Thermal Investigation of Ammonioborite (NH4)3[B_(15)O_(20)(OH)_8] · 4H2O

摘要

The thermal behavior of ammonioborite (NH4)3B_(15)O_(20)COH)8] · 4H2O is investigated using thermal X-ray diffraction, differential thermal analysis (DTA) in air and vacuum, and thermogravimetry. It is shown that the decomposition of the mineral (dehydration, dehydroxylation, deammoniation) proceeds in several stages, and the dehydration is accompanied by the amorphization. The thermal expansion of ammonioborite is sharply anisotropic. As in the case of other hydrous pentaborates, the thermal expansion is maximum in the direction in which pentaborate groups alternate with ammonium cations.