[en] Copper-exchanged SAPO-34 (Cu-SAPO-34) provides excellent catalytic activity and hydrothermal sta-bility in the selective catalytic reduction (SCR) of NOxby using NH3as a reductant. Here, we find that the6-membered ring (6MR) site is the most energetically favorable for a Cu+ion while the 8-memberedring (8MR) sites are less favorable by about 0.5 eV with respect to the 6MR site in Cu-SAPO-34. Uponadsorption of molecular species (H2O, O, OH, O2), the energy differences between Cu in the 8MR and 6MRsites decreases and almost disappears. Further, a thermodynamic phase diagram study shows that a Cu+ion bound to a single H2O molecule is the most stable species at low oxygen potential values while aCu2+ion bound to 2 OH species is more stable when the oxygen chemical potential is sufficiently high. Bycomparing Cu K-edge XANES between Cu-SSZ-13 and Cu-SAPO-34 with Cu in different oxidation states,we conclude that it is difficult to differentiate the simulated XANES of Cu in these structures at a givenoxidation state. By studying the Cu K-edge XANES of several favorable structures in Cu-SAPO-34 in thepresence of adspecies, the simulated XANES results capture the real trend of the edge shift with oxidationstate and gives new insights into the experimentally determined XANES of Cu-SAPO-34 obtained understandard SCR conditions.

[en] Here, to gain insight into inelastic deformation mechanisms for shocked hexagonal close-packed (hcp) metals, particularly the role of crystal anisotropy, magnesium (Mg) single crystals were subjected to shock compression and release along the a-axis to 3.0 and 4.8 GPa elastic impact stresses. Wave profiles measured at several thicknesses, using laser interferometry, show a sharply peaked elastic wave followed by the plastic wave. Additionally, a smooth and featureless release wave is observed following peak compression. When compared to wave profiles measured previously for c-axis Mg, the elastic wave amplitudes for a-axis Mg are lower for the same propagation distance, and less attenuation of elastic wave amplitude is observed for a given peak stress. The featureless release wave for a-axis Mg is in marked contrast to the structured features observed for c-axis unloading. Numerical simulations, using a time-dependent anisotropic modeling framework, showed that the wave profiles calculated using prismatic slip or (101̄2) twinning, individually, do not match the measured compression profiles for a-axis Mg. However, a combination of slip and twinning provides a good overall match to the measured compression profiles. In contrast to compression,prismatic slip alone provides a reasonable match to the measured release wave profiles; (101̄2) twinning due to its uni-directionality is not activated during release. The experimental results and wave profile simulations for a-axis Mg presented here are quite different from the previously published c-axis results, demonstrating the important role of crystal anisotropy on the time-dependent inelastic deformation of Mg single crystals under shock compression and release.

[en] Delicately engineering well-defined noble metal aerogels with favorable structural and compositional features is of vital importance for wide applications. Here, we reported a one-pot and facile method for synthesizing core–shell PdPb@Pd hydrogels/aerogels with multiply-twinned grains and an ordered intermetallic phase using sodium hypophosphite as a multifunctional reducing agent. Due to the accelerated gelation kinetics induced by increased reaction temperature and the specific function of sodium hypophosphite, the formation of hydrogels can be completed within 4 h. As a result, owing to their unique porous structure and favorable geometric and electronic effects, the optimized PdPb@Pd aerogels exhibit enhanced electrochemical performance towards ethylene glycol oxidation with a mass activity of 5.8 times higher than Pd black.

[en] Gallium oxide is a promising semiconductor for its potential as a material in the field of power electronics. The effects of iridium impurities on undoped, Mg-doped, and Ca-doped gallium oxides were investigated with IR spectroscopy. In undoped and Ca-doped β-Ga₂O₃, IR peaks at 3313, 3450, and 3500 cm^-1 are tentatively assigned to O–H bond-stretching modes of IrH complexes. Mg-, Ca-, and Fe-doped samples show an Ir⁴⁺ electronic transition feature at 5148 cm^-1. By measuring the strength of this feature vs photoexcitation, the Ir^3+/4+ donor level was determined to lie 2.2–2.3 eV below the conduction band minimum. Ga₂O₃:Mg also has a range of sidebands between 5100 and 5200 cm^-1, attributed to IrMg pairs. Polarized IR measurements show that the 5248 cm^-1 peak is anisotropic, weakest for light polarized along the c axis, consistent with Lenyk et al. [J. Appl. Phys. 125, 045703 (2019)].

[en] Intermittency of wind energy poses a great challenge for power system operation and control. Wind curtailment might be necessary at the certain operating condition to keep the line flow within the limit. Remedial Action Scheme (RAS) offers quick control action mechanism to keep reliability and security of the power system operation with high wind energy integration. In this paper, a new RAS is developed to maximize the wind energy integration without compromising the security and reliability of the power system based on specific utility requirements. A new Distributed Linear State Estimation (DLSE) is also developed to provide the fast and accurate input data for the proposed RAS. A distributed computational architecture is designed to guarantee the robustness of the cyber system to support RAS and DLSE implementation. The proposed RAS and DLSE is validated using the modified IEEE-118 Bus system. Simulation results demonstrate the satisfactory performance of the DLSE and the effectiveness of RAS. Real-time cyber-physical testbed has been utilized to validate the cyber-resiliency of the developed RAS against computational node failure.

[en] To understand the elastic-plastic deformation response of shock-compressed molybdenum (Mo) – a body-centered cubic (BCC) metal, single crystal samples were shocked along the [100] crystallographic orientation to an elastic impact stress of 12.5 GPa. Elastic-plastic wave profiles, measured at different propagation distances ranging between ~0.23 to 2.31 mm using laser interferometry, showed a time-dependent material response. Within experimental scatter, the measured elastic wave amplitudes were nearly constant over the propagation distances examined. These data point to a large and rapid elastic wave attenuation near the impact surface, before reaching a threshold value (elastic limit) of ~3.6 GPa. Numerical simulations of the measured wave profiles, performed using a dislocation-based continuum model, suggested that (110)<111> and/or (112)<111> slip systems are operative under shock loading. In contrast to shocked metal single crystals with close-packed structures, the measured wave profiles in Mo single crystals could not be explained in terms of dislocation multiplication alone. A dislocation generation mechanism, operative for shear stresses larger than that at the elastic limit, was required to model the rapid elastic wave attenuation and to provide a good overall match to the measured wave profiles. However, the physical basis for this mechanism was not established for the high-purity single crystal samples used in this study. As a result, the numerical simulations also suggested that Mo single crystals do not work harden significantly under shock loading in contrast to the behavior observed under quasi-static loading.

[en] Nuclear wastes generated from reprocessing of used nuclear fuel tend to contain a large fraction of rare earth (RE, e.g., Nd³⁺), transition (TM, e.g., Mo⁶⁺, Zr⁴⁺), alkali (A, e.g., Cs⁺), and alkaline earth cations (AE, e.g., Ba²⁺, Sr²⁺). Various strategies have been considered for immobilizing such waste streams, varying from nominally crystal-free glass to glass-ceramic to multi-phase ceramic waste forms. For glass and glass-ceramic waste forms, the added glass-forming system is generally alkali-alkaline earth-aluminoborosilicate (i.e., Na-Ca-Al-B-Si oxide). In a US-UK collaborative project, summarized here, we investigated the glass structure and crystallization dependence on compositional changes in simulated nuclear waste glasses and glass-ceramics. Compositions ranged in complexity from five – to – eight oxides. Specifically, the roles of Mo and rare earths are investigated, since a proposed glass-ceramic waste form contains crystalline phases such as powellite [(AE,A,RE)MoO₄] and oxyapatite [(RE,AE,A)₁₀Si₆O₂₆], and the precipitation of molybdenum phases is known to be affected by the rare earth concentration in the glass. Additionally, the effects of other chemical additions have been systematically investigated, including Zr, Ru, P, and Ti. A series of studies were also undertaken to ascertain the effect of the RE size on glass structure and on partitioning to crystal phases, investigating similarities and differences in glasses containing single RE oxides of Sc, Y, La, Ce, Nd, Sm, Er, Yb, or Lu. Finally, the effect of charge compensation was investigated by considering not only the commonly assessed peralkaline glass but also metaluminous and peraluminous compositions. Glass structure and crystallization studies were conducted by spectroscopic methods (i.e., Raman, X-ray absorption, nuclear magnetic resonance (NMR), optical absorption, photoluminescence, photoluminescence excitation, X-ray photoelectron spectroscopy), microscopy (i.e., scanning electron microscopy, transmission electron microscopy, electron probe microanalysis), scattering (i.e., X-ray and neutron diffraction, small angle measurements), and physical characterization (i.e., differential thermal analysis, liquidus, viscosity, density). This paper will give an overview of the research program and some example unpublished results on glass-ceramic crystallization kinetics, microstructure, and Raman spectra, as well as some examples of the effects of rare earths on the absorption, luminescence, and NMR spectra of starting glasses. Finally, the formal collaboration described here has resulted in the generation of a large number of results, some of which are still in the process of being published as separate studies.

[en] Since 2002, Washington State University has been building radiochemistry as a component of its overall chemistry program. Using an aggressive hiring strategy and leveraged funds from the state of Washington and federal agencies, six radiochemistry faculty members have been added to give a total of seven radiochemists out of a department of twenty-five faculty members. These faculty members contribute to a diverse curriculum in radiochemistry, and the Chemistry Department now enjoys a significant increase in the number of trainees, the quantity of research expenditures, and the volume and quality of peer-reviewed scientific literature generated by the radiochemistry faculty and the trainees. These three factors are essential for sustaining the radiochemistry education and research program at any academic institution.

[en] The crystallization and mechanical behavior of a hafnium-containing bulk amorphous alloy (Hf_28.35Zr_28.35Cu_15.3Ni_12.5Nb_5.0Al_10.0Y_0.5) was investigated and compared with a Hf-free alloy (Zr_56.7Cu_15.3Ni_12.5Nb_5.0Al_10.0Y_0.5) to understand the role of hafnium. Although the overall behavior of both alloys has similarities both in the as-received and heat-treated states, details of the physical, thermal, and mechanical properties are influenced by the incorporation of hafnium. Differential scanning calorimetry (DSC) results for the hafnium-containing alloy showed a glass transition at 440 deg. C and three exothermic peaks at 511, 559, 664 deg. C which correspond to primary and secondary crystallization. The increase in glass transition and the first crystallization temperature, compared to the Hf-free alloy, indicates stabilization of the amorphous state. Samples were heat-treated at various temperatures to examine the crystallization of various intermetallic phases. The phases were identified using X-ray diffraction (XRD) and the sizes varied between 100 and 200 nm, as observed by field emission scanning electron microscopy (FESEM), for samples heat-treated at 700 and 800 deg. C. The Vickers microhardness increased with heat-treatment from 5.2 to 7.2 GPa. Quasi-static compression tests showed decrease in failure stresses from 1843 MPa (as-received) to 994 MPa (heat-treated at 535 deg. C). The failure stress increased to 1661 MPa for the sample heat-treated at 800 deg. C, similar to the Hf-free alloy. Fracture morphologies changed from typical vein-type in as-received samples to smooth facets in heat-treated samples indicating embrittlement. Failure mechanism changes from shear banding in the as-received amorphous samples to void formation and coalescence in the heat-treated samples

[en] Plate impact experiments were carried out to examine the high strain-rate tensile response of alumina-aluminum (Al) composites with tailored microstructures. A novel processing technique was used to fabricate interpenetrating phase alumina-aluminum composites with controlled microstructures. Fused deposition modeling (FDM), a commercially available rapid prototyping technique, was used to produce the controlled porosity mullite ceramic preforms. Alumina-Al composites were then processed via reactive metal infiltration of porous mullite ceramics. With this approach, both the micro as well as the macro structures can be designed via computer aided design (CAD) to tailor the properties of the composites. Two sets of dynamic tensile experiments were performed. In the first, the metal content was varied between 23 and 39 wt. percent. In the second, the microstructure was varied while holding the metal content nearly constant. Samples with higher metal content, as expected, displayed better spall resistance. For a given metal content, samples with finer metal diameter showed better spall resistance. Relationship of the microstructural parameters on the dynamic tensile response of the structured composites is discussed here