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1

Method of operating a thermal engine powered by a chemical reaction  

DOEpatents

The invention involves a novel method of increasing the efficiency of a thermal engine. Heat is generated by a non-linear chemical reaction of reactants, said heat being transferred to a thermal engine such as Rankine cycle power plant. The novel method includes externally perturbing one or more of the thermodynamic variables of said non-linear chemical reaction. 7 figs.

Ross, J.; Escher, C.

1988-06-07

2

Method and apparatus for obtaining enhanced production rate of thermal chemical reactions  

DOEpatents

The present invention is a method and apparatus (vessel) for providing a heat transfer rate from a reaction chamber through a wall to a heat transfer chamber substantially matching a local heat transfer rate of a catalytic thermal chemical reaction. The key to the invention is a thermal distance defined on a cross sectional plane through the vessel inclusive of a heat transfer chamber, reaction chamber and a wall between the chambers. The cross sectional plane is perpendicular to a bulk flow direction of the reactant stream, and the thermal distance is a distance between a coolest position and a hottest position on the cross sectional plane. The thermal distance is of a length wherein the heat transfer rate from the reaction chamber to the heat transfer chamber substantially matches the local heat transfer rate.

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Wegeng, Robert S [Richland, WA; Gao, Yufei [Kennewick, WA

2003-04-01

3

Solar photo-thermal catalytic reactions to produce high value chemicals  

SciTech Connect

This report presents a summary of the research work accomplished to date on the utilization of solar photo-thermal energy to convert low cost chemical feedstocks into high $-value chemical products. The rationale is that the solar IR-VIS-UV spectrum is unique, supplying endothermic reaction energy as well as VIS-UV for photochemical activation. Chemical market analysis and product price distribution focused attention on speciality chemicals with prices >$1.00/lb, and a synthesis sequence of n-paraffins to aromatics to partial oxidized products. The experimental work has demonstrated that enhanced reaction effects result from VIS-UV irradiation of catalytically active V2O5/SiO2. Experiments of the past year have been on dehydrogenation and dehydrocyclization of n-paraffins to olefins and aromatics with preference for the latter. Recent results using n-hexane produced 95% conversion with 56% benzene; it is speculated that aromatic yield should reach {approximately}70% by further optimization. Pilot- and commercial-scale reactor configurations have been examined; the odds-on-favorite being a shallow fluid-bed of catalyst with incident radiation from the top. Sequencing for maximum cost effectiveness would be day-time endothermic followed by night-time exothermic reactions to produce the products.

Prengle, H.W. Jr.; Wentworth, W.E. [Houston Univ., TX (United States)] [Houston Univ., TX (United States)

1992-04-01

4

Mass Transfer with Chemical Reaction on Flow Past an Accelerated Vertical Plate with Variable Temperature and Thermal Radiation  

NASA Astrophysics Data System (ADS)

An exact solution of an unsteady radiative flow past a uniformly accelerated infinite vertical plate with variable temperature and mass diffusion is presented here, taking into account the homogeneous chemical reaction of first order. The plate temperature as well as concentration near the plate is raised linearly with time. The dimensionless governing equations are solved using the Laplace-transform technique. The velocity, temperature and concentration fields are studied for different physical parameters such as the thermal Grashof number, mass Grashof number, Schmidt number, Prandtl number, radiation parameter, chemical reaction parameter and time. It is observed that the velocity increases with increasing values of the thermal Grashof number or mass Grashof number. But the trend is just reversed with respect to the thermal radiation parameter. It is also observed that the velocity increases with the decreasing chemical reaction parameter

Muthucumaraswamy, R.; Balachandran, P.; Ganesan, K.

2013-08-01

5

Solar photo-thermal catalytic reactions to produce high value chemicals.  

National Technical Information Service (NTIS)

This report presents a summary of the research work accomplished to date on the utilization of solar photo-thermal energy to convert low cost chemical feedstocks into high $-value chemical products. The rationale is that the solar IR-VIS-UV spectrum is un...

H. W. Prengle W. E. Wentworth

1992-01-01

6

Application of a reversible chemical reaction system to solar thermal power plants  

NASA Technical Reports Server (NTRS)

Three distributed dish solar thermal power systems using various applications of SO2/SO3 chemical energy storage and transport technology were comparatively assessed. Each system features various roles for the chemical system: (1) energy storage only, (2) energy transport, or (3) energy transport and storage. These three systems were also compared with the dish-Stirling, using electrical transport and battery storage, and the central receiver Rankine system, with thermal storage, to determine the relative merit of plants employing a thermochemical system. As an assessment criterion, the busbar energy costs were compared. Separate but comparable solar energy cost computer codes were used for distributed receiver and central receiver systems. Calculations were performed for capacity factors ranging from 0.4 to 0.8. The results indicate that SO2/SO3 technology has the potential to be more cost effective in transporting the collected energy than in storing the energy for the storage capacity range studied (2-15 hours)

Hanseth, E. J.; Won, Y. S.; Seibowitz, L. P.

1980-01-01

7

Application of a reversible chemical reaction system to solar thermal power plants  

NASA Astrophysics Data System (ADS)

Three distributed dish solar thermal power systems using various applications of SO2/SO3 chemical energy storage and transport technology were comparatively assessed. Each system features various roles for the chemical system: (1) energy storage only, (2) energy transport, or (3) energy transport and storage. These three systems were also compared with the dish-Stirling, using electrical transport and battery storage, and the central receiver Rankine system, with thermal storage, to determine the relative merit of plants employing a thermochemical system. As an assessment criterion, the busbar energy costs were compared. Separate but comparable solar energy cost computer codes were used for distributed receiver and central receiver systems. Calculations were performed for capacity factors ranging from 0.4 to 0.8. The results indicate that SO2/SO3 technology has the potential to be more cost effective in transporting the collected energy than in storing the energy for the storage capacity range studied (2-15 hours)

Hanseth, E. J.; Won, Y. S.; Seibowitz, L. P.

1980-08-01

8

Chemical reactions with aerosols  

NASA Astrophysics Data System (ADS)

Chemical reactions of aerosol droplets with vapors are discussed. Examples are given in which liquid aerosols of 1-octadecene of narrow size distribution are converted to 1,2-dibromooctadecane with bromine vapor. It was shown that the chemical reaction in the droplet controls the kinetics of this process. The application of chemical reactions with aerosols to the formation of pure, uniform spherical particles of metal oxides is also described. Droplets of metal alkoxides rapidly react with water vapor to yield well-defined powders. The technique was used to prepare titanium dioxide, aluminum oxide, and particles consisting of both metal oxides. This procedure allows generation of powders of predetermined size and composition.

Matijevi?, Egon

9

Chemical Reactions and Pancakes  

NSDL National Science Digital Library

Students will compare ingredients in two different pancake recipes, then taste the difference. We will talk about the chemical reaction that happened when the recipes are mixed and why there are bubbles in the pancakes.

10

Translated chemical reaction networks.  

PubMed

Many biochemical and industrial applications involve complicated networks of simultaneously occurring chemical reactions. Under the assumption of mass action kinetics, the dynamics of these chemical reaction networks are governed by systems of polynomial ordinary differential equations. The steady states of these mass action systems have been analyzed via a variety of techniques, including stoichiometric network analysis, deficiency theory, and algebraic techniques (e.g., Gröbner bases). In this paper, we present a novel method for characterizing the steady states of mass action systems. Our method explicitly links a network's capacity to permit a particular class of steady states, called toric steady states, to topological properties of a generalized network called a translated chemical reaction network. These networks share their reaction vectors with their source network but are permitted to have different complex stoichiometries and different network topologies. We apply the results to examples drawn from the biochemical literature. PMID:24610094

Johnston, Matthew D

2014-05-01

11

Method and apparatus for obtaining enhanced production rate of thermal chemical reactions  

DOEpatents

Reactors and processes are disclosed that can utilize high heat fluxes to obtain fast, steady-state reaction rates. Porous catalysts used in conjunction with microchannel reactors to obtain high rates of heat transfer are also disclosed. Reactors and processes that utilize short contact times, high heat flux and low pressure drop are described. Improved methods of steam reforming are also provided.

Tonkovich, Anna Lee Y. (Pasco, WA); Wang, Yong (Richland, WA); Wegeng, Robert S. (Richland, WA); Gao, Yufei (Kennewick, WA)

2006-05-16

12

Chemical reaction dynamics  

PubMed Central

Understanding the motions of the constituent atoms in reacting molecules lies at the heart of chemistry and is the central focus of chemical reaction dynamics. The most detailed questions one can ask are about the evolution of molecules prepared in a single quantum state to products in individual states, and both calculations and experiments are providing such detailed understanding of increasingly complex systems. A central goal of these studies is uncovering the essential details of chemical change by removing the averaging over the initial conditions that occurs in many cases. Such information provides an exquisite test of theory and helps paint pictures of complicated chemical transformations. The goal of this Special Feature is to provide a snapshot of a portion of the field of chemical reaction dynamics. Much of the work presented here emphasizes a close interplay of experiment and theory in ways that sharpen the conclusions of both and animate future studies. The articles do not completely cover the rich field of chemical reaction dynamics but rather provide a glimpse of some of the emerging insights.

Crim, F. Fleming

2008-01-01

13

Chemical Reactions at Surfaces  

SciTech Connect

Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

Michael Henderson and Nancy Ryan Gray

2010-04-14

14

Chemical Reaction Effects on MHD Flow Past a Linearly Accelerated Vertical Plate with Variable Temperature and Mass Diffusion in the Presence of Thermal Radiation  

NASA Astrophysics Data System (ADS)

An exact solution of first order chemical reaction effects on a radiative flow past a linearly accelerated infinite isothermal vertical plate with variable mass diffusion, under the action of a transversely applied magnetic field has been presented. The plate temperature is raised linearly with time and the concentration level near the plate is also raised to C'w linearly with time. The dimensionless governing equations are tackled using the Laplace-transform technique. The velocity, temperature and concentration fields are studied for different physical parameters such as the magnetic field parameter, radiation parameter, chemical reaction parameter, thermal Grashof number, mass Grashof number, Schmidt number, Prandtl number and time. It is observed that velocity increases with decreasing magnetic field parameter or radiation parameter. But the trend is just reversed with respect to the chemical reaction parameter

Muthucumaraswamy, R.; Geetha, E.

2013-08-01

15

Mass Transfer with Chemical Reaction.  

ERIC Educational Resources Information Center

Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

DeCoursey, W. J.

1987-01-01

16

A review of reaction rates and thermodynamic and transport properties for the 11-species air model for chemical and thermal nonequilibrium calculations to 30000 K  

NASA Technical Reports Server (NTRS)

Reaction rate coefficients and thermodynamic and transport properties are provided for the 11-species air model which can be used for analyzing flows in chemical and thermal nonequilibrium. Such flows will likely occur around currently planned and future hypersonic vehicles. Guidelines for determining the state of the surrounding environment are provided. Approximate and more exact formulas are provided for computing the properties of partially ionized air mixtures in such environments.

Gupta, Roop N.; Yos, Jerrold M.; Thompson, Richard A.

1989-01-01

17

Strontium isotopes as an indicator of water-rock reaction for the Coupled Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) Experimental Facility at DUSEL  

Microsoft Academic Search

The Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) Experimental Facility is a proposed facility at the DUSEL-Homestake that will be used to investigate reactive transport, heat transfer and the resulting biological responses within a natural fractured rock. As part of THMCB facility design we are characterizing the current geochemical conditions and developing geochemical and isotopic indicators for fluid flow paths and reaction rates. The proposed

K. Maher; N. J. Olsen; C. Harris; T. L. Jones; M. E. Conrad; E. L. Sonnenthal; D. Elsworth; N. Uzunlar; B. J. Mailloux; R. P. Lowell

2010-01-01

18

Microfabricated electrochemiluminescence cell for chemical reaction detection  

DOEpatents

A detector cell for a silicon-based or non-silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The detector cell is an electrochemiluminescence cell constructed of layers of silicon with a cover layer of glass, with spaced electrodes located intermediate various layers forming the cell. The cell includes a cavity formed therein and fluid inlets for directing reaction fluid therein. The reaction chamber and detector cell may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The ECL cell may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

Northrup, M. Allen (Berkeley, CA); Hsueh, Yun-Tai (Davis, CA); Smith, Rosemary L. (Davis, CA)

2003-01-01

19

Chemical Reactions: Investigating Exothermic and Endothermic Reactions  

NSDL National Science Digital Library

This activity is an inquiry-based investigation where students discover the indicators of chemical reactions (endothermic and exothermic) by collecting data and using that data to develop a testable question for further experimentation.

20

Microfabricated sleeve devices for chemical reactions  

DOEpatents

A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and non-silicon based materials to provide the thermal properties desired. For example, the chamber may combine a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

Northrup, M. Allen (Berkeley, CA)

2003-01-01

21

Desalination of Thermal Water from Ixtapan De La Sal, Mex. By Means of Chemical Reactions, Ultrasound and Flotation Cell  

NASA Astrophysics Data System (ADS)

It is an excellent process because, the sodium chloride was converted into AgCl and calcium, sodium sulfate. The silver can be recovery from AgCl and from the final solution. Only it is necessary to design new tests in order to improve the time duration process and chemical reactive dose. Because for the equipment used, the process can be scaled to a largest seawater desalination. The bactericidal effect of the process and ultrasound is very important because the final water could be drinkable without harmful bacteria. Only spores and fungus remained 0.35% using ultrasound. The same process could be good for the seawater desalination because the chemical reactions are the same.

Abrego, Josef.

22

Chemical Energy Storage for Solar Thermal Conversion. Final Report.  

National Technical Information Service (NTIS)

The technical and economic aspects of using reversible chemical reactions to store energy in Solar Thermal Electric Conversion (STEC) facilities have been studied. The study included identification of nine promising chemical reactions from a list of over ...

R. D. Smith

1979-01-01

23

Monotonicity in chemical reaction systems  

Microsoft Academic Search

This article discusses the question of when the dynamical systems arising from chemical reaction networks are monotone, preserving an order induced by some proper cone. The reaction systems studied are defined by the reaction network structure while the kinetics is only constrained very weakly. Necessary and sufficient conditions on cones preserved by these systems are presented. Linear coordinate changes which

Murad Banaji

2009-01-01

24

More on Chemical Reaction Balancing.  

ERIC Educational Resources Information Center

A previous article stated that only the matrix method was powerful enough to balance a particular chemical equation. Shows how this equation can be balanced without using the matrix method. The approach taken involves writing partial mathematical reactions and redox half-reactions, and combining them to yield the final balanced reaction. (JN)

Swinehart, D. F.

1985-01-01

25

Thermal hyperspectral chemical imaging  

NASA Astrophysics Data System (ADS)

Several chemical compounds have their strongest spectral signatures in the thermal region. This paper presents three push-broom thermal hyperspectral imagers. The first operates in MWIR (2.8-5 ?m) with 35 nm spectral resolution. It consists of uncooled imaging spectrograph and cryogenically cooled InSb camera, with spatial resolution of 320/640 pixels and image rate to 400 Hz. The second imager covers LWIR in 7.6-12 ?m with 32 spectral bands. It employs an uncooled microbolometer array and spectrograph. These imagers have been designed for chemical mapping in reflection mode in industry and laboratory. An efficient line-illumination source has been developed, and it makes possible thermal hyperspectral imaging in reflection with much higher signal and SNR than is obtained from room temperature emission. Application demonstrations including sorting of dark plastics and mineralogical mapping of drill cores are presented. The third imager utilizes a cryo-cooled MCT array with precisely temperature stabilized optics. The optics is not cooled, but instrument radiation is suppressed by special filtering and corrected by BMC (Background-Monitoring-on-Chip) method. The approach provides excellent sensitivity in an instrument which is portable and compact enough for installation in UAVs. The imager has been verified in 7.6 to 12.3 ?m to provide NESR of 18 mW/(m2 sr ?m) at 10 ?m for 300 K target with 100 spectral bands and 384 spatial samples. It results in SNR of higher than 500. The performance makes possible various applications from gas detection to mineral exploration and vegetation surveys. Results from outdoor and airborne experiments are shown.

Holma, Hannu; Hyvärinen, Timo; Mattila, Antti-Jussi; Kormano, Ilkka

2012-05-01

26

Speeding chemical reactions by focusing  

NASA Astrophysics Data System (ADS)

We present numerical results for a chemical reaction of colloidal particles which are transported by a laminar fluid and are focused by periodic obstacles in such a way that the two components are well mixed and consequently the chemical reaction is speeded up. The roles of the various system parameters (diffusion coefficients, reaction rate, and obstacles sizes) are studied. We show that focusing speeds up the reaction from the diffusion limited rate ~t-1/2 to very close to the perfect mixing rate, ~t-1.

Lacasta, A. M.; Ramírez-Piscina, L.; Sancho, J. M.; Lindenberg, K.

2013-04-01

27

Prediction of thermal hazards of chemical reactions 1 Based on a paper published in German in Praxis der Sicherheitstechnik, Vol. 4, DECHEMA, Frankfurt a.M., 1997. 1  

Microsoft Academic Search

A large number of products of the chemical industry are produced using potentially hazardous reactions. The experimental investigation of the hazards of all reactions involved in production processes would be very expensive. The primary reactions—desired reactions which are part of the process—and the secondary reactions—undesired successive or side reactions—should both be considered. In this paper the methods of prediction of

Theodor Grewer; David J. Frurip; B. Keith Harrison

1999-01-01

28

Thermal, Photon and Electron-Induced Chemical Reactions of Sulfur and Nitrogen Containing Adsorbates on Transition Metal Surfaces  

NASA Astrophysics Data System (ADS)

The photon-induced desorption of SO_ {rm 2(a)} from Ag(111) at 106 K was measured in situ as a function of wavelength and correlated with literature results for the absorptivity and photoelectron yield of bulk and (111) silver, respectively. Photodesorption is attributed to metal-to-adsorbate electron transfer. The initial photodesorption rate was measured at (313 +/- 10) nm as a function of initial coverage. The initial rates were analyzed and found to increase monotonically up to 1 ML and then the sharply decrease as multilayers form. Initial rates were also measured at (313 +/- 10) nm as a function of photon flux and surface temperature for an initial coverage of 1 ML. The initial rates were found to be temperature independent between 106-138 K and to increase linearly with the incident photon flux. Average rates were found to be strongly dependent on substrate temperature. The interaction of SO_2 with electrons (with kinetic energy of about 54 eV) was measured as a function of coverage. From 0 up to 1 ML, only electron stimulated desorption was found. Above 1 ML, electron induced decomposition of physisorbed layers was readily observed. This is attributed to strong quenching of excited molecules in the first layer by the metal surface. For 1 ML, the dependence of the initial desorption rate on electron energy was investigated. A threshold of ~20 eV was found; the ESD process is explained by a mechanism involving ionization from the oxygen 2s atomic orbital followed by quenching and desorption by the Antoniweicz mechanism. The interaction of chemisorbed azomethane on Ag(111) at 106 K with low energy electrons (0-50 eV) was also investigated. In contrast with SO_2, adsorbed CH _3N_2CH _3 is found to readily dissociate upon electron irradiation to gaseous N_2 and C _1-C_2 hydrocarbons. The electron energy dependence of the electron induced decomposition (EID) reaction was measured and found to be about 10 eV. The EID process is attributed to ionization of chemisorbed molecules with subsequent quenching to repulsive states in the H_3C-(N)_2 bond potential. The thermal decomposition of methanethiol was investigated on Ni(111) and (100). CH_3 SH is found to dissociate upon adsorption to form a thiomethoxy intermediate. The thiomethoxy decomposes by C-S bond scission to form a short lived CH_ {rm 3(a)}, which undergoes hydrogenation to desorbing methane and dehydrogenation to CH _{rm x} fragments. A strong stabilization effect by preadsorbed sulfur on C-S and C -H bond activation was found.

Castro-Rosario, Miguel Eduardo

29

Influence of fluctuating thermal and mass diffusion on unsteady MHD buoyancy-driven convection past a vertical surface with chemical reaction and Soret effects  

NASA Astrophysics Data System (ADS)

The influence of thermal radiation and first-order chemical reaction on unsteady MHD convective flow, heat and mass transfer of a viscous incompressible electrically conducting fluid past a semi-infinite vertical flat plate in the presence of transverse magnetic field under oscillatory suction and heat source in slip-flow regime is studied. The dimensionless governing equations for this investigation are formulated and solved analytically using two-term harmonic and non-harmonic functions. Comparisons with previously published work on special cases of the problem are performed and results are found to be in excellent agreement. A parametric study illustrating the effects of various physical parameters on the fluid velocity, temperature and concentration fields as well as skin-friction coefficient, the Nusselt and Sherwood numbers in terms of amplitude and phase is conducted. The numerical results of this parametric study are presented graphically and in tabular form to highlight the physical aspects of the problem.

Pal, Dulal; Talukdar, Babulal

2012-04-01

30

A review of reaction rates and thermodynamic and transport properties for an 11-species air model for chemical and thermal nonequilibrium calculations to 30000 K  

NASA Technical Reports Server (NTRS)

Reaction rate coefficients and thermodynamic and transport properties are reviewed and supplemented for the 11-species air model which can be used for analyzing flows in chemical and thermal nonequilibrium up to temperatures of 3000 K. Such flows will likely occur around currently planned and future hypersonic vehicles. Guidelines for determining the state of the surrounding environment are provided. Curve fits are given for the various species properties for their efficient computation in flowfield codes. Approximate and more exact formulas are provided for computing the properties of partially ionized air mixtures in a high energy environment. Limitations of the approximate mixing laws are discussed for a mixture of ionized species. An electron number-density correction for the transport properties of the charged species is obtained. This correction has been generally ignored in the literature.

Gupta, Roop N.; Yos, Jerrold M.; Thompson, Richard A.; Lee, Kam-Pui

1990-01-01

31

Programmability of Chemical Reaction Networks  

NASA Astrophysics Data System (ADS)

Motivated by the intriguing complexity of biochemical circuitry within individual cells we study Stochastic Chemical Reaction Networks (SCRNs), a formal model that considers a set of chemical reactions acting on a finite number of molecules in a well-stirred solution according to standard chemical kinetics equations. SCRNs have been widely used for describing naturally occurring (bio)chemical systems, and with the advent of synthetic biology they become a promising language for the design of artificial biochemical circuits. Our interest here is the computational power of SCRNs and how they relate to more conventional models of computation. We survey known connections and give new connections between SCRNs and Boolean Logic Circuits, Vector Addition Systems, Petri nets, Gate Implementability, Primitive Recursive Functions, Register Machines, Fractran, and Turing Machines. A theme to these investigations is the thin line between decidable and undecidable questions about SCRN behavior.

Cook, Matthew; Soloveichik, David; Winfree, Erik; Bruck, Jehoshua

32

Chemical and Thermal Analysis.  

National Technical Information Service (NTIS)

Thermal decomposition activation energies have been determined using two methods of Thermogravimetric Analysis (TGA), with good correlation being obtained between the two techniques. Initial heating curves indicated a two-component system for Coflon (i.e....

J. W. Bulluck R. A. Rushing

1994-01-01

33

Chemical and Thermal Analysis.  

National Technical Information Service (NTIS)

During the past six months we have conducted significant research in several domains in order to clarify and understanding the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. We organized numerous analytical studies with...

J. W. Bulluck R. A. Rushing

1995-01-01

34

Strain-induced chemical reactions  

SciTech Connect

The uniaxial displacements at leading edges of detonation fronts in solids create large shear-strains. These bend the covalent bonds, and cause piezoelectric effects, thereby closing the HOMO-LUMO energy gaps, and leading to ultra-fast athermal chemical reactions. Specific examples are discussed: ammonium, azide, and nitrate ions; and PETN. It is shown that their properties are consistent with the proposed mechanism. [copyright]American Institute of Physics

Gilman, J.J. (Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States))

1994-07-10

35

Thermal Plasma Chemical Vapor Deposition  

Microsoft Academic Search

Diamond has many unrivaled properties and has great application potentials in modern industry. Among various metastable chemical vapor deposition methods for producing diamond, thermal plasma chemical vapor deposition has shown advantages of offering high growth rates and high quality. However, systematic parametric studies are needed for optimization of the process. This study investigates the effects of substrate materials, substrate temperatures,

Zhipeng Lu

1991-01-01

36

Binary counting with chemical reactions.  

PubMed

This paper describes a scheme for implementing a binary counter with chemical reactions. The value of the counter is encoded by logical values of "0" and "1" that correspond to the absence and presence of specific molecular types, respectively. It is incremented when molecules of a trigger type are injected. Synchronization is achieved with reactions that produce a sustained three-phase oscillation. This oscillation plays a role analogous to a clock signal in digital electronics. Quantities are transferred between molecular types in different phases of the oscillation. Unlike all previous schemes for chemical computation, this scheme is dependent only on coarse rate categories for the reactions ("fast" and "slow"). Given such categories, the computation is exact and independent of the specific reaction rates. Although conceptual for the time being, the methodology has potential applications in domains of synthetic biology such as biochemical sensing and drug delivery. We are exploring DNA-based computation via strand displacement as a possible experimental chassis. PMID:21121058

Kharam, Aleksandra; Jiang, Hua; Riedel, Marc; Parhi, Keshab

2011-01-01

37

A Novel Solar Thermal Cycle with Chemical Looping Combustion  

Microsoft Academic Search

In this paper, we have proposed a thermal cycle with the integration of chemical-looping combustion and solar thermal energy with the temperature of about 500-600°C. Chemical-looping combustion may be carried out in two successive reactions between a reduction of hydrocarbon fuel with metal oxides and a reduced metal with oxygen in the air. This loop of chemical reactions is substituted

Hui Hong; Hongguang Jin

2005-01-01

38

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

Work during the past three years has included significant research in several areas aimed at further clarification of the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. Among the areas investigated were the crystallinity changes associated with both the Coflon and Tefzel after various simulated environmental exposures using X-Ray diffraction analysis. We have found that significant changes in polymer crystallinity levels occur as a function of the exposures. These crystallinity changes may have important consequences on the fracture, fatigue, tensile, and chemical resistance of the materials. We have also noted changes in the molecular weight distribution and the increased crosslinking of the Coflon material using Gel Permeation Chromatographic Analysis. Again these changes may result in variations in the mechanical and chemical properties in the material. We conducted numerous analytical studies with methods including X-ray Diffraction, Gel Permeation Chromatography, Fourier Transform Infrared Spectroscopy, and Differential Scanning Calorimetry. We investigated a plethora of aged samples of both Tefzel and Coflon that were forwarded from MERL. Pressurized tests were performed on powdered PVDF in a modified Fluid A, which we will call A-2. In this case the ethylene diamine concentration was increased to 3 percent in methanol. Coflon pipe sections and powdered Coflon were exposed in pressure cells at 1700 psi at three separate test temperatures.

Bulluck, J. W.; Rushing, R. A.

1997-01-01

39

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

Work has included significant research in several areas aimed at further clarification of the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. Among the areas investigated were the crystallinity changes associated with both the Coflon and Tefzel after various simulated environmental exposures using X-Ray diffraction analysis. We have found that significant changes in polymer crystallinity levels occur as a function of the exposures. These crystallinity changes may have important consequences on the fracture, fatigue, tensile, and chemical resistance of the materials. We have also noted changes in the molecular weight distribution of the Coflon material using a dual detector Gel Permeation Analysis. Again these changes may result in variation in the mechanical and chemical properties in the material. We conducted numerous analytical studies with methods including X-Ray Diffraction, Gel Permeation Chromatography, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis, and Differential Scanning Calorimetry. We investigated a number of aged samples of both Tefzel and Coflon that were forwarded from MERL. Pressurized tests were performed in a modified Fluid G, which we will call G2. In this case the ethylene diamine concentration was increased to 3 percent in methanol. Coflon pipe sections and powdered Coflon were exposed in pressure cells at 1700 psi at three separate test temperatures, 70 C, 110 C, and 130 C. The primary purpose of the pressure tests in Fluid G2 was to further elucidate the aging mechanism of PVDF degradation.

Bulluck, J. W.; Rushing, R. A.; Thornton, C. P.

1996-01-01

40

Chemical energy storage system for SEGS solar thermal power plant  

Microsoft Academic Search

In October 1988, a symposium was held in Helendale, California, to discuss thermal energy storage (TES) concepts applicable to medium temperature (200 to 400 C) solar thermal electric power plants, in general, and the solar electric generating system (SEGS) plants developed by Luz International, in particular. Chemical reaction energy storage based on the reversible reaction between metal oxides and metal

D. R. Brown; J. L. Lamarche; G. E. Spanner

1991-01-01

41

Learning to Predict Chemical Reactions  

PubMed Central

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles respectively are not high-throughput, are not generalizable or scalable, or lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry dataset consisting of 1630 full multi-step reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval, problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of non-productive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal (http://cdb.ics.uci.edu) under the Toolkits section.

Kayala, Matthew A.; Azencott, Chloe-Agathe; Chen, Jonathan H.

2011-01-01

42

Learning to predict chemical reactions.  

PubMed

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal ( http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

Kayala, Matthew A; Azencott, Chloé-Agathe; Chen, Jonathan H; Baldi, Pierre

2011-09-26

43

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

During the past six months we have conducted significant research in several domains in order to clarify and understanding the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. We organized numerous analytical studies with methods including Fourier Transform Infrared Spectroscopy, Dynamic Mechanical Analysis, Differential Scanning Calorimetry, and Stress Relaxation experiments. In addition we have reanalyzed previous thermogravimetric data concerning the rate of deplasticization of Coflon pipe. We investigated a number of aged samples of both Tefzel and Coflon that were forwarded from MERL. We conducted stress relaxation experiments of Coflon pipe at several temperatures and determined an activation energy. We also examined the dynamic mechanical response PVDF during deplasticization and during methanol plasticization. We performed numerous DSC analyses to research the changing crystalline morphology. We have noted significant changes in crystallinity upon aging for both PVDF and Tefzel. Little variation in elemental composition was noted for many of the aged Coflon and Tefzel samples tested.

Bulluck, J. W.; Rushing, R. A.

1995-01-01

44

Chemical reactions at aqueous interfaces  

NASA Astrophysics Data System (ADS)

Interfaces or phase boundaries are a unique chemical environment relative to individual gas, liquid, or solid phases. Interfacial reaction mechanisms and kinetics are often at variance with homogeneous chemistry due to mass transfer, molecular orientation, and catalytic effects. Aqueous interfaces are a common subject of environmental science and engineering research, and three environmentally relevant aqueous interfaces are investigated in this thesis: 1) fluorochemical sonochemistry (bubble-water), 2) aqueous aerosol ozonation (gas-water droplet), and 3) electrolytic hydrogen production and simultaneous organic oxidation (water-metal/semiconductor). Direct interfacial analysis under environmentally relevant conditions is difficult, since most surface-specific techniques require relatively `extreme' conditions. Thus, the experimental investigations here focus on the development of chemical reactors and analytical techniques for the completion of time/concentration-dependent measurements of reactants and their products. Kinetic modeling, estimations, and/or correlations were used to extract information on interfacially relevant processes. We found that interfacial chemistry was determined to be the rate-limiting step to a subsequent series of relatively fast homogeneous reactions, for example: 1) Pyrolytic cleavage of the ionic headgroup of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorbed to cavitating bubble-water interfaces during sonolysis was the rate-determining step in transformation to their inorganic constituents carbon monoxide, carbon dioxide, and fluoride; 2) ozone oxidation of aqueous iodide to hypoiodous acid at the aerosol-gas interface is the rate-determining step in the oxidation of bromide and chloride to dihalogens; 3) Electrolytic oxidation of anodic titanol surface groups is rate-limiting for the overall oxidation of organics by the dichloride radical. We also found chemistry unique to the interface, for example: 1) Adsorption of dilute PFOS(aq) and PFOA(aq) to acoustically cavitating bubble interfaces was greater than equilibrium expectations due to high-velocity bubble radial oscillations; 2) Relative ozone oxidation kinetics of aqueous iodide, sulfite, and thiosulfate were at variance with previously reported bulk aqueous kinetics; 3) Organics that directly chelated with the anode surface were oxidized by direct electron transfer, resulting in immediate carbon dioxide production but slower overall oxidation kinetics. Chemical reactions at aqueous interfaces can be the rate-limiting step of a reaction network and often display novel mechanisms and kinetics as compared to homogeneous chemistry.

Vecitis, Chad David

45

Strontium isotopes as an indicator of water-rock reaction for the Coupled Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) Experimental Facility at DUSEL  

NASA Astrophysics Data System (ADS)

The Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) Experimental Facility is a proposed facility at the DUSEL-Homestake that will be used to investigate reactive transport, heat transfer and the resulting biological responses within a natural fractured rock. As part of THMCB facility design we are characterizing the current geochemical conditions and developing geochemical and isotopic indicators for fluid flow paths and reaction rates. The proposed experimental site is located at a depth of 4850 feet, primarily in the Homestake and Poorman Formations. At the experimental site, these formations are a quartz-chlorite-siderite iron formation and alumina-poor metapelite, respectively. Water samples from fractures and boreholes indicate that the pore fluid is a dilute Na-HCO3 water. The strontium isotope 87Sr/86Sr composition of surface waters is approximately 0.7106 based on stream water collected near the DUSEL site. The 87Sr/86Sr of subsurface waters sampled from fractures and boreholes throughout the mine varies from 0.7144 to 0.8145. 87Sr/86Sr and strontium concentrations suggest that calcite precipitation removes strontium and calcium from solution at shallow depths in the mine (< 3000 ft), consistent with pervasive calcite accumulation observed in the tunnels at these levels. 87Sr/86Sr values generally increase with depth and are highest in slow flowing fractures where they approach the isotopic value of the Poorman Formation (ca. 0.83±0.06). Collectively the data suggest that the Sr isotopic composition of the mine water is controlled by the flow rate of water and the extent of exchange with the surrounding rock matrix. Additionally, 87Sr/86Sr and temperature are positively correlated in the Poorman and Homestake Formations suggesting that temperature may be an additional tracer for fluid flow. Other isotopic tracers including 234U/238U, ?18O, ?D, ?13C and ?30Si are also being evaluated for use in the THMCB experimental facility.

Maher, K.; Olsen, N. J.; Harris, C.; Jones, T. L.; Conrad, M. E.; Sonnenthal, E. L.; Elsworth, D.; Uzunlar, N.; Mailloux, B. J.; Lowell, R. P.

2010-12-01

46

Analysis of Symmetry in Chemical Reactions.  

National Technical Information Service (NTIS)

The authors investigated the effect of the symmetry of the electronic and nuclear motion in chemical reactions. The analysis focuses on concerted reactions which are defined to be describable by a single transition matrix. The transition matrix for rearra...

T. F. George J. Ross

1971-01-01

47

Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions  

ERIC Educational Resources Information Center

A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different…

Schultz, Emeric

2008-01-01

48

2005 Chemical Reactions at Surfaces  

SciTech Connect

The Gordon Research Conference (GRC) on 2005 Chemical Reactions at Surfaces was held at Ventura Beach Marriott, Ventura California from February 13, 2005 through February 18, 2005. The Conference was well-attended with 124 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, 'free time' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field.

Cynthia M. Friend

2006-03-14

49

Classification of Chemical Reactions: Stages of Expertise  

Microsoft Academic Search

In this study we explore the strategies that undergraduate and graduate chemistry students use when engaged in classification tasks involving symbolic and microscopic (particulate) representations of different chemical reactions. We were specifically interested in characterizing the basic features to which students pay attention when classifying chemical reactions at the symbolic and microscopic levels. We identified the categories that students create

Marilyne Stains; Vicente Talanquer

2007-01-01

50

Chemical Kinetics: Rate of Reaction  

NSDL National Science Digital Library

This site offers an interactive tutorial that emphasizes graphical interpretation of chemical kinetics. The stoichiometric coefficients for a chemical equation are determined by comparing the slopes of concentration-time plots for the reactants and products. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

51

Thermal Plasma Chemical Vapor Deposition  

NASA Astrophysics Data System (ADS)

Diamond has many unrivaled properties and has great application potentials in modern industry. Among various metastable chemical vapor deposition methods for producing diamond, thermal plasma chemical vapor deposition has shown advantages of offering high growth rates and high quality. However, systematic parametric studies are needed for optimization of the process. This study investigates the effects of substrate materials, substrate temperatures, substrate pre-treatment methods, precursor concentrations, and process pressures on the initial nucleation, growth rate, morphology, and quality of the diamond films under thermal plasma conditions. X-ray diffraction, optical microscopy, scanning electron microscopy, and Raman spectroscopy have been used for the diamond film characterization. Thermal plasmas have been also used to deposit homoepitaxial diamond films at high growth rates. High quality macro-sized diamond crystals have been grown on {100} and {110} oriented natural type IIa diamond seeds. Raman spectra reveal that the diamond deposit is of high quality. Laue X-ray diffraction patterns show that the diamond grown on the seed is single crystal and oriented epitaxially with the underlying seed crystal. The gas phase chemistry has been calculated using computer code SOLGASMIX to determine the equilibrium gaseous composition in thermal plasmas. Key species concentrations have been obtained under various pressure conditions. Although kinetic factors have not been taken into account, equilibrium conditions offer an estimation of the process justified by the "frozen chemistry" associated with the fast quenching in the boundary layer. Due to the strong emission of the highly luminous plasma plumes, it has been difficult to measure the in -situ substrate temperature distribution with conventional infrared optical pyrometers. A new technique has been developed to obtain the surface temperature distribution of the substrate by combining the experimental temperature measurements of an array of thermocouples imbedded in the substrate and analytical solutions of the two-dimensional heat conduction equation. This method enables an indirect determination of the substrate temperature distribution.

Lu, Zhipeng

52

Thermal, chemical, and mechanical cookoff modeling  

SciTech Connect

A Thermally Reactive, Elastic-plastic eXplosive code, TREX, has been developed to analyze coupled thermal, chemical and mechanical effects associated with cookoff simulation of confined or unconfined energetic materials. In confined systems, pressure buildup precedes thermal runaway, and unconfined energetic material expands to relieve high stress. The model was developed based on nucleation, decomposition chemistry, and elastic/plastic mechanical behavior of a material with a distribution of internal defects represented as clusters of spherical inclusions. A local force balance, with mass continuity constraints, forms the basis of the model requiring input of temperature and reacted gas fraction. This constitutive material model has been incorporated into a quasistatic mechanics code SANTOS as a material module which predicts stress history associated with a given strain history. The thermal-chemical solver XCHEM has been coupled to SANTOS to provide temperature and reacted gas fraction. Predicted spatial history variables include temperature, chemical species, solid/gas pressure, solid/gas density, local yield stress, and gas volume fraction. One-Dimensional Time to explosion (ODTX) experiments for TATB and PBX 9404 (HMX and NC) are simulated using global multistep kinetic mechanisms and the reactive elastic-plastic constitutive model. Pressure explosions, rather than thermal runaway, result in modeling slow cookoff experiments of confined conventional energetic materials such as TATB. For PBX 9404, pressure explosions also occur at fast cookoff conditions because of low temperature reactions of nitrocellulose resulting in substantial pressurization. A demonstrative calculation is also presented for reactive heat flow in a hollow, propellant-filled, stainless steel cylinder, representing a rocket motor. This example simulation show

Hobbs, M.L.; Baer, M.R.; Gross, R.J.

1994-08-01

53

Method and apparatus for controlling gas evolution from chemical reactions  

DOEpatents

The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846. 8 figs.

Skorpik, J.R.; Dodson, M.G.

1999-05-25

54

Method and apparatus for controlling gas evolution from chemical reactions  

DOEpatents

The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846.

Skorpik, James R. (Kennewick, WA); Dodson, Michael G. (Richland, WA)

1999-01-01

55

Solar thermal harvesting for enhanced photocatalytic reactions.  

PubMed

The Shockley-Queisser limit predicts a maximum efficiency of 30% for single junction photovoltaic (PV) cells. The rest of the solar energy is lost as heat and due to phenomena such as reflection and transmission through the PV and charge carrier recombination. In the case of photocatalysis, this maximum value is smaller since the charge carriers should be transferred to acceptor molecules rather than conductive electrodes. With this perspective, we realize that at least 70% of the solar energy is available to be converted into heat. This is specifically useful for photocatalysis, since heat can provide more kinetic energy to the reactants and increase the number of energetic collisions leading to the breakage of chemical bonds. Even in natural photosynthesis, at the most 6% of the solar spectrum is used to produce sugar and the rest of the absorbed photons are converted into heat in a process called transpiration. The role of this heating component is often overlooked; in this paper, we demonstrate a coupled system of solar thermal and photocatalytic decontamination of water by titania, the most widely used photocatalyst for various photo reactions. The enhancement of this photothermal process over solely photocatalytic water decontamination is demonstrated to be 82% at 1× sun. Our findings suggest that the combination of solar thermal energy capture with photocatalysis is a suitable strategy to utilize more of the solar spectrum and improve the overall performance. PMID:24480846

Hashemi, Seyyed Mohammad Hosseini; Choi, Jae-Woo; Psaltis, Demetri

2014-03-21

56

Thermal, chemical, and mechanical cookoff modeling.  

National Technical Information Service (NTIS)

A Thermally Reactive, Elastic-plastic eXplosive code, TREX, has been developed to analyze coupled thermal, chemical and mechanical effects associated with cookoff simulation of confined or unconfined energetic materials. In confined systems, pressure buil...

M. L. Hobbs M. R. Baer R. J. Gross

1994-01-01

57

Semiclassical methods in chemical reaction dynamics.  

National Technical Information Service (NTIS)

Semiclassical approximations, simple as well as rigorous, are formulated in order to be able to describe gas phase chemical reactions in large systems. We formulate a simple but accurate semiclassical model for incorporating multidimensional tunneling in ...

S. Keshavamurthy

1994-01-01

58

Modeling of turbulent chemical reaction  

NASA Technical Reports Server (NTRS)

Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.

Chen, J.-Y.

1995-01-01

59

Thermo-chemical dynamics and chemical quasi-equilibrium of plasmas in thermal non-equilibrium  

SciTech Connect

We examine both processes of ionization by electron and heavy-particle impact in spatially uniform plasmas at rest in the absence of external forces. A singular perturbation analysis is used to study the following physical scenario, in which thermal relaxation becomes much slower than chemical reactions. First, electron-impact ionization is investigated. The dynamics of the system rapidly becomes close to a slow dynamics manifold that allows for defining a unique chemical quasi-equilibrium for two-temperature plasmas and proving that the second law of thermodynamics is satisfied. Then, all ionization reactions are taken into account simultaneously, leading to a surprising conclusion: the inner layer for short time scale (or time boundary layer) directly leads to thermal equilibrium. Global thermo-chemical equilibrium is reached within a short time scale, involving only chemical reactions, even if thermal relaxation through elastic collisions is assumed to be slow.

Massot, Marc [Laboratoire EM2C, UPR 288 CNRS - Ecole Centrale Paris (France); Graille, Benjamin [Laboratoire de Mathematiques d'Orsay, UMR 8628 CNRS - Universite Paris-Sud (France); Magin, Thierry E. [Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics (Belgium)

2011-05-20

60

Tracking thermal fronts with temperature-sensitive, chemically reactive tracers  

SciTech Connect

Los Alamos is developing tracer techniques using reactive chemicals to track thermal fronts in fractured geothermal reservoirs. If a nonadsorbing tracer flowing from the injection to production well chemically reacts, its reaction rate will be a strong function of temperature. Thus the extent of chemical reaction will be greatest early in the lifetime of the system, and less as the thermal front progresses from the injection to production well. Early laboratory experiments identified tracers with chemical kinetics suitable for reservoirs in the temperature range of 75 to 100/sup 0/C. Recent kinetics studies have focused on the kinetics of hydrolysis of derivatives of bromobenzene. This class of reactions can be used in reservoirs ranging in temperature from 150 to 275/sup 0/C, which is of greater interest to the geothermal industry. Future studies will include laboratory adsorption experiments to identify possibly unwanted adsorption on granite, development of sensitive analytical techniques, and a field demonstration of the reactive tracer concept.

Robinson, B.A.; Birdsell, S.A.

1987-01-01

61

Entropy Generation in a Chemical Reaction  

ERIC Educational Resources Information Center

Entropy generation in a chemical reaction is analysed without using the general formalism of non-equilibrium thermodynamics at a level adequate for advanced undergraduates. In a first approach to the problem, the phenomenological kinetic equation of an elementary first-order reaction is used to show that entropy production is always positive. A…

Miranda, E. N.

2010-01-01

62

Chemical Principles Revisited: Annotating Reaction Equations.  

ERIC Educational Resources Information Center

Urges chemistry teachers to have students annotate the chemical reactions in aqueous-solutions that they see in their textbooks and witness in the laboratory. Suggests this will help students recognize the reaction type more readily. Examples are given for gas formation, precipitate formation, redox interaction, acid-base interaction, and…

Tykodi, R. J.

1987-01-01

63

Heterogeneous chemical reactions: Preparation of monodisperse latexes  

NASA Technical Reports Server (NTRS)

It is demonstrated that a photoinitiated emulsion polymerization can be carried out to a significant conversion in a SPAR rocket prototype polymerization vessel within the six minutes allowed for the experiment. The percentage of conversion was determined by both dilatometry and gravimetric methods with good agreement. The experimental results lead to the following conclusions: (1) emulsion polymerizations can be carried out to conversions as high as 75%, using a stable micellized styrene-SLS system plus photoinitiator; (2) dilatometry can be used to accurately determine both the rate and conversion of polymerization; (3) thermal expansion due to the light source and heat of reaction is small and can be corrected for if necessary; (4) although seeded emulsion polymerizations are unfavorable in photoinitiation, as opposed to chemical initiation, polymerizations can be carried out to at least 15% conversion using 7940A seed particles, with 0.05% solids; and (5) photoinitiation should be used to initiate polymerization in the SPAR rocket experiments because of the mechanical simplicity of the experiment.

Vanderhoff, J. W.; Micale, F. J.; El-Aasser, M. S.; Sterk, A. A.; Bethke, G. W.

1977-01-01

64

Chemical Reactions in Supercritical Carbon Dioxide  

NASA Astrophysics Data System (ADS)

Utilizing supercritical fluids as environmentally benign solvents for chemical synthesis is one of the new approaches in the "greening" of chemistry. Carbon dioxide is the most widely used gas for supercritical fluid studies because of its moderate critical constants, nontoxic nature, and availability in pure form. One unique property of supercritical carbon dioxide (sc-CO2) is its high solubility for fluorinated compounds. Thus sc-CO2 can be used to replace Freons that are conventionally used as solvents for synthesis of perfluoro-polymers. Another property of sc-CO2 is its miscibility with gases such as H2. Heterogeneous reactions involving these gases may become homogeneous reactions in sc-CO2. Reactions in sc-CO2 may offer several advantages including controlling phase behavior and products, increasing speed of reactions, and obtaining specific reaction channels. This paper describes the following nine types of chemical reactions reported in the literature utilizing sc-CO2 as a solvent to illustrate the unique properties of the supercritical fluid reaction systems: (i) hydrogenation and hydroformylation, (ii) synthesis of organometallic compounds, (iii) metal chelation and extraction, (iv) preparation of inorganic nanoparticles, (v) stereo-selectivity of lipase-catalyzed reactions, (vi) asymmetric catalytic hydrogenation, (vii) polymerization, (viii) Diels-Alder reaction, and (ix) free radical reactions.

Wai, Chien M.; Hunt, Fred; Ji, Min; Chen, Xiaoyuan

1998-12-01

65

Chemical preconcentrator with integral thermal flow sensor  

DOEpatents

A chemical preconcentrator with integral thermal flow sensor can be used to accurately measure fluid flow rate in a microanalytical system. The thermal flow sensor can be operated in either constant temperature or constant power mode and variants thereof. The chemical preconcentrator with integral thermal flow sensor can be fabricated with the same MEMS technology as the rest of the microanlaytical system. Because of its low heat capacity, low-loss, and small size, the chemical preconcentrator with integral thermal flow sensor is fast and efficient enough to be used in battery-powered, portable microanalytical systems.

Manginell, Ronald P. (Albuquerque, NM); Frye-Mason, Gregory C. (Cedar Crest, NM)

2003-01-01

66

Chemical Changes in Lipids Produced by Thermal Processing.  

ERIC Educational Resources Information Center

Describes heat effects on lipids, indicating that the chemical and physical changes that occur depend on the lipid's composition and conditions of treatment. Thermolytic and oxidation reactions, thermal/oxidative interaction of lipids with other food components and the chemistry of frying are considered. (JN)

Nawar, Wassef W.

1984-01-01

67

Chemical Changes in Carbohydrates Produced by Thermal Processing.  

ERIC Educational Resources Information Center

Discusses chemical changes that occur in the carbohydrates found in food products when these products are subjected to thermal processing. Topics considered include browning reactions, starch found in food systems, hydrolysis of carbohydrates, extrusion cooking, processing of cookies and candies, and alterations in gums. (JN)

Hoseney, R. Carl

1984-01-01

68

Memory Switches in Chemical Reaction Space  

PubMed Central

Just as complex electronic circuits are built from simple Boolean gates, diverse biological functions, including signal transduction, differentiation, and stress response, frequently use biochemical switches as a functional module. A relatively small number of such switches have been described in the literature, and these exhibit considerable diversity in chemical topology. We asked if biochemical switches are indeed rare and if there are common chemical motifs and family relationships among such switches. We performed a systematic exploration of chemical reaction space by generating all possible stoichiometrically valid chemical configurations up to 3 molecules and 6 reactions and up to 4 molecules and 3 reactions. We used Monte Carlo sampling of parameter space for each such configuration to generate specific models and checked each model for switching properties. We found nearly 4,500 reaction topologies, or about 10% of our tested configurations, that demonstrate switching behavior. Commonly accepted topological features such as feedback were poor predictors of bistability, and we identified new reaction motifs that were likely to be found in switches. Furthermore, the discovered switches were related in that most of the larger configurations were derived from smaller ones by addition of one or more reactions. To explore even larger configurations, we developed two tools: the “bistabilizer,” which converts almost-bistable systems into bistable ones, and frequent motif mining, which helps rank untested configurations. Both of these tools increased the coverage of our library of bistable systems. Thus, our systematic exploration of chemical reaction space has produced a valuable resource for investigating the key signaling motif of bistability.

Ramakrishnan, Naren; Bhalla, Upinder S.

2008-01-01

69

Stochastic Generator of Chemical Structure. 3. Reaction Network Generation  

SciTech Connect

A new method to generate chemical reaction network is proposed. The particularity of the method is that network generation and mechanism reduction are performed simultaneously using sampling techniques. Our method is tested for hydrocarbon thermal cracking. Results and theoretical arguments demonstrate that our method scales in polynomial time while other deterministic network generator scale in exponential time. This finding offers the possibility to investigate complex reacting systems such as those studied in petroleum refining and combustion.

FAULON,JEAN-LOUP; SAULT,ALLEN G.

2000-07-15

70

Runaway chemical reaction exposes community to highly toxic chemicals.  

PubMed

The U.S. Chemical Safety and Hazard Investigation Board (CSB) conducted a comprehensive investigation of a runaway chemical reaction at MFG Chemical (MFG) in Dalton, Georgia on April 12, 2004 that resulted in the uncontrolled release of a large quantity of highly toxic and flammable allyl alcohol and allyl chloride into the community. Five people were hospitalized and 154 people required decontamination and treatment for exposure to the chemicals. This included police officers attempting to evacuate the community and ambulance personnel who responded to 911 calls from residents exposed to the chemicals. This paper presents the findings of the CSB report (U.S. Chemical Safety and Hazard Investigation Board (CSB), Investigation Report: Toxic Chemical Vapor Cloud Release, Report No. 2004-09-I-GA, Washington DC, April 2006) including a discussion on tolling practices; scale-up of batch reaction processes; Process Safety Management (PSM) and Risk Management Plan (RMP) implementation; emergency planning by the company, county and the city; and emergency response and mitigation actions taken during the incident. The reactive chemical testing and atmospheric dispersion modeling conducted by CSB after the incident and recommendations adopted by the Board are also discussed. PMID:18313843

Kaszniak, Mark; Vorderbrueggen, John

2008-11-15

71

Chemical Characterization and Reactivity of Fuel-Oxidizer Reaction Product  

NASA Technical Reports Server (NTRS)

Fuel-oxidizer reaction product (FORP), the product of incomplete reaction of monomethylhydrazine and nitrogen tetroxide propellants prepared under laboratory conditions and from firings of Shuttle Reaction Control System thrusters, has been characterized by chemical and thermal analysis. The composition of FORP is variable but falls within a limited range of compositions that depend on three factors: the fuel-oxidizer ratio at the time of formation; whether the composition of the post-formation atmosphere is reducing or oxidizing; and the reaction or post-reaction temperature. A typical composition contains methylhydrazinium nitrate, ammonium nitrate, methylammonium nitrate, and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. Thermal decomposition reactions of the FORP compositions used in this study were unremarkable. Neither the various compositions of FORP, the pure major components of FORP, nor mixtures of FORP with propellant system corrosion products showed any unusual thermal activity when decomposed under laboratory conditions. Off-limit thruster operations were simulated by rapid mixing of liquid monomethylhydrazine and liquid nitrogen tetroxide in a confined space. These tests demonstrated that monomethylhydrazine, methylhydrazinium nitrate, ammonium nitrate, or Inconel corrosion products can induce a mixture of monomethylhydrazine and nitrogen tetroxide to produce component-damaging energies. Damaging events required FORP or metal salts to be present at the initial mixing of monomethylhydrazine and nitrogen tetroxide.

David, Dennis D.; Dee, Louis A.; Beeson, Harold D.

1997-01-01

72

Perspective: Bimolecular chemical reaction dynamics in liquids.  

PubMed

Bimolecular reactions in the gas phase exhibit rich and varied dynamical behaviour, but whether a profound knowledge of the mechanisms of isolated reactive collisions can usefully inform our understanding of reactions in liquid solutions remains an open question. The fluctuating environment in a liquid may significantly alter the motions of the reacting particles and the flow of energy into the reaction products after a transition state has been crossed. Recent experimental and computational studies of exothermic reactions of CN radicals with organic molecules indicate that many features of the gas-phase dynamics are retained in solution. However, observed differences may also provide information on the ways in which a solvent modifies fundamental chemical mechanisms. This perspective examines progress in the use of time-resolved infra-red spectroscopy to study reaction dynamics in liquids, discusses how existing theories can guide the interpretation of experimental data, and suggests future challenges for this field of research. PMID:24606343

Orr-Ewing, Andrew J

2014-03-01

73

Computer Animation of a Chemical Reaction.  

ERIC Educational Resources Information Center

Taking a prototype chemical reaction (molecular hydrogen plus hydrogen atom), constructs an accurate semiempirical, generalized diatomics-in-molecules potential energy surface, calculates motions of these atoms on this surface using REACTS trajectory program, and presents results as moving picture on a microcomputer graphics system. Provides…

Eaker, Charles W.; Jacobs, Edwin L.

1982-01-01

74

CHEMICAL REACTIONS INDUCED BY UNDERGROUND NUCLEAR EXPLOSIONS  

Microsoft Academic Search

As part of the general program for study of potential industrial and ; civil applications of nuclear explosions (Plowshare Program), chemical reactions ; useful for the recovery of nuclear energy are discussed. Three problems are ; considered. First, the mechanism for the transfer of explosive energy to the ; medium is discussed and the results of calculations of useful explosive

G. H. Higgins; D. E. Rawson; W. Z. Wade

1961-01-01

75

CO Chain-Reaction Chemical Laser Research.  

National Technical Information Service (NTIS)

A chain-reaction CO chemical laser fueled by carbon monosulfide (CS) and molecular oxygen (O2) has been demonstrated. Initiation by the chain carriers (either O-atoms or S-atoms) is necessary; the chain length lambda* increases rapidly with CS/CS2 fuel mo...

W. Q. Jeffers H. Y. Ageno C. E. Wiswall

1976-01-01

76

Thermal reaction processes in a relativistic QED plasma drop  

SciTech Connect

The equilibrium size and temperature limits of thermally and chemically equilibrated e{sup +}e{sup -{gamma}} plasma drops are investigated at a given energy content. For a plasma to be equilibrated it must be opaque to electron and photon interactions. The opaqueness condition is determined by comparing plasma size with the mean free electron and photon paths. We calculate those paths using thermal Lorentz-invariant reaction rates for pair production and electron (positron) and photon scattering. The range of the corresponding plasma temperature and size is evaluated numerically. Considering the energy and size we find that the opaque and equilibrated plasma drop may be experimentally attainable.

Kuznetsova, Inga; Habs, Dieter; Rafelski, Johann [Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States) and Department fuer Physik der Ludwig-Maximilians, Universitaet Muenchen und Maier-Leibnitz-Laboratorium, Am Coulombwall 1, 85748 Garching (Germany)

2010-03-01

77

Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions  

PubMed Central

Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions.

SUZUKI, Toshinori

2013-01-01

78

Multidimensional thermal-chemical cookoff modeling  

Microsoft Academic Search

Multidimensional thermal\\/chemical modeling is an essential step in the development of a predictive capability for cookoff of energetic materials in systems subjected to abnormal thermal environments. COYOTE II is a state-of-the-art two- and three-dimensional finite element code for the solution of heat conduction problems including surface-to-surface thermal radiation heat transfer and decomposition chemistry. Multistep finite rate chemistry is incorporated into

M. R. Baer; R. J. Gross; D. K. Gartling; M. L. Hobbs

1994-01-01

79

Thermal, chemical, and mechanical cookoff modeling  

Microsoft Academic Search

A Thermally Reactive, Elastic-plastic eXplosive code, TREX, has been developed to analyze coupled thermal, chemical and mechanical effects associated with cookoff simulation of confined or unconfined energetic materials. In confined systems, pressure buildup precedes thermal runaway, and unconfined energetic material expands to relieve high stress. The model was developed based on nucleation, decomposition chemistry, and elastic\\/plastic mechanical behavior of a

M. L. Hobbs; M. R. Baer; R. J. Gross

1994-01-01

80

Neutral theory of chemical reaction networks  

NASA Astrophysics Data System (ADS)

To what extent do the characteristic features of a chemical reaction network reflect its purpose and function? In general, one argues that correlations between specific features and specific functions are key to understanding a complex structure. However, specific features may sometimes be neutral and uncorrelated with any system-specific purpose, function or causal chain. Such neutral features are caused by chance and randomness. Here we compare two classes of chemical networks: one that has been subjected to biological evolution (the chemical reaction network of metabolism in living cells) and one that has not (the atmospheric planetary chemical reaction networks). Their degree distributions are shown to share the very same neutral system-independent features. The shape of the broad distributions is to a large extent controlled by a single parameter, the network size. From this perspective, there is little difference between atmospheric and metabolic networks; they are just different sizes of the same random assembling network. In other words, the shape of the degree distribution is a neutral characteristic feature and has no functional or evolutionary implications in itself; it is not a matter of life and death.

Lee, Sang Hoon; Bernhardsson, Sebastian; Holme, Petter; Kim, Beom Jun; Minnhagen, Petter

2012-03-01

81

Minimum Energy Pathways for Chemical Reactions  

NASA Technical Reports Server (NTRS)

Computed potential energy surfaces are often required for computation of such parameters as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method to obtain accurate energetics, gives useful results for a number of chemically important systems. The talk will focus on a number of applications to reactions leading to NOx and soot formation in hydrocarbon combustion.

Walch, S. P.; Langhoff, S. R. (Technical Monitor)

1995-01-01

82

Chemical energy storage system for SEGS solar thermal power plant  

NASA Astrophysics Data System (ADS)

In October 1988, a symposium was held in Helendale, California, to discuss thermal energy storage (TES) concepts applicable to medium temperature (200 to 400 C) solar thermal electric power plants, in general, and the solar electric generating system (SEGS) plants developed by Luz International, in particular. Chemical reaction energy storage based on the reversible reaction between metal oxides and metal hydroxides was identified as a leading candidate for meeting Luz International's cost and performance requirements. The principal objectives of this study were to identify the design conditions, requirements, and potential feasibility for a chemical energy storage system applied to a SEGS solar thermal power plant. The remaining sections of this report begin by providing an overview of the chemical reaction energy storage concept and a SEGS solar thermal power plant. Subsequent sections describe the initial screening of alternative evaporation energy sources and the more detailed evaluation of design alternatives considered for the preferred evaporation energy source. The final sections summarize the results, conclusions, and recommendations.

Brown, D. R.; Lamarche, J. L.; Spanner, G. E.

1991-09-01

83

Stochastic flux analysis of chemical reaction networks  

PubMed Central

Background Chemical reaction networks provide an abstraction scheme for a broad range of models in biology and ecology. The two common means for simulating these networks are the deterministic and the stochastic approaches. The traditional deterministic approach, based on differential equations, enjoys a rich set of analysis techniques, including a treatment of reaction fluxes. However, the discrete stochastic simulations, which provide advantages in some cases, lack a quantitative treatment of network fluxes. Results We describe a method for flux analysis of chemical reaction networks, where flux is given by the flow of species between reactions in stochastic simulations of the network. Extending discrete event simulation algorithms, our method constructs several data structures, and thereby reveals a variety of statistics about resource creation and consumption during the simulation. We use these structures to quantify the causal interdependence and relative importance of the reactions at arbitrary time intervals with respect to the network fluxes. This allows us to construct reduced networks that have the same flux-behavior, and compare these networks, also with respect to their time series. We demonstrate our approach on an extended example based on a published ODE model of the same network, that is, Rho GTP-binding proteins, and on other models from biology and ecology. Conclusions We provide a fully stochastic treatment of flux analysis. As in deterministic analysis, our method delivers the network behavior in terms of species transformations. Moreover, our stochastic analysis can be applied, not only at steady state, but at arbitrary time intervals, and used to identify the flow of specific species between specific reactions. Our cases study of Rho GTP-binding proteins reveals the role played by the cyclic reverse fluxes in tuning the behavior of this network.

2013-01-01

84

Internal Active Thermal Control System (IATCS) Sodium Bicarbonate/Carbonate Buffer in an Open Aqueous Carbon Dioxide System and Corollary Electrochemical/Chemical Reactions Relative to System pH Changes  

NASA Technical Reports Server (NTRS)

The International Space Station (ISS) Internal Active Thermal Control System (IATCS) experienced a number of chemical changes driven by system absorption of CO2 which altered the coolant’s pH. The natural effects of the decrease in pH from approximately 9.2 to less than 8.4 had immediate consequences on system corrosion rates and corrosion product interactions with specified coolant constituents. The alkalinity of the system was increased through the development and implementation of a carbonate/bicarbonate buffer that would increase coolant pH to 9.0 – 10.0 and maintain pH above 9.0 in the presence of ISS cabin concentrations of CO2 up to twenty times higher than ground concentrations. This paper defines how a carbonate/bicarbonate buffer works in an open carbon dioxide system and summarizes the analyses performed on the buffer for safe and effective application in the on-orbit system. The importance of the relationship between the cabin environment and the IATCS is demonstrated as the dominant factor in understanding the system chemistry and pH trends before and after addition of the carbonate/bicarbonate buffer. The paper also documents the corollary electrochemical and chemical reactions the system has experienced and the rationale for remediation of these effects with the addition of the carbonate/bicarbonate buffer.

Stegman, Thomas W.; Wilson, Mark E.; Glasscock, Brad; Holt, Mike

2014-01-01

85

Study of the Interaction of ZDDP and Dispersants Using X-ray Absorption Near Edge Structure Spectroscopy—Part 1: Thermal Chemical Reactions  

Microsoft Academic Search

The interactions of ZDDP and different dispersants have been investigated both in oil solutions and on steel substrates at 150–185?°C. X-ray absorption near edge structure (XANES) spectroscopy at P and S L-edge and K-edge has been used to identify the chemical species both in solution and on the surface of the steel. It was found that noticeable ZDDP decomposition in

Z. Zhang; M. Kasrai; G. M. Bancroft; E. S. Yamaguchi

2003-01-01

86

Reactions in microemulsions: Effect of thermal fluctuations on reaction kinetics  

NASA Astrophysics Data System (ADS)

In this paper we address the generic effects arising from the interplay of thermal fluctuations and reactions. This is accomplished by considering specifically the kinetics of reactions effected in microemulsion media. In the first part of this paper we consider the kinetics of the reaction A+B-->Ø in bicontinuous microemulsion media, wherein the solutes A and B are assumed to be preferentially attracted to water and oil, respectively, and Ø constitutes an inert product. We formulate the diffusion and reaction of these solutes in a field-theoretical framework within which the fluctuations of the background microemulsion are embedded. We then employ mean-field arguments and a perturbative Wilson-type renormalization group (RG) approach to discern the relevance, at long length scales, of the background fluctuations. Our analysis indicates that the dynamic fluctuations of the microemulsion prove irrelevant in impacting the asymptotic kinetics of the reaction. In view of the fact that our field-theoretic approach enables us to probe only the long time characteristics, moreover, only in the weak-coupling limit, in the second part of this paper we analyze similar issues in the context of the droplet phase of microemulsions. This enables us to surmount some of the restrictions placed upon the results of the first part of this paper. In the second part, our analysis focuses upon a simpler reaction, viz., A-->Ø, wherein the solute A which is present only in the water phase is anhiliated upon contact with the fluctuating interfaces of the droplets. We employ a standard diffusion equation framework to formulate the transport and reaction of A. The fluctuations of the microemulsion are manifest in the boundary condition positing the vanishing concentration of A. We then employ a perturbation scheme to the solution of the diffusion equation, and thereby discern the explicit effects of the fluctuations of the sinks. Our formulation enables, in a sequentially improvable asymptotic manner, the explicit computation of the time-dependent and the steady state fluctuation contributions to the reaction rate.

Ganesan, Venkat; Fredrickson, Glenn H.

2000-08-01

87

The smallest chemical reaction system with bistability  

PubMed Central

Background Bistability underlies basic biological phenomena, such as cell division, differentiation, cancer onset, and apoptosis. So far biologists identified two necessary conditions for bistability: positive feedback and ultrasensitivity. Results Biological systems are based upon elementary mono- and bimolecular chemical reactions. In order to definitely clarify all necessary conditions for bistability we here present the corresponding minimal system. According to our definition, it contains the minimal number of (i) reactants, (ii) reactions, and (iii) terms in the corresponding ordinary differential equations (decreasing importance from i-iii). The minimal bistable system contains two reactants and four irreversible reactions (three bimolecular, one monomolecular). We discuss the roles of the reactions with respect to the necessary conditions for bistability: two reactions comprise the positive feedback loop, a third reaction filters out small stimuli thus enabling a stable 'off' state, and the fourth reaction prevents explosions. We argue that prevention of explosion is a third general necessary condition for bistability, which is so far lacking discussion in the literature. Moreover, in addition to proving that in two-component systems three steady states are necessary for bistability (five for tristability, etc.), we also present a simple general method to design such systems: one just needs one production and three different degradation mechanisms (one production, five degradations for tristability, etc.). This helps modelling multistable systems and it is important for corresponding synthetic biology projects. Conclusion The presented minimal bistable system finally clarifies the often discussed question for the necessary conditions for bistability. The three necessary conditions are: positive feedback, a mechanism to filter out small stimuli and a mechanism to prevent explosions. This is important for modelling bistability with simple systems and for synthetically designing new bistable systems. Our simple model system is also well suited for corresponding teaching purposes.

Wilhelm, Thomas

2009-01-01

88

Computed Potential Energy Surfaces for Chemical Reactions  

NASA Technical Reports Server (NTRS)

A manuscript describing the calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction, which were described in the last progress report, has been accepted for publication in J. Chem. Phys., and a copy of the manuscript is included in the appendix. The production of (1)CH2 in this reaction is important in hydrocarbon combustion since (1)CH2 is highly reactive and would be expected to insert into N2, possibly leading to a new source for prompt NO(x) (vide infra). During the last six months new calculations have been carried out for the NH2 + NO system, which is important in the thermal de-NO(x) process.

Heinemann, K.; Walch, Stephen P.; Levin, Eugene

1993-01-01

89

Thermal field theory with nonuniform chemical potential  

NASA Astrophysics Data System (ADS)

We investigate thermal one-loop effective potentials in multiflavor models with chemical potentials. We study four-dimensional models in which each flavor has different global U(1) charges. Accordingly they have different chemical potentials. We call these “nonuniform chemical potentials,” which are organized into a diagonal matrix ?^. The mass matrix at a vacuum does not commute with ?^. We find that the effective potential is divided into three parts. The first part is the Coleman-Weinberg potential. The UV divergence resides only in this part. The second is the correction to the Coleman-Weinberg potential that is independent of temperature, and the third depends on both temperature and ?^. Our result is a generalization of the thermal potentials in previous studies for models with single and multiflavors with (uniform) chemical potentials, and it reproduces all the known results correctly.

Arai, Masato; Kobayashi, Yoshishige; Sasaki, Shin

2013-12-01

90

Chemical Reactions on Ice Surfaces; Experimental and Theoretical Studies  

Microsoft Academic Search

Surfaces of ice particles in the stratosphere and troposphere are now widely recognized to heterogeneously catalyze chemical reactions that lead to changes in the chemical composition of the atmosphere, however, not much is known about the reaction mechanisms, their time scales, or why ice is required for the reactions. We address these issues with respect to heterogeneous chlorine activation reactions

Franz Geiger

2002-01-01

91

Nonlinear magnetoacoustic wave propagation with chemical reactions  

NASA Astrophysics Data System (ADS)

The magnetoacoustic problem with an application to sound wave propagation through electrically conducting fluids such as the ocean in the Earth's magnetic field, liquid metals, or plasmas has been addressed taking into account several simultaneous chemical reactions. Using continuum balance equations for the total mass, linear momentum, energy; as well as Maxwell's electrodynamic equations, a nonlinear beam equation has been developed to generalize the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation for a fluid with linear viscosity but nonlinear and diffraction effects. Thermodynamic parameters are used and not tailored to only an adiabatic fluid case. The chemical kinetic equations build on a relaxing media approach presented, for example, by K. Naugolnukh and L. Ostrovsky [Nonlinear Wave Processes in Acoustics (Cambridge Univ. Press, Cambridge, 1998)] for a linearized single reaction and thermodynamic pressure equation of state. Approximations for large and small relaxation times and for magnetohydrodynamic parameters [Korsunskii, Sov. Phys. Acoust. 36 (1990)] are examined. Additionally, Cattaneo's equation for heat conduction and its generalization for a memory process rather than a Fourier's law are taken into account. It was introduced for the heat flux depends on the temperature gradient at an earlier time to generate heat pulses of finite speed.

Margulies, Timothy Scott

2002-11-01

92

Anodic Reactions in the Ca/CaCrO sub 4 Thermal Battery.  

National Technical Information Service (NTIS)

The reaction of Ca with a CaCrO sub 4 -(LiCl-KCl eutectic) solution at temperatures of 400 exp 0 C to 500 exp 0 C was studied to better understand the nature of the chemical reactions and electrochemical processes that occur in the Ca/CaCrO sub 4 thermal ...

R. A. Guidotti F. W. Reinhardt

1985-01-01

93

Thermal maps of gases in heterogeneous reactions  

NASA Astrophysics Data System (ADS)

More than 85 per cent of all chemical industry products are made using catalysts, the overwhelming majority of which are heterogeneous catalysts that function at the gas-solid interface. Consequently, much effort is invested in optimizing the design of catalytic reactors, usually by modelling the coupling between heat transfer, fluid dynamics and surface reaction kinetics. The complexity involved requires a calibration of model approximations against experimental observations, with temperature maps being particularly valuable because temperature control is often essential for optimal operation and because temperature gradients contain information about the energetics of a reaction. However, it is challenging to probe the behaviour of a gas inside a reactor without disturbing its flow, particularly when trying also to map the physical parameters and gradients that dictate heat and mass flow and catalytic efficiency. Although optical techniques and sensors have been used for that purpose, the former perform poorly in opaque media and the latter perturb the flow. NMR thermometry can measure temperature non-invasively, but traditional approaches applied to gases produce signals that depend only weakly on temperature are rapidly attenuated by diffusion or require contrast agents that may interfere with reactions. Here we present a new NMR thermometry technique that circumvents these problems by exploiting the inverse relationship between NMR linewidths and temperature caused by motional averaging in a weak magnetic field gradient. We demonstrate the concept by non-invasively mapping gas temperatures during the hydrogenation of propylene in reactors packed with metal nanoparticles and metal-organic framework catalysts, with measurement errors of less than four per cent of the absolute temperature. These results establish our technique as a non-invasive tool for locating hot and cold spots in catalyst-packed gas-solid reactors, with unprecedented capabilities for testing the approximations used in reactor modelling.

Jarenwattananon, Nanette N.; Glöggler, Stefan; Otto, Trenton; Melkonian, Arek; Morris, William; Burt, Scott R.; Yaghi, Omar M.; Bouchard, Louis-S.

2013-10-01

94

Plasmon-driven sequential chemical reactions in an aqueous environment.  

PubMed

Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H(+) in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight. PMID:24958029

Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

2014-01-01

95

Plasmon-driven sequential chemical reactions in an aqueous environment  

PubMed Central

Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H+ in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight.

Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

2014-01-01

96

Chemical energy storage system for SEGS solar thermal power plant  

NASA Astrophysics Data System (ADS)

The Pacific Northwest Laboratory evaluated the potential feasibility of using chemical energy storage at the Solar Electric Generating System (SEGS) power plants developed by Luz International. Like sensible or latent heat energy storage systems, chemical energy storage can be beneficially applied to solar thermal power plants to dampen the impact of cloud transients, extend the daily operating period, and/or allow a higher fraction of power production to occur during high-valued peak demand periods. Higher energy storage densities make chemical energy storage a potentially attractive option. The results of the evaluation indicated that a system based on the reversible reaction, CaO + H2O = Ca(OH)2, could be technically and economically feasible for this application, but many technical and economic issues must be resolved.

Brown, D. R.; Lamarche, J. L.; Spanner, G. E.

1992-04-01

97

Reaction pathways for the thermal decomposition of methyl butanoate.  

PubMed

In recent years, biodiesel fuels, consisting of long-chain alkyl (methyl, ethyl, propyl) esters, have emerged as viable alternatives to petroleum-based fuels. From a combustion chemistry standpoint, there is great interest in developing accurate reaction models for these new molecules that can be used to predict their behaviors in various regimes. In this paper, we report a detailed study of the unimolecular decomposition pathways of methyl butanoate (MB), a short-chain ester that contains the basic chemical structure of biodiesel fuels. Using ab initio/DFT methods, we identified five homolytic fissions of C-C and C-O bonds and five hydrogen transfer reactions. Rate constants were determined using the G3B3 theory coupled with both variational transition state theory and Rice-Ramsperger-Kassel-Marcus/master equation simulations with hindered rotation corrections. Branching ratios in the temperature range 1500-2200 K indicate that the main pathway for thermal decomposition of MB is the reaction CH3CH2CH2C(?O)OCH3 ? C2H5 + CH2C(?O)OCH3. The results, in terms of reaction pathways and rate constants, can be used for future development of mechanisms for long alkyl-chain esters. PMID:23679139

Akbar Ali, Mohamad; Violi, Angela

2013-06-21

98

GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

Green chemical synthesis through catalysis and alternate reaction conditions Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

99

Coupled Thermal-Chemical-Mechanical Modeling of Validation Cookoff Experiments  

SciTech Connect

The cookoff of energetic materials involves the combined effects of several physical and chemical processes. These processes include heat transfer, chemical decomposition, and mechanical response. The interaction and coupling between these processes influence both the time-to-event and the violence of reaction. The prediction of the behavior of explosives during cookoff, particularly with respect to reaction violence, is a challenging task. To this end, a joint DoD/DOE program has been initiated to develop models for cookoff, and to perform experiments to validate those models. In this paper, a series of cookoff analyses are presented and compared with data from a number of experiments for the aluminized, RDX-based, Navy explosive PBXN-109. The traditional thermal-chemical analysis is used to calculate time-to-event and characterize the heat transfer and boundary conditions. A reaction mechanism based on Tarver and McGuire's work on RDX{sup 2} was adjusted to match the spherical one-dimensional time-to-explosion data. The predicted time-to-event using this reaction mechanism compares favorably with the validation tests. Coupled thermal-chemical-mechanical analysis is used to calculate the mechanical response of the confinement and the energetic material state prior to ignition. The predicted state of the material includes the temperature, stress-field, porosity, and extent of reaction. There is little experimental data for comparison to these calculations. The hoop strain in the confining steel tube gives an estimation of the radial stress in the explosive. The inferred pressure from the measured hoop strain and calculated radial stress agree qualitatively. However, validation of the mechanical response model and the chemical reaction mechanism requires more data. A post-ignition burn dynamics model was applied to calculate the confinement dynamics. The burn dynamics calculations suffer from a lack of characterization of the confinement for the flaw-dominated failure mode experienced in the tests. High-pressure burning rates are needed for more detailed post-ignition studies. Sub-models for chemistry, mechanical response and burn dynamics need to be validated against data from less complex experiments. The sub-models can then be used in integrated analysis for comparison with experimental data taken during integrated tests.

ERIKSON,WILLIAM W.; SCHMITT,ROBERT G.; ATWOOD,A.I.; CURRAN,P.D.

2000-11-27

100

Bimolecular chemical reactions on weighted complex networks.  

PubMed

We investigate the kinetics of bimolecular chemical reactions A+A?0 and A+B?0 on weighted scale-free networks (WSFNs) with degree distribution P(k)?k^{-?} . On WSFNs, a weight w{ij} is assigned to the link between node i and j . We consider the symmetric weight given as w{ij}=(k{i}k{j})^{?} , where k{i} and k{j} are the degree of node i and j . The hopping probability T{ij} of a particle from node i to j is then given as T{ij}?(k{i}k{j})^{?} . From a mean-field analysis, we analytically show in the thermodynamic limit that the kinetics of A+A?0 and A+B?0 are identical and there exist two crossover ? values, ?{1c}=?-2 and ?{2c}=(?-3)/2 . The density of particles ?(t) algebraically decays in time t as t^{-?} with ?=1 for ?

Kwon, Sungchul; Choi, Woosik; Kim, Yup

2010-08-01

101

Distinguishing solid bitumens formed by thermochemical sulfate reduction and thermal chemical alteration  

Microsoft Academic Search

Insoluble solid bitumens are organic residues that can form by the thermal chemical alteration (TCA) or thermochemical sulfate reduction (TSR) of migrated petroleum. TCA may actually encompass several low temperature processes, such as biodegradation and asphaltene precipitation, followed by thermal alteration. TSR is an abiotic redox reaction where petroleum is oxidized by sulfate. It is difficult to distinguish solid bitumens

Simon R. Kelemen; Clifford C. Walters; Peter J. Kwiatek; Mobae Afeworki; Michael Sansone; Howard Freund; Robert J. Pottorf; Hans G. Machel; Tongwei Zhang; Geoffrey S. Ellis; Yongchun Tang; Kenneth E. Peters

2008-01-01

102

Shock initiated thermal and chemical responses of HMX crystal from ReaxFF molecular dynamics simulation.  

PubMed

To gain an atomistic-level understanding of the thermal and chemical responses of condensed energetic materials under thermal shock, we developed a thermal shock reactive dynamics (TS-RD) computational protocol using molecular dynamics simulation coupled with ReaxFF force field. ?-Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) was selected as a a target explosive due to its wide usage in the military and industry. The results show that a thermal shock initiated by a large temperature gradient between the "hot" region and the "cold" region results in thermal expansion of the particles and induces a thermal-mechanical wave propagating back and forth in the system with an averaged velocity of 3.32 km s(-1). Heat propagating along the direction of thermal shock leads to a temperature increment of the system and thus chemical reaction initiation. Applying a continuum reactive heat conduction model combined with the temperature distribution obtained from the RD simulation, a heat conduction coefficient is derived as 0.80 W m(-1) K(-1). The chemical reaction mechanisms during thermal shock were analyzed, showing that the reaction is triggered by N-NO2 bond breaking followed by HONO elimination and ring fission. The propagation rates of the reaction front and reaction center are obtained to be 0.069 and 0.038 km s(-1), based on the time and spatial distribution of NO2. The pressure effect on the thermal shock was also investigated by employing uniaxial compression before the thermal shock. We find that compression significantly accelerates thermal-mechanical wave propagation and heat conduction, resulting in higher temperature and more excited molecules and thus earlier initiation and faster propagation of chemical reactions. PMID:24899535

Zhou, Tingting; Song, Huajie; Liu, Yi; Huang, Fenglei

2014-07-21

103

Investigating Factors Influencing Rates of Chemical Reactions  

NSDL National Science Digital Library

This activity is a lab investigation in which students observe the rate of generation of hydrogen gas from a reaction, and then modify the procedure to compare another variable affecting the rate of this reaction.

Derickson, Paula

104

Semiclassical methods in chemical reaction dynamics  

SciTech Connect

Semiclassical approximations, simple as well as rigorous, are formulated in order to be able to describe gas phase chemical reactions in large systems. We formulate a simple but accurate semiclassical model for incorporating multidimensional tunneling in classical trajectory simulations. This model is based on the existence of locally conserved actions around the saddle point region on a multidimensional potential energy surface. Using classical perturbation theory and monitoring the imaginary action as a function of time along a classical trajectory we calculate state-specific unimolecular decay rates for a model two dimensional potential with coupling. Results are in good comparison with exact quantum results for the potential over a wide range of coupling constants. We propose a new semiclassical hybrid method to calculate state-to-state S-matrix elements for bimolecular reactive scattering. The accuracy of the Van Vleck-Gutzwiller propagator and the short time dynamics of the system make this method self-consistent and accurate. We also go beyond the stationary phase approximation by doing the resulting integrals exactly (numerically). As a result, classically forbidden probabilties are calculated with purely real time classical trajectories within this approach. Application to the one dimensional Eckart barrier demonstrates the accuracy of this approach. Successful application of the semiclassical hybrid approach to collinear reactive scattering is prevented by the phenomenon of chaotic scattering. The modified Filinov approach to evaluating the integrals is discussed, but application to collinear systems requires a more careful analysis. In three and higher dimensional scattering systems, chaotic scattering is suppressed and hence the accuracy and usefulness of the semiclassical method should be tested for such systems.

Keshavamurthy, S.

1994-12-01

105

The effect of chemical reaction on liquid round free jet  

Microsoft Academic Search

In the fluid engineering field, chemical reaction frequently occur. Sodium-water chain reaction in the sodium cooled nuclear reactor can make an explosion that causes the accident during the operation of nuclear reactor. Therefore, it is very important to investigate the characteristic of this chemically reacting type of jet to achieve the reliable design of industrial reactor. Although a number of

Seong Dae Hong; Okamoto Koji; Madarame Haruki

2002-01-01

106

Chemical kinetics computer program for static and flow reactions  

NASA Technical Reports Server (NTRS)

General chemical kinetics computer program for complex gas mixtures has been developed. Program can be used for any homogeneous reaction in either one dimensional flow or static system. It is flexible, accurate, and easy to use. It can be used for any chemical system for which species thermodynamic data and reaction rate constant data are known.

Bittker, D. A.; Scullin, V. J.

1972-01-01

107

A DFT analysis of thermal decomposition reactions important to natural products.  

PubMed

The thermal decomposition reactions of several important natural flavor and fragrance chemicals have been investigated using density functional theory (DFT, B3LYP/6-31G*). Retro-aldol reactions of glucose, fructose, hernandulcin, epihernandulcin, [3]-gingerol, and [4]-isogingerol; retro-carbonyl-ene reactions of isopulegol, lavandulol, isolyratol, and indicumenone; and pyrolytic syn elimination reactions of linalyl acetate, alpha-terpinyl acetate, and bornyl acetate, have been carried out. The calculations indicate activation enthalpies of around 30 kcal/mol for the retro-aldol reactions and for retro-carbonyl-ene reactions, comparable to pericyclic reactions such as the Cope rearrangement and electrocyclic reactions, and therefore important reactions at elevated temperatures (e.g., boiling aqueous solutions, gas-chromatograph injection ports). Activation enthalpies for pyrolytic eliminations are around 40 kcal/mol and are unlikely to occur during extraction or GC analysis. PMID:20734926

Setzer, William N

2010-07-01

108

Computed potential energy surfaces for chemical reactions  

NASA Technical Reports Server (NTRS)

The objective was to obtain accurate potential energy surfaces (PES's) for a number of reactions which are important in the H/N/O combustion process. The interest in this is centered around the design of the SCRAM jet engine for the National Aerospace Plane (NASP), which was envisioned as an air-breathing hydrogen-burning vehicle capable of reaching velocities as large as Mach 25. Preliminary studies indicated that the supersonic flow in the combustor region of the scram jet engine required accurate reaction rate data for reactions in the H/N/O system, some of which was not readily available from experiment. The most important class of combustion reactions from the standpoint of the NASP project are radical recombinaton reactions, since these reactions result in most of the heat release in the combustion process. Theoretical characterizations of the potential energy surfaces for these reactions are presented and discussed.

Walch, Stephen P.

1990-01-01

109

Heat-of-Reaction Chemical Heat Pumps.  

National Technical Information Service (NTIS)

Chemical heat pumps are mechanically driven heat pumps with working fluids that undergo chemical changes or are heat-driven heat pumps in which either the driver (heat engine) or heat pump utilizes a reactive working fluid. As such, chemical heat pumps ca...

C. Bliem L. Kirol

1988-01-01

110

Rate constants for chemical reactions in high-temperature nonequilibrium air  

NASA Technical Reports Server (NTRS)

In the nonequilibrium atmospheric chemistry regime that will be encountered by the proposed Aeroassisted Orbital Transfer Vehicle in the upper atmosphere, where air density is too low for thermal and chemical equilibrium to be maintained, the detailed high temperature air chemistry plays a critical role in defining radiative and convective heating loads. Although vibrational and electronic temperatures remain low (less than 15,000 K), rotational and translational temperatures may reach 50,000 K. Attention is presently given to the effects of multiple temperatures on the magnitudes of various chemical reaction rate constants, for the cases of both bimolecular exchange reactions and collisional excitation and dissociation reactions.

Jaffe, R. L.

1986-01-01

111

Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction.  

ERIC Educational Resources Information Center

Describes a dramatic chemical demonstration in which chemicals that are black and white combine to produce a colorless liquid. Reactants include tincture of iodine, bleach, white vinegar, Epsom salt, vitamin C tablets, and liquid laundry starch. (DDR)

Wright, Stephen W.

2002-01-01

112

Chemical reactivity test for thermal stability  

SciTech Connect

Lawrence Livermore National Laboratory (LLNL) has developed a thermal stability test procedure that is currently being evaluated by the Department of Defense (DOD) Explosives Safety Board as an equivalent alternate test to the DOD Technical Bulletin 700-2 {open_quotes}Thermal Stability Test at 75{degrees}C{close_quotes}. The LLNL Chemical Reactivity Test (CRT) is significantly more severe than the existing {open_quotes}Thermal Stability Test at 75{degrees}C{close_quotes} and is also quantitative in nature. It has been approved by the Department of Energy (DOE) Explosives Safety Committee as an equivalent alternate thermal stability test and has been in use by LLNL for over 30 years. It is currently used by other DOE and DOD organizations as the standard small-scale safety test for determining thermal stability and material compatibility. The LLNL CRT is run on a 0.250 gm sample for 22 hours at 120{degrees}C rather than the 50 gm sample for 48 hours at 75{degrees}C as required for the Thermal Stability Test. Thus the CRT is a much more severe test since it is run at 120{degrees}C rather than 75{degrees}C. Simple Arrhenius kinetics predict a material decomposition rate of approximately 25 times greater at 120{degrees}C than at 75{degrees}C. Any material under test that exhibits gas evolution exceeding 4 cc/gm (approximately 0.8 % decomposition) is considered suspect and additional testing and/or evaluation is then performed to determine if the material is thermally unstable. In addition to the CRT being significantly more severe and quantitative, there are significant other advantages for using the CRT. These include: (1) the increased safety afforded to operating personnel and equipment by using a fraction of the test material, (2) the cost savings associated with reduced sample heating time and the use of less sample material, and (3) the reduced amount of post-test waste produced.

Prokosch, D.W.; Garcia, F.

1994-07-01

113

Coarse grain model for coupled thermo-mechano-chemical processes and its application to pressure-induced endothermic chemical reactions  

NASA Astrophysics Data System (ADS)

We extend a thermally accurate model for coarse grain dynamics (Strachan and Holian 2005 Phys. Rev. Lett. 94 014301) to enable the description of stress-induced chemical reactions in the degrees of freedom internal to the mesoparticles. Similar to the breathing sphere model, we introduce an additional variable that describes the internal state of the particles and whose dynamics is governed both by an internal potential energy function and by interparticle forces. The equations of motion of these new variables are derived from a Hamiltonian and the model exhibits two desired features: total energy conservation and Galilean invariance. We use a simple model material with pairwise interactions between particles and study pressure-induced chemical reactions induced by hydrostatic and uniaxial compression. These examples demonstrate the ability of the model to capture non-trivial processes including the interplay between mechanical, thermal and chemical processes of interest in many applications.

Antillon, Edwin; Banlusan, Kiettipong; Strachan, Alejandro

2014-03-01

114

Systems of Chemical Equations as Reasonable Reaction Mechanisms  

NASA Astrophysics Data System (ADS)

This paper demonstrates that chemical equations may be operated like a kind of LEGO game, with construction of the systems of chemical equations. In my teaching experience, these systems of chemical equations are able to help students to understand the reaction routes. Six general principles of creating the systems are formulated. Three examples from inorganic chemistry are considered and discussed in detail.

Dorozhkin, Sergey V.

2001-07-01

115

FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

The chemical research in the late 1990's witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into the atmo...

116

The Mystery Reaction: A Lesson on Chemical Reactions  

NSDL National Science Digital Library

This teaching resource was developed by a K-12 science teacher in the American Physiologycal Society's 2006 Frontiers in Physiology Program. For more information on this program, please visit www.frontiersinphys.org. The purpose of this lesson is to design an investigation and conduct an experiment that will allow students to explore the differences between physical and chemical changes. In this investigation, they are given the opportunity to develop a list of evidence for determining whether or not a chemical change has occurred.

Tonya Williams (Kelly Miller Middle School)

2006-08-01

117

Computed potential energy surfaces for chemical reactions  

NASA Technical Reports Server (NTRS)

A new global potential energy surface (PES) is being generated for O(P-3) + H2 yields OH + H. This surface is being fit using the rotated Morse oscillator method, which was used to fit the previous POL-CI surface. The new surface is expected to be more accurate and also includes a much more complete sampling of bent geometries. A new study has been undertaken of the reaction N + O2 yields NO + O. The new studies have focused on the region of the surface near a possible minimum corresponding to the peroxy form of NOO. A large portion of the PES for this second reaction has been mapped out. Since state to state cross sections for the reaction are important in the chemistry of high temperature air, these studies will probably be extended to permit generation of a new global potential for reaction.

Walch, Stephen P.; Levin, Eugene

1993-01-01

118

Solar-Thermal Fluid-Wall Reaction Processing.  

National Technical Information Service (NTIS)

The present invention provides a method for carrying out high temperature thermal dissociation reactions requiring rapid-heating and short residence times using solar energy. In particular, the present invention provides a method for carrying out high tem...

A. A. Lewandowski A. W. Weimer C. Bingham J. K. Dahl K. J. R. Buechler W. Grothe

2006-01-01

119

Kinetics of Chemical Reactions in Flames  

NASA Technical Reports Server (NTRS)

In part I of the paper the theory of flame propagation is developed along the lines followed by Frank-Kamenetsky and one of the writers. The development of chain processes in flames is considered. A basis is given for the application of the method of stationary concentrations to reactions in flames; reactions with branching chains are analyzed. The case of a diffusion coefficient different from the coefficient of temperature conductivity is considered.

Zeldovich, Y.; Semenov, N.

1946-01-01

120

Developing Secondary Students' Conceptions of Chemical Reactions: The Introduction of Chemical Equilibrium.  

ERIC Educational Resources Information Center

Describes an empirical study concerning the introduction of the concept of chemical equilibrium in chemistry classrooms in a way which challenges students' initial conceptions of chemical reactions. Contains 23 references. (DDR)

Van Driel, Jan H.; De Vos, Wobbe; Verloop, Nico; Dekkers, Hetty

1998-01-01

121

Chemical, Thermal, and Dynamic Mechanical Properties of Five Adhesives.  

National Technical Information Service (NTIS)

The chemical, thermal, and dynamic mechanical properties of five adhesives have been determined. The analyses performed include the determination of the amount and identity of the unbound chemicals extracted from the cured adhesives, the swell ratio, the ...

G. K. Baker

1978-01-01

122

Computed potential energy surfaces for chemical reactions  

NASA Technical Reports Server (NTRS)

The work on the NH + NO system which was described in the last progress report was written up and a draft of the manuscript is included in the appendix. The appendix also contains a draft of a manuscript on an Ar + H + H surface. New work which was completed in the last six months includes the following: (1) calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction; (2) calculations for the NH2 + O reaction; (3) calculations for the CH3 + O2 reaction; and (4) calculations for CH3O and the two decomposition channels--CH2OH and H + H2CO. Detailed descriptions of this work will be given in manuscripts; however, brief descriptions of the CH3 + OH and CH3 + O2 projects are given.

Heinemann, K.; Walch, Stephen P.

1992-01-01

123

Chemical Reactions Studied by Crossed Beam Techniques.  

National Technical Information Service (NTIS)

Interaction potentials for the H-heavy rare gases, O-Ar and O2-Ar systems have been determined by measuring the total cross section as a function of the energy in the thermal energy range. Information on the potential curves of alkali atom - alkali ion, d...

G. G. Volpi

1973-01-01

124

Direct imaging of covalent bond structure in single-molecule chemical reactions.  

PubMed

Observing the intricate chemical transformation of an individual molecule as it undergoes a complex reaction is a long-standing challenge in molecular imaging. Advances in scanning probe microscopy now provide the tools to visualize not only the frontier orbitals of chemical reaction partners and products, but their internal covalent bond configurations as well. We used noncontact atomic force microscopy to investigate reaction-induced changes in the detailed internal bond structure of individual oligo-(phenylene-1,2-ethynylenes) on a (100) oriented silver surface as they underwent a series of cyclization processes. Our images reveal the complex surface reaction mechanisms underlying thermally induced cyclization cascades of enediynes. Calculations using ab initio density functional theory provide additional support for the proposed reaction pathways. PMID:23722428

de Oteyza, Dimas G; Gorman, Patrick; Chen, Yen-Chia; Wickenburg, Sebastian; Riss, Alexander; Mowbray, Duncan J; Etkin, Grisha; Pedramrazi, Zahra; Tsai, Hsin-Zon; Rubio, Angel; Crommie, Michael F; Fischer, Felix R

2013-06-21

125

Drying with Chemical Reaction in Cocoa Beans  

Microsoft Academic Search

Desirable flavor qualities of cocoa are dependent on how the cocoa beans are fermented, dried, and roasted. During fermentation and drying, polyphenols such as leucocyanidin and apecatechin are oxidized by polyphenols oxidase to form o-quinone, which later react nonenzymatically with a hydroquinone in a condensation reaction to form browning products and moisture. The objective of this article is to model

Wan Ramli Wan Daud; Meor Zainal Meor Talib; Tin Mar Kyi

2007-01-01

126

Potential energy surfaces for chemical reactions  

Microsoft Academic Search

The research completed spans a rather broad range of chemistry. Taken as a body it conforms well to our goal of three years ago to contribute in a significant way to the fundamental underpinnings of combustion chemistry. It includes the reaction of methane with molecular oxygen, research on protonated ethane and the hydronium ion, aluminum atom-unsaturated hydrocarbon systems, the infrared

1990-01-01

127

THERMAL AND CHEMICAL EVOLUTION OF COLLAPSING FILAMENTS  

SciTech Connect

Intergalactic filaments form the foundation of the cosmic web that connect galaxies together, and provide an important reservoir of gas for galaxy growth and accretion. Here we present very high resolution two-dimensional simulations of the thermal and chemical evolution of such filaments, making use of a 32 species chemistry network that tracks the evolution of key molecules formed from hydrogen, oxygen, and carbon. We study the evolution of filaments over a wide range of parameters including the initial density, initial temperature, strength of the dissociating UV background, and metallicity. In low-redshift, Z Almost-Equal-To 0.1 Z{sub Sun} filaments, the evolution is determined completely by the initial cooling time. If this is sufficiently short, the center of the filament always collapses to form a dense, cold core containing a substantial fraction of molecules. In high-redshift, Z = 10{sup -3} Z{sub Sun} filaments, the collapse proceeds much more slowly. This is mostly due to the lower initial temperatures, which lead to a much more modest increase in density before the atomic cooling limit is reached, making subsequent molecular cooling much less efficient. Finally, we study how the gravitational potential from a nearby dwarf galaxy affects the collapse of the filament and compare this to NGC 5253, a nearby starbursting dwarf galaxy thought to be fueled by the accretion of filament gas. In contrast to our fiducial case, a substantial density peak forms at the center of the potential. This peak evolves faster than the rest of the filament due to the increased rate at which chemical species form and cooling occurs. We find that we achieve similar accretion rates as NGC 5253 but our two-dimensional simulations do not recover the formation of the giant molecular clouds that are seen in radio observations.

Gray, William J. [Lawrence Livermore National Laboratory, P.O. Box 808, L-038, Livermore, CA 94550 (United States); Scannapieco, Evan [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1494 (United States)

2013-05-10

128

Electronic excitations by chemical reactions on metal surfaces  

Microsoft Academic Search

Dissipation of chemical energy released in exothermic reactions at metal surfaces may happen adiabatically by creation of phonons or non-adiabatically by excitation of the electronic system of the metal or the reactants. In the past decades, the only direct experimental evidence for such non-adiabatic reactions has been exoelectron emission into vacuum and surface chemiluminescence which are observed in a special

Hermann Nienhaus

2002-01-01

129

Evaluated Chemical Kinetic Rate Constants for Various Gas Phase Reactions  

Microsoft Academic Search

The available information, up to mid-1972, for the rate constants of a series of gas phase chemical reactions has been evaluated critically. For each reaction, relevant thermodynamic data are presented and values for the equilibrium constant expressed in mathematical form. Kinetic data are presented in tabular and graphical form together with a discussion of the pertinent details. Recommended rate constant

Keith Schofield

1973-01-01

130

Cu-free click cycloaddition reactions in chemical biology†  

PubMed Central

Bioorthogonal chemical reactions are paving the way for new innovations in biology. These reactions possess extreme selectivity and biocompatibility, such that their participating reagents can form covalent bonds within richly functionalized biological systems—in some cases, living organisms. This tutorial review will summarize the history of this emerging field, as well as recent progress in the development and application of bioorthogonal copper-free click cycloaddition reactions.

Jewett, John C.

2010-01-01

131

Results of the 2010 Survey on Teaching Chemical Reaction Engineering  

ERIC Educational Resources Information Center

A survey of faculty teaching the chemical reaction engineering course or sequence during the 2009-2010 academic year at chemical engineering programs in the United States and Canada reveals change in terms of content, timing, and approaches to teaching. The report consists of two parts: first, a statistical and demographic characterization of the…

Silverstein, David L.; Vigeant, Margot A. S.

2012-01-01

132

Laser cutting with chemical reaction assist  

DOEpatents

A method for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation.

Gettemy, Donald J. (Los Alamos, NM) [Los Alamos, NM

1992-01-01

133

Laser cutting with chemical reaction assist  

DOEpatents

A method is described for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation. 1 figure.

Gettemy, D.J.

1992-11-17

134

LIGAND: Database of Chemical Compounds and Reactions in Biological Pathways  

NSDL National Science Digital Library

The Institute for Chemical Research at Kyoto University provides this frequently updated and well-documented database of enzyme reactions. With more than 9,300 entries, the LIGAND Chemical Database includes over 3,700 entries for enzymes (the Enzyme Reaction Database) and 5,600 entries for compounds (Chemical Compound Database). The database is searchable by keyword using DBGET (which supports numerous other databases and gene catalogs as well) and is accompanied by clear instructions. The LIGAND database, updated weekly, may be downloaded via anonymous FTP.

135

Photo-thermal chemical vapor deposition growth of graphene  

Microsoft Academic Search

The growth of graphene on Ni using a photo-thermal chemical vapor deposition (PT-CVD) technique is reported. The non-thermal equilibrium nature of PT-CVD process resulted in a much shorter duration in both heating up and cooling down stages, thus allowing for a reduction in the overall growth time. Despite the reduced time for synthesis compared to standard thermal chemical vapor deposition

Y. Y. Tan; K. D. G. I. Jayawardena; A. A. D. T. Adikaari; L. W. Tan; J. V. Anguita; S. J. Henley; V. Stolojan; J. D. Carey; S. R. P. Silva

2012-01-01

136

A robustness screen for the rapid assessment of chemical reactions  

NASA Astrophysics Data System (ADS)

In contrast to the rapidity with which scientific information is published, the application of new knowledge often remains slow, and we believe this to be particularly true of newly developed synthetic organic chemistry methodology. Consequently, methods to assess and identify robust chemical reactions are desirable, and would directly facilitate the application of newly reported synthetic methodology to complex synthetic problems. Here, we describe a simple process for assessing the likely scope and limitations of a chemical reaction beyond the idealized reaction conditions initially reported. Using simple methods and common analytical techniques we demonstrate a rapid assessment of an established chemical reaction, and also propose a simplified analysis that may be reported alongside new synthetic methodology.

Collins, Karl D.; Glorius, Frank

2013-07-01

137

Thermal oxidative degradation reactions of perfluoroalklethers  

NASA Technical Reports Server (NTRS)

The objective of this contract was to investigate the mechanisms operative in thermal and thermal oxidative degradation of Fomblin Z and hexafluoropropene oxide derived fluids and the effect of alloys and additives upon these processes. The nature of arrangements responsible for the inherent thermal oxidative instability of the Fomblin Z fluids has not been established. It was determined that this behavior was not associated with hydrogen end-groups or peroxy linkages. The degradation rate of these fluids at elevated temperatures in oxidizing atmospheres was found to be dependent on the surface/volume ratio. Once a limiting ratio was reached, a steady rate appeared to be attained. Based on elemental analysis and oxygen consumption data, -CF2OCF2CF2O-, not -CF2CF2O-, is one of the major arrangements present. The action of the M-50 and Ti(4 Al, 4 Mn) alloys was found to be much more drastic in the case of Fomblin Z fluids than that observed for the hexalfuoropropane oxide derived materials. The effectiveness of antioxidation/anticorrosion additives, P-3 and phospha-s-triazine, in the presence of metal alloys was very limited at 316 C; at 288 C the additives arrested almost completely the fluid degradation. The phospha-s-triazine appeared to be at least twice as effective as the P-3 compound; it also protected the coupon better. The Ti(4 Al, 4 Mn) alloy degraded the fluid mainly by chain scission processes; this took place to a much lesser degree with M-50.

Paciorek, K. L.; Harris, D. H.; Smythe, M. E.; Kratzer, R. H.

1983-01-01

138

Coupled Thermal-Chemical-Mechanical Modeling of Validation Cookoff Experiments  

Microsoft Academic Search

The cookoff of energetic materials involves the combined effects of several physical and chemical processes. These processes include heat transfer, chemical decomposition, and mechanical response. The interaction and coupling between these processes influence both the time-to-event and the violence of reaction. The prediction of the behavior of explosives during cookoff, particularly with respect to reaction violence, is a challenging task.

WILLIAM W. ERIKSON; ROBERT G. SCHMITT; A. I. ATWOOD; P. D. CURRAN

2000-01-01

139

Analysis of the Reaction Rate Coefficients for Slow Bimolecular Chemical Reactions  

NASA Astrophysics Data System (ADS)

Simple bimolecular reactions A_1+A_2A_3+A_4 are analyzed within the framework of the Boltzmann equation in the initial stage of a chemical reaction with the system far from chemical equilibrium. The Chapman-Enskog methodology is applied to determine the coefficients of the expansion of the distribution functions in terms of Sonine polynomials for peculiar molecular velocities. The results are applied to the reaction H_2 +ClHCl+H, and the influence of the non-Maxwellian distribution and of the activation-energy dependent reactive cross sections upon the forward and reverse reaction rate coefficients are discussed.

Kremer, Gilberto M.; Silva, Tiago G.

2012-12-01

140

Thermal oxidative degradation reactions of perfluoroalkylethers  

NASA Technical Reports Server (NTRS)

The mechanisms operative in thermal oxidative degradation of Fomblin Z and hexafluoropropene oxide derived fluids and the effect of alloys and additives upon these processes are investigated. The nature of arrangements responsible for the inherent thermal oxidative instability of the Fomblin Z fluids is not established. It was determined that this behavior is not associated with hydrogen end groups or peroxy linkages. The degradation rate of these fluids at elevated temperatures in oxidizing atmospheres is dependent on the surface/volume ratio. Once a limiting ratio is reached, a steady rate appears to be attained. Based on elemental analysis and oxygen consumption data, CF2OCF2CF2O2, no. CF2CF2O, is one of the major arrangements present. The action of the M-50 and Ti(4 Al, 4 Mn) alloys is much more drastic in the case of Fomblin Z fluids than that observed for the hexafluoropropene derived materials. The effectiveness of antioxidation anticorrosion additives, P-3 and phospha-s-triazine, in the presence of metal alloys is very limited at 316 C; at 288 C the additives arrested almost completely the fluid degradation. The phospha-s-triazine appears to be at least twice as effective as the P-3 compound; it also protected the coupon better. The Ti(4 Al, 4 Mn) alloy degraded the fluid mainly by chain scission processes this takes place to a much lesser degree with M-50.

Paciorek, K. L.; Ito, T. I.; Kratzer, R. H.

1981-01-01

141

Advanced deposition model for thermal activated chemical vapor deposition  

NASA Astrophysics Data System (ADS)

Thermal Activated Chemical Vapor Deposition (TACVD) is defined as the formation of a stable solid product on a heated substrate surface from chemical reactions and/or dissociation of gaseous reactants in an activated environment. It has become an essential process for producing solid film, bulk material, coating, fibers, powders and monolithic components. Global market of CVD products has reached multi billions dollars for each year. In the recent years CVD process has been extensively used to manufacture semiconductors and other electronic components such as polysilicon, AlN and GaN. Extensive research effort has been directed to improve deposition quality and throughput. To obtain fast and high quality deposition, operational conditions such as temperature, pressure, fluid velocity and species concentration and geometry conditions such as source-substrate distance need to be well controlled in a CVD system. This thesis will focus on design of CVD processes through understanding the transport and reaction phenomena in the growth reactor. Since the in situ monitor is almost impossible for CVD reactor, many industrial resources have been expended to determine the optimum design by semi-empirical methods and trial-and-error procedures. This approach has allowed the achievement of improvements in the deposition sequence, but begins to show its limitations, as this method cannot always fulfill the more and more stringent specifications of the industry. To resolve this problem, numerical simulation is widely used in studying the growth techniques. The difficulty of numerical simulation of TACVD crystal growth process lies in the simulation of gas phase and surface reactions, especially the latter one, due to the fact that very limited kinetic information is available in the open literature. In this thesis, an advanced deposition model was developed to study the multi-component fluid flow, homogeneous gas phase reactions inside the reactor chamber, heterogeneous surface reactions on the substrate surface, conductive, convective, inductive and radiative heat transfer, species transport and thereto-elastic stress distributions. Gas phase and surface reactions are studied thermodynamically and kinetically. Based on experimental results, detailed reaction mechanisms are proposed and the deposition rates are predicted. The deposition model proposed could be used for other experiments with similar operating conditions. Four different growth systems are presented in this thesis to discuss comprehensive transport phenomena in crystal growth from vapor. The first is the polysilicon bulk growth by modified Siemens technique in which a silicon tube is used as the starting material. The research effort has been focused on system design, geometric and operating parameters optimization, and heterogeneous and homogeneous silane pyrolysis analysis. The second is the GaN thin film growth by iodine vapor phase epitaxy technique. Heat and mass transport is studied analytically and numerically. Gas phase and surface reactions are analyzed thermodynamically and kinetically. Quasi-equilibrium and kinetic deposition models are developed to predict the growth rate. The third one is the AlN thin film growth by halide vapor phase epitaxy technique. The effects of gas phase and surface reactions on the crystal growth rate and deposition uniformity are studied. The last one is the AlN sublimation growth system. The research effort has been focused on the effect of thermal environment evolution on the crystal growth process. The thermoelastic stress formed in the as-grown AlN crystal is also calculated.

Cai, Dang

142

Single-molecule chemical reaction reveals molecular reaction kinetics and dynamics.  

PubMed

Understanding the microscopic elementary process of chemical reactions, especially in condensed phase, is highly desirable for improvement of efficiencies in industrial chemical processes. Here we show an approach to gaining new insights into elementary reactions in condensed phase by combining quantum chemical calculations with a single-molecule analysis. Elementary chemical reactions in liquid-phase, revealed from quantum chemical calculations, are studied by tracking the fluorescence of single dye molecules undergoing a reversible redox process. Statistical analyses of single-molecule trajectories reveal molecular reaction kinetics and dynamics of elementary reactions. The reactivity dynamic fluctuations of single molecules are evidenced and probably arise from either or both of the low-frequency approach of the molecule to the internal surface of the SiO2 nanosphere or the molecule diffusion-induced memory effect. This new approach could be applied to other chemical reactions in liquid phase to gain more insight into their molecular reaction kinetics and the dynamics of elementary steps. PMID:24963600

Zhang, Yuwei; Song, Ping; Fu, Qiang; Ruan, Mingbo; Xu, Weilin

2014-01-01

143

Threshold resonances in ultracold chemical reactions  

NASA Astrophysics Data System (ADS)

We analyze the effects of near threshold resonances on the low energy behavior of cross sections for reactive scattering systems with reaction a barrier (e.g. Cl + H2, D + H2). We find an anomalous behavior when a resonance pole is very close to the threshold of the entrance channel. For inelastic processes, including reactive ones, the anomalous energy dependence of the cross sections is given by ?˜E-3/2. However, at vanishingly low energies, the standard Wigner's threshold behavior (?˜E-1/2) is eventually recovered, but limiting to much narrower range of energies. When the cross sections are averaged to obtain rate coefficients, the anomalous behavior persists; indeed, we find an intermediate regime of ultralow temperatures, where the inelastic rate coefficients behave as K˜1/T.

Côté, Robin; Simbotin, Ionel; Ghosal, Subhas

2012-06-01

144

Imaging chemical reactions - 3D velocity mapping  

NASA Astrophysics Data System (ADS)

Visualising a collision between an atom or a molecule or a photodissociation (half-collision) of a molecule on a single particle and single quantum level is like watching the collision of billiard balls on a pool table: Molecular beams or monoenergetic photodissociation products provide the colliding reactants at controlled velocity before the reaction products velocity is imaged directly with an elaborate camera system, where one should keep in mind that velocity is, in general, a three-dimensional (3D) vectorial property which combines scattering angles and speed. If the processes under study have no cylindrical symmetry, then only this 3D product velocity vector contains the full information of the elementary process under study.

Chichinin, A. I.; Gericke, K.-H.; Kauczok, S.; Maul, C.

145

Automatic NMR-Based Identification of Chemical Reaction Types in Mixtures of Co-Occurring Reactions  

PubMed Central

The combination of chemoinformatics approaches with NMR techniques and the increasing availability of data allow the resolution of problems far beyond the original application of NMR in structure elucidation/verification. The diversity of applications can range from process monitoring, metabolic profiling, authentication of products, to quality control. An application related to the automatic analysis of complex mixtures concerns mixtures of chemical reactions. We encoded mixtures of chemical reactions with the difference between the 1H NMR spectra of the products and the reactants. All the signals arising from all the reactants of the co-occurring reactions were taken together (a simulated spectrum of the mixture of reactants) and the same was done for products. The difference spectrum is taken as the representation of the mixture of chemical reactions. A data set of 181 chemical reactions was used, each reaction manually assigned to one of 6 types. From this dataset, we simulated mixtures where two reactions of different types would occur simultaneously. Automatic learning methods were trained to classify the reactions occurring in a mixture from the 1H NMR-based descriptor of the mixture. Unsupervised learning methods (self-organizing maps) produced a reasonable clustering of the mixtures by reaction type, and allowed the correct classification of 80% and 63% of the mixtures in two independent test sets of different similarity to the training set. With random forests (RF), the percentage of correct classifications was increased to 99% and 80% for the same test sets. The RF probability associated to the predictions yielded a robust indication of their reliability. This study demonstrates the possibility of applying machine learning methods to automatically identify types of co-occurring chemical reactions from NMR data. Using no explicit structural information about the reactions participants, reaction elucidation is performed without structure elucidation of the molecules in the mixtures.

Latino, Diogo A. R. S.; Aires-de-Sousa, Joao

2014-01-01

146

Computed potential energy surfaces for chemical reactions  

NASA Technical Reports Server (NTRS)

The minimum energy path for the addition of a hydrogen atom to N2 is characterized in CASSCF/CCI calculations using the (4s3p2d1f/3s2p1d) basis set, with additional single point calculations at the stationary points of the potential energy surface using the (5s4p3d2f/4s3p2d) basis set. These calculations represent the most extensive set of ab initio calculations completed to date, yielding a zero point corrected barrier for HN2 dissociation of approx. 8.5 kcal mol/1. The lifetime of the HN2 species is estimated from the calculated geometries and energetics using both conventional Transition State Theory and a method which utilizes an Eckart barrier to compute one dimensional quantum mechanical tunneling effects. It is concluded that the lifetime of the HN2 species is very short, greatly limiting its role in both termolecular recombination reactions and combustion processes.

Walch, Stephen P.

1988-01-01

147

Thermal isolation of microchip reaction chambers for rapid non-contact DNA amplification  

NASA Astrophysics Data System (ADS)

This paper describes further optimization of a non-contact, infrared-mediated system for microchip DNA amplification via the polymerase chain reaction (PCR). The optimization is focused on heat transfer modeling and subsequent fabrication of thermally isolated reaction chambers in glass devices that are uniquely compatible with non-contact thermal control. With a thermal conductivity approximately an order of magnitude higher than many plastics, glass is not the obvious substrate of choice for rapid thermal cycling in microfluidic chambers, yet it is preferable in terms of optical clarity, solvent compatibility and chemical inertness. Based on predictions of a lumped capacity heat transfer analysis, it is shown here that post-bonding, patterned etching of surrounding glass from microfluidic reaction chambers provides enhancements as high as 3.6- and 7.5-fold in cooling and heating rates, respectively, over control devices with the same chamber designs. These devices are then proven functional for rapid DNA amplification via PCR, in which 25 thermal cycles are completed in only 5 min in thermally isolated PCR chambers of 270 nL volume, representing the fastest static PCR in glass devices reported to date. Amplification of the 500-base pair fragment of ?-DNA was confirmed by capillary gel electrophoresis. In addition to rapid temperature control, the fabrication scheme presented, which is compatible with standard photolithography and wet etching techniques, provides a simple alternative for general thermal management in glass microfluidic devices without metallization.

Easley, Christopher J.; Humphrey, Joseph A. C.; Landers, James P.

2007-09-01

148

Ultrarapid flashlamp pyrolysis: Thermal versus photochemical reaction pathways  

Microsoft Academic Search

A xenon flashlamp has been used to rapidly heat organic substrates coated onto graphite particles by conversion of photochemical energy into thermal energy within the graphite particles, resulting in heating rates of 10⁵C\\/s (i.e., ultrarapid pyrolysis). The compounds chosen for ultrarapid pyrolysis have been carefully selected to verify whether the reported reactions are due to photochemical or thermal activation. Bibenzyl

J. H. Penn; W. H. Owens; L. J. Shadle

2009-01-01

149

The role of products and a reverse reaction in analysis of nonequilibrium effects in a bimolecular chemical reaction in a dilute gas  

NASA Astrophysics Data System (ADS)

A thermally activated bimolecular reaction in a dilute gas is analyzed. The Shizgal-Karplus perturbation method of solution of the Boltzmann equation for reactions A+A?B+B and A+A?B+B is used to obtain the analytical expressions for the nonequilibrium temperatures of reactants and for the rate of chemical reaction. For both the reactions the temperatures of components obtained within one and two Sonines approximations depend on concentration of products. The rate constant of chemical reaction depends on concentration of products for the first reaction only and for the second reaction is constant. The analytical results for the temperature of the reactant A are compared with those obtained from the Monte Carlo computer simulations with use of the Bird method. It is shown that all analytical expressions simplify to those previously discussed if the concentration of products is negligible.

Cukrowski, A. S.

2000-01-01

150

Mining chemical reactions using neighborhood behavior and condensed graphs of reactions approaches.  

PubMed

This work addresses the problem of similarity search and classification of chemical reactions using Neighborhood Behavior (NB) and Condensed Graphs of Reaction (CGR) approaches. The CGR formalism represents chemical reactions as a classical molecular graph with dynamic bonds, enabling descriptor calculations on this graph. Different types of the ISIDA fragment descriptors generated for CGRs in combination with two metrics--Tanimoto and Euclidean--were considered as chemical spaces, to serve for reaction dissimilarity scoring. The NB method has been used to select an optimal combination of descriptors which distinguish different types of chemical reactions in a database containing 8544 reactions of 9 classes. Relevance of NB analysis has been validated in generic (multiclass) similarity search and in clustering with Self-Organizing Maps (SOM). NB-compliant sets of descriptors were shown to display enhanced mapping propensities, allowing the construction of better Self-Organizing Maps and similarity searches (NB and classical similarity search criteria--AUC ROC--correlate at a level of 0.7). The analysis of the SOM clusters proved chemically meaningful CGR substructures representing specific reaction signatures. PMID:22894688

de Luca, Aurélie; Horvath, Dragos; Marcou, Gilles; Solov'ev, Vitaly; Varnek, Alexandre

2012-09-24

151

STM CONTROL OF CHEMICAL REACTIONS: Single-Molecule Synthesis  

NASA Astrophysics Data System (ADS)

The fascinating advances in single atom/molecule manipulation with a scanning tunneling microscope (STM) tip allow scientists to fabricate atomic-scale structures or to probe chemical and physical properties of matters at an atomic level. Owing to these advances, it has become possible for the basic chemical reaction steps, such as dissociation, diffusion, adsorption, readsorption, and bond-formation processes, to be performed by using the STM tip. Complete sequences of chemical reactions are able to induce at a single-molecule level. New molecules can be constructed from the basic molecular building blocks on a one-molecule-at-a-time basis by using a variety of STM manipulation schemes in a systematic step-by-step manner. These achievements open up entirely new opportunities in nanochemistry and nanochemical technology. In this review, various STM manipulation techniques useful in the single-molecule reaction process are reviewed, and their impact on the future of nanoscience and technology are discussed.

Hla, Saw-Wai; Rieder, Karl-Heinz

2003-10-01

152

RPMDRATE: Bimolecular chemical reaction rates from ring polymer molecular dynamics  

NASA Astrophysics Data System (ADS)

We present RPMDRATE, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions. Program summaryProgram title: RPMDrate Catalogue identifier: AENW_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENW_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: MIT license No. of lines in distributed program, including test data, etc.: 94512 No. of bytes in distributed program, including test data, etc.: 1395674 Distribution format: tar.gz Programming language: Fortran 90/95, Python (version 2.6.x or later, including any version of Python 3, is recommended). Computer: Not computer specific. Operating system: Any for which Python, Fortran 90/95 compiler and the required external routines are available. Has the code been vectorized or parallelized?: The program can efficiently utilize 4096+ processors, depending on problem and available computer. At low temperatures, 110 processors are reasonable for a typical umbrella integration run with an analytic potential energy function and gradients on the latest x86-64 machines. RAM: 256 Mb Classification: 16.12. External routines: NumPy (http://numpy.scipy.org, version 1.5.0 or later is recommended). FFTW3 (http://www.fftw.org, version 3.3 or later is recommended). Nature of problem: The RPMDrate program calculates thermal bimolecular rate coefficients of thermally activated atom-diatom and more complex bimolecular chemical reactions in the gas phase. Solution method: The RPMD rate is calculated using the Bennett-Chandler factorization as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (transmission coefficient) factor. A key feature of this procedure is that it does not require that one calculate the absolute quantum mechanical partition function of the reactants or the transition state. The centroid density QTST rate is calculated from the potential of mean force along the reaction coordinate using umbrella integration. The reaction coordinate is taken to be an interpolating function that connects two dividing surfaces: one located in the asymptotic reactant valley and the other located in the transition state region. The Hessian of the collective reaction coordinate is obtained analytically. The transmission coefficient is calculated from the RPMD simulations with the hard constraint along the reaction coordinate. Restrictions: The applicability of RPMDrate is restricted to global potential energy surfaces with gradients. In the current release, they should be provided by Python callable objects. Unusual features: Simple and user-friendly input system provided by Python syntax. Additional comments: Test calculations for the H+H2 reactions were performed using the Boothroyd-Keogh-Martin-Peterson-2 (BKMP2) potential energy surface (PES) [1]. PESs for the H+CH4,OH+CH4 and H+C2H6 reactions are taken from the online POTLIB library [2]. PESs are included within the distribution package as Fortran subroutines. Implementations of the colored-noise, generalized Langevin equation (GLE) thermostats [3-5] have been included in the current release. The distribution contains example data and a detailed manual describing the use of RPMDrate. Running time: Highly dependent on the input parameters. The running time of RPMDrate depends mainly on the complexity of the potential energy surface and number of ring polymer beads. For the H+H2, H+CH4, and OH+CH4 test calculations given (with 128 ring polymer beads and analytic gradients), the running time is

Suleimanov, Yu. V.; Allen, J. W.; Green, W. H.

2013-03-01

153

Asymmetric chemical reactions by polarized quantum beams  

NASA Astrophysics Data System (ADS)

One of the most attractive hypothesis for the origin of homochirality in terrestrial bio-organic compounds (L-amino acid and D-sugar dominant) is nominated as "Cosmic Scenario"; a chiral impulse from asymmetric excitation sources in space triggered asymmetric reactions on the surfaces of such space materials as meteorites or interstellar dusts prior to the existence of terrestrial life. 1) Effective asymmetric excitation sources in space are proposed as polarized quantum beams, such as circularly polarized light and spin polarized electrons. Circularly polarized light is emitted as synchrotron radiation from tightly captured electrons by intense magnetic field around neutron stars. In this case, either left-or right-handed polarized light can be observed depending on the direction of observation. On the other hand, spin polarized electrons is emitted as beta-ray in beta decay from radioactive nuclei or neutron fireballs in supernova explosion. 2) The spin of beta-ray electrons is longitudinally polarized due to parity non-conservation in the weak interaction. The helicity (the the projection of the spin onto the direction of kinetic momentum) of beta-ray electrons is universally negative (left-handed). For the purpose of verifying the asymmetric structure emergence in bio-organic compounds by polarized quantum beams, we are now carrying out laboratory simulations using circularly polarized light from synchrotron radiation facility or spin polarized electron beam from beta-ray radiation source. 3,4) The target samples are solid film or aqueous solution of racemic amino acids. 1) K.Kobayashi, K.Kaneko, J.Takahashi, Y.Takano, in Astrobiology: from simple molecules to primitive life; Ed. V.Basiuk; American Scientific Publisher: Valencia, 2008. 2) G.A.Gusev, T.Saito, V.A.Tsarev, A.V.Uryson, Origins Life Evol. Biosphere. 37, 259 (2007). 3) J.Takahashi, H.Shinojima, M.Seyama, Y.Ueno, T.Kaneko, K.Kobayashi, H.Mita, M.Adachi, M.Hosaka, M.Katoh, Int. J. Mol. Sci. 10, 3044 (2009). 4) V.I.Burkov, L.A.Goncharova, G.A.Gusev, H.Hashimoto, F.Kaneko, T.Kaneko, K. Kobayashi, H.Mita, E.V.Moiseenko, T.Ogawa, N.G.Poluhina, T.Saito, S.Shima, J.Takahashi, M.Tanaka, Y.Tao, V.A.Tsarev, J.Xu, H.Yabuta, K.Yagi-Watanabe, H.Yan, G.Zhang, Origins Life Evol. Biosphere, 39 295 (2009).

Takahashi, Jun-Ichi; Kobayashi, Kensei

154

Analysis of Nonequilibrium Effects in a Bimolecular Chemical Reaction in a Dilute Gas  

NASA Astrophysics Data System (ADS)

We analyze a thermally activated bimolecular reaction in a dilute gas proceeding with introduction of the Prigogine--Xhrouet model (PX) for the reactive cross section. We use the Shizgal--Karplus perturbation method of solution of the Boltzmann equation for reactions A + A ? B + B and A + A ? B + B to obtain the analytical expressions for the nonequilibrium temperatures of reagents and for the rate of chemical reaction. We present the results obtained within one and two Sonine polynomials approximations. The rate constant of chemical reaction depends on concentration of products for the first reaction only and for the second reaction is constant. The analytical results for the temperature of the reagent A and its value in the beginning of reaction for the product B are compared with those obtained from the Monte Carlo computer simulations with use of the Bird method. It is shown that the nonequilibrium effects in Shizgal--Karplus temperatures and in decrease of the chemical constant rate are more pronounced than for the lines-of-centers model. For the PX model the rate constant can be decreased even 4 times.

Cukrowski, Andrzej S.; Fritzsche, Siegfried

2003-07-01

155

Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems  

PubMed Central

The detailed behavior of many molecular processes in the cell, such as protein folding, protein complex assembly, and gene regulation, transcription and translation, can often be accurately captured by stochastic chemical kinetic models. We investigate a novel computational problem involving these models – that of finding the most-probable sequence of reactions that connects two or more states of the system observed at different times. We describe an efficient method for computing the probability of a given reaction sequence, but argue that computing most-probable reaction sequences is EXPSPACE-hard. We develop exact (exhaustive) and approximate algorithms for finding most-probable reaction sequences. We evaluate these methods on test problems relating to a recently-proposed stochastic model of folding of the Trp-cage peptide. Our results provide new computational tools for analyzing stochastic chemical models, and demonstrate their utility in illuminating the behavior of real-world systems.

Salehi, Maryam; Perkins, Theodore J.

2010-01-01

156

Phase Separation in Binary Mixtures with Chemical Reactions  

NASA Astrophysics Data System (ADS)

This paper is the second in a two-stage exposition on phase separation in binary (AB) mixtures with simple chemical reactions, which involve only the components A and B of the mixture. In this paper, we present details of our modelling, which employs the master equation formalism, for a number of different reactions. We also present detailed numerical results which supplement those in our previous paper (S. Puri and H. L. Frisch, J. Phys. A27, 6027 (1994)).

Puri, Sanjay; Frisch, Harry L.

157

Surface light-induced drift affected by chemical reactions  

Microsoft Academic Search

Surface light-induced drift caused by backscattering from rough surfaces can be strongly affected by surface-enhanced state-specific chemical reactions. Expressions for the drift fluxes of the incident resonant-gas component and of the reaction product are presented. A resulting asymmetry in the spatial distributions of the components in a ssT-shaped enclosure is discussed, as a possible sensitive tool for studying the state

M. A. Vaksman; A. Ben-Reuven

1992-01-01

158

Mass transfer and chemical reactions in reactive deformable bubble swarms  

NASA Astrophysics Data System (ADS)

A hybrid numerical/experimental technique was developed for the study of the impact of the multiphase hydrodynamics on mass transfer and chemical reactions at deformable interfaces. Different material properties and flow conditions can yield flows with qualitatively different mass transfer and transport characteristics. As many (bio-) reaction systems exhibit sensitivity to mass transport in general, and mixing specifically, it is possible to control their product distribution by tailoring the system parameters.

Koynov, Athanas; Tryggvason, Grétar; Schlüter, Michael; Khinast, Johannes G.

2006-03-01

159

Channel flow of a Maxwell fluid with chemical reaction  

NASA Astrophysics Data System (ADS)

This work is concerned with the two-dimensional boundary layer flow of an upper-convected Maxwell (UCM) fluid in a channel with chemical reaction. The walls of the channel are porous. Employing similarity transformations the governing non-linear partial differential equations are reduced into non-linear ordinary differential equations. The resulting ordinary differential equations are solved analytically using homotopy analysis method (HAM). Expressions for series solutions are derived. The convergence of the obtained series solutions are shown explicitly. The effects of Reynold’s number Re, Deborah number De, Schmidt number Sc and chemical reaction parameter ? on the velocity and the concentration fields are shown through graphs and discussed.

Hayat, T.; Abbas, Z.

2008-01-01

160

Chemical reactions in viscous liquids under space conditions  

NASA Astrophysics Data System (ADS)

A long-term human flight needs a large-size space ships with artificial self-regulating ecological life-support system. The best way for creation of large-size space ship is a synthesis of light construction on Earth orbit, that does not need a high energy transportation carriers from Earth surface. The construction can be created by the way of chemical polymerisation reaction under space environment. But the space conditions are very specific for chemical reactions. A high vacuum, high energy particles, X-rays, UV- and VUV-irradiations, atomic oxygen, microgravity have a significant influence on chemical reactions. Polymerisation reactions in liquid active mixture were studied in simulated space environment. The epoxy resins based on Bisphenol A and amine curing agents were investigated under vacuum, microwave plasma discharge and ion beam. An acceleration of polymerisation reaction with free radicals formation was observed. The polymerisation reaction can be carried out under space environment. The study was supported by Alexander von Humboldt Foundation (A. Kondyurin) and European Space Agency, ESTEC (contract 17083/03/NL/Sfe "Space Environmental Effects on the Polymerisation of Composite Structures").

Kondyurin, A.; Lauke, B.; Richter, E.

161

Oxidation behavior of silicon carbide based biomorphic ceramics prepared by chemical vapor infiltration and reaction technique  

Microsoft Academic Search

The oxidation behavior of biomorphic SiC based ceramics with different microstructure and composition was studied at 1450°C in airflow for 50h by thermal gravimetric analysis (TGA). SiC with amorphous, coarse grain, crystalline and fine grain crystalline microstructures as well as SiC–Si3N4 composite ceramics were processed from paper preforms by chemical vapor infiltration and reaction technique. The ceramics were characterized by

H. Ghanem; E. Alkhateeb; H. Gerhard; N. Popovska

2009-01-01

162

Preparation and thermal conductivity of CuO nanofluid via a wet chemical method  

NASA Astrophysics Data System (ADS)

In this article, a wet chemical method was developed to prepare stable CuO nanofluids. The influences of synthesis parameters, such as kinds and amounts of copper salts, reaction time, were studied. The thermal conductivities of CuO nanofluids were also investigated. The results showed that different copper salts resulted in different particle morphology. The concentration of copper acetate and reaction time affected the size and shape of clusters of primary nanoparticles. Nanofluids with different microstructures could be obtained by changing the synthesis parameters. The thermal conductivities of CuO nanofluids increased with the increase of particle loading.

Zhu, Haitao; Han, Dongxiao; Meng, Zhaoguo; Wu, Daxiong; Zhang, Canying

2011-12-01

163

Preparation and thermal conductivity of CuO nanofluid via a wet chemical method.  

PubMed

In this article, a wet chemical method was developed to prepare stable CuO nanofluids. The influences of synthesis parameters, such as kinds and amounts of copper salts, reaction time, were studied. The thermal conductivities of CuO nanofluids were also investigated. The results showed that different copper salts resulted in different particle morphology. The concentration of copper acetate and reaction time affected the size and shape of clusters of primary nanoparticles. Nanofluids with different microstructures could be obtained by changing the synthesis parameters. The thermal conductivities of CuO nanofluids increased with the increase of particle loading. PMID:21711693

Zhu, Haitao; Han, Dongxiao; Meng, Zhaoguo; Wu, Daxiong; Zhang, Canying

2011-01-01

164

Preparation and thermal conductivity of CuO nanofluid via a wet chemical method  

PubMed Central

In this article, a wet chemical method was developed to prepare stable CuO nanofluids. The influences of synthesis parameters, such as kinds and amounts of copper salts, reaction time, were studied. The thermal conductivities of CuO nanofluids were also investigated. The results showed that different copper salts resulted in different particle morphology. The concentration of copper acetate and reaction time affected the size and shape of clusters of primary nanoparticles. Nanofluids with different microstructures could be obtained by changing the synthesis parameters. The thermal conductivities of CuO nanofluids increased with the increase of particle loading.

2011-01-01

165

Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories  

NASA Technical Reports Server (NTRS)

This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

Gokoglu, Suleyman A.

1988-01-01

166

Modeling of forced flow/thermal gradient chemical vapor infiltration.  

National Technical Information Service (NTIS)

The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conve...

T. L. Starr A. W. Smith

1992-01-01

167

Researches on Preliminary Chemical Reactions in Spark-Ignition Engines  

NASA Technical Reports Server (NTRS)

Chemical reactions can demonstrably occur in a fuel-air mixture compressed in the working cylinder of an Otto-cycle (spark ignition) internal-combustion engine even before the charge is ignited by the flame proceeding from the sparking plug. These are the so-called "prelinminary reactions" ("pre-flame" combustion or oxidation), and an exact knowledge of their characteristic development is of great importance for a correct appreciation of the phenomena of engine-knock (detonation), and consequently for its avoidance. Such reactions can be studied either in a working engine cylinder or in a combustion bomb. The first method necessitates a complicated experimental technique, while the second has the disadvantage of enabling only a single reaction to be studied at one time. Consequently, a new series of experiments was inaugurated, conducted in a motored (externally-driven) experimental engine of mixture-compression type, without ignition, the resulting preliminary reactions being detectable and measurable thermometrically.

Muehlner, E.

1943-01-01

168

On the role of chemical reactions in initiating ultraviolet laser ablation in poly(methyl methacrylate)  

SciTech Connect

The role of chemical reactions is investigated versus the thermal and mechanical processes occurring in a polymer substrate during irradiation by a laser pulse and subsequent ablation. Molecular dynamics simulations with an embedded Monte Carlo based reaction scheme were used to study ultraviolet ablation of poly(methyl methacrylate) at 157 nm. We discuss the onset of ablation, the mechanisms leading to ablation, and the role of stress relaxation of the polymer matrix during ablation. Laser induced heating and chemical decomposition of the polymer substrate are considered as ablation pathways. It is shown that heating the substrate can set off ablation via mechanical failure of the material only for very short laser pulses. For longer pulses, the mechanism of ejection is thermally driven limited by the critical number of bonds broken in the substrate. Alternatively, if the photon energy goes towards direct bond breaking, it initiates chemical reactions, polymer unzipping, and formation of gaseous products, leading to a nearly complete decomposition of the top layers of substrates. The ejection of small molecules has a hollowing out effect on the weakly connected substrates which can lead to lift-off of larger chunks. Excessive pressure buildup upon the creation of gaseous molecules does not lead to enhanced yield. The larger clusters are thermally ejected, and an entrainment of larger polymer fragments in gaseous molecules is not observed.

Prasad, Manish; Conforti, Patrick F.; Garrison, Barbara J. [Department of Chemistry, 104 Chemistry Building, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

2007-05-15

169

Reduction of chemical reaction networks through delay distributions  

NASA Astrophysics Data System (ADS)

Accurate modelling and simulation of dynamic cellular events require two main ingredients: an adequate description of key chemical reactions and simulation of such chemical events in reasonable time spans. Quite logically, posing the right model is a crucial step for any endeavour in Computational Biology. However, more often than not, it is the associated computational costs which actually limit our capabilities of representing complex cellular behaviour. In this paper, we propose a methodology aimed at representing chains of chemical reactions by much simpler, reduced models. The abridgement is achieved by generation of model-specific delay distribution functions, consecutively fed to a delay stochastic simulation algorithm. We show how such delay distributions can be analytically described whenever the system is solely composed of consecutive first-order reactions, with or without additional ``backward'' bypass reactions, yielding an exact reduction. For models including other types of monomolecular reactions (constitutive synthesis, degradation, or ``forward'' bypass reactions), we discuss why one must adopt a numerical approach for its accurate stochastic representation, and propose two alternatives for this. In these cases, the accuracy depends on the respective numerical sample size. Our model reduction methodology yields significantly lower computational costs while retaining accuracy. Quite naturally, computational costs increase alongside network size and separation of time scales. Thus, we expect our model reduction methodologies to significantly decrease computational costs in these instances. We anticipate the use of delays in model reduction will greatly alleviate some of the current restrictions in simulating large sets of chemical reactions, largely applicable in pharmaceutical and biological research.

Barrio, Manuel; Leier, André; Marquez-Lago, Tatiana T.

2013-03-01

170

Program Helps To Determine Chemical-Reaction Mechanisms  

NASA Technical Reports Server (NTRS)

General Chemical Kinetics and Sensitivity Analysis (LSENS) computer code developed for use in solving complex, homogeneous, gas-phase, chemical-kinetics problems. Provides for efficient and accurate chemical-kinetics computations and provides for sensitivity analysis for variety of problems, including problems involving honisothermal conditions. Incorporates mathematical models for static system, steady one-dimensional inviscid flow, reaction behind incident shock wave (with boundary-layer correction), and perfectly stirred reactor. Computations of equilibrium properties performed for following assigned states: enthalpy and pressure, temperature and pressure, internal energy and volume, and temperature and volume. Written in FORTRAN 77 with exception of NAMELIST extensions used for input.

Bittker, D. A.; Radhakrishnan, K.

1995-01-01

171

Favorite Demonstration: Demonstrating Indigo Carmine Oxidation-Reduction Reactions--A Choreography for Chemical Reactions  

NSDL National Science Digital Library

The indigo carmine demonstration (Ferguson et al. 1973), also referred to as a traffic-light demonstration (Flinn Scientific 2007a), is an example of a set of oxidation-reduction reactions that occurs within one solution. This type of demonstration can be used to introduce the concept of chemical reaction to undergraduate nonscience majors. Through their observations guided by the instructor, students begin to develop and construct the following concepts: color changes, reaction rates, reversible reactions, energy requirements (endothermic/exothermic), and equilibrium.

Majerich, David M.; Schmuckler, Joseph S.

2008-03-01

172

Jet quenching and holographic thermalization with a chemical potential  

NASA Astrophysics Data System (ADS)

We investigate jet quenching of virtual gluons and thermalization of a strongly-coupled plasma with a non-zero chemical potential via the gauge/gravity duality. By tracking a charged shell falling in an asymptotic AdS d+1 background for d = 3 and d = 4, which is characterized by the AdS-Reissner-Nordström-Vaidya (AdS-RN-Vaidya) geometry, we extract a thermalization time of the medium with a non-zero chemical potential. In addition, we study the falling string as the holographic dual of a virtual gluon in the AdS-RN-Vaidya spacetime. The stopping distance of the massless particle representing the tip of the falling string in such a spacetime could reveal the jet quenching of an energetic light probe traversing the medium in the presence of a chemical potential. We find that the stopping distance decreases when the chemical potential is increased in both AdS-RN and AdS-RN-Vaidya spacetimes, which correspond to the thermalized and thermalizing media respectively. Moreover, we find that the soft gluon with an energy comparable to the thermalization temperature and chemical potential in the medium travels further in the non-equilibrium plasma. The thermalization time obtained here by tracking a falling charged shell does not exhibit, generically, the same qualitative features as the one obtained studying non-local observables. This indicates that — holographically — the definition of thermalization time is observer dependent and there is no unambiguos definition.

Caceres, Elena; Kundu, Arnab; Yang, Di-Lun

2014-03-01

173

Modeling pore collapse and chemical reactions in shock-loaded HMX crystals  

NASA Astrophysics Data System (ADS)

The localization of deformation in shock-loaded crystals of high explosive material leads to the formation of hot spots, which, if hot enough, initiate chemical reactions. The collapse of microscopic pores contained within a crystal is one such process that localizes energy and generates hot spots. Given the difficulty of resolving the details of pore collapse in shock compression experiments, it is useful to study the problem using direct numerical simulation. In this work, we focus on simulating the shock-induced closure of a single pore in crystalline ?-HMX using a multiphysics finite element code. To address coupled thermal-mechanical-chemical responses, the model incorporates a crystal-mechanics-based description of thermoelasto-viscoplasticity, the crystal melting behavior, and transformation kinetics for a single-step decomposition reaction. The model is applied to stress wave amplitudes of up to 11 GPa to study the details of pore collapse, energy localization, and the early stages of reaction initiation.

Austin, R. A.; Barton, N. R.; Howard, W. M.; Fried, L. E.

2014-05-01

174

2011 Chemical Reactions at Surfaces Gordon Research Conference  

SciTech Connect

The Gordon Research Conference on Chemical Reactions at Surfaces is dedicated to promoting and advancing the fundamental science of interfacial chemistry and physics by providing surface scientists with the foremost venue for presentation and discussion of research occurring at the frontiers of their fields.

Peter Stair

2011-02-11

175

Chemical Reactions at the Au/InP Interface.  

National Technical Information Service (NTIS)

Chemical reactions at the Au/InP interface were investigated in the temperature range 25 510C by x-ray diffractometry, scanning electron microscopy and energy dispersive X-ray analysis. The samples were prepared by depositing gold films onto clean InP(100...

C. T. Tsai R. S. Williams

1986-01-01

176

Pyrimidine-specific chemical reactions useful for DNA sequencing.  

PubMed Central

Potassium permanganate reacts selectively with thymidine residues in DNA (1) while hydroxylamine hydrochloride at pH 6 specifically attacks cytosine (2). We have adopted these reactions for use with the chemical sequencing method developed by Maxam and Gilbert (3). Images

Rubin, C M; Schmid, C W

1980-01-01

177

Chemical reaction engineering using molecularly imprinted polymeric catalysts  

Microsoft Academic Search

Enzymes play an important role as highly specific catalysts in biotechnology [J. Biotechnol. 66 (1998) 3; Hydrolases in Organic Synthesis, Wiley, New York, 1999] as well as in chemical reaction engineering [J. Biotechnol. 59 (1997) 11; Trends Biotechnol. 13 (7) (1995) 253]. However, the drawbacks of these biomaterials are poor durability and relatively high costs of production. Thus, the technique

Oliver Brüggemann

2001-01-01

178

Characterization of Thermally Degraded Energetic Materials: Mechanical and Chemical Behavior  

SciTech Connect

We report the results of recent experiments on thermally degraded HMX and HMX/binder materials. Small-scale samples were heated confined in either constant-volume or load- controlled configurations. A main emphasis of the work reported here is developing an understanding of the complex coupling of the mechanical and chemical responses during thermal degradation.

Miller, J.C.; Renlund, A.M.; Schmitt, R.G.; Wellman, G.W.

1998-12-04

179

A fully coupled thermal, chemical, mechanical cookoff model  

Microsoft Academic Search

Cookoff modeling of confined energetic materials involves the coupling of thermal, chemical and mechanical effects. In the past, modeling has focussed on the prediction of thermal runaway with little regard to the effects of mechanical behavior of the energetic material. To address the mechanical response of the energetic material, a constitutive submodel has been developed which can be incorporated into

M. L. Hobbs; M. R. Baer; R. J. Gross

1994-01-01

180

Chemical Reactions on Ice Surfaces; Experimental and Theoretical Studies  

NASA Astrophysics Data System (ADS)

Surfaces of ice particles in the stratosphere and troposphere are now widely recognized to heterogeneously catalyze chemical reactions that lead to changes in the chemical composition of the atmosphere, however, not much is known about the reaction mechanisms, their time scales, or why ice is required for the reactions. We address these issues with respect to heterogeneous chlorine activation reactions on ice which ultimately lead to stratospheric ozone depletion. Studies using second harmonic generation (SHG) are presented first. The equilibrium basal (0001) face of ice Ih is held under stratospherically relevant conditions, and chlorine activation reactions are studied using submonolayer reactant amounts. In another set of experiments, the adsorption of HCl on ice, a key step required for chlorine activation, is examined using chemical ionization mass spectrometry (CIMS). The ice is formed by freezing from the melt inside a flow tube reactor and is polycrystalline; HCl partial pressures are held between 1 10^9 and 1 x 10^6 Torr, and the experiments are performed under stratospherically relevant temperature and pressure conditions. Finally, ab initio calculations on water clusters representative of an adsorption site on the basal ice surface and Car-Parrinello Molecular Dynamics (CPMD) simulations on ice slabs having a varying number of dangling OH groups help us develop a molecular level picture of how ice surfaces are involved in stratospheric ozone depletion.

Geiger, Franz

2002-03-01

181

Mixing, chemical reaction and flow field development in ducted rockets  

SciTech Connect

Calculations have been made of the three-dimensional mixing, chemical reaction, and flow field development in a typical ducted rocket configuration. The governing partial differential equations are numerically solved by an iterative finite-difference solution procedure. The physical models include the k approx. epsilon turbulence model, one-step reaction, and mixing controlled chemical reaction rate. Radiation is neglected. The mean flow structure, fuel dispersal patterns, and temperature field are presented in detail for a base configuration with 0.058 m (2 in.) dome height, 45/sup 0/ side arm inclination, and with gaseous ethylene injected from the dome plate at an eccentric location. In addition, the influences of the geometrical parameters such as dome height, inclination of the side arms, and location of the fuel injector are studied.

Vanka, S.P.; Craig, R.R.; Stull, F.D.

1984-09-01

182

Multiscale stochastic simulations of chemical reactions with regulated scale separation  

SciTech Connect

We present a coupling of multiscale frameworks with accelerated stochastic simulation algorithms for systems of chemical reactions with disparate propensities. The algorithms regulate the propensities of the fast and slow reactions of the system, using alternating micro and macro sub-steps simulated with accelerated algorithms such as ? and R-leaping. The proposed algorithms are shown to provide significant speedups in simulations of stiff systems of chemical reactions with a trade-off in accuracy as controlled by a regulating parameter. More importantly, the error of the methods exhibits a cutoff phenomenon that allows for optimal parameter choices. Numerical experiments demonstrate that hybrid algorithms involving accelerated stochastic simulations can be, in certain cases, more accurate while faster, than their corresponding stochastic simulation algorithm counterparts.

Koumoutsakos, Petros, E-mail: petros@ethz.ch [Chair of Computational Science, Clausiusstrasse 33, ETH Zurich, CH-8092 (Switzerland)] [Chair of Computational Science, Clausiusstrasse 33, ETH Zurich, CH-8092 (Switzerland); Feigelman, Justin [Chair of Computational Science, Clausiusstrasse 33, ETH Zurich, CH-8092 (Switzerland)] [Chair of Computational Science, Clausiusstrasse 33, ETH Zurich, CH-8092 (Switzerland)

2013-07-01

183

Chemical reaction mediated self-assembly of PTCDA into nanofibers  

NASA Astrophysics Data System (ADS)

Uniform and crystalline nanofibers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), an insoluble organic semiconducting molecule, have been achieved by self-assembling the molecules using chemical reaction mediated conversion of an appropriately designed soluble precursor, perylene tetracarboxylic acid (PTCA) using carbodiimide chemistry.Uniform and crystalline nanofibers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), an insoluble organic semiconducting molecule, have been achieved by self-assembling the molecules using chemical reaction mediated conversion of an appropriately designed soluble precursor, perylene tetracarboxylic acid (PTCA) using carbodiimide chemistry. Electronic supplementary information (ESI) available: Synthesis protocols and schemes, plausible mechanism of reaction, additional TEM images, TEM images for stability of fibers after extraction in DCM and aqueous potassium carbonate, detailed FTIR spectra, mass spectroscopy, and XRD of fibers of PTCDA. See DOI: 10.1039/c1nr10579e

Sayyad, Arshad S.; Balakrishnan, Kaushik; Ajayan, Pulickel M.

2011-09-01

184

KINETICS: A computer program to analyze chemical reaction data. Revision 2  

SciTech Connect

KINETICS (Version 3.2) is a copyrighted, user-friendly kinetics analysis computer program designed for reactions such-as kerogen or polymer decomposition. It can fit rate parameters to chemical reaction data (rate or cumulative reacted) measured at a series of constant temperatures, constant heating rates, or arbitrary thermal histories. The program uses two models with conversion-dependent Azrhenius parameters and two models with activation energy distributions. The discrete distribution model fits an average frequency factor and relative fractions and activation energies for up to 25 parallel, fast-order reactions. The Gaussian distribution model fits a frequency factor, activation energy, Gaussian distribution parameter, and reaction order for up to 3 parallel reactions. For both distribution models, if the experiments are at a series of constant heating rates, the program uses a very fast approximate fitting procedure to determine possible initial parameter-estimates for the subsequent nonlinear regression analysis. This increases the probability that the regression analysis will properly. converge with a minimum of computer time. Once convergence is reached by the discrete model, the parameter space is further systematically searched to achieve global convergence. With the Gaussian model, the calculated rates or integrals can be convoluted with an experimental tracer signal during the nonlinear regression to account for dispersion effects often found in real chemical reaction data. KINETICS can also be used in an application mode to calculate reaction rates and integrals for previously determined Gaussian or discrete, parameters, using an arbitrary thermal history. Four additional models have been incorporated for the kinetics analysis of polymers and other materials, including some kerogens, which have a reaction-rate profile that is narrower than that for a single first-order reaction.

Braun, R.L.; Burnham, A.K.

1994-09-01

185

Biodegradable multifunctional oil production chemicals: Thermal polyaspartates.  

National Technical Information Service (NTIS)

The paper deals with biodegradable oil production chemicals. Control of both mineral scale and corrosion with a single, environmentally acceptable material is an ambitious goal. Polyaspartate polymers represent a significant milestone in the attainment of...

R. J. Ross P. D. Ravenscroft

1996-01-01

186

Chemical energy storage system for SEGS solar thermal power plant  

Microsoft Academic Search

The Pacific Northwest Laboratory evaluated the potential feasibility of using chemical energy storage at the Solar Electric Generating System (SEGS) power plants developed by Luz International. Like sensible or latent heat energy storage systems, chemical energy storage can be beneficially applied to solar thermal power plants to dampen the impact of cloud transients, extend the daily operating period, and\\/or allow

D. R. Brown; J. L. Lamarche; G. E. Spanner

1992-01-01

187

Chemical, Electrical and Thermal Characterization of Nanoceramic Silicon Carbide  

Microsoft Academic Search

Silicon carbide (SiC) is a lightweight high bandgap semiconductor material that can maintain dimensional and chemical stability in adverse environments and very high temperatures. These properties make it suitable for high temperature thermoelectric converters. At the Center for Irradiaton of Materials (CIM) we design, manufacture and fabricate nanoceramic SiC, and perform electrical, thermal and chemical characterization of the material using

Hervie Martin; Malek Abunaemeh; Cydale Smith; Claudiu Muntele; Satilmish Budak; Daryush Ila

2009-01-01

188

Chemical analyses of selected thermal springs and wells in Wyoming  

SciTech Connect

Basic chemical data for 27 selected thermal well and springs in Wyoming are presented. The samples were gathered from 1979 through 1982 in an effort to define geothermal resources in Wyoming. The basic data for the 27 analyzed samples generally include location, temperature, flow, date analyzed, and a description of what the sample is from. The chemical analyses for the sample are listed.

Heasler, H.P.

1984-06-01

189

Robust Stochastic Chemical Reaction Networks and Bounded Tau-Leaping  

PubMed Central

Abstract The behavior of some stochastic chemical reaction networks is largely unaffected by slight inaccuracies in reaction rates. We formalize the robustness of state probabilities to reaction rate deviations, and describe a formal connection between robustness and efficiency of simulation. Without robustness guarantees, stochastic simulation seems to require computational time proportional to the total number of reaction events. Even if the concentration (molecular count per volume) stays bounded, the number of reaction events can be linear in the duration of simulated time and total molecular count. We show that the behavior of robust systems can be predicted such that the computational work scales linearly with the duration of simulated time and concentration, and only polylogarithmically in the total molecular count. Thus our asymptotic analysis captures the dramatic speedup when molecular counts are large, and shows that for bounded concentrations the computation time is essentially invariant with molecular count. Finally, by noticing that even robust stochastic chemical reaction networks are capable of embedding complex computational problems, we argue that the linear dependence on simulated time and concentration is likely optimal.

2009-01-01

190

Information-Theoretical Complexity Analysis of Selected Elementary Chemical Reactions  

NASA Astrophysics Data System (ADS)

We investigate the complexity of selected elementary chemical reactions (namely, the hydrogenic-abstraction reaction and the identity SN2 exchange reaction) by means of the following single and composite information-theoretic measures: disequilibrium (D), exponential entropy(L), Fisher information (I), power entropy (J), I-D, D-L and I-J planes and Fisher-Shannon (FS) and Lopez-Mancini-Calbet (LMC) shape complexities. These quantities, which are functionals of the one-particle density, are computed in both position (r) and momentum (p) spaces. The analysis revealed that the chemically significant regions of these reactions can be identified through most of the single information-theoretic measures and the two-component planes, not only the ones which are commonly revealed by the energy, such as the reactant/product (R/P) and the transition state (TS), but also those that are not present in the energy profile such as the bond cleavage energy region (BCER), the bond breaking/forming regions (B-B/F) and the charge transfer process (CT). The analysis of the complexities shows that the energy profile of the abstraction reaction bears the same information-theoretical features of the LMC and FS measures, however for the identity SN2 exchange reaction does not hold a simple behavior with respect to the LMC and FS measures. Most of the chemical features of interest (BCER, B-B/F and CT) are only revealed when particular information-theoretic aspects of localizability (L or J), uniformity (D) and disorder (I) are considered.

Molina-Espíritu, M.; Esquivel, R. O.; Dehesa, J. S.

191

Investigation of chemical reactions in solution using API-MS  

NASA Astrophysics Data System (ADS)

The general concepts, advantages, and applications of on-line and off-line screening to organic reaction mechanistic studies applying API-MS are reviewed. An overview is presented of the development and the present stage of connected microreactors to API ion-sources. Examples of the successful application of API in revealing, elucidating, and helping to consolidate several proposed mechanisms of organic reactions are summarized. Finally, a variety of outstanding features and advantages that make API-MS the most suitable tool for the fast screening of intermediates directly from solution, and the exceptional gains in chemical information for organic chemists are also emphasized.

Santos, Leonardo Silva; Knaack, Larissa; Metzger, Jürgen O.

2005-11-01

192

Electrochemical Reactions During Ru Chemical Mechanical Planarization and Safety Considerations  

NASA Astrophysics Data System (ADS)

We analyzed electrochemical reactions during ruthenium (Ru) chemical mechanical planarization (CMP) using a potentiostat and a quartz crystal microbalance, and considered the potential safety issues. We evaluated the valence number derived from Faraday's law using the dissolution mass change of Ru and total coulomb consumption in the electrochemical reactions for Ru in acidic solution and slurry. The valence numbers of dissolved Ru ions were distributed in the range of 2 to 3.5. As toxic ruthenium tetroxide (RuO4) has a valence number of 8, we were able to conclude that no toxic RuO4 was produced in the actual Ru CMP.

Shima, Shohei; Wada, Yutaka; Tokushige, Katsuhiko; Fukunaga, Akira; Tsujimura, Manabu

2011-05-01

193

Thermal impurity reactions and structural changes in slightly carbonated hydroxyapatite  

Microsoft Academic Search

Lattice and surface impurity reactions and structural changes induced by them in slightly carbonated hydroxyapatite (SCHA)\\u000a treated at 25–1100ºC were comprehensively studied. The SCHA was processed by a conventional wet synthesis at a high possible\\u000a temperature (96ºC) using ammonium containing parent reagents. IR-spectroscopy, XRD, TG-DTA technique and mass spectrometric\\u000a thermal analysis (MSTA) were employed for characterization of the samples. $$

Z. Z. Zyman; D. V. Rokhmistrov; V. I. Glushko; I. G. Ivanov

2009-01-01

194

Modeling of Thermal-Hydrological-Chemical Laboratory Experiments  

SciTech Connect

The emplacement of heat-generating nuclear waste in the potential geologic repository at Yucca Mountain, Nevada, will result in enhanced water-rock interaction around the emplacement drifts. Water present in the matrix and fractures of the rock around the drift may vaporize and migrate via fractures to cooler regions where condensation would occur. The condensate would react with the surrounding rock, resulting in mineral dissolution. Mineralized water flowing under gravity back towards the heat zone would boil, depositing the dissolved minerals. Such mineral deposition would reduce porosity and permeability above the repository, thus altering the flow paths of percolating water. The objective of this research is to use coupled thermal-hydrological-chemical (THC) models to simulate previously conducted laboratory experiments involving tuff dissolution and mineral precipitation in a boiling, unsaturated fracture. Numerical simulations of tuff dissolution and fracture plugging were performed using a modified version of the TOUGHREACT code developed at LBNL by T. Xu and K. Pruess. The models consider the transport of heat, water, gas and dissolved constituents, reactions between gas, mineral and aqueous phases, and the coupling of porosity and permeability to mineral dissolution and precipitation. The model dimensions and initial fluid chemistry, rock mineralogy, permeability, and porosity were defined using the experimental conditions. A 1-D plug-flow model was used to simulate dissolution resulting from reaction between deionized water and crushed ash flow tuff. A 2-D model was developed to simulate the flow of mineralized water through a planar fracture within a block of ash flow tuff where boiling conditions led to mineral precipitation. Matrix blocks were assigned zero permeability to confine fluid flow to the fracture, and permeability changes in the fracture were specified using the porosity cubic law relationship.

P. F. Dobson; T. J. Kneafsey; E. L. Sonnenthal; Nicolas Spycher

2001-05-31

195

A fully coupled thermal, chemical, mechanical cookoff model  

SciTech Connect

Cookoff modeling of confined energetic materials involves the coupling of thermal, chemical and mechanical effects. In the past, modeling has focussed on the prediction of thermal runaway with little regard to the effects of mechanical behavior of the energetic material. To address the mechanical response of the energetic material, a constitutive submodel has been developed which can be incorporated into thermal-chemical-mechanical analysis. This work presents development of this submodel and its incorporation into a fully coupled one-dimensional, thermal-chemical-mechanical computer code to simulate thermal initiation of energetic materials. Model predictions include temperature, chemical species, stress, strain, solid/gas pressure, solid/gas density, yield function, and gas volume fraction. Sample results from a scaled aluminum tube filled with RDX exposed to a constant temperature bath at 500 K will be displayed. The micromechanical submodel is based on bubble mechanics which describes nucleation, decomposition, and elastic/plastic mechanical behavior. This constitutive material description requires input of temperatures and reacted fraction of the energetic material as provided by the reactive heat flow code, XCHEM, and the mechanical response is predicted using a quasistatic mechanics code, SANTOS. A parametric sensitivity analysis indicates that a small degree of decomposition causes significant pressurization of the energetic material, which implies that cookoff modeling must consider the strong interaction between thermal-chemistry and mechanics. This document consists of view graphs from the poster session.

Hobbs, M.L.; Baer, M.R.; Gross, R.J.

1994-05-01

196

A Review of Study on Thermal Energy Transport System by Synthesis and Decomposition Reactions of Methanol  

NASA Astrophysics Data System (ADS)

The study on thermal energy transport system by synthesis and decomposition reactions of methanol was reviewed. To promote energy conservation and global environment protection, a two-step liquid-phase methanol synthesis process, which starts with carbonylation of methanol to methyl formate, then followed by the hydrogenolysis of the formate, was studied to recover wasted or unused discharged heat from industrial sources for the thermal energy demands of residential and commercial areas by chemical reactions. The research and development of the system were focused on the following three points. (1) Development of low-temperature decomposition and synthetic catalysts, (2) Development of liquid phase reactor (heat exchanger accompanying chemical reaction), (3) Simulation of the energy transport efficiency of entire system which contains heat recovery and supply sections. As the result of the development of catalyst, promising catalysts which agree with the development purposes for the methyl formate decomposition reaction and the synthetic reaction are being developed though some studies remain for the methanol decomposition and synthetic reactions. In the fundamental development of liquid phase reactor, the solubilities of CO and H2 gases in methanol and methyl formate were measured by the method of total pressure decrease due to absorption under pressures up to 1500kPa and temperatures up to 140°C. The diffusivity of CO gas in methanol was determined by measuring the diameter and solution time of single CO bubbles in methanol. The chemical reaction rate of methanol synthesis by hydrogenolysis of methyl formate was measured using a plate-type of Raney copper catalyst in a reactor with rectangular channel and in an autoclave reactor. The reaction characteristics were investigated by carrying out the experiments at various temperatures, flow rates and at various catalyst development conditions. We focused on the effect of Raney copper catalyst thickness on the liquid-phase chemical reaction by varying the development time of the catalyst. Investigation results of the catalyst such as surface area, pore radius, lattice size, and photographs of scanning electron microscope (SEM) were also given. In the simulation of energy transport efficiency of this system, by simulating the energy transfer system using two-step liquid phase methanol decomposition and synthetic reactions, and comparing with the technology so far, it can be expected that an innovative energy transfer system is possible to realize.

Liu, Qiusheng; Yabe, Akira; Kajiyama, Shiro; Fukuda, Katsuya

197

Evaluation on thermal explosion induced by slightly exothermic interface reaction.  

PubMed

An asphalt-salt mixture (ASM), which once caused a fire and explosion in a reprocessing plant, was prepared by imitating the real bituminization process of waste on a lab scale to evaluate its actual thermal hazards. Heat flux reaction calorimeters were used to measure the release of heat for the simulated ASM at a constant heating rate and at a constant temperature, respectively. Experimental results show that the reaction in the ASM below about 250 degrees C is a slightly exothermic interface reaction between the asphalt and the salt particles contained in the asphalt, and that the heat release rate increases sharply above about 250 degrees C due to melting of the salt particles. The reaction rates were formulated on the basis of an assumed reaction model, and the kinetic parameters were determined. Using the model with the kinetic parameters, temperature changes with time and drum-radius axes for the ASM-filled drum were numerically simulated assuming a one-dimensional infinite cylinder system, where the drum was being cooled at an ambient temperature of 50 degrees C. The minimum filling temperature, at which the runaway reaction (MFTRR) can occur for the simulated ASM in the drum is about 194 degrees C. Furthermore, a very good linear correlation exists between this MFTRR and the initial radius of salt particles formed in the bituminization product. The critical filling temperature to the runaway reaction is about 162 degrees C for the asphalt-salt mixture, containing zero-size salt particles, filled in the same drum at an ambient temperature of 50 degrees C. Thus, the runaway reaction will never occur in the drum filled with the asphalt-salt mixture under the conditions of the filling temperature below 162 degrees C and a constant ambient temperature of 50 degrees C. As a consequence, the ASM explosion occurred in the reprocessing plant likely was due to a slightly exothermically reaction and self heating. PMID:15363527

Yu, Ma-Hong; Li, Yong-Fu; Sun, Jin-Hua; Hasegawa, Kazutoshi

2004-09-10

198

Chemical reaction fouling model for single-phase heat transfer  

SciTech Connect

A fouling model was developed on the premise that the chemical reaction for generation of precursor can take place in the bulk fluid, in the thermalboundary layer, or at the fluid/wall interface, depending upon the interactive effects of flu id dynamics, heat and mass transfer, and the controlling chemical reaction. The analysis was used to examine the experimental data for fouling deposition of polyperoxides produced by autoxidation of indene in kerosene. The effects of fluid and wall temperatures for two flow geometries were analyzed. The results showed that the relative effects of physical parameters on the fouling rate would differ for the three fouling mechanisms; therefore, it is important to identify the controlling mechanism in applying the closed-flow-loop data to industrial conditions.

Panchal, C.B. [Argonne National Lab., IL (United States); Watkinson, A.P. [British Columbia Univ., Vancouver, BC (Canada)

1993-08-01

199

Crossed molecular beam studies of atmospheric chemical reaction dynamics  

SciTech Connect

The dynamics of several elementary chemical reactions that are important in atmospheric chemistry are investigated. The reactive scattering of ground state chlorine or bromine atoms with ozone molecules and ground state chlorine atoms with nitrogen dioxide molecules is studied using a crossed molecular beams apparatus with a rotatable mass spectrometer detector. The Cl + O{sub 3} {yields} ClO + O{sub 2} reaction has been studied at four collision energies ranging from 6 kcal/mole to 32 kcal/mole. The derived product center-of-mass angular and translational energy distributions show that the reaction has a direct reaction mechanism and that there is a strong repulsion on the exit channel. The ClO product is sideways and forward scattered with respect to the Cl atom, and the translational energy release is large. The Cl atom is most likely to attack the terminal oxygen atom of the ozone molecule. The Br + O{sub 3} {yields} ClO + O{sub 2} reaction has been studied at five collision energies ranging from 5 kcal/mole to 26 kcal/mole. The derived product center-of-mass angular and translational energy distributions are quite similar to those in the Cl + O{sub 3} reaction. The Br + O{sub 3} reaction has a direct reaction mechanism similar to that of the Cl + O{sub 3} reaction. The electronic structure of the ozone molecule seems to play the central role in determining the reaction mechanism in atomic radical reactions with the ozone molecule. The Cl + NO{sub 2} {yields} ClO + NO reaction has been studied at three collision energies ranging from 10.6 kcal/mole to 22.4 kcal/mole. The center-of-mass angular distribution has some forward-backward symmetry, and the product translational energy release is quite large. The reaction proceeds through a short-lived complex whose lifetime is less than one rotational period. The experimental results seem to show that the Cl atom mainly attacks the oxygen atom instead of the nitrogen atom of the NO{sub 2} molecule.

Zhang, Jingsong

1993-04-01

200

A microvascular system for chemical reactions using surface waste heat.  

PubMed

Coffee-powered chemistry: Low-grade waste heat on surfaces can be used to drive chemical reactions, including the regeneration of a CO2 capture solution. Flowing two-phase heat transfer has been implemented within microvascular systems. This stripping system can be adapted to pre-fabricated surfaces, as demonstrated by a coffee mug containing a 1.2?m long microchannel. MEA=monoethanolamine. PMID:24307247

Nguyen, Du Thai; Esser-Kahn, Aaron P

2013-12-16

201

Separation of the isotopes of boron by chemical exchange reactions  

DOEpatents

The isotopes of boron, .sup.10 B and .sup.11 B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF.sub.3 and a liquid BF.sub.3 . donor molecular addition complex formed between BF.sub.3 gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone.

McCandless, Frank P. (Bozeman, MT); Herbst, Ronald S. (Idaho Falls, ID)

1995-01-01

202

Exploring chemical diversity via a modular reaction pairing strategy  

PubMed Central

Summary The efficient synthesis of an 80-member library of unique benzoxathiazocine 1,1-dioxides by a microwave-assisted, intermolecular nucleophilic aromatic substitution (SNAr) diversification pathway is reported. Eight benzofused sultam cores were generated by means of a sulfonylation/SNAr/Mitsunobu reaction pairing protocol, and subsequently diversified by intermolecular SNAr with ten chiral, non-racemic amine/amino alcohol building blocks. Computational analyses were employed to explore and evaluate the chemical diversity of the library.

Loh, Joanna K; Yoon, Sun Young; Samarakoon, Thiwanka B; Rolfe, Alan; Porubsky, Patrick; Neuenswander, Benjamin; Lushington, Gerald H

2012-01-01

203

Exploring chemical reaction mechanisms through harmonic Fourier beads path optimization  

NASA Astrophysics Data System (ADS)

Here, we apply the harmonic Fourier beads (HFB) path optimization method to study chemical reactions involving covalent bond breaking and forming on quantum mechanical (QM) and hybrid QM/molecular mechanical (QM/MM) potential energy surfaces. To improve efficiency of the path optimization on such computationally demanding potentials, we combined HFB with conjugate gradient (CG) optimization. The combined CG-HFB method was used to study two biologically relevant reactions, namely, L- to D-alanine amino acid inversion and alcohol acylation by amides. The optimized paths revealed several unexpected reaction steps in the gas phase. For example, on the B3LYP/6-31G(d,p) potential, we found that alanine inversion proceeded via previously unknown intermediates, 2-iminopropane-1,1-diol and 3-amino-3-methyloxiran-2-ol. The CG-HFB method accurately located transition states, aiding in the interpretation of complex reaction mechanisms. Thus, on the B3LYP/6-31G(d,p) potential, the gas phase activation barriers for the inversion and acylation reactions were 50.5 and 39.9 kcal/mol, respectively. These barriers determine the spontaneous loss of amino acid chirality and cleavage of peptide bonds in proteins. We conclude that the combined CG-HFB method further advances QM and QM/MM studies of reaction mechanisms.

Khavrutskii, Ilja V.; Smith, Jason B.; Wallqvist, Anders

2013-10-01

204

Automation of the Maxam-Gilbert chemical sequencing reactions.  

PubMed

A practical automated method of Maxam-Gilbert chemical sequencing reactions that uses solid-phase chromatography methods to purify DNA following chemical modification and cleavage is described in this report. The automation has primarily been made possible by using specially designed BioPak mini-columns, compatible with the Biomek 1000 automated workstation, which can be utilized in a manner similar to that of standard pipet tips. This automated chromatographic sequencing method produces rapid and reliable data as verified by sequencing a known human factor IX exon VIII gene fragment. The procedure presented in this report is a prototype for a single-fragment reaction and can easily be expanded to perform reactions on as many as 8 fragments at a time. The automation eliminates the tedious and time-consuming steps in the original method and increases the rate of sequence acquisition. This technology makes the Maxam-Gilbert chemical sequencing protocol more accessible, especially in large-scale, automated sequencing projects. PMID:8074875

Boland, E J; Pillai, A; Odom, M W; Jagadeeswaran, P

1994-06-01

205

APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems  

SciTech Connect

Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a glass like'' material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

Nguyen, H.D.

1991-11-01

206

APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems  

SciTech Connect

Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a ``glass like`` material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

Nguyen, H.D.

1991-11-01

207

Physio-chemical reactions in recycle aggregate concrete.  

PubMed

Concrete waste constitutes the major proportion of construction waste at about 50% of the total waste generated. An effective way to reduce concrete waste is to reuse it as recycled aggregate (RA) for the production of recycled aggregate concrete (RAC). This paper studies the physio-chemical reactions of cement paste around aggregate for normal aggregate concrete (NAC) and RAC mixed with normal mixing approach (NMA) and two-stage mixing approach (TSMA) by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Four kinds of physio-chemical reactions have been recorded from the concrete samples, including the dehydration of C(3)S(2)H(3), iron-substituted ettringite, dehydroxylation of CH and development of C(6)S(3)H at about 90 degrees C, 135 degrees C, 441 degrees C and 570 degrees C, respectively. From the DSC results, it is confirmed that the concrete samples with RA substitution have generated less amount of strength enhancement chemical products when compared to those without RA substitution. However, the results from the TSMA are found improving the RAC quality. The pre-mix procedure of the TSMA can effectively develop some strength enhancing chemical products including, C(3)S(2)H(3), ettringite, CH and C(6)S(3)H, which shows that RAC made from the TSMA can improve the hydration processes. PMID:18718710

Tam, Vivian W Y; Gao, X F; Tam, C M; Ng, K M

2009-04-30

208

Reversible chemical reactions for single-color multiplexing microscopy.  

PubMed

Recent developments in biology demand an increasing number of simultaneously imaged structures with standard fluorescence microscopy. However, the number of multiplexed channels is limited for most multiplexing modalities, such as spectral multiplexing or fluorescence-lifetime imaging. We propose extending the number of imaging channels by using chemical reactions, controlling the emissive state of fluorescent dyes. As proof of concept, we reversibly switch a fluorescent copper sensor to enable successive imaging of two different structures in the same spectral channel. We also show that this chemical multiplexing is orthogonal to existing methods. By using two different dyes, we combine chemical with spectral multiplexing for the simultaneous imaging of four different structures with only two spectrally different channels. We characterize and discuss the approach and provide perspectives for extending imaging modalities in stimulated emission depletion microscopy, for which spectral multiplexing is technically demanding. PMID:24753024

Brox, Dominik; Schwering, Michael; Engelhardt, Johann; Herten, Dirk-Peter

2014-08-01

209

Chemical-Decomposition Models for the Thermal Explosion of Confined HMX, TATB, RDX, and TNT Explosives.  

National Technical Information Service (NTIS)

Chemical decomposition models have been deduced from the available chemical kinetic data on the thermal decomposition of HMX, TATB, RDX, and TNT. A thermal conduction model is used in which the thermal conductivity of the reacting explosive decreases line...

R. R. McGuire C. M. Tarver

1981-01-01

210

Raman studies of chemically and thermally reduced graphene oxide  

NASA Astrophysics Data System (ADS)

Reduced graphene oxides were synthesized by chemical reduction of graphite oxide using hydrazine hydrate as well as by high temperature-high vacuum thermal exfoliation at 900-1100°C. The samples were characterized using Raman spectroscopy. From the Raman spectra, it is inferred that hydrazine reduced and thermally exfoliated samples were found to consist of two and three to five layers. The change in the amount of sp2 rings present in GO with increase in exfoliation temperature is studied.

Sahoo, Madhusmita; Antony, Rajini P.; Mathews, Tom; Dash, S.; Tyagi, A. K.

2013-02-01

211

A microfabricated suspended-tube chemical reactor for thermally efficient fuel processing  

Microsoft Academic Search

We present a suspended-tube chemical reactor\\/heat exchanger for high-temperature fuel processing in micro energy conversion systems, primarily for hydrogen production in portable fuel cell systems. This reactor, designed to thermally isolate a high-temperature reaction zone, consists of four free-standing silicon nitride tubes comprising two independent U-shaped fluidic channels. Portions of the tubes are encased in silicon to enable heat exchange

Leonel R. Arana; Samuel B. Schaevitz; Aleksander J. Franz; Martin A. Schmidt; Klavs F. Jensen

2003-01-01

212

Sodium-Water Reaction and Thermal Hydraulics at Gas-Liquid Interface: Numerical Interpretation of Experimental Observations  

SciTech Connect

In a sodium-cooled fast reactor development, coupled phenomena of thermal-hydraulics and chemical reaction of sodium and water vapor are of importance from the safety viewpoint. However, the sodium-water reaction (SWR) phenomena are generally complex and the experimental measurement technology is not well matured. Therefore, a numerical simulation is used for the investigation of the SWR. In this paper, a new computer program has been developed and the SWR in a counter-flow diffusion flame is studied by a numerical simulations and an experiment as well. In the computer program, Navier-Stokes equations and chemical reaction equations are solved interactively. In addition, a dynamic equation of airborne particulates is coupled with the governing equations of thermal hydraulics. A source of the particulates is the chemical reaction products, i.e. sodium hydroxide and sodium oxide. The SWR experiment is decided based on the numerical simulation. To obtain a stable reaction flame and to measure the temperature and reaction product distributions, the flow field in the experimental cell needs to be optimized. The numerical simulation is useful for designing experiments of complex phenomena and for obtaining the data. The computations are compared with experimental data. It has been demonstrated that the computational fluid dynamics code coupled with chemical reaction well predict the SWR. (authors)

Yamaguchi, Akira; Takata, Takashi [Osaka University, 1-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Ohshima, Hiroyuki; Suda, Kazunori [Japan Atomic Energy Agency (Japan)

2006-07-01

213

EFFECTS OF THERMAL TREATMENTS ON THE CHEMICAL REACTIVITY OF TRICHLOROETHYLENE  

EPA Science Inventory

A series of experiments was completed to investigate abiotic degradation and reaction product formation of trichloroethylene (TCE) when heated. A quartz-tube apparatus was used to study short residence time and high temperature conditions that are thought to occur during thermal ...

214

The influence of overlap interactions on chemical reactions in confinement  

NASA Astrophysics Data System (ADS)

Chemical reactions are often carried out in nano-structured materials due to their large surface area per unit mass. It is, however, difficult to understand fully the role of the nano-structure in many reactions due to the superposition of multiple effects. Such effects include: the reduced dimensionality of the system, the heterogeneity of the pore surfaces, the selective adsorption of reactants/products, catalytic effects, and transport limitations. Experimental studies often show many of these effects at the same time, making the results difficult to interpret. In this work we present results of density functional theory calculations illustrating the influence of overlap interactions (shape-catalytic effects) on chemical reactions. In particular, we show the effect of confinement in small pores on the rates of rotational isomerizations of n-butane, 1-butene and 1,3-butadiene. We find that the rates of these transitions change as the double exponential of the pore size in the molecular sieving limit. These results are a first step towards an integrated model for the design of catalytic materials.

Santiso, Erik E.; Gubbins, Keith E.; George, Aaron M.; Buongiorno Nardelli, Marco

2007-03-01

215

Mechano-chemical coupling in Belousov-Zhabotinskii reactions  

NASA Astrophysics Data System (ADS)

Mechano-chemical coupling has been recently recognised as an important effect in various systems as chemical reactivity can be controlled through an applied mechanical loading. Namely, Belousov-Zhabotinskii reactions in polymer gels exhibit self-sustained oscillations and have been identified to be reasonably controllable and definable to the extent that they can be harnessed to perform mechanical work at specific locations. In this paper, we use our theoretical work of nonlinear mechano-chemical coupling and investigate the possibility of providing an explanation of phenomena found in experimental research by means of this theory. We show that mechanotransduction occurs as a response to both static and dynamic mechanical stimulation, e.g., volume change and its rate, as observed experimentally and discuss the difference of their effects on oscillations. Plausible values of the quasi-stoichiometric parameter f of Oregonator model are estimated together with its dependence on mechanical stimulation. An increase in static loading, e.g., pressure, is predicted to have stimulatory effect whereas dynamic loading, e.g., rate of volume change, is predicted to be stimulatory only up to a certain threshold. Further, we offer a physically consistent explanation of the observed phenomena why some Belousov-Zhabotinskii gels require an additional mechanical stimulation to show emergence of oscillation or why "revival" of oscillations in Belousov-Zhabotinskii reactions is possible together with indications for further experimental setups.

Klika, Václav; Grmela, Miroslav

2014-03-01

216

Nuclear field shift effect in chemical exchange reactions  

NASA Astrophysics Data System (ADS)

The classic theory of stable isotope fractionation in chemical exchange reactions has been established by Bigeleisen, Mayer, and Urey in 1947. The theory was based on the difference of molecular vibrational energies of isotopomers that are proportional to the respective masses, and hence, results in mass-dependent isotope effect only. In 1996, this conventional mass-dependent theory has been expanded by Bigeleisen to include a mass-independent term named the nuclear field shift effect. The nuclear field shift is an isotope shift in orbital electrons, which results from the isotopic difference in nuclear size and shape. The new equation defined by Bigeleisen (at a constant temperature) can be simply expressed as, ln ? = ? A + (? m/mm') B, where ? is the isotope separation factor, ? isotopic difference in mean-square nuclear charge radius, ?m difference between isotopic masses m and m'. A and B are scaling factors of the nuclear field shift effect and the conventional mass effect, respectively. Since this new theory was presented, the mass-independent isotope fractionation of various elements, e.g, Ti, Cr, Ni, Zn, Sr, Zr, Mo, Ru, Cd, Te, Ba, Nd, Sm, Gd, Yb, and U, found in chemical exchange systems has been successfully explained as the nuclear field shift effect. In our most recent studies, the nuclear field shift effect of Cr, Mo, Ru, Cd, and Te isotopes has been found in laboratory scale experiments. The isotopes of these elements were fractionated by using a liquid-liquid extraction system (a ligand exchange system) at room temperature. The isotopic analysis was performed by the multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) with a typical precision of <100 ppm (at ENS Lyon or UC Davis). Isotope enrichment factors did not show mass-dependent trend, but possessed a similar variation of their nuclear charge radii. For Cr, we tested a different chemical exchange system (a redox system): at high temperature (723-1023 K), an eutectic melt was contacted with a liquid metal. In this system, the nuclear field shift effect of Cr was also found. All these experimental results suggest that the nuclear field shift effect may occur in every chemical exchange reaction at various temperatures to various degrees. Therefore, isotopic anomalies found in a natural system might be partly or largely affected by the nuclear field shift effect via chemical reactions occurred in the nature. In order to clarify the degree and significance of its contribution, we may need to pay more attention to the nuclear field shift effect created chemically.

Fujii, T.; Moynier, F.; Yin, Q.; Albarède, F.

2007-12-01

217

Fuels and chemicals from biomass using solar thermal energy  

NASA Technical Reports Server (NTRS)

The significant nearer term opportunities for the application of solar thermal energy to the manufacture of fuels and chemicals from biomass are summarized, with some comments on resource availability, market potential and economics. Consideration is given to the production of furfural from agricultural residues, and the role of furfural and its derivatives as a replacement for petrochemicals in the plastics industry.

Giori, G.; Leitheiser, R.; Wayman, M.

1981-01-01

218

Modeling of forced flow\\/thermal gradient chemical vapor infiltration  

Microsoft Academic Search

The forced flow\\/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used

T. L. Starr; A. W. Smith

1992-01-01

219

Modeling thermal\\/chemical\\/mechanical response of energetic materials  

Microsoft Academic Search

An overview of modeling at Sandia National Laboratories is presented which describes coupled thermal, chemical and mechanical response of energetic materials. This modeling addresses cookoff scenarios for safety assessment studies in systems containing energetic materials. Foundation work is discussed which establishes a method for incorporating chemistry and mechanics into multidimensional analysis. Finite element analysis offers the capabilities to simultaneously resolve

M. R. Baer; M. L. Hobbs; R. J. Gross

1995-01-01

220

Engineered Barrier Systems Thermal-Hydraulic-Chemical Column Test Report  

SciTech Connect

The Engineered Barrier System (EBS) Thermal-Hydraulic-Chemical (THC) Column Tests provide data needed for model validation. The EBS Degradation, Flow, and Transport Process Modeling Report (PMR) will be based on supporting models for in-drift THC coupled processes, and the in-drift physical and chemical environment. These models describe the complex chemical interaction of EBS materials, including granular materials, with the thermal and hydrologic conditions that will be present in the repository emplacement drifts. Of particular interest are the coupled processes that result in mineral and salt dissolution/precipitation in the EBS environment. Test data are needed for thermal, hydrologic, and geochemical model validation and to support selection of introduced materials (CRWMS M&O 1999c). These column tests evaluated granular crushed tuff as potential invert ballast or backfill material, under accelerated thermal and hydrologic environments. The objectives of the THC column testing are to: (1) Characterize THC coupled processes that could affect performance of EBS components, particularly the magnitude of permeability reduction (increases or decreases), the nature of minerals produced, and chemical fractionation (i.e., concentrative separation of salts and minerals due to boiling-point elevation). (2) Generate data for validating THC predictive models that will support the EBS Degradation, Flow, and Transport PMR, Rev. 01.

W.E. Lowry

2001-12-13

221

Friction and thermal phenomena in chemical mechanical polishing  

Microsoft Academic Search

The friction and thermal phenomenon was investigated to verify the effect of temperature on the material removal mechanism in chemical mechanical polishing (CMP). To this end, the polishing of various materials, temperature measurement by way of infrared ray camera, frictional force measurement and real contact area measurement experiment were conducted. From the results of these experiments, we concluded that the

H. j. Kim; H. y. Kim; H. d. Jeong; E. s. Lee; Y. j. Shin

2002-01-01

222

Exploring Chemical and Thermal Non-equilibrium in Nitrogen Arcs  

NASA Astrophysics Data System (ADS)

Plasma torches operating with nitrogen are of special importance as they can operate with usual tungsten based refractory electrodes and offer radical rich non-oxidizing high temperature environment for plasma chemistry. Strong gradients in temperature as well as species densities and huge convective fluxes lead to varying degrees of chemical non-equilibrium in associated regions. An axi-symmetric two-temperature chemical non-equilibrium model of a nitrogen plasma torch has been developed to understand the effects of thermal and chemical non-equilibrium in arcs. A 2-D finite volume CFD code in association with a non-equilibrium property routine enabled extraction of steady state self-consistent distributions of various plasma quantities inside the torch under various thermal and chemical non-equilibrium conditions. Chemical non-equilibrium has been incorporated through computation of diffusive and convective fluxes in each finite volume cell in every iteration and associating corresponding thermodynamic and transport properties through the scheme of 'chemical non-equilibrium parameter' introduced by Ghorui et. al. Recombination coefficient data from Nahar et. al. and radiation data from Krey and Morris have been used in the simulation. Results are presented for distributions of temperature, pressure, velocity, current density, electric potential, species densities and chemical non-equilibrium effects. Obtained results are compared with similar results under LTE.

Ghorui, S.; Das, A. K.

2012-12-01

223

Anodic reactions in the Ca/CaCrO4 thermal battery  

NASA Astrophysics Data System (ADS)

The reaction of Ca with a CaCrO4-(LiCl-KCl eutectic) solution at temperatures of 400(0)C to 500(0)C was studied to better understand the nature of the chemical reactions and electrochemical processes that occur in the Ca/CaCrO4 thermal battery at the anode during activation and discharge. Limited tests also were conducted with a CaCrO4-(CaCl2-NaCl-KCl eutectic) solution at 550(0)C. Ca/CaCrO4 and CaLi2/CaCrO4 single cells were tested to observe the relative performance differences of Ca and CaLi2 anodes. The discharged cells were analyzed by optical microscopy, electron microprobe, Auger electron spectroscopy, and secondary-ion mass spectroscopy. These analytical data were used in conjunction with the results of chemical-reaction experiments to propose a discharge mechanism for the Ca/CaCrO4 thermal battery, consistent with experimental observations.

Guidotti, R. A.; Reinhardt, F. W.

1985-09-01

224

Chemical characteristics of mineral trioxide aggregate and its hydration reaction  

PubMed Central

Mineral trioxide aggregate (MTA) was developed in early 1990s and has been successfully used for root perforation repair, root end filling, and one-visit apexification. MTA is composed mainly of tricalcium silicate and dicalcium silicate. When MTA is hydrated, calcium silicate hydrate (CSH) and calcium hydroxide is formed. Formed calcium hydroxide interacts with the phosphate ion in body fluid and form amorphous calcium phosphate (ACP) which finally transforms into calcium deficient hydroxyapatite (CDHA). These mineral precipitate were reported to form the MTA-dentin interfacial layer which enhances the sealing ability of MTA. Clinically, the use of zinc oxide euginol (ZOE) based materials may retard the setting of MTA. Also, the use of acids or contact with excessive blood should be avoided before complete set of MTA, because these conditions could adversely affect the hydration reaction of MTA. Further studies on the chemical nature of MTA hydration reaction are needed.

2012-01-01

225

Bioconjugate functionalization of thermally carbonized porous silicon using a radical coupling reaction.  

PubMed

The high stability of Salonen's thermally carbonized porous silicon (TCPSi) has attracted attention for environmental and biochemical sensing applications, where corrosion-induced zero point drift of porous silicon-based sensor elements has historically been a significant problem. Prepared by the high temperature reaction of porous silicon with acetylene gas, the stability of this silicon carbide-like material also poses a challenge--many sensor applications require a functionalized surface, and the low reactivity of TCPSi has limited the ability to chemically modify its surface. This work presents a simple reaction to modify the surface of TCPSi with an alkyl carboxylate. The method involves radical coupling of a dicarboxylic acid (sebacic acid) to the TCPSi surface using a benzoyl peroxide initiator. The grafted carboxylic acid species provides a route for bioconjugate chemical modification, demonstrated in this work by coupling propylamine to the surface carboxylic acid group through the intermediacy of pentafluorophenol and 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC). The stability of the carbonized porous Si surface, both before and after chemical modification, is tested in phosphate buffered saline solution and found to be superior to either hydrosilylated (with undecylenic acid) or thermally oxidized porous Si surfaces. PMID:20967329

Sciacca, Beniamino; Alvarez, Sara D; Geobaldo, Francesco; Sailor, Michael J

2010-12-01

226

Bioconjugate functionalization of thermally carbonized porous silicon using a radical coupling reaction†  

PubMed Central

The high stability of Salonen’s thermally carbonized porous silicon (TCPSi) has attracted attention for environmental and biochemical sensing applications, where corrosion-induced zero point drift of porous silicon-based sensor elements has historically been a significant problem. Prepared by the high temperature reaction of porous silicon with acetylene gas, the stability of this silicon carbide-like material also poses a challenge—many sensor applications require a functionalized surface, and the low reactivity of TCPSi has limited the ability to chemically modify its surface. This work presents a simple reaction to modify the surface of TCPSi with an alkyl carboxylate. The method involves radical coupling of a dicarboxylic acid (sebacic acid) to the TCPSi surface using a benzoyl peroxide initiator. The grafted carboxylic acid species provides a route for bioconjugate chemical modification, demonstrated in this work by coupling propylamine to the surface carboxylic acid group through the intermediacy of pentafluorophenol and 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC). The stability of the carbonized porous Si surface, both before and after chemical modification, is tested in phosphate buffered saline solution and found to be superior to either hydrosilylated (with undecylenic acid) or thermally oxidized porous Si surfaces.

Sciacca, Beniamino; Alvarez, Sara D.; Geobaldo, Francesco; Sailor, Michael J.

2011-01-01

227

Thermal reaction studies of organic model compound-mineral matter interactions in solids  

SciTech Connect

The solid-state chemistry of silica-immobilized phenethyl phenyl ethers is being investigated in the presence of interdispersed aluininosilicates at temperatures relevant to coal processing to gain a better understanding of the impact of mineral matter on pyrolysis and liquefaction mechanisms. Results demonstrate the dramatic effect that aluminosilicates can have in altering the normal thermal reaction pathways for these models of ether linkages in lignin and low rank coals. An investigation of the chemistry of these model compounds at low temperatures (ca. 150-200{degrees}C) in the presence of aluminosilicates, including montmorillonite, is currently being investigated to delineate the chemical transformations that can occur during lignin maturation.

Buchanan, A.C. III; Britt, P.F.; Thomas, K.B.

1995-07-01

228

Anthropogenic reaction parameters - the missing link between chemical intuition and the available chemical space.  

PubMed

How do skilled synthetic chemists develop good intuitive expertise? Why can we only access such a small amount of the available chemical space-both in terms of the reactions used and the chemical scaffolds we make? We argue here that these seemingly unrelated questions have a common root and are strongly interdependent. We performed a comprehensive analysis of organic reaction parameters dating back to 1771 and discovered that there are several anthropogenic factors that limit reaction parameters and thus the scope of synthetic chemistry. Nevertheless, many of the anthropogenic limitations such as narrow parameter space and the opportunity for rapid and clear feedback on the progress of reactions appear to be crucial for the acquisition of valid and reliable chemical intuition. In parallel, however, all of these same factors represent limitations for the exploration of available chemistry space and we argue that these are thus at least partly responsible for limited access to new chemistries. We advocate, therefore, that the present anthropogenic boundaries can be expanded by a more conscious exploration of "off-road" chemistry that would also extend the intuitive knowledge of trained chemists. PMID:24877159

Keser?, György M; Soós, Tibor; Kappe, C Oliver

2014-07-01

229

Selective Rapid Thermal Chemical Vapor Deposition of Titanium Silicide.  

NASA Astrophysics Data System (ADS)

Scaling of MOSFET device dimensions into the deep submicron regime requires source/drain junction depths on the order of a few tens of nanometers. Considerable work has been carried out to form such ultra-shallow junctions. Formation of reliable, low resistivity contacts to these junctions is also a challenging task. The presently available self -aligned silicide technology suffers from substrate consumption during silicide formation, which makes the process unsuited for ultra-shallow junctions. Selective rapid thermal chemical vapor deposition of TiSi_2 is one of the promising alternatives currently considered for contact formation. In this process, Ti and Si are provided in the gas phase. The process relies on the hypothesis that by supplying optimum amounts of Ti and Si, substrate consumption can be minimized or eliminated. In previous studies as well as this one, the source gas for Ti has been TiCl_4. For Si, SiH _4 and rm SiH_2Cl_2 have both been considered. From the beginning, the objective of this work has been to increase fundamental understanding on selective chemical vapor deposition of TiSi_2. The work includes investigations of TiSi _2 nucleation on Si, reaction pathways, selectivity and chamber contamination. Nucleation studies in this work emphasize surface preparation for TiSi_2 . In-situ cleaning as well as in-situ selective deposition of different layers prior to TiSi_2 deposition have been investigated. As part of these studies, a new in-situ low temperature surface cleaning method using rm SiH_2Cl_2/H _2 has been developed. Potential mechanisms that retard TiSi_2 nucleation below 800^circC have been proposed. Results suggest that surface morphology may be a key factor in TiSi_2 nucleation. Silicon substrate etching during TiSi_2 deposition has been studied in detail via thermodynamic equilibrium simulations. It has been determined that Si etching occurs via formation of SiCl_4 and SiCl_2. Hydrogen has been determined as an extremely useful ingredient to suppress substrate etching. The simulation results have also been confirmed by experiments. Silicon substrate consumption has been studied under different deposition temperatures and using different gas compositions. A process window for consumption -free TiSi_2 deposition has been determined. Deposition selectivity with respect to silicon dioxide and silicon nitride has been investigated. A novel approach that combines SiH_4 and rm SiH_2Cl_2 has been developed for enhanced selectivity.

Ren, Xiaowei

1995-01-01

230

Thermal conversion of biomass to valuable fuels, chemical feedstocks and chemicals  

DOEpatents

A continuous process for the conversion of biomass to form a chemical feedstock is described. The biomass and an exogenous metal oxide, preferably calcium oxide, or metal oxide precursor are continuously fed into a reaction chamber that is operated at a temperature of at least 1400.degree. C. to form reaction products including metal carbide. The metal oxide or metal oxide precursor is capable of forming a hydrolizable metal carbide. The reaction products are quenched to a temperature of 800.degree. C. or less. The resulting metal carbide is separated from the reaction products or, alternatively, when quenched with water, hydolyzed to provide a recoverable hydrocarbon gas feedstock.

Peters, William A. (Lexington, MA); Howard, Jack B. (Winchester, MA); Modestino, Anthony J. (Hanson, MA); Vogel, Fredreric (Villigen PSI, CH); Steffin, Carsten R. (Herne, DE)

2009-02-24

231

Predicting Formation Damage in Aquifer Thermal Energy Storage Systems Utilizing a Coupled Hydraulic-Thermal-Chemical Reservoir Model  

NASA Astrophysics Data System (ADS)

In aquifer thermal energy storage (ATES) systems, large amounts of energy can be stored by injecting hot water into deep or intermediate aquifers. In a seasonal production-injection cycle, water is circulated through a system comprising the porous aquifer, a production well, a heat exchanger and an injection well. This process involves large temperature and pressure differences, which shift chemical equilibria and introduce or amplify mechanical processes. Rock-fluid interaction such as dissolution and precipitation or migration and deposition of fine particles will affect the hydraulic properties of the porous medium and may lead to irreversible formation damage. In consequence, these processes determine the long-term performance of the ATES system and need to be predicted to ensure the reliability of the system. However, high temperature and pressure gradients and dynamic feedback cycles pose challenges on predicting the influence of the relevant processes. Within this study, a reservoir model comprising a coupled hydraulic-thermal-chemical simulation was developed based on an ATES demonstration project located in the city of Berlin, Germany. The structural model was created with Petrel, based on data available from seismic cross-sections and wellbores. The reservoir simulation was realized by combining the capabilities of multiple simulation tools. For the reactive transport model, COMSOL Multiphysics (hydraulic-thermal) and PHREEQC (chemical) were combined using the novel interface COMSOL_PHREEQC, developed by Wissmeier & Barry (2011). It provides a MATLAB-based coupling interface between both programs. Compared to using COMSOL's built-in reactive transport simulator, PHREEQC additionally calculates adsorption and reaction kinetics and allows the selection of different activity coefficient models in the database. The presented simulation tool will be able to predict the most important aspects of hydraulic, thermal and chemical transport processes relevant to formation damage in ATES systems. We would like to present preliminary results of the structural reservoir model and the hydraulic-thermal-chemical coupling for the demonstration site. Literature: Wissmeier, L. and Barry, D.A., 2011. Simulation tool for variably saturated flow with comprehensive geochemical reactions in two- and three-dimensional domains. Environmental Modelling & Software 26, 210-218.

Müller, Daniel; Regenspurg, Simona; Milsch, Harald; Blöcher, Guido; Kranz, Stefan; Saadat, Ali

2014-05-01

232

Parameter estimation in complex flows with chemical reactions  

NASA Astrophysics Data System (ADS)

The estimation of unknown parameters in engineering and scientific models continues to be of great importance in order to validate them to available experimental data. These parameters of concern cannot be known beforehand, but must be measured experimentally, variables such as chemical species concentrations, pressures, or temperatures as examples. Particularly, in chemically reacting flows, the estimation of kinetic rate parameters from experimentally determined values is in great demand and not well understood. New parameter optimization algorithms have been developed from a Gauss-Newton formulation for the estimation of reaction rate parameters in several different complex flow applications. A zero-dimensional parameter estimation methodology was used in conjunction with a parameter sensitivity study and then applied to three-dimensional flow models. This new parameter estimation technique was applied to three-dimensional models for chemical vapor deposition of silicon carbide and gallium arsenide semiconductor materials. The parameter estimation for silicon carbide for several different operating points was in close agreement to experiment. The parameter estimation for gallium arsenide proved to be very accurate, being within four percent of the experimental data. New parameter estimation algorithms were likewise created for a three-dimensional multiphase model for methanol spray combustion. The kinetic rate parameters delivered results in close agreement to experiment for profiles of combustion species products. In addition, a new parameter estimation method for the determination of spray droplet sizes and velocities is presented. The results for methanol combustion chemical species profiles are in good agreement to experiment for several different droplet sizes. Lastly, the parameter estimation method was extended to a bio-kinetic application, namely mitochondrial cells, that are cardiac or respiratory cells found in animals and humans. The results for the electrochemical parameters examined again show very close agreement to the experimental values. The usual method of determining chemical reaction rates by measurement is lengthy and time consuming, especially where the chemistry and chemical processes are of a more complex nature. This computational method and associated algorithms has shown to deliver accurate correlations to the experimental data for three-dimensional models, demonstrated in these new unique applications of the technique.

Robinson, Daniel J.

233

Laser enhanced chemical reaction studies. Technical progress report  

SciTech Connect

A powerful infrared diode laser probe was used to determine final states of small (2-5 atom) molecules produced by collisions, photofragmentation, or chemical reactions with spectral resolution 0.0003 cm{sup {minus}1} and time resolution 10{sup {minus}7}s. Besides picturing the vibrational rotational quantum states of product molecules, this also provides a picture of the translational motion of recoiling fragments through the infrared Doppler line width profile. This method was used to probe collisions between cool bath molecules and vibrationally hot molecules, in order to understand the quenching mechanism for unimolecular chemical reactions. Long-range collisions appear to dominate production of bath molecules which become vibrationally excited during this quenching process. Glimpses are being provided of the separate behavior of translational and rotational degrees of freedom of recoiling bath molecules during relaxation of highly vibrationally excited donors. A study was completed of collisions between hot H atoms and CO{sub 2}, by measuring probability for excitation of the antisymmetric vibrational overtone level CO{sub 2}(00{sup 0}2). Comparison with a 00{sup 0}1 fundamental level study suggests that translational and rotational energy distributions in this collision can be described by classical mechanics, but that vibrational excitation probabilities require full quantum treatment. Relaxation of hot pyrazine by CO{sub 2} was studied. Multiphoton ionization studies have been begun.

Flynn, G.

1993-12-31

234

Following a chemical reaction using high-harmonic interferometry.  

PubMed

The study of chemical reactions on the molecular (femtosecond) timescale typically uses pump laser pulses to excite molecules and subsequent probe pulses to interrogate them. The ultrashort pump pulse can excite only a small fraction of molecules, and the probe wavelength must be carefully chosen to discriminate between excited and unexcited molecules. The past decade has seen the emergence of new methods that are also aimed at imaging chemical reactions as they occur, based on X-ray diffraction, electron diffraction or laser-induced recollision--with spectral selection not available for any of these new methods. Here we show that in the case of high-harmonic spectroscopy based on recollision, this apparent limitation becomes a major advantage owing to the coherent nature of the attosecond high-harmonic pulse generation. The coherence allows the unexcited molecules to act as local oscillators against which the dynamics are observed, so a transient grating technique can be used to reconstruct the amplitude and phase of emission from the excited molecules. We then extract structural information from the amplitude, which encodes the internuclear separation, by quantum interference at short times and by scattering of the recollision electron at longer times. The phase records the attosecond dynamics of the electrons, giving access to the evolving ionization potentials and the electronic structure of the transient molecule. In our experiment, we are able to document a temporal shift of the high-harmonic field of less than an attosecond (1 as = 10(-18) s) between the stretched and compressed geometry of weakly vibrationally excited Br(2) in the electronic ground state. The ability to probe structural and electronic features, combined with high time resolution, make high-harmonic spectroscopy ideally suited to measuring coupled electronic and nuclear dynamics occurring in photochemical reactions and to characterizing the electronic structure of transition states. PMID:20671706

Wörner, H J; Bertrand, J B; Kartashov, D V; Corkum, P B; Villeneuve, D M

2010-07-29

235

Irreversible bimolecular chemical reactions on directed scale-free networks.  

PubMed

Kinetics of irreversible bimolecular chemical reactions A+A?0 and A+B?0 on directed scale-free networks with the in-degree distribution P(in)(k)?k(-?)(in) and the out-degree distribution P(out)(?)??(-?)(out) are investigated. Since the correlation between k and ? of each node generally exists in directed networks, we control the correlation (k?) with the probability r?[0,1] by two different algorithms for the construction of the directed networks, i.e., the so-called k and ? algorithms. For r=1, the k algorithm gives (k?)=(k(2)), whereas the ? algorithm gives (k?)=(?(2). For r=0, (k?)=(k)(?) for both algorithms. The kinetics of both reactions are analyzed using heterogeneous mean-field (HMF) theory and Monte Carlo simulations. The density of particles (?) algebraically decays in time t as ?(t)?t(-?). The kinetics of both reactions are determined by the same rate equation, d?/dt=a?(2)+b?(?-1), apart from coefficients. The exponent ? is determined by the algorithm: ?=?(in) for the k algorithm (r?0) and ?=?(min) for the ? algorithm (r>0), where ?(min) is the smaller exponent between ?(in) and ?(out). For ?>3, one observes the ordinary mean-field kinetics, ??1/t (?=1). In contrast, for ?<3, ?(t) anomalously decays with ?=1/(?-2). The HMF predictions are confirmed by the simulations on quenched directed networks. PMID:24229156

Kwon, Sungchul; Kim, Yup

2013-10-01

236

Irreversible bimolecular chemical reactions on directed scale-free networks  

NASA Astrophysics Data System (ADS)

Kinetics of irreversible bimolecular chemical reactions A+A?0 and A+B?0 on directed scale-free networks with the in-degree distribution Pin(k)˜k-?in and the out-degree distribution Pout(?)˜?-?out are investigated. Since the correlation between k and ? of each node generally exists in directed networks, we control the correlation with the probability r?[0,1] by two different algorithms for the construction of the directed networks, i.e., the so-called k and ? algorithms. For r=1, the k algorithm gives =, whereas the ? algorithm gives =. For r=0, = for both algorithms. The kinetics of both reactions are analyzed using heterogeneous mean-field (HMF) theory and Monte Carlo simulations. The density of particles (?) algebraically decays in time t as ?(t)˜t-?. The kinetics of both reactions are determined by the same rate equation, d?/dt=a?2+b??-1, apart from coefficients. The exponent ? is determined by the algorithm: ?=?in for the k algorithm (r?0) and ?=?min for the ? algorithm (r>0), where ?min is the smaller exponent between ?in and ?out. For ?>3, one observes the ordinary mean-field kinetics, ?˜1/t (?=1). In contrast, for ?<3, ?(t) anomalously decays with ?=1/(?-2). The HMF predictions are confirmed by the simulations on quenched directed networks.

Kwon, Sungchul; Kim, Yup

2013-10-01

237

Coupled thermal/chemical/mechanical modeling of energetic materials in ALE3D  

SciTech Connect

We must improve our ability to model the response of energetic ma@ to thmnal stimuli and the processes involved m the energetic response. Traditionally, the analyses of energeuc have mvolved coupled thermal chemical reaction codes. This provides only a reasonable estimate of the dw and location of ensuing rapid reaction. To predict the violence of the reaction, the m cal motion must be included in the wide range of time scales as with the th@ hazard. Ile ALE3D code has been modified to the hazards associated with heaung energetic ma@ in weapons. We have merged the thermal models from TOPAZ3D and the chemistry models &vel@ in Chemical TOPAZ into ALE3D. We have developed and use an impMt time step option to efficiently and accurately compute the hours that the energetic material can take to react. Since on these longer fim scales materials can be expected to have signifimt motion, it is even more important to provide high- ordcr advection for all components, including the chemical species. We will show an example cook-off problem to illustrate these capabilities.

Nichols, A.L.; Couch, R.; Maltby, J.D.; McCallen, R.C.; Otero, I.; Sharp, R.

1996-10-01

238

Chemical Vapor Deposition of Turbine Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

Ceramic thermal barrier coatings extend the operating temperature range of actively cooled gas turbine components, therefore increasing thermal efficiency. Performance and lifetime of existing ceram ic coatings are limited by spallation during heating and cooling cycles. Spallation of the ceramic is a function of its microstructure, which is determined by the deposition method. This research is investigating metalorganic chemical vapor deposition (MOCVD) of yttria stabilized zirconia to improve performance and reduce costs relative to electron beam physical vapor deposition. Coatings are deposited in an induction-heated, low-pressure reactor at 10 microns per hour. The coating's composition, structure, and response to the turbine environment will be characterized.

Haven, Victor E.

1999-01-01

239

Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.  

SciTech Connect

A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2010-06-01

240

Chemical Reactions and Mechanical Properties of the Directly Bonded Ge-Si Interface  

NASA Astrophysics Data System (ADS)

In this study, chemical reactions and mechanical properties of directly bonded Ge-Si interfaces are investigated. The Ge-Si bonded interface has been systematically characterized as a function of the thermal budget (200 °C and 300 °C), which demonstrated that the formation of a thin GeO2 cap layer by radical pre-treatment can reduce the generation rate of voids at the bonded interface significantly. Patterning of one of the wafers prior to bonding can help to achieve high bonding quality thanks to enhanced out-diffusion of reaction by-products and stress reduction at the bonded interface. Both numerical modeling and structural analysis show that the presence of diffusion path (channels) at the bonded interfaces result in a maximum bond strength and minimum stress at the bonded interface.

Byun, Ki Yeol; Ferain, Isabelle; Yu, Ran; Colinge, Cindy

2011-12-01

241

The quantum dynamics of electronically nonadiabatic chemical reactions  

NASA Technical Reports Server (NTRS)

Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally adiabatic functions in various quantum scattering algorithms.

Truhlar, Donald G.

1993-01-01

242

Latest findings on the dynamics of the simplest chemical reaction  

NASA Astrophysics Data System (ADS)

This paper focuses on recent progress in the understanding of the H + H2 reaction and its isotopic variants. The detailed agreement between theory and experiment attained during the last years is emphasized and major experimental and theoretical advances are highlighted. The excellent description of most experimental findings, from state-resolved cross-sections to thermal rate constants, provided by the available quantum mechanical (QM) treatments, as well as the good overall behaviour of classical mechanics are underlined. Debated issues on short-lived complexes and delayed scattering, resonances and interferences, geometric-phase (GP) effects, or product rotational distributions are discussed. Finally, some prospects for future research on this prototypic system are presented.

Bañares, Luis; Aoiz, F. J.; Herrero, Victor J.

2006-01-01

243

Thermal stresses in chemically hardening elastic media with application to the molding process  

NASA Technical Reports Server (NTRS)

A method has been formulated for the determination of thermal stresses in materials which harden in the presence of an exothermic chemical reaction. Hardening is described by the transformation of the material from an inviscid liquid-like state into an elastic solid, where intermediate states consist of a mixture of the two, in a ratio which is determined by the degree of chemical reaction. The method is illustrated in terms of an infinite slab cast between two rigid mold surfaces. It is found that the stress component normal to the slab surfaces vanishes in the residual state, so that removal of the slab from the mold leaves the remaining residual stress unchanged. On the other hand, the residual stress component parallel to the slab surfaces does not vanish. Its distribution is described as a function of the parameters of the hardening process.

Levitsky, M.; Shaffer, B. W.

1974-01-01

244

Dynamic solvent effects on activated chemical reactions. I. Classical effects of reaction path curvature  

SciTech Connect

In gas phase reactions, dynamical recrossings across a phase space dividing surface induced by nonlinear reaction path curvature coupling leads to the breakdown of the fundamental dynamical approximation of classical transition state theory (TST). In the following study, we examine the nature of this breakdown for chemical reaction dynamics occurring in solution. As a model system, we consider the collinear [ital A]+[ital BC] reaction where reaction path curvature increases as the mass of [ital B] becomes small compared to the mass of [ital A] and [ital C]. We use a London--Eyring--Polanyi--Sato (LEPS) potential to describe the solute interaction and model the influence of the solvent by using a generalized Langevin equation that is further represented by a system of coupled harmonic oscillators. Exact classical rate constants are compared to those obtained from conventional TST and canonical variational transition state theory (CVT) as a function of solvent friction coupling. A harmonic TST analysis at the saddle point of the full system (solute plus solvent) with an optimum dividing surface containing both solute and solvent degrees of freedom returns the Grote--Hynes expression for the rate. For the case of no solvent coupling, both TST and CVT are identical and fail to account for the dynamical recrossings induced by reaction path curvature. At intermediate couplings, CVT provides an improvement to the TST estimate and agrees with dynamical simulation results. All estimates of the rate constant approach each other asymptotically at large couplings. The results are interpreted in terms of recrossings in the extended system (solute and solvent coordinates).

Schenter, G.K.; McRae, R.P.; Garrett, B.C. (Molecular Science Research Center, Pacific Northwest Laboratory, Richland, Washington 99352 (United States))

1992-12-15

245

A Thermal Desorption Chemical Ionization Ion Trap Mass Spectrometer for the Chemical Characterization of Ultrafine Aerosol Particles  

Microsoft Academic Search

The development of a thermal desorption chemical ionization ion trap mass spectrometer for the chemical characterization of ultrafine aerosol particles is reported and first experimental results are presented. Atmospheric particles are size-classified and collected using a unipolar charger, a radial differential mobility analyzer and an electrostatic precipitator, and analyzed after thermal desorption and chemical ionization using an ion trap mass

Andreas Held; G. Jeffrey Rathbone; James N. Smith

2009-01-01

246

Thermalization with a chemical potential from AdS spaces  

NASA Astrophysics Data System (ADS)

The time-scale of thermalization in holographic dual models with a chemical potential in diverse number of dimensions is systematically investigated using the gauge/gravity duality. We consider a model with a thin-shell of charged dust collapsing from the boundary toward the bulk interior of asymptotically anti-de Sitter (AdS) spaces. In the outer region there is a Reissner-Nordström-AdS black hole (RNAdS-BH), while in the inner region there is an anti-de Sitter space. We consider renormalized geodesic lengths and minimal area surfaces as probes of thermalization, which in the dual quantum field theory (QFT) correspond to two-point functions and expectation values of Wilson loops, respectively. We show how the behavior of these extensive probes changes for charged black holes in comparison with Schwarzschild-AdS black holes (AdS-BH), for different values of the black hole mass and charge. The full range of values of the chemical potential over temperature ratio in the dual QFT is investigated. In all cases, the structure of the thermalization curves shares similar features with those obtained from the AdS-BH. On the other hand, there is an important difference in comparison with the AdS-BH: the thermalization times obtained from the renormalized geodesic lengths and the minimal area surfaces are larger for the RNAdS-BH, and they increase as the black hole charge increases.

Galante, Damián; Schvellinger, Martin

2012-07-01

247

Chemical Reactions in the Processing of Mosi2 + Carbon Compacts  

NASA Technical Reports Server (NTRS)

Hot-pressing of MoSi2 powders with carbon at high temperatures reduces the siliceous grain boundary phase in the resultant compact. The chemical reactions in this process were examined using the Knudsen cell technique. A 2.3 wt pct oxygen MoSi2 powder and a 0.59 wt pct oxygen MoSi2 powder, both with additions of 2 wt pct carbon, were examined. The reduction of the siliceous grain boundary phase was examined at 1350 K and the resultant P(SiO)/P(CO) ratios interpreted in terms of the SiO(g) and CO(g) isobars on the Si-C-O predominance diagram. The MoSi2 + carbon mixtures were then heated at the hot-pressing temperature of 2100 K. Large weight losses were observed and could be correlated with the formation of a low-melting eutectic and the formation and vaporization of SiC.

Jacobson, Nathan S.; Lee, Kang N.; Maloy, Stuart A.; Heuer, Arthur H.

1993-01-01

248

Fischer-Tropsch reaction on a thermally conductive and reusable silicon carbide support.  

PubMed

The Fischer-Tropsch (FT) process, in which synthesis gas (syngas) derived from coal, natural gas, and biomass is converted into synthetic liquid fuels and chemicals, is a strongly exothermic reaction, and thus, a large amount of heat is generated during the reaction that could severely modify the overall selectivity of the process. In this Review, we report the advantages that can be offered by different thermally conductive supports, that is, carbon nanomaterials and silicon carbide, pure or doped with different promoters, for the development of more active and selective FT catalysts. This Review follows a discussion regarding the clear trend in the advantages and drawbacks of these systems in terms of energy efficiency and catalytic performance for this most-demanded catalytic process. It is demonstrated that the use of a support with an appropriate pore size and thermal conductivity is an effective strategy to tune and improve the activity of the catalyst and to improve product selectivity in the FT process. The active phase and the recovery of the support, which also represents a main concern in terms of the large amount of FT catalyst used and the cost of the active cobalt phase, is also discussed within the framework of this Review. It is expected that a thermally conductive support such as ?-SiC will not only improve the development of the FT process, but that it will also be part of a new support for different catalytic processes for which high catalytic performance and selectivity are strongly needed. PMID:24616239

Liu, Yuefeng; Ersen, Ovidiu; Meny, Christian; Luck, Francis; Pham-Huu, Cuong

2014-05-01

249

On-chip isothermal, chemical cycling polymerase chain reaction (ccPCR)  

NASA Astrophysics Data System (ADS)

We demonstrate a novel ccPCR technique for microfluidic DNA amplification where temperature is held constant in space and time. The polymerase chain reaction is a platform of choice for biological assays and typically based on a three-step thermal cycling: DNA denaturation, primers annealing and extension by an enzyme. We here demonstrate a novel technique where high concentration chemical denaturants (solvents) denature DNA. We leverage the high electrophoretic mobility of DNA and the electrical neutrality of denaturants to achieve chemical cycling. We focus DNA with isotachophoresis (ITP); a robust electrophoretic preconcentration technique which generates strong electric field gradients and protects the sample from dispersion. We apply a pressure-driven flow to balance electromigration velocity and keep the DNA sample stationary in a microchannel. We drive the DNA through a series of high denaturant concentration zones. DNA denatures at high denaturant concentration. At low denaturant concentration, the enzyme creates complementary strands. DNA reaction kinetics are slower than buffer reactions involved in ITP. We demonstrate successful ccPCR amplification for detection of E. Coli. The ccPCR has the potential for simpler chemistry than traditional PCR.

Persat, Alexandre; Santiago, Juan

2008-11-01

250

Scaling laws for pulsed chain-reaction chemical lasers  

NASA Astrophysics Data System (ADS)

Scaling laws for pulsed chain-reaction chemical lasers are deduced with the use of a two-level vibrational model. The performance of a saturated laser depends only on the parameter K = t sub cd/t sub p, where t sub cd and t sub p are the characteristic collisional deactivation and characteristic pumping times, respectively. The normalized output energy per unit volume per pulse of a saturated HF chain-reaction laser is 2E/Epsilon H sub 2,0 = K(1 + 0(K)), where E is output energy per unit volume per pulse, Epsilon is energy per mole of photons, and H sub 2, 0 is the initial concentration of H sub 2 in moles per unit volume. In the range 0.02 < or = thi << 1 the normalized output energy from a saturated HF laser can be expressed as 2E/Epsilon H sub 2, 0 = thi, where thi approx. = (F/F sub 2) sub 0 1/2(F sub 2/H sub 2)0(1 + 0.094(F sub 2/H sub 2) sub 0) to the minus 1/2 power. In the latter regime the product Et sub e is a constant for a saturated laser (t sub e = pulse length). Corrections for multiple vibrational levels are given in an Appendix.

Mirels, H.; Hofland, R., Jr.; Whittier, J. S.

1981-08-01

251

The Thermal Reaction Battery. Part II. Preparation and Pyrolysis of Some Aromatic Hydrazones and Hydrazonium Salts.  

National Technical Information Service (NTIS)

Organic compounds that can be thermally degraded to yield permanently liquid solvents for ionizable salts for use in the proposed thermal reaction battery continue to receive attention. It was confirmed that benzaldehyde phenylhydrazone undergoes pyrolysi...

F. M. Dewey

1968-01-01

252

Chloroaluminum phthalocyanine thin films: chemical reaction and molecular orientation.  

PubMed

The chemical transformation of the polar chloroaluminum phthalocyanine, AlClPc, to ?-(oxo)bis(phthalocyaninato)aluminum(III), (PcAl)2O, in thin films on indium tin oxide is studied and its influence on the molecular orientation is discussed. The studies were conducted using complementary spectroscopic techniques: Raman spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In addition, density functional theory calculations were performed in order to identify specific vibrations and to monitor the product formation. The thin films of AlClPc were annealed in controlled environmental conditions to obtain (PcAl)2O. It is shown that the chemical transformation in the thin films can proceed only in the presence of water. The influence of the reaction and the annealing on the molecular orientation was studied with Raman spectroscopy and NEXAFS spectroscopy in total electron yield and partial electron yield modes. The comparison of the results obtained from these techniques allows the determination of the molecular orientation of the film as a function of the probing depth. PMID:23494276

Latteyer, Florian; Peisert, Heiko; Uihlein, Johannes; Basova, Tamara; Nagel, Peter; Merz, Michael; Schuppler, Stefan; Chassé, Thomas

2013-05-01

253

Thermal, chemical, and mechanical response of rigid polyurethane foam  

SciTech Connect

Rigid polyurethane foams are frequently used as encapsulants to isolate and support thermally sensitive components within weapon systems. When exposed to abnormal thermal environments, such as fire, the polyurethane foam decomposes to form products having a wide distribution of molecular weights and can dominate the overall thermal response of the system. Mechanical response of the decomposing foam, such as thermal expansion under various loading conditions created by gas generation, remains a major unsolved problem. A constitutive model of the reactive foam is needed to describe the coupling between mechanical response and chemical decomposition of foam exposed to environments such as fire. Towards this end, a reactive elastic-plastic constitutive model based on bubble mechanics describing nucleation, decomposition chemistry, and elastic/plastic mechanical behavior of rigid polyurethane foam has been developed. A local force balance, with mass continuity constraints, forms the basis of the constitutive model requiring input of temperature and the fraction of the material converted to gas. This constitutive model provides a stress-strain relationship which is applicable for a broad class of reacting materials such as explosives, propellants, pyrotechnics, and decomposing foams. The model is applied to a block of foam exposed to various thermal fluxes. The model is also applied to a sphere of foam confined in brass. The predicted mechanical deformation of the foam block and sphere are shown to qualitatively agree with experimental observations.

Hobbs, M.L.

1997-12-01

254

A Comprehensive Chemical Kinetic Reaction Mechanism for Oxidation and Pyrolysis of Propane and Propene  

Microsoft Academic Search

Abstract—A detailed chemical kinetic reaction mechanism is developed to describe the oxidation and pyrolysis of propane and propene. The mechanism consists of 163 elementary reactions among 4l chemical species. New rate expressions are developed for a number of reactions of propane, propene, and intermediate hydrocarbon species with radicals including H, 0, and OH. The mechanism is tested by comparisons between

CHARLES K. WESTBROOK; WILLIAM J. PITZ

1984-01-01

255

MODEL OF CHEMICAL REACTION EQUILIBRIUM OF SULFURIC ACID SALTS OF TRIOCTYLAMINE  

Microsoft Academic Search

The chemical reaction of trioctylamine (TOA) and sulfuric acid in organic solvent\\/aqueous solution was carried out. TOA salt products of various kinds were obtained based on different conditions of operation and organic solvents. An equilibrium model, based on the chemical reaction of sulfuric acid and trioctylamine, is proposed. The equilibrium constants of various reactions of trioctylamine and sulfuric acid were

MAW-LING WANG; KWAN-HUA HU

1993-01-01

256

Transport Properties of a Kinetic Model for Chemical Reactions without Barriers  

SciTech Connect

A kinetic model of the Boltzmann equation for chemical reactions without energy barrier is considered here with the aim of evaluating the reaction rate and characterizing the transport coefficient of shear viscosity for the reactive system. The Chapman-Enskog solution of the Boltzmann equation is used to compute the chemical reaction effects, in a flow regime for which the reaction process is close to the final equilibrium state. Some numerical results are provided illustrating that the considered chemical reaction without energy barrier can induce an appreciable influence on the reaction rate and on the transport coefficient of shear viscosity.

Alves, Giselle M. [Escola Tecnica, Universidade Federal do Parana, Curitiba (Brazil); Kremer, Gilberto M. [Departamento de Fisica, Universidade Federal do Parana, Curitiba (Brazil); Soares, Ana Jacinta [Departamento de Matematica, Universidade do Minho, Braga (Portugal)

2011-05-20

257

Possible application of solar-thermal energy in the chemical industry  

NASA Astrophysics Data System (ADS)

Eight chemicals are identified that require substantial amounts of nonrecoverable energy for their production. The chemicals are: ethylene, vinyl chloride, styrene, propylene, butadiene, isoprene, hydrogen, and phosphorus. These chemicals are used to produce a wealth of products such as plastics, rubbers and fertilizers. In most cases, these energy intensive materials are at the top of a pyramid of subsequent, exothermic reactions and products that do not require additional thermal energy except for separation processes. Their production at present is centralized and done on a large scale, and most of the organics are produced in refineries where hydrocarbon energy is abundant. This association with refineries means at present that direct substitution of solar energy for hydrocarbon fired heaters may not be convenient, even though scientifically feasible. Other solar energy applications are production of caustic soda from thermodynamic cycles, ethylene from ethanol, and butadiene from ethanol.

Martin, L. R.

1982-06-01

258

Reaction and Transport Phenomena in Non-Thermal Equilibrium Plasmas  

NASA Astrophysics Data System (ADS)

The research presented in this dissertation pursued two independent but connected directions. The first was to expand our understanding of the important microscopic phenomena in low temperature plasma systems and of their influence on the observed processing characteristics. The second was to incorporate these microscopic phenomena into a continuum model which allows simulation of the important reaction and transport phenomena at reasonable computational costs. In the process, low temperature plasmas were considered from a thermodynamic view point on a continuum level through the generalized bracket formalism and from a microscopic viewpoint via an analytical solution of the Boltzmann kinetic equation. The continuum model developed, via solution of the Boltzmann kinetic equation, represents an extension to the previous continuum models by allowing for a direct calculation of the parameters based on the kinetic theory governing the microscopic phenomena and for a non-Maxwellian electron energy distribution. The key assumptions for the model validity are a small free path for the electrons, implying a reasonably high pressure, and a dominating electric field. The results from the kinetic theory based model are consistent with previous continuum model results under the assumption of a Maxwellian electron energy distribution. However, there is a large richness of phenomenology that is included in the kinetic model, taking into account the parameter dependence on the simulation variables and the more general non-Maxwellian energy distribution of the electrons, that is not available in previous continuum models. In addition, the current work revealed an inconsistency in the previous model results which suggests that although the model system used in both the previous and the current work is a good representation of the overall reaction and transport phenomena in a glow discharge, it does not adequately represent the ionization chemistry of real chemical systems. The kinetic theory based model developed in this dissertation represents an important step in the continuing investigation of the role played by the microscopic structure of the plasma in determining the macroscopic transport and reaction phenomena.

Gustafson, John Burton

259

Chemical Kinetic Reaction Mechanisms for Combustion of Hydrocarbon and Other Types of Chemical Fuels  

DOE Data Explorer

The central feature of the Combustion Chemistry project at LLNL is the development, validation, and application of detailed chemical kinetic reaction mechanisms for the combustion of hydrocarbon and other types of chemical fuels. For the past 30 years, LLNL's Chemical Sciences Division has built hydrocarbon mechanisms for fuels from hydrogen and methane through much larger fuels including heptanes and octanes. Other classes of fuels for which models have been developed include flame suppressants such as halons and organophosphates, and air pollutants such as soot and oxides of nitrogen and sulfur. Reaction mechanisms have been tested and validated extensively through comparisons between computed results and measured data from laboratory experiments (e.g., shock tubes, laminar flames, rapid compression machines, flow reactors, stirred reactors) and from practical systems (e.g., diesel engines, spark-ignition engines, homogeneous charge, compression ignition (HCCI) engines). These kinetic models are used to examine a wide range of combustion systems.[Taken from https://www-pls.llnl.gov/?url=science_and_technology-chemistry-combustion

260

Millimeter-wave imaging of thermal and chemical signatures.  

SciTech Connect

Development of a passive millimeter-wave (mm-wave) system is described for remotely mapping thermal and chemical signatures of process effluents with application to arms control and nonproliferation. Because a large amount of heat is usually dissipated in the air or waterway as a by-product of most weapons of mass destruction facilities, remote thermal mapping may be used to detect concealed or open facilities of weapons of mass destruction. We have developed a focal-plane mm-wave imaging system to investigate the potential of thermal mapping. Results of mm-wave images obtained with a 160-GHz radiometer system are presented for different target scenes simulated in the laboratory. Chemical and nuclear facilities may be identified by remotely measuring molecular signatures of airborne molecules emitted from these facilities. We have developed a filterbank radiometer to investigate the potential of passive spectral measurements. Proof of principle is presented by measuring the HDO spectral line at 80.6 GHz with a 4-channel 77-83 GHz radiometer.

Gopalsami, N.

1999-03-30

261

Concentration fluctuations in a mesoscopic oscillating chemical reaction system  

NASA Astrophysics Data System (ADS)

Under sustained pumping, kinetics of macroscopic nonlinear biochemical reaction systems far from equilibrium either can be in a stationary steady state or can execute sustained oscillations about a fixed mean. For a system of two dynamic species X and Y, the concentrations nx and ny will be constant or will repetitively trace a closed loop in the (nx, ny) phase plane, respectively. We study a mesoscopic system with nx and ny very small; hence the occurrence of random fluctuations modifies the deterministic behavior and the law of mass action is replaced by a stochastic model. We show that nx and ny execute cyclic random walks in the (nx, ny) plane whether or not the deterministic kinetics for the corresponding macroscopic system represents a steady or an oscillating state. Probability distributions and correlation functions for nx(t) and ny(t) show quantitative but not qualitative differences between states that would appear as either oscillating or steady in the corresponding macroscopic systems. A diffusion-like equation for probability P(nx, ny, t) is obtained for the two-dimensional Brownian motion in the (nx, ny) phase plane. In the limit of large nx, ny, the deterministic nonlinear kinetics derived from mass action is recovered. The nature of large fluctuations in an oscillating nonequilibrium system and the conceptual difference between "thermal stochasticity" and "temporal complexity" are clarified by this analysis. This result is relevant to fluorescence correlation spectroscopy and metabolic reaction networks. fluorescence correlation spectroscopy | limit cycle | nanobiochemistry | nonequilibrium steady state | random walk

Qian, Hong; Saffarian, Saveez; Elson, Elliot L.

2002-08-01

262

Relaxation of chemical reactions to stationary states in the chemical affinities space  

NASA Astrophysics Data System (ADS)

Using the mass balance equations for chemical reactions, we show how the system relaxes toward a steady-state in and out of the Onsager region. In the chemical affinities space, after fast transients, the relaxation process is a straight line when operating in the Onsager region, while out of this regime, the evolution of the system is such that the projections of the evolution equations for the forces and the shortest path on the flows coincide. For spatially extended systems, similar results are valid for the evolution of the thermodynamic mode (i.e., the mode with wave-number k = 0). These results allow us to obtain the expression for the affine connection of the space covered by the thermodynamic forces, close to the steady-states. Through the affine connection, the nonlinear closure equations are derived.

Sonnino, Giorgio

2010-12-01

263

No electron left behind: a rule-based expert system to predict chemical reactions and reaction mechanisms.  

PubMed

Predicting the course and major products of arbitrary reactions is a fundamental problem in chemistry, one that chemists must address in a variety of tasks ranging from synthesis design to reaction discovery. Described here is an expert system to predict organic chemical reactions based on a knowledge base of over 1500 manually composed reaction transformation rules. Novel rule extensions are introduced to enable robust predictions and describe detailed reaction mechanisms at the level of electron flows in elementary reaction steps, ensuring that all reactions are properly balanced and atom-mapped. The core reaction prediction functionalities of this expert system are illustrated with applications including: (1) prediction of detailed reaction mechanisms; (2) computer-based learning in organic chemistry; (3) retrosynthetic analysis; and (4) combinatorial library design. Select applications are available via http://cdb.ics.uci.edu. PMID:19719121

Chen, Jonathan H; Baldi, Pierre

2009-09-01

264

Thermal reactions of aromatics with CaO. Technical progress report, September 1, 1981April 30, 1982  

Microsoft Academic Search

Research in this period focussed on understanding the calcination chemistry of CaO and its relation to the activity of CaO for pyrolysis of aromatic compounds. The main objectives are to arrive at a set of optimal calcination conditions under which to prepare CaO samples for systematic studies of the thermal reactions of aromatics with CaO, and to relate the chemical

J. P. Longwell; C. K. Lai; G. C. Williams; W. A. Peters

1982-01-01

265

A Two-Photon Induced Chemical Reaction in AgCl.  

National Technical Information Service (NTIS)

Two photon absorptions have been observed in a variety of materials. The only reported instances of the initiation of chemical reactions by such an absorption are polymerization reactions of organic molecules. We wish to report the two photon absorption b...

D. L. Rousseau G. E. Leroi G. L. Link

1965-01-01

266

Thermal activation and reaction of allyl alcohol on Ni(100)  

NASA Astrophysics Data System (ADS)

The thermal chemistry of allyl alcohol (CH 2CHCH 2OH) on a Ni(100) single-crystal surface was studied by the temperature programmed desorption (TPD) and the X-ray photoelectron spectroscopy (XPS). The allyl alcohol adsorbs molecularly on the metal surface at 100 K. Intact molecular desorption from the surface occurs at temperatures around 180 K, but some molecules exhibit chemical reactivity on the surface: activation of the O sbnd H, C dbnd C, and C sbnd O bonds produces ?1(O)-allyloxy CH 2dbnd CHCH 2O (a), ?2(C, C) allyl alcohol (C (a)H 2C (a)HCH 2OH), and ?3(C, C, O)-alkoxide (C (a)H 2sbnd C (a)CH 2 O (a)) intermediates. Further thermal activation of allyl alcohol on the surface yields propylene (CH 2CHCH 3), 1-propanol (CH 3CH 2CH 2OH), propanal (CH 3CH 2CHO), and combustion and dehydrogenation products (H 2O, H 2, and CO). Propylene desorbs from the surface at temperatures of around 270 K. Hydrogenation to the ?3(C, C, O)-alkoxide intermediate leads to the production of propanal which desorbs from the surface around 320 K, while hydrogenation of the ?2(C, C) allyl alcohol intermediate produces 1-propanol, which desorbs at around 310 K. The co-adsorption of hydrogen atoms on the surface enhances the formation of the saturated alcohol, while co-adsorption of oxygen enhances the formation of both the saturated alcohol and the saturated aldehydes.

Zhao, Qing; Deng, Rongping; Zaera, Francisco

2011-07-01

267

Atomistic-scale simulations of the initial chemical events in the thermal initiation of triacetonetriperoxide.  

PubMed

To study the initial chemical events related to the detonation of triacetonetriperoxide (TATP), we have performed a series of molecular dynamics (MD) simulations. In these simulations we used the ReaxFF reactive force field, which we have extended to reproduce the quantum mechanics (QM)-derived relative energies of the reactants, products, intermediates, and transition states related to the TATP unimolecular decomposition. We find excellent agreement between the QM-predicted reaction products and those observed from 100 independent ReaxFF unimolecular MD cookoff simulations. Furthermore, the primary reaction products and average initiation temperature observed in these 100 independent unimolecular cookoff simulations match closely with those observed from a TATP condensed-phase cookoff simulation, indicating that unimolecular decomposition dominates the thermal initiation of the TATP condensed phase. Our simulations demonstrate that thermal initiation of condensed-phase TATP is entropy-driven (rather than enthalpy-driven), since the initial reaction (which mainly leads to the formation of acetone, O(2), and several unstable C(3)H(6)O(2) isomers) is almost energy-neutral. The O(2) generated in the initiation steps is subsequently utilized in exothermic secondary reactions, leading finally to formation of water and a wide range of small hydrocarbons, acids, aldehydes, ketones, ethers, and alcohols. PMID:16076213

van Duin, Adri C T; Zeiri, Yehuda; Dubnikova, Faina; Kosloff, Ronnie; Goddard, William A

2005-08-10

268

Chemical reactions between aluminum and fly ash during synthesis and reheating of Al-fly ash composite  

SciTech Connect

Thermodynamic analysis indicates that there is the possibility of chemical reactions between aluminum melt and cenosphere fly ash particles. These particles contain alumina, silica, and iron oxide, which, during solidification processing of aluminum-fly ash composites or during holding of such composites at temperatures above the melting temperature of the aluminum, are likely to undergo chemical reduction. These chemical reactions between the fly ash and molten aluminum have been studied by metallographic examination, differential thermal analysis (DTA), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and X-ray analysis after holding the aluminum-fly ash composites for different periods above the liquidus temperature. The experiments indicate that there is progressive reduction of silica and mullite in the fly ash, and formation of alumina with holding time of composites at a temperature of 850 C. The walls of the cenosphere fly ash particles progressively disintegrate into discrete particles as the reaction progresses. The rate of chemical reaction was high at the start of holding the composite at a temperature of 850 C, and then the rate significantly decreased with time. The reaction was almost complete after 10 hours.

Guo, R.Q.; Rohatgi, P.K. [Univ. of Wisconsin, Milwaukee, WI (United States). Dept. of Materials

1998-06-01

269

A Case Study in Chemical Kinetics: The OH + CO Reaction.  

ERIC Educational Resources Information Center

Reviews some important properties of the bimolecular reaction between the hydroxyl radical and carbon monoxide. Investigates the kinetics of the reaction, the temperature and pressure dependence of the rate constant, the state-to-state dynamics of the reaction, and the reverse reaction. (MVL)

Weston, Ralph E., Jr.

1988-01-01

270

Final Technical Report "Energy Partitioning in Elementary Chemical Reactions"  

SciTech Connect

This is the final technical report of the subject grant. It describes the scientific results obtained during the reporting period. These results are focused on the reactions of atomic oxygen with terminal alkenes. We have studied the production of vinoxy in these reactions. We have characterized the energy disposal in the reactions and have elaborated the reaction mechanism.

Richard Bersohn (deceased); James J. Valentini (reporting investigator)

2005-10-03

271

Thermal and fast neutron detection in chemical vapor deposition single-crystal diamond detectors  

SciTech Connect

Recently, a compact solid-state neutron detector capable of simultaneously detecting thermal and fast neutrons was proposed [M. Marinelli et al., Appl. Phys. Lett. 89, 143509 (2006)]. Its design is based on a p-type/intrinsic/metal layered structure obtained by Microwave Plasma Chemical Vapor Deposition (CVD) of homoepitaxial diamond followed by thermal evaporation of an Al contact and a {sup 6}LiF converting layer. Fast neutrons are directly detected in the CVD diamond bulk, since they have enough energy to produce the {sup 12}C(n,{alpha}){sup 9}Be reaction in diamond. Thermal neutrons are instead converted into charged particles in the {sup 6}LiF layer through the {sup 6}Li(n,{alpha})T nuclear reaction. These charged particles are then detected in the diamond layer. The thickness of the {sup 6}LiF converting layer and the CVD diamond sensing layer affect the counting efficiency and energy resolution of the detector both for low- (thermal) and high-energy neutrons. An analysis is carried out on the dynamics of the {sup 6}Li(n,{alpha})T and the {sup 12}C(n,{alpha}){sup 9}Be reactions products, and the distribution of the energy released inside the sensitive layer is calculated. The detector counting efficiency and energy resolution were accordingly derived as a function of the thickness of the {sup 6}LiF and CVD diamond layers, both for thermal and fast neutrons, thus allowing us to choose the optimum detector design for any particular application. Comparison with experimental results is also reported.

Almaviva, S.; Marinelli, M.; Milani, E.; Prestopino, G.; Tucciarone, A.; Verona, C.; Verona-Rinati, G. [Dipartimento di Ingegneria Meccanica, Universita di Roma 'Tor Vergata', Via del Politecnico 1, I-00133 Roma (Italy); Angelone, M.; Lattanzi, D.; Pillon, M. [Associazione EURATOM-ENEA sulla Fusione, Via E. Fermi 45, I-00044 Frascati (Roma) (Italy); Montereali, R. M.; Vincenti, M. A. [ENEA-FIS C.R. Frascati, Via E. Fermi 45, I-00044 Frascati (Roma) (Italy)

2008-03-01

272

Non-adiabatic effects within a single thermally averaged potential energy surface: Thermal expansion and reaction rates of small molecules  

NASA Astrophysics Data System (ADS)

At non-zero temperature and when a system has low-lying excited electronic states, the ground-state Born-Oppenheimer approximation breaks down and the low-lying electronic states are involved in any chemical process. In this work, we use a temperature-dependent effective potential for the nuclei which can accommodate the influence of an arbitrary number of electronic states in a simple way, while at the same time producing the correct Boltzmann equilibrium distribution for the electronic part. With the help of this effective potential, we show that thermally activated low-lying electronic states can have a significant effect in molecular properties for which electronic excitations are oftentimes ignored. We study the thermal expansion of the Manganese dimer, Mn2, where we find that the average bond length experiences a change larger than the present experimental accuracy upon the inclusion of the excited states into the picture. We also show that, when these states are taken into account, reaction-rate constants are modified. In particular, we study the opening of the ozone molecule, O3, and show that in this case the rate is modified as much as a 20% with respect to the ground-state Born-Oppenheimer prediction.

Alonso, J. L.; Castro, A.; Clemente-Gallardo, J.; Echenique, P.; Mazo, J. J.; Polo, V.; Rubio, A.; Zueco, D.

2012-12-01

273

Point defect dynamics and evolution of chemical reactions in alanates by anelastic spectroscopy.  

PubMed

We report the first measurements of elastic modulus and energy dissipation in Ti-doped and undoped sodium aluminum hydride. It is shown that the chemical reactions that occur by varying the sample temperatures or by aging most sensitively affect the elastic constants, such that the modulus variations allow the time and temperature evolution of decomposition to be monitored. After a well-defined thermal treatment at 436 K, a thermally activated relaxation process appears at 70 K in the kilohertz range, denoting the existence of a new species, likely involving hydrogen, having a very high mobility, that is, 10(3) jumps/s at the peak temperature corresponding to a relaxation rate of about 10(11) s(-1) at room temperature. The activation energy of the process is 0.126 eV and the preexponential factor 7 x 10(-14) s, which is typical of point defect relaxation. The peak is very broad with respect to a single Debye process, indicating strong interaction or/and multiple jumping type of the mobile entity. The present data suggest that the models aiming at interpreting the decomposition reactions and kinetics should take into account the indicated point-defect dynamics and stoichiometry defects. PMID:16851077

Palumbo, Oriele; Cantelli, Rosario; Paolone, Annalisa; Jensen, Craig M; Srinivasan, Sesha S

2005-01-27

274

Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks  

SciTech Connect

This is an annual technical report for the work done over the last year (period ending 9/30/2004) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a procedure to speed up the training of NPCA. The developed procedure is based on the non-parametric statistical technique of kernel smoothing. When this smoothing technique is implemented as a Neural Network, It is know as Generalized Regression Neural Network (GRNN). We present results of implementing GRNN on a test problem. In addition, we present results of an in house developed 2-D CFD code that will be used through out the project period.

Nelson Butuk

2004-12-01

275

Chemical reactions between Venus' surface and atmosphere - An update. (Invited)  

NASA Astrophysics Data System (ADS)

The surface of Venus, at ~740K, is hot enough to allow relatively rapid chemical reactions between it and the atmosphere, i.e. weathering. Venus chemical weathering has been explored in detail [1], to the limits of available data. New data from Venus Express (VEx) and new ideas from exoplanets have sparked a modest renewal of interest in Venus weathering. Venus' surface cannot be observed in visible light, but there are several NIR ';windows' through its atmosphere that allow surface imaging. The VIRTIS spectrometer on VEx viewed the surface through one window [2]; emissivity variations among lava flows on Imdr and Themis Regios have been explained as varying degrees of weathering, and thus age [3]. The VMC camera on VEx also provides images through a NIR window, which suggest variable degrees of weathering on some basaltic plains [4]. Indirect evidence for weathering may come from varying SO2 abundance at Venus' cloud tops; repeated rapid increases and gradual declines may represent volcanic eruptions followed by weathering to form sulfate minerals [5]. Continued geochemical modeling relevant to Venus weathering is motivated by expolanet studies [6]. Models have been extended to hypothetical exo-Venuses of different temperatures and surface compositions [7]. The idea that Venus' atmosphere composition can be buffered by reaction with its surface was explored in detail, and the derived constraint extended to other types of planets [8]. Several laboratories are investigating Venus weathering, motivated in part by the hope that they can provide real constraints on timescales of Venus volcanism [3]. Aveline et al. [9] are extending early studies [10] by reacting rocks and minerals with concentrated SO2 (to accelerate reaction rates to allow detectability of products). Kohler et al. [11] are investigating the stability of metals and chalcogenides as possible causes of the low-emissivity surfaces at high elevations. Berger and Aigouy [12] studied rock alteration on a hypothetical early Venus with a water-rich atmosphere. Martin et al. [13] investigated the fate of weathered rock when heated (by igneous or impact events). Our understanding of Venus' geological history is stymied by a lack of data - spacecraft observations of and/or at its surface. VMC on VEx may continue to provide new data on surface emissivity, but their interpretation is inherently ambiguous. Laboratory experiments seem the most promising approach - attempting to quantify rates of weathering and thus volcanism [3], and (with luck) framing significant problems that can be directly answered by spacecraft observations. [1] Fegley B.Jr. et al. (1997) In Venus II. U. Ariz. Press. p. 591. [2] Helbert J. et al. (2008) GRL 35, L11201. [3] Smrekar S.E et al. (2010) Science 328, 605-608. [4] Basilevsky A.T. et al. (2012) Icarus 217, 434-450. [5] Marcq E. et al. (2013) Nature Geoscience 6, 25-28. [6] Kane S.R. et al. (2013) Astrophysical J. 770, L20. [7] Schaefer L. & Fegley B.Jr. (2011) Astrophysical J. 729, 6. [8] Treiman A.H. & Bullock M.A. (2012) Icarus 217, 534-541. [9] Aveline D.C. et al. (2011) Lunar Planet. Sci. Conf. 42, Abstr. #2165. [10] Fegley B.Jr. & Prinn R.G. (1989) Nature 337, 55-58. [11] Kohler E. et al. (2012) Lunar Planet. Sci. Conf. 43, Abstr. #2749. [12] Berger G. & Aigouy T. (2011) Lunar Planet. Sci. Conf. 42, Abstr. #1660. [13] Martin A.M. et al. (2012) Earth Planet. Sci. Lett. 331-332, 291-304.

Treiman, A. H.

2013-12-01

276

Examination of lignocellulosic fibers for chemical, thermal, and separations properties: Addressing thermo-chemical stability issues  

NASA Astrophysics Data System (ADS)

Natural fiber-plastic composites incorporate thermoplastic resins with fibrous plant-based materials, sometimes referred to as biomass. Pine wood mill waste has been the traditional source of natural fibrous feedstock. In anticipation of a waste wood shortage other fibrous biomass materials are being investigated as potential supplements or replacements. Perennial grasses, agricultural wastes, and woody biomass are among the potential source materials. As these feedstocks share the basic chemical building blocks; cellulose, hemicellulose, and lignin, they are collectively called lignocellulosics. Initial investigation of a number of lignocellulosic materials, applied to fiber-plastic composite processing and material testing, resulted in varied results, particularly response to processing conditions. Less thermally stable lignocellulosic filler materials were physically changed in observable ways: darkened color and odor. The effect of biomass materials' chemical composition on thermal stability was investigated an experiment involving determination of the chemical composition of seven lignocellulosics: corn hull, corn stover, fescue, pine, soy hull, soy stover, and switchgrass. These materials were also evaluated for thermal stability by thermogravimetric analysis. The results of these determinations indicated that both chemical composition and pretreatment of lignocellulosic materials can have an effect on their thermal stability. A second study was performed to investigate what effect different pretreatment systems have on hybrid poplar, pine, and switchgrass. These materials were treated with hot water, ethanol, and a 2:1 benzene/ethanol mixture for extraction times of: 1, 3, 6, 12, and 24 hours. This factorial experiment demonstrated that both extraction time and medium have an effect on the weight percent of extractives removed from all three material types. The extracted materials generated in the above study were then subjected to an evaluation of thermal stability by thermogravimetric analysis in a subsequent experiment. Overlay plots, combining individual weight loss curves, demonstrate that the experimental factors, solvent system and extraction time, produce effects on the thermal stability of the treated biomass samples. These data also indicated that the individual lignocellulosic materials had unique responses to the type of solvent used for pretreatment. Increasing extraction time had either no correlation with or a positive effect on thermal stability of the biomass samples.

Johnson, Carter David

277

Variation in thermal performance and reaction norms among populations of Drosophila melanogaster.  

PubMed

The major goal of evolutionary thermal biology is to understand how variation in temperature shapes phenotypic evolution. Comparing thermal reaction norms among populations from different thermal environments allows us to gain insights into the evolutionary mechanisms underlying thermal adaptation. Here, we have examined thermal adaptation in six wild populations of the fruit fly (Drosophila melanogaster) from markedly different natural environments by analyzing thermal reaction norms for fecundity, thorax length, wing area, and ovariole number under ecologically realistic fluctuating temperature regimes in the laboratory. Contrary to expectation, we found only minor differences in the thermal optima for fecundity among populations. Differentiation among populations was mainly due to differences in absolute (and partly also relative) thermal fecundity performance. Despite significant variation among populations in the absolute values of morphological traits, we observed only minor differentiation in their reaction norms. Overall, the thermal reaction norms for all traits examined were remarkably similar among different populations. Our results therefore suggest that thermal adaptation in D. melanogaster predominantly involves evolutionary changes in absolute trait values rather than in aspects of thermal reaction norms. PMID:24299409

Klepsatel, Peter; Gáliková, Martina; De Maio, Nicola; Huber, Christian D; Schlötterer, Christian; Flatt, Thomas

2013-12-01

278

Optomechanical manipulation of chemical reactions on the nanoscale with optofluidic nanotweezers  

NASA Astrophysics Data System (ADS)

Chemical reactions are often described as a progression along a reaction coordinate. Waveguide evanescent fields generate an electromagnetic force that spans tens of nanometers and have been used previously to trap protein molecules. Applying this force along a reaction coordinate could radically alter the chemical reaction by modifying the activation energy or biasing the reaction towards a specific pathway. Here, we show that the adsorption of proteins onto carbon nanotubes can be controlled with opto-mechanical forces. An analytic model for the reaction was developed, the predictions of which were explored by probing the energy barrier under various experimental conditions.

O'Dell, Dakota; Serey, Xavier; Erickson, David

2014-03-01

279

Thermal and chemical degradation of inorganic membrane materials. Topical report  

SciTech Connect

This report describes the results of a literature review to evaluate the long-term thermal and chemical degradation of inorganic membranes that are being developed to separate gaseous products produced by the gasification or combustion of coal in fixed-, fluidized-, and entrained-bed gasifiers, direct coal-fired turbines, and pressurized-fluidized-bed combustors. Several impurities, such as H{sub 2}S, NH{sub 3}, SO{sub 2}, NO{sub x}, and trace metal compounds are generated during coal conversion, and they must be removed from the coal gas or the combustor flue gas to meet environmental standards. The use of membranes to separate these noxious gases is an attractive alternative to their removal by sorbents such as zinc titanate or calcium oxide. Inorganic membranes that have a high separation efficiency and exhibit both thermal and chemical stability would improve the economics of power generation from coal. The U.S. Department of Energy is supporting investigations to develop inorganic membranes for separating hydrogen from coal gas streams and noxious impurities from hot coal- and flue-gas streams. Membrane materials that have been investigated in the past include glass (silica), alumina, zirconia, carbon, and metals (Pd and Pt).

Krishnan, G.N.; Sanjurjo, A.; Wood, B.J.; Lau, K.H.

1994-04-01

280

Chemical kinetic performance losses for a hydrogen laser thermal thruster  

NASA Technical Reports Server (NTRS)

Projected requirements for efficient, economical, orbit-raising propulsion systems have generated investigations into several potentially high specific impulse, moderate thrust, advanced systems. One of these systems, laser thermal propulsion, utilizes a high temperature plasma as the enthalpy source. The plasma is sustained by a focused laser beam which maintains the plasma temperature at levels near 20,000 K. Since such temperature levels lead to total dissociation and high ionization, the plasma thruster system potentially has a high specific impulse decrement due to recombination losses. The nozzle flow is expected to be sufficiently nonequilibrium to warrant concern over the achievable specific impluse. This investigation was an attempt at evaluation of those losses. The One-Dimensional Kinetics (ODK) option of the Two-Dimensional Kinetics (TDK) Computer Program was used with a chemical kinetics rate set obtained from available literature to determine the chemical kinetic energy losses for typical plasma thruster conditions. The rates were varied about the nominal accepted values to band the possible losses. Kinetic losses were shown to be highly significant for a laser thermal thruster using hydrogen. A 30 percent reduction in specific impulse is possible simply due to the inability to completely extract the molecular recombination energy.

Mccay, T. D.; Dexter, C. E.

1985-01-01

281

A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions  

NASA Astrophysics Data System (ADS)

This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing NE equilibrium reactions and a set of reactive transport equations of M- NE kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.

Zhang, Fan; Yeh, Gour-Tsyh; Parker, Jack C.; Brooks, Scott C.; Pace, Molly N.; Kim, Young-Jin; Jardine, Philip M.; Watson, David B.

2007-06-01

282

Optical thin films grown by surface chemical reaction for high-power lasers  

NASA Astrophysics Data System (ADS)

We prepared optical thin films grown with surface chemical reactions using TiCl4 and H2O for TiO2. The nonuniformity of thickness distribution was under 1% over 240 mm in diameter. The structure of TiO2 film grown at 25 degrees Celsius was amorphous. The structure changed into polycrystalline with an increase of growth temperature up to 400 degrees Celsius. Secondary ion mass spectrometry showed that chloride residents presented in the films at every growth temperature. However, these chloride residents could be removed by thermal annealing at 400 degrees Celsius. The TiO2 film at the growth temperature of 25 degrees Celsius had a laser-induced damage threshold of 5 J/cm2 for 1-ns, 1064 nm laser pulse. The damage threshold of TiO2 films decreased at higher growth temperature. Chloride in the films had no influence on the laser-induced damage threshold.

Zaitsu, Shin-ichi; Motokoshi, Shinji; Jitsuno, Takahisa; Nakatsuka, Masahiro; Yamanaka, Tatsuhiko

2000-04-01

283

Performance and cost of energy transport and storage systems for dish applications using reversible chemical reactions  

NASA Technical Reports Server (NTRS)

The use of reversible chemical reactions for energy transport and storage for parabolic dish networks is considered. Performance and cost characteristics are estimated for systems using three reactions (sulfur-trioxide decomposition, steam reforming of methane, and carbon-dioxide reforming of methane). Systems are considered with and without storage, and in several energy-delivery configurations that give different profiles of energy delivered versus temperature. Cost estimates are derived assuming the use of metal components and of advanced ceramics. (The latter reduces the costs by three- to five-fold). The process that led to the selection of the three reactions is described, and the effects of varying temperatures, pressures, and heat exchanger sizes are addressed. A state-of-the-art survey was performed as part of this study. As a result of this survey, it appears that formidable technical risks exist for any attempt to implement the systems analyzed in this study, especially in the area of reactor design and performance. The behavior of all components and complete systems under thermal energy transients is very poorly understood. This study indicates that thermochemical storage systems that store reactants as liquids have efficiencies below 60%, which is in agreement with the findings of earlier investigators.

Schredder, J. M.; Fujita, T.

1984-01-01

284

Computational Analyses of Complex Flows with Chemical Reactions  

NASA Astrophysics Data System (ADS)

The heat and mass transfer phenomena in micro-scale for the mass transfer phenomena on drug in cylindrical matrix system, the simulation of oxygen/drug diffusion in a three dimensional capillary network, and a reduced chemical kinetic modeling of gas turbine combustion for Jet propellant-10 have been studied numerically. For the numerical analysis of the mass transfer phenomena on drug in cylindrical matrix system, the governing equations are derived from the cylindrical matrix systems, Krogh cylinder model, which modeling system is comprised of a capillary to a surrounding cylinder tissue along with the arterial distance to veins. ADI (Alternative Direction Implicit) scheme and Thomas algorithm are applied to solve the nonlinear partial differential equations (PDEs). This study shows that the important factors which have an effect on the drug penetration depth to the tissue are the mass diffusivity and the consumption of relevant species during the time allowed for diffusion to the brain tissue. Also, a computational fluid dynamics (CFD) model has been developed to simulate the blood flow and oxygen/drug diffusion in a three dimensional capillary network, which are satisfied in the physiological range of a typical capillary. A three dimensional geometry has been constructed to replicate the one studied by Secomb et al. (2000), and the computational framework features a non-Newtonian viscosity model for blood, the oxygen transport model including in oxygen-hemoglobin dissociation and wall flux due to tissue absorption, as well as an ability to study the diffusion of drugs and other materials in the capillary streams. Finally, a chemical kinetic mechanism of JP-10 has been compiled and validated for a wide range of combustion regimes, covering pressures of 1atm to 40atm with temperature ranges of 1,200 K--1,700 K, which is being studied as a possible Jet propellant for the Pulse Detonation Engine (PDE) and other high-speed flight applications such as hypersonic missiles. The comprehensive skeletal mechanism consists of 58 species and 315 reactions including in CPD, Benzene formation process by the theory for polycyclic aromatic hydrocarbons (PAH) and soot formation process on the constant volume combustor, premixed flame characteristics.

Bae, Kang-Sik

285

Effect of chemical vapor infiltration on erosion and thermal properties of porous carbon\\/carbon composite thermal insulation  

Microsoft Academic Search

A highly porous carbon\\/carbon composite, known as carbon bonded carbon fiber (CBCF) and used as thermal insulation, was densified by chemical vapor infiltration (CVI). The erosion resistance, thermal conductivity and thermal expansion coefficient were measured with interest to utilization of the CVI densified composite as erosion protection in furnaces that employ inert gas quenching. It was found that the erosion

R. I Baxter; R. D Rawlings; N Iwashita; Y Sawada

2000-01-01

286

Thermal effects on the diffusive layer convection instability of an exothermic acid-base reaction front  

NASA Astrophysics Data System (ADS)

A buoyancy-driven hydrodynamic instability appearing when an aqueous acid solution of HCl overlies a denser alkaline aqueous solution of NaOH in a vertically oriented Hele-Shaw cell is studied both experimentally and theoretically. The peculiarity of this reactive convection pattern is its asymmetry with regard to the initial contact line between the two solutions as convective plumes develop in the acidic solution only. We investigate here by a linear stability analysis (LSA) of a reaction-diffusion-convection model of a simple A+B?C reaction the relative role of solutal versus thermal effects in the origin and location of this instability. We show that heat effects are much weaker than concentration-related ones such that the heat of reaction only plays a minor role on the dynamics. Computation of density profiles and of the stability analysis eigenfunctions confirm that the convective motions result from a diffusive layer convection mechanism whereby a locally unstable density stratification develops in the upper acidic layer because of the difference in the diffusion coefficients of the chemical species. The growth rate and wavelength of the pattern are determined experimentally as a function of the Brinkman parameter of the problem and compare favorably with the theoretical predictions of both LSA and nonlinear simulations.

Almarcha, C.; Trevelyan, P. M. J.; Grosfils, P.; De Wit, A.

2013-09-01

287

Chemical-decomposition models for the thermal explosion of confined HMX, TATB, RDX, and TNT explosives  

Microsoft Academic Search

Chemical decomposition models have been deduced from the available chemical kinetic data on the thermal decomposition of HMX, TATB, RDX, and TNT. A thermal conduction model is used in which the thermal conductivity of the reacting explosive decreases linearly with the mass fraction reacted to that of the gaseous products. These reactive heat flow models are used to predict the

R. R. McGuire; C. M. Tarver

1981-01-01

288

Thermal reactions of starch with long-chain unsaturated fatty acids. Part 2. Linoleic acid  

Microsoft Academic Search

The significance and numerous applications of products resulting from reactions of starch with fatty acids induced our interest in checking thermal reaction of potato starch with linoleic acid. Behaviour of the starch–linoleic acid blends was monitored by means of thermogravimetric (TG), differential thermogravimetric (DTG), and differential scanning calorimetric (DSC) methods. The reaction carried out on conventional heating provided mixture of

Janusz Kapusniak; Przemyslaw Siemion

2007-01-01

289

Study on thermal crosslinking reaction of o-naphthoquinone diazides and application to electrodeposition positive photoresist  

Microsoft Academic Search

The thermal reactions of o-naphthoquinone diazide (NQD) compounds as a material for photoresists were studied in comparison with their photochemical reactions. An NQD compound decomposed at around 140°C and further reacted in the presence of an alcohol in the solution to yield an indenecarboxylic ester. The photochemical reaction of the NQD compound with alcohol also provided the same ester in

Kenji Miyagawa; Keisuke Naruse; Shinsuke Ohnishi; Koji Yamaguchi; Kenji Seko; Nobushige Numa; Naozumi Iwasawa

2001-01-01

290

Detailed Chemical Kinetic Reaction Mechanisms for Incineration of Organophosphorus and Fluoro-Organophosphorus Compounds  

Microsoft Academic Search

A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previous kinetic models of organophosphorus compounds such as TMP, DMMP and DIMP that are often used as surrogates to predict incineration of GB. Kinetic

P A Glaude; C Melius; W J Pitz; C K Westbrook

2001-01-01

291

Application of the shock tube unsteady expansion wave technique to the study of chemical reactions  

Microsoft Academic Search

An unsteady expansion wave was generated through rupture of a secondary diaphragm by an incident shock wave in a shock tube to study the three-body recombination of iodine atoms. The application to chemical reaction studies has been made possible through an extension of the usable flow time, and a theoretical treatment enables the effect of coupling of chemical reaction to

W. H. Beck; J. C. Mackie

1978-01-01

292

Acid-Base Chemistry According to Robert Boyle: Chemical Reactions in Words as well as Symbols  

ERIC Educational Resources Information Center

Examples of acid-base reactions from Robert Boyle's "The Sceptical Chemist" are used to illustrate the rich information content of chemical equations. Boyle required lengthy passages of florid language to describe the same reaction that can be done quite simply with a chemical equation. Reading or hearing the words, however, enriches the student's…

Goodney, David E.

2006-01-01

293

Influence of Chemical Reactions on the Mobility of Radionuclides in the Terrestrial Environment.  

National Technical Information Service (NTIS)

The influence of the kinetics of chemical and physico-chemical reactions on the mobility of radionuclides in the terrestrial environment has been studied theoretically by application of the COLUMN2 computer code. A variety of reaction systems has been ana...

L. Carlsen O. J. Nielsen P. Bo C. Ditlevsen

1986-01-01

294

Design criteria for extraction with chemical reaction and liquid membrane permeation  

NASA Technical Reports Server (NTRS)

The design criteria for heterogeneous chemical reactions in liquid/liquid systems formally correspond to those of classical physical extraction. More complex models are presented which describe the material exchange at the individual droplets in an extraction with chemical reaction and in liquid membrane permeation.

Bart, H. J.; Bauer, A.; Lorbach, D.; Marr, R.

1988-01-01

295

CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

The chemical research during the last decade has witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into ...

296

Heat-of-Reaction Chemical Heat Pumps: Possible Configurations.  

National Technical Information Service (NTIS)

Chemical heat pumps utilize working fluids which undergo reversible chemical changes. Mechanically driven reactive heat pump cycles or, alternatively, heat driven heat pumps in which either heat engine or heat pump working fluid is reactive, are considere...

L. D. Kirol

1986-01-01

297

SUBSTITUTION REACTIONS FOR THE DETOXIFICATION OF HAZARDOUS CHEMICALS  

EPA Science Inventory

Chemical Treatment is one of several treatment techniques used for the remediation of toxic and hazardous chemicals. Chemical treatment in this report is defined as substitution of halogens by hydrogens for the conversion of halogenated organic toxicant into its native hydrocarb...

298

Chemical Characterization and Reactivity Testing of Fuel-Oxidizer Reaction Product (Test Report)  

NASA Technical Reports Server (NTRS)

The product of incomplete reaction of monomethylhydrazine (MMH) and nitrogen tetroxide (NTO) propellants, or fuel-oxidizer reaction product (FORP), has been hypothesized as a contributory cause of an anomaly which occurred in the chamber pressure (PC) transducer tube on the Reaction Control Subsystem (RCS) aft thruster 467 on flight STS-51. A small hole was found in the titanium-alloy PC tube at the first bend below the pressure transducer. It was surmised that the hole may have been caused by heat and pressure resulting from ignition of FORP. The NASA Johnson Space Center (JSC) White Sands Test Facility (WSTF) was requested to define the chemical characteristics of FORP, characterize its reactivity, and simulate the events in a controlled environment which may have lead to the Pc-tube failure. Samples of FORP were obtained from the gas-phase reaction of MMH with NTO under laboratory conditions, the pulsed firings of RCS thrusters with modified PC tubes using varied oxidizer or fuel lead times, and the nominal RCS thruster firings at WSTF and Kaiser-Marquardt. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC), ion chromatography (IC), inductively coupled plasma (ICP) spectrometry, thermogravimetric analysis (TGA) coupled to FTIR (TGA/FTIR), and mechanical impact testing were used to qualitatively and quantitatively characterize the chemical, thermal, and ignition properties of FORP. These studies showed that the composition of FORP is variable but falls within a limited range of compositions that depends on the fuel loxidizer ratio at the time of formation, composition of the post-formation atmosphere (reducing or oxidizing), and reaction or postreaction temperature. A typical composition contains methylhydrazinium nitrate (MMHN), ammonium nitrate (AN), methylammonium nitrate (MAN), and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. The thermal decomposition reactions of FORP compositions used in this study were unremarkable, Neither the various compositions of FORP, the pure major components of FORP, nor mixtures of FORP with propellant-system corrosion products showed any unusual thermal activity when decomposed under laboratory conditions. Off-limit thruster operations were simulated by rapid mixing of liquid MMH and liquid NTO in a confined space. The test hardware was constructed with pressure- and temperature-measurement devices to determine if the expected fuel oxidizer reaction would result in increased energy release when FORP, FORP constituents, or propellant-system corrosion products were present. These tests demonstrated that FORP, MMHN, AN, or Inconel corrosion products can induce a mixture of MMH and NTO to produce component-damaging energies. The simulation-test program was not extensive enough to provide statistical probabilities for these events but did show that such events can occur. Damaging events required FORP or metal salts to be present at the initial mixing of MMH and NTO. Based on the results of these studies, it is suggested that removal or mitigation of a buildup of these materials may decrease the incidence of these high-energy, potentially damaging events.

1996-01-01

299

Chemical Diffusivity and Wave Propagation in Surface Reactions: Analysis of the Bistable Monomer-Dimer Reaction Model  

NASA Astrophysics Data System (ADS)

Spatial pattern formation and wave propagation in surface reactions is controlled in part by chemical diffusion of the adsorbed reactant species. While in the simplest treatment, the chemical diffusion coefficients are taken as constant, the diffusion of one species is in fact influenced by the presence of coadsorbed species(M. Tammaro, M. Sabella, and J.W. Evans, J. Chem. Phys. 103 (1995) 10277; M. Tammaro and J.W. Evans, J. Chem. Phys. (submitted)). We thus develop an appropriate theory for chemical diffusion in mixed adlayers of mobile species. This theory is used to analyze the propagation of chemical waves associated with the displacement of the CO-poisoned state by a reactive steady state in the monomer-dimer model for CO-oxidation. We find good agreement between "exact" simulation results and those obtained from reaction-diffusion equations incorporating an appropriate description of the non-linear chemical diffusion.

Tammaro, M.; Evans, J. W.

1997-03-01

300

Using Drawing Technology to Assess Students' Visualizations of Chemical Reaction Processes  

NASA Astrophysics Data System (ADS)

In this study, we investigated how students used a drawing tool to visualize their ideas of chemical reaction processes. We interviewed 30 students using thinking-aloud and retrospective methods and provided them with a drawing tool. We identified four types of connections the students made as they used the tool: drawing on existing knowledge, incorporating dynamic aspects of chemical processes, linking a visualization to the associated chemical phenomenon, and connecting between the visualization and chemistry concepts. We also compared students who were able to create dynamic visualizations with those who only created static visualizations. The results indicated a relationship between students constructing a dynamic view of chemical reaction processes and their understanding of chemical reactions. This study provides insights into the use of visualizations to support instruction and assessment to facilitate students' integrated understanding of chemical reactions.

Chang, Hsin-Yi; Quintana, Chris; Krajcik, Joseph

2014-06-01

301

Scanning thermal lithography for nanopatterning of polymers : transient heat transport and thermal chemical functionalization across the length scales  

Microsoft Academic Search

The research described in this Thesis comprises the development of Scanning Thermal Lithography (SThL) as an alternative approach for the spatially controlled, highly localized thermal chemical surface modification of polymer films for the development of e.g. (bio)sensors. In the Thesis, the range of thermal transport from heated AFM probes in contact with polymer surfaces is assessed. Proximity effects of thermally

Joost Duvigneau

2011-01-01

302

Iteration Scheme for Implicit Calculations of Kinetic and Equilibrium Chemical Reactions in Fluid Dynamics  

NASA Astrophysics Data System (ADS)

An iteration scheme for the implicit treatment of equilibrium chemical reactions in partial equilibrium flow has previously been described (J. D. Ramshaw and A. A. Amsden, J. Comput. Phys.59, 484 (1985); 71 , 224 (1987)). Here we generalize this scheme to kinetic reactions as well as equilibrium reactions. This extends the applicability of the scheme to problems with kinetic reactions that are fast in some regions of the flow field but slow in others. The resulting scheme thereby provides a single unified framework for the implicit treatment of an arbitrary number of coupled equilibrium and kinetic reactions in chemically reacting fluid flow.

Ramshaw, J. D.; Chang, C. H.

1995-02-01

303

Iteration scheme for implicit calculations of kinetic and equilibrium chemical reactions in fluid dynamics  

SciTech Connect

An iteration scheme for the implicit treatment of equilibrium chemical reactions in partial equilibrium flow has previously been described. Here we generalize this scheme to kinetic reactions as well as equilibrium reactions. This extends the applicability of the scheme to problems with kinetic reactions that are fast in regions of the flow field but slow in others. The resulting scheme thereby provides a single unified framework for the implicit treatment of an arbitrary number of coupled equilibrium and kinetic reactions in chemically reacting fluid flow. 10 refs., 2 figs.

Ramshaw, J.D.; Chang, C.H. [Idaho National Engineering Lab., ID (United States)] [Idaho National Engineering Lab., ID (United States)

1995-02-01

304

Direct observation of chemical reactions on single gold nanocrystals using surface plasmon spectroscopy  

Microsoft Academic Search

Heterogeneous catalysts have been pivotal to the development of the modern chemical industry and are essential for catalysing many industrial reactions. However, reaction rates are different for every individual catalyst particle and depend upon each particle's morphology and size, crystal structure and composition. Measuring the rates of reaction on single nanocrystals will enable the role of catalyst structure to be

Carolina Novo; Alison M. Funston; Paul Mulvaney

2008-01-01

305

A Unified Approach to the Study of Chemical Reactions in Freshman Chemistry.  

ERIC Educational Resources Information Center

Provides rationale and objectives for presenting chemical reactions in a unified, logical six-stage approach rather than a piecemeal approach. Stages discussed include: introduction, stable electronic configurations and stable oxidation states, reactions between two free elements, ion transfer/proton transfer reactions, double displacement…

Cassen, T.; DuBois, Thomas D.

1982-01-01

306

Impact of organic-mineral matter interactions on thermal reaction pathways for coal model compounds  

SciTech Connect

Coal is a complex, heterogeneous solid that includes interdispersed mineral matter. However, knowledge of organic-mineral matter interactions is embryonic, and the impact of these interactions on coal pyrolysis and liquefaction is incomplete. Clay minerals, for example, are known to be effective catalysts for organic reactions. Furthermore, clays such as montmorillonite have been proposed to be key catalysts in the thermal alteration of lignin into vitrinite during the coalification process. Recent studies by Hatcher and coworkers on the evolution of coalified woods using microscopy and NMR have led them to propose selective, acid-catalyzed, solid state reaction chemistry to account for retained structural integrity in the wood. However, the chemical feasibility of such reactions in relevant solids is difficult to demonstrate. The authors have begun a model compound study to gain a better molecular level understanding of the effects in the solid state of organic-mineral matter interactions relevant to both coal formation and processing. To satisfy the need for model compounds that remain nonvolatile solids at temperatures ranging to 450 C, model compounds are employed that are chemically bound to the surface of a fumed silica (Si-O-C{sub aryl}linkage). The organic structures currently under investigation are phenethyl phenyl ether (C{sub 6}H{sub 5}CH{sub 2}CH{sub 2}OC{sub 6}H{sub 5}) derivatives, which serve as models for {beta}-alkyl aryl ether units that are present in lignin and lignitic coals. The solid-state chemistry of these materials at 200--450 C in the presence of interdispersed acid catalysts such as small particle size silica-aluminas and montmorillonite clay will be reported. Initial focus will be on defining the potential impact of these interactions on coal pyrolysis and liquefaction.

Buchanan, A.C. III; Britt, P.F.; Struss, J.A. [Oak Ridge National Lab., TN (United States). Chemical and Analytical Sciences Div.

1995-07-01

307

Study of chemical reactions under the influence of ultrasound  

NASA Astrophysics Data System (ADS)

At Los Alamos, the author is interested in sonochemistry because there is potential for accelerating reactions involving the synthesis of certain nitro compounds and for reducing the possibility of decomposition under milder reaction conditions. The author has initiated the study of the nitration of 2,4-dihydro-3H-1,2,4-triazol-3-one with concentrated nitric acid under sonication. The preparation of 4,5-tetrazine, and oxidation of 3,6-diamino-1,2,4,5-tetrazine were also studied. Sonication reaction conditions and results of these reactions under ultrasound are discussed in detail.

Lee, Kien-Yin

308

New measurements of astrophysical (?,n) reaction rates using a quasi-thermal photon bath from bremsstrahlung  

NASA Astrophysics Data System (ADS)

The astrophysical reaction rates for the (?, n) photodisintegration reactions of 204Pb, 196,198,204Hg, and 197Au will be determined using a quasi-thermal photon bath which is produced from bremsstrahlung. Here we present the first part of this experiment. The reaction 197Au(?,n)196Au is discussed in detail because this reaction was measured in several experiments using different experimental techniques. .

Vogt, K.; Babilon, M.; Bayer, W.; Denefleh, K.; Enders, J.; Galaviz, D.; Hartmann, T.; Hutter, C.; Mohr, P.; Volz, S.; Zilges, A.

2001-04-01

309

Modeling of forced flow/thermal gradient chemical vapor infiltration  

SciTech Connect

The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by some to be unsuitable for such components. The major concern Is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification. A one-dimensional process model, described in a previous interim report, has demonstrated good agreement with experimental results in predicting overall densification time and density uniformity during processing and the effect of various fiber architectures and operating parameters on these process issues. This model is fundamentally unsuitable for more complex geometries, however, and extension to two- and three-dimensions is necessary. This interim report summarizes our progress since the previous interim report toward development of a ``finite volume`` model for FCVI.

Starr, T.L.; Smith, A.W. [Oak Ridge National Lab., TN (United States)

1992-09-01

310

Modeling of forced flow/thermal gradient chemical vapor infiltration  

SciTech Connect

The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by some to be unsuitable for such components. The major concern Is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification. A one-dimensional process model, described in a previous interim report, has demonstrated good agreement with experimental results in predicting overall densification time and density uniformity during processing and the effect of various fiber architectures and operating parameters on these process issues. This model is fundamentally unsuitable for more complex geometries, however, and extension to two- and three-dimensions is necessary. This interim report summarizes our progress since the previous interim report toward development of a finite volume'' model for FCVI.

Starr, T.L.; Smith, A.W. (Oak Ridge National Lab., TN (United States))

1992-09-01

311

Chemical and microstructural characterization of thermally grown alumina scales  

SciTech Connect

An experimental program has been initiated to evaluate the chemical, microstructural, and mechanical integrity of thermally grown oxide scales to establish requirements for improved corrosion performance in terms of composition, structure, and properties. Iron aluminides of several compositions were selected for the study. Oxidation studies were conducted in air and oxygen environments at 1000{degrees}C. The results showed that the scaling kinetics followed a parabolic rate law but that the rates in early stages of oxidation were significantly greater than in later stages; the difference could be attributed to the presence of fast-growing transient iron oxides in the layer during the early stages. Further, scale failure occurred via gross spallation, scale cracking, and nodule formation and was influenced by alloy composition. Auger electron spectroscopy of Ar-exposed specimens of ternary Fe-Cr-Al alloy showed sulfur on the gas/scale side of the interface; the sulfur decreased as the exposure time increased. Raman spectroscopy and ruby fluorescence were used to examine the scale development as a function of oxidation temperature. Ruby-line shift is used to examine phase transformations in alumina and to calculate compressive strains in thermally grown scales.

Natesan, K.; Richier, C.; Veal, B.W. [and others

1995-09-01

312

Vicher: A Virtual Reality Based Educational Module for Chemical Reaction Engineering.  

ERIC Educational Resources Information Center

A virtual reality application for undergraduate chemical kinetics and reactor design education, Vicher (Virtual Chemical Reaction Model) was originally designed to simulate a portion of a modern chemical plant. Vicher now consists of two programs: Vicher I that models catalyst deactivation and Vicher II that models nonisothermal effects in…

Bell, John T.; Fogler, H. Scott

1996-01-01

313

Numerical simulation of the thermal-gradient chemical vapor infiltration process for production of fiber-reinforced ceramic composite  

Microsoft Academic Search

A numerical model was developed in order to describe the thermal-gradient chemical vapor infiltration (CVI) for the production of SiCW\\/Al2O3 composite. The proposed model considered reaction, diffusion and deposition of alumina within the porous preform. The cubic array of disconnected cylinders model was proposed in order to represent the porous structure of the preform and the composite. The experimental results

Teruoki Tago; Motoaki Kawase; Yoshiaki Ikuta; Kenji Hashimoto

2001-01-01

314

Kinetic energy release in thermal ion–molecule reactions: The Nb2+–(benzene) single charge–transfer reaction  

Microsoft Academic Search

We have adapted the techniques originally developed to measure ion kinetic energies in ion cyclotron resonance (ICR) spectrometry to study the single charge–transfer reaction of Nb2+ with benzene under thermal conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The partitioning of reaction exothermicity among the internal and translational modes available is consistent with a long-distance electron-transfer mechanism,

James R. Gorda; Ben S. Freiser; Steven W. Buckner

1991-01-01

315

Kinetic energy release in thermal ion-molecule reactions: The Nb2 + -(benzene) single charge-transfer reaction  

Microsoft Academic Search

We have adapted the techniques originally developed to measure ion kinetic energies in ion cyclotron resonance (ICR) spectrometry to study the single charge--transfer reaction of Nb{sup 2+} with benzene under thermal conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The partitioning of reaction exothermicity among the internal and translational modes available is consistent with a long-distance electron-transfer

James R. Gord; Ben S. Freiser; Steven W. Buckner

1991-01-01

316

Chemical oxygen-iodine laser (COIL) thermal management  

NASA Astrophysics Data System (ADS)

The chemical oxygen-iodine laser (COIL) has been studied at the Phillips Laboratory since its invention in 1978. One of the most difficult challenges in COIL technology is to produce constant power for more than a few seconds; an essential feature for most applications. The key to developing a laser with these operational characteristics is management of the heat released during the production of singlet delta oxygen. Approximately 10 joules is deposited into the singlet delta oxygen generator (SOG) for every joule extracted as laser power. A recent test series demonstrated run times of 120 seconds at 9 kW by controlling the SOG reaction temperature with a flowing aqueous solution of cold hydroperoxide (BHP). This method of managing the energy released is quite effective but requires a large reservoir of cold BHP.

Truesdell, Keith A.; Helms, Charles A.; Longergan, Thomas; Wisniewski, Charles F.; Scott, Joseph E.; Healey, Keith P.

1995-03-01

317

Chemical reactions on metal oxide surfaces investigated by vibrational spectroscopy  

Microsoft Academic Search

The most successful method to unravel the microscopic mechanisms governing reactions in heterogeneous catalysis is the “surface science” approach which is based on well-controlled studies on model catalysts (usually single crystal surfaces) under ultrahigh vacuum (UHV) conditions [G. Ertl, Angew. Chem. 47 (2008) 3524]. In this review our recent vibrational spectroscopic studies on selected model reactions at various single-crystalline metal

Yuemin Wang; Christof Wöll

2009-01-01

318

A kinetic mechanism inducing oscillations in simple chemical reactions networks.  

PubMed

It is known that a kinetic reaction network in which one or more secondary substrates are acting as cofactors may exhibit an oscillatory behavior. The aim of this work is to provide a description of the functional form of such a cofactor action guaranteeing the onset of oscillations in sufficiently simple reaction networks. PMID:20462291

Coatleven, Julien; Altafini, Claudio

2010-04-01

319

CHEMICAL REACTIONS OF AQUATIC HUMIC MATERIALS WITH SELECTED OXIDANTS  

EPA Science Inventory

A study was conducted to identify the specific organic reaction products of natural aquatic humic materials with selected oxidants (KMnO4, HOCl, Cl02, O3 and monochloramine). Reaction products were identified by GC/MS after solvent extraction and derivatization. The two most reac...

320

Chemical Reactions of Aquatic Humic Materials with Selected Oxidants.  

National Technical Information Service (NTIS)

A study was conducted to identify the specific organic reaction products of natural aquatic humic materials with selected oxidants (KMnO4, HOCl, Cl02, O3 and monochloramine). Reaction products were identified by GC/MS after solvent extraction and derivati...

A. A. Stevens D. S. Millington J. D. Johnson R. F. Christman

1983-01-01

321

Interdiffusion reaction in the CrN interlayer in the NiCrAlY\\/CrN\\/DSM11 system during thermal treatment  

Microsoft Academic Search

During thermal treatment, a series of chemical reactions took place in the CrN interlayer in the NiCrAlY\\/CrN\\/DSM11 system. The CrN phase in the interlayer was first transformed to intermediate AlN and Cr2N phases during vacuum heat treatment, and thereafter both changed to TiN phase after thermal exposure. The formation of TiN is beneficial to the suppression of elemental interdiffusion. With

W. Z. Li; Q. M. Wang; J. Gong; C. Sun; X. Jiang

2009-01-01

322

Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.  

SciTech Connect

This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2009-08-01

323

Study of chemical reactions under the influence of ultrasound  

SciTech Connect

At Los Alamos the author is interested in sonochemistry because there is potential for accelerating reactions involving the synthesis of certain nitro compounds and for reducing the possibility of decomposition under milder reaction conditions. The author has initiated the study of the nitration of 2,4-dihydro-3H-1,2,4-triazol-3-one with concentrated nitric acid under sonication. The preparation of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine, and oxidation of 3,6-diamino-1,2,4,5-tetrazine were also studied. Sonication reaction conditions and results of these reactions under ultrasound are discussed in detail.

Lee, Kien-Yin

1993-07-01

324

Study of chemical reactions under the influence of ultrasound  

SciTech Connect

At Los Alamos the author is interested in sonochemistry because there is potential for accelerating reactions involving the synthesis of certain nitro compounds and for reducing the possibility of decomposition under milder reaction conditions. The author has initiated the study of the nitration of 2,4-dihydro-3H-1,2,4-triazol-3-one with concentrated nitric acid under sonication. The preparation of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine, and oxidation of 3,6-diamino-1,2,4,5-tetrazine were also studied. Sonication reaction conditions and results of these reactions under ultrasound are discussed in detail.

Lee, Kien-Yin.

1993-01-01

325

Lagrangian simulation of mixing-controlled chemical reactions  

NASA Astrophysics Data System (ADS)

A Lagrangian framework is developed to simulate the mixing-limited bimolecular second-order reactions in laboratory-scale porous media. The core is to define the interaction radius of reactant molecule, which controls the probability of reactions and is affected by the property of the medium, reactants and fluids. The simulated particle dynamics is checked against the kinetics for both diffusion-controlled and well-mixed reactions. The influence of anomalous transport on mixing and hence reaction is also evaluated, where both the space and time fractional-derivative models are considered. Applicability of the simulator is further tested by simulating the breakthrough curves and snapshots for different products observed in previous laboratory experiments.

Zhang, Y.

2010-12-01

326

Thermally Stable Nanocatalyst for High Temperature Reactions: Pt-Mesoporous Silica Core-Shell Nanoparticles  

SciTech Connect

Recent advances in colloidal synthesis enabled the precise control of size, shape and composition of catalytic metal nanoparticles, allowing their use as model catalysts for systematic investigations of the atomic-scale properties affecting catalytic activity and selectivity. The organic capping agents stabilizing colloidal nanoparticles, however, often limit their application in high-temperature catalytic reactions. Here we report the design of a high-temperature stable model catalytic system that consists of Pt metal core coated with a mesoporous silica shell (Pt{at}mSiO{sub 2}). While inorganic silica shells encaged the Pt cores up to 750 C in air, the mesopores directly accessible to Pt cores made the Pt{at}mSiO{sub 2} nanoparticles as catalytically active as bare Pt metal for ethylene hydrogenation and CO oxidation. The high thermal stability of Pt{at}mSiO{sub 2} nanoparticles permitted high-temperature CO oxidation studies, including ignition behavior, which was not possible for bare Pt nanoparticles because of their deformation or aggregation. The results suggest that the Pt{at}mSiO{sub 2} nanoparticles are excellent nanocatalytic systems for high-temperature catalytic reactions or surface chemical processes, and the design concept employed in the Pt{at}mSiO{sub 2} core-shell catalyst can be extended to other metal-metal oxide compositions.

Joo, Sang Hoon; Park, J.Y.; Tsung, C.-K.; Yamada, Y.; Yang, P.; Somorjai, G.A.

2008-10-25

327

Thermally stable Pt/mesoporous silica core-shell nanocatalysts for high-temperature reactions  

NASA Astrophysics Data System (ADS)

Recent advances in colloidal synthesis enabled the precise control of the size, shape and composition of catalytic metal nanoparticles, enabling their use as model catalysts for systematic investigations of the atomic-scale properties affecting catalytic activity and selectivity. The organic capping agents stabilizing colloidal nanoparticles, however, often limit their application in high-temperature catalytic reactions. Here, we report the design of a high-temperature-stable model catalytic system that consists of a Pt metal core coated with a mesoporous silica shell (Pt@mSiO2). Inorganic silica shells encaged the Pt cores up to 750?C in air and the mesopores providing direct access to the Pt core made the Pt@mSiO2 nanoparticles as catalytically active as bare Pt metal for ethylene hydrogenation and CO oxidation. The high thermal stability of Pt@mSiO2 nanoparticles enabled high-temperature CO oxidation studies, including ignition behaviour, which was not possible for bare Pt nanoparticles because of their deformation or aggregation. The results suggest that the Pt@mSiO2 nanoparticles are excellent nanocatalytic systems for high-temperature catalytic reactions or surface chemical processes, and the design concept used in the Pt@mSiO2 core-shell catalyst can be extended to other metal/metal oxide compositions.

Joo, Sang Hoon; Park, Jeong Young; Tsung, Chia-Kuang; Yamada, Yusuke; Yang, Peidong; Somorjai, Gabor A.

2009-02-01

328

Light hydrocarbons in hydrothermal and magmatic fumaroles: hints of catalytic and thermal reactions  

NASA Astrophysics Data System (ADS)

Volcanic gaseous mixtures emitted from active volcanoes frequently show variable amounts of saturated (alkanes), unsaturated (alkenes) and aromatic volatile hydrocarbons. Three major patterns of distributions can be recognized, apparently related to the chemical-physical environment of formation of the gas exhalations: alkane-rich, low-temperature gas emissions from recently active volcanic areas; aromatic-rich hydrothermal manifestations; and alkene-rich, ‘magmatic’ fumaroles on active volcanoes. Thermodynamic data, together with theoretical and practical findings from the petroleum industry, point to two main types of reactions occurring in these volcanic environments: cracking and reforming. Cracking processes, mainly caused by thermal effects, occur when hydrocarbon-bearing hydrothermal fluids enter and mix with a hot and dry, rapidly rising magmatic gas phase. The most probable products are light alkenes with carbon numbers decreasing with increasing reaction temperatures. The presence of aromatic species in hydrothermal fluids can be linked to reforming processes, catalysed by several possible agents, such as smectites and zeolites, generally present in the hydrothermally altered volcanic terranes, and facilitated by long residence times in a hydrothermal envelope.

Capaccioni, Bruno; Martini, Marino; Mangani, Filippo

1995-02-01

329

A Petri net approach to the study of persistence in chemical reaction networks.  

PubMed

Persistence is the property, for differential equations in R(n), that solutions starting in the positive orthant do not approach the boundary of the orthant. For chemical reactions and population models, this translates into the non-extinction property: provided that every species is present at the start of the reaction, no species will tend to be eliminated in the course of the reaction. This paper provides checkable conditions for persistence of chemical species in reaction networks, using concepts and tools from Petri net theory, and verifies these conditions on various systems which arise in the modeling of cell signaling pathways. PMID:17869313

Angeli, David; De Leenheer, Patrick; Sontag, Eduardo D

2007-12-01

330

Thermal-Energy Negative Ion-Molecule Reactions.  

National Technical Information Service (NTIS)

Some results of quantitative studies of negative ion reactions with neutrals by the recently developed flowing afterglow technique have been discussed. The versatility of the method allows a wide variety of reactants to be investigated. The laboratory stu...

E. E. Ferguson

1970-01-01

331

Thermal, chemical, and mechanical response of rigid polyurethane foam  

Microsoft Academic Search

Rigid polyurethane foams are frequently used as encapsulants to isolate and support thermally sensitive components within weapon systems. When exposed to abnormal thermal environments, such as fire, the polyurethane foam decomposes to form products having a wide distribution of molecular weights and can dominate the overall thermal response of the system. Mechanical response of the decomposing foam, such as thermal

1997-01-01

332

Ab initio chemical kinetics for the HCCO + OH reaction  

NASA Astrophysics Data System (ADS)

The mechanism for the reaction of HCCO and OH has been investigated at different high-levels of theory. The reaction was found to occur on singlet and triplet potential energy surfaces with multiple accessible paths. Rate constants predicted by variational RRKM/ME calculations show that the reaction on both surfaces occurs primarily by barrierless OH attack at both C atoms producing excited intermediates which fragment to produce predominantly CO and 1,3HCOH with kS = 3.12 × 10-8T-0.59exp[-73.0/T] and kT = 6.29 × 10-11T0.13exp[108/T] cm3 molecule-1 s-1 at T = 300-2000 K, independent of pressure at P < 76 000 Torr.

Mai, Tam V.-T.; Raghunath, P.; Le, Xuan T.; Huynh, Lam K.; Nam, Pham-Cam; Lin, M. C.

2014-01-01

333

Energy storage and transport by reversible chemical reactions  

NASA Astrophysics Data System (ADS)

Reversible thermochemical reactions are one of the possibilities to store and transport high temperature heat (800 K up to 1300 K). There are open cycles and closed cycles. Some reversible systems are described, as the SO2-SO3 system. A typical example of open cycle is the reaction for water decomposition. Results of a pilot plant to verify the decomposition of sulfuric acid are described; the technological feasibility of this method for hydrogen production is shown. The possibility to use other high temperature sources, as solar energy is discussed.

Beghi, G.

334

Chemical reaction and equilibration mechanisms in detonation waves  

SciTech Connect

Experimental and theoretical evidence for the nonequilibrium Zeldovich-von Neumann-Doring (NEZND) theory of self-sustaining detonation is presented. High density, high temperature transition state theory is used to calculate unimolecular reaction rate constants for the initial decomposition of gaseous norbornene, liquid nitromethane, and solid, single crystal pentaerythritol tetranitrate as functions of shock temperature. The calculated rate constants are compared to those derived from experimental induction time measurements at various shock and detonation states. Uncertainties in the calculated shock and von Neumann spike temperatures are the main drawbacks to calculating these reaction rates. Nanosecond measurements of the shock temperatures of unreacted explosives are necessary to reduce these uncertainties.

Tarver, C. M., LLNL

1997-07-01

335

The hydroperoxyl radical in atmospheric chemical dynamics - Reaction with carbon monoxide.  

NASA Technical Reports Server (NTRS)

Discussion of laboratory measurements which indicate that the reaction of the thermalized HO(2) radical with CO is exceedingly slow and that this reaction should not, therefore, be of any significance in atmospheric chemistry. The large discrepancy between the new results and data obtained earlier by Westenberg and de Haas (1972) is explained in terms of the reacting hydroperoxyl radical being in a non-Boltzmann distribution in the former study. It appears that the most important reactions of thermalized HO(2) in the atmosphere are those involving the trace gases of NO and sulfur dioxide.

Davis, D. D.; Payne, W. A.; Stief, L. J.

1973-01-01

336

LSENS, a general chemical kinetics and sensitivity analysis code for gas-phase reactions: User's guide  

NASA Technical Reports Server (NTRS)

A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS, are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include static system, steady, one-dimensional, inviscid flow, shock initiated reaction, and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method, which works efficiently for the extremes of very fast and very slow reaction, is used for solving the 'stiff' differential equation systems that arise in chemical kinetics. For static reactions, sensitivity coefficients of all dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters can be computed. This paper presents descriptions of the code and its usage, and includes several illustrative example problems.

Radhakrishnan, Krishnan; Bittker, David A.

1993-01-01

337

A new approximate method for the stochastic simulation of chemical systems: the representative reaction approach.  

PubMed

We have developed two new approximate methods for stochastically simulating chemical systems. The methods are based on the idea of representing all the reactions in the chemical system by a single reaction, i.e., by the "representative reaction approach" (RRA). Discussed in the article are the concepts underlying the new methods along with flowchart with all the steps required for their implementation. It is shown that the two RRA methods {with the reaction 2A ?> B as the representative reaction (RR)} perform creditably with regard to accuracy and computational efficiency, in comparison to the exact stochastic simulation algorithm (SSA) developed by Gillespie and are able to successfully reproduce at least the first two moments of the probability distribution of each species in the systems studied. As such, the RRA methods represent a promising new approach for stochastically simulating chemical systems. PMID:22108838

Kadam, Shantanu; Vanka, Kumar

2012-01-30

338

An approximate Riemann solver for thermal and chemical nonequilibrium flows  

NASA Technical Reports Server (NTRS)

Among the many methods available for the determination of inviscid fluxes across a surface of discontinuity, the flux-difference-splitting technique that employs Roe-averaged variables has been used extensively by the CFD community because of its simplicity and its ability to capture shocks exactly. This method, originally developed for perfect gas flows, has since been extended to equilibrium as well as nonequilibrium flows. Determination of the Roe-averaged variables for the case of a perfect gas flow is a simple task; however, for thermal and chemical nonequilibrium flows, some of the variables are not uniquely defined. Methods available in the literature to determine these variables seem to lack sound bases. The present paper describes a simple, yet accurate, method to determine all the variables for nonequilibrium flows in the Roe-average state. The basis for this method is the requirement that the Roe-averaged variables form a consistent set of thermodynamic variables. The present method satisfies the requirement that the square of the speed of sound be positive.

Prabhu, Ramadas K.

1994-01-01

339

ACTIVE MEDIA: Chemical hydrogen fluoride laser on a thermal chain explosion initiated by resonance IR radiation  

NASA Astrophysics Data System (ADS)

Characteristics of a chemical H2—F2 laser initiated by resonant vibrational excitation of HF molecules upon the development of a thermal chain branching reaction are theoretically studied. After the addition of N2F2 or F2SO3 molecules with partial pressure of 20 Torr to the HF: H2: F2: O2: He = 0.5: 76: 228: 23: 100-Torr mixture, a specific output energy of a hydrogen fluoride laser initiated by a 2-?s pulse from an H2—F2 laser with the energy density of 0.01-10 J cm-2 amounted to 30-60 J litre-1, exceeding the specific initiation energy by a factor of 100 —4000.

Igoshin, Valerii I.; Pichugin, S. Yu; Stukalina, I. L.

2000-07-01

340

Theoretical Studies of Chemical Reactions following Electronic Excitation  

NASA Technical Reports Server (NTRS)

The use of multi-configurational wave functions is demonstrated for several processes: tautomerization reactions in the ground and excited states of the DNA base adenine, dissociation of glycine molecule after electronic excitation, and decomposition/deformation of novel rare gas molecules HRgF. These processes involve bond brealung/formation and require multi-configurational approaches that include dynamic correlation.

Chaban, Galina M.

2003-01-01

341

Enhanced Oxidation and Solvolysis Reactions in Chemically Inert Microheterogeneous Systems.  

National Technical Information Service (NTIS)

In the second year of contract, the following parts of the original project have been accomplished: 1. Model calculations of the kinetics of the decomposition of H2O2 in H2O and fitting of the model of sequence and rates of reactions to the experimental r...

A. M. Braun

1987-01-01

342

Theoretical Chemical Dynamics Studies of Elementary Combustion Reactions.  

National Technical Information Service (NTIS)

The objective of this research was to develop and apply methods for more accurate predictions of reaction rates based on high-level quantum chemistry. We have developed and applied efficient, robust methods for fitting global ab initio potential energy su...

D. L. Thompson

2009-01-01

343

Chemical Principles Revisited. Redox Reactions and the Electropotential Axis.  

ERIC Educational Resources Information Center

This paper suggests a nontraditional pedagogic approach to the subject of redox reactions and electrode potentials suitable for freshman chemistry. Presented is a method for the representation of galvanic cells without the introduction of the symbology and notation of conventional cell diagrams. (CW)

Vella, Alfred J.

1990-01-01

344

Transient modeling of chemical vapor infiltration of methane using multi-step reaction and deposition models  

Microsoft Academic Search

Based on multi-step reaction and deposition models including the hydrogen inhibition model of pyrocarbon growth, transient 2D simulations of chemical vapor infiltration of methane were carried out by a finite element method (FEM) coupling the mass transfer (by convection and diffusion) and the evolutive surface area model with gas-phase and surface chemical reactions. The continuous infiltration, pyrolysis and deposition of

Aijun Li; Olaf Deutschmann

2007-01-01

345

Chemical reactions in protoplanetary accretion disks. IV. Multicomponent dust mixture  

Microsoft Academic Search

We consider the different major components of the dust mixture in protostellar accretion disks and the development of their structure and chemical composition as the disk material slowly migrates inwards during the viscous phase of the disk evolution. It is shown that the amorphous structure of the dust grains from the parent molecular cloud is converted by annealing at about

H.-P. Gail

1998-01-01

346

Chemical reactions in protoplanetary accretion disks IV. Multicomponent dust mixture  

Microsoft Academic Search

We consider the different major components of the dust mixture in protostellar accretion disks and the development of their structure and chemical composition as the disk material slowly migrates inwards during the viscous phase of the disk evolution. It is shown that the amorphous structure of the dust grains from the parent molecular cloud is converted by anneal- ing at

H.-P. Gail

347

Single-molecule chemical reactions on DNA origami  

Microsoft Academic Search

DNA nanotechnology and particularly DNA origami, in which long, single-stranded DNA molecules are folded into predetermined shapes, can be used to form complex self-assembled nanostructures. Although DNA itself has limited chemical, optical or electronic functionality, DNA nanostructures can serve as templates for building materials with new functional properties. Relatively large nanocomponents such as nanoparticles and biomolecules can also be integrated

Niels V. Voigt; Thomas Tørring; Alexandru Rotaru; Mikkel F. Jacobsen; Jens B. Ravnsbæk; Ramesh Subramani; Wael Mamdouh; Jørgen Kjems; Andriy Mokhir; Flemming Besenbacher; Kurt Vesterager Gothelf

2010-01-01

348

Supercritical fluid phase separations induced by chemical reactions.  

National Technical Information Service (NTIS)

Our statistical mechanical studies predict that a chemically reactive system containing species composed of C, H, N, O atoms can exhibit a phase separation into a N2-rich and a N2-poor phase. This paper is concerned with the effect of the fluid phase sepa...

F. H. Ree, J. A. Viecelli, M. van Thiel

1997-01-01

349

Chemical-biological reactions common to teratogenesis and mutagenesis  

PubMed Central

Cytotoxic chemicals have in common the ability to act specifically on cells in cycle. Bacteria are more sensitive in the exponential growth phase than when growing slowly in media. Similar observations have been made on a variety of systems ranging from bacteria, yeast, higher plants and invertebrates to vertebrates including primates. The embryo and fetus are highly susceptible to cytotoxic agents because they have continuous groups of cells in the growth phase. Acutely toxic doses may cause cellular death and result in developmental defects or fetal death. Cytotoxic agents can be grouped as alkylating agents, electrophilic reactants, antimetabolites, intercalating agents, amino acid antagonists, spindle poisons, and an additional group of chemicals which covalently bind to DNA. These cytotoxic groups of chemicals may also be mutagenic by interacting with DNA to produce changes in sequences of nucleotides resulting in heritable defects either in a somatic cell line or in a germinal cell line. The mechanisms of chemical-induced teratogenicity and mutagenicity are similar. This commonality is further discussed in the text.

Harbison, Raymond D.

1978-01-01

350

X-ray Microspectroscopy and Chemical Reactions in Soil Microsites  

SciTech Connect

Soils provide long-term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid-phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earth's surface. In the context of historical developments in soil analytical techniques, we describe applications of bulk-sample and spatially resolved synchrotron X-ray absorption spectroscopy (XAS) for characterizing chemical species of contaminants in soils, and for determining the uniqueness of trace-element reactivity in different soil microsites. Spatially resolved X-ray techniques provide opportunities for following chemical changes within soil microsites that serve as highly localized chemical micro- (or nano-)reactors of unique composition. An example of this microreactor concept is shown for micro-X-ray absorption near edge structure analysis of metal sulfide oxidation in a contaminated soil. One research challenge is to use information and principles developed from microscale soil chemistry for predicting macroscale and field-scale behavior of soil contaminants.

D Hesterberg; M Duff; J Dixon; M Vepraskas

2011-12-31

351

Modeling the Thermal Destruction of Chemical Warfare Agents Bound on Building Materials  

Microsoft Academic Search

In the event of a terrorist attack with chemical warfare agents (CWAs), large quantities of materials, both indoor and outdoor, may be treated with thermal incineration during the site remediation process. CWAs in general are not particularly thermally stable and decompose readily in a high temperature combustion environment. Potential difficulties exist, however, in thermally processing waste materials from a post-CWA

P. Lemieux; J. Wood

352

Product distributions for some thermal energy charge transfer reactions of rare gas ions  

NASA Technical Reports Server (NTRS)

Ion cyclotron resonance methods were used to measure the product distributions for thermal-energy charge-transfer reactions of He(+), Ne(+), and Ar(+) ions with N2, O2, CO, NO, CO2, and N2O. Except for the He(+)-N2 reaction, no molecular ions were formed by thermal-energy charge transfer from He(+) and Ne(+) with these target molecules. The propensity for dissociative ionization channels in these highly exothermic charge-transfer reactions at thermal energies contrasts with the propensity for formation of parent molecular ions observed in photoionization experiments and in high-energy charge-transfer processes. This difference is explained in terms of more stringent requirements for energy resonance and favorable Franck-Condon factors at thermal ion velocities.

Anicich, V. G.; Laudenslager, J. B.; Huntress, W. T., Jr.; Futrell, J. H.

1977-01-01

353

Experimental simulation of chemical reactions between ZDDP tribofilms and steel surfaces during friction processes  

Microsoft Academic Search

Friction tests are performed in a controlled environment (Ultra High Vacuum), between steel surfaces and a ZDDP tribofilm\\u000a at different contact severities. According to AES analyses, evidence of chemical reactions activated by friction is given.\\u000a The reaction of the ZDDP tribofilm with the native iron oxide could partially explain its antiwear behavior.

C. Minfray; T. Le Mogne; A. A. Lubrecht; J.-M. Martin

2006-01-01

354

Everyday Chemical Reactions: A Writing Assignment to Promote Synthesis of Concepts and Relevance in Chemistry  

Microsoft Academic Search

Capturing the interest of students in required chemistry courses is a problem for which many solutions have been proposed and described. The solution proposed here is the use of a writing assignment on everyday chemical reactions. Students select their own organic reaction and apply concepts learned throughout the semester to understanding it. The assignment requires the synthesis of many concepts

Abby L. Parrill

2000-01-01

355

Thermal, Mechanical and Chemical Analysis for VELOX -Verification Experiments for Lunar Oxygen Production  

NASA Astrophysics Data System (ADS)

One major aspect for the development of a long-term human presence on the moon will be sustainability and autonomy of any kind of a permanent base. Important resources, such as breathable air and water for the survival of the crew on the lunar surface will have to be extracted in-situ from the lunar regolith, the major resource on the Moon, which covers the first meter of the lunar surface and contains about 45 At the DLR Bremen we are interested in a compact and flexible lab experimenting facility, which shall demonstrate the feasibility of this process by extracting oxygen out of lunar Regolith, respectively soil simulants and certain minerals in the laboratory case. For this purpose, we have investigated important boundary conditions such as temperatures during the process, chemical reaction characteristics and material properties for the buildup of the facility and established basic requirements which shall be analyzed within this paper. These requirements have been used for the concept development and outline of the facility, which is currently under construction and will be subject to initial tests in the near future. This paper will focus mainly on the theoretical aspects of the facility development. Great effort has been put into the thermal and mechanical outline and pre-analysis of components and the system in a whole. Basic aspects that have been investigated are: 1. Selection of suitable materials for the furnace chamber configuration to provide a high-temperature capable operating mode. 2. Theoretical heat transfer analysis of the designed furnace chamber assembly with subsequent validation with the aid of measured values of the constructed demonstration plant. 3. Description of chemical conversion processes for Hydrogen reduction of Lunar Regolith with corresponding analysis of thermal and reaction times under different boundary conditions. 4. Investigation of the high-temperature mechanical behavior of the constructed furnace chamber with regard to thermal stability and especially to the hermetically sealed reactor due to internal Hydrogen atmosphere. In the end, we will give a first glimpse into the development of the test setup and first test results on the way to a superior test set-up and infrastructure with pre-and post-processing units such as feeding and extraction units and analysis of reaction products.

Lange, Caroline; Ksenik, Eugen; Braukhane, Andy; Richter, Lutz

356

Design of potential energy surfaces for chemical reactions  

SciTech Connect

The design of potential energy surfaces for two systems is considered. The first study presented is for the abstraction reaction F + H/sub 2/ ..-->.. HF + H and the exchange reaction H' + FH ..-->.. FH' + H and their related isotopic analogs. Several surfaces are proposed which incorporate both experimental and ab initio information. The new surfaces are of the form of the extended London-Eyring-Polanyi method but with angle-and distance-dependent Sato parameters and an added three-center term. The first new surface is fit using empirical data in the entrance channel but only ab initio data in the exit channel. Preliminary studies on the role of dynamical bottlenecks in the exit-channel are used to locate the crucial regions of the surface where accurate calculations are needed. A second surface is a slightly modified version of the first in which experimental information is used to recalibrate the abstraction exit channel. Two additional surfaces presented here are designed to test the effect of a higher entrance-channel saddle point on the dynamics. A study of potential energy surfaces for the reaction CH/sub 3/ + H/sub 2/ ..-->.. CH/sub 4/ + H is also presented. This includes a thorough analysis of existing surfaces and dynamics calculations using slightly modified forms of these surfaces. Two new surfaces are calibrated using both ab initio and experimental data. Rate constants, activation energies, and kinetic isotope effects calculated using the new surfaces are compared to experiment.

Steckler, R.

1986-01-01

357

On the feasibility of chemical reactions in the presence of siloxane-based surfactants  

Microsoft Academic Search

Siloxane-containing surfactants have been tested as stabilizers for the preparation of polymer nanoparticles by three types\\u000a of chemical reactions. Two crosslinking reactions were used to obtain silicone elastomers particles: one involved HO-terminated\\u000a polydimethylsiloxane and tetraethoxysilane, while the other one was a crosslinking via polyhydrosilylation. The third reaction\\u000a was a linear polycondensation between a diamine and a siloxane dialdehyde. The monitoring

Carmen Racles; Maria Cazacu; Gabriela Hitruc; Thierry Hamaide

2009-01-01

358

Thermal oxidative degradation reactions of linear perfluoroalky lethers  

NASA Technical Reports Server (NTRS)

Thermal and thermal oxidative stability studies were performed on linear perfluoro alkyl ether fluids. The effect on degradation by metal catalysts and degradation inhibitors are reported. The liner perfluoro alkylethers are inherently unstable at 316 C in an oxidizing atmosphere. The metal catalysts greatly increased the rate of degradation in oxidizing atmospheres. In the presence of these metals in an oxidizing atmosphere, the degradation inhibitors were highly effective in arresting degradation at 288 C. However, the inhibitors had only limited effectiveness at 316 C. The metals promote degradation by chain scission. Based on elemental analysis and oxygen consumption data, the linear perfluoro alkylether fluids have a structural arrangement based on difluoroformyl and tetrafluoroethylene oxide units, with the former predominating.

Jones, W. R., Jr.; Paciorek, K. J. L.; Ito, T. I.; Kratzer, R. H.

1982-01-01

359

Numerical modeling of coupled thermal chemical reactive transport: simulation of a heat storage system  

NASA Astrophysics Data System (ADS)

As a carbon-free energy supply technology, the operation time and final energy output of thermal solar power plants can be greatly extended if efficient thermal storage systems are applied. One of the proposed design of such system is to utilize reversible thermochemical reactions and its embedded reaction enthalpy, e.g. the Ca(OH)2/CaO hydration circle, in a fixed-bed gas-solid reactor (Schaube et al. 2011) The modeling of such a storage system involves multiple strongly-coupled physical and chemical processes. Seepage velocity is calculated by the nonlinear Forchheimer law. Gas phase density and viscosity are temperature, pressure and composition dependent. Also, heat transfer between gas and solid phases is largely influenced by the exothermal heat produced by the hydration of calcium oxide. Numerical solution of four governing PDEs include the mass balance, reactive transport, heat balance equations for gas and solid phases, which are implemented into the open source scientific software OpenGeoSys in a monolithic way. Based on it, a 2D numerical model, considering the boundary heat loss of the system, was set up to simulate the energy-storage and release circle. The high performance computing techniques were employed in two stages. First, the dynamic behavior of the heat storage system is simulated on a parallel platform. Second, a large number of processors are employed to perform sensitivity analysis, whereas the reaction rates and efficiency factor of heat transfer are parameterized so that the measured and simulated temperature profile fit with each other. The model showed that heat transfer coefficient between solid and gas phase, grain size of the filling material will influence the final performance greatly. By varying these factors, the calibrated model will be further applied to optimize the design of such energy storage system.

Shao, H.; Watanabe, N.; Singh, A. K.; Nagel, T.; Linder, M.; Woerner, A.; Kolditz, O.

2012-12-01

360

Site-selective reactions of imperfectly matched DNA with small chemical molecules: applications in mutation detection  

Microsoft Academic Search

The last decade has witnessed many exciting scientific publications associated with site-selective reactions of small chemical molecules with imperfectly matched DNA. Typical examples are carbodiimide, hydroxylamine, potassium permanganate, osmium tetroxide, chemical tagging probes, biotinylated, chemiluminescent and fluorescent probes, and all of them selectively react with imperfectly matched DNA. More recently, some therapeutic agents including DNA intercalating drugs and groove binders

Chinh T Bui; Kylee Rees; Andreana Lambrinakos; Abdulkerim Bedir; Richard G. H Cotton

2002-01-01

361

WORKSHOP ON STATUS OF TEST METHODS FOR ASSESSING POTENTIAL OF CHEMICALS TO INDUCE RESPIRATORY ALLERGIC REACTIONS  

EPA Science Inventory

Because of the association between allergy and asthma and the increasing incidence of morbidity and mortality due to asthma, there is growing concern over the potential of industrial chemicals to produce allergic reactions in the respiratory tract. Two classes of chemicals have b...

362

Indoor Volatile Organic Compounds and Chemical Sensitivity Reactions  

PubMed Central

Studies of unexplained symptoms observed in chemically sensitive subjects have increased the awareness of the relationship between neurological and immunological diseases due to exposure to volatile organic compounds (VOCs). However, there is no direct evidence that links exposure to low doses of VOCs and neurological and immunological dysfunction. We review animal model data to clarify the role of VOCs in neuroimmune interactions and discuss our recent studies that show a relationship between chronic exposure of C3H mice to low levels of formaldehyde and the induction of neural and immune dysfunction. We also consider the possible mechanisms by which VOC exposure can induce the symptoms presenting in patients with a multiple chemical sensitivity.

Win-Shwe, Tin-Tin; Arashidani, Keiichi; Kunugita, Naoki

2013-01-01

363

Influence of antioxidants on polyethylene chemical crosslinking reaction  

Microsoft Academic Search

The influence of antioxidants on the chemical crosslinking of crosslinked polyethylene (XLPE) was investigated. Experiments were conducted using XLPE specimens crosslinked at various temperatures with added phenolic, sulfur-type and amine-type antioxidants. Specimens were characterized by measuring the gel fraction and the content of crosslinking byproducts, acetophenone, cumyl alcohol and ?-methyl styrene. It was found that sulfur-type antioxidant has the strongest

Yasuo Sekii; Yuichi Idei; Kiyotaka Asakawa

2001-01-01

364

Chemical reactions for a deuteration network (Vastel+, 2012)  

NASA Astrophysics Data System (ADS)

The ground-state rotational ortho-D2H+(1,1,1-0,0,0) transition at 1476.6GHz in the prestellar core 16293E has been searched for with the Herschel/HIFI instrument, within the CHESS (Chemical HErschel Surveys of Star forming regions) Key Program. The line has not been detected at the 21mK.km/s level (3 sigma integrated line intensity). We used the ortho-H2D+ 110-111 transition and para-D2H+ 110-101 transition detected in this source to determine an upper limit on the ortho-to-para D2H+ ratio as well as the para-D2H+/ortho-H2D+ ratio from a non-LTE analysis. We then compared our chemical modeling with the observations in order to estimate the CO depletion as well as the H2 density and kinetic temperature at the position observed. The chemical network is provided in the kida.dat file. (1 data file).

Vastel, C.; Caselli, P.; Ceccarelli, C.; Bacmann, A.; Lis, D. C.; Caux, E.; Codella, C.; Beckwith, J. A.; Ridley, T.

2012-09-01

365

Thermal reactions of 2-iodoethanol on Cu(1 0 0)  

NASA Astrophysics Data System (ADS)

Temperature-programmed reaction/desorption, X-ray photoelectron spectroscopy, and reflection-absorption infrared spectroscopy have been employed to investigate the reactions of ICH 2CH 2OH on Cu(1 0 0) under ultrahigh-vacuum conditions. ICH 2CH 2OH can dissociate on Cu(1 0 0) at 100 K, forming a -CH 2CH 2OH surface intermediate. Density functional theory calculations predict that the -CH 2CH 2OH is most probably adsorbed on atop site. -CH 2CH 2OH on Cu(1 0 0) further decomposes to yield C 2H 4 below 270 K. No evidence shows the formation of -CH 2CH 2O- intermediate in the reactions of ICH 2CH 2OH on Cu(1 0 0) in contrast to the decomposition of BrCH 2CH 2OH on Cu(1 0 0) and ICH 2CH 2OH on Ag(1 1 1) and Ag(1 1 0), exhibiting the effects of carbon-halogen bonds and metal surfaces.

Liao, Yung-Hsuan; Chen, Chia-Yuan; Fu, Tao-Wei; Wang, Ching-Yung; Fan, Liang-Jen; Yang, Yaw-Wen; Lin, Jong-Liang

2006-01-01

366

Ultralocalized thermal reactions in subnanoliter droplets-in-air  

PubMed Central

Miniaturized laboratory-on-chip systems promise rapid, sensitive, and multiplexed detection of biological samples for medical diagnostics, drug discovery, and high-throughput screening. Within miniaturized laboratory-on-chips, static and dynamic droplets of fluids in different immiscible media have been used as individual vessels to perform biochemical reactions and confine the products. Approaches to perform localized heating of these individual subnanoliter droplets can allow for new applications that require parallel, time-, and space-multiplex reactions on a single integrated circuit. Our method positions droplets on an array of individual silicon microwave heaters on chip to precisely control the temperature of droplets-in-air, allowing us to perform biochemical reactions, including DNA melting and detection of single base mismatches. We also demonstrate that ssDNA probe molecules can be placed on heaters in solution, dried, and then rehydrated by ssDNA target molecules in droplets for hybridization and detection. This platform enables many applications in droplets including hybridization of low copy number DNA molecules, lysing of single cells, interrogation of ligand–receptor interactions, and rapid temperature cycling for amplification of DNA molecules.

Salm, Eric; Guevara, Carlos Duarte; Dak, Piyush; Dorvel, Brian Ross; Reddy, Bobby; Alam, Muhammad Ashraf; Bashir, Rashid

2013-01-01

367

The mineralogic evolution of the Martian surface through time: Implications from chemical reaction path modeling studies  

NASA Technical Reports Server (NTRS)

Chemical reaction path calculations were used to model the minerals that might have formed at or near the Martian surface as a result of volcano or meteorite impact driven hydrothermal systems; weathering at the Martian surface during an early warm, wet climate; and near-zero or sub-zero C brine-regolith reactions in the current cold climate. Although the chemical reaction path calculations carried out do not define the exact mineralogical evolution of the Martian surface over time, they do place valuable geochemical constraints on the types of minerals that formed from an aqueous phase under various surficial and geochemically complex conditions.

Plumlee, G. S.; Ridley, W. I.; Debraal, J. D.; Reed, M. H.

1993-01-01

368

Thermal and chemical evolution of The Geysers geothermal system, California  

SciTech Connect

Fluid inclusions and mineral assemblages provide a reward of the thermal and chemical changes that occurred during the evolution of The Geysers geothermal system. The data document the presence of an extensive liquid dominated geothermal system that developed in response to felsite intrusion and its evolution to a vapor-dominated regime. Temperatures within the early liquid-dominated system ranged from 175 C at a distance of 7200 feet from the felsite to more than 350 C near the contact while salinities varied from 5 equivalent weight percent NaCl (at a distance of 5500 feet) to more than 26 weight percent NaCl. As temperatures around the felsite declined, the liquid-dominated system collapsed upon itself. Downward migration of the low salinity waters resulted in dilution of the fluids present in regions now occupied by the caprock and normal vapor-dominated reservoir. In contrast, dilution was minor in rocks now hosting the high-temperature vapor-dominated reservoir. This suggests that low permeabilities are the primary reason for the development of the high-temperature reservoir. Boiling within the caprock produced late-stage veins of calcite and quartz. As the fluid boiled off, condensate was trapped as low salinity fluid inclusions. Within the main body of the reservoir, a liquid phase with salinities of up to 7 equivalent weight percent NaCl persisted to temperatures between 250 and 270 C. However, except for the presence of vapor-rich inclusions, little evidence of boiling within the reservoir rocks was preserved.

Moore, J.N.

1992-01-01

369

Rate-Controlled Constrained-Equilibrium Theory of Chemical Reactions  

NASA Astrophysics Data System (ADS)

The Rate-Controlled Constrained-Equilibrium (RCCE) method for simplifying the treatment of reactions in complex systems is summarized and the selection of constraints for both close-to and far-from equilibrium systems is discussed. Illustrative examples of RCCE calculations of carbon monoxide concentrations in the exhaust products of an internal combustion engine and ignition delays for methane-oxygen mixtures in a constant volume adiabatic chamber are given and compared with ``detailed'' calculations. The advantages of RCCE calculations over ``detailed'' calculations are discussed.

Keck, James C.

2008-08-01

370

Tracking chemical reactions on the surface of filamentous phage using mass spectrometry.  

PubMed

Chemical modification of phage libraries has allowed the in vitro evolution of ligands having properties not provided by natural polypeptides. The development of novel and more diverse chemical reactions on phage was hampered by the lack of analytical methods to efficiently monitor the reaction products on the more than 10?000 kDa large filamentous phage particles. Herein, we present a strategy to detect chemically modified peptides on phage based on enzymatic release of peptide from phage and mass spectrometry analysis. PMID:24291807

Chen, Shiyu; Touati, Jeremy; Heinis, Christian

2014-05-25

371

Kinetics of sulphuric alkylation reactions: study of two reaction steps and modelling using chemical families grouping.  

National Technical Information Service (NTIS)

Isobutane/olefins sulphuric alkylation is used in the petroleum industry to prepare fuels with high octane numbers. Although the alkylation reaction/process has been considered by numerous investigators, relatively few results have been published concerni...

L. E. Pizarro Borges

1995-01-01

372

Systematic trends in photonic reagent induced reactions in a homologous chemical family.  

PubMed

The growing use of ultrafast laser pulses to induce chemical reactions prompts consideration of these pulses as "photonic reagents" in analogy to chemical reagents. This work explores the prospect that photonic reagents may affect systematic trends in dissociative ionization reactions of a homologous family of halomethanes, much as systematic outcomes are often observed for reactions between homologous families of chemical reagents and chemical substrates. The experiments in this work with photonic reagents of varying pulse energy and linear spectral chirp reveal systematic correlations between observable ion yields and the following set of natural variables describing the substrate molecules: the ionization energy of the parent molecule, the appearance energy of each fragment ion, and the relative strength of carbon-halogen bonds in molecules containing two different halogens. The results suggest that reactions induced by photonic reagents exhibit systematic behavior analogous to that observed in reactions driven by chemical reagents, which provides a basis to consider empirical "rules" for predicting the outcomes of photonic reagent induced reactions. PMID:23909915

Tibbetts, Katharine Moore; Xing, Xi; Rabitz, Herschel

2013-08-29

373

Chemical reactions in the interstellar medium: The HOC+ ? HCO+ Isomerization Reaction catalyzed by H2  

NASA Astrophysics Data System (ADS)

The present work studies the catalytic effect of molecular hydrogen on the hydrogen transfer from O bounded to C bounded in HOC+ . For this purpose, the reactions with and without hydrogen assistance were studied. The potential energy surface of this reaction was studied using Density Functional Theory methods (PBE/TVZP). The energy barrier was found to be significantly lower than that of the isolated system: An energy profile in function of the intrinsic reaction coordinate was obtained and used to get the reaction force profile and reaction work, which in turn is used to characterize the reaction mechanism. The main contribution to the activation barrier in the uncatalyzed isomerization is W1= 24,42 kcal/mol and can be attributed to structural changes, which the system suffers in order to reach the transition state. This fact is not modified by the introduction of H2, where the main contribution again is W 1 = 8.38 kcal/mol.This shows that the hydrogen catalyst has no special effect over a specific region, but homogenously lowers W1 and W2.

Vogt-Geisse, S.; Toro-Labbe, A.

374

Detailed Chemical Kinetic Reaction Mechanisms for Incineration of Organophosphorus and Fluoro-Organophosphorus Compounds  

SciTech Connect

A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previous kinetic models of organophosphorus compounds such as TMP, DMMP and DIMP that are often used as surrogates to predict incineration of GB. Kinetic models of the three surrogates and GB are then used to predict their consumption in a perfectly stirred reactor fueled by natural gas to simulate incineration of these chemicals. Computed results indicate that DIMP is the only one of these surrogates that adequately describes combustion of GB under comparable conditions. The kinetic pathways responsible for these differences in reactivity are identified and discussed. The most important reaction in GB and DIMP that makes them more reactive than TMP or DMMP is found to be a six-center molecular elimination reaction producing propene.

Glaude, P A; Melius, C; Pitz, W J; Westbrook, C K

2001-12-13

375

Chemical reaction pathways affecting stratospheric and mesospheric ozone  

NASA Astrophysics Data System (ADS)

Catalytic cycles and other chemical pathways affecting ozone are normally estimated empirically in atmospheric models. In this work we have automatically quantified such processes by applying a newly developed analysis package called the "Pathway Analysis Program" (PAP). It used modeled chemical rates and concentrations as input. These were supplied by the "Module Efficiently Calculating the Chemistry of the Atmosphere" MECCA box model, itself initialized by the Free University of Berlin Climate Middle Atmosphere Model with Chemistry. We analyzed equatorial, midlatitude and high-latitude locations over 24-hour periods during spring in both hemispheres. We present results for locations in the lower stratosphere, upper stratosphere and midmesosphere. Oxygen photolysis dominated (>99%) in situ ozone production in the equatorial lower stratosphere, in the upper stratosphere and in the mesosphere. In the lower stratosphere midlatitudes the "ozone smog cycle" (already established in the troposphere) rivaled oxygen photolysis as an in situ ozone source in both hemispheres. However, absolute ozone production rates in midlatitudes were rather slow compared with at the equator, typically 16-50 ppt ozone/day. In the equatorial lower stratosphere, five catalytic sinks were important (each contributing at least 5% to chemical ozone loss): a HOx cycle, a HOBr cycle and its HOCl analog, a water-HOx cycle and a mixed chlorine-bromine cycle. Important in midlatitudes were the HOx cycle, a NOx cycle, the HOBr cycle and the mixed chlorine-bromine cycle. In lower-stratosphere high latitudes, the chlorine dimer cycle and the mixed chlorine-bromine cycle dominated in both hemispheres. A variant on the latter, involving BrCl formation, also featured. In the upper stratosphere high latitudes (where strong negative ozone trends are observed), a nitrogen cycle, a chlorine cycle, and a mixed chlorine-nitrogen cycle were found. In the mesosphere, three closely related HOx cycles dominated ozone loss.

Grenfell, J. Lee; Lehmann, Ralph; Mieth, Peter; Langematz, Ulrike; Steil, Benedikt

2006-09-01

376

Theoretical Chemical Dynamics Studies of Elementary Combustion Reactions  

SciTech Connect

The objective of this research was to develop and apply methods for more accurate predictions of reaction rates based on high-level quantum chemistry. We have developed and applied efficient, robust methods for fitting global ab initio potential energy surfaces (PESs) for both spectroscopy and dynamics calculations and for performing direct dynamics simulations. Our approach addresses the problem that high-level quantum calculations are often too costly in computer time for practical applications resulting in the use of levels of theory that are often inadequate for reactions. A critical objective was to develop practical methods that require the minimum number of electronic structure calculations for acceptable fidelity to the ab initio PES. Our method does this by a procedure that determines the optimal configurations at which ab initio points are computed, and that ensures that the final fitted PES is uniformly accurate to a prescribed tolerance. Our fitting methods can be done automatically, with little or no human intervention, and with no prior knowledge of the topology of the PES. The methods are based on local fitting schemes using interpolating moving least-squares (IMLS). IMLS has advantages over the very effective modified-Shepard methods developed by Collins and others in that higher-order polynomials can be used and does not require derivatives but can benefit from them if available.

Donald L. Thompson

2009-09-30

377

Thermal Proton Transfer Reactions in Ultraviolet Matrix-Assisted Laser Desorption/Ionization  

NASA Astrophysics Data System (ADS)

One of the reasons that thermally induced reactions are not considered a crucial mechanism in ultraviolet matrix-assisted laser desorption ionization (UV-MALDI) is the low ion-to-neutral ratios. Large ion-to-neutral ratios (10-4) have been used to justify the unimportance of thermally induced reactions in UV-MALDI. Recent experimental measurements have shown that the upper limit of the total ion-to-neutral ratio is approximately 10-7 at a high laser fluence and less than 10-7 at a low laser fluence. Therefore, reexamining the possible contributions of thermally induced reactions in MALDI may be worthwhile. In this study, the concept of polar fluid was employed to explain the generation of primary ions in MALDI. A simple model, namely thermal proton transfer, was used to estimate the ion-to-neutral ratios in MALDI. We demonstrated that the theoretical calculations of ion-to-neutral ratios exhibit the same trend and similar orders of magnitude compared with those of experimental measurements. Although thermal proton transfer may not generate all of the ions observed in MALDI, the calculations demonstrated that thermally induced reactions play a crucial role in UV-MALDI.

Chu, Kuan Yu; Lee, Sheng; Tsai, Ming-Tsang; Lu, I.-Chung; Dyakov, Yuri A.; Lai, Yin Hung; Lee, Yuan-Tseh; Ni, Chi-Kung

2014-03-01

378

Thermal proton transfer reactions in ultraviolet matrix-assisted laser desorption/ionization.  

PubMed

One of the reasons that thermally induced reactions are not considered a crucial mechanism in ultraviolet matrix-assisted laser desorption ionization (UV-MALDI) is the low ion-to-neutral ratios. Large ion-to-neutral ratios (10(-4)) have been used to justify the unimportance of thermally induced reactions in UV-MALDI. Recent experimental measurements have shown that the upper limit of the total ion-to-neutral ratio is approximately 10(-7) at a high laser fluence and less than 10(-7) at a low laser fluence. Therefore, reexamining the possible contributions of thermally induced reactions in MALDI may be worthwhile. In this study, the concept of polar fluid was employed to explain the generation of primary ions in MALDI. A simple model, namely thermal proton transfer, was used to estimate the ion-to-neutral ratios in MALDI. We demonstrated that the theoretical calculations of ion-to-neutral ratios exhibit the same trend and similar orders of magnitude compared with those of experimental measurements. Although thermal proton transfer may not generate all of the ions observed in MALDI, the calculations demonstrated that thermally induced reactions play a crucial role in UV-MALDI. PMID:24395022

Chu, Kuan Yu; Lee, Sheng; Tsai, Ming-Tsang; Lu, I-Chung; Dyakov, Yuri A; Lai, Yin Hung; Lee, Yuan-Tseh; Ni, Chi-Kung

2014-03-01

379

Exploring the limits of ultrafast polymerase chain reaction using liquid for thermal heat exchange: A proof of principle  

PubMed Central

Thermal ramp rate is a major limiting factor in using real-time polymerase chain reaction (PCR) for routine diagnostics. We explored the limits of speed by using liquid for thermal exchange rather than metal as in traditional devices, and by testing different polymerases. In a clinical setting, our system equaled or surpassed state-of-the-art devices for accuracy in amplifying DNA?RNA of avian influenza, cytomegalovirus, and human immunodeficiency virus. Using Thermococcus kodakaraensis polymerase and optimizing both electrical and chemical systems, we obtained an accurate, 35 cycle amplification of an 85-base pair fragment of E. coli O157:H7 Shiga toxin gene in as little as 94.1 s, a significant improvement over a typical 1 h PCR amplification.

Maltezos, George; Johnston, Matthew; Taganov, Konstantin; Srichantaratsamee, Chutatip; Gorman, John; Baltimore, David; Chantratita, Wasun; Scherer, Axel

2010-01-01

380

Radical-neutral chemical reactions studied at low temperature with VUV synchrotron photoionization mass spectrometry  

NASA Astrophysics Data System (ADS)

A pulsed Laval nozzle apparatus employing tunable VUV synchrotron photoionization and quadrupole mass spectrometry for the study of radical-neutral chemical reactions of importance for modeling the atmosphere of Titan and the outer planets is described. The apparatus enables the study of low-temperature kinetics and isomer-resolved product branching of highly reactive radicals with unsaturated hydrocarbons reactions. The low-temperature branching ratio for the reaction of the ethynyl radical (C2H) with allene (C3H4) has been measured for the first time at 79 K. This reaction is found to yield 1,4-pentadiyne as the major reaction product (50+10%), followed by ethynylallene (28+10%) and methyldiacetylene (22+10%) via H-atom elimination from the initially formed C5H5 adduct. The derived branching ratios can be directly used to predict the chemical evolution of Titan's atmosphere.

Soorkia, Satchin; Leone, Stephen R.; Wilson, Kevin R.

2012-11-01

381

Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents  

NASA Astrophysics Data System (ADS)

We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom.

Dzhioev, Alan A.; Kosov, Daniel S.; von Oppen, Felix

2013-04-01

382

Charge exchange and chemical reactions with trapped thorium ions  

NASA Astrophysics Data System (ADS)

Most atomic nuclei have excitation energies ranging from keV to MeV. A unique exception is the ^229Th nucleus, which has an excited state just several eV above the nuclear ground state.ootnotetextB. R. Beck et al., Phys. Rev. Lett. 98, 142501 (2007). Th^3+ provides a convenient level structure for laser cooling in an rf Paul trap.ootnotetextC. J. Campbell et al., Phys. Rev. Lett 102, 233004 (2009). Unlike many ions commonly utilized in precision measurements, the trap lifetime of Th^3+ is limited to only several minutes. This is a severe limitation to experiments involving ^229Th as it is only available in minute quantities. Here we have studied the loss mechanisms by introduction of various contaminants and analyzed reaction products using trapped ion mass spectrometry techniques.ootnotetextL. R. Churchill et al., Phys. Rev. A 83, 012710 (2011).

Depalatis, Michael; Churchill, Layne; Chapman, Michael

2011-06-01

383

Molecular beam studies of hot atom chemical reactions: Reactive scattering of energetic deuterium atoms  

SciTech Connect

A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H/sub 2/ /minus/> DH + H and the substitution reaction D + C/sub 2/H/sub 2/ /minus/> C/sub 2/HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible. 18 refs., 9 figs.

Continetti, R.E.; Balko, B.A.; Lee, Y.T.

1989-02-01

384

Nonequilibrium effects on the rate of bimolecular chemical reaction in a dilute gas  

NASA Astrophysics Data System (ADS)

The perturbation solution of the Boltzmann equation in a dilute gas shows that the rate constant of chemical reaction A+ A ? B+ B is diminished due to nonequilibrium effects. For the line-of-centers model, the relative decrease ? of the reaction rate can reach even nearly 45% (for a small reduced threshold energy ?* and a large molar fraction xB). For slow reactions this method is valid and ? does not depend on xB. The appropriate equilibrium expressions for reaction rate (with: (a) the temperature of the system T, (b) the nonequilibrium Shizgal-Karplus temperatures TA and TB) are used for this analysis.

Cukrowski, A. S.; Fritzsche, S.; Fort, J.

2001-06-01

385

Shock wave and modeling study of the thermal decomposition reactions of pentafluoroethane and 2-H-heptafluoropropane.  

PubMed

The thermal decomposition reactions of CF3CF2H and CF3CFHCF3 have been studied in shock waves by monitoring the appearance of CF2 radicals. Temperatures in the range 1400-2000 K and Ar bath gas concentrations in the range (2-10) × 10(-5) mol cm(-3) were employed. It is shown that the reactions are initiated by C-C bond fission and not by HF elimination. Differing conclusions in the literature about the primary decomposition products, such as deduced from experiments at very low pressures, are attributed to unimolecular falloff effects. By increasing the initial reactant concentrations in Ar from 60 to 1000 ppm, a retardation of CF2 formation was observed while the final CF2 yields remained close to two CF2 per C2F5H or three CF2 per C3F7H decomposed. This is explained by secondary bimolecular reactions which lead to comparably stable transient species like CF3H, releasing CF2 at a slower rate. Quantum-chemical calculations and kinetic modeling help to identify the reaction pathways and provide estimates of rate constants for a series of primary and secondary reactions in the decomposition mechanism. PMID:24352693

Cobos, C J; Sölter, L; Tellbach, E; Troe, J

2014-06-01

386

Comparative thermal conductivity measurement of chemical vapor deposition grown graphene supported on substrate  

NASA Astrophysics Data System (ADS)

We develop a comparative thermal conductivity measurement technique based on miniature differential thermocouples and measure the temperature dependence of the thermal conductivity of chemical vapor deposition grown graphene supported on glass or SiO2 substrate in the temperature range of 180-420 K. For all 28 investigated samples, the obtained room temperature values of the thermal conductivity are bounded between 1800 and 2200 W/m K. Compared with other techniques, we find that a significant improvement in accuracy of our measurements is because of the absence of chemical doping/contamination from micro-fabrication procedures. Our results are confirmed using scanning thermal microscopy.

Sidorov, Anton N.; Benjamin, Daniel K.; Foy, Christopher

2013-12-01

387

Chemical and thermal response of Jupiter's atmosphere following the impact of comet Shoemaker-Levy 9  

NASA Astrophysics Data System (ADS)

IN July 1994, the collisions of the fragments of comet Shoemaker-Levy 9 with Jupiter resulted in dramatic changes in the planet's atmosphere. Observations of the events suggest that the composition and thermal properties of the atmosphere were considerably modified at the impact sites, with the changes persisting for times lasting from minutes to weeks (see, for example, refs 1-4). Here we report observations of the impact sites at millimetre wavelengths, which reveal strong emission lines associated with carbon monoxide, carbonyl sulphide and carbon monosulphide. The abundance of carbon monoxide in the jovian atmosphere is normally very low5; carbonyl sulphide and carbon monosulphide, on the other hand, have not hitherto been detected. We find that the largest fragments (G and K) each produced approximately 1014g of carbon monoxide, 3 x 1012g of carbonyl sulphide and 3 x 1011g of carbon monosulphide, most probably by shock-induced chemical reactions6. Our observations also place firm constraints on the thermal response of Jupiter's stratosphere to the impacts.

Lellouch, E.; Paubert, G.; Moreno, R.; Festou, M. C.; Bézard, B.; Bockelée-Morvan, D.; Colom, P.; Crovisier, J.; Encrenaz, T.; Gautier, D.; Marten, A.; Despois, D.; Strobel, D. F.; Sievers, A.

1995-02-01

388

Investigation of shock-induced and shock-assisted chemical reactions in molybdenum-silicon powder mixtures  

NASA Astrophysics Data System (ADS)

In this research, chemical reactions occurring in molybdenum and silicon powder mixtures under "shock-induced" (those occurring during the high-pressure shock state) and "shock-assisted" (those occurring subsequent to the shock event, but due to bulk temperature increases) conditions were investigated. Differences in the densities and yield strengths of the two constituents, in addition to the large heat of reaction associated with molybdenum disilicide (MoSi2) formation can lead to shock-induced as well as shock-assisted reactions, which make this an ideal system to delineate the kinetics and mechanisms of reactions occurring in shock-compressed powder mixtures. Shock recovery experiments performed on Mo + 2 Si powder mixtures employing cylindrical implosion geometry showed thermally initiated reactions. A mixed phase eutectic type microstructure of MoSi2 and Mo 5Si3, resulting from reaction occurring due to melting of both reactants, was observed in axial regions of the cylindrical compacts. In regions surrounding the mach stem, melting of only silicon and reaction occurring via dissolution and re-precipitation forming MoSi2 spherules surrounding molybdenum particles in a melted and solidified silicon matrix was observed. The planar pressure shock recovery geometry showed a single phase MoSi2, microstructure formed due to a solid-state pressure-induced reaction process. The time-resolved instrumented experiments were performed using a single stage gas gun in the velocity range of 500 m/s to 1 km/s, and employed poly-vinyl di-flouride (PVDF) stress gauges placed at the front and rear surfaces of the powder to determine the crush strength, densification history, and reaction initiation threshold conditions. Time-resolved experiments performed on ˜58% dense Mo + 2 Si powder mixtures at input stresses less than 4 GPa, showed characteristics of powder densification and dispersed propagated wave stress profiles with rise time >˜40 nanoseconds. At input stress between 4--6 GPa, the powder mixtures showed a sharp rise time (<˜10 ns) of propagated wave profile and an expanded state of products revealing conclusive evidence of shock-induced reaction. At input stresses greater than 6 GPa, the powder mixtures showed a lower rise time and transition to a low-compressibility (melt) state indicating lack of shock-induced reaction. The results of this work show that (a) premature formation of a melt phase restricts mixing between reactants and inhibits "shock-induced" reaction initiation, although "shock-assisted" reactions can still occur in time scales of thermal equilibrium, and (b) the crush strength of powder mixtures is the most important parameter that controls initiation of a "shock-induced" reaction. Reaction synthesis experiments conducted on 55--95% dense Mo + 2 Si powder mixture compacts under an applied electric field showed that SHS reactions that would have normally become extinguished without the application of electric field, were observed to be self-sustained. Under such conditions, the reaction kinetics were observed to be enhanced and the reaction products showed a highly refined microstructure.

Vandersall, Kevin Stewart

1999-10-01

389

Influence of reaction heat on time dependent processes in a chemically reacting binary mixture  

NASA Astrophysics Data System (ADS)

In this paper we study time dependent problems, like the propagation of sound waves or the behavior of small local wave disturbances induced by spontaneous internal fluctuations, in a binary mixture undergoing a chemical reaction of type A + A ? B + B. The study is developed at the hydrodynamic Euler level, in a chemical regime of fast reactive process in which the chemical reaction is close to its final equilibrium state. The hydrodynamic state of the mixture is described by the balance equations for the mass densities of both constituents A and B, together with the conservation laws for the momentum and total energy of the mixture. The progress of the chemical reaction is specified by an Arrhenius-type reaction rate which defines the net balance between production and consumption of each constituent. Assuming that the considered time dependent problems induce weak macroscopic deviations, the hydrodynamic equations are linearized through a normal mode expansion of the state variables around the equilibrium state. From the dispersion relation of the normal modes, we determine the free and forced phase velocities as well as the attenuation coefficients of the waves. We show that the dispersion and absorption of these waves depend explicitly on the heat of the chemical reaction, the concentrations of the constituents and the activation energy through the exponential factor of Arrhenius law.

Marques, Wilson, Jr.; Kremer, Gilberto M.; Soares, Ana Jacinta

2012-11-01

390

Chemical reactions of ultracold alkali-metal dimers in the lowest-energy 3? state  

NASA Astrophysics Data System (ADS)

We show that the interaction of polar alkali-metal dimers in the quintet spin state leads to the formation of a deeply bound reaction complex. The reaction complex can decompose adiabatically into homonuclear alkali-metal dimers (for all molecules except KRb) and into alkali-metal trimers (for all molecules). We show that there are no barriers for these chemical reactions. This means that all alkali-metal dimers in the a3?+ state are chemically unstable at ultracold temperature, and the use of an optical lattice to segregate the molecules and suppress losses may be necessary. In addition, we calculate the minimum-energy path for the chemical reactions of alkali-metal hydrides. We find that the reaction of two molecules is accelerated by a strong attraction between the alkali-metal atoms, leading to a barrierless process that produces hydrogen atoms with large kinetic energy. We discuss the unique features of the chemical reactions of ultracold alkali-metal dimers in the a3?+ electronic state.

Tomza, Micha?; Madison, Kirk W.; Moszynski, Robert; Krems, Roman V.

2013-11-01

391

[Study on the chemical reaction of DNA with Congo red].  

PubMed

The interaction of deoxyribonucleic acid(DNA) and Congo red (GGH) was investigated by UV-Vis spectrophotometry in Tris-HCl solution (pH 4.56). When DNA was added into GGH solution, the color of the system changed from red to purple, which indicated the formation of the DNA-GGH complex. The maximum absorption of the complex is at 600 nm. The molar absorptivity measured at this wavelength epsilon = 1.41 x 10(5) L x cm(-1) mol(-1), the maximum binding number is n = 32, and the detection limit is c = 8.04 x 10(-8) mol x L(-1). The basic reaction condition of best pH value, time, and temperature, and the interference of different materials on the system were also studied. The ionic strength could affect the absorption of the system. The interaction of small molecule and DNA, the molecule structure, and the relationship between the molecule conformation and the distribution of electron cloud were studied. PMID:16830404

Chi, Yan-hua; Zhuang, Jia; Xue, Qi-bin; Li, Ke-an

2006-01-01

392

Separation of chemical reaction intermediates by metal-organic frameworks.  

PubMed

HPLC columns custom-packed with metal-organic framework (MOF) materials are used for the separation of four small intermediates and byproducts found in the commercial synthesis of an important active pharmaceutical ingredient in methanol. In particular, two closely related amines can be separated in the methanol reaction medium using MOFs, but not with traditional C18 columns using an optimized aqueous mobile phase. Infrared spectroscopy, UV-vis spectroscopy, X-ray diffraction, and thermogravimetric analysis are used in combination with molecular dynamic simulations to study the separation mechanism for the best-performing MOF materials. It is found that separation with ZIF-8 is the result of an interplay between the thermodynamic driving force for solute adsorption within the framework pores and the kinetics of solute diffusion into the material pores, while the separation with Basolite F300 is achieved because of the specific interactions between the solutes and Fe(3+) sites. This work, and the exceptional ability to tailor the porous properties of MOF materials, points to prospects for using MOF materials for the continuous separation and synthesis of pharmaceutical compounds. PMID:21626684

Centrone, Andrea; Santiso, Erik E; Hatton, T Alan

2011-08-22

393

Variational principles for describing chemical reactions: Condensed reactivity indices  

NASA Astrophysics Data System (ADS)

Two recent papers [P. W. Ayers and R. G. Parr, J. Am. Chem. Soc. 122, 2010 (2000); 123, 2007 (2001)] have shown how variational principles for the energy may be used to derive and elucidate the significance of the chemical reactivity indices of density-functional theory. Here, similar ideas are applied, yielding a systematic, mathematically rigorous, and physically sound approach to condensed reactivity indices. First, we use the variational principle for the energy to derive an expression for the condensed Fukui function index in terms of the condensed hardness kernel. Next, we address an important open problem pertaining to condensed reactivity indices: when (if ever) is the condensed Fukui function for an atom in a molecule negative? In particular, our analysis confirms the observation, hitherto based only on computational evidence, that the Hirshfeld partitioning is optimal for obtaining non-negative Fukui functions. We also hypothesize that the strong diagonal dominance of the condensed hardness kernel is sufficient for the non-negativity of the Fukui function. Errors in the partitioning of molecules into atoms and inadequate treatment of correlation are pinpointed as the most likely causes of negative condensed Fukui functions. We conclude by noting that the condensed Fukui functions are, in some respects, more appropriate indicators of a molecular site's reactivity than the Fukui function itself.

Ayers, Paul W.; Morrison, Robert C.; Roy, Ram K.

2002-05-01

394

Kilometer-scale chemical reaction boundary patterns and deformation in sedimentary rocks  

NASA Astrophysics Data System (ADS)

We use three-dimensional (3D) seismic data to image patterns developed by kilometer-scale chemical reaction boundaries to demonstrate that chemical patterns are scaleable phenomena. The patterns develop in biosiliceous marine successions due to the dissolution of opal-A (biogenic silica) and reprecipitation as opal-CT (Crystobalite and Tridymite) during burial. The reaction boundary patterns comprise roughly circular regions where the reaction boundary has preferentially advanced. These regions are up to 2.7 km wide, and c. 50-200 m in height and are termed cells. The cells form by amalgamation with adjacent juvenile cells. They also form by the incorporation of much smaller regions surrounding the cells where the chemical change has already occurred that we term 'satellites' (50 m wide). The reaction results in enhanced rates of sediment compaction hence differential advancement of reaction boundaries causes differential subsidence of the overburden, inducing folding and faulting of the overburden above the cellular promontories. We propose three potential mechanisms for the development of kilometer-scale reaction boundary patterns: (a) mass transport of silica by advection (b) perturbation of isotherms as a result of convective or conductive heat transport or (c) establishment of a positive feedback loop between fluid production due to the reaction, hydraulic fracturing and the upward and lateral transport of fluids. This study provides the first insights into how strongly patterned diagenetic reaction boundaries evolve at a basin scale, an initial conceptualization of the potential range of reaction boundary morphologies that could exist in this diagenetic system, and the likely mechanisms that could control them. Furthermore it demonstrates that the discipline of 'seismic diagenesis' could represent a completely new approach for the study of chemical diagenetic processes in sedimentary rocks.

Davies, Richard J.; Cartwright, Joe A.

2007-10-01

395

Chemical reactions studied at ultra-low temperature in liquid helium clusters  

SciTech Connect

Low-temperature reaction rates are important ingredients for astrophysical reaction networks modeling the formation of interstellar matter in molecular clouds. Unfortunately, such data is difficult to obtain by experimental means. In an attempt to study low-temperature reactions of astrophysical interest, we have investigated relevant reactions at ultralow temperature in liquid helium droplets. Being prepared by supersonic expansion of helium gas at high pressure through a nozzle into a vacuum, large helium clusters in the form of liquid droplets constitute nano-sized reaction vessels for the study of chemical reactions at ultra-low temperature. If the normal isotope {sup 4}He is used, the helium droplets are superfluid and characterized by a constant temperature of 0.37 K. Here we present results obtained for Mg, Al, and Si reacting with O{sub 2}. Mass spectrometry was employed to characterize the reaction products. As it may be difficult to distinguish between reactions occurring in the helium droplets before they are ionized and ion-molecule reactions taking place after the ionization, additional techniques were applied to ensure that the reactions actually occurred in the helium droplets. This information was provided by measuring the chemiluminescence light emitted by the products, the evaporation of helium atoms by the release of the reaction heat, or by laser-spectroscopic identification of the reactants and products.

Huisken, Friedrich; Krasnokutski, Serge A. [Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the University of Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena (Germany)

2012-11-27

396

Chemical reactions studied at ultra-low temperature in liquid helium clusters  

NASA Astrophysics Data System (ADS)

Low-temperature reaction rates are important ingredients for astrophysical reaction networks modeling the formation of interstellar matter in molecular clouds. Unfortunately, such data is difficult to obtain by experimental means. In an attempt to study low-temperature reactions of astrophysical interest, we have investigated relevant reactions at ultralow temperature in liquid helium droplets. Being prepared by supersonic expansion of helium gas at high pressure through a nozzle into a vacuum, large helium clusters in the form of liquid droplets constitute nano-sized reaction vessels for the study of chemical reactions at ultra-low temperature. If the normal isotope 4He is used, the helium droplets are superfluid and characterized by a constant temperature of 0.37 K. Here we present results obtained for Mg, Al, and Si reacting with O2. Mass spectrometry was employed to characterize the reaction products. As it may be difficult to distinguish between reactions occurring in the helium droplets before they are ionized and ion-molecule reactions taking place after the ionization, additional techniques were applied to ensure that the reactions actually occurred in the helium droplets. This information was provided by measuring the chemiluminescence light emitted by the products, the evaporation of helium atoms by the release of the reaction heat, or by laser-spectroscopic identification of the reactants and products.

Huisken, Friedrich; Krasnokutski, Serge A.

2012-11-01

397

Transport in chemical vapor deposition reactors: A two-dimensional model including multicomponent and thermal diffusion, and species interdiffusion  

SciTech Connect

The chemical vapor deposition (CVD) process that consists of depositing coatings of silicon nitride from silicon tetrafluoride and ammonia at low-pressure is modeled in a reactor simulation. Combined effects of surface chemical kinetics, multicomponent diffusion, convection, thermal diffusion, species interdiffusion, and variable properties are included in a reactor model. Full multicomponent diffusion is included by solving the StefanMaxwell equations. Species interdiffusion and thermal diffusion are included in the energy and species conservation equations. Results are for five gas phase species with two surface reactions specified for the deposition. Distributions of radial and axial components of velocity, species, temperature, and deposition rate and deposition profile are obtained in a tube reactor. Effects of the combined transport mechanisms noted above are determined. The decomposition of NH{sub 3} into N{sub 2} and H2{sub 2} retards deposition of silicon nitride and dilutes the incoming reactants. This dilution is strongly enhanced by thermal diffusion since the direction of the temperature gradient causes the light species generated by the surface reactions to remain near the surface resulting in smaller and nonmonotonic deposition rates. The effects of a ramp in the surface temperature on the deposition rate and profile and on the transport processes are also determined.

Evans, G. [Sandia National Labs., Livermore, CA (United States); Greif, R. [California Univ., Berkeley, CA (United States). Dept. of Mechanical Engineering

1994-11-01

398

Coupling quantum interpretative techniques: another look at chemical mechanisms in organic reactions.  

PubMed

A cross ELF-NCI analysis is tested over prototypical organic reactions. The synergetic use of ELF and NCI enables the understanding of reaction mechanisms since each method can respectively identify regions of strong and weak electron pairing. Chemically intuitive results are recovered and enriched by the identification of new features. Non covalent interactions are found to foresee the evolution of the reaction from the initial steps. Within NCI, no topological catastrophe is observed as changes are continuous to such an extent that future reaction steps can be predicted from the evolution of the initial NCI critical points. Indeed, strong convergences through the reaction paths between ELF and NCI critical points enable to identify key interactions at the origin of the bond formation. VMD scripts enabling the automatic generation of movies depicting the cross NCI/ELF analysis along a reaction path (or following a Born-Oppenheimer molecular dynamics trajectory) are provided as S.I. PMID:23185140

Gillet, Natacha; Chaudret, Robin; Contreras-Garc?a, Julia; Yang, Weitao; Silvi, Bernard; Piquemal, Jean-Philip

2012-11-13

399

The Role of Comprehensive Detailed Chemical Kinetic Reaction Mechanisms in Combustion Research  

SciTech Connect

Recent developments by the authors in the field of comprehensive detailed chemical kinetic reaction mechanisms for hydrocarbon fuels are reviewed. Examples are given of how these mechanisms provide fundamental chemical insights into a range of combustion applications. Practical combustion consists primarily of chemical heat release from reactions between a fuel and an oxidizer, and computer simulations of practical combustion systems have become an essential tool of combustion research (Westbrook et al., 2005). At the heart of most combustion simulations, the chemical kinetic submodel frequently is the most detailed, complex and computationally costly part of a system model. Historically, the chemical submodel equations are solved using time-implicit numerical algorithms, due to the extreme stiffness of the coupled rate equations, with a computational cost that varies roughly with the cube of the number of chemical species in the model. While early mechanisms (c. 1980) for apparently simple fuels such as methane (Warnatz, 1980) or methanol (Westbrook and Dryer, 1979) included perhaps 25 species, current detailed mechanisms for much larger, more complex fuels such as hexadecane (Fournet et al., 2001; Ristori et al., 2001; Westbrook et al., 2008) or methyl ester methyl decanoate (Herbinet et al., 2008) have as many as 2000 or even 3000 species. Rapid growth in capabilities of modern computers has been an essential feature in this rapid growth in the size and complexity of chemical kinetic reaction mechanisms.

Westbrook, C K; Pitz, W J; Curran, H J; Mehl, M

2008-07-16

400

Can information of chemical reaction propagate with plasmonic waveguide and be detected at remote terminal of nanowire?  

NASA Astrophysics Data System (ADS)

We attempt to provide experimental and theoretical evidence that information of chemical reaction can propagate with plasmonic waveguide along the nanowire and be detected at the remote terminal of nanowire, where the chemical reaction is the surface catalyzed reaction of DMAB produced from PATP assisted by surface plasmon polaritons.

Sun, Mengtao; Hou, Yanxue; Xu, Hongxing

2011-10-01

401

Reaction and spontaneity: the influence of meaning from everyday language on fourth year undergraduates’ interpretations of some simple chemical phenomena  

Microsoft Academic Search

Fourteen fourth?year undergraduate chemistry students were interviewed in the context of some simple chemical phenomena to find out their concepts of ‘reaction’ and ‘spontaneous’. The students were asked to discuss and to decide in four situations whether or not a chemical reaction had taken place and then, if one had, to decide whether or not the reaction was spontaneous. The

M. Gabriela; T. C. Ribeiro; Duarte J. V. Costa Pereira; Roger Maskill

1990-01-01

402

Competition between charge exchange and chemical reaction - The D2/+/ + H system  

NASA Technical Reports Server (NTRS)

Study of the special features of molecular charge exchange and its competition with chemical reaction in the case of the D2(+) + H system. The trajectory surface hopping (TSH) model proposed by Tully and Preston (1971) is used to study this competition for a number of reactions involving the above system. The diatomics-in-molecules zero-overlap approximation is used to calculate the three adiabatic surfaces - one triplet and two singlet - which are needed to describe this system. One of the significant results of this study is that the chemical reaction and charge exchange are strongly coupled. It is also found that the number of trajectories passing into the chemical regions of the three surfaces depends very strongly on the surface crossings.-

Preston, R. K.; Cross, R. J., Jr.

1973-01-01

403

Simple Models for Nonequilibrium Effects in Bimolecular Chemical Reaction in a Dilute Gas  

NASA Astrophysics Data System (ADS)

Two models for reactive cross sections are introduced to analyze non-equilibrium effects connected with proceeding of the bimolecular chemical reaction A+A ? B+B in a dilute gas: 1. Line-of-Centers model LC, 2. the reverse model rLC leading to negative values of the Arrhenius activation energy. The perturbation method of solution of the Boltzmann equation is used to obtain analytical expressions for the rate constant of chemical reaction and for the nonequilibrium Shizgal--Karplus temperatures. It is shown that if the molar fraction of product is large enough the relative change of the rate of chemical reaction is constant, i.e. does not depend on the molar fraction. Replacing the equilibrium temperature by the nonequilibrium one (depending on the molar fraction) in the equilibrium equations for forward and reverse rate constants confirms these results.

Cukrowski, Andrzej S.; Fort, Joaquim; Fritzsche, Siegfried

2002-04-01

404

Optical thin films grown by surface chemical reaction for high-power lasers  

NASA Astrophysics Data System (ADS)

We developed a novel coating method using chemical reactions of gaseous reactants on a surface. A self-limiting nature of surface chemical reactions allows precisely controlled growth of films with high uniformity and controllability of thickness over large area. The nonuniformity of thickness distribution was under 1% over 240 mm in diameter. The film thickness had proportional relationship with a number of chemical reactions. TiO2 films at growth temperature of 25 degree(s)C had a laser-induced damage threshold of 5 J/cm2 for 1-ns, 1.06-micrometers laser pulses. The laser damage resistance of TiO2 films decreased at higher growth temperature. TiO2 films grown at the high temperature had higher crystallinity. We clarified that the laser damages resulted from the local sites that absorbed the laser energy.

Zaitsu, Shin-ichi; Motokoshi, Shinji; Jitsuno, Takahisa; Nakatsuka, Masahiro; Yamanaka, Tatsuhiko

2001-04-01

405

Finite volume model for forced flow/thermal gradient chemical vapor infiltration.  

National Technical Information Service (NTIS)

The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successfully technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the con...

T. L. Starr A. W. Smith

1991-01-01

406

A nanochannel fabrication technique using chemical-mechanical polishing (CMP) and thermal oxidation  

NASA Technical Reports Server (NTRS)

We have developed a new nanochannel fabrication technique using chemical-mechanical polishing (CMP) and thermal oxidation. With this technique, it is possible to control the width, length, and depth of the nanochannels without the need for nanolithography.

Lee, C.; Yang, E. H.; Myung, N. V.; George, T.

2003-01-01

407

Comparison of thermal flow and chemical shrink processes for 193 nm contact hole patterning  

NASA Astrophysics Data System (ADS)

This paper compares thermal shrink properties of contact holes and chemical shrink performance for 193 nm lithography. Pitch dependence, shrink properties, contact hole circularity, sidewall roughness, and process window are also discussed. Thermal flow process exhibited more pitch dependence than chemical shrink process. Thermal shrink rate increased substantially at higher bake temperatures. Contact holes in defocused area shrunk non-evenly and DOF deteriorated upon heating. In chemical shrink process, shrink rate was hardly influenced by mixing bake temperature, contact holes from center focus to defocus area shrunk evenly preserving effective DOF and MEF became smaller at smaller CD. Chemical shrink has clear advantages over thermal flow process and sub-70 nm contact holes were obtained with iso-dense overlap DOF 0.25 ?m by optimizing resist formulations and process conditions. Application of shrink processes will pave the way for the next generation LSI production.

Kudo, Takanori; Antonio, Charito; Sagan, John; Chakrapani, Srinivasan; Parthasarathy, Deepa; Hong, Sungeun; Thiyagarajan, Muthiah; Cao, Yi; Padmanaban, Munirathna

2009-03-01

408

Reaction hazard analysis for the thermal decomposition of cumene hydroperoxide in the presence of sodium hydroxide  

Microsoft Academic Search

Organic peroxides have caused many serious explosions and fires that were promoted by thermal instability, chemical pollutants,\\u000a and even mechanical shock. Cumene hydroperoxide (CHP) has been employed in polymerization and for producing phenol and dicumyl\\u000a peroxide (DCPO). Differential scanning calorimetry (DSC) has been used to assess the thermal hazards associated with CHP contacting\\u000a sodium hydroxide (NaOH). Thermokinetic parameters, such as

Y.-P. Chou; J.-Y. Huang; J.-M. Tseng; S.-Y. Cheng; C.-M. Shu

2008-01-01

409

On the curvature in logarithmic plots of rate coefficients for chemical reactions  

PubMed Central

In terms of the reduced potential energy barrier ? = ?uTS/kT, the rate coefficients for chemical reactions are usually expressed as proportional to e-?. The coupling between vibrational modes of the medium to the reaction coordinate leads to a proportionality of the regularized gamma function of Euler Q(a,?) = ?(a,?)/?(a), with a being the number of modes coupled to the reaction coordinate. In this work, the experimental rate coefficients at various temperatures for several chemical reactions were fitted to the theoretical expression in terms of Q(a,?) to determine the extent of its validity and generality. The new expression affords lower deviations from the experimental points in 29 cases out of 38 and it accounts for the curvature in the logarithmic plots of rate coefficients versus inverse temperature. In the absence of tunneling, conventional theories predict the curvature of these plots to be identically zero.

2011-01-01

410

CHEMICAL AND BIOLOGICAL TREATMENT OF THERMALLY CONDITIONED SLUDGE RECYCLE LIQUORS  

EPA Science Inventory

The objective of this research project was to demonstrate and evaluate the feasibility of treating undiluted heat treatment liquor prior to its rerouting back to the head of the sewage treatment plant. Chemical and biological treatment processes were studied. Chemical treatment w...

411

Thermal–hydrologic–mechanical–chemical processes in the evolution of engineered geothermal reservoirs  

Microsoft Academic Search

In a companion paper [Taron J, Elsworth D, Min K-B. Numerical simulation of thermal–hydrologic–mechanical–chemical processes in deformable, fractured porous media. Int J Rock Mech Min Sci 2009; doi:10.1016\\/j.ijrmms.2009.01.008] we introduced a new methodology and numerical simulator for the modeling of thermal–hydrologic–mechanical–chemical processes in dual-porosity media. In this paper we utilize the model to examine some of the dominant behaviors and

Joshua Taron; Derek Elsworth

2009-01-01

412

Modeling of multiphase flow with solidification and chemical reaction in materials processing  

NASA Astrophysics Data System (ADS)

Understanding of multiphase flow and related heat transfer and chemical reactions are the keys to increase the productivity and efficiency in industrial processes. The objective of this thesis is to utilize the computational approaches to investigate the multiphase flow and its application in the materials processes, especially in the following two areas: directional solidification, and pyrolysis and synthesis. In this thesis, numerical simulations will be performed for crystal growth of several III-V and II-VI compounds. The effects of Prandtl and Grashof numbers on the axial temperature profile, the solidification interface shape, and melt flow are investigated. For the material with high Prandtl and Grashof numbers, temperature field and growth interface will be significantly influenced by melt flow, resulting in the complicated temperature distribution and curved interface shape, so it will encounter tremendous difficulty using a traditional Bridgman growth system. A new design is proposed to reduce the melt convection. The geometric configuration of top cold and bottom hot in the melt will dramatically reduce the melt convection. The new design has been employed to simulate the melt flow and heat transfer in crystal growth with large Prandtl and Grashof numbers and the design parameters have been adjusted. Over 90% of commercial solar cells are made from silicon and directional solidification system is the one of the most important method to produce multi-crystalline silicon ingots due to its tolerance to feedstock impurities and lower manufacturing cost. A numerical model is developed to simulate the silicon ingot directional solidification process. Temperature distribution and solidification interface location are presented. Heat transfer and solidification analysis are performed to determine the energy efficiency of the silicon production furnace. Possible improvements are identified. The silicon growth process is controlled by adjusting heating power and moving the side insulation layer upward. It is possible to produce high quality crystal with a good combination of heating and cooling. SiC based ceramic materials fabricated by polymer pyrolysis and synthesis becomes a promising candidate for nuclear applications. To obtain high uniformity of microstructure/concentration fuel without crack at high operating temperature, it is important to understand transport phenomena in material processing at different scale levels. In our prior work, a system level model based on reactive porous media theory was developed to account for the pyrolysis process in uranium-ceramic nuclear fabrication In this thesis, a particle level mesoscopic model based on the Smoothed Particle Hydrodynamics (SPH) is developed for modeling the synthesis of filler U3O8 particles and SiC matrix. The system-level model provides the thermal boundary conditions needed in the particle level simulation. The evolution of particle concentration and structure as well as composition of composite produced will be investigated. Since the process temperature and heat flux play the important roles in material quality and uniformity, the effects of heating rate at different directions, filler particle size and distribution on uniformity and microstructure of the final product are investigated. Uncertainty issue is also discussed. For the multiphase flow with directional solidification, a system level based on FVM is established. In this model, melt convection, temperature distribution, phase change and solidification interface can be investigated. For the multiphase flow with chemical reaction, a particle level model based on SPH method is developed to describe the pyrolysis and synthesis process of uranium-ceramic nuclear fuel. Due to its mesh-free nature, SPH can easily handle the problems with multi phases and components, large deformation, chemical reactions and even solidifications. A multi-scale meso-macroscopic approach, which combine a mesoscopic model based on SPH method and macroscopic model based on FVM, FEM and FDM, can be applied to even more com

Wei, Jiuan

413

Chemical additives to control expansion of alkali-silica reaction gel: proposed mechanisms of control  

Microsoft Academic Search

Calcium chloride, lithium chloride, and acetone have previously been shown to affect expansion caused by alkali-silica reaction (ASR), a deleterious reaction occurring between reactive siliceous minerals present in some aggregate and the strongly alkaline pore solution in concrete. Here, the effect of these chemical additives was examined by transmission soft X-ray microscopy and a quantitative elemental analysis, using ICP-OES. In

K. E. Kurtis; P. J. M. Monteiro

2003-01-01

414

A free boundary problem describing reaction–diffusion problems in chemical vapor infiltration of pyrolytic carbon  

Microsoft Academic Search

In this paper we consider chemical vapor deposition of pyrolytic carbon from methane in hot wall reactors. Especially, we deal with the interaction of homogeneous gas-phase and heterogeneous surface reactions. The resulting mathematical model is composed of a system of reaction–diffusion equations in a corner domain supplied with the Gibbs–Thomson law, which describes the movement of the free boundary, arising

W. Merz; P. Rybka

2004-01-01

415

Diffusion-controlled chemical reactions modeled by continuous-time random walks  

Microsoft Academic Search

In the kinetic theory of pseudo-first-order diffusion-controlled chemical reactions, the diffusion motion of one component can be suppressed as long as the relative diffusion coefficient is assigned to the other component. The continuous-time-random-walk (CTWR) treatment of the pseudo-first-order reactions reaffirmed this well-known notion in the case of an exponential jump time distribution. In the case of a long-tail jump time

W. P. Helman; K. Funabashi

1979-01-01

416

Chemical modelling of Alkali Silica reaction: Influence of the reactive aggregate size distribution  

Microsoft Academic Search

This article presents a new model which aims at predicting the expansion induced by Alkali Silica Reaction (ASR) and describing\\u000a the chemical evolution of affected concretes. It is based on the description of the transport and reaction of alkalis and\\u000a calcium ions within a Relative Elementary Volume (REV). It takes into account the influence of the reactive aggregate size\\u000a grading

S. Poyet; A. Sellier; B. Capra; G. Foray; J.-M. Torrenti; H. Cognon; E. Bourdarot

2007-01-01

417

Simulation of Chemical Isomerization Reaction Dynamics on a NMR Quantum Simulator  

NASA Astrophysics Data System (ADS)

Quantum simulation can beat current classical computers with minimally a few tens of qubits. Here we report an experimental demonstration that a small nuclear-magnetic-resonance quantum simulator is already able to simulate the dynamics of a prototype laser-driven isomerization reaction using engineered quantum control pulses. The experimental results agree well with classical simulations. We conclude that the quantum simulation of chemical reaction dynamics not computable on current classical computers is feasible in the near future.

Lu, Dawei; Xu, Nanyang; Xu, Ruixue; Chen, Hongwei; Gong, Jiangbin; Peng, Xinhua; Du, Jiangfeng

2011-07-01

418

Optimal path of the consecutive chemical reactions xA?yB?zC  

NASA Astrophysics Data System (ADS)

The optimal path of the consecutive chemical reactions xA?yB?zC (x, y and z are the orders of chemical reactions) is analyzed numerically by taking temperature as a control variable, using the optimal-control theory based on Bak et al's work (2002 J. Phys. Chem. A 106 10961-4). Starting with pure A and maximizing the yield of B at the end of the given process duration, the optimal path starts with a branch at infinite temperature. A curve in which switching from this temperature to a lower temperature is possible is derived. For given parameters, there is a unique 'maximal useful time' that results in the highest possible yield of B. If a duration longer than this is specified, all reactions should be shut off during that excess amount of time in the optimal path. A numerical example for the optimal path is provided by the Taylor method. Finally, the results obtained are compared with the results of A?B?C (the orders of chemical reactions are all equal to 1) (Bak et al 2002 J. Phys. Chem. A 106 10961-4). When the orders of chemical reactions are taken into account, the optimal time sequences of the concentrations change markedly, the maximum obtainable yield is smaller, the initial values of co-state variables are bigger and the optimal phase trajectory changes.

Chen, Lingen; Song, Hanjiang; Sun, Fengrui

2009-05-01

419

Persistence of transition-state structure in chemical reactions driven by fields oscillating in time  

NASA Astrophysics Data System (ADS)

Chemical reactions subjected to time-varying external forces cannot generally be described through a fixed bottleneck near the transition-state barrier or dividing surface. A naive dividing surface attached to the instantaneous, but moving, barrier top also fails to be recrossing-free. We construct a moving dividing surface in phase space over a transition-state trajectory. This surface is recrossing-free for both Hamiltonian and dissipative dynamics. This is confirmed even for strongly anharmonic barriers using simulation. The power of transition-state theory is thereby applicable to chemical reactions and other activated processes even when the bottlenecks are time dependent and move across space.

Craven, Galen T.; Bartsch, Thomas; Hernandez, Rigoberto

2014-04-01

420

THE LIFETIME OF AEROSOLS IN AMBIENT AIR: CONSIDERATION OF THE EFFECTS OF SURFACTANTS AND CHEMICAL REACTIONS  

SciTech Connect

The relatively long lifetime of droplets in atmospheric haze and fog in comparison with similar droplets of pure water is attributed to the presence of a monolayer of surfactant film and to the accumulation Of soluble salts from chemical reactions. The lifetime of these droplets is a significant factor in the evaluation of the role of heterogeneous aqueous chemical reactions occurring in the troposphere. Several mechanisms of SO{sub 2} oxidation in the presence of liquid water are investigated. It is shown that soot-catalyzed oxidation of sulfur dioxide could be responsible for the high level of sulfate concentration observed in the coastal industrial areas.

Toossi, R.; Novakov, T.

1984-04-01

421

A study of the effects of solid phase reactions on the thermal degradation and ballistic properties of solid propellants  

NASA Technical Reports Server (NTRS)

The thermal stability of perchlorate composite propellants was studied at 135 and 170 C. The experimental efforts were concentrated on determining the importance of heterogeneous oxidizer-fuel reactions in the thermal degradation process. The experimental approach used to elucidate the mechanisms by which the oxidizer fuel composites thermally degrade was divided into two parts: (1) keeping the fuel constant and varying the nature of the oxidizers, and (2) holding the oxidizer constant and varying the fuel components. The fuel component primarily utilized in the first phase was polyethylene. Oxidizers included KClO4, KClO3, NH4ClO4 and NH4ClO4 doped with materials such as chlorate, phosphate and arsenate. In the second phase the oxidizer used was primarily NH4ClO4 while the fuels included saturated and unsaturated polybutadiene prepolymers and a series of bonding agents. Techniques employed in the current study include thermogravimetric measurements, differential thermal analysis, infrared, mass spectrometry, electron microscopy, and appropriate wet chemical analysis.

Schmidt, W. G.

1974-01-01

422

A coupled THC model of the FEBEX in situ test with bentonite swelling and chemical and thermal osmosis.  

PubMed

The performance assessment of a geological repository for radioactive waste requires quantifying the geochemical evolution of the bentonite engineered barrier. This barrier will be exposed to coupled thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. This paper presents a coupled THC model of the FEBEX (Full-scale Engineered Barrier EXperiment) in situ test which accounts for bentonite swelling and chemical and thermal osmosis. Model results attest the relevance of thermal osmosis and bentonite swelling for the geochemical evolution of the bentonite barrier while chemical osmosis is found to be almost irrelevant. The model has been tested with data collected after the dismantling of heater 1 of the in situ test. The model reproduces reasonably well the measured temperature, relative humidity, water content and inferred geochemical data. However, it fails to mimic the solute concentrations at the heater-bentonite and bentonite-granite interfaces because the model does not account for the volume change of bentonite, the CO(2)(g) degassing and the transport of vapor from the bentonite into the granite. The inferred HCO(3)(-) and pH data cannot be explained solely by solute transport, calcite dissolution and protonation/deprotonation by surface complexation, suggesting that such data may be affected also by other reactions. PMID:21783271

Zheng, Liange; Samper, Javier; Montenegro, Luis

2011-09-25

423

A coupled THC model of the FEBEX in situ test with bentonite swelling and chemical and thermal osmosis  

SciTech Connect

The performance assessment of a geological repository for radioactive waste requires quantifying the geochemical evolution of the bentonite engineered barrier. This barrier will be exposed to coupled thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. This paper presents a coupled THC model of the FEBEX (Full-scale Engineered Barrier EXperiment) in situ test which accounts for bentonite swelling and chemical and thermal osmosis. Model results attest the relevance of thermal osmosis and bentonite swelling for the geochemical evolution of the bentonite barrier while chemical osmosis is found to be almost irrelevant. The model has been tested with data collected after the dismantling of heater 1 of the in situ test. The model reproduces reasonably well the measured temperature, relative humidity, water content and inferred geochemical data. However, it fails to mimic the solute concentrations at the heater-bentonite and bentonite-granite interfaces because the model does not account for the volume change of bentonite, the CO{sub 2}(g) degassing and the transport of vapor from the bentonite into the granite. The inferred HCO{sub 3}{sup -} and pH data cannot be explained solely by solute transport, calcite dissolution and protonation/deprotonation by surface complexation, suggesting that such data may be affected also by other reactions.