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 ZrOCl
2
and
NH
4
H
2
PO
4
salts with KNO
3
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(PO
4
)
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 KZr
2
(PO
4
)
3
of
NASICON structure or the layered compound
K
2
Zr(PO
4
)
2
. The solids obtained were
characterized by X-ray diffraction,
1
H and
31
P NMR
spectroscopy. A correlation of
31
P chemical shift and the mean
electronegativity of the obtained solids has been
proposed.
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