Thermal behavior of acid phosphate salts Ca2MH7(PO4)4⋅2H2O (M = K+, NH4 +) and CaK3H(PO4)2

Abstract

New knowledge about various aspects of little-known acid salts is of great scientific and practical importance in view of their potential application in different areas such as proton conductors. For the first time, the thermal behavior of three acid phosphate salts, dicalcium potassium heptahydrogen tetrakis(phosphate) dihydrate (Ca2KH7(PO4)4⋅2H2O), dicalcium ammonium heptahydrogen tetrakis(phosphate) dihydrate (Ca2(NH4)H7(PO4)4⋅2H2O) and calcium tripotassium hydrogenbis(phosphate) (CaK3H(PO4)2), has been investigated. By means of simultaneous thermogravimetry, differential thermal and mass spectrometry analyses (TG/DTA/MS) he schemes of their thermal decomposition have been proposed. The two isostructural compounds Ca2KH7(PO4)4⋅2H2O and Ca2(NH4)H7(PO4)4⋅2H2O are stable up to 90 – 95 ◦C and then undergo multiple-steps thermal decomposition process owing to dehydration of the crystallization water and dehydration-condensation. The anhydrous salt CaK3H(PO4)2 exhibits very high thermal stability up to 530 ◦C. The products of the thermal decomposition have been identified.