Molten salt preparation of K–Zr ternary phosphates

Abstract

Mixed phosphates of K and Zr have been prepared by means of the reactions of hydrated ZrOCl₂ and NH₄H₂PO₄ salts with KNO₃ in the temperature range 250–550 °C. Molten salt reactions were studied by thermogravimetry and mass spectrometry of the evolved gases. Thermal analysis of the ternary mixture demonstrated that a strongly exothermic mass loss occurs at ca. 250 °C, due to the reaction producing a KHZr(PO₄)₂ phase. Depending on the reaction conditions, different solids can be obtained, including dispersed zirconia superficially doped with phosphate or crystalline ternary phosphates such as KZr₂(PO₄)₃ of NASICON structure or the layered compound K₂Zr(PO₄)₂ . The solids obtained were characterized by X-ray diffraction, ¹H and ³¹P NMR spectroscopy. A correlation of ³¹P chemical shift and the mean electronegativity of the obtained solids has been proposed.

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