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This paper introduces the results of hydrolytic stability tests and radiation resistance tests of phosphate molybdates and phosphate tungstates Na_1−xZr₂(PO₄)_3−x(XO₄)_x, X = Mo, W (0 ≤ x ≤ 0.5). The ceramics characterized by relatively high density (more than 97.5%) were produced by spark plasma sintering (SPS) of submicron powders obtained by sol–gel synthesis. The study focused on hydrolytic resistance of the ceramics in static mode at room temperature. After 28 days of testing in distilled water, the normalized leaching rate was determined. It was found that the ceramics demonstrated high hydrolytic resistance in static mode: the normalized leaching rates for Mo- and W-containing ceramics were 31·10⁻⁶ and 3.36·10⁻⁶ g·cm⁻²·day⁻¹, respectively. The ceramics demonstrated high resistance to irradiation with 167 MeV Xe⁺²⁶ multiple-charged ions at fluences ranging from 1·10¹² to 6·10¹³ cm⁻². The Mo-containing Na_0.5Zr₂(PO₄)_2.5(XO₄)_0.5 ceramics were shown to have higher radiation resistance than phosphate tungstates. Radiation was shown to trigger an increase in leaching rates for W and Mo in the crystal structure of NZP ceramics. Full article

The structure, microstructure, coefficient of thermal expansion (CTE), and mechanical properties of Na_1+2xZr_2−xCo_x(PO₄)₃ ceramics (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were studied. Na_1+2xZr_2−xCo_x(PO₄)₃ submicron powders with the NaZr₂(PO₄)₃ structure (NZP, kosnarite type) were obtained by the solid-phase method. The starting reagents (NaNO₃, ZrOCl₂·8H₂O, NH₄H₂PO₄, CoCl₂·6H₂O, ethanol) were mixed with the addition of ethyl alcohol. The resulting mixtures were annealed at 600 °C (20 h) and 700 °C (20 h). The obtained phosphates crystallized in the expected structure of the NaZr₂(PO₄)₃ type (trigonal system, space group R$\overline{3}$c). Thermal expansion of the powders was studied with high-temperature X-ray diffraction at temperatures ranging from 25 to 700 °C. CTEs were calculated, and their dependence on the cobalt content was analyzed. Na_1+2xZr_2−xCo_x(PO₄)₃ ceramics with high relative density (93.67–99.70%) were obtained by Spark Plasma Sintering (SPS). Ceramics poor in cobalt (x = 0.1) were found to have a high relative density (98.87%) and a uniform fine-grained microstructure with a grain size of 0.5–1 µm. Bigger cobalt content leads to a smaller relative density of ceramics. During the sintering of ceramics with high cobalt content, anomalous grain growth was observed. The powder compaction rate was shown to be determined by creep and diffusion intensity in the Na_1+2xZr_2−xCo_x(PO₄)₃ crystal lattice. SPS activation energy in ceramics increased as the cobalt content grew. The microhardness and fracture toughness of ceramics did not depend on their cobalt content. Full article

Crystalline ceramics are intensively investigated as effective materials in various nuclear energy applications, such as inert matrix and accident tolerant fuels and nuclear waste immobilization. This paper presents an analysis of the current status of work in this field of material sciences. We have considered inorganic materials characterized by different structures, including simple oxides with fluorite structure, complex oxides (pyrochlore, murataite, zirconolite, perovskite, hollandite, garnet, crichtonite, freudenbergite, and P-pollucite), simple silicates (zircon/thorite/coffinite, titanite (sphen), britholite), framework silicates (zeolite, pollucite, nepheline /leucite, sodalite, cancrinite, micas structures), phosphates (monazite, xenotime, apatite, kosnarite (NZP), langbeinite, thorium phosphate diphosphate, struvite, meta-ankoleite), and aluminates with a magnetoplumbite structure. These materials can contain in their composition various cations in different combinations and ratios: Li–Cs, Tl, Ag, Be–Ba, Pb, Mn, Co, Ni, Cu, Cd, B, Al, Fe, Ga, Sc, Cr, V, Sb, Nb, Ta, La, Ce, rare-earth elements (REEs), Si, Ti, Zr, Hf, Sn, Bi, Nb, Th, U, Np, Pu, Am and Cm. They can be prepared in the form of powders, including nano-powders, as well as in form of monolith (bulk) ceramics. To produce ceramics, cold pressing and sintering (frittage), hot pressing, hot isostatic pressing and spark plasma sintering (SPS) can be used. The SPS method is now considered as one of most promising in applications with actual radioactive substances, enabling a densification of up to 98–99.9% to be achieved in a few minutes. Characteristics of the structures obtained (e.g., syngony, unit cell parameters, drawings) are described based upon an analysis of 462 publications. Full article

Calcium (titanium, zirconium) hexaorthophosphates with a [NZP] (sodium zirconium phosphate) structure belonging to the NaSiCon (Na Superionic Conductor) family were deposited by atmospheric plasma spraying onto the surfaces of Ti6Al4V substrates. (NaSiCon sensu strictu refers to solids with the chemical formula Na_1+xZr₂Si_xP_3−xO₁₂, 0 < x < 3. In a broader sense, it is also used for similar compounds where Na, Zr and/or Si are replaced by isovalent elements). The microstructure of the coatings revealed the incongruent melting of the precursor material as ascertained by electron probe microanalysis (EPMA). The adhesion of the coatings to the substrate surface was within the limits specified for biomedical coatings. The solubility of the coatings was tested by immersion in 0.2 molar tris–hydroxymethyl–amino–methane–HCl (TRIS–HCl) buffer and found to be at least one order of magnitude lower than that of conventional hydroxylapatite coatings deposited under comparable conditions. In vitro biocompatibility tests with primary rat bone marrow cells (BMCs) showed a substantial cell proliferation in the presence of fetal bovine serum. Animal tests confirmed that coatings based on calcium (titanium, zirconium) hexaorthophosphates applied to Ti6Al4V rods implanted in the femoral medulla of sheep led to the strong neoformation of dense bone at a stable interface implant-bioceramic coating without coating delamination. Hence, based on their multifarious advantageous properties in the biomedical context, CaTi_4-xZr_x(PO₄)₆ ceramics may be considered the ‘Sleeping Beauty’ of osseoconductive coatings for the stem of hip endoprostheses and dental root implants, osteosynthetic fixation devices, and bioelectric devices including bone growth stimulators. Full article