Phase changes during heating of magnesium ammonium phosphate hexahydrate and magnesium hydrogen phosphate trihydrate to high temperatures

Abstract

Magnesium ammonium phosphate hexahydrate MgNH₄PO₄,6H₂O and magnesium hydrogen phosphate trihydrate MgHPO₄,3H₂O have been heated to temperatures up to 1220° and X-ray powder photographs taken of the products. Both substances decompose during the process and gradually change first into an amorphous phase and then into crystalline magnesium pyrophosphate. The incandescence which appears on the ignition of these substances may be associated with the dimerisation of the ion HPO₄^2–.