Alumina Paste Sublimation Suppression Barrier for Thermoelectric Device

NASA Technical Reports Server (NTRS)

Caillat, Thierry (Inventor); Paik, Jong-Ah (Inventor)

2014-01-01

Alumina as a sublimation suppression barrier for a Zintl thermoelectric material in a thermoelectric power generation device operating at high temperature, e.g. at or above 1000K, is disclosed. The Zintl thermoelectric material may comprise Yb.sub.14MnSb.sub.11. The alumina may be applied as an adhesive paste dried and cured on a substantially oxide free surface of the Zintl thermoelectric material and polished to a final thickness. The sublimation suppression barrier may be finalized by baking out the alumina layer on the Zintl thermoelectric material until it becomes substantially clogged with ytterbia.

Structurally complex Zintl compounds for high temperature thermoelectric power generation

NASA Astrophysics Data System (ADS)

Zevalkink, Alexandra; Pomrehn, Gregory; Gibbs, Zachary; Snyder, Jeffrey

2014-03-01

Zintl phases, characterized by covalently-bonded substructures surrounded by highly electropositive cations, exhibit many of the characteristics desired for thermoelectric applications. Recently, we demonstrated promising thermoelectric performance (zT values between 0.4 and 0.9) in a class of Zintl antimonides that share a common structural motif: anionic moieties resembling infinite chains of linked tetrahedra. These compounds (A5M2 Sb6 and A3 M Sb3 compounds where A = Ca or Sr and M = Al, Ga and In) crystallize as four distinct, but closely related chain-forming structure types. Their large unit cells lead to exceptionally low lattice thermal conductivity due to the containment of heat in low velocity optical phonon modes. Here, we show that chemical substitutions on the A and M sites can be used to control the electronic and thermal transport properties and optimize the thermoelectric figure of merit. Doping with alio-valent elements allows for rational control of the carrier concentration, while isoelectronic substitutions can be used to fine-tune the intrinsic properties. A combination of Density Functional calculations and classical transport models was used to explain the experimentally observed transport properties of these compounds.

Different Topological Quantum States in Ternary Zintl compounds: BaCaX (X = Si, Ge, Sn and Pb)

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

Wang, Lin-Lin; Kaminski, Adam; Canfield, Paul C.

Topological quantum states require stringent combination of crystal symmetry and spin–orbit coupling (SOC) strength. Here in this paper, we report that the ternary Zintl compound series BaCaX (X = Si, Ge, Sn and Pb, Group IV) in the same crystal structure having eight valence electrons per formula unit can host two different topological quantum phases, controlled by atomic size and SOC strength. BaCaSi is a nodal-line semimetal (NLSM) with band inversion protected by mirror symmetry and hosts a strong topological insulator (TI) state when SOC is turned on, thus, a NLSM-TI phase. Moving to larger atomic sizes and heavier atoms,more » BaCaGe and BaCaSn are normal insulators (NIs); then, with the strongest SOC in BaCaPb, a different band inversion is induced, giving a strong TI phase without the need of NLSM. Thus, we also predict two types of topological transitions in a phase diagram for BaCaX: (1) NLSM-TI to NI, then to TI by tuning atomic size and SOC strength via alloying, and (2) NI or TI to NLSM-TI via pressure.« less

Different Topological Quantum States in Ternary Zintl compounds: BaCaX (X = Si, Ge, Sn and Pb)

DOE PAGES

Wang, Lin-Lin; Kaminski, Adam; Canfield, Paul C.; ...

2017-12-14

Topological quantum states require stringent combination of crystal symmetry and spin–orbit coupling (SOC) strength. Here in this paper, we report that the ternary Zintl compound series BaCaX (X = Si, Ge, Sn and Pb, Group IV) in the same crystal structure having eight valence electrons per formula unit can host two different topological quantum phases, controlled by atomic size and SOC strength. BaCaSi is a nodal-line semimetal (NLSM) with band inversion protected by mirror symmetry and hosts a strong topological insulator (TI) state when SOC is turned on, thus, a NLSM-TI phase. Moving to larger atomic sizes and heavier atoms,more » BaCaGe and BaCaSn are normal insulators (NIs); then, with the strongest SOC in BaCaPb, a different band inversion is induced, giving a strong TI phase without the need of NLSM. Thus, we also predict two types of topological transitions in a phase diagram for BaCaX: (1) NLSM-TI to NI, then to TI by tuning atomic size and SOC strength via alloying, and (2) NI or TI to NLSM-TI via pressure.« less

Roles of cations, electronegativity difference, and anionic interlayer interactions in the metallic versus nonmetallic character of Zintl phases related to arsenic.

PubMed

Alemany, Pere; Llunell, Miquel; Canadell, Enric

2008-10-01

A first-principles Density Functional Theory study of several layered solids structurally related to rhombohedral arsenic has been carried out. The electronic structures of rhombohedral arsenic, CaSi(2), CaAl(2)Si(2), KSnSb, and SrSn(2)As(2) are discussed in detail, emphasizing on the origins of their metallic or nonmetallic behaviours. It is found that all of these systems are metallic except KSnSb. Electronegativity differences between the elements in the anionic sublattice and/or direct interlayer interactions play the main role in controlling the conductivity behavior. CaSi(2) exhibits a peculiar feature since the cation directly influences the conductivity but is not essential for its appearance. Cation-anion interactions are shown to have an important covalent contribution, but despite this fact and the metallic character found for most of these phases, the Zintl approach still provides a valid approximation to their electronic structure. (c) 2008 Wiley Periodicals, Inc.

The unusual chemical bonding and thermoelectric properties of a new type Zintl phase compounds Ba3Al2As4

NASA Astrophysics Data System (ADS)

Yang, Gui; Zhang, Guangbiao; Wang, Chao; Wang, Yuanxu

2016-07-01

Ba3Al2As4 exhibits an unusual anisotropic electrical conductivity, that is, the electrical conductivity along the chain is smaller than those along other two directions. The results is conflict with previous conclusion for Ca5M2Pn6. Earlier studies on Ca5M2Pn6 showed that a higher electrical conductivity could be obtained along the chain. The band decomposed charge density is used to explain such unusual behavior. Our calculations indicate the existence of a conductive pathway near the Fermi level is responsible for the electrons transport. Further, the Ba-As bonding of Ba3Al2As4 has some degree covalency which is novel for the Zintl compounds.

Hydrogenation properties of KSi and NaSi Zintl phases.

PubMed

Tang, Wan Si; Chotard, Jean-Noël; Raybaud, Pascal; Janot, Raphaël

2012-10-14

The recently reported KSi-KSiH(3) system can store 4.3 wt% of hydrogen reversibly with slow kinetics of several hours for complete absorption at 373 K and complete desorption at 473 K. From the kinetics measured at different temperatures, the Arrhenius plots give activation energies (E(a)) of 56.0 ± 5.7 kJ mol(-1) and 121 ± 17 kJ mol(-1) for the absorption and desorption processes, respectively. Ball-milling with 10 wt% of carbon strongly improves the kinetics of the system, i.e. specifically the initial rate of absorption becomes about one order of magnitude faster than that of pristine KSi. However, this fast absorption causes a disproportionation into KH and K(8)Si(46), instead of forming the KSiH(3) hydride from a slow absorption. This disproportionation, due to the formation of stable KH, leads to a total loss of reversibility. In a similar situation, when the pristine Zintl NaSi phase absorbs hydrogen, it likewise disproportionates into NaH and Na(8)Si(46), indicating a very poorly reversible reaction.

Na(23)K(9)Tl(15.3): An Unusual Zintl Compound Containing Apparent Tl(5)(7)(-), Tl(4)(8)(-), Tl(3)(7)(-), and Tl(5)(-) Anions.

PubMed

Dong, Zhen-Chao; Corbett, John D.

1996-05-22

Reaction of the neat elements in tantalum containers at 400 degrees C and then 150 degrees C gives the pure title phase. X-ray crystallography shows that the hexagonal structure (P6(3)/mmc, Z = 2, a = 11.235(1) Å, b = 30.133(5) Å) contains relatively high symmetry clusters Tl(5)(7)(-) (D(3)(h)()), Tl(4)(8)(-) (C(3)(v)(), approximately T(d)), and the new Tl(3)(7)(-) (D(infinity)(h)()) plus Tl(5)(-), the last two disordered over the same elongated site in 1:2 proportions. Cation solvation of these anions is tight and specific, providing good Coulombic trapping of weakly bound electrons on the isolated cluster anions. The observed disorder makes the compound structurally a Zintl phase with a closed shell electron count. EHMO calculations on the novel Tl(3)(7)(-) reveal some bonding similarities with the isoelectronic CO(2), with two good sigma(s,p) bonding and two weakly bonding pi MO's. The Tl-Tl bond lengths therein (3.14 Å) are evidently consistent with multiple bonding. The weak temperature-independent paramagnetism and metallic conductivity (rho(293) approximately 90 &mgr;Omega.cm) of the phase are discussed.

Eu9Cd4-xCM2+x-y□ySb9: Ca9Mn4Bi9-type structure stuffed with coinage metals (Cu, Ag, and Au) and the challenges with classical valence theory in describing these possible zintl phases.

PubMed

Kazem, Nasrin; Hurtado, Antonio; Klobes, Benedikt; Hermann, Raphaël P; Kauzlarich, Susan M

2015-02-02

The synthesis, crystal structure, magnetic properties, and europium Mössbauer spectroscopy of the new members of the 9-4-9 Zintl family of Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb(9) (CM = coinage metal: Au, Ag, and Cu) are reported. These compounds crystallize in the Ca(9)Mn(4)Bi(9) structure type (9-4-9) with the 4g interstitial site almost half-occupied by coinage metals; these are the first members in the 9-4-9 family where the interstitial positions are occupied by a monovalent metal. All previously known compounds with this structure type include divalent interstitials where these interstitials are typically the same as the transition metals in the anionic framework. Single-crystal magnetic susceptibility data indicate paramagnetic behavior for all three compounds with antiferromagnetic ordering below 10 K (at 100 Oe) that shifts to lower temperature (<7 K) by applying a 3 T magnetic field. (151)Eu Mössbauer spectra were collected on polycrystalline powder samples of Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb(9) at 50 and 6.5 K in order to evaluate the valence of Eu cations. Although the Zintl formalism states that the five crystallographically distinct Eu sites in Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb9 should bear Eu(2+), the Mössbauer spectral isomer shifts are clearly indicative of both 2+ and 3+ valence of the Eu cations with the Cu- and Au-containing compounds showing higher amounts of Eu(3+). This electronic configuration leads to an excess of negative charge in these compounds that contradicts the expected valence-precise requirement of Zintl phases. The spectra obtained at 6.5 K reveal magnetic ordering for both Eu(2+) and Eu(3+). The field dependence of Eu(2+) indicates two distinct magnetic sublattices, with higher and lower fields, and of a small field for Eu(3+). The site symmetry of the five Eu sites is not distinguishable from the Mössbauer data.

Synthesis of Nine-atom Deltahedral Zintl Ions of Germanium and their Functionalization with Organic Groups

PubMed Central

Gillett-Kunnath, Miriam M.; Sevov, Slavi C.

2012-01-01

Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later.1,2 Their redox chemistry is even younger, just about ten years old, but despite this short history these deltahedral clusters ions E9n- (E = Si, Ge, Sn, Pb; n = 2, 3, 4) have already shown interesting and diverse reactivity and have been at the forefront of rapidly developing and exciting new chemistry.3-6 Notable milestones are the oxidative coupling of Ge94- clusters to oligomers and infinite chains,7-19 their metallation,14-16,20-25 capping by transition-metal organometallic fragments,26-34 insertion of a transition-metal atom at the center of the cluster which is sometimes combined with capping and oligomerization,35-47 addition of main-group organometallic fragments as exo-bonded substituents,48-50 and functionalization with various organic residues by reactions with organic halides and alkynes.51-58 This latter development of attaching organic fragments directly to the clusters has opened up a new field, namely organo-Zintl chemistry, that is potentially fertile for further synthetic explorations, and it is the step-by-step procedure for the synthesis of germanium-divinyl clusters described herein. The initial steps outline the synthesis of an intermetallic precursor of K4Ge9 from which the Ge94- clusters are extracted later in solution. This involves fused-silica glass blowing, arc-welding of niobium containers, and handling of highly air-sensitive materials in a glove box. The air-sensitive K4Ge9 is then dissolved in ethylenediamine in the box and then alkenylated by a reaction with Me3SiC≡CSiMe3. The reaction is followed by electrospray mass spectrometry while the resulting solution is used for obtaining single crystals containing the functionalized clusters [H2C=CH-Ge9-CH=CH2]2-. For this purpose the solution is centrifuged, filtered, and carefully layered with a toluene solution of 18-crown-6. Left undisturbed for a few days, the so-layered solutions produced orange crystalline blocks of [K(18-crown-6)]2[Ge9(HCCH2)2]•en which were characterized by single-crystal X-ray diffraction. The process highlights standard reaction techniques, work-up, and analysis towards functionalized deltahedral Zintl clusters. It is hoped that it will help towards further development and understanding of these compounds in the community at large. PMID:22349121

Organo-Zintl-based superatoms: [Ge9(CHO)3] and [Ge9(CHO)

NASA Astrophysics Data System (ADS)

Reddy, G. Naaresh; Jena, Puru; Giri, Santanab

2017-10-01

A systematic study, based on density functional theory and different hybrid functionals for exchange-correlation potential, shows that the electron affinities of organo-zintl clusters [Ge9(R)n] [R = CHO; n = 1, 3] are close to that of chlorine (3.6 eV) and iodine (3.0 eV). A detailed study of the molecular orbitals of these complexes, when compared to those of Al13-, Cl- and I-, confirm that they behave as superatoms, mimicking the chemistry of halogens. This study expands the scope of superatoms by including a new class of pseudo-halogens based on ligated organo-Zintl ions.

Synthesis of Ge-nanoparticles in organic solution

NASA Astrophysics Data System (ADS)

Pugsley, Andrew James

Much interest is focused on the synthesis of semiconductor particles from organic solution, in order to provide luminescent tracers for biological assays. However, group IV semiconductors have been largely neglected be cause of the lack of suitable nanoparticle formation reactions by solution-phase chemistries. A potentially useful new route to solution-based synthesis of nanocrystalline-Si,Ge involves the reaction between Zintl phases (NaSi, Mg 2Ge) that formally contain anionic semiconducting group species (Si-, Ge4-) and liquid phase SiCU, GeCU, etc. Luminescent nanoparticles formed by these reactions in organic solvents (e.g. diglyme) have been decribed in work from the Kauzlarich group at UC Davis (California, USA). The aim of this project has been to characterise the structural chemistry and luminescent properties of the products of the reaction, as well as following the course of the reaction in situ via synchrotron measurements. The product of the reaction has been characterised by TEM and x-ray absorption spectroscopy as well as other techniques. In order to analyse the x-ray absorption spectroscopy data, a number of model compounds have been studied, including the precursor material which was previously uncharacterised by this technique. An in situ reaction cell has been designed and built and used at a number of synchrotron beamlines to follow the course of the reaction. It has been found that the presence of even low concentrations of water can greatly affect the formation reaction, this is described herein.

Thermoelectric Performance and Defect Chemistry in n-Type Zintl KGaSb 4

DOE PAGES

Ortiz, Brenden R.; Gorai, Prashun; Stevanovic, Vladan; ...

2017-05-08

The rise of high-throughput calculations has accelerated the discovery of promising classes of thermoelectric materials. In prior work, we identified the n-type Zintl pnictides as one such material class. To date, however, a lack of detailed defect calculations and chemical intuition has led the community to investigate p-type Zintls almost exclusively. Here, we investigate the synthesis, thermoelectric properties, and defect structure of the complex Zintl KGaSb 4. We find that KGaSb 4 is successfully doped n-type with Ba and has the potential for p-type doping with Zn. Our calculations reveal the fundamental defect structure in KGaSb 4 that enables n-typemore » and p-type doping. We find that Ba doped KGaSb4 exhibits high electronic mobility (~50 cm 2V -1s -1) and near minimum lattice thermal conductivity (<0.5 Wm -1K -1) at 400 °C. Samples doped with 1.5% Ba achieve zT > 0.9 at 400 °C, promising for a previously unstudied material. Here, we also briefly investigate the series of alloys between KGaSb 4 and KAlSb 4, finding that a full solid solution exists. Altogether our work reinforces motivation for the exploration of n-type Zintl materials, especially in tandem with high-throughput defect calculations to inform selection of effective dopants and systems amenable to n-type transport.« less

Thermoelectric Performance and Defect Chemistry in n-Type Zintl KGaSb 4

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

Ortiz, Brenden R.; Gorai, Prashun; Stevanovic, Vladan

The rise of high-throughput calculations has accelerated the discovery of promising classes of thermoelectric materials. In prior work, we identified the n-type Zintl pnictides as one such material class. To date, however, a lack of detailed defect calculations and chemical intuition has led the community to investigate p-type Zintls almost exclusively. Here, we investigate the synthesis, thermoelectric properties, and defect structure of the complex Zintl KGaSb 4. We find that KGaSb 4 is successfully doped n-type with Ba and has the potential for p-type doping with Zn. Our calculations reveal the fundamental defect structure in KGaSb 4 that enables n-typemore » and p-type doping. We find that Ba doped KGaSb4 exhibits high electronic mobility (~50 cm 2V -1s -1) and near minimum lattice thermal conductivity (<0.5 Wm -1K -1) at 400 °C. Samples doped with 1.5% Ba achieve zT > 0.9 at 400 °C, promising for a previously unstudied material. Here, we also briefly investigate the series of alloys between KGaSb 4 and KAlSb 4, finding that a full solid solution exists. Altogether our work reinforces motivation for the exploration of n-type Zintl materials, especially in tandem with high-throughput defect calculations to inform selection of effective dopants and systems amenable to n-type transport.« less

Designing, Describing and Disseminating New Materials by using the Network Topology Approach.

PubMed

Öhrström, Lars

2016-09-19

This Concept article describes how network topology analysis is applied to different fields of solid-state chemistry. Its usefulness is demonstrated by examples from metal-organic frameworks, group 14 allotropes and related compounds, ice polymorphs, zeolites, supramolecular (organic) solid-state chemistry, Zintl phases, and cathode materials for Li-ion batteries. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Eu2P7X and Ba2As7X (X = Br, I): Chiral double-Zintl salts containing heptapnictotricyclane clusters

NASA Astrophysics Data System (ADS)

Dolyniuk, Juli-Anna; Lee, Shannon; Tran, Nhon; Wang, Jian; Wang, Lin-Lin; Kovnir, Kirill

2018-07-01

Chiral double Zintl salts present tunable crystal structures with enhanced structural flexibilities and potential for applications requiring chiral control and enantioselectivity. To accompany the chiral Sr2P7I and Sr2P7Br double Zintl salts reported by us previously, six new chiral Zintl salts of the form Ba2-ySryAs7I (y = 0, 0.23, 2), Eu2P7I, Eu2P7Br, and Eu1.3Ba0.7P7Br have been synthesized and characterized by single crystal X-ray diffraction and SEM-EDS analyses. All new compounds crystallize in the Sohncke space group P213 (No. 198) with variations of P73- (heptaphosphanortricyclane) or As73- (heptaarsanortricyclane) clusters surrounded by alkaline-earth or Eu cations and halogen anions. Band structure calculations predict semiconducting properties for all synthesized compounds. Diffuse reflectance UV-vis spectroscopy indicates that Eu2P7I is a direct bandgap semiconductor with Eg of 1.7 eV.

Structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr, Ba)

NASA Astrophysics Data System (ADS)

Benahmed, A.; Bouhemadou, A.; Alqarni, B.; Guechi, N.; Al-Douri, Y.; Khenata, R.; Bin-Omran, S.

2018-05-01

First-principles calculations were performed to investigate the structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr, Ba) using two complementary approaches based on density functional theory. The pseudopotential plane-wave method was used to explore the structural and elastic properties whereas the full-potential linearised augmented plane wave approach was used to study the structural, electronic, optical and thermoelectric properties. The calculated structural parameters are in good consistency with the corresponding measured ones. The single-crystal and polycrystalline elastic constants and related properties were examined in details. The electronic properties, including energy band dispersions, density of states and charge-carrier effective masses, were computed using Tran-Blaha modified Becke-Johnson functional for the exchange-correlation potential. It is found that both studied compounds are direct band gap semiconductors. Frequency-dependence of the linear optical functions were predicted for a wide photon energy range up to 15 eV. Charge carrier concentration and temperature dependences of the basic parameters of the thermoelectric properties were explored using the semi-classical Boltzmann transport model. Our calculations unveil that the studied compounds are characterised by a high thermopower for both carriers, especially the p-type conduction is more favourable.

Pressure-induced structural transformations of the Zintl phase sodium silicide

NASA Astrophysics Data System (ADS)

Cabrera, Raúl Quesada; Salamat, Ashkan; Barkalov, Oleg I.; Leynaud, Olivier; Hutchins, Peter; Daisenberger, Dominik; Machon, Denis; Sella, Andrea; Lewis, Dewi W.; McMillan, Paul F.

2009-09-01

The high-pressure behaviour of NaSi has been studied using Raman spectroscopy and angle-dispersive synchrotron X-ray diffraction to observe the onset of structural phase transformations and potential oligomerisation into anionic Si nanoclusters with extended dimensionality. Our studies reveal a first structural transformation occurring at 8-10 GPa, followed by irreversible amorphisation above 15 GPa, suggesting the formation of Si-Si bonds with oxidation of the Si - species and reduction of Na + to metallic sodium. We have combined our experimental studies with DFT calculations to assist in the analysis of the structural behaviour of NaSi at high pressure.

Structural and thermoelectric properties of zintl-phase CaLiPn (Pn=As, Sb, Bi)

NASA Astrophysics Data System (ADS)

Chandran, Anoop K.; Gudelli, Vijay Kumar; Sreeparvathy, P. C.; Kanchana, V.

2016-11-01

First-principles calculations were carried out to study the structural, mechanical, dynamical and transport properties of zintl phase materials CaLiPn (Pn=As, Sb and Bi). We have used two different approaches to solve the system based on density functional theory. The plane wave pseudopotential approach has been used to study the structural and dynamical properties whereas, full potential linear augment plane wave method is used to examine the electronic structure, mechanical and thermoelectric properties. The calculated ground-state properties agree quite well with experimental values. The computed electronic structure shows the investigated compounds to be direct band gap semiconductors. Further, we have calculated the thermoelectric properties of all the investigated compounds for both the carriers at various temperatures. We found a high thermopower for both the carriers, especially n-type doping to be more favourable, which enabled us to predict that CaLiPn might have promising applications as a good thermoelectric material. Further, the phonon dispersion curves of the investigated compounds showed flat phonon modes and we also find lower optical and acoustic modes to cut each other at the lower frequency range, which further indicate the investigated compounds to possess reasonably low thermal conductivity. We have also analysed the low value of the thermal conductivity through the empirical relations and discussions are presented here.

Electronic structure calculation by nonlinear optimization: Application to metals

NASA Astrophysics Data System (ADS)

Benedek, R.; Min, B. I.; Woodward, C.; Garner, J.

1988-04-01

There is considerable interest in the development of novel algorithms for the calculation of electronic structure (e.g., at the level of the local-density approximation of density-functional theory). In this paper we consider a first-order equation-of-motion method. Two methods of solution are described, one proposed by Williams and Soler, and the other base on a Born-Dyson series expansion. The extension of the approach to metallic systems is outlined and preliminary numerical calculations for Zintl-phase NaTl are presented.

Study on anisotropy of n-type Mg3Sb2-based thermoelectric materials

NASA Astrophysics Data System (ADS)

Song, Shaowei; Mao, Jun; Shuai, Jing; Zhu, Hangtian; Ren, Zhensong; Saparamadu, Udara; Tang, Zhongjia; Wang, Bo; Ren, Zhifeng

2018-02-01

The recent discovery of a high thermoelectric figure of merit (ZT) in an n-type Mg3Sb2-based Zintl phase triggered an intense research effort to pursue even higher ZT. Based on our previous report on Mg3.1Nb0.1Sb1.5Bi0.49Te0.01, we report here that partial texturing in the (001) plane is achieved by double hot pressing, which is further confirmed by the rocking curves of the (002) plane. The textured samples of Mg3.1Nb0.1Sb1.5Bi0.49Te0.01 show a much better average performance in the (00l) plane. Hall mobility is significantly improved to ˜105 cm2 V-1 s-1 at room temperature in the (00l) plane due to texturing, resulting in higher electrical conductivity, a higher power factor of ˜18 μW cm-1 K-2 at room temperature, and also higher average ZT. This work shows that texturing is good for higher thermoelectric performance, suggesting that single crystals of n-type Mg3Sb2-based Zintl compounds are worth pursuing.

Semiconducting Ba 3Sn 3Sb 4 and Metallic Ba 7–xSn 11Sb 15–y ( x = 0.4, y = 0.6) Zintl Phases

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

Chen, Haijie; Narayan, Awadhesh; Stoumpos, Constantinos C.

In this paper, we report the discovery of two ternary Zintl phases Ba 3Sn 3Sb 4 and Ba 7-xSn 11Sb 15-y, (x = 0.4, y = 0.6). Ba 3Sn 3Sb 4 adopts the monoclinic space group P2 1/c with a = 14.669(3) Å, b = 6.9649(14) Å, c = 13.629(3) Å, and β = 104.98(3)°. It features a unique corrugated two-dimensional (2D) structure consisting of [Sn 3Sb 4] 6- layers extending along the ab plane with Ba 2+ atoms sandwiched between them. The non-stoichiometric Ba 6.6Sn 11Sb 14.4 has a complex one-dimensional (1D) structure adopting the orthorhombic space group Pnma,more » with unit cell parameters a = 37.964(8) Å, b = 4.4090(9) Å and c = 24.682(5) Å. It consists of large double Sn-Sb ribbons separated by Ba 2+ atoms. Ba3Sn3Sb4 is an n-type semiconductor which has a narrow energy gap of ~0.18 eV and a room temperature carrier concentration of ~4.2 × 10 18 cm -3. Lastly, Ba 6.6Sn 11Sb 14.4 is determined to be a metal with electrons being the dominant carriers.« less

Semiconducting Ba 3Sn 3Sb 4 and Metallic Ba 7–xSn 11Sb 15–y ( x = 0.4, y = 0.6) Zintl Phases

DOE PAGES

Chen, Haijie; Narayan, Awadhesh; Stoumpos, Constantinos C.; ...

2017-11-08

In this paper, we report the discovery of two ternary Zintl phases Ba 3Sn 3Sb 4 and Ba 7-xSn 11Sb 15-y, (x = 0.4, y = 0.6). Ba 3Sn 3Sb 4 adopts the monoclinic space group P2 1/c with a = 14.669(3) Å, b = 6.9649(14) Å, c = 13.629(3) Å, and β = 104.98(3)°. It features a unique corrugated two-dimensional (2D) structure consisting of [Sn 3Sb 4] 6- layers extending along the ab plane with Ba 2+ atoms sandwiched between them. The non-stoichiometric Ba 6.6Sn 11Sb 14.4 has a complex one-dimensional (1D) structure adopting the orthorhombic space group Pnma,more » with unit cell parameters a = 37.964(8) Å, b = 4.4090(9) Å and c = 24.682(5) Å. It consists of large double Sn-Sb ribbons separated by Ba 2+ atoms. Ba3Sn3Sb4 is an n-type semiconductor which has a narrow energy gap of ~0.18 eV and a room temperature carrier concentration of ~4.2 × 10 18 cm -3. Lastly, Ba 6.6Sn 11Sb 14.4 is determined to be a metal with electrons being the dominant carriers.« less

Aromaticity and Antiaromaticity in Zintl Clusters

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

Sun, Zhong -Ming; Liu, Chao; Popov, Ivan Aleksandrovich

Originally, the concepts of aromaticity and antiaromaticity were introduced to explain the stability and reactivity of unsaturated organic compounds. Since then, they have been extended to other species with delocalized electrons including various saturated systems, organometallic compounds, and even inorganic clusters and molecules. In this study, we focus on the most recent progress of using these concepts to guide experimental synthesis and rationalize geometrical and electronic structures of a particular family of polyanions composed of Group 14 and 15 elements, namely Zintl clusters.

Aromaticity and Antiaromaticity in Zintl Clusters

DOE PAGES

Sun, Zhong -Ming; Liu, Chao; Popov, Ivan Aleksandrovich; ...

2018-05-18

Originally, the concepts of aromaticity and antiaromaticity were introduced to explain the stability and reactivity of unsaturated organic compounds. Since then, they have been extended to other species with delocalized electrons including various saturated systems, organometallic compounds, and even inorganic clusters and molecules. In this study, we focus on the most recent progress of using these concepts to guide experimental synthesis and rationalize geometrical and electronic structures of a particular family of polyanions composed of Group 14 and 15 elements, namely Zintl clusters.

Synthesis, structure, and bonding of two lanthanum indium germanides with novel structures and properties

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

Guloy, A.M.; Corbett, J.D.

1996-04-24

The new tetragonal phases La{sub 3}In{sub 4}Ge and La{sub 3}InGe are obtained from high-temperature reactions of the elements in welded Ta followed by annealing. The structures of both were established by single-crystal X-ray diffraction in tetragonal space group I4/mcm (Z = 4 and 16, {alpha} = 8.5165(3) and 12.3083(2) {Angstrom}, c = 11.9024(4) and 16.0776(4) {Angstrom}, respectively). La{sub 3}In{sub 4}Ge contains layers or slabs of three-connected indium built of puckered 8-rings and 4-rings, or of squashed tetrahedra ({open_quotes}butterflies{close_quotes}) interlinked at all vertices, and these are separated by layers of La and isolated Ge. The phase is deficient of being amore » Zintl phase by three electrons per formula unit and is better described in terms of an alternate optimized and delocalized bonding picture and an open-shell metallic better described in terms of an alternate optimized and delocalized bonding picture and an open-shell metallic behavior for the In slabs. The more complex La{sub 3}InGe, isostructural with Gd{sub 3}Ga{sub 2}, is also layered. This phase contains pairs of mixed-occupancy (0.75 In, 0.25 Ge) sites separated by 3.020 {Angstrom}, as well as isolated In and Ge atoms. The former appear to be fully reduced closed-shell atoms (relative to the bonded Ga dimers in Gd{sub 3}Ga{sub 2}) that are held in somewhat close proximity by cation matrix effects. The compound appears to be semiconducting and thus is a classical Zintl phase, (La{sup +3}){sub 3}In{sup {minus}5}Ge{sup {minus}4} in the simplest oxidation state notation. High Coulomb energies are presumably important for the nature of the bonding and the stabilities of both compounds.« less

Copper Selenidophosphates Cu4P2Se6, Cu4P3Se4, Cu4P4Se3, and CuP2Se, Featuring Zero-, One-, and Two-Dimensional Anions.

PubMed

Kuhn, Alexander; Schoop, Leslie M; Eger, Roland; Moudrakovski, Igor; Schwarzmüller, Stefan; Duppel, Viola; Kremer, Reinhard K; Oeckler, Oliver; Lotsch, Bettina V

2016-08-15

Five new compounds in the Cu/P/Se phase diagram have been synthesized, and their crystal structures have been determined. The crystal structures of these compounds comprise four previously unreported zero-, one-, and two-dimensional selenidophosphate anions containing low-valent phosphorus. In addition to two new modifications of Cu4P2Se6 featuring the well-known hexaselenidohypodiphosphate(IV) ion, there are three copper selenidophosphates with low-valent P: Cu4P3Se4 contains two different new anions, (i) a monomeric (zero-dimensional) selenidophosphate anion [P2Se4](4-) and (ii) a one-dimensional selenidophosphate anion [Formula: see text], which is related to the well-known gray-Se-like [Formula: see text] Zintl anion. Cu4P4Se3 contains one-dimensional [Formula: see text] polyanions, whereas CuP2Se contains the 2D selenidophosphate [Formula: see text] polyanion. It consists of charge-neutral CuP2Se layers separated by a van der Waals gap which is very rare for a Zintl-type phase. Hence, besides black P, CuP2Se constitutes a new possible source of 2D oxidized phosphorus containing layers for intercalation or exfoliation experiments. Additionally, the electronic structures and some fundamental physical properties of the new compounds are reported. All compounds are semiconducting with indirect band gaps of the orders of around 1 eV. The phases reported here add to the structural diversity of chalcogenido phosphates. The structural variety of this family of compounds may translate into a variety of tunable physical properties.

LiBSi2: a tetrahedral semiconductor framework from boron and silicon atoms bearing lithium atoms in the channels.

PubMed

Zeilinger, Michael; van Wüllen, Leo; Benson, Daryn; Kranak, Verina F; Konar, Sumit; Fässler, Thomas F; Häussermann, Ulrich

2013-06-03

Silicon swallows up boron: The novel open tetrahedral framework structure (OTF) of the Zintl phase LiBSi2 was made by applying high pressure to a mixture of LiB and elemental silicon. The compound represents a new topology in the B-Si net (called tum), which hosts Li atoms in the channels (see picture). LiBSi2 is the first example where B and Si atoms form an ordered common framework structure with B engaged exclusively in heteronuclear B-Si contacts.

Ca4As3 – a new binary calcium arsenide

PubMed Central

Hoffmann, Andrea V.; Hlukhyy, Viktor; Fässler, Thomas F.

2015-01-01

The crystal structure of the binary compound tetra­calcium triarsenide, Ca4As3, was investigated by single-crystal X-ray diffraction. Ca4As3 crystallizes in the Ba4P3 structure type and is thus a homologue of isotypic Sr4As3. The unit cell contains 32 Ca2+ cations, 16 As3− isolated anions and four centrosymmetric [As2]4– dumbbells. The As atoms in each of the dumbbells are connected by a single bond, thus this calcium arsenide is a Zintl phase. PMID:26870427

Stability, electronic structures and thermoelectric properties of binary Zn–Sb materials

DOE PAGES

He, Xin; Fu, Yuhao; Singh, David J.; ...

2016-11-03

We report first principles studies of the binary Zn–Sb phases in relation to thermoelectric properties and chemical stability. We identify the unknown structure of the Zn 3Sb 2 phase using particle swarm optimization, finding a tetragonal structure different from the hexagonal Mg 3Sb 2 and the hexagonal or cubic Ca 3Sb 2 phases. All the phases are found to be semiconducting with bandgaps in the range of 0.06–0.77 eV. This semiconducting behavior is understood in Zintl terms as a balance between the Zn:Sb and Sb 3-:½(Sb 2) 4- ratios in the stable crystal structures. With the exception of Zn 3Sbmore » 2, which has a small gap, all the compounds have electronic properties favorable for thermoelectric performance.« less

Thermoelectric properties of the Ca(5)Al(2-x)In(x)Sb(6) solid solution.

PubMed

Zevalkink, Alex; Swallow, Jessica; Ohno, Saneyuki; Aydemir, Umut; Bux, Sabah; Snyder, G Jeffrey

2014-11-14

Zintl phases are attractive for thermoelectric applications due to their complex structures and bonding environments. The Zintl compounds Ca(5)Al(2)In(x)Sb(6)and Ca(5)Al(2)In(x)Sb(6) have both been shown to have promising thermoelectric properties, with zT values of 0.6 and 0.7, respectively, when doped to control the carrier concentration. Alloying can often be used to further improve thermoelectric materials in cases when the decrease in lattice thermal conductivity outweighs reductions to the electronic mobility. Here we present the high temperature thermoelectric properties of the Ca(5)Al(2-x)In(x)Sb(6)solid solution. Undoped and optimally Zn-doped samples were investigated. X-ray diffraction confirms that a full solid solution exists between the Al and In end-members. We find that the Al : In ratio does not greatly influence the carrier concentration or Seebeck effect. The primary effect of alloying is thus increased scattering of both charge carriers and phonons, leading to significantly reduced electronic mobility and lattice thermal conductivity at room temperature. Ultimately, the figure of merit is unaffected by alloying in this system, due to the competing effects of reduced mobility and lattice thermal conductivity.

Antibonding Holes Induce Good Thermoelectric Properties of p-type Ca5Ga2As6

NASA Astrophysics Data System (ADS)

Yu, Qingxiu; Wang, Yuan Xu; Shao, Hehong

2017-07-01

The arrangement of anionic tetrahedra in Zintl compounds plays a key role in determining their thermoelectric properties. We manifest this idea by investigating the crystal structure, electronic structure, and thermoelectric properties of the Zintl compounds Ca3GaAs3 and Ca5Ga2As6. By comparing various properties of Ca3GaAs3 and Ca5Ga2As6, we found that with decreasing calcium content from Ca3GaAs3 to Ca5Ga2As6, the two adjacent covalent chains formed by GaAs4 tetrahedra are connected by As-As bonds. In Ca5Ga2As6, the appearance of such As-As bonds not only supports the charge balance but also provides two nearly degenerate bands at the top of its valence bands. These two bands determine the thermoelectric behavior of p-type Ca5Ga2As6. The calculated band-decomposed charge density shows that the two bands have a π* antibonding feature of the As pz orbital. Our calculations also reveal that the formation or non-formation of As-As bonds plays an important role in the difference in the thermoelectric properties between Ca3GaAs3 and Ca5Ga2As6. The optimal carrier concentration for achieving the highest thermoelectric performance was explored by calculating the trends in their thermoelectric properties with the carrier concentration. Our work may stimulate further experimental and theoretical work to increase understanding of Zintl chemistry and improve the thermoelectric performance of Zintl compounds.

Synthesis, crystal structures, and physical properties of the new Zintl phases A{sub 21}Zn{sub 4}Pn{sub 18} (A=Ca, Eu; Pn=As, Sb)—Versatile arrangements of [ZnPn{sub 4}] tetrahedra

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

Suen, Nian-Tzu; Wang, Yi; Bobev, Svilen, E-mail: bobev@udel.edu

Four new Zintl phases, Ca{sub 21}Zn{sub 4}As{sub 18}, Ca{sub 21}Zn{sub 4}Sb{sub 18}, Eu{sub 21}Zn{sub 4}As{sub 18} and Eu{sub 21}Zn{sub 4}Sb{sub 18} have been synthesized by metal flux reactions. Their structures have been established from single-crystal X-ray diffraction. Despite the similar chemical makeup and the identical formulae, the structures of the four compounds are not the same—Ca{sub 21}Zn{sub 4}As{sub 18}, Ca{sub 21}Zn{sub 4}Sb{sub 18} and Eu{sub 21}Zn{sub 4}As{sub 18} crystallize in the monoclinic space group C2/m (No. 12, Z=4) with the β-Ca{sub 21}Mn{sub 4}Sb{sub 18} structure type, while Eu{sub 21}Zn{sub 4}Sb{sub 18} adopts the Ba{sub 21}Cd{sub 4}Sb{sub 18} structure type withmore » the orthorhombic space group Cmce (No. 64, Z=8). Both structures are based on ZnAs{sub 4} or ZnSb{sub 4} tetrahedra, linked in slightly different ways, and Ca{sup 2+} and Eu{sup 2+} cations that fill the space between them. The structural relationships between the title compounds and other known ternary phases with intricate structures are discussed. Electrical resistivity measurement on single-crystalline Eu{sub 21}Zn{sub 4}Sb{sub 18} suggests an intrinsic semiconductor behavior with a band gap of ca. 0.2 eV. The temperature dependent DC magnetization measurement on the same material indicates Curie–Weiss paramagnetism in the high-temperature regime, and a spontaneous antiferromagnetic ordering below 8 K. The calculated effective moments of Eu confirm the divalent Eu{sup 2+} ground state, as expected from the Zintl–Klemm concept. - Graphical abstract: The four new Zintl phases—Ca{sub 21}Zn{sub 4}As{sub 18}, Ca{sub 21}Zn{sub 4}Sb{sub 18}, Eu{sub 21}Zn{sub 4}As{sub 18}, and Eu{sub 21}Zn{sub 4}Sb{sub 18}—crystallize in two structure types, showing the versatility in the arrangements of ZnAs{sub 4} and ZnSb{sub 4} tetrahedra. - Highlights: • Ca{sub 21}Zn{sub 4}As{sub 18}, Ca{sub 21}Zn{sub 4}Sb{sub 18}, Eu{sub 21}Zn{sub 4}As{sub 18}, and Eu{sub 21}Zn{sub 4}Sb{sub 18} are new compounds in the respective ternary phase diagrams. • They form with structure types, showing the versatility in the arrangements of ZnAs{sub 4} and ZnSb{sub 4} tetrahedra. • For both structures, the valence electron count follows the Zintl–Klemm rules.« less

Studies on the reactivity of [Ge9]4- towards [Fe(cot)(CO)3]: synthesis and characterization of [Ge8Fe(CO)3]3- and of the anionic organometallic species [Fe(cot)(CO)3]-.

PubMed

Zhou, Binbin; Goicoechea, Jose M

2010-09-24

Reaction of cyclooctatetraene (COT) iron(II) tricarbonyl, [Fe(cot)(CO)(3)], with one equivalent of K(4)Ge(9) in ethylenediamine (en) yielded the cluster anion [Ge(8)Fe(CO)(3)](3-) which was crystallographically-characterized as a [K(2,2,2-crypt)](+) salt in [K(2,2,2-crypt)](3)[Ge(8)Fe(CO)(3)]. The chemically-reduced organometallic species [Fe(η(3)-C(8)H(8))(CO)(3)](-) was also isolated as a side-product from this reaction as [K(2,2,2-crypt)][Fe(η(3)-C(8)H(8))(CO)(3)]. Both species were further characterized by EPR and IR spectroscopy and electrospray mass spectrometry. The [Ge(8)Fe(CO)(3)](3-) cluster anion represents an unprecedented functionalized germanium Zintl anion in which the nine-atom precursor cluster has lost a vertex, which has been replaced by a transition-metal moiety.

New insights into the application of the valence rules in Zintl phases—Crystal and electronic structures of Ba{sub 7}Ga{sub 4}P{sub 9}, Ba{sub 7}Ga{sub 4}As{sub 9}, Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 6}CaAl{sub 4}Sb{sub 9}, and Ba{sub 6}CaGa{sub 4}Sb{sub 9}

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

He, Hua; Stoyko, Stanislav; Bobev, Svilen, E-mail: bobev@udel.edu

Crystals of three new ternary pnictides—Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9} have been prepared by reactions of the respective elements in molten Al or Pb fluxes. Single-crystal X-ray diffraction studies reveal that the three phases are isotypic, crystallizing in the orthorhombic Ba{sub 7}Ga{sub 4}Sb{sub 9}-type structure (space group Pmmn, Pearson symbol oP40, Z=2), for which only the prototype is known. The structure is based on TrPn{sub 4} tetrahedra (Tr=Al, Ga; Pn=P, As, Sb), connected in an intricate scheme into 1D-ribbons. Long interchain Pn–Pn bonds (d{sub P–P}>3.0 Å; d{sub As–As}>3.1 Å; d{sub Sb–Sb}>3.3 Å)more » account for the realization of 2D-layers, separated by Ba{sup 2+} cations. Applying the classic valance rules to rationalize the bonding apparently fails, and Ba{sub 7}Ga{sub 4}Sb{sub 9} has long been known as a metallic Zintl phase. Earlier theoretical calculations, both empirical and ab-initio, suggest that the possible metallic properties originate from filled anti-bonding Pn–Pn states, and the special roles of the “cations” in this crystal structure. To experimentally probe this hypothesis, we sought to synthesize the ordered quaternary phases Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga). Single-crystal X-ray diffraction work confirms Ba{sub 6.145(3)}Ca{sub 0.855}Al{sub 4}Sb{sub 9} and Ba{sub 6.235(3)}Ca{sub 0.765}Ga{sub 4}Sb{sub 9}, with Ca atoms preferably substituting Ba on one of the three available sites. The nuances of the five crystal structures are discussed, and the chemical bonding in Ba{sub 7}Ga{sub 4}As{sub 9} is interrogated by tight-binding linear muffin-tin orbital calculations. - Graphical abstract: The new Zintl phases—Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9}, and their quaternary variants Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga)—crystallize in the Ba{sub 7}Ga{sub 4}Sb{sub 9} structure type. The structures are based on TrPn{sub 4} tetrahedra (a perspective of the crystal structure is shown, as viewed along the c axis). - Highlights: • Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9} are new compounds in the respective phase diagrams. • The quaternary phases Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga) show nearly ordered Ba/Ca distribution. • Very weak Pn–Pn bonds and pairing distortion are observed for Ba{sub 7}Ga{sub 4}Pn{sub 9} (Pn=P, As).« less

A low temperature solution phases synthesis for silicon quantum dots

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

Bley, R.A.; Yang, Chung-Sung; Kauzlarich, S.M.

Silicon nanoparticles are of interest because of their optoelectronic properties. This warrants finding new methods for making these clusters which are more economical and allow for greater versatility in their mechanical and chemical manipulation. We have produced silicon nanoclusters using a low temperature solution phase method. Our approach uses the Zintl salts KSi, NaSi or Mg{sub 2}Si as the source of silicon anion, This is reacted with tetrachlorosilane, the silicon cation source, in appropriate solvents. These nanoclusters have been terminated with various organic groups via reaction with alkyl-Li or alkylgrignard reagents. High resolution TEM, FTIR, and Raman spectroscopy have beenmore » used to establish the size, structure and surface composition of the particles. UV-vis and photoluminescence have been used to investigate their optical properties. The effect of termination on the photoluminescence will be discussed in detail.« less

Synthesis and structural characterization of the Zintl phases Na{sub 3}Ca{sub 3}TrPn{sub 4}, Na{sub 3}Sr{sub 3}TrPn{sub 4}, and Na{sub 3}Eu{sub 3}TrPn{sub 4} (Tr=Al, Ga, In; Pn=P, As, Sb)

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

Wang, Yi; Suen, Nian-Tzu; College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002

15 new quaternary Zintl phases have been synthesized by solid-state reactions from the respective elements, and their structures have been determined by single-crystal X-ray diffraction. Na{sub 3}E{sub 3}TrPn{sub 4} (E=Ca, Sr, Eu; Tr=Al, Ga, In; Pn=P, As, Sb) crystallize in the hexagonal crystal system with the non-centrosymmetric space group P6{sub 3}mc (No. 186). The structure represents a variant of the K{sub 6}HgS{sub 4} structure type (Pearson index hP22) and features [TrPn{sub 4}]{sup 9–} tetrahedral units, surrounded by Na{sup +} and Ca{sup 2+}, Sr{sup 2+}, Eu{sup 2+} cations. The nominal formula rationalization [Na{sup +}]{sub 3}[E{sup 2+}]{sub 3}[TrPn{sub 4}]{sup 9–} follows themore » octet rule, suggesting closed-shell configurations for all atoms and intrinsic semiconducting behavior. However, structure refinements for several members hint at disorder and mixing of cations that potentially counteract the optimal valence electron count. - Graphical abstract: The hexagonal, non-centrosymmetric structure of Na{sub 3}E{sub 3}TrPn{sub 4} (E=Ca, Sr, Eu; Tr=Al, Ga, In; Pn=P, As, Sb) features [TrPn{sub 4}]{sup 9–} tetrahedral units, surrounded by Na{sup +} and Ca{sup 2+}, Sr{sup 2+}, Eu{sup 2+} cations. - Highlights: • 15 quaternary phosphides, arsenides, and antimonides are synthesized and structurally characterized. • The structure is a variant of the hexagonal K{sub 6}HgS{sub 4}-type, with distinctive pattern for the cations. • Occupational and/or positional disorder of yet unknown origin exists for some members of the series.« less

Valence State Driven Site Preference in the Quaternary Compound Ca5MgAgGe5: An Electron-Deficient Phase with Optimized Bonding

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

Ponou, Simeon; Lidin, Sven; Zhang, Yuemei

The quaternary phase Ca5Mg0.95Ag1.05(1)Ge5 (3) was synthesized by high-temperature solid-state techniques, and its crystal structure was determined by single-crystal diffraction methods in the orthorhombic space group Pnma – Wyckoff sequence c12 with a = 23.1481(4) Å, b = 4.4736(1) Å, c = 11.0128(2) Å, V = 1140.43(4) Å3, Z = 4. The crystal structure can be described as linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaMGe (TiNiSi-type; M = Mg, Ag) structures. Hence, 3 is a hettotype of the hitherto missing n = 3 member of the structure series with the general formula R2+nT2X2+n, previously describedmore » with n = 1, 2, and 4. The member with n = 3 was predicted in the space group Cmcm – Wyckoff sequence f5c2. The experimental space group Pnma (in the nonstandard setting Pmcn) corresponds to a klassengleiche symmetry reduction of index two of the predicted space group Cmcm. This transition originates from the switching of one Ge and one Ag position in the TiNiSi-related slab, a process that triggers an uncoupling of each of the five 8f sites in Cmcm into two 4c sites in Pnma. The Mg/Ag site preference was investigated using VASP calculations and revealed a remarkable example of an intermetallic compound for which the electrostatic valency principle is a critical structure-directing force. The compound is deficient by one valence electron according to the Zintl concept, but LMTO electronic structure calculations indicate electronic stabilization and overall bonding optimization in the polyanionic network. Other stability factors beyond the Zintl concept that may account for the electronic stabilization are discussed.« less

Lithiation-induced zinc clustering of Zn 3, Zn 12, and Zn 18 units in Zintl-like Ca ~30Li 3+xZn 60-x (x=0.44-1.38)

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

Lin, Qisheng

2014-11-14

Zinc clusters are not common for binary intermetallics with relatively low zinc content, but this work shows that zinc clustering can be triggered by lithiation, as exemplified by Ca ~30Li 3+xZn 60-x, P6/mmm, Z = 1, which can be directly converted from CaZn 2. Two end members of the solid solution (x = 0.44 and 1.38) were established and structurally characterized by single-crystal X-ray diffraction analyses: Ca 30Li 3.44(6)Zn59.56(6), a = 15.4651(9) Å, c = 9.3898(3) Å; Ca 30.45(2)Li 4.38(6)Zn 58.62(6), a = 15.524(3) Å, c = 9.413(2) Å. The structures of Ca ~30Li 3+xZn 60-x feature a condensed anionicmore » network of Zn3 triangles, lithium-centered Zn12 icosahedra, and arachno-(Zn,Li)18 tubular clusters that are surrounded respectively by Ca 14, Ca 20, and Ca 30 polyhedra. These polyhedra share faces and form a clathrate-like cationic framework. The specific occupation of lithium in the structure is consistent with theoretical “coloring” analyses. Analysis by the linear muffin-tin orbital (LMTO) method within the atomic sphere approximation reveals that Ca ~30Li 3+xZn 60-x is a metallic, Zintl-like phase with an open-shell electronic structure. The contribution of Ca–Zn polar covalent interactions is about 41%.« less

Ab initio computational study on the lattice thermal conductivity of Zintl clathrates [Si19P4] Cl4 and Na4[Al4Si19

NASA Astrophysics Data System (ADS)

Härkönen, Ville J.; Karttunen, Antti J.

2016-08-01

The lattice thermal conductivity of silicon clathrate framework Si23 and two Zintl clathrates, [Si19P4] Cl4 and Na4[Al4Si19] , is investigated by using an iterative solution of the linearized Boltzmann transport equation in conjunction with ab initio lattice dynamical techniques. At 300 K, the lattice thermal conductivities for Si23, [Si19P4] Cl4 , and Na4[Al4Si19] were found to be 43 W/(m K), 25 W/(m K), and 2 W/(m K), respectively. In the case of Na4[Al4Si19] , the order-of-magnitude reduction in the lattice thermal conductivity was found to be mostly due to relaxation times and group velocities differing from Si23 and [Si19P4] Cl4 . The difference in the relaxation times and group velocities arises primarily due to the phonon spectrum at low frequencies, resulting eventually from the differences in the second-order interatomic force constants (IFCs). The obtained third-order IFCs were rather similar for all materials considered here. The present findings are similar to those obtained earlier for some skutterudites. The predicted lattice thermal conductivity of Na4[Al4Si19] is in line with the experimentally measured thermal conductivity of recently synthesized type-I Zintl clathrate Na8[Al8Si38] (polycrystalline samples).

Synthesis and characterization of P-doped amorphous and nanocrystalline Si

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

Wang, Jialing; Ganguly, Shreyashi; Sen, Sabyasachi

Intentional impurity doping lies at the heart of the silicon technology. The dopants provide electrons or holes as necessary carriers of the electron current and can significantly modify the electric, optical and magnetic properties of the semiconductors. P-doped amorphous Si (a-Si) was prepared by a solid state and solution metathesis reaction of a P-doped Zintl phase precursor, NaSi 0.99P 0.01, with an excess of NH 4X (X = Br, I). After the salt byproduct was removed from the solid state reaction, the a-Si material was annealed at 600 °C under vacuum for 2 h, resulting in P-doped nanocrystalline Si (nc-Si)more » material embedded in a-Si matrix. The product from the solution reaction also shows a combination of nc-Si embedded in a-Si; however, it was fully converted to nc-Si after annealing under argon at 650 °C for 30 min. Powder X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) show the amorphous nature of the P-doped Si material before the annealing and the nanocrystallinity after the annealing. Fourier Transform Infrared (FTIR) spectroscopy shows that the P-doped Si material surface is partially capped by H and O or with solvent. Finally, electron microprobe wavelength dispersive spectroscopy (WDS) as well as energy dispersive spectroscopy (EDS) confirm the presence of P in the Si material. 29Si and 31P solid state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy data provide the evidence of P doping into the Si structure with the P concentration of approximately 0.07 at.%.« less

Engineering half-Heusler thermoelectric materials using Zintl chemistry

NASA Astrophysics Data System (ADS)

Zeier, Wolfgang G.; Schmitt, Jennifer; Hautier, Geoffroy; Aydemir, Umut; Gibbs, Zachary M.; Felser, Claudia; Snyder, G. Jeffrey

2016-06-01

Half-Heusler compounds based on XNiSn and XCoSb (X = Ti, Zr or Hf) have rapidly become important thermoelectric materials for converting waste heat into electricity. In this Review, we provide an overview on the electronic properties of half-Heusler compounds in an attempt to understand their basic structural chemistry and physical properties, and to guide their further development. Half-Heusler compounds can exhibit semiconducting transport behaviour even though they are described as ‘intermetallic’ compounds. Therefore, it is most useful to consider these systems as rigid-band semiconductors within the framework of Zintl (or valence-precise) compounds. These considerations aid our understanding of their properties, such as the bandgap and low hole mobility because of interstitial Ni defects in XNiSn. Understanding the structural and bonding characteristics, including the presence of defects, will help to develop different strategies to improve and design better half-Heusler thermoelectric materials.

Addition of a thallium vertex to empty and centered nine-atom deltahedral zintl ions of germanium and tin.

PubMed

Rios, Daniel; Gillett-Kunnath, Miriam M; Taylor, Jacob D; Oliver, Allen G; Sevov, Slavi C

2011-03-21

Nickel atoms were inserted into nine-atom deltahedral Zintl ions of E(9)(4-) (E = Ge, Sn) via reactions with Ni(cod)(2) (cod = cyclooctadiene), and [Ni@Sn(9)](3-) was structurally characterized. Both the empty and the Ni-centered clusters react with TlCp (Cp = cyclopentadienyl anion) and add a thallium vertex to form the deltahedral ten-atom closo-species [E(9)Tl](3-) and [Ni@E(9)Tl](3-), respectively. The structures of [Ge(9)Tl](3-) and [Ni@Sn(9)Tl](3-) showed that, as expected, the geometry of the ten-atom clusters is that of a bicapped square antiprism where the Tl-atom occupies one of the two capping vertices. This illustrates that centering a nine-atom cluster with a nickel atom does not change its reactivity toward TlCp. All compounds were characterized by electrospray mass spectrometry.

Investigation of phase evolution of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) by in situ synchrotron high-temperature powder diffraction

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

Ouyang, Xin; Huang, Saifang; School of Materials Science and Technology, China University of Geosciences

2014-03-15

In situ synchrotron X-ray powder diffraction was used to study the high-temperature phase evolution of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) precursors prepared via solid-state and sol–gel methods. After the precursors are heated to 1225 °C, the CCTO phase is the main phase observed in the calcined powder, with the presence of some minor impurities. Comparing the two precursors, we found that the onset temperature for the CCTO phase formation is 800 °C in the sol–gel precursor, lower than that in the solid-state precursor (875 °C). Intermediate phases were only observed in the sol–gel precursor. Both precursors are able to bemore » calcined to sub-micrometric sized powders. Based on the synchrotron data along with differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), the phase formation sequence and mechanism during calcination are proposed in this study. -- Graphical abstract: The in situ synchrotron HT-XRD patterns of CCTO sol–gel and solid-state precursor. Highlights: • Phase formation sequence/mechanism in two CCTO precursors has been established. • Formation temperature of CCTO via sol–gel method is lower than solid-state method. • Intermediate phases are only observed in the sol–gel precursor. • Both precursors are able to be calcined into sub-micrometric sized powders.« less

Amorphous and nanocrystalline luminescent Si and Ge obtained via a solid-state chemical metathesis synthesis route

NASA Astrophysics Data System (ADS)

McMillan, Paul F.; Gryko, Jan; Bull, Craig; Arledge, Richard; Kenyon, Anthony J.; Cressey, Barbara A.

2005-03-01

A new solid-state metathesis synthesis route was applied to obtain bulk samples of amorphous or microcrystalline Si and Ge. The method involves reaction of Zintl phases such as NaSi or NaGe, with ammonium or metal (e.g., CuCl, CoBr 2) halides. The driving force for the solid-state reaction is provided by the formation of alkali halides and the transition metals or metal silicides, or gaseous ammonia and hydrogen. The semiconductors were purified by washing to remove other solid products. The amorphous semiconductors were obtained in bulk form from reactions carried out at 200-300 °C. Syntheses at higher temperatures gave rise to microcrystalline semiconductors, or to micro-/nanocrystalline particles contained within the amorphous material. Similar crystalline/amorphous composites were obtained after heat treatment of bulk amorphous materials.

Investigation of phase evolution of CaCu3Ti4O12 (CCTO) by in situ synchrotron high-temperature powder diffraction

NASA Astrophysics Data System (ADS)

Ouyang, Xin; Huang, Saifang; Zhang, Weijun; Cao, Peng; Huang, Zhaohui; Gao, Wei

2014-03-01

In situ synchrotron X-ray powder diffraction was used to study the high-temperature phase evolution of CaCu3Ti4O12 (CCTO) precursors prepared via solid-state and sol-gel methods. After the precursors are heated to 1225 °C, the CCTO phase is the main phase observed in the calcined powder, with the presence of some minor impurities. Comparing the two precursors, we found that the onset temperature for the CCTO phase formation is 800 °C in the sol-gel precursor, lower than that in the solid-state precursor (875 °C). Intermediate phases were only observed in the sol-gel precursor. Both precursors are able to be calcined to sub-micrometric sized powders. Based on the synchrotron data along with differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), the phase formation sequence and mechanism during calcination are proposed in this study.

Simultaneous constraint and phase conversion processing of oxide superconductors

DOEpatents

Li, Qi; Thompson, Elliott D.; Riley, Jr., Gilbert N.; Hellstrom, Eric E.; Larbalestier, David C.; DeMoranville, Kenneth L.; Parrell, Jeffrey A.; Reeves, Jodi L.

2003-04-29

A method of making an oxide superconductor article includes subjecting an oxide superconductor precursor to a texturing operation to orient grains of the oxide superconductor precursor to obtain a highly textured precursor; and converting the textured oxide superconducting precursor into an oxide superconductor, while simultaneously applying a force to the precursor which at least matches the expansion force experienced by the precursor during phase conversion to the oxide superconductor. The density and the degree of texture of the oxide superconductor precursor are retained during phase conversion. The constraining force may be applied isostatically.

Structural and electronic properties of Genm- and KGen- Zintl anions (n=3-10;m=2-4) from density functional theory

NASA Astrophysics Data System (ADS)

Li, Si-Dian; Guo, Qiao-Ling; Zhao, Xiu-Feng; Wu, Hai-Shun; Jin, Zhi-Hao

2002-07-01

Structural optimizations and frequency analyses have been performed on free Genm- and KGen- (n=3-10, m=2-4) Zintl anions and ionization potentials and electron affinities calculated for KGen using the density functional theory (DFT) of Becke's three-parameter hybrid functional with the Perdew/Wang 91 expression. The DFT results obtained for small clusters (n=3-5) are further checked with both the second-order Moller-Plesset perturbation theory (MP2) and the configuration interaction calculations with all single and double substitutions from the Hartree-Fock reference determinant (CISD). Free Gen2- anions are found to share the same geometries as naked Zintl anions observed in solids with a systematical expansion in bond lengths within about 5%. Intensive searches indicate that two isomers, a tricapped trigonal prism (D3h) and a slightly distorted tricapped trigonal prism (C2v), exist for Ge92- and Ge93-, while nido-Ge94- clearly favors the monocapped antisquare prism (C4v) structure. HOMO-LUMO energy gaps >2.23 eV are obtained for Genm- series at the DFT level, except Ge93- which has a much narrower energy gap of 1.16 eV. The calculated Gibbs free energy change of Ge92-+Ge94-=2 Ge93- conversion reaction involving nonagermanides has the value of Delta]G[deg=-2.91 x105 J mol-1, providing the first quantum chemistry evidence that the geometrically deduced mixed valent couple of Ge92- and Ge94- in a previous study is thermodynamically unstable compared to two Ge93- anions. The calculated stabilization energies of Gen2-, Gen-, and Gen exhibit similar variation trends, clearly indicating a maximum at n=7, a minimum at n=8, and an obvious recovery at n=9 and 10. The calculated normal vibrational frequencies reproduce the six observed Raman peaks of naked Ge52- with an averaged discrepancy of 11 cm-1. Face-capped or edge-capped deltahedral structures are predicted for binary KGen- anions and KGen and K2Gen neutrals. The magic numbers at n=5, 9, and 10 obtained in both stabilization energies and ionization potentials well reproduce the abundance distributions of KGen- observed in time-of-flight mass spectra. The validity of the Zintl-Klemm-Busmann principle in KGen and K2Gen neutrals is supported by the finding that sizable electron transfers from K atoms to Gen nuclei occur in these clusters and the Gen nuclei approach corresponding structures of free closo-Gen2- anions.

Semiconductor Clathrates: In Situ Studies of Their High Pressure, Variable Temperature and Synthesis Behavior

NASA Astrophysics Data System (ADS)

Machon, D.; McMillan, P. F.; San-Miguel, A.; Barnes, P.; Hutchins, P. T.

In situ studies have provided valuable new information on the synthesis mechanisms, low temperature properties and high pressure behavior of semiconductor clathrates. Here we review work using synchrotron and laboratory X-ray diffraction and Raman scattering used to study mainly Si-based clathrates under a variety of conditions. During synthesis of the Type I clathrate Na8Si46 by metastable thermal decomposition from NaSi in vacuum, we observe an unusual quasi-epitaxial process where the clathrate structure appears to nucleate and grow directly from the Na-deficient Zintl phase surface. Low temperature X-ray studies of the guest-free Type II clathrate framework Si136 reveal a region of negative thermal expansion behavior as predicted theoretically and analogous to that observed for diamond-structured Si. High pressure studies of Si136 lead to metastable production of the β-Sn structured Si-II phase as well as perhaps other metastable crystalline materials. High pressure investigations of Type I clathrates show evidence for a new class of apparently isostructural densification transformations followed by amorphization in certain cases.

Synthesis and characterization of the divalent samarium Zintl-phases SmMg 2Bi 2 and SmMg 2Sb 2

DOE PAGES

Ramirez, D.; Gallagher, A.; Baumbach, R.; ...

2015-08-29

Here, single crystals of LnMg 2Bi 2 (Ln = Yb, Eu, Sm) and SmMg 2Sb 2 were synthesized using Mg-Bi metal and Mg-Sb metal fluxes, respectively. The crystal structures are of the CaAl 2Si 2 type with space group P3 m1 (#164, Z = 1): SmMg 2Bi 2 ( a = 4.7745(1)Å, c = 7.8490(2)Å), EuMg 2Bi 2 ( a = 4.7702(1)Å, c = 7.8457(2) Å), YbMg 2Bi 2 ( a = 4.7317(2)Å, c = 7.6524(3) Å), and SmMg 2Sb 2 ( a = 4.6861(1) Å, c = 7.7192(2) Å). Heat capacity, electrical transport, and magnetization of all bismuth containingmore » phases were measured. The materials behave as “poor metals” with resistivity between 2 and 10 mΩ·cm. Temperature independent Van Vleck paramagnetism is observed in SmMg 2Bi 2 indicative of divalent samarium (Sm 2+) ions.« less

Amorphous and nanocrystalline luminescent Si and Ge obtained via a solid-state chemical metathesis synthesis route

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

McMillan, Paul F.; Gryko, Jan; Bull, Craig

A new solid-state metathesis synthesis route was applied to obtain bulk samples of amorphous or microcrystalline Si and Ge. The method involves reaction of Zintl phases such as NaSi or NaGe, with ammonium or metal (e.g., CuCl, CoBr{sub 2}) halides. The driving force for the solid-state reaction is provided by the formation of alkali halides and the transition metals or metal silicides, or gaseous ammonia and hydrogen. The semiconductors were purified by washing to remove other solid products. The amorphous semiconductors were obtained in bulk form from reactions carried out at 200-300{sup o}C. Syntheses at higher temperatures gave rise tomore » microcrystalline semiconductors, or to micro-/nanocrystalline particles contained within the amorphous material. Similar crystalline/amorphous composites were obtained after heat treatment of bulk amorphous materials.« less

Chromospheric Response during the Precursor and the Main Phase of a B6.4 Flare on 2005 August 20

NASA Astrophysics Data System (ADS)

Awasthi, Arun Kumar; Rudawy, Pawel; Falewicz, Robert; Berlicki, Arkadiusz; Liu, Rui

2018-05-01

Solar flare precursors depict a constrained rate of energy release, in contrast to the imminent rapid energy release, which calls for a different regime of plasma processes to be at play. Due to the subtle emission during the precursor phase, its diagnostics remain delusive, revealing either nonthermal electrons (NTEs) or thermal conduction to be the driver. In this regard, we investigate the chromospheric response during various phases of a B6.4 flare on 2005 August 20. Spatiotemporal investigation of flare ribbon enhancement during the precursor phase, carried out using spectra images recorded in several wavelength positions on the Hα line profile, revealed its delayed response (180 s) compared to the X-ray emission, as well as a sequential increment in the width of the line profile, which are indicative of a slow heating process. However, the energy contained in the Hα emission during the precursor phase can reach as high as 80% of that estimated during the main phase. Additionally, the plasma hydrodynamics during the precursor phase, resulting from the application of a single-loop one-dimensional model, revealed the presence of a power-law extension in the model-generated X-ray spectra, with a flux lower than the RHESSI background. Therefore, our multiwavelength diagnostics and hydrodynamical modeling of the precursor emission indicates the role of a two-stage process. First, reconnection-triggered NTEs, although too small in flux to overcome the observational constraints, thermalize in the upper chromosphere. This leads to the generation of a slow conduction front, which causes plasma heating during the precursor phase.

Multiwavelength Diagnostics of the Precursor and Main Phases of an M1.8 Flare on 2011 April 22

NASA Technical Reports Server (NTRS)

Awasthi, A. K.; Jain, R.; Gadhiya, P. D.; Aschwanden, M. J.; Uddin, W.; Srivastava, A. K.; Chandra, R.; Gopalswamy, N.; Nitta, N. V.; Yashiro, S.;

Pressure-induced structural transformations of the Zintl phase sodium silicide

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

Cabrera, Raul Quesada; Salamat, Ashkan; Barkalov, Oleg I.

The high-pressure behaviour of NaSi has been studied using Raman spectroscopy and angle-dispersive synchrotron X-ray diffraction to observe the onset of structural phase transformations and potential oligomerisation into anionic Si nanoclusters with extended dimensionality. Our studies reveal a first structural transformation occurring at 8-10 GPa, followed by irreversible amorphisation above 15 GPa, suggesting the formation of Si-Si bonds with oxidation of the Si{sup -} species and reduction of Na{sup +} to metallic sodium. We have combined our experimental studies with DFT calculations to assist in the analysis of the structural behaviour of NaSi at high pressure. - Abstract: The high-pressuremore » behaviour of NaSi has been studied using Raman spectroscopy and angle-dispersive synchrotron X-ray diffraction. Our studies reveal a first structural transformation occurring at 8-10 GPa, followed by irreversible amorphisation, suggesting the formation of Si-Si bonds with oxidation of the Si{sup -} species and reduction of Na{sup +} to metallic sodium. We have combined our experimental studies with DFT calculations to assist in the analysis of the structural behaviour of NaSi at high pressure. Display Omitted« less

The relationship between the electronic structure and thermoelectric properties of Zintl compounds M2Zn5As4 (M = K, Rb).

PubMed

Yang, Gui; Yang, Jueming; Yan, Yuli; Wang, Yuanxu

2014-03-28

The electronic structure and the thermoelectric properties of M2Zn5As4 (M = K, Rb) are studied by the first principles and the semiclassical BoltzTraP theory. It is determined that they are semiconductors with an indirect band gap of about 1 eV, which is much larger than that of Ca5Al2Sb6 (0.50 eV). The calculated electronic localization function indicates that they are typical Zintl bonding compounds. The combination of heavy and light bands near the valence band maximum may improve their thermoelectric performance. Rb2Zn5As4 exhibits relatively large Seebeck coefficients, high electrical conductivities, and the large "maximum" thermoelectric figures of merit (ZeT). Compared with Ca5Al2Sb6, the highest ZeT of Rb2Zn5As4 appears at relatively low carrier concentration. For Rb2Zn4As5, the p-type doping may achieve a higher thermoelectric performance than n-type doping. The thermoelectric properties of Rb2Zn5As4 are possibly superior to those of Ca5Al2Sb6.

High Temperature Electronic and Thermal Transport Properties of EuGa2- x In x Sb2

NASA Astrophysics Data System (ADS)

Chanakian, Sevan; Weber, Rochelle; Aydemir, Umut; Ormeci, Alim; Fleurial, Jean-Pierre; Bux, Sabah; Snyder, G. Jeffrey

2017-08-01

The Zintl phase EuGa2Sb2 was synthesized via ball milling followed by hot pressing. The crystal structure of EuGa2Sb2 is comprised of a 3-D network of polyanionic [Ga2Sb2]2- tunnels filled with Eu cations that provide charge balance (Eu2+[Ga2Sb2]2-). Here we report the temperature-dependent resistivity, Hall Effect, Seebeck coefficient and thermal conductivity for EuGa2- x In x Sb2 ( x = 0, 0.05, 0.1) from 300 K to 775 K. Experimental results demonstrate that the material is a p-type semiconductor. However, a small band gap (˜0.1 eV) prevents EuGa2Sb2 from having high zT at higher temperatures. Isoelectronic substitution of In on the Ga site leads to point defect scattering of holes and phonons, thus reducing thermal conductivity and resulting in a slight improvement in zT.

Increased KPI containing amyloid precursor protein in experimental autoimmune encephalomyelitis brains.

PubMed

Beilin, Orit; Karussis, Dimitrios M; Korczyn, Amos D; Gurwitz, David; Aronovich, Ramona; Mizrachi-Kol, Rachel; Chapman, Joab

2007-04-16

Amyloid precursor protein can be translated from three alternatively spliced mRNAs. We measured levels of amyloid precursor protein isoforms containing the Kunitz protease inhibitor domain (KPIAPP), and amyloid precursor protein without the Kunitz protease inhibitor domain (KPIAPP) in brain homogenates of acute experimental autoimmune encephalomyelitis mice. At the preclinical phase of the disease, both KPIAPP and KPIAPP levels were significantly higher in homogenates from brains of autoimmune encephalomyelitis mice, whereas at the acute phase of the disease only KPIAPP remained significantly elevated compared with controls. At the recovery phase, no differences were observed between the groups. The early and isoform-specific elevation of KPIAPP in autoimmune encephalomyelitis mice suggests a possible role for amyloid precursor protein in the immune response mediating the disease.

Phase transitions in colloidal fluids: Kinetically or thermodynamically controlled?

NASA Astrophysics Data System (ADS)

Duran-Olivencia, Miguel A.; Yatsyshin, Peter; Lutsko, James F.; Kalliadasis, Serafim

2017-11-01

In recent years, a flurry of experimental observations suggests that most phase transitions occur in a multistage manner and via intermediate phases. These precursors to the final phase are commonly understood as the local minima of the free energy of the system. Inherently, the classical paradigm of nucleation has no capacity to describe neither the origin nor the role played by these precursors in the nucleation pathway. Here we present a systematic theoretical framework capable of describing the precursor phases in a self-consistent way. We demonstrate that nucleation precursors can appear even in situations involving a single free-energy barrier. This contradicts previous phenomenological approaches, which always characterise intermediate phases as the minima of a complex free-energy landscape. We show that a kinetically-induced mechanism temporarily stabilises an intermediate phase, which thus is not the result of a local minimum of the free energy but a consequence of the entropic cost of cluster formation. Moreover, the appearance of precursors does not seem to influence the overall nucleation time, which is governed by the free-energy barrier. The mechanism uncovered in this study can be used to explain recently reported experimental findings in crystallisation. European Research Council - Advanced Grant No. 247031; Engineering and Physical Sciences Research Council - Grant Nos. EP/L020564 and EP/L025159.

Synthesis and Characterization of Some Alkaline-Earth-Oxide Nanoparticles

NASA Astrophysics Data System (ADS)

Singh, Jitendra Pal; Lim, Weon Cheol; Won, Sung Ok; Song, Jonghan; Chae, Keun Hwa

2018-04-01

The present work reports the synthesis of MgO and CaO nanoparticles by using the sol-gel autocombustion method. The annealing of the precursor at 1200 °C was observed to lead the formation of MgO nanoparticles having average crystallite size of 31 nm. Annealing the precursor at same temperature produced materials having a CaO phase with a minor impure phase of calcium carbonate ( 3%). The crystallite size corresponding to the CaO phase was 38 nm. A change of thermal history in the precursor was observed not to result in an improvement of the CaO phase. The change of thermal history in the precursor gave rise to mixed phases of CaCO3 and Ca(OH)2 rather than the phase of CaO. Further, annealing at 1200 °C for 12 h resulted in the formation of the CaO phase along with almost 1 - 5% of calcium hydroxide as an impurity phase. X-ray absorption spectroscopic measurements carried out on these materials revealed that the local electronic/atomic structure of these oxides was not only affected by the impurity phases but also influenced by the carbaneous impurities attached to the crystallites.

Precursor composites for oxygen dispersion hardened silver sheathed superconductor composites

DOEpatents

Podtburg, E.R.

1999-06-22

An oxide superconductor composite having improved texture and durability is disclosed. The oxide superconductor composite includes an oxide superconductor phase substantially surrounded with/by a noble metal matrix, the noble metal matrix comprising a metal oxide in an amount effective to form metal oxide domains that increase hardness of the composite. The composite is characterized by a degree of texture at least 10% greater than a comparable oxide superconductor composite lacking metal oxide domains. An oxide superconducting composite may be prepared by oxidizing the precursor composite under conditions effective to form solute metal oxide domains within the silver matrix and to form a precursor oxide in the precursor alloy phase; subjecting the oxidized composite to a softening anneal under conditions effective to relieve stress within the noble metal phase; and converting the oxide precursor into an oxide superconductor. 1 fig.

Precursor composites for oxygen dispersion hardened silver sheathed superconductor composites

DOEpatents

Podtburg, Eric R.

1999-01-01

An oxide superconductor composite having improved texture and durability. The oxide superconductor composite includes an oxide superconductor phase substantially surrounded with/by a noble metal matrix, the noble metal matrix comprising a metal oxide in an amount effective to form metal oxide domains that increase hardness of the composite. The composite is characterized by a degree of texture at least 10% greater than a comparable oxide superconductor composite lacking metal oxide domains. An oxide superconducting composite may be prepared by oxidizing the precursor composite under conditions effective to form solute metal oxide domains within the silver matrix and to form a precursor oxide in the precursor alloy phase; subjecting the oxidized composite to a softening anneal under conditions effective to relieve stress within the noble metal phase; and converting the oxide precursor into an oxide superconductor.

Gas-phase kinetics modifies the CCN activity of a biogenic SOA.

PubMed

Vizenor, A E; Asa-Awuku, A A

2018-02-28

Our current knowledge of cloud condensation nuclei (CCN) activity and the hygroscopicity of secondary organic aerosol (SOA) depends on the particle size and composition, explicitly, the thermodynamic properties of the aerosol solute and subsequent interactions with water. Here, we examine the CCN activation of 3 SOA systems (2 biogenic single precursor and 1 mixed precursor SOA system) in relation to gas-phase decay. Specifically, the relationship between time, gas-phase precursor decay and CCN activity of 100 nm SOA is studied. The studied SOA systems exhibit a time-dependent growth of CCN activity at an instrument supersaturation of ∼0.2%. As such, we define a critical activation time, t 50 , above which a 100 nm SOA particle will activate. The critical activation time for isoprene, longifolene and a mixture of the two precursor SOA is 2.01 hours, 2.53 hours and 3.17 hours, respectively. The activation times are then predicted with gas-phase kinetic data inferred from measurements of precursor decay. The gas-phase prediction of t 50 agrees well with CCN measured t 50 (within 0.05 hours of the actual critical times) and suggests that the gas-to-particle phase partitioning may be more significant for SOA CCN prediction than previously thought.

Supramolecular Assembly of Single-Source Metal-Chalcogenide Nanocrystal Precursors.

PubMed

Smith, Stephanie C; Bryks, Whitney; Tao, Andrea R

2018-05-28

In this Feature Article, we discuss our recent work in the synthesis of novel supramolecular precursors for semiconductor nanocrystals. Metal chalcogenolates that adopt liquid crystalline phases are employed as single-source precursors that template the growth of shaped solid-state nanocrystals. Supramolecular assembly is programmed by both precursor chemical composition and molecular parameters such alkyl chain length, steric bulk, and the intercalation of halide ions. Here, we explore the various design principles that enable the rational synthesis of these single-source precursors, their liquid crystalline phases, and the various semiconductor nanocrystal products that can be generated by thermolysis, ranging from highly anisotropic two-dimensional nanosheets and nanodisks to spheres.

Precursor preparation for Ca-Al layered double hydroxide to remove hexavalent chromium coexisting with calcium and magnesium chlorides

NASA Astrophysics Data System (ADS)

Zhong, Lihua; He, Xiaoman; Qu, Jun; Li, Xuewei; Lei, Zhiwu; Zhang, Qiwu; Liu, Xinzhong

2017-01-01

Al(OH)3 and Ca(OH)2 powders are co-ground to prepare a precursor which hydrates into a layered double hydroxide (LDH) phase by agitation in aqueous solution with target hexavalent chromium (Cr(VI)) at room temperature, to achieve an obvious improvement in removal efficiency of Cr(VI) through an easy incorporation into the structure. Although the prepared precursor transforms into LDH phases also when agitated in the solutions of calcium and magnesium chlorides, it incorporates Cr(VI) preferentially to the chloride salts when they coexist. The adsorption isotherm and kinetic studies show that the phenomena occurring on the Al-Ca precursor fit a pseudo-second-order kinetics with a Langmuir adsorption capacity of 59.45 mg/g. Besides, characterizations of the prepared precursor and the samples after adsorption are also performed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Transmission electron microscope (TEM) to understand the reason of the preferential incorporation of Cr(VI) to the coexisting chloride salts during the LDH phase formation. Ca-Al precursor (C3A) was agitated in a hexavalent chromium (Cr(VI)) solution to form Al-Ca-CrO4 LDH product. Ca-Al-CrO4 LDH phase occurred preferentially to Ca-Al-MCl2 LDH phases in the solutions of calcium and magnesium chlorides, it incorporates Cr(VI) preferentially to the chloride salts when they coexist.

Characteristics of a Steadily Operating Metal Combustor

DTIC Science & Technology

1976-08-01

Physique, Serie 7, Vol. 17, p. 510-576, 1899. 18. Zintl, E., Harder, A., and Dauth, B., "Gitterstruktur Der Oxyde , Sulfide, Selenide Und Telluride Des...ethyl alcohol were added to the cylinder along with three drops of alizarin Red S indicator (1%). The solution was titrated with thorium nitrate until...the appearance of a faint pink color. The thorium nitrate precipitated thorium fluoride which is insoluble in ethyl alcohol , and the indicator detected

Role of Precursor-Conversion Chemistry in the Crystal-Phase Control of Catalytically Grown Colloidal Semiconductor Quantum Wires.

PubMed

Wang, Fudong; Buhro, William E

2017-12-26

Crystal-phase control is one of the most challenging problems in nanowire growth. We demonstrate that, in the solution-phase catalyzed growth of colloidal cadmium telluride (CdTe) quantum wires (QWs), the crystal phase can be controlled by manipulating the reaction chemistry of the Cd precursors and tri-n-octylphosphine telluride (TOPTe) to favor the production of either a CdTe solute or Te, which consequently determines the composition and (liquid or solid) state of the Bi x Cd y Te z catalyst nanoparticles. Growth of single-phase (e.g., wurtzite) QWs is achieved only from solid catalysts (y ≪ z) that enable the solution-solid-solid growth of the QWs, whereas the liquid catalysts (y ≈ z) fulfill the solution-liquid-solid growth of the polytypic QWs. Factors that affect the precursor-conversion chemistry are systematically accounted for, which are correlated with a kinetic study of the composition and state of the catalyst nanoparticles to understand the mechanism. This work reveals the role of the precursor-reaction chemistry in the crystal-phase control of catalytically grown colloidal QWs, opening the possibility of growing phase-pure QWs of other compositions.

Non-aqueous solution preparation of doped and undoped lixmnyoz

DOEpatents

Boyle, Timothy J.; Voigt, James A.

1997-01-01

A method for generation of phase-pure doped and undoped Li.sub.x Mn.sub.y O.sub.z precursors. The method of this invention uses organic solutions instead of aqueous solutions or nonsolution ball milling of dry powders to produce phase-pure precursors. These precursors can be used as cathodes for lithium-polymer electrolyte batteries. Dopants may be homogeneously incorporated to alter the characteristics of the powder.

MicroRNA-like RNAs from the same miRNA precursors play a role in cassava chilling responses.

PubMed

Zeng, Changying; Xia, Jing; Chen, Xin; Zhou, Yufei; Peng, Ming; Zhang, Weixiong

2017-12-07

MicroRNAs (miRNAs) are known to play important roles in various cellular processes and stress responses. MiRNAs can be identified by analyzing reads from high-throughput deep sequencing. The reads realigned to miRNA precursors besides canonical miRNAs were initially considered as sequencing noise and ignored from further analysis. Here we reported a small-RNA species of phased and half-phased miRNA-like RNAs different from canonical miRNAs from cassava miRNA precursors detected under four distinct chilling conditions. They can form abundant multiple small RNAs arranged along precursors in a tandem and phased or half-phased fashion. Some of these miRNA-like RNAs were experimentally confirmed by re-amplification and re-sequencing, and have a similar qRT-PCR detection ratio as their cognate canonical miRNAs. The target genes of those phased and half-phased miRNA-like RNAs function in process of cell growth metabolism and play roles in protein kinase. Half-phased miR171d.3 was confirmed to have cleavage activities on its target gene P-glycoprotein 11, a broad substrate efflux pump across cellular membranes, which is thought to provide protection for tropical cassava during sharp temperature decease. Our results showed that the RNAs from miRNA precursors are miRNA-like small RNAs that are viable negative gene regulators and may have potential functions in cassava chilling responses.

Process for preparing zinc oxide-based sorbents

DOEpatents

Gangwal, Santosh Kumar [Cary, NC; Turk, Brian Scott [Durham, NC; Gupta, Raghubir Prasad [Durham, NC

2011-06-07

The disclosure relates to zinc oxide-based sorbents, and processes for preparing and using them. The sorbents are preferably used to remove one or more reduced sulfur species from gas streams. The sorbents comprise an active zinc component, optionally in combination with one or more promoter components and/or one or more substantially inert components. The active zinc component is a two phase material, consisting essentially of a zinc oxide (ZnO) phase and a zinc aluminate (ZnAl.sub.2O.sub.4) phase. Each of the two phases is characterized by a relatively small crystallite size of typically less than about 500 Angstroms. Preferably the sorbents are prepared by converting a precursor mixture, comprising a precipitated zinc oxide precursor and a precipitated aluminum oxide precursor, to the two-phase, active zinc oxide containing component.

The structure of Na{sub 3}SbTe{sub 3}: How ionic and covalent bonding forces work together

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

Lin, Jianhua; Miller, G.J.

1994-12-01

The compound Na{sub 3}SbTe{sub 3} has been synthesized from the elements and characterized by single crystal X-ray diffraction. Na{sub 3}SbTe{sub 3} is cubic, crystallizing in the cP28 structure type (isomorphous with Na{sub 3}AsS{sub 3}); space group P2{sub 1}3 (No. 198); a=9.6114(9) {angstrom}; Z = 4; R1 = 0.0324; wR2 = 0.0561 (I {le} 2{sigma}(I)). The structure consists of isolated sodium cations and trigonal pyramidal [SbTe{sub 3}]{sup {minus}3} anions with a Sb-Te bond length of 2.787(1) {angstrom} and a Te-Sb-Te bond angle of 100.0(1){degrees}. The structure is related to both the Li{sub 3}Bi and K{sub 3}AsS{sub 4}-type structures. Both lattice energymore » and semiempirical electronic structure calculations are utilized to evaluate various local and long-range structural aspects of this Zintl phase.« less

In situ synthesis studies of silicon clathrates

NASA Astrophysics Data System (ADS)

Hutchins, Peter Thomas

Solid state clathrates have shown considerable potential as a new class of materials over the past 30 years. Experimental and theoretical studies have shown that precise tuning and synthetic control of these materials, may lead to desirable properties. Very little is known about the mechanism of formation of the clathrates and so the desire to have accurate synthetic control was, until now, unrealistic. This thesis address the problem using in situ synchrotron x-ray techniques. In this study, experiments were designed to utilise time-resolved in situ diffraction techniques and high temperature 23Na NMR, in efforts to understand the mechanism of formation for this class of expanded framework materials. A complex high vacuum capillary synthesis cell was designed for loading under inert conditions and operation under high vacuum at station 6.2 of the SRS Daresbury. The cell was designed to operate in conjunction with a custom made furnace capable of temperatures in excess of 1000 C, as well as a vacuum system capable of 10"5 bar. The clathrate system was studied in situ, using rapid data collection to elucidate the mechanism of formation. The data were analysed using Rietveld methods and showed a structural link between the monoclinic, C2/c, Zintl precursors and the cubic, Pm3n, clathrate I phase. The phases were found to be linked by relation of the sodium planes in the silicide and the sodium atoms resident at cages centres in the clathrate system. This evidence suggests the guest species is instrumental in formation of the clathrate structure by templating the formation of the cages in the structure. Solid state 23Na NMR was utilised to complete specially design experiments, similar to those complete in situ using synchrotron x-ray techniques. The experiments showed increased spherical symmetry of the alkali metal sites and suggested increased mobility of the guest atoms during heating. In addition, cyclic heating experiments using in situ diffraction showed reversible reintroduction of the guest species on heating and cooling, during formation and subsequent dissipation of the clathrate structure. The realisation of the synthesis of a guest free type II clathrate and the theoretical prediction of negative thermal expansion behaviour at low temperature prompted the use of laboratory x-ray diffraction and a liquid helium cryostat to test the prediction. Careful study of the region from 20 to 200 K showed a region of zero or negative thermal expansion in the predicted region the effect observed showed good agreement with theory.

Thermal shock resistance ceramic insulator

DOEpatents

Morgan, Chester S.; Johnson, William R.

1980-01-01

Thermal shock resistant cermet insulators containing 0.1-20 volume % metal present as a dispersed phase. The insulators are prepared by a process comprising the steps of (a) providing a first solid phase mixture of a ceramic powder and a metal precursor; (b) heating the first solid phase mixture above the minimum decomposition temperature of the metal precursor for no longer than 30 minutes and to a temperature sufficiently above the decomposition temperature to cause the selective decomposition of the metal precursor to the metal to provide a second solid phase mixture comprising particles of ceramic having discrete metal particles adhering to their surfaces, said metal particles having a mean diameter no more than 1/2 the mean diameter of the ceramic particles, and (c) densifying the second solid phase mixture to provide a cermet insulator having 0.1-20 volume % metal present as a dispersed phase.

Zinc oxide-based sorbents and processes for preparing and using same

DOEpatents

Gangwal, Santosh Kumar; Turk, Brian Scott; Gupta, Raghubir Prasad

2005-10-04

Zinc oxide-based sorbents, and processes for preparing and using them are provided, wherein the sorbents are preferably used to remove one or more reduced sulfur species from gas streams. The sorbents contain an active zinc component, optionally in combination with one or more promoter components and/or one or more substantially inert components. The active zinc component is a two phase material, consisting essentially of a zinc oxide (ZnO) phase and a zinc aluminate (ZnAl.sub.2 O.sub.4) phase. Each of the two phases is characterized by a relatively small crystallite size of typically less than about 500 Angstroms. Preferably the sorbents are prepared by converting a precursor mixture, containing a precipitated zinc oxide precursor and a precipitated aluminum oxide precursor, to the two-phase, active zinc oxide containing component.

Zinc-oxide-based sorbents and processes for preparing and using same

DOEpatents

Gangwal, Santosh Kumar; Turk, Brian Scott; Gupta, Raghubir Prasael

2010-03-23

Zinc oxide-based sorbents, and processes for preparing and using them are provided. The sorbents are preferably used to remove one or more reduced sulfur species from gas streams. The sorbents comprise an active zinc component, optionally in combination with one or more promoter components and/or one or more substantially inert components. The active zinc component is a two phase material, consisting essentially of a zinc oxide (ZnO) phase and a zinc aluminate (ZnAl.sub.2O.sub.4) phase. Each of the two phases is characterized by a relatively small crystallite size of typically less than about 500 Angstroms. Preferably the sorbents are prepared by converting a precursor mixture, comprising a precipitated zinc oxide precursor and a precipitated aluminum oxide precursor, to the two-phase, active zinc oxide containing component.

Influence of carboxylic acid type on microstructure and magnetic properties of polymeric complex sol-gel driven NiFe2O4

NASA Astrophysics Data System (ADS)

Hessien, M. M.; Mostafa, Nasser Y.; Abd-Elkader, Omar H.

2016-01-01

Citric, oxalic and tartaric acids were used for synthesis of NiFe2O4 using polymeric complex precursor route. The dry precursor gels were calcined at various temperatures (400-1100 °C) for 2 h. All carboxylic acids produce iron-deficient NiFe2O4 with considerable amount of α-Fe2O3 at 400 °C. Increase in the annealing temperature caused reaction of α-Fe2O3 with iron-deficient ferrite phase. The amount of initially formed α-Fe2O3 is directly correlated with stability constant and inversely correlated with the decomposition temperature of Fe(III) carboxylate precursors. In case of tartaric acid precursor, single phase of the ferrite was obtained at 450 °C. However, in case of oxalic acid and citric acid precursors, single phase ferrite was obtained at 550 °C and 700 °C, respectively. The lattice parameters were increased with increasing annealing temperature and with decreasing the amount of α-Fe2O3. Maximum saturation magnetization (55 emu/g) was achieved using tartaric acid precursor annealed at 1100 °C.

Nonequilibrium Phase Precursors during a Photoexcited Insulator-to-Metal Transition in V2O3

NASA Astrophysics Data System (ADS)

Singer, Andrej; Ramirez, Juan Gabriel; Valmianski, Ilya; Cela, Devin; Hua, Nelson; Kukreja, Roopali; Wingert, James; Kovalchuk, Olesya; Glownia, James M.; Sikorski, Marcin; Chollet, Matthieu; Holt, Martin; Schuller, Ivan K.; Shpyrko, Oleg G.

2018-05-01

Here, we photoinduce and directly observe with x-ray scattering an ultrafast enhancement of the structural long-range order in the archetypal Mott system V2O3 . Despite the ultrafast increase in crystal symmetry, the change of unit cell volume occurs an order of magnitude slower and coincides with the insulator-to-metal transition. The decoupling between the two structural responses in the time domain highlights the existence of a transient photoinduced precursor phase, which is distinct from the two structural phases present in equilibrium. X-ray nanoscopy reveals that acoustic phonons trapped in nanoscale twin domains govern the dynamics of the ultrafast transition into the precursor phase, while nucleation and growth of metallic domains dictate the duration of the slower transition into the metallic phase. The enhancement of the long-range order before completion of the electronic transition demonstrates the critical role the nonequilibrium structural phases play during electronic phase transitions in correlated electrons systems.

Precursor preparation for Ca-Al layered double hydroxide to remove hexavalent chromium coexisting with calcium and magnesium chlorides

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

Zhong, Lihua; He, Xiaoman; Qu, Jun

Al(OH){sub 3} and Ca(OH){sub 2} powders are co-ground to prepare a precursor which hydrates into a layered double hydroxide (LDH) phase by agitation in aqueous solution with target hexavalent chromium (Cr(VI)) at room temperature, to achieve an obvious improvement in removal efficiency of Cr(VI) through an easy incorporation into the structure. Although the prepared precursor transforms into LDH phases also when agitated in the solutions of calcium and magnesium chlorides, it incorporates Cr(VI) preferentially to the chloride salts when they coexist. The adsorption isotherm and kinetic studies show that the phenomena occurring on the Al-Ca precursor fit a pseudo-second-order kineticsmore » with a Langmuir adsorption capacity of 59.45 mg/g. Besides, characterizations of the prepared precursor and the samples after adsorption are also performed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Transmission electron microscope (TEM) to understand the reason of the preferential incorporation of Cr(VI) to the coexisting chloride salts during the LDH phase formation. - Graphical abstract: Activated Ca-Al hydroxides (C{sub 3}A) transformed into Ca-Al-OH compound when agitated in water. Ca-Al precursor (C{sub 3}A) was agitated in a hexavalent chromium (Cr(VI)) solution to form Al-Ca-CrO{sub 4} LDH product. Ca-Al-CrO{sub 4} LDH phase occurred preferentially to Ca-Al-MCl{sub 2} LDH phases in the solutions of calcium and magnesium chlorides, it incorporates Cr(VI) preferentially to the chloride salts when they coexist. - Highlights: • Activated Ca-Al hydroxides transformed into LDH when agitated in water with some inorganic substances. • Hexavalent Cr was incorporated in the LDH structure at high adsorption capacity. • Ca-Al-Cr LDH phase occurred preferentially to Ca-Al-MCl{sub 2} LDH phases with coexistence. • The prepared Ca-Al hydroxides had high performance as adsorbent even with high salinity of the solution.« less

Synthesis, characterization, microstructure, optical and magnetic properties of strontium cobalt carbonate precursor and Sr2Co2O5 oxide material

NASA Astrophysics Data System (ADS)

Agilandeswari, K.; Ruban Kumar, A.

2014-04-01

Sr2Co2O5 ceramic synthesized by the coprecipitation of strontium cobalt carbonate method. XRD analysis shows the single phase strontianite precursor and decomposed oxide product as orthorhombic structure of Sr2Co2O5. Thermal analysis proves the Sr2Co2O5 phase formation temperature of 800 °C. SEM image indicates crystalline rod shaped carbonate precursor transformed to oxide as porous diffused sphere shape particles. Optical band gap it reveals the strontium cobalt carbonate precursor as insulating material and the Sr2Co2O5 as semiconducting nature. The room temperature magnetic study indicates the carbonate precursor as paramagnetic but its oxide Sr2Co2O5 as superparamagnetic behavior.

Non-aqueous solution preparation of doped and undoped Li{sub x}Mn{sub y}O{sub z}

DOEpatents

Boyle, T.J.; Voigt, J.A.

1997-05-20

A method is described for generation of phase-pure doped and undoped Li{sub x}Mn{sub y}O{sub z} precursors. The method of this invention uses organic solutions instead of aqueous solutions or nonsolution ball milling of dry powders to produce phase-pure precursors. These precursors can be used as cathodes for lithium-polymer electrolyte batteries. Dopants may be homogeneously incorporated to alter the characteristics of the powder. 1 fig.

Compliant Interfacial Layers in Thermoelectric Devices

NASA Technical Reports Server (NTRS)

Firdosy, Samad A. (Inventor); Li, Billy Chun-Yip (Inventor); Ravi, Vilupanur A. (Inventor); Fleurial, Jean-Pierre (Inventor); Caillat, Thierry (Inventor); Anjunyan, Harut (Inventor)

2017-01-01

A thermoelectric power generation device is disclosed using one or more mechanically compliant and thermally and electrically conductive layers at the thermoelectric material interfaces to accommodate high temperature differentials and stresses induced thereby. The compliant material may be metal foam or metal graphite composite (e.g. using nickel) and is particularly beneficial in high temperature thermoelectric generators employing Zintl thermoelectric materials. The compliant material may be disposed between the thermoelectric segments of the device or between a thermoelectric segment and the hot or cold side interconnect of the device.

Nanoscale Transforming Mineral Phases in Fresh Nacre.

PubMed

DeVol, Ross T; Sun, Chang-Yu; Marcus, Matthew A; Coppersmith, Susan N; Myneni, Satish C B; Gilbert, Pupa U P A

2015-10-21

Nacre, or mother-of-pearl, the iridescent inner layer of many mollusk shells, is a biomineral lamellar composite of aragonite (CaCO3) and organic sheets. Biomineralization frequently occurs via transient amorphous precursor phases, crystallizing into the final stable biomineral. In nacre, despite extensive attempts, amorphous calcium carbonate (ACC) precursors have remained elusive. They were inferred from non-nacre-forming larval shells, or from a residue of amorphous material surrounding mature gastropod nacre tablets, and have only once been observed in bivalve nacre. Here we present the first direct observation of ACC precursors to nacre formation, obtained from the growth front of nacre in gastropod shells from red abalone (Haliotis rufescens), using synchrotron spectromicroscopy. Surprisingly, the abalone nacre data show the same ACC phases that are precursors to calcite (CaCO3) formation in sea urchin spicules, and not proto-aragonite or poorly crystalline aragonite (pAra), as expected for aragonitic nacre. In contrast, we find pAra in coral.

Influence of thermal treatment on the formation of zirconia nanostructured powder by thermal decomposition of different precursors

NASA Astrophysics Data System (ADS)

Stoia, Marcela; Barvinschi, Paul; Barbu-Tudoran, Lucian; Negrea, Adina; Barvinschi, Floricica

2013-10-01

The paper presents some results concerning the preparation of zirconia powders starting from ZrOCl2·8H2O by using two synthesis methods: (a) precipitation with NH3, at 90 °C, and (b) thermal decomposition of carboxylate precursors, obtained in the reaction of zirconium nitrate and two different alcohols, 1,3-propanediol (PD) and poly(vinyl alcohol) (PVA), at 150 °C. The precursors obtained at different temperatures have been characterized by thermal analysis (TG, DTA) and FT-IR spectroscopy. DTA analysis evidenced very clearly the transition temperatures between zirconia crystalline phases. The precursors have been annealed at different temperatures in order to obtain zirconia powders and the as obtained powders have been characterized by means of X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). In case of precipitation method the presence of the tetragonal phase was observed at 400 °C, while the monoclinic phase appears at temperatures higher than 400 °C, becoming major crystalline phase starting with 700 °C. In case of the powders prepared by thermal decomposition of carboxylate precursors, the tetragonal phase was formed at temperatures below 700 °C, when the monoclinic phase begin to crystallize as secondary phase, in a higher proportion for the samples synthesized with 1,3-propanediol. All powders annealed at 1200 °C are pure monoclinic zirconia. SEM images have evidenced for the zirconia powders annealed at 1000 °C particles with diameters up to 150 nm, agglomerated in micrometer-sized aggregates, more individualized and homogenous than that obtained in the case of zirconia powder synthesized with poly(vinyl alcohol).

On the difficulties of detecting PP precursors

NASA Astrophysics Data System (ADS)

Lessing, Stephan; Thomas, Christine; Saki, Morvarid; Schmerr, Nicholas; Vanacore, Elizabeth

2015-06-01

The PP precursors are seismic waves that form from underside reflections of P waves off discontinuities in the upper mantle transition zone (MTZ). These seismic phases are used to map discontinuity topography, sharpness, and impedance contrasts; the resulting structural variations are then often interpreted as evidence for temperature and/or mineralogy variations within the mantle. The PP precursors as well as other seismic phases have been used to establish the global presence of seismic discontinuities at 410 and 660 km depth. Intriguingly, in more than 80 per cent of PP precursor observations the seismic wave amplitudes are significantly weaker than the amplitudes predicted by seismic reference models. Even more perplexing is the observation that 1-5 per cent of all earthquakes (which are 20-25 per cent of earthquakes with clear PP waveforms) do not show any evidence for the PP precursors from the discontinuities even in the presence of well-developed PP waveforms. Non-detections are found in six different data sets consisting of tens to hundreds of events. We use synthetic modelling to examine a suite of factors that could be responsible for the absence of the PP precursors. The take-off angles for PP and the precursors differ by only 1.2-1.5°; thus source-related complexity would affect PP and the precursors. A PP wave attenuated in the upper mantle would increase the relative amplitude of the PP precursors. Attenuation within the transition zone could reduce precursor amplitudes, but this would be a regional phenomenon restricted to particular source receiver geometries. We also find little evidence for deviations from the theoretical travel path of seismic rays expected for scattered arrivals. Factors that have a strong influence include the stacking procedures used in seismic array techniques in the presence of large, interfering phases, the presence of topography on the discontinuities on the order of tens of kilometres, and 3-D lateral heterogeneity in the velocity and density changes with depth across the transition zone. We also compare the observed precursors' amplitudes with seismic models from calculations of phase equilibria and find that a seismic velocity model derived from a pyrolite composition reproduces the data better than the currently available 1-D earth models. This largely owes to the pyrolite models producing a stronger minimum in the reflection coefficient across the epicentral distances where the reduction in amplitudes of the PP precursors is observed. To suppress the precursors entirely in a small subset of earthquakes, other effects, such as localized discontinuity topography and seismic signal processing effects are required in addition to the changed velocity model.

Non-noble electrocatalysts for alkaline fuel cells

NASA Technical Reports Server (NTRS)

Sarangapani, S.; Lessner, P.; Manoukian, M.; Giner, J.

1989-01-01

The doping of solid phase precursors followed by pyrolysis or the copyrolysis of gas phase precursors has allowed us to produce catalysts with good activity toward oxygen reduction. Efforts are currently underway to better understand the reasons for the catalytic activity of the bulk doped catalysts with a view toward further improving their activity.

Observations of Electron-driven Evaporation in a Flare Precursor

NASA Astrophysics Data System (ADS)

Li, Dong; Li, Ying; Su, Wei; Huang, Yu; Ning, Zongjun

2018-02-01

We investigate the relationship between the blueshifts of a hot emission line and the nonthermal emissions in microwave and hard X-ray (HXR) wavelengths in the precursor of a solar flare on 2014 October 27. The flare precursor is identified as a small but well-developed peak in the soft X-ray and extreme-ultraviolet passbands before the GOES flare onset, which is accompanied by a pronounced burst in microwave 17 and 34 GHz and in HXR 25–50 keV. The slit of the Interface Region Imaging Spectrograph (IRIS) stays on one ribbon-like transient during the flare precursor phase, which shows visible nonthermal emissions in Nobeyama Radioheliograph and RHESSI images. The IRIS spectroscopic observations show that the hot line of Fe XXI 1354.09 Å (log T ∼ 7.05) displays blueshifts, while the cool line of Si IV 1402.77 Å (log T ∼ 4.8) exhibits redshifts. The blueshifts and redshifts are well correlated with each other, indicative of an explosive chromospheric evaporation during the flare precursor phase combining a high nonthermal energy flux with a short characteristic timescale. In addition, the blueshifts of Fe XXI 1354.09 Å are well correlated with the microwave and HXR emissions, implying that the explosive chromospheric evaporation during the flare precursor phase is driven by nonthermal electrons.

New stable ternary alkaline-earth metal Pb(II) oxides: Ca / Sr / BaPb 2 O 3 and BaPbO 2

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

Li, Yuwei; Zhang, Lijun; Singh, David J.

The different but related chemical behaviors of Pb(II) oxides compared to Sn(II) oxides, and the existence of known alkali/alkali-earth metal Sn(II) ternary phases, suggest that there should be additional ternary Pb(II) oxide phases. Here, we report structure searches on the ternary alkaline-earth metal Pb(II) oxides leading to four new phases. These are two ternary Pb(II) oxides, SrPb 2O 3 and BaPb 2O 3, which have larger chemical potential stability ranges compared with the corresponding Sn(II) oxides, and additionally two other ternary Pb(II) oxides, CaPb 2O 3 and BaPbO 2, for which there are no corresponding Sn(II) oxides. Those Pb(II) oxidesmore » are stabilized by Pb-rich conditions. These structures follow the Zintl behavior and consist of basic structural motifs of (PbO 3) 4- anionic units separated and stabilized by the alkaline-earth metal ions. They show wide band gaps ranging from 2.86 to 3.12 eV, and two compounds (CaPb 2O 3 and SrPb 2O 3) show rather light hole effective masses (around 2m 0). The valence band maxima of these compounds have a Pb-6s/O-2p antibonding character, which may lead to p-type defect (or doping) tolerant behavior. This then suggests alkaline-earth metal Pb(II) oxides may be potential p-type transparent conducting oxides.« less

New stable ternary alkaline-earth metal Pb(II) oxides: Ca / Sr / BaPb 2 O 3 and BaPbO 2

DOE PAGES

Li, Yuwei; Zhang, Lijun; Singh, David J.

2017-10-16

The different but related chemical behaviors of Pb(II) oxides compared to Sn(II) oxides, and the existence of known alkali/alkali-earth metal Sn(II) ternary phases, suggest that there should be additional ternary Pb(II) oxide phases. Here, we report structure searches on the ternary alkaline-earth metal Pb(II) oxides leading to four new phases. These are two ternary Pb(II) oxides, SrPb 2O 3 and BaPb 2O 3, which have larger chemical potential stability ranges compared with the corresponding Sn(II) oxides, and additionally two other ternary Pb(II) oxides, CaPb 2O 3 and BaPbO 2, for which there are no corresponding Sn(II) oxides. Those Pb(II) oxidesmore » are stabilized by Pb-rich conditions. These structures follow the Zintl behavior and consist of basic structural motifs of (PbO 3) 4- anionic units separated and stabilized by the alkaline-earth metal ions. They show wide band gaps ranging from 2.86 to 3.12 eV, and two compounds (CaPb 2O 3 and SrPb 2O 3) show rather light hole effective masses (around 2m 0). The valence band maxima of these compounds have a Pb-6s/O-2p antibonding character, which may lead to p-type defect (or doping) tolerant behavior. This then suggests alkaline-earth metal Pb(II) oxides may be potential p-type transparent conducting oxides.« less

Tannins and terpenoids as major precursors of Suwannee River fulvic acid

USGS Publications Warehouse

Leenheer, Jerry A.; Rostad, Colleen E.

2004-01-01

Suwannee River fulvic acid (SRFA) was fractionated into 7 fractions by normal-phase chromatography on silica gel followed by reverse-phase fractionation on XAD-8 resin that produced 18 subfractions. Selected major subfractions were characterized by 13C-nuclear magnetic resonance (NMR), infrared spectrometry, and elemental analyses. 13C-NMR spectra of the subfractions were more indicative of precursor structures than unfractionated SRFA, and gave spectral profiles that indicated SRFA mass was about equally split between tannin precursors and terpenoid precursors. Lignin precursors were minor components. Synthesis of 13C-NMR data with elemental data for subfractions derived from both tannin and terpenoid precursors revealed high ring contents and low numbers of carbon per rings which is indicative of fused ring structures that are extensively substituted with carboxyl and methyl groups. These results ruled out extended chain structures for SRFA. This information is useful for determining sources and properties of fulvic acid in drinking water supplies as tannins are more reactive with chlorine to produce undesirable disinfection by-products than are terpenoids.

Structural comparison of nickel electrodes and precursor phases

NASA Technical Reports Server (NTRS)

Cornilsen, Bahne C.; Shan, Xiaoyin; Loyselle, Patricia

1989-01-01

Researchers summarize previous Raman spectroscopic results and discuss important structural differences in the various phases of active mass and active mass precursors. Raman spectra provide unique signatures for these phases, and allow one to distinguish each phase, even when the compound is amorphous to x rays (i.e., does not scatter x rays because of a lack of order and/or small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging are discussed. The oxidation states and dopant contents are explained in terms of the nonstoichiometric structures.

Cathodes and electrolytes for rechargeable magnesium batteries and methods of manufacture

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

Kumta, Prashant N.; Saha, Partha; Datta, Moni Kanchan

The invention relates to Chevrel-phase materials and methods of preparing these materials utilizing a precursor approach. The Chevrel-phase materials are useful in assembling electrodes, e.g., cathodes, for use in electrochemical cells, such as rechargeable batteries. The Chevrel-phase materials have a general formula of Mo 6Z 8 and the precursors have a general formula of M xMo 6Z 8. The cathode containing the Chevrel-phase material in accordance with the invention can be combined with a magnesium-containing anode and an electrolyte.

Bound Volatile Precursors in Genotypes in the Pedigree of 'Marion' Blackberry (Rubus Sp.)

USDA-ARS?s Scientific Manuscript database

Glycosidically bound volatiles and precursors in genotypes representing the pedigree for 'Marion' blackberry were investigated over two growing seasons. The volatile precursors were isolated using a C18 solid-phase extraction column. After enzymatic hydrolysis, the released volatiles were analyzed u...

Nanoscale Transforming Mineral Phases in Fresh Nacre

DOE PAGES

DeVol, Ross T.; Sun, Chang-Yu; Marcus, Matthew A.; ...

2015-09-24

Nacre, or mother-of-pearl, the iridescent inner layer of many mollusk shells, is a biomineral lamellar composite of aragonite (CaCO 3) and organic sheets. Biomineralization frequently occurs via transient amorphous precursor phases, crystallizing into the final stable biomineral. In nacre, despite extensive attempts, amorphous calcium carbonate (ACC) precursors have remained elusive. They were inferred from non-nacre-forming larval shells, or from a residue of amorphous material surrounding mature gastropod nacre tablets, and have only once been observed in bivalve nacre. Here we present the first direct observation of ACC precursors to nacre formation, obtained from the growth front of nacre in gastropodmore » shells from red abalone (Haliotis rufescens), using synchrotron spectromicroscopy. Surprisingly, the abalone nacre data show the same ACC phases that are precursors to calcite (CaCO 3) formation in sea urchin spicules, and not proto-aragonite or poorly crystalline aragonite (pAra), as expected for aragonitic nacre. In contrast, we find pAra in coral.« less

Wet-chemical synthesis of different bismuth telluride nanoparticles using metal organic precursors - single source vs. dual source approach.

PubMed

Bendt, Georg; Weber, Anna; Heimann, Stefan; Assenmacher, Wilfried; Prymak, Oleg; Schulz, Stephan

2015-08-28

Thermolysis of the single source precursor (Et2Bi)2Te in DIPB at 80 °C yielded phase-pure Bi4Te3 nanoparticles, while mixtures of Bi4Te3 and elemental Bi were formed at higher temperatures. In contrast, cubic Bi2Te particles were obtained by thermal decomposition of Et2BiTeEt in DIPB. Moreover, a dual source approach (hot injection method) using the reaction of Te(SiEt3)2 and Bi(NMe2)3 was applied for the synthesis of different pure Bi-Te phases including Bi2Te, Bi4Te3 and Bi2Te3, which were characterized by PXRD, REM, TEM and EDX. The influence of reaction temperature, precursor molar ratio and thermolysis conditions on the resulting material phase was verified. Moreover, reactions of alternate bismuth precursors such as Bi(NEt2)3, Bi(NMeEt)3 and BiCl3 with Te(SiEt3)2 were investigated.

Effect of Group-III precursors on unintentional gallium incorporation during epitaxial growth of InAlN layers by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Kim, Jeomoh; Ji, Mi-Hee; Detchprohm, Theeradetch; Dupuis, Russell D.; Fischer, Alec M.; Ponce, Fernando A.; Ryou, Jae-Hyun

2015-09-01

Unintentional incorporation of gallium (Ga) in InAlN layers grown with different molar flow rates of Group-III precursors by metalorganic chemical vapor deposition has been experimentally investigated. The Ga mole fraction in the InAl(Ga)N layer was increased significantly with the trimethylindium (TMIn) flow rate, while the trimethylaluminum flow rate controls the Al mole fraction. The evaporation of metallic Ga from the liquid phase eutectic system between the pyrolized In from injected TMIn and pre-deposited metallic Ga was responsible for the Ga auto-incorporation into the InAl(Ga)N layer. The theoretical calculation on the equilibrium vapor pressure of liquid phase Ga and the effective partial pressure of Group-III precursors based on growth parameters used in this study confirms the influence of Group-III precursors on Ga auto-incorporation. More Ga atoms can be evaporated from the liquid phase Ga on the surrounding surfaces in the growth chamber and then significant Ga auto-incorporation can occur due to the high equilibrium vapor pressure of Ga comparable to effective partial pressure of input Group-III precursors during the growth of InAl(Ga)N layer.

Two-dimensional ultra-thin SiO(x) (0 < x < 2) nanosheets with long-term cycling stability as lithium ion battery anodes.

PubMed

Sun, Lin; Su, Tingting; Xu, Lei; Liu, Meipin; Du, Hong-Bin

2016-03-21

Ultra-thin SiO(x) (0 < x < 2) nanosheets were obtained via a convenient solvothermal route from a Zintl compound CaSi2. After carbon coating, the SiOx@C nanosheet anodes exhibit high capacity, good rate and superior cycling performance for high-capacity lithium ion battery applications. The specific capacity can be maintained as high as 760 mA h g(-1) with almost no capacity decay after 400 cycles at a current density of 0.5 A g(-1).

Structural Evolution of Iron Antimonides from Amorphous Precursors to Crystalline Products Studied by Total Scattering Techniques.

PubMed

Bauers, Sage R; Wood, Suzannah R; Jensen, Kirsten M Ø; Blichfeld, Anders B; Iversen, Bo B; Billinge, Simon J L; Johnson, David C

2015-08-05

Homogeneous reaction precursors may be used to form several solid-state compounds inaccessible by traditional synthetic routes, but there has been little development of techniques that allow for a priori prediction of what may crystallize in a given material system. Here, the local structures of FeSbx designed precursors are determined and compared with the structural motifs of their crystalline products. X-ray total scattering and atomic pair distribution function (PDF) analysis are used to show that precursors that first nucleate a metastable FeSb3 compound share similar local structure to the product. Interestingly, precursors that directly crystallize to thermodynamically stable FeSb2 products also contain local structural motifs of the metastable phase, despite their compositional disagreement. While both crystalline phases consist of distorted FeSb6 octahedra with Sb shared between either two or three octahedra as required for stoichiometry, a corner-sharing arrangement indicative of AX3-type structures is the only motif apparent in the PDF of either precursor. Prior speculation was that local composition controlled which compounds nucleate from amorphous intermediates, with different compositions favoring different local arrangements and hence different products. This data suggests that local environments in these amorphous intermediates may not be very sensitive to overall composition. This can provide insight into potential metastable phases which may form in a material system, even with a precursor that does not crystallize to the kinetically stabilized product. Determination of local structure in homogeneous amorphous reaction intermediates from techniques such as PDF can be a valuable asset in the development of systematic methods to prepare targeted solid-state compounds from designed precursors.

Synthesis and Characterization of the First Liquid Single Source Precursors for the Deposition of Ternary Chalcopyrite (CuInS2) Thin Film Materials

NASA Technical Reports Server (NTRS)

Banger, Kulbinder K.; Cowen, Jonathan; Hepp, Aloysius

2002-01-01

Molecular engineering of ternary single source precursors based on the [{PBu3}2Cu(SR')2In(SR')2] architecture have afforded the first liquid CIS ternary single source precursors (when R = Et, n-Pr), which are suitable for low temperature deposition (< 350 C). Thermogravimetric analyses (TGA) and modulated-differential scanning calorimetry (DSC) confirm their liquid phase and reduced stability. X-ray diffraction studies, energy dispersive analyzer (EDS), and scanning electron microscopy (SEM) support the formation of the single-phase chalcopyrite CuInS2 at low temperatures.

Insight into the optoelectronic and thermoelectric properties of Ca-based Zintl phase CaCd2X2 (X = P, As) from first principles calculation

NASA Astrophysics Data System (ADS)

Belfarh, T.; Batouche, M.; Seddik, T.; Uğur, G.; Omran, S. Bin; Bouhemadou, A.; Sandeep; Wang, Xiaotian; Sun, Xiao-Wei; Khenata, R.

2018-06-01

We have studied the structural, optical, electronic and thermoelectric properties of the CaCd2X2 (X = P, As) compounds by using the full-potential augmented plane wave plus local orbitals method (FP-APW + lo). The exchange-correlation potential was treated using both the gradient generalized approximation (WC-GGA) and local density approximation (LDA). The estimated structural parameters, including the lattice parameters and internal coordinates agree well with the available experimental data. Our computed band structure shows that both studied compounds are semiconductors, with direct band gaps (Γ-Γ) of approximately 1.78 eV and 1.2 eV for CaCd2P2 and CaCd2As2, respectively, using GGA-TB-mBJ approach. The calculated optical spectra reveal a strong response of these materials in the energy range between the visible light and extreme UV regions, making them a good candidate for optoelectronic devices. Thermoelectric parameters, such as thermal conductivity, electrical conductivity, Seebeck coefficient, power factor and figure of merit were calculated. We note that both the CaCd2P2 and CaCd2As2 compounds show promising thermoelectric properties.

Y2O3-MgO Nano-Composite Synthesized by Plasma Spraying and Thermal Decomposition of Solution Precursors

NASA Astrophysics Data System (ADS)

Muoto, Chigozie Kenechukwu

This research aims to identify the key feedstock characteristics and processing conditions to produce Y2O3-MgO composite coatings with high density and hardness using solution precursor plasma spray (SPPS) and suspension plasma spray (SPS) processes, and also, to explore the phenomena involved in the production of homogenized nano-composite powders of this material system by thermal decomposition of solution precursor mixtures. The material system would find potential application in the fabrication of components for optical applications such as transparent windows. It was shown that a lack of major endothermic events during precursor decomposition and the resultant formation of highly dense particles upon pyrolysis are critical precursor characteristics for the deposition of dense and hard Y2O3-MgO coatings by SPPS. Using these principles, a new Y2O3-MgO precursor solution was developed, which yielded a coating with Vickers hardness of 560 Hv. This was a considerable improvement over the hardness of the coatings obtained using conventional solution precursors, which was as low as 110 Hv. In the thermal decomposition synthesis process, binary solution precursor mixtures of: yttrium nitrate (Y[n]) or yttrium acetate (Y[a]), with magnesium nitrate (Mg[n]) or magnesium acetate (Mg[a]) were used in order to study the effects of precursor chemistry on the structural characteristics of the resultant Y2O3-MgO powders. The phase domains were coarse and distributed rather inhomogeneously in the materials obtained from the Y[n]Mg[n] and Y[a]Mg[a] mixtures; finer and more homogeneously-distributed phase domains were obtained for ceramics produced from the Y[a]Mg[n] and Y[n]Mg[a] mixtures. It was established that these phenomena were related to the thermal characteristics for the decomposition of the precursors and their effect on phase separation during oxide crystallization. Addition of ammonium acetate to the Y[n[Mg[n] mixture changed the endothermic process to exothermic and improved the dispersion of the component phases. Two suspension types, made with powders synthesized from the Y[n]Mg[n] and Y[n]Mg[a] precursor mixtures were sprayed by SPS. The densities and hardnesses of the coatings deposited using the two powder types were similar. However, the microstructure of coatings deposited using the Y[n]Mg[a]-synthesized powder exhibited some eutectic configuration which was not observed in the coatings deposited using the Y[n]Mg[n]-synthesized powder.

­­Secondary organic aerosol formation from photo-oxidation of wood combustion emissions: Characterization of gas phase precursors and their link to SOA budget

NASA Astrophysics Data System (ADS)

Bhattu, D.; Stefenelli, G.; Zotter, P.; Zhou, J.; Nussbaumer, T.; Bertrand, A.; Marchand, N.; Termine-Roussel, B.; Baltensperger, U.; Slowik, J.; Prevot, A. S.; El-Haddad, I.; Dommen, J.

2016-12-01

Current legislation limits the emission of particulate matter, but does not regulate the precursors potentially forming secondary organic aerosol (SOA). Recent literature has shown that only 22 non-traditional SOA precursors from residential wood combustion explains 84-116% of the observed SOA mass whereas traditional precursors in the models account for only 3-27% of the SOA mass (Bruns et al., 2016). Investigation of gas phase emissions from wood combustion and their SOA formation potential have largely focused on single combustion devices with limited operating conditions. As, both primary emissions and SOA formation is a strong function of device type, load, fuel and operating conditions, we have performed a detailed chamber study investigating the gas-phase precursors from beech wood using three combustion devices namely a pellet boiler (combustion conditions: optimum, lack and excess of oxygen), an industrial wood chip grate boiler (30% and 100% power), and a log wood stove (varying fuel load and moisture content) using a potential aerosol mass reactor (PAM) with varying OH exposure. The short residence time in the reactor allowed a time resolved picture of SOA production potential and reduced wall losses. The main aim of this study is to characterize the primary and aged gaseous emissions and investigate their SOA formation potential depending on their mass yield, molecular structures, functional groups and OH reactivity in order to ascertain the contribution of residential wood burning in total carbonaceous OA budget. The physical and chemical effects of different OA aging conditions were monitored using an SMPS, an Aethalometer, an HR-ToF-AMS, as well as a PTR-ToF-MS and other gas monitors. In pellet boiler, significant SOA mass enhancement is observed in excess oxygen conditions compared to optimum and oxygen deprived conditions. Highest gas phase emissions from wood stove are observed at cold start (start of each burn cycle) and lowest in burn out phase (end of each burn cycle). Despite of the comparable total gas phase emissions, the compositional space of wood stove emissions is largely occupied by SOA precursors compared to pellet boiler. Finally we will determine effective SOA mass yield of the speciated and unspeciated precursors and assess the extent to which SOA mass closure can be achieved.

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

Du, Mao -Hua; Singh, David J.; Zhang, Lijun

Oxides with good p-type conductivity have been long sought after to achieve high performance all-oxide optoelectronic devices. Divalent Sn(II) based oxides are promising candidates because of their rather dispersive upper valence bands caused by the Sn-5s/O-2p anti-bonding hybridization. There are so far few known Sn(II) oxides being p-type conductive suitable for device applications. Here, we present via first-principles global optimization structure searches a material design study for a hitherto unexplored Sn(II)-based system, ternary alkaline-earth metal Sn(II) oxides in the stoichiometry of MSn 2O 3 (M = Mg, Ca, Sr, Ba). We identify two stable compounds of SrSn 2O 3 andmore » BaSn 2O 3, which can be stabilized by Sn-rich conditions in phase stability diagrams. Their structures follow the Zintl behaviour and consist of basic structural motifs of SnO 3 tetrahedra. Unexpectedly they show distinct electronic properties with band gaps ranging from 1.90 (BaSn 2O 3) to 3.15 (SrSn 2O 3) eV, and hole effective masses ranging from 0.87 (BaSn 2O 3) to above 6.0 (SrSn 2O 3) m0. Further exploration of metastable phases indicates a wide tunability of electronic properties controlled by the details of the bonding between the basic structural motifs. Lastly, this suggests further exploration of alkaline-earth metal Sn(II) oxides for potential applications requiring good p-type conductivity such as transparent conductors and photovoltaic absorbers.« less

The influence of different locations of sputter guns on the morphological and structural properties of Cu-In-Ga precursors and Cu(In,Ga)Se2 thin films

NASA Astrophysics Data System (ADS)

Wang, J.; Zhu, J.; He, Y. X.

2014-01-01

The influence of two different locations of sputter guns on the morphological and structural properties of Cu-In-Ga precursors and Cu(In,Ga)Se2 (CIGS) thin films was investigated. All the precursors contained cauliflower-like nodules, whereas smaller subnodules were observed on the background. All the precursors revealed apparent three-layered structures, and voids were observed at the CIGS/SLG interface of Sets 1 and 2 films rather than Set 3 film. EDS results indicated that all CIGS thin films were Cu-deficient. Based on the grazing incidence X-ray diffraction (GIXRD) patterns, as-selenized films showed peaks corresponding to the chalcopyrite-type CIGS structure. Depth-resolved Raman spectra showed the formation of a dominant CIGS phase inside the films for all the as-selenized samples investigated, and of an ordered vacancy compound (OVC) phase like Cu(In,Ga)3Se5 or Cu(In,Ga)2Se3.5 at the surface and/or CIGS/SLG interface region of Sets 2 and 3 films. No evidence was obtained on the presence of an OVC phase in Set 1 CIGS film, which may be speculated that long-time annealing is contributed to suppress the growth of OVC phases. The results of the present work suggest that the metallic precursors deposited with the upright-location sputter gun might be more appropriate to prepare CIGS thin films than those sputtered with the titled-location gun.

Investigation of optimal route to fabricate submicron-sized Sm{sub 2}Fe{sub 17} particles with reduction-diffusion method

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

Okada, Shusuke, E-mail: shusuke-okada@aist.go.jp; Takagi, Kenta; Ozaki, Kimihiro

Submicron-sized Sm{sub 2}Fe{sub 17} powder samples were fabricated by a non-pulverizing process through reduction-diffusion of precursors prepared by a wet-chemical technique. Three precursors having different morphologies, which were micron-sized porous Sm-Fe oxide-impregnated iron nitrate, acicular goethite impregnated-samarium nitrate, and a conventional Sm-Fe coprecipitate, were prepared and subjected to hydrogen reduction and reduction-diffusion treatment to clarify whether these precursors could be convert to Sm{sub 2}Fe{sub 17} without impurity phases and which precursor is the most attractive for producing submicron-sized Sm{sub 2}Fe{sub 17} powder. As a result, all three precursors were successfully converted to Sm{sub 2}Fe{sub 17} powders without impurity phases, andmore » the synthesis route using iron-oxide particle-impregnated samarium oxide was revealed to have the greatest potential among the three routes.« less

Precursor directed synthesis - ``molecular'' mechanisms in the Soft Chemistry approaches and their use for template-free synthesis of metal, metal oxide and metal chalcogenide nanoparticles and nanostructures

NASA Astrophysics Data System (ADS)

Seisenbaeva, Gulaim A.; Kessler, Vadim G.

2014-05-01

This review provides an insight into the common reaction mechanisms in Soft Chemistry processes involved in nucleation, growth and aggregation of metal, metal oxide and chalcogenide nanoparticles starting from metal-organic precursors such as metal alkoxides, beta-diketonates, carboxylates and their chalcogene analogues and demonstrates how mastering the precursor chemistry permits us to control the chemical and phase composition, crystallinity, morphology, porosity and surface characteristics of produced nanomaterials.This review provides an insight into the common reaction mechanisms in Soft Chemistry processes involved in nucleation, growth and aggregation of metal, metal oxide and chalcogenide nanoparticles starting from metal-organic precursors such as metal alkoxides, beta-diketonates, carboxylates and their chalcogene analogues and demonstrates how mastering the precursor chemistry permits us to control the chemical and phase composition, crystallinity, morphology, porosity and surface characteristics of produced nanomaterials. To Professor David Avnir on his 65th birthday.

Effect of Group-III precursors on unintentional gallium incorporation during epitaxial growth of InAlN layers by metalorganic chemical vapor deposition

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

Kim, Jeomoh, E-mail: jkim610@gatech.edu; Ji, Mi-Hee; Detchprohm, Theeradetch

2015-09-28

Unintentional incorporation of gallium (Ga) in InAlN layers grown with different molar flow rates of Group-III precursors by metalorganic chemical vapor deposition has been experimentally investigated. The Ga mole fraction in the InAl(Ga)N layer was increased significantly with the trimethylindium (TMIn) flow rate, while the trimethylaluminum flow rate controls the Al mole fraction. The evaporation of metallic Ga from the liquid phase eutectic system between the pyrolized In from injected TMIn and pre-deposited metallic Ga was responsible for the Ga auto-incorporation into the InAl(Ga)N layer. The theoretical calculation on the equilibrium vapor pressure of liquid phase Ga and the effectivemore » partial pressure of Group-III precursors based on growth parameters used in this study confirms the influence of Group-III precursors on Ga auto-incorporation. More Ga atoms can be evaporated from the liquid phase Ga on the surrounding surfaces in the growth chamber and then significant Ga auto-incorporation can occur due to the high equilibrium vapor pressure of Ga comparable to effective partial pressure of input Group-III precursors during the growth of InAl(Ga)N layer.« less

Monodisperse Iron Oxide Nanoparticles by Thermal Decomposition: Elucidating Particle Formation by Second-Resolved in Situ Small-Angle X-ray Scattering

PubMed Central

2017-01-01

The synthesis of iron oxide nanoparticles (NPs) by thermal decomposition of iron precursors using oleic acid as surfactant has evolved to a state-of-the-art method to produce monodisperse, spherical NPs. The principles behind such monodisperse syntheses are well-known: the key is a separation between burst nucleation and growth phase, whereas the size of the population is set by the precursor-to-surfactant ratio. Here we follow the thermal decomposition of iron pentacarbonyl in the presence of oleic acid via in situ X-ray scattering. This method allows reaction kinetics and precursor states to be followed with high time resolution and statistical significance. Our investigation demonstrates that the final particle size is directly related to a phase of inorganic cluster formation that takes place between precursor decomposition and particle nucleation. The size and concentration of clusters were shown to be dependent on precursor-to-surfactant ratio and heating rate, which in turn led to differences in the onset of nucleation and concentration of nuclei after the burst nucleation phase. This first direct observation of prenucleation formation of inorganic and micellar structures in iron oxide nanoparticle synthesis by thermal decomposition likely has implications for synthesis of other NPs by similar routes. PMID:28572705

Thin Film CuInS2 Prepared by Spray Pyrolysis with Single-Source Precursors

NASA Technical Reports Server (NTRS)

Jin, Michael H.; Banger, Kulinder K.; Harris, Jerry D.; Cowen, Jonathan E.; Hepp, Aloysius F.; Lyons, Valerie (Technical Monitor)

2002-01-01

Both horizontal hot-wall and vertical cold-wall atmospheric chemical spray pyrolysis processes deposited near single-phase stoichiometric CuInS2 thin films. Single-source precursors developed for ternary chalcopyrite materials were used for this study, and a new liquid phase single-source precursor was tested with a vertical cold-wall reactor. The depositions were carried out under an argon atmosphere, and the substrate temperature was kept at 400 C. Columnar grain structure was obtained with vapor deposition, and the granular structure was obtained with (liquid) droplet deposition. Conductive films were deposited with planar electrical resistivities ranging from 1 to 30 Omega x cm.

Vaporization of a mixed precursors in chemical vapor deposition for YBCO films

NASA Technical Reports Server (NTRS)

Zhou, Gang; Meng, Guangyao; Schneider, Roger L.; Sarma, Bimal K.; Levy, Moises

1995-01-01

Single phase YBa2Cu3O7-delta thin films with T(c) values around 90 K are readily obtained by using a single source chemical vapor deposition technique with a normal precursor mass transport. The quality of the films is controlled by adjusting the carrier gas flow rate and the precursor feed rate.

Mechanically activated synthesis of PZT and its electromechanical properties

NASA Astrophysics Data System (ADS)

Liu, X.; Akdogan, E. K.; Safari, A.; Riman, R. E.

2005-08-01

Mechanical activation was successfully used to synthesize nanostructured phase-pure Pb(Zr0.7Ti0.3)O3 (PZT) powders. Lead zirconium titanium (PbZrTi) hydrous oxide precursor, synthesized from chemical co-precipitation, was mechanically activated in a NaCl matrix. The synthesized PZT particles were characterized by using X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, laser-light diffraction, and nitrogen adsorption. Thermogravimetric analysis and differential thermal analysis were used to monitor dehydration and phase transformation of PbZrTi hydrous oxide precursor during mechanical activation. The best mechanical activation conditions corresponded to mechanically activating PbZrTi hydrous oxide precursor in a NaCl matrix with a NaCl/precursor weight ratio of 4:1 for 8 h. These conditions resulted in a dispersible phase-pure PZT powder with a median secondary-particle size of ˜110 nm. The properties of PZT 70/30 from mechanically activated powder, as measured on discs sintered at 1150 °C for 2 h, were found to be in close conformity to those obtained by a conventional mixed oxide solid state reaction route.

Material State Awareness for Composites Part I: Precursor Damage Analysis Using Ultrasonic Guided Coda Wave Interferometry (CWI).

PubMed

Patra, Subir; Banerjee, Sourav

2017-12-16

Detection of precursor damage followed by the quantification of the degraded material properties could lead to more accurate progressive failure models for composite materials. However, such information is not readily available. In composite materials, the precursor damages-for example matrix cracking, microcracks, voids, interlaminar pre-delamination crack joining matrix cracks, fiber micro-buckling, local fiber breakage, local debonding, etc.-are insensitive to the low-frequency ultrasonic guided-wave-based online nondestructive evaluation (NDE) or Structural Health Monitoring (SHM) (~100-~500 kHz) systems. Overcoming this barrier, in this article, an online ultrasonic technique is proposed using the coda part of the guided wave signal, which is often neglected. Although the first-arrival wave packets that contain the fundamental guided Lamb wave modes are unaltered, the coda wave packets however carry significant information about the precursor events with predictable phase shifts. The Taylor-series-based modified Coda Wave Interferometry (CWI) technique is proposed to quantify the stretch parameter to compensate the phase shifts in the coda wave as a result of precursor damage in composites. The CWI analysis was performed on five woven composite-fiber-reinforced-laminate specimens, and the precursor events were identified. Next, the precursor damage states were verified using high-frequency Scanning Acoustic Microscopy (SAM) and optical microscopy imaging.

Irreversible phase transitions due to laser-based T-jump heating of precursor Eu:ZrO{sub 2}/Tb:Y{sub 2}O{sub 3} core/shell nanoparticles

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

Gunawidjaja, Ray; Diez-y-Riega, Helena; Eilers, Hergen, E-mail: eilers@wsu.edu

2015-09-15

Amorphous precursors of Eu-doped-ZrO{sub 2}/Tb-doped-Y{sub 2}O{sub 3} (p-Eu:ZrO{sub 2}/p-Tb:Y{sub 2}O{sub 3}) core/shell nanoparticles are rapidly heated to temperatures between 200 °C and 950 °C for periods between 2 s and 60 s using a CO{sub 2} laser. During this heating process the nanoparticles undergo irreversible phase changes. The fluorescence spectra due to Eu{sup 3+} dopants in the core and Tb{sup 3+} dopants in the shell are used to identify distinct phases within the material and to generate time/temperature phase diagrams. Such phase diagrams can potentially help to determine unknown time/temperature histories in thermosensor applications. - Graphical abstract: A CO{sub 2}more » laser is used for rapid heating of p-Eu:ZrO{sub 2}/p-Tb:Y{sub 2}O{sub 3} core/shell nanoparticles. Optical spectra are used to identify distinct phases and to determine its thermal history. - Highlights: • Synthesized oxide precursors of lanthanide doped core/shell nanoparticles. • Heated core/shell nanoparticles via laser-based T-jump technique. • Observed time- and temperature-dependent irreversible phase transition.« less

Nucleation and Epitaxy-Mediated Phase Transformation of a Precursor Cadmium Carbonate Phase at the Calcite/Water Interface

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

Riechers, Shawn L.; Rosso, Kevin M.; Kerisit, Sebastien N.

Mineral nucleation can be catalyzed by the presence of mineral substrates; however, the mechanisms of heterogeneous nucleation remain poorly understood. A combination of in situ time-sequenced measurements and nano-manipulation experiments were performed using atomic force microscopy (AFM) to probe the mechanisms of heteroepitaxial nucleation of otavite (CdCO3) on calcite (CaCO3) single crystals that exposed the (10-14) surface. Otavite and calcite are isostructural carbonates that display a 4% lattice mismatch, based on their (10-14) surface areas. AFM observations revealed a two-stage process in the nucleation of cadmium carbonate surface precipitates. As evidenced by changes in height, shape, growth behavior, and frictionmore » signal of the precipitates, a precursor phase was observed to initially form on the surface and subsequently undergo an epitaxy-mediated phase transformation to otavite, which then grew epitaxially. Nano-manipulation experiments, in which the applied force was increased progressively until precipitates were removed from the surface, showed that adhesion of the precursor phase to the substrate was distinctively weaker than that of the epitaxial phase, consistent with that of an amorphous phase. These findings demonstrate for the first time that heterogeneous mineral nucleation can follow a non-classical pathway like that found in homogenous aqueous conditions.« less

Crystalline oxides on semiconductors: A structural transition of the interface phase

NASA Astrophysics Data System (ADS)

Walker, F. J.; Buongiorno-Nardelli, Marco; Billman, C. A.; McKee, R. A.

2004-03-01

The growth of crystalline oxides on silicon is facilitated by the preparation of a surface phase of alkaline earth silicide. We describe how the surface phase serves as a precursor of the final interface phase using reflection high energy electron diffraction (RHEED) and density functional theory (DFT). RHEED intensity oscillations of the growth of BaSrO show layer-by-layer build up of the oxide on the interface. The 2x1 symmetry of the surface precursor persists up to 3 ML BaSrO coverage at which point a 1x1 pattern characteristic of the rock-salt structure of BaSrO is observed. Prior to 3 ML growth of alkaline earth oxide, DFT calculations and RHEED show that the surface precursor persists as the interface phase and induces large displacements in the growing oxide layer away from the rock-salt structure and having a 2x1 symmetry. These distortions of the rock-salt structure are energetically unfavorable and become more unfavorable as the oxide thickness increases. At 3 ML, the stability of the rock-salt structure drives a structural transformation of the film and the interface phase to a structure that is distinct from the surface precursor. Research sponsored jointly by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory under contract DE-AC05-00OR22725 with UT-Battelle, LLC and at the University of Tennessee under contract DE-FG02-01ER45937. Calculations have been performed on CCS supercomputers at Oak Ridge National Laboratory.

The role of low-energy electrons in focused electron beam induced deposition: four case studies of representative precursors

PubMed Central

Thorman, Rachel M; Kumar T. P., Ragesh; Fairbrother, D Howard

2015-01-01

Summary Focused electron beam induced deposition (FEBID) is a single-step, direct-write nanofabrication technique capable of writing three-dimensional metal-containing nanoscale structures on surfaces using electron-induced reactions of organometallic precursors. Currently FEBID is, however, limited in resolution due to deposition outside the area of the primary electron beam and in metal purity due to incomplete precursor decomposition. Both limitations are likely in part caused by reactions of precursor molecules with low-energy (<100 eV) secondary electrons generated by interactions of the primary beam with the substrate. These low-energy electrons are abundant both inside and outside the area of the primary electron beam and are associated with reactions causing incomplete ligand dissociation from FEBID precursors. As it is not possible to directly study the effects of secondary electrons in situ in FEBID, other means must be used to elucidate their role. In this context, gas phase studies can obtain well-resolved information on low-energy electron-induced reactions with FEBID precursors by studying isolated molecules interacting with single electrons of well-defined energy. In contrast, ultra-high vacuum surface studies on adsorbed precursor molecules can provide information on surface speciation and identify species desorbing from a substrate during electron irradiation under conditions more representative of FEBID. Comparing gas phase and surface science studies allows for insight into the primary deposition mechanisms for individual precursors; ideally, this information can be used to design future FEBID precursors and optimize deposition conditions. In this review, we give a summary of different low-energy electron-induced fragmentation processes that can be initiated by the secondary electrons generated in FEBID, specifically, dissociative electron attachment, dissociative ionization, neutral dissociation, and dipolar dissociation, emphasizing the different nature and energy dependence of each process. We then explore the value of studying these processes through comparative gas phase and surface studies for four commonly-used FEBID precursors: MeCpPtMe3, Pt(PF3)4, Co(CO)3NO, and W(CO)6. Through these case studies, it is evident that this combination of studies can provide valuable insight into potential mechanisms governing deposit formation in FEBID. Although further experiments and new approaches are needed, these studies are an important stepping-stone toward better understanding the fundamental physics behind the deposition process and establishing design criteria for optimized FEBID precursors. PMID:26665061

The role of low-energy electrons in focused electron beam induced deposition: four case studies of representative precursors.

PubMed

Thorman, Rachel M; Kumar T P, Ragesh; Fairbrother, D Howard; Ingólfsson, Oddur

2015-01-01

Focused electron beam induced deposition (FEBID) is a single-step, direct-write nanofabrication technique capable of writing three-dimensional metal-containing nanoscale structures on surfaces using electron-induced reactions of organometallic precursors. Currently FEBID is, however, limited in resolution due to deposition outside the area of the primary electron beam and in metal purity due to incomplete precursor decomposition. Both limitations are likely in part caused by reactions of precursor molecules with low-energy (<100 eV) secondary electrons generated by interactions of the primary beam with the substrate. These low-energy electrons are abundant both inside and outside the area of the primary electron beam and are associated with reactions causing incomplete ligand dissociation from FEBID precursors. As it is not possible to directly study the effects of secondary electrons in situ in FEBID, other means must be used to elucidate their role. In this context, gas phase studies can obtain well-resolved information on low-energy electron-induced reactions with FEBID precursors by studying isolated molecules interacting with single electrons of well-defined energy. In contrast, ultra-high vacuum surface studies on adsorbed precursor molecules can provide information on surface speciation and identify species desorbing from a substrate during electron irradiation under conditions more representative of FEBID. Comparing gas phase and surface science studies allows for insight into the primary deposition mechanisms for individual precursors; ideally, this information can be used to design future FEBID precursors and optimize deposition conditions. In this review, we give a summary of different low-energy electron-induced fragmentation processes that can be initiated by the secondary electrons generated in FEBID, specifically, dissociative electron attachment, dissociative ionization, neutral dissociation, and dipolar dissociation, emphasizing the different nature and energy dependence of each process. We then explore the value of studying these processes through comparative gas phase and surface studies for four commonly-used FEBID precursors: MeCpPtMe3, Pt(PF3)4, Co(CO)3NO, and W(CO)6. Through these case studies, it is evident that this combination of studies can provide valuable insight into potential mechanisms governing deposit formation in FEBID. Although further experiments and new approaches are needed, these studies are an important stepping-stone toward better understanding the fundamental physics behind the deposition process and establishing design criteria for optimized FEBID precursors.

Fabrication of Lanthanum Telluride 14-1-11 Zintl High-Temperature Thermoelectric Couple

NASA Technical Reports Server (NTRS)

Ravi, Vilupanur A.; Li, Billy Chun-Yip; Fleurial, Pierre; Star, Kurt

2010-01-01

The development of more efficient thermoelectric couple technology capable of operating with high-grade heat sources up to 1,275 K is key to improving the performance of radioisotope thermoelectric generators. Lanthanum telluride La3-xTe4 and 14-1-11 Zintls (Yb14MnSb11) have been identified as very promising materials. The fabrication of advanced high-temperature thermoelectric couples requires the joining of several dissimilar materials, typically including a number of diffusion bonding and brazing steps, to achieve a device capable of operating at elevated temperatures across a large temperature differential (up to 900 K). A thermoelectric couple typically comprises a heat collector/ exchanger, metallic interconnects on both hot and cold sides, n-type and ptype conductivity thermoelectric elements, and cold-side hardware to connect to the cold-side heat rejection and provide electrical connections. Differences in the physical, mechanical, and chemical properties of the materials that make up the thermoelectric couple, especially differences in the coefficients of thermal expansion (CTE), result in undesirable interfacial stresses that can lead to mechanical failure of the device. The problem is further complicated by the fact that the thermoelectric materials under consideration have large CTE values, are brittle, and cracks can propagate through them with minimal resistance. The inherent challenge of bonding brittle, high-thermal-expansion thermoelectric materials to a hot shoe material that is thick enough to carry the requisite electrical current was overcome. A critical advantage over prior art is that this device was constructed using all diffusion bonds and a minimum number of assembly steps. The fabrication process and the materials used are described in the following steps: (1) Applying a thin refractory metal foil to both sides of lanthanum telluride. To fabricate the n-type leg of the advanced thermoelectric couple, the pre-synthesized lanthanum telluride coupon was diffusion bonded to the metal foil using a thin adhesion layer. (2) Repeating a similar process for the 14-1-11 Zintl p-type leg of the advanced thermoelectric couple. (3) Bonding thick CTE-matched metal plates on the metallized lanthanum telluride and Yb14MnSb11 to form the hot and cold sides of the thermoelectric couple. The calculated conversion efficiency of such an advanced couple would be about 10.5 percent, about 35 percent better than heritage radioisotope thermoelectric technology that relies on Si-Ge alloys. In addition, unlike Si-Ge alloys, these materials can be combined with many other thermoelectric materials optimized for operation at lower temperatures to achieve conversion efficiency in excess of 15 percent (a factor of 2 increase over heritage technology).

Morphology and stability in a half-metallic ferromagnetic CrO 2 compound of nanoparticles synthesized via a polymer precursor

NASA Astrophysics Data System (ADS)

Biswas, S.; Ram, S.

2004-11-01

Nanoparticles of stable CrO2 of a half-metallic ferromagnet are synthesized with a novel chemical method involving a Cr4+-polymer composite precursor. A single phase CrO2 of D4h 14 : P42 / mnm tetragonal crystal structure (lattice parameters a = 0.4250 and c = 0.3190 nm) lies after firing the precursor at 350 °C for 1 h in air. Microstructure reveals single domain CrO2 particles of thin platelets (aspect ratio ∼1) of average 50 nm diameter and 35 nm thickness. In air, unless heating at temperatures above 500 °C, no due CrO2 → Cr2O3 phase transformation encounters. The results are presented in terms of X-ray diffraction and thermal or thermogravimetric analysis of precursor and derived CrO2 powder.

Formation of crystalline InGaO₃(ZnO)n nanowires via the solid-phase diffusion process using a solution-based precursor.

PubMed

Guo, Yujie; Van Bilzen, Bart; Locquet, Jean Pierre; Seo, Jin Won

2015-12-11

One-dimensional single crystalline InGaO3(ZnO)n (IGZO) nanostructures have great potential for various electrical and optical applications. This paper demonstrates for the first time, to our knowledge, a non-vacuum route for the synthesis of IGZO nanowires by annealing ZnO nanowires covered with solution-based IGZO precursor. This method results in nanowires with highly periodic IGZO superlattice structure. The phase transition of IGZO precursor during thermal treatment was systematically studied. Transmission electron microscopy studies reveal that the formation of the IGZO structure is driven by anisotropic inter-diffusion of In, Ga, and Zn atoms, and also by the crystallization of the IGZO precursor. Optical measurements using cathodoluminescence and UV-vis spectroscopy confirm that the nanowires consist of the IGZO compound with wide optical band gap and suppressed luminescence.

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

DeVol, Ross T.; Sun, Chang-Yu; Marcus, Matthew A.

Nacre, or mother-of-pearl, the iridescent inner layer of many mollusk shells, is a biomineral lamellar composite of aragonite (CaCO 3) and organic sheets. Biomineralization frequently occurs via transient amorphous precursor phases, crystallizing into the final stable biomineral. In nacre, despite extensive attempts, amorphous calcium carbonate (ACC) precursors have remained elusive. They were inferred from non-nacre-forming larval shells, or from a residue of amorphous material surrounding mature gastropod nacre tablets, and have only once been observed in bivalve nacre. Here we present the first direct observation of ACC precursors to nacre formation, obtained from the growth front of nacre in gastropodmore » shells from red abalone (Haliotis rufescens), using synchrotron spectromicroscopy. Surprisingly, the abalone nacre data show the same ACC phases that are precursors to calcite (CaCO 3) formation in sea urchin spicules, and not proto-aragonite or poorly crystalline aragonite (pAra), as expected for aragonitic nacre. In contrast, we find pAra in coral.« less

Atomically resolved calcium phosphate coating on a gold substrate.

PubMed

Metoki, Noah; Baik, Sung-Il; Isheim, Dieter; Mandler, Daniel; Seidman, David N; Eliaz, Noam

2018-05-10

Some articles have revealed that the electrodeposition of calcium phosphate (CaP) coatings entails a precursor phase, similarly to biomineralization in vivo. The chemical composition of the initial layer and its thickness are, however, still arguable, to the best of our knowledge. Moreover, while CaP and electrodeposition of metal coatings have been studied utilizing atom-probe tomography (APT), the electrodeposition of CaP ceramics has not been heretofore studied. Herein, we present an investigation of the CaP deposition on a gold substrate. Using APT and transmission electron microscopy (TEM) it is found that a mixture of phases, which could serve as transient precursor phases to hydroxyapatite (HAp), can be detected. The thickness of these phases is tens of nanometers, and they consist of amorphous CaP (ACP), dibasic calcium phosphate dihydrate (DCPD), and octacalcium phosphate (OCP). This demonstrates the value of using atomic-resolved characterization techniques for identifying the precursor phases. It also indicates that the kinetics of their transformation into the more stable HAp is not too fast to enable their observation. The coating gradually displays higher Ca/P atomic ratios, a porous nature, and concomitantly a change in its density.

The μ3 model of acids and bases: extending the Lewis theory to intermetallics.

PubMed

Stacey, Timothy E; Fredrickson, Daniel C

2012-04-02

A central challenge in the design of new metallic materials is the elucidation of the chemical factors underlying the structures of intermetallic compounds. Analogies to molecular bonding phenomena, such as the Zintl concept, have proven very productive in approaching this goal. In this Article, we extend a foundational concept of molecular chemistry to intermetallics: the Lewis theory of acids and bases. The connection is developed through the method of moments, as applied to DFT-calibrated Hückel calculations. We begin by illustrating that the third and fourth moments (μ(3) and μ(4)) of the electronic density of states (DOS) distribution tune the properties of a pseudogap. μ(3) controls the balance of states above and below the DOS minimum, with μ(4) then determining the minimum's depth. In this way, μ(3) predicts an ideal occupancy for the DOS distribution. The μ(3)-ideal electron count is used to forge a link between the reactivity of transition metals toward intermetallic phase formation, and that of Lewis acids and bases toward adduct formation. This is accomplished through a moments-based definition of acidity which classifies systems that are electron-poor relative to the μ(3)-ideal as μ(3)-acidic, and those that are electron-rich as μ(3)-basic. The reaction of μ(3) acids and bases, whether in the formation of a Lewis acid/base adduct or an intermetallic phase, tends to neutralize the μ(3) acidity or basicity of the reactants. This μ(3)-neutralization is traced to the influence of electronegativity differences at heteroatomic contacts on the projected DOS curves of the atoms involved. The role of μ(3)-acid/base interactions in intermetallic phases is demonstrated through the examination of 23 binary phases forming between 3d metals, the stability range of the CsCl type, and structural trends within the Ti-Ni system.

[Simultaneous determination of nine perfluorinated compound precursors in atmospheric precipitation by solid phase extraction and ultra performance liquid chromatography with tandem mass spectrometry].

PubMed

Zhang, Ming; Tang, Fangliang; Xu, Jianfen; Yu, Bo; Zhang, Wei; Yao, Jianliang; Hu, Minhua

2017-10-08

A high-throughput detection method has been developed for the determination of nine perfluorinated compound precursors (PFCPs) in atmospheric precipitation by solid phase extraction-ultra performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (SPE-UPLC-ESI-MS/MS). The atmospheric precipitation samples were concentrated and purified with HLB solid phase extraction cartridges. The UPLC separation was performed on an HSS T 3 column (100 mm×2.1 mm, 1.7 μm) utilizing a gradient elution program of methanol and water as the mobile phases at a flow rate of 0.2 mL/min. The MS/MS detection was performed under negative electrospray ionization (ESI - ) in multiple reaction monitoring (MRM) mode. Good linearity was observed in the range of 0.05-5.00 μg/L, 0.50-50.0 μg/L or 5.00-500 μg/L with correlation coefficients from 0.9921 to 0.9995. The limits of detection (LODs) for the nine perfluorinated compound precursors were in the ranges of 0.05-7.9 ng/L. The recoveries ranged from 76.0% to 106% with the relative standard deviations between 0.72% and 13.7%. This method is characterized by high sensitivity and precision, extensive analytical range and quick analytical rate, and can be applied for the analysis of perfluorinated compound precursors in atmospheric precipitation.

Synthesis of stable TiO2 nanotubes: effect of hydrothermal treatment, acid washing and annealing temperature.

PubMed

López Zavala, Miguel Ángel; Lozano Morales, Samuel Alejandro; Ávila-Santos, Manuel

2017-11-01

Effect of hydrothermal treatment, acid washing and annealing temperature on the structure and morphology of TiO 2 nanotubes during the formation process was assessed. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy analysis were conducted to describe the formation and characterization of the structure and morphology of nanotubes. Hydrothermal treatment of TiO 2 precursor nanoparticles and acid washing are fundamental to form and define the nanotubes structure. Hydrothermal treatment causes a change in the crystallinity of the precursor nanoparticles from anatase phase to a monoclinic phase, which characterizes the TiO 2 nanosheets structure. The acid washing promotes the formation of high purity nanotubes due to Na + is exchanged from the titanate structure to the hydrochloric acid (HCl) solution. The annealing temperature affects the dimensions, structure and the morphology of the nanotubes. Annealing temperatures in the range of 400 °C and 600 °C are optimum to maintain a highly stable tubular morphology of nanotubes. Additionally, nanotubes conserve the physicochemical properties of the precursor Degussa P25 nanoparticles. Temperatures greater than 600 °C alter the morphology of nanotubes from tubular to an irregular structure of nanoparticles, which are bigger than those of the precursor material, i.e., the crystallinity turn from anatase phase to rutile phase inducing the collapse of the nanotubes.

Methods for forming particles

DOEpatents

Fox, Robert V.; Zhang, Fengyan; Rodriguez, Rene G.; Pak, Joshua J.; Sun, Chivin

2016-06-21

Single source precursors or pre-copolymers of single source precursors are subjected to microwave radiation to form particles of a I-III-VI.sub.2 material. Such particles may be formed in a wurtzite phase and may be converted to a chalcopyrite phase by, for example, exposure to heat. The particles in the wurtzite phase may have a substantially hexagonal shape that enables stacking into ordered layers. The particles in the wurtzite phase may be mixed with particles in the chalcopyrite phase (i.e., chalcopyrite nanoparticles) that may fill voids within the ordered layers of the particles in the wurtzite phase thus produce films with good coverage. In some embodiments, the methods are used to form layers of semiconductor materials comprising a I-III-VI.sub.2 material. Devices such as, for example, thin-film solar cells may be fabricated using such methods.

New precursors for direct synthesis of single phase Na- and K-{beta}{double_prime}-aluminas for use in AMTEC systems

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

Cook, R.L.; MacQueen, D.B.; Bader, K.E.

1997-12-31

Alkali Metal Thermoelectric Converters (AMTEC) are efficient direct energy conversion devices that depend on the use of highly conductive beta-alumina membranes for their operation. The key component of the AMTEC system is a highly conductive Na-{beta}{double_prime}-alumina solid electrolyte which conducts sodium ions from the high to low temperature zone, thereby generating electricity. AMTEC cells convert thermal to electrical energy by using heat to produce and maintain an alkali metal concentration gradient across the ion transporting BASE membrane. They have developed a method for producing pure phase Na-{beta}{double_prime}-alumina and K-{beta}{double_prime}-alumina powders from single phase nano-sized carboxylato-alumoxanes precursors. Sodium or potassium ionsmore » (the mobile ions) and either Mg{sup 2+} or Li{sup +} ions (which stabilize the {beta}{double_prime}-alumina structure) can be atomically dispersed into the carboxylato-alumoxane lattice at low (< 100 C) temperature. Calculation of the carboxylato-alumoxane precursors at 1,200--1,500 C produces pure phase {beta}{double_prime}-alumina powders.« less

Nanoceramic -Metal Matrix Composites by In-Situ Pyrolysis of Organic Precursors in a Liquid Melt

NASA Astrophysics Data System (ADS)

Sudarshan; Surappa, M. K.; Ahn, Dongjoon; Raj, Rishi

2008-12-01

We show the feasibility of introducing a dispersion of a refractory ceramic phase into metals by stirring a powder of an organic polymer into a magnesium melt and having it convert into a ceramic within the melt by in-situ pyrolysis of the polymer. The pyrolysis is a highly reactive process, accompanied by the evolution of hydrogen, which disperses the ceramic phase into nanoscale constituents. In the present experiments, a polysilazane-based precursor, which is known to yield an amorphous ceramic constituted from silicon, carbon, and nitrogen, was used. Five weight percent of the precursor (which has a nominal ceramic yield of 75 to 85 wt pct) produced a twofold increase in the room-temperature yield strength and reduced the steady-state strain rate at 450 °C by one to two orders of magnitude, relative to pure magnesium. This polymer-based in-situ process (PIP) for processing metal-matrix composites (MMCs) is likely to have great generality, because many different kinds of organic precursors, for producing oxide, carbides, nitrides, and borides, are commercially available. Also, the process would permit the addition of large volume fractions of the ceramic, enabling the nanostructural design, and production of MMCs with a wide range of mechanical properties, meant especially for high-temperature applications. An important and noteworthy feature of the present process, which distinguishes it from other methods, is that all the constituents of the ceramic phase are built into the organic molecules of the precursor ( e.g., polysilazanes contain silicon, carbon, and nitrogen); therefore, a reaction between the polymer and the host metal is not required to produce the dispersion of the refractory phase.

On-fiber furan formation from volatile precursors: a critical example of artefact formation during Solid-Phase Microextraction.

PubMed

Adams, An; Van Lancker, Fien; De Meulenaer, Bruno; Owczarek-Fendor, Agnieszka; De Kimpe, Norbert

2012-05-15

For the analysis of furan, a possible carcinogen formed during thermal treatment of food, Solid-Phase Microextraction (SPME) is a preferred and validated sampling method. However, when volatile furan precursors are adsorbed on the carboxen/PDMS fiber, additional amounts of furan can be formed on the fiber during thermal desorption, as shown here for 2-butenal and furfural. No significant increase in furan amounts was found upon heating the furan precursor 2-butenal, indicating that the furan amounts formed during precursor heating experiments are negligible as compared to the additional amounts of furan formed during fiber desorption. This artefactual furan formation increased with increasing desorption time, but especially with increasing desorption temperature. Although this effect was most pronounced on the Carboxen/PDMS SPME-fiber, it was also noted on two other SPME-fibers tested (PDMS and DVB/Carboxen/PDMS). The general impact on furan data from food and model systems in literature will depend on the amounts of volatile precursors present, but will probably remain limited. However, considering the importance of this worldwide food contaminant, special care has to be taken during SPME-analysis of furan. Especially when performing precursor studies, static headspace sampling should preferably be applied for furan analysis. Copyright © 2012 Elsevier B.V. All rights reserved.

Template-assisted mineral formation via an amorphous liquid phase precursor route

NASA Astrophysics Data System (ADS)

Amos, Fairland F.

The search for alternative routes to synthesize inorganic materials has led to the biomimetic route of producing ceramics. In this method, materials are manufactured at ambient temperatures and in aqueous solutions with soluble additives and insoluble matrix, similar to the biological strategy for the formation of minerals by living organisms. Using this approach, an anionic polypeptide additive was used to induce an amorphous liquid-phase precursor to either calcium carbonate or calcium phosphate. This precursor was then templated on either organic or inorganic substrates. Non-equilibrium morphologies, such as two-dimensional calcium carbonate films, one-dimensional calcium carbonate mesostructures and "molten" calcium phosphate spherulites were produced, which are not typical of the traditional (additive-free) solution grown crystals in the laboratory. In the study of calcium carbonate, the amorphous calcium carbonate mineral formed via the liquid-phase precursor, either underwent a dissolution-recrystallization event or a pseudo-solid-state transformation to produce different morphologies and polymorphs of the mineral. Discrete or aggregate calcite crystals were formed via the dissolution of the amorphous phase to allow the reprecipitation of the stable crystal. Non-equilibrium morphologies, e.g., films, mesotubules and mesowires were templated using organic and inorganic substrates and compartments. These structures were generated via an amorphous solid to crystalline solid transformation. Single crystalline tablets and mesowires of aragonite, which are reported to be found only in nature as skeletal structures of marine organisms, such as mollusk nacre and echinoderm teeth, were successfully synthesized. These biomimetic structures were grown via the polymer-induced liquid-phase precursor route in the presence of magnesium. Only low magnesium-bearing calcite was formed in the absence of the polymer. A similar approach of using a polymeric additive was implemented in calcium phosphate. Spherulitic crystals and films, seemingly formed from a molten state, were produced. These structures served as nucleating surfaces for the radial formation of calcium oxalate minerals. The composite calcium phosphate-calcium oxalate assemblies are similar to the core-shell structures found in certain kidney stones.

Effects of intergranular phase on the coercivity for MnBi magnets prepared by spark plasma sintering

NASA Astrophysics Data System (ADS)

Cao, J.; Huang, Y. L.; Hou, Y. H.; Zhang, G. Q.; Shi, Z. Q.; Zhong, Z. C.; Liu, Z. W.

2018-05-01

MnBi magnets with a high content of low temperature phase (LTP) and excellent magnetic properties were prepared by spark plasma sintering (SPS) using ball milling powders as precursors without magnetic purification. A complicated intergranular phase, which contains Mn phase, Bi phase, MnO phase, and even amorphous phase in MnBi magnets, was characterized and reported systematically. It was found that the formation of intergranular phase which was contributed by ball milling precursors and sintering mechanism, jointly, had important influence on the magnetic properties. The appropriate content of intergranular phase was beneficial in improving the coercivity due to the strong magnetic isolation effects. The optimum magnetic properties with Mr=26.0 emu/g, Hci= 7.11 kOe and (BH)max=1.53 MGOe at room temperature, and a maximum value Hci= 25.37 kOe at 550 K can be obtained. Strongly favorable magnetic properties make SPSed MnBi magnets an attractive candidate material for small permanent magnets used in high-temperature applications.

Synthesis, structure, and bonding of BaTl4. Size effects on encapsulation of cations in electron-poor metal networks.

PubMed

Dai, Jing-Cao; Gupta, Shalabh; Corbett, John D

2011-01-03

The synthesis, structure, and bonding of BaTl(4) are described [C2/m, Z = 4, a = 12.408(3), b = 5.351(1), c = 10.383(2) Å, β = 116.00(3)°]. Pairs of edge-sharing Tl pentagons are condensed to generate a network of pentagonal biprisms along b that encapsulate Ba atoms. Alternating levels of prisms along c afford six more bifunctional Tl atoms about the waists of the biprisms, giving Ba a coordination number of 16. Each Tl atom is bonded to five to seven other Tl atoms and to three to five Ba atoms. There is also strong evidence that Hg substitutes preferentially in the shared edges of the Tl biprisms in BaHg(0.80)Tl(3.20) to generate more strongly bound Hg(2) dimers. Cations that are too small relative to the dimensions of the surrounding polyanionic network make this BaTl(4) structure (and for SrIn(4) and perhaps EuIn(4) as well) one stable alternative to tetragonal BaAl(4)-type structures in which cations are bound in larger hexagon-faced nets, as for BaIn(4) and SrGa(4). Characteristic condensation and augmentation of cation-centered prismatic units is common among many relatively cation- and electron-poor, polar derivatives of Zintl phases gain stability. At the other extreme, the large family of Frank-Kasper phases in which the elements exhibit larger numbers of bonded neighbors are sometimes referred to as orbitally rich.

Design of ternary alkaline-earth metal Sn(II) oxides with potential good p-type conductivity

DOE PAGES

Du, Mao -Hua; Singh, David J.; Zhang, Lijun; ...

2016-04-19

Oxides with good p-type conductivity have been long sought after to achieve high performance all-oxide optoelectronic devices. Divalent Sn(II) based oxides are promising candidates because of their rather dispersive upper valence bands caused by the Sn-5s/O-2p anti-bonding hybridization. There are so far few known Sn(II) oxides being p-type conductive suitable for device applications. Here, we present via first-principles global optimization structure searches a material design study for a hitherto unexplored Sn(II)-based system, ternary alkaline-earth metal Sn(II) oxides in the stoichiometry of MSn 2O 3 (M = Mg, Ca, Sr, Ba). We identify two stable compounds of SrSn 2O 3 andmore » BaSn 2O 3, which can be stabilized by Sn-rich conditions in phase stability diagrams. Their structures follow the Zintl behaviour and consist of basic structural motifs of SnO 3 tetrahedra. Unexpectedly they show distinct electronic properties with band gaps ranging from 1.90 (BaSn 2O 3) to 3.15 (SrSn 2O 3) eV, and hole effective masses ranging from 0.87 (BaSn 2O 3) to above 6.0 (SrSn 2O 3) m0. Further exploration of metastable phases indicates a wide tunability of electronic properties controlled by the details of the bonding between the basic structural motifs. Lastly, this suggests further exploration of alkaline-earth metal Sn(II) oxides for potential applications requiring good p-type conductivity such as transparent conductors and photovoltaic absorbers.« less

Lyotropic liquid crystalline L3 phase silicated nanoporous monolithic composites and their production

DOEpatents

McGrath, Kathryn M.; Dabbs, Daniel M.; Aksay, Ilhan A.; Gruner, Sol M.

2003-10-28

A mesoporous ceramic material is provided having a pore size diameter in the range of about 10-100 nanometers produced by templating with a ceramic precursor a lyotropic liquid crystalline L.sub.3 phase consisting of a three-dimensional, random, nonperiodic network packing of a multiple connected continuous membrane. A preferred process for producing the inesoporous ceramic material includes producing a template of a lyotropic liquid crystalline L.sub.3 phase by mixing a surfactant, a co-surfactant and hydrochloric acid, coating the template with an inorganic ceramic precursor by adding to the L.sub.3 phase tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS) and then converting the coated template to a ceramic by removing any remaining liquids.

Tailoring the synthesis of supported Pd catalysts towards desired structure and size of metal particles.

PubMed

Suresh, Gatla; Radnik, Jörg; Kalevaru, Venkata Narayana; Pohl, Marga-Martina; Schneider, Matthias; Lücke, Bernhard; Martin, Andreas; Madaan, Neetika; Brückner, Angelika

2010-05-14

In a systematic study, the influence of different preparation parameters on phase composition and size of metal crystallites and particles in Pd-Cu/TiO(2) and Pd-Sb/TiO(2) catalyst materials has been explored. Temperature and atmosphere of thermal pretreatment (pure He or 10% H(2)/He), nature of metal precursors (chlorides, nitrates or acetates) as well as of ammonium additives (ammonium sulfate, nitrate, carbonate) and urea were varied with the aim of tailoring the synthesis procedure for the preferential formation of metal particles with similar size and structure as observed recently in active catalysts after long-term equilibration under catalytic reaction conditions in acetoxylation of toluene to benzylacetate. Among the metal precursors and additives, the chloride metal precursors and (NH(4))(2)SO(4) were most suitable. Upon thermal pretreatment of Pd-Sb or Pd-Cu precursors, chloroamine complexes of Pd and Cu are formed, which decompose above 220 degrees C to metallic phases independent of the atmosphere. In He, metallic Pd particles were formed with both the co-components. In H(2)/He flow, Pd-Cu precursors were converted to core-shell particles with a Cu shell and a Pd core, while Sb(1)Pd(1) and Sb(7)Pd(20) alloy phases were formed in the presence of Sb. Metal crystallites of about 40 nm agglomerate to particles of up to 150 nm in He and to even larger size in H(2)/He.

Effect of phase assemblage of precursor on the fabrication process and properties of Bi2223 tape sheathed with Ag-alloy

NASA Astrophysics Data System (ADS)

Nakamura, Y.; Shioiri, T.; Kurihara, C.; Machida, T.; Inada, R.; Oota, A.

2008-09-01

The use of alloy sheath is effective to increase the strength of Ag-sheathed Bi2223 tapes. However, the Jc value of alloy sheathed tapes was not high enough since the undesired reaction to form impurity phases and the change in formation rate of Bi2223 were disturbed by the microstructure of the filaments . In this study, the effect of 2223 contents in precursor on the formation and property of Bi2223 tapes sheathed with Ag-Mg alloy was investigated. The conversion rate of Bi2223 from Bi2212 was increased by the addition of Bi2223 phase in precursor but the conversion rate in Ag-Mg alloy sheathed tapes was slower than that in the Ag-Cu alloy sheathed tapes. This reduction of conversion speed of Bi2223 may be attributed to the decrease in the growth rate of Bi2223 crystals in Ag-Mg alloy sheath. Since the tapes with small Bi2223 crystals after first sintering showed many outgrowths after final sintering, the formation of outgrowth would be caused in the case of small crystal size. The Jc value of 2.2 × 10 4 A/cm 2 was achieved in the samples using the precursor with 10 wt.% 2223. The high Jc value can be achieved by the proper control of precursor condition including the contents of Bi2223 and corresponding heat treatment pattern in Ag-Mg alloy sheathed tapes.

Early T-cell precursor acute lymphoblastic leukaemia in children treated in AIEOP centres with AIEOP-BFM protocols: a retrospective analysis.

PubMed

Conter, Valentino; Valsecchi, Maria Grazia; Buldini, Barbara; Parasole, Rosanna; Locatelli, Franco; Colombini, Antonella; Rizzari, Carmelo; Putti, Maria Caterina; Barisone, Elena; Lo Nigro, Luca; Santoro, Nicola; Ziino, Ottavio; Pession, Andrea; Testi, Anna Maria; Micalizzi, Concetta; Casale, Fiorina; Pierani, Paolo; Cesaro, Simone; Cellini, Monica; Silvestri, Daniela; Cazzaniga, Giovanni; Biondi, Andrea; Basso, Giuseppe

2016-02-01

Early T-cell precursor acute lymphoblastic leukaemia was recently recognised as a distinct leukaemia and reported as associated with poor outcomes. We aimed to assess the outcome of early T-cell precursor acute lymphoblastic leukaemia in patients from the Italian Association of Pediatric Hematology Oncology (AIEOP) centres treated with AIEOP-Berlin-Frankfurt-Münster (AIEOP-BFM) protocols. In this retrospective analysis, we included all children aged from 1 to less than 18 years with early T-cell precursor acute lymphoblastic leukaemia immunophenotype diagnosed between Jan 1, 2008, and Oct 31, 2014, from AIEOP centres. Early T-cell precursors were defined as being CD1a and CD8 negative, CD5 weak positive or negative, and positive for at least one of the following antigens: CD34, CD117, HLADR, CD13, CD33, CD11b, or CD65. Treatment was based on AIEOP-BFM acute lymphoblastic leukaemia 2000 (NCT00613457) or AIEOP-BFM acute lymphoblastic leukaemia 2009 protocols (European Clinical Trials Database 2007-004270-43). The main differences in treatment and stratification of T-cell acute lymphoblastic leukaemia between the two protocols were that in the 2009 protocol only, pegylated L-asparaginase was substituted for Escherichia coli L-asparaginase, patients with prednisone poor response received an additional dose of cyclophosphamide at day 10 of phase IA, and high minimal residual disease at day 15 assessed by flow cytometry was used as a high-risk criterion. Outcomes were assessed in terms of event-free survival, disease-free survival, and overall survival. Early T-cell precursor acute lymphoblastic leukaemia was diagnosed in 49 patients. Compared with overall T-cell acute lymphoblastic leukaemia, it was associated with absence of molecular markers for PCR detection of minimal residual disease in 25 (56%) of 45 patients; prednisone poor response in 27 (55%) of 49 patients; high minimal residual disease at day 15 after starting therapy in 25 (64%) of 39 patients (bone marrow blasts ≥ 10%, by flow cytometry); no complete remission after phase IA in 7 (15%) of 46 patients (bone marrow blasts ≥ 5%, morphologically); and high PCR minimal residual disease (≥ 5 × 10(-4)) at day 33 after starting therapy in 17 (85%) of 20 patients with markers available. Overall, 38 (78%) of 49 patients are in continuous complete remission, including 13 of 18 after haemopoietic stem cell transplantation, with three deaths in induction, five deaths after haemopoietic stem cell transplantation, and three relapses. Severe adverse events in the 2009 study were reported in 10 (30%) of 33 patients with early T-cell precursor acute lymphoblastic leukaemia versus 24 (15%) of 164 patients without early T-cell precursor acute lymphoblastic leukaemia and life-threatening events in induction phase IA occurred in 4 (12%) of 33 patients with early T-cell precursor acute lymphoblastic leukaemia versus 7 (4%) of 164 patients without early T-cell precursor acute lymphoblastic leukaemia. No difference was seen in the subsequent consolidation phase IB of protocol I. Early T-cell precursor acute lymphoblastic leukaemia is characterised by poor early response to conventional induction treatment. Consolidation phase IB, based on cyclophosphamide, 6-mercaptopurine, and ara-C at conventional (non-high) doses is effective in reducing minimal residual disease. Although the number of patients and observational time are limited, patients with early T-cell precursor acute lymphoblastic leukaemia treated with current BFM stratification and treatment strategy have a favourable outcome compared with earlier reports. The role of innovative therapies and haemopoietic stem cell therapy in early T-cell precursor acute lymphoblastic leukaemia needs to be assessed. None. Copyright © 2016 Elsevier Ltd. All rights reserved.

Comparative examination of titania nanocrystals synthesized by peroxo titanic acid approach from different precursors.

PubMed

Liu, Yong-Jun; Aizawa, Mami; Wang, Zheng-Ming; Hatori, Hiroaki; Uekawa, Naofumi; Kanoh, Hirofumi

2008-06-15

Titanium dioxide nanocrystalline particles were synthesized by peroxo titanium acid (PTA) approach from titanium alkoxide and inorganic salt precursors, and their structural and surface properties, porosities, and photocatalytic activities were comparatively examined by XRD, TG/DTA, DRIFT, UV-vis, low temperature N(2) adsorption, and methyl orange (MO) degradation. It was found that nanoparticles with single anatase phase can be obtained from alkoxide precursor even near room temperature if synthesis conditions are appropriately controlled. PTA-derived anatase nanoparticles from titanium alkoxide precursor have smaller crystalline sizes and better porosities, and contain less amount of peroxo group and no organic impurities as compared to those from TiCl(4) precursor. The advantages in structural property, porosity, and surface properties (few deficiencies) lead to a much better photocatalytic activity for TiO(2) nanoparticles from titanium alkoxide precursor in comparison with those from TiCl(4) precursor.

High Tc superconducting films from metallo-organic precursors

NASA Astrophysics Data System (ADS)

Davison, W. W.; Shyu, S. G.; Buchanan, R. C.

High Tc superconducting films of heavy metal soaps (derived from carboxylic acid precursors) have been prepared on Si and other substrates. The precursors were synthesized and mixed in appropriate molar ratios to form the high Tc compound YBa2Cu3O(7-x), using a high boiling point common solvent base. The precursor solution was deposited by a spin casting technique on the substrates. Film thicknesses of 0.1-1.0 micron were achieved after heat treatment at 550-850 C at not longer than 4 hours. Films were analyzed as to orientation, appropriate phase, interfacial reaction, and superconducting properties.

Synthesis of liquid crystalline epoxy monomers

NASA Astrophysics Data System (ADS)

Fabia, J.; Galina, H.; Mossety-Leszczak, B.; Ulanski, J.; Wojciechowski, Piotr; Wlochowicz, Andrzej

2002-06-01

A two-stage method of synthesis of liquid-crystalline diepoxy monomers has been developed. In the first stage, esterification of 4-hydroxyphenyl-4-hydroxybenzoate or 4,4'- biphenol or 4,4'-dihydroxyazobenzene was carried out using 4-penetenoic acid. The resulting olefinic precursors were oxidized with m-chloroperoxybenzoic acid to introduce the epoxy groups. The structure of products was confirmed by FT- IR and 1H NMR. Examinations on a polarization microscope with a hot plate confirmed the presence of mesomorphic phases in both the precursors and monomers. The phase transition temperatures were in the range of 73.5 (at cooling) to 128.0 degree(s)C for olefinic precursors and in the range 57.1 (at cooling) to 143 degree(s)C for epoxy compounds, as determined by DSC and thermo-optical analysis (TOA).

Phase formation of V{sub 2}O{sub 5}.xNb{sub 2}O{sub 5} compounds via gels and freeze-dried precursors

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

Langbein, Hubert; Mayer-Uhma, Tobias

2009-03-05

An X-ray powder diffraction study of the phase formation in the system V{sub 2}O{sub 5}/Nb{sub 2}O{sub 5} is performed. Freeze-dried ammonium vanadate and ammonium oxalato niobate, alkoxide-derived xerogels and a mixture of active oxides are used as precursors to compare the resulting phase composition. Thermal decomposition of the freeze-dried precursor is monitored with DTA/TG and mass spectrometry. In the quasi-binary system V{sub 2}O{sub 5}-Nb{sub 2}O{sub 5} metastable VNbO{sub 5}, V{sub 4}Nb{sub 18}O{sub 55}, VNb{sub 9}O{sub 25} and solid solutions of V{sub 2}O{sub 5} in TT-Nb{sub 2}O{sub 5} as also thermodynamically stable VNb{sub 9}O{sub 25} exist. The thermal decomposition of freeze-driedmore » vanadate-oxalatoniobate solution allows the synthesis of all these phases in a relative simple manner. Structural relationships between an intermediate phase and the product, or, in the case of solid-state reactions, between one of the starting oxide and the product, favour the desired reaction. Therefore, the structure of a former phase influences or directs the structure of the product similar to a topotactic reaction.« less

Morphology control of anisotropic BaTiO 3 and BaTiOF 4 using organic-inorganic interaction

NASA Astrophysics Data System (ADS)

Masuda, Yoshitake; Tanaka, Yuki; Gao, Yanfeng; Koumoto, Kunihito

2009-01-01

We proposed a novel concept for morphology control of barium titanate precursor to fabricate platy particles. Organic molecules play an essential role in the crystallization of BaTiOF 4 to synthesize multi-needle particles, polyhedron particles or platy particles in an aqueous solution. Precursors were successfully transformed to barium titanate single phase by annealing. Platy barium titanate precursor particles are expected for future multilayer ceramic capacitors.

Precursor Mediated Synthesis of Nanostructured Silicas: From Precursor-Surfactant Ion Pairs to Structured Materials.

PubMed

Hesemann, Peter; Nguyen, Thy Phung; Hankari, Samir El

2014-04-11

The synthesis of nanostructured anionic-surfactant-templated mesoporous silica (AMS) recently appeared as a new strategy for the formation of nanostructured silica based materials. This method is based on the use of anionic surfactants together with a co-structure-directing agent (CSDA), mostly a silylated ammonium precursor. The presence of this CSDA is necessary in order to create ionic interactions between template and silica forming phases and to ensure sufficient affinity between the two phases. This synthetic strategy was for the first time applied in view of the synthesis of surface functionalized silica bearing ammonium groups and was then extended on the formation of materials functionalized with anionic carboxylate and bifunctional amine-carboxylate groups. In the field of silica hybrid materials, the "anionic templating" strategy has recently been applied for the synthesis of silica hybrid materials from cationic precursors. Starting from di- or oligosilylated imidazolium and ammonium precursors, only template directed hydrolysis-polycondensation reactions involving complementary anionic surfactants allowed accessing structured ionosilica hybrid materials. The mechanistic particularity of this approach resides in the formation of precursor-surfactant ion pairs in the hydrolysis-polycondensation mixture. This review gives a systematic overview over the various types of materials accessed from this cooperative ionic templating approach and highlights the high potential of this original strategy for the formation of nanostructured silica based materials which appears as a complementary strategy to conventional soft templating approaches.

Understanding and Tailoring Grain Growth of Lead-Halide Perovskite for Solar Cell Application.

PubMed

Ma, Yongchao; Liu, Yanliang; Shin, Insoo; Hwang, In-Wook; Jung, Yun Kyung; Jeong, Jung Hyun; Park, Sung Heum; Kim, Kwang Ho

2017-10-04

The fundamental mechanism of grain growth evolution in the fabrication process from the precursor phase to the perovskite phase is not fully understood despite its importance in achieving high-quality grains in organic-inorganic hybrid perovskites, which are strongly affected by processing parameters. In this work, we investigate the fundamental conversion mechanism from the precursor phase of perovskite to the complete perovskite phase and how the intermediate phase promotes growth of the perovskite grains during the fabrication process. By monitoring the morphological evolution of the perovskite during the film fabrication process, we observed a clear rod-shaped intermediate phase in the highly crystalline perovskite and investigated the role of the nanorod intermediate phase on the growth of the grains of the perovskite film. Furthermore, on the basis of these findings, we developed a simple and effective method to tailor grain properties including the crystallinity, size, and number of grain boundaries, and then utilized the film with the tailored grains to develop perovskite solar cells.

A Dual-Phase Ceramic Membrane with Extremely High H2 Permeation Flux Prepared by Autoseparation of a Ceramic Precursor.

PubMed

Cheng, Shunfan; Wang, Yanjie; Zhuang, Libin; Xue, Jian; Wei, Yanying; Feldhoff, Armin; Caro, Jürgen; Wang, Haihui

2016-08-26

A novel concept for the preparation of multiphase composite ceramics based on demixing of a single ceramic precursor has been developed and used for the synthesis of a dual-phase H2 -permeable ceramic membrane. The precursor BaCe0.5 Fe0.5 O3-δ decomposes on calcination at 1370 °C for 10 h into two thermodynamically stable oxides with perovskite structures: the cerium-rich oxide BaCe0.85 Fe0.15 O3-δ (BCF8515) and the iron-rich oxide BaCe0.15 Fe0.85 O3-δ (BCF1585), 50 mol % each. In the resulting dual-phase material, the orthorhombic perovskite BCF8515 acts as the main proton conductor and the cubic perovskite BCF1585 as the main electron conductor. The dual-phase membrane shows an extremely high H2 permeation flux of 0.76 mL min(-1)  cm(-2) at 950 °C with 1.0 mm thickness. This auto-demixing concept should be applicable to the synthesis of other ionic-electronic conducting ceramics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of SiO2 substitution on wettability of laser deposited Ca-P biocoating on Ti-6Al-4V.

PubMed

Yang, Yuling; Paital, Sameer R; Dahotre, Narendra B

2010-09-01

Silicon (Si) substitution in the crystal structure of calcium phosphate (CaP) ceramics has proved to generate materials with improved bioactivity than their stoichiometric counterpart. In light of this, in the current work, 100 wt% hydroxyapatite (HA) precursor and 25 wt% SiO(2)-HA precursors were used to prepare bioactive coatings on Ti-6Al-4V substrates by a laser cladding technique. The effects of SiO(2) on phase constituents, crystallite size, surface roughness, and surface energy of the CaP coatings were studied. Furthermore, on the basis of these results, the effects and roles of SiO(2) substitution in HA were systematically discussed. X-ray diffraction analysis of the coated samples indicated the presence of various phases such as CaTiO(3), Ca(2)SiO(4), Ca(3)(PO(4))(2), TiO(2) (Anatase), and TiO(2) (Rutile). The addition of SiO(2) in the HA precursor resulted in the refinement of grain size. Confocal laser microscopy characterization of the surface morphology demonstrated an improved surface roughness for samples with 25 wt% SiO(2)-HA precursor compared to the samples with 100 wt% HA precursor processed at 125 cm/min laser speed. The addition of SiO(2) in the HA precursor resulted in the highest surface energy, increased hydrophilicity, and improved biomineralization as compared to the control (untreated Ti-6Al-4V) and the sample with 100 wt% HA as precursor. The microstructural evolution observed using a scanning electron microscopy indicated that the addition of SiO(2) in the HA precursor resulted in the presence of reduced cracking across the cross-section of the bioceramic coating.

Nanostructures produced by phase-separation during growth of (III-V).sub.1-x(IV.sub.2).sub.x alloys

DOEpatents

Norman, Andrew G [Evergreen, CO; Olson, Jerry M [Lakewood, CO

2007-06-12

Nanostructures (18) and methods for production thereof by phase separation during metal organic vapor-phase epitaxy (MOVPE). An embodiment of one of the methods may comprise providing a growth surface in a reaction chamber and introducing a first mixture of precursor materials into the reaction chamber to form a buffer layer (12) thereon. A second mixture of precursor materials may be provided into the reaction chamber to form an active region (14) on the buffer layer (12), wherein the nanostructure (18) is embedded in a matrix (16) in the active region (14). Additional steps are also disclosed for preparing the nanostructure (18) product for various applications.

Preparation of tungsten oxide

DOEpatents

Bulian, Christopher J [Yankton, SD; Dye, Robert C [Los Alamos, NM; Son, Steven F [Los Alamos, NM; Jorgensen, Betty S [Jemez Springs, NM; Perry, W Lee [Jemez Springs, NM

2009-09-22

Tungsten trioxide hydrate (WO.sub.3.H.sub.2O) was prepared from a precursor solution of ammonium paratungstate in concentrated aqueous hydrochloric acid. The precursor solution was rapidly added to water, resulting in the crash precipitation of a yellow white powder identified as WO.sub.3.H.sub.2O nanosized platelets by x-ray diffraction and scanning electron microscopy. Annealing of the powder at 200.degree. C. provided cubic phase WO.sub.3 nanopowder, and at 400.degree. C. provided WO.sub.3 nanopowder as a mixture of monoclinic and orthorhombic phases.

Nanocomposite and method of making thereof

DOEpatents

Tangirala, Ravisubhash; Milliron, Delia J.; Llordes, Anna

2016-03-15

An embodiment of an inorganic nanocomposite includes a nanoparticle phase and a matrix phase. The nanoparticle phase includes nanoparticles that are arranged in a repeating structure. In an embodiment, the nanoparticles have a spherical or pseudo-spherical shape and are incompatible with hydrazine. In another embodiment, the nanoparticles have neither a spherical nor pseudo-spherical shape. The matrix phase lies between the nanoparticles of the nanoparticle phase. An embodiment of a method of making an inorganic nanocomposite of the present invention includes forming a nanoparticle superlattice on a substrate. The nanoparticle superlattice includes nanoparticles. Each nanoparticle has organic ligands attached to a surface of the nanoparticle. The organic ligands separate adjacent nanoparticles within the nanoparticle superlattice. The method also includes forming a solution that includes an inorganic precursor. The nanoparticle superlattice is placed in the solution for a sufficient time for the inorganic precursor to replace the organic ligands.

Terminal Transient Phase of Chaotic Transients

NASA Astrophysics Data System (ADS)

Lilienkamp, Thomas; Parlitz, Ulrich

2018-03-01

Transient chaos in spatially extended systems can be characterized by the length of the transient phase, which typically grows quickly with the system size (supertransients). For a large class of these systems, the chaotic phase terminates abruptly, without any obvious precursors in commonly used observables. Here we investigate transient spatiotemporal chaos in two different models of this class. By probing the state space using perturbed trajectories we show the existence of a "terminal transient phase," which occurs prior to the abrupt collapse of chaotic dynamics. During this phase the impact of perturbations is significantly different from the earlier transient and particular patterns of (non)susceptible regions in state space occur close to the chaotic trajectories. We therefore hypothesize that even without perturbations proper precursors for the collapse of chaotic transients exist, which might be highly relevant for coping with spatiotemporal chaos in cardiac arrhythmias or brain functionality, for example.

Role of precursors and coating polymers in sol-gel chemistry toward enhanced selectivity and efficiency in solid phase microextraction.

PubMed

Bagheri, Habib; Piri-Moghadam, Hamed; Ahdi, Tayebeh

2012-09-12

To evaluate the selectivity and efficiency of solid phase microextraction (SPME) fiber coatings, synthesized by sol-gel technology, roles of precursors and coating polymers were extensively investigated. An on-line combination of capillary microextraction (CME) technique and high performance liquid chromatography (HPLC) was set up to perform the investigation. Ten different fiber coatings were synthesized in which five of them contained only the precursor and the rests were prepared using both the precursor and coating polymer. All the coatings were chemically bonded to the inner surface of copper tubes, intended to be used as the CME device and already functionalized by self-assembly monolayers of 3-(mercaptopropyl)trimethoxysilane (3MPTMOS). The selected precursors included tetramethoxysilane (TMOS), 3-(trimethoxysilyl)propylmethacrylate (TMSPMA), 3-(triethoxysilyl)-propylamine (TMSPA), 3MPTMOS, [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane (EPPTMOS) while poly(ethyleneglycol) (PEG) was chosen as the coating polymer. The effects of different precursors on the extraction efficiency and selectivity, was studied by selecting a list of compounds ranging from non-polar to polar ones, i.e. polycyclic aromatic hydrocarbon, herbicides, estrogens and triazines. The results from CME-HPLC analysis revealed that there is no significant difference between precursors, except TMOS, in which has the lowest extraction efficiency. Most of the selected precursors have rather similar interactions toward the selected analytes which include Van der Walls, dipole-dipole and hydrogen bond while TMOS has only dipole-dipole interaction and therefore the least efficiency. TMOS is silica but the other sorbents are organically modified silica (ORMOSIL). Our investigation revealed that it is rather impossible to prepare a selective coating using conventional sol-gel methodologies. The comparison study performed among the fiber coatings contained only a precursor and those synthesized by a precursor along with coating polymer proved that the extraction efficiency obtained for all coatings are the same. This is an indication that by selecting the appropriate precursor there is no need to use any coating polymer. In overall, a fiber coating in sol-gel process could be synthesize with no coating polymer which leads to faster, easier, cheaper and more controllable synthesis. Copyright © 2012 Elsevier B.V. All rights reserved.

Apparatus for fabricating continuous lengths of superconductor

DOEpatents

Kroeger, Donald M.; List, III, Frederick A.

2002-01-01

A process and apparatus for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor comprising a layer of said superconducting precursor powder between said first substrate ribbon and said second substrates ribbon. The layered superconductor is then heat treated to establish the superconducting phase of said superconductor precursor powder.

Apparatus for fabricating continuous lengths of superconductor

DOEpatents

Kroeger, Donald M.; List, III, Frederick A.

2001-01-01

A process and apparatus for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor comprising a layer of said superconducting precursor powder between said first substrate ribbon and said second substrates ribbon. The layered superconductor is then heat treated to establish the superconducting phase of said superconductor precursor powder.

Continuous lengths of oxide superconductors

DOEpatents

Kroeger, Donald M.; List, III, Frederick A.

2000-01-01

A layered oxide superconductor prepared by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon. A continuous length of a second substrate ribbon is overlaid on the first substrate ribbon. Sufficient pressure is applied to form a bound layered superconductor precursor powder between the first substrate ribbon and the second substrate ribbon. The layered superconductor precursor is then heat treated to establish the oxide superconducting phase. The layered oxide superconductor has a smooth interface between the substrate and the oxide superconductor.

Precursor directed synthesis--"molecular" mechanisms in the Soft Chemistry approaches and their use for template-free synthesis of metal, metal oxide and metal chalcogenide nanoparticles and nanostructures.

PubMed

Seisenbaeva, Gulaim A; Kessler, Vadim G

2014-06-21

This review provides an insight into the common reaction mechanisms in Soft Chemistry processes involved in nucleation, growth and aggregation of metal, metal oxide and chalcogenide nanoparticles starting from metal-organic precursors such as metal alkoxides, beta-diketonates, carboxylates and their chalcogene analogues and demonstrates how mastering the precursor chemistry permits us to control the chemical and phase composition, crystallinity, morphology, porosity and surface characteristics of produced nanomaterials.

A phase coherence approach to identifying co-located earthquakes and tremor

NASA Astrophysics Data System (ADS)

Hawthorne, J. C.; Ampuero, J.-P.

2018-05-01

We present and use a phase coherence approach to identify seismic signals that have similar path effects but different source time functions: co-located earthquakes and tremor. The method used is a phase coherence-based implementation of empirical matched field processing, modified to suit tremor analysis. It works by comparing the frequency-domain phases of waveforms generated by two sources recorded at multiple stations. We first cross-correlate the records of the two sources at a single station. If the sources are co-located, this cross-correlation eliminates the phases of the Green's function. It leaves the relative phases of the source time functions, which should be the same across all stations so long as the spatial extent of the sources are small compared with the seismic wavelength. We therefore search for cross-correlation phases that are consistent across stations as an indication of co-located sources. We also introduce a method to obtain relative locations between the two sources, based on back-projection of interstation phase coherence. We apply this technique to analyse two tremor-like signals that are thought to be composed of a number of earthquakes. First, we analyse a 20 s long seismic precursor to a M 3.9 earthquake in central Alaska. The analysis locates the precursor to within 2 km of the mainshock, and it identifies several bursts of energy—potentially foreshocks or groups of foreshocks—within the precursor. Second, we examine several minutes of volcanic tremor prior to an eruption at Redoubt Volcano. We confirm that the tremor source is located close to repeating earthquakes identified earlier in the tremor sequence. The amplitude of the tremor diminishes about 30 s before the eruption, but the phase coherence results suggest that the tremor may persist at some level through this final interval.

Identifying precursors and aqueous organic aerosol formation pathways during the SOAS campaign

NASA Astrophysics Data System (ADS)

Sareen, Neha; Carlton, Annmarie G.; Surratt, Jason D.; Gold, Avram; Lee, Ben; Lopez-Hilfiker, Felipe D.; Mohr, Claudia; Thornton, Joel A.; Zhang, Zhenfa; Lim, Yong B.; Turpin, Barbara J.

2016-11-01

Aqueous multiphase chemistry in the atmosphere can lead to rapid transformation of organic compounds, forming highly oxidized, low-volatility organic aerosol and, in some cases, light-absorbing (brown) carbon. Because liquid water is globally abundant, this chemistry could substantially impact climate, air quality, and health. Gas-phase precursors released from biogenic and anthropogenic sources are oxidized and fragmented, forming water-soluble gases that can undergo reactions in the aqueous phase (in clouds, fogs, and wet aerosols), leading to the formation of secondary organic aerosol (SOAAQ). Recent studies have highlighted the role of certain precursors like glyoxal, methylglyoxal, glycolaldehyde, acetic acid, acetone, and epoxides in the formation of SOAAQ. The goal of this work is to identify additional precursors and products that may be atmospherically important. In this study, ambient mixtures of water-soluble gases were scrubbed from the atmosphere into water at Brent, Alabama, during the 2013 Southern Oxidant and Aerosol Study (SOAS). Hydroxyl (OH⚫) radical oxidation experiments were conducted with the aqueous mixtures collected from SOAS to better understand the formation of SOA through gas-phase followed by aqueous-phase chemistry. Total aqueous-phase organic carbon concentrations for these mixtures ranged from 92 to 179 µM-C, relevant for cloud and fog waters. Aqueous OH-reactive compounds were primarily observed as odd ions in the positive ion mode by electrospray ionization mass spectrometry (ESI-MS). Ultra high-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) spectra and tandem MS (MS-MS) fragmentation of these ions were consistent with the presence of carbonyls and tetrols. Products were observed in the negative ion mode and included pyruvate and oxalate, which were confirmed by ion chromatography. Pyruvate and oxalate have been found in the particle phase in many locations (as salts and complexes). Thus, formation of pyruvate/oxalate suggests the potential for aqueous processing of these ambient mixtures to form SOAAQ.

Ionospheric parameters as the precursors of disturbed geomagnetic conditions

NASA Astrophysics Data System (ADS)

Blagoveshchensky, D. V.; Sergeeva, M. A.; Kozlovsky, A.

2017-12-01

Geomagnetic storms and substorms are the principal elements of the disturbed Space Weather conditions. The aim of the study was to reveal the ionospheric precursors that can be used to forecast geomagnetic disturbance beginning. To study the ionospheric processes before, during and after magnetic storms and substorms data from Sodankylä Geophysical Observatory was used (geomagnetic coordinates: 64.1oN, 119.2oE). In earlier works the Main Effect (ME) was revealed for substorms. It consists of the following steps: (a) the increase of critical frequency foF2 from its quiet median before and during the substorm growth phase, four-five hours before To moment that is the moment of the expansion phase onset, (b) the foF2 decrease to the level lower than its median just after To and until Te that is the moment of the end of the expansion phase, (c) the issue ;a; repeated during the recovery phase (d) two bell-shape spikes in the cutoff frequency values foEs: first spike occurs three hours before To, second spike - during the expansion phase within the interval between To and Te. In the present work it is shown that ME manifestations can be used as precursors of magnetic substorms at high-latitudes (geomagnetic latitudes 50oN-65oN). In particular, the foF2 growth some hours before To can be used as a precursor of substorm development. The first foEs bell-shaped spike also can be used for short-term forecasting, two-three hours in advance of a substorm. Furthermore, the storms between 2008 and 2012 were studied. It was revealed that the similar ME also takes place in the case of magnetic storms but within the different time scale. More specifically, the first ME maximum in foF2 values occurs one-two days before the storm beginning and can be used as its precursor. In addition, the foEs spike takes place approximately ten hours before a storm and also can be used for the prediction of the storm beginning.

Templating Influence of Molecular Precursors on Pr(OH)3 Nanostructures.

PubMed

Hemmer, Eva; Cavelius, Christian; Huch, Volker; Mathur, Sanjay

2015-07-06

Four new praseodymium alkoxo and amido compounds ([Pr3(μ3-OtBu)2(μ2-OtBu)3(OtBu)4(HOtBu)2] (1), [Pr{OC(tBu)3}3(THF)] (2), [PrCl{N(SiMe3)2}2(THF)]2 (3), and [PrCl{OC(tBu)3}2(THF)]2 (4)) were synthesized and structurally characterized by single-crystal X-ray diffraction analysis. Application of these compounds in solvothermal synthesis of praseodymium oxide/hydroxide nanostructures showed their templating influence on the morphology and phase composition of the resulting solid-state materials. Differential reactivity of the chosen alkoxide ligands toward water and the different arrangements of metal-oxygen units in the studied precursor compounds strongly influenced the kinetics of hydrolysis and cross-condensation reactions as manifested in the morphological changes and phase composition of the final products. Thermal decomposition studies of 1-4 confirmed their conversion into the corresponding oxide phases. Activation of compounds 1, 2, and 4 by either a base or a stoichiometric amount of water showed the distinct influence of their chemical configuration on the obtained nanopowders: whereas 1 solely produced nanorods of Pr(OH)3, 2 predominantly formed a mixture of rod-shaped and spherical particles. The solvothermal decomposition of 4 resulted in Pr(OH)2Cl or PrOCl due to the presence of Cl ligands in the molecular precursor. The resultant materials were thoroughly characterized to demonstrate the relationship between precursor chemistry and the processing parameters that are clearly manifested in the morphology and phase of the final ceramics.

Processing strategy for water-gun seismic data from the Gulf of Mexico

USGS Publications Warehouse

Lee, Myung W.; Hart, Patrick E.; Agena, Warren F.

2000-01-01

In order to study the regional distribution of gas hydrates and their potential relationship to a large-scale sea-fl oor failures, more than 1,300 km of near-vertical-incidence seismic profi les were acquired using a 15-in3 water gun across the upper- and middle-continental slope in the Garden Banks and Green Canyon regions of the Gulf of Mexico. Because of the highly mixed phase water-gun signature, caused mainly by a precursor of the source arriving about 18 ms ahead of the main pulse, a conventional processing scheme based on the minimum phase assumption is not suitable for this data set. A conventional processing scheme suppresses the reverberations and compresses the main pulse, but the failure to suppress precursors results in complex interference between the precursors and primary refl ections, thus obscuring true refl ections. To clearly image the subsurface without interference from the precursors, a wavelet deconvolution based on the mixedphase assumption using variable norm is attempted. This nonminimum- phase wavelet deconvolution compresses a longwave- train water-gun signature into a simple zero-phase wavelet. A second-zero-crossing predictive deconvolution followed by a wavelet deconvolution suppressed variable ghost arrivals attributed to the variable depths of receivers. The processing strategy of using wavelet deconvolution followed by a secondzero- crossing deconvolution resulted in a sharp and simple wavelet and a better defi nition of the polarity of refl ections. Also, the application of dip moveout correction enhanced lateral resolution of refl ections and substantially suppressed coherent noise.

Effect of efferent activation on binaural frequency selectivity.

PubMed

Verhey, Jesko L; Kordus, Monika; Drga, Vit; Yasin, Ifat

2017-07-01

Binaural notched-noise experiments indicate a reduced frequency selectivity of the binaural system compared to monaural processing. The present study investigates how auditory efferent activation (via the medial olivocochlear system) affects binaural frequency selectivity in normal-hearing listeners. Thresholds were measured for a 1-kHz signal embedded in a diotic notched-noise masker for various notch widths. The signal was either presented in phase (diotic) or in antiphase (dichotic), gated with the noise. Stimulus duration was 25 ms, in order to avoid efferent activation due to the masker or the signal. A bandpass-filtered noise precursor was presented prior to the masker and signal stimuli to activate the efferent system. The silent interval between the precursor and the masker-signal complex was 50 ms. For comparison, thresholds for detectability of the masked signal were also measured in a baseline condition without the precursor and, in addition, without the masker. On average, the results of the baseline condition indicate an effectively wider binaural filter, as expected. For both signal phases, the addition of the precursor results in effectively wider filters, which is in agreement with the hypothesis that cochlear gain is reduced due to the presence of the precursor. Copyright © 2017 Elsevier B.V. All rights reserved.

Synthesis and optical properties of Mg-Al layered double hydroxides precursor powders

NASA Astrophysics Data System (ADS)

Lin, Chia-Hsuan; Chu, Hsueh-Liang; Hwang, Weng-Sing; Wang, Moo-Chin; Ko, Horng-Huey

2017-12-01

The synthesis and optical properties of Mg-Al layered double hydroxide (LDH) precursor powders were investigated using X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution TEM (HRTEM), UV-transmission spectrometer, and fluorescence spectrophotometer. The FT-IR results show that the intense absorption at around 1363-1377 cm-1 can be assigned to the antisymmetric ν3 mode of interlayer carbonate anions because the LDH phase contains some CO32-. The XRD results show that all of the Mg-Al LDH precursor powders contain only a single phase of [Mg0.833Al0.167(OH)2](CO3)0.083.(H2O)0.75 but have broad and weak intensities of peaks. All of Mg-Al LDHs precursor powders before calcination have the same photoluminescence (PL) spectra. Moreover, these spectra were excited at λex = 235 nm, and the broad emission band was in the range 325-650 nm. In the range, there were relatively strong intensity at around 360, 407 and 510 nm, respectively.

Precursor Ion Scan Mode-Based Strategy for Fast Screening of Polyether Ionophores by Copper-Induced Gas-Phase Radical Fragmentation Reactions.

PubMed

Crevelin, Eduardo J; Possato, Bruna; Lopes, João L C; Lopes, Norberto P; Crotti, Antônio E M

2017-04-04

The potential of copper(II) to induce gas-phase fragmentation reactions in macrotetrolides, a class of polyether ionophores produced by Streptomyces species, was investigated by accurate-mass electrospray tandem mass spectrometry (ESI-MS/MS). Copper(II)/copper(I) transition directly induced production of diagnostic acylium ions with m/z 199, 185, 181, and 167 from α-cleavages of [macrotetrolides + Cu] 2+ . A UPLC-ESI-MS/MS methodology based on the precursor ion scan of these acylium ions was developed and successfully used to identify isodinactin (1), trinactin (2), and tetranactin (3) in a crude extract of Streptomyces sp. AMC 23 in the precursor ion scan mode. In addition, copper(II) was also used to induce radical fragmentation reactions in the carboxylic acid polyether ionophore nigericin. The resulting product ions with m/z 755 and 585 helped to identify nigericin in a crude extract of Streptomyces sp. Eucal-26 by means of precursor ion scan experiments, demonstrating that copper-induced fragmentation reactions can potentially identify different classes of polyether ionophores rapidly and selectively.

Magnéli phases Ti{sub 4}O{sub 7} and Ti{sub 8}O{sub 15} and their carbon nanocomposites via the thermal decomposition-precursor route

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

Conze, S., E-mail: susan.conze@ikts.fraunhofer.de; Veremchuk, I.; Reibold, M.

2015-09-15

A new synthetic approach for producing nano-powders of the Magnéli phases Ti{sub 4}O{sub 7}, Ti{sub 8}O{sub 15} and their carbon nanocomposites by thermal decomposition-precursor route is proposed. The formation mechanism of the single-phase carbon nanocomposites (Ti{sub 4}O{sub 7}/C and Ti{sub 8}O{sub 15}/C) from metal–organic precursors is studied using FT-IR, elemental analysis, TG, STA-MS and others. The synthesis parameters and conditions were optimized to prepare the target oxides with the desired microstructure and physical properties. The electrical and transport properties of Ti{sub 4}O{sub 7}/C and Ti{sub 8}O{sub 15}/C are investigated. These nano-materials are n-type semiconductors with relatively low thermal conductivity inmore » contrast to the bulk species. The nanostructured carbon nanocomposites of Magnéli phases achieve a low thermal conductivity close to 1 W/m K at RT. The maximum ZT{sub 570} {sub °C} values are 0.04 for Ti{sub 4}O{sub 7}/C powder nanocomposite and 0.01 for Ti{sub 8}O{sub 15}/C bulk nanocomposite. - Graphical abstract: From the precursor to the produced titanium oxide pellet and its microstructure (SEM, TEM micrographs) as well as results of phase and thermoelectric analyses. - Highlights: • Magnéli phases Ti{sub 4}O{sub 7}/Ti{sub 8}O{sub 15} via thermal decomposition-precursor route is proposed. • The formation mechanism of the nanocomposites Ti{sub 4}O{sub 7}/C and Ti{sub 8}O{sub 15}/C are investigated. • Microstructure of Ti{sub 4}O{sub 7}/C and Ti{sub 8}O{sub 15}/C are examined. • The electrical and transport properties of Ti{sub 4}O{sub 7}/C and Ti{sub 8}O{sub 15}/C are investigated. • The maximum figure of mertit ZT{sub 570} {sub °C} of Ti{sub 4}O{sub 7}/C and Ti{sub 8}O{sub 15}/C are 0.01 and 0.04.« less

Overview of the amorphous precursor phase strategy in biomineralization

NASA Astrophysics Data System (ADS)

Weiner, Steve; Mahamid, Julia; Politi, Yael; Ma, Yurong; Addadi, Lia

2009-06-01

It was assumed for a long time that organisms produce minerals directly from a saturated solution. A few exceptions were known, including the well documented mineralized teeth of the chiton. In 1997 it was demon-strated that sea urchin larvae form their calcitic spicules by first depositing a highly unstable mineral phase called amorphous calcium carbonate. This strategy has since been shown to be used by animals from other phyla and for both aragonite and calcite. Recent evidence shows that vertebrate bone mineral may also be formed via a precursor phase of amorphous calcium carbonate. This strategy thus appears to be widespread. The challenge now is to understand the mechanisms by which these unstable phases are initially formed, how they are temporarily stabilized and how they are destabilized and transform into a crystalline mature product.

In Vivo Formation of Cubic Phase in Situ after Oral Administration of Cubic Phase Precursor Formulation Provides Long Duration Gastric Retention and Absorption for Poorly Water-Soluble Drugs.

PubMed

Pham, Anna C; Hong, Linda; Montagnat, Oliver; Nowell, Cameron J; Nguyen, Tri-Hung; Boyd, Ben J

2016-01-04

Lipid-based liquid crystalline systems based on the combination of digestible and nondigestible lipids have been proposed as potential sustained release delivery systems for oral delivery of poorly water-soluble drugs. The potential for cubic phase liquid crystal formation to induce dramatically extended gastric retention in vivo has been shown previously to strongly influence the resulting pharmacokinetics of incorporated drug. In vitro studies showing the in situ formation of cubic phase from a disordered precursor comprising a mixture of digestible and nondigestible lipids under enzymatic digestion have also recently been reported. Combining both concepts, here we show the potential for such systems to form in vivo, increasing gastric retention, and providing a sustained release effect for a model poorly water-soluble drug cinnarizine. A mixture of phytantriol and tributyrin at an 85:15 mass ratio, shown previously to form cubic phase under the influence of digestion, induced a similar pharmacokinetic profile to that in the absence of tributyrin, but completely different from tributyrin alone. The gastric retention of the formulation, assessed using micro-X-ray CT imaging, was also consistent with the pharmacokinetic behavior, where phytantriol alone and with 15% tributyrin was greater than that of tributyrin in the absence of phytantriol. Thus, the concept of precursor lipid systems that form cubic phase in situ during digestion in vivo has been demonstrated and opens new opportunities for sustained release of poorly water-soluble drugs.

Formation of complex precursors of amino acids by irradiation of simulated interstellar media with heavy ions

NASA Astrophysics Data System (ADS)

Kobayashi, K.; Suzuki, N.; Taniuchi, T.; Kaneko, T.; Yoshida, S.

A wide variety of organic compounds have been detected in such extraterrestrial bodies as meteorites and comets Amino acids were identified in the extracts from Murchison meteorite and other carbonaceous chondrites It is hypothesized that these compounds are originally formed in ice mantles of interstellar dusts ISDs in molecular clouds by cosmic rays and ultraviolet light UV Formation of amino acid precursors by high energy protons or UV irradiation of simulated ISDs was reported by several groups The amino acid precursors were however not well-characterized We irradiated a frozen mixture of methanol ammonia and water with heavy ions to study possible organic compounds abiotically formed in molecular clouds by cosmic rays A mixture of methanol ammonia and water was irradiated with carbon beams 290 MeV u from a heavy ion accelerator HIMAC of National Institute of Radiological Sciences Japan Irradiation was performed either at room temperature liquid phase or at 77 K solid phase The products were characterized by gel filtration chromatography GFC FT-IR pyrolysis PY -GC MS etc Amino acids were analyzed by HPLC and GC MS after acid hydrolysis or the products Amino acids such as glycine and alanine were identified in the products in both the cases of liquid phase and solid phase irradiation Energy yields G-values of glycine were 0 014 liquid phase and 0 007 solid phase respectively Average molecular weights of the products were estimated as to 2300 in both the case Aromatic hydrocarbons N-containing heterocyclic

Single-phase ceramics with La 1- xSr xGa 1- yMg yO 3- δ composition from precursors obtained by mechanosynthesis

NASA Astrophysics Data System (ADS)

Moure, A.; Castro, A.; Tartaj, J.; Moure, C.

Dense ceramics with La 0.80Sr 0.20Ga 0.85Mg 0.15O 2.825 and La 0.80Sr 0.15Ga 0.85Mg 0.20O 2.825 compositions have been prepared by sintering of mechanosynthesized precursors. The perovskite is synthesized after 85 h of milling in a planetary mill. Single phases have been obtained at conditions that are not possible if traditional solid-state reaction (SSR) method is used. The influence of milling time and composition in the reactivity of the precursors is studied. Highest purity is obtained in Sr = 0.15 and Mg = 0.20 composition, with relative density higher than 97%. The total elimination of typical secondary phases for these compositions, as SrLaGaO 4 and SrLaGa 3O 7, allows the total conductivity of the ceramics to be improved. The influence of the grain size and the nature of the grain boundaries on the electrical characteristic of the ceramics are also discussed.

Effect of Precursor Selection on the Photocatalytic Performance of Indium Oxide Nanomaterials for Gas-Phase CO 2 Reduction

DOE PAGES

Hoch, Laura B.; He, Le; Qiao, Qiao; ...

2016-06-01

Nonstoichiometric indium oxide nanoparticles, In 2O 3–x(OH)y, have been shown to function as active photocatalysts for gas-phase CO 2 reduction under simulated solar irradiation. We demonstrate that the choice of starting material has a strong effect on the photocatalytic activity of indium oxide nanoparticles. We also examine three indium oxide materials prepared via the thermal decomposition of either indium(III) hydroxide or indium(III) nitrate and correlate their stability and photocatalytic activity to the number and type of defect present in the material. Furthermore, we use 13CO 2 isotope-tracing experiments to clearly identify the origins of the observed carbon-containing products. Significantly, wemore » find that the oxidizing nature of the precursor anion has a substantial impact on the defect formation within the sample. Our study demonstrates the importance of surface defects in designing an active heterogeneous photocatalyst and provides valuable insight into key parameters for the precursor design, selection, and performance optimization of materials for gas-phase CO 2 reduction.« less

Preparation of TiO₂ nanocrystallite powders coated with 9 mol% ZnO for cosmetic applications in sunscreens.

PubMed

Ko, Horng-Huey; Chen, Hui-Ting; Yen, Feng-Ling; Lu, Wan-Chen; Kuo, Chih-Wei; Wang, Moo-Chin

2012-01-01

The preparation of TiO(2) nanocrystallite powders coated with and without 9 mol% ZnO has been studied for cosmetic applications in sunscreens by a co-precipitation process using TiCl(4) and Zn(NO(3))(2)·6H(2)O as starting materials. XRD results show that the phases of anatase TiO(2) and rutile TiO(2) coexist for precursor powders without added ZnO (T-0Z) and calcined at 523 to 973 K for 2 h. When the T-0Z precursor powders are calcined at 1273 K for 2 h, only the rutile TiO(2) appears. In addition, when the TiO(2) precursor powders contain 9 mol% ZnO (T-9Z) are calcined at 873 to 973 K for 2 h, the crystallized samples are composed of the major phase of rutile TiO(2) and the minor phases of anatase TiO(2) and Zn(2)Ti(3)O(8). The analyses of UV/VIS/NIR spectra reveal that the absorption of the T-9Z precursor powders after being calcined has a red-shift effect in the UV range with increasing calcination temperature. Therefore, the TiO(2) nanocrystallite powders coated with 9 mol% ZnO can be used as the attenuate agent in the UV-A region for cosmetic applications in sunscreens.

Preparation of TiO2 Nanocrystallite Powders Coated with 9 mol% ZnO for Cosmetic Applications in Sunscreens

PubMed Central

Ko, Horng-Huey; Chen, Hui-Ting; Yen, Feng-Ling; Lu, Wan-Chen; Kuo, Chih-Wei; Wang, Moo-Chin

2012-01-01

The preparation of TiO2 nanocrystallite powders coated with and without 9 mol% ZnO has been studied for cosmetic applications in sunscreens by a co-precipitation process using TiCl4 and Zn(NO3)2·6H2O as starting materials. XRD results show that the phases of anatase TiO2 and rutile TiO2 coexist for precursor powders without added ZnO (T-0Z) and calcined at 523 to 973 K for 2 h. When the T-0Z precursor powders are calcined at 1273 K for 2 h, only the rutile TiO2 appears. In addition, when the TiO2 precursor powders contain 9 mol% ZnO (T-9Z) are calcined at 873 to 973 K for 2 h, the crystallized samples are composed of the major phase of rutile TiO2 and the minor phases of anatase TiO2 and Zn2Ti3O8. The analyses of UV/VIS/NIR spectra reveal that the absorption of the T-9Z precursor powders after being calcined has a red-shift effect in the UV range with increasing calcination temperature. Therefore, the TiO2 nanocrystallite powders coated with 9 mol% ZnO can be used as the attenuate agent in the UV-A region for cosmetic applications in sunscreens. PMID:22408415

Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid

NASA Astrophysics Data System (ADS)

Tan, Y.; Lim, Y. B.; Altieri, K. E.; Seitzinger, S. P.; Turpin, B. J.

2011-06-01

Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA). Acetic acid is an important intermediate in aqueous methylglyoxal oxidation and a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. Altieri et al. (2008) proposed that acetic acid was the precursor of oligoesters observed in methylglyoxal oxidation. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid at concentrations relevant to atmospheric waters (20 μM-10 mM) was oxidized by OH radical. Products were analyzed by ion chromatography (IC), electrospray ionization mass spectrometry (ESI-MS), and IC-ESI-MS. The formation of glyoxylic, glycolic, and oxalic acids were observed. In contrast to methylglyoxal oxidation, succinic acid and oligomers were not detected. Using results from these and methylglyoxal + OH radical experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols.

Precursor Mediated Synthesis of Nanostructured Silicas: From Precursor-Surfactant Ion Pairs to Structured Materials

PubMed Central

Hesemann, Peter; Nguyen, Thy Phung; Hankari, Samir El

2014-01-01

The synthesis of nanostructured anionic-surfactant-templated mesoporous silica (AMS) recently appeared as a new strategy for the formation of nanostructured silica based materials. This method is based on the use of anionic surfactants together with a co-structure-directing agent (CSDA), mostly a silylated ammonium precursor. The presence of this CSDA is necessary in order to create ionic interactions between template and silica forming phases and to ensure sufficient affinity between the two phases. This synthetic strategy was for the first time applied in view of the synthesis of surface functionalized silica bearing ammonium groups and was then extended on the formation of materials functionalized with anionic carboxylate and bifunctional amine-carboxylate groups. In the field of silica hybrid materials, the “anionic templating” strategy has recently been applied for the synthesis of silica hybrid materials from cationic precursors. Starting from di- or oligosilylated imidazolium and ammonium precursors, only template directed hydrolysis-polycondensation reactions involving complementary anionic surfactants allowed accessing structured ionosilica hybrid materials. The mechanistic particularity of this approach resides in the formation of precursor-surfactant ion pairs in the hydrolysis-polycondensation mixture. This review gives a systematic overview over the various types of materials accessed from this cooperative ionic templating approach and highlights the high potential of this original strategy for the formation of nanostructured silica based materials which appears as a complementary strategy to conventional soft templating approaches. PMID:28788602

The role of amorphous precursors in the crystallization of La and Nd carbonates

NASA Astrophysics Data System (ADS)

Vallina, Beatriz; Rodriguez-Blanco, Juan Diego; Brown, Andrew P.; Blanco, Jesus A.; Benning, Liane G.

2015-07-01

Crystalline La and Nd carbonates can be formed from poorly-ordered nanoparticulate precursors, termed amorphous lanthanum carbonate (ALC) and amorphous neodymium carbonate (ANC). When reacted in air or in aqueous solutions these precursors show highly variable lifetimes and crystallization pathways. We have characterized these precursors and the crystallization pathways and products with solid-state, spectroscopic and microscopic techniques to explain the differences in crystallization mechanisms between the La and Nd systems. ALC and ANC consist of highly hydrated, 10-20 nm spherical nanoparticles with a general formula of REE2(CO3)3.5H2O (REE = La, Nd). The stabilities differ by ~2 orders of magnitude, with ANC being far more stable than ALC. This difference is due to the Nd3+ ion having a far higher hydration energy compared to the La3+ ion. This, together with temperature and reaction times, leads to clear differences not only in the kinetics and mechanisms of crystallization of the amorphous precursor La- and Nd-carbonate phases but also in the resulting crystallite sizes and morphologies of the end products. All crystalline La and Nd carbonates developed spherulitic morphologies when crystallization occurred from hydrous phases in solution at temperatures above 60 °C (La system) and 95 °C (Nd system). We suggest that spherulitic growth occurs due to a rapid breakdown of the amorphous precursors and a concurrent rapid increase in supersaturation levels in the aqueous solution. The kinetic data show that the crystallization pathway for both La and Nd carbonate systems is dependent on the reaction temperature and the ionic potential of the REE3+ ion.Crystalline La and Nd carbonates can be formed from poorly-ordered nanoparticulate precursors, termed amorphous lanthanum carbonate (ALC) and amorphous neodymium carbonate (ANC). When reacted in air or in aqueous solutions these precursors show highly variable lifetimes and crystallization pathways. We have characterized these precursors and the crystallization pathways and products with solid-state, spectroscopic and microscopic techniques to explain the differences in crystallization mechanisms between the La and Nd systems. ALC and ANC consist of highly hydrated, 10-20 nm spherical nanoparticles with a general formula of REE2(CO3)3.5H2O (REE = La, Nd). The stabilities differ by ~2 orders of magnitude, with ANC being far more stable than ALC. This difference is due to the Nd3+ ion having a far higher hydration energy compared to the La3+ ion. This, together with temperature and reaction times, leads to clear differences not only in the kinetics and mechanisms of crystallization of the amorphous precursor La- and Nd-carbonate phases but also in the resulting crystallite sizes and morphologies of the end products. All crystalline La and Nd carbonates developed spherulitic morphologies when crystallization occurred from hydrous phases in solution at temperatures above 60 °C (La system) and 95 °C (Nd system). We suggest that spherulitic growth occurs due to a rapid breakdown of the amorphous precursors and a concurrent rapid increase in supersaturation levels in the aqueous solution. The kinetic data show that the crystallization pathway for both La and Nd carbonate systems is dependent on the reaction temperature and the ionic potential of the REE3+ ion. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01497b

The effect of replacing pnictogen elements on the physical properties SrMg2 {{\\boldsymbol{X}}}_{2} ({\\boldsymbol{X}}=N, P, As, Sb, Bi) Zintl compounds

NASA Astrophysics Data System (ADS)

Murtaza, G.; Ahad Khan, Abdul; Yaseen, M.; Laref, A.; Ullah, Naeem; Rahman, Inayat ur

2018-04-01

Not Available Project supported by a grant from the “Research Center of Female Scientific and Medical Colleges”, the Deanship of Scientific Research, King Saud University. Yaseen M is thankful to Higher Education Commission (HEC), Pakistan for funding (Grant No. 6410/Punjab/NRPU/R&D/HEC/2016), and also this study is made possible by the support of the United States Government and the American people through the United States Agency for International Development (USAID). The contents are the sole responsibility of National University of Sciences and Technology and do not necessarily reflect the views of USAID or the United States Government.

Near-infrared–driven decomposition of metal precursors yields amorphous electrocatalytic films

PubMed Central

Salvatore, Danielle A.; Dettelbach, Kevan E.; Hudkins, Jesse R.; Berlinguette, Curtis P.

2015-01-01

Amorphous metal-based films lacking long-range atomic order have found utility in applications ranging from electronics applications to heterogeneous catalysis. Notwithstanding, there is a limited set of fabrication methods available for making amorphous films, particularly in the absence of a conducting substrate. We introduce herein a scalable preparative method for accessing oxidized and reduced phases of amorphous films that involves the efficient decomposition of molecular precursors, including simple metal salts, by exposure to near-infrared (NIR) radiation. The NIR-driven decomposition process provides sufficient localized heating to trigger the liberation of the ligand from solution-deposited precursors on substrates, but insufficient thermal energy to form crystalline phases. This method provides access to state-of-the-art electrocatalyst films, as demonstrated herein for the electrolysis of water, and extends the scope of usable substrates to include nonconducting and temperature-sensitive platforms. PMID:26601148

Zintl phase with a layered network structure, KSi/sub 3/As/sub 3/

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

Hurng, W.M.; Corbett, J.D.; Wang, S.L.

The title compound is obtained in high yield from a two-step reaction of K with Si in sealed tantalum and then of that product with As in silica at 800-900/sup 0/C. Ion exchange with NaI at 500 /sup 0/C gives the sodium derivative. The structure of the purple KSi/sub 3/A/sub 3/ crystals has been established by x-ray diffraction means at room temperature (orthorhombic, space group Pbam, Z = 4, a = 10.010 (4) A, b = 19.139 (8) A, c = 3.664 (1) A, R = 0.044 for 674 reflections, 2theta < 55/sup 0/). The infinity /sup 2/(Si/sub 3/As/sub 3/)/supmore » -/ anion layers may be generated by Si-Si bonding between puckered Si/sub 3/As/sub 3/(As) rings to form chains followed by side-by-side condensation of these to sheets. The structure may be derived from the layered structure of SiAs in a concerted way through reductive ring opening and Si-Si bond formation. Comparisons are also made with more reduced Si-As anion chains and clusters and with the closely related Li/sub 3/NaSi/sub 6/. K/sub 2/SiAs/sub 2/ has also been synthesized and shown to be isostructural with K/sub 2/SiP/sub 2/. 20 references, 4 figures, 4 tables.« less

Synthesis, Crystal and Electronic Structures of the Pnictides AE 3TrPn 3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

DOE PAGES

Stoyko, Stanislav; Voss, Leonard; He, Hua; ...

2015-09-24

New ternary arsenides AE 3TrAs 3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr 3GaP 3 and Ba 3AlP 3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr 3AlAs 3 and Ba 3AlAs 3 adopt the Ba 3AlSb 3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr 3GaP 3 and Ba 3AlP 3. Likewise, the compounds Sr 3GaAs 3 and Ba 3GaAs 3 crystallize with the Ba 3GaSb 3-type structure (Pearson symbol oP56, space groupmore » Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn 4 and GaPn 4 tetrahedra (Pn = pnictogen, i.e., P or As), separated by the alkaline-earth Sr 2+ and Ba 2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE 2+] 3[Tr 3+][Pn 3-] 3, or rather [AE 2+] 6[Tr 2Pn 6] 12-, i.e., as Zintl phases.« less

Yb14MgBi11: structure, thermoelectric properties and the effect of the structure on low lattice thermal conductivity.

PubMed

Hu, Yufei; Kauzlarich, Susan M

2017-03-21

Zintl phases Yb 14 MnSb 11 and Yb 14 MgSb 11 , which share the same complex structure type, have been demonstrated as the best p-type thermoelectric materials for the high temperature region (800-1200 K). A new iso-structural compound, Yb 14 MgBi 11 , was synthesized in order to investigate the structure and thermoelectric properties of the Bi analogs. Yb 14 MgBi 11 crystallizes in the Ca 14 AlSb 11 structure-type with the space group I4 1 /acd [a = 16.974(2) Å, c = 22.399(4) Å, V = 6454(2) Å 3 , R 1 /wR 2 = 0.0238/0.0475]. The structure follows the previous description of this structure type and the trend observed in previous analogs. Thermoelectric properties of Yb 14 MgBi 11 are measured together with Yb 14 MnBi 11 and both compounds are metallic. Compared to Yb 14 MgSb 11 , Yb 14 MgBi 11 has a higher carrier concentration with a similar mobility and effective mass. The lattice thermal conductivity of Yb 14 MgBi 11 is extremely low, which is as low as 0.16-0.36 W(mK) -1 . The zT values of Yb 14 MgBi 11 and Yb 14 MnBi 11 reach 0.2 at 875 K.

Coated electroactive materials

DOEpatents

Amine, Khalil; Abouimrane, Ali

2016-08-30

A process includes suspending an electroactive material in a solvent, suspending or dissolving a carbon precursor in the solvent; and depositing the carbon precursor on the electroactive material to form a carbon-coated electroactive material. Compositions include a graphene-coated electroactive material prepared from a solution phase mixture or suspension of an electroactive material and graphene, graphene oxide, or a mixture thereof.

Live imaging of heart tube development in mouse reveals alternating phases of cardiac differentiation and morphogenesis

PubMed Central

Ivanovitch, Kenzo; Temiño, Susana

2017-01-01

During vertebrate heart development, two progenitor populations, first and second heart fields (FHF, SHF), sequentially contribute to longitudinal subdivisions of the heart tube (HT), with the FHF contributing the left ventricle and part of the atria, and the SHF the rest of the heart. Here, we study the dynamics of cardiac differentiation and morphogenesis by tracking individual cells in live analysis of mouse embryos. We report that during an initial phase, FHF precursors differentiate rapidly to form a cardiac crescent, while limited morphogenesis takes place. In a second phase, no differentiation occurs while extensive morphogenesis, including splanchnic mesoderm sliding over the endoderm, results in HT formation. In a third phase, cardiac precursor differentiation resumes and contributes to SHF-derived regions and the dorsal closure of the HT. These results reveal tissue-level coordination between morphogenesis and differentiation during HT formation and provide a new framework to understand heart development. PMID:29202929

Phase transitions and their energetics in calcite biominerals

NASA Astrophysics Data System (ADS)

Gilbert, Pupa

2013-03-01

Biominerals include mollusk shells and the skeletons of algae, sponges, corals, sea urchins and most other animals. The function of biominerals are diverse: mechanical support, attack, defense, grinding, biting, and chewing, gravitational and magnetic field sensing, light focusing, and many others. The exquisite nanostructure of biominerals is directly controlled by the organisms, which have evolved to master the chemico-physical aspects of mineralization. By controlling the inorganic precursor nanoparticle size, packing, and phase transitions, organisms efficiently fill space, produce tough and hard structures, with micro- or macroscopic morphology optimized for their functions. Specifically, this talk will address two key questions: Q: How are the beautiful biomineral morphologies achieved? A: Using amorphous precursor phases, with phase transitions kinetically regulated (retarded) by proteins. Q: How do organisms co-orient their single-crystalline biominerals? A: Controlling the propagation of crystallinity one nanoparticle at a time, not atom-by-atom.

Hybridized 1T/2H MoS2 Having Controlled 1T Concentrations and its use in Supercapacitors.

PubMed

Thi Xuyen, Nguyen; Ting, Jyh-Ming

2017-12-06

Molybdenum disulfide (MoS 2 ) nanoflowers consisting of hybridized 1T/2H phases have been synthesized by using a microwave-assisted hydrothermal (MTH) method. The concentration of the 1T phase, ranging from 40 % to 73 %, is controlled by simply adjusting the ratio of the Mo and S precursors. By using the hybridized 1T/2H MoS 2 as an electrode material, it was demonstrated that the resulting supercapacitor performance is dominated by the 1T phase concentration. It was found that a supercapacitor with 73 % 1T phase exhibits excellent capacitance of 259 F g -1 and great cyclic stability after 1000 cycles. The formation mechanism of the MHT-synthesized hybridized 1T/2H MoS 2 is also reported. More importantly, the mechanism also explains the observed relationship between the 1T phase concentration and the ratio of the Mo and S precursors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Possible mechanisms for four regimes associated with cold events over East Asia

NASA Astrophysics Data System (ADS)

Yang, Zifan; Huang, Wenyu; Wang, Bin; Chen, Ruyan; Wright, Jonathon S.; Ma, Wenqian

2017-09-01

Circulation patterns associated with cold events over East Asia during the winter months of 1948-2014 are classified into four regimes by applying a k-means clustering method based on the area-weighted pattern correlation. The earliest precursor signals for two regimes are anticyclonic anomalies, which evolve into Ural and central Siberian blocking-like circulation patterns. The earliest precursor signals for the other two regimes are cyclonic anomalies, both of which evolve to amplify the East Asian trough (EAT). Both the blocking-like circulation patterns and amplified EAT favor the initialization of cold events. On average, the blocking-related regimes tend to last longer. The lead time of the earliest precursor signal for the central Siberian blocking-related regime is only 4 days, while those for the other regimes range from 16 to 18 days. The North Atlantic Oscillation plays essential roles both in triggering the precursor for the Ural blocking-related regime and in amplifying the precursors for all regimes. All regimes preferentially occur during the positive phase of the Eurasian teleconnection pattern and the negative phase of the El Niño-Southern Oscillation. For three regimes, surface cooling is primarily due to reduced downward infrared radiation and enhanced cold advection. For the remaining regime, which is associated with the southernmost cooling center, sensible and latent heat release and horizontal cold advection dominate the East Asian cooling.

Rapid formation of phase-clean 110 K (Bi-2223) powders derived via freeze-drying process

DOEpatents

Balachandran, Uthamalingam

1996-01-01

A process for the preparation of amorphous precursor powders for Pb-doped Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x (2223) includes a freeze-drying process incorporating a splat-freezing step. The process generally includes splat freezing a nitrate solution of Bi, Pb, Sr, Ca, and Cu to form flakes of the solution without any phase separation; grinding the frozen flakes to form a powder; freeze-drying the frozen powder; heating the dried powder to form a dry green precursor powders; denitrating the green-powders; heating the denitrated powders to form phase-clean Bi-2223 powders. The grain boundaries of the 2223 grains appear to be clean, leading to good intergrain contact between 2223 grains.

Rapid formation of phase-clean 110 K (Bi-2223) powders derived via freeze-drying process

DOEpatents

Balachandran, U.

1996-06-04

A process for the preparation of amorphous precursor powders for Pb-doped Bi{sub 2}Sr{sub 2} Ca{sub 2}Cu{sub 3}O{sub x} (2223) includes a freeze-drying process incorporating a splat-freezing step. The process generally includes splat freezing a nitrate solution of Bi, Pb, Sr, Ca, and Cu to form flakes of the solution without any phase separation; grinding the frozen flakes to form a powder; freeze-drying the frozen powder; heating the dried powder to form a dry green precursor powders; denitrating the green-powders; heating the denitrated powders to form phase-clean Bi-2223 powders. The grain boundaries of the 2223 grains appear to be clean, leading to good intergrain contact between 2223 grains. 11 figs.

Structural and optical characterization of Eu3+ doped beta-Ga2O3 nanoparticles using a liquid-phase precursor method.

PubMed

Kim, Moung-O; Kang, Bongkyun; Yoon, Daeho

2013-08-01

Eu3+ doped beta-Ga2O3 and non-doped beta-Ga2O3 nanoparticles were synthesized at 800 degrees C using a liquid-phase precursor (LPP) method, with different annealing times and Eu3+ ion concentrations. Eu3+ doped beta-Ga2O3 nanoparticles showed broad XRD peaks, revealing a second phase compared with the non-doped beta-Ga2O3 nanoparticles. The cathode luminescence (CL) spectra of beta-Ga2O3 and Eu3+ doped beta-Ga2O3 nanoparticles showed a broad band emission (300-500 nm) of imperfection and two component emissions. The luminescence quenching properties of Eu3+ dopant ion concentration appeared gradually beyond 5 mol% in our investigation.

Multiple reaction monitoring (MRM)-profiling for biomarker discovery applied to human polycystic ovarian syndrome.

PubMed

Cordeiro, Fernanda B; Ferreira, Christina R; Sobreira, Tiago Jose P; Yannell, Karen E; Jarmusch, Alan K; Cedenho, Agnaldo P; Lo Turco, Edson G; Cooks, R Graham

2017-09-15

We describe multiple reaction monitoring (MRM)-profiling, which provides accelerated discovery of discriminating molecular features, and its application to human polycystic ovary syndrome (PCOS) diagnosis. The discovery phase of the MRM-profiling seeks molecular features based on some prior knowledge of the chemical functional groups likely to be present in the sample. It does this through use of a limited number of pre-chosen and chemically specific neutral loss and/or precursor ion MS/MS scans. The output of the discovery phase is a set of precursor/product transitions. In the screening phase these MRM transitions are used to interrogate multiple samples (hence the name MRM-profiling). MRM-profiling was applied to follicular fluid samples of 22 controls and 29 clinically diagnosed PCOS patients. Representative samples were delivered by flow injection to a triple quadrupole mass spectrometer set to perform a number of pre-chosen and chemically specific neutral loss and/or precursor ion MS/MS scans. The output of this discovery phase was a set of 1012 precursor/product transitions. In the screening phase each individual sample was interrogated for these MRM transitions. Principal component analysis (PCA) and receiver operating characteristic (ROC) curves were used for statistical analysis. To evaluate the method's performance, half the samples were used to build a classification model (testing set) and half were blinded (validation set). Twenty transitions were used for the classification of the blind samples, most of them (N = 19) showed lower abundances in the PCOS group and corresponded to phosphatidylethanolamine (PE) and phosphatidylserine (PS) lipids. Agreement of 73% with clinical diagnosis was found when classifying the 26 blind samples. MRM-profiling is a supervised method characterized by its simplicity, speed and the absence of chromatographic separation. It can be used to rapidly isolate discriminating molecules in healthy/disease conditions by tailored screening of signals associated with hundreds of molecules in complex samples. Copyright © 2017 John Wiley & Sons, Ltd.

Synthesis of phase-pure and monodisperse iron oxide nanoparticles by thermal decomposition

NASA Astrophysics Data System (ADS)

Hufschmid, Ryan; Arami, Hamed; Ferguson, R. Matthew; Gonzales, Marcela; Teeman, Eric; Brush, Lucien N.; Browning, Nigel D.; Krishnan, Kannan M.

2015-06-01

Superparamagnetic iron oxide nanoparticles (SPIONs) are used for a wide range of biomedical applications requiring precise control over their physical and magnetic properties, which are dependent on their size and crystallographic phase. Here we present a comprehensive template for the design and synthesis of iron oxide nanoparticles with control over size, size distribution, phase, and resulting magnetic properties. We investigate critical parameters for synthesis of monodisperse SPIONs by organic thermal decomposition. Three different, commonly used, iron containing precursors (iron oleate, iron pentacarbonyl, and iron oxyhydroxide) are evaluated under a variety of synthetic conditions. We compare the suitability of these three kinetically controlled synthesis protocols, which have in common the use of iron oleate as a starting precursor or reaction intermediate, for producing nanoparticles with specific size and magnetic properties. Monodisperse particles were produced over a tunable range of sizes from approximately 2-30 nm. Reaction parameters such as precursor concentration, addition of surfactant, temperature, ramp rate, and time were adjusted to kinetically control size and size-distribution, phase, and magnetic properties. In particular, large quantities of excess surfactant (up to 25 : 1 molar ratio) alter reaction kinetics and result in larger particles with uniform size; however, there is often a trade-off between large particles and a narrow size distribution. Iron oxide phase, in addition to nanoparticle size and shape, is critical for establishing magnetic properties such as differential susceptibility (dm/dH) and anisotropy. As an example, we show the importance of obtaining the required size and iron oxide phase for application to Magnetic Particle Imaging (MPI), and describe how phase purity can be controlled. These results provide much of the information necessary to determine which iron oxide synthesis protocol is best suited to a particular application.

Controlled synthesis of Co2C nanochains using cobalt laurate as precursor: Structure, growth mechanism and magnetic properties

NASA Astrophysics Data System (ADS)

Zhang, Yajing; Zhu, Yuan; Wang, Kangjun; Li, Da; Wang, Dongping; Ding, Fu; Meng, Dan; Wang, Xiaolei; Choi, Chuljin; Zhang, Zhidong

2018-06-01

Cobalt carbides (Co2C and Co3C) nanocomposites exhibit interesting hard magnetic property, controlled synthesis of individual phase facilitates to clarify the magnetism of each, but it is difficult to obtain the single phase. We present a new approach to address this issue via a polyol refluxing process, using cobalt laurate as the precursor. The single phase Co2C magnetic nanochains self-assembled by nanoparticles are synthesized. The precursor is the key factor for controlling the growth kinetics of the Co2C nanochains. Cobalt, instead of cobalt carbides, is produced if cobalt chloride, acetate and acetylacetonate replace cobalt laurate as the precursor, respectively. The evolution of the growth process has been studied. In the formation of Co2C, first fcc-Co produces, then it transforms into Co2C by carbon diffusion process, and the produced carbon first exists in disordered state and then a small amount of them transforms into graphite. Saturation magnetization (Ms) of Co2C nanochains obtained at 300 °C for 20, 60, and 180 min are 27.1, 18.9, and 10.9 emu g-1, respectively. The decrease of Ms caused by increasing carbon content, and the carbon content are much larger than the stoichiometric ratio value of Co2C (9.2 wt%). The Co2C nanochains have mesoporous pore of 3.8 nm and the specific surface area of 48.6 m2 g-1.

Metal stabilization mechanism of incorporating lead-bearing sludge in kaolinite-based ceramics.

PubMed

Lu, Xingwen; Shih, Kaimin

2012-02-01

The feasibility and mechanism of incorporating simulated lead-laden sludge into low-cost ceramic products was investigated by observing the reaction of lead with two kaolinite-based precursors under sintering conditions. To investigate the phase transformation process of lead, lead oxide (PbO) mixed with a kaolinite or mullite precursor were fired at 500-950°C for 3h. Detailed X-ray diffraction analysis of sintered products revealed that both precursors had crystallochemically incorporated lead into the lead feldspar (PbAl(2)Si(2)O(8)) crystalline structure. By mixing lead oxide with kaolinite, lead feldspar begins to crystallize at 700°C; maximum incorporation of lead into this structure occurred at 950°C. However, two intermediate phases, Pb(4)Al(4)Si(3)O(16) and a polymorph of lead feldspar, were detected at temperatures between 700 and 900°C. By sintering lead oxide with the mullite precursor, lead feldspar was detected at temperatures above 750°C, and an intermediate phase of Pb(4)Al(4)Si(3)O(16) was observed in the temperature range of 750-900°C. This study compared the lead leachabilities of PbO and lead feldspar using a prolonged leaching test (at pH 2.9 for 23d) modified from the toxicity characteristic leaching procedure. The results indicate the superiority of lead feldspar in stabilizing lead and suggest a promising and reliable strategy to stabilize lead in ceramic products. Copyright © 2011 Elsevier Ltd. All rights reserved.

Tuning the morphology, luminescence and magnetic properties of hexagonal-phase NaGdF4: Yb, Er nanocrystals via altering the addition sequence of the precursors

NASA Astrophysics Data System (ADS)

Zhao, Shuwen; Xia, Donglin; Zhao, Ruimin; Zhu, Hao; Zhu, Yiru; Xiong, Yuda; Wang, Youfa

2017-01-01

Hexagonal-phase NaGdF4: Yb, Er upconversion nanocrystals (UCNCs) with tunable morphology and properties were successfully prepared via a thermal decomposition method. The influences of the adding sequence of the precursors on the morphology, chemical composition, luminescence and magnetic properties were investigated by transmission electron microscopy (TEM), inductively coupled plasma-atomic emission spectrometry (ICP-AES), upconversion (UC) spectroscopy, and a vibrating sample magnetometer (VSM). It was found that the resulting nanocrystals, with different sizes ranging from 24 to 224 nm, are in the shape of spheres, hexagonal plates and flakes; moreover, the composition percentage of Yb3+-Er3+ and Gd3+ ions was found to vary in a regular pattern with the adding sequence. Furthermore, the intensity ratios of emission colors (f g/r, f g/p), and the magnetic mass susceptibility of hexagonal-phase NaGdF4: Yb, Er nanocrystals change along with the composition of the nanocrystals. A positive correlation between the susceptibility and f g/r of NaGdF4: Yb, Er was proposed. The decomposition processes of the precursors were investigated by a thermogravimetric (TG) analyzer. The result indicated that the decomposition of the resolved lanthanide trifluoroacetate is greatly different from lanthanide trifluoroacetate powder. It is of tremendous help to recognize the decomposition process of the precursors and to understand the related reaction mechanism.

On the mixing and evaporation of secondary organic aerosol components.

PubMed

Loza, Christine L; Coggon, Matthew M; Nguyen, Tran B; Zuend, Andreas; Flagan, Richard C; Seinfeld, John H

2013-06-18

The physical state and chemical composition of an organic aerosol affect its degree of mixing and its interactions with condensing species. We present here a laboratory chamber procedure for studying the effect of the mixing of organic aerosol components on particle evaporation. The procedure is applied to the formation of secondary organic aerosol (SOA) from α-pinene and toluene photooxidation. SOA evaporation is induced by heating the chamber aerosol from room temperature (25 °C) to 42 °C over 7 h and detected by a shift in the peak diameter of the SOA size distribution. With this protocol, α-pinene SOA is found to be more volatile than toluene SOA. When SOA is formed from the two precursors sequentially, the evaporation behavior of the SOA most closely resembles that of SOA from the second parent hydrocarbon, suggesting that the structure of the mixed SOA resembles a core of SOA from the initial precursor coated by a layer of SOA from the second precursor. Such a core-and-shell configuration of the organic aerosol phases implies limited mixing of the SOA from the two precursors on the time scale of the experiments, consistent with a high viscosity of at least one of the phases.

Impact of Gas-Phase Mechanisms on Weather Research Forecasting Model with Chemistry (WRF/Chem) Predictions: Mechanism Implementation and Comparative Evaluation

EPA Science Inventory

Gas-phase mechanisms provide important oxidant and gaseous precursors for secondary aerosol formation. Different gas-phase mechanisms may lead to different predictions of gases, aerosols, and aerosol direct and indirect effects. In this study, WRF/Chem-MADRID simulations are cond...

Structural and spectroscopic characterization of irreversible phase changes in rapidly heated precursors of europium-doped titania nanoparticles

NASA Astrophysics Data System (ADS)

Gunawidjaja, Ray; Anderson, Benjamin R.; Eilers, Hergen

2018-02-01

We observe temperature-dependent phase changes in a precursor of europium-doped titania (p-Eu:TiO2) that is prepared via precipitation and is laser-heated to temperatures between 473 K and 1246 K within sub-second heating durations. The phase changes are characterized using X-ray diffraction and site-selective photoluminescence spectroscopy. We find that upon heating, the initially amorphous p-Eu:TiO2 first transforms into the anatase phase and then into a mixed anatase/rutile phase. These phase transformations change the local environment of the dopant Eu3+ ions resulting in modifications to the Eu3+ ions spectroscopic properties, with the modifications occurring for calcination temperatures above approximately 573 K following sub-second durations. These results demonstrate the temperature sensing ability of p-Eu:TiO2 nanoparticles for use in sub-second heating events. Moreover, at 573 K this temperature is lower than other host materials that we have evaluated (i.e., La2O3, ZrO2 and Y2O3).

Benzimidazole Based Aerogel Materials

NASA Technical Reports Server (NTRS)

Rhine, Wendell E. (Inventor); Mihalcik, David (Inventor)

2016-01-01

The present invention provides aerogel materials based on imidazoles and polyimidazoles. The polyimidazole based aerogel materials can be thermally stable up to 500 C or more, and can be carbonized to produce a carbon aerogel having a char yield of 60% or more, specifically 70% or more. The present invention also provides methods of producing polyimidazole based aerogel materials by reacting at least one monomer in a suitable solvent to form a polybenzimidazole gel precursor solution, casting the polybenzimidazole gel precursor solution into a fiber reinforcement phase, allowing the at least one gel precursor in the precursor solution to transition into a gel material, and drying the gel materials to remove at least a portion of the solvent, to obtain an polybenzimidazole-based aerogel material.

Biosynthesis and characterization of silver nanoparticles prepared from two novel natural precursors by facile thermal decomposition methods

NASA Astrophysics Data System (ADS)

Goudarzi, Mojgan; Mir, Noshin; Mousavi-Kamazani, Mehdi; Bagheri, Samira; Salavati-Niasari, Masoud

2016-09-01

In this work, two natural sources, including pomegranate peel extract and cochineal dye were employed for the synthesis of silver nanoparticles. The natural silver complex from pomegranate peel extract resulted in nano-sized structures through solution-phase method, but this method was not efficient for cochineal dye-silver precursor and the as-formed products were highly agglomerated. Therefore, an alternative facile solid-state approach was investigated as for both natural precursors and the results showed successful production of well-dispersed nanoparticles with narrow size distribution for cochineal dye-silver precursor. The products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy dispersive X-ray microanalysis (EDX), and Transmission Electron Microscopy (TEM).

Electron beam induced deposition of silicon nanostructures from a liquid phase precursor.

PubMed

Liu, Yin; Chen, Xin; Noh, Kyong Wook; Dillon, Shen J

2012-09-28

This work demonstrates electron beam induced deposition of silicon from a SiCl(4) liquid precursor in a transmission electron microscope and a scanning electron microscope. Silicon nanodots of tunable size are reproducibly grown in controlled geometries. The volume of these features increases linearly with deposition time. The results indicate that secondary electrons generated at the substrate surface serve as the primary source of silicon reduction. However, at high current densities the influence of the primary electrons is observed to retard growth. The results demonstrate a new approach to fabricating silicon nanostructures and provide fundamental insights into the mechanism for liquid phase electron beam induced deposition.

Electron beam induced deposition of silicon nanostructures from a liquid phase precursor

NASA Astrophysics Data System (ADS)

Liu, Yin; Chen, Xin; Noh, Kyong Wook; Dillon, Shen J.

2012-09-01

This work demonstrates electron beam induced deposition of silicon from a SiCl4 liquid precursor in a transmission electron microscope and a scanning electron microscope. Silicon nanodots of tunable size are reproducibly grown in controlled geometries. The volume of these features increases linearly with deposition time. The results indicate that secondary electrons generated at the substrate surface serve as the primary source of silicon reduction. However, at high current densities the influence of the primary electrons is observed to retard growth. The results demonstrate a new approach to fabricating silicon nanostructures and provide fundamental insights into the mechanism for liquid phase electron beam induced deposition.

Magnesium-aspartate-based crystallization switch inspired from shell molt of crustacean

PubMed Central

Tao, Jinhui; Zhou, Dongming; Zhang, Zhisen; Xu, Xurong; Tang, Ruikang

2009-01-01

Many animals such as crustacean periodically undergo cyclic molt of the exoskeleton. During this process, amorphous calcium mineral phases are biologically stabilized by magnesium and are reserved for the subsequent rapid formation of new shell tissue. However, it is a mystery how living organisms can regulate the transition of the precursor phases precisely. We reveal that the shell mineralization from the magnesium stabilized precursors is associated with the presence of Asp-rich proteins. It is suggested that a cooperative effect of magnesium and Asp-rich compound can result into a crystallization switch in biomineralization. Our in vitro experiments confirm that magnesium increases the lifetime of amorphous calcium carbonate and calcium phosphate in solution so that the crystallization can be temporarily switched off. Although Asp monomer alone inhibits the crystallization of pure amorphous calcium minerals, it actually reduces the stability of the magnesium-stabilized precursors to switch on the transformation from the amorphous to crystallized phases. These modification effects on crystallization kinetics can be understood by an Asp-enhanced magnesium desolvation model. The interesting magnesium-Asp-based switch is a biologically inspired lesson from nature, which can be developed into an advanced strategy to control material fabrications. PMID:20007788

Magnesium-aspartate-based crystallization switch inspired from shell molt of crustacean.

PubMed

Tao, Jinhui; Zhou, Dongming; Zhang, Zhisen; Xu, Xurong; Tang, Ruikang

2009-12-29

Many animals such as crustacean periodically undergo cyclic molt of the exoskeleton. During this process, amorphous calcium mineral phases are biologically stabilized by magnesium and are reserved for the subsequent rapid formation of new shell tissue. However, it is a mystery how living organisms can regulate the transition of the precursor phases precisely. We reveal that the shell mineralization from the magnesium stabilized precursors is associated with the presence of Asp-rich proteins. It is suggested that a cooperative effect of magnesium and Asp-rich compound can result into a crystallization switch in biomineralization. Our in vitro experiments confirm that magnesium increases the lifetime of amorphous calcium carbonate and calcium phosphate in solution so that the crystallization can be temporarily switched off. Although Asp monomer alone inhibits the crystallization of pure amorphous calcium minerals, it actually reduces the stability of the magnesium-stabilized precursors to switch on the transformation from the amorphous to crystallized phases. These modification effects on crystallization kinetics can be understood by an Asp-enhanced magnesium desolvation model. The interesting magnesium-Asp-based switch is a biologically inspired lesson from nature, which can be developed into an advanced strategy to control material fabrications.

Multiday production of condensing organic aerosol mass in urban and forest outflow

DOE PAGES

Lee-Taylor, J.; Hodzic, A.; Madronich, S.; ...

2014-07-03

Secondary organic aerosol (SOA) production in air masses containing either anthropogenic or biogenic (terpene-dominated) emissions is investigated using the explicit gas-phase chemical mechanism generator GECKO-A. Simulations show several-fold increases in SOA mass continuing for several days in the urban outflow, even as the initial air parcel is diluted into the regional atmosphere. The SOA mass increase in the forest outflow is more modest (∼50%) and of shorter duration (1–2 days). The production in the urban outflow stems from continuing oxidation of gas-phase precursors which persist in equilibrium with the particle phase, and can be attributed to multigenerational reaction products ofmore » both aromatics and alkanes. In particular we find large contributions from substituted maleic anhydrides and multi-substituted peroxide-bicyclic alkenes. The results show that the predicted production is a robust feature of our model even under changing atmospheric conditions, and contradict the notion that SOA undergoes little mass production beyond a short initial formation period. The results imply that anthropogenic aerosol precursors could influence the chemical and radiative characteristics of the atmosphere over an extremely wide region, and that SOA measurements near precursor sources may routinely underestimate this influence.« less

Amorphous surface layer versus transient amorphous precursor phase in bone - A case study investigated by solid-state NMR spectroscopy.

PubMed

Von Euw, Stanislas; Ajili, Widad; Chan-Chang, Tsou-Hsi-Camille; Delices, Annette; Laurent, Guillaume; Babonneau, Florence; Nassif, Nadine; Azaïs, Thierry

2017-09-01

The presence of an amorphous surface layer that coats a crystalline core has been proposed for many biominerals, including bone mineral. In parallel, transient amorphous precursor phases have been proposed in various biomineralization processes, including bone biomineralization. Here we propose a methodology to investigate the origin of these amorphous environments taking the bone tissue as a key example. This study relies on the investigation of a bone tissue sample and its comparison with synthetic calcium phosphate samples, including a stoichiometric apatite, an amorphous calcium phosphate sample, and two different biomimetic apatites. To reveal if the amorphous environments in bone originate from an amorphous surface layer or a transient amorphous precursor phase, a combined solid-state nuclear magnetic resonance (NMR) experiment has been used. The latter consists of a double cross polarization 1 H→ 31 P→ 1 H pulse sequence followed by a 1 H magnetization exchange pulse sequence. The presence of an amorphous surface layer has been investigated through the study of the biomimetic apatites; while the presence of a transient amorphous precursor phase in the form of amorphous calcium phosphate particles has been mimicked with the help of a physical mixture of stoichiometric apatite and amorphous calcium phosphate. The NMR results show that the amorphous and the crystalline environments detected in our bone tissue sample belong to the same particle. The presence of an amorphous surface layer that coats the apatitic core of bone apatite particles has been unambiguously confirmed, and it is certain that this amorphous surface layer has strong implication on bone tissue biogenesis and regeneration. Questions still persist on the structural organization of bone and biomimetic apatites. The existing model proposes a core/shell structure, with an amorphous surface layer coating a crystalline bulk. The accuracy of this model is still debated because amorphous calcium phosphate (ACP) environments could also arise from a transient amorphous precursor phase of apatite. Here, we provide an NMR spectroscopy methodology to reveal the origin of these ACP environments in bone mineral or in biomimetic apatite. The 1 H magnetization exchange between protons arising from amorphous and crystalline domains shows unambiguously that an ACP layer coats the apatitic crystalline core of bone et biomimetic apatite platelets. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A sintering study on the β-spodumene-based glass ceramics prepared from gel-derived precursor powders with LiF additive

NASA Astrophysics Data System (ADS)

Wang, Moo-Chin; Wu, Nan-Chung; Yang, Sheng; Wen, Shaw-Bing

2002-01-01

Beta-spodumene (Li2O·Al2O3·4SiO2, LAS) powders were prepared by a sol-gel process using Si(OC2H5)4, Al(OC4H9)3, and LiNO3 as precursors and LiF as a sintering aid agent. Dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED) were utilized to study the sintering, phase transformation, microstructure, and properties of the β-spodumene glass-ceramics prepared from the gel-derived precursor powders with and without LiF additives. For the LAS precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4 wt pct LiF and sintered at 1050 °C for 5 hours the crystalline phases were β-spodumene and β-eucryptite (Li2O·Al2O3·2SiO2). When the LiF content was 5 wt pct and the sintering process was carried out at 1050 °C for 5 hours, the crystalline phases were β-spodumene, β-eucryptite (triclinic), and eucryptite (rhombohedral (hex.)) phases. With the LiF additive increased from 0.5 to 4 wt pct and sintering at 1050 °C for 5 hours, the open porosity of the sintered bodies decrease from 30 to 2.1 pct. The grains size is about to 4 to 5 µm when pellect LAS compact contains LiF 3 wt pct as sintered at 1050 °C for 5 hours. The grains size grew to 8 to 25 µm with a remarkable discontinuous grain growth for pellet LAS compact contain LiF 5 wt pct sintered at 1050 °C for 5 hours. Relative densities greater than 90 pct could be obtained for the LAS precursor powders with LiF > 2 wt pct when sintered at 1050 °C for 5 hours. The coefficient of thermal expansion of the sintered bodies decreased from 8.3 × 10-7 to 5.2 × 10-7/°C (25 °C to 900 °C) as the LiF addition increased from 0 to 5 wt pct.

Strategies to indium nitride and gallium nitride nanoparticles: Low-temperature, solution-phase and precursor routes

NASA Astrophysics Data System (ADS)

Dingman, Sean Douglas

I present new strategies to low-temperature solution-phase synthesis of indium and gallium nitride (InN and GaN) ceramic materials. The strategies include: direct conversion of precursor molecules to InN by pyrolysis, solution-phase synthesis of nanostructured InN fibers via molecular precursors and co-reactants, and synthesis of powders through reactions derived from molten-salt chemistry. Indium nitride powders are prepared by pyrolysis of the precursors R 2InN3 (R = t-Bu (1), i-Amyl(2), Et(3), i-Pr( 4)). The precursors are synthesized via azide-alkoxide exchange of R2InOMe with Me3SiN3. The precursors are coordination polymers containing five-coordinate indium centers. Pyrolysis of 1 and 2 under N2 at 400°C yields powders consisting primarily of InN with average crystal sizes of 15--35 nm. 1 yields nanocrystalline InN with average particle sizes of 7 nm at 250°C. 3 and 4 yield primarily In metal from pyrolysis. Refluxing 1 in diisopropylbenzene (203°C) in the presence of primary amines yields InN nanofibers 10--100 nm in length. InN nanofibers of up to 1 mum can be synthesized by treating 1 with 1,1-dimethylhydrazine (DMHy) The DMHy appears to control the fiber length by acting as a secondary source of active nitrogen in order to sustain fiber growth. The resulting fibers are attached to droplets of indium metal implying a solution-liquid-solid growth mechanism. Precursor 4 yields crystalline InN whiskers when reacted with DMHy. Reactions of 4 with reducing agents such as HSnBu3, yield InN nanoparticles with an average crystallite size of 16 nm. Gallium precursors R2GaN3 (R = t-Bu( 5), Me3SiCH2(6) and i-Pr( 7)), synthesized by azide-alkoxide exchange, are found to be inert toward solution decomposition and do not yield GaN. These compounds are molecular dimers and trimers unlike the indium analogs. Compound 6 displays a monomer-dimer equilibrium in benzene solution, but exists as a solid-state trimer. InN powders are also synthesized by reactions of InCl3 and LiNH2 in a molten alkali-halide eutectic, KBr: Liar (60:40), at 400°C. The molten salt acts as an appropriate recrystallization medium for InN. Large InN platelets up to 500 nm could be synthesized. This is a significant step in finding mild reaction conditions that yield large InN crystals.

Aqueous-phase mechanism for secondary organic aerosol ...

EPA Pesticide Factsheets

Isoprene emitted by vegetation is an important precursor of secondary organic aerosol (SOA), but the mechanism and yields are uncertain. Aerosol is prevailingly aqueous under the humid conditions typical of isoprene-emitting regions. Here we develop an aqueous-phase mechanism for isoprene SOA formation coupled to a detailed gas-phase isoprene oxidation scheme. The mechanism is based on aerosol reactive uptake coefficients (γ) for water-soluble isoprene oxidation products, including sensitivity to aerosol acidity and nucleophile concentrations. We apply this mechanism to simulation of aircraft (SEAC4RS) and ground-based (SOAS) observations over the southeast US in summer 2013 using the GEOS-Chem chemical transport model. Emissions of nitrogen oxides (NOx  ≡  NO + NO2) over the southeast US are such that the peroxy radicals produced from isoprene oxidation (ISOPO2) react significantly with both NO (high-NOx pathway) and HO2 (low-NOx pathway), leading to different suites of isoprene SOA precursors. We find a mean SOA mass yield of 3.3 % from isoprene oxidation, consistent with the observed relationship of total fine organic aerosol (OA) and formaldehyde (a product of isoprene oxidation). Isoprene SOA production is mainly contributed by two immediate gas-phase precursors, isoprene epoxydiols (IEPOX, 58 % of isoprene SOA) from the low-NOx pathway and glyoxal (28 %) from both low- and high-NOx pathways. This speciation is consistent with observati

Glass precursor approach to high-temperature superconductors

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.

1992-01-01

The available studies on the synthesis of high T sub c superconductors (HTS) via the glass precursor approach were reviewed. Melts of the Bi-Sr-Ca-Cu-O system as well as those doped with oxides of some other elements (Pb, Al, V, Te, Nb, etc.) could be quenched into glasses which, on further heat treatments under appropriate conditions, crystallized into the superconducting phase(s). The nature of the HTS phase(s) formed depends on the annealing temperature, time, atmosphere, and the cooling rate and also on the glass composition. Long term annealing was needed to obtain a large fraction of the 110 K phase. The high T sub c phase did not crystallize out directly from the glass matrix, but was preceded by the precipitation of other phases. The 110 K HTS was produced at high temperatures by reaction between the phases formed at lower temperatures resulting in multiphase material. The presence of a glass former such as B2O3 was necessary for the Y-Ba-Cu-O melt to form a glass on fast cooling. A discontinuous YBa2Cu3O(7-delta) HTS phase crystallized out on heat treatment of this glass. Attempts to prepare Tl-Ba-Ca-Cu-O system in the glassy state were not successful.

Investigation of Chemically Vapor Deposited Tantalum for Medium Caliber Gun Barrel Protection

DTIC Science & Technology

2008-10-01

electrodeposition ) by December 31, 2006. As a result of this ordinance, several efforts were initiated to investigate the use of environmentally...catalyzed reactions (i.e., heterogeneous as compared to homogeneous where the reactions nucleate in the gas phase). The occurrence of a chemical reaction...Precursor Desorption of Volatile Surface Reaction Products Adsorption of Film Precursor Nucleation and Growth Transport Transport Figure 2. Schematic

Atomic insights into nanoparticle formation of hydroxyfluorinated anatase featuring titanium vacancies

DOE PAGES

Li, Wei; Body, Monique; Legein, Christophe; ...

2016-06-28

Anatase TiO 2 with exposed highly reactive (001) surface is commonly prepared using solution-based synthesis in the presence of a fluorinating agent acting as a structure directing agent. Here, the solvothermal reaction of titanium tetraisopropoxide in the presence of aqueous HF has resulted in the stabilization of an oxyhydroxyfluorinated anatase phase featuring cationic vacancies. In the present work, we have studied its formation mechanism, revealing a solid-state transformation of a highly defective anatase phase having a hydroxyfluoride composition that subsequently evolves through an oxolation reaction into an oxyhydroxyfluoride phase. Importantly, this work confirms that titanium alkoxide precursors can react withmore » HF via a fluorolysis process yielding fluorinated molecular precursors, which further condense to produce new composition and structural features deviating from a well ordered anatase network.« less

Microwave-assisted synthesis of porous carbon-titania and highly crystalline titania nanostructures.

PubMed

Parker, Alison; Marszewski, Michal; Jaroniec, Mietek

2013-03-01

Porous carbon-titania and highly crystalline titania nanostructured materials were obtained through a microwave-assisted one-pot synthesis. Resorcinol and formaldehyde were used as carbon precursors, triblock copolymer Pluronic F127 as a stabilizing agent, and titanium isopropoxide as a titania precursor. This microwave-assisted one-pot synthesis involved formation of carbon spheres according to the recently modified Stöber method followed by hydrolysis and condensation of titania precursor. This method afforded carbon-titania composite materials containing anatase phase with specific surface areas as high as 390 m(2) g(-1). The pure nanostructured titania, obtained after removal of carbon through calcination of the composite material in air, was shown to be the anatase phase with considerably higher degree of crystallinity and the specific surface area as high as 130 m(2) g(-1). The resulting titania, because of its high surface area, well-developed porosity, and high crystallinity, is of great interest for catalysis, water treatment, lithium batteries, and other energy-related applications.

Bortezomib with chemotherapy is highly active in advanced B-precursor acute lymphoblastic leukemia: Therapeutic Advances in Childhood Leukemia & Lymphoma (TACL) Study.

PubMed

Messinger, Yoav H; Gaynon, Paul S; Sposto, Richard; van der Giessen, Jeannette; Eckroth, Elena; Malvar, Jemily; Bostrom, Bruce C

2012-07-12

Therapy of relapsed pediatric acute lymphoblastic leukemia (ALL) is hampered by low remission rates and high toxicity, especially in second and subsequent relapses. Our phase 1 study, T2005-003, showed that the combination of bortezomib with vincristine, dexamethasone, pegylated asparaginase, and doxorubicin had acceptable toxicity. We report the phase 2 expansion of this combination in patients with relapsed ALL who failed 2-3 previous regimens. Twenty-two patients with relapsed ALL were treated with bortezomib combined with this regimen; their ages ranged from 1 to 22 years, and they had either B-precursor ALL (n = 20) or T-cell ALL (n = 2). Grade 3 peripheral neuropathy developed in 2 (9%) patients. After 3 patients died from bacterial infections, treatment with vancomycin, levofloxacin, and voriconazole prophylaxis resulted in no further infectious mortality in the last 6 patients. Fourteen patients achieved complete remission (CR), and 2 achieved CR without platelet recovery, for an overall 73% response rate, meeting predefined criteria allowing for early closure. B-precursor patients faired best, with 16 of 20 (80%) CR + CR without platelet recovery, whereas the 2 patients with T-cell ALL did not respond. Thus, this combination of bortezomib with chemotherapy is active in B-precursor ALL, and prophylactic antibiotics may be useful in reducing mortality. Bortezomib merits further evaluation in combination therapy in pediatric B-precursor ALL. This study is registered at http://www.clinicaltrials.gov as NCT00440726.

Current challenges for pre-earthquake electromagnetic emissions: shedding light from micro-scale plastic flow, granular packings, phase transitions and self-affinity notion of fracture process

NASA Astrophysics Data System (ADS)

Eftaxias, K.; Potirakis, S. M.

2013-10-01

Are there credible electromagnetic (EM) potential earthquake (EQ) precursors? This a question debated in the scientific community and there may be legitimate reasons for the critical views. The negative view concerning the existence of EM potential precursors is enhanced by features that accompany their observation which are considered as paradox ones, namely, these signals: (i) are not observed at the time of EQs occurrence and during the aftershock period, (ii) are not accompanied by large precursory strain changes, (iii) are not accompanied by simultaneous geodetic or seismological precursors and (iv) their traceability is considered problematic. In this work, the detected candidate EM potential precursors are studied through a shift in thinking towards the basic science findings relative to granular packings, micron-scale plastic flow, interface depinning, fracture size effects, concepts drawn from phase transitions, self-affine notion of fracture and faulting process, universal features of fracture surfaces, recent high quality laboratory studies, theoretical models and numerical simulations. We try to contribute to the establishment of strict criteria for the definition of an emerged EM anomaly as a possibly EQ-related one, and to the explanation of potential precursory EM features which have been considered as paradoxes. A three-stage model for EQ generation by means of pre-EQ fracture-induced EM emissions is proposed. The claim that the observed EM potential precursors may permit a real-time and step-by-step monitoring of the EQ generation is tested.

OBSERVATIONS OF MAGNETIC FLUX-ROPE OSCILLATION DURING THE PRECURSOR PHASE OF A SOLAR ERUPTION

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

Zhou, G. P.; Wang, J. X.; Zhang, J., E-mail: gpzhou@nao.cas.cn, E-mail: wangjx@nao.cas.cn, E-mail: jzhang7@gmu.edu

2016-05-20

Based on combined observations from the Interface Region Imaging Spectrograph (IRIS) spectrometer with the coronal emission line of Fe xxi at 1354.08 Å and SDO /AIA images in multiple passbands, we report the finding of the precursor activity manifested as the transverse oscillation of a sigmoid, which is likely a pre-existing magnetic flux rope (MFR), that led to the onset of an X class flare and a fast halo coronal mass ejection (CME) on 2014 September 10. The IRIS slit is situated at a fixed position that is almost vertical to the main axis of the sigmoid structure that hasmore » a length of about 1.8 × 10{sup 5} km. This precursor oscillation lasts for about 13 minutes in the MFR and has velocities in the range of [−9, 11] km s{sup −1} and a period of ∼280 s. Our analysis, which is based on the temperature, density, length, and magnetic field strength of the observed sigmoid, indicates that the nature of the oscillation is a standing wave of fast magnetoacoustic kink mode. We further find that the precursor oscillation is excited by the energy released through an external magnetic reconnection between the unstable MFR and the ambient magnetic field. It is proposed that this precursor activity leads to the dynamic formation of a current sheet underneath the MFR that subsequently reconnects to trigger the onset of the main phase of the flare and the CME.« less

Structural comparison of nickel electrodes and precursor phases

NASA Technical Reports Server (NTRS)

Cornilsen, Bahne C.; Shan, Xiaoyin; Loyselle, Patricia

1989-01-01

A summary of previous Raman spectroscopic results and a discussion of important structural differences in the various phases of active mass and active mass precurors are presented. Raman spectra provide unique signatures for these phases, and allow one to distinguish each phase, even when the compound is amorphous to X-rays (i.e., does not scatter X-rays because of a lack of order and/or small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging will be discussed and related to electrode properties. Important structural differences include NiO2 layer stacking, nonstoichiometry (especially cation-deficit nonstoichiometry), disorder, dopant content, and water content. The results indicate that optimal nickel active mass is non-close packed and nonstoichiometric. The formation process transforms precursor phases into this structure. Therefore, the precursor disorder, or lack thereof, influences this final active mass structure and the rate of formation. Aging processes induce structural change which is believed to be detrimental. The role of cobalt addition can be appreciated in terms of structures favored or stabilized by the dopant. In recent work, the in situ Raman technique to characterize the critical structural parameters was developed. An in situ method relates structure, electrochemistry, and preparation. In situ Raman spectra of cells during charge and discharge, either during cyclic voltammetry or under constant current conditions were collected. With the structure-preparation knowledge and the in situ Raman tool, it will be possible to define the structure-property-preparation relations in more detail. This instrumentation has application to a variety of electrode systems.

Characterization of nanosized TiO2 synthesized inside a porous glass ceramic monolith by metallo-organic decomposition process

NASA Astrophysics Data System (ADS)

Mazali, Italo Odone; Alves, Oswaldo Luiz

2005-01-01

This work reports the preparation of TiO2 by decomposition of a metallo-organic precursor (MOD process) in the pores of an α-NbPO5 glass-ceramic monolith (PGC-NbP) and the study of the TiO2 anatase-rutile transition phase. The impregnation of titanium di-(propoxy)-di-(2-ethylhexanoate) in the PGC-NbP was confirmed by diffuse reflectance infrared spectroscopy. In the restrictive porous environment the decomposition of the metallo-organic compound exhibits a lower initial decomposition temperature but a higher final decomposition temperature, in comparison to the free precursor. The pure TiO2 rutile phase is formed only above 700 °C when the titanium precursor is decomposed outside the pores. The TiO2 anatase obtained inside the PGC-NbP was stabilized up to 750 °C and exhibits a smaller average crystallite size in comparison with the MOD process performed without PGC-NbP. Furthemore, the temperature of the TiO2 anatase-rutile transformation depends on crystallite size, which was provided by XRD and Raman spectroscopy. The precursor impregnation-decomposition cycle revealed a linear mass increment inside PGC-NbP. Micro-Raman spectroscopy shows the presence of a gradient concentration of the TiO2 inside the PGC-NbP. The use of the MOD process in the PGC-NbP pores has several advantages: control of the amount and the nature of the phase formed and preservation of the pore structure of PGC-NbP for subsequent treatments and reactions.

Nilotinib and Combination Chemotherapy in Treating Patients With Newly Diagnosed Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia or Blastic Phase Chronic Myelogenous Leukemia

ClinicalTrials.gov

2015-10-29

B-cell Adult Acute Lymphoblastic Leukemia; Blastic Phase Chronic Myelogenous Leukemia; Chronic Myelogenous Leukemia, BCR-ABL1 Positive; Philadelphia Chromosome Positive Adult Precursor Acute Lymphoblastic Leukemia; Untreated Adult Acute Lymphoblastic Leukemia

Method for forming solar cell materials from particulars

DOEpatents

Eberspacher, Chris; Pauls, Karen Lea

2001-01-01

Materials in bulk and film forms are prepared from fine particulate precursors such as single-phase, mixed-metal oxides; multi-phase, mixed-metal particles comprising a metal oxide; multinary metal particles; mixtures of such particles with other particles; and particulate materials intercalated with other materials.

Czochralski growth of LaPd2Al2 single crystals

NASA Astrophysics Data System (ADS)

Doležal, P.; Rudajevová, A.; Vlášková, K.; Kriegner, D.; Václavová, K.; Prchal, J.; Javorský, P.

2017-10-01

The present study is focused on the preparation of single crystalline LaPd2Al2 by the Czochralski method. Differential scanning calorimetry (DSC) and energy dispersive X-ray spectroscopy (EDX) analyses reveal that LaPd2Al2 is an incongruently melting phase which causes difficulties for the preparation of single crystalline LaPd2Al2 by the Czochralski method. Therefore several non-stoichiometric polycrystalline samples were studied for its preparation. Finally the successful growth of LaPd2Al2 without foreign phases has been achieved by using a non-stoichiometric precursor with atomic composition 22:39:39 (La:Pd:Al). X-ray powder diffraction, EDX analysis and DSC were used for the characterisation. A single crystalline sample was separated from the ingot prepared by the Czochralski method using the non-stoichiometric precursor. The presented procedure for the preparation of pure single phase LaPd2Al2 could be modified for other incongruently melting phases.

Monoterpene oxidation in an oxidative flow reactor: SOA yields and the relationship between bulk gas-phase properties and organic aerosol growth

NASA Astrophysics Data System (ADS)

Friedman, B.; Link, M.; Farmer, D.

2016-12-01

We use an oxidative flow reactor (OFR) to determine the secondary organic aerosol (SOA) yields of five monoterpenes (alpha-pinene, beta-pinene, limonene, sabinene, and terpinolene) at a range of OH exposures. These OH exposures correspond to aging timescales of a few hours to seven days. We further determine how SOA yields of beta-pinene and alpha-pinene vary as a function of seed particle type (organic vs. inorganic) and seed particle mass concentration. We hypothesize that the monoterpene structure largely accounts for the observed variance in SOA yields for the different monoterpenes. We also use high-resolution time-of-flight chemical ionization mass spectrometry to calculate the bulk gas-phase properties (O:C and H:C) of the monoterpene oxidation systems as a function of oxidant concentrations. Bulk gas-phase properties can be compared to the SOA yields to assess the capability of the precursor gas-phase species to inform the SOA yields of each monoterpene oxidation system. We find that the extent of oxygenated precursor gas-phase species corresponds to SOA yield.

Nazca-South America Subduction Zone Reflectivity from P'P' Precursors

NASA Astrophysics Data System (ADS)

Gu, Y. J.; Schultz, R.

2012-12-01

Much of what is known about mantle owes to the interpretation of its reflectivity structure. On the global scale mantle stratifications have been attributed to mineralogical phase changes of olivine; two widely observed examples are the 410 and 660 km discontinuities. Among the various seismological tools, results from longer-period SS/PP precursors and high frequency receiver functions are routinely compared to increase the confidence of the recovered mantle stratifications. The former are lower frequency approaches with complex Fresnel zones, while constraints on receiver distribution hinder analysis in oceanic regions for the latter. P'P' precursors are a promising high frequency alternative, capable of resolving small-scale structures (resolution of ~5 km vertically, 200 km laterally) in the mantle, owing to its short-period nature (~1Hz), shallow angle of incidence and nearly symmetric Fresnel zone. However, P'P' precursors are known for several complications: phase triplication (PKiKPPKiKP, PKIKPPKIKP, PKPPKPab and PKPPKPbc) and the maximum-phase Fresnel zones result in strong scattering and asymmetric arrivals. Much of these concerns are alleviated through revamped processing techniques involving stacking, deconvolution, Radon transform and migration. We utilize P'P' precursors to constrain the mantle structure and layering beneath the Nazca-South America subduction zone. Our migration profiles reveal both olivine (e.g., 410, 520, 660) and garnet related transitions in the mantle, with constraints on the sharpness of these transitions. Observations of a depressed 660 are attributed to thermal variations, showing the spatial extent of the impinging Nazca slab. Prominent 520 arrivals near subducted slab material suggest this transition is sharpened to a thickness resonant with P'P' (~10km). The possibility of chemical heterogeneity is evidenced near the top of the mantle transition zone through complicated 410 amplitudes. The existence, depth, sharpness and strength of these reflectors/discontinuities offer new constraints on the dynamics and mineralogy of the mantle.

Spinel formation for stabilizing simulated nickel-laden sludge with aluminum-rich ceramic precursors.

PubMed

Shih, Kaimin; White, Tim; Leckie, James O

2006-08-15

The feasibility of stabilizing nickel-laden sludge from commonly available Al-rich ceramic precursors was investigated and accomplished with high nickel incorporation efficiency. To simulate the process, nickel oxide was mixed alternatively with gamma-alumina, corundum, kaolinite, and mullite and was sintered from 800 to 1480 degrees C. The nickel aluminate spinel (NiAl2O4) was confirmed as the stabilization phase for nickel and crystallized with efficiencies greater than 90% for all precursors above 1250 degrees C and 3-h sintering. The nickel-incorporation reaction pathways with these precursors were identified, and the microstructure and spinel yield were investigated as a function of sintering temperature with fixed sintering time. This study has demonstrated a promising process for forming nickel spinel to stabilize nickel-laden sludge from a wide range of inexpensive ceramic precursors, which may provide an avenue for economically blending waste metal sludges via the building industry processes to reduce the environmental hazards of toxic metals. The correlation of product textures and nickel incorporation efficiencies through selection of different precursors also provides the option of tailoring property-specific products.

CuInS2 Films Deposited by Aerosol-Assisted Chemical Vapor Deposition Using Ternary Single-Source Precursors

NASA Technical Reports Server (NTRS)

Jin, Michael; Banger, Kal; Harris, Jerry; Hepp, Aloysius

2003-01-01

Polycrystalline CuInS2 films were deposited by aerosol-assisted chemical vapor deposition using both solid and liquid ternary single-source precursors (SSPs) which were prepared in-house. Films with either (112) or (204/220) preferred orientation, had a chalcopyrite structure, and (112)-oriented films contained more copper than (204/220)-oriented films. The preferred orientation of the film is likely related to the decomposition and reaction kinetics associated with the molecular structure of the precursors at the substrate. Interestingly, the (204/220)-oriented films were always In-rich and were accompanied by a secondary phase. From the results of post-growth annealing, etching experiments, and Raman spectroscopic data, the secondary phase was identified as an In-rich compound. On the contrary, (112)-oriented films were always obtained with a minimal amount of the secondary phase, and had a maximum grain size of about 0.5 micron. Electrical and optical properties of all the films grown were characterized. They all showed p-type conduction with an electrical resistivity between 0.1 and 30 Omega-cm, and an optical band gap of approximately 1.46 eV +/- 0.02, as deposited. The material properties of deposited films revealed this methodology of using SSPs for fabricating chalcopyrite-based solar cells to be highly promising.

Multiday production of condensing organic aerosol mass in urban and forest outflow

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

Lee-Taylor, J.; Hodzic, A.; Madronich, S.

2015-01-16

Secondary organic aerosol (SOA) production in air masses containing either anthropogenic or biogenic (terpene-dominated) emissions is investigated using the explicit gas-phase chemical mechanism generator GECKO-A. Simulations show several-fold increases in SOA mass continuing for multiple days in the urban outflow, even as the initial air parcel is diluted into the regional atmosphere. The SOA mass increase in the forest outflow is more modest (~50%) and of shorter duration (1–2 days). The multiday production in the urban outflow stems from continuing oxidation of gas-phase precursors which persist in equilibrium with the particle phase, and can be attributed to multigenerational reaction productsmore » of both aromatics and alkanes, especially those with relatively low carbon numbers (C4–15). In particular we find large contributions from substituted maleic anhydrides and multi-substituted peroxide-bicyclic alkenes. The results show that the predicted production is a robust feature of our model even under changing atmospheric conditions and different vapor pressure schemes, and contradict the notion that SOA undergoes little mass production beyond a short initial formation period. The results imply that anthropogenic aerosol precursors could influence the chemical and radiative characteristics of the atmosphere over an extremely wide region, and that SOA measurements near precursor sources may routinely underestimate this influence.« less

Multiday production of condensing organic aerosol mass in urban and forest outflow

DOE PAGES

Lee-Taylor, J.; Hodzic, A.; Madronich, S.; ...

2015-01-16

Secondary organic aerosol (SOA) production in air masses containing either anthropogenic or biogenic (terpene-dominated) emissions is investigated using the explicit gas-phase chemical mechanism generator GECKO-A. Simulations show several-fold increases in SOA mass continuing for multiple days in the urban outflow, even as the initial air parcel is diluted into the regional atmosphere. The SOA mass increase in the forest outflow is more modest (~50%) and of shorter duration (1–2 days). The multiday production in the urban outflow stems from continuing oxidation of gas-phase precursors which persist in equilibrium with the particle phase, and can be attributed to multigenerational reaction productsmore » of both aromatics and alkanes, especially those with relatively low carbon numbers (C4–15). In particular we find large contributions from substituted maleic anhydrides and multi-substituted peroxide-bicyclic alkenes. The results show that the predicted production is a robust feature of our model even under changing atmospheric conditions and different vapor pressure schemes, and contradict the notion that SOA undergoes little mass production beyond a short initial formation period. Here, the results imply that anthropogenic aerosol precursors could influence the chemical and radiative characteristics of the atmosphere over an extremely wide region, and that SOA measurements near precursor sources may routinely underestimate this influence.« less

Chemical beam epitaxy of GaAs1-xNx using MMHy and DMHy precursors, modeled by ab initio study of GaAs(100) surfaces stability over As2, H2 and N2

NASA Astrophysics Data System (ADS)

Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

2017-06-01

Using ab initio calculations, a simple model for GaAs1-xNx vapor-phase epitaxy on (100) surface of GaAs was created. By studying As2 and H2 molecules adsorptions and As/N atom substitutions on (100) GaAs surfaces, we obtain a relative stability diagram of all stable surfaces under varying As2, H2, and N2 conditions. We previously proved that this model could describe the vapor-phase epitaxy of GaAs1-x Nx with simple, fully decomposed, precursors. In this paper, we show that in more complex reaction conditions using monomethylhydrazine (MMHy), and dimethylhydrazine (DMHy), it is still possible to use our model to obtain an accurate description of the temperature and pressure stability domains for each surfaces, linked to chemical beam epitaxy (CBE) growth conditions. Moreover, the different N-incorporation regimes observed experimentally at different temperature can be explain and predict by our model. The use of MMHy and DMHy precursors can also be rationalized. Our model should then help to better understand the conditions needed to obtain an high quality GaAs1-xNx using vapor-phase epitaxy.

Crystal nucleation and metastable bcc phase in charged colloids: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Ji, Xinqiang; Sun, Zhiwei; Ouyang, Wenze; Xu, Shenghua

2018-05-01

The dynamic process of homogenous nucleation in charged colloids is investigated by brute-force molecular dynamics simulation. To check if the liquid-solid transition will pass through metastable bcc, simulations are performed at the state points that definitely lie in the phase region of thermodynamically stable fcc. The simulation results confirm that, in all of these cases, the preordered precursors, acting as the seeds of nucleation, always have predominant bcc symmetry consistent with Ostwald's step rule and the Alexander-McTague mechanism. However, the polymorph selection is not straightforward because the crystal structures formed are not often determined by the symmetry of intermediate precursors but have different characters under different state points. The region of the state point where bcc crystal structures of large enough size are formed during crystallization is narrow, which gives a reasonable explanation as to why the metastable bcc phase in charged colloidal suspensions is rarely detected in macroscopic experiments.

Single-phase and well-dispersed Cu1.75S nanocrystals by ambient pressure diethylene glycol solution synthesis

NASA Astrophysics Data System (ADS)

Zheng, Xuerong; Jin, Zhengguo; Liu, Hui; Wang, Yueqiu; Wang, Xin; Du, Haiyan

2013-02-01

Single-phase, well-dispersed Cu1.75S nanocrystals were synthesized by an ambient pressure, hydrazine hydrate and ethylenediamine co-assisted diethylene glycol based solution chemical process using copper chloride and thioacetamide as precursors at the temperature range from 180 to 210 °C. Influence of hydrazine hydrate and ethylenediamine adding amounts, synthetic temperature on crystal growth, size distribution and optical properties of the synthesized Cu1.75S nanocrystals were investigated by XRD, TEM, HRTEM, EDX and UV-vis measurements. The synthetic reaction at above 200 °C grew flaky-shaped nanocrystals with relatively narrow size distribution. The formation of single-phase Cu1.75S nanocrystals in the diethylene glycol based solution process might be involved in the presence of intermediate [Cu(en)n]1+ and [Cu(NH3)4]2+ complexes in reaction solution, providing a stable Cu(I) and Cu(II) valent-mixed precursor.

Fullerene-like WS(2) nanoparticles and nanotubes by the vapor-phase synthesis of WCl(n) and H(2)S.

PubMed

Margolin, A; Deepak, F L; Popovitz-Biro, R; Bar-Sadan, M; Feldman, Y; Tenne, R

2008-03-05

Inorganic fullerene-like (IF) nanoparticles and nanotubes of WS(2) were synthesized by a gas phase reaction starting from WCl(n) (n = 4, 5, 6) and H(2)S. The effect of the various metal chloride precursors on the formation of the products was investigated during the course of the study. Various parameters have been studied to understand the growth and formation of the IF-WS(2) nanoparticles and nanotubes. The parameters that have been studied include flow rates of the various carrier gases, heating of the precursor metal chlorides and the temperature at which the reactions were carried out. The best set of conditions wherein maximum yields of the high quality pure-phase IF-WS(2) nanoparticles and nanotubes are obtained have been identified. A detailed growth mechanism has been outlined to understand the course of formation of the various products of WS(2).

Fullerene-like WS2 nanoparticles and nanotubes by the vapor-phase synthesis of WCln and H2S

NASA Astrophysics Data System (ADS)

Margolin, A.; Deepak, F. L.; Popovitz-Biro, R.; Bar-Sadan, M.; Feldman, Y.; Tenne, R.

2008-03-01

Inorganic fullerene-like (IF) nanoparticles and nanotubes of WS2 were synthesized by a gas phase reaction starting from WCln (n = 4, 5, 6) and H2S. The effect of the various metal chloride precursors on the formation of the products was investigated during the course of the study. Various parameters have been studied to understand the growth and formation of the IF-WS2 nanoparticles and nanotubes. The parameters that have been studied include flow rates of the various carrier gases, heating of the precursor metal chlorides and the temperature at which the reactions were carried out. The best set of conditions wherein maximum yields of the high quality pure-phase IF-WS2 nanoparticles and nanotubes are obtained have been identified. A detailed growth mechanism has been outlined to understand the course of formation of the various products of WS2.

Large scale synthesis of nanostructured zirconia-based compounds from freeze-dried precursors

NASA Astrophysics Data System (ADS)

Gómez, A.; Villanueva, R.; Vie, D.; Murcia-Mascaros, S.; Martínez, E.; Beltrán, A.; Sapiña, F.; Vicent, M.; Sánchez, E.

2013-01-01

Nanocrystalline zirconia powders have been obtained at the multigram scale by thermal decomposition of precursors resulting from the freeze-drying of aqueous acetic solutions. This technique has equally made possible to synthesize a variety of nanostructured yttria or scandia doped zirconia compositions. SEM images, as well as the analysis of the XRD patterns, show the nanoparticulated character of those solids obtained at low temperature, with typical particle size in the 10-15 nm range when prepared at 673 K. The presence of the monoclinic, the tetragonal or both phases depends on the temperature of the thermal treatment, the doping concentration and the nature of the dopant. In addition, Rietveld refinement of the XRD profiles of selected samples allows detecting the coexistence of the tetragonal and the cubic phases for high doping concentration and high thermal treatment temperatures. Raman experiments suggest the presence of both phases also at relatively low treatment temperatures.

The 520 km Discontinuity: No Longer Just the Middle Child of the Transition Zone

NASA Astrophysics Data System (ADS)

Houser, C.; Williams, Q.

2008-12-01

The 520 km discontinuity is more difficult to image and changes character laterally more relative to its siblings the 410 km and 660 km discontinuities. The 520 km discontinuity is thought to result from the phase change of β-spinel to γ-spinel, a transition which has a smaller impedance contrast than the olivine to β-spinel or the γ-spinel to perovskite and periclase transitions that are associated with the 410 km and 660 km discontinuities, respectively. In addition, there are gradual phase changes occurring in the pyroxene component of the mantle between the 410 km and 660 km discontinuity which complicate imaging and interpretation of the 520 km discontinuity. The best global coverage of discontinuity depth comes from the stacking of SS precursors, seismic phases that bounce off the discontinuities and arrive as precursors to the main SS phase. A recent study by Houser et al. (2008) contains the largest compilation of SS precursor measurements. However, since the 520 km discontinuity is not ubiquitously observed, its characteristics were not addressed. Here, we examine the geographic distribution (which is global, but not even) of high quality 520 km discontinuity measurements derived from precursors. The principal result is that the depth of the 520 km discontinuity has a higher correlation with tomographically-imaged high and low seismic velocities than either the 410 km or 660 km discontinuities. This stronger temperature sensitivity is in accord with determinations of the Clapeyron slopes of the differing transitions. Furthermore, this correlation is observed in a wide range of tectonic environments, and the prospect thus exists that the 520 km discontinuity will, where it is observed, provide a tighter bound on temperature within the transition zone than either of the other major discontinuities. Furthermore, improved constraints on the temperature distribution at depth may produce improved insight into the relative roles of thermal and compositional effects on the 660 km disctoninuity.

Life Cycle Assessment of III-V Precursors for Photovoltaic and Semiconductor Applications

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

Horowitz, Kelsey A; Smith, Brittany L.; Babbitt, Callie W.

This study provides detailed information on the manufacture of III-V metal organic vapor phase epitaxy precursors through extensive literature and patent research. This data informed a cradle-to-gate life cycle assessment of these chemicals. Reported impacts include cumulative energy demand and greenhouse gas emissions. The results were interpreted to identify sources of environmental burden within the life cycle and were compared to energy demand reported in previous studies.

Metal inks

DOEpatents

Ginley, David S; Curtis, Calvin J; Miedaner, Alex; van Hest, Marinus Franciscus Antonius Maria; Kaydanova, Tatiana

2014-02-04

Self-reducing metal inks and systems and methods for producing and using the same are disclosed. In an exemplary embodiment, a method may comprise selecting metal-organic (MO) precursor, selecting a reducing agent, and dissolving the MO precursor and the reducing agent in an organic solvent to produce a metal ink that remains in a liquid phase at room temperature. Metal inks, including self-reducing and fire-through metal inks, are also disclosed, as are various applications of the metal inks.

A rapid method to extract Seebeck coefficient under a large temperature difference

NASA Astrophysics Data System (ADS)

Zhu, Qing; Kim, Hee Seok; Ren, Zhifeng

2017-09-01

The Seebeck coefficient is one of the three important properties in thermoelectric materials. Since thermoelectric materials usually work under large temperature difference in real applications, we propose a quasi-steady state method to accurately measure the Seebeck coefficient under large temperature gradient. Compared to other methods, this method is not only highly accurate but also less time consuming. It can measure the Seebeck coefficient in both the temperature heating up and cooling down processes. In this work, a Zintl material (Mg3.15Nb0.05Sb1.5Bi0.49Te0.01) was tested to extract the Seebeck coefficient from room temperature to 573 K. Compared with a commercialized Seebeck coefficient measurement device (ZEM-3), there is ±5% difference between those from ZEM-3 and this method.

Isolation and Versatile Derivatization of an Unsaturated Anionic Silicon Cluster (Siliconoid)

PubMed Central

Willmes, Philipp; Leszczyńska, Kinga; Heider, Yannic; Abersfelder, Kai; Zimmer, Michael; Huch, Volker

2016-01-01

Abstract The characteristic features of bulk silicon surfaces are echoed in the related partially substituted—and thus unsaturated—neutral silicon clusters (siliconoids). The incorporation of siliconoids into more‐extended frameworks is promising owing to their unique electronic features, but further developments in this regard are limited by the notable absence of functionalized siliconoid derivatives until now. Herein we report the isolation and full characterization of the lithium salt of an anionic R5Si6‐siliconoid, thus providing the missing link between silicon‐based Zintl anions and siliconoid clusters. Proof‐of‐principle for the high potential of this species for the efficient transfer of the intact unsaturated R5Si6 moiety is demonstrated by clean reactions with representative electrophiles of Groups 13, 14, and 15. PMID:26800440

Lanthanide-Substituted Magnetite Nanoparticles Using a New Mixed Precursor Method by Thermoanaerobacter ethanolicus

NASA Astrophysics Data System (ADS)

Moon, J.; Roh, Y.; Yeary, L. W.; Lauf, R. J.; Phelps, T. J.

2006-12-01

A metal reducing bacterium, Thermoanaerobacter ethanolicus successfully converted the precursor of L (lanthanide)-mixed akaganeite (LxFe1-xOOH) phase to L-substituted magnetite (LyFe3-yO4) while avoiding the potentially toxic effects of soluble L-ions. Antibiotic elements, lanthanide (Nd, Gd, Tb, Ho, and Er)-substituted magnetites were produced by microbial fermentation using LxFe1-xOOH, where x was up to 0.02 which is equivalent to 0.72 mM. Combining lanthanides into the akaganeite precursor phase mitigated some of the toxicity when compared to the traditional method by using pure akaganeite and the dissolved L-salt form. This new technique showed that an upper limit of L-concentrations between 0.02 and 0.1 mM might suppress bacterial activity. At the equivalent L-cation mole fraction, the traditional method increased the concentration of soluble toxic L ions in the final media. The precursor method enabled production of microbially synthesized L- substituted magnetite with an L-concentration 36-fold greater than could be obtained when the lanthanides were added as soluble salts. These results were confirmed by protein assay. The increase of L-concentration in the magnetite evidently manipulates its physical properties such as decreasing Curie temperature and decreasing saturation magnetism of L-substituted magnetite. This mixed precursor method can therefore be used to extend the application for nanofermentation and other bacterial synthesis fields where there is a need for economically low-energy consumable microbial production of nanoscale materials that should involve toxic or inhibitory elements to bacterial growth.

Fabrication and Characterization of CZTS Thin Films Prepared by the Sulfurization of RF-Sputtered Stacked Metal Precursors

NASA Astrophysics Data System (ADS)

Abusnina, Mohamed; Moutinho, Helio; Al-Jassim, Mowafak; DeHart, Clay; Matin, Mohammed

2014-09-01

In this work, Cu2ZnSnS4 (CZTS) thin films were prepared by the sulfurization of metal precursors deposited sequentially via radio frequency magnetron sputtering on Mo-coated soda-lime glass. The stack order of the precursors was Mo/Zn/Sn/Cu. Sputtered precursors were annealed in sulfur atmosphere with nine different conditions to study the impact of sulfurization time and substrate temperature on the structural, morphological, and optical properties of the final CZTS films. X-ray fluorescence was used to determine the elemental composition ratio of the metal precursors. Final CZTS films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). XRD and EDS were combined to investigate the films' structure and to identify the presence of secondary phases. XRD analysis indicated an improvement in film crystallinity with an increase of the substrate temperature and annealing times. Also indicated was the minimization and/or elimination of secondary phases when the films experienced longer annealing time. EDS revealed slight Sn loss in films sulfurized at 550°C; however, an increase of the sulfurization temperature to 600°C did not confirm these results. SEM study showed that films treated with higher temperatures exhibited dense morphology, indicating the completion of the sulfurization process. The estimated absorption coefficient was on the order of 104 cm-1 for all CZTS films, and the values obtained for the optical bandgap energy of the films were between 1.33 eV and 1.52 eV.

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

NASA Astrophysics Data System (ADS)

Cook, Ryan D.; Lin, Ying-Hsuan; Peng, Zhuoyu; Boone, Eric; Chu, Rosalie K.; Dukett, James E.; Gunsch, Matthew J.; Zhang, Wuliang; Tolic, Nikola; Laskin, Alexander; Pratt, Kerri A.

2017-12-01

Organic aerosol formation and transformation occurs within aqueous aerosol and cloud droplets, yet little is known about the composition of high molecular weight organic compounds in cloud water. Cloud water samples collected at Whiteface Mountain, New York, during August-September 2014 were analyzed by ultra-high-resolution mass spectrometry to investigate the molecular composition of dissolved organic carbon, with a focus on sulfur- and nitrogen-containing compounds. Organic molecular composition was evaluated in the context of cloud water inorganic ion concentrations, pH, and total organic carbon concentrations to gain insights into the sources and aqueous-phase processes of the observed high molecular weight organic compounds. Cloud water acidity was positively correlated with the average oxygen : carbon ratio of the organic constituents, suggesting the possibility for aqueous acid-catalyzed (prior to cloud droplet activation or during/after cloud droplet evaporation) and/or radical (within cloud droplets) oxidation processes. Many tracer compounds recently identified in laboratory studies of bulk aqueous-phase reactions were identified in the cloud water. Organosulfate compounds, with both biogenic and anthropogenic volatile organic compound precursors, were detected for cloud water samples influenced by air masses that had traveled over forested and populated areas. Oxidation products of long-chain (C10-12) alkane precursors were detected during urban influence. Influence of Canadian wildfires resulted in increased numbers of identified sulfur-containing compounds and oligomeric species, including those formed through aqueous-phase reactions involving methylglyoxal. Light-absorbing aqueous-phase products of syringol and guaiacol oxidation were observed in the wildfire-influenced samples, and dinitroaromatic compounds were observed in all cloud water samples (wildfire, biogenic, and urban-influenced). Overall, the cloud water molecular composition depended on air mass source influence and reflected aqueous-phase reactions involving biogenic, urban, and biomass burning precursors.

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

Cook, Ryan D.; Lin, Ying-Hsuan; Peng, Zhuoyu

Organic aerosol formation and transformation occurs within aqueous aerosol and cloud droplets, yet little is known about the composition of high molecular weight organic compounds in cloud water. Cloud water samples collected at Whiteface Mountain, New York, during August-September 2014 were analyzed by ultra-high-resolution mass spectrometry to investigate the molecular composition of dissolved organic carbon, with a focus on sulfur- and nitrogen-containing compounds. Organic molecular composition was evaluated in the context of cloud water inorganic ion concentrations, pH, and total organic carbon concentrations to gain insights into the sources and aqueous-phase processes of the observed high molecular weight organic compounds.more » Cloud water acidity was positively correlated with the average oxygen : carbon ratio of the organic constituents, suggesting the possibility for aqueous acid-catalyzed (prior to cloud droplet activation or during/after cloud droplet evaporation) and/or radical (within cloud droplets) oxidation processes. Many tracer compounds recently identified in laboratory studies of bulk aqueous-phase reactions were identified in the cloud water. Organosulfate compounds, with both biogenic and anthropogenic volatile organic compound precursors, were detected for cloud water samples influenced by air masses that had traveled over forested and populated areas. Oxidation products of long-chain (C 10-12) alkane precursors were detected during urban influence. Influence of Canadian wildfires resulted in increased numbers of identified sulfur-containing compounds and oligomeric species, including those formed through aqueous-phase reactions involving methylglyoxal. Light-absorbing aqueous-phase products of syringol and guaiacol oxidation were observed in the wildfire-influenced samples, and dinitroaromatic compounds were observed in all cloud water samples (wildfire, biogenic, and urban-influenced). Overall, the cloud water molecular composition depended on air mass source influence and reflected aqueous-phase reactions involving biogenic, urban, and biomass burning precursors.« less

Out-of-equilibrium Sm Fe based phases

NASA Astrophysics Data System (ADS)

Djéga-Mariadassou, C.; Bessais, L.

2008-02-01

Structure and magnetic properties of nanocrystalline P6/mmm out-of-equilibrium precursors of hard magnetic R-3m Sm2(Fe,M)17C (M=Ga,Si,) and I4/mmm Sm(Fe,Co,Ti)11 equilibrium phases, are presented. Their structure is explained with a model ground on the R1 - s T5 + 2 s formula (R=rare-earth, s=vacancy rate, T=transition metal) where s Sm atoms are statistically substituted by s transition metal pairs. The Rietveld analysis (RA) provides the stoichiometry of the precursors, 1:9 and 1:10, respectively precursor of 2:17 and 1:12 phases. The interpretation of the Mössbauer spectra of the 1:9 and 1:10 phases, is based on the correlation between δ and the Wigner Seitz Cell volumes, calculated from the structural parameters. The δ behaviour of each crystallographic site versus Co content, defines the Co location while it confirms that of Si and Ga obtained by RA. Substitution occurs in 3 g site, whatever Co or M. The Sm(Fe,Co,Ti)10 and Sm(Fe,M)9C Curie temperature (Tc) are compared to those of the equilibrium phases, the effects of Fe substitution and C addition are discussed. The maximum μ 0Hc is obtained for low M or Co content, for auto-coherent diffraction domain size ˜30 nm. SmFe8.75Ga0.25C and SmFe8.75Si0.25C with Tc of 680 and 690 K, show respectively Mr and μ 0Hc of 58 emu/g, 27 kOe and 95 emu/g, 15 kOe, values higher than those obtained for Sm2(Fe,M)17 carbides.

Ferroelectric/ferrimagnetic composite ceramics with depressed interfacial reaction and low dielectric loss

NASA Astrophysics Data System (ADS)

Zheng, Hui; Weng, Wenjian; Han, Gaorong; Du, Piyi

2014-10-01

(1-x)BaTiO3/xNi0.5Zn0.5Fe2O4 (NZFO) ferroelectric/ferrimagnetic composite ceramics with restricted interfacial reaction were prepared by adopting fine NZFO precursors synthesized by combustion method. The dielectric dispersion, loss, and conductivity are significantly reduced at most compositions, particularly at concentrations below the percolation threshold. At x = 0.3, a frequency-stable permittivity of 2300 and a low loss of 0.04 at 1 kHz is realized. The recovery of the dielectric/electric properties is attributed to the interfacial amorphous phase introduced by the fine NZFO precursors, which can act as barrier for ionic inter-diffusion between the two phases and hopping conduction among ferrites.

Calcination and solid state reaction of ceramic-forming components to provide single-phase superconducting materials having fine particle size

DOEpatents

Balachandran, Uthamalingam; Poeppel, Roger B.; Emerson, James E.; Johnson, Stanley A.

1992-01-01

An improved method for the preparation of single phase, fine grained ceramic materials from precursor powder mixtures where at least one of the components of the mixture is an alkali earth carbonate. The process consists of heating the precursor powders in a partial vacuum under flowing oxygen and under conditions where the partial pressure of CO.sub.2 evolved during the calcination is kept to a very low level relative to the oxygen. The process has been found particularly suitable for the preparation of high temperature copper oxide superconducting materials such as YBa.sub.2 Cu.sub.3 O.sub.x "123" and YBa.sub.2 Cu.sub.4 O.sub.8 "124".

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

Seinfeld, John H.

This project addressed the following research need in the Atmospheric System Research (ASR) Science and Program Plan: "Measurements downwind of urban sources of aerosol particles and precursor gases have shown that the mass concentration of secondary organic aerosol (SOA) can be several-fold greater than can be explained on the basis of current model calculations using observed precursor concentrations. ASR will continue conducting laboratory experiments on both gas-phase and aqueous-phase SOA formation to characterize the particle formation and the organic gases that react to form new organic aerosol material on aerosol seeds. ASR will use these experiments to guide the developmentmore » of comprehensive chemical mechanisms... to guide the development of parameterizations that are simple enough to be applied to aerosol life cycle models."« less

Synthesis and structural properties of (Y, Sr)(Ti, Fe, Nb)O3-δ perovskite nanoparticles fabricated by modified polymer precursor method

NASA Astrophysics Data System (ADS)

Miruszewski, T.; Gdaniec, P.; Karczewski, J.; Bochentyn, B.; Szaniawska, K.; Kupracz, P.; Prześniak-Welenc, M.; Kusz, B.

2016-09-01

The yttrium, iron and niobium doped-SrTiO3 powders have been successfully fabricated by a modified low-temperature synthesis method from a polymer complex. The usage of strontium hydroxide precursor instead of conventional strontium nitrate or strontium carbonate provides to the possibility of significant decrease of annealing temperature. It allows to prepare a material with sphere-shape grains of nanometric size (15-70 nm). The results of thermal analysis indicate that the crystallization of precursor takes place at different stages. The product after heat treatment at 600 °C for 3 h in air was also characterized by X-Ray diffraction method (XRD) and Fourier transform - infrared spectroscopy (FT-IR). After the crystallization and the impurity removal process, a single-phase material was obtained in case of all analyzed samples. The morphology of obtained nano-powders was also studied by a scanning electron microscopy (SEM). It can be concluded, that this method allows obtaining a perovskite phase of a metal doped SrTiO3 with nanometric particles.

Spectroscopic Identification of p-CHLORO-α-METHYLBENZYL Radical in the Gas Phase

NASA Astrophysics Data System (ADS)

Lee, Seung Woon; Lee, Gi Woo; Lee, Sang Kuk

2009-06-01

We report the first spectroscopic identification of the p-fluoro-α-methylbenzyl radical in the gas phase. Precursor p-fluoro-ethylbenzene seeded in a large amount of inert carrier gas helium was electrically discharged to produce the benzyl-type radicals in a corona excited supersonic expansion using a pinhole-type glass nozzle, from which the vibronic emission spectrum was recorded in the visible region using a long path monochromator. From an analysis of the spectrum observed, we found the formation of p-fluoro-α-methylbenzyl radical as well as p-fluorobenzyl radical in the jet from the precursor. After eliminating the bands belonging to p-fluorobenzyl radical using the known data, we identified spectroscopically the formation of the p-fluoro-α-methylbenzyl radical, in which the energy of the D_1 → D_0 electronic transition and a few vibrational mode frequencies in the ground electronic state were determined by comparison with those from an ab initio calculation and with those from the known data of the precursor. S. K. Lee and D. Y. Baek Chem. Phys. Lett. 301(3-4), 407-412 (1999).

High-Resolution P'P' Precursor Imaging of Nazca-South America Plate Boundary Zones and Inferences for Transition Zone Temperature and Composition

NASA Astrophysics Data System (ADS)

Gu, Y. J.; Schultz, R.

2013-12-01

Knowledge of upper mantle transition zone stratification and composition is highly dependent on our ability to efficiently extract and properly interpret small seismic arrivals. A promising high-frequency seismic phase group particularly suitable for a global analysis is P'P' precursors, which are capable of resolving mantle structures at vertical and lateral resolution of approximately 5 and 200 km, respectively, owing to their shallow incidence angle and small, quasi-symmetric Fresnel zones. This study presents a simultaneous analysis of SS and P'P' precursors based on deconvolution, Radon transform and depth migration. Our multi-resolution survey of the mantle near Nazca-South America subduction zone reveals both olivine and garnet related transitions at depth below 400 km. We attribute a depressed 660 to thermal variations, whereas compositional variations atop the upper-mantle transition zone are needed to explain the diminished or highly complex reflected/scattered signals from the 410 km discontinuity. We also observe prominent P'P' reflections within the transition zone, especially near the plate boundary zone where anomalously high reflection amplitudes result from a sharp (~10 km thick) mineral phase change resonant with the dominant frequency of the P'P' precursors. Near the base of the upper mantle, the migration of SS precursors shows no evidence of split reflections near the 660-km discontinuity, but potential majorite-ilmenite (590-640 km) and ilmenite-perovskite transitions (740-750 km) are identified based on similarly processed high-frequency P'P' precursors. At nominal mantle temperatures these two phase changes may be seismically indistinguishable, but colder mantle conditions from the descending Nazca plate, the presence of water and variable Fe contents may cause sufficient separation for a reliable analysis. In addition, our preliminary results provide compelling evidence for multiple shallow lower-mantle reflections (at ~800 km) along the elongated plate boundary zones of South America. Slab stagnation at the base of the transition zone could play a key role, though a proper interpretation of this finding would likely entail compositional (rather than strictly thermal) variations in the vicinity of the descending oceanic crust and lithosphere. Overall, the resolution and sensitivity differences between low/intermediate- S and high-frequency P wave reflections are key considerations toward reconciling seismic and mineralogical models of transition zone structure, both at the study location and worldwide.

Precursor routes to quaternary intermetallics: Synthesis, crystal structure, and physical properties of clathrate-II Cs8Na16Al24Si112

NASA Astrophysics Data System (ADS)

Wei, Kaya; Dong, Yongkwan; Nolas, George S.

2016-05-01

A new quaternary clathrate-II composition, Cs8Na16Al24Si112, was synthesized by kinetically controlled thermal decomposition (KCTD) employing both NaSi and NaAlSi as the precursors and CsCl as a reactive flux. The crystal structure and composition of Cs8Na16Al24Si112 were investigated using both Rietveld refinement and elemental analysis, and the temperature dependent transport properties were investigated. Our results indicate that KCTD with multiple precursors is an effective method for the synthesis of multinary inorganic phases that are not easily accessible by traditional solid-state synthesis or crystal growth techniques.

Synthesis and Photoluminescence Characteristics of Eu(3+)-Doped Molybdates Nanocrystals.

PubMed

Li, Fuhai; Yu, Lixin; Wei, Shuilin; Sun, Jiaju; Chen, Weiqing; Sun, Wei

2015-12-01

In this paper, the Eu(3+)-doped molybdate (CaMoO4, ZnMoO4 and BaMoO4) phosphors have been prepared by a hydrothermal method through modulating the pH value of the precursor solution (pH = 8, 10, and 12, respectively). The crystalline phase, morphology, photoluminescent properties of the prepared samples were systematically characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence (PL) spectra. The results indicate that the photoluminescence and morphology can be affected by the precursor solution. And the growth of the ZnMoO4 crystals also can be affected by the pH value of the precursor solution.

Analysis and identification of astaxanthin and its carotenoid precursors from Xanthophyllomyces dendrorhous by high-performance liquid chromatography.

PubMed

Lu, Mingbo; Zhang, Yang'e; Zhao, Chunfang; Zhou, Pengpeng; Yu, Longjiang

2010-01-01

This study presents an HPLC method for simultaneous analysis of astaxanthin and its carotenoid precursors from Xanthophyllomyces dendrorhous. The HPLC method is accomplished by employing a C18 column and the mobile phase methanol/water/acetonitrile/ dichloromethane (70:4:13:13, v/v/v/v). Astaxanthin is quantified by detection at 480 nm. The carotenoid precursors are identified by LC-APCI-MS and UV-vis absorption spectra. Peaks showed in the HPLC chromatogram are identified as carotenoids in the monocyclic biosynthetic pathway or their derivatives. In the monocyclic carotenoid pathway, 3,3'-dihydroxy-beta,psi-carotene-4,4'-dione (DCD) is produced through gamma-carotene and torulene.

Imaging measurements of atomic iron concentration with laser-induced fluorescence in a nanoparticle synthesis flame reactor

NASA Astrophysics Data System (ADS)

Hecht, C.; Kronemayer, H.; Dreier, T.; Wiggers, H.; Schulz, C.

2009-01-01

The iron-atom concentration distribution as well as the gas-phase temperature was measured via laser-induced fluorescence (LIF) during iron-oxide nanoparticle synthesis in a low-pressure hydrogen/oxygen/argon flame reactor using ironpentacarbonyl (Fe(CO)5) as precursor. Temperature measurements based on multi-line NO-LIF imaging are used to correct for temperature-dependent ground-state populations. The concentration measurement is calibrated based on line-of-sight absorption measurements. The influence of the precursor on the flame is observed at precursor concentrations larger than 70 ppm as the flame front moves closer to the burner surface with increasing Fe(CO)5 concentration.

Spectroscopic evidence of α-methylbenzyl radical in the gas phase

NASA Astrophysics Data System (ADS)

Lee, Gi Woo; Ahn, Hyeon Geun; Kim, Tae Kyu; Lee, Sang Kuk

2008-11-01

We report the observation of the spectroscopic evidence of the α-methylbenzyl radical in a corona excited supersonic expansion using a pinhole-type glass nozzle for the first time. The precursors, toluene, ethylbenzene, and isopropylbenzene, seeded in a large amount of inert carrier gas helium, were electrically discharged to produce benzyl-type radicals as a result of the breaking off of a C-H or a C-C bond from the alkyl chain. The vibronic emission spectra, obtained in the visible region from the precursors, were compared to identify the species generated in the corona discharge of the precursors, from which we found the spectroscopic evidence of the α-methylbenzyl radical.

Tuning the optical properties of ZnO nanorods by variation of precursor concentration through hydrothermal method

NASA Astrophysics Data System (ADS)

Kumari, Lakshmi; Kar, Asit Kumar

2018-05-01

ZnO nanorods with varying precursor concentration have been successfully synthesized by the hydrothermal method. The effect of the precursor concentration on the structural, morphological and optical properties of the resulting nanorods was investigated by means of X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), UV-Vis spectroscopy and photoluminescence (PL) spectroscopy. The crystalline structural characterization demonstrated that the synthesized materials crystallize in pure ZnO wurtzite structure without any other secondary phase. SEM micrographs demonstrate nanorod type features in all the samples. In addition, they show that increase of precursor concentration changes the length and diameter of nanorods. The UV-Vis studies show a strong absorption band in UV region at 373 nm attributed to the band-edge absorption of wurtzite hexagonal ZnO, blue shifted relative to its bulk form (380 nm). The PL spectra of obtained nanorods excited at 360 nm present broad visible emission. Moreover, as the visible region (from 510 to 550 nm) is concerned, it is speculated that the increase of the precursor concentration affects strongly the kind of interstitial defects (Oi, Zni and Vo) formed in ZnO nanorods. The luminescence intensity decreases with the increase of precursor concentration.

Transition Metal Dichalcogenide Growth via Close Proximity Precursor Supply

NASA Astrophysics Data System (ADS)

O'Brien, Maria; McEvoy, Niall; Hallam, Toby; Kim, Hye-Young; Berner, Nina C.; Hanlon, Damien; Lee, Kangho; Coleman, Jonathan N.; Duesberg, Georg S.

2014-12-01

Reliable chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) is currently a highly pressing research field, as numerous potential applications rely on the production of high quality films on a macroscopic scale. Here, we show the use of liquid phase exfoliated nanosheets and patterned sputter deposited layers as solid precursors for chemical vapour deposition. TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup. A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented. Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, scanning electron microscopy and electrical transport measurements reveal the high quality of the TMD samples produced. Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components.

Thermal Studies of New Precursors to Indium-tin Oxides for Use as Sensor Materials in the Detection of NO(x)

NASA Technical Reports Server (NTRS)

Goldsby, J. C.; Kacik, T.; Hockensmith, C. M.

1999-01-01

Control of combustion product emissions in both sub and super-sonic jet engines can be facilitated by measurement of NO(x) levels with metal oxide sensors, In2O3, metal-doped SnO2, and SnO, (as well as other materials) show resistivity changes in the presence of NO(x), but often their sensitivity, stability, and selectivity are low. This study was designed to develop new synthetic pathways to precursors that produce high purity, two phase In2O3-SnO2. The precursors were formed by complexation of tin with any oxide ligands to give the ammonium salt (NH4). Thermal studies of these precursors were carried out by thermal gravimetry (TG) and differential scanning calorimetry (DSC). Further studies by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR) were also conducted.

Subeutectic Synthesis of Epitaxial Si-NWs with Diverse Catalysts Using a Novel Si Precursor

PubMed Central

2010-01-01

The applicability of a novel silicon precursor with respect to reasonable nanowire (NW) growth rates, feasibility of epitaxial NW growth and versatility with respect to diverse catalysts was investigated. Epitaxial growth of Si-NWs was achieved using octochlorotrisilane (OCTS) as Si precursor and Au as catalyst. In contrast to the synthesis approach with SiCl4 as precursor, OCTS provides Si without the addition of H2. By optimizing the growth conditions, effective NW synthesis is shown for alternative catalysts, in particular, Cu, Ag, Ni, and Pt with the latter two being compatible to complementary metal-oxide-semiconductor technology. As for these catalysts, the growth temperatures are lower than the lowest liquid eutectic; we suggest that the catalyst particle is in the solid state during NW growth and that a solid-phase diffusion process, either in the bulk, on the surface, or both, must be responsible for NW nucleation. PMID:20843058

Synthesis, Dielectric, Electrical and Optical characterization of ZnO synthesized by chemical route using polymer precursors

NASA Astrophysics Data System (ADS)

Mishra, Raman; Bajpai, P. K.

2011-11-01

Nano-size ZnO (particle size 7.8 nm) have been prepared from a versatile, efficient and technically simple polymer matrix based precursor solution. The precursor solution constituted of zinc nitrates with polymer PVA in presence of mono-/disaccharides. Annealing the precursor mass at 900 °C single phase zinc oxide nano-particles are obtained. X-ray diffraction analysis confirms hexagonal crystal structure with lattice parameter a = b = 3.261 A0, c = 5.220 A0. The estimated average particle size obtained from XRD data is ≈7.8 nm. The impedance analysis reveals that the grain resistance decreases with increase in temperature as expected for a semi-conducting material. The relaxation is polydispersive and conduction is mainly through grains. Optical properties and AC/DC conduction activation energies are estimated from Arrhenius plots and conduction mechanism is discussed.

Role of Elemental Sulfur in Forming Latent Precursors of H2S in Wine.

PubMed

Jastrzembski, Jillian A; Allison, Rachel B; Friedberg, Elle; Sacks, Gavin L

2017-12-06

The level of hydrogen sulfide (H 2 S) can increase during abiotic storage of wines, and potential latent sources of H 2 S are still under investigation. We demonstrate that elemental sulfur (S 0 ) residues on grapes not only can produce H 2 S during fermentation but also can form precursors capable of generating additional H 2 S after bottle storage for 3 months. H 2 S could be released from S 0 -derived precursors by addition of a reducing agent (TCEP), but not by addition of strong brine to induce release of H 2 S from metal sulfide complexes. The size of the TCEP-releasable pool varied among yeast strains. Using the TCEP assay, multiple polar S 0 -derived precursors were detected following normal-phase preparative chromatography. Using reversed-phase liquid chromatography and high-resolution mass spectrometry, we detected an increase in the levels of diglutathione trisulfane (GSSSG) and glutathione disulfide (GSSG) in S 0 -fermented red wine and an increase in the levels of glutathione S-sulfonate (GSSO 3 - ) and tetrathionate (S 4 O 6 2- ) in S 0 -fermented white wine as compared to controls. GSSSG, but not S 4 O 6 2- , was shown to evolve H 2 S in the presence of TCEP. Pathways for the formation of GSSSG, GSSG, GSSO 3 - , and S 4 O 6 2- from S 0 are proposed.

Cryptic color change in a crab spider (Misumena vatia): identification and quantification of precursors and ommochrome pigments by HPLC.

PubMed

Riou, Mickaël; Christidès, Jean-Philippe

2010-04-01

Mimicry is used widely by arthropods to survive in a hostile environment. Often mimicry is associated with the production of chemical compounds such as pigments. In crab spiders, the change of color is based on a complex physiological process that still is not understood. The aim of this study was to identify and quantify the ommochrome pigments and precursors responsible for the color change in the mimetic crab spider Misumena vatia (Thomisidae). A modified high performance reverse phase ion-pair chromatography technique enabled us to separate and quantify the ommochrome pigments, their precursors, and related metabolites in individual spiders. Compounds such as tryptophan, kynurenine, and kynurenic acid occurred only or mainly in white crab spiders. In contrast, compounds such as 3-hydroxy-kynurenine, xanthommatin, and ommatin D occurred only or mainly in yellow crab spiders. Factor analysis ranked the different color forms in accordance with their metabolites. The biochemical results enabled us to associate the different phases of formation of pigment granules with specific metabolites. Yellow crab spiders contain many unknown ommochrome-like compounds not present in white crab spiders. We also found large quantities of decarboxylated xanthommatin, whose role as precursor of new pathways in ommochrome synthesis needs to be assessed. The catabolism of ommochromes, a process occurring when spiders revert from yellow to white, warrants further study.

The influence of the precursor compositional ratio on Cu2ZnSnS4 films prepared by using sulfurization of the metallic precursor

NASA Astrophysics Data System (ADS)

Amal, Muhamad I.; Kim, Kyoo Ho

2013-12-01

Cu2ZnSnS4 (CZTS) films were prepared by using the sulfurization of sputtered metallic precursors. The compositional ratio of the CZTS films was slightly different compared to their initial metallic precursors due to elemental loss during annealing. The Cu/(Zn+Sn) ratio for the CZTS-1, CZTS-2 and CZTS-3 films were 0.91, 1.06 and 1.21, respectively. In addition, all films had a compositional ratio of Zn/Sn >1. The grain sizes of the CZTS films increased with increasing Cu ratio. X-ray diffraction and Raman spectroscopy showed that the CZTS films with an excess of copper and zinc had secondary phases of Cu2SnS3 and ZnS. The optical band gap and absorption coefficient for all CZTS films in the range of the experimental compositions were calculated to be 1.5 eV and >104 cm-1, respectively. The presence of secondary phases related to compositional ratio in the CZTS films influenced the electrical properties. The CZTS-1 film with a Cu-poor and Zn-rich composition whose a carrier concentration, an electrical mobility, and a resistivity values were 2.29 × 1018 cm-3, 10.29 cm2 V-1 s-1, 3.16 Ω cm, is the most suitable for solar-cell applications.

OM-VPE growth of Mg-doped GaAs. [OrganoMetallic-Vapor Phase Epitaxy

NASA Technical Reports Server (NTRS)

Lewis, C. R.; Dietze, W. T.; Ludowise, M. J.

1982-01-01

The epitaxial growth of Mg-doped GaAs by the organometallic vapor phase epitaxial process (OM-VPE) has been achieved for the first time. The doping is controllable over a wide range of input fluxes of bis (cyclopentadienyl) magnesium, (C5H5)2Mg, the organometallic precursor to Mg.

Nucleation, growth and evolution of calcium phosphate films on calcite.

PubMed

Naidu, Sonia; Scherer, George W

2014-12-01

Marble, a stone composed of the mineral calcite, is subject to chemically induced weathering in nature due to its relatively high dissolution rate in acid rain. To protect monuments and sculpture from corrosion, we are investigating the application of thin layers of hydroxyapatite (HAP) onto marble. The motivation for using HAP is its low dissolution rate and crystal and lattice compatibility with calcite. A mild, wet chemical synthesis route, in which diammonium hydrogen phosphate salt was reacted with marble, alone and with cationic and anionic precursors under different reaction conditions, was used to produce inorganic HAP layers on marble. Nucleation and growth on the calcite substrate was studied, as well as metastable phase evolution, using scanning electron microscopy, grazing incidence X-ray diffraction, and atomic force microscopy. Film nucleation was enhanced by surface roughness. The rate of nucleation and the growth rate of the film increased with cationic (calcium) and anionic (carbonate) precursor additions. Calcium additions also influenced phase formation, introducing a metastable phase (octacalcium phosphate) and a different phase evolution sequence. Copyright © 2014 Elsevier Inc. All rights reserved.

Ferromagnetism in spin-coated cobalt-doped TiO2 thin films and the role of crystalline phases

NASA Astrophysics Data System (ADS)

Salazar Cuaila, J. L.; Alayo, W.; Avellaneda, César O.

2017-11-01

Two sets of Cobalt-doped (1-10% at) TiO2 thin films, for different molar concentrations of the Ti precursor (0.3 and 0.5 mol/L), have been deposited onto Si substrates by combining the Sol Gel process and the Spin Coating technique. The structure of the samples was studied by X-ray reflectivity (XRR) and X-ray diffraction (XRD) and their magnetic properties were analyzed by magnetization measurements as a function of the applied magnetic field. The XRR results provided the thickness and interfacial roughness of the films, while XRD patterns revealed the crystalline phases and lattice parameters. Room temperature ferromagnetic behaviour was observed for some of the atomic Co concentrations by the magnetization measurements. This behaviour has been correlated to the crystalline phases, which were found to be modified by both the molar ratio of Ti precursor and the concentration of the Co dopant. A suppression of ferromagnetism is observed for some atomic Co fractions and it was attributed to the presence of secondary crystalline phases.

Formation of complex organic molecules in cold objects: the role of gas-phase reactions

NASA Astrophysics Data System (ADS)

Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney

2015-04-01

While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ≳ 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.

The stannylphosphide anion reagent sodium bis(triphenylstannyl) phosphide: synthesis, structural characterization, and reactions with indium, tin, and gold electrophiles.

PubMed

Cummins, Christopher C; Huang, Chao; Miller, Tabitha J; Reintinger, Markus W; Stauber, Julia M; Tannou, Isabelle; Tofan, Daniel; Toubaei, Abouzar; Velian, Alexandra; Wu, Gang

2014-04-07

Treatment of P4 with in situ generated [Na][SnPh3] leads to the formation of the sodium monophosphide [Na][P(SnPh3)2] and the Zintl salt [Na]3[P7]. The former was isolated in 46% yield as the crystalline salt [Na(benzo-15-crown-5)][P(SnPh3)2] and used to prepare the homoleptic phosphine P(SnPh3)3, isolated in 67% yield, as well as the indium derivative (XL)2InP(SnPh3)2 (XL = S(CH2)2NMe2), isolated in 84% yield, and the gold complex (Ph3P)AuP(SnPh3)2. The compounds [Na(benzo-15-crown-5)][P(SnPh3)2], P(SnPh3)3, (XL)2InP(SnPh3)2, and (Ph3P)AuP(SnPh3)2 were characterized using multinuclear NMR spectroscopy and X-ray crystallography. The bonding in (Ph3P)AuP(SnPh3)2 was dissected using natural bond orbital (NBO) methods, in response to the observation from the X-ray crystal structure that the dative P:→Au bond is slightly shorter than the shared electron-pair P-Au bond. The bonding in (XL)2InP(SnPh3)2 was also interrogated using (31)P and (13)C solid-state NMR and computational methods. Co-product [Na]3[P7] was isolated in 57% yield as the stannyl heptaphosphide P7(SnPh3)3, following salt metathesis with ClSnPh3. Additionally, we report that treatment of P4 with sodium naphthalenide in dimethoxyethane at 22 °C is a convenient and selective method for the independent synthesis of Zintl ion [Na]3[P7]. The latter was isolated as the silylated heptaphosphide P7(SiMe3)3, in 67% yield, or as the stannyl heptaphosphide P7(SnPh3)3 in 65% yield by salt metathesis with ClSiMe3 or ClSnPh3, respectively.

Amorphous Calcium Carbonate in Biomineralization: Stable and Precursor Phases

NASA Astrophysics Data System (ADS)

Weiner, S.

2003-12-01

The biological formation of the crystalline polymorphs of calcium carbonate, aragonite and calcite, is widespread. The less stable polymorphs, vaterite and monohydrocalcite are also formed by some organisms. Surprisingly, the highly unstable phase, amorphous calcium carbonate (ACC), is formed by a variety of organisms from different phyla. Most of these are stable at least within the lifetime of the organism. The stable forms all have a stoichiometry of CaCO3.H2O. Despite the fact that they do not diffract X-rays. Studies of their short range order by EXAFS, reveal species specific variations in the number and distances of atoms that surround the calcium ion. Proteins extracted from stable biogenic ACC are able to stabilize the phase in vitro. ACC has also been identified as a transient precursor phase during the formation of the calcitic larval spicule of the sea urchin and the formation of the larval shell of a bivalve. The transient form has little or no water associated with the CaCO3. Preliminary EXAFS data suggest that the short range order of the sea urchin spicule transient ACC resembles calcite. Proteins extracted from these spicules are able to stabilize ACC provided Mg is present in the solution. As the mollusks and the echinoderms are on two different branches of the animal phylogenetic tree, it is conceivable that the strategy of using ACC as a precursor phase at least for larval mineralization may be widespread. It has yet to be shown that it is used by adults of either phylum. The manner in which organisms precipitate, stabilize and destabilize if necessary, this highly metastable phase of calcium carbonate presents many fascinating and enigmatic questions, whose solutions could well contribute to a better understanding of basic processes in biomineralization. For more details and references, see Addadi, L., Raz, S. and Weiner, S. (2003). Taking advantage of disorder: Amorphous calcium carbonate and its roles in biomineralization. Adv. Mat.15, 959-970.

THE ARECIBO L-BAND FEED ARRAY ZONE OF AVOIDANCE SURVEY. I. PRECURSOR OBSERVATIONS THROUGH THE INNER AND OUTER GALAXY

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

Henning, P. A.; McIntyre, T.; Day, F.

The Arecibo L-band Feed Array (ALFA) is being used to conduct a low-Galactic latitude survey, to map the distribution of galaxies and large-scale structures behind the Milky Way through detection of galaxies' neutral hydrogen (H I) 21 cm emission. This Zone of Avoidance (ZOA) survey finds new H I galaxies which lie hidden behind the Milky Way, and also provides redshifts for partially obscured galaxies known at other wavelengths. Before the commencement of the full survey, two low-latitude precursor regions were observed, totaling 138 deg{sup 2}, with 72 H I galaxies detected. Detections through the inner Galaxy generally have nomore » cataloged counterparts in any other waveband, due to the heavy extinction and stellar confusion. Detections through the outer Galaxy are more likely to have Two Micron All Sky Survey counterparts. We present the results of these precursor observations, including a catalog of the detected galaxies, with their H I parameters. The survey sensitivity is well described by a flux- and linewidth-dependent signal-to-noise ratio of 6.5. ALFA ZOA galaxies, which also have H I measurements in the literature, show good agreement between our measurements and previous work. The inner Galaxy precursor region was chosen to overlap the H I Parkes Zone of Avoidance Survey, so ALFA performance could be quickly assessed. The outer Galaxy precursor region lies north of the Parkes sky. Low-latitude large-scale structure in this region is revealed, including an overdensity of galaxies near l = 183{sup 0} and between 5000-6000 km s{sup -1} in the ZOA. The full ALFA ZOA survey will be conducted in two phases: a shallow survey using the observing techniques of the precursor observations, and also a deep phase with much longer integration time, with thousands of galaxies predicted for the final catalog.« less

Applying the polarity rapid assessment method to characterize nitrosamine precursors and to understand their removal by drinking water treatment processes.

PubMed

Liao, Xiaobin; Bei, Er; Li, Shixiang; Ouyang, Yueying; Wang, Jun; Chen, Chao; Zhang, Xiaojian; Krasner, Stuart W; Suffet, I H Mel

2015-12-15

Some N-nitrosamines (NAs) have been identified as emerging disinfection by-products during water treatment. Thus, it is essential to understand the characteristics of the NA precursors. In this study, the polarity rapid assessment method (PRAM) and the classical resin fractionation method were studied as methods to fractionate the NA precursors during drinking water treatment. The results showed that PRAM has much higher selectivity for NA precursors than the resin approach. The normalized N-nitrosodimethylamine formation potential (NDMA FP) and N-nitrosodiethylamine (NDEA) FP of four resin fractions was at the same level as the average yield of the bulk organic matter whereas that of the cationic fraction by PRAM showed 50 times the average. Thus, the cationic fraction was shown to be the most important NDMA precursor contributor. The PRAM method also helped understand which portions of the NA precursor were removed by different water treatment processes. Activated carbon (AC) adsorption removed over 90% of the non-polar PRAM fraction (that sorbs onto the C18 solid phase extraction [SPE] cartridge) of NDMA and NDEA precursors. Bio-treatment removed 80-90% of the cationic fraction of PRAM (that is retained on the cation exchange SPE cartridge) and 40-60% of the non-cationic fractions. Ozonation removed 50-60% of the non-polar PRAM fraction of NA precursors and transformed part of them into the polar fraction. Coagulation and sedimentation had very limited removal of various PRAM fractions of NA precursors. Copyright © 2015 Elsevier Ltd. All rights reserved.

Phase stabilities of pyrite-related MTCh compounds (M=Ni, Pd, Pt; T=Si, Ge, Sn, Pb; Ch=S, Se, Te): A systematic DFT study

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

Bachhuber, Frederik; School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland; Krach, Alexander

2015-03-15

Pyrite-type and related systems appear for a wide range of binary and ternary combinations of transition metals and main group elements that form Zintl type dumbbell anion units. Those representatives with 20 valence electrons exhibit an extraordinary structural flexibility and interesting properties as low-gap semiconductors or thermoelectric and electrode materials. This work is devoted to the systematic exploration of novel compounds within the class of MTCh compounds (M=Ni, Pd, Pt; T=Si, Ge, Sn, Pb; Ch=S, Se, Te) by means of density functional calculations. Their preferred structures are predicted from an extended scheme of colored pyrites and marcasites. To determine theirmore » stabilities, competing binary MT{sub 2} and MCh{sub 2} boundary phases are taken into account as well as ternary M{sub 3}T{sub 2}Ch{sub 2} and M{sub 2}T{sub 3}Ch{sub 3} systems. Recently established stability diagrams are presented to account for MTCh ordering phenomena with a focus on a not-yet-reported ordering variant of the NiAs{sub 2} type. Due to the good agreement with experimental data available for several PtTCh systems, the predictions for the residual systems are considered sufficiently accurate. - Graphical abstract: Compositional and structural stability of MTCh compounds is investigated from first principle calculations. A conceptional approach is presented to study and predict novel stable and metastable compounds and structures of low gap semiconductors with TCh dumbbell units that are isoelectronic and structurally related to pyrite (FeS{sub 2}). - Highlights: • Study of compositional stability of MTCh vs. M{sub 3}T{sub 2}Ch{sub 2} and M{sub 2}T{sub 3}Ch{sub 3} compounds. • Study of structural stability of known and novel MTCh compounds. • Prediction of novel stable and metastable structures and compounds isoelectronic to pyrite, FeS{sub 2}.« less

Low-temperature thermoelectric, galvanomagnetic, and thermodynamic properties of the type-I clathrate Ba8AuxSi46-x

NASA Astrophysics Data System (ADS)

Aydemir, U.; Candolfi, C.; Ormeci, A.; Oztan, Y.; Baitinger, M.; Oeschler, N.; Steglich, F.; Grin, Yu.

2011-11-01

Polycrystalline samples of the clathrate Ba8AuxSi46-x were synthesized for 0.2 ⩽ x ⩽ 10. The homogeneity range of the type-I clathrate phase was determined to be 3.63 ⩽ x ⩽ 6.10 after annealing at 900 °C, while a lower Au concentration (x ≈ 2.2) was obtained by steel-quenching. Quasisingle phase materials were obtained for 4.10 ⩽ x ⩽ 6.10. In this composition range, thermoelectric properties, including electrical resistivity, thermopower, and thermal conductivity, were investigated between 2 and 350 K. These experiments were complemented by low-temperature specific heat and Hall-effect measurements (2-300 K). First-principles calculations were carried out to determine the evolution of the electronic structure as a function of x. Both theoretical and experimental results evidence a progressive evolution, with the Au content, from a metallic-like behavior towards a highly doped semiconducting state which develops around x = 5.43. At this concentration, a crossover from n- to p-type conduction occurs, suggesting that the present system satisfies the Zintl-Klemm concept, which predicts a transition at x = 5.33. This crossover is traced by Hall-effect data indicating a dominant electronlike response for x ⩽ 5.43, which turns into a holelike signal at higher x values. Analysis of the data based on a single-parabolic-band model under the assumption of a single scattering mechanism of the charge carriers proved to adequately describe the transport properties in the compositional range investigated. Interestingly, the temperature dependence of the lattice thermal conductivity is strongly influenced by the Au concentration: the typical behavior of crystalline insulators in the n-type compounds evolves into a glasslike dependence in the p-type samples. The series Ba8AuxSi46-x thus provides an excellent testing ground for the interplay between crystal structure, electronic properties, and lattice thermal conductivity in type-I clathrates.

An effective approach to synthesize monolayer tungsten disulphide crystals using tungsten halide precursor

NASA Astrophysics Data System (ADS)

Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap; Tanemura, Masaki

2016-02-01

The synthesis of large-area monolayer tungsten disulphide (WS2) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS2 crystals using tungsten hexachloride (WCl6) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl6 in ethanol was drop-casted on SiO2/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS2 crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS2 single crystalline monolayer can be grown using the WCl6 precursor. Our finding shows an easier and effective approach to grow WS2 monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.

Amorphous calcium carbonate: A precursor phase for aragonite in shell disease of the pearl oyster.

PubMed

Huang, Jingliang; Liu, Chuang; Xie, Liping; Zhang, Rongqing

2018-02-26

Amorphous calcium carbonate (ACC) has long been shown to act as an important constituent or precursor phase for crystalline material in mollusks. However, the presence and the role of ACC in bivalve shell formation are not fully studied. In this study, we found that brown deposits containing heterogeneous calcium carbonates were precipitated when a shell disease occurred in the pearl oyster Pinctada fucata. Calcein-staining of the brown deposits indicated that numerous amorphous calcium deposits were present, which was further confirmed by Fourier-transform infrared spectroscopy (FTIR), Raman spectrum and X-ray difraction (XRD) analyses. So we speculate that ACC plays an important role in rapid calcium carbonate precipitation during shell repair process in diseased oysters. Copyright © 2018 Elsevier Inc. All rights reserved.

Role of precursor crystal structure on electrochemical performance of carbide-derived carbon electrodes

NASA Astrophysics Data System (ADS)

Palazzo, Benjamin; Norris, Zach; Taylor, Greg; Yu, Lei; Lofland, Samuel; Hettinger, Jeffrey

2015-03-01

Binary carbides with hexagonal and cubic crystal structures have been synthesized by reactive magnetron sputtering of vanadium and other transition metals in acetylene or methane gas mixed with argon. The binary carbides are converted to carbide-derived carbon (CDC) films using chlorine gas in a post-deposition process in an external vacuum reaction furnace. Residual chlorine has been removed using an annealing step in a hydrogen atmosphere. The CDC materials have been characterized by x-ray diffraction, x-ray fluorescence, and scanning electron microscopy. The performance of the CDC materials in electrochemical device applications has been measured with the hexagonal phase precursor demonstrating a significantly higher specific capacitance in comparison to that of the cubic phase. We report these results and pore-size distributions of these and similar materials.

Automated electrochemical assembly of the protected potential TMG-chitotriomycin precursor based on rational optimization of the carbohydrate building block.

PubMed

Nokami, Toshiki; Isoda, Yuta; Sasaki, Norihiko; Takaiso, Aki; Hayase, Shuichi; Itoh, Toshiyuki; Hayashi, Ryutaro; Shimizu, Akihiro; Yoshida, Jun-ichi

2015-03-20

The anomeric arylthio group and the hydroxyl-protecting groups of thioglycosides were optimized to construct carbohydrate building blocks for automated electrochemical solution-phase synthesis of oligoglucosamines having 1,4-β-glycosidic linkages. The optimization study included density functional theory calculations, measurements of the oxidation potentials, and the trial synthesis of the chitotriose trisaccharide. The automated synthesis of the protected potential N,N,N-trimethyl-d-glucosaminylchitotriomycin precursor was accomplished by using the optimized building block.

Synthesis and characterization of WO3 nanowires and metal nanoparticle-WO3 nanowire composites

NASA Astrophysics Data System (ADS)

Szabó, Mária; Pusztai, Péter; Leino, Anne-Riikka; Kordás, Krisztián; Kónya, Zoltán; Kukovecz, Ákos

2013-07-01

Tungsten-trioxide nanowire bundles were prepared using a simple hydrothermal method. Sodium-tungstate was used as precursor and sodium-sulfate as structure directing agent. All the reflections of the X-ray diffractogram of the synthesized wires belong to the hexagonal phase of the tungsten trioxide. The nanowires were successfully decorated with metal nanoparticles by wet impregnation. The TEM investigation showed that using different metal precursors resulted in different particle sizes and coverage on the surface.

Novel in situ resistance measurement for the investigation of CIGS growth in a selenization process

NASA Astrophysics Data System (ADS)

Liu, Wei; Tian, Jian-Guo; Li, Zu-Bin; He, Qing; Li, Feng-Yan; Li, Chang-Jian; Sun, Yun

2009-03-01

During the selenization process of CIGS thin films, the relation between the element loss rate and the precursor depositions are analyzed. The growth of the CIGS thin films during the selenization process is investigated by the novel in situ resistance measurement, by which the formation of compound semiconductors can be observed directly and simultaneously. Their structures, phase evolutions and element losses are analyzed by XRD and XRF. Based on the experimental results, it can be concluded that the phase transforms have nothing to do with the deposition sequences of precursors, while the element loss rates are related to the deposition sequences in this process. In addition, element loss mechanisms of CIGS thin films prepared by the selenization process are analyzed by the phase evolutions and chemical combined path in the In, Ga-Se reaction processes. Moreover it is verified that the element losses are depressed by increasing the ramping-up rate finally. The results provide effective methods to fabricate high-quality CIGS thin films with low element losses.

Ketonization of levulinic acid and γ-valerolactone to hydrocarbon fuel precursors

DOE PAGES

Lilga, Michael A.; Padmaperuma, Asanga B.; Auberry, Deanna L.; ...

2017-06-21

We studied a new process for direct conversion of either levulinic acid (LA) or γ-valerolactone (GVL) to hydrocarbon fuel precursors. The process involves passing an aqueous solution of LA or GVL containing a reducing agent, such as ethylene glycol or formic acid, over a ketonization catalyst at 380–400 °C and atmospheric pressure to form a biphasic liquid product. The organic phase is significantly oligomerized and deoxygenated and comprises a complex mixture of open-chain alkanes and olefins, aromatics, and low concentrations of ketones, alcohols, ethers, and carboxylates or lactones. Carbon content in the aqueous phase decreases with decreasing feed rate; themore » aqueous phase can be reprocessed through the same catalyst to form additional organic oils to improve carbon yield. Catalysts are readily regenerated to restore initial activity. Furthermore, the process might be valuable in converting cellulosics to biorenewable gasoline, jet, and diesel fuels as a means to decrease petroleum use and decrease greenhouse gas emissions.« less

Lu2O3-SiO2-ZrO2 Coatings for Environmental Barrier Application by Solution Precursor Plasma Spraying and Influence of Precursor Chemistry

NASA Astrophysics Data System (ADS)

Darthout, Émilien; Quet, Aurélie; Braidy, Nadi; Gitzhofer, François

2014-02-01

As environmental barrier coatings are subjected to thermal stress in gas turbine engines, the introduction of a secondary phase as zircon (ZrSiO4) is likely to increase the stress resistance of Lu2Si2O7 coatings generated by induction plasma spraying using liquid precursors. In a first step, precursor chemistry effect is investigated by the synthesis of ZrO2-SiO2 nanopowders by induction plasma nanopowder synthesis technique. Tetraethyl orthosilicate (TEOS) as silicon precursor and zirconium oxynitrate and zirconium ethoxide as zirconium precursors are mixed in ethanol and produce a mixture of tetragonal zirconia and amorphous silica nanoparticles. The use of zirconium ethoxide precursor results in zirconia particles with diameter below 50 nm because of exothermic thermal decomposition of the ethoxide and its high boiling point with respect to solvent, while larger particles are formed when zirconium oxynitrate is employed. The formation temperature of zircon from zirconia and silica oxides is found at 1425 °C. Second, coatings are synthesized in Lu2O3-ZrO2-SiO2 system. After heat treatment, the doping effect of lutetium on zirconia grains totally inhibits the zircon formation. Dense coatings are obtained with the use of zirconium ethoxide because denser particles with a homogeneous diameter distribution constitute the coating.

Mechanical mixtures of metal oxides and phosphorus pentoxide as novel precursors for the synthesis of transition-metal phosphides.

PubMed

Guo, Lijuan; Zhao, Yu; Yao, Zhiwei

2016-01-21

This study presents a new type of precursor, mechanical mixtures of metal oxides (MOs) and phosphorus pentoxide (P2O5) are used to synthesize Ni2P, Co2P and MoP phosphides by the H2 reduction method. In addition, this is first report of common solid-state P2O5 being used as a P source for the synthesis of metal phosphides. The traditional precursors are usually prepared via a complicated preparation procedure involving dissolution, drying and calcination steps. However, these novel MOs/P2O5 precursors can be obtained only by simple mechanical mixing of the starting materials. Furthermore, unlike the direct transformation from amorphous phases to phosphides, various specific intermediates were involved in the transformation from MOs/P2O5 to phosphides. It is worthy to note that the dispersions of Ni2P, Co2P and MoP obtained from MOs/P2O5 precursors were superior to those of the corresponding phosphides prepared from the abovementioned traditional precursors. It is suggested that the morphology of the as-prepared metal phosphides might be inherited from the corresponding MOs. Based on the results of XRD, XPS, SEM and TEM, the formation pathway of phosphides can be defined as MOs/P2O5 precursors → complex intermediates (metals, metal phosphates and metal oxide-phosphates) → metal phosphides.

Aqueous-phase mechanism for secondary organic aerosol formation from isoprene: application to the southeast United States and co-benefit of SO2 emission controls

EPA Science Inventory

Isoprene emitted by vegetation is an important precursor of secondary organic aerosol (SOA), but the mechanism and yields are uncertain. Aerosol is prevailingly aqueous under the humid conditions typical of isoprene-emitting regions. Here we develop an aqueous-phase mechanism for...

77 FR 35862 - Approval and Promulgation of Implementation Plans; State of Florida: New Source; Review...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-15

... Resource Management, to EPA in two separate SIP revisions on October 19, 2007, and July 1, 2011. These SIP...) Implementation Rule NSR Update Phase II (hereafter referred to as the ``Ozone Implementation NSR Update'' or ``Phase II Rule'') recognizing nitrogen oxide (NO X ) as an ozone precursor, among other requirements. In...

Electromagnetic Whistler Precursors at Supercritical Interplanetary Shocks

NASA Technical Reports Server (NTRS)

Wilson, L. B., III

2012-01-01

We present observations of electromagnetic precursor waves, identified as whistler mode waves, at supercritical interplanetary shocks using the Wind search coil magnetometer. The precursors propagate obliquely with respect to the local magnetic field, shock normal vector, solar wind velocity, and they are not phase standing structures. All are right-hand polarized with respect to the magnetic field (spacecraft frame), and all but one are right-hand polarized with respect to the shock normal vector in the normal incidence frame. Particle distributions show signatures of specularly reflected gyrating ions, which may be a source of free energy for the observed modes. In one event, we simultaneously observe perpendicular ion heating and parallel electron acceleration, consistent with wave heating/acceleration due to these waves.

Discovery of composite diopside-magnetite lamellae in discrete olivine crytals from Colorado Plateau diatremes: indication of former hydrous ringwoodite

NASA Astrophysics Data System (ADS)

Sakamaki, K.; Sato, Y.; Marshall, E. W., IV; Ogasawara, Y.

2016-12-01

We investigate composite diopside (Di) + magnetite (Mt) lamellae in olivine crystals from Oligocene diatremes of serpentinized ultramafic microbreccia located at Buell Park (AZ) and Green Knobs (NM) in the Colorado Plateau, and propose their genesis as breakdown products of precursor hydrous ringwoodite (γ-olivine) lamellae coexisting with α-olivine host. Among a hundred olivines (2-5 mm across, Fo89-93 in mol%) from both localities, the Di + Mt composite lamellae are recognized in only 15 of relatively Fe-rich grains (Fo89-91.5). The olivine host contains minor amounts of Ca (< 0.01 wt% CaO), Mn, Ni, and Co. Lamellar Di (Di95) contains minor amounts of Al, Na, Cr, Mn, and Ni. Lamellar Mt contains Cr (5.0-43.0 wt% Cr2O3) with minor amounts of Si, Ti, Al, Mn, Ni, and Co. The area fractions of olivine host and the lamellae in a typical grain (sample no. BP02-3) were measured at 98.8 % of the host and 1.2 % of the lamellae that are composed of Di:Mt = 85:15 to 53:47, average 66:34. The estimated average CaO content in a lamella reaches 17 wt% and the reintegrated CaO in the host and the lamellae is 0.22 wt%.We propose that Fe3+ in lamellar Mt was produced by dehydration of hydrous precursor phase via the reaction, Fe2+ + OH- = Fe3+ + O2- + 1/2H2. Converting Fe3+ into Fe2+ in the precursor phase based on this reaction, the composition satisfies the stoichiometry of olivine (X2TO4). Thus, the pre-existing phase certainly is of hydrous and contains Ca and other components with olivine stoichiometry. The most likely phase is lamellar hydrous ringwoodite. The precursor phase, hydrous ringwoodite, might have occurred as lamellae with α-olivine host and have probably decomposed by the following reaction, (1+X+Y+Z) hydrous ringwoodite → α-olivine + X Di + Y Mt + Z H2 (where X:Y:Z=2:1:1). The composite Di-Mt lamellae after hydrous ringwoodite lamellae in α-olivine host certainly suggest the materials originated from a deep mantle setting at least 300 km.

Near white light emission of silicon nanocrystals

NASA Astrophysics Data System (ADS)

Lee, Soojin; Han, Il-Ki; Cho, Woon-Jo

2003-11-01

Silicon nanoparticles in the range from 2 nm to 5 nm was prepared from Zintl salt, soldium silicide (NaSi) by sonochemical method. This synthesis permits the reaction completed as fast as in a few hours and the easy alkyl-modification of nanocrystals surface at room temperature and ambient pressure. The average size of nanoparticles measured by the dynamic light scattering analysis was 2.7 nm. The high-resolution transmission electron micrograph cofirmed the material identity of nanoparticles as crystalline silicon. FT-IR spectra are consistent with the surface states of nanocrystals that is chlorine- or butyl-capped. The emission peak center moved to longer wavelength (up to 430 nm) with the reaction time, under a 325 nm excitation. The luminescence of silicon colloids looks bright bluish-white under excitation using a commercial low-intensity UV lamp.

{[Ga(en){sub 3}]{sub 2}(Ge{sub 2}Te{sub 15})}n : a polymeric semiconducting polytelluride with boat-shaped Te{sub 8}{sup 4-} rings and cross-shaped Te{sub 5}{sup 6-} units.

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

Zhang, Q.; Malliakas, C. D.; Kanatzidis, M. G.

2009-11-11

The reaction of the Zintl compound K{sub 4}Ge{sub 9} with Te and Ga{sub 2}Te{sub 3} in ethylenediamine (en) at 190 C gave the germanium polytelluride {l_brace}[Ga(en){sub 3}]{sub 2}[(GeTe){sub 2}(Te{sub 5}){sup 6-}(Te{sub 8}){sup 4-}]{r_brace}n (1). The single-crystal structure analysis revealed that 1 has two different polytelluride fragments: cross-shaped 36-e- TeTe{sub 4}{sup 6-} anions and boat-shaped 52-e- Te{sup 8}{sup 4-} rings. The new material is a p-type semiconductor at room temperature and switches to n-type at 380 K.

Qualification of a sublimation tool applied to the case of metalorganic chemical vapor deposition of In{sub 2}O{sub 3} from In(tmhd){sub 3} as a solid precursor

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

Szkutnik, P. D., E-mail: pierre.szkutnik@cea.fr; Jiménez, C.; Angélidès, L.

2016-02-15

A solid delivery system consisting of a source canister, a gas management, and temperature controlled enclosure designed and manufactured by Air Liquide Electronics Systems was tested in the context of gas-phase delivery of the In(tmhd){sub 3} solid precursor. The precursor stream was delivered to a thermal metalorganic chemical vapor deposition reactor to quantify deposition yield under various conditions of carrier gas flow and sublimation temperature. The data collected allowed the determination of characteristic parameters such as the maximum precursor flow rate (18.2 mg min{sup −1} in specified conditions) and the critical mass (defined as the minimum amount of precursor ablemore » to attain the maximum flow rate) found to be about 2.4 g, as well as an understanding of the influence of powder distribution inside the canister. Furthermore, this qualification enabled the determination of optimal delivery conditions which allowed for stable and reproducible precursor flow rates over long deposition times (equivalent to more than 47 h of experiment). The resulting In{sub 2}O{sub 3} layers was compared with those elaborated via pulsed liquid injection obtained in the same chemical vapor deposition chamber and under the same deposition conditions.« less

Grafting strategy to develop single site titanium on an amorphous silica surface.

PubMed

Capel-Sanchez, M C; Blanco-Brieva, G; Campos-Martin, J M; de Frutos, M P; Wen, W; Rodriguez, J A; Fierro, J L G

2009-06-16

Titanium/silica systems were prepared by grafting a titanium alkoxide (titanium isopropoxide and titanium (triethanolaminate) isopropoxide) precursor onto amorphous silica. The grafting process, which consisted of the hydrolysis of the Ti precursor by the hydroxyl groups on the silica surface, yielded samples containing Ti-loadings of 1-1.6 wt %. The as synthesized and calcined TiO(2)-SiO(2) samples were characterized by UV-vis, FTIR, XPS, and XANES spectroscopic techniques. These systems were tested in the liquid-phase epoxidation of oct-1-ene with hydrogen peroxide reaction. Spectroscopic data indicated that titanium anchoring takes place by reaction between the alkoxide precursor and surface OH groups of the silica substrate. The nature of surface titanium species generated by chemical grafting depends largely on the titanium precursor employed. Thus, the titanium isopropoxide precursor yields tetrahedrally coordinated polymeric titanium species, which give rise to a low-efficiency catalyst. However, if an atrane precursor (titanium (triethanolaminate) isopropoxide) is employed, isolated titanium species are obtained. The fact that these species remain isolated even after calcination is due to the protective effect of the triethanolaminate ligand that avoids titanium polymerization. These differences in the titanium environment have a pivotal role in the performance of these systems in the epoxidation of alkenes with hydrogen peroxide.

Grafting Strategy to Develop Single Site Titanium on an Amorphous Silica Surface

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

Capel-Sanchez, M.; Blanco-Brieva, G; Campos-Martin, J

2009-01-01

Titanium/silica systems were prepared by grafting a titanium alkoxide (titanium isopropoxide and titanium (triethanolaminate) isopropoxide) precursor onto amorphous silica. The grafting process, which consisted of the hydrolysis of the Ti precursor by the hydroxyl groups on the silica surface, yielded samples containing Ti-loadings of 1-1.6 wt %. The as synthesized and calcined TiO2-SiO2 samples were characterized by UV-vis, FTIR, XPS, and XANES spectroscopic techniques. These systems were tested in the liquid-phase epoxidation of oct-1-ene with hydrogen peroxide reaction. Spectroscopic data indicated that titanium anchoring takes place by reaction between the alkoxide precursor and surface OH groups of the silica substrate.more » The nature of surface titanium species generated by chemical grafting depends largely on the titanium precursor employed. Thus, the titanium isopropoxide precursor yields tetrahedrally coordinated polymeric titanium species, which give rise to a low-efficiency catalyst. However, if an atrane precursor (titanium (triethanolaminate) isopropoxide) is employed, isolated titanium species are obtained. The fact that these species remain isolated even after calcination is due to the protective effect of the triethanolaminate ligand that avoids titanium polymerization. These differences in the titanium environment have a pivotal role in the performance of these systems in the epoxidation of alkenes with hydrogen peroxide.« less

Size and Morphology Controlled Synthesis of Boehmite Nanoplates and Crystal Growth Mechanisms

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

Zhang, Xin; Cui, Wenwen; Page, Katharine L.

The aluminum oxyhydroxide boehmite is an important crystalline phase in nature and industry. We report development of a flexible additive-free hydrothermal synthesis method to prepare high quality boehmite nanoplates with sizes ranging from under 20 nm to 5 um via using hydrated alumina gels and amorphous powders as precursors. The size and morphology of the boehmite nanoplates was systematically varied between hexagonal and rhombic by adjusting precursor concentrations, pH, and the synthesis temperature, due to face-specific effects. The transformation mechanism is consistent with dissolution and reprecipitation, and involves transitory initial appearance of metastable gibbsite that is later consumed upon nucleationmore » of boehmite. Detailed X-ray pair distribution characterization of the solids over time showed similarities in short-range order that suggest linkages in local chemistry and bonding topology between the precursors and product boehmite, yet also that precursor-specific differences in long-range order appear to manifest subtle changes in resulting boehmite characteristics, suggesting that the rate and extent of water release or differences in the resulting solubilized aluminate speciation leads to slightly different polymerization and condensation pathways. The findings suggest that during dissolution of the precursor that precursor-specific dehydration or solution speciation could be important aspects of the transformation impacting the molecular level details of boehmite nucleation and growth.« less

Applying polarity rapid assessment method and ultrafiltration to characterize NDMA precursors in wastewater effluents.

PubMed

Chen, Chao; Leavey, Shannon; Krasner, Stuart W; Mel Suffet, I H

2014-06-15

Certain nitrosamines in water are disinfection byproducts that are probable human carcinogens. Nitrosamines have diverse and complex precursors that include effluent organic matter, some anthropogenic chemicals, and natural (likely non-humic) substances. An easy and selective tool was first developed to characterize nitrosamine precursors in treated wastewaters, including different process effluents. This tool takes advantages of the polarity rapid assessment method (PRAM) and ultrafiltration (UF) (molecular weight distribution) to locate the fractions with the strongest contributions to the nitrosamine precursor pool in the effluent organic matter. Strong cation exchange (SCX) and C18 solid-phase extraction cartridges were used for their high selectivity for nitrosamine precursors. The details of PRAM operation, such as cartridge clean-up, capacity, pH influence, and quality control were included in this paper, as well as the main parameters of UF operation. Preliminary testing of the PRAM/UF method with effluents from one wastewater treatment plant gave very informative results. SCX retained 45-90% of the N-nitrosodimethylamine (NDMA) formation potential (FP)-a measure of the precursors-in secondary and tertiary wastewater effluents. These results are consistent with NDMA precursors likely having a positively charged amine group. C18 adsorbed 30-45% of the NDMAFP, which indicates that a substantial portion of these precursors were non-polar. The small molecular weight (MW) (<1 kDa) and large MW (>10 kDa) fractions obtained from UF were the primary contributors to NDMAFP. The combination of PRAM and UF brings important information on the characteristics of nitrosamine precursors in water with easy operation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Atmospheric new particle formation at the research station Melpitz, Germany: connection with gaseous precursors and meteorological parameters

NASA Astrophysics Data System (ADS)

Größ, Johannes; Hamed, Amar; Sonntag, André; Spindler, Gerald; Elina Manninen, Hanna; Nieminen, Tuomo; Kulmala, Markku; Hõrrak, Urmas; Plass-Dülmer, Christian; Wiedensohler, Alfred; Birmili, Wolfram

2018-02-01

This paper revisits the atmospheric new particle formation (NPF) process in the polluted Central European troposphere, focusing on the connection with gas-phase precursors and meteorological parameters. Observations were made at the research station Melpitz (former East Germany) between 2008 and 2011 involving a neutral cluster and air ion spectrometer (NAIS). Particle formation events were classified by a new automated method based on the convolution integral of particle number concentration in the diameter interval 2-20 nm. To study the relevance of gaseous sulfuric acid as a precursor for nucleation, a proxy was derived on the basis of direct measurements during a 1-month campaign in May 2008. As a major result, the number concentration of freshly produced particles correlated significantly with the concentration of sulfur dioxide as the main precursor of sulfuric acid. The condensation sink, a factor potentially inhibiting NPF events, played a subordinate role only. The same held for experimentally determined ammonia concentrations. The analysis of meteorological parameters confirmed the absolute need for solar radiation to induce NPF events and demonstrated the presence of significant turbulence during those events. Due to its tight correlation with solar radiation, however, an independent effect of turbulence for NPF could not be established. Based on the diurnal evolution of aerosol, gas-phase, and meteorological parameters near the ground, we further conclude that the particle formation process is likely to start in elevated parts of the boundary layer rather than near ground level.

Antimony-ligated dysprosium single-molecule magnets as catalysts for stibine dehydrocoupling† †Electronic supplementary information (ESI) available: Synthetic details, spectroscopic characterization for all compounds, X-ray crystallography details and crystallographic information files, computational details. CCDC 1484570–1484573 and 1485316. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc04465d Click here for additional data file. Click here for additional data file.

PubMed Central

Pugh, Thomas

2017-01-01

Single-molecule magnets (SMMs) are coordination compounds that exhibit magnetic bistability below a characteristic blocking temperature. Research in this field continues to evolve from its fundamental foundations towards applications of SMMs in information storage and spintronic devices. Synthetic chemistry plays a crucial role in targeting the properties that could ultimately produce SMMs with technological potential. The ligands in SMMs are invariably based on non-metals; we now report a series of dysprosium SMMs (in addition to their magnetically dilute analogues embedded in yttrium matrices) that contain ligands with the metalloid element antimony as the donor atom, i.e. [(η5-Cp′2Dy){μ-Sb(H)Mes}]3 (1-Dy) and [(η5-Cp′2Dy)3{μ-(SbMes)3Sb}] (2-Dy), which contain the stibinide ligand [Mes(H)Sb]– and the unusual Zintl-like ligand [Sb4Mes3]3–, respectively (Cp′ = methylcyclopentadienyl; Mes = mesityl). The zero-field anisotropy barriers in 1-Dy and 2-Dy are U eff = 345 cm–1 and 270 cm–1, respectively. Stabilization of the antimony-ligated SMMs is contingent upon careful control of reaction time and temperature. With longer reaction times and higher temperatures, the stibine pro-ligands are catalytically dehydrocoupled by the rare-earth precursor complexes. NMR spectroscopic studies of the yttrium-catalysed dehydrocoupling reactions reveal that 1-Y and 2-Y are formed during the catalytic cycle. By implication, 1-Dy and 2-Dy should also be catalytic intermediates, hence the nature of these complexes as SMMs in the solid-state and as catalysts in solution introduces a strategy whereby new molecular magnets can be identified by intercepting species formed during catalytic reactions. PMID:28451326

Engineering Particle Surface Chemistry and Electrochemistry with Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Jackson, David Hyman Kentaro

Atomic layer deposition (ALD) is a vapor phase thin film coating technique that relies on sequential pulsing of precursors that undergo self-limited surface reactions. The self- limiting reactions and gas phase diffusion of the precursors together enable the conformal coating of microstructured particles with a high degree of thickness and compositional control. ALD may be used to deposit thin films that introduce new functionalities to a particle surface. Examples of new functionalities include: chemical reactivity, a mechanically strong protective coating, and an electrically resistive layer. The coatings properties are often dependent on the bulk properties and microstructure of the particle substrate, though they usually do not affect its bulk properties or microstructure. Particle ALD finds utility in the ability to synthesize well controlled, model systems, though it is expensive due to the need for costly metal precursors that are dangerous and require special handling. Enhanced properties due to ALD coating of particles in various applications are frequently described empirically, while the details of their enhancement mechanisms often remain the focus of ongoing research in the field. This study covers the various types of particle ALD and attempts to describe them from the unifying perspective of surface science.

Effect of cetyl trimethyl ammonium bromide concentration on structure, morphology and carbon dioxide adsorption capacity of calcium hydroxide based sorbents

NASA Astrophysics Data System (ADS)

Hlaing, Nwe Ni; Vignesh, K.; Sreekantan, Srimala; Pung, Swee-Yong; Hinode, Hirofumi; Kurniawan, Winarto; Othman, Radzali; Thant, Aye Aye; Mohamed, Abdul Rahman; Salim, Chris

2016-02-01

Calcium hydroxide (Ca(OH)2) has been proposed as an important material for industrial, architectural, and environmental applications. In this study, calcium acetate was used as a precursor and cetyl trimethyl ammonium bromide (CTAB) was used as a surfactant to synthesize Ca(OH)2 based adsorbents for carbon dioxide (CO2) capture. The effect of CTAB concentration (0.2-0.8 M) on the structure, morphology and CO2 adsorption performance of Ca(OH)2 was studied in detail. The synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), BET surfaced area and thermogravimetry-differential thermal analysis (TG-DTA) techniques. The phase purity, crystallite size, Brunauer-Emmett-Teller (BET) surface area and CO2 adsorption performance of Ca(OH)2 precursor adsorbents were significantly increased when the concentration of CTAB was increased. XRD results showed that pure Ca(OH)2 phase was obtained at the CTAB concentration of 0.8 M. TGA results exhibited that 0.8 M of CTAB-assisted Ca(OH)2 precursor adsorbent possessed a residual carbonation conversion of ∼56% after 10 cycles.

Ternary arsenides ATt{sub 3}As{sub 3} (A=K, Rb; Tt=Ge, Sn) with layered structures

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

Khatun, Mansura; Stoyko, Stanislav S.; Mar, Arthur, E-mail: arthur.mar@ualberta.ca

2016-06-15

The four ternary arsenides ATt{sub 3}As{sub 3} (A=K, Rb; Tt=Ge, Sn) were obtained by reaction of the elements at 600–650 °C. They adopt an orthorhombic structure (space group Pnma, Z=4, with cell parameters ranging from a=9.9931(11) Å, b=3.7664(4) Å, c=18.607(2) Å for KGe{sub 3}As{sub 3} to a=10.3211(11) Å, b=4.0917(4) Å, c=19.570(2) Å for RbSn{sub 3}As{sub 3}) containing corrugated [Tt{sub 3}As{sub 3}] layers built from Tt-centred trigonal pyramids and tetrahedra forming five-membered rings decorated with As handles. They can be considered to be Zintl phases with Tt atoms in +4, +3, and +1 oxidation states. Band structure calculations predict that thesemore » compounds are semiconductors with narrow band gaps (0.71 eV in KGe{sub 3}As{sub 3}, 0.50 eV in KSn{sub 3}As{sub 3}). - Graphical abstract: Ternary arsenides ATt{sub 3}As{sub 3} (A=K, Rb; Tt=Ge, Sn) contain corrugated layers with Tt atoms in three different oxidation states and are narrow band gap semiconductors. Display Omitted - Highlights: • ATt{sub 3}As{sub 3} (A=K, Rb; Tt=Ge, Sn) contains Tt atoms in three oxidation states. • The structure differs from NaGe{sub 3}P{sub 3} in terms of layer stacking arrangement. • The compounds are predicted to be narrow band gap semiconductors.« less

High-time resolved measurements of biogenic and anthropogenic secondary organic aerosol precursors and products in urban air

NASA Astrophysics Data System (ADS)

Flores, Rosa M.; Doskey, Paul V.

2016-04-01

Volatile organic compounds (VOCs), which are present in the atmosphere entirely in the gas phase are directly emitted by biogenic (~1089 Tg yr-1) and anthropogenic sources (~185 Tg yr-1). However, the sources and molecular speciation of intermediate VOCs (IVOCs), which are for the most part also present almost entirely in the gas phase, are not well characterized. The VOCs and IVOCs participate in reactions that form ozone and semivolatile OC (SVOC) that partition into the aerosol phase. Formation and evolution of secondary organic aerosol (SOA) are part of a complex dynamic process that depends on the molecular speciation and concentration of VOCs, IVOCs, primary organic aerosol (POA), and the level of oxidants (NO3, OH, O3). The current lack of understanding of OA properties and their impact on radiative forcing, ecosystems, and human health is partly due to limitations of models to predict SOA production on local, regional, and global scales. More accurate forecasting of SOA production requires high-temporal resolution measurement and molecular characterization of SOA precursors and products. For the subject study, the IVOCs and aerosol-phase organic matter were collected using the high-volume sampling technique and were analyzed by multidimensional gas chromatography with time-of-flight mass spectrometry (GCxGC-ToFMS). The IVOCs included terpenes, terpenoids, n-alkanes, branched alkanes, isoprenoids, alkylbenzenes, cycloalkylbenzenes, PAH, alkyl PAH, and an unresolved complex mixture (UCM). Diurnal variations of OA species containing multiple oxygenated functionalities and selected SOA tracers of isorprene, α-pinene, toluene, cyclohexene, and n-dodecane oxidation were also quantified. The data for SOA precursor and oxidation products presented here will be useful for evaluating the ability of molecular-specific SOA models to forecast SOA production in and downwind of urban areas.

JAK/Stat signaling regulates heart precursor diversification in Drosophila

PubMed Central

Johnson, Aaron N.; Mokalled, Mayssa H.; Haden, Tom N.; Olson, Eric N.

2011-01-01

Intercellular signal transduction pathways regulate the NK-2 family of transcription factors in a conserved gene regulatory network that directs cardiogenesis in both flies and mammals. The Drosophila NK-2 protein Tinman (Tin) was recently shown to regulate Stat92E, the Janus kinase (JAK) and Signal transducer and activator of transcription (Stat) pathway effector, in the developing mesoderm. To understand whether the JAK/Stat pathway also regulates cardiogenesis, we performed a systematic characterization of JAK/Stat signaling during mesoderm development. Drosophila embryos with mutations in the JAK/Stat ligand upd or in Stat92E have non-functional hearts with luminal defects and inappropriate cell aggregations. Using strong Stat92E loss-of-function alleles, we show that the JAK/Stat pathway regulates tin expression prior to heart precursor cell diversification. tin expression can be subdivided into four phases and, in Stat92E mutant embryos, the broad phase 2 expression pattern in the dorsal mesoderm does not restrict to the constrained phase 3 pattern. These embryos also have an expanded pericardial cell domain. We show the E(spl)-C gene HLHm5 is expressed in a pattern complementary to tin during phase 3 and that this expression is JAK/Stat dependent. In addition, E(spl)-C mutant embryos phenocopy the cardiac defects of Stat92E embryos. Mechanistically, JAK/Stat signals activate E(spl)-C genes to restrict Tin expression and the subsequent expression of the T-box transcription factor H15 to direct heart precursor diversification. This study is the first to characterize a role for the JAK/Stat pathway during cardiogenesis and identifies an autoregulatory circuit in which tin limits its own expression domain. PMID:21965617

High crystalline Cu2ZnSnS4 semiconductor prepared from low toxicity ethanol-based precursors

NASA Astrophysics Data System (ADS)

Munir, Badrul; Prastyo, Bayu Eko; Nurjaya, Dwi Marta; Muslih, Ersan Yudhapratama; Alfauzan, Sahri Karim

2017-01-01

At this moment, we present a new, cost-effective, and environmentally friendly method of preparing a high crystalline Cu2ZnSnS4 (CZTS) absorber layer for thin film solar cells using ethanol-based solutions. Ethanolamine (ETA) and 2-mercaptopropionic acid (MPA) were studied as a stabilizer and to improve wetting ability of the precursors during the deposition process. Cu2ZnSnS4 precursors are deposited onto soda lime glass using spin coater in different molar of cations in the precursor. The effects of a precursor system, ethanol-ETA-MPA, and ethanol-MPA, on the structure, morphology, composition and optical properties of CZTS thin films have been investigated in details. X-ray diffraction and energy-dispersive X-ray spectroscopy analyses confirmed the successful fabrication of high crystalline Cu2ZnSnS4 kesterite phase. The crystallinity of CZTS is continue increasing before reaching 2.2 molar cations of the ethanol-MPA precursors. The crystallinity of ethanol-ETA-MPA precursors remains similar in the experiment using 1.2 molar and 1.6 molars. The highest crystallinity was achieved using 2 molar cations of the ethanol-MPA precursor. Its band gap energy is found to be around 1.4 eV. The SEM micrographs of CZTS film shows the average grain size around 1.5 µm and some porosity which indicated the room of improvement. The high-crystallinity CZTS achieved in the present study brings a low-cost absorber semiconductor one step closer to practical use.

Phase Transformation of Droplets into Particles and Nucleation in Atmospheric Pressure Discharges

NASA Astrophysics Data System (ADS)

Iqbal, M. M.; Stallard, C. P.; Dowling, D. P.; Turner, M. M.

2013-09-01

We investigate the mechanism of phase transformation of liquid precursor droplets into nano-particulates in an atmospheric pressure discharge (APD). This phase transformation is possible when the solid to a liquid mass ratio of slurry droplet reaches a threshold value. The behaviour of phase transformation of a single slurry droplet of HMDSO is described by developing a numerical model under the saturation condition of evaporation. It is observed from the temporal evolution of inner radius (Ri) of a single slurry droplet that its value approaches zero before the entire shifting of a liquid phase and which explains with an expansion in the crust thickness (Ro - Ri) . The solid traces of nano-particles are observed experimentally on the surface coating depositions because the time for transferring the slurry droplet of HMDSO into solid state is amplified with an increment in the radii of droplets and the entire phase transition occurs within residence time for the nano-sized liquid droplets. The GDE coupled with discharge plasma is numerically solved to describe the mechanism of nucleation of nano-sized particles in APD plasma under similar conditions of the experiment. The growth of nucleation in APD plasma depends on the type of liquid precursor, such as HMDSO, TEOS and water, which is verified with a sharp peak in the nucleation rate and saturation ratio. Science Foundation Ireland under Grant No. 08/SRC/I1411.

Phase Composition of Samarium Niobate and Tantalate Thin Films Prepared by Sol-Gel Method

NASA Astrophysics Data System (ADS)

Bruncková, H.; Medvecký, Ľ.; Múdra, E.; Kovalčiková, A.; Ďurišin, J.; Šebek, M.; Girman, V.

2017-12-01

Samarium niobate SmNbO4 (SNO) and tantalate SmTaO4 (STO) thin films ( 100 nm) were prepared by sol-gel/spin-coating process on alumina substrates with PZT interlayer and annealing at 1000°C. The precursors of films were synthesized using Nb or Ta tartrate complexes. The improvement of the crystallinity of monoclinic M'-SmTaO4 phase via heating was observed through the coexistence of small amounts of tetragonal T-SmTa7O19 phase in STO precursor at 1000°C. The XRD results of SNO and STO films confirmed monoclinic M-SmNbO4 and M'-SmTaO4 phases, respectively, with traces of orthorhombic O-SmNbO4 (in SNO). In STO film, the single monoclinic M'-SmTaO4 phase was revealed. The surface morphology and topography of thin films were investigated by SEM and AFM analysis. STO film was smoother with roughness 3.2 nm in comparison with SNO (6.3 nm). In the microstructure of SNO film, small spherical ( 50 nm) and larger cuboidal particles ( 100 nm) of the SmNbO4 phase were observed. In STO, compact clusters composed of fine spherical SmTaO4 particles ( 20-50 nm) were found. Effect of samarium can contribute to the formation different polymorphs of these films for the application to environmental electrolytic thin film devices.

Effects of poling over the orthorhombic-tetragonal phase transition temperature in compositionally homogeneous (K,Na)NbO3-based ceramics

NASA Astrophysics Data System (ADS)

Morozov, M. I.; Kungl, H.; Hoffmann, M. J.

2011-03-01

Li-, Ta-, and Mn-modified (K,Na)NbO3 ceramics with various compositional homogeneity have been prepared by conventional and precursor methods. The homogeneous ceramic has demonstrated a sharper peak in temperature dependent piezoelectric response. The dielectric and piezoelectric properties of the homogeneous ceramics have been characterized at the experimental subcoercive electric fields near the temperature of the orthorhombic-tetragonal phase transition with respect to poling in both phases. Poling in the tetragonal phase is shown to enhance the low-signal dielectric and piezoelectric properties in the orthorhombic phase.

In Situ High Temperature High Pressure MAS NMR Study on the Crystallization of AlPO 4 -5

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

Zhao, Zhenchao; Xu, Suochang; Hu, Mary Y.

2016-01-28

A damped oscillating crystallization process of AlPO4-5 at the presence of small amount of water is demonstrated by in situ high temperature high pressure multinuclear MAS NMR. Crystalline AlPO4-5 is formed from an intermediate semicrystalline phase via continuous rearrangement of the local structure of amorphous precursor gel. Activated water catalyzes the rearrangement via repeatedly hydrolysis and condensation reaction. Strong interactions between organic template and inorganic species facilitate the ordered rearrangement. During the crystallization process, excess water, phosphate, and aluminums are expelled from the precursor. The oscillating crystallization reflects mass transportation between the solid and liquid phase during the crystallization process.more » This crystallization process is also applicable to AlPO4-5 crystallized in the presence of a relatively large amount of water.« less

Precursor wave structure, prereversal vertical drift, and their relative roles in the development of post sunset equatorial spread-F

NASA Astrophysics Data System (ADS)

Abdu, Mangalathayil; Sobral, José; alam Kherani, Esfhan; Batista, Inez S.; Souza, Jonas

2016-07-01

The characteristics of large-scale wave structure in the equatorial bottomside F region that are present during daytime as precursor to post sunset development of the spread F/plasma bubble irregularities are investigated in this paper. Digisonde data from three equatorial sites in Brazil (Fortaleza, Sao Luis and Cachimbo) for a period of few months at low to medium/high solar activity phases are analyzed. Small amplitude oscillations in the F layer true heights, representing wave structure in polarization electric field, are identified as upward propagating gravity waves having zonal scale of a few hundred kilometers. Their amplitudes undergo amplification towards sunset, and depending on the amplitude of the prereversal vertical drift (PRE) they may lead to post sunset generation of ESF/plasma bubble irregularities. On days of their larger amplitudes they appear to occur in phase coherence on all days, and correspondingly the PRE vertical drift velocities are larger than on days of the smaller amplitudes of the wave structure that appear at random phase on the different days. The sustenance of these precursor waves structures is supported by the relatively large ratio (approaching unity) of the F region-to- total field line integrated Pedersen conductivities as calculated using the SUPIM simulation of the low latitude ionosphere. This study examines the role of the wave structure relative to that of the prereversal vertical drift in the post sunset spread F irregularity development.

Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid and methylglyoxal

NASA Astrophysics Data System (ADS)

Tan, Y.; Lim, Y. B.; Altieri, K. E.; Seitzinger, S. P.; Turpin, B. J.

2012-01-01

Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including pyruvate, oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA). Acetic acid plays a central role in the aqueous oxidation of methylglyoxal and it is a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid (20 μM-10 mM) was oxidized by OH radicals, and pyruvic acid and methylglyoxal experimental samples were analyzed using new analytical methods, in order to better understand the formation of SOA from acetic acid and methylglyoxal. Glyoxylic, glycolic, and oxalic acids formed from acetic acid and OH radicals. In contrast to the aqueous OH radical oxidation of methylglyoxal, the aqueous OH radical oxidation of acetic acid did not produce succinic acid and oligomers. This suggests that the methylgloxal-derived oligomers do not form through the acid catalyzed esterification pathway proposed previously. Using results from these experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols.

Determination of 15 N-nitrosodimethylamine precursors in different water matrices by automated on-line solid-phase extraction ultra-high-performance-liquid chromatography tandem mass spectrometry.

PubMed

Farré, Maria José; Insa, Sara; Mamo, Julian; Barceló, Damià

2016-08-05

A new methodology based on on-line solid-phase extraction (SPE) ultra-high-performance-liquid chromatography coupled to a triple quadrupole mass spectrometer (UHPLC-MS-MS) for the determination of 15 individual anthropogenic N-nitrosodimethylamine (NDMA) precursors was developed. On-line SPE was performed by passing 2mL of the water sample through a Hypersil GOLD aQ column and chromatographic separation was done using a Kinetex Biphenyl column using methanol and 0.1% formic acid aqueous solution as a mobile phase. For unequivocal identification and confirmation, two selected reaction monitoring (SRM) transitions were monitored per compound. Quantification was performed by internal standard approach and matrix match calibration. The main advantages of the developed method are high sensitivity (limits of detection in the sub ng/L range), selectivity due to the use of tandem mass spectrometry, precision and minimum sample manipulation as well as fast analytical response. Process efficiency and recovery were also evaluated for all the target compounds. As part of the validation procedure, the method was applied in a sampling campaign for the analysis of influent and secondary effluent of a wastewater treatment plant (WWTP) in Girona, Spain. Additionally, the effluent from a nanofiltration (NF) membrane system used for water recycling was monitored. The percentage of NDMA formation explained by the measured precursors was also quantified. Copyright © 2016 Elsevier B.V. All rights reserved.

Structural and Mössbauer characterization of the ball milled Fe x(Cr 2O 3) 1- x system

NASA Astrophysics Data System (ADS)

Biondo, Valdecir; de Medeiros, Suzana Nóbrega; Paesano, Andrea, Jr.; Ghivelder, Luis; Hallouche, Bachir; da Cunha, João Batista Marimon

2009-08-01

The Fe x(Cr 2O 3) 1- x system, with 0.10 ≤ X ≤ 0.80, was mechanically processed for 24 h in a high-energy ball-mill. In order to examine the possible formation of iron-chromium oxides and alloys, the milled samples were, later, thermally annealed in inert (argon) and reducing (hydrogen) atmospheres. The as-milled and annealed products were characterized by X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy and magnetization. The as-milled samples showed the formation of an Fe 1+ YCr 2- YO 4- δ nanostructured and disordered spinel phase, the α 1-Fe(Cr) and α 2-Cr(Fe) solid solutions and the presence of non-exhausted precursors. For the samples annealed in inert atmosphere, the chromite (FeCr 2O 4) formation and the recrystallization of the precursors were verified. The hydrogen treated samples revealed the reduction of the spinel phase, with the phase separation of the chromia phase and retention of the Fe-Cr solid solutions. All the samples, either as-milled or annealed, presented the magnetization versus applied field curves typical for superparamagnetic systems.

Arginine pathways and the inflammatory response: interregulation of nitric oxide and polyamines: review article.

PubMed

Satriano, J

2004-07-01

An early response to an acute inflammatory insult, such as wound healing or experimental glomerulonephritis, is the conversion of arginine to the cytostatic molecule nitric oxide (NO). This 'anti-bacterial' phase is followed by the conversion of arginine to ornithine, which is the precursor for the pro-proliferative polyamines as well as proline for the production of extracellular matrix. This latter, pro-growth phase constitutes a 'repair' phase response. The temporal switch of arginine as a substrate for the cytostatic iNOS/NO axis to the pro-growth arginase/ ornithine/polyamine and proline axis is subject to regulation by inflammatory cytokines as well as interregulation by the arginine metabolites themselves. Arginine is also the precursor for another biogenic amine, agmatine. Here we describe the capacity of these three arginine pathways to interregulate, and propose a model whereby agmatine has the potential to serve in the coordination of the early and repair phase pathways of arginine in the inflammatory response by acting as a gating mechanism at the transition from the iNOS/NO axis to the arginase/ODC/polyamine axis. Due to the pathophysiologic and therapeutic potential, we will further examine the antiproliferative effects of agmatine on the polyamine pathway.

The elusive indigo precursors in woad (Isatis tinctoria L.)--identification of the major indigo precursor, isatan A, and a structure revision of isatan B.

PubMed

Oberthür, Christine; Schneider, Bernd; Graf, Heidemarie; Hamburger, Matthias

2004-01-01

A metabolite-profiling study of shock-frozen leaves of Isatis tinctoria L., an old indigo dye plant and medicinal herb, revealed a complex pattern of indigo-forming compounds with higher polarities than the known indigo precursors isatan B and indican. These highly unstable compounds underwent rapid post-harvest transformation and were not detected in air-dried leaves. The major indigo precursor, named isatan A (4), was isolated by rapid normal-phase and gel chromatography, along with isatan B (3). A full spectral data set of 3 showed that the previous structure assignment as 'indoxyl-5-ketogluconate' has to be revised to 1H-indol-3-yl beta-D-ribohex-3-ulopyranoside. Isatan A (4) was identified as 1H-indol-3-yl 6'-O-(carboxyacetyl)-beta-D-ribohex-3'-ulopyranoside. In aqueous solution, glycosides 3 and 4 occur as hydrates and undergo rapid hydrolysis under very mild acidic or basic conditions.

Synthesizing and characterization of titanium diboride for composite bipolar plates in PEM fuel cell

NASA Astrophysics Data System (ADS)

Duddukuri, Ramesh

This research deals with the synthesis and characterization of titanium diboride (TiB2) from novel carbon coated precursors. This work provides information on using different boron sources and their effect on the resulting powders of TiB2. The process has two steps in which the oxide powders were first coated with carbon by cracking of a hydrocarbon gas, propylene (C3H6) and then, mixed with boron carbide and boric acid powders in a stoichiometric ratio. These precursors were treated at temperatures in the range of 1200--1400° C for 2 h in flowing Argon atmosphere to synthesize TiB2. The process utilizes a carbothermic reduction reaction of novel carbon coated precursor that has potential of producing high-quality powders (sub-micrometer and high purity). Single phase TiB2 powders produced, were compared with commercially available titanium diboride using X-ray diffraction and Transmission electron microscopy obtained from boron carbide and boric acid containing carbon coated precursor.

Processing approach towards the formation of thin-film Cu(In,Ga)Se2

DOEpatents

Beck, Markus E.; Noufi, Rommel

2003-01-01

A two-stage method of producing thin-films of group IB-IIIA-VIA on a substrate for semiconductor device applications includes a first stage of depositing an amorphous group IB-IIIA-VIA precursor onto an unheated substrate, wherein the precursor contains all of the group IB and group IIIA constituents of the semiconductor thin-film to be produced in the stoichiometric amounts desired for the final product, and a second stage which involves subjecting the precursor to a short thermal treatment at 420.degree. C.-550.degree. C. in a vacuum or under an inert atmosphere to produce a single-phase, group IB-III-VIA film. Preferably the precursor also comprises the group VIA element in the stoichiometric amount desired for the final semiconductor thin-film. The group IB-IIIA-VIA semiconductor films may be, for example, Cu(In,Ga)(Se,S).sub.2 mixed-metal chalcogenides. The resultant supported group IB-IIIA-VIA semiconductor film is suitable for use in photovoltaic applications.

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

DOE PAGES

Cook, Ryan D.; Lin, Ying-Hsuan; Peng, Zhuoyu; ...

2017-12-21

Organic aerosol formation and transformation occurs within aqueous aerosol and cloud droplets, yet little is known about the composition of high molecular weight organic compounds in cloud water. Cloud water samples collected at Whiteface Mountain, New York, during August-September 2014 were analyzed by ultra-high-resolution mass spectrometry to investigate the molecular composition of dissolved organic carbon, with a focus on sulfur- and nitrogen-containing compounds. Organic molecular composition was evaluated in the context of cloud water inorganic ion concentrations, pH, and total organic carbon concentrations to gain insights into the sources and aqueous-phase processes of the observed high molecular weight organic compounds.more » Cloud water acidity was positively correlated with the average oxygen : carbon ratio of the organic constituents, suggesting the possibility for aqueous acid-catalyzed (prior to cloud droplet activation or during/after cloud droplet evaporation) and/or radical (within cloud droplets) oxidation processes. Many tracer compounds recently identified in laboratory studies of bulk aqueous-phase reactions were identified in the cloud water. Organosulfate compounds, with both biogenic and anthropogenic volatile organic compound precursors, were detected for cloud water samples influenced by air masses that had traveled over forested and populated areas. Oxidation products of long-chain (C 10-12) alkane precursors were detected during urban influence. Influence of Canadian wildfires resulted in increased numbers of identified sulfur-containing compounds and oligomeric species, including those formed through aqueous-phase reactions involving methylglyoxal. Light-absorbing aqueous-phase products of syringol and guaiacol oxidation were observed in the wildfire-influenced samples, and dinitroaromatic compounds were observed in all cloud water samples (wildfire, biogenic, and urban-influenced). Overall, the cloud water molecular composition depended on air mass source influence and reflected aqueous-phase reactions involving biogenic, urban, and biomass burning precursors.« less

Precursor dynamics in the ferroelectric phase transition of barium titanate single crystals studied by Brillouin light scattering

NASA Astrophysics Data System (ADS)

Ko, Jae-Hyeon; Kim, Tae Hyun; Roleder, K.; Rytz, D.; Kojima, Seiji

2011-09-01

The acoustic anomalies and precursor dynamics of high-quality barium titanate single crystals were investigated by Brillouin light scattering and the birefringence measurements in the paraelectric phase above the cubic-to-tetragonal ferroelectric phase transition temperature (Tc). Two elastic stiffness coefficients C11 and C44, the related sound velocities, and their absorption coefficients were determined from Tc to 400∘C for the first time. The longitudinal acoustic (LA) mode showed a substantial softening over a wide temperature range above Tc which was accompanied by a remarkable increase in the acoustic damping as well as growth of central peaks. The broad central peak (CP) exhibited a two-mode and one-mode behavior in the paraelectric and ferroelectric phase, respectively, which was consistent with recent far-infrared reflectivity measurements and first-principle-based calculations [Ponomareva , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.77.012102 77, 012102 (2008)]. The acoustic anomalies and CP behavior were correlated with the anomalous birefringence, piezoelectric effect, and the deviation of the Curie-Weiss law observed from the same crystal. This strongly indicates similarity between the dynamics of polar clusters in typical ferroelectrics and the dynamics of polar nanoregions in relaxors, consistent with recent acoustic emission measurements [Dul’kin , Appl. Phys. Lett.APPLAB0003-695110.1063/1.3464968 97, 032903 (2010)]. The relaxation times estimated from the central peak and the LA mode anomalies exhibited similar temperature dependences with comparable orders of magnitude, indicating that the polarization fluctuations due to the precursor polar clusters couples to the LA mode through density fluctuations. All these anomalies share common microscopic origin, correlated Ti off-centered motions forming polar clusters having local symmetry breaking in the paraelectric phase. The existence of the polar clusters were directly evidenced by the temperature evolution of the precise birefringence map. The narrow central peak within ±5 GHz proposed before was not confirmed to exist in the present study.

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

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

Cook, Ryan D.; Lin, Ying-Hsuan; Peng, Zhuoyu

Organic aerosol formation and transformation occurs within aqueous aerosol and cloud droplets, yet little is known about the composition of high molecular weight organic compounds in cloud water. Cloud water samples collected at Whiteface Mountain, New York, during August-September 2014 were analyzed by ultra-high-resolution mass spectrometry to investigate the molecular composition of dissolved organic carbon, with a focus on sulfur- and nitrogen-containing compounds. Organic molecular composition was evaluated in the context of cloud water inorganic ion concentrations, pH, and total organic carbon concentrations to gain insights into the sources and aqueous-phase processes of the observed high molecular weight organic compounds.more » Cloud water acidity was positively correlated with the average oxygen : carbon ratio of the organic constituents, suggesting the possibility for aqueous acid-catalyzed (prior to cloud droplet activation or during/after cloud droplet evaporation) and/or radical (within cloud droplets) oxidation processes. Many tracer compounds recently identified in laboratory studies of bulk aqueous-phase reactions were identified in the cloud water. Organosulfate compounds, with both biogenic and anthropogenic volatile organic compound precursors, were detected for cloud water samples influenced by air masses that had traveled over forested and populated areas. Oxidation products of long-chain (C 10-12) alkane precursors were detected during urban influence. Influence of Canadian wildfires resulted in increased numbers of identified sulfur-containing compounds and oligomeric species, including those formed through aqueous-phase reactions involving methylglyoxal. Light-absorbing aqueous-phase products of syringol and guaiacol oxidation were observed in the wildfire-influenced samples, and dinitroaromatic compounds were observed in all cloud water samples (wildfire, biogenic, and urban-influenced). Overall, the cloud water molecular composition depended on air mass source influence and reflected aqueous-phase reactions involving biogenic, urban, and biomass burning precursors.« less

Enhancement of photoluminescence intensity of GaAs with cubic GaS chemical vapor deposited using a structurally designed single-source precursor

NASA Technical Reports Server (NTRS)

Macinnes, Andrew N.; Power, Michael B.; Barron, Andrew R.; Jenkins, Phillip P.; Hepp, Aloysius F.

1993-01-01

A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster /(t-Bu)GaS/4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron and Rutherford backscattering spectroscopies.

High-yield sol-gel synthesis of well-dispersed, colorless ZrO(2) nanocrystals.

PubMed

Mizuno, Mikihisa; Sasaki, Yuichi; Lee, Sungkil; Katakura, Hitoshi

2006-08-15

A 93% high-yield synthesis of well-dispersed, colorless zirconium dioxide (ZrO(2)) nanocrystals is reported. In this synthesis, hydrolysis and condensation reactions of zirconium(IV) tert-butoxide in the presence of oleic acid (100 degrees C) formed ZrO(2) precursors. The ZrO(2) precursors were made of -Zr-O-Zr- networks surrounded by oleic acid molecules. Annealing (280 degrees C) the precursors dispersed in dioctyl ether caused crystallization of the -Zr-O-Zr- networks, thereby generating 4 nm ZrO(2) nanocrystals stabilized with oleic acid. The particles were highly crystalline and tetragonal phase. A dense ZrO(2) nanocrystal dispersion in toluene (280 mg/mL) showed a transmittance of about 90% (3 mm optical path length) in the whole visible region.

Obtaining aluminas from the thermal decomposition of their different precursors: An {sup 27}Al MAS NMR and X-ray powder diffraction studies

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

Chagas, L.H.; De Carvalho, G.S.G.; San Gil, R.A.S.

2014-01-01

Graphical abstract: - Highlights: • We synthesized three precursors of alumina from different methods. • The calcination of the precursors generated several alumina polymorphs. • XRD and NMR were used for structural investigation of the polymorphs. • The synthesis route determines the structural and textural properties of the solids. - Abstract: A commercial sample of Boehmite was used as precursor of alumina polymorphs. For comparison, three other precursors were synthesized from different methods. Particularly, the use of excess of urea promoted a very crystalline form of basic aluminum carbonate. The characteristics of the four precursors were investigated by thermal, vibrationalmore » and X-ray powder diffraction (XRD) analysis. Additionally, the nuclear magnetic resonance, with magic angle spinning ({sup 27}Al MAS NMR), was used to verify the coordination of aluminum cations. Each precursor was calcined at various temperatures generating alumina polymorphs, which were structurally analyzed by XRD and {sup 27}Al MAS NMR. Due to interest in catalysis supports, special attention was given to the γ-Al{sub 2}O{sub 3} phase, which in addition to structural investigation was subjected to textural analysis. The results showed that, from different synthesis procedures and common route of calcination, one can obtain materials with the same composition but with different structural and textural properties, which in turn can significantly influence the performance of a supported catalyst.« less

Aqueous phase oligomerization of α,β-unsaturated carbonyls and acids investigated using ion mobility spectrometry coupled to mass spectrometry (IMS-MS)

NASA Astrophysics Data System (ADS)

Renard, Pascal; Tlili, Sabrine; Ravier, Sylvain; Quivet, Etienne; Monod, Anne

2016-04-01

One of the current essential issues to unravel our ability to forecast future climate change and air quality, implies a better understanding of natural processes leading to secondary organic aerosol (SOA) formation, and in particular the formation and fate of oligomers. The difficulty in characterizing macromolecules is to discern between large oxygenated molecules from series of oligomers containing repeated small monomers of diverse structures. In the present study, taking advantage from previously established radical vinyl oligomerization of methyl vinylketone (MVK) in the aqueous phase, where relatively simple oligomers containing up to 14 monomers were observed, we have investigated the same reactivity on several other unsaturated water soluble organic compounds (UWSOCs) and on a few mixtures of these precursor compounds. The technique used to characterize the formed oligomers was a traveling wave ion mobility spectrometry coupled to a hybrid quadrupole - time of flight mass spectrometer (IMS-MS) fitted with an electrospray source and ultra-high performance liquid chromatography (UPLC). The technique allows for an additional separation, especially for large ions, containing long carbon chains. We have shown the efficiency of the IMS-mass spectrometry technique to detect oligomers derived from MVK photooxidation in the aqueous phase. The results were then compared to other oligomers, derived from ten other individual biogenic UWSOCs. The technique allowed distinguishing between different oligomers arising from different precursors. It also clearly showed that compounds bearing a non-conjugated unsaturation did not provide oligomerization. Finally, it was shown that the IMS-mass spectrometry technique, applied to mixtures of unsaturated conjugated precursors, exhibited the ability of these precursors to co-oligomerize, i.e. forming only one complex oligomer system bearing monomers of different structures. The results are discussed in terms of atmospheric implications for the detection of oligomers in complex chamber and/or field samples.

Cytometry of DNA Replication and RNA Synthesis: Historical Perspective and Recent Advances Based on “Click Chemistry”

PubMed Central

Darzynkiewicz, Zbigniew; Traganos, Frank; Zhao, Hong; Halicka, H. Dorota; Li, Jiangwei

2011-01-01

This review covers progress in the development of cytometric methodologies designed to assess DNA replication and RNA synthesis. The early approaches utilizing autoradiography to detect incorporation of 3H- or 14C-labeled thymidine were able to identify the four fundamental phases of the cell cycle G1, S, G2, and M, and by analysis of the fraction of labeled mitosis (FLM), to precisely define the kinetics of cell progression through these phases. Analysis of 3H-uridine incorporation and RNA content provided the means to distinguish quiescent G0 from cycling G1 cells. Subsequent progress in analysis of DNA replication was based on the use of BrdU as a DNA precursor and its detection by the quenching of the fluorescence intensity of DNA-bound fluorochromes such as Hoechst 33358 or acridine orange as measured by flow cytometry. Several variants of this methodology have been designed and used in studies to detect anticancer drug-induced perturbations of cell cycle kinetics. The next phase of method development, which was particularly useful in studies of the cell cycle in vivo, including clinical applications, relied on immunocytochemical detection of incorporated halogenated DNA or RNA precursors. This approach however was hampered by the need for DNA denaturation, which made it difficult to concurrently detect other cell constituents for multiparametric analysis. The recently introduced “click chemistry” approach has no such limitation and is the method of choice for analysis of DNA replication and RNA synthesis. This method is based on the use of 5-ethynyl-2′deoxyuridine (EdU) as a DNA precursor or 5-ethynyluridine (EU) as an RNA precursor and their detection with fluorochrome-tagged azides utilizing a copper (I) catalyzed [3+2] cycloaddition. Several examples are presented that illustrate incorporation of EdU or EU in cells subjected to DNA damage detected as histone H2AX phosphorylation that have been analyzed by flow or laser scanning cytometry. PMID:21425239

Efficient nitrogen incorporation in GaAs using novel metal organic As-N precursor di-tertiary-butyl-arsano-amine (DTBAA)

NASA Astrophysics Data System (ADS)

Sterzer, E.; Beyer, A.; Duschek, L.; Nattermann, L.; Ringler, B.; Leube, B.; Stegmüller, A.; Tonner, R.; von Hänisch, C.; Stolz, W.; Volz, K.

2016-04-01

III/V semiconductors containing small amounts of nitrogen (N; dilute nitrides) are discussed in the context of different solar cell and laser applications. The efficiency of these devices is negatively affected by carbon (C) incorporation, which comes either from the direct C-N bond in the N precursor unsymmetrical 1,1-dimethylhydrazine (UDMHy) used conventionally or from the alkyl groups of the conventional precursors for gallium (Ga), indium and arsenic (As) containing carbon. This C is incorporated together with the N due to the strength of the C-N bond. A further important issue in dilute nitride growth is the very low N incorporation efficiency in the crystal from UDMHy, which can be as little as 1% of the N supplied in the gas phase. Therefore, new metal organic chemicals have to be synthesized and their growth characteristics and suitability for dilute nitride growth have to be explored. This work presents the chemical di-tertiary-butyl-arsano-amine (DTBAA), which was synthesized, purified and tested as an N precursor for metal organic vapor phase epitaxy (MOVPE). Computational investigations show β-hydrogen and isobutane elimination to be the main reaction channel in the gas phase with high reaction barriers and absence of small fragments containing C as products. The loss of N via N2, as in UDMHy, can be excluded for unimolecular reactions of DTBAA. The Ga(NAs)/GaAs heterostructures were grown by MOVPE as initial test material and a systematic N incorporation study is presented in this paper. It is shown that high quality Ga(NAs) can be grown using DTBAA. The N incorporation was confirmed by high resolution X-ray diffraction and photoluminescence studies. All samples grown exhibit as grown room temperature photoluminescence and smooth surface morphologies. Furthermore, DTBAA shows extremely high N incorporation efficiency, which makes this molecule a very promising candidate for further research into dilute nitride material growth.

Large scale synthesis of nanostructured zirconia-based compounds from freeze-dried precursors

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

Gomez, A.; Villanueva, R.; Vie, D.

2013-01-15

Nanocrystalline zirconia powders have been obtained at the multigram scale by thermal decomposition of precursors resulting from the freeze-drying of aqueous acetic solutions. This technique has equally made possible to synthesize a variety of nanostructured yttria or scandia doped zirconia compositions. SEM images, as well as the analysis of the XRD patterns, show the nanoparticulated character of those solids obtained at low temperature, with typical particle size in the 10-15 nm range when prepared at 673 K. The presence of the monoclinic, the tetragonal or both phases depends on the temperature of the thermal treatment, the doping concentration and themore » nature of the dopant. In addition, Rietveld refinement of the XRD profiles of selected samples allows detecting the coexistence of the tetragonal and the cubic phases for high doping concentration and high thermal treatment temperatures. Raman experiments suggest the presence of both phases also at relatively low treatment temperatures. - Graphical abstract: Zr{sub 1-x}A{sub x}O{sub 2-x/2} (A=Y, Sc; 0{<=}x{<=}0.12) solid solutions have been prepared as nanostructured powders by thermal decomposition of precursors obtained by freeze-drying, and this synthetic procedure has been scaled up to the 100 g scale. Highlights: Black-Right-Pointing-Pointer Zr{sub 1-x}A{sub x}O{sub 2-x/2} (A=Y, Sc; 0{<=}x{<=}0.12) solid solutions have been prepared as nanostructured powders. Black-Right-Pointing-Pointer The synthetic method involves the thermal decomposition of precursors obtained by freeze-drying. Black-Right-Pointing-Pointer The temperature of the thermal treatment controls particle sizes. Black-Right-Pointing-Pointer The preparation procedure has been scaled up to the 100 g scale. Black-Right-Pointing-Pointer This method is appropriate for the large-scale industrial preparation of multimetallic systems.« less

A Review of Single Source Precursors for the Deposition of Ternary Chalcopyrite Materials

NASA Technical Reports Server (NTRS)

Banger, K. K.; Cowen, J.; Harris, J.; McClarnon, R.; Hehemann, D. G.; Duraj, S. A.; Scheiman, D.; Hepp, A. F.

2002-01-01

The development of thin-film solar cells on flexible, lightweight, space-qualified durable substrates (i.e. Kapton) provides an attractive solution to fabricating solar arrays with high specific power, (W/kg). The syntheses and thermal modulation of ternary single source precursors, based on the [{LR}2Cu(SR')2In(SR')2] architecture in good yields are described. Thermogravimetric analyses (TGA) and Low temperature Differential Scanning Caloriometry, (DSC) demonstrate that controlled manipulation of the steric and electronic properties of either the group five-donor and/or chalcogenide moiety permits directed adjustment of the thermal stability and physical properties of the precursors. TGA-Evolved Gas Analysis, confirms that single precursors decompose by the initial extrusion of the sulphide moiety, followed by the loss of the neutral donor group, (L) to release the ternary chalcopyrite matrix. X-ray diffraction studies, EDS and SEM on the non-volatile pyrolized material demonstrate that these derivatives afford single-phase CuInS2/CuInSe2 materials at low temperature. Thin-film fabrication studies demonstrate that these single source precursors can be used in a spray chemical vapor deposition process, for depositing CuInS2 onto flexible polymer substrates at temperatures less than 400 C.

An effective approach to synthesize monolayer tungsten disulphide crystals using tungsten halide precursor

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

Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap, E-mail: kalita.golap@nitech.ac.jp

2016-02-01

The synthesis of large-area monolayer tungsten disulphide (WS{sub 2}) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS{sub 2} crystals using tungsten hexachloride (WCl{sub 6}) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl{sub 6} in ethanol was drop-casted on SiO{sub 2}/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS{sub 2} crystals on the substrate. The crystalmore » geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS{sub 2} single crystalline monolayer can be grown using the WCl{sub 6} precursor. Our finding shows an easier and effective approach to grow WS{sub 2} monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.« less

Infrared gas phase study on plasma-polymer interactions in high-current diffuse dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Liu, Y.; Welzel, S.; Starostin, S. A.; van de Sanden, M. C. M.; Engeln, R.; de Vries, H. W.

2017-06-01

A roll-to-roll high-current diffuse dielectric barrier discharge at atmospheric pressure was operated in air and Ar/N2/O2 gas mixtures. The exhaust gas from the discharge was studied using a high-resolution Fourier-transform infrared spectrometer in the range from 3000 to 750 cm-1 to unravel the plasma-polymer interactions. The absorption features of HxNyOz, COx, and HCOOH (formic acid) were identified, and the relative densities were deduced by fitting the absorption bands of the detected molecules. Strong interactions between plasma and polymer (Polyethylene-2,6-naphthalate, or PEN) in precursor-free oxygen-containing gas mixtures were observed as evidenced by a high COx production. The presence of HCOOH in the gas effluent, formed through plasma-chemical synthesis of COx, turns out to be a sensitive indicator for etching. By adding tetraethylorthosilicate precursor in the plasma, dramatic changes in the COx production were measured, and two distinct deposition regimes were identified. At high precursor flows, a good agreement with the precursor combustion and the COx production was observed, whereas at low precursor flows an etching-deposition regime transpires, and the COx production is dominated by polymer etching.

A high yield reverse micelle synthesis of catalysts and catalyst precursors

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

Linehan, J.C.; Matson, D.W.; Darab, J.G.

1995-04-01

Reverse micelles or water-in-oil microemulsions have been prepared using a mixed AOT/SDS surfactant to increase the stability of the microemulsion and thereby allow a high loading of particle-forming precursors in the aqueous cores. The Modified Reverse Micelles (MRM), as these new binary surfactant microemulsions are called, have proven useful for the laboratory-scale synthesis of nanoscale metals, metal oxides, metal sulfides, and mixed metal materials. The system allows control over the phase and size of the precipitated crystallites and is ideal for producing nanocrystalline powders and suspensions.

Electrochemical vapor deposition of semiconductors from gas phase with a solid membrane cell.

PubMed

Cho, Sung Ki; Fan, Fu-Ren F; Bard, Allen J

2015-05-27

We demonstrate the feasibility of semiconductor deposition via the electrochemical reduction of gaseous precursors by the use of an anhydrous proton-conducting membrane, the solid acid CsHSO4, at 165 °C. This membrane electrode assembly was operated within the oxidation of hydrogen on a porous Pt anode and the deposition of Si or Ge under bias at the cathode from chloride-based gaseous precursors; SiCl4 and GeCl4 in an Ar flow with a reduction potential over -1.0 V (vs RHE).

Influence of Boehmite Precursor on Aluminosilicate Aerogel Pore Structure, Phase Stability and Resistance to Densification at High Temperatures

NASA Technical Reports Server (NTRS)

Hurwitz, Frances I.; Guo, Haiquan; Newlin, Katy N.

2011-01-01

Aluminosilicate aerogels are of interest as constituents of thermal insulation systems for use at temperatures higher than those attainable with silica aerogels. It is anticipated that their effectiveness as thermal insulators will be influenced by their morphology, pore size distribution, physical and skeletal densities. The present study focuses on the synthesis of aluminosilicate aerogel from a variety of Boehmite (precursors as the Al source, and tetraethylorthosilicate (TEOS) as the Si source, and the influence of starting powder on pore structure and thermal stability.

High-pressure CVD Growth of InN and Indium-rich Group III-nitride Compound Semiconductors for Novel Mid- and Far-infrared Detectors and Emitters

DTIC Science & Technology

2010-02-01

conditions. The TMI and trimethylgallium ( TMG ) precursors are injected simultaneously c) growth surface response via PARS signal The link between...ternary or quaternary alloys such as InGaN or InGaAlN is illustrated in Fig. 10. Here, the injection of the metal precursors, TMI and TMG , are separated...digital InGaN alloy formation, for the control of phase segregations, as well as to adjust the injection parameter to the different TMI and TMG growth

Hydrothermal synthesis of bismuth germanium oxide

DOEpatents

Boyle, Timothy J.

2016-12-13

A method for the hydrothermal synthesis of bismuth germanium oxide comprises dissolving a bismuth precursor (e.g., bismuth nitrate pentahydrate) and a germanium precursor (e.g., germanium dioxide) in water and heating the aqueous solution to an elevated reaction temperature for a length of time sufficient to produce the eulytite phase of bismuth germanium oxide (E-BGO) with high yield. The E-BGO produced can be used as a scintillator material. For example, the air stability and radioluminescence response suggest that the E-BGO can be employed for medical applications.

Peroxyl radical reactions with carotenoids in microemulsions: Influence of microemulsion composition and the nature of peroxyl radical precursor.

PubMed

El-Agamey, Ali; McGarvey, David J

2016-01-01

The reactions of acetylperoxyl radicals with different carotenoids (7,7'-dihydro-β-carotene and ζ-carotene) in SDS and CTAC microemulsions of different compositions were investigated using laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy. The primary objective of this study was to explore the influence of microemulsion composition and the type of surfactant used on the yields and kinetics of various transients formed from the reaction of acetylperoxyl radicals with carotenoids. Also, the influence of the site (hydrocarbon phases or aqueous phase) of generation of the peroxyl radical precursor was examined by using 4-acetyl-4-phenylpiperidine hydrochloride (APPHCl) and 1,1-diphenylacetone (11DPA) as water-soluble and lipid-soluble peroxyl radical precursors, respectively. LFP of peroxyl radical precursors with 7,7'-dihydro-β-carotene (77DH) in different microemulsions gives rise to the formation of three distinct transients namely addition radical (λmax=460 nm), near infrared transient1 (NIR, λmax=700 nm) and 7,7'-dihydro-β-carotene radical cation (77DH(•+), λmax=770 nm). In addition, for ζ-carotene (ZETA) two transients (near infrared transient1 (NIR1, λmax=660 nm) and ζ-carotene radical cation (ZETA(•+), λmax=730-740 nm)) are generated following LFP of peroxyl radical precursors in the presence of ζ-carotene (ZETA) in different microemulsions. The results show that the composition of the microemulsion strongly influences the observed yield and kinetics of the transients formed from the reactions of peroxyl radicals (acetylperoxyl radicals) with carotenoids (77DH and ZETA). Also, the type of surfactant used in the microemulsions influences the yield of the transients formed. The dependence of the transient yields and kinetics on microemulsion composition (or the type of surfactant used in the microemulsion) can be attributed to the change of the polarity of the microenvironment of the carotenoid. Furthermore, the nature of the peroxyl radical precursor used (water-soluble or lipid-soluble peroxyl radical precursors) has little influence on the yields and kinetics of the transients formed from the reaction of peroxyl radicals with carotenoids. In the context of the interest in carotenoids as radical scavenging antioxidants, the fates of the addition radicals (formed from the reaction of carotenoid with peroxyl radicals) and carotenoid radical cations are discussed. Copyright © 2015 Elsevier Inc. All rights reserved.

Colloidal nickel/gallium nanoalloys obtained from organometallic precursors in conventional organic solvents and in ionic liquids: noble-metal-free alkyne semihydrogenation catalysts

NASA Astrophysics Data System (ADS)

Schütte, Kai; Doddi, Adinarayana; Kroll, Clarissa; Meyer, Hajo; Wiktor, Christian; Gemel, Christian; van Tendeloo, Gustaaf; Fischer, Roland A.; Janiak, Christoph

2014-04-01

Efforts to replace noble-metal catalysts by low-cost alternatives are of constant interest. The organometallic, non-aqueous wet-chemical synthesis of various hitherto unknown nanocrystalline Ni/Ga intermetallic materials and the use of NiGa for the selective semihydrogenation of alkynes to alkenes are reported. Thermal co-hydrogenolysis of the all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in high-boiling organic solvents mesitylene and n-decane in molar ratios of 1 : 1, 2 : 3 and 3 : 1 yields the nano-crystalline powder materials of the over-all compositions NiGa, Ni2Ga3 and Ni3Ga, respectively. Microwave induced co-pyrolysis of the same precursors without additional hydrogen in the ionic liquid [BMIm][BF4] (BMIm = 1-butyl-3-methyl-imidazolium) selectively yields the intermetallic phases NiGa and Ni3Ga from the respective 1 : 1 and 3 : 1 molar ratios of the precursors. The obtained materials are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), IR, powder X-ray diffraction (PXRD) and atomic absorption spectroscopy (AAS). The single-source precursor [Ni(GaCp*)(PMe3)3] with a fixed Ni : Ga stoichiometry of 1 : 1 was employed as well. In comparison with the co-hydrogenolytic dual precursor source approach it turned out to be less practical due to inefficient nickel incorporation caused by the parasitic formation of stable [Ni(PMe3)4]. The use of ionic liquid [BMIm][BF4] as a non-conventional solvent to control the reaction and stabilize the nanoparticles proved to be particularly advantageous and stable colloids of the nanoalloys NiGa and Ni3Ga were obtained. A phase-selective Ni/Ga colloid synthesis in conventional solvents and in the presence of surfactants such as hexadecylamine (HDA) was not feasible due to the undesired reactivity of HDA with GaCp* leading to inefficient gallium incorporation. Recyclable NiGa nanoparticles selectively semihydrogenate 1-octyne and diphenylacetylene (tolan) to 1-octene and diphenylethylene, respectively, with a yield of about 90% and selectivities of up to 94 and 87%. Ni-NPs yield alkanes with a selectivity of 97 or 78%, respectively, under the same conditions.Efforts to replace noble-metal catalysts by low-cost alternatives are of constant interest. The organometallic, non-aqueous wet-chemical synthesis of various hitherto unknown nanocrystalline Ni/Ga intermetallic materials and the use of NiGa for the selective semihydrogenation of alkynes to alkenes are reported. Thermal co-hydrogenolysis of the all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in high-boiling organic solvents mesitylene and n-decane in molar ratios of 1 : 1, 2 : 3 and 3 : 1 yields the nano-crystalline powder materials of the over-all compositions NiGa, Ni2Ga3 and Ni3Ga, respectively. Microwave induced co-pyrolysis of the same precursors without additional hydrogen in the ionic liquid [BMIm][BF4] (BMIm = 1-butyl-3-methyl-imidazolium) selectively yields the intermetallic phases NiGa and Ni3Ga from the respective 1 : 1 and 3 : 1 molar ratios of the precursors. The obtained materials are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), IR, powder X-ray diffraction (PXRD) and atomic absorption spectroscopy (AAS). The single-source precursor [Ni(GaCp*)(PMe3)3] with a fixed Ni : Ga stoichiometry of 1 : 1 was employed as well. In comparison with the co-hydrogenolytic dual precursor source approach it turned out to be less practical due to inefficient nickel incorporation caused by the parasitic formation of stable [Ni(PMe3)4]. The use of ionic liquid [BMIm][BF4] as a non-conventional solvent to control the reaction and stabilize the nanoparticles proved to be particularly advantageous and stable colloids of the nanoalloys NiGa and Ni3Ga were obtained. A phase-selective Ni/Ga colloid synthesis in conventional solvents and in the presence of surfactants such as hexadecylamine (HDA) was not feasible due to the undesired reactivity of HDA with GaCp* leading to inefficient gallium incorporation. Recyclable NiGa nanoparticles selectively semihydrogenate 1-octyne and diphenylacetylene (tolan) to 1-octene and diphenylethylene, respectively, with a yield of about 90% and selectivities of up to 94 and 87%. Ni-NPs yield alkanes with a selectivity of 97 or 78%, respectively, under the same conditions. Electronic supplementary information (ESI) available: Ni-Ga phase diagrams, EDX (XPS) of NP1-NP8, table of Ni : Ga ratios, TG of Ni-Ga SSPs, analysis of NP4, dec. of [Ni(GaCp*)3(PCy3)] with characterization, local resolution EDX of NP3-IL, Ni-NP characterization from Ni(COD)2 and details of (semi-)hydrogenation catalysis. See DOI: 10.1039/c4nr00111g

Monitoring of precursor landslide surface deformation using InSAR image in Kuchi-Sakamoto, Shizuoka Prefecture, Japan

NASA Astrophysics Data System (ADS)

Sato, H. P.; Nakajima, H.; Nakano, T.; Daimaru, H.

2014-12-01

Synthetic Aperture Radar (SAR) is the technique to obtain ground surface images using microwave that is emitted from and received on the antenna. The Kuchi-Sakamoto area, 2.2 km2 in precipitous mountains, central Japan, has suffered from frequent landslides, and slow landslide surface deformation has been monitored by on-site extensometer; however, such the monitoring method cannot detect the deformation in the whole area. Because satellite InSAR is effective tool to monitor slow landslide suface deformation, it is a promising tool for detecting precursor deformation and preparing effective measures against serious landslide disasters. In this study Advanced Land Observing Satellite (ALOS) / Phased Array type L-band SAR (PALSAR) data were used, and InSAR images were produced from the PALSAR data that were observed between 5 Sep 2008 and 21 Oct 2008 (from descending orbit) and between 20 Jul 2008 and 7 Sep 2009 (from ascending orbit). InSAR image from descending orbit was found to detect clear precursor landslide surface deformation on a slope; however, InSAR image on ascending orbit did not always detect clear precursor deformation. It is thought to be related with atmospheric moisture condition, length of observation baseline and so on. Furthermore, after phase unwrapping on InSAR images, 2.5-dimensional deformation was analized. This analysis needed both ascending and descending InSAR images and culculated quasi east-west deformation component (Figs. (a) and (b)) and quasi up-down deformation component (Figs. (c) and (d)). The resulting 2.5D calculation gave westward deformation and mixture of upward and downward deformations on the precursor landslide surface deformation slope (blue circles in Figs. (c) and (d)), where remarkable disrupted deep landslide occurred during Nov 2012 and 25 Jun 2013, judging from result of airborne LiDAR survey and field survey; the occurrence date is not precisely identified. The figure remains the issue that eliminating "real" precursor deformation from other candidate deformations. Preparation of this paper was supported by part of Individual Research Fund in College of Humanities and Sciences, Nihon University and part of Grants-in-Aid for Scientific Research, Challenging Exploratory (#25560185, Principal Investigator: Dr. Hiromu Daimaru).

Externally triggered microcapsules

NASA Technical Reports Server (NTRS)

Mosier, Benjamin (Inventor); Morrison, Dennis R. (Inventor)

2011-01-01

Disclosed are microcapsules comprising a polymer shell enclosing one or more immiscible liquid phases in which a drug or drug precursor are contained in a liquid phase. The microparticles also contain magnetic particles that can be heated by application of an external magnetic field and thus heated to a predetermined Curie temperature. Heating of the particles melts the polymer shell and releases the drug without causing heating of surrounding tissues.

Level 3 material characterization of NARC HRPF, HRHU, HRHF, and HRPU

NASA Technical Reports Server (NTRS)

Tobias, Mark E.

1993-01-01

The North American Rayon Corporation (NARC) precursor was developed, qualified, and characterized for Space Shuttle nozzle carbon-cloth phenolic ablative materials in three distinct phases. The characterization phase includes thermal and structural material property analysis and comparisons. This report documents the thermal and structural material property characterization performed by Southern Research Institute (SRI) on the two NARC baseline and two crossover materials.

Electrostimulation of rat callus cells and human lymphocytes in vitro

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

Aro, H.; Eerola, E.; Aho, A.J.

1984-01-01

Asymmetrical pulsing low voltage current was supplied via electrodes to cultured rat fracture callus cells and human peripheral blood lymphocytes. The (/sup 3/H)thymidine incorporation of the callus cells and 5-(/sup 125/I)iodo-2'-deoxyuridine incorporation of the lymphocytes were determined. The growth pattern of callus cells (estimated by cellular density) did not respond to electrical stimulation. However, the uptake of (/sup 3/H)thymidine was increased at the early phase of cell proliferation and inhibited at later phases of proliferation. The (/sup 3/H)thymidine uptake of confluent callus cell cultures did not respond to electrical stimulation. Lymphocytes reacted in a similar way; stimulated cells took upmore » more DNA precursor than control cells at the early phase of stimulation. During cell division, induced by the mitogens phytohemagglutinin and Concanavalin-A, the uptake of DNA precursor by stimulated cells was constantly inhibited. The results suggest that electrical stimuli affect the uptake mechanisms of cell membranes. The duality of the effect seems to be dependent on the cell cycle.« less

Ab initio 27Al NMR chemical shifts and quadrupolar parameters for Al2O3 phases and their precursors

NASA Astrophysics Data System (ADS)

Ferreira, Ary R.; Küçükbenli, Emine; Leitão, Alexandre A.; de Gironcoli, Stefano

2011-12-01

The gauge-including projector augmented wave (GIPAW) method, within the density functional theory (DFT) generalized gradient approximation (GGA) framework, is applied to compute solid state NMR parameters for 27Al in the α, θ, and κ aluminium oxide phases and their gibbsite and boehmite precursors. The results for well established crystalline phases compare very well with available experimental data and provide confidence in the accuracy of the method. For γ-alumina, four structural models proposed in the literature are discussed in terms of their ability to reproduce the experimental spectra also reported in the literature. Among the considered models, the Fd3¯m structure proposed by Paglia [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.71.224115 71, 224115 (2005)] shows the best agreement. We attempt to link the theoretical NMR parameters to the local geometry. Chemical shifts depend on coordination number but no further correlation is found with geometrical parameters. Instead, our calculations reveal that, within a given coordination number, a linear correlation exists between chemical shifts and Born effective charges.

Dissociation of protonated N-(3-phenyl-2H-chromen-2-ylidene)-benzenesulfonamide in the gas phase: cyclization via sulfonyl cation transfer.

PubMed

Wang, Shanshan; Dong, Cheng; Yu, Lian; Guo, Cheng; Jiang, Kezhi

2016-01-15

In the tandem mass spectrometry of protonated N-(3-phenyl-2H-chromen-2-ylidene)benzenesulfonamides, the precursor ions have been observed to undergo gas-phase dissociation via two competing channels: (a) the predominant channel involves migration of the sulfonyl cation to the phenyl C atom and the subsequent loss of benzenesulfinic acid along with cyclization reaction, and (b) the minor one involves dissociation of the precursor ion to give an ion/neutral complex of [sulfonyl cation/imine], followed by decomposition to afford sulfonyl cation or the INC-mediated electron transfer to give an imine radical cation. The proposed reaction channels have been supported by theoretical calculations and D-labeling experiments. The gas-phase cyclization reaction originating from the N- to C-sulfonyl cation transfer has been first reported to the best of our knowledge. For the substituted sulfonamides, the presence of electron-donating groups (R(2) -) at the C-ring effectively facilitates the reaction channel of cyclization reaction, whereas that of electron-withdrawing groups inhibits this pathway. Copyright © 2015 John Wiley & Sons, Ltd.

Designing high-performance layered thermoelectric materials through orbital engineering

PubMed Central

Zhang, Jiawei; Song, Lirong; Madsen, Georg K. H.; Fischer, Karl F. F.; Zhang, Wenqing; Shi, Xun; Iversen, Bo B.

2016-01-01

Thermoelectric technology, which possesses potential application in recycling industrial waste heat as energy, calls for novel high-performance materials. The systematic exploration of novel thermoelectric materials with excellent electronic transport properties is severely hindered by limited insight into the underlying bonding orbitals of atomic structures. Here we propose a simple yet successful strategy to discover and design high-performance layered thermoelectric materials through minimizing the crystal field splitting energy of orbitals to realize high orbital degeneracy. The approach naturally leads to design maps for optimizing the thermoelectric power factor through forming solid solutions and biaxial strain. Using this approach, we predict a series of potential thermoelectric candidates from layered CaAl2Si2-type Zintl compounds. Several of them contain nontoxic, low-cost and earth-abundant elements. Moreover, the approach can be extended to several other non-cubic materials, thereby substantially accelerating the screening and design of new thermoelectric materials. PMID:26948043

Thermal conversion of an iron nitride-silicon nitride precursor into a ferromagnetic nanocomposite

NASA Astrophysics Data System (ADS)

Maya, L.; Thompson, J. R.; Song, K. J.; Warmack, R. J.

1998-01-01

Iron nitride films, FeN, in a pure form and in the form of a nanocomposite in silicon nitride were prepared by reactive sputtering using iron or iron disilicide, respectively, as targets in a nitrogen plasma. Iron nitride decomposes into the elements by heating in vacuum to 800 °C. Intermediate phases such as Fe2N or Fe4N form at lower temperatures. The nanocomposites contain the iron phases as particles with an average size of ˜5 nm dispersed in the amorphous silicon nitride matrix. The magnetic properties of the nanocomposites were established. The precursor FeN-Si3N4 film is paramagnetic, while the Fe-Si3N4, obtained by heating in vacuum, is ferromagnetic and shows typical superparamagnetic behavior. These films are of interest as recording media with superior chemical and mechanical stability and may be encoded by localized heating.

In situ production of titanium dioxide nanoparticles in molten salt phase for thermal energy storage and heat-transfer fluid applications

NASA Astrophysics Data System (ADS)

Lasfargues, Mathieu; Bell, Andrew; Ding, Yulong

2016-06-01

In this study, TiO2 nanoparticles (average particle size 16 nm) were successfully produced in molten salt phase and were showed to significantly enhance the specific heat capacity of a binary eutectic mixture of sodium and potassium nitrate (60/40) by 5.4 % at 390 °C and 7.5 % at 445 °C for 3.0 wt% of precursors used. The objective of this research was to develop a cost-effective alternate method of production which is potentially scalable, as current techniques utilized are not economically viable for large quantities. Enhancing the specific heat capacity of molten salt would promote more competitive pricing for electricity production by concentrating solar power plant. Here, a simple precursor (TiOSO4) was added to a binary eutectic mixture of potassium and sodium nitrate, heated to 450 °C, and cooled to witness the production of nanoparticles.

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

Kabalka, George W

The goal of this research was on the development of new, rapid, and efficient synthetic methods for incorporating short-lived radionuclides into agents of use in measuring dynamic processes. The initial project period (Year 1) was focused on the preparation of stable, solid state precursors that could be used to efficiently incorporate short-lived radioisotopes into small molecules of use in biological applications (environmental, plant, and animal). The investigation included development and evaluation of new methods for preparing carbon-carbon and carbon-halogen bonds for use in constructing the substrates to be radiolabeled. The second phase (Year 2) was focused on developing isotope incorporationmore » techniques using the stable, boronated polymeric precursors. The final phase (Year 3), was focused on the preparation of specific radiolabeled agents and evaluation of their biodistribution using micro-PET and micro-SPECT. In addition, we began the development of a new series of polymeric borane reagents based on polyethylene glycol backbones.« less

Titanium Dioxide Coating Prepared by Use of a Suspension-Solution Plasma-Spray Process

NASA Astrophysics Data System (ADS)

Du, Lingzhong; Coyle, Thomas W.; Chien, Ken; Pershin, Larry; Li, Tiegang; Golozar, Mehdi

2015-08-01

Titanium dioxide coatings were prepared from titanium isopropoxide solution containing nano TiO2 particles by use of a plasma-spray process. The effects of stand-off distance on coating composition and microstructure were investigated and compared with those for pure solution precursor and a water-based suspension of TiO2. The results showed that the anatase content of the coating increased with increasing stand-off distance and the rate of deposition decreased with increasing spray distance. Anatase nanoparticles in solution were incorporated into the coatings without phase transformation whereas most of the TiO2 in the precursor solution was transformed into rutile. The microstructure of preserved anatase particles bound by rutile improved the efficiency of deposition of the coating. The amount of anatase phase can be adjusted by variation of the ratio of solution to added anatase TiO2 nanoparticles.

Physical Principles of Skeletal Minerals Revealed with Spectromicroscopy

ScienceCinema

Gilbert, Pupa [U of Wisconsin-Madison, Wisconsin, United States

2017-12-09

Skeletal elements of marine and terrestrial organisms have the most fascinating nano-to-macro-structures, attracting the attention of physicists, biologists, chemists, and materials scientists. Using X-PEEM spectromicroscopy we revealed some of the fundamental mechanisms leading to the formation of these biominerals. Specifically, we addressed the following questions and provided the answers: 1Q) How do teeth, bones, and echinoderm and mollusk shells acquire their unusual, curved and complex morphology, if they are composed of single crystals? 1A) Via amorphous precursor phases; 2Q) How does crystallinity propagate through the amorophous precursor phases in sea urchin spicules and teeth? 2A) By secondary nucleation, following random walk patterns; 3Q) How does iridescent mother-of-pearl become ordered? 3A) Gradually, through a kinetic mechanisms in which fastest growing single-crystals win the competition for space, thus end up being approximately co-oriented.

Space Shuttle main engine product improvement

NASA Technical Reports Server (NTRS)

Lucci, A. D.; Klatt, F. P.

1985-01-01

The current design of the Space Shuttle Main Engine has passed 11 certification cycles, amassed approximately a quarter million seconds of engine test time in 1200 tests and successfully launched the Space Shuttle 17 times of 51 engine launches through May 1985. Building on this extensive background, two development programs are underway at Rocketdyne to improve the flow of hot gas through the powerhead and evaluate the changes to increase the performance margins in the engine. These two programs, called Phase II+ and Technology Test Bed Precursor program are described. Phase II+ develops a two-tube hot-gas manifold that improves the component environment. The Precursor program will evaluate a larger throat main combustion chamber, conduct combustion stability testing of a baffleless main injector, fabricate an experimental weld-free heat exchanger tube, fabricate and test a high pressure oxidizer turbopump with an improved inlet, and develop and test methods for reducing temperature transients at start and shutdown.

Motion of the guest ion as precursor to the first-order phase transition in the cage system GdB6

NASA Astrophysics Data System (ADS)

Iwasa, Kazuaki; Igarashi, Ryosuke; Saito, Kotaro; Laulhé, Claire; Orihara, Toshihiko; Kunii, Satoru; Kuwahara, Keitaro; Nakao, Hironori; Murakami, Youichi; Iga, Fumitoshi; Sera, Masafumi; Tsutsui, Satoshi; Uchiyama, Hiroshi; Baron, Alfred Q. R.

2011-12-01

The motion of guest Gd ions in oversized boron cages in GdB6 was investigated from phonon spectra measurements obtained by inelastic x-ray scattering. The measured phonon modes soften by about 10% from 300 K down to TN=16 K, in particular, the longitudinal phonon for the propagation vector q1=(1/2,0,0) that characterizes the distorted structure below TN. Besides, the dispersion relation curves show kinklike anomalies at qk=(0.38,0.38,0). The observed results imply that the motion of the guest Gd ion interplays with the f electrons magnetoelastically and with carriers via Fermi surface nesting. The anomalous properties previously reported for this material far above TN originate from the strong electron-phonon coupling, which causes the motion of guest ions as precursors to the first-order phase transition.

Ab initio molecular dynamics of atomic-scale surface reactions: insights into metal organic chemical vapor deposition of AlN on graphene.

PubMed

Sangiovanni, D G; Gueorguiev, G K; Kakanakova-Georgieva, A

2018-06-19

Metal organic chemical vapor deposition (MOCVD) of group III nitrides on graphene heterostructures offers new opportunities for the development of flexible optoelectronic devices and for the stabilization of conceptually-new two-dimensional materials. However, the MOCVD of group III nitrides is regulated by an intricate interplay of gas-phase and surface reactions that are beyond the resolution of experimental techniques. We use density-functional ab initio molecular dynamics (AIMD) with van der Waals corrections to identify atomistic pathways and associated electronic mechanisms driving precursor/surface reactions during metal organic vapor phase epitaxy at elevated temperatures of aluminum nitride on graphene, considered here as model case study. The results presented provide plausible interpretations of atomistic and electronic processes responsible for delivery of Al, C adatoms, and C-Al, CHx, AlNH2 admolecules on pristine graphene via precursor/surface reactions. In addition, the simulations reveal C adatom permeation across defect-free graphene, as well as exchange of C monomers with graphene carbon atoms, for which we obtain rates of ∼0.3 THz at typical experimental temperatures (1500 K), and extract activation energies Eexca = 0.28 ± 0.13 eV and attempt frequencies Aexc = 2.1 (×1.7±1) THz via Arrhenius linear regression. The results demonstrate that AIMD simulations enable understanding complex precursor/surface reaction mechanisms, and thus propose AIMD to become an indispensable routine prediction-tool toward more effective exploitation of chemical precursors and better control of MOCVD processes during synthesis of functional materials.

E-beam and UV induced fabrication of CeO2, Eu2O3 and their mixed oxides with UO2

NASA Astrophysics Data System (ADS)

Pavelková, Tereza; Vaněček, Vojtěch; Jakubec, Ivo; Čuba, Václav

2016-07-01

CeO2, Eu2O3 and mixed oxides of CeO2-UO2, Eu2O3-UO2 were fabricated. The preparative method was based on the irradiation of aqueous solutions containing cerium/europium (and uranyl) nitrates and ammonium formate. In the course of irradiation, the solid phase (precursor) was precipitated. The composition of irradiated solutions significantly affected the properties of precursor formed in the course of the irradiation. However, subsequent heat treatment of (amorphous) precursors at temperatures ≤650 °C invariably resulted in the formation of powder oxides with well-developed nanocrystals with linear crystallite size 13-27 nm and specific surface area 10-46 m2 g-1. The applicability of both ionizing (e-beam) and non-ionizing (UV) radiation was studied.

Bi-Sr-Ca-Cu-O and Pb-Bi-Sr-Ca-Cu-O superconductor films via an electrodeposition process

NASA Astrophysics Data System (ADS)

Maxfield, M.; Eckhardt, H.; Iqbal, Z.; Reidinger, F.; Baughman, R. H.

1989-05-01

A novel electrochemical process has been developed for the formation of superconducting films. Using this process, superconducting films of Bi2Sr2Ca1Cu2O8 and (Pb,Bi)2Sr2Ca1Cu2O8 have been formed. The process consists of simultaneously depositing the metallic constituents of the superconductor from a single electrolyte, and thermally oxidizing the resulting precursors film to form the superconducting phase. Application of -4 to -5 V vs Ag/Ag(+) to a conductive cathode substrate which is immersed in an electrolyte containing salts of all of the metals reduces the metal cations, causing then to deposit on the cathode as a metallic film precursor. Precursor films having desired stoichiometries were obtained by regulating the electrolyte bath composition.

Mechanochemical approach for synthesis of layered double hydroxides

NASA Astrophysics Data System (ADS)

Zhang, Xiaoqing; Li, Shuping

2013-06-01

In this paper, a mechanochemical approach is used to prepare layered double hydroxides (LDHs). This approach involves manually grinding the precursor, nitrates and then the hydrothermal treatment. The study indicates that grinding leads to the incomplete formation of LDHs phase, LDHs-M. The reaction degree of precursor salts to LDHs after grinding depends on the melting points of the precursors. As expected, hydrothermal treatment is beneficial for the good crystallization and regularity of LDHs. Especially, the effect of hydrothermal treatment has been emphatically explored. The hydration of LDHs-M, increment of zeta potentials and the complete exchange of NO3- by CO32- anions occur successively or in parallel during the hydrothermal treatment. It can be found that combination of grinding and hydrothermal treatment gives rise to the formation of uniform and monodispersed particles of LDHs.

Advanced transition metal phosphide materials from single-source molecular precursors

NASA Astrophysics Data System (ADS)

Colson, Adam Caleb

In this thesis, the feasibility of employing organometallic single-source precursors in the preparation of advanced transition metal pnictide materials such as colloidal nanoparticles and films has been investigated. In particular, the ternary FeMnP phase was targeted as a model for preparing advanced heterobimetallic phosphide materials, and the iron-rich Fe3P phase was targeted due to its favorable ferromagnetic properties as well as the fact that the preparation of advanced Fe3P materials has been elusive by commonly used methods. Progress towards the synthesis of advanced Fe2--xMn xP nanomaterials and films was facilitated by the synthesis of the novel heterobimetallic complexes FeMn(CO)8(mu-PR1R 2) (R1 = H, R2 = H or R1 = H, R2 = Ph), which contain the relatively rare mu-PH2 and mu-PPhH functionalities. Iron rich Fe2--xMnxP nanoparticles were obtained by thermal decomposition of FeMn(CO)8(mu-PH 2) using solution-based synthetic methods, and empirical evidence suggested that oleic acid was responsible for manganese depletion. Films containing Fe, Mn, and P with the desired stoichiometric ratio of 1:1:1 were prepared using FeMn(CO)8(mu-PH2) in a simple low-pressure metal-organic chemical vapor deposition (MOCVD) apparatus. Although the elemental composition of the precursor was conserved in the deposited film material, spectroscopic evidence indicated that the films were not composed of pure-phase FeMnP, but were actually mixtures of crystalline FeMnP and amorphous FeP and Mn xOy. A new method for the preparation of phase-pure ferromagnetic Fe 3P films on quartz substrates has also been developed. This approach involved the thermal decomposition of the single-source precursors H 2Fe3(CO)9PR (R = tBu or Ph) at 400 °C. The films were deposited using a simple home-built MOCVD apparatus and were characterized using a variety of analytical methods. The films exhibited excellent phase purity, as evidenced by X-ray diffraction, X-ray photoelectron spectroscopy, and field-dependent magnetization measurements, the results of which were all in good agreement with measurements obtained from bulk Fe3P. As-deposited Fe3P films were found to be amorphous, and little or no magnetic hysteresis was observed in plots of magnetization versus applied field. Annealing the Fe3P films at 550 °C resulted in improved crystallinity as well as the observation of magnetic hysteresis.

Molding mineral within microporous hydrogels by a polymer-induced liquid-precursor (PILP) process.

PubMed

Cheng, Xingguo; Gower, Laurie B

2006-01-01

Natural biominerals often have exquisite morphologies, where the cells exercise a high degree of crystallographic control through secretion of biological macromolecules and regulation of ion transport. One important example is the sea urchin spine. It has recently been shown to be formed through deposition of a transient amorphous calcium carbonate (ACC) precursor phase that later transforms to single-crystalline calcite, ultimately forming an elaborate three-dimensional microporous calcium carbonate structure with interconnected pores. Macromolecules associated with the mineral phase are thought to play a key role in regulating this transformation. The work described here mimics this type of morphological control by "molding" an amorphous calcium carbonate precursor within a porous poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel that has been prepared as a negative replica from the void space of an urchin spine. Using an acidic biomimetic polymer as a process-directing agent, we show that polyaspartic acid induces amorphous calcium carbonate (ACC) nanoparticles, which have fluidic character and therefore are able to infiltrate the PHEMA hydrogel replica and coalesce into the convoluted morphology that replicates the original microporous structure of the sea urchin spine. By "molding" calcium carbonate into a complex morphology at room temperature, using a precursor process that is induced by a biomimetic acidic macromolecule, the PILP process is a useful in vitro model for examining different aspects of the amorphous-to-crystalline transformation process that is apparently used by a variety of biomineralizing organisms. For example, although we were able to replicate the overall morphology of the spine, it had polycrystalline texture; further studies with this system will focus on controlling the nucleation event, which may help to elucidate how such a convoluted structure can be prepared with single-crystalline texture via an amorphous precursor. Through a better understanding of the mechanisms used by organisms to regulate crystal properties, such biomimetic processes can lead to the synthesis of materials with superior electronic, mechanical, and optical properties.

Characterizations of maghemite thin films prepared by a sol-gel method

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

Lau, L. N., E-mail: lau7798@gmail.com; Ibrahim, N. B., E-mail: baayah@ukm.edu.my

2015-09-25

Iron is one of the abundant elements of Mother Nature and its compound, iron oxide is an interesting material to study since its discovery in the form of magnetite. It can exist in many phases such as hematite and maghemite, this unique nature has put it as a potential candidate in various applications. The aim of this work is to study the influence of different precursor concentrations on the microstructural and magnetic properties of iron oxide thin film. All samples were prepared via the sol-gel method followed by a spin coating technique on quartz substrates. Iron oxide films were confirmedmore » as maghemite phase from X-ray diffraction patterns. The film morphology was examined by a field emission scanning electron microscope and it showed non-systematic value of average grain size and film thickness throughout the study. Hysteresis loop further confirmed that maghemite is a magnetic material when it was characterized by a vibrating sample magnetometer. The coercivity did not show any correlation with molarity. Nevertheless, it increased as the precursor concentration of the film increased due to the domain behaviour. In conclusion, maghemite thin films were successfully synthesized by the sol-gel method with different precursor concentrations in this work.« less

Synthesis and hydration behavior of calcium zirconium aluminate (Ca{sub 7}ZrAl{sub 6}O{sub 18}) cement

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

Kang, Eun-Hee; Yoo, Jun-Sang; Kim, Bo-Hye

2014-02-15

Calcium zirconium aluminate (Ca{sub 7}ZrAl{sub 6}O{sub 18}) cements were prepared by solid state reaction and polymeric precursor methods, and their phase evolution, morphology, and hydration behavior were investigated. In polymeric precursor method, a nearly single phase Ca{sub 7}ZrAl{sub 6}O{sub 18} was obtained at relatively lower temperature (1200 °C) whereas in solid state reaction, a small amount of CaZrO{sub 3} coexisted with Ca{sub 7}ZrAl{sub 6}O{sub 18} even at higher temperature (1400 °C). Unexpectedly, Ca{sub 7}ZrAl{sub 6}O{sub 18} synthesized by polymeric precursor process was the large-sized and rough-shaped powder. The planetary ball milling was employed to control the particle size and shape.more » The hydration behavior of Ca{sub 7}ZrAl{sub 6}O{sub 18} was similar to that of Ca{sub 3}Al{sub 2}O{sub 6} (C3A), but the hydration products were Ca{sub 3}Al{sub 2}O{sub 6}·6H{sub 2}O (C3AH6) and several intermediate products. Thus, Zr (or ZrO{sub 2}) stabilized the intermediate hydration products of C3A.« less

High rate capability of a BaTiO3-decorated LiCoO2 cathode prepared via metal organic decomposition

NASA Astrophysics Data System (ADS)

Teranishi, Takashi; Katsuji, Naoto; Yoshikawa, Yumi; Yoneda, Mika; Hayashi, Hidetaka; Kishimoto, Akira; Yoda, Koji; Motobayashi, Hidefumi; Tasaki, Yuzo

2016-10-01

Metal organic decomposition (MOD) using octylic acid salts was applied to synthesize a BaTiO3-LiCoO2 (BT-LC) composite powder. The Ba and Ti octylates were utilized as metal precursors, in an attempt to synthesize homogeneous BT nanoparticles on the LC matrix. The BT-LC composite, having a phase-separated composite structure without any impurity phase, was successfully obtained by optimizing the MOD procedure. The composite prepared using octylate precursors exhibited a sharper distribution and better dispersibility of decorated BT particles. Additionally, the average particle size of the decorated BTs using metal octylate was reduced to 23.3 nm, compared to 44.4 nm from conventional processes using Ba acetate as well as Ti alkoxide as precursors. The composite cathode displayed better cell performance than its conventional counterpart; the discharge capacity of the metal octylate-derived specimen was 55.6 mAh/g at a 50C rate, corresponding to 173% of the capacity of the conventional specimen (32.2 mAh/g). The notable improvement in high rate capability obtained in this study, compared with the conventional route, was attributed to the higher density of the triple junction formed by the BT-LC-electrolyte interface.

ZnS, CdS and HgS nanoparticles via alkyl-phenyl dithiocarbamate complexes as single source precursors.

PubMed

Onwudiwe, Damian C; Ajibade, Peter A

2011-01-01

The synthesis of II-VI semiconductor nanoparticles obtained by the thermolysis of certain group 12 metal complexes as precursors is reported. Thermogravimetric analysis of the single source precursors showed sharp decomposition leading to their respective metal sulfides. The structural and optical properties of the prepared nanoparticles were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) UV-Vis and photoluminescence spectroscopy. The X-ray diffraction pattern showed that the prepared ZnS nanoparticles have a cubic sphalerite structure; the CdS indicates a hexagonal phase and the HgS show the presence of metacinnabar phase. The TEM image demonstrates that the ZnS nanoparticles are dot-shaped, the CdS and the HgS clearly showed a rice and spherical morphology respectively. The UV-Vis spectra exhibited a blue-shift with respect to that of the bulk samples which is attributed to the quantum size effect. The band gap of the samples have been calculated from absorption spectra and werefound to be about 4.33 eV (286 nm), 2.91 eV (426 nm) and 4.27 eV (290 nm) for the ZnS, CdS and HgS samples respectively.

ZnS, CdS and HgS Nanoparticles via Alkyl-Phenyl Dithiocarbamate Complexes as Single Source Precursors

PubMed Central

Onwudiwe, Damian C.; Ajibade, Peter A.

2011-01-01

The synthesis of II-VI semiconductor nanoparticles obtained by the thermolysis of certain group 12 metal complexes as precursors is reported. Thermogravimetric analysis of the single source precursors showed sharp decomposition leading to their respective metal sulfides. The structural and optical properties of the prepared nanoparticles were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) UV-Vis and photoluminescence spectroscopy. The X-ray diffraction pattern showed that the prepared ZnS nanoparticles have a cubic sphalerite structure; the CdS indicates a hexagonal phase and the HgS show the presence of metacinnabar phase. The TEM image demonstrates that the ZnS nanoparticles are dot-shaped, the CdS and the HgS clearly showed a rice and spherical morphology respectively. The UV-Vis spectra exhibited a blue-shift with respect to that of the bulk samples which is attributed to the quantum size effect. The band gap of the samples have been calculated from absorption spectra and werefound to be about 4.33 eV (286 nm), 2.91 eV (426 nm) and 4.27 eV (290 nm) for the ZnS, CdS and HgS samples respectively. PMID:22016607

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

Wildfire, Christina; Sabolsky, Edward M.; Spencer, Michael J.

The rapid synthesis of yttrium aluminum garnet (Y 3Al 15O 12, YAG) powder was investigated through the use of microwave irradiation of the oxide precursor system. For this investigation, an external hybrid heating source was not used. Instead, the rapid heating of the precursor materials (yttria and alumina powders, which are typically transparent to 2.45 GHz microwaves) was initiated by mixing an intrinsic absorbing material (carbon) into the original oxide precursors. The effect of the carbon characteristics, such as carbon source, concentration, particle size, and agglomerate microstructure were evaluated on the efficiency of coupling and resultant oxide reaction. The microwavemore » power was varied to optimize the YAG conversion and eliminate intermediate phase formation. Interactions between the conductive carbon particles and the dielectric oxides within the microwave exposure produced local arching and micro-plasma formation within the powder bed, resulting in the rapid formation of the refractory YAG composition. This optimal conduction led to temperatures of 1000°C that could be achieved in less than 5 min resulting in the formation of > 90 vol% YAG. The understanding of a conductor/dielectric particulate system here, provided insight into possible application of similar systems where microwave irradiation could be used for enhanced solid-state formation, local melting events, and gas phase reactions with a composite powder media.« less

Review of Urban Secondary Organic Aerosol Formation from Gasoline and Diesel Motor Vehicle Emissions.

PubMed

Gentner, Drew R; Jathar, Shantanu H; Gordon, Timothy D; Bahreini, Roya; Day, Douglas A; El Haddad, Imad; Hayes, Patrick L; Pieber, Simone M; Platt, Stephen M; de Gouw, Joost; Goldstein, Allen H; Harley, Robert A; Jimenez, Jose L; Prévôt, André S H; Robinson, Allen L

2017-02-07

Secondary organic aerosol (SOA) is formed from the atmospheric oxidation of gas-phase organic compounds leading to the formation of particle mass. Gasoline- and diesel-powered motor vehicles, both on/off-road, are important sources of SOA precursors. They emit complex mixtures of gas-phase organic compounds that vary in volatility and molecular structure-factors that influence their contributions to urban SOA. However, the relative importance of each vehicle type with respect to SOA formation remains unclear due to conflicting evidence from recent laboratory, field, and modeling studies. Both are likely important, with evolving contributions that vary with location and over short time scales. This review summarizes evidence, research needs, and discrepancies between top-down and bottom-up approaches used to estimate SOA from motor vehicles, focusing on inconsistencies between molecular-level understanding and regional observations. The effect of emission controls (e.g., exhaust aftertreatment technologies, fuel formulation) on SOA precursor emissions needs comprehensive evaluation, especially with international perspective given heterogeneity in regulations and technology penetration. Novel studies are needed to identify and quantify "missing" emissions that appear to contribute substantially to SOA production, especially in gasoline vehicles with the most advanced aftertreatment. Initial evidence suggests catalyzed diesel particulate filters greatly reduce emissions of SOA precursors along with primary aerosol.

Combining single source chemical vapour deposition precursors to explore the phase space of titanium oxynitride thin films.

PubMed

Rees, Kelly; Lorusso, Emanuela; Cosham, Samuel D; Kulak, Alexander N; Hyett, Geoffrey

2018-02-14

In this paper we report on a novel chemical vapour deposition approach to the formation and control of composition of mixed anion materials, as applied to titanium oxynitride thin films. The method used is the aerosol assisted chemical vapour deposition (AACVD) of a mixture of single source precursors. To explore the titanium-oxygen-nitrogen system the single source precursors selected were tetrakis(dimethylamido) titanium and titanium tetraisopropoxide which individually are precursors to thin films of titanium nitride and titanium dioxide respectively. However, by combining these precursors in specific ratios in a series of AACVD reactions at 400 °C, we are able to deposit thin films of titanium oxynitride with three different structure types and a wide range of compositions. Using this precursor system we can observe films of nitrogen doped anatase, with 25% anion doping of nitrogen; a new composition of pseudobrookite titanium oxynitride with a composition of Ti 3 O 3.5 N 1.5 , identified as being a UV photocatalyst; and rock-salt titanium oxynitride in the range TiO 0.41 N 0.59 to TiO 0.05 N 0.95 . The films were characterised using GIXRD, WDX and UV-vis spectroscopy, and in the case of the pseudobrookite films, assessed for photocatalytic activity. This work shows that a so-called dual single-source CVD approach is an effective method for the deposition of ternary mixed anion ceramic films through simple control of the ratio of the precursors, while keeping all other experimental parameters constant.

Electron interactions with the heteronuclear carbonyl precursor H2FeRu3(CO)13 and comparison with HFeCo3(CO)12: from fundamental gas phase and surface science studies to focused electron beam induced deposition.

PubMed

P, Ragesh Kumar T; Weirich, Paul; Hrachowina, Lukas; Hanefeld, Marc; Bjornsson, Ragnar; Hrodmarsson, Helgi Rafn; Barth, Sven; Fairbrother, D Howard; Huth, Michael; Ingólfsson, Oddur

2018-01-01

In the current contribution we present a comprehensive study on the heteronuclear carbonyl complex H 2 FeRu 3 (CO) 13 covering its low energy electron induced fragmentation in the gas phase through dissociative electron attachment (DEA) and dissociative ionization (DI), its decomposition when adsorbed on a surface under controlled ultrahigh vacuum (UHV) conditions and exposed to irradiation with 500 eV electrons, and its performance in focused electron beam induced deposition (FEBID) at room temperature under HV conditions. The performance of this precursor in FEBID is poor, resulting in maximum metal content of 26 atom % under optimized conditions. Furthermore, the Ru/Fe ratio in the FEBID deposit (≈3.5) is higher than the 3:1 ratio predicted. This is somewhat surprising as in recent FEBID studies on a structurally similar bimetallic precursor, HFeCo 3 (CO) 12 , metal contents of about 80 atom % is achievable on a routine basis and the deposits are found to maintain the initial Co/Fe ratio. Low temperature (≈213 K) surface science studies on thin films of H 2 FeRu 3 (CO) 13 demonstrate that electron stimulated decomposition leads to significant CO desorption (average of 8-9 CO groups per molecule) to form partially decarbonylated intermediates. However, once formed these intermediates are largely unaffected by either further electron irradiation or annealing to room temperature, with a predicted metal content similar to what is observed in FEBID. Furthermore, gas phase experiments indicate formation of Fe(CO) 4 from H 2 FeRu 3 (CO) 13 upon low energy electron interaction. This fragment could desorb at room temperature under high vacuum conditions, which may explain the slight increase in the Ru/Fe ratio of deposits in FEBID. With the combination of gas phase experiments, surface science studies and actual FEBID experiments, we can offer new insights into the low energy electron induced decomposition of this precursor and how this is reflected in the relatively poor performance of H 2 FeRu 3 (CO) 13 as compared to the structurally similar HFeCo 3 (CO) 12 .

Electron interactions with the heteronuclear carbonyl precursor H2FeRu3(CO)13 and comparison with HFeCo3(CO)12: from fundamental gas phase and surface science studies to focused electron beam induced deposition

PubMed Central

P, Ragesh Kumar T; Weirich, Paul; Hrachowina, Lukas; Hanefeld, Marc; Bjornsson, Ragnar; Hrodmarsson, Helgi Rafn; Barth, Sven; Fairbrother, D Howard; Huth, Michael

2018-01-01

In the current contribution we present a comprehensive study on the heteronuclear carbonyl complex H2FeRu3(CO)13 covering its low energy electron induced fragmentation in the gas phase through dissociative electron attachment (DEA) and dissociative ionization (DI), its decomposition when adsorbed on a surface under controlled ultrahigh vacuum (UHV) conditions and exposed to irradiation with 500 eV electrons, and its performance in focused electron beam induced deposition (FEBID) at room temperature under HV conditions. The performance of this precursor in FEBID is poor, resulting in maximum metal content of 26 atom % under optimized conditions. Furthermore, the Ru/Fe ratio in the FEBID deposit (≈3.5) is higher than the 3:1 ratio predicted. This is somewhat surprising as in recent FEBID studies on a structurally similar bimetallic precursor, HFeCo3(CO)12, metal contents of about 80 atom % is achievable on a routine basis and the deposits are found to maintain the initial Co/Fe ratio. Low temperature (≈213 K) surface science studies on thin films of H2FeRu3(CO)13 demonstrate that electron stimulated decomposition leads to significant CO desorption (average of 8–9 CO groups per molecule) to form partially decarbonylated intermediates. However, once formed these intermediates are largely unaffected by either further electron irradiation or annealing to room temperature, with a predicted metal content similar to what is observed in FEBID. Furthermore, gas phase experiments indicate formation of Fe(CO)4 from H2FeRu3(CO)13 upon low energy electron interaction. This fragment could desorb at room temperature under high vacuum conditions, which may explain the slight increase in the Ru/Fe ratio of deposits in FEBID. With the combination of gas phase experiments, surface science studies and actual FEBID experiments, we can offer new insights into the low energy electron induced decomposition of this precursor and how this is reflected in the relatively poor performance of H2FeRu3(CO)13 as compared to the structurally similar HFeCo3(CO)12. PMID:29527432

Preparation & characterization of high purity Cu2 ZnSn(SxSe1-x)4 nanoparticles

NASA Astrophysics Data System (ADS)

Negash, Bethlehem G.

Research in thin film solar cells applies novel techniques to synthesize cost effective and highly efficient absorber materials in order to generate electricity directly from solar energy. Of these materials, copper zinc tin sulfoselenide (Cu2ZnSn(SxSe1-x) 4) nanoparticles have shown great promise in solar cell applications due to optimal material properties as well as low cost & relative abundance of materials.1,2 Sulfoselenide nanoparticles have also a broader impact in other industries including electronics3, LED 4, and biomedical research5. Of the many routes of manufacturing these class of semiconductors, colloidal synthesis of Cu 2ZnSn(SxSe1-x)4 offers a scalable, low cost and high-throughput route for manufacturing high efficiency thin-film solar cells. Hydrazine processed Cu2ZnSn(SxSe1-x )4 devices have reached a record power conversion efficiency (PCE) of 12.6%, much higher than the 9.6% reported for physical vapor deposition (PVD) systems.6,7. Despite high efficiencies, wet synthesis of nanoparticles, however, is made more complicated in multi-element, quaternary and quinary systems such as copper zinc tin sulfoselenide (CZTSSe) and copper indium gallium diselenide (CIGSe). One major disadvantage in these systems is growth of the desired quaternary or quinary phase in competition with unwanted binary and ternary phases with low energy of formation.8,9 Moreover, various reaction parameters such as reaction time, temperature, and choice of ligand also affect, chemical as well as physical properties of resulting nanoparticles. Understanding of the formation mechanisms of the particles is necessary in order to address some of these challenges in wet synthesis of CZTSSe nanoparticles. In this study, we investigate synthesis conditions & reaction parameters which yield high purity Cu2ZnSn(SxSe1-x) 4 nanoparticles as well as attempt to understand the growth mechanism of these nanoparticles. This was achieved by manipulating anion precursor preparation routes as well order in which precursors are introduced into a reaction system. We report a new solution based sulfoselenide preparation route which has been used to synthesize high purity Cu2ZnSn(S xSe1-x)4 nanoparticles. Uniform phase Cu 2ZnSn(SxSe1-x)4 nanoparticles were successfully synthesized over a wide range of varying chalcogen ratios. It was found that anion precursor solution plays a key role in determining the morphology & phase purity of the final nanoparticles, as observed from X-ray Diffraction (XRD) and Raman spectroscopy. A uniform sulfoselenide solution is needed to produce high purity Cu2ZnSn(SxSe1-x )4 nanoparticles with narrow phase distribution. Moreover, the relative reactivity of each anion must be balanced in order to yield uniform phase nanoparticles. The findings of this study as well as the reported mixed chalcogen precursor preparation route can be applied in various industries, including photovoltaics to produce uniform phase, solution processed sulfoselenide nanoparticles.

Sulfur and Hydrogen Isotope Anomalies in Meteorite Sulfonic Acids

NASA Technical Reports Server (NTRS)

Cooper, George W.; Thiemens, Mark H.; Jackson, Teresa L.; Chang, Sherwood

1997-01-01

Intramolecular carbon, hydrogen, and sulfur isotope ratios were measured on a homologous series of organic sulfonic acids discovered in the Murchison meteorite. Mass-independent sulfur isotope fractionations were observed along with high deuterium/hydrogen ratios. The deuterium enrichments indicate formation of the hydrocarbon portion of these compounds in a low-temperature environment that is consistent with that of interstellar clouds. Sulfur-33 enrichments observed in methanesulfonic acid could have resulted from gas-phase ultraviolet irradiation of a precursor, carbon disulfide. The source of the sulfonic acid precursors may have been the reactive interstellar molecule carbon monosulfide.

Theoretical investigation of M@Pb122- and M@Sn122- Zintl clusters (M = Lrn+, Lun+, La3+, Ac3+ and n = 0, 1, 2, 3).

PubMed

Joshi, Meenakshi; Chandrasekar, Aditi; Ghanty, Tapan K

2018-06-06

The positions of lawrencium (Lr), lutetium (Lu), actinium (Ac) and lanthanum (La) in the periodic table have been a controversial topic for quite some time. According to studies carried out by different groups with their justifications, these elements may potentially be placed in the d-block, p-block or all four in a 15 element f-block. The present work looks into this issue from a new perspective, which involves encapsulation of these four elements into Zintl ion clusters, Pb122- and Sn122-, followed by the determination of the structural, thermodynamic and electronic properties of these endohedral M@Pb122- and M@Sn122- clusters (M = Lrn+, Lun+ with n = 0, 1, 2, 3) using first principles based density functional theory (DFT). These parameters are compared with similar clusters encapsulated La3+ and Ac3+ ions in order to seek out similarities and differences to draw conclusions about their placement in the periodic table. For the first time the structural, energetic, and electronic properties of these metal atom/ion encapsulated Pb122- and Sn122- clusters have been investigated thoroughly. Structural parameters such as bond distances, geometry and symmetry, electronic properties viz. the density of states, the molecular orbital ordering, the electron localization function, bond critical point properties and charge distributions have been analyzed. Additionally, the thermodynamic property of the binding energy during the encapsulation process has also been calculated. All M@Pb12+ and M@Sn12+ (M = Lr and Lu) clusters form stable 18 bonding electron magic number systems with shell closing. They show negative values of binding energy and relatively large HOMO-LUMO energy gaps indicating the stability of such clusters. All the calculated parameters for Lr encapsulated clusters closely match with the corresponding calculated parameters of Lu encapsulated clusters, confirming the similarity between Lr and Lu metal atoms in various oxidation states, though their atomic ground state valence electronic configurations are different. The effect of spin orbit coupling has also been investigated using the ZORA approach. It is interesting to discover that La and Ac showed striking similarities to Lr and Lu with respect to all the properties investigated and have formed a stable 18-electron system.

Synthesis of Er-doped Lu2O3 nanoparticles and transparent ceramics

NASA Astrophysics Data System (ADS)

Serivalsatit, K.; Wasanapiarnpong, T.; Kucera, C.; Ballato, J.

2013-05-01

Transparent rare earth-doped Lu2O3 ceramics have received much attention for use in solid-state scintillator and laser applications. The fabrication of these ceramics, however, requires ultrafine and uniform powders as precursors. Presented here is the synthesis of Er-doped Lu2O3 nanopowders by a solution precipitation method using Er-doped lutetium sulfate solution and hexamethylenetetramine as a precipitant and the fabrication of Er-doped Lu2O3 transparent ceramics from these nanopowders. The precipitated precursors were calcined at 1100 °C for 4 h in order to convert the precursors into Lu2O3 nanoparticles with an average particle size of 60 nm. Thermal decomposition and phase evolution of the precursors were studied by simultaneous thermal analysis (STA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Er-doped Lu2O3 transparent ceramics were fabricated from these nanopowders using vacuum sintering followed by hot isostatic pressing at 1700 °C for 8 h. The transparent ceramics exhibit an optical transmittance of 78% at a wavelength of 1.55 μm.

Cross influences of ozone and sulfate precursor emissions changes on air quality and climate

PubMed Central

Unger, Nadine; Shindell, Drew T.; Koch, Dorothy M.; Streets, David G.

2006-01-01

Tropospheric O3 and sulfate both contribute to air pollution and climate forcing. There is a growing realization that air quality and climate change issues are strongly connected. To date, the importance of the coupling between O3 and sulfate has not been fully appreciated, and thus regulations treat each pollutant separately. We show that emissions of O3 precursors can dramatically affect regional sulfate air quality and climate forcing. At 2030 in an A1B future, increased O3 precursor emissions enhance surface sulfate over India and China by up to 20% because of increased levels of OH and gas-phase SO2 oxidation rates and add up to 20% to the direct sulfate forcing for that region relative to the present day. Hence, O3 precursors impose an indirect forcing via sulfate, which is more than twice the direct O3 forcing itself (compare −0.61 vs. +0.35 W/m2). Regulatory policy should consider both air quality and climate and should address O3 and sulfate simultaneously because of the strong interaction between these species. PMID:16537360

Precursor Routes to Complex Ternary Intermetallics: Single-Crystal and Microcrystalline Preparation of Clathrate-I Na8Al8Si38 from NaSi + NaAlSi.

PubMed

Dong, Yongkwan; Chai, Ping; Beekman, Matt; Zeng, Xiaoyu; Tritt, Terry M; Nolas, George S

2015-06-01

Single crystals of the ternary clathrate-I Na8Al8Si38 were synthesized by kinetically controlled thermal decomposition (KCTD), and microcrystalline Na8Al8Si38 was synthesized by spark plasma sintering (SPS) using a NaSi + NaAlSi mixture as the precursor. Na8AlxSi46-x compositions with x ≤ 8 were also synthesized by SPS from precursor mixtures of different ratios. The crystal structure of Na8Al8Si38 was investigated using both Rietveld and single-crystal refinements. Temperature-dependent transport and UV/vis measurements were employed in the characterization of Na8Al8Si38, with diffuse-reflectance measurement indicating an indirect optical gap of 0.64 eV. Our results indicate that, when more than one precursor is used, both SPS and KCTD are effective methods for the synthesis of multinary inorganic phases that are not easily accessible by traditional solid-state synthesis or crystal growth techniques.

Observations of Electromagnetic Whistler Precursors at Supercritical Interplanetary Shocks

NASA Technical Reports Server (NTRS)

Wilson, L. B., III; Koval, A.; Szabo, Adam; Breneman, A.; Cattell, C. A.; Goetz, K.; Kellogg, P. J.; Kersten, K.; Kasper, J. C.; Maruca, B. A.;

(GaIn)(NAs) growth using di-tertiary-butyl-arsano-amine (DTBAA)

NASA Astrophysics Data System (ADS)

Sterzer, E.; Ringler, B.; Nattermann, L.; Beyer, A.; von Hänisch, C.; Stolz, W.; Volz, K.

2017-06-01

III/V semiconductors containing small amounts of Nitrogen (N) are very interesting for a variety of optoelectronic applications. Unfortunately, the conventionally used N precursor 1,1-dimethylhydrazine (UDMHy) has an extremely low N incorporation efficiency in GaAs when grown using metal organic vapor phase epitaxy. Alloying Ga(NAs) with Indium (In) even leads to an exponential reduction of N incorporation. The huge amount of UDMHy in turn changes drastically the growth conditions. Furthermore, the application of this material is still hampered by the large carbon incorporation, most probably originating from the metal organic precursors. Hence, novel precursors for dilute nitride growth are needed. This paper will show (GaIn)(NAs) growth studies with the novel precursor di-tertiary-butyl-arsano-amine in combination with tri-ethyl-gallium and tri-methyl-indium. We show an extremely high N incorporation efficiency in the In containing (GaIn)(NAs). The (GaIn)(NAs) samples investigated in this study have been examined using high resolution X-Ray diffraction, room temperature photoluminescence and atomic force microscope measurements as well as secondary ion mass spectrometry.

ACBC to Balcite: Bioinspired Synthesis of a Highly Substituted High-Temperature Phase from an Amorphous Precursor

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

Whittaker, Michael L.; Joester, Derk

2017-04-28

Energy-efficient synthesis of materials locked in compositional and structural states far from equilibrium remains a challenging goal, yet biomineralizing organisms routinely assemble such materials with sophisticated designs and advanced functional properties, often using amorphous precursors. However, incorporation of organics limits the useful temperature range of these materials. Herein, the bioinspired synthesis of a highly supersaturated calcite (Ca0.5Ba0.5CO3) called balcite is reported, at mild conditions and using an amorphous calcium–barium carbonate (ACBC) (Ca1- x Ba x CO3·1.2H2O) precursor. Balcite not only contains 50 times more barium than the solubility limit in calcite but also displays the rotational disorder on carbonate sitesmore » that is typical for high-temperature calcite. It is significantly harder (30%) and less stiff than calcite, and retains these properties after heating to elevated temperatures. Analysis of balcite local order suggests that it may require the formation of the ACBC precursor and could therefore be an example of nonclassical nucleation. These findings demonstrate that amorphous precursor pathways are powerfully enabling and provide unprecedented access to materials far from equilibrium, including high-temperature modifications by room-temperature synthesis.« less

Alternative group V precursors for CVD applications

NASA Astrophysics Data System (ADS)

Lum, R. M.; Klingert, J. K.

1991-01-01

The chemical vapor deposition (CVD) techniques used to grow III/V semiconductors films, such as metalorganic vapor phase epitaxy (MOVPE), hydride VPE, chemical beam epitaxy (CBE) and gas source molecular beam epitaxy (GS-MBE), all use hydrides (AsH 3 and PH 3) as the Group V source. However, the hydrides are extremely toxic gases which are stored under high pressure (200-2000 psi). To reduce the safety hazards associated with these gases, alternative Group V precursors have been investigated. Organoarsenic and phosphorous compounds have received the most attention as replacements for AsH 3 and PH 3 because they are typically low vapor pressure liquids, and thus present significantly lower exposure risks than the hydrides. For AsH 3 these have included the methyl, ethyl and butyl-based derivatives RnAsH 3- n, with varying degrees ( n = 1-3) of hydrogen atom substitution. In this paper the growth properties, thermochemistry and toxicity of the various alkylarsine precursors are compared with arsine. Data are presented on the impact of the thermochemistry of these compounds on film electrical properties, and on the effects of precursor composition and purity on overall film quality. The suitability of alternative As-precursors for device applications is demonstrated, and selection criteria are presented for the most effective alkylarsine compound for a particular CVD growth process.

Ultrasmall Zeolite L Crystals Prepared from Highly-Interdispersed Alkali-Silicate Precursors.

PubMed

Li, Rui; Linares, Noemi; Sutjianto, James G; Chawla, Aseem; Garcia Martinez, Javier; Rimer, Jeffrey D

2018-06-19

The preparation of nanosized zeolites is critical for applications where mass transport limitations within microporous networks hinder their performance. Oftentimes the ability to generate ultrasmall zeolite crystals is dependent upon the use of expensive organics with limited commercial relevance. Here, we report the generation of zeolite L crystals with uniform sizes less than 30 nm using a facile, organic-free method. Time-resolved analysis of precursor assembly and evolution during nonclassical crystallization highlights key differences among silicon sources. Our findings reveal that a homogenous dispersion of potassium ions throughout silicate precursors is critical to enhancing the rate of nucleation and facilitating the formation of ultrasmall crystals. Intimate contact between the inorganic structure-directing agent and silica leads to the formation of a metastable nonporous phase, identified as KAlSi2O6, which undergoes an intercrystalline transformation to zeolite L. The presence of highly-interdispersed alkali-silicate precursors is seemingly integral to a reduced zeolite induction time and may facilitate the development of ultrasmall crystals. Given the general difficulty of achieving nanosized crystals in zeolite synthesis, it is likely that using well-dispersed precursors does not have the same effect on all framework types; however, in select cases it may provide an alternative strategy for optimizing zeolite synthesis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Engineered glass seals for solid-oxide fuel cells

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

Surdoval, Wayne; Lara-Curzio, Edgar; Stevenson, Jeffry

2017-02-07

A seal for a solid oxide fuel cell includes a glass matrix having glass percolation therethrough and having a glass transition temperature below 650.degree. C. A deformable second phase material is dispersed in the glass matrix. The second phase material can be a compliant material. The second phase material can be a crushable material. A solid oxide fuel cell, a precursor for forming a seal for a solid oxide fuel cell, and a method of making a seal for a solid oxide fuel cell are also disclosed.

Hydrothermal synthesis and characterization of Si and Sr co-substituted hydroxyapatite nanowires using strontium containing calcium silicate as precursors.

PubMed

Zhang, Na; Zhai, Dong; Chen, Lei; Zou, Zhaoyong; Lin, Kaili; Chang, Jiang

2014-04-01

In the absence of any organic surfactants and solvents, the silicon (Si) and strontium (Sr) co-substituted hydroxyapatite [Ca10(PO4)6(OH)2, Si/Sr-HAp] nanowires were synthesized via hydrothermal treatment of the Sr-containing calcium silicate (Sr-CS) powders as the precursors in trisodium phosphate (Na3PO4) aqueous solution. The morphology, phase, chemical compositions, lattice constants and the degradability of the products were characterized. The Si/Sr-HAp nanowires with diameter of about 60nm and up to 2μm in length were obtained after hydrothermal treatment of the Sr-CS precursors. The Sr and Si substitution amount of the HAp nanowires could be well regulated by facile tailoring the Sr substitution level of the precursors and the reaction ratio of the precursor/solution, respectively. The SiO4 tetrahedra and Sr(2+) ions occupied the crystal sites of the HAp, and the lattice constants increased apparently with the increase of the substitution amount. EDS mapping also suggested the uniform distribution of Si and Sr in the synthetic nanowires. Moreover, the Si/Sr-substitution apparently improved the degradability of the HAp materials. Our study suggested that the precursor transformation method provided a facile approach to synthesize the Si/Sr co-substituted HAp nanowires with controllable substitution amount, and the synthetic Si/Sr-HAp nanowires might be used as bioactive materials for hard tissue regeneration applications. Copyright © 2014 Elsevier B.V. All rights reserved.

Analysis of PKP scattering using mantle mixing simulations and axisymmetric 3D waveforms

NASA Astrophysics Data System (ADS)

Haugland, Samuel M.; Ritsema, Jeroen; van Keken, Peter E.; Nissen-Meyer, Tarje

2018-03-01

The scattering of PKP waves in the lower mantle produces isolated signals before the PKIKP phase. We explore whether these so-called PKIKP precursors can be related to wave scattering off mid ocean ridge basalt (MORB) fragments that have been advected in the deep mantle throughout geologic time. We construct seismic models of small-scale (>20 km) heterogeneity in the lower mantle informed by mantle mixing simulations from Brandenburg et al. (2008) and generate PKIKP precursors using 3D, axisymmetric waveform simulations up to 0.75 Hz. We consider two end-member geodynamic models with fundamentally different distributions of MORB in the lower mantle. Our results suggest that the accumulation of MORB at the base of the mantle is a viable hypothesis for the origin of PKP scattering. We find that the strength of the PKIKP precursor amplitudes is consistent with P wave speed heterogeneity of 0.1-0.2%, as reported previously. The radial distribution of MORB has a profound effect on the strength of PKIKP precursors. Simulation of PKIKP precursors for models with an increasing MORB concentration in the lowermost 500 km of the mantle appears to reproduce most accurately the strength of PKIKP precursors in Global Seismic Network waveforms. These models assume that MORB has an excess density of at least 7%. Additional simulations of more complex geodynamic models will better constrain the geodynamic conditions to explain the significant variability of PKP scattering strength.

Controllable synthesis of mesoporous carbon nanospheres and Fe-N/carbon nanospheres as efficient oxygen reduction electrocatalysts

NASA Astrophysics Data System (ADS)

Wei, Jing; Liang, Yan; Zhang, Xinyi; Simon, George P.; Zhao, Dongyuan; Zhang, Jin; Jiang, Sanping; Wang, Huanting

2015-03-01

The synthesis of mesoporous carbon nanospheres (MCNs), especially with diameters below 200 nm remains a great challenge due to weak interactions between the carbon precursors and soft templates, as well as the uncontrollable cross-linking rate of carbon precursors. Herein, we demonstrate a simple acid-assisted, hydrothermal synthesis approach to synthesizing such uniform MCNs with well controlled diameters ranging from 20 to 150 nm under highly acidic conditions (2 M HCl). Both the carbon precursor and the template are partly protonated under such conditions and show additional Coulombic interactions with chloride ions (acts as mediators). This kind of enhanced interaction is similar to that of the ``I+X-S+'' mechanism in the synthesis of mesoporous metal oxide, which can effectively retard the cross-linking rate of resol molecules and avoid macroscopic phase separation during the hydrothermal synthesis. Due to their uniform spherical morphology, small diameter, and high surface areas, MCNs can be modified with Fe and N species via impregnation of cheap precursors (ferric nitrate and dicyandiamide), which are further converted into nonprecious electrocatalysts for oxygen reduction reactions. The resulting Fe-N/MCNs exhibit high catalytic activities, long-term stability and improved methanol tolerance under alkaline conditions, which can be potentially used in direct methanol fuel cells and metal-air batteries.The synthesis of mesoporous carbon nanospheres (MCNs), especially with diameters below 200 nm remains a great challenge due to weak interactions between the carbon precursors and soft templates, as well as the uncontrollable cross-linking rate of carbon precursors. Herein, we demonstrate a simple acid-assisted, hydrothermal synthesis approach to synthesizing such uniform MCNs with well controlled diameters ranging from 20 to 150 nm under highly acidic conditions (2 M HCl). Both the carbon precursor and the template are partly protonated under such conditions and show additional Coulombic interactions with chloride ions (acts as mediators). This kind of enhanced interaction is similar to that of the ``I+X-S+'' mechanism in the synthesis of mesoporous metal oxide, which can effectively retard the cross-linking rate of resol molecules and avoid macroscopic phase separation during the hydrothermal synthesis. Due to their uniform spherical morphology, small diameter, and high surface areas, MCNs can be modified with Fe and N species via impregnation of cheap precursors (ferric nitrate and dicyandiamide), which are further converted into nonprecious electrocatalysts for oxygen reduction reactions. The resulting Fe-N/MCNs exhibit high catalytic activities, long-term stability and improved methanol tolerance under alkaline conditions, which can be potentially used in direct methanol fuel cells and metal-air batteries. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00331h

Microstructures and Mechanical Properties of Two-Phase Alloys Based on NbCr(2)

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

Cady, C.M.; Chen, K.C.; Kotula, P.G.

A two-phase, Nb-Cr-Ti alloy (bee+ C15 Laves phase) has been developed using several alloy design methodologies. In effort to understand processing-microstructure-property relationships, diffment processing routes were employed. The resulting microstructure and mechanical properties are discussed and compared. Plasma arc-melted samples served to establish baseline, . . . as-cast properties. In addition, a novel processing technique, involving decomposition of a supersaturated and metastable precursor phase during hot isostatic pressing (HIP), was used to produce a refined, equilibrium two-phase microstructure. Quasi-static compression tests as a ~ function of temperature were performed on both alloy types. Different deformation mechanisms were encountered based uponmore » temperature and microstructure.« less

The 3R polymorph of CaSi{sub 2}

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

Nedumkandathil, Reji; Benson, Daryn E.; Grins, Jekabs

The Zintl phase CaSi{sub 2} commonly occurs in the 6R structure where puckered hexagon layers of Si atoms are stacked in an AA′BB′CC′ fashion. In this study we show that sintering of CaSi{sub 2} in a hydrogen atmosphere (30 bar) at temperatures between 200 and 700 °C transforms 6R-CaSi{sub 2} quantitatively into 3R-CaSi{sub 2}. In the 3R polymorph (space group R-3m (no. 166), a=3.8284(1), c=15.8966(4), Z=3) puckered hexagon layers are stacked in an ABC fashion. The volume per formula unit is about 3% larger compared to 6R-CaSi{sub 2}. First principles density functional calculations reveal that 6R and 3R-CaSi{sub 2} aremore » energetically degenerate at zero Kelvin. With increasing temperature 6R-CaSi{sub 2} stabilizes over 3R because of its higher entropy. This suggests that 3R-CaSi{sub 2} should revert to 6R at elevated temperatures, which however is not observed up to 800 °C. 3R-CaSi{sub 2} may be stabilized by small amounts of incorporated hydrogen and/or defects. - Graphical abstract: The common 6R form of CaSi{sub 2} can be transformed quantitatively into 3R-CaSi{sub 2} upon sintering in a hydrogen atmosphere. - Highlights: • Quantitative and reproducible bulk synthesis of the rare 3R polymorph of CaSi{sub 2}. • Clarification of the energetic relation between 3R and conventional 6R form. • 3R-CaSi{sub 2} is presumably stabilized by small amounts of incorporated hydrogen and/or defects.« less

Perspective: Web-based machine learning models for real-time screening of thermoelectric materials properties

NASA Astrophysics Data System (ADS)

Gaultois, Michael W.; Oliynyk, Anton O.; Mar, Arthur; Sparks, Taylor D.; Mulholland, Gregory J.; Meredig, Bryce

2016-05-01

The experimental search for new thermoelectric materials remains largely confined to a limited set of successful chemical and structural families, such as chalcogenides, skutterudites, and Zintl phases. In principle, computational tools such as density functional theory (DFT) offer the possibility of rationally guiding experimental synthesis efforts toward very different chemistries. However, in practice, predicting thermoelectric properties from first principles remains a challenging endeavor [J. Carrete et al., Phys. Rev. X 4, 011019 (2014)], and experimental researchers generally do not directly use computation to drive their own synthesis efforts. To bridge this practical gap between experimental needs and computational tools, we report an open machine learning-based recommendation engine (http://thermoelectrics.citrination.com) for materials researchers that suggests promising new thermoelectric compositions based on pre-screening about 25 000 known materials and also evaluates the feasibility of user-designed compounds. We show this engine can identify interesting chemistries very different from known thermoelectrics. Specifically, we describe the experimental characterization of one example set of compounds derived from our engine, RE12Co5Bi (RE = Gd, Er), which exhibits surprising thermoelectric performance given its unprecedentedly high loading with metallic d and f block elements and warrants further investigation as a new thermoelectric material platform. We show that our engine predicts this family of materials to have low thermal and high electrical conductivities, but modest Seebeck coefficient, all of which are confirmed experimentally. We note that the engine also predicts materials that may simultaneously optimize all three properties entering into zT; we selected RE12Co5Bi for this study due to its interesting chemical composition and known facile synthesis.

An improved soft-chemistry approach to the preparation of spinel powders

NASA Astrophysics Data System (ADS)

Cook, Ronald

2007-04-01

Spinel powders for the production of transparent polycrystalline ceramic windows have been produced using a number of traditional ceramic and sol-gel methods. We have demonstrated that magnesium aluminate spinel powders produced from the reaction of organo-magnesium compounds with surface modified boehmite precursors can be used to produce high quality transparent spinel parts. In previous work, the spinel powders were prepared by the reaction of surface-modified boehmite nanoparticles with magnesium acetylacetonate. While the magnesium acetylacetonate can produce small quantities of high quality spinel powders, it use for large scale production of spinel powders is problematic. Through a thermodynamic analysis we have identified a new high-purity, low-cost, low-toxicity organomagnesium compound that reacts the with surface modified boehmite nanoparticles to produce a spinel precursor. The magnesium doped precursor readily transforms into pure phase spinel at temperature between 900°C and 1200°C.

Carbon-11 choline: synthesis, purification, and brain uptake inhibition by 2-dimethylaminoethanol

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

Rosen, M.A.; Jones, R.M.; Yano, Y.

We report an improved method for the synthesis and purification of (11C)methylcholine from the precursors (11C)methyliodide and 2-dimethylaminoethanol (deanol). Preparation time, including purification, is 35 min postbombardment. Forty millicuries of purified injectable (11C)choline were produced with a measured specific activity of greater than 300 Ci/mmol and a radiochemical purity greater than 98%. The decay corrected radiochemical yield for the synthesis and purification was approximately 50%. Residual precursor deanol, which inhibits brain uptake of choline, is removed by a rapid preparative high performance liquid chromatography (HPLC) method using a reverse phase cyano column with a biologically compatible 100% water eluent. Evaporationmore » alone did not completely remove the deanol precursor. Brain uptake of the (11C)choline product was six times greater after HPLC removal of deanol because doses of less than 1 microgram/kg significantly inhibit (14C)choline brain uptake.« less

Precision synthesis of colloidal inorganic nanocrystals using metal and metalloid amides

NASA Astrophysics Data System (ADS)

Yarema, Maksym; Caputo, Riccarda; Kovalenko, Maksym V.

2013-08-01

Rational selection of molecular precursors is the key consideration in the synthesis of inorganic nanocrystals and nanoparticles. This review highlights the state-of-the-art and future potential of metal amides as precursors in the solution-phase synthesis of monodisperse colloidal nanocrystals of metals and metal alloys, as well as metal oxides and chalcogenides. We exclusively focus on homoleptic metal and metalloid alkylamides M(NR2)n and silylamides M[N(SiMe3)2]n as predominant choice of element-nitrogen bonded precursors, which are often advantageous to commonly used metal-oxygen and metal-carbon bonded counterparts. In particular, these amides are highly reactive in oxidation, reduction and metathesis reactions; they are oxygen-free, easy-to-make and/or commercially available. A comprehensive literature review is complemented by our theoretical studies on the thermal stability of metal silylamides using molecular dynamics simulations.

Somatic and germinal cells' interrelationship in the course of seminiferous tubule maturation in man.

PubMed

Kula, K; Romer, T E; Wlodarczyk, W P

1980-02-01

Certain successive phases of seminiferous tubule maturation were observed in a transsection of a Leydig cell adenoma-bearing testis of a boy with precocious puberty. Massively accumulated Leydig cells may stimulate the maturation of Sertoli cells, as indicated by progressive replacement of Sertoli cell precursors by mature Sertoli cells at a distance closer to the adenoma. On the other hand, tubules less advanced in maturation contained a higher number of somatic cells than those more advanced in maturation. Leydig-cell-dependent maturation of Sertoli cells may be in competition with Certoli cell multiplication, or numerous undifferentiated somatic cells may undergo a natural elimination in the course of tubular maturation. An inverse relation between the number of Sertoli cell precursors and the number of meiotic spermatocytes suggests that quantitative reduction of Sertoli cell precursors may be important for the intratubular milieu necessary for the onset of the first meiosis in man.

Process for coating an object with silicon carbide

NASA Technical Reports Server (NTRS)

Levin, Harry (Inventor)

1989-01-01

A process for coating a carbon or graphite object with silicon carbide by contacting it with silicon liquid and vapor over various lengths of contact time. In the process, a stream of silicon-containing precursor material in gaseous phase below the decomposition temperature of said gas and a co-reactant, carrier or diluent gas such as hydrogen is passed through a hole within a high emissivity, thin, insulating septum into a reaction chamber above the melting point of silicon. The thin septum has one face below the decomposition temperature of the gas and an opposite face exposed to the reaction chamber. The precursor gas is decomposed directly to silicon in the reaction chamber. A stream of any decomposition gas and any unreacted precursor gas from said reaction chamber is removed. The object within the reaction chamber is then contacted with silicon, and recovered after it has been coated with silicon carbide.

On the role of precursor powder composition in controlling microstructure, flux pinning, and the critical current density of Ag/Bi2Sr2CaCu2Ox conductors

NASA Astrophysics Data System (ADS)

Li, Pei; Naderi, Golsa; Schwartz, Justin; Shen, Tengming

2017-03-01

Precursor powder composition is known to strongly affect the critical current density (J c) of Ag/Bi2Sr2CaCu2Ox (Bi-2212) wires. However, reasons for such J c dependence have not yet been fully understood, compromising our ability to achieve further optimization. We systematically examined superconducting properties, microstructural evolution and phase transformation, and grain boundaries of Bi-2212 conductors fabricated from precursor powders with a range of compositions using a combination of transport-current measurements, a quench technique to freeze microstructures at high temperatures during heat treatment, and scanning transmission electron microscopy (STEM). Samples include both dip-coated tapes and round wires, among which a commercial round wire carries a high J c of 7600 A mm-2 at 4.2 K, self-field and 2600 A mm-2 at 4.2 K, 20 T, respectively. In the melt, this high-J c conductor, made using a composition of Bi2.17Sr1.94Ca0.89Cu2Ox, contains a uniform dispersion of fine alkaline-earth cuprate (AEC) and copper-free solid phases, whereas several low-J c conductors contain large AEC particles. Such significant differences in the phase morphologies in the melt are accompanied by a drastic difference in the formation kinetics of Bi-2212 during recrystallization cooling. STEM studies show that Bi-2212 grain colonies in the high-J c conductors have a high density of Bi2Sr2CuO y (Bi-2201) intergrowths, whereas a low-J c conductor, made using Bi2.14Sr1.66Ca1.24Cu1.96O x , is nearly free of them. STEM investigation shows grain boundaries in low-J c conductors are often insulated with a Bi-rich amorphous phase. High-J c conductors also show higher flux-pinning strength, which we ascribe to their higher Bi-2201 intergrowth density.

Nucleation Behavior of Oxygen-Acetylene Torch-Produced Diamond Films

NASA Technical Reports Server (NTRS)

Roberts, F. E.

2003-01-01

A mechanism is presented for the nucleation of diamond in the combustion flame environment. A series of six experiments and two associated simulations provide results from which the mechanism was derived. A substantial portion of the prior literature was reviewed and the data and conclusions from the previous experimenters were found to support the proposed mechanism. The nucleation mechanism builds on the work of previous researchers but presents an approach to nucleation in a detail and direction not fully presented heretofore. This work identifies the gas phase as the controlling environment for the initial formation steps leading to nucleation. The developed mechanism explains some of the difficulty which has been found in producing single crystal epitaxial films. An experiment which modified the initial gas phase precursor using methane and carbon monoxide is presented. Addition of methane into the precursor gases was found to be responsible for pillaring of the films. Atomic force microscopy surface roughness data provides a reasonable look at suppression of nucleation by carbon monoxide. Surface finish data was taken on crystals which were open to the nucleation environment and generally parallel to the substrate surface. The test surfaces were measured as an independent measure of the instantaneous nucleation environent. A gas flow and substrate experiment changed the conditions on the surface of the sample by increasing the gas flow rate while remaining on a consistent point of the atomic constituent diagram, and by changing the carbide potential of the substrate. Two tip modification experiments looked at the behavior of gas phase nucleation by modifying the shape and behavior of the flame plasma in which the diamond nucleation is suspected to occur. Diamond nucleation and growth was additionally examined using a high-velocity oxygen fuel gun and C3H6 as the fuel gas phase precursor with addition of carbon monoxide gas 01 addition of liquid toluene.

Inorganic nanofibers with tailored placement of nanocatalysts for hydrogen production via alkaline hydrolysis of glucose.

PubMed

Hansen, Nathaniel S; Ferguson, Thomas E; Panels, Jeanne E; Park, Ah-Hyung Alissa; Joo, Yong Lak

2011-08-12

Monoaxial silica nanofibers containing iron species as well as coaxial nanofibers with a pure silica core and a silica shell containing high concentrations of iron nanocrystals were fabricated via electrospinning precursor solutions, followed by thermal treatment. Tetraethyl-orthosilicate (TEOS) and iron nitrate (Fe(NO(3))(3)) were used as the precursors for the silica and iron phases, respectively. Thermal treatments of as-spun precursor fibers were applied to generate nanocrystals of iron with various oxidation states (pure iron and hematite). Scanning electron microscopy (SEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to probe the fiber morphology and crystal structures. The results indicated that the size, phase, and placement of iron nanocrystals can be tuned by varying the precursor concentration, thermal treatment conditions, and processing scheme. The resulting nanofiber/metal systems obtained via both monoaxial and coaxial electrospinning were applied as catalysts to the alkaline hydrolysis of glucose for the production of fuel gas. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and bulk weight change in a furnace with residual gas analysis (RGA) were used to evaluate the performance of the catalysts for various ratios of both Fe to Si, and catalyst to glucose, and the oxidation state of the iron nanocrystals. The product gas is composed of mostly H(2) (>96 mol%) and CH(4) with very low concentrations of CO(2) and CO. Due to the clear separation of reaction temperature for H(2) and CH(4) production, pure hydrogen can be obtained at low reaction temperatures. Our coaxial approach demonstrates that placing the iron species selectively near the fiber surface can lead to two to three fold reduction in catalytic consumption compared to the monoaxial fibers with uniform distribution of catalysts.

Per- and polyfluoroalkyl substances (PFASs) in San Francisco Bay wildlife: Temporal trends, exposure pathways, and notable presence of precursor compounds.

PubMed

Sedlak, Margaret D; Benskin, Jonathan P; Wong, Adam; Grace, Richard; Greig, Denise J

2017-10-01

Concentrations of perfluorooctane sulfonate (PFOS) in San Francisco Bay (SF Bay) wildlife have historically been among the highest reported globally. To track continuing exposures to PFASs and assess the impact of the 2002 phase-out of production of PFOS and related chemicals in the US, nine perfluoroalkyl carboxylic acids (PFCAs; C4-C12), three perfluoroalkyl sulfonic acids (PFSAs; C4, C6, C8) and perfluorooctane sulfonamide (PFOSA, a PFOS precursor) were measured in SF Bay cormorant eggs in 2012 and harbor seal serum sampled between 2009 and 2014. PFOS remained the dominant perfluoroalkyl acid (PFAA) in both cormorant eggs (36.1-466 ng/g) and seals (12.6-796 ng/g) from 2012 and 2014, respectively. Concentrations in seal and bird eggs from the South Bay have declined approximately 70% in both matrices. To elucidate potential pathways of exposure, prey fish, sediments and wastewater effluent were analyzed for PFASs, and in the case of sediment and effluent, a suite of PFAA precursors. PFOS was the dominant PFAA in prey fish and sediment. In effluent, different mixtures of PFAAs were measured, with PFOS, PFHxA, and PFOA detected in the highest concentrations. Polyfluoroalkyl phosphate diesters (PFCA-precursors) were observed at concentrations over an order of magnitude higher than PFCAs in sediment, highlighting their importance as a potential, on-going source of PFCAs to SF Bay wildlife. These findings suggest that the PFOS phase-out has resulted in reduced burdens to wildlife in SF Bay, but that exposure to diverse and incompletely characterized PFASs continues. Copyright © 2017 Elsevier Ltd. All rights reserved.

Structural, chemical and optical evaluation of Cu-doped ZnO nanoparticles synthesized by an aqueous solution method

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

Iribarren, A., E-mail: augusto@imre.oc.uh.cu; Hernández-Rodríguez, E.; Maqueira, L.

Highlights: • Cu-doped ZnO nanoparticles obtained by chemical synthesis. • Substitutional or interstitial Cu into ZnO lead specific structural, chemical, and optical changes. • Incorporation efficiency of Cu atoms in ZnO as a function of the Cu concentration in the precursor dissolution. - Abstract: In this work a study of ZnO and Cu-doped ZnO nanoparticles obtained by chemical synthesis in aqueous media was carried out. Structural analysis gave the dominant presence of wurtzite ZnO phase forming a solid solution Zn{sub 1−x}Cu{sub x}O. For high Cu doping CuO phase is also present. For low Cu concentration the lattice shrinks due tomore » Cu atoms substitute Zn atoms. For high Cu concentration the lattice enlarges due to predominance of interstitial Cu. From elemental analysis we determined and analyzed the incorporation efficiency of Cu atoms in Zn{sub 1−x}Cu{sub x}O as a function of the Cu concentration in the precursor dissolution. Combining structural and chemical results we described the Cu/Zn precursor concentrations r{sub w} in which the solid solution of Cu in ZnO is predominant. In the region located at r{sub w} ≈ 0.2–0.3 it is no longer valid. For Cu/Zn precursor concentration r{sub w} > 0.3 interstitial Cu dominates, and some amount of copper oxide appears. As the Cu concentration increases, the effective size of nanoparticles decreases. Photoluminescence (PL) measurements of the Cu-doped ZnO nanoparticles were carried out and analyzed.« less

A facile way to control phase of tin selenide flakes by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wang, Zhigang; Pang, Fei

2018-06-01

Although two-dimensional (2D) tin selenides are attracting intense attentions, studies on its phase transition are still relatively few. Here we report a facile way to control the phase growth of tin selenide flakes on mica and SiO2/Si by only adjusting nominal Sn:Se ratio, which refers to the amount of loaded SnO2 and Se precursors. High normal Sn:Se ratio induced SnSe flakes, conversely SnSe2 flakes formed. It could be used as a practical guide to selectively synthesize pure phase of single crystalline 2D layered chalcogenide materials similar to tin selenides.

Effect of chain length on thermal conversion of alkoxy-substituted copper phthalocyanine precursors.

PubMed

Fukuda, Takamitsu; Kikukawa, Yuu; Tsuruya, Ryota; Fuyuhiro, Akira; Ishikawa, Naoto; Kobayashi, Nagao

2011-11-21

A series of dialkoxy-substituted copper phthalocyanine (CuPc) precursors (4a-4d) have been prepared by treating phthalonitrile with the corresponding lithium alkoxide under mild conditions. The precursors exhibited high solubilities in common organic solvents, including acetone, toluene, tetrahydrofuran (THF), CH(2)Cl(2), and CHCl(3). Elongation of the alkoxy chains improved the solubilities of the precursors effectively, and accordingly, the butoxy-substituted derivative (4d) showed the highest solubility among 4a-4d. X-ray crystallography clarified that the conjugated skeletons of 4a-4d are all isostructural, and have two alkoxy groups in a syn-conformation fashion, leading to highly bent structures. Thermal conversions of the precursors examined by thermogravimetry (TG) and differential thermal analysis (DTA) demonstrate that 4a was converted into CuPc via two distinct exothermic processes in the 200-250 °C temperature range, while 4d exhibits only one exothermic signal in the DTA. In the field emission scanning electron microscopy (FESEM) images of 4a, the presence of two types of distinct crystal morphology (prismatic and plate-like crystals) can be recognized, implying that the two observed exothermic processes in the DTA can be attributed to the different crystal morphologies of the samples rather than the step-by-step elimination of the alkoxy groups. The thermal formation of CuPc from the precursors has been unambiguously confirmed by X-ray powder diffraction, UV-vis spectroscopy, and elemental analysis. The precursors were converted into CuPc at lower temperature with increasing chain length, presumably because of the increased void volume in the crystals. Thermal conversion performed in the solution phase results in a bright blue-colored solution with prominent absorption bands in the 650-700 nm region, strongly supporting the formation of CuPc.

Study on Precursor Activity of the X1.6 Flare in the Great AR 12192 with SDO , IRIS , and Hinode

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

Bamba, Yumi; Lee, Kyoung-Sun; Imada, Shinsuke

The physical properties and their contribution to the onset of a solar flare are still uncleare even though chromospheric brightening is considered a precursor phenomenon of a flare. Many studies suggested that photospheric magnetic field changes cause destabilization of large-scale coronal structure. We aim to understand how a small photospheric change contributes to a flare and to reveal how the intermediary chromosphere behaves in the precursor phase. We analyzed the precursor brightening of the X1.6 flare on 2014 October 22 in the AR 12192 using the Interface Region Imaging Spectrograph ( IRIS ) and Hinode /EUV Imaging Spectrometer (EIS) data.more » We investigated a localized jet with the strong precursor brightening, and compared the intensity, Doppler velocity, and line width in C ii, Mg ii k, and Si iv lines by IRIS and He ii, Fe xii, and Fe xv lines by Hinode /EIS. We also analyzed the photospheric magnetic field and chromospheric/coronal structures using the Solar Dynamics Observatory ( SDO )/Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly. We found a significant blueshift (∼100 km s{sup −1}), which is related to the strong precursor brightening over a characteristic magnetic field structure, and the blueshift was observed at all of the temperatures. This might indicate that the flow is accelerated by Lorentz force. Moreover, the large-scale coronal loop that connects the foot points of the flare ribbons was destabilized just after the precursor brightening with the blueshift. It suggests that magnetic reconnection locally occurred in the lower chromosphere and it triggered magnetic reconnection of the X1.6 flare in the corona.« less

Study on Precursor Activity of the X1.6 Flare in the Great AR 12192 with SDO, IRIS, and Hinode

NASA Astrophysics Data System (ADS)

Bamba, Yumi; Lee, Kyoung-Sun; Imada, Shinsuke; Kusano, Kanya

2017-05-01

The physical properties and their contribution to the onset of a solar flare are still uncleare even though chromospheric brightening is considered a precursor phenomenon of a flare. Many studies suggested that photospheric magnetic field changes cause destabilization of large-scale coronal structure. We aim to understand how a small photospheric change contributes to a flare and to reveal how the intermediary chromosphere behaves in the precursor phase. We analyzed the precursor brightening of the X1.6 flare on 2014 October 22 in the AR 12192 using the Interface Region Imaging Spectrograph (IRIS) and Hinode/EUV Imaging Spectrometer (EIS) data. We investigated a localized jet with the strong precursor brightening, and compared the intensity, Doppler velocity, and line width in C II, Mg II k, and Si IV lines by IRIS and He II, Fe xii, and Fe xv lines by Hinode/EIS. We also analyzed the photospheric magnetic field and chromospheric/coronal structures using the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly. We found a significant blueshift (˜100 km s-1), which is related to the strong precursor brightening over a characteristic magnetic field structure, and the blueshift was observed at all of the temperatures. This might indicate that the flow is accelerated by Lorentz force. Moreover, the large-scale coronal loop that connects the foot points of the flare ribbons was destabilized just after the precursor brightening with the blueshift. It suggests that magnetic reconnection locally occurred in the lower chromosphere and it triggered magnetic reconnection of the X1.6 flare in the corona.

Upper Mantle Discontinuity Structure Beneath the Western Atlantic Ocean and Eastern North America from SS Precursors

NASA Astrophysics Data System (ADS)

Schmerr, N. C.; Beghein, C.; Kostic, D.; Baldridge, A. M.; West, J. D.; Nittler, L. R.; Bull, A. L.; Montesi, L.; Byrne, P. K.; Hummer, D. R.; Plescia, J. B.; Elkins-Tanton, L. T.; Lekic, V.; Schmidt, B. E.; Elkins, L. J.; Cooper, C. M.; ten Kate, I. L.; Van Hinsbergen, D. J. J.; Parai, R.; Glass, J. B.; Ni, J.; Fuji, N.; McCubbin, F. M.; Michalski, J. R.; Zhao, C.; Arevalo, R. D., Jr.; Koelemeijer, P.; Courtier, A. M.; Dalton, H.; Waszek, L.; Bahamonde, J.; Schmerr, B.; Gilpin, N.; Rosenshein, E.; Mach, K.; Ostrach, L. R.; Caracas, R.; Craddock, R. A.; Moore-Driskell, M. M.; Du Frane, W. L.; Kellogg, L. H.

2015-12-01

Seismic discontinuities within the mantle arise from a wide range of mechanisms, including changes in mineralogy, major element composition, melt content, volatile abundance, anisotropy, or a combination of the above. In particular, the depth and sharpness of upper mantle discontinuities at 410 and 660 km depth are attributed to solid-state phase changes sensitive to both mantle temperature and composition, where regions of thermal heterogeneity produce topography and chemical heterogeneity changes the impedance contrast across the discontinuity. Seismic mapping of this topography and sharpness thus provides constraint on the thermal and compositional state of the mantle. The EarthScope USArray is providing unprecedented access to a wide variety of new regions previously undersampled by the SS precursors. This includes the boundary between the oceanic plate in the western Atlantic Ocean and continental margin of eastern North America. Here we use a seismic array approach to image the depth, sharpness, and topography of the upper mantle discontinuities, as well as other possible upper mantle reflectors beneath this region. This array approach utilizes seismic waves that reflect off the underside of a mantle discontinuity and arrive several hundred seconds prior to the SS seismic phase as precursory energy. In this study, we collected high-quality broadband data SS precursors data from shallow focus (< 30 km deep), mid-Atlantic ridge earthquakes recorded by USArray seismometers in Alaska. We generated 4th root vespagrams to enhance the SS precursors and determine how they sample the mantle. Our data show detection of localized structure on the discontinuity boundaries as well as additional horizons, such as the X-discontinuity and a potential reflection from a discontinuity near the depth of the lithosphere-asthenosphere boundary. These structures are related to the transition from predominantly old ocean lithosphere to underlying continental lithosphere, as while deeper reflectors are associated with the subduction of the ancient Farallon slab. A comparison of the depth of upper mantle discontinuities to changes in seismic velocity and anisotropy will further quantify the relationship to mantle flow, compositional layering, and phases changes.

Heterometallic molecular precursors for a lithium-iron oxide material: synthesis, solid state structure, solution and gas-phase behaviour, and thermal decomposition.

PubMed

Han, Haixiang; Wei, Zheng; Barry, Matthew C; Filatov, Alexander S; Dikarev, Evgeny V

2017-05-02

Three heterometallic single-source precursors with a Li : Fe = 1 : 1 ratio for a LiFeO 2 oxide material are reported. Heterometallic compounds LiFeL 3 (L = tbaoac (1), ptac (2), and acac(3)) have been obtained on a large scale, in nearly quantitative yields by one-step reactions that employ readily available reagents. The heterometallic precursor LiFe(acac) 3 (3) with small, symmetric substituents on the ligand (acac = pentane-2,4-dionate), maintains a 1D polymeric structure in the solid state that limits its volatility and prevents solubility in non-coordinating solvents. The application of the unsymmetrical ligands, tbaoac (tert-butyl acetoacetate) and ptac (1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedionate), that exhibit different bridging properties at the two ends of the ligand, allowed us to change the connectivity pattern within the heterometallic assembly. The latter was demonstrated by structural characterization of heterometallic complexes LiFe(tbaoac) 3 (1) and LiFe(ptac) 3 (2) that consist of discrete heterocyclic tetranuclear molecules Li 2 Fe 2 L 6 . The compounds are highly volatile and exhibit a congruent sublimation character. DART mass spectrometric investigation revealed the presence of heterometallic molecules in the gas phase. The positive mode spectra are dominated by the presence of [M - L] + peaks (M = Li 2 Fe 2 L 6 ). In accord with their discrete molecular structure, complexes 1 and 2 are highly soluble in nearly all common solvents. In order to test the retention of the heterometallic structure in solution, the diamagnetic analog of 1, LiMg(tbaoac) 3 (4), has been isolated. Its tetranuclear molecular structure was found to be isomorphous to that of the iron counterpart. 1 H and 7 Li NMR spectroscopy unambiguously confirmed the presence of heterometallic molecules in solutions of non-coordinating solvents. The heterometallic precursor 1 was shown to exhibit clean thermal decomposition in air that results in phase-pure α-modification of layered oxide LiFeO 2 , the prospective cathode material for lithium ion batteries.

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

Sherman, Andrew J

A heterogeneous body having ceramic rich cermet regions in a more ductile metal matrix. The heterogeneous bodies are formed by thermal spray operations on metal substrates. The thermal spray operations apply heat to a cermet powder and project it onto a solid substrate. The cermet powder is composed of complex composite particles in which a complex ceramic-metallic core particle is coated with a matrix precursor. The cermet regions are generally comprised of complex ceramic-metallic composites that correspond approximately to the core particles. The cermet regions are approximately lenticular shaped with an average width that is at least approximately twice themore » average thickness. The cermet regions are imbedded within the matrix phase and generally isolated from one another. They have obverse and reverse surfaces. The matrix phase is formed from the matrix precursor coating on the core particles. The amount of heat applied during the formation of the heterogeneous body is controlled so that the core particles soften but do not become so fluid that they disperse throughout the matrix phase. The force of the impact on the surface of the substrate tends to flatten them. The flattened cermet regions tend to be approximately aligned with one another in the body.« less

Anticipating flash-floods: Multi-scale aspects of the social response

NASA Astrophysics Data System (ADS)

Lutoff, Céline; Creutin, Jean-Dominique; Ruin, Isabelle; Borga, Marco

2016-10-01

This paper aims at exploring the anticipation phase before a flash flood, corresponding to the time between the first climatic signs and the peak-flow. We focus the analysis on people's behaviors observing how they use this period to organize themselves for facing the event. The analysis is made through the definition of three specific scales: the timeliness scale, an analytical scale of anticipatory actions and the scale of human response network. Using a cross-scale and cross level analysis enables to define different phases in the anticipation period where different kind of environmental precursors are mobilized by the actors in order to make sense of the situation and adapt. Three main points deserve attention at the end: firstly, the concepts of timeliness, anticipatory actions and crisis network scales enable to understand differently what happens both physically and socially during an extreme event; secondly, analyzing the precursors shows that each level of crisis network uses different kinds of signs for estimating the situation, organizing and reacting; thirdly, there is a potential for improvement in observation on both social and physical processes at different scales, for verifying the theory of the anticipatory phases.

Kinetic effects in InP nanowire growth and stacking fault formation: the role of interface roughening.

PubMed

Chiaramonte, Thalita; Tizei, Luiz H G; Ugarte, Daniel; Cotta, Mônica A

2011-05-11

InP nanowire polytypic growth was thoroughly studied using electron microscopy techniques as a function of the In precursor flow. The dominant InP crystal structure is wurtzite, and growth parameters determine the density of stacking faults (SF) and zinc blende segments along the nanowires (NWs). Our results show that SF formation in InP NWs cannot be univocally attributed to the droplet supersaturation, if we assume this variable to be proportional to the ex situ In atomic concentration at the catalyst particle. An imbalance between this concentration and the axial growth rate was detected for growth conditions associated with larger SF densities along the NWs, suggesting a different route of precursor incorporation at the triple phase line in that case. The formation of SFs can be further enhanced by varying the In supply during growth and is suppressed for small diameter NWs grown under the same conditions. We attribute the observed behaviors to kinetically driven roughening of the semiconductor/metal interface. The consequent deformation of the triple phase line increases the probability of a phase change at the growth interface in an effort to reach local minima of system interface and surface energy.

Method for producing microcomposite powders using a soap solution

DOEpatents

Maginnis, Michael A.; Robinson, David A.

1996-01-01

A method for producing microcomposite powders for use in superconducting and non-superconducting applications. A particular method to produce microcomposite powders for use in superconducting applications includes the steps of: (a) preparing a solution including ammonium soap; (b) dissolving a preselected amount of a soluble metallic such as silver nitrate in the solution including ammonium soap to form a first solution; (c) adding a primary phase material such as a single phase YBC superconducting material in particle form to the first solution; (d) preparing a second solution formed from a mixture of a weak acid and an alkyl-mono-ether; (e) adding the second solution to the first solution to form a resultant mixture; (f) allowing the resultant mixture to set until the resultant mixture begins to cloud and thicken into a gel precipitating around individual particles of the primary phase material; (g) thereafter drying the resultant mixture to form a YBC superconducting material/silver nitrate precursor powder; and (h) calcining the YBC superconducting material/silver nitrate precursor powder to convert the silver nitrate to silver and thereby form a YBC/silver microcomposite powder wherein the silver is substantially uniformly dispersed in the matrix of the YBC material.

Investigation on structural properties of M-type strontium hexaferrite synthesized in presence of neem and aloe-vera plant leaves extract

NASA Astrophysics Data System (ADS)

Solanki, Neha; Jotania, Rajshree B.

2017-05-01

M-type strontium hexaferrite powder samples were synthesized using a green synthesis route with and without presence of Aloe vera and Neem leaves extract. The dry brownish precursors of strontium hexaferrite were recovered from a mixed solution of metal salts and leaves extract, heated at 100 °C. The obtained precursors were pre-heated at 500 °C for 4 hrs. followed by final heating at 950 °C for 4 hrs. in a muffle furnace to obtain SrFe12O19 hexaferrite powder. The obtained SrFe12O19 hexaferrite powder samples characterized at room temperature in order to check phase purity and structural properties. XRD analysis confirms that samples prepared without and with Aloe vera leaves extract (heated at 950 °C for 4 hrs.) show formation of α-Fe2O3 and M-phase; while the sample prepared in presence of Neem leaves extract (heated at 950 °C for 4 hrs.) show formation of mono phase of strontium hexaferrite. Lattice parameter (a) and cell volume (V) are found to increase in the samples prepared in presence of Aloe vera and Neem leaves extract.

Relative Contributions of Regional and Sector Emissions to the Radiative Forcing of Aerosol-Radiation and Aerosol-Cloud Interactions Based on the AeroCOM Phase III/HTAP2 Experiment

NASA Astrophysics Data System (ADS)

Takemura, T.; Chin, M.

2014-12-01

It is important to understand relative contributions of each regional and sector emission of aerosols and their precursor gases to the regional and global mean radiative forcing of aerosol-radiation and aerosol-cloud interactions. This is because it is useful for international cooperation on controls of air pollution and anthropogenic climate change along most suitable reduction path of their emissions from each region and sector. The Task Force on Hemispheric Transport of Air Pollution (TF HTAP) under the United Nations researches the intercontinental transport of air pollutants including aerosols with strong support of the Aerosol Comparisons between Observations and Models (AeroCOM). The ongoing AeroCOM Phase III/HTAP2 experiment assesses relative contributions of regional and sector sources of aerosols and their precursor gases to the air quality using global aerosol transport models with latest emission inventories. In this study, the extended analyses on the relative contributions of each regional and sector emission to the radiative forcing of aerosol-radiation and aerosol-cloud interactions are done from the AeroCOM Phase III/HTAP2 experiment. Simulated results from MIROC-SPRINTARS and other some global aerosol models participating in the the AeroCOM Phase III/HTAP2 experiment are assessed. Acknowledgements: This study is based on the AeroCOM Phase III/HTAP2 experiment and partly supported by the Environment Research and Technology Development Fund (S-12-3) of the Ministry of the Environment, Japan.

Synthesis of fullerene-like tantalum disulfide nanoparticles by a gas-phase reaction and laser ablation.

PubMed

Schuffenhauer, Christoph; Parkinson, Bruce A; Jin-Phillipp, Neng Yun; Joly-Pottuz, Lucile; Martin, Jean-Michel; Popovitz-Biro, Ronit; Tenne, Reshef

2005-11-01

Motivated by the discovery of the C(60) molecule (buckminsterfullerene), the search for inorganic counterparts of this closed-cage nanostructure started in 1992 with the discovery of nested fullerene-like nanoparticles of WS(2). Inorganic fullerene-like (IF) materials have since been found in numerous two-dimensional compounds and are available in a variety of shapes that offer major applications such as in lubricants and nanocomposites. Various synthetic methodologies have been employed to achieve the right conditions for the constricted or templated growth needed for the occurrence of this new phase. In this study, IF-TaS(2) is produced from a volatile chloride precursor in the gas phase and in small yield by room temperature laser ablation both in argon and in liquid CS(2). For the gas-phase reaction, a high yield of IF nanoparticles was obtained between 400 and 600 degrees C with a low concentration of the precursor gas. The average size and the yield of the IF-TaS(2) nanoparticles decrease with temperature. Above 600 degrees C, IF nanoparticles were found in low yields and at sizes below 20 nm. The stability of the IF nanoparticles produced by the gas-phase reaction is discussed in the light of two existing theoretical models. Laser ablation in argon leads to IF nanoparticles filled with clusters of TaS(2). Agglomeration of the nanoparticles can be avoided by laser ablation in liquid CS(2).

Impact of stacking order on the microstructural properties of Cu2ZnGeSe4 thin film absorber layer

NASA Astrophysics Data System (ADS)

Mary, G. Swapna; Chandra, G. Hema; Sunil, M. Anantha; Subbaiah, Y. P. Venkata; Gupta, Mukul; Rao, R. Prasada

2018-05-01

Six possible multiple stacks of Cu-ZnSe-Ge with selenium incorporation at a precursor stage were prepared using electron beam evaporation followed by vacuum selenization at 475 °C for 30 min to investigate the role of stacking order on the growth and properties of Cu2ZnGeSe4 films. The X-ray diffraction measurements affirm the existence of various binary and ternary phases (ZnSe, Cu2Se, GeSe2 and Cu2GeSe3) for all the precursor stacks. These phases are completely diminished after selenization at 475 °C except a minor co-existence of ZnSe (111) phase along with dominant Cu2ZnGeSe4 (112) phase for stack A: (Cu/Se/ZnSe/Se/Ge/Se) × 4. The Raman measurements for selenized multiple stack A, revealed two major A3, A1 modes at 206 cm-1 and 176 cm-1 and one minor E5 mode at 270 cm-1 corresponding to CZGSe phase. The surface morphology and the elemental distribution across the thickness found to vary significantly with the change of stacking order. The selenized multiple stacks A films shows densely packed flake and capsule shaped grains. The selenized stack A found to have a direct energy band gap of 1.60 eV, showing p-type conductivity with a Hall mobility of 22 cm2 (Vs)-1.

Characteristics of aerosol pollution during heavy haze events in Suzhou, China

NASA Astrophysics Data System (ADS)

Tian, M.; Wang, H. B.; Chen, Y.; Yang, F. M.; Zhang, X. H.; Zou, Q.; Zhang, R. Q.; Ma, Y. L.; He, K. B.

2015-11-01

A comprehensive measurement was carried out to analyze the heavy haze events in Suzhou in January 2013 when extremely severe haze pollution occurred in many cities in China especially in the East. Hourly concentrations of PM2.5, chemical composition (including water-soluble inorganic ions, OC, and EC), and gas-phase precursors were obtained via on-line monitoring system. Based on these data, detailed aerosol composition, light extinction and gas-phase precursors were analyzed to understand the characteristics of the haze events, moreover, the formation mechanism of nitrate and sulfate in PM2.5 and the regional sources deduced from trajectory and PSCF were discussed to explore the origin of the heavy aerosol pollution. The results showed that frequent haze events were occurred on January 2013 and the concentrations of PM2.5 often exceeded 150 μg m-3 during the haze occurrence, with a maximum concentration of 324 μg m-3 on 14 January 2013. Unfavorable weather conditions (high RH, and low rainfall, wind speed and atmospheric pressure), high concentration of secondary aerosol species (including SO42-, NO3-, NH4+, and SOC) and precursors were observed during the haze events. Additionally, OM, (NH4)2SO4, NH4NO3 were demonstrated to be the major contributors to the visibility impairment but the share differed from haze events. This study also found that the high concentration of sulfate might be explained by the heterogeneous reactions in the aqueous surface layer of pre-existing particles or in cloud processes while nitrate might be mainly formed through homogeneous gas-phase reactions. The results of trajectory clustering and the PSCF method manifested that aerosol pollutions in the studied areas were mainly affected by local activities and surrounding sources transported from nearby cities.

Influences of Silver and Zinc Contents in the Stannite Ag2ZnSnS4 Photoelectrodes on Their Photoelectrochemical Performances in the Salt-Water Solution.

PubMed

Cheng, Kong-Wei; Hong, Shu-Wei

2018-06-13

The multicomponent metal sulphide (stannite Ag2ZnSnS4) samples were grown onto the conductive metal oxide coated glass substrates by using the sulfurization of co-sputtering silver-zinc-tin precursors. Several [Ag]/[Zn+Sn] and [Zn]/[Sn] ratios were set in the metal precursors to investigate their influences on the crystal phases, microstructures and physical properties of the stannite Ag2ZnSnS4 samples. The results of the crystal phases and compositions of samples showed that the stannite Ag2ZnSnS4 phase can be obtained using the two-step sulfurization process, which maintained the silver-zinc-tin precursors at 160C for 1 hour and then kept them at 450oC for 30 minutes under sulfur/nitrogen atmosphere. N-type stannite Ag2ZnSnS4 samples with the carrier concentrations of 5.54x1012 - 9.11x1012 cm-3 can be obtained. High resistivities of Ag2ZnSnS4 samples were observed due to the low values of carrier concentration. Increasing the silver content in the sample can improve its PEC performance due to the decrease in the sample resistivity. The ratio of [Ag]/[Zn+Sn] kept at 0.8 and ratio of [Zn]/[Sn] set at 0.90 in the stannite Ag2ZnSnS4 sample had the highest photoelectrochemical performance of 0.31 mA.cm-2 with the potential set at 1.23 V vs. relative hydrogen electrode applied on the sample because of it having the lowest charge transfer resistance in electrolyte.

NUCLEIC ACID AND PROTEIN METABOLISM DURING THE MITOTIC CYCLE IN VICIA FABA

PubMed Central

Woodard, John; Rasch, Ellen; Swift, Hewson

1961-01-01

In order to investigate some of the cytochemical processes involved in interphase growth and culminating in cell division, a combined autoradiographic and microphotometric study of nucleic acids and proteins was undertaken on statistically seriated cells of Vicia faba root meristems. Adenine-8-C14 and uridine-H3 were used as ribonucleic acid (RNA) precursors, thymidine-H3 as a deoxyribonucleic acid (DNA) precursor, and phenylalanine-3-C14 as a protein precursor. Stains used in microphotometry were Feulgen (DNA), azure B (RNA), pH 2.0 fast green (total protein), and pH 8.1 fast green (histone). The autoradiographic data (representing rate of incorporation per organelle) and the microphotometric data (representing changes in amounts of the various components) indicate that the mitotic cycle may be divided into several metabolic phases, three predominantly anabolic (net increase), and a fourth phase predominantly catabolic (net decrease). The anabolic periods are: 1. Telophase to post-telophase during which there are high rates of accumulation of cytoplasmic and nucleolar RNA and nucleolar and chromosomal total protein. 2. Post-telophase to preprophase characterized by histone synthesis and a diphasic synthesis of DNA with the peak of synthesis at mid-interphase and a minor peak just preceding prophase. The minor peak is coincident with a relatively localized DNA synthesis in several chromosomal regions. This period is also characterized by minimal accumulations of cytoplasmic RNA and chromosomal and nucleolar total protein and RNA. 3. Preprophase to prophase in which there are again high rates of accumulation of cytoplasmic RNA, and nucleolar and chromosomal total protein and RNA. The catabolic phase is: 4. The mitotic division during which there are marked losses of cytoplasmic RNA and chromosomal and nucleolar total protein and RNA. PMID:13786522

Viral Infection Induces Expression of Novel Phased MicroRNAs from Conserved Cellular MicroRNA Precursors

PubMed Central

Zhang, Jiayao; Zhao, Shuqi; Zheng, Hong; Gao, Ge; Wei, Liping; Li, Yi

2011-01-01

RNA silencing, mediated by small RNAs including microRNAs (miRNAs) and small interfering RNAs (siRNAs), is a potent antiviral or antibacterial mechanism, besides regulating normal cellular gene expression critical for development and physiology. To gain insights into host small RNA metabolism under infections by different viruses, we used Solexa/Illumina deep sequencing to characterize the small RNA profiles of rice plants infected by two distinct viruses, Rice dwarf virus (RDV, dsRNA virus) and Rice stripe virus (RSV, a negative sense and ambisense RNA virus), respectively, as compared with those from non-infected plants. Our analyses showed that RSV infection enhanced the accumulation of some rice miRNA*s, but not their corresponding miRNAs, as well as accumulation of phased siRNAs from a particular precursor. Furthermore, RSV infection also induced the expression of novel miRNAs in a phased pattern from several conserved miRNA precursors. In comparison, no such changes in host small RNA expression was observed in RDV-infected rice plants. Significantly RSV infection elevated the expression levels of selective OsDCLs and OsAGOs, whereas RDV infection only affected the expression of certain OsRDRs. Our results provide a comparative analysis, via deep sequencing, of changes in the small RNA profiles and in the genes of RNA silencing machinery induced by different viruses in a natural and economically important crop host plant. They uncover new mechanisms and complexity of virus-host interactions that may have important implications for further studies on the evolution of cellular small RNA biogenesis that impact pathogen infection, pathogenesis, as well as organismal development. PMID:21901091

Elastic excitations in BaTiO3 single crystals and ceramics: Mobile domain boundaries and polar nanoregions observed by resonant ultrasonic spectroscopy

NASA Astrophysics Data System (ADS)

Salje, Ekhard K. H.; Carpenter, Michael A.; Nataf, Guillaume F.; Picht, Gunnar; Webber, Kyle; Weerasinghe, Jeevaka; Lisenkov, S.; Bellaiche, L.

2013-01-01

The dynamic properties of elastic domain walls in BaTiO3 were investigated using resonance ultrasonic spectroscopy (RUS). The sequence of phase transitions is characterized by minima in the temperature dependence of RUS resonance frequencies and changes in Q factors (resonance damping). Damping is related to the friction of mobile twin boundaries (90° ferroelectric walls) and distorted polar nanoregions (PNRs) in the cubic phase. Damping is largest in the tetragonal phase of ceramic materials but very low in single crystals. Damping is also small in the low-temperature phases of the ceramic sample and slightly increases with decreasing temperature in the single crystal. The phase angle between the real and imaginary part of the dynamic response function changes drastically in the cubic and tetragonal phases and remains constant in the orthorhombic phase. Other phases show a moderate dependence of the phase angle on temperature showing systematic changes of twin microstructures. Mobile twin boundaries (or sections of twin boundaries such as kinks inside twin walls) contribute strongly to the energy dissipation of the forced oscillation while the reduction in effective modulus due to relaxing twin domains is weak. Single crystals and ceramics show strong precursor softening in the cubic phase related to polar nanoregions (PNRs). The effective modulus decreases when the transition point of the cubic-tetragonal transformation is approached from above. The precursor softening follows temperature dependence very similar to recent results from Brillouin scattering. Between the Burns temperature (≈586 K) and Tc at 405 K, we found a good fit of the squared RUS frequency [˜Δ (C11-C12)] to a Vogel-Fulcher process with an activation energy of ˜0.2 eV. Finally, some first-principles-based effective Hamiltonian computations were carried out in BaTiO3 single domains to explain some of these observations in terms of the dynamics of the soft mode and central mode.

Implications of Low Volatility SOA and Gas-Phase Fragmentation Reactions on SOA Loadings and their Spatial and Temporal Evolution in the Atmosphere

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

Shrivastava, ManishKumar B.; Zelenyuk, Alla; Imre, Dan

2013-04-27

Recent laboratory and field measurements by a number of groups show that secondary organic aerosol (SOA) evaporates orders of magnitude slower than traditional models assume. In addition, chemical transport models using volatility basis set (VBS) SOA schemes neglect gas-phase fragmentation reactions, which are known to be extremely important. In this work, we present modeling studies to investigate the implications of non-evaporating SOA and gas-phase fragmentation reactions. Using the 3-D chemical transport model, WRF-Chem, we show that previous parameterizations, which neglect fragmentation during multi-generational gas-phase chemistry of semi-volatile/inter-mediate volatility organics ("aging SIVOC"), significantly over-predict SOA as compared to aircraft measurements downwindmore » of Mexico City. In sharp contrast, the revised models, which include gas-phase fragmentation, show much better agreement with measurements downwind of Mexico City. We also demonstrate complex differences in spatial SOA distributions when we transform SOA to non-volatile secondary organic aerosol (NVSOA) to account for experimental observations. Using a simple box model, we show that for same amount of SOA precursors, earlier models that do not employ multi-generation gas-phase chemistry of precursors ("non-aging SIVOC"), produce orders of magnitude lower SOA than "aging SIVOC" parameterizations both with and without fragmentation. In addition, traditional absorptive partitioning models predict almost complete SOA evaporation at farther downwind locations for both "non-aging SIVOC" and "aging SIVOC" with fragmentation. In contrast, in our revised approach, SOA transformed to NVSOA implies significantly higher background concentrations as it remains in particle phase even under highly dilute conditions. This work has significant implications on understanding the role of multi-generational chemistry and NVSOA formation on SOA evolution in the atmosphere.« less

Facile synthesis of p-type Zn-doped α-Fe2O3 films for solar water splitting

NASA Astrophysics Data System (ADS)

Kuo, Chun-Lin; Hsu, Yu-Kuei; Lin, Yan-Gu

2014-10-01

A facile and simple fabrication of Zn-doped α-Fe2O3 thin films as a photocathode for solar hydrogen generation was proposed in this report. Transparent Zn-doped α-Fe2O3 films were prepared by a deposition-annealing (DA) process using nontoxic iron(III) chloride as the Fe precursor and zinc chloride as a acceptor dopant, followed by annealing at 550 °C in air. In terms of the structural examination of as-grown samples, X-ray diffraction analysis demonstrated an increase in the lattice parameters of Zn incorporated in Fe2O3 by substituting Fe in the host lattice. No second phase was determined, indicating no phase separation in the ternary materials. Energy dispersive spectroscopy results demonstrated that Zn, Fe, and O elements existed in the deposits. Furthermore, impedance measurements show that the Zn-dopant serves as an hole acceptor and increases the acceptor concentration by increasing concentration of zinc precursor. Significantly, the photoelectrochemical measurements exhibited remarkable cathodic current, corresponding to the reduction reaction of hydrogen. Finally, the optimum photocurrent can be achieved by controlled variation of the Fe and Zni precursor concentration, annealing conditions, and the number of DA cycles. According to our investigation, the understandings of morphology effect on PEC activity give the blueprint for materials design in the application of solar hydrogen.

Synthesis and characterization of micro/nanoscopic Pb(Zr0.52Ti0.48)O3 fibers by electrospinning

NASA Astrophysics Data System (ADS)

Wang, Y.; Furlan, R.; Ramos, I.; Santiago-Aviles, J. J.

Micro/nanoscopic Pb(Zr0.52Ti0.48)O3 fibers were synthesized from commercially available zirconium n-pro-poxide, titanium isopropoxide, and lead 2-ethylhexanoate. Using xylene as a solvent, they were mixed to form a precursor solution with a suitable viscosity for electrospinning. The solution was analyzed using thermo-gravimetric and differential thermal methods. Ultra-fine fibers and mats were electrostatically drawn from the precursor solution. The as-deposited materials were sintered for 2 h at 400, 500, 600, 700 and 800 °C, respectively. Sintered mats or fibers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), Raman micro-spectrometry and scanning-probe microscopy (SPM). The SEM results revealed that the fibers had diameters varying from hundreds of nanometers to 10 μm. Using AES, the elements Pb, Zr, Ti and O, as well as residual C, were detected on the surface of the fibers. Raman and XRD spectra indicated that the precursors began to transform into the intermediate pyrochlore phase at 400 °C, followed by the perovskite Pb(Zr0.52Ti0.48)O3 phase above 600 °C. Scanning-probe microscopy (SPM), operated in the piezo-response imaging mode, revealed spontaneous polarization domains in the fibers, with diameters ranging from 100 to 500 nm.

Solid-state synthesis of YAG powders through microwave coupling of oxide/carbon particulate mixtures

DOE PAGES

Wildfire, Christina; Sabolsky, Edward M.; Spencer, Michael J.; ...

2017-06-14

The rapid synthesis of yttrium aluminum garnet (Y 3Al 15O 12, YAG) powder was investigated through the use of microwave irradiation of the oxide precursor system. For this investigation, an external hybrid heating source was not used. Instead, the rapid heating of the precursor materials (yttria and alumina powders, which are typically transparent to 2.45 GHz microwaves) was initiated by mixing an intrinsic absorbing material (carbon) into the original oxide precursors. The effect of the carbon characteristics, such as carbon source, concentration, particle size, and agglomerate microstructure were evaluated on the efficiency of coupling and resultant oxide reaction. The microwavemore » power was varied to optimize the YAG conversion and eliminate intermediate phase formation. Interactions between the conductive carbon particles and the dielectric oxides within the microwave exposure produced local arching and micro-plasma formation within the powder bed, resulting in the rapid formation of the refractory YAG composition. This optimal conduction led to temperatures of 1000°C that could be achieved in less than 5 min resulting in the formation of > 90 vol% YAG. The understanding of a conductor/dielectric particulate system here, provided insight into possible application of similar systems where microwave irradiation could be used for enhanced solid-state formation, local melting events, and gas phase reactions with a composite powder media.« less

Assembling a supercapacitor electrode with dual metal oxides and activated carbon using a liquid phase plasma.

PubMed

Ki, Seo Jin; Jeon, Ki-Joon; Park, Young-Kwon; Park, Hyunwoong; Jeong, Sangmin; Lee, Heon; Jung, Sang-Chul

2017-12-01

Developing supercapacitor electrodes at an affordable cost while improving their energy and/or power density values is still a challenging task. This study introduced a recipe which assembled a novel electrode composite using a liquid phase plasma that was applied to a reactant solution containing an activated carbon (AC) powder with dual metal precursors of iron and manganese. A comparison was made between the composites doped with single and dual metal components as well as among those synthesized under different precursor concentrations and plasma durations. The results showed that increasing the precursor concentration and plasma duration raised the content of both metal oxides in the composites, whereas the deposition conditions were more favorable to iron oxide than manganese oxide, due to its higher standard potential. The composite treated with the longest plasma duration and highest manganese concentration was superior to the others in terms of cyclic stability and equivalent series resistance. In addition, the new composite selected out of them showed better electrochemical performance than the raw AC material only and even two types of single metal-based composites, owing largely to the synergistic effect of the two metal oxides. Therefore, the proposed methodology can be used to modify existing and future composite electrodes to improve their performance with relatively cheap host and guest materials. Copyright © 2017 Elsevier Ltd. All rights reserved.

Structure comparison of PMN-PT and PMN-PZT nanocrystals prepared by gel-combustion method at optimized temperatures

NASA Astrophysics Data System (ADS)

Ghasemifard, M.; Hosseini, S. M.; Bagheri-Mohagheghi, M. M.; Shahtahmasbi, N.

2009-09-01

We have synthesized and were performed a comparison of structures and optical properties between relaxor ferroelectric PMN-PT and PMN-PZT nanopowders. A gel-combustion method has been used to synthesize PMN-PT and PMN-PZT nanocrystalline with the perovskite structure. The precursors employed in the gel-combustion process were lead nitrate, magnesium acetate, niobium ammonium oxalate and zirconium nitrate. The nanopowders were characterized using the X-ray diffraction (XRD) and transmission electron microscopy (TEM) observation. Fourier transform infrared (FTIR) spectroscopy was employed to monitor the transformation of precursor solutions during the thermal reactions leading to the formation of perovskite phase.

Emission of discrete vortex rings by a vibrating grid in superfluid 3He-B: a precursor to quantum turbulence.

PubMed

Bradley, D I; Clubb, D O; Fisher, S N; Guénault, A M; Haley, R P; Matthews, C J; Pickett, G R; Tsepelin, V; Zaki, K

2005-07-15

We report a transition in the vorticity generated by a grid moving in the B phase of superfluid 3He at T

Highly ordered nanocomposites via a monomer self-assembly in situ condensation approach

DOEpatents

Gin, D.L.; Fischer, W.M.; Gray, D.H.; Smith, R.C.

1998-12-15

A method for synthesizing composites with architectural control on the nanometer scale is described. A polymerizable lyotropic liquid-crystalline monomer is used to form an inverse hexagonal phase in the presence of a second polymer precursor solution. The monomer system acts as an organic template, providing the underlying matrix and order of the composite system. Polymerization of the template in the presence of an optional cross-linking agent with retention of the liquid-crystalline order is carried out followed by a second polymerization of the second polymer precursor within the channels of the polymer template to provide an ordered nanocomposite material. 13 figs.

Three-dimensional morphology of GaP-GaAs nanowires revealed by transmission electron microscopy tomography.

PubMed

Verheijen, Marcel A; Algra, Rienk E; Borgström, Magnus T; Immink, George; Sourty, Erwan; Enckevort, Willem J P van; Vlieg, Elias; Bakkers, Erik P A M

2007-10-01

We have investigated the morphology of heterostructured GaP-GaAs nanowires grown by metal-organic vapor-phase epitaxy as a function of growth temperature and V/III precursor ratio. The study of heterostructured nanowires with transmission electron microscopy tomography allowed the three-dimensional morphology to be resolved, and discrimination between the effect of axial (core) and radial (shell) growth on the morphology. A temperature- and precursor-dependent structure diagram for the GaP nanowire core morphology and the evolution of the different types of side facets during GaAs and GaP shell growth were constituted.

Highly ordered nanocomposites via a monomer self-assembly in situ condensation approach

DOEpatents

Gin, Douglas L.; Fischer, Walter M.; Gray, David H.; Smith, Ryan C.

1998-01-01

A method for synthesizing composites with architectural control on the nanometer scale is described. A polymerizable lyotropic liquid-crystalline monomer is used to form an inverse hexagonal phase in the presence of a second polymer precursor solution. The monomer system acts as an organic template, providing the underlying matrix and order of the composite system. Polymerization of the template in the presence of an optional cross-linking agent with retention of the liquid-crystalline order is carried out followed by a second polymerization of the second polymer precursor within the channels of the polymer template to provide an ordered nanocomposite material.

Thermodynamic analysis of vapor-phase epitaxy of CdTe using a metallic Cd source

NASA Astrophysics Data System (ADS)

Iso, Kenji; Murakami, Hisashi; Koukitu, Akinori

2017-07-01

Thermodynamic analysis of CdTe growth using cost-effective metallic Cd and dialkyl telluride was performed. The major vapor species at source zone in equilibrium were gaseous Cd for the group-II precursor, and Te2 and H2Te for the group-VI precursors. The driving force for the CdTe deposition was still positive even at 650 °C. This indicates that CdTe formation from gaseous Cd can proceed thermodynamically. Furthermore, the calculations showed that CdTe decomposes at higher temperature and increasing the II/VI ratio increases the limit of the growth temperature, which coincides with the experimental results.

Monolithic microfluidic concentrators and mixers

DOEpatents

Frechet, Jean M.; Svec, Frantisek; Yu, Cong; Rohr, Thomas

2005-05-03

Microfluidic devices comprising porous monolithic polymer for concentration, extraction or mixing of fluids. A method for in situ preparation of monolithic polymers by in situ initiated polymerization of polymer precursors within microchannels of a microfluidic device and their use for solid phase extraction (SPE), preconcentration, concentration and mixing.

ORIGIN OF CARBON IN POLYCHLORINATED DIOXINS AND FURANS FORMED DURING SOOTING COMBUSTION

EPA Science Inventory

The paper discusses results of an investigation on the importance of solid- and gas-phase carbon precursors for the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) during sooting combustion. Experiments were performed in an entrained flow reactor (EFR)...

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

Yusoff, Yusriha Mohd; Salimi, Midhat Nabil Ahmad; Anuar, Adilah

Many studies have been carried out in order to prepare hydroxyapatite (HAp) by various methods. In this study, we focused on the preparation of HAp nanoparticles by using sol-gel technique in which few parameters are optimized which were stirring rate, aging time and sintering temperature. HAp nanoparticles were prepared by using precursors of calcium nitrate tetrahydrate, Ca(NO{sub 3}){sub 2}.4H{sub 2}O and phosphorous pentoxide, P{sub 2}O{sub 5}. Both precursors are mixed in ethanol respectively before they were mixed together in which it formed a stable sol. Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Scanning electron microscopy (SEM) were used formore » its characterization in terms of functional group, phase composition, crystallite size and morphology of the nanoparticles produced. FTIR spectra showed that the functional groups that present in all five samples were corresponding to the formation of HAp. Besides, XRD shows that only one phase was formed which was hydroxyapatite. Meanwhile, SEM shows that the small particles combine together to form agglomeration.« less

Preparation of hydroxyapatite nanoparticles by sol-gel method with optimum processing parameters

NASA Astrophysics Data System (ADS)

Yusoff, Yusriha Mohd; Salimi, Midhat Nabil Ahmad; Anuar, Adilah

2015-05-01

Many studies have been carried out in order to prepare hydroxyapatite (HAp) by various methods. In this study, we focused on the preparation of HAp nanoparticles by using sol-gel technique in which few parameters are optimized which were stirring rate, aging time and sintering temperature. HAp nanoparticles were prepared by using precursors of calcium nitrate tetrahydrate, Ca(NO3)2.4H2O and phosphorous pentoxide, P2O5. Both precursors are mixed in ethanol respectively before they were mixed together in which it formed a stable sol. Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Scanning electron microscopy (SEM) were used for its characterization in terms of functional group, phase composition, crystallite size and morphology of the nanoparticles produced. FTIR spectra showed that the functional groups that present in all five samples were corresponding to the formation of HAp. Besides, XRD shows that only one phase was formed which was hydroxyapatite. Meanwhile, SEM shows that the small particles combine together to form agglomeration.

Mechanistic Understanding of Tungsten Oxide In-Plane Nanostructure Growth via Sequential Infiltration Synthesis

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

Kim, Jae Jin; Suh, Hyo Seon; Zhou, Chun

Tungsten oxide (WO3-x) nanostructures with hexagonal in-plane arrangements were fabricated by sequential infiltration synthesis (SIS), using the selective interaction of gas phase precursors with functional groups in one domain of a block copolymer (BCP) self-assembled template. Such structures are highly desirable for various practical applications and as model systems for fundamental studies. The nanostructures were characterized by cross-sectional scanning electron microscopy, grazing-incidence small/wide-angle X-ray scattering (GISAXS/GIWAXS), and X-ray absorption near edge structure (XANES) measurements at each stage during the SIS process and subsequent thermal treatments, to provide a comprehensive picture of their evolution in morphology, crystallography and electronic structure. Inmore » particular, we discuss the critical role of SIS Al2O3 seeds toward modifying the chemical affinity and free volume in a polymer for subsequent infiltration of gas phase precursors. The insights into SIS growth obtained from this study are valuable to the design and fabrication of a wide range of targeted nanostructures.« less

Induction of labor in a contemporary obstetric cohort.

PubMed

Laughon, S Katherine; Zhang, Jun; Grewal, Jagteshwar; Sundaram, Rajeshwari; Beaver, Julie; Reddy, Uma M

2012-06-01

We sought to describe details of labor induction, including precursors and methods, and associated vaginal delivery rates. This was a retrospective cohort study of 208,695 electronic medical records from 19 hospitals across the United States, 2002 through 2008. Induction occurred in 42.9% of nulliparas and 31.8% of multiparas and elective or no recorded indication for induction at term occurred in 35.5% and 44.1%, respectively. Elective induction at term in multiparas was highly successful (vaginal delivery 97%) compared to nulliparas (76.2%). For all precursors, cesarean delivery was more common in nulliparas in the latent compared to active phase of labor. Regardless of method, vaginal delivery rates were higher with a ripe vs unripe cervix, particularly for multiparas (86.6-100%). Induction of labor was a common obstetric intervention. Selecting appropriate candidates and waiting longer for labor to progress into the active phase would make an impact on decreasing the national cesarean delivery rate. Published by Mosby, Inc.

Custom-designed nanomaterial libraries for testing metal oxide toxicity

PubMed Central

Pokhrel, Suman; Nel, André E.; Mädler, Lutz

2014-01-01

Conspectus Advances in aerosol technology over the past 10 years have provided methods that enable the generation and design of ultrafine nanoscale materials for different applications. The particles are produced combusting a precursor solution and its chemical reaction in the in the gas phase. Flame spray pyrolysis (FSP) is a highly versatile technique for single step and scalable synthesis of nanoscale materials. New innovations in particle synthesis using FSP technology and its precursor chemistry have enabled flexible dry synthesis of loosely-agglomerated highly crystalline ultrafine powders (porosity ≥ 90%) of binary, ternary and mixed binary or ternary oxides. The flame spray pyrolysis lies at the intersection of combustion science, aerosols technology and materials chemistry. The interdisciplinary research is not only inevitable but is becoming increasingly crucial in the design of nanoparticles (NPs) made in the gas phase. The increasing demand especially in the bio-applications for particles with specific material composition, high purity and crystallinity can be often fulfilled with the fast, single step FSP technique. PMID:23194152

Discovery of the 3-Imino-1,2,4-thiadiazinane 1,1-Dioxide Derivative Verubecestat (MK-8931)–A β-Site Amyloid Precursor Protein Cleaving Enzyme 1 Inhibitor for the Treatment of Alzheimer’s Disease

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

Scott, Jack D.; Li, Sarah W.; Brunskill, Andrew P. J.

Verubecestat 3 (MK-8931), a diaryl amide-substituted 3-imino-1,2,4-thiadiazinane 1,1-dioxide derivative, is a high-affinity β-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitor currently undergoing Phase 3 clinical evaluation for the treatment of mild to moderate and prodromal Alzheimer’s disease. Although not selective over the closely related aspartyl protease BACE2, verubecestat has high selectivity for BACE1 over other key aspartyl proteases, notably cathepsin D, and profoundly lowers CSF and brain Aβ levels in rats and nonhuman primates and CSF Aβ levels in humans. In this annotation, we describe the discovery of 3, including design, validation, and selected SAR around the novel iminothiadiazinanemore » dioxide core as well as aspects of its preclinical and Phase 1 clinical characterization.« less

In situ production of titanium dioxide nanoparticles in molten salt phase for thermal energy storage and heat-transfer fluid applications.

PubMed

Lasfargues, Mathieu; Bell, Andrew; Ding, Yulong

In this study, TiO 2 nanoparticles (average particle size 16 nm) were successfully produced in molten salt phase and were showed to significantly enhance the specific heat capacity of a binary eutectic mixture of sodium and potassium nitrate (60/40) by 5.4 % at 390 °C and 7.5 % at 445 °C for 3.0 wt% of precursors used. The objective of this research was to develop a cost-effective alternate method of production which is potentially scalable, as current techniques utilized are not economically viable for large quantities. Enhancing the specific heat capacity of molten salt would promote more competitive pricing for electricity production by concentrating solar power plant. Here, a simple precursor (TiOSO 4 ) was added to a binary eutectic mixture of potassium and sodium nitrate, heated to 450 °C, and cooled to witness the production of nanoparticles.

First principles kinetic Monte Carlo study on the growth patterns of WSe2 monolayer

NASA Astrophysics Data System (ADS)

Nie, Yifan; Liang, Chaoping; Zhang, Kehao; Zhao, Rui; Eichfeld, Sarah M.; Cha, Pil-Ryung; Colombo, Luigi; Robinson, Joshua A.; Wallace, Robert M.; Cho, Kyeongjae

2016-06-01

The control of domain morphology and defect level of synthesized transition metal dichalcogenides (TMDs) is of crucial importance for their device applications. However, current TMDs synthesis by chemical vapor deposition and molecular beam epitaxy is in an early stage of development, where much of the understanding of the process-property relationships is highly empirical. In this work, we use a kinetic Monte Carlo coupled with first principles calculations to study one specific case of the deposition of monolayer WSe2 on graphene, which can be expanded to the entire TMD family. Monolayer WSe2 domains are investigated as a function of incident flux, temperature and precursor ratio. The quality of the grown WSe2 domains is analyzed by the stoichiometry and defect density. A phase diagram of domain morphology is developed in the space of flux and the precursor stoichiometry, in which the triangular compact, fractal and dendritic domains are identified. The phase diagram has inspired a new synthesis strategy for large TMD domains with improved quality.

Induction of Labor in a Contemporary Obstetric Cohort

PubMed Central

Laughon, S. Katherine; Zhang, Jun; Grewal, Jagteshwar; Sundaram, Rajeshwari; Beaver, Julie; Reddy, Uma M.

2012-01-01

Objective To describe details of labor induction, including precursors and methods, and associated vaginal delivery rates. Study Design A retrospective cohort study of 208,695 electronic medical records from 19 hospitals across the United States, 2002–2008. Results Induction occurred in 42.9% of nulliparas and 31.8% of multiparas and elective or no recorded indication for induction at term occurred in 35.5% and 44.1%, respectively. Elective induction at term in multiparas was highly successful (vaginal delivery 97%) compared to nulliparas (76.2%). For all precursors, cesarean delivery was more common in nulliparas in the latent compared to active phase of labor. Regardless of method, vaginal delivery rates were higher with a ripe versus unripe cervix, particularly for multiparas (86.6 – 100%). Conclusions Induction of labor was a common obstetric intervention. Selecting appropriate candidates and waiting longer for labor to progress into the active phase would make an impact on decreasing the national cesarean delivery rate. PMID:22520652

Spherical boron nitride particles and method for preparing them

DOEpatents

Phillips, Jonathan; Gleiman, Seth S.; Chen, Chun-Ku

2003-11-25

Spherical and polyhedral particles of boron nitride and method of preparing them. Spherical and polyhedral particles of boron nitride are produced from precursor particles of hexagonal phase boron nitride suspended in an aerosol gas. The aerosol is directed to a microwave plasma torch. The torch generates plasma at atmospheric pressure that includes nitrogen atoms. The presence of nitrogen atoms is critical in allowing boron nitride to melt at atmospheric pressure while avoiding or at least minimizing decomposition. The plasma includes a plasma hot zone, which is a portion of the plasma that has a temperature sufficiently high to melt hexagonal phase boron nitride. In the hot zone, the precursor particles melt to form molten particles that acquire spherical and polyhedral shapes. These molten particles exit the hot zone, cool, and solidify to form solid particles of boron nitride with spherical and polyhedral shapes. The molten particles can also collide and join to form larger molten particles that lead to larger spherical and polyhedral particles.

Phases of LiMn1.84V0.06Ti0.1O4 cathode material

NASA Astrophysics Data System (ADS)

Zainol, N. H.; Kamarulzaman, N.; Osman, Z.; Fadzil, A. F. M.; Yahya, N. F.

2017-09-01

In this work, LiMn1.84V0.06Ti0.1O4 was prepared via a combustion method using citric acid as a reductant. The precursor obtained was annealed at 700 °C for 24h in a furnace. The thermal profile of the precursor was obtained by simultaneous thermogravimetric analysis (STA). The observed material was characterized by X-ray Diffraction (XRD) and found to be pure and single-phase of cubic structure. The electrochemical performance of LiMn1.84V0.06Ti0.1O4 cathode material was studied by applying a constant current of 1.0 mA at a voltage range of 4.2 to 2.5 V. The specific capacity of LiMn1.84V0.06Ti0.1O4 cathode material at the 1st cycle shows the value of 95mAh/g which is less than the specific capacity of LiMn2O4, which is 117 mAh/g.

The rational design of a Au(I) precursor for focused electron beam induced deposition

PubMed Central

Marashdeh, Ali; Tiesma, Thiadrik; van Velzen, Niels J C; Harder, Sjoerd; Havenith, Remco W A; De Hosson, Jeff T M

2017-01-01

Au(I) complexes are studied as precursors for focused electron beam induced processing (FEBIP). FEBIP is an advanced direct-write technique for nanometer-scale chemical synthesis. The stability and volatility of the complexes are characterized to design an improved precursor for pure Au deposition. Aurophilic interactions are found to play a key role. The short lifetime of ClAuCO in vacuum is explained by strong, destabilizing Au–Au interactions in the solid phase. While aurophilic interactions do not affect the stability of ClAuPMe3, they leave the complex non-volatile. Comparison of crystal structures of ClAuPMe3 and MeAuPMe3 shows that Au–Au interactions are much weaker or partially even absent for the latter structure. This explains its high volatility. However, MeAuPMe3 dissociates unfavorably during FEBIP, making it an unsuitable precursor. The study shows that Me groups reduce aurophilic interactions, compared to Cl groups, which we attribute to electronic rather than steric effects. Therefore we propose MeAuCO as a potential FEBIP precursor. It is expected to have weak Au–Au interactions, making it volatile. It is stable enough to act as a volatile source for Au deposition, being stabilized by 6.5 kcal/mol. Finally, MeAuCO is likely to dissociate in a single step to pure Au. PMID:29354346

Droplet size prediction in ultrasonic nebulization for non-oxide ceramic powder synthesis.

PubMed

Muñoz, Mariana; Goutier, Simon; Foucaud, Sylvie; Mariaux, Gilles; Poirier, Thierry

2018-03-01

Spray pyrolysis process has been used for the synthesis of non-oxide ceramic powders from liquid precursors in the Si/C/N system. Particles with a high thermal stability and with variable composition and size distribution have been obtained. In this process, the mechanisms involved in precursor decomposition and gas phase recombination of species are still unknown. The final aim of this work consists in improving the whole process comprehension by an experimental/modelling approach that helps to connect the synthesized particles characteristics to the precursor properties and process operating parameters. It includes the following steps: aerosol formation by a piezoelectric nebulizer, its transport and the chemical-physical phenomena involved in the reaction processes. This paper focuses on the aerosol characterization to understand the relationship between the liquid precursor properties and the liquid droplet diameter distribution. Liquids with properties close to the precursor of interest (hexamethyldisilazane) have been used. Experiments have been performed using a shadowgraphy technique to determine the drop size distribution of the aerosol. For all operating parameters of the nebulizer device and liquids used, bimodal droplet size distributions have been obtained. Correlations proposed in the literature for the droplet size prediction by ultrasonic nebulization were used and adapted to the specific nebulizer device used in this study, showing rather good agreement with experimental values. Copyright © 2017 Elsevier B.V. All rights reserved.

The rational design of a Au(I) precursor for focused electron beam induced deposition.

PubMed

Marashdeh, Ali; Tiesma, Thiadrik; van Velzen, Niels J C; Harder, Sjoerd; Havenith, Remco W A; De Hosson, Jeff T M; van Dorp, Willem F

2017-01-01

Au(I) complexes are studied as precursors for focused electron beam induced processing (FEBIP). FEBIP is an advanced direct-write technique for nanometer-scale chemical synthesis. The stability and volatility of the complexes are characterized to design an improved precursor for pure Au deposition. Aurophilic interactions are found to play a key role. The short lifetime of ClAuCO in vacuum is explained by strong, destabilizing Au-Au interactions in the solid phase. While aurophilic interactions do not affect the stability of ClAuPMe 3 , they leave the complex non-volatile. Comparison of crystal structures of ClAuPMe 3 and MeAuPMe 3 shows that Au-Au interactions are much weaker or partially even absent for the latter structure. This explains its high volatility. However, MeAuPMe 3 dissociates unfavorably during FEBIP, making it an unsuitable precursor. The study shows that Me groups reduce aurophilic interactions, compared to Cl groups, which we attribute to electronic rather than steric effects. Therefore we propose MeAuCO as a potential FEBIP precursor. It is expected to have weak Au-Au interactions, making it volatile. It is stable enough to act as a volatile source for Au deposition, being stabilized by 6.5 kcal/mol. Finally, MeAuCO is likely to dissociate in a single step to pure Au.

Analysis of the amyloid precursor protein role in neuritogenesis reveals a biphasic SH-SY5Y neuronal cell differentiation model.

PubMed

da Rocha, Joana Fernandes; da Cruz e Silva, Odete A B; Vieira, Sandra Isabel

2015-07-01

The existence of an intrinsic programme controlling neuritogenesis and activated during early neuronal differentiation and regeneration stages is well established. However, the identity and role of each molecular player and event, as well as how such a programme is modified by environmental signals, remain a focus of research. The amyloid precursor protein (APP) is a neuromodulator of the developing and mature nervous system, although in a highly complex manner which is far from clear. To study APP-induced neuritogenesis, the retinoic acid (RA)-induced SH-SY5Y cell differentiation model was first minutely characterized in terms of RA dose, morphological outputs and relevant biochemical markers. The findings reported here unveiled two differentiation phases for the 10 μM RA dose: 1-4 (4 days excluded) and 4-8 days, clearly defined by fold increases in the ratio between APP and acetylated Tubulin. Moreover, we describe, for the first time, a unique peak of secreted APP (sAPP)/APP ratio in the first phase. Subsequent APP and sAPP modulations confirmed that a high sAPP/APP ratio potentiates the elongation of smaller processes at the earlier neuritogenic phase. This sAPP/APP ratio drops in the second phase, as holoAPP levels increase to assist the maintenance of the longer neurites, potentially via their stabilization. © 2015 International Society for Neurochemistry.

Liquid-phase explosive crystallization of electron-beam-evaporated a-Si films induced by flash lamp annealing

NASA Astrophysics Data System (ADS)

Ohdaira, Keisuke; Matsumura, Hideki

2013-01-01

We succeed in the formation of micrometer-order-thick polycrystalline silicon (poly-Si) films through the flash-lamp-induced liquid-phase explosive crystallization (EC) of precursor a-Si films prepared by electron-beam (EB) evaporation. The velocity of the explosive crystallization (vEC) is estimated to be ˜14 m/s, which is close to the velocity of the liquid-phase epitaxy (LPE) of Si at a temperature around the melting point of a-Si of 1418 K. Poly-Si films formed have micrometer-order-long grains stretched along a lateral crystallization direction, and X-ray diffraction (XRD) and electron diffraction pattern measurements reveal that grains in poly-Si films tend to have a particular orientation. These features are significantly different from our previous results: the formation of poly-Si films containing randomly-oriented 10-nm-sized fine grains formed from a-Si films prepared by catalytic chemical vapor deposition (Cat-CVD) or sputtering. One possible reason for the emergence of a different EC mode in EB-evaporated a-Si films is the suppression of solid-phase nucleation (SPN) during Flash Lamp Annealing (FLA) due to tensile stress which precursor a-Si films originally hold. Poly-Si films formed from EB-evaporated a-Si films would contribute to the realization of high-efficiency thin-film poly-Si solar cells because of large and oriented grains.

Eu(2+)-Activated Phase-Pure Oxonitridosilicate Phosphor in a Ba-Si-O-N System via Facile Silicate-Assisted Routes Designed by First-Principles Thermodynamic Simulation.

PubMed

Yun, Young Jun; Kim, Jin Kyu; Ju, Ji Young; Choi, Seul Ki; Park, Woon Ik; Jung, Ha-Kyun; Kim, Yongseon; Choi, Sungho

2016-09-06

Eu(2+)-activated single phase Ba(2+)-oxonitridosilicate phosphors were prepared under a mild synthetic condition via silicate precursors, and their luminescent properties were investigated. Both the preferred oxonitridosilicate formation as for the available host compounds and thermodynamic stability within the Ba-Si-O-N system were elucidated in detail by the theoretical simulation based on the first-principles density functional theory. Those results can visualize the optimum synthetic conditions for Eu(2+)-activated highly luminescent Ba(2+)-oxonitridosilicates, especially Ba3Si6O12N2, as promising conversion phosphors for white LEDs, including Ba3Si6O9N4 and BaSi2O2N2 phases. To prove the simulated design rule, we synthesized the Ba3Si6O12N2:Eu(2+) phosphor using various silicate precursors, Ba2Si4O10, Ba2Si3O8, and BaSiO3, in a carbothermal reduction ambient and finally succeeded in obtaining a phase of pure highly luminescent oxonitridosilicate phosphor without using any solid-state nitride addition and/or high pressure synthetic procedures. Our study provides useful guidelines for robust synthetic procedures for developing thermally stable rare-earth-ion activated oxonitridosilicate phosphors and an established simulation method that can be effectively applied to other multigas systems.

Enhanced quality thin film Cu(In,Ga)Se.sub.2 for semiconductor device applications by vapor-phase recrystallization

DOEpatents

Tuttle, John R.; Contreras, Miguel A.; Noufi, Rommel; Albin, David S.

1994-01-01

Enhanced quality thin films of Cu.sub.w (In,Ga.sub.y)Se.sub.z for semiconductor device applications are fabricated by initially forming a Cu-rich, phase-separated compound mixture comprising Cu(In,Ga):Cu.sub.x Se on a substrate to form a large-grain precursor and then converting the excess Cu.sub.x Se to Cu(In,Ga)Se.sub.2 by exposing it to an activity of In and/or Ga, either in vapor In and/or Ga form or in solid (In,Ga).sub.y Se.sub.z. Alternatively, the conversion can be made by sequential deposition of In and/or Ga and Se onto the phase-separated precursor. The conversion process is preferably performed in the temperature range of about 300.degree.-600.degree. C., where the Cu(In,Ga)Se.sub.2 remains solid, while the excess Cu.sub.x Se is in a liquid flux. The characteristic of the resulting Cu.sub.w (In,Ga).sub.y Se.sub.z can be controlled by the temperature. Higher temperatures, such as 500.degree.-600.degree. C., result in a nearly stoichiometric Cu(In,Ga)Se.sub.2, whereas lower temperatures, such as 300.degree.-400.degree. C., result in a more Cu-poor compound, such as the Cu.sub.z (In,Ga).sub.4 Se.sub.7 phase.

Enhanced quality thin film Cu(In,Ga)Se[sub 2] for semiconductor device applications by vapor-phase recrystallization

DOEpatents

Tuttle, J.R.; Contreras, M.A.; Noufi, R.; Albin, D.S.

1994-10-18

Enhanced quality thin films of Cu[sub w](In,Ga[sub y])Se[sub z] for semiconductor device applications are fabricated by initially forming a Cu-rich, phase-separated compound mixture comprising Cu(In,Ga):Cu[sub x]Se on a substrate to form a large-grain precursor and then converting the excess Cu[sub x]Se to Cu(In,Ga)Se[sub 2] by exposing it to an activity of In and/or Ga, either in vapor In and/or Ga form or in solid (In,Ga)[sub y]Se[sub z]. Alternatively, the conversion can be made by sequential deposition of In and/or Ga and Se onto the phase-separated precursor. The conversion process is preferably performed in the temperature range of about 300--600 C, where the Cu(In,Ga)Se[sub 2] remains solid, while the excess Cu[sub x]Se is in a liquid flux. The characteristic of the resulting Cu[sub w](In,Ga)[sub y]Se[sub z] can be controlled by the temperature. Higher temperatures, such as 500--600 C, result in a nearly stoichiometric Cu(In,Ga)Se[sub 2], whereas lower temperatures, such as 300--400 C, result in a more Cu-poor compound, such as the Cu[sub z](In,Ga)[sub 4]Se[sub 7] phase. 7 figs.

Efficient colloidal route to pure phase kesterite Cu2ZnSnS4 (CZTS) nanocrystals with controlled shape and structure

NASA Astrophysics Data System (ADS)

Jain, Shefali; Chawla, Parul; Sharma, Shailesh Narain; Singh, Dinesh; Vijayan, N.

2018-07-01

This work reports the synthesis of varied shaped Cu2ZnSnS4 (CZTS) nano inks in a most stable kesterite phase via a hot injection colloidal route. CZTS nanoparticles of varied shape were synthesized by using various capping ligands with the introduction of butylamine as a new capping ligand and two different sulfur precursors respectively. The shape of the as-synthesized kesterite CZTS nanocrystals can be well controlled in the form of nanofibers, spherical nanoparticles, nano hexagons, nanotriangles, and nanodiscs. A detailed analysis of the effects of various capping ligand and sulfur source on reaction conditions to obtain pure phase kesterite CZTS nanocrystals for different shapes is explained using LaMer's diagram. It has been found that the choice of sulfur precursor also plays an important role in determining the symmetry and orientation of the plane of the CZTS nanocrystals. Due to different morphology and capping ligands present on the surface, diverse surface properties were obtained which was confirmed by contact angle measurements. The variation in the band gap was also found with changes in morphology of kesterite phased CZTS nanoparticles. Due to variations obtained in band gap, changes in I-V characteristics were also observed which may leads different CZTS nanoparticles to have their potential applications in different regime other than photovoltaics like sensors, photocatalysis etc.

Laboratory management of cervical intraepithelial neoplasia: proposing a new paradigm.

PubMed

Herfs, Michael; Crum, Christopher P

2013-03-01

Since the discovery of human papillomavirus (HPV) type 16 in early 80s, the link between HPV and cervical cancer has been established with certainty, a function of the discovery and cloning of a range of HPV types associated with both cancer precursors (cervical intraepithelial neoplasia or CIN) and carcinomas and extensive epidemiologic, clinical, pathologic, and experimental data. These accumulated results have culminated in new paradigms of cancer prevention through screening and triage. Despite this, the management of women with CIN is still suboptimal and the overtreatment of these conditions still occurs, largely due to the lack of clarity regarding which precancerous lesions are most likely to progress in grade. Recently, a discrete population of cuboidal cells was discovered at the cervical squamocolumnar junction, the anatomic site where the large majority of HPV-related (pre)neoplastic lesions develop. These cells seem to be embryonic in nature and participate both in benign metaplasias and the initial phase of precancer development. This review summarizes the historical evolution of precursor management, assesses the potential role of this and other discoveries in segregating lower from higher-risk precursors, and examines their potential impact on the management of women with real or potential cervical cancer precursors.

An integrated scheme for the simultaneous determination of biogenic amines, precursor amino acids, and related metabolites by liquid chromatography with electrochemical detection.

PubMed

Oka, K; Kojima, K; Togari, A; Nagatsu, T; Kiss, B

1984-06-08

A new method using high-performance liquid chromatography with electrochemical detection (HPLC-ED) for the simultaneous determination of monoamines, their precursor amino acids, and related major metabolites in small samples of brain tissue weighing from 0.5 to 50 mg is described. The method is based on the preliminary isolation of monoamines (dopamine, norepinephrine, epinephrine, and serotonin), their precursor amino acids (tyrosine, 3,4-dihydroxyphenylalanine, tryptophan and 5-hydroxytryptophan), and their major metabolites (3-methoxytyramine, normetanephrine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, vanillylmandelic acid, 3-methoxy-4-hydroxyphenylethyleneglycol, and 5-hydroxyindoleacetic acid) by chromatography on small columns of Amberlite CG-50 and Dowex 50W, and by ethyl acetate extraction. All the compounds in the four isolated fractions were measured by HPLC-ED on a reversed-phase column under four different conditions. The sensitivity was from 0.1 to 40 pmol, depending on the substances analysed. This newly established method was applied to the study of the effects of an aromatic L-amino acid decarboxylase inhibitor (NSD-1015) and a monoamine oxidase inhibitor (pargyline) on the levels of monoamines, their precursor amino acids and their major metabolites in brain regions of mice.

CVD of SiC and AlN using cyclic organometallic precursors

NASA Technical Reports Server (NTRS)

Interrante, L. V.; Larkin, D. J.; Amato, C.

1992-01-01

The use of cyclic organometallic molecules as single-source MOCVD precursors is illustrated by means of examples taken from our recent work on AlN and SiC deposition, with particular focus on SiC. Molecules containing (AlN)3 and (SiC)2 rings as the 'core structure' were employed as the source materials for these studies. The organoaluminum amide, (Me2AlNH2)3, was used as the AlN source and has been studied in a molecular beam sampling apparatus in order to determine the gas phase species present in a hot-wall CVD reactor environment. In the case of SiC CVD, a series of disilacyclobutanes (Si(XX')CH2)2 (with X and X' = H, CH3, and CH2SiH2CH3), were examined in a cold-wall, hot-stage CVD reactor in order to compare their relative reactivities and prospective utility as single-source CVD precursors. The parent compound, disilacyclobutane, (SiH2CH2)2, was found to exhibit the lowest deposition temperature (ca. 670 C) and to yield the highest purity SiC films. This precursor gave a highly textured, polycrystalline film on the Si(100) substrates.

EFFECTS OF PRECURSOR SOLUTION MODIFICATION ON THE CRYSTALLINITY AND ELECTRICAL PROPERTIES OF Na0.5Bi0.5TiO3-BiFeO3 BASED THIN FILM

NASA Astrophysics Data System (ADS)

Sui, Huiting; Yang, Changhong; Wang, Gaoyun; Feng, Chao

2014-07-01

For chemical solution decomposition process, the precursor solution is a basic factor affecting the quality of the deposited-film. In this paper, we choose (l00)-oriented 0.7[(Bi0.95Ce0.05)0.5Na0.5(Ti0.99Fe0.01)O3]-0.3BiFe0.97Mn0.03O3(0.7NBTCeFe-0.3BFOMn) thin films prepared by various precursor solutions for investigation. The roles of precursor solution modification on crystallinity, ferroelectric and dielectric properties are characterized. With the addition of polyethylene glycol into the solution, phase-pure perovskite structure can be obtained. Furthermore, when the volume ratio for the solvents (ethylene glycol to acetic acid) is modified as 2:1, enhanced ferroelectricity can be achieved with a remanent polarization (Pr) of 27.5 μC/cm2, which coincides well with the capacitance-voltage curve with relatively sharp feature. Also, the 0.7NBTCeFe-0.3BFOMn film exhibits a dielectric constant (ɛr) of 576 and dielectric loss (tan δ) of 0.123 at 100 kHz.

Surface defects on the Gd{sub 2}Zr{sub 2}O{sub 7} oxide films grown on textured NiW technical substrates by chemical solution method

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

Zhao, Y., E-mail: yuezhao@sjtu.edu.cn

2017-02-15

Epitaxial growth of oxide thin films has attracted much interest because of their broad applications in various fields. In this study, we investigated the microstructure of textured Gd{sub 2}Zr{sub 2}O{sub 7} films grown on (001)〈100〉 orientated NiW alloy substrates by a chemical solution deposition (CSD) method. The aging effect of precursor solution on defect formation was thoroughly investigated. A slight difference was observed between the as-obtained and aged precursor solutions with respect to the phase purity and global texture of films prepared using these solutions. However, the surface morphologies are different, i.e., some regular-shaped regions (mainly hexagonal or dodecagonal) weremore » observed on the film prepared using the as-obtained precursor, whereas the film prepared using the aged precursor exhibits a homogeneous structure. Electron backscatter diffraction and scanning electron microscopy analyses showed that the Gd{sub 2}Zr{sub 2}O{sub 7} grains present within the regular-shaped regions are polycrystalline, whereas those present in the surrounding are epitaxial. Some polycrystalline regions ranging from several micrometers to several tens of micrometers grew across the NiW grain boundaries underneath. To understand this phenomenon, the properties of the precursors and corresponding xerogel were studied by Fourier transform infrared spectroscopy and coupled thermogravimetry/differential thermal analysis. The results showed that both the solutions mainly contain small Gd−Zr−O clusters obtained by the reaction of zirconium acetylacetonate with propionic acid during the precursor synthesis. The regular-shaped regions were probably formed by large Gd−Zr−O frameworks with a metastable structure in the solution with limited aging time. This study demonstrates the importance of the precise control of chemical reaction path to enhance the stability and homogeneity of the precursors of the CSD route. - Highlights: •We investigate microstructure of Gd{sub 2}Zr{sub 2}O{sub 7} films grown by a chemical solution route. •The aging effect of precursor solution on formation of surface defect was thoroughly studied. •Gd−Zr−O clusters are present in the precursor solutions.« less

An Automatic Phase-Change Detection Technique for Colloidal Hard Sphere Suspensions

NASA Technical Reports Server (NTRS)

McDowell, Mark; Gray, Elizabeth; Rogers, Richard B.

2005-01-01

Colloidal suspensions of monodisperse spheres are used as physical models of thermodynamic phase transitions and as precursors to photonic band gap materials. However, current image analysis techniques are not able to distinguish between densely packed phases within conventional microscope images, which are mainly characterized by degrees of randomness or order with similar grayscale value properties. Current techniques for identifying the phase boundaries involve manually identifying the phase transitions, which is very tedious and time consuming. We have developed an intelligent machine vision technique that automatically identifies colloidal phase boundaries. The algorithm utilizes intelligent image processing techniques that accurately identify and track phase changes vertically or horizontally for a sequence of colloidal hard sphere suspension images. This technique is readily adaptable to any imaging application where regions of interest are distinguished from the background by differing patterns of motion over time.

Wettability control on fluid-fluid displacements in patterned microfluidics

NASA Astrophysics Data System (ADS)

Zhao, B.; MacMinn, C. W.; Juanes, R.

2015-12-01

Two-phase flow in porous media is important in many natural and industrial processes like geologic CO2 sequestration, enhanced oil recovery, and water infiltration in soil. While it is well known that the wetting properties of porous media can vary drastically depending on the type of media and the pore fluids, the effect of wettability on fluid displacement continues to challenge our microscopic and macroscopic descriptions. Here we conduct two-phase flow experiments via radial displacement of viscous silicone oil by water, in planar microfluidic devices patterned with vertical posts. These devices allow for visualization of flow through a complex but well-defined microstructure. In addition, the surface energy of the devices can be tuned over a wide range of contact angles, allowing us to access different wettability conditions. We use a fluorescent dye to measure the in-plane water saturation. We perform constant-rate injection experiments with highly unfavorable mobility contrast (viscosity of injected water is 350 times less than the displaced silicone oil) at injection rates over four orders of magnitude. We focus on three particular wetting conditions: drainage (θ=120°), weak imbibition (θ=60°), and strong imbibition (θ=7°). In drainage, we observe a transition from viscous fingering at high capillary numbers to a morphology that, in contrast with conventional knowledge, is different from capillary fingering. In weak imbibition, we observe an apparent stabilization of flow instabilities, as a result of cooperative invasion at the pore scale. In strong imbibition, we find that the flow behavior is heavily influenced by a precursor front that emanates from the main imbibition front. The nature of the precursor front depends on the capillary number. At intermediate capillary numbers, the precursor front consists primarily of corner flow that connects the surface of neighboring posts, forming ramified fingers. The progress of corner flow is overtaken by the spreading of precursor film (~1 um thick) at lower capillary numbers. The ensuing main imbibition front preferentially invades areas already coated by the precursor film, forming a more compact invasion pattern. Our work demonstrates the important, yet intricate, impact of wettability on the morphology of fluid-fluid displacement in porous media.

Non-noble electrocatalysts for alkaline fuel cells

NASA Technical Reports Server (NTRS)

Sarangapani, S.; Lessner, P.; Manoukian, M.; Giner, J.

1989-01-01

Carbons activated with macrocyclics have attracted increasing attention as alternative electrocatalysts for oxygen reduction. Initial activity of these catalysts is good, but performance declines rapidly. Pyrolyzing the macrocyclic on the carbon support leads to enhanced stability and the catalysts retain good activity. The approach described is designed to develop bulk doped catalysts with similar structures to pyrolyzed macrocyclic catalysts. The transition metal and coordinated ligands are dispersed throughout the bulk of the conductive carbon skeleton. Two approaches to realizing this concept are being pursued, both involving the doping of carbon precursors. In one approach, the precursor is a solid phase carbon-containing ion-exchange resin. The precursor is doped with a transition metal and/or nitrogen, and the resulting mixture is pyrolyzed. In the other approach, the precursor is a gas-phase hydrocarbon. This is introduced with a transition metal species and nitrogen species into a reactor and pyrolyzed. Several studies have been conducted to determine if there is a synergistic effect between the transition metal and nitrogen and the effect of different methods of introducing the metal-nitrogen (M-N) coordination on performance. One approach was to introduce the metal and nitrogen separately, for example, by sequentially doping FeCl3 and NH4OH into the resin. Catalysts were prepared from an undoped ion-exchange resin, a resin doped only with N, a resin doped only with Fe, and a resin doped with both Fe and N. Introduction of nitrogen alone has no beneficial effect on the performance of the catalysts. The introduction of the Fe alone significantly improves the performance in both the high and low current density regions. When both Fe and N are introduced, the performance at lower current densities (catalytic activity) is increased beyond that of the Fe-doped carbon, but the performance at higher current densities is similar to the carbon containing only Fe. Catalysts prepared from resins-Fe(bipy)3SO4 precursors have performance that is only slightly less then CoTMPP adsorbed and pyroloyzed on Vulcan XC-72. Their performance is much better than carbons which have had the N and Fe introduced separately.

Sensitivity analysis of seismic waveforms to upper-mantle discontinuities using the adjoint method

NASA Astrophysics Data System (ADS)

Koroni, Maria; Bozdağ, Ebru; Paulssen, Hanneke; Trampert, Jeannot

2017-09-01

Using spectral-element simulations of wave propagation, we investigated the sensitivity of seismic waveforms, recorded on transverse components, to upper-mantle discontinuities in 1-D and 3-D background models. These sensitivity kernels, or Fréchet derivatives, illustrate the spatial sensitivity to model parameters, of which those for shear wave speed and the surface topography of internal boundaries are discussed in this paper. We focus on the boundaries at 400 and 670 km depth of the mantle transition zone. SS precursors have frequently been used to infer the topography of upper-mantle discontinuities. These seismic phases are underside reflections off these boundaries and are usually analysed in the distance range of 110°-160°. This distance range is chosen to minimize the interference from other waves. We show sensitivity kernels for consecutive time windows at three characteristic epicentral distances within the 110°-160° range. The sensitivity kernels are computed with the adjoint method using synthetic data. From our simulations we can draw three main conclusions: (i) The exact Fréchet derivatives show that in all time windows, and also in those centred on the SS precursors, there is interference from other waves. This explains the difficulty reported in the literature to correct for 3-D shear wave speed perturbations, even if the 3-D structure is perfectly known. (ii) All studies attempting to map the topography of the 400 and 670 km discontinuities to date assume that the traveltimes of SS precursors can be linearly decomposed into a 3-D elastic structure and a topography part. We recently showed that such a linear decomposition is not possible for SS precursors, and the sensitivity kernels presented in this paper explain why. (iii) In agreement with previous work, we show that other parts of the seismograms have greater sensitivity to upper-mantle discontinuities than SS precursors, especially multiply bouncing S waves exploiting the S-wave triplications due to the mantle transition zone. These phases can potentially improve the inference of global topographic variations of the upper-mantle discontinuities in the context of full waveform inversion in a joint inversion for (an)elastic parameters and topography.

COMPARISON OF MERCURY CAPTURE EFFICIENCIES OF THREE DIFFERENT IN SITU GENERATED SORBENTS

EPA Science Inventory

Three different sorbent materials (Ti, Si and Ca based) were compared for their mercury capture efficiencies in an entrained flow reactor. Agglomerated particles with a high specific surface area were generated in situ by injecting gas phase sorbent precursors into a high tempera...

The Abundance of SiC2 in Carbon Star Envelopes⋆: Evidence that SiC2 is a gas-phase precursor of SiC dust

PubMed Central

Massalkhi, Sarah; Agúndez, M.; Cernicharo, J.; Velilla Prieto, L.; Goicoechea, J. R.; Quintana-Lacaci, G.; Fonfría, J. P.; Alcolea, J.; Bujarrabal, V.

2017-01-01

Context Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si–C bond detected in C-rich AGB stars are SiC2, SiC, and Si2C. To date, the ring molecule SiC2 has been observed in a handful of evolved stars, while SiC and Si2C have only been detected in the C-star envelope IRC +10216. Aims We aim to study how widespread and abundant SiC2, SiC, and Si2C are in envelopes around C-rich AGB stars and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars. Methods We carried out sensitive observations with the IRAM 30m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiC2, SiC, and Si2C in the λ 2 mm band. We performed non-LTE excitation and radiative transfer calculations based on the LVG method to model the observed lines of SiC2 and to derive SiC2 fractional abundances in the observed envelopes. Results We detect SiC2 in most of the sources, SiC in about half of them, and do not detect Si2C in any source, at the exception of IRC +10216. Most of these detections are reported for the first time in this work. We find a positive correlation between the SiC and SiC2 line emission, which suggests that both species are chemically linked, the SiC radical probably being the photodissociation product of SiC2 in the external layer of the envelope. We find a clear trend in which the denser the envelope, the less abundant SiC2 is. The observed trend is interpreted as an evidence of efficient incorporation of SiC2 onto dust grains, a process which is favored at high densities owing to the higher rate at which collisions between particles take place. Conclusions The observed behavior of a decline in the SiC2 abundance with increasing density strongly suggests that SiC2 is an important gas-phase precursor of SiC dust in envelopes around carbon stars. PMID:29628518

The Abundance of SiC2 in Carbon Star Envelopes: Evidence that SiC2 is a gas-phase precursor of SiC dust.

PubMed

Massalkhi, Sarah; Agúndez, M; Cernicharo, J; Velilla Prieto, L; Goicoechea, J R; Quintana-Lacaci, G; Fonfría, J P; Alcolea, J; Bujarrabal, V

2018-03-01

Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si-C bond detected in C-rich AGB stars are SiC 2 , SiC, and Si 2 C. To date, the ring molecule SiC 2 has been observed in a handful of evolved stars, while SiC and Si 2 C have only been detected in the C-star envelope IRC +10216. We aim to study how widespread and abundant SiC 2 , SiC, and Si 2 C are in envelopes around C-rich AGB stars and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars. We carried out sensitive observations with the IRAM 30m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiC 2 , SiC, and Si 2 C in the λ 2 mm band. We performed non-LTE excitation and radiative transfer calculations based on the LVG method to model the observed lines of SiC 2 and to derive SiC 2 fractional abundances in the observed envelopes. We detect SiC 2 in most of the sources, SiC in about half of them, and do not detect Si 2 C in any source, at the exception of IRC +10216. Most of these detections are reported for the first time in this work. We find a positive correlation between the SiC and SiC 2 line emission, which suggests that both species are chemically linked, the SiC radical probably being the photodissociation product of SiC 2 in the external layer of the envelope. We find a clear trend in which the denser the envelope, the less abundant SiC 2 is. The observed trend is interpreted as an evidence of efficient incorporation of SiC 2 onto dust grains, a process which is favored at high densities owing to the higher rate at which collisions between particles take place. The observed behavior of a decline in the SiC 2 abundance with increasing density strongly suggests that SiC 2 is an important gas-phase precursor of SiC dust in envelopes around carbon stars.

Organic/inorganic hybrid coatings for anticorrosion

NASA Astrophysics Data System (ADS)

He, Zhouying

Compared to organic coatings, organic-inorganic hybrid coatings can potentially improve the anticorrosion performance. The organic phase provides the excellent mechaincal and barrier properties while the inorganic phase acts as an adhesion promoter and corrosion inhibitor. Despite that many studies on alkoxylsilane-based hybrid coatings have been developed and studied, their weatherability and anticorrosion performance has been rarely evaluated. On the other hand, organic-inorganic hybrid coatings based on mixed sol-gel precursors have received much less attention compared to alkoxylsilane-based hybrid coatings. In the first part, polyurethane hybrid coatings with a unique hybrid crosslinked structure as an improved unicoat were successfully prepared. The effect of polyesters on physical properties of the hybrid coatings was studied. Polyurethane coatings derived from cycloaliphatic polyester show comparable properties than those derived from the commercially viable aromatic polyester. Introducing the polysiloxane part into the polyurethane coatings enhanced the crosslinking density, Tg, mechanical properties, and general coating properties. The increased adhesion between the hybrid coating and the substrate make the hybrid coating a good candidate for anticorrosion application, which is shown by electrochemical impedance spectroscopy (EIS). The degradation mechanism of the polyurethane/polysiloxane hybrid coatings under various weathering conditions was shown to be the scission of the urethane and ester groups in the organic phase along with reorganizing and rearranging of the inorganic phase. The anticorrosion performance of the cycloaliphatic hybrid was much better than that of aromatic based hybrid under outdoor weathering based on visual observation and EIS analysis. Acid undercutting is an issue for TEOS based hybrid coating. In the second part, design of experiments (DOEs) was used to statistically investigate on the effect of sol-gel precursors. The synergistic effect of the mixed sol-gel precursors was shown to enhance the overall properties and was also observed structurally by SAXS and SEM. The improved resistance to the acid undercutting was observed for mixed sol-gel precursors based hybrids. The application of hybrids provides excellent anticorrosive properties as observed in salt spray and EIS study. The formation of Al2O3 protective layer as well as M-O-Al covalent bond provided the basis for excellent corrosion protection on Al substrate. However, the generation of Fe ions as corrosion product caused the accumulation of electrolyte, which resulted in the delamination of the coating on steel substrate. In this way, the corrosion of steel substrate is much faster than that of Al substrate. The maintenance of high impedance and corresponding resistance and capacitance based on EIS results further confirmed the great anticorrosion performance of hybrids on both Al and steel substrate.

A novel HPLC-MRM strategy to discover unknown and long-term metabolites of stanozolol for expanding analytical possibilities in doping-control.

PubMed

Wang, Zhe; Zhou, Xinmiao; Liu, Xin; Dong, Ying; Zhang, Jinlan

2017-01-01

Stanozolol is one of the most commonly abused anabolic androgenic steroids (AAS) by athletes and usually detected by its parent drug and major metabolites. However, its metabolic pathway is complex, varied and individually different, it is important to characterize its overall metabolic profiles and discover new and long-term metabolites for the aims of expanding detection windows. High performance liquid chromatography coupled with triple quadrupole mass spectrometer (HPLC-MS/MS) was used to analyze the human urine after oral administration of stanozolol. Multiple reaction monitoring (MRM), one of the scan modes of triple quadrupole mass spectrometer showing extremely high sensitivity was well used to develop a strategy for metabolic profiles characterization and long-term metabolites detection based on typical precursor to product ion transitions of parent drug and its major metabolites. Utilizing the characteristic fragment ions of stanozolol and its major metabolites as the product ions, and speculating unknown precursor ions based on the possible phase I and phase II metabolic reactions in human body, the metabolite profiles of stanozolol could be comprehensively discovered, especially for those unknown and low concentration metabolites in human urine. Then these metabolites were further well structure identified by targeted high resolution MS/MS scan of quadrupole-time of flight mass spectrometry (Q-TOF). Applying this strategy, 27 phase I and 21 phase II metabolites of stanozolol were identified, in which 13 phase I and 14 phase II metabolites have not been reported previously. The 9 out of 48 metabolites could be detected over 15days post drug administration. This strategy could be employed effectively to characterize AAS metabolic profiles and discover unknown and long-term metabolites in sports drug testing. Copyright © 2016 Elsevier B.V. All rights reserved.

Electronic structure and thermoelectric performance of Zintl compound Sr{sub 3}GaSb{sub 3}: A first-principles study

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

Feng Shi, Qing; Li Yan, Yu; Xu Wang, Yuan, E-mail: wangyx@henu.edu.cn

2014-01-06

By using first-principles method and Boltzmann theory, we simulated the thermoelectric transport properties of p-type and n-type Sr{sub 3}GaSb{sub 3}. It is found that the thermoelectric figure-of merit (ZT) of n-type Sr{sub 3}GaSb{sub 3} is probably better than that of p-type, mainly due to its large band degeneracy. Moreover, a high ZT value of 1.74 at 850 K can be achieved for n-type Sr{sub 3}GaSb{sub 3} along the yy direction, corresponding to the carrier concentration 3.5 × 10{sup 20} e cm{sup −3}. We propose that the high ZT value of experimentally synthesized p-type Sr{sub 3}GaSb{sub 3} is originated from appearing of the larger numbermore » of band valley on the top of valence bands.« less

Self-assembled SnO2 micro- and nanosphere-based gas sensor thick films from an alkoxide-derived high purity aqueous colloid precursor

NASA Astrophysics Data System (ADS)

Kelp, G.; Tätte, T.; Pikker, S.; Mändar, H.; Rozhin, A. G.; Rauwel, P.; Vanetsev, A. S.; Gerst, A.; Merisalu, M.; Mäeorg, U.; Natali, M.; Persson, I.; Kessler, V. G.

2016-03-01

Tin oxide is considered to be one of the most promising semiconductor oxide materials for use as a gas sensor. However, a simple route for the controllable build-up of nanostructured, sufficiently pure and hierarchical SnO2 structures for gas sensor applications is still a challenge. In the current work, an aqueous SnO2 nanoparticulate precursor sol, which is free of organic contaminants and sorbed ions and is fully stable over time, was prepared in a highly reproducible manner from an alkoxide Sn(OR)4 just by mixing it with a large excess of pure neutral water. The precursor is formed as a separate liquid phase. The structure and purity of the precursor is revealed using XRD, SAXS, EXAFS, HRTEM imaging, FTIR, and XRF analysis. An unconventional approach for the estimation of the particle size based on the quantification of the Sn-Sn contacts in the structure was developed using EXAFS spectroscopy and verified using HRTEM. To construct sensors with a hierarchical 3D structure, we employed an unusual emulsification technique not involving any additives or surfactants, using simply the extraction of the liquid phase, water, with the help of dry butanol under ambient conditions. The originally generated crystalline but yet highly reactive nanoparticles form relatively uniform spheres through self-assembly and solidify instantly. The spheres floating in butanol were left to deposit on the surface of quartz plates bearing sputtered gold electrodes, producing ready-for-use gas sensors in the form of ca. 50 μm thick sphere-based-films. The films were dried for 24 h and calcined at 300 °C in air before use. The gas sensitivity of the structures was tested in the temperature range of 150-400 °C. The materials showed a very quickly emerging and reversible (20-30 times) increase in electrical conductivity as a response to exposure to air containing 100 ppm of H2 or CO and short (10 s) recovery times when the gas flow was stopped.Tin oxide is considered to be one of the most promising semiconductor oxide materials for use as a gas sensor. However, a simple route for the controllable build-up of nanostructured, sufficiently pure and hierarchical SnO2 structures for gas sensor applications is still a challenge. In the current work, an aqueous SnO2 nanoparticulate precursor sol, which is free of organic contaminants and sorbed ions and is fully stable over time, was prepared in a highly reproducible manner from an alkoxide Sn(OR)4 just by mixing it with a large excess of pure neutral water. The precursor is formed as a separate liquid phase. The structure and purity of the precursor is revealed using XRD, SAXS, EXAFS, HRTEM imaging, FTIR, and XRF analysis. An unconventional approach for the estimation of the particle size based on the quantification of the Sn-Sn contacts in the structure was developed using EXAFS spectroscopy and verified using HRTEM. To construct sensors with a hierarchical 3D structure, we employed an unusual emulsification technique not involving any additives or surfactants, using simply the extraction of the liquid phase, water, with the help of dry butanol under ambient conditions. The originally generated crystalline but yet highly reactive nanoparticles form relatively uniform spheres through self-assembly and solidify instantly. The spheres floating in butanol were left to deposit on the surface of quartz plates bearing sputtered gold electrodes, producing ready-for-use gas sensors in the form of ca. 50 μm thick sphere-based-films. The films were dried for 24 h and calcined at 300 °C in air before use. The gas sensitivity of the structures was tested in the temperature range of 150-400 °C. The materials showed a very quickly emerging and reversible (20-30 times) increase in electrical conductivity as a response to exposure to air containing 100 ppm of H2 or CO and short (10 s) recovery times when the gas flow was stopped. Electronic supplementary information (ESI) available: IR spectrum of additives found in the residual butanol layer formed during precursor preparation. See DOI: 10.1039/c5nr07942j

A LOW COST CATALYTIC FILTER FOR SIMULTANEOUS VOC AND PARTICULATE REMOVAL - PHASE II

EPA Science Inventory

Emissions of VOC's are subject to control by the EPA both because VOC's are regarded as ozone precursors and because many specific VOC's are hazardous air pollutants (HAP's) under the Clean Air Act Amendments. A number of industries generate offgases with both fine particul...

Experimental study of the replacement of calcite by calcium sulphates

NASA Astrophysics Data System (ADS)

Ruiz-Agudo, E.; Putnis, C. V.; Hövelmann, J.; Álvarez-Lloret, P.; Ibáñez-Velasco, A.; Putnis, A.

2015-05-01

Among the most relevant mineral replacement reactions are those involving sulphates and carbonates, which have important geological and technological implications. Here it is shown experimentally that during the interaction of calcite (CaCO3) cleavage surfaces with sulphate-bearing acidic solutions, calcite is ultimately replaced by gypsum (CaSO4 2H2O) and anhydrite (CaSO4), depending on the reaction temperature. Observations suggest that this occurs most likely via an interface-coupled dissolution-precipitation reaction, in which the substrate is replaced pseudomorphically by the product. At 120 and 200 °C gypsum and/or bassanite (CaSO4·0.5H2O) form as precursor phases for the thermodynamically stable anhydrite. Salinity promotes the formation of less hydrated precursor phases during the replacement of calcite by anhydrite. The reaction stops before equilibrium with respect to calcite is reached and during the course of the reaction most of the bulk solutions are undersaturated with respect to the precipitating phase(s). A mechanism consisting of the dissolution of small amounts of solid in a thin layer of fluid at the mineral-fluid interface and the subsequent precipitation of the product phase from this layer is in agreement with these observations. PHREEQC simulations performed in the framework of this mechanism highlight the relevance of transport and surface reaction kinetics on the volume change associated with the CaCO3-CaSO4 replacement. Under our experimental conditions, this reaction occurs with a positive volume change, which ultimately results in passivation of the unreacted substrate before calcite attains equilibrium with respect to the bulk solution.

Precursor Ion–Ion Aggregation in the Brust–Schiffrin Synthesis of Alkanethiol Nanoparticles

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

Graham, Trent R.; Renslow, Ryan; Govind, Niranjan

Tetraoctylammonium bromide is used in the Brust-Schiffrin nanoparticle synthesis to phase-transfer chloroaurate ions from the aqueous phase to the organic phase. While it is established that the quaternary ammonium complex self-associates in the organic phase, the actual self-assembled structure is debated. We have confirmed the presence of ion-ion aggregates through quantitative 1H Nuclear Magnetic Resonance spectroscopy (NMR), pulsed field gradient, diffusion-ordered NMR (DOSY-NMR) and density functional theory (DFT) based NMR shift calculations. Tetraoctylammonium complexes (TOA-X, where X = Br, Cl, AuCl4-xBrx, AuBr4/Br and AuCl4-xBrx/Br) were investigated to measure the extraction of water into the organic phase. 1H NMR and DFTmore » based NMR shielding calculations indicated that deshielding of water is due to hydration of the anion and not the formation of the aqueous core of a reverse micelle. DOSYNMR results were consistent with the formation of small aggregates at typical Brust-Schiffrin synthesis concentrations. The extent of aggregation correlated with the size and electronegativity of the anion and was analyzed with a modified, isodesmic, indefinite aggregation model. The substitution of bromoauric acid for chlororoauric acid at conditions emulating the Brust-Schiffrin synthesis increased the aggregation of the quaternary ammonium complex. The increase in aggregation corresponded with an increase in the size of the produced nanoparticles from 4.3 to 4.6 nm. Understanding the selfassembly and supramolecular structure of precursors in the Brust-Schiffrin synthesis will enable further refinement of models that predict the growth of noble metal nanoparticles.« less

Preparation of plutonium-bearing ceramics via mechanically activated precursor

NASA Astrophysics Data System (ADS)

Chizhevskaya, S. V.; Stefanovsky, S. V.

2000-07-01

The problem of excess weapons plutonium disposition is suggested to be solved by means of its incorporation in stable ceramics with high chemical durability and radiation resistivity. The most promising host phases for plutonium as well as uranium and neutron poisons (gadolinium, hafnium) are zirconolite, pyrochlore, zircon, zirconia [1,2], and murataite [3]. Their production requires high temperatures and a fine-grained homogeneous precursor to reach final waste form with high quality and low leachability. Currently various routes to homogeneous products preparation such as sol-gel technology, wet-milling, and grinding in a ball or planetary mill are used. The best result demonstrates sol-gel technology but this route is very complicated. An alternative technology for preparation of ceramic precursors is the treatment of the oxide batch with high mechanical energy [4]. Such a treatment produces combination of mechanical (fine milling with formation of various defects, homogenization) and chemical (split bonds with formation of active centers—free radicals, ion-radicals, etc.) effects resulting in higher reactivity of the activated batch.

Combinatorial Optimization of Heterogeneous Catalysts Used in the Growth of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Cassell, Alan M.; Verma, Sunita; Delzeit, Lance; Meyyappan, M.; Han, Jie

2000-01-01

Libraries of liquid-phase catalyst precursor solutions were printed onto iridium-coated silicon substrates and evaluated for their effectiveness in catalyzing the growth of multi-walled carbon nanotubes (MWNTs) by chemical vapor deposition (CVD). The catalyst precursor solutions were composed of inorganic salts and a removable tri-block copolymer (EO)20(PO)70(EO)20 (EO = ethylene oxide, PO = propylene oxide) structure-directing agent (SDA), dissolved in ethanol/methanol mixtures. Sample libraries were quickly assayed using scanning electron microscopy after CVD growth to identify active catalysts and CVD conditions. Composition libraries and focus libraries were then constructed around the active spots identified in the discovery libraries to understand how catalyst precursor composition affects the yield, density, and quality of the nanotubes. Successful implementation of combinatorial optimization methods in the development of highly active, carbon nanotube catalysts is demonstrated, as well as the identification of catalyst formulations that lead to varying densities and shapes of aligned nanotube towers.

Synthesis and Study of Gel Calcined Cd-Sn Oxide Nanocomposites

NASA Astrophysics Data System (ADS)

De, Arijit; Kundu, Susmita

2016-07-01

Cd-Sn oxide nanocomposites were synthesized by sol-gel method from precursor sol containing Cd:Sn = 2:1 and 1:1 mol ratio. Instead of coprecipitation, a simple novel gel calcination route was followed. Cd (NO3)2. 4H2O and SnCl4. 5H2O were used as starting materials. Gel was calcined at 1050 °C for 2 h to obtain nanocomposites. XRD analysis reveals the presence of orthorhombic, cubic Cd2SnO4 along with orthorhombic, hexagonal CdSnO3 phases in both the composites. SEM and TEM studies indicate the development of nanocomposites of different shapes suggesting different degrees of polymerization in precursor sol of different composition. UV-Vis absorption spectra show a blue shift for both the composites compared to bulk values. Decrease of polarization with frequency, dipole contribution to the polarization, and more sensitivity to ethanol vapor were observed for the nanocomposite derived from precursor sol containing Cd:Sn = 2:1 mol ratio.

A Real-Time Earthquake Precursor Detection Technique Using TEC from a GPS Network

NASA Astrophysics Data System (ADS)

Alp Akyol, Ali; Arikan, Feza; Arikan, Orhan

2016-07-01

Anomalies have been observed in the ionospheric electron density distribution prior to strong earthquakes. However, most of the reported results are obtained by earthquake analysis. Therefore, their implementation in practice is highly problematic. Recently, a novel earthquake precursor detection technique based on spatio-temporal analysis of Total Electron Content (TEC) data obtained from Turkish National Permanent GPS Network (TNPGN) is developed by IONOLAB group (www.ionolab.org). In the present study, the developed detection technique is implemented in a causal setup over the available data set in test phase that enables the real time implementation. The performance of the developed earthquake prediction technique is evaluated by using 10 fold cross validation over the data obtained in 2011. Among the 23 earthquakes that have magnitudes higher than 5, the developed technique can detect precursors of 14 earthquakes while producing 8 false alarms. This study is supported by TUBITAK 115E915 and Joint TUBITAK 114E092 and AS CR 14/001 projects.

Multi-Step Crystallization of Barium Carbonate: Rapid Interconversion of Amorphous and Crystalline Precursors.

PubMed

Whittaker, Michael L; Smeets, Paul J M; Asayesh-Ardakani, Hasti; Shahbazian-Yassar, Reza; Joester, Derk

2017-12-11

The direct observation of amorphous barium carbonate (ABC), which transforms into a previously unknown barium carbonate hydrate (herewith named gortatowskite) within a few hundred milliseconds of formation, is described. In situ X-ray scattering, cryo-, and low-dose electron microscopy were used to capture the transformation of nanoparticulate ABC into gortatowskite crystals, highly anisotropic sheets that are up to 1 μm in width, yet only about 10 nm in thickness. Recrystallization of gortatowskite to witherite starts within 30 seconds. We describe a bulk synthesis and report a first assessment of the composition, vibrational spectra, and structure of gortatowskite. Our findings indicate that transient amorphous and crystalline precursors can play a role in aqueous precipitation pathways that may often be overlooked owing to their extremely short lifetimes and small dimensions. However, such transient precursors may be integral to the formation of more stable phases. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Single-Source Molecular Precursor for Synthesis of CdS Nanoparticles and Nanoflowers

NASA Astrophysics Data System (ADS)

Salavati-Niasari, Masoud; Sobhani, Azam

2012-04-01

CdS Semiconductor nanostructures were synthesized by using two different methods. Using triphenylphosphine (C18H15P) and oleylamine (C18H37N) as surfactant, CdS semiconductor nanocrystals with a size ranging from 30 to 90 nm can be synthesized by thermal decomposition of precursor [bis(thiosemicarbazide)cadmium(II)]. CdS nanoflowers were synthesized via hydrothermal decomposition of [bis(thiosemicarbazide) cadmium(II)] without any surfactant. X-ray diffraction (XRD) patterns confirm that the resulting samples were a pure hexagonal phase of CdS. The optical property test indicates that the absorption peak of the samples shifts towards short wavelength, and the blue shift phenomenon might be ascribed to the quantum effect.

Preparation and electrochemical properties of NiO-Co3O4 composite as electrode materials for supercapacitors

NASA Astrophysics Data System (ADS)

Wang, X. W.; Zheng, D. L.; Yang, P. Z.; Wang, X. E.; Zhu, Q. Q.; Ma, P. F.; Sun, L. Y.

2017-01-01

The precursor of NiO-Co3O4 composites was synthesized via a simple hydrothermal process. After that, the precursor was calcined at 300 °C for 3 h to obtain the composite powders. The powders calcined at 300 °C showed amorphous, and the powders calcined at 400 °C and 500 °C for comparison showed the composite phase of NiO and Co3O4. The composite products showed a microstructure of micro-spheres. For the samples calcined at 300 °C for 3 h, the specific capacitance reached 801 F g-1 at a current density of 1 A g-1.

[Disorder of porphyrin metabolism in thallium intoxication (author's transl)].

PubMed

Graben, N; Doss, M; Klöppel, H A

1978-08-04

A 19-year old male ingested in suicidal attempt 750 mg of thallium. He developed the characteristic symptoms of thallium intoxication. During the acute phase the urinary excretion of porphyrins and porphyrin precursors was largely increased. The percentage distribution of the individual metabolites of heme synthesis revealed a preponderance of kopro- and uroporphyrin. This constellation (kopro- greater than uro- greater than tricarboxylic porphyrin) differs appreciably from that one in lead intoxication. The observation of increased urinary excretion of porphyrins and their precursors in a possibly particular spectrum in thallium intoxication is of special interest for differential-diagnostic reasoning. In each case of a toxic disorder of porphyrin metabolism thallium intoxication ought to be considered a possible cause.

Complex impedance analyses and magnetoelectric effect in ferrite ferroelectric composite ceramics

NASA Astrophysics Data System (ADS)

Patankar, K. K.; Kanade, S. A.; Padalkar, D. S.; Chougule, B. K.

2007-02-01

Magnetoelectric (ME) composites yBa0.8Pb0.2TiO3 (1-y)CuFe2O4 are prepared by ceramic method. The component phases are prepared from two different routes, viz. CuFe2O4 (ferrite phase) is prepared by oxalate precursor route and Ba0.8Pb0.2TiO3 (ferroelectric phase) by solid-state reaction route. No intermediate phases are observed in the composites containing these ferrite and ferroelectric phases. ME conversion factor (measure of ME effect) is found to be enhanced compared to those reported in the composites, in which the component phases were prepared by only one route, i.e. solid-state reaction route. The results on ME conversion are well accounted by measuring the complex impedance and analyzing their Nyquist plots.

Structural and Na-ion conduction characteristics of Na 3PS xSe 4–x

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

Bo, Shou -Hang; Wang, Yan; Ceder, Gerbrand

The recent discovery of the isostructrual cubic Na 3PS 4 and Na 3PSe 4 as fast Na-ion conductors provided a general structural framework for the exploration of new sodium superionic conductors. In this work, we systematically investigated the structures and ionic conduction characteristics of a series of compounds with the general chemical formula of Na 3PS xSe 4–x. Synthesis of Na 3PS 4 under different conditions (e.g., temperature, reaction vessel, mass of the precursors) reveals the reactivity of the precursors with the reaction tubes, producing different polymorphs. X-ray diffraction studies on the solid solution phases Na 3PS xSe 4–x identifiedmore » a tetragonal-to-cubic phase transition with increasing Se concentration. This observation is consistent with the computed stability of the tetragonal and cubic polymorphs, where the energy difference between the two polymorphs becomes very close to zero in Se-rich compositions. Furthermore, ab initio molecular dynamic simulations suggest that the fast Na-ion conduction in Na 3PS xSe 4–x may not be causally related with the symmetry or the composition of these phases. The formation of defects, instead, enables fast Na-ion conduction in this class of materials.« less

Structural and Na-ion conduction characteristics of Na 3 PS x Se 4-x

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

Bo, Shou-Hang; Wang, Yan; Ceder, Gerbrand

The recent discovery of the isostructrual cubic Na 3PS 4 and Na 3PSe 4 as fast Na-ion conductors provided a general structural framework for the exploration of new sodium superionic conductors. In this work, we systematically investigated the structures and ionic conduction characteristics of a series of compounds with the general chemical formula of Na 3PS xSe 4-x. Synthesis of Na 3PS 4 under different conditions (e.g., temperature, reaction vessel, mass of the precursors) reveals the reactivity of the precursors with the reaction tubes, producing different polymorphs. X-ray diffraction studies on the solid solution phases Na 3PS xSe 4-x more » identified a tetragonal-to-cubic phase transition with increasing Se concentration. This observation is consistent with the computed stability of the tetragonal and cubic polymorphs, where the energy difference between the two polymorphs becomes very close to zero in Se-rich compositions. Furthermore, ab initio molecular dynamic simulations suggest that the fast Na-ion conduction in Na 3PS xSe 4-x may not be causally related with the symmetry or the composition of these phases. The formation of defects, instead, enables fast Na-ion conduction in this class of materials.« less

Similarities and differences of serotonin and its precursors in their interactions with model membranes studied by molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Wood, Irene; Martini, M. Florencia; Pickholz, Mónica

2013-08-01

In this work, we report a molecular dynamics (MD) simulations study of relevant biological molecules as serotonin (neutral and protonated) and its precursors, tryptophan and 5-hydroxy-tryptophan, in a fully hydrated bilayer of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyl-choline (POPC). The simulations were carried out at the fluid lamellar phase of POPC at constant pressure and temperature conditions. Two guest molecules of each type were initially placed at the water phase. We have analyzed, the main localization, preferential orientation and specific interactions of the guest molecules within the bilayer. During the simulation run, the four molecules were preferentially found at the water-lipid interphase. We found that the interactions that stabilized the systems are essentially hydrogen bonds, salt bridges and cation-π. None of the guest molecules have access to the hydrophobic region of the bilayer. Besides, zwitterionic molecules have access to the water phase, while protonated serotonin is anchored in the interphase. Even taking into account that these simulations were done using a model membrane, our results suggest that the studied molecules could not cross the blood brain barrier by diffusion. These results are in good agreement with works that show that serotonin and Trp do not cross the BBB by simple diffusion.

Theory of nonlinear, distortive phenomena in solids: Martensitic, crack, and multiscale structures-phenomenology and physics. Progress summary, 1991--1994

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

Sethna, J.P.; Krumhansl, J.A.

1994-08-01

We have identified tweed precursors to martensitic phase transformations as a spin glass phase due to composition variations, and used simulations and exact replica theory predictions to predict diffraction peaks and model phase diagrams, and provide real space data for comparison to transmission electron micrograph images. We have used symmetry principles to derive the crack growth laws for mixed-mode brittle fracture, explaining the results for two-dimensional fracture and deriving the growth laws in three dimensions. We have used recent advances in dynamical critical phenomena to study hysteresis in disordered systems, explaining the return-point-memory effect, predicting distributions for Barkhausen noise, andmore » elucidating the transition from athermal to burst behavior in martensites. From a nonlinear lattice-dynamical model of a first-order transition using simulations, finite-size scaling, and transfer matrix methods, it is shown that heterophase transformation precursors cannot occur in a pure homogeneous system, thus emphasizing the role of disorder in real materials. Full integration of nonlinear Landau-Ginzburg continuum theory with experimental neutron-scattering data and first-principles calculations has been carried out to compute semi-quantitative values of the energy and thickness of twin boundaries in InTl and FePd martensites.« less

New Approach for Gas Phase Synthesis and Growth Mechanism of MoS2 Fullerene-like Nanoparticles

NASA Astrophysics Data System (ADS)

Zak, Alla; Feldman, Yishay; Alperovich, Vladimir; Rosentsveig, Rita; Tenne, Reshef

2002-10-01

Inorganic fullerene-like (hollow onion-like) nanoparticles (IF) and nanotubes are of significant interest over the past few years due to their unusual crystallographic morphology and their interesting physical properties. The synthesis of inorganic fullerene-like spherical MoS2 nanoparticles (IF-MoS2) of 5-300nm in diameter was studied in the present work. This process is based on the previous formation of suboxide (MoO3-x) 5-300nm nanoparticles and their subsequent sulfidization. During the sulfidization process the overall geometrical parameters of the suboxide nanoparticles are preserved. The oxide nanoparticles were obtained in-situ by the condensation of the evaporated MoO3 powder precursor. The condensation was provoked not by cooling (conventional method for nano-size particle formation), but by a chemical reaction (partial reduction of the MoO3 vapor by hydrogen). In this case the vapor pressure of the product (MoO2) was much lower than that of the precursor (MoO3). Based on the comprehensive understanding of the IF-MoS2 growth mechanism from MoO3 powder, a gas phase reactor, which allowed reproducible preparation of a pure IF-MoS2 phase (up to 100mg/batch) with controllable sizes, is demonstrated. Further scale-up of this production is underway.

Structural and Na-ion conduction characteristics of Na 3PS xSe 4–x

DOE PAGES

Bo, Shou -Hang; Wang, Yan; Ceder, Gerbrand

2016-05-19

The recent discovery of the isostructrual cubic Na 3PS 4 and Na 3PSe 4 as fast Na-ion conductors provided a general structural framework for the exploration of new sodium superionic conductors. In this work, we systematically investigated the structures and ionic conduction characteristics of a series of compounds with the general chemical formula of Na 3PS xSe 4–x. Synthesis of Na 3PS 4 under different conditions (e.g., temperature, reaction vessel, mass of the precursors) reveals the reactivity of the precursors with the reaction tubes, producing different polymorphs. X-ray diffraction studies on the solid solution phases Na 3PS xSe 4–x identifiedmore » a tetragonal-to-cubic phase transition with increasing Se concentration. This observation is consistent with the computed stability of the tetragonal and cubic polymorphs, where the energy difference between the two polymorphs becomes very close to zero in Se-rich compositions. Furthermore, ab initio molecular dynamic simulations suggest that the fast Na-ion conduction in Na 3PS xSe 4–x may not be causally related with the symmetry or the composition of these phases. The formation of defects, instead, enables fast Na-ion conduction in this class of materials.« less

Preparation and effect of thermal treatment on Gd2O3:SiO2 nanocomposite

NASA Astrophysics Data System (ADS)

Ahlawat, Rachna

2015-04-01

Rare earth oxides have been extensively investigated due to their fascinating properties such as enhanced luminescence efficiency, lower lasing threshold, high-performance luminescent devices, drug-carrying vehicle, contrast agent in magnetic resonance imaging (MRI), up-conversion materials, catalysts and time-resolved fluorescence (TRF) labels for biological detection etc. Nanocomposites of silica gadolinium oxide have been successfully synthesized by sol-gel process using hydrochloric acid as a catalyst. Gd(NO3)3ṡ6H2O and tetraethyl orthosilicate (TEOS) were used as precursors to obtain powdered form of gadolinum oxide:silica (Gd2O3:SiO2) composite. The powdered samples having 2.8 mol% Gd2O3 were annealed at 500°C and 900°C temperature for 6 h and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and transmission electron microscope (TEM). The effect of annealing on the phase evolution of the composite system has been discussed in detail. It was found that the sintering of gadolinium precursor plays a pivotal role to obtain crystalline phase of Gd2O3. Cubic phase of gadolinium oxide was developed for annealed sample at 900°C (6 h) with an average grain size 12 nm.

Cd(1-x)Zn(x)O [0.05 ≤x≤ 0.26] synthesized by vapor-diffusion induced hydrolysis and co-nucleation from aqueous metal salt solutions.

PubMed

Schwenzer, Birgit; Neilson, James R; Jeffries, Stacie M; Morse, Daniel E

2011-02-14

Nanoparticulate Cd(1-x)Zn(x)O (x = 0, 0.05-0.26, 1) is synthesized in a simple two-step synthesis approach. Vapor-diffusion induced catalytic hydrolysis of two molecular precursors at low temperature induces co-nucleation and polycondensation to produce bimetallic layered hydroxide salts (M = Cd, Zn) as precursor materials which are subsequently converted to Cd(1-x)Zn(x)O at 400 °C. Unlike ternary materials prepared by standard co-precipitation procedures, all products presented here containing < 30 mol% Zn(2+) ions are homogeneous in elemental composition on the micrometre scale. This measured compositional homogeneity within the samples, as determined by energy dispersive spectroscopy and inductively coupled plasma spectroscopy, is a testimony to the kinetic control achieved by employing slow hydrolysis conditions. In agreement with this observation, the optical properties of the materials obey Vegard's Law for a homogeneous solid solution of Cd(1-x)Zn(x)O, where x corresponds to the values determined by inductively coupled plasma analysis, even though powder X-ray diffraction shows phase separation into a cubic mixed metal oxide phase and a hexagonal ZnO phase at all doping levels.

Micro-structural evolution and biomineralization behavior of carbon nanofiber/bioactive glass composites induced by precursor aging time.

PubMed

Jia, Xiaolong; Tang, Tianhong; Cheng, Dan; Zhang, Cuihua; Zhang, Ran; Cai, Qing; Yang, Xiaoping

2015-12-01

Bioactive glass (BG)-containing carbon nanofibers (CNFs) are promising orthopaedic biomaterials. Herein, CNF composites were produced from electrospinning of polyacrylonitrile (PAN)/BG sol-gel precursor solution, followed by carbonization. Choosing 58S-type BG (mol%: 58.0% SiO2-26.3% CaO-15.7% P2O5) as the model, micro-structural evolution of CNF/BG composites was systematically evaluated in relating to aging times of BG precursor solution. With aging time prolonging, BG precursors underwent morphological changes from small sol clusters with loosely and randomly branched structure to highly crosslinked Si-network structure, showing continuous increase in solution viscosity. BG precursor solution with low viscosity could mix well with PAN solution, resulting in CNF composite with homogeneously distributed BG component. Whereas, BG precursor gel with densely crosslinked Si-network structure led to uneven distribution of BG component along final CNFs due to its significant phase separation from PAN component. Meanwhile, BG nanoparticles in CNFs demonstrated micro-structural evolution that they transited from weak to strong crystal state along with longer aging time. Biomineralization in simulated body fluid and in vitro osteoblasts proliferation were then applied to determine the bioactivity of CNF/BG composites. CNF/BG composites prepared from shorter aging time could induce both faster apatite deposition and cell proliferation rate. It was suggested weakly crystallized BG nanoparticles along CNFs dissolved fast and was able to provide numerous nucleation sites for apatite deposition, which also favored the proliferation of osteoblasts cells. Aging time could thus be a useful tool to regulate the biological features of CNF/BG composites. Copyright © 2015 Elsevier B.V. All rights reserved.

Biosynthesis of sesquiterpenes in grape berry exocarp of Vitis vinifera L.: evidence for a transport of farnesyl diphosphate precursors from plastids to the cytosol

PubMed Central

May, Bianca; Lange, B. Markus; Wüst, Matthias

2013-01-01

The participation of the mevalonic acid (MVA) and 1-deoxy-D-xylulose 5-phosphate/2-C-methyl-D-erythritol-4-phosphate (DOXP/MEP) pathways in sesquiterpene biosynthesis of grape berries was investigated. There is an increasing interest in this class of terpenoids, since the oxygenated sesquiterpene rotundone was identified as the peppery aroma impact compound in Australian Shiraz wines. To investigate precursor supply pathway utilization, in vivo feeding experiments were performed with the deuterium labeled, pathway specific, precursors [5,5-2H2]-1-deoxy-D-xylulose and [5,5-2H2]-mevalonic acid lactone. Head Space-Solid Phase Micro Extraction-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS) analysis of the generated volatile metabolites demonstrated that de novo sesquiterpene biosynthesis is mainly located in the grape berry exocarp (skin), with no detectable activity in the mesocarp (flesh) of the Lemberger variety. Interestingly, precursors from both the (primarily) cytosolic MVA and plastidial DOXP/MEP pathways were incorporated into grape sesquiterpenes in the varieties Lemberger, Gewürztraminer and Syrah. Our labeling data provide evidence for a homogenous, cytosolic pool of precursors for sesquiterpene biosynthesis, indicating that a transport of precursors occurs mostly from plastids to the cytosol. The labeling patterns of the sesquiterpene germacrene D were in agreement with a cyclization mechanism analogous to that of a previously cloned enantioselective (R)-germacrene D synthase from Solidago canadensis. This observation was subsequently confirmed by enantioselective GC-MS analysis demonstrating the exclusive presence of (R)-germacrene D, and not the (S)-enantiomer, in grape berries. PMID:23954075

Mixed-ligand approach to design of heterometallic single-source precursors with discrete molecular structure.

PubMed

Lieberman, Craig M; Navulla, Anantharamulu; Zhang, Haitao; Filatov, Alexander S; Dikarev, Evgeny V

2014-05-05

Heterometallic single-source precursors for the Pb/Fe = 1:1 oxide materials, PbFe(β-dik)4 (β-dik = hexafluoroacetylacetonate (hfac, 1), acetylacetonate (acac, 2), and trifluoroacetylacetonate (tfac, 4)), have been isolated by three different solid-state synthetic methods. The crystal structures of heterometallic diketonates 1, 2, and 4 were found to contain polymeric chains built on alternating [Fe(β-dik)2] and [Pb(β-dik)2] units that are held together by bridging M-O interactions. Heterometallic precursors are highly volatile, but soluble only in coordinating solvents, in which they dissociate into solvated homometallic fragments. In order to design the heterometallic precursor with a proper metal/metal ratio and with a discrete molecular structure, we used a combination of two different diketonate ligands. Heteroleptic complex Pb2Fe2(hfac)6(acac)2 (5) has been obtained by optimized stoichiometric reaction of an addition of homo-Fe(acac)2 to heterometallic Pb2Fe(hfac)6 (3) diketonate that can be run in solution on a high scale. The combination of two ligands with electron-withdrawing and electron-donating groups allows changing the connectivity pattern within the heterometallic assembly and yields the precursor with a discrete tetranuclear structure. In accord with its molecular structure, heteroleptic complex 5 is soluble even in noncoordinating solvents and was found to retain its heterometallic structure in solution. Thermal decomposition of heterometallic precursors in air at 750 °C resulted in the target Pb2Fe2O5 oxide, a prospective multiferroic material. Prolonging the annealing time or increasing the decomposition temperature leads to another phase-pure lead-iron oxide PbFe12O19 that is a representative of the important family of magnetic hexaferrites.

Biosynthesis of sesquiterpenes in grape berry exocarp of Vitis vinifera L.: evidence for a transport of farnesyl diphosphate precursors from plastids to the cytosol.

PubMed

May, Bianca; Lange, B Markus; Wüst, Matthias

2013-11-01

The participation of the mevalonic acid (MVA) and 1-deoxy-d-xylulose 5-phosphate/2-C-methyl-d-erythritol-4-phosphate (DOXP/MEP) pathways in sesquiterpene biosynthesis of grape berries was investigated. There is an increasing interest in this class of terpenoids, since the oxygenated sesquiterpene rotundone was identified as the peppery aroma impact compound in Australian Shiraz wines. To investigate precursor supply pathway utilization, in vivo feeding experiments were performed with the deuterium labeled, pathway specific, precursors [5,5-(2)H2]-1-deoxy-d-xylulose and [5,5-(2)H2]-mevalonic acid lactone. Head Space-Solid Phase Micro Extraction-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS) analysis of the generated volatile metabolites demonstrated that de novo sesquiterpene biosynthesis is mainly located in the grape berry exocarp (skin), with no detectable activity in the mesocarp (flesh) of the Lemberger variety. Interestingly, precursors from both the (primarily) cytosolic MVA and plastidial DOXP/MEP pathways were incorporated into grape sesquiterpenes in the varieties Lemberger, Gewürztraminer and Syrah. Our labeling data provide evidence for a homogenous, cytosolic pool of precursors for sesquiterpene biosynthesis, indicating that a transport of precursors occurs mostly from plastids to the cytosol. The labeling patterns of the sesquiterpene germacrene D were in agreement with a cyclization mechanism analogous to that of a previously cloned enantioselective (R)-germacrene D synthase from Solidago canadensis. This observation was subsequently confirmed by enantioselective GC-MS analysis demonstrating the exclusive presence of (R)-germacrene D, and not the (S)-enantiomer, in grape berries. Copyright © 2013 Elsevier Ltd. All rights reserved.

Supplementation with tocotrienol-rich fraction alters the plasma levels of Apolipoprotein A-I precursor, Apolipoprotein E precursor, and C-reactive protein precursor from young and old individuals.

PubMed

Heng, Eng Chee; Karsani, Saiful Anuar; Abdul Rahman, Mariati; Abdul Hamid, Noor Aini; Hamid, Zalina; Wan Ngah, Wan Zurinah

2013-10-01

Tocotrienol possess beneficial effects not exhibited by tocopherol. In vitro studies using animal models have suggested that these effects are caused via modulation of gene and protein expression. However, human supplementation studies using tocotrienol-rich isomers are limited. This study aims to identify plasma proteins that changed in expression following tocotrienol-rich fraction (TRF) supplementation within two different age groups. Subjects were divided into two age groups-32 ± 2 (young) and 52 ± 2 (old) years old. Four subjects from each group were assigned with TRF (78% tocotrienol and 22% tocopherol, 150 mg/day) or placebo capsules for 6 months. Fasting plasma were obtained at 0, 3, and 6 months. Plasma tocopherol and tocotrienol levels were determined. Plasma proteome was resolved by 2DE, and differentially expressed proteins identified by MS. The expressions of three proteins were validated by Western blotting. Six months of TRF supplementation significantly increased plasma levels of tocopherols and tocotrienols. Proteins identified as being differentially expressed were related to cholesterol homeostasis, acute-phase response, protease inhibitor, and immune response. The expressions of Apolipoprotein A-I precursor, Apolipoprotein E precursor, and C-reactive protein precursor were validated. The old groups showed more proteins changing in expression. TRF appears to not only affect plasma levels of tocopherols and tocotrienols, but also the levels of plasma proteins. The identity of these proteins may provide insights into how TRF exerts its beneficial effects. They may also be potentially developed into biomarkers for the study of the effects and effectiveness of TRF supplementation.

Essential elucidation for preparation of supported nickel phosphide upon nickel phosphate precursor

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

Liu, Xuguang, E-mail: liuxuguang@qust.edu.cn; Xu, Lei; Zhang, Baoquan

2014-04-01

Preparation of supported nickel phosphide (Ni{sub 2}P) depends on nickel phosphate precursor, generally related to its chemical composition and supports. Study of this dependence is essential and meaningful for the preparation of supported Ni{sub 2}P with excellent catalytic activity. The chemical nature of nickel phosphate precursor is revealed by Raman and UV–vis spectra. It is found that initial P/Ni mole ratio ≥0.8 prohibits the Ni-O-Ni bridge bonding (i.e., nickel oxide). This chemical bonding will not result in Ni{sub 2}P structure, verified by XRD characterization results. The alumina (namely, γ-Al{sub 2}O{sub 3}, θ-Al{sub 2}O{sub 3}, or α-Al{sub 2}O{sub 3}) with distinctmore » physiochemical properties also results in diverse chemical nature of nickel phosphate, and then different nickel phosphides. The influence of alumina support on producing Ni{sub 2}P was explained by the theory of surface energy heterogeneity, calculated by the NLDFT method based on N{sub 2}-sorption isotherm. The uniform surface energy of α-Al{sub 2}O{sub 3} results only in the nickel phosphosate precursor and thus the Ni{sub 2}P phase. - Graphical abstract: Surface energy heterogeneity in alumina (namely α-Al{sub 2}O{sub 3}, θ-Al{sub 2}O{sub 3}, and γ-Al{sub 2}O{sub 3}) supported multi-oxidic precursors with different reducibilities and thus diverse nickel phosphides (i.e., Ni{sub 3}P, Ni{sub 12}P{sub 5}, Ni{sub 2}P). - Highlights: • Preparing pure Ni{sub 2}P. • Elucidating nickel phosphate precursor. • Associating with surface energy.« less

Comparative Study of Rhodamine B degradation by Tio2 nanoparticles synthesized from titanium sec butoxide and its chloroacetato derivatves.

PubMed

Ambreen, S; Pandey, N D; Pandey, A

2017-07-31

TiO2 has been well recognized as a proficient photocatalyst. TiO2 nanoparticles have been synthesized from titanium sec butoxide (1) and its monochloroacetate derived compounds. The modifications of Ti(OsBu)4 with monochloroacetic acid in 1:1 and 1:2 molar ratios afforded Ti(OsBu)3(OOCCH2Cl) (2) and Ti(OsBu)2(OOCCH2Cl)2 (3), respectively. The use of monochloroacetic acid as a modifier allows the control of both the degree of condensation and oligomerization of the precursor. The cross linking of the gel and connectivity of the molecular building blocks are lowered in these heteroleptic alkoxides which results in the formation of gels instead of crystalline precipitate. This modification of the precursors leads to the generation of new building blocks which significantly affect the properties of the resulting TiO2. TiO2 powders were prepared via sol-gel method from these precursors and calcined at 400°C and 600°C for 4 h. Phase and morphology of the prepared metal oxide nanoparticles were studied. XRD patterns showed TiO2 in anatase phase. After coating with the surfactant trioctyl phosphinoxide (TOPO), TiO2 particles were dispersed in chloroform to study the particle size and distribution. The optical properties were studied by UV-VIS drs. The photocatalytic activity was studied over the degradation of Rhodamine B under UV radiation.