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Borosilicate glasses are widely used for radioactive waste disposal due to their ability to incorporate a variety of contaminants and radionuclides while exhibiting high durability in various disposal scenarios. This research evaluated the dissolution of borosilicate glass using both single-pass-flow-through (ASTM C1662-18) and product consistency test (ASTM C1285-21) methods with different solutions, including a cementitious-contacted water (called grout-contacted, GC, from this point) and solutions with varying levels of dissolved cementitious species such as Si, Ca, Al. The results indicated that the presence of Ca plays a crucial role in suppressing glass corrosion, as evidenced by the slower normalized dissolution rates, which were one order of magnitude lower for boron and two orders of magnitude lower for rhenium, observed in both Ca-amended and GC solutions compared to the pH 12 buffer solution. This effect is attributed to the formation of a dense, low-porosity, and strongly bonded calcium silicate hydrate (CSH) layer on the glass surface, which implies that a glass corrosion process is influenced by ion exchange involving alkali ions Na+, K+, Ca2+, and hydrogen-containing species. A small number of glass particles treated in the GC solution showed minor corrosion pits in the form of shallow craters with an average diameter of approximately 500 μm. This observation is correlated with a significant reduction, 2000 to 3000 times lower, in the cumulative volume of glass pores, indicating that smaller pore voids were "sealed" in the presence of Ca2+ ions, likely attributed to the formation of CSH precipitation or other corrosion products such as calcium carbonate saturated from the grout solution. These findings suggest that the presence of dissolved Ca in the GC solution can slow down the dissolution of borosilicate glass, contrary to the expected trend of higher dissolution rates resulting from exposure to high alkaline and thus higher pH solutions. [ABSTRACT FROM AUTHOR]

Flash sintering (FS) is a potentially rapid and low‐cost manufacturing technique for advanced ceramics. There are still many unknowns about ceramic FS, especially for highly conductive high‐temperature ceramics (HTC), which often display decreased bulk conductivity with increasing temperature. This study qualitatively characterizes the flash behavior of highly conductive HTC materials using zirconium nitride (ZrN) as an example. The effects of processing parameters (e.g., DC voltage/electrical field strength, voltage ramp rate, post‐flash holding time, mechanical pressure, sample milling, and choice of electrode materials) on ZrN flash behavior are also qualitatively studied and linked to samples microstructure and hardness. It is observed that best densification was achieved using 5 min Spex‐milled ZrN powder under 25 MPa of applied pressure and constant 8 V DC. The potential mechanism for ZrN FS and the similarity and difference from FS of conventional oxides like YSZ have been proposed based on experimental observations, and the directions for future research are also pointed out. [ABSTRACT FROM AUTHOR]

In this study, we report the synthesis of a new cubic neodymium-rhenium metallic alloy NdRe2 through the utilization of high pressure and laser heating in a diamond anvil cell. NdRe2 crystallizes in the … space group with a lattice parameter equal to 7.486 (2) Å and Z = 8 at 24 (1) GPa and 2,200 (100) K. It was studied using high-pressure single-crystal X-ray diffraction. The compound crystallizes in the cubic MgCu2 structure type. Its successful synthesis further proves that high-pressure high-temperature conditions can be used to obtain alloys holding a Laves phase structure. Ab initio calculations were done to predict the mechanical properties of the material. We also discuss the usage of extreme conditions to synthesize and study materials present in the nuclear waste. [ABSTRACT FROM AUTHOR]

A binary, three-dimensional (3D), foldable, Metal–Organic Framework (MOF) of formula {[trans-Ni(H2O)2(μ-4,4′-bpy)2](ClO4)2}n (1), with CdSO4 (65 8), cds, topology, based on four-connected (4-c) square-planar single Ni2+ ion nodes and two-connected (2-c) linear rigid 4,4′-bipyridine (4,4′-bpy) ligands, was synthesized and structurally characterized via single crystal X-ray crystallography. The 41° dihedral angle between two distinct coordination environments within the 3D network of 1 produced the self-dual topology of Ni2+ nodes. Two rectangular 1D channels ran parallel to the crystallographic a-axis and b-axis, respectively, creating a 44.2% volume porosity, probed by gas (N2, CO2, and H2) sorption studies. The PXRD, FT-IR, Raman, EDS, and SEM methods were employed for the study of 1. A thermogravimetric analysis (TGA) showed that coordinated water molecules were readily removed upon heating, whereas the 3D lattice remained intact up to 370 °C. [ABSTRACT FROM AUTHOR]

Gadolinium aluminate perovskite (GdAlO3) was studied at high pressures of up to 23 GPa in a diamond anvil cell (DAC) using monochromatic synchrotron X-ray powder diffraction. Evidence of a pressure-induced phase transformation from orthorhombic (Pbnm) to rhombohedral (R 3 ¯ c) structure was observed at 21 GPa and further proved by DFT calculations. Before phase transition, the volumetric ratio of polyhedron A and B (i.e., VA/VB for ABX3 general notation) in the Pbnm phase continuously increased towards the ideal value of five at the transition, indicating a pressure-induced decrease in the structural distortion as opposed to the trend in many other orthorhombic perovskites (e.g., CaSnO3, CaGeO3, MgSiO3 and NaMgF3). Pressure–volume data of the Pbnm phase were fitted to the third-order Birch–Murnaghan equation of state yielding a bulk modulus (Ko) of 216 ± 7 GPa with a pressure derivative of the bulk modulus ( K o ′ ) of 5.8 GPa (fixed). This work confirms the pressure-induced phase transformation from orthorhombic to a higher symmetry structure previously predicted in GdAlO3 perovskite. [ABSTRACT FROM AUTHOR]