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The structure, microstructure, coefficient of thermal expansion (CTE), and mechanical properties of Na1+2xZr2−xCox(PO4)3 ceramics (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were studied. Na1+2xZr2−xCox(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 R3¯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. Na1+2xZr2−xCox(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 Na1+2xZr2−xCox(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.

The structure, microstructure, coefficient of thermal expansion (CTE), and mechanical properties of Na1+2xZr2−xCox(PO4)3 ceramics (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were studied. Na1+2xZr2−xCox(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 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. Na1+2xZr2−xCox(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 Na1+2xZr2−xCox(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. [ABSTRACT FROM AUTHOR]

The crystal-chemical approach has been applied to design materials with regulated thermal expansion. To that end, model simulations have been performed for compositions of phosphates that yield solid solutions of the following type Na1 + 2xZr2 –xCux(PO4)3 and Ca0.5 +xZr2 –xCux(PO4)3, 0.1 ≤ x ≤ 0.5 with the expected structure of NaZr2(PO4)3 (NZP). The new phosphates have been prepared by solid-state reactions and characterized by X‑ray diffraction, IR spectroscopy, and scanning electron microscopy. The compounds have been shown to crystallize in the NZP structure, with a particle size from 0.1 to 1 μm. The thermal expansion of the compounds has been studied by high-temperature X-ray diffraction in the temperature range from 25 to 700°C. Linear, average, and volume coefficients of thermal expansion and anisotropy of thermal expansion have been calculated and analyzed in relation to composition of Na, Zr, Cu and Ca, Zr, Cu phosphates in the studied sets. [ABSTRACT FROM AUTHOR]

Abstract—: Ca0.75 + 0.5xZr1.5Fe0.5(PO4)3 -x(SiO4)x (x = 0-0.5) solid solutions have been synthesized by a sol-gel process and characterized by X-ray diffraction, IR spectroscopy, and differential scanning calorimetry. As expected, the synthesized phosphatosilicates crystallize in a NaZr2(PO4)3-type structure (trigonal symmetry, sp. gr. Rc). The thermal expansion of the solid solutions has been studied by high-temperature X-ray diffraction in the temperature range from 25 to 800°C. Their thermal expansion parameters have been calculated and analyzed as functions of composition. High-density ceramics based on the Ca0.875Zr1.5Fe0.5(PO4)2.75(SiO4)0.25 phosphatosilicate have been produced by spark plasma sintering and their structure and properties have been studied in detail. [ABSTRACT FROM AUTHOR]

Ca0.5(1 + x)Zr2-xFex(PO4)3 phosphates have been synthesized by a sol-gel process. The individual compounds and solid solutions obtained crystallize in the NaZr2(PO4)3 structure (trigonal symmetry, sp. gr. R3¯). Using high-temperature X-ray diffraction, we have determined their thermal expansion parameters in the temperature range from 25 to 800°C. With increasing x, the magnitudes of their linear thermal expansion coefficients and thermal expansion anisotropy decrease. Most of the synthesized phosphates can be rated as low-thermal-expansion compounds and can be regarded as materials capable of withstanding thermal “stress.” [ABSTRACT FROM AUTHOR]

Preliminary data were obtained on the immobilization of various heterovalent ions present in the two selected high-level nuclear waste compositions. The entire set of ions present in the waste compositions were immobilized into sodium zirconium phosphate (NZP) structure. The waste loading was in the range 5-25%. The two types of wasteforms loaded with the simulated high-level waste compositions were characterized by powder X-ray diffraction, FT-IR, TGA/DTA, and scanning electron microscopy. The difference in the compositions of the two simulated wastes was reflected in the waste loading percentage and the crystallization of the wasteforms into NZP structure. Up to 12% waste loading, single phase isostructural with NZP was obtained as a major product in the case of the first waste composition. An increase in the waste loading led to the segregation of ZrPO as a secondary phase. With the second waste composition, an NZP-like phase was obtained as the major product even at 25% waste loading. [ABSTRACT FROM AUTHOR]

Abstract: Chromium-containing NASICON-related phosphates of the type Na(1+x)Cr x M(2−x)P3O12) (M=Ti, Hf, Zr) have been synthesised by solid state reaction and structurally characterised by Rietveld refinement of the powder X-ray diffraction data. Materials of composition A(1+x)/2Cr x Zr(2−x)P3O12 (A=Cd, Ca, Sr), have also been prepared and characterised. The crystal structure of Na(1+x)Cr x M(2−x)P3O12 corresponds to R-3c symmetry for x values ranging from 0.15 to 2.00, whereas compounds of composition A(1+x)/2Cr x Zr(2−x)P3O12 corresponding to R-3c are obtained when x ≤1.00 for Sr2+ and Ca2+, and x ≤1.50 for Cd2+. The polarizing effect of the two different metal ions A and M on the phosphorus atom and the P–O bond was studied by both 31P MAS NMR and infrared spectroscopy and shows that the electron density on the phosphorus, and thus the strength of the P–O bonds, are affected by both the interstitial (A) and the structural (M) metal ions. [Copyright &y& Elsevier]