A new hydrothermal fluoro-zircon

Abstract

A zircon exhibiting original properties was synthesized under autogenous pressure at 150 °C for a few tens of hours. Silicon vacancies in the form of tetrahedral nests [F _n (OH) _4–n ] were identified by coupling ¹ H NMR CRAMPS and thermogravimetry. A Rietveld refinement of the structure was performed. The mechanism of the hydrothermal synthesis involves heterocondensation reactions between the Si(OH) ₄ species and a fluoro-zirconium complex rich in fluorine. Annealing of this fluoro-zircon above 500 °C produces, according to the heating profile, either monoclinic or tetragonal zirconia with a plate-like morphology having an acicular network texture.