The solid state phase transformation of potassium sulfate

TL;DR

This study investigates the phase transformation of potassium sulfate, including water loss during heating, effects of metal impurities, and the transformation's thermal characteristics.

Contribution

It provides new insights into the phase transformation temperature, water loss, and impurity incorporation in potassium sulfate crystals.

Findings

Mass loss of up to 1% due to water during initial heating.

Transformation temperature is 581.3°C, independent of heating rate for pure K2SO4.

Cu and Fe impurities are incorporated significantly, affecting phase behavior.

Abstract

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 K2SO4. Only in the first heating run of K2SO4 that has not yet released water, pretransitional thermal effects can be observed in the DTA curve. If K2SO4 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 K2SO4, the phase transformation temperature is independent on heating rate 581.3 deg. C and the enthalpy of transformation is (5.8+/-0.2) kJ/mol.