Dielectric behaviour of water adsorbed by partially dehydrated potassium chrome alum

Abstract

Measurements of the real and imaginary parts of the complex dielectric constant have been made in the range 40 Hz–5 MHz during exposure of partially-dehydrated KCr alum, containing 6 of the original 12 moles of water of crystallization per mole KCr(SO₄)₂, to water vapour at 27 and 38°C. As the amount of water taken up by the residue increases, two regions of dispersion and absorption appear; the lower frequency region, characterized by a single relaxation time, is attributed to water of hydration formed during rehydration, and the higher frequency region, characterized by a distribution of relaxation times, is attributed to adsorbed water in equilibrium with water vapour. The relaxation times of the adsorbed water and water of hydration are compared with those for ice.