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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Amorphous 1-D nanowires of calcium phosphate/pyrophosphate: A demonstration of oriented self-growth of amorphous minerals

Amorphous inorganic solids are traditionally isotropic, thus, it is believed that they only grow in a non-preferential way without the assistance of regulators, leading to the morphologies of nanospheres or irregular aggregates of nanoparticles. However, in the presence of (ortho)phosphate (Pi) and pyrophosphate ions (PPi) which have synergistic roles in biomineralization, the highly elongated amorphous nanowires (denoted ACPPNs) form in a regulator-free aqueous solution (without templates, additives, organics, etc). Based on thorough characterization and tracking of the formation process (e.g., Cryo-TEM, spherical aberration correction high resolution TEM, solid state NMR, high energy resolution monochromated STEM-EELS), the microstructure and its preferential growth behavior are elucidated. In ACPPNs, amorphous calcium orthophosphate and amorphous calcium pyrophosphate are distributed at separated but close sites. The ACPPNs grow via either the preferential attachment of ~2 nm nanoclusters in a 1-dimension way, or the transformation of bigger nanoparticles, indicating an inherent driving force-governed process. Here, we propose that the anisotropy of ACPPNs microstructure, which is corroborated experimentally, causes their oriented growth. This study proves that, unlike the conventional view, amorphous minerals can form via oriented growth without external regulation, demonstrating a novel insight into the structures and growth behaviors of amorphous minerals.

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NASA NTRS2023

Investigating the Role of Incident Ion Flux in Solar Wind Space Weathering of Carbon-Rich Asteroidal Regolith Via H+ and He+ Irradiation of the Murchison Meteorite

We present results from a set of low and high flux 1 keV/amu H + and He + irradiation experiments performed on slabs of the Murchison CM2 carbonaceous chondrite. The low flux conditions for H + and He + irradiation were ~1-1.5 orders of magnitude lower than the high flux conditions, and each experiment was irradiated to a total fluence between ~3 × 10 16 to ~6 × 10 16 ions/cm 2 . Irradiation-induced changes in the surface chemistry and optical properties of the Murchison samples were evaluated using in situ X-ray photoelectron spectroscopy (XPS) and visible and near-infrared spectroscopy (VNIR). We characterized the microstructure and composition of ion damaged rims in focused ion beam (FIB) cross-sections extracted from olivine and matrix material in each irradiated Murchison slab using transmission electron microscopy (TEM). XPS results suggest that both low flux and high flux H + and He + irradiation cause minor sputtering of surface carbon as well as a reduction in the valence state of iron, from Fe 3+ to Fe 2+ . Slope bluing is observed in VNIR spectra of the irradiated samples which may reflect carbonization and dehydrogenation of organic species and contrasts with reddening trends associated with npFe 0 formation. Although we do not observe a strong flux-dependence on the crystallinity of ion-damaged olivine, TEM analyses reveal a variety of microstructures in all olivine FIB-sections, suggesting that crystallographic orientation affects amorphization efficiency. Analyses of matrix FIB-sections indicate that phyllosilicate alteration is mainly driven by He+ irradiation, where the higher incident flux leads to greater amorphization and the formation of more distinct ion-damaged layers, similar to smooth layers in returned Ryugu particles. TEM results also provide some evidence that higher ion flux leads to greater vesiculation, with He + irradiation being more efficient at vesiculation than H + irradiation, and that higher ion flux may promote the segregation of Mg and Si into laterally extensive lenses and layers in olivine samples. We discuss the implications of these findings for constraining the role that ion flux plays in the development of space weathering characteristics in silicate phases present in carbonaceous asteroidal regoliths. These results will be important for understanding the complexity of this process and how it operates on carbon-rich airless bodies like asteroids Bennu and Ryugu.

meteorites↗
DOE OSTI2014

Numerical study of the effects of surface topography and chemistry on the wetting transition using the string method

Droplets on a solid surface patterned with microstructures can exhibit the composite Cassie-Baxter (CB) state or the wetted Wenzel state. The stability of the CB state is determined by the energy barrier separating it from the wetted state. In this work, we study the CB to Wenzel transition using the string method [E et al., J. Chem. Phys. 126, 164103 (2007); W. Ren and E. Vanden-Eijnden, J. Chem. Phys. 138, 134105 (2013)]. We compute the transition states and energy barriers for a three-dimensional droplet on patterned surfaces. The liquid-vapor coexistence is modeled using the mean field theory. Numerical results are obtained for surfaces patterned with straight pillars and nails, respectively. It is found that on both type of surfaces, wetting occurs via infiltration of the liquid in a single groove. The reentrant geometry of nails creates large energy barrier for the wetting of the solid surface compared to straight pillars. We also study the effect of surface chemistry, pillar height, and inter-pillar spacing on the energy barrier and compare it with nails.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Chrome-free qandilite (Mg 2 TiO 4 ) refractory aggregates: Role of titania source and evaluation of thermal expansion coefficient

As used chrome-based refractories may contain toxic Cr 6+ , the chrome-free Mg 2 TiO 4 phase is being considered which is known to improve hot strength and resistance to thermal shock and slag corrosion. As in situ Mg 2 TiO 4 formation generates porosity, preformed aggregates are desirable. Dilatometric studies revealed that when dead burned magnesia is combined with industrial anatase instead of rutile, it expanded less (1% versus 7.2%) and the reaction occurred earlier (965°C compared to 1120°C). After sintering at 1,600°C, rutile produced an aggregate with 3.8% open porosity, whereas anatase led to 0 % porosity and a bulk density of 3.24g/cm 3 with a thermal expansion coefficient (70–1,600°C) of 13.5×10 -6 K -1 . Moreover, replacing rutile by anatase eliminates the undesirable MgTiO 3 phase. The anatase-based aggregate consisted of a Mg 2 TiO 4 matrix with residual unreacted MgO and an intergranular, refractory CaTiO 3 phase. In conclusion, the rutile-based aggregate was deemed unsuitable due to a low-melting microstructure of forsterite contiguous with CaTiO 3 .

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

Supercritical Fluid Adsorption to Weakly Attractive Solids: Universal Scaling Laws

In this study, adsorption of light hydrocarbons (C1–C3) confined in the pores of silica aerogel (nominal density 0.2 g/cm 3 ) was studied experimentally and by computer simulation. Five isotherms of ethane (25.0, 32.0, 32.3, 33.0, and 35.0 °C) were obtained over a temperature range including the critical temperature of the bulk fluid (T c = 32.18 °C) to ~220 bar by the vibrating tube densimetry (VTD) method, which yields unique information impossible to obtain by excess sorption measurements. Two isotherms (35 and 50 °C) of methane adsorption in SiO 2 aerogel were measured far above its critical temperature, T c = -82.59 °C, at 0–150 bar using a gravimetric method. The experimental pore fluid properties of methane, ethane, propane, and CO 2 (obtained earlier by VTD for the same SiO 2 aerogel sample) show behavior conforming to the principle of corresponding states over the entire covered reduced temperature ranges from T r = 0.976 to T r = 1.696. The magnitudes of the excess adsorption maxima and the reduced fluid densities where the maxima occur for C1–C3 hydrocarbons and CO 2 are similar functions of the reduced temperature. This behavior indicates that, at least under the conditions covered in this work, the differences in molecular size and shape have only minor impacts on the solid–fluid interactions underlying the adsorption behavior. Lastly, these findings are supported by large-scale GCMC simulations of a lattice gas confined in the pores of a computer representation of the SiO 2 aerogel framework, yielding excess adsorption isotherms in good agreement with experimental measurements, as well as the underlying microstructures of the adsorbed fluids.

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

Effects of Sea Spray on the Dynamics and Microphysics of an Idealized Tropical Cyclone

The effect of sea spray particles (SSP) on the intensity and microphysical structure of an idealized tropical cyclone (TC) is investigated using the Weather Research and Forecasting Model with a new spectral bin microphysics package. The SSP size distribution in the hurricane boundary layer is calculated using a Lagrangian–Eulerian bin-microphysics model (LEM) with high spatial resolution and extremely high drop size resolution. Sea spray ascending in updrafts within the eyewall of a TC dramatically increases the concentration of cloud drops within a wide range of sizes and decreases the effective drop radius to the values typical of polluted continental clouds. At the same time, the presence of spray drops of a few hundred microns in radii trigger intense rain just above cloud base. As a result, sea spray creates clouds that have a unique combination of maritime and continental properties. Outside the eyewall, clouds remain extremely maritime. SSP are shown to increase substantially the maximum vertical velocity, the cloud water content, and the mass contents of ice particles within the eyewall. As a result, SSP lead to TC intensification, axis symmetrization, and a decrease in eyewall radius. We found a new mechanism where wind-generated sea spray particles invigorate the inner cloud bands by nucleating more cloud droplets, which leads to more water vapor condensation and greater latent heating. The dependence of this process on surface wind speed constitutes a positive feedback loop that can lead to higher hurricane intensity. The results of simulations of cloud microstructure in the hurricane eyewall are supported by observations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Influence of oxide impurities on the chemical tuning of the thermoelectric properties of substitution derivatives of RuIn{sub 3}

A systematic investigation on tuning the charge carrier concentration by substitution of the Ru position in RuIn{sub 3} is performed. Samples with nominal composition Ru{sub 0.95}T{sub 0.05}In{sub 3} (T=Re, Rh, Ir) were synthesized via liquid–solid-reaction and subsequent spark plasma sintering treatment. The chemical composition was characterized by X-ray, metallographic and microstructure analysis revealing solid solutions in the samples with Rh and Ir, whereas Re cannot be incorporated in RuIn{sub 3}. Minor oxide impurities in the commercially available starting elements, the homogeneity range of RuIn{sub 3} and the redox potentials of the participating elements are the key for interpreting the observed lattice parameters and the corresponding composition. Both, substitutions with Rh or Ir and Re inclusions in RuIn{sub 3} lead independently to a significant decrease of the total thermal conductivity down to approximately one half of the value observed for binary RuIn{sub 3}, prepared with commercially available starting materials. The electrical resistivity was reduced by substitution and the temperature dependence changes from semiconductor-like, for RuIn{sub 3}, to metal-like in the substitution derivatives. At the same time the sign change in the thermopower at high temperatures, characteristic for binary RuIn{sub 3}, is suppressed, attaining only electrons as majority carriers. - Graphical abstract: Microstructure (perpendicular to the pressure axis; polarized light) of polycrystalline Ru{sub 0.95}Rh{sub 0.05}In{sub 3} (a), Ru{sub 0.95}Ir{sub 0.05}In{sub 3} (b) and Ru{sub 0.95}Re{sub 0.05}In{sub 3} (c) samples after SPS treatment. - Highlights: • Substitution solid solutions of RuIn{sub 3} were prepared via liquid–solid-reaction. • Chemistry of oxide impurities is crucial for explanation of experimental results. • Thermodynamic calculations support the observation of In{sub 2}O{sub 3} or ZnO as impurities. • Electrical resistivity is reduced by substitution. • Temperature dependence of resistivity changes from semiconductor- to metal-like.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Structural investigation of self-irradiation damaged AmO{sub 2}

Studying self-irradiated materials is an ideal means to investigate the effect of the damage on material structure and to better understand the behavior of irradiated nuclear fuels. In this context, X-ray diffraction, X-ray absorption spectroscopy and transmission electron microscopy have been used to investigate self-irradiation damaged AmO{sub 2}. Combining these techniques allows studying the microstructure and the variation of the fluorite structure at both short-range and long-range order. Thus, the increase of both interatomic distances and lattice parameter was shown, as well as the presence of nanometer sized He bubbles and dislocation loops. As confirmed by the observed high-level of crystallinity, the fluorite structure exhibits a high radiation tolerance, which is confirmed by the low increase of the lattice parameter. This could be explained by a self-annealing mechanism of the created defects at room temperature. - Graphical abstract: The structure of damaged AmO2 (36 dpa) has been studied by XRD, XAS and TEM. Thus, the effects of the self-irradiation on the oxidation state, the lattice distances, the structural disorder, the radiation stability and the microstructure have been discussed. - Highlights: • The structure of highly self-irradiated AmO{sub 2} (36 dpa) was studied by XAS and TEM. • XRD, EXAFS and TEM confirm the high stability of the fluorite structure. • XRD and EXAFS show an increase of 0.3% of the structural distances. • XANES shows that Am is tetravalent as well as the Np recoil nucleus. • The presence of He bubbles was evidenced by TEM.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Polymorph (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}RE{sub 3}F{sub 10}·xH{sub 2}O (RE = Ho-Lu, Y) and REF{sub 3} nanocrystals: Hydrothermal synthesis, characterization and luminescence

Graphical abstract: A hydrothermal system is developed to prepare one new polymorph of (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}RE{sub 3}F{sub 10}·xH{sub 2}O and known rare earth fluorides involving REF{sub 3} nanocrystals under mild condition. Highlights: ► A new polymorph of (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}RE{sub 3}F{sub 10}·xH{sub 2}O has been synthesized. ► The RE{sup 3+} radius decides the shape evolution and phase control for REF{sub 3} NCs. ► The RE{sup 3+} radius has influence on the microstructure and morphology of REF{sub 3} NCs. -- Abstract: In this paper, a solvents-thermal system is developed to prepare one new polymorph of (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}Ho{sub 3}F{sub 10}·xH{sub 2}O and rare earth fluorides REF{sub 3} nanocrystals under mild condition. It is found that the ionic radius of RE{sup 3+} is the key factor responsible for the shape evolution and phase control for rare earth fluorides nanocrystals at selected temperatures, which has an influence on the microstructure and morphology of the products to some extent. With the increase of the atomic number, the shape of fluoride changes from hexagonal REF{sub 3} phase (RE = La, Sm) to orthorhombic REF{sub 3} phase (RE = Eu-Dy), and finally to diamond structure (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}Ho{sub 3}F{sub 10}·xH{sub 2}O (RE = Ho, Er, Tm, Yb, Lu, Y). In addition, the characteristic energy level transition {sup 5}D{sub 0}–{sup 7}F{sub 1} of Eu{sup 3+} splits into 585 and 591 nm emission peaks, and the dominant peak is the orange emission at 591 nm.

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

How Microstructure and Pore Moisture Affect Strength Gain in Portlandite-Enriched Composites That Mineralize CO 2

Binders containing portlandite (Ca(OH) 2 ) can take up carbon dioxide (CO 2 ) from dilute flue gas streams (<15% CO 2 , v/v), thereby forming carbonate compounds with binding attributes. While the carbonation of portlandite particulates is straightforward, it remains unclear how CO 2 transport into monoliths is affected by microstructure and pore moisture content. Therefore, this study elucidates the influences of pore saturation and CO 2 diffusivity on the carbonation kinetics and strength evolution of portlanditeenriched composites (“mortars”). To assess the influences of microstructure, composites hydrated to different extents and conditioned to different pore saturation levels (S w ) were exposed to dilute CO 2 . First, reducing saturation increases the gas diffusivity and carbonation kinetics so long as saturation exceeds a critical value (S w,c ≈ 0.10) independent of microstructural attributes. Second, careful analysis reveals that both traditional cement hydration and carbonation offer similar levels of strengthening, the magnitude of which can be estimated from the extent of each reaction. As a result, portlandite-enriched binders offer cementation performance that is similar to traditional materials while offering an embodied CO 2 footprint that is more than 50 % smaller. Furthermore, these insights are foundational to create new “low-CO 2 ” cementation agents via in situ CO 2 mineralization (utilization) using dilute CO 2 waste streams.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Microstructure and thermal conductivity of surfactant-free NiO nanostructures

High purity, nanometer sized surfactant-free nickel oxide (NiO) particles were produced in gram scale using a solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), gas pycnometry and gas adsorption analysis (BET). The average particle size of the as-synthesized NiO increases significantly with the preheating temperature of the furnace, while the specific surface area decreases. A BET specific surface area of {approx}100 m{sup 2}/g was obtained for NiO nanoparticles with size as small as 3 nm synthesized at 300 Degree-Sign C. The thermal conductivity ({kappa}) of pressed pellets of the synthesized NiO nanoparticles obtained using spark plasma sintering (SPS) and uniaxial hot pressing is drastically decreased ({approx}60%) compared to that of NiO single crystal. This strong reduction in {kappa} with particle size suggests the suitability of the synthesized surfactant-free NiO nanoparticles for use as nanoinclusions when designing high performance materials for waste heat recovery. - Graphical abstract: Highly efficient phonon scattering by surfactant-free NiO nanostructures obtained by solution combustion of a mixture of nickel (II) nitrate hexahydrate (oxidizer) and urea (fuel) at various temperatures. Highlights: Black-Right-Pointing-Pointer Fast synthesis of surfactant-free NiO nanoparticles with controllable size. Black-Right-Pointing-Pointer High specific surface area for NiO nanoparticles with size range from 3 to 7 nm. Black-Right-Pointing-Pointer Strong reduction of the thermal conductivity with decreasing particle size. Black-Right-Pointing-Pointer NiO as nanoinclusions in high performance materials for energy conversion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Impact of cobalt doping on structural and magnetic properties of zinc oxide nanocomposites synthesized by mechanical ball-milling method

A series of zinc oxide (ZnO) semiconductor nanocomposite samples doped with different concentrations of cobalt (Co) were successfully synthesized via simple and highly effective mechanical ball-milling method using suitable precursors. All doped nanocomposites crystallized in hexagonal wurtzite formation of ZnO. No alteration in the wurtzite structure, with no evidence of any segregated secondary phase(s) was detected with increasing doping concentrations. This result unambiguously verified the substitution of Zn 2+ sites by Co 2+ ions in the ZnO host lattice for different doping concentrations. Moreover, room temperature ferromagnetic behavior was observed in all doped nanocomposite samples in the reported work. Present study clearly shows that mechanical ball-milling is a facile, inexpensive, eco-friendly method to synthesize crystalline and magnetic Co doped ZnO nanocomposites for next generation spin-based devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Link statistics of dislocation network during strain hardening

Dislocations are line defects in crystals that multiply and self-organize into a complex network during strain hardening. The length of dislocation links, connecting neighboring nodes within this network, contains crucial information about the evolving dislocation microstructure. By analyzing data from Discrete Dislocation Dynamics (DDD) simulations in face-centered cubic (fcc) Cu, we characterize the statistical distribution of link lengths of dislocation networks during strain hardening on individual slip systems. Here, our analysis reveals that link lengths on active slip systems follow a double-exponential distribution, while those on inactive slip systems conform to a single-exponential distribution. The distinctive long tail observed in the double-exponential distribution is attributed to the stress-induced bowing out of long links on active slip systems, a feature that disappears upon removal of the applied stress. We further demonstrate that both observed link length distributions can be explained by extending a one-dimensional Poisson process to include different growth functions. Specifically, the double-exponential distribution emerges when the growth rate for links exceeding a critical length becomes super-linear, which aligns with the physical phenomenon of long links bowing out under stress. This work advances our understanding of dislocation microstructure evolution during strain hardening and elucidates the underlying physical mechanisms governing its formation.

Crystal plasticity↗
DOE OSTI2012

Investigations on hydrogen storage properties of Mg{sub 2}Ni+x wt% LaMg{sub 2}Ni (x=0, 10, 20, 30) composites

Mg{sub 2}Ni+x wt% LaMg{sub 2}Ni (x=0, 10, 20, 30) composites have been prepared by ball milling Mg{sub 2}Ni and LaMg{sub 2}Ni hydrides. X-ray Diffraction indicates that the composites consist of LaH{sub 3} and Mg{sub 2}NiH{sub 4} phases. Mg{sub 2}NiH{sub 4} phase transforms between with Mg{sub 2}Ni phase during hydriding/dehydriding cycling, while the LaH{sub 3} phase exists still after dehydriding process. Backscatter Electron results reveal that the LaH{sub 3} phase, which is decomposed from hydrided LaMg{sub 2}Ni, distributes in Mg{sub 2}Ni alloy homogeneously after ball milling procedure. Hydriding/Dehydriding measurements indicate significant improvement in reversible hydrogen storage properties of the composites over Mg{sub 2}Ni at low temperature. At 473 K, the hydrogen storage capacity of Mg{sub 2}Ni+20 wt% LaMg{sub 2}Ni composite reaches 3.22 wt% and can reversely desorb hydrogen completely, while the pure Mg{sub 2}Ni hydride is hardly desorbs hydrogen at this temperature. The improvement in the hydrogen storage properties is attributed to the existence of LaH{sub 3} phase in the composites. - Graphical abstract: The Mg{sub 2}Ni + x wt% LaMg{sub 2}Ni (x=10, 20, 30) composites display enhancement on reversible hydrogen storage properties compared with that of pure Mg{sub 2}Ni. Highlights: Black-Right-Pointing-Pointer Tittle La is introduced into Mg{sub 2}Ni alloy without multiphase created. Black-Right-Pointing-Pointer La is introduced into Mg{sub 2}Ni by hydrogen decomposed ball-milling. Black-Right-Pointing-Pointer Reversible hydrogen storage properties at low temperature are improved. Black-Right-Pointing-Pointer Hydrogen storage capacity of composites is beyond 3 wt% at 473 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Mg dopant in Cu{sub 2}SnSe{sub 3}: An n-type former and a promoter of electrical mobility up to 387 cm{sup 2} V{sup −1} s{sup −1}

Mg-doped Cu{sub 2}SnSe{sub 3} bulk materials with the (Cu{sub 2−x}Mg{sub x})SnSe{sub 3} (Mg-x-CTSe) formula at x=0, 0.05, 0.1, 0.15, and 0.2 were prepared at 550 °C for 2 h with soluble sintering aids of Sb{sub 2}S{sub 3} and Te. Defect chemistry was studied by measuring structural and electrical properties of Mg-doped Cu{sub 2}SnSe{sub 3} as a function of dopant concentration. Mg-x-CTSe pellets show p-type at x=0, 0.05 and 0.1 and n-type at x=0.15 and 0.2. The low hole concentration of 3.2×10{sup 17} cm{sup −3} and high mobility of 387 cm{sup 2} V{sup −1} s{sup −1} were obtained for (Cu{sub 2−x}Mg{sub x})SnSe{sub 3} bulks at x=0.1 (5% Mg) as compared to 2.2×10{sup 18} cm{sup −3} and 91 cm{sup 2} V{sup −1} s{sup −1} for the undoped one. The explanation based upon the Mg-to-Cu antisite donor defect for the changes in electrical property was declared. A high Mg content for Mg-x-CTSe at x≥0.1 can lead to the formation of second phases. The study in bulk Mg-x-CTSe has been based upon defect states and is consistent and supported by the data of structural and electrical properties. - Graphical abstract: The effects of extrinsic doping of Mg{sup 2+} on the electrical properties of Cu{sub 2}SnSe{sub 3} bulks. - Highlights: • p-Type Mg-CTSe with n{sub p} of 3.2×10{sup 17} cm{sup −3} and μ{sub p} of 387 cm{sup 2} V{sup −1} s{sup −1} was obtained. • This p-type occurred for 5%Mg-doped CTSe with the (Cu{sub 1.9}Mg{sub 0.1})SnSe{sub 3} formula. • Mg dopant acts as a donor to lower n{sub p} and an accelerator to increase mobility. • High Mg content leads to the p-to-n transitions. • Defect was explored by measuring electrical property and lattice parameter.

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

Bayesian Learning of Adatom Interactions from Atomically Resolved Imaging Data

Atomic structures and adatom geometries of surfaces encode information about the thermodynamics and kinetics of the processes that lead to their formation, and which can be captured by a generative physical model. In this work, we develop a workflow based on a machine-learning-based analysis of scanning tunneling microscopy images to reconstruct the atomic and adatom positions, and a Bayesian optimization procedure to minimize statistical distance between the chosen physical models and experimental observations. We optimize the parameters of a 2- and 3-parameter Ising model describing surface ordering and use the derived generative model to make predictions across the parameter space. For concentration dependence, we compare the predicted morphologies at different adatom concentrations with the dissimilar regions on the sample surfaces that serendipitously had different adatom concentrations. The proposed workflow can be used to reconstruct the thermodynamic models and associated uncertainties from the experimental observations of materials microstructures. The code used in the manuscript is available at https://github.com/saimani5/Adatom_interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Electro-carburization of mild steel through two-step reaction in molten-salt electrolyte

The rapid carburization of mild steel is demonstrated via the electrochemical deposition of solid carbon, followed by thermochemical iron-carbon (Fe-C) reaction using a molten lithium-potassium carbonate (LiKCO 3 ) salt electrolyte and carbon dioxide as the carbon source. Depth-dependent microstructural and compositional changes in the steel are shown to be controlled by the applied cell voltage and reaction temperatures. Reaction temperatures above the Fe-C eutectoid temperature promote faster carburization due to carbon dissolution into austenite. The carbon deposition rate is regulated by the applied cell voltage: At - 2.4 V, carbon deposition occurs much faster than its diffusion into the steel, resulting in the accumulation of a carbon-rich layer exceeding 1 mm, which does not diffuse into the steel. In contrast, at - 1.8 V, all deposited carbon effectively diffuses into the steel, leaving a minimal external deposit. In both cases, carbon ingress forms a carbide-rich surface layer and precipitates additional carbides along the grain boundaries within the steel electrode. This method offers a potential approach to increase the carbon content of mild or low-carbon steel feedstocks, such as scrap or direct reduced iron, for industrial applications.

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

Sintering and characterization of SrBi{sub 2}Ta{sub 2}O{sub 9} obtained by high-pressure processing at low temperatures

High-pressure processing is a very attractive approach for the production of materials with new and/or improved properties. In this work, pressures in the order of 7.7 GPa and 2.5 GPa were induced in SrBi{sub 2}Ta{sub 2}O{sub 9} samples at different temperatures placed in a specific reaction cell and generated different effects on phase formation. The microstructural evolution during high-pressure processing was investigated by scanning electron microscopy in association with energy dispersion spectroscopy and with the support of an X-ray diffraction analyzer. Frequency response analysis was used to obtain the dielectric curves by electrochemical impedance spectroscopy. A SrBi{sub 2}Ta{sub 2}O{sub 9} single-phase sample, treated at 2.5 GPa and 900 °C, was used to evaluate the electrical properties, obtaining a dielectric response similar to SrBi{sub 2}Ta{sub 2}O{sub 9} samples sintered by conventional processes at temperatures above 1000 °C. In addition, by this method, it was possible to obtain ceramics with uniform microstructure and a relative density of 93%. - Highlights: • The first production of SrBi{sub 2}Ta{sub 2}O{sub 9} using the technique of high-pressure processing. • The ability to produce single-phase SrBi{sub 2}Ta{sub 2}O{sub 9} treated at 2.5 GPa and 900 °C. • The electrical properties are compatible with SBT sintered at high temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗