structural applications. Ingots of AlMo0.5NbTa0.5TiZr were cast by vacuum arc melting followed by hot isostatic pressing (HIP) and homogenization at 1400 °C for 24 hrs with a furnace cool of 10 °C/min. The resulting microstructure was characterized at multiple length scales using x-ray diffraction (XRD), scanning transmission electron microscopy (SEM), conventional and scanning transmission electron microscopy (TEM and STEM), and x-ray energy dispersive spectroscopy (XEDS). The microstructure was found to consist of a periodic, coherent two phase mixture, where a disordered bcc phase is aligned orthogonally in an ordered B2 phase. Through microstructural evolution heat treatment studies, the nanoscale interpenetrating microstructure was discovered to form via a conditional spinodal reaction pathway involving a congruent ordering transformation preceding spinodal decomposition. In order to gain a comprehensive understanding of the true morphology of these phases and obtain a novel perspective of 3D elemental segregation in the HEA, STEM-high angle annular darkfield (HAADF) micrographs and XEDS spectral images were utilized in the tomographic reconstruction of the microstructure, which was inherently difficult to observe through conventional characterization techniques. The microstructure of the alloy was ultimately refined by incremental variations to the base alloy composition in an effort to remove deleterious intermetallic phases adversely affecting ductility. Despite the excellent compressive strength across a wide range of temperatures and the ability to tailor the microstructure by compositional modifications, microstructural and phase transformations in the desired operating temperature range indicate that the AlMo0.5NbTa0.5TiZr alloy may not be a suitable material for high temperature aerospace structural components.

Assessment of a new method for the analysis of decomposition gases of polymers by a combining thermogravimetric solid-phase extraction and thermal desorption gas chromatography mass spectrometry.

PubMed

Duemichen, E; Braun, U; Senz, R; Fabian, G; Sturm, H

2014-08-08

For analysis of the gaseous thermal decomposition products of polymers, the common techniques are thermogravimetry, combined with Fourier transformed infrared spectroscopy (TGA-FTIR) and mass spectrometry (TGA-MS). These methods offer a simple approach to the decomposition mechanism, especially for small decomposition molecules. Complex spectra of gaseous mixtures are very often hard to identify because of overlapping signals. In this paper a new method is described to adsorb the decomposition products during controlled conditions in TGA on solid-phase extraction (SPE) material: twisters. Subsequently the twisters were analysed with thermal desorption gas chromatography mass spectrometry (TDS-GC-MS), which allows the decomposition products to be separated and identified using an MS library. The thermoplastics polyamide 66 (PA 66) and polybutylene terephthalate (PBT) were used as example polymers. The influence of the sample mass and of the purge gas flow during the decomposition process was investigated in TGA. The advantages and limitations of the method were presented in comparison to the common analysis techniques, TGA-FTIR and TGA-MS. Copyright © 2014 Elsevier B.V. All rights reserved.

Understanding paper degradation: identification of products of cellulosic paper decomposition at the wet-dry "tideline" interface using GC-MS.

PubMed

Sladkevich, Sergey; Dupont, Anne-Laurence; Sablier, Michel; Seghouane, Dalila; Cole, Richard B

2016-11-01

Cellulose paper degradation products forming in the "tideline" area at the wet-dry interface of pure cellulose paper were analyzed using gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) and high-resolution electrospray ionization-mass spectrometry (ESI-MS, LTQ Orbitrap) techniques. Different extraction protocols were employed in order to solubilize the products of oxidative cellulose decomposition, i.e., a direct solvent extraction or a more laborious chromophore release and identification (CRI) technique aiming to reveal products responsible for paper discoloration in the tideline area. Several groups of low molecular weight compounds were identified, suggesting a complex pathway of cellulose decomposition in the tidelines formed at the cellulose-water-oxygen interface. Our findings, namely the appearance of a wide range of linear saturated carboxylic acids (from formic to nonanoic), support the oxidative autocatalytic mechanism of decomposition. In addition, the identification of several furanic compounds (which can be, in part, responsible for paper discoloration) plus anhydro carbohydrate derivatives sheds more light on the pathways of cellulose decomposition. Most notably, the mechanisms of tideline formation in the presence of molecular oxygen appear surprisingly similar to pathways of pyrolytic cellulose degradation. More complex chromophore compounds were not detected in this study, thereby revealing a difference between this short-term tideline experiment and longer-term cellulose aging.

Synthesis, characterization, thermal and explosive properties of potassium salts of trinitrophloroglucinol.

PubMed

Wang, Liqiong; Chen, Hongyan; Zhang, Tonglai; Zhang, Jianguo; Yang, Li

2007-08-17

Three different substituted potassium salts of trinitrophloroglucinol (H(3)TNPG) were prepared and characterized. The salts are all hydrates, and thermogravimetric analysis (TG) and elemental analysis confirmed that these salts contain crystal H2O and that the amount crystal H2O in potassium salts of H3TNPG is 1.0 hydrate for mono-substituted potassium salts of H3TNPG [K(H2TNPG)] and di-substituted potassium salt of H3TNPG [K2(HTNPG)], and 2.0 hydrate for tri-substituted potassium salt of H3TNPG [K3(TNPG)]. Their thermal decomposition mechanisms and kinetic parameters from 50 to 500 degrees C were studied under a linear heating rate by differential scanning calorimetry (DSC). Their thermal decomposition mechanisms undergo dehydration stage and intensive exothermic decomposition stage. FT-IR and TG studies verify that their final residua of decomposition are potassium cyanide or potassium carbonate. According to the onset temperature of the first exothermic decomposition process of dehydrated salts, the order of the thermal stability from low to high is from K(H2TNPG) and K2(HTNPG) to K3(TNPG), which is conform to the results of apparent activation energy calculated by Kissinger's and Ozawa-Doyle's method. Sensitivity test results showed that potassium salts of H3TNPG demonstrated higher sensitivity properties and had greater explosive probabilities.

Analysis on Vertical Scattering Signatures in Forestry with PolInSAR

NASA Astrophysics Data System (ADS)

Guo, Shenglong; Li, Yang; Zhang, Jingjing; Hong, Wen

2014-11-01

We apply accurate topographic phase to the Freeman-Durden decomposition for polarimetric SAR interferometry (PolInSAR) data. The cross correlation matrix obtained from PolInSAR observations can be decomposed into three scattering mechanisms matrices accounting for the odd-bounce, double-bounce and volume scattering. We estimate the phase based on the Random volume over Ground (RVoG) model, and as the initial input parameter of the numerical method which is used to solve the parameters of decomposition. In addition, the modified volume scattering model introduced by Y. Yamaguchi is applied to the PolInSAR target decomposition in forest areas rather than the pure random volume scattering as proposed by Freeman-Durden to make best fit to the actual measured data. This method can accurately retrieve the magnitude associated with each mechanism and their vertical location along the vertical dimension. We test the algorithms with L- and P- band simulated data.

Materials on the brink: unprecedented transforming materials

DTIC Science & Technology

2013-09-10

2013 56.00 Shenqiang Ren\\, Manfred Wuttig. Spinodal synthesis of PZT /NFO magnetoelectric, Applied Physics Letters, (08 2007): 83501. doi: 02/06/2013... PZT . This material was discovered through a combinatorial search. Rabe et al. have used first principles methods to show that this morphotropic...temperature. James et al. have suggested a new strategy for energy recovery from waste heat using this alloy. • Discovery of a new fatigue -free shape

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baidakov, Vladimir G., E-mail: baidakov@itp.uran.ru; Tipeev, Azat O.

The method of molecular dynamics simulation has been used to investigate the phase decay of a metastable Lennard-Jones face-centered cubic crystal at positive and negative pressures. It is shown that at high degrees of metastability, crystal decay proceeds through the spontaneous formation and growth of new-phase nuclei. It has been found that there exists a certain boundary temperature. Below this temperature, the crystal phase disintegrates as the result of formation of voids, and above, as a result of formation of liquid droplets. The boundary temperature corresponds to the temperature of cessation of a crystal–liquid phase equilibrium when the melting linemore » comes in contact with the spinodal of the stretched liquid. The results of the simulations are interpreted in the framework of classical nucleation theory. The thermodynamics of phase transitions in solids has been examined with allowance for the elastic energy of stresses arising owing to the difference in the densities of the initial and the forming phases. As a result of the action of elastic forces, at negative pressures, the boundary of the limiting superheating (stretching) of a crystal approaches the spinodal, on which the isothermal bulk modulus of dilatation becomes equal to zero. At the boundary of the limiting superheating (stretching), the shape of liquid droplets and voids is close to the spherical one.« less

HCOOH decomposition on Pt(111): A DFT study

DOE PAGES

Scaranto, Jessica; Mavrikakis, Manos

2015-10-13

Formic acid (HCOOH) decomposition on transition metal surfaces is important for hydrogen production and for its electro-oxidation in direct HCOOH fuel cells. HCOOH can decompose through dehydrogenation leading to formation of CO 2 and H 2 or dehydration leading to CO and H 2O; because CO can poison metal surfaces, dehydrogenation is typically the desirable decomposition path. Here we report a mechanistic analysis of HCOOH decomposition on Pt(111), obtained from a plane wave density functional theory (DFT-PW91) study. We analyzed the dehydrogenation mechanism by considering the two possible pathways involving the formate (HCOO) or the carboxyl (COOH) intermediate. We alsomore » considered several possible dehydration paths leading to CO formation. We studied HCOO and COOH decomposition both on the clean surface and in the presence of other relevant co-adsorbates. The results suggest that COOH formation is energetically more difficult than HCOO formation. In contrast, COOH dehydrogenation is easier than HCOO decomposition. Here, we found that CO 2 is the main product through both pathways and that CO is produced mainly through the dehydroxylation of the COOH intermediate.« less

HCOOH decomposition on Pt(111): A DFT study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scaranto, Jessica; Mavrikakis, Manos

Formic acid (HCOOH) decomposition on transition metal surfaces is important for hydrogen production and for its electro-oxidation in direct HCOOH fuel cells. HCOOH can decompose through dehydrogenation leading to formation of CO 2 and H 2 or dehydration leading to CO and H 2O; because CO can poison metal surfaces, dehydrogenation is typically the desirable decomposition path. Here we report a mechanistic analysis of HCOOH decomposition on Pt(111), obtained from a plane wave density functional theory (DFT-PW91) study. We analyzed the dehydrogenation mechanism by considering the two possible pathways involving the formate (HCOO) or the carboxyl (COOH) intermediate. We alsomore » considered several possible dehydration paths leading to CO formation. We studied HCOO and COOH decomposition both on the clean surface and in the presence of other relevant co-adsorbates. The results suggest that COOH formation is energetically more difficult than HCOO formation. In contrast, COOH dehydrogenation is easier than HCOO decomposition. Here, we found that CO 2 is the main product through both pathways and that CO is produced mainly through the dehydroxylation of the COOH intermediate.« less

Phase separation of comb polymer nanocomposite melts.

PubMed

Xu, Qinzhi; Feng, Yancong; Chen, Lan

2016-02-07

In this work, the spinodal phase demixing of branched comb polymer nanocomposite (PNC) melts is systematically investigated using the polymer reference interaction site model (PRISM) theory. To verify the reliability of the present method in characterizing the phase behavior of comb PNCs, the intermolecular correlation functions of the system for nonzero particle volume fractions are compared with our molecular dynamics simulation data. After verifying the model and discussing the structure of the comb PNCs in the dilute nanoparticle limit, the interference among the side chain number, side chain length, nanoparticle-monomer size ratio and attractive interactions between the comb polymer and nanoparticles in spinodal demixing curves is analyzed and discussed in detail. The results predict two kinds of distinct phase separation behaviors. One is called classic fluid phase boundary, which is mediated by the entropic depletion attraction and contact aggregation of nanoparticles at relatively low nanoparticle-monomer attraction strength. The second demixing transition occurs at relatively high attraction strength and involves the formation of an equilibrium physical network phase with local bridging of nanoparticles. The phase boundaries are found to be sensitive to the side chain number, side chain length, nanoparticle-monomer size ratio and attractive interactions. As the side chain length is fixed, the side chain number has a large effect on the phase behavior of comb PNCs; with increasing side chain number, the miscibility window first widens and then shrinks. When the side chain number is lower than a threshold value, the phase boundaries undergo a process from enlarging the miscibility window to narrowing as side chain length increases. Once the side chain number overtakes this threshold value, the phase boundary shifts towards less miscibility. With increasing nanoparticle-monomer size ratio, a crossover of particle size occurs, above which the phase separation is consistent with that of chain PNCs. The miscibility window for this condition gradually narrows while the other parameters of the PNCs system are held constant. These results indicate that the present PRISM theory can give molecular-level details of the underlying mechanisms of the comb PNCs. It is hoped that the results can be used to provide useful guidance for the future design control of novel, thermodynamically stable comb PNCs.

Magnetite Formation from Thermal Decomposition of Siderite: Implications for Inorganic Magnetite Formation in Martian Meteorite ALH84001

NASA Technical Reports Server (NTRS)

Morris, RIchard V.

2002-01-01

A biogenic mechanism for formation of a subpopulation magnetite in Martian meteorite ALH84001 has been suggested [McKay et al., 1996; Thomas-Keprta, et al., 2000]. We are developing experimental evidence for an alternating working hypothesis, that the subpopulation was produced inorganically by the thermal decomposition of siderite [Golden et al., 2000].

Studies on thermal decomposition behaviors of polypropylene using molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Huang, Jinbao; He, Chao; Tong, Hong; Pan, Guiying

2017-11-01

Polypropylene (PP) is one of the main components of waste plastics. In order to understand the mechanism of PP thermal decomposition, the pyrolysis behaviour of PP has been simulated from 300 to 1000 K in periodic boundary conditions by molecular dynamic method, based on AMBER force field. The simulation results show that the pyrolysis process of PP can mostly be divided into three stages: low temperature pyrolysis stage, intermediate temperature stage and high temperature pyrolysis stage. PP pyrolysis is typical of random main-chain scission, and the possible formation mechanism of major pyrolysis products was analyzed.

Decomposition and extraction: a new framework for visual classification.

PubMed

Fang, Yuqiang; Chen, Qiang; Sun, Lin; Dai, Bin; Yan, Shuicheng

2014-08-01

In this paper, we present a novel framework for visual classification based on hierarchical image decomposition and hybrid midlevel feature extraction. Unlike most midlevel feature learning methods, which focus on the process of coding or pooling, we emphasize that the mechanism of image composition also strongly influences the feature extraction. To effectively explore the image content for the feature extraction, we model a multiplicity feature representation mechanism through meaningful hierarchical image decomposition followed by a fusion step. In particularly, we first propose a new hierarchical image decomposition approach in which each image is decomposed into a series of hierarchical semantical components, i.e, the structure and texture images. Then, different feature extraction schemes can be adopted to match the decomposed structure and texture processes in a dissociative manner. Here, two schemes are explored to produce property related feature representations. One is based on a single-stage network over hand-crafted features and the other is based on a multistage network, which can learn features from raw pixels automatically. Finally, those multiple midlevel features are incorporated by solving a multiple kernel learning task. Extensive experiments are conducted on several challenging data sets for visual classification, and experimental results demonstrate the effectiveness of the proposed method.

Out-of-equilibrium processes in suspensions of oppositely charged colloids: liquid-to-crystal nucleation and gel formation

NASA Astrophysics Data System (ADS)

Sanz, Eduardo

2009-03-01

We study the kinetics of the liquid-to-crystal transformation and of gel formation in colloidal suspensions of oppositely charged particles. We analyse, by means of both computer simulations and experiments, the evolution of a fluid quenched to a state point of the phase diagram where the most stable state is either a homogeneous crystalline solid or a solid phase in contact with a dilute gas. On the one hand, at high temperatures and high packing fractions, close to an ordered-solid/disordered-solid coexistence line, we find that the fluid-to-crystal pathway does not follow the minimum free energy route. On the other hand, a quench to a state point far from the ordered-crystal/disordered-crystal coexistence border is followed by a fluid-to-solid transition through the minimum free energy pathway. At low temperatures and packing fractions we observe that the system undergoes a gas-liquid spinodal decomposition that, at some point, arrests giving rise to a gel-like structure. Both our simulations and experiments suggest that increasing the interaction range favors crystallization over vitrification in gel-like structures. [4pt] In collaboration with Chantal Valeriani, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands and SUPA, School of Physics, University of Edinburgh, JCMB King's Buildings, Mayfield Road, Edinburgh EH9 3JZ, UK; Teun Vissers, Andrea Fortini, Mirjam E. Leunissen, and Alfons van Blaaderen, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University; Daan Frenke, FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands and Department of Chemistry, University of Cambridge, Lensfield Road, CB2 1EW, Cambridge, UK; and Marjolein Dijkstra, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University.

Phase-field-based lattice Boltzmann model for incompressible binary fluid systems with density and viscosity contrasts.

PubMed

Zu, Y Q; He, S

2013-04-01

A lattice Boltzmann model (LBM) is proposed based on the phase-field theory to simulate incompressible binary fluids with density and viscosity contrasts. Unlike many existing diffuse interface models which are limited to density matched binary fluids, the proposed model is capable of dealing with binary fluids with moderate density ratios. A new strategy for projecting the phase field to the viscosity field is proposed on the basis of the continuity of viscosity flux. The new LBM utilizes two lattice Boltzmann equations (LBEs): one for the interface tracking and the other for solving the hydrodynamic properties. The LBE for interface tracking can recover the Chan-Hilliard equation without any additional terms; while the LBE for hydrodynamic properties can recover the exact form of the divergence-free incompressible Navier-Stokes equations avoiding spurious interfacial forces. A series of 2D and 3D benchmark tests have been conducted for validation, which include a rigid-body rotation, stationary and moving droplets, a spinodal decomposition, a buoyancy-driven bubbly flow, a layered Poiseuille flow, and the Rayleigh-Taylor instability. It is shown that the proposed method can track the interface with high accuracy and stability and can significantly and systematically reduce the parasitic current across the interface. Comparisons with momentum-based models indicate that the newly proposed velocity-based model can better satisfy the incompressible condition in the flow fields, and eliminate or reduce the velocity fluctuations in the higher-pressure-gradient region and, therefore, achieve a better numerical stability. In addition, the test of a layered Poiseuille flow demonstrates that the proposed scheme for mixture viscosity performs significantly better than the traditional mixture viscosity methods.

Microstructure and thermal stability of Cu/Zr0.3Al0.7N/Zr0.2Al0.8N/Al34O60N6 cermet-based solar selective absorbing coatings

NASA Astrophysics Data System (ADS)

Meng, Jian-ping; Guo, Rui-rui; Li, Hu; Zhao, Lu-ming; Liu, Xiao-peng; Li, Zhou

2018-05-01

Solar selective absorbing coatings play a valuable role in photo-thermal conversion for high efficiency concentrating solar power systems (CSP). In this paper, a novel Cu/Zr0.3Al0.7N/Zr0.2Al0.8N/Al34O60N6 cermet-based solar selective absorbing coating was successfully deposited by ion beam assisted deposition. The optical properties, microstructure and element distribution in depth were investigated by spectroscopic ellipsometry, UV-vis-NIR spectrophotometer, transmission electron microscope (TEM) and Auger electron spectroscopy (AES), respectively. A high absorptance of 0.953 and a low thermal emittance of 0.079 at 400 °C are obtained by the integral computation according to the whole reflectance from 300 nm to 28,800 nm. After annealing treatment at 400 °C (in vacuum) for 192 h, the deposited coating exhibits the high thermal stability. Whereas, the photothermal conversion efficiency decreases from 12.10 to 6.86 due to the emittance increase after annealing at 600 °C for 192 h. Meanwhile, the nitrogen atom in the Zr0.3Al0.7N sub-layer diffuses toward the adjacent sub-layer due to the spinodal decomposition of metastable c-ZrAlN and the phase transition from c-AlN to h-AlN, which leads to the composition of the Zr0.3Al0.7N sub-layer deviates the initial design. This phenomenon has a guide effect for the thermal-stability improvement of cermet coatings. Additionally, a serious diffusion between copper and silicon substrate also contributes to the emittance increase.

Average structure and M2 site configurations in C2/c clinopyroxenes along the Di-En join

NASA Astrophysics Data System (ADS)

Tribaudino, M.; Benna, P.; Bruno, E.

1989-12-01

In order to clarify the structural configurations observed in Diss in the Ca-rich region of the Di-En join (in which TEM observations show neither exsolution microstructures nor evidence of spinodal decomposition) single crystals large enough for X-ray diffraction analyses, with composition (Ca0.66Mg0.34)MgSi2O6, have been equilibrated close to the solvus at T=1350° C for 317 h, and quenched at room temperature. The refinement in C2/c space group shows that in the M2 site Ca and Mg are fully ‘ordered’ in two split positions (M2occ: 0.66 Ca; M2'occ: 0.34 Mg). Since the average structure shows a relevant elongation of anisotropic thermal ellipsoids of the O2 and O3 oxygen atoms, the refinement has been carried out according to a split model for O2 and O3 atoms: Ca appears 8-coordinated (as in diopside) and Mg shows a sixfold coordination similar to that of high-pigeonite. This coordination for Mg is significantly different from the fourfold coordination (Zn-like in Zn-cpx) proposed previously and it is a more probable coordination for Mg from a crystalchemical point of view. The same results were obtained refining a Di80En20 cpx, equilibrated at T=1230° C, according to the same O-split model. The data support the coexistence of a Di-like configuration for Ca and of a highPig-like configuration for Mg away from the solvus also. At T very near to T solidus the different configurations, observed at room temperature in the quenched samples, should converge and Ca and Mg should retain a single disordered configuration in the M2 site.

Supersonic beams at high particle densities: model description beyond the ideal gas approximation.

PubMed

Christen, Wolfgang; Rademann, Klaus; Even, Uzi

2010-10-28

Supersonic molecular beams constitute a very powerful technique in modern chemical physics. They offer several unique features such as a directed, collision-free flow of particles, very high luminosity, and an unsurpassed strong adiabatic cooling during the jet expansion. While it is generally recognized that their maximum flow velocity depends on the molecular weight and the temperature of the working fluid in the stagnation reservoir, not a lot is known on the effects of elevated particle densities. Frequently, the characteristics of supersonic beams are treated in diverse approximations of an ideal gas expansion. In these simplified model descriptions, the real gas character of fluid systems is ignored, although particle associations are responsible for fundamental processes such as the formation of clusters, both in the reservoir at increased densities and during the jet expansion. In this contribution, the various assumptions of ideal gas treatments of supersonic beams and their shortcomings are reviewed. It is shown in detail that a straightforward thermodynamic approach considering the initial and final enthalpy is capable of characterizing the terminal mean beam velocity, even at the liquid-vapor phase boundary and the critical point. Fluid properties are obtained using the most accurate equations of state available at present. This procedure provides the opportunity to naturally include the dramatic effects of nonideal gas behavior for a large variety of fluid systems. Besides the prediction of the terminal flow velocity, thermodynamic models of isentropic jet expansions permit an estimate of the upper limit of the beam temperature and the amount of condensation in the beam. These descriptions can even be extended to include spinodal decomposition processes, thus providing a generally applicable tool for investigating the two-phase region of high supersaturations not easily accessible otherwise.

Decreases in Soil Moisture and Organic Matter Quality Suppress Microbial Decomposition Following a Boreal Forest Fire

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holden, Sandra R.; Berhe, Asmeret A.; Treseder, Kathleen K.

Climate warming is projected to increase the frequency and severity of wildfires in boreal forests, and increased wildfire activity may alter the large soil carbon (C) stocks in boreal forests. Changes in boreal soil C stocks that result from increased wildfire activity will be regulated in part by the response of microbial decomposition to fire, but post-fire changes in microbial decomposition are poorly understood. Here, we investigate the response of microbial decomposition to a boreal forest fire in interior Alaska and test the mechanisms that control post-fire changes in microbial decomposition. We used a reciprocal transplant between a recently burnedmore » boreal forest stand and a late successional boreal forest stand to test how post-fire changes in abiotic conditions, soil organic matter (SOM) composition, and soil microbial communities influence microbial decomposition. We found that SOM decomposing at the burned site lost 30.9% less mass over two years than SOM decomposing at the unburned site, indicating that post-fire changes in abiotic conditions suppress microbial decomposition. Our results suggest that moisture availability is one abiotic factor that constrains microbial decomposition in recently burned forests. In addition, we observed that burned SOM decomposed more slowly than unburned SOM, but the exact nature of SOM changes in the recently burned stand are unclear. Finally, we found no evidence that post-fire changes in soil microbial community composition significantly affect decomposition. Taken together, our study has demonstrated that boreal forest fires can suppress microbial decomposition due to post-fire changes in abiotic factors and the composition of SOM. Models that predict the consequences of increased wildfires for C storage in boreal forests may increase their predictive power by incorporating the observed negative response of microbial decomposition to boreal wildfires.« less

Hydrated electron based decomposition of perfluorooctane sulfonate (PFOS) in the VUV/sulfite system.

PubMed

Gu, Yurong; Liu, Tongzhou; Wang, Hongjie; Han, Huili; Dong, Wenyi

2017-12-31

As one of the most reactive species, hydrated electron (e aq - ) is promising for reductive decomposition of recalcitrant organic pollutants, such as perfluorooctane sulfonate (PFOS). In this study, PFOS decomposition using a vacuum ultraviolet (VUV)/sulfite system was systematically investigated in comparison with sole VUV and ultraviolet (UV)/sulfite systems. A fast and nearly complete (97.3%) PFOS decomposition was observed within 4h from its initial concentration of 37.2μM in the VUV/sulfite system. The observed rate constant (k obs ) for PFOS decomposition in the studied system was 0.87±0.0060h -1 , which was nearly 7.5 and 2 folds faster than that in sole VUV and UV/sulfite systems, respectively. Compared to previously studied UV/sulfite system, VUV/sulfite system enhanced PFOS decomposition in both weak acidic and alkaline pH conditions. In weak acidic condition (pH6.0), PFOS predominantly decomposed via direct VUV photolysis, whereas in alkaline condition (pH>9.0), PFOS decomposition was mainly induced by e aq - generated from both sulfite and VUV photolytic reactions. At a fixed initial solution pH (pH10.0), PFOS decomposition kinetics showed a positive linear dependence with sulfite dosage. The co-presence of humic acid (HA) and NO 3 - obviously suppressed PFOS decomposition, whereas HCO 3 - showed marginal inhibition. A few amount of short chain perfluorocarboxylic acids (PFCAs) were detected in PFOS decomposition process, and a high defluorination efficiency (75.4%) was achieved. These results suggested most fluorine atoms in PFOS molecule ultimately mineralized into fluoride ions, and the mechanisms for PFOS decomposition in the VUV/sulfite system were proposed. Copyright © 2017 Elsevier B.V. All rights reserved.

Potential macro-detritivore range expansion into the subarctic stimulates litter decomposition: a new positive feedback mechanism to climate change?

PubMed

van Geffen, Koert G; Berg, Matty P; Aerts, Rien

2011-12-01

As a result of low decomposition rates, high-latitude ecosystems store large amounts of carbon. Litter decomposition in these ecosystems is constrained by harsh abiotic conditions, but also by the absence of macro-detritivores. We have studied the potential effects of their climate change-driven northward range expansion on the decomposition of two contrasting subarctic litter types. Litter of Alnus incana and Betula pubescens was incubated in microcosms together with monocultures and all possible combinations of three functionally different macro-detritivores (the earthworm Lumbricus rubellus, isopod Oniscus asellus, and millipede Julus scandinavius). Our results show that these macro-detritivores stimulated decomposition, especially of the high-quality A. incana litter and that the macro-detritivores tested differed in their decomposition-stimulating effects, with earthworms having the largest influence. Decomposition processes increased with increasing number of macro-detritivore species, and positive net diveristy effects occurred in several macro-detritivore treatments. However, after correction for macro-detritivore biomass, all interspecific differences in macro-detritivore effects, as well as the positive effects of species number on subarctic litter decomposition disappeared. The net diversity effects also appeared to be driven by variation in biomass, with a possible exception of net diversity effects in mass loss. Based on these results, we conclude that the expected climate change-induced range expansion of macro-detritivores into subarctic regions is likely to result in accelerated decomposition rates. Our results also indicate that the magnitude of macro-detritivore effects on subarctic decomposition will mainly depend on macro-detritivore biomass, rather than on macro-detritivore species number or identity.

Understanding Litter Input Controls on Soil Organic Matter Turnover and Formation are Essential for Improving Carbon-Climate Feedback Predictions for Arctic, Tundra Ecosystems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wallenstein, Matthew

The Arctic region stored vast amounts of carbon (C) in soils over thousands of years because decomposition has been limited by cold, wet conditions. Arctic soils now contain roughly as much C that is contained in all other soils across the globe combined. However, climate warming could unlock this oil C as decomposition accelerates and permafrost thaws. In addition to temperature-driven acceleration of decomposition, several additional processes could either counteract or augment warming-induced SOM losses. For example, increased plant growth under a warmer climate will increase organic matter inputs to soils, which could fuel further soil decomposition by microbes, butmore » will also increase the production of new SOM. Whether Arctic ecosystems store or release carbon in the future depends in part on the balance between these two counteracting processes. By differentiating SOM decomposition and formation and understanding the drivers of these processes, we will better understand how these systems function. We did not find evidence of priming under current conditions, defined as an increase in the decomposition of native SOM stocks. This suggests that decomposition is unlikely to be further accelerated through this mechanism. We did find that decomposition of native SOM did occur when nitrogen was added to these soils, suggesting that nitrogen limits decomposition in these systems. Our results highlight the resilience and extraordinary C storage capacity of these soils, and suggest shrub expansion may partially mitigate C losses from decomposition of old SOM as Arctic soils warm.« less

Infrared spectroscopy of radiation-chemical transformation of n-hexane on a beryllium surface

NASA Astrophysics Data System (ADS)

Gadzhieva, N. N.

2017-07-01

The radiation-chemical decomposition of n-hexane in a Be- n-hexane system under the effect of γ-irradiation at room temperature is studied by infrared reflection-absorption spectroscopy. In the absorbed dose range 5 kGy ≤ Vγ ≤ 50 kGy, intermediate surface products of radiation-heterogeneous decomposition of n-hexane (beryllium alkyls, π-olefin complexes, and beryllium hydrides) are detected. It is shown that complete radiolysis occurs at Vγ = 30 kGy; below this dose, decomposition of n-hexane occurs only partially, while higher doses lead to steady-state saturation. The radiation-chemical yield of the final decomposition product—molecular hydrogen—is determined to be G ads(H2) = 24.8 molecules/100 eV. A possible mechanism of this process is discussed.

Moisture drives surface decomposition in thawing tundra

NASA Astrophysics Data System (ADS)

Hicks Pries, Caitlin E.; Schuur, E. A. G.; Vogel, Jason G.; Natali, Susan M.

2013-07-01

Permafrost thaw can affect decomposition rates by changing environmental conditions and litter quality. As permafrost thaws, soils warm and thermokarst (ground subsidence) features form, causing some areas to become wetter while other areas become drier. We used a common substrate to measure how permafrost thaw affects decomposition rates in the surface soil in a natural permafrost thaw gradient and a warming experiment in Healy, Alaska. Permafrost thaw also changes plant community composition. We decomposed 12 plant litters in a common garden to test how changing plant litter inputs would affect decomposition. We combined species' tissue-specific decomposition rates with species and tissue-level estimates of aboveground net primary productivity to calculate community-weighted decomposition constants at both the thaw gradient and warming experiment. Moisture, specifically growing season precipitation and water table depth, was the most significant driver of decomposition. At the gradient, an increase in growing season precipitation from 200 to 300 mm increased mass loss of the common substrate by 100%. At the warming experiment, a decrease in the depth to the water table from 30 to 15 cm increased mass loss by 100%. At the gradient, community-weighted decomposition was 21% faster in extensive than in minimal thaw, but was similar when moss production was included. Overall, the effect of climate change and permafrost thaw on surface soil decomposition are driven more by precipitation and soil environment than by changes to plant communities. Increasing soil moisture is thereby another mechanism by which permafrost thaw can become a positive feedback to climate change.

Variable diffusion rates during exsolution coarsening in the presence of fluids.

NASA Astrophysics Data System (ADS)

Putnis, Andrew; Prent, Alexander

2017-04-01

The scale of exsolution textures in mineral solid solutions has long been used as an indicator of thermal history during cooling. The theory of spinodal decomposition in an anisotropic solid and subsequent coarsening of exsolution textures as a function of temperature and cooling rate is well developed (see Petrishcheva et al., 2009 and Abart et al., 2009 for a review of the Cahn-Hilliard theory). For the case of exsolution in the alkali feldspar solid solution [(Na,K)AlSi3O8] the characteristic texture shows compositional fluctuations in Na,K with a wavelength that depends on the cooling rate. The cooling rate is determined from knowledge of the Na-K interdiffusion coefficient, assuming that the unmixing is simply due to the interdiffusion of Na and K in an otherwise fixed tetrahedral Al,Si framework. Cryptoperthites and mesoperthites with a periodic lamellar microstructure are considered to be the end-result of such a solid-state exsolution process. Later-stage fluid infiltration results in patch perthites that are formed at a sharp replacement front by a dissolution-precipitation mechanism (Parsons et al., 2015). Patch perthites have an easily recognizable texture and are clear indicators of a reaction with an aqueous solution. The distinction is thus drawn between crypto- and meso-perthite showing periodic lamellae, associated with a solid-state exsolution process, and the patch perthite showing irregular domains of Na-rich and K-rich feldspars associated with a fluid mediated reprecipitation process. However, the presence of fluids can also enhance the coarsening of lamellar exsolution textures, retaining an apparently solid-state microstructure but with a length scale that is dependent on local recrystallization driven by fluid infiltration. Examples will be given from alkali feldspars in granitic rocks where it is clearly demonstrable that cooling rates cannot be inferred from such exsolution textures. The variability in Na,K diffusion rates and thus different length scales of exsolution are likely to be due to the efficiency of diffusional transport through a fluid phase, which is influenced by differences in fluid-induced micro- and nano-porosity. Abart R. et al. (2009) Am. J. Sci. 309, 450-475. Petrishcheva E. and Abart R. (2009) Am. J. Sci, 309, 431-449. Parsons I. et al., (2015) Am. Min. 100, 1277-1303.

Nano-defect management in directed self-assembly of block copolymers (Conference Presentation)

NASA Astrophysics Data System (ADS)

Azuma, Tsukasa; Seino, Yuriko; Sato, Hironobu; Kasahara, Yusuke; Kodera, Katsuyoshi; Jiravanichsakul, Phubes; Hayakawa, Teruaki; Yoshimoto, Kenji; Takenaka, Mikihito

2017-03-01

Directed self-assembly (DSA) of block copolymers (BCPs) has been expected to become one of the most promising next generation lithography candidates for sub-15 nm line patterning and sub-20 nm contact hole patterning. In order to provide the DSA lithography to practical use in advanced semiconductor device manufacturing, defect mitigation in the DSA materials and processes is the primary challenge. We need to clarify the defect generation mechanism using in-situ measurement of self-assembling processes of BCPs in cooperation with modeling approaches to attain the DSA defect mitigation. In this work, we thus employed in-situ atomic force microscope (AFM) and grazing-incidence small angle X-ray scattering (GI-SAXS) and investigated development of surface morphology as well as internal structure during annealing processes. Figure 1 shows series of the AFM images of PMAPOSS-b-PTFEMA films during annealing processes. The images clearly show that vitrified sponge-like structure without long-range order in as-spun film transforms into lamellar structure and that the long range order of the lamellar structure increases with annealing temperature. It is well-known that ordering processes of BCPs from disordered state in bulk progress via nucleation and growth. In contrary to the case of bulk, the observed processes seem to be spinodal decomposition. This is because the structure in as-spun film is not the concentration fluctuation of disordered state but the vitrified sponge-like structure. The annealing processes induce order-order transition from non-equilibrium ordered-state to the lamellar structure. The surface tension assists the transition and directs the orientation. Figure 2 shows scattering patterns of (a) vicinity of film top and (b) whole sample of the GI-SAXS. We can find vertically oriented lamellar structure in the vicinity of film top while horizontally oriented lamellar structures in the vicinity of film bottom, indicating that the GI-SAXS measurement can clarify the variation of the morphologies in depth direction and that the surface tension affects the orientation of the lamellar structure. Finally a combination of the time development data in the in-situ AFM and the GI-SAXS is used to develop a kinetic modeling for prediction of dynamical change in three-dimensional nano-structures. A part of this work was funded by the New Energy and Industrial Technology Development Organization (NEDO) in Japan under the EIDEC project.

Emissions of volatile organic compounds during the decomposition of plant litter

NASA Astrophysics Data System (ADS)

Gray, Christopher M.; Monson, Russell K.; Fierer, Noah

2010-09-01

Volatile organic compounds (VOCs) are emitted during plant litter decomposition, and such VOCs can have wide-ranging impacts on atmospheric chemistry, terrestrial biogeochemistry, and soil ecology. However, we currently have a limited understanding of the relative importance of biotic versus abiotic sources of these VOCs and whether distinct types of litter emit different types and quantities of VOCs during decomposition. We analyzed VOCs emitted by microbes or by abiotic mechanisms during the decomposition of litter from 12 plant species in a laboratory experiment using proton transfer reaction mass spectrometry (PTR-MS). Net emissions from litter with active microbial populations (non-sterile litters) were between 0 and 11 times higher than emissions from sterile controls over a 20-d incubation period, suggesting that abiotic sources of VOCs are generally less important than biotic sources. In all cases, the sterile and non-sterile litter treatments emitted different types of VOCs, with methanol being the dominant VOC emitted from litters during microbial decomposition, accounting for 78 to 99% of the net emissions. We also found that the types of VOCs released during biotic decomposition differed in a predictable manner among litter types with VOC profiles also changing as decomposition progressed over time. These results show the importance of incorporating both the biotic decomposition of litter and the species-dependent differences in terrestrial vegetation into global VOC emission models.

Ecological role of reindeer summer browsing in the mountain birch (Betula pubescens ssp. czerepanovii) forests: effects on plant defense, litter decomposition, and soil nutrient cycling.

PubMed

Stark, Sari; Julkunen-Tiitto, Riitta; Kumpula, Jouko

2007-03-01

Mammalian herbivores commonly alter the concentrations of secondary compounds in plants and, by this mechanism, have indirect effects on litter decomposition and soil carbon and nutrient cycling. In northernmost Fennoscandia, the subarctic mountain birch (Betula pubescens ssp. czerepanovii) forests are important pasture for the semidomestic reindeer (Rangifer tarandus). In the summer ranges, mountain birches are intensively browsed, whereas in the winter ranges, reindeer feed on ground lichens, and the mountain birches remain intact. We analyzed the effect of summer browsing on the concentrations of secondary substances, litter decomposition, and soil nutrient pools in areas that had been separated as summer or winter ranges for at least 20 years, and we predicted that summer browsing may reduce levels of secondary compounds in the mountain birch and, by this mechanism, have an indirect effect on the decomposition of mountain birch leaf litter and soil nutrient cycling. The effect of browsing on the concentration of secondary substances in the mountain birch leaves varied between different years and management districts, but in some cases, the concentration of condensed tannins was lower in the summer than in the winter ranges. In a reciprocal litter decomposition trial, both litter origin and emplacement significantly affected the litter decomposition rate. Decomposition rates were faster for the litter originating from and placed into the summer range. Soil inorganic nitrogen (N) concentrations were higher in the summer than in the winter ranges, which indicates that reindeer summer browsing may enhance the soil nutrient cycling. There was a tight inverse relationship between soil N and foliar tannin concentrations in the winter range but not in the summer range. This suggests that in these strongly nutrient-limited ecosystems, soil N availability regulates the patterns of resource allocation to condensed tannins in the absence but not in the presence of browsing.

Mechanical and Assembly Units of Viral Capsids Identified via Quasi-Rigid Domain Decomposition

PubMed Central

Polles, Guido; Indelicato, Giuliana; Potestio, Raffaello; Cermelli, Paolo; Twarock, Reidun; Micheletti, Cristian

2013-01-01

Key steps in a viral life-cycle, such as self-assembly of a protective protein container or in some cases also subsequent maturation events, are governed by the interplay of physico-chemical mechanisms involving various spatial and temporal scales. These salient aspects of a viral life cycle are hence well described and rationalised from a mesoscopic perspective. Accordingly, various experimental and computational efforts have been directed towards identifying the fundamental building blocks that are instrumental for the mechanical response, or constitute the assembly units, of a few specific viral shells. Motivated by these earlier studies we introduce and apply a general and efficient computational scheme for identifying the stable domains of a given viral capsid. The method is based on elastic network models and quasi-rigid domain decomposition. It is first applied to a heterogeneous set of well-characterized viruses (CCMV, MS2, STNV, STMV) for which the known mechanical or assembly domains are correctly identified. The validated method is next applied to other viral particles such as L-A, Pariacoto and polyoma viruses, whose fundamental functional domains are still unknown or debated and for which we formulate verifiable predictions. The numerical code implementing the domain decomposition strategy is made freely available. PMID:24244139

An investigation on the modelling of kinetics of thermal decomposition of hazardous mercury wastes.

PubMed

Busto, Yailen; M G Tack, Filip; Peralta, Luis M; Cabrera, Xiomara; Arteaga-Pérez, Luis E

2013-09-15

The kinetics of mercury removal from solid wastes generated by chlor-alkali plants were studied. The reaction order and model-free method with an isoconversional approach were used to estimate the kinetic parameters and reaction mechanism that apply to the thermal decomposition of hazardous mercury wastes. As a first approach to the understanding of thermal decomposition for this type of systems (poly-disperse and multi-component), a novel scheme of six reactions was proposed to represent the behaviour of mercury compounds in the solid matrix during the treatment. An integration-optimization algorithm was used in the screening of nine mechanistic models to develop kinetic expressions that best describe the process. The kinetic parameters were calculated by fitting each of these models to the experimental data. It was demonstrated that the D₁-diffusion mechanism appeared to govern the process at 250°C and high residence times, whereas at 450°C a combination of the diffusion mechanism (D₁) and the third order reaction mechanism (F3) fitted the kinetics of the conversions. The developed models can be applied in engineering calculations to dimension the installations and determine the optimal conditions to treat a mercury containing sludge. Copyright © 2013 Elsevier B.V. All rights reserved.

DFT study of hydrogen production from formic acid decomposition on Pd-Au alloy nanoclusters

NASA Astrophysics Data System (ADS)

Liu, D.; Gao, Z. Y.; Wang, X. C.; Zeng, J.; Li, Y. M.

2017-12-01

Recently, it has been reported that the hydrogen production rate of formic acid decomposition can be significantly increased using Pd-Au binary alloy nano-catalysts [Wang et al. J. Mater. Chem. A 1 (2013) 12721-12725]. To explain the reaction mechanism of this alloy catalysis method, formic acid decomposition reactions on pure Pd and Pd-Au alloy nanoclusters are studied via density functional theory simulations. The simulation results indicate that the addition of inert element Au would not influence formic acid decomposition on Pd surface sites of Pd-Au alloy nanoclusters. On the other hand, the existence of Au surface sites brings relative weak hydrogen atom adsorption. On Pd-Au alloy nanoclusters, the dissociated hydrogen atoms from formic acid are easier to combine as hydrogen molecules than that on pure Pd clusters. Via the synergetic effect between Pd and Au, both formic acid decomposition and hydrogen production are events with large probability, which eventually results in high hydrogen production rate.

Kinetics of Thermal Decomposition of Ammonium Perchlorate by TG/DSC-MS-FTIR

NASA Astrophysics Data System (ADS)

Zhu, Yan-Li; Huang, Hao; Ren, Hui; Jiao, Qing-Jie

2014-01-01

The method of thermogravimetry/differential scanning calorimetry-mass spectrometry-Fourier transform infrared (TG/DSC-MS-FTIR) simultaneous analysis has been used to study thermal decomposition of ammonium perchlorate (AP). The processing of nonisothermal data at various heating rates was performed using NETZSCH Thermokinetics. The MS-FTIR spectra showed that N2O and NO2 were the main gaseous products of the thermal decomposition of AP, and there was a competition between the formation reaction of N2O and that of NO2 during the process with an iso-concentration point of N2O and NO2. The dependence of the activation energy calculated by Friedman's iso-conversional method on the degree of conversion indicated that the AP decomposition process can be divided into three stages, which are autocatalytic, low-temperature diffusion and high-temperature, stable-phase reaction. The corresponding kinetic parameters were determined by multivariate nonlinear regression and the mechanism of the AP decomposition process was proposed.

Stabilization of the Thermal Decomposition of Poly(Propylene Carbonate) Through Copper Ion Incorporation and Use in Self-Patterning

NASA Astrophysics Data System (ADS)

Spencer, Todd J.; Chen, Yu-Chun; Saha, Rajarshi; Kohl, Paul A.

2011-06-01

Incorporation of copper ions into poly(propylene carbonate) (PPC) films cast from γ-butyrolactone (GBL), trichloroethylene (TCE) or methylene chloride (MeCl) solutions containing a photo-acid generator is shown to stabilize the PPC from thermal decomposition. Copper ions were introduced into the PPC mixtures by bringing the polymer mixture into contact with copper metal. The metal was oxidized and dissolved into the PPC mixture. The dissolved copper interferes with the decomposition mechanism of PPC, raising its decomposition temperature. Thermogravimetric analysis shows that copper ions make PPC more stable by up to 50°C. Spectroscopic analysis indicates that copper ions may stabilize terminal carboxylic acid groups, inhibiting PPC decomposition. The change in thermal stability based on PPC exposure to patterned copper substrates was used to provide a self-aligned patterning method for PPC on copper traces without the need for an additional photopatterning registration step. Thermal decomposition of PPC is then used to create air isolation regions around the copper traces. The spatial resolution of the self-patterning PPC process is limited by the lateral diffusion of the copper ions within the PPC. The concentration profiles of copper within the PPC, patterning resolution, and temperature effects on the PPC decomposition have been studied.

Traveling waves in a spring-block chain sliding down a slope

NASA Astrophysics Data System (ADS)

Morales, J. E.; James, G.; Tonnelier, A.

2017-07-01

Traveling waves are studied in a spring slider-block model. We explicitly construct front waves (kinks) for a piecewise-linear spinodal friction force. Pulse waves are obtained as the matching of two traveling fronts with identical speeds. Explicit formulas are obtained for the wavespeed and the wave form in the anticontinuum limit. The link with localized waves in a Burridge-Knopoff model of an earthquake fault is briefly discussed.

Traveling waves in a spring-block chain sliding down a slope.

PubMed

Morales, J E; James, G; Tonnelier, A

2017-07-01

Traveling waves are studied in a spring slider-block model. We explicitly construct front waves (kinks) for a piecewise-linear spinodal friction force. Pulse waves are obtained as the matching of two traveling fronts with identical speeds. Explicit formulas are obtained for the wavespeed and the wave form in the anticontinuum limit. The link with localized waves in a Burridge-Knopoff model of an earthquake fault is briefly discussed.

Reaction Mechanisms of Energetic Materials in the Condensed Phase: Long-term Aging, Munition Safety and Condensed-Phase Processes in Propellants and Explosives

DTIC Science & Technology

2009-03-31

Journal of the American Society for Mass Spectrometry, 2002. 13(2): p. 135- 143 . 7. Delcorte, A., P. Bertrand, and B.J. Garrison, Collision cascade and...TNCHP. 49, 50 The presence of the keto group in K6 appears to promote a more direct reaction to the gaseous decomposition products. Decomposition

The relative importance of decomposition and transport mechanisms in accounting for soil organic carbon profiles

NASA Astrophysics Data System (ADS)

Guenet, B.; Eglin, T.; Vasilyeva, N.; Peylin, P.; Ciais, P.; Chenu, C.

2013-04-01

Soil is the major terrestrial reservoir of carbon and a substantial part of this carbon is stored in deep layers, typically deeper than 50 cm below the surface. Several studies underlined the quantitative importance of this deep soil organic carbon (SOC) pool and models are needed to better understand this stock and its evolution under climate and land-uses changes. In this study, we tested and compared three simple theoretical models of vertical transport for SOC against SOC profiles measurements from a long-term bare fallow experiment carried out by the Central-Chernozem State Natural Biosphere Reserve in the Kursk Region of Russia. The transport schemes tested are diffusion, advection and both diffusion and advection. They are coupled to three different formulations of soil carbon decomposition kinetics. The first formulation is a first order kinetics widely used in global SOC decomposition models; the second one, so-called "priming" model, links SOC decomposition rate to the amount of fresh organic matter, representing the substrate interactions. The last one is also a first order kinetics, but SOC is split into two pools. Field data are from a set of three bare fallow plots where soil received no input during the past 20, 26 and 58 yr, respectively. Parameters of the models were optimised using a Bayesian method. The best results are obtained when SOC decomposition is assumed to be controlled by fresh organic matter (i.e., the priming model). In comparison to the first-order kinetic model, the priming model reduces the overestimation in the deep layers. We also observed that the transport scheme that improved the fit with the data depended on the soil carbon mineralisation formulation chosen. When soil carbon decomposition was modelled to depend on the fresh organic matter amount, the transport mechanism which improved best the fit to the SOC profile data was the model representing both advection and diffusion. Interestingly, the older the bare fallow is, the lesser the need for diffusion is, suggesting that stabilised carbon may not be transported within the profile by the same mechanisms than more labile carbon.

Polymethacrylic acid as a new precursor of CuO nanoparticles

NASA Astrophysics Data System (ADS)

Hosny, Nasser Mohammed; Zoromba, Mohamed Shafick

2012-11-01

Polymethacrylic acid and its copper complexes have been synthesized and characterized. These complexes have been used as precursors to produce CuO nanoparticles by thermal decomposition in air. The stages of decompositions and the calcination temperature of the precursors have been determined from thermal analyses (TGA). The obtained CuO nanoparticles have been characterized by X-ray diffraction (XRD), scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). XRD showed a monoclinic structure with particle size 8-20 nm for the synthesized copper oxide nanoparticles. These nanoparticles are catalytically active in decomposing hydrogen peroxide and a mechanism of decomposition has been suggested.

gamma-Irradiation effects on the thermal decomposition behaviour and IR absorption spectra of piperacillin

NASA Astrophysics Data System (ADS)

Mahfouz, R. M.; Gaffar, M. A.; Abu El-Fadl, A.; Hamad, Ar. G. K.

2003-11-01

The thermal decomposition behaviour of unirradiated and pre-gamma-irradiated piperacillin (pipril) as a semi-synthetic penicillin antibiotic has been studied in the temperature range of (273-1072 K). The decomposition was found to proceed through three major steps both for unirradiated and gamma-irradiated samples. Neither appearance nor disappearance of new bands in the IR spectrum of piperacillin was recorded as a result of gamma-irradiation but only a decrease in the intensity of most bands was observed. A degradation mechanism was suggested to explain the bond rupture and the decrease in the intensities of IR bands of gamma-irradiated piperacillin.

On the mechanism of penetration of ovicidal fungi through egg-shells of parasitic nematodes. Decomposition of chitinous and ascaroside layers.

PubMed

Kunert, J

1992-01-01

The decomposition of egg-shells of Ascaris lumbricoides L. was studied microscopically using topochemical methods in a set of 32 strains of soil ovicidal fungi. It was found that even fungi displaying minimal chitinolytic activity in tests on purified chitin in vitro are able to dissolve chitin of egg-shells during the attack on live eggs. Fungi without any chitinolytic activity penetrate probably only the mechanically damaged eggs. None of the studied fungi was capable of degrading enzymatically the glycolipid (ascaroside) layer of the egg-shell which remained intact after digestion of all other components of the egg.

Clathrate hydrates in cometary nuclei and porosity

NASA Technical Reports Server (NTRS)

Smoluchowski, R.

1988-01-01

Possible mechanisms of formation and decomposition of CO2-clathrate hydrate in cometary nuclei are discussed. As far as it is known, this is the only clathrate hydrate which is unstable at low temperatures. Calculation shows that, in accord with other evidence, neither volume nor grain boundary diffusion in the clathrate lattice can be responsible for the rate of these reactions and that a surface mechanism with the attendant sensitivity to pressure must play a crucial role. Density changes accompanying CO2-clathrate decomposition and formation can lead to microporosity and enhanced brittleness or even to fracture of cometary nuclei at low temperatures. Other clathrate hydrates and mixed clathrates are also discussed.

Functionally dissimilar neighbors accelerate litter decomposition in two grass species.

PubMed

Barbe, Lou; Jung, Vincent; Prinzing, Andreas; Bittebiere, Anne-Kristel; Butenschoen, Olaf; Mony, Cendrine

2017-05-01

Plant litter decomposition is a key regulator of nutrient recycling. In a given environment, decomposition of litter from a focal species depends on its litter quality and on the efficiency of local decomposers. Both may be strongly modified by functional traits of neighboring species, but the consequences for decomposition of litter from the focal species remain unknown. We tested whether decomposition of a focal plant's litter is influenced by the functional-trait dissimilarity to the neighboring plants. We cultivated two grass species (Brachypodium pinnatum and Elytrigia repens) in experimental mesocosms with functionally similar and dissimilar neighborhoods, and reciprocally transplanted litter. For both species, litter quality increased in functionally dissimilar neighborhoods, partly as a result of changes in functional traits involved in plant-plant interactions. Furthermore, functional dissimilarity increased overall decomposer efficiency in one species, probably via complementarity effects. Our results suggest a novel mechanism of biodiversity effects on ecosystem functioning in grasslands: interspecific functional diversity within plant communities can enhance intraspecific contributions to litter decomposition. Thus, plant species might better perform in diverse communities by benefiting from higher remineralization rates of their own litter. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Fungal community structure of fallen pine and oak wood at different stages of decomposition in the Qinling Mountains, China.

PubMed

Yuan, Jie; Zheng, Xiaofeng; Cheng, Fei; Zhu, Xian; Hou, Lin; Li, Jingxia; Zhang, Shuoxin

2017-10-24

Historically, intense forest hazards have resulted in an increase in the quantity of fallen wood in the Qinling Mountains. Fallen wood has a decisive influence on the nutrient cycling, carbon budget and ecosystem biodiversity of forests, and fungi are essential for the decomposition of fallen wood. Moreover, decaying dead wood alters fungal communities. The development of high-throughput sequencing methods has facilitated the ongoing investigation of relevant molecular forest ecosystems with a focus on fungal communities. In this study, fallen wood and its associated fungal communities were compared at different stages of decomposition to evaluate relative species abundance and species diversity. The physical and chemical factors that alter fungal communities were also compared by performing correspondence analysis according to host tree species across all stages of decomposition. Tree species were the major source of differences in fungal community diversity at all decomposition stages, and fungal communities achieved the highest levels of diversity at the intermediate and late decomposition stages. Interactions between various physical and chemical factors and fungal communities shared the same regulatory mechanisms, and there was no tree species-specific influence. Improving our knowledge of wood-inhabiting fungal communities is crucial for forest ecosystem conservation.

Bulk Diffusion via a ``kick-out'' method for Lithium in the decomposition reaction LiAlH4/Li3AlH6

NASA Astrophysics Data System (ADS)

Rolih, Biljana; Ozolins, Vidvuds; Ozolins Team

2013-03-01

In the pursuit to find a practical system for hydrogen storage, complex metal hydrides have long been considered as viable candidates due to their high hydrogen content. However, some of the challenges faced with these types of systems are poor thermodynamics or kinetics. The underlying mechanisms, and their limiting processes, for the decomposition of these materials need to be understood. From experimental work on the decomposition of hydrogen storage materials, it has been suggested that bulk diffusion of metal species is the bottleneck for hydrogen release. In this work is the dehydrogenation we investigated the system LiAlH4  LiAlH6 with favorable hydrogen release (5.3 wt %), at moderate temperatures. Using first-principles density functional theory we found the defects facilitating mass transport by calculating individual formation energies, highest concentrations, and activation barriers for defect mobility. The mass transport of Lithium is found to be mediated by a ``kick-out'' mechanism. The results are used to further our understanding of the fundamental mechanism of mass transport and evaluate the possibility of kinetics as the limiting process in this reaction.

Study of thermal decomposition mechanisms and low-level detection of explosives using pulsed photoacoustic technique

NASA Astrophysics Data System (ADS)

Yehya, F.; Chaudhary, A. K.; Srinivas, D.; Muralidharan, K.

2015-11-01

We report a novel time-resolved photoacoustic-based technique for studying the thermal decomposition mechanisms of some secondary explosives such as RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), picric acid, 4,6-dinitro-5-(4-nitro-1 H-imidazol-1-yl)-1 H-benzo[ d] [1-3] triazole, and 5-chloro-1-(4-nitrophenyl)-1 H-tetrazole. A comparison of the thermal decomposition mechanisms of these secondary explosives was made by detecting NO2 molecules released under controlled pyrolysis between 25 and 350 °C. The results show excellent agreement with the thermogravimetric and differential thermal analysis (TGA-DTA) results. A specially designed PA cell made of stainless steel was filled with explosive vapor and pumped using second harmonic, i.e., λ = 532 nm, pulses of duration 7 ns at a 10 Hz repetition rate, obtained using a Q-switched Nd:YAG laser. The use of a combination of PA and TGA-DTA techniques enables the study of NO2 generation, and this method can be used to scale the performance of these explosives as rocket fuels. The minimum detection limits of the four explosives were 38 ppmv to 69 ppbv, depending on their respective vapor pressures.

On formation mechanism of Pd-Ir bimetallic nanoparticles through thermal decomposition of [Pd(NH3)4][IrCl6

NASA Astrophysics Data System (ADS)

Asanova, Tatyana I.; Asanov, Igor P.; Kim, Min-Gyu; Gerasimov, Evgeny Yu.; Zadesenets, Andrey V.; Plyusnin, Pavel E.; Korenev, Sergey V.

2013-10-01

The formation mechanism of Pd-Ir nanoparticles during thermal decomposition of double complex salt [Pd(NH3)4][IrCl6] has been studied by in situ X-ray absorption (XAFS) and photoelectron (XPS) spectroscopies. The changes in the structure of the Pd and Ir closest to the surroundings and chemical states of Pd, Ir, Cl, and N atoms were traced in the range from room temperature to 420 °C in inert atmosphere. It was established that the thermal decomposition process is carried out in 5 steps. The Pd-Ir nanoparticles are formed in pyramidal/rounded Pd-rich (10-200 nm) and dendrite Ir-rich (10-50 nm) solid solutions. A d charge depletion at Ir site and a gain at Pd, as well as the intra-atomic charge redistribution between the outer d and s and p electrons of both Ir and Pd in Pd-Ir nanoparticles, were found to occur.

Solid solutions of platinum(II) and palladium(II) oxalato-complex salt as precursors of nanoalloys

NASA Astrophysics Data System (ADS)

Zadesenets, A. V.; Asanova, T. I.; Vikulova, E. S.; Filatov, E. Yu.; Plyusnin, P. E.; Baidina, I. A.; Asanov, I. P.; Korenev, S. V.

2013-03-01

A solid solution of platinum (II) and palladium (II) oxalato-complex salt, (NH4)2[Pt0.5Pd0.5(C2O4)2]·2H2O, has been synthesized and studied as a precursor for preparing bimetallic PtPd nanoparticles through its thermal decomposition. The smallest homogenous bimetallic PtPd nanoparticles were found to form in hydrogen and helium atmospheres. The annealing temperature and time have low effect on the bimetallic particles size. Comparative analysis of structural and thermal properties of the solid solution and individual Pt, Pd oxalato-complex salts was performed to investigate a mechanism of thermal decomposition of (NH4)2[Pt0.5Pd0.5(C2O4)2]·2H2O. Based on in situ X-ray photoemission spectroscopy investigation it was proposed a mechanism of formation of bimetallic PtPd nanoparticles from the solid-solution oxalato-complex salt during thermal decomposition.

Decomposition mechanisms and kinetics of novel energetic molecules BNFF-1 and ANFF-1: quantum-chemical modeling.

PubMed

Tsyshevsky, Roman V; Kuklja, Maija M

2013-07-18

Decomposition mechanisms, activation barriers, Arrhenius parameters, and reaction kinetics of the novel explosive compounds, 3,4-bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole (BNFF-1), and 3-(4-amino-1,2,5-oxadiazol-3-yl)-4-(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole (ANFF-1) were explored by means of density functional theory with a range of functionals combined with variational transition state theory. BNFF-1 and ANFF-1 were recently suggested to be good candidates for insensitive high energy density materials. Our modeling reveals that the decomposition initiation in both BNFF-1 and ANFF-1 molecules is triggered by ring cleavage reactions while the further process is defined by a competition between two major pathways, the fast C-NO₂ homolysis and slow nitro-nitrite isomerization releasing NO. We discuss insights on design of new energetic materials with targeted properties gained from our modeling.

First-principles study on the initial decomposition process of CH3NH3PbI3

NASA Astrophysics Data System (ADS)

Xue, Yuanbin; Shan, Yueyue; Xu, Hu

2017-09-01

Hybrid perovskites are promising materials for high-performance photovoltaics. Unfortunately, hybrid perovskites readily decompose in particular under humid conditions, and the mechanisms of this phenomenon have not yet been fully understood. In this work, we systematically studied the possible mechanisms and the structural properties during the initial decomposition process of MAPbI3 (MA = CH3NH3+) using first-principles calculations. The theoretical results show that it is energetically favorable for PbI2 to nucleate and crystalize from the MAPbI3 matrix ahead of other decomposition products. Additionally, the structural instability is an intrinsic property of MAPbI3, regardless of whether the system is exposed to humidity. We find that H2O could facilitate the desorption of gaseous components, acting as a catalyst to transfer the H+ ion. These results provide insight into the cause of the instability of MAPbI3 and may improve our understanding of the properties of hybrid perovskites.

A Light-Induced Reaction with Oxygen Leads to Chromophore Decomposition and Irreversible Photobleaching in GFP-Type Proteins.

PubMed

Grigorenko, Bella L; Nemukhin, Alexander V; Polyakov, Igor V; Khrenova, Maria G; Krylov, Anna I

2015-04-30

Photobleaching and photostability of proteins of the green fluorescent protein (GFP) family are crucially important for practical applications of these widely used biomarkers. On the basis of simulations, we propose a mechanism for irreversible bleaching in GFP-type proteins under intense light illumination. The key feature of the mechanism is a photoinduced reaction of the chromophore with molecular oxygen (O2) inside the protein barrel leading to the chromophore's decomposition. Using quantum mechanics/molecular mechanics (QM/MM) modeling we show that a model system comprising the protein-bound Chro(-) and O2 can be excited to an electronic state of the intermolecular charge-transfer (CT) character (Chro(•)···O2(-•)). Once in the CT state, the system undergoes a series of chemical reactions with low activation barriers resulting in the cleavage of the bridging bond between the phenolic and imidazolinone rings and disintegration of the chromophore.

Leaf Litter Mixtures Alter Microbial Community Development: Mechanisms for Non-Additive Effects in Litter Decomposition

PubMed Central

Chapman, Samantha K.; Newman, Gregory S.; Hart, Stephen C.; Schweitzer, Jennifer A.; Koch, George W.

2013-01-01

To what extent microbial community composition can explain variability in ecosystem processes remains an open question in ecology. Microbial decomposer communities can change during litter decomposition due to biotic interactions and shifting substrate availability. Though relative abundance of decomposers may change due to mixing leaf litter, linking these shifts to the non-additive patterns often recorded in mixed species litter decomposition rates has been elusive, and links community composition to ecosystem function. We extracted phospholipid fatty acids (PLFAs) from single species and mixed species leaf litterbags after 10 and 27 months of decomposition in a mixed conifer forest. Total PLFA concentrations were 70% higher on litter mixtures than single litter types after 10 months, but were only 20% higher after 27 months. Similarly, fungal-to-bacterial ratios differed between mixed and single litter types after 10 months of decomposition, but equalized over time. Microbial community composition, as indicated by principal components analyses, differed due to both litter mixing and stage of litter decomposition. PLFA biomarkers a15∶0 and cy17∶0, which indicate gram-positive and gram-negative bacteria respectively, in particular drove these shifts. Total PLFA correlated significantly with single litter mass loss early in decomposition but not at later stages. We conclude that litter mixing alters microbial community development, which can contribute to synergisms in litter decomposition. These findings advance our understanding of how changing forest biodiversity can alter microbial communities and the ecosystem processes they mediate. PMID:23658639

Soil organic matter decomposition follows plant productivity response to sea-level rise

NASA Astrophysics Data System (ADS)

Mueller, Peter; Jensen, Kai; Megonigal, James Patrick

2015-04-01

The accumulation of soil organic matter (SOM) is an important mechanism for many tidal wetlands to keep pace with sea-level rise. SOM accumulation is governed by the rates of production and decomposition of organic matter. While plant productivity responses to sea-level rise are well understood, far less is known about the response of SOM decomposition to accelerated sea-level rise. Here we quantified the effects of sea-level rise on SOM decomposition by exposing planted and unplanted tidal marsh monoliths to experimentally manipulated flood duration. The study was performed in a field-based mesocosm facility at the Smithsonian Global Change Research Wetland, a micro tidal brackish marsh in Maryland, US. SOM decomposition was quantified as CO2 efflux, with plant- and SOM-derived CO2 separated using a stable carbon isotope approach. Despite the dogma that decomposition rates are inversely related to flooding, SOM mineralization was not sensitive to varying flood duration over a 35 cm range in surface elevation in unplanted mesocoms. In the presence of plants, decomposition rates were strongly and positively related to aboveground biomass (p≤0.01, R2≥0.59). We conclude that rates of soil carbon loss through decomposition are driven by plant responses to sea level in this intensively studied tidal marsh. If our result applies more generally to tidal wetlands, it has important implications for modeling carbon sequestration and marsh accretion in response to accelerated sea-level rise.

Characteristic of root decomposition in a tropical rainforest in Sarawak, Malaysi

NASA Astrophysics Data System (ADS)

Ohashi, Mizue; Makita, Naoki; Katayam, Ayumi; Kume, Tomonori; Matsumoto, Kazuho; Khoon Kho, L.

2016-04-01

Woody roots play a significant role in forest carbon cycling, as up to 60 percent of tree photosynthetic production can be allocated to belowground. Root decay is one of the main processes of soil C dynamics and potentially relates to soil C sequestration. However, much less attention has been paid for root litter decomposition compared to the studies of leaf litter because roots are hidden from view. Previous studies have revealed that physico-chemical quality of roots, climate, and soil organisms affect root decomposition significantly. However, patterns and mechanisms of root decomposition are still poorly understood because of the high variability of root properties, field environment and potential decomposers. For example, root size would be a factor controlling decomposition rates, but general understanding of the difference between coarse and fine root decompositions is still lacking. Also, it is known that root decomposition is performed by soil animals, fungi and bacteria, but their relative importance is poorly understood. In this study, therefore, we aimed to characterize the root decomposition in a tropical rainforest in Sarawak, Malaysia, and clarify the impact of soil living organisms and root sizes on root litter decomposition. We buried soil cores with fine and coarse root litter bags in soil in Lambir Hills National Park. Three different types of soil cores that are covered by 1.5 cm plastic mesh, root-impermeable sheet (50um) and fungi-impermeable sheet (1um) were prepared. The soil cores were buried in February 2013 and collected 4 times, 134 days, 226 days, 786 days and 1151 days after the installation. We found that nearly 80 percent of the coarse root litter was decomposed after two years, whereas only 60 percent of the fine root litter was decomposed. Our results also showed significantly different ratio of decomposition between different cores, suggesting the different contribution of soil living organisms to decomposition process.

Methanol Oxidation on Pt3Sn(111) for Direct Methanol Fuel Cells: Methanol Decomposition.

PubMed

Lu, Xiaoqing; Deng, Zhigang; Guo, Chen; Wang, Weili; Wei, Shuxian; Ng, Siu-Pang; Chen, Xiangfeng; Ding, Ning; Guo, Wenyue; Wu, Chi-Man Lawrence

2016-05-18

PtSn alloy, which is a potential material for use in direct methanol fuel cells, can efficiently promote methanol oxidation and alleviate the CO poisoning problem. Herein, methanol decomposition on Pt3Sn(111) was systematically investigated using periodic density functional theory and microkinetic modeling. The geometries and energies of all of the involved species were analyzed, and the decomposition network was mapped out to elaborate the reaction mechanisms. Our results indicated that methanol and formaldehyde were weakly adsorbed, and the other derivatives (CHxOHy, x = 1-3, y = 0-1) were strongly adsorbed and preferred decomposition rather than desorption on Pt3Sn(111). The competitive methanol decomposition started with the initial O-H bond scission followed by successive C-H bond scissions, (i.e., CH3OH → CH3O → CH2O → CHO → CO). The Brønsted-Evans-Polanyi relations and energy barrier decomposition analyses identified the C-H and O-H bond scissions as being more competitive than the C-O bond scission. Microkinetic modeling confirmed that the vast majority of the intermediates and products from methanol decomposition would escape from the Pt3Sn(111) surface at a relatively low temperature, and the coverage of the CO residue decreased with an increase in the temperature and decrease in partial methanol pressure.

Catalytic Decomposition of Hydroxylammonium Nitrate Ionic Liquid: Enhancement of NO Formation.

PubMed

Chambreau, Steven D; Popolan-Vaida, Denisia M; Vaghjiani, Ghanshyam L; Leone, Stephen R

2017-05-18

Hydroxylammonium nitrate (HAN) is a promising candidate to replace highly toxic hydrazine in monopropellant thruster space applications. The reactivity of HAN aerosols on heated copper and iridium targets was investigated using tunable vacuum ultraviolet photoionization time-of-flight aerosol mass spectrometry. The reaction products were identified by their mass-to-charge ratios and their ionization energies. Products include NH 3 , H 2 O, NO, hydroxylamine (HA), HNO 3 , and a small amount of NO 2 at high temperature. No N 2 O was detected under these experimental conditions, despite the fact that N 2 O is one of the expected products according to the generally accepted thermal decomposition mechanism of HAN. Upon introduction of iridium catalyst, a significant enhancement of the NO/HA ratio was observed. This observation indicates that the formation of NO via decomposition of HA is an important pathway in the catalytic decomposition of HAN.

Activation energy and energy density: a bioenergetic framework for assessing soil organic matter stability

NASA Astrophysics Data System (ADS)

Williams, E. K.; Plante, A. F.

2017-12-01

The stability and cycling of natural organic matter depends on the input of energy needed to decompose it and the net energy gained from its decomposition. In soils, this relationship is complicated by microbial enzymatic activity which decreases the activation energies associated with soil organic matter (SOM) decomposition and by chemical and physical protection mechanisms which decreases the concentrations of the available organic matter substrate and also require additional energies to overcome for decomposition. In this study, we utilize differential scanning calorimetry and evolved CO2 gas analysis to characterize differences in the energetics (activation energy and energy density) in soils that have undergone degradation in natural (bare fallow), field (changes in land-use), chemical (acid hydrolysis), and laboratory (high temperature incubation) experimental conditions. We will present this data in a novel conceptual framework relating these energy dynamics to organic matter inputs, decomposition, and molecular complexity.

Kinetics of non-isothermal decomposition of cinnamic acid

NASA Astrophysics Data System (ADS)

Zhao, Ming-rui; Qi, Zhen-li; Chen, Fei-xiong; Yue, Xia-xin

2014-07-01

The thermal stability and kinetics of decomposition of cinnamic acid were investigated by thermogravimetry and differential scanning calorimetry at four heating rates. The activation energies of this process were calculated from analysis of TG curves by methods of Flynn-Wall-Ozawa, Doyle, Distributed Activation Energy Model, Šatava-Šesták and Kissinger, respectively. There are only one stage of thermal decomposition process in TG and two endothermic peaks in DSC. For this decomposition process of cinnamic acid, E and log A[s-1] were determined to be 81.74 kJ mol-1 and 8.67, respectively. The mechanism was Mampel Power law (the reaction order, n = 1), with integral form G(α) = α (α = 0.1-0.9). Moreover, thermodynamic properties of Δ H ≠, Δ S ≠, Δ G ≠ were 77.96 kJ mol-1, -90.71 J mol-1 K-1, 119.41 kJ mol-1.

Automatic network coupling analysis for dynamical systems based on detailed kinetic models.

PubMed

Lebiedz, Dirk; Kammerer, Julia; Brandt-Pollmann, Ulrich

2005-10-01

We introduce a numerical complexity reduction method for the automatic identification and analysis of dynamic network decompositions in (bio)chemical kinetics based on error-controlled computation of a minimal model dimension represented by the number of (locally) active dynamical modes. Our algorithm exploits a generalized sensitivity analysis along state trajectories and subsequent singular value decomposition of sensitivity matrices for the identification of these dominant dynamical modes. It allows for a dynamic coupling analysis of (bio)chemical species in kinetic models that can be exploited for the piecewise computation of a minimal model on small time intervals and offers valuable functional insight into highly nonlinear reaction mechanisms and network dynamics. We present results for the identification of network decompositions in a simple oscillatory chemical reaction, time scale separation based model reduction in a Michaelis-Menten enzyme system and network decomposition of a detailed model for the oscillatory peroxidase-oxidase enzyme system.

Formation and decomposition of ethane, propane, and carbon dioxide hydrates in silica gel mesopores under high pressure.

PubMed

Aladko, E Ya; Dyadin, Yu A; Fenelonov, V B; Larionov, E G; Manakov, A Yu; Mel'gunov, M S; Zhurko, F V

2006-10-05

The experimental data on decomposition temperatures for the gas hydrates of ethane, propane, and carbon dioxide dispersed in silica gel mesopores are reported. The studies were performed at pressures up to 1 GPa. It is shown that the experimental dependence of hydrate decomposition temperature on the size of pores that limit the size of hydrate particles can be described on the basis of the Gibbs-Thomson equation only if one takes into account changes in the shape coefficient that is present in the equation; in turn, the value of this coefficient depends on a method of mesopore size determination. A mechanism of hydrate formation in mesoporous medium is proposed. Experimental data providing evidence of the possibility of the formation of hydrate compounds in hydrophobic matrixes under high pressure are reported. Decomposition temperature of those hydrate compounds is higher than that for the bulk hydrates of the corresponding gases.

Stream ecosystem integrity is impaired by logging and shifting agriculture in a global megadiversity center (Sarawak, Borneo).

PubMed

Jinggut, Tajang; Yule, Catherine M; Boyero, Luz

2012-10-15

In common with most of Borneo, the Bakun region of Sarawak is currently subject to heavy deforestation mainly due to logging and, to a lesser extent, traditional slash-and-burn farming practices. This has the potential to affect stream ecosystems, which are integrators of environmental change in the surrounding terrestrial landscape. This study evaluated the effects of both types of deforestation by using functional and structural indicators (leaf litter decomposition rates and associated detritivores or 'shredders', respectively) to compare a fundamental ecosystem process, leaf litter decomposition, within logged, farmed and pristine streams. Slash-and-burn agricultural practices increased the overall rate of decomposition despite a decrease in shredder species richness (but not shredder abundance) due to increased microbial decomposition. In contrast, decomposition by microbes and invertebrates was slowed down in the logged streams, where shredders were less abundant and less species rich. This study suggests that shredder communities are less affected by traditional agricultural farming practices, while modern mechanized deforestation has an adverse effect on both shredder communities and leaf breakdown. Copyright © 2012 Elsevier B.V. All rights reserved.

Study on Kinetic Mechanism of Bastnaesite Concentrates Decomposition Using Calcium Hydroxide

NASA Astrophysics Data System (ADS)

Cen, Peng; Wu, Wenyuan; Bian, Xue

2018-06-01

The thermal decomposition of bastnaesite concentrates using calcium hydroxide was studied. Calcium hydroxide can effectively inhibit the emission of fluorine during roasting by transforming it to calcium fluoride. The decomposition rate increased with increasing reaction temperature and amount of calcium hydroxide. The decomposition kinetics were investigated. The decomposition reaction was determined to be a heterogeneous gas-solid reaction, and it followed an unreacted shrinking core model. By means of the integrated rate equation method, the reaction was proven to be kinetically first order. Different reaction models were fit to the experimental data to determine the reaction control process. The chemical reaction at the phase interface controlled the reaction rate in the temperatures ranging from 673 K to 773 K (400 °C to 500 °C) with an apparent activation energy of 82.044 kJ·mol-1. From 773 K to 973 K (500 °C to 700 °C), diffusion through the solid product's layer became the determining step, with a lower activation energy of 15.841 kJ·mol-1.

Controllable pneumatic generator based on the catalytic decomposition of hydrogen peroxide

NASA Astrophysics Data System (ADS)

Kim, Kyung-Rok; Kim, Kyung-Soo; Kim, Soohyun

2014-07-01

This paper presents a novel compact and controllable pneumatic generator that uses hydrogen peroxide decomposition. A fuel micro-injector using a piston-pump mechanism is devised and tested to control the chemical decomposition rate. By controlling the injection rate, the feedback controller maintains the pressure of the gas reservoir at a desired pressure level. Thermodynamic analysis and experiments are performed to demonstrate the feasibility of the proposed pneumatic generator. Using a prototype of the pneumatic generator, it takes 6 s to reach 3.5 bars with a reservoir volume of 200 ml at the room temperature, which is sufficiently rapid and effective to maintain the repetitive lifting of a 1 kg mass.

Controllable pneumatic generator based on the catalytic decomposition of hydrogen peroxide.

PubMed

Kim, Kyung-Rok; Kim, Kyung-Soo; Kim, Soohyun

2014-07-01

This paper presents a novel compact and controllable pneumatic generator that uses hydrogen peroxide decomposition. A fuel micro-injector using a piston-pump mechanism is devised and tested to control the chemical decomposition rate. By controlling the injection rate, the feedback controller maintains the pressure of the gas reservoir at a desired pressure level. Thermodynamic analysis and experiments are performed to demonstrate the feasibility of the proposed pneumatic generator. Using a prototype of the pneumatic generator, it takes 6 s to reach 3.5 bars with a reservoir volume of 200 ml at the room temperature, which is sufficiently rapid and effective to maintain the repetitive lifting of a 1 kg mass.

Plasma-catalyst hybrid reactor with CeO2/γ-Al2O3 for benzene decomposition with synergetic effect and nano particle by-product reduction.

PubMed

Mao, Lingai; Chen, Zhizong; Wu, Xinyue; Tang, Xiujuan; Yao, Shuiliang; Zhang, Xuming; Jiang, Boqiong; Han, Jingyi; Wu, Zuliang; Lu, Hao; Nozaki, Tomohiro

2018-04-05

A dielectric barrier discharge (DBD) catalyst hybrid reactor with CeO 2 /γ-Al 2 O 3 catalyst balls was investigated for benzene decomposition at atmospheric pressure and 30 °C. At an energy density of 37-40 J/L, benzene decomposition was as high as 92.5% when using the hybrid reactor with 5.0wt%CeO 2 /γ-Al 2 O 3 ; while it was 10%-20% when using a normal DBD reactor without a catalyst. Benzene decomposition using the hybrid reactor was almost the same as that using an O 3 catalyst reactor with the same CeO 2 /γ-Al 2 O 3 catalyst, indicating that O 3 plays a key role in the benzene decomposition. Fourier transform infrared spectroscopy analysis showed that O 3 adsorption on CeO 2 /γ-Al 2 O 3 promotes the production of adsorbed O 2 - and O 2 2‒ , which contribute benzene decomposition over heterogeneous catalysts. Nano particles as by-products (phenol and 1,4-benzoquinone) from benzene decomposition can be significantly reduced using the CeO 2 /γ-Al 2 O 3 catalyst. H 2 O inhibits benzene decomposition; however, it improves CO 2 selectivity. The deactivated CeO 2 /γ-Al 2 O 3 catalyst can be regenerated by performing discharges at 100 °C and 192-204 J/L. The decomposition mechanism of benzene over CeO 2 /γ-Al 2 O 3 catalyst was proposed. Copyright © 2017 Elsevier B.V. All rights reserved.

Mass-Spectrometric Studies of Catalytic Chemical Vapor Deposition Processes of Organic Silicon Compounds Containing Nitrogen

NASA Astrophysics Data System (ADS)

Morimoto, Takashi; Ansari, S. G.; Yoneyama, Koji; Nakajima, Teppei; Masuda, Atsushi; Matsumura, Hideki; Nakamura, Megumi; Umemoto, Hironobu

2006-02-01

The mechanism of catalytic chemical vapor deposition (Cat-CVD) processes for hexamethyldisilazane (HMDS) and trisdimethylaminosilane (TDMAS), which are used as source gases to prepare SiNx or SiCxNy films, was studied using three different mass spectrometric techniques: ionization by Li+ ion attachment, vacuum-ultraviolet radiation and electron impact. The results for HMDS show that Si-N bonds dissociate selectively, although Si-C bonds are weaker, and (CH3)3SiNH should be one of the main precursors of deposited films. This decomposition mechanism did not change when NH3 was introduced, but the decomposition efficiency was slightly increased. Similar results were obtained for TDMAS.

Short-term Dynamics of Photopriming Increase Carbon Loss During Litter Decomposition

NASA Astrophysics Data System (ADS)

Lin, Y.; King, J. Y.; Karlen, S. D.; Ralph, J.

2017-12-01

Solar radiation plays a key role in carbon (C) cycling by increasing the decomposition rates of plant litter through photodegradation. This process is particularly important in drylands where solar radiation is high and microbial activity may be limited by water availability. One mechanism of photodegradation may be the facilitation of microbial decomposition of litter by altering litter chemistry and consequently degradability, termed photopriming. However, it remains unclear to what extent photopriming contributes to litter decomposition. We evaluated photopriming by ultraviolet (UV) radiation through two laboratory experiments. In one experiment, we found that four months of UV exposure increased mass loss by 3-4% compared to dark treatment in two of three litter species commonly found in California oak savanna; however, UV exposure did not alter litter degradability as measured by microbial respiration in an incubation study. UV exposure had limited effects on lignin and other cell wall structures, but one month of microbial decomposition in the dark significantly reduced lignin β-aryl ether inter-unit linkages and acetylated xylans, which interestingly was the same pattern seen in litter exposed to UV radiation under field conditions and may account for the significant effects of UV exposure on litter mass loss observed in situ. These results indicate that microbial decomposition, not abiotic photodegradation, was ultimately responsible for changes in litter chemistry observed in the field. In a separate experiment, litter of a common grass was incubated for 128 days under either alternating UV radiation and dark conditions at two-day intervals or continuous darkness. During the second half of the experiment, alternating UV exposure increased CO2 production by 35% compared to continuous darkness, suggesting that UV exposure induces subtle but important changes in litter chemistry that facilitate microbial decomposition on a temporal scale of days. Together the results point to microbial facilitation as the primary mechanism of photodegradation and suggest that photopriming is governed by short-term dynamics at the litter-microbe interface. The C cycling associated with these short-term dynamics may be especially sensitive to anticipated increases in drought conditions in drylands.

Energy & Energetics

DTIC Science & Technology

2012-06-22

mechanical and structural failure and decomposition in ultra-fast time regimes. Our research teams are exploring novel ways to convert mechanical ...energy to thermal energy by examining initiation mechanisms , multi-phase combustion, detonation and the mechanisms that lead to the release of energy...understanding of the mechanisms of structural stability by doping Fe in LiCoPO4 and effectiveness of HFiP in stopping further oxidation of electrolytes are

Research@ARL: Energy & Energetics

DTIC Science & Technology

2012-06-01

enabling us to probe chemical, mechanical and structural failure and decomposition in ultra-fast time regimes. Our research teams are exploring novel ways...to convert mechanical energy to thermal energy by examining initiation mechanisms , multi-phase combustion, detonation and the mechanisms that lead...storage life. The understanding of the mechanisms of structural stability by doping Fe in LiCoPO4 and effectiveness of HFiP in stopping further

Study on the decomposition of trace benzene over V2O5-WO3 ...

EPA Pesticide Factsheets

Commercial and laboratory-prepared V2O5–WO3/TiO2-based catalysts with different compositions were tested for catalytic decomposition of chlorobenzene （ClBz） in simulated flue gas. Resonance enhanced multiphoton ionization-time of flight mass spectrometry (REMPI-TOFMS) was employed to measure real-time, trace concentrations of ClBz contained in the flue gas before and after the catalyst. The effects of various parameters, including vanadium content of the catalyst, the catalyst support, as well as the reaction temperature on decomposition of ClBz were investigated. The results showed that the ClBz decomposition efficiency was significantly enhanced when nano-TiO2 instead of conventional TiO2 was used as the catalyst support. No promotion effects were found in the ClBz decomposition process when the catalysts were wet-impregnated with CuO and CeO2. Tests with different concentrations (1,000, 500, and 100 ppb) of ClBz showed that ClBz-decomposition efficiency decreased with increasing concentration, unless active sites were plentiful. A comparison between ClBz and benzene decomposition on the V2O5–WO3/TiO2-based catalyst and the relative kinetics analysis showed that two different active sites were likely involved in the decomposition mechanism and the V=O and V-O-Ti groups may only work for the degradation of the phenyl group and the benzene ring rather than the C-Cl bond. V2O5-WO3/TiO2 based catalysts, that have been used for destruction of a wide variet

Dry-season ultraviolet radiation primes litter for wet season decomposition in a Mediterranean grassland

NASA Astrophysics Data System (ADS)

Baker, N. R.; Allison, S. D.

2013-12-01

Traditional decomposition models developed in mesic ecosystems often consistently underestimate rates of decomposition in more arid ecosystems such as deserts and Mediterranean grasslands. Photodegradation of plant litter by ultraviolet radiation (UV) is hypothesized to be one of the mechanisms accounting for the greater-than-expected rates of decomposition observed in these ecosystems. Putatively, photodegradation preferentially degrades complex aromatic compounds in litter such as lignin, whose decomposition is considered a rate-limiting step in the microbial decomposition of plant litter. This study tested the effects of attenuated ultraviolet radiation on the decomposition of two litter types over the course of a year in a Southern California Mediterranean grassland. The two types of litter differed primarily in lignin content to test for a differential effect of UV on high-lignin versus low-lignin litter. Rates of litter mass loss, changes in litter chemistry, and changes in microbial activity and microbial biomass were observed, and assays of extracellular enzymes were conducted at 5 points through the year, beginning during the dry season and continuing until the end of the following dry season. Litter exposed to attenuated ultraviolet radiation during the dry season had lower rates of mass loss than litter exposed to ambient radiation (6.1% vs. 8.6%, respectively, p < 0.04). Extracellular enzyme activities were significantly affected by UV attenuation, as low lignin samples exposed to attenuated UV displayed elevated cellulase enzyme activity potential during the wet season, while high lignin samples displayed decreased oxidative enzyme activity potential during the wet season. For example, potential activity of the cellulase cellobiohydrolase in low-lignin, ambient UV samples was 5286 μmol/hr*g during the wet season, compared to 7969 μmol/hr*g in attenuated UV samples (p < 0.003). Conversely, potential activity of the oxidative enzyme peroxidase in high-lignin, ambient UV samples was 85.9 μmol/hr*g during the wet season, compared to 44.1 μmol/hr*g in attenuated UV samples (p < 0.028). This increased potential cellulase activity under attenuated UV may indicate that dry season photodegradation primes low-lignin litter for wet season decomposition, reducing the selective pressure for microbial decomposers to invest in costly extracellular enzyme production. Similarly, the reduced potential oxidative enzyme activity in high-lignin samples exposed to attenuated UV may indicate that photodegradation is necessary to facilitate the breakdown of more complex compounds such as lignin by microbial decomposers. We conclude that while abiotic factors such as photodegradation can have a significant effect on the mechanisms of plant matter decomposition in semiarid ecosystems, these effects are not only restricted to the dry season and may also facilitate wet season decomposition.

Theory of competitive solvation of polymers by two solvents and entropy-enthalpy compensation in the solvation free energy upon dilution with the second solvent.

PubMed

Dudowicz, Jacek; Freed, Karl F; Douglas, Jack F

2015-06-07

We develop a statistical mechanical lattice theory for polymer solvation by a pair of relatively low molar mass solvents that compete for binding to the polymer backbone. A theory for the equilibrium mixture of solvated polymer clusters {AiBCj} and free unassociated molecules A, B, and C is formulated in the spirit of Flory-Huggins mean-field approximation. This theoretical framework enables us to derive expressions for the boundaries for phase stability (spinodals) and other basic properties of these polymer solutions: the internal energy U, entropy S, specific heat CV, extent of solvation Φsolv, average degree of solvation 〈Nsolv〉, and second osmotic virial coefficient B2 as functions of temperature and the composition of the mixture. Our theory predicts many new phenomena, but the current paper applies the theory to describe the entropy-enthalpy compensation in the free energy of polymer solvation, a phenomenon observed for many years without theoretical explanation and with significant relevance to liquid chromatography and other polymer separation methods.

Aggregation Pattern Transitions by Slightly Varying the Attractive/Repulsive Function

PubMed Central

Cheng, Zhao; Zhang, Hai-Tao; Chen, Michael Z. Q.; Zhou, Tao; Valeyev, Najl V.

2011-01-01

Among collective behaviors of biological swarms and flocks, the attractive/repulsive (A/R) functional links between particles play an important role. By slightly changing the cutoff distance of the A/R function, a drastic transition between two distinct aggregation patterns is observed. More precisely, a large cutoff distance yields a liquid-like aggregation pattern where the particle density decreases monotonously from the inside to the outwards within each aggregated cluster. Conversely, a small cutoff distance produces a crystal-like aggregation pattern where the distance between each pair of neighboring particles remains constant. Significantly, there is an obvious spinodal in the variance curve of the inter-particle distances along the increasing cutoff distances, implying a legible transition pattern between the liquid-like and crystal-like aggregations. This work bridges the aggregation phenomena of physical particles and swarming of organisms in nature upon revealing some common mechanism behind them by slightly varying their inter-individual attractive/repulsive functions, and may find its potential engineering applications, for example, in the formation design of multi-robot systems and unmanned aerial vehicles (UAVs). PMID:21799776

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hiratsuka, Tatsumasa; Tanaka, Hideki, E-mail: tanaka@cheme.kyoto-u.ac.jp; Miyahara, Minoru T., E-mail: miyahara@cheme.kyoto-u.ac.jp

Capillary condensation in the regime of developing hysteresis occurs at a vapor pressure, P{sub cond}, that is less than that of the vapor-like spinodal. This is because the energy barrier for the vapor-liquid transition from a metastable state at P{sub cond} becomes equal to the energy fluctuation of the system; however, a detailed mechanism of the spontaneous transition has not been acquired even through extensive experimental and simulation studies. We therefore construct accurate atomistic silica mesopore models for MCM-41 and perform molecular simulations (gauge cell Monte Carlo and grand canonical Monte Carlo) for argon adsorption on the models at subcriticalmore » temperatures. A careful comparison between the simulation and experiment reveals that the energy barrier for the capillary condensation has a critical dimensionless value, W{sub c}{sup *} = 0.175, which corresponds to the thermal fluctuation of the system and depends neither on the mesopore size nor on the temperature. We show that the critical energy barrier W{sub c}{sup *} controls the capillary condensation pressure P{sub cond} and also determines a boundary between the reversible condensation/evaporation regime and the developing hysteresis regime.« less

Theory of Liquid Film Growth and Wetting Instabilities on Graphene

NASA Astrophysics Data System (ADS)

Sengupta, Sanghita; Nichols, Nathan S.; Del Maestro, Adrian; Kotov, Valeri N.

2018-06-01

We investigate wetting phenomena near graphene within the Dzyaloshinskii-Lifshitz-Pitaevskii theory for light gases of hydrogen, helium, and nitrogen in three different geometries where graphene is either affixed to an insulating substrate, submerged or suspended. We find that the presence of graphene has a significant effect in all configurations. When placed on a substrate, the polarizability of graphene can increase the strength of the total van der Waals force by a factor of 2 near the surface, enhancing the propensity towards wetting. In a suspended geometry unique to two-dimensional materials, where graphene is able to wet on only one side, liquid film growth becomes arrested at a critical thickness, which may trigger surface instabilities and pattern formation analogous to spinodal dewetting. The existence of a mesoscopic critical film with a tunable thickness provides a platform for the study of a continuous wetting transition, as well as the engineering of custom liquid coatings. These phenomena are robust to some mechanical deformations and are also universally present in doped graphene and other two-dimensional materials, such as monolayer dichalcogenides.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aytug, Tolga; Lupini, Andrew R.; Jellison, Gerald E.

The design of multifunctional coatings impact impact the performance of many optical systems and components. Such coatings should be mechanically robust, and combine user-defined optical and wetting functions with scalable fabrication formulations. By taking cues from the properties of some natural biological structures, we report here the formation of low-refractive index antireflective glass films that embody omni-directional optical properties over a wide range of wavelengths, while also possessing specific wetting capabilities. The coatings comprise an interconnected network of nanoscale pores surrounded by a nanostructured silica framework. These structures result from a novel fabrication method that utilizes metastable spinodal phase separationmore » in glass-based materials. The approach not only enables design of surface microstructures with graded-index antireflection characteristics, where the surface reflection is suppressed through optical impedance matching between interfaces, but also facilitates self-cleaning ability through modification of the surface chemistry. Based on near complete elimination of Fresnel reflections (yielding >95% transmission through a single-side coated glass) and corresponding increase in broadband transmission, the fabricated nanostructured surfaces are found to promote a general and an invaluable ~3–7% relative increase in current output of multiple direct/indirect bandgap photovoltaic cells. Moreover, these antireflective surfaces also demonstrate superior resistance against mechanical wear and abrasion. Unlike conventional counterparts, the present antireflective coatings are essentially monolithic, enabling simultaneous realization of graded index anti-reflectivity, self-cleaning capability, and mechanical stability within the same surface. Moreover, the concept represents a fundamental basis for development of advanced coated optical quality products, especially where environmental exposure is required.« less

Dynamic Responses and Initial Decomposition under Shock Loading: A DFTB Calculation Combined with MSST Method for β-HMX with Molecular Vacancy.

PubMed

He, Zheng-Hua; Chen, Jun; Ji, Guang-Fu; Liu, Li-Min; Zhu, Wen-Jun; Wu, Qiang

2015-08-20

Despite extensive efforts on studying the decomposition mechanism of HMX under extreme condition, an intrinsic understanding of mechanical and chemical response processes, inducing the initial chemical reaction, is not yet achieved. In this work, the microscopic dynamic response and initial decomposition of β-HMX with (1 0 0) surface and molecular vacancy under shock condition, were explored by means of the self-consistent-charge density-functional tight-binding method (SCC-DFTB) in conjunction with multiscale shock technique (MSST). The evolutions of various bond lengths and charge transfers were analyzed to explore and understand the initial reaction mechanism of HMX. Our results discovered that the C-N bond close to major axes had less compression sensitivity and higher stretch activity. The charge was transferred mainly from the N-NO2 group along the minor axes and H atom to C atom during the early compression process. The first reaction of HMX primarily initiated with the fission of the molecular ring at the site of the C-N bond close to major axes. Further breaking of the molecular ring enhanced intermolecular interactions and promoted the cleavage of C-H and N-NO2 bonds. More significantly, the dynamic response behavior clearly depended on the angle between chemical bond and shock direction.

Multi-scale Methods in Quantum Field Theory

NASA Astrophysics Data System (ADS)

Polyzou, W. N.; Michlin, Tracie; Bulut, Fatih

2018-05-01

Daubechies wavelets are used to make an exact multi-scale decomposition of quantum fields. For reactions that involve a finite energy that take place in a finite volume, the number of relevant quantum mechanical degrees of freedom is finite. The wavelet decomposition has natural resolution and volume truncations that can be used to isolate the relevant degrees of freedom. The application of flow equation methods to construct effective theories that decouple coarse and fine scale degrees of freedom is examined.

The decomposition of peroxynitrite to nitroxyl anion (NO−) and singlet oxygen in aqueous solution

PubMed Central

Khan, Ahsan Ullah; Kovacic, Dianne; Kolbanovskiy, Alexander; Desai, Mehul; Frenkel, Krystyna; Geacintov, Nicholas E.

2000-01-01

The mechanism of decomposition of peroxynitrite (OONO−) in aqueous sodium phosphate buffer solution at neutral pH was investigated. The OONO− was synthesized by directly reacting nitric oxide with superoxide anion at pH 13. The hypothesis was explored that OONO−, after protonation at pH 7.0 to HOONO, decomposes into 1O2 and HNO according to a spin-conserved unimolecular mechanism. Small aliquots of the concentrated alkaline OONO− solution were added to a buffer solution (final pH 7.0–7.2), and the formation of 1O2 and NO− in high yields was observed. The 1O2 generated was trapped as the transannular peroxide (DPAO2) of 9,10-diphenylanthracene (DPA) dissolved in carbon tetrachloride. The nitroxyl anion (NO−) formed from HNO (pKa 4.5) was trapped as nitrosylhemoglobin (HbNO) in an aqueous methemoglobin (MetHb) solution. In the presence of 25 mM sodium bicarbonate, which is known to accelerate the rate of decomposition of OONO−, the amount of singlet oxygen trapped was reduced by a factor of ≈2 whereas the yield of trapping of NO− by methemoglobin remained unaffected. Because NO3− is known to be the ultimate decomposition product of OONO−, these results suggest that the nitrate anion is not formed by a direct isomerization of OONO−, but by an indirect route originating from NO−. PMID:10716721

Computational Elucidation of Selectivities and Mechanisms Performed by Organometallic and Bioinorganic Catalysts

NASA Astrophysics Data System (ADS)

Grandner, Jessica Marie

Computational methods were used to determine the mechanisms and selectivities of organometallic-catalyzed reactions. The first half of the dissertation focuses on the study of metathesis catalysts in collaboration with the Grubbs group at CalTech. Chapter 1 describes the studies of the decomposition modes of several ruthenium-based metathesis catalysts. These studies were performed to better understand the decomposition of such catalysts in order to prevent decomposition (Chapter 1.2) or utilize decomposed catalysts for alternative reactions (Chapter 1.1). Chapter 2.1 describes the computational investigation of the origins of stereoretentive metathesis with ruthenium-based metathesis catalysts. These findings were then used to computationally design E-selective metathesis catalysts (Chapter 2.2). While the first half of the dissertation was centered around ruthenium catalysts, the second half of the dissertation pertains to iron-catalyzed reaction, in particular, iron-catalyzed reactions by P450 enzymes. The elements of Chapter 3 concentrate on the stereo- and chemo-selectivity of P450-catalyzed C-H hydroxylations. By combining multiple computational methods, the inherent activity of the iron-oxo catalyst and the influence of the active site on such reactions were illuminated. These discoveries allow for the engineering of new substrates and mutant enzymes for tailored C-H hydroxylation. While the mechanism of C-H hydroxylations catalyzed by P450 enzymes has been well studied, there are several P450-catalyzed transformations for which the mechanism is unknown. The components of Chapter 4 describe the use of computations to determine the mechanisms of complex, multi-step reactions catalyzed by P450s. The determination of these mechanisms elucidates how these enzymes react with various functional groups and substrate architectures and allows for a better understanding of how drug-like compounds may be broken down by human P450s.

Theoretical study of the reaction mechanism of CH₃NO₂ with NO₂, NO and CO: the bimolecular reactions that cannot be ignored.

PubMed

Zhang, Ji-Dong; Kang, Li-Hua; Cheng, Xin-Lu

2015-01-01

The intriguing decompositions of nitro-containing explosives have been attracting interest. While theoretical investigations have long been concentrated mainly on unimolecular decompositions, bimolecular reactions have received little theoretical attention. In this paper, we investigate theoretically the bimolecular reactions between nitromethane (CH3NO2)-the simplest nitro-containing explosive-and its decomposition products, such as NO2, NO and CO, that are abundant during the decomposition process of CH3NO2. The structures and potential energy surface (PES) were explored at B3LYP/6-31G(d), B3P86/6-31G(d) and MP2/6-311 + G(d,p) levels, and energies were refined using CCSD(T)/cc-pVTZ methods. Quantum chemistry calculations revealed that the title reactions possess small barriers that can be comparable to, or smaller than, that of the initial decomposition reactions of CH3NO2. Considering that their reactants are abundant in the decomposition process of CH3NO2, we consider bimolecular reactions also to be of great importance, and worthy of further investigation. Moreover, our calculations show that NO2 can be oxidized by CH3NO2 to NO3 radical, which confirms the conclusion reached formerly by Irikura and Johnson [(2006) J Phys Chem A 110:13974-13978] that NO3 radical can be formed during the decomposition of nitramine explosives.

Impact of cycling at low temperatures on the safety behavior of 18650-type lithium ion cells: Combined study of mechanical and thermal abuse testing accompanied by post-mortem analysis

NASA Astrophysics Data System (ADS)

Friesen, Alex; Horsthemke, Fabian; Mönnighoff, Xaver; Brunklaus, Gunther; Krafft, Roman; Börner, Markus; Risthaus, Tim; Winter, Martin; Schappacher, Falko M.

2016-12-01

The impact of cycling at low temperatures on the thermal and mechanical abuse behavior of commercial 18650-type lithium ion cells was compared to fresh cells. Post-mortem analyses revealed a deposition of high surface area lithium (HSAL) metal on the graphite surface accompanied by severe electrolyte decomposition. Heat wait search (HWS) tests in an accelerating rate calorimeter (ARC) were performed to investigate the thermal abuse behavior of aged and fresh cells under quasi-adiabatic conditions, showing a strong shift of the onset temperature for exothermic reactions. HSAL deposition promotes the reduction of the carbonate based electrolyte due to the high reactivity of lithium metal with high surface area, leading to a thermally induced decomposition of the electrolyte to produce volatile gaseous products. Nail penetration tests showed a change in the thermal runaway (TR) behavior affected by the decomposition reaction. This study indicates a greater thermal hazard for LIB cells at higher SOC and experiencing aging at low temperature.

First-principles and thermodynamic analysis of trimethylgallium (TMG) decomposition during MOVPE growth of GaN

NASA Astrophysics Data System (ADS)

Sekiguchi, K.; Shirakawa, H.; Yamamoto, Y.; Araidai, M.; Kangawa, Y.; Kakimoto, K.; Shiraishi, K.

2017-06-01

We analyzed the decomposition mechanisms of trimethylgallium (TMG) used for the gallium source of GaN fabrication based on first-principles calculations and thermodynamic analysis. We considered two conditions. One condition is under the total pressure of 1 atm and the other one is under metal organic vapor phase epitaxy (MOVPE) growth of GaN. Our calculated results show that H2 is indispensable for TMG decomposition under both conditions. In GaN MOVPE, TMG with H2 spontaneously decomposes into Ga(CH3) and Ga(CH3) decomposes into Ga atom gas when temperature is higher than 440 K. From these calculations, we confirmed that TMG surely becomes Ga atom gas near the GaN substrate surfaces.

Decomposition of a symmetric second-order tensor

NASA Astrophysics Data System (ADS)

Heras, José A.

2018-05-01

In the three-dimensional space there are different definitions for the dot and cross products of a vector with a second-order tensor. In this paper we show how these products can uniquely be defined for the case of symmetric tensors. We then decompose a symmetric second-order tensor into its ‘dot’ part, which involves the dot product, and the ‘cross’ part, which involves the cross product. For some physical applications, this decomposition can be interpreted as one in which the dot part identifies with the ‘parallel’ part of the tensor and the cross part identifies with the ‘perpendicular’ part. This decomposition of a symmetric second-order tensor may be suitable for undergraduate courses of vector calculus, mechanics and electrodynamics.

Investigation of induced unimolecular decomposition for development of visible chemical lasers. Quarterly progress report, 1 August 1976--30 October 1976

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piper, L G; Taylor, R L

This report summarizes progress during the second quarterly period of the subject contract. The methods available for the production of excited electronic states following azide decomposition are summarized. It is concluded that an experiment designed to study the kinetics of and branching ratios for electronically excited products from azide radicals reactions will be most productive in elucidating excitation mechanisms for potential chemical lasers. A flow reactor is described in which these studies may be undertaken. The major feature of this apparatus is a clean azide radical source based upon the thermal decomposition of solid, ionic azides. The contruction of themore » experimental apparatus has been started.« less

Lyman α photolysis of solid nitromethane (CH3NO2) and D3-nitromethane (CD3NO2)--untangling the reaction mechanisms involved in the decomposition of model energetic materials.

PubMed

Maksyutenko, Pavlo; Muzangwa, Lloyd G; Jones, Brant M; Kaiser, Ralf I

2015-03-21

Solid nitromethane (CH3NO2) along with its isotopically labelled counterpart D3-nitromethane (CD3NO2) ices were exposed to Lyman α photons to investigate the mechanism involved in the decomposition of energetic materials in the condensed phase. The chemical processes in the ices were monitored online and in situ via infrared spectroscopy complimented by temperature programmed desorption studies utilizing highly sensitive reflectron time-of-flight mass spectrometry coupled with pulsed photoionization (ReTOF-PI) at 10.49 eV. The infrared data revealed the formation of cis-methylnitrite (CH3ONO), formaldehyde (H2CO), water (H2O), carbon monoxide (CO), and carbon dioxide (CO2). Upon sublimation of the irradiated samples, three classes of higher molecular weight products, which are uniquely formed in the condensed phase, were identified via ReTOF-PI: (i) nitroso compounds [nitrosomethane (CH3NO), nitrosoethane (C2H5NO), nitrosopropane (C3H7NO)], (ii) nitrite compounds [methylnitrite (CH3ONO), ethylnitrite (C2H5ONO), propylnitrite (C3H7ONO)], and (iii) higher molecular weight molecules [CH3NONOCH3, CH3NONO2CH3, CH3OCH2NO2, ONCH2CH2NO2]. The mechanistical information obtained in the present study suggest that the decomposition of nitromethane in the condensed phase is more complex compared to the gas phase under collision-free conditions opening up not only hitherto unobserved decomposition pathways of nitromethane (hydrogen atom loss, oxygen atom loss, retro carbene insertion), but also the blocking of several initial decomposition steps due to the 'matrix cage effect'.

Characterization of corncob-derived biochar and pyrolysis kinetics in comparison with corn stalk and sawdust.

PubMed

Liu, Xuan; Zhang, Yang; Li, Zifu; Feng, Rui; Zhang, Yaozhong

2014-10-01

In this study, thermal and physicochemical characterization results of corncob (CC) and its derived biochars were analyzed and differentiated from sawdust (SD) and cornstalk (CS). The pyrolysis temperature shows the largest effect on the yield of biochar produced compare with residing time, heating rate, and feedstock particle size. The CC-derived biochars produced at temperatures ranging from 300 to 600°C were analyzed. The CC was thermochemically altered to a stable biochar when the pyrolysis temperature was set to over 500°C. To deduce the reaction mechanism of the CC during the major thermal decomposition stage, 16 mechanisms in solid-state reactions were applied. The reaction order and nucleation mechanisms described the thermal decomposition of the CC. By using the best-fitted mechanisms, the kinetic parameters were calculated. The weight active energy of the CC was 122.42kJ/mol, which was the lowest value compared to those of CS and SD. Copyright © 2014 Elsevier Ltd. All rights reserved.

Decomposition mechanism of an artemisinin-type compound via hemin-electrocatalysis.

PubMed

Chen, H Y; Chen, Y; Zhu, S M; Bian, N S; Shan, F; Li, Y

1999-01-01

The interaction between a typical derivative of artemisinin and hemin was investigated by electrochemical and spectroelectrochemical methods. This derivative can be reduced via hemin-catalysis at the glassy carbon electrode, the cathodic overpotential is decreased by ca. 650 mV. A HPLC method for separating the products of the catalytic reaction was established. They were identified either in H(2)O-CH(3)CN solution or in tetrahydrofuran, respectively. The structures of these products show that the hemin-catalyzed decomposition of an artemisinin-type compound on the glassy carbon or reticulated vitreous carbon electrode can be achieved by both electrochemical reduction and rearrangement. The conclusion that the reaction of artemisinin with hemin is a critical step in the antimalarial mechanism of artemisinin can be drawn.

Decomposition reactions of (hydroxyalkyl) nitrosoureas and related compounds: possible relationship to carcinogenicity.

PubMed

Singer, S S

1985-08-01

(Hydroxyalkyl)nitrosoureas and the related cyclic carbamates N-nitrosooxazolidones are potent carcinogens. The decompositions of four such compounds, 1-nitroso-1-(2-hydroxyethyl)urea (I), 3-nitrosooxazolid-2-one (II), 1-nitroso-1-(2-hydroxypropyl)urea (III), and 5-methyl-3-nitrosooxazolid-2-one (IV), in aqueous buffers at physiological pH were studied to determine if any obvious differences in decomposition pathways could account for the variety of tumors obtained from these four compounds. The products predicted by the literature mechanisms for nitrosourea and nitrosooxazolidone decompositions (which were derived from experiments at pH 10-12) were indeed the products formed, including glycols, active carbonyl compounds, epoxides, and, from the oxazolidones, cyclic carbonates. Furthermore, it was shown that in pH 6.4-7.4 buffer epoxides were stable reaction products. However, in the presence of hepatocytes, most of the epoxide was converted to glycol. The analytical methods developed were then applied to the analysis of the decomposition products of some related dialkylnitrosoureas, and similar results were obtained. The formation of chemically reactive secondary products and the possible relevance of these results to carcinogenesis studies are discussed.

Unusual behavior in the reactivity of 5-substituted-1H-tetrazoles in a resistively heated microreactor

PubMed Central

Gutmann, Bernhard; Glasnov, Toma N; Razzaq, Tahseen; Goessler, Walter; Roberge, Dominique M

2011-01-01

Summary The decomposition of 5-benzhydryl-1H-tetrazole in an N-methyl-2-pyrrolidone/acetic acid/water mixture was investigated under a variety of high-temperature reaction conditions. Employing a sealed Pyrex glass vial and batch microwave conditions at 240 °C, the tetrazole is comparatively stable and complete decomposition to diphenylmethane requires more than 8 h. Similar kinetic data were obtained in conductively heated flow devices with either stainless steel or Hastelloy coils in the same temperature region. In contrast, in a flow instrument that utilizes direct electric resistance heating of the reactor coil, tetrazole decomposition was dramatically accelerated with rate constants increased by two orders of magnitude. When 5-benzhydryl-1H-tetrazole was exposed to 220 °C in this type of flow reactor, decomposition to diphenylmethane was complete within 10 min. The mechanism and kinetic parameters of tetrazole decomposition under a variety of reaction conditions were investigated. A number of possible explanations for these highly unusual rate accelerations are presented. In addition, general aspects of reactor degradation, corrosion and contamination effects of importance to continuous flow chemistry are discussed. PMID:21647324

Vacancy-induced initial decomposition of condensed phase NTO via bimolecular hydrogen transfer mechanisms at high pressure: a DFT-D study.

PubMed

Liu, Zhichao; Wu, Qiong; Zhu, Weihua; Xiao, Heming

2015-04-28

Density functional theory with dispersion-correction (DFT-D) was employed to study the effects of vacancy and pressure on the structure and initial decomposition of crystalline 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (β-NTO), a high-energy insensitive explosive. A comparative analysis of the chemical behaviors of NTO in the ideal bulk crystal and vacancy-containing crystals under applied hydrostatic compression was considered. Our calculated formation energy, vacancy interaction energy, electron density difference, and frontier orbitals reveal that the stability of NTO can be effectively manipulated by changing the molecular environment. Bimolecular hydrogen transfer is suggested to be a potential initial chemical reaction in the vacancy-containing NTO solid at 50 GPa, which is prior to the C-NO2 bond dissociation as its initiation decomposition in the gas phase. The vacancy defects introduced into the ideal bulk NTO crystal can produce a localized site, where the initiation decomposition is preferentially accelerated and then promotes further decompositions. Our results may shed some light on the influence of the molecular environments on the initial pathways in molecular explosives.

Effects of magnesium-based hydrogen storage materials on the thermal decomposition, burning rate, and explosive heat of ammonium perchlorate-based composite solid propellant.

PubMed

Liu, Leili; Li, Jie; Zhang, Lingyao; Tian, Siyu

2018-01-15

MgH 2 , Mg 2 NiH 4 , and Mg 2 CuH 3 were prepared, and their structure and hydrogen storage properties were determined through X-ray photoelectron spectroscopy and thermal analyzer. The effects of MgH 2 , Mg 2 NiH 4 , and Mg 2 CuH 3 on the thermal decomposition, burning rate, and explosive heat of ammonium perchlorate-based composite solid propellant were subsequently studied. Results indicated that MgH 2 , Mg 2 NiH 4 , and Mg 2 CuH 3 can decrease the thermal decomposition peak temperature and increase the total released heat of decomposition. These compounds can improve the effect of thermal decomposition of the propellant. The burning rates of the propellant increased using Mg-based hydrogen storage materials as promoter. The burning rates of the propellant also increased using MgH 2 instead of Al in the propellant, but its explosive heat was not enlarged. Nonetheless, the combustion heat of MgH 2 was higher than that of Al. A possible mechanism was thus proposed. Copyright © 2017. Published by Elsevier B.V.

Microbial genomics, transcriptomics and proteomics: new discoveries in decomposition research using complementary methods.

PubMed

Baldrian, Petr; López-Mondéjar, Rubén

2014-02-01

Molecular methods for the analysis of biomolecules have undergone rapid technological development in the last decade. The advent of next-generation sequencing methods and improvements in instrumental resolution enabled the analysis of complex transcriptome, proteome and metabolome data, as well as a detailed annotation of microbial genomes. The mechanisms of decomposition by model fungi have been described in unprecedented detail by the combination of genome sequencing, transcriptomics and proteomics. The increasing number of available genomes for fungi and bacteria shows that the genetic potential for decomposition of organic matter is widespread among taxonomically diverse microbial taxa, while expression studies document the importance of the regulation of expression in decomposition efficiency. Importantly, high-throughput methods of nucleic acid analysis used for the analysis of metagenomes and metatranscriptomes indicate the high diversity of decomposer communities in natural habitats and their taxonomic composition. Today, the metaproteomics of natural habitats is of interest. In combination with advanced analytical techniques to explore the products of decomposition and the accumulation of information on the genomes of environmentally relevant microorganisms, advanced methods in microbial ecophysiology should increase our understanding of the complex processes of organic matter transformation.

Reactive molecular dynamics simulation of solid nitromethane impact on (010) surfaces induced and nonimpact thermal decomposition.

PubMed

Guo, Feng; Cheng, Xin-lu; Zhang, Hong

2012-04-12

Which is the first step in the decomposition process of nitromethane is a controversial issue, proton dissociation or C-N bond scission. We applied reactive force field (ReaxFF) molecular dynamics to probe the initial decomposition mechanisms of nitromethane. By comparing the impact on (010) surfaces and without impact (only heating) for nitromethane simulations, we found that proton dissociation is the first step of the pyrolysis of nitromethane, and the C-N bond decomposes in the same time scale as in impact simulations, but in the nonimpact simulation, C-N bond dissociation takes place at a later time. At the end of these simulations, a large number of clusters are formed. By analyzing the trajectories, we discussed the role of the hydrogen bond in the initial process of nitromethane decompositions, the intermediates observed in the early time of the simulations, and the formation of clusters that consisted of C-N-C-N chain/ring structures.

Active sites and mechanisms for H2O2 decomposition over Pd catalysts

PubMed Central

Plauck, Anthony; Stangland, Eric E.; Dumesic, James A.; Mavrikakis, Manos

2016-01-01

A combination of periodic, self-consistent density functional theory (DFT-GGA-PW91) calculations, reaction kinetics experiments on a SiO2-supported Pd catalyst, and mean-field microkinetic modeling are used to probe key aspects of H2O2 decomposition on Pd in the absence of cofeeding H2. We conclude that both Pd(111) and OH-partially covered Pd(100) surfaces represent the nature of the active site for H2O2 decomposition on the supported Pd catalyst reasonably well. Furthermore, all reaction flux in the closed catalytic cycle is predicted to flow through an O–O bond scission step in either H2O2 or OOH, followed by rapid H-transfer steps to produce the H2O and O2 products. The barrier for O–O bond scission is sensitive to Pd surface structure and is concluded to be the central parameter governing H2O2 decomposition activity. PMID:27006504

Kinetics of methane hydrate decomposition studied via in situ low temperature X-ray powder diffraction.

PubMed

Everett, S Michelle; Rawn, Claudia J; Keffer, David J; Mull, Derek L; Payzant, E Andrew; Phelps, Tommy J

2013-05-02

Gas hydrate is known to have a slowed decomposition rate at ambient pressure and temperatures below the melting point of ice. As hydrate exothermically decomposes, gas is released and water of the clathrate cages transforms into ice. Based on results from the decomposition of three nominally similar methane hydrate samples, the kinetics of two regions, 180-200 and 230-260 K, within the overall decomposition range 140-260 K, were studied by in situ low temperature X-ray powder diffraction. The kinetic rate constants, k(a), and the reaction mechanisms, n, for ice formation from methane hydrate were determined by the Avrami model within each region, and activation energies, E(a), were determined by the Arrhenius plot. E(a) determined from the data for 180-200 K was 42 kJ/mol and for 230-260 K was 22 kJ/mol. The higher E(a) in the colder temperature range was attributed to a difference in the microstructure of ice between the two regions.

Synergies from using higher order symplectic decompositions both for ordinary differential equations and quantum Monte Carlo methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matuttis, Hans-Georg; Wang, Xiaoxing

Decomposition methods of the Suzuki-Trotter type of various orders have been derived in different fields. Applying them both to classical ordinary differential equations (ODEs) and quantum systems allows to judge their effectiveness and gives new insights for many body quantum mechanics where reference data are scarce. Further, based on data for 6 × 6 system we conclude that sampling with sign (minus-sign problem) is probably detrimental to the accuracy of fermionic simulations with determinant algorithms.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brezov, D. S.; Mladenova, C. D.; Mladenov, I. M., E-mail: mladenov@bio21.bas.bg

In this paper we obtain the Lie derivatives of the scalar parameters in the generalized Euler decomposition with respect to arbitrary axes under left and right deck transformations. This problem can be directly related to the representation of the angular momentum in quantum mechanics. As a particular example, we calculate the angular momentum and the corresponding quantum hamiltonian in the standard Euler and Bryan representations. Similarly, in the hyperbolic case, the Laplace-Beltrami operator is retrieved for the Iwasawa decomposition. The case of two axes is considered as well.

Hydrazine vapor detonations

NASA Technical Reports Server (NTRS)

Pedley, M. D.; Bishop, C. V.; Benz, F. J.; Bennett, C. A.; Mcclenagan, R. D.

1988-01-01

The detonation velocity and cell widths for hydrazine decomposition were measured over a wide range of temperatures and pressures. The detonation velocity in pure hydrazine was within 5 percent of the calculated C-J velocity. The detonation cell width measurements were interpreted using the Zeldovich-Doering-von Neumann model with a detailed reaction mechanism for hydrazine decomposition. Excellent agreement with experimental data for pure hydrazine was obtained using the empirical relation that detonation cell width was equal to 29 times the kinetically calculated reaction zone length.

Thermochemical and kinetic analysis of the thermal decomposition of monomethylhydrazine: an elementary reaction mechanism.

PubMed

Sun, Hongyan; Law, Chung K

2007-05-17

The reaction kinetics for the thermal decomposition of monomethylhydrazine (MMH) was studied with quantum Rice-Ramsperger-Kassel (QRRK) theory and a master equation analysis for pressure falloff. Thermochemical properties were determined by ab initio and density functional calculations. The entropies, S degrees (298.15 K), and heat capacities, Cp degrees (T) (0 < or = T/K < or = 1500), from vibrational, translational, and external rotational contributions were calculated using statistical mechanics based on the vibrational frequencies and structures obtained from the density functional study. Potential barriers for internal rotations were calculated at the B3LYP/6-311G(d,p) level, and hindered rotational contributions to S degrees (298.15 K) and Cp degrees (T) were calculated by solving the Schrödinger equation with free rotor wave functions, and the partition coefficients were treated by direct integration over energy levels of the internal rotation potentials. Enthalpies of formation, DeltafH degrees (298.15 K), for the parent MMH (CH3NHNH2) and its corresponding radicals CH3N*NH2, CH3NHN*H, and C*H2NHNH2 were determined to be 21.6, 48.5, 51.1, and 62.8 kcal mol(-1) by use of isodesmic reaction analysis and various ab initio methods. The kinetic analysis of the thermal decomposition, abstraction, and substitution reactions of MMH was performed at the CBS-QB3 level, with those of N-N and C-N bond scissions determined by high level CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) calculations. Rate constants of thermally activated MMH to dissociation products were calculated as functions of pressure and temperature. An elementary reaction mechanism based on the calculated rate constants, thermochemical properties, and literature data was developed to model the experimental data on the overall MMH thermal decomposition rate. The reactions of N-N and C-N bond scission were found to be the major reaction paths for the modeling of MMH homogeneous decomposition at atmospheric conditions.

Decomposition of toluene in a steady-state atmospheric-pressure glow discharge

NASA Astrophysics Data System (ADS)

Trushkin, A. N.; Grushin, M. E.; Kochetov, I. V.; Trushkin, N. I.; Akishev, Yu. S.

2013-02-01

Results are presented from experimental studies of decomposition of toluene (C6H5CH3) in a polluted air flow by means of a steady-state atmospheric pressure glow discharge at different water vapor contents in the working gas. The experimental results on the degree of C6H5CH3 removal are compared with the results of computer simulations conducted in the framework of the developed kinetic model of plasma chemical decomposition of toluene in the N2: O2: H2O gas mixture. A substantial influence of the gas flow humidity on toluene decomposition in the atmospheric pressure glow discharge is demonstrated. The main mechanisms of the influence of humidity on C6H5CH3 decomposition are determined. The existence of two stages in the process of toluene removal, which differ in their duration and the intensity of plasma chemical decomposition of C6H5CH3 is established. Based on the results of computer simulations, the composition of the products of plasma chemical reactions at the output of the reactor is analyzed as a function of the specific energy deposition and gas flow humidity. The existence of a catalytic cycle in which hydroxyl radical OH acts a catalyst and which substantially accelerates the recombination of oxygen atoms and suppression of ozone generation when the plasma-forming gas contains water vapor is established.

Decomposition Mechanism of C5F10O: An Environmentally Friendly Insulation Medium.

PubMed

Zhang, Xiaoxing; Li, Yi; Xiao, Song; Tang, Ju; Tian, Shuangshuang; Deng, Zaitao

2017-09-05

SF 6 , the most widely used electrical-equipment-insulation gas, has serious greenhouse effects. C 5 F 10 O has attracted much attention as an alternative gas in recent two years, but the environmental impact of its decomposition products is unclear. In this work, the decomposition characteristics of C 5 F 10 O were studied based on gas chromatography-mass spectrometry and density functional theory. We found that the amount of decomposition products of C 5 F 10 O, namely, CF 4 , C 2 F 6 , C 3 F 6 , C 3 F 8 , C 4 F 10 , and C 6 F 14 , increased with increased number of discharges. Under a high-energy electric field, the C-C bond of C 5 F 10 O between carbonyl carbon and α-carbon atoms was most likely to break and generate CF 3 CO•, C 3 F 7 • or C 3 F 7 CO•, CF 3 • free radicals. CF 3 •, and C 3 F 7 • free radicals produced by the breakage more easily recombined to form small molecular products. By analyzing the ionization parameters, toxicity, and environmental effects of C 5 F 10 O and its decomposition products, we found that C 5 F 10 O gas mixtures exhibit great decomposition and environmental characteristics with low toxicity, with great potential to replace SF 6 .

Effect of sulfation on the surface activity of CaO for N2O decomposition

NASA Astrophysics Data System (ADS)

Wu, Lingnan; Hu, Xiaoying; Qin, Wu; Dong, Changqing; Yang, Yongping

2015-12-01

Limestone addition to circulating fluidized bed boilers for sulfur removal affects nitrous oxide (N2O) emission at the same time, but mechanism of how sulfation process influences the surface activity of CaO for N2O decomposition remains unclear. In this paper, we investigated the effect of sulfation on the surface properties and catalytic activity of CaO for N2O decomposition using density functional theory calculations. Sulfation of CaO (1 0 0) surface by the adsorption of a single gaseous SO2 or SO3 molecule forms stable local CaSO3 or CaSO4 on the CaO (1 0 0) surface with strong hybridization between the S atom of SOx and the surface O anion. The formed local CaSO3 increases the barrier energy of N2O decomposition from 0.989 eV (on the CaO (1 0 0) surface) to 1.340 eV, and further sulfation into local CaSO4 remarkably increases the barrier energy to 2.967 eV. Sulfation from CaSO3 into CaSO4 is therefore the crucial step for deactivating the surface activity for N2O decomposition. Completely sulfated CaSO4 (0 0 1) and (0 1 0) surfaces further validate the negligible catalytic ability of CaSO4 for N2O decomposition.

Direct vs. Microclimate-Driven Effects of Tree Species Diversity on Litter Decomposition in Young Subtropical Forest Stands.

PubMed

Seidelmann, Katrin N; Scherer-Lorenzen, Michael; Niklaus, Pascal A

2016-01-01

Effects of tree species diversity on decomposition can operate via a multitude of mechanism, including alterations of microclimate by the forest canopy. Studying such effects in natural settings is complicated by the fact that topography also affects microclimate and thus decomposition, so that effects of diversity are more difficult to isolate. Here, we quantified decomposition rates of standard litter in young subtropical forest stands, separating effects of canopy tree species richness and topography, and quantifying their direct and micro-climate-mediated components. Our litterbag study was carried out at two experimental sites of a biodiversity-ecosystem functioning field experiment in south-east China (BEF-China). The field sites display strong topographical heterogeneity and were planted with tree communities ranging from monocultures to mixtures of 24 native subtropical tree species. Litter bags filled with senescent leaves of three native tree species were placed from Nov. 2011 to Oct. 2012 on 134 plots along the tree species diversity gradient. Topographic features were measured for all and microclimate in a subset of plots. Stand species richness, topography and microclimate explained important fractions of the variations in litter decomposition rates, with diversity and topographic effects in part mediated by microclimatic changes. Tree stands were 2-3 years old, but nevertheless tree species diversity explained more variation (54.3%) in decomposition than topography (7.7%). Tree species richness slowed litter decomposition, an effect that slightly depended on litter species identity. A large part of the variance in decomposition was explained by tree species composition, with the presence of three tree species playing a significant role. Microclimate explained 31.4% of the variance in decomposition, and was related to lower soil moisture. Within this microclimate effect, species diversity (without composition) explained 8.9% and topography 34.4% of variance. Topography mainly affected diurnal temperature amplitudes by varying incident solar radiation.

Direct vs. Microclimate-Driven Effects of Tree Species Diversity on Litter Decomposition in Young Subtropical Forest Stands

PubMed Central

Seidelmann, Katrin N.; Scherer-Lorenzen, Michael; Niklaus, Pascal A.

2016-01-01

Effects of tree species diversity on decomposition can operate via a multitude of mechanism, including alterations of microclimate by the forest canopy. Studying such effects in natural settings is complicated by the fact that topography also affects microclimate and thus decomposition, so that effects of diversity are more difficult to isolate. Here, we quantified decomposition rates of standard litter in young subtropical forest stands, separating effects of canopy tree species richness and topography, and quantifying their direct and micro-climate-mediated components. Our litterbag study was carried out at two experimental sites of a biodiversity-ecosystem functioning field experiment in south-east China (BEF-China). The field sites display strong topographical heterogeneity and were planted with tree communities ranging from monocultures to mixtures of 24 native subtropical tree species. Litter bags filled with senescent leaves of three native tree species were placed from Nov. 2011 to Oct. 2012 on 134 plots along the tree species diversity gradient. Topographic features were measured for all and microclimate in a subset of plots. Stand species richness, topography and microclimate explained important fractions of the variations in litter decomposition rates, with diversity and topographic effects in part mediated by microclimatic changes. Tree stands were 2–3 years old, but nevertheless tree species diversity explained more variation (54.3%) in decomposition than topography (7.7%). Tree species richness slowed litter decomposition, an effect that slightly depended on litter species identity. A large part of the variance in decomposition was explained by tree species composition, with the presence of three tree species playing a significant role. Microclimate explained 31.4% of the variance in decomposition, and was related to lower soil moisture. Within this microclimate effect, species diversity (without composition) explained 8.9% and topography 34.4% of variance. Topography mainly affected diurnal temperature amplitudes by varying incident solar radiation. PMID:27490180

Reaction mechanisms in cellulose pyrolysis: a literature review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molton, P.M.; Demmitt, T.F.

1977-08-01

A bibliographic review of 195 references is presented outlining the history of the research into the mechanisms of cellulose pyrolysis. Topics discussed are: initial product identification, mechanism of initial formation of levoglucosan, from cellulose and from related compounds, decomposition of cellulose to other compounds, formation of aromatics, pyrolysis of levoglucosan, crosslinking of cellulose, pyrolytic reactions of cellulose derivatives, and the effects of inorganic salts on the pyrolysis mechanism. (JSR)

Thermochemical properties of nanometer CL-20 and PETN fabricated using a mechanical milling method

NASA Astrophysics Data System (ADS)

Song, Xiaolan; Wang, Yi; An, Chongwei

2018-06-01

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and pentaerythritol tetranitrate (PETN), with mean sizes of 73.8 nm and 267.7 nm, respectively, were fabricated on a high-energy ball-mill. Scanning electron microscope (SEM) analysis was used to image the micron-scale morphology of nano-explosives, and the particle size distribution was calculated using the statistics of individual particle sizes obtained from the SEM images. Analyses, such as X-ray diffractometer (XRD), infrared spectroscopy (IR), and X-ray photoelectron spectroscopy (XPS), were also used to confirm whether the crystal phase, molecular structure, and surface elements changed after a long-term milling process. The results were as expected. Thermal analysis was performed at different heating rates. Parameters, such as the activation energy (ES), activation enthalpy (ΔH≠), activation free energy (ΔG≠), activation entropy (ΔS≠), and critical temperature of thermal explosion (Tb), were calculated to determine the decomposition courses of the explosives. Moreover, the thermal decomposition mechanisms of nano CL-20 and nano PETN were investigated using thermal-infrared spectrometry online (DSC-IR) analysis, by which their gas products were also detected. The results indicated that nano CL-20 decomposed to CO2 and N2O and that nano PETN decayed to NO2, which implied a remarkable difference between the decomposition mechanisms of the two explosives. In addition, the mechanical sensitivities of CL-20 and PETN were tested, and the results revealed that nano-explosives were more insensitive than raw ones, and the possible mechanism for this was discussed. Thermal sensitivity was also investigated with a 5 s bursting point test, from which the 5 s bursting point (T5s) and the activation of the deflagration were obtained.

The Chemical Decomposition of 5-aza-2′-deoxycytidine (Decitabine): Kinetic Analyses and Identification of Products by NMR, HPLC, and Mass Spectrometry

PubMed Central

Rogstad, Daniel K.; Herring, Jason L.; Theruvathu, Jacob A.; Burdzy, Artur; Perry, Christopher C.; Neidigh, Jonathan W.; Sowers, Lawrence C.

2014-01-01

The nucleoside analog 5-aza-2′-deoxycytidine (Decitabine, DAC) is one of several drugs in clinical use that inhibit DNA methyltransferases, leading to a decrease of 5-methylcytosine in newly replicated DNA and subsequent transcriptional activation of genes silenced by cytosine methylation. In addition to methyltransferase inhibition, DAC has demonstrated toxicity and potential mutagenicity, and can induce a DNA-repair response. The mechanisms accounting for these events are not well understood. DAC is chemically unstable in aqueous solutions, but there is little consensus between previous reports as to its half-life and corresponding products of decomposition at physiological temperature and pH, potentially confounding studies on its mechanism of action and long-term use in humans. Here we have employed a battery of analytical methods to estimate kinetic rates and to characterize DAC decomposition products under conditions of physiological temperature and pH. Our results indicate that DAC decomposes into a plethora of products, formed by hydrolytic opening and deformylation of the triazine ring, in addition to anomerization and possibly other changes in the sugar ring structure. We also discuss the advantages and problems associated with each analytical method used. The results reported here will facilitate ongoing studies and clinical trials aimed at understanding the mechanisms of action, toxicity, and possible mutagenicity of DAC and related analogs. PMID:19480391

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopes, E.S.N.; Cremasco, A.; Afonso, C.R.M.

Aging heat treatment can be a good way to optimize mechanical properties, changing the microstructure, and hence, the mechanical behavior of Ti alloys. The effects of aging heat treatments on {beta}-type Ti-30Nb alloy were investigated to evaluate the kinetics of {alpha}'' {yields} {alpha} + {beta} transformation. The results obtained from differential scanning calorimetry and high-temperature X-ray diffraction experiments indicated the complete decomposition of orthorhombic {alpha}'' phase at close to 300 deg. C, followed by {alpha} phase precipitation at 470 deg. C. The aging heat treatments also enabled us to observe a transformation sequence {alpha}'' {yields} {beta} + {omega} {yields} {beta}more » + {omega} + {alpha}, indicating martensite decomposition and {omega} phase precipitation at 260 deg. C after 2 h, followed by {alpha} phase nucleation after heating at 400 deg. C for 1 h. The elastic modulus and Vickers hardness of Ti-30Nb alloy were found to be very sensitive to the microstructural changes caused by heat treatment. - Highlights: {yields} DSC and XRD shed light on the {alpha}'' decomposition and nucleation of {omega} and {alpha} phases. {yields} Aging allows for {alpha}''{yields}{beta} transformation and nucleation of {omega} dispersed in the {beta} matrix. {yields} During aging, {alpha}'' interplanar distances are reduced to enable {beta} phase nucleation. {yields} Mechanical behavior is dependent on the microstructure and the phases in the alloy. {yields} It is not possible to obtain high strength and low elastic modulus by applying aging.« less

Chemical decomposition of 5-aza-2'-deoxycytidine (Decitabine): kinetic analyses and identification of products by NMR, HPLC, and mass spectrometry.

PubMed

Rogstad, Daniel K; Herring, Jason L; Theruvathu, Jacob A; Burdzy, Artur; Perry, Christopher C; Neidigh, Jonathan W; Sowers, Lawrence C

2009-06-01

The nucleoside analogue 5-aza-2'-deoxycytidine (Decitabine, DAC) is one of several drugs in clinical use that inhibit DNA methyltransferases, leading to a decrease of 5-methylcytosine in newly replicated DNA and subsequent transcriptional activation of genes silenced by cytosine methylation. In addition to methyltransferase inhibition, DAC has demonstrated toxicity and potential mutagenicity, and can induce a DNA-repair response. The mechanisms accounting for these events are not well understood. DAC is chemically unstable in aqueous solutions, but there is little consensus between previous reports as to its half-life and corresponding products of decomposition at physiological temperature and pH, potentially confounding studies on its mechanism of action and long-term use in humans. Here, we have employed a battery of analytical methods to estimate kinetic rates and to characterize DAC decomposition products under conditions of physiological temperature and pH. Our results indicate that DAC decomposes into a plethora of products, formed by hydrolytic opening and deformylation of the triazine ring, in addition to anomerization and possibly other changes in the sugar ring structure. We also discuss the advantages and problems associated with each analytical method used. The results reported here will facilitate ongoing studies and clinical trials aimed at understanding the mechanisms of action, toxicity, and possible mutagenicity of DAC and related analogues.

Uncertainty propagation in orbital mechanics via tensor decomposition

NASA Astrophysics Data System (ADS)

Sun, Yifei; Kumar, Mrinal

2016-03-01

Uncertainty forecasting in orbital mechanics is an essential but difficult task, primarily because the underlying Fokker-Planck equation (FPE) is defined on a relatively high dimensional (6-D) state-space and is driven by the nonlinear perturbed Keplerian dynamics. In addition, an enormously large solution domain is required for numerical solution of this FPE (e.g. encompassing the entire orbit in the x-y-z subspace), of which the state probability density function (pdf) occupies a tiny fraction at any given time. This coupling of large size, high dimensionality and nonlinearity makes for a formidable computational task, and has caused the FPE for orbital uncertainty propagation to remain an unsolved problem. To the best of the authors' knowledge, this paper presents the first successful direct solution of the FPE for perturbed Keplerian mechanics. To tackle the dimensionality issue, the time-varying state pdf is approximated in the CANDECOMP/PARAFAC decomposition tensor form where all the six spatial dimensions as well as the time dimension are separated from one other. The pdf approximation for all times is obtained simultaneously via the alternating least squares algorithm. Chebyshev spectral differentiation is employed for discretization on account of its spectral ("super-fast") convergence rate. To facilitate the tensor decomposition and control the solution domain size, system dynamics is expressed using spherical coordinates in a noninertial reference frame. Numerical results obtained on a regular personal computer are compared with Monte Carlo simulations.

Combustion modeling and kinetic rate calculations for a stoichiometric cyclohexane flame. 1. Major reaction pathways.

PubMed

Zhang, Hongzhi R; Huynh, Lam K; Kungwan, Nawee; Yang, Zhiwei; Zhang, Shaowen

2007-05-17

The Utah Surrogate Mechanism was extended in order to model a stoichiometric premixed cyclohexane flame (P = 30 Torr). Generic rates were assigned to reaction classes of hydrogen abstraction, beta scission, and isomerization, and the resulting mechanism was found to be adequate in describing the combustion chemistry of cyclohexane. Satisfactory results were obtained in comparison with the experimental data of oxygen, major products and important intermediates, which include major soot precursors of C2-C5 unsaturated species. Measured concentrations of immediate products of fuel decomposition were also successfully reproduced. For example, the maximum concentrations of benzene and 1,3-butadiene, two major fuel decomposition products via competing pathways, were predicted within 10% of the measured values. Ring-opening reactions compete with those of cascading dehydrogenation for the decomposition of the conjugate cyclohexyl radical. The major ring-opening pathways produce 1-buten-4-yl radical, molecular ethylene, and 1,3-butadiene. The butadiene species is formed via beta scission after a 1-4 internal hydrogen migration of 1-hexen-6-yl radical. Cascading dehydrogenation also makes an important contribution to the fuel decomposition and provides the exclusive formation pathway of benzene. Benzene formation routes via combination of C2-C4 hydrocarbon fragments were found to be insignificant under current flame conditions, inferred by the later concentration peak of fulvene, in comparison with benzene, because the analogous species series for benzene formation via dehydrogenation was found to be precursors with regard to parent species of fulvene.

A detailed kinetic modeling study of toluene oxidation in a premixed laminar flame

PubMed Central

Tian, Zhenyu; Pitz, William J.; Fournet, René; Glaude, Pierre-Alexander; Battin-Leclerc, Frédérique

2013-01-01

An improved chemical kinetic model for the toluene oxidation based on experimental data obtained in a premixed laminar low-pressure flame with vacuum ultraviolet (VUV) photoionization and molecular beam mass spectrometry (MBMS) techniques has been proposed. The present mechanism consists of 273 species up to chrysene and 1740 reactions. The rate constants of reactions of toluene decomposition, reaction with oxygen, ipso-additions and metatheses with abstraction of phenylic H-atom are updated; new pathways of C4 + C2 species giving benzene and fulvene are added. Based on the experimental observations, combustion intermediates such as fulvenallene, naphtol, methylnaphthalene, acenaphthylene, 2-ethynylnaphthalene, phenanthrene, anthracene, 1-methylphenanthrene, pyrene and chrysene are involved in the present mechanism. The final toluene model leads to an overall satisfactory agreement between the experimentally observed and predicted mole fraction profiles for the major products and most combustion intermediates. The toluene depletion is governed by metathese giving benzyl radicals, ipso-addition forming benzene and metatheses leading to C6H4CH3 radicals. A sensitivity analysis indicates that the unimolecular decomposition via the cleavage of a methyl C-H bond has a strong inhibiting effect, while decomposition via C-C bond breaking, ipso-addition of H-atom to toluene, decomposition of benzyl radicals and reactions related to C6H4CH3 radicals have promoting effect for the consumption of toluene. Moreover, flow rate analysis is performed to illustrate the formation pathways of mono- and polycyclic aromatics. PMID:23762016

Hysteresis and Phase Transitions in a Lattice Regularization of an Ill-Posed Forward-Backward Diffusion Equation

NASA Astrophysics Data System (ADS)

Helmers, Michael; Herrmann, Michael

2018-03-01

We consider a lattice regularization for an ill-posed diffusion equation with a trilinear constitutive law and study the dynamics of phase interfaces in the parabolic scaling limit. Our main result guarantees for a certain class of single-interface initial data that the lattice solutions satisfy asymptotically a free boundary problem with a hysteretic Stefan condition. The key challenge in the proof is to control the microscopic fluctuations that are inevitably produced by the backward diffusion when a particle passes the spinodal region.

Impact of OH Radical-Initiated H2CO3 Degradation in the Earth's Atmosphere via Proton-Coupled Electron Transfer Mechanism.

PubMed

Ghoshal, Sourav; Hazra, Montu K

2016-02-04

The decomposition of isolated carbonic acid (H2CO3) molecule into CO2 and H2O (H2CO3 → CO2 + H2O) is prevented by a large activation barrier (>35 kcal/mol). Nevertheless, it is surprising that the detection of the H2CO3 molecule has not been possible yet, and the hunt for the free H2CO3 molecule has become challenging not only in the Earth's atmosphere but also on Mars. In view of this fact, we report here the high levels of quantum chemistry calculations investigating both the energetics and kinetics of the OH radical-initiated H2CO3 degradation reaction to interpret the loss of the H2CO3 molecule in the Earth's atmosphere. It is seen from our study that proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) are the two mechanisms by which the OH radical initiates the degradation of the H2CO3 molecule. Moreover, the PCET mechanism is potentially the important one, as the effective barrier, defined as the difference between the zero point vibrational energy (ZPE) corrected energy of the transition state and the total energy of the isolated starting reactants in terms of bimolecular encounters, for the PCET mechanism at the CCSD(T)/6-311++G(3df,3pd) level of theory is ∼3 to 4 kcal/mol lower than the effective barrier height associated with the HAT mechanism. The CCSD(T)/6-311++G(3df,3pd) level predicted effective barrier heights for the degradations of the two most stable conformers of H2CO3 molecule via the PCET mechanism are only ∼2.7 and 4.3 kcal/mol. A comparative reaction rate analysis at the CCSD(T)/6-311++G(3df,3pd) level of theory has also been carried out to explore the potential impact of the OH radical-initiated H2CO3 degradation relative to that from water (H2O), formic acid (FA), acetic acid (AA) and sulfuric acid (SA) assisted H2CO3 → CO2 + H2O decomposition reactions in both the Earth's troposphere and stratosphere. The comparison of the reaction rates reveals that, although the atmospheric concentration of the OH radical is substantially lower than the concentrations of the H2O, FA, AA in the Earth's atmosphere, nevertheless, the OH radical-initiated H2CO3 degradation reaction has significant impact, especially toward the loss of the H2CO3 molecule in the Earth's atmosphere. In clean environments, which exist in greater numbers in comparison to the polluted environments of the Earth's atmosphere, the impact of the OH radical-initiated H2CO3 degradation reaction is seen to be comparable to that from a competing pathway which utilizes hydrogen bonded molecules such as H2O, FA or AA to catalyze the H2CO3 decomposition. Similarly, in the polluted environments, and especially in the Earth's troposphere, although the reactions rates for the OH radical-initiated H2CO3 degradation and FA-assisted H2CO3 decomposition are comparable within a factor of ∼15, nevertheless, the AA-assisted H2CO3 decomposition reaction is appeared to be the dominant channel. This follows only because of slightly greater catalytic efficiency of the AA over FA upon the H2CO3 → CO2 + H2O decomposition reaction. In contrary, although the catalytic efficiencies of SA, FA, and AA upon the H2CO3 decomposition reaction are similar to each other and the concentrations of both the SA and OH radical in the Earth's atmosphere are more-or-less equal to each other, but nevertheless, the SA-assisted H2CO3 decomposition reaction cannot compete with the OH radical-initiated H2CO3 degradation reaction.

Active Mechanism of the Interphase Film-Forming Process for an Electrolyte Based on a Sulfolane Solvent and a Chelato-Borate Complexe.

PubMed

Li, Chunlei; Wang, Peng; Li, Shiyou; Zhao, Dongni; Zhao, Qiuping; Liu, Haining; Cui, Xiao-Ling

2018-06-14

Electrolytes based on sulfolane (SL) solvents and lithium bis(oxalato)borate (LiBOB) chelato-borate complexes have been reported many times for use in advanced lithium-ion batteries due to their many advantages. This study aims to clarify the active mechanism of the interphase film-forming process to optimize the properties of these batteries by experimental analysis and theoretical calculations. The results indicate that the self-repairing film-forming process during the first cycle is divided into three stages: the initial film formation with an electric field force of ~1.80 V, the further growth of the preformation solid electrolyte interface (SEI) film at ~1.73 V, and the final formation of a complete SEI film at a potential below 0.7 V. Additionally, we can deduce that the decomposition of LiBOB and SL occurs throughout nearly the entire process of the formation of the SEI film. The decomposition product of BOB- anions tends to form films with an irregular structure, while the decomposition product of SL is in favor of the formation of a uniform SEI film.

Theoretical study on stabilization mechanisms of nitrate esters using aromatic amines as stabilizers.

PubMed

Sun, Zhi-Dan; Fu, Xiao-Long; Yu, Hong-Jian; Fan, Xue-Zhong; Ju, Xue-Hai

2017-10-05

The propellants of nitrate esters can be stabilized by some aromatic amines practically. To probe the mechanism of this phenomenon, we performed DFT calculations on: (1) The decompositions of nitrate esters (with and without the catalysis of NO 2 ) and (2) the reaction between the stabilizers and the nitro dioxide (NO 2 is released during the storage of nitrate esters). The structures on the reaction paths (reactants, intermediates and products) were optimized at the (U)B3LYP/6-31G** level. It was shown that NO 2 lowers the activation energy barrier in the decomposition of nitrate ester by 11.82-17.86kJ/mol and efficiently catalyzes the rupture of ONO 2 bond. However, the aromatic amines, typical stabilizers for nitrate esters, can easily eliminate NO 2 with activation barriers as low as 27-113kJ/mol (with one exception of 128kJ/mol). These values are, for most cases, lower or much lower than the activation energy barriers for reactions between nitrate esters and NO 2 (127-137kJ/mol). Consequently, the stabilizers can block the NO 2 catalysis for the decompositions of nitrate esters. Copyright © 2017 Elsevier B.V. All rights reserved.

Forest height estimation from mountain forest areas using general model-based decomposition for polarimetric interferometric synthetic aperture radar images

NASA Astrophysics Data System (ADS)

Minh, Nghia Pham; Zou, Bin; Cai, Hongjun; Wang, Chengyi

2014-01-01

The estimation of forest parameters over mountain forest areas using polarimetric interferometric synthetic aperture radar (PolInSAR) images is one of the greatest interests in remote sensing applications. For mountain forest areas, scattering mechanisms are strongly affected by the ground topography variations. Most of the previous studies in modeling microwave backscattering signatures of forest area have been carried out over relatively flat areas. Therefore, a new algorithm for the forest height estimation from mountain forest areas using the general model-based decomposition (GMBD) for PolInSAR image is proposed. This algorithm enables the retrieval of not only the forest parameters, but also the magnitude associated with each mechanism. In addition, general double- and single-bounce scattering models are proposed to fit for the cross-polarization and off-diagonal term by separating their independent orientation angle, which remains unachieved in the previous model-based decompositions. The efficiency of the proposed approach is demonstrated with simulated data from PolSARProSim software and ALOS-PALSAR spaceborne PolInSAR datasets over the Kalimantan areas, Indonesia. Experimental results indicate that forest height could be effectively estimated by GMBD.

Monolithic graded-refractive-index glass-based antireflective coatings. Broadband/omnidirectional light harvesting and self-cleaning characteristics

DOE PAGES

Aytug, Tolga; Lupini, Andrew R.; Jellison, Gerald E.; ...

2015-04-23

The design of multifunctional coatings impact impact the performance of many optical systems and components. Such coatings should be mechanically robust, and combine user-defined optical and wetting functions with scalable fabrication formulations. By taking cues from the properties of some natural biological structures, we report here the formation of low-refractive index antireflective glass films that embody omni-directional optical properties over a wide range of wavelengths, while also possessing specific wetting capabilities. The coatings comprise an interconnected network of nanoscale pores surrounded by a nanostructured silica framework. These structures result from a novel fabrication method that utilizes metastable spinodal phase separationmore » in glass-based materials. The approach not only enables design of surface microstructures with graded-index antireflection characteristics, where the surface reflection is suppressed through optical impedance matching between interfaces, but also facilitates self-cleaning ability through modification of the surface chemistry. Based on near complete elimination of Fresnel reflections (yielding >95% transmission through a single-side coated glass) and corresponding increase in broadband transmission, the fabricated nanostructured surfaces are found to promote a general and an invaluable ~3–7% relative increase in current output of multiple direct/indirect bandgap photovoltaic cells. Moreover, these antireflective surfaces also demonstrate superior resistance against mechanical wear and abrasion. Unlike conventional counterparts, the present antireflective coatings are essentially monolithic, enabling simultaneous realization of graded index anti-reflectivity, self-cleaning capability, and mechanical stability within the same surface. Moreover, the concept represents a fundamental basis for development of advanced coated optical quality products, especially where environmental exposure is required.« less

Room-temperature ferromagnetic transitions and the temperature dependence of magnetic behaviors in FeCoNiCr-based high-entropy alloys

NASA Astrophysics Data System (ADS)

Na, Suok-Min; Yoo, Jin-Hyeong; Lambert, Paul K.; Jones, Nicholas J.

2018-05-01

High-entropy alloys (HEAs) containing multiple principle alloying elements exhibit unique properties so they are currently receiving great attention for developing innovative alloy designs. In FeCoNi-based HEAs, magnetic behaviors strongly depend on the addition of alloying elements, usually accompanied by structural changes. In this work, the effect of non-magnetic components on the ferromagnetic transition and magnetic behaviors in equiatomic FeCoNiCrX (X=Al, Ga, Mn and Sn) HEAs was investigated. Alloy ingots of nominal compositions of HEAs were prepared by arc melting and the button ingots were cut into discs for magnetic measurements as functions of magnetic field and temperature. The HEAs of FeCoNiCrMn and FeCoNiCrSn show typical paramagnetic behaviors, composed of solid solution FCC matrix, while the additions of Ga and Al in FeCoNiCr exhibit ferromagnetic behaviors, along with the coexistence of FCC and BCC phases due to spinodal decomposition. The partial phase transition in both HEAs with the additions of Ga and Al would enhance ferromagnetic properties due to the addition of the BCC phase. The saturation magnetization for the base alloy FeCoNiCr is 0.5 emu/g at the applied field of 20 kOe (TC = 104 K). For the HEAs of FeCoNiCrGa and FeCoNiCrAl, the saturation magnetization significantly increased to 38 emu/g (TC = 703 K) and 25 emu/g (TC = 277 K), respectively. To evaluate the possibility of solid solution FCC and BCC phases in FeCoNiCr-type HEAs, we introduced a parameter of valence electron concentration (VEC). The proposed rule for solid solution formation by the VEC was matched with FeCoNiCr-type HEAs.

Cascades, ``Blobby'' Turbulence, and Target Pattern Formation in Elastic Systems: A New Take on Classic Themes in Plasma Turbulence

NASA Astrophysics Data System (ADS)

Fan, Xiang

2017-10-01

Concerns central to understanding turbulence and transport include: 1) Dynamics of dual cascades in EM turbulence; 2) Understanding `negative viscosity phenomena' in drift-ZF systems; 3) The physics of blobby turbulence (re: SOL). Here, we present a study of a simple model - that of Cahn-Hilliard Navier-Stokes (CHNS) Turbulence - which sheds important new light on these issues. The CHNS equations describe the motion of binary fluid undergoing a second order phase transition and separation called spinodal decomposition. The CHNS system and 2D MHD are analogous, as they both contain a vorticity equation and a ``diffusion'' equation. The CHNS system differs from 2D MHD by the appearance of negative diffusivity, and a nonlinear dissipative flux. An analogue of the Alfven wave exists in the 2D CHNS system. DNS shows that mean square concentration spectrum Hkψ scales as k - 7 / 3 in the elastic range. This suggests an inverse cascade of Hψ . However, the kinetic energy spectrum EkK scales as k-3 , as in the direct enstrophy cascade range for a 2D fluid (not MHD!). The resolution is that the feedback of capillarity acts only at blob interfaces. Thus, as blob merger progresses, the packing fraction of interfaces decreases, thus explaining the weakened surface tension feedback and the outcome for EkK. We also examine the evolution of scalar concentration in a single eddy in the Cahn-Hilliard system. This extends the classic problem of flux expulsion in 2D MHD. The simulation results show that a target pattern is formed. Target pattern is a meta stable state, since the band merger process continues on a time scale exponentially long relative to the eddy turnover time. Band merger resembles step merger in drift-ZF staircases. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Award Number DE-FG02-04ER54738.

Our Magnetic Universe: The Nature of High Polarization Prompt Gamma Ray Bursts and the Origin of Dark Energy

NASA Astrophysics Data System (ADS)

Greyber, Howard D.

2011-01-01

The author's "Strong” Magnetic Field model (SMF), created in 1961, is an approach identical to that urged for study by Zel'dovich in 1983. SMF is described in my 2005 paper, published in the CD of the Proceedings of the 22nd Texas Relativistic Astrophysics Symposium (also existing in Astro-ph0509223). A first order phase transition called the Spinodal Decomposition Instability causes a rapid exponential growth of the fluctuations at Combination Time. One of several important results from SMF is the very early generation, soon after Combination Time, of an intense, relativistic stable "storage current loop” in most active galaxies and quasars that was formed by gravitational collapse of the huge pre-galactic plasma cloud in the presence of the primordial magnetic field. This suggests that gamma ray bursts (GRB) are created, similar to what happens on Earth at an accelerator, by a beam on target (BOT) process. A dense target, like a white dwarf, neutron star, planet, et al, crossing the beam, causes the optical transient or "fireball” that is observed at the site of a gamma ray burst (GRB). The extremely powerful "storage current ring", or loop current, heats the target into a plasma blob. The plasma blob is accelerated, exits the current ring, passing through the enormous ordered magnetic field around the current loop, thus inducing the polarization that has been observed. An Appendix explains the Origin of Dark Energy according to the SMF model, which, uniquely, derives the Origin of Magnetic Fields occurring at Combination Time, (NOT far later when galaxies form, as believed by most astrophysicists for over eight decades), and also uses a comment by Albert Einstein. That result produces the unique Supercluster Topology where almost all the mass is on a shell surrounding an extremely high vacuum, explaining the current Accelerating Expansion observed in our universe.

Mass loss and chemical structures of wheat and maize straws in response to ultraviolet-B radiation and soil contact.

PubMed

Zhou, Guixiang; Zhang, Jiabao; Mao, Jingdong; Zhang, Congzhi; Chen, Lin; Xin, Xiuli; Zhao, Bingzi

2015-10-01

The role of photodegradation, an abiotic process, has been largely overlooked during straw decomposition in mesic ecosystems. We investigated the mass loss and chemical structures of straw decomposition in response to elevated UV-B radiation with or without soil contact over a 12-month litterbag experiment. Wheat and maize straw samples with and without soil contact were exposed to three radiation levels: a no-sunlight control, ambient solar UV-B, and artificially elevated UV-B radiation. A block control with soil contact was not included. Compared with the no-sunlight control, UV-B radiation increased the mass loss by 14-19% and the ambient radiation by 9-16% for wheat and maize straws without soil contact after 12 months. Elevated UV-B exposure decreased the decomposition rates of both wheat and maize straws when in contact with soil. Light exposure resulted in decreased O-alkyl carbons and increased alkyl carbons for both the wheat and maize straws compared with no-sunlight control. The difference in soil contact may influence the contribution of photodegradation to the overall straw decomposition process. These results indicate that we must take into account the effects of photodegradation when explaining the mechanisms of straw decomposition in mesic ecosystems.

Limited-memory adaptive snapshot selection for proper orthogonal decomposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oxberry, Geoffrey M.; Kostova-Vassilevska, Tanya; Arrighi, Bill

2015-04-02

Reduced order models are useful for accelerating simulations in many-query contexts, such as optimization, uncertainty quantification, and sensitivity analysis. However, offline training of reduced order models can have prohibitively expensive memory and floating-point operation costs in high-performance computing applications, where memory per core is limited. To overcome this limitation for proper orthogonal decomposition, we propose a novel adaptive selection method for snapshots in time that limits offline training costs by selecting snapshots according an error control mechanism similar to that found in adaptive time-stepping ordinary differential equation solvers. The error estimator used in this work is related to theory boundingmore » the approximation error in time of proper orthogonal decomposition-based reduced order models, and memory usage is minimized by computing the singular value decomposition using a single-pass incremental algorithm. Results for a viscous Burgers’ test problem demonstrate convergence in the limit as the algorithm error tolerances go to zero; in this limit, the full order model is recovered to within discretization error. The resulting method can be used on supercomputers to generate proper orthogonal decomposition-based reduced order models, or as a subroutine within hyperreduction algorithms that require taking snapshots in time, or within greedy algorithms for sampling parameter space.« less

Thermal decomposition pathways of hydroxylamine: theoretical investigation on the initial steps.

PubMed

Wang, Qingsheng; Wei, Chunyang; Pérez, Lisa M; Rogers, William J; Hall, Michael B; Mannan, M Sam

2010-09-02

Hydroxylamine (NH(2)OH) is an unstable compound at room temperature, and it has been involved in two tragic industrial incidents. Although experimental studies have been carried out to study the thermal stability of hydroxylamine, the detailed decomposition mechanism is still in debate. In this work, several density functional and ab initio methods were used in conjunction with several basis sets to investigate the initial thermal decomposition steps of hydroxylamine, including both unimolecular and bimolecular reaction pathways. The theoretical investigation shows that simple bond dissociations and unimolecular reactions are unlikely to occur. The energetically favorable initial step of decomposition pathways was determined as a bimolecular isomerization of hydroxylamine into ammonia oxide with an activation barrier of approximately 25 kcal/mol at the MPW1K level of theory. Because hydroxylamine is available only in aqueous solutions, solvent effects on the initial decomposition pathways were also studied using water cluster methods and the polarizable continuum model (PCM). In water, the activation barrier of the bimolecular isomerization reaction decreases to approximately 16 kcal/mol. The results indicate that the bimolecular isomerization pathway of hydroxylamine is more favorable in aqueous solutions. However, the bimolecular nature of this reaction means that more dilute aqueous solution will be more stable.

Thermal decomposition of condensed-phase nitromethane from molecular dynamics from ReaxFF reactive dynamics.

PubMed

Han, Si-ping; van Duin, Adri C T; Goddard, William A; Strachan, Alejandro

2011-05-26

We studied the thermal decomposition and subsequent reaction of the energetic material nitromethane (CH(3)NO(2)) using molecular dynamics with ReaxFF, a first principles-based reactive force field. We characterize the chemistry of liquid and solid nitromethane at high temperatures (2000-3000 K) and density 1.97 g/cm(3) for times up to 200 ps. At T = 3000 K the first reaction in the decomposition of nitromethane is an intermolecular proton transfer leading to CH(3)NOOH and CH(2)NO(2). For lower temperatures (T = 2500 and 2000 K) the first reaction during decomposition is often an isomerization reaction involving the scission of the C-N bond the formation of a C-O bond to form methyl nitrate (CH(3)ONO). Also at very early times we observe intramolecular proton transfer events. The main product of these reactions is H(2)O which starts forming following those initiation steps. The appearance of H(2)O marks the beginning of the exothermic chemistry. Recent quantum-mechanics-based molecular dynamics simulations on the chemical reactions and time scales for decomposition of a crystalline sample heated to T = 3000 K for a few picoseconds are in excellent agreement with our results, providing an important, direct validation of ReaxFF.

Laser augmented decomposition. II. D/sub 3/BPF/sub 3/. [Deuterium effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chien, K.R.; Bauer, S.H.

1976-06-17

The study of the accelerated decomposition of H/sub 3/BPF/sub 3/ induced by laser radiation (930-950 cm/sup -1/ was extended to the fully deuterated species. While in all essential respects the kinetics of the ir photolysis for the two compounds are identical, the few differences which were uncovered proved crucial in pointing to interesting features of the mechanism. These verified predictions were based on a normal mode analysis for the distribution of potential energy among the internal coordinates. For the laser augmented decomposition, E/sub a//sup L/ = 3.5 +- 1 kcal/mol, compared with E/sub a//sup th/ = 29.3 kcal/mol for themore » thermal process. The quantum efficiency is low, approximately 4 x 10/sup 4/ photons/molecule decomposed. The rates of decomposition depend on the isotopic content and are sensitively dependent on the frequency of the irradiating line. For example, with P(24) large fractionation ratios were found for D/sub 3/BPF/sub 3/ vs. H/sub 3/BPF/sub 3/, and small differences for D/sub 3//sup 11/BPF/sub 3/ vs. D/sub 3//sup 10/BPF/sub 3/. The levels of decomposition induced by the sequential three-photon absorption have been semiquantitatively accounted for.« less

Effect of the carbon coating in Fe-C-TiO(2) photocatalyst on phenol decomposition under UV irradiation via photo-Fenton process.

PubMed

Tryba, Beata; Morawski, Antoni W; Inagaki, Michio; Toyoda, Masahiro

2006-08-01

Fe-C-TiO(2) photocatalysts which contained the residue carbon (0.2-3.3 mass%) were prepared from a mixture of TiO(2) and FeC(2)O(4) through the heating at 673-1173 K in Ar. These photocatalysts did not show a high adsorption of phenol, but they were active in photo-Fenton reactions during decomposition of phenol under UV irradiation with addition of H(2)O(2). It was proved that Fe(2+) governed the photoactivity of Fe-C-TiO(2) photocatalysts, it decreased with heat-treatment temperature above 773 K. For comparison, Fe-TiO(2) photocatalyst was prepared by heating TiO(2) and FeC(2)O(4) at 823 K in air for 3h. Phenol decomposition was going much slower on Fe-TiO(2) photocatalyst in comparison with Fe-C-TiO(2), of which mechanism was different, on the former phenol was decomposed by the radical reaction, on the latter through a complex reaction with iron and intermediates of phenol decomposition. Therefore carbon-coating TiO(2) was found to be advantageous for mounting iron and its application for the phenol decomposition via photo-Fenton process.

Mass loss and chemical structures of wheat and maize straws in response to ultraviolet-B radiation and soil contact

PubMed Central

Zhou, Guixiang; Zhang, Jiabao; Mao, Jingdong; Zhang, Congzhi; Chen, Lin; Xin, Xiuli; Zhao, Bingzi

2015-01-01

The role of photodegradation, an abiotic process, has been largely overlooked during straw decomposition in mesic ecosystems. We investigated the mass loss and chemical structures of straw decomposition in response to elevated UV-B radiation with or without soil contact over a 12-month litterbag experiment. Wheat and maize straw samples with and without soil contact were exposed to three radiation levels: a no-sunlight control, ambient solar UV-B, and artificially elevated UV-B radiation. A block control with soil contact was not included. Compared with the no-sunlight control, UV-B radiation increased the mass loss by 14–19% and the ambient radiation by 9–16% for wheat and maize straws without soil contact after 12 months. Elevated UV-B exposure decreased the decomposition rates of both wheat and maize straws when in contact with soil. Light exposure resulted in decreased O-alkyl carbons and increased alkyl carbons for both the wheat and maize straws compared with no-sunlight control. The difference in soil contact may influence the contribution of photodegradation to the overall straw decomposition process. These results indicate that we must take into account the effects of photodegradation when explaining the mechanisms of straw decomposition in mesic ecosystems. PMID:26423726

Thermal decomposition of europium sulfates Eu2(SO4)3·8H2O and EuSO4

NASA Astrophysics Data System (ADS)

Denisenko, Yu. G.; Khritokhin, N. A.; Andreev, O. V.; Basova, S. A.; Sal'nikova, E. I.; Polkovnikov, A. A.

2017-11-01

Reactions of europium sulfates Eu2(SO4)3·8H2O and EuSO4 complete decomposition were studied by Simultaneous Thermal Analysis. It was revealed that one-step dehydratation of Eu2(SO4)3·8H2O crystallohydrate is accompanied by the formation of amorphous anhydrous europium sulfate Eu2(SO4)3. Crystallization of amorphous europium (III) sulfate occurs at 381.1 °C (in argon) and 391.3 °C (in air). The average enthalpy values for dehydratation reaction of Eu2(SO4)3·8H2O (ΔH° = 141.1 kJ/mol), decomposition reactions of Eu2(SO4)3 (ΔH = 463.1 kJ/mol), Eu2O2SO4 (ΔH = 378.4 kJ/mol) and EuSO4 (ΔH = 124.1 kJ/mol) were determined. The step process mechanisms of thermal decomposition of europium (III) sulfate in air and europium (II) sulfate in inert atmosphere were established and justified. The kinetic parameters of complete thermal decomposition of europium (III) sulfate octahydrate were calculated by Kissinger model. The standard enthalpies of compound formation were calculated using thermal effects and formation enthalpy data for binary compounds.

Decomposition of toluene in a steady-state atmospheric-pressure glow discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trushkin, A. N.; Grushin, M. E.; Kochetov, I. V.

Results are presented from experimental studies of decomposition of toluene (C{sub 6}H{sub 5}CH{sub 3}) in a polluted air flow by means of a steady-state atmospheric pressure glow discharge at different water vapor contents in the working gas. The experimental results on the degree of C{sub 6}H{sub 5}CH{sub 3} removal are compared with the results of computer simulations conducted in the framework of the developed kinetic model of plasma chemical decomposition of toluene in the N{sub 2}: O{sub 2}: H{sub 2}O gas mixture. A substantial influence of the gas flow humidity on toluene decomposition in the atmospheric pressure glow discharge ismore » demonstrated. The main mechanisms of the influence of humidity on C{sub 6}H{sub 5}CH{sub 3} decomposition are determined. The existence of two stages in the process of toluene removal, which differ in their duration and the intensity of plasma chemical decomposition of C{sub 6}H{sub 5}CH{sub 3} is established. Based on the results of computer simulations, the composition of the products of plasma chemical reactions at the output of the reactor is analyzed as a function of the specific energy deposition and gas flow humidity. The existence of a catalytic cycle in which hydroxyl radical OH acts a catalyst and which substantially accelerates the recombination of oxygen atoms and suppression of ozone generation when the plasma-forming gas contains water vapor is established.« less

Stability analysis of gyroscopic systems with delay via decomposition

NASA Astrophysics Data System (ADS)

Aleksandrov, A. Yu.; Zhabko, A. P.; Chen, Y.

2018-05-01

A mechanical system describing by the second order linear differential equations with a positive parameter at the velocity forces and with time delay in the positional forces is studied. Using the decomposition method and Lyapunov-Krasovskii functionals, conditions are obtained under which from the asymptotic stability of two auxiliary first order subsystems it follows that, for sufficiently large values of the parameter, the original system is also asymptotically stable. Moreover, it is shown that the proposed approach can be applied to the stability investigation of linear gyroscopic systems with switched positional forces.

Comment on “A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states” [J. Chem. Phys. 142, 124312 (2015)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harding, Lawrence B.; Klippenstein, Stephen J.

2015-10-28

We discuss the recent report of a roaming type mechanism for the decomposition of the Criegee intermediate. We show that the predicted barrier height for this new pathway is too low by ∼30 kcal/mol owing to an inconsistent use of spin-restricted and spin-unrestricted calculations. As a result, this new pathway is not expected to compete significantly with the well-known dioxirane pathways for the decomposition of the Criegee intermediate.

A transient semimetallic layer in detonating nitromethane

NASA Astrophysics Data System (ADS)

Reed, Evan J.; Riad Manaa, M.; Fried, Laurence E.; Glaesemann, Kurt R.; Joannopoulos, J. D.

2008-01-01

Despite decades of research, the microscopic details and extreme states of matter found within a detonating high explosive have yet to be elucidated. Here we present the first quantum molecular-dynamics simulation of a shocked explosive near detonation conditions. We discover that the wide-bandgap insulator nitromethane (CH3NO2) undergoes chemical decomposition and a transformation into a semimetallic state for a limited distance behind the detonation front. We find that this transformation is associated with the production of charged decomposition species and provides a mechanism to explain recent experimental observations.

Ab initio molecular dynamics simulations of the initial stages of solid-electrolyte interphase formation on lithium ion battery graphitic anodes.

PubMed

Leung, Kevin; Budzien, Joanne L

2010-07-07

The decomposition of ethylene carbonate (EC) during the initial growth of solid-electrolyte interphase (SEI) films at the solvent-graphitic anode interface is critical to lithium ion battery operations. Ab initio molecular dynamics simulations of explicit liquid EC/graphite interfaces are conducted to study these electrochemical reactions. We show that carbon edge terminations are crucial at this stage, and that achievable experimental conditions can lead to surprisingly fast EC breakdown mechanisms, yielding decomposition products seen in experiments but not previously predicted.