Thermolysis of Hydrated Antimony Pentoxide

Abstract

The thermolysis of hydrated antimony pentoxide (HAP) has been studied in the temperature range from 25 to 1000°C using a variety of experimental techniques: thermogravimetry, X-ray diffraction, pycnometry, elemental microanalysis, and mass spectrometry. The composition and structure of the forming phases have been determined. It has been shown that the initial stages of HAP thermolysis, in the temperature range 24–500°C, include dehydration processes and the formation of anhydrous antimony pentoxide, Sb₂O₅. At temperatures above 500°C, the process includes oxygen removal, the reduction of Sb(V) to Sb(III), and the formation of Sb₆O₁₃ and Sb₂O₄. The pyrochlore structure of HAP (sp. gr. Fd3m) has been shown to persist in the course of the phase transformations at temperatures below 700°C. Analysis of our experimental data has allowed us to propose a model for crystallographic site occupancies in the pyrochlore-type structure of the phases obtained and determine their temperature stability ranges.