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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Phase evolution during reactive flash sintering of Li 6.25 Al 0.25 La 3 Zr 2 O 12 starting from a chemically prepared powder

Here, reactive flash sintering (RFS) of a chemically prepared multiphase precursor powder was performed to fabricate Li 6.25 Al 0.25 La 3 Zr 2 O 12 (Al-LLZO) ceramics. This approach allowed for obtaining single-phase dense samples in a remarkably short processing time of 30 s, at a furnace temperature of 600 °C, with an electric field of 50 V cm -1 and a current limit of 150 mA mm -2 . The ceramics display high bulk conductivity of 0.18 mS cm -1 at room temperature. Furthermore, phase evolution is studied by in-situ X-ray diffraction during: i) conventional heating and ii) RFS under current rate mode. As expected, the intermediate phases progressively dissolved into the Al-LLZO matrix by conventional heating. On the other hand, RFS promoted the growth of the intermediate La 2 Zr 2 O 7 , an effect that was overcome by the thermally driven formation of Al-LLZO at higher temperatures. The observed different reaction pathway suggests that RFS can be used for stabilizing phases that are not thermodynamically favored upon conventional heating.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tuning the hydrogenation of CO 2 to CH 4 over mechano-chemically prepared palladium supported on ceria

CO 2 methanation reactivity, reaction mechanism, and surface structure were investigated on a mechanochemically prepared Pd/CeO 2 catalyst (PdAcCeO 2 -M), where an oxidative pretreatment (-o) increased methane yield by a factor of two compared to a reductive pretreatment (-h). Methanation rates were maintained for over 48 h and further increased upon oxidative regeneration treatments. The surface species of both PdAcCeO 2 -M-o and PdAcCeO 2 -M-h were explored via in situ CO 2 and CO hydrogenation DRIFTS, where CO hydrogenation effectively models the dissociative CO 2 mechanism (CO 2 → CO → CH 4 ). PdAcCeO 2 -M-o yielded distinct Pd-CO adsorption and the absence of monodentate carbonate at ~ 1400 cm -1 , while AP-XPS showed that PdAcCeO 2 -M-o yielded a unique Pd δ+ contribution at 335.9 eV. By gaining insights from various in situ spectroscopic techniques, and by breaking the CO 2 hydrogenation mechanism into piecewise steps, a deeper understanding of the direct CO 2 reduction towards methane and CO over mechanochemically prepared Pd/CeO 2 catalysts was obtained.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Chemical Preparation, Crystal Structure Reinvestigation and Vibrational Study of CoNa 3 P 3 O 10 ·12H 2 O and X-ray Characterization of the New Anhydrous Triphosphate CoNa 3 P 3 O 10

The triphosphate dodecahydrate of cobalt and sodium CoNa 3 P 3 O 10 ·12H 2 O was prepared by the ion exchange resin process. Its structure was studied by X-ray diffraction and determined in the monoclinic space group P12 1 /c1 with the unit-cell parameters a = 14.6650(5) Å, b=9.1916(3) Å, c = 15.0239(5) Å,β =90.2210(10)°, Z = 4 and V = 2025.13(12) Å 3 . The thermal dehydration of this compound was performed, leading to an anhydrous new form, CoNa 3 P 3 O 10 , which was characterized by X-ray diffraction. The obtained CoNa 3 P 3 O 10 crystallized in monoclinic space group P21/n with the unit-cell parameters a=15,3774 Å, b=7,6988 A°, c=14,2832A°, β=92,9115°. The characteristic IR wavenumbers of the P 3 O 10 5- ions observed in the vibrational spectra were calculated using isotopic substitutions, which confirms the existence of these groups in the studied compound. A comparison between the IR and Raman wavenumbers of CoNa 3 P 3 O 10 ·12H 2 O, CoNa 3 P 3 O 10 and Na 5 P 3 O 10 ·12H 2 was performed. A kinetic study was also made for CoNa 3 P 3 O 10 ·12H 2 O.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Portable Sample Preparation For Chemical and Biological Analysis

Preparing samples for chemical or biological analysis is often time consuming and a critical step function to assure an accurate analysis. This invention provides an automated, hands-free, highly accurate device to prepare industrial, chemical, or biological samples for instrumental analysis methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Structure and Properties of SiO{sub x} Films Prepared by Chemical Etching of Amorphous Alloy Ribbons

The structure and the physical properties of amorphous SiO{sub x} films prepared by chemical etching of an iron-based amorphous ribbon alloy have been studied. The neutron diffraction and also the atomicforce and electron microscopy show that the prepared visually transparent films have amorphous structure, exhibit dielectric properties, and their morphology is similar to that of opals. The samples have been studied by differential scanning calorimetry, Raman and IR spectroscopy before and after their heat treatment. It is found that annealing of the films in air at a temperature of 1273 K leads to a change in their chemical compositions: an amorphous SiO{sub 2} compound with inclusions of SiO{sub 2} nanocrystals (crystobalite) forms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Abrupt GaP/Si hetero-interface using bistepped Si buffer

We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Charge transfer in crystalline germanium/monolayer MoS 2 heterostructures prepared by chemical vapor deposition

Heterostructuring provides novel opportunities for exploring emergent phenomena and applications by developing designed properties beyond those of homogeneous materials. Advances in nanoscience enable the preparation of heterostructures formed incommensurate materials. Two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides, are of particular interest due to their distinct physical characteristics. There have been recent changes in new research areas related to 2D/2D heterostructures. But, other heterostructures such as 2D/three-dimensional (3D) materials have not been thoroughly studied yet although the growth of 3D materials on 2D materials creating 2D/3D heterostructures with exceptional carrier transport properties has been reported. Here also we report a novel heterostructure composed of Ge and monolayer MoS 2 , prepared by chemical vapor deposition. A single crystalline Ge (110) thin film was grown on monolayer MoS 2 . The electrical characteristics of Ge and MoS 2 in the Ge/MoS 2 heterostructure were remarkably different from those of isolated Ge and MoS 2 . The field-effect conductivity type of the monolayer MoS 2 is converted from n-type to p-type by growth of the Ge thin film on top of it. Undoped Ge on MoS 2 is highly conducting. The observations can be explained by charge transfer in the heterostructure as opposed to chemical doping via the incorporation of impurities, based on our first-principles calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Online chemical adsorption studies of Hg, Tl, and Pb on SiO 2 and Au surfaces in preparation for chemical investigations on Cn, Nh, and Fl at TASCA

Online gas-solid adsorption studies with single-atom quantities of Hg, Tl, and Pb, the lighter homologs of the superheavy elements (SHE) copernicium (Cn, Z=112), nihonium (Nh, Z=113), and flerovium (Fl, Z=114), were carried out using short-lived radioisotopes. The interaction with Au and SiO 2 surfaces was studied and the overall chemical yield was determined. Here, suitable radioisotopes were produced in fusion-evaporation reactions, isolated in the gas-filled recoil separator TASCA, and flushed rapidly to an adjacent setup of two gas chromatography detector arrays covered with SiO 2 (first array) and Au (second array). While Tl and Pb adsorbed on the SiO 2 surface, Hg interacts only weakly and reached the Au-covered array. Our results contribute to elucidating the influence of relativistic effects on chemical properties of the heaviest elements by providing experimental data on these lighter homologs.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2016

Study of the crystallographic phase change on copper (I) selenide thin films prepared through chemical bath deposition by varying the pH of the solution

Copper (I) selenide thin films with orthorhombic and cubic structure were deposited on glass substrates by using the chemical bath deposition technique. The effects of the solution pH on the films growth and subsequently the structural, optical and electrical properties of the films were studied. Films with orthorhombic structure were obtained from baths wherein both metal complex and hydroxide coexist; while films with cubic structure were obtained from baths where the metal hydroxide there is no present. The structural modifications are accompanied by changes in bandgap energy, morphology and electrical resistivity of the films. - Graphical abstract: “Study of the crystallographic phase change on copper (I) selenide thin films prepared through chemical bath deposition by varying the pH of the solution” by M. G. Sandoval-Paz, C. A. Rodríguez, P. F. Porcile-Saavedra, C. Trejo-Cruz. Display Omitted - Highlights: • Copper (I) selenide thin films were obtained by chemical bath deposition. • Orthorhombic to cubic phase change was induced by varying the reaction solution pH. • Orthorhombic phase is obtained mainly from a hydroxides cluster mechanism. • Cubic phase is obtained mainly from an ion by ion mechanism. • Structural, optical and electrical properties are presented as a function of pH.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Local structure analysis of diluted magnetic semiconductor Co and Al co-doped ZnO nanoparticles

In this study, Co and Al ions co-doped ZnO nanoparticles (Zn(Al, Co)O NPs) were prepared by our original chemical preparation method. The obtained samples prepared by this method, were encapsulated in amorphous SiO{sub 2}. X-ray diffraction (XRD) results showed Zn(Al, Co)O NPs had a single-phase nature with hexagonal wurtzite structure. These particle sizes could be controlled to be approximately 30 nm. We investigate the effect that the increase in the carrier has on the magnetization by doping Al to Co-doped ZnO NPs. The local structures were qualitatively analyzed using X-ray absorption fine structure (XAFS) measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Structural and electronic switching of a single crystal 2D metal-organic framework prepared by chemical vapor deposition

The incorporation of metal-organic frameworks into advanced devices remains a desirable goal, but progress is hindered by difficulties in preparing large crystalline metal-organic framework films with suitable electronic performance. We demonstrate the direct growth of large-area, high quality, and phase pure single metal-organic framework crystals through chemical vapor deposition of a dimolybdenum paddlewheel precursor, Mo 2 (INA) 4 . These exceptionally uniform, high quality crystals cover areas up to 8600 µm 2 and can be grown down to thicknesses of 30 nm. Moreover, scanning tunneling microscopy indicates that the Mo 2 (INA) 4 clusters assemble into a two-dimensional, single-layer framework. Devices are readily fabricated from single vapor-phase grown crystals and exhibit reversible 8-fold changes in conductivity upon illumination at modest powers. Moreover, we identify vapor-induced single crystal transitions that are reversible and responsible for 30-fold changes in conductivity of the metal-organic framework as monitored by in situ device measurements. Gas-phase methods, including chemical vapor deposition, show broader promise for the preparation of high-quality molecular frameworks, and may enable their integration into devices, including detectors and actuators.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1971

Automated Drug Identification for Urban Hospitals

Many urban hospitals are becoming overloaded with drug abuse cases requiring chemical analysis for identification of drugs. In this paper, the requirements for chemical analysis of body fluids for drugs are determined and a system model for automated drug analysis is selected. The system as modeled, would perform chemical preparation of samples, gas-liquid chromatographic separation of drugs in the chemically prepared samples, infrared spectrophotometric analysis of the drugs, and would utilize automatic data processing and control for drug identification. Requirements of cost, maintainability, reliability, flexibility, and operability are considered.

Shirley, Donna L.↗
NASA NTRS1977

Heterogeneous chemical reactions: Preparation of monodisperse latexes

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

Vanderhoff, J. W.↗
DOE OSTI2015

Low temperature carrier transport study of monolayer MoS{sub 2} field effect transistors prepared by chemical vapor deposition under an atmospheric pressure

Large size monolayer Molybdenum disulphide (MoS{sub 2}) was successfully grown by chemical vapor deposition method under an atmospheric pressure. The electrical transport properties of the fabricated back-gate monolayer MoS{sub 2} field effect transistors (FETs) were investigated under low temperatures; a peak field effect mobility of 59 cm{sup 2}V{sup −1}s{sup −1} was achieved. With the assist of Raman measurement under low temperature, this work identified the mobility limiting factor for the monolayer MoS{sub 2} FETs: homopolar phonon scattering under low temperature and electron-polar optical phonon scattering at room temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Structural and optical properties of nano-structured CdS thin films prepared by chemical bath deposition

Cadmium sulfide (CdS) thin films have been deposited on conducting glass substrates by chemical bath deposition (CBD) technique. The effect of precursor concentration on the structural, morphological, compositional, and optical properties of the CdS films has been studied. Crystal structure of these CdS films is characterized by X-ray diffraction (XRD) and it reveals polycrystalline structure with mixture of cubic and wurtzite phases with grain size decreasing as precursor concentration is increased. Optical studies reveal that the CdS thin films have high transmittance in visible spectral region reaching 90% and the films possess direct optical band gap that decreases from 2.46 to 2.39 eV with decreasing bath concentration. Our study suggests that growth is nucleation controlled.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Annealing effect on Cu{sub 2}S thin films prepared by chemical bath deposition

In present work Cu{sub 2}S thin film fabricated on glass substrate by simple, cost effective chemical bath deposition method subsequently it annealed at 150°C. These films were studied for their structural, optical and electrical properties using X-ray diffraction, UV-vis spectrophotometer and I-V system. The results show successful synthesis of Cu{sub 2}S thin films and improvement in crystalline nature of the thin film which resulted in reduced bad gap and resistance of the film. Thus these thin films prove to be a promising candidate for solar cell application.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1984

A morphological study of silicon carbide prepared by chemical vapor deposition

Surface morphologies of SiC deposits obtained via chemical vapor deposition (CVD) were studied as functions of substrate surface temperature and the concentration of the silicon and carbon source material, methyltrichlorosilane. Substrates of graphite and alpha-SiC crystals were used. Explanations of the observed morphologies on graphite substrates and their marked changes with temperature are given in terms of chemical kinetics and mass transport arguments. The results of thermodynamic calculations were used to help explain the observed morphologies of the deposits on alpha-SiC substrates.

Tsui, P.↗