The solid state phase transformation of potassium sulfate

摘要

Potassium sulfate single crystals that are grown from aqueous solutions lose, upon the first heating, up to 1% of mass that is assumed to be water. This mass loss occurs in the vicinity of the PT from orthorhombic to hexagonal K_2SO_4. Only in the first heating run of K_2SO_4 that has not yet released water, pretransitional thermal effects can be observed in the DTA curve. If K_2SO_4 crystals are grown from solutions containing 4 wt% Cd, Cu, or Fe, only Cu or Fe can be incorporated significantly with concentrations of several 0.1%. The phase transformation temperature measured for such solid solutions depends on the heating rate. For pure K_2SO_4, the phase transformation temperature is independent of heating rate 581.3℃ and the enthalpy of transformation is (5.8 ± 0.2) kJ/mol.