Kinetics of vapour phase hydration of magnesium oxide. Part 3.—Effect of iron oxides in solid solution

Abstract

The hydration of magnesiowustite, both ferrous and ferric types, containing 5 atom % iron was measured under identical conditions as in part 2 for MgO. Iron oxides in solid solution in MgO cause initial nucleation of the reaction to be greatly protracted. However, the remainder of the reaction for magnesiowustites of similar particle size follows reaction kinetics similar to those for MgO with respect to temperature and water vapour pressure. Activation energies for stoichiometric (i.e., ferrous), and non-stoichiometric (i.e., mainly ferric) magnesiowustites are 14.4 and 20.4 kcal/mole respectively. A “quasi-solution” mechanism is suggested for the hydration reaction of MgO and magnesiowustite governed by phase-boundary reaction kinetics. The progress of the phase-boundary reaction may be directly influenced by the effects of Fe²⁺ and Fe³⁺ on the MgO lattice.