Heats of immersion of pure and doped magnesia in cyclohexane. Effects of micropores

Abstract

Heats of immersion of pure and doped magnesia in cyclohexane were measured at 35°C for samples heated at different temperatures in vacuo. For the pure samples, rise in temperature of thermal treatment leads to a gradual decrease in the heats of immersion normalized per unit area (h¹, ergs cm^–2), till a certain limiting value of 44.5 ergs cm^–2 is reached. Pore structure analyses lead to certain correlations between the heat of immersion and the fraction of the total surface located in micropores. Pores which could effectively play a role in altering the heat of immersion were assessed to possess a mean hydraulic radius of 10 Å or less. Doping on the surface leads to the same behaviour, except that the decline in the heat of immersion is followed by an increase in the hⁱ values for the high temperature samples heated at or above 560°C. For the doped samples, formation of a solid solution between Li⁺ and Mg²⁺, and a spinel between Al³⁺ and Mg²⁺ complicates the results obtained.