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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Development of a continuous synthesis process for carbamazepine using validated in-line Raman spectroscopy and kinetic modelling for disturbance simulation

Mitigation of failure modes in the continuous synthesis (CS) of a drug substance (DS) has the potential to widen the adoption of continuous manufacturing (CM) technologies by the pharmaceutical industry. Here, this work demonstrates the development of a robust continuous process for the synthesis of carbamazepine (CBZ), an essential medicine as per the World Health Organization (WHO), facilitated by kinetic modelling and monitored by in-line Raman spectroscopy. Accurate kinetic modelling and the use of validated process analytical technology (PAT) models for quantitative measurement were found to play an important role in developing CS of drug substances. Kinetic data for the formation of CBZ from iminostilbene (ISB) were collected by batch reaction sampling and high-performance liquid chromatography (HPLC) analysis. A non-linear solver and iterative method was applied to determine two sets of Arrhenius parameters simultaneously for the reaction system by minimizing the standard error of the model fit. The start-up and dynamic equilibrium stages for the CS of CBZ using a continuous stirred tank reactor (CSTR) were modelled based on the batch kinetic data and employed to optimize conversion and simulate process disturbances. An in-line Raman spectroscopy method was successfully developed, validated, and integrated to determine the concentrations of CBZ and ISB within the operating range for the CS. The CS kinetic model was evaluated experimentally from startup to dynamic equilibrium over 10 residence times with monitoring by HPLC and in-line Raman spectroscopy. The developed kinetic model in tandem with in-line Raman spectroscopy successfully predicted disturbances due to changes in process variables and can serve as a useful tool in the future design of advanced process control strategies for the continuous synthesis of CBZ.

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

Interlayer Triplet Energy Transfer in Dion–Jacobson Two-Dimensional Lead Halide Perovskites Containing Naphthalene Diammonium Cations

Recently, hybrid perovskites have gained attention as sensitizers for molecular triplet generation. Layered, two-dimensional (2D) perovskites are especially well-suited for this purpose because the triplet donor (inorganic framework) and triplet acceptor (organic layer) are self-assembled into adjacent sheets, so that with the appropriate energetics, triplets can be driven across the interface. Here we examine interlayer energy transfer in a series of mixed-halide Dion–Jacobson 2D perovskites containing divalent naphthalene cations. We find that the sensitized phosphorescence in these compounds is dominated by naphthalene triplet excimer emission, but when the inorganic exciton is tuned near resonance with the naphthalene triplet, naphthalene monomer phosphorescence competes with triplet excimer formation. The interlayer energy-transfer process is further revealed by ultrafast transient absorption spectroscopy through kinetic variations in triplet excimer formation times. Ultimately, gaining control over interlayer interactions in 2D perovskites through cation design will help uncover new functions and applications for these materials.

2D perovskite↗
NASA NTRS1992

Reaction layer formation at the graphite/copper-chromium alloy interface

Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, auger electron spectroscopy, and x ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

Devincent, Sandra M.↗
NASA NTRS1993

Reaction layer formation at the graphite/copper-chromium alloy interface

Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, Auger electron spectroscopy, and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

Devincent, Sandra M.↗
NASA NTRS1990

Characterization of Iridium Coated Rhenium Used in High-Temperature, Radiation-Cooled Rocket Thrusters

Materials used for radiation-cooled rocket thrusters must be capable of surviving under extreme conditions of high-temperatures and oxidizing environments. While combustion efficiency is optimized at high temperatures, many refractory metals are unsuitable for thruster applications due to rapid material loss from the formation of volatile oxides. This process occurs during thruster operation by reaction of the combustion products with the material surface. Aerojet Technical Systems has developed a thruster cone chamber constructed of Re coated with Ir on the inside surface where exposure to the rocket exhaust occurs. Re maintains its structural integrity at high temperature and the Ir coating is applied as an oxidation barrier. Ir also forms volatile oxide species (IrO2 and IrO3) but at a considerably slower rate than Re. In order to understand the performance limits of Ir-coated Re thrusters, we are investigating the interdiffusion and oxidation kinetics of Ir/Re. The formation of iridium and rhenium oxides has been monitored in situ by Raman spectroscopy during high temperature exposure to oxygen. For pure Ir, the growth of oxide films as thin as approximately 200 A could be easily detected and the formation of IrO2 was observed at temperatures as low as 600 C. Ir/Re diffusion test specimens were prepared by magnetron sputtering of Ir on Re substrates. Concentration profiles were determined by sputter Auger depth profiles of the heat treated specimens. Significant interdiffusion was observed at temperatures as low as 1000 C. Measurements of the activation energy suggest that below 1350 C, the dominant diffusion path is along defects, most likely grain boundaries, rather than bulk diffusion through the grains. The phases that form during interdiffusion have been examined by x ray diffraction. Analysis of heated test specimens indicates that the Ir-Re reaction produces a solid solution phase of Ir dissolved in the HCP structure of Re.

Stulen, R. H.↗
NASA NTRS2010

Cryogenic Carbonate Formation on Mars: Clues from Stable Isotope Variations Seen in Experimental Studies

Discoveries of large deposits of sedimentary materials on the planet Mars by landers and orbiters have confirmed the widely held hypothesis that water has played a crucial role in the development of the martian surface. Recent studies have indicated that both water ice and liquid water may have been present and in the case of water ice perhaps is still present on or near the surface of Mars. However, there remains much controversy about the prevailing atmospheric conditions and climate of Mars during its history and whether liquid water existed on the martian surface simply during discrete geological events or whether this water was present over relatively much longer geologic time periods. The recent identification of Ca-rich carbonate by the Phoenix lander as well as its measurement of the isotopic composition of atmospheric CO2 has shown the importance of understanding the carbonates on Mars as an important sink of atmospheric carbon. This work compliments that of our past experiments where we produced cryogenic calcite in open containers, as analogs for terrestrial aufeis formation, and as a means for evaluating the fractionation of C-13 in CO2 during bicarbonate freezing [13]. Unlike our previous experiments in which carbonates were grown in ambient laboratory condition in open containers (atmospheric pressure and composition), this work attempts to quantify the amount of delta C-13 enrichment possible in both fluids and secondary carbonates formed from freezing of bicarbonate fluids under martian-like atmospheric conditions. Morphologic textures of produced carbonates in these experiments are also examined under SEM in order to identify the effect that the cryogenic freezing process has on the mineral's mineralogy. Understanding the role of kinetic isotope fractionation during formation of carbonates under martian-like conditions will aid in our ability to quantify the isotopic composition of the carbonate sink furthering our ability to model the climate history of Mars.

Socki, Richard A.↗
NASA NTRS1998

Rejoining and misrejoining of radiation-induced chromatin breaks. IV. Charged particles

We have recently reported the kinetics of chromosome rejoining and exchange formation in human lymphocytes exposed to gamma rays using the techniques of fluorescence in situ hybridization (FISH) and premature chromosome condensation (PCC). In this paper, we have extended previous measurements to cells exposed to charged particles. Our goal was to determine differences in chromatin break rejoining and misrejoining after exposure to low- and high-linear energy transfer (LET) radiation. Cells were irradiated with hydrogen, neon, carbon or iron ions in the LET range 0.3-140 keV/microm and were incubated at 37 degrees C for various times after exposure. Little difference was observed in the yield of early prematurely condensed chromosome breaks for the different ions. The kinetics of break rejoining was exponential for all ions and had similar time constants, but the residual level of unrejoined breaks after prolonged incubation was higher for high-LET radiation. The kinetics of exchange formation was also similar for the different ions, but the yield of chromosome interchanges measured soon after exposure was higher for high-LET particles, suggesting that a higher fraction of DNA breaks are misrejoined quickly. On the other hand, the rate of formation of complete exchanges was slightly lower for densely ionizing radiation. The ratios between the yields of different types of aberrations observed at 10 h postirradiation in prematurely condensed chromosome preparations were dependent on LET. We found significant differences between the yields of aberrations measured in interphase (after repair) and metaphase for densely ionizing radiation. This difference might be caused by prolonged mitotic delay and/or interphase death. Overall, the results point out significant differences between low- and high-LET radiation for the formation of chromosome aberrations.

NASA Center JSC↗
DOE OSTI2020

Development of an autothermal formate-based hydrogen generator: From optimization of formate dehydrogenation conditions to thermal integration with Fuel Cells

Formate received significant attention for storing H2 in chemical bonds using the concept of H2 carriers. In this report, hydrogen generation from formate was optimized systematically by varying reaction variables. Initial mass activity with a turnover frequency of 3200 molH2 molPd–1 h–1 and 92% H2 yield were obtained in sodium formate (7 M 2.0 mL) dehydrogenation over Pd(3 wt %)/C at 80 °C. Influence of formate cations (Na, K, and NH4) on dehydrogenation was also elucidated, presenting that the fastest initial reaction kinetics was achieved with ammonium formate, whereas the highest H2 yield was obtained with potassium formate (PF) in multiple catalyst recycle tests. Finally, an on-site power generation system was integrated, where a proton exchange membrane fuel cell (PEMFC) was operated in conjunction with H2 produced from the custom developed semibatch dehydrogenation reactors. The system operation was demonstrated with continuous feeding of PF to generate H2 and power on demand without an external heat source by utilizing waste heat produced from the PEMFC in a highly efficient manner.

formate dehydrogenation, optimization of reaction ↗
NASA NTRS1989

Superconducting Bi1.5Pb0.5Sr2Ca2Cu3O(x) ceramics by rapid melt quenching and glass crystallization

A glass of nominal Bi(1.5)Pb(0.5)Sr2Ca2Cu3O(x) composition, prepared by rapid quenching of the melt, showed a glass transition temperature of 383 C, crystallization temperature of 446 C, melting temperature of 855 C, and bulk density of 5.69 g/cu cm in air. The activation energy for crystallization of the glass was estimated to be 292kJ/mol from non-isothermal DSC. On heating in oxygen, the glass showed a slow and continuous weight gain starting at approximately 530 C which reached a plateau at approximately 820 C. The weight gained during heating was retained on cooling to ambient conditions indicating an irreversible oxidation step. The influence of annealing conditions on the formation of various phases in the glass has been investigated. The Bi(2)Sr(2)Ca(0)Cu(1)O(6) phase crystallized out first followed by formation of other phases at higher temperatures. The high-T(sub c) phase, isostructural with Bi(2)Sr(2)Ca(2)Cu(3)O(10) was not detected below 840 C, but its fraction increased with the annealing time at 840 C. A sample annealed at 840 C for 243h in air and furnace cooled showed the highest T(sub c)(R=0) of 107.2K and a narrow transition width, delta T(sub c)(10 to 90 percent), of approximately 2 K. The high T(sub c) phase does not seem to crystallize out directly from the glass but is rather produced at high temperature by reaction between the phases formed at lower temperatures. The kinetics of 110K phase formation was sluggish. It appears that the presence of lead helps in the formation and/or stabilization of the 110 K phase.

Bansal, Narottam P.↗
DOE OSTI2021

Shock tube investigation of high-temperature, extremely-rich oxidation of several co-optima biofuels for spark-ignition engines

To reduce the reliance on fossil fuels in the transportation sector and increase combustion efficiency, the Co-Optima initiative from US Department of Energy identified the top 10 biofuels for downsized, boosted, spark-ignition engines. Most of these biofuels have detailed reaction mechanisms available in literature developed based on studies at temperatures lower than 1700 K and an equivalence ratio of less than five. As such, the performance of these detailed mechanisms at high temperature and extremely rich conditions are unknown. It is important to validate kinetic mechanisms at these conditions because they are conducive to soot formation. Prediction of soot by chemical kinetic models relies on the prediction of underlying benchmark species like carbon monoxide and ethylene. In this work, we conduct high temperature (1700–2050 K) and high equivalence ratio(Φ=8.6) oxidation of these biofuels, namely 2,4,4-trimethyl-1-pentene (α-diisobutylene), ethanol, cyclopentanone, methyl acetate, and 2-methylfuran, blended in ethylene behind reflected shock waves at 4–4.7 atm pressure. Carbon monoxide and ethylene time histories are measured simultaneously using a continuous feedback quantum cascade laser near 4.9 µm and a tunable CO 2 gas laser at 10.532 nm, respectively. Results show that ethanol blend forms more carbon monoxide than other biofuels and consumes ethylene faster than the biofuel blends in the temperature range considered. Overall, the performance of different mechanisms in literature are evaluated against the experimental results. The novel reaction mechanism ‘the Co-Optima model’, which includes the sub mechanisms for all the biofuels in this study, was found to be the best mechanism for the experimental conditions studied.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2025

Data-Driven Mapping of the Cesium Cadmium Bromide Phase Space Utilizing a Soft-Chemistry Approach

Soft-chemistry techniques provide a versatile approach to synthesizing inorganic materials under mild conditions, enabling access to compositions and structures that are challenging to achieve through traditional thermodynamically driven solid-state methods. However, these solution-based routes often result in phase competition, requiring precise control over reaction conditions to achieve selective product formation. While one-variable-at-a-time (OVAT) approaches have traditionally been used for phase selection, data-driven strategies are emerging as more efficient methods for navigating complex synthetic spaces. Ternary metal halides, such as cesium cadmium bromides (Cs–Cd–Br), are of growing interest due to their potential in wide and ultrawide band gap applications. Unlike the well-studied cesium lead halide phases, the compositional diversity and solution-based synthesis of ternary Cs–Cd–Br phases remain largely unexplored. This study systematically investigates the synthetic phase space of the Cs–Cd–Br system by constructing a data-driven phase map. Using a common set of precursors and a standardized experimental procedure, we successfully synthesize all four known Cs–Cd–Br phases—CsCdBr 3 , Cs 2 CdBr 4 , Cs 3 CdBr 5 , and Cs 7 Cd 3 Br 13 —each exhibiting distinct structures, morphologies, and optical properties. Our findings highlight the potential of soft-chemistry methods for expanding the library of ternary metal halides and provide key insights into the thermodynamic and kinetic factors governing phase formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Solitary Magnetic Structures at Quasi–Parallel Collisionless Shocks: Formation

Solitary magnetic structures known as SLAMS (short large-amplitude magnetic structures) have been considered as essential elements of collisionless shocks with quasi-parallel geometries. Yet the physics underlying their formation remains an open question. In this paper, we use measurements from the magnetospheric multiscale mission combined with fully kinetic simulations to study the formation of SLAMS. We find that gyro-resonance between solar wind ions and right-hand circularly polarized electromagnetic waves results in magnetic field amplification. Gyro-trapping by the growing magnetic field builds up the plasma density that further enhances the current and field. The solitary nature of SLAMS stems from a beat-like magnetic field envelope where the maximum sets the initial location for nonlinear growth. Our results present a conceptual advance on SLAMS, and may shed new light on the open question of magnetic field amplification at astrophysical shocks.

58 GEOSCIENCES↗
DOE OSTI2024

Wire directed energy deposition of steel-aluminum structures using cold metal transfer process

In this study, a sharp transition from 316L stainless steel to 4043 aluminum alloy was fabricated using wire directed energy deposition (DED) via the cold metal transfer (CMT) process. The CMT process with its inherently low heat input, led to a significant reduction in intermetallic thickness at the bi-metallic interface compared to blown powder DED technique reported in the literature resulting in superior properties when compared to those of dissimilar steel-aluminum welds. Thermo-kinetic modeling confirmed that the intermetallic formation is through a classical nucleation and growth mechanism, and the fraction and thickness can be controlled by adjusting CMT process parameters to kinetically arrest or minimize the intermetallic formation. These findings underscore the efficacy of CMT-based wire DED for fabrication of steel-aluminum bi-metallic structures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Galvanic Transformation Dynamics in Heterostructured Nanoparticles

Corrosion is a significant problem for the stability of structural metals and potentially for functional nanomaterials in operating environments. When two metals with different electrochemical potentials form a junction, galvanic corrosion occurs, resulting in the sacrificial dissolution of the metal with a higher oxidation potential (lower electrode potential). In this report it is shown that bimetallic hetero-nanostructures composed of phase-segregated metals undergo galvanic corrosion in aqueous environments. Such selective etching of the sacrificial metal in heterojunction particles leads to the formation of unusual and kinetically stabilized half-spheroid particles. By using a fluid cell and in situ scanning transmission electron microscopy, a two-stage corrosion process can be observed where the Cu experiences a fractal breakdown before the Ag corrodes due to the lack of a protective oxide layer. However, when treated with a mild Ar plasma, the stability of these structures against corrosion is enhanced due to the conversion of the amorphous native oxide to a denser, thin layer of CuO on the Cu surface. Taken together, this work highlights the importance of considering the effects of galvanic corrosion on the stability of multicomponent nanoparticles, and it shows how mass transport in a nanoscale system is influenced by redox processes.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Carbonate clumped isotope analysis (Δ 47 ) of 21 carbonate standards determined via gas‐source isotope‐ratio mass spectrometry on four instrumental configurations using carbonate‐based standardization and multiyear data sets

Rationale Clumped isotope geochemistry examines the pairing or clumping of heavy isotopes in molecules and provides information about the thermodynamic and kinetic controls on their formation. The first clumped isotope measurements of carbonate minerals were first published 15 years ago, and since then, interlaboratory offsets have been observed, and laboratory and community practices for measurement, data analysis, and instrumentation have evolved. Here we briefly review historical and recent developments for measurements, share Tripati Lab practices for four different instrument configurations, test a recently published proposal for carbonate‐based standardization on multiple instruments using multi‐year data sets, and report values for 21 different carbonate standards that allow for recalculations of previously published data sets. Methods We examine data from 4628 standard measurements on Thermo MAT 253 and Nu Perspective IS mass spectrometers, using a common acid bath (90°C) and small‐sample (70°C) individual reaction vessels. Each configuration was investigated by treating some standards as anchors (working standards) and the remainder as unknowns (consistency standards). Results We show that different acid digestion systems and mass spectrometer models yield indistinguishable results when instrument drift is well characterized. For linearity correction, mixed gas‐and‐carbonate standardization or carbonate‐only standardization yields similar results. No difference is observed in the use of three or eight working standards for the construction of transfer functions. Conclusions We show that all configurations yield similar results if instrument drift is robustly characterized and validate a recent proposal for carbonate‐based standardization using large multiyear data sets. Δ 47 values are reported for 21 carbonate standards on both the absolute reference frame (ARF; also refered to as the Carbon Dioxide Equilibrated Scale or CDES) and the new InterCarb‐Carbon Dioxide Equilibrium Scale (I‐CDES) reference frame, facilitating intercomparison of data from a diversity of labs and instrument configurations and restandardization of a broad range of sample sets between 2006, when the first carbonate measurements were published, and the present.

58 GEOSCIENCES↗
DOE OSTI2026

Role of Chemical Disorder in High Temperature Dislocation Glide in Refractory Multi-principal Element Alloys

Refractory multi-principal element alloys (RMPEAs) combine a chemically disordered lattice with a structurally ordered, single‐phase body‐centered cubic (bcc) crystal structure. Chemical fluctuations in these alloys give rise to significant energy barriers that impede dislocation motion. In this study, we use phase field dislocation dynamics to examine how spatial temperature fluctuations compete with randomness in energy barriers to affect the motion of long screw dislocations in three equi-atomic MoNbTa‐based RMPEAs: MoNbTa, MoNbTaW, and MoNbTaVW. Over a wide range of homologous temperatures (T h ≈ 0–0.6), we determined a screw dislocation ‘flow stress’ as the minimum applied stress to sustain continuous motion over a long excursion distance within a fixed timeframe. All three RMPEAs exhibit temperature dependent flow stress with three characteristic glide regimes: at low homologous temperatures, flow stress drops sharply, and screw glide remains planar and rectilinear; at intermediate homologous temperatures, the flow stress levels off as glide becomes planar but wavy; and at high homologous temperatures, flow stress plateaus as screws exhibit nonplanar, three‐dimensional motion. Glide kinetics and transition temperatures are controlled by the chemically induced fluctuations in the energy landscape. The rectilinear to wavy transition temperature is controlled by statistically weakest local barriers in the glide plane, whereas the wavy to 3D transition temperature is governed by statistically strongest local barriers. At low and intermediate homologous temperatures, the relative spread in energy barriers governs glide behavior by controlling the local kinetics of kink pair formation and kink pinning. At high homologous temperatures, the average barrier height governs the glide behavior by controlling the number of out-of-plane excursions during 3D glide. These findings reveal how random chemical fluctuations determine screw‐driven plasticity in RMPEAs, providing critical insight for the design of high temperature structural alloys.

Defects↗
DOE OSTI2021

Preliminary Studies of UV Photolysis of Gas-phase CH3I in Air: Time-resolved Infrared Identification of Methanol and Formaldehyde Products

Halogen-bearing compounds are known to photolyze under UV radiation; analysis of degradation products is of interest for both safety and environmental considerations. Time-resolved infrared spectroscopy was used in the laboratory to study the UV-photolysis of methyl iodide. Photolysis products methanol (CH3OH) and formaldehyde (HCHO) were clearly identified in a time-resolved manner. Preliminary kinetic models predict the formation of both CH3OH and HCHO.

Hughey, Kendall D.↗
DOE OSTI2024

On the product phases and the reaction kinetics of carbothermic reduction of UO 2 +C at relatively low temperatures

The synthesis of UC using carbothermic reduction of UO 2 and C mixtures has been well studied at high temperatures. However, the product phase behavior of carbothermic reduction at low temperatures (≤1773 K) is not well studied. Such a study is important as low temperatures permit single phase UC synthesis without forming secondary higher carbides, and it further supports the knowledge base of the process that needs to be used for transuranic elements such as plutonium that have high vapor pressures at elevated temperatures. Therefore, a low temperature carbothermic reduction of two different C/UO 2 molar ratios under inert and reducing environments have been studied here. Two different sample holding crucibles, alumina (Al 2 O 3 ) and graphite, were also used here to differentiate the hypostoichiometric (UC 1-a ) and oxygen dissolved (UC 1-x O x ) uranium monocarbide phases adding more details on the two systems. Also, the reaction kinetics involved in the formation of UC via the carbothermic reduction of UO 2 +C using product phases instead of evolved gases such as carbon monoxide is reported here. Under inert atmospheres but with significant oxygen partial pressures, the low temperature carbothermic reduction of UO 2 +C produced up to 90 wt.% UC 1-x O x type oxycarbides as was confirmed by Xray powder diffraction. Reducing Ar-4%H 2 environments at these temperatures were not successful in synthesizing UC as it reduces the amount of C required for the carbothermic reduction, leaving UC phase at a non-equilibrium state. Inert atmospheres with low or negligible oxygen partial pressures on the other hand produced near stoichiometric UC at high phase purity, especially at 1673 – 1773 K temperature range. An activation energy of 377±75 kJmol -1 was also calculated using product phase concentrations of the carbothermic reduction of UO 2 +C under these inert Ar (g) atmospheres.

36 MATERIALS SCIENCE↗