Kinetics of Hydration of Monocaldum Aluminate

Abstract

Hydration of CaAl 2 O 4 (CA) was studied by calorimetry, analysis of the liquid phase, measurement of the combined water, and electron microscopy. During the induction period, the solution remains almost unchanged and is equilibrated temporarily with both superficially intrusion‐hydrated CA particles and Al(OH) 3 gel formed by dissociation of Al(OH) 4 – ions, the solubility of the Al(OH) 3 gel being 10 –4.24 molkg –1 at 25°C, while the intrusion‐hydrated layer on the CA particles grows following a nearly linear law to reach a critical thickness (∼3 nm at 10° to 20°C, or 12 nm at 30°C). At this point destruction of the layer occurs, nuclei of hydrous compounds are generated, and the induction period terminates. Subsequent reaction proceeds in accordance with the rate equation of Schiller based on the dissolution‐crystallization mechanism.