Dielectric behaviour of adsorbed water during dehydration of potassium chrome alum
Abstract
Dielectric measurements at 4 MHz have been used to investigate the behaviour of adsorbed water during dehydration of potassium chrome alum at –23° to 70 °C, in vacuo and in air. The dielectric absorption is generally independent of changes in surface area during dehydration, and anomalous behaviour at temperatures below ca. 30 °C is attributed to formation of a partly amorphous product. The rate of dehydration is controlled by diffusion of water vapour, according to the equation, α=k1(t½–ti½), where α is the fractional decomposition and ti is the apparent induction period. Activation energies derived from the variations of k1 and ti with temperature are 11·5 ± 0·2 and 15 ± 2 kcal mol–1 respectively.