EFFECT OF PHOSPHORIC ACID ON THERMAL PHASE TRANSFORMATION OF CRYSTALLINE ALUMINIUM PHOSPHATES

Abstract

The effect of phosphoric acid on thermal transformation of crystal-line aluminium orthophosphate (AlPO₄) has been investigated by means of PXD, TG-DTA, MAS-NMR, and SEM. The used crystal forms of AlPO₄ were berlinite, tridymite-form, and cristobalite-form. Tridymite- and cristobalite-form in the presence of phosphoric acid were exothermaly transformed to berlinite at 150 °C Cristobalite-form more easily changed to berlinite than tridymite-form The phosphoric acid plays an important role in the phase transformation of tridymite- or cristobalite-form (high temperature-phases) to berlinite (low temperature-phase) at low temperature.