Thermal decomposition of colemanite

Abstract

Thermal decomposition of colemanite Ca[B 3O 4(OH) 3]H 2O monocrystals has been investigated by thermal, X-ray, IR and optical microscopy methods at normal as well as at elevated temperatures. Investigations have revealed that thermal decomposition of colemanite occurs in the whole volume of the crystal and is divided into two independent stages: (1) formation of H 2O from OH groups and (2) breaking of H 2O and borate chains bonds and then removal of both kinds of water from the anhydrous phase of the preserved borate structure. Each process corresponds to a separate DTA peak, the second being accompanied also by loss of weight due to explosive water escape. This represents a rare event of dehydroxylation with distinct separation of H 2O formation and removal of water molecules from the parent substance.