Sintering of the Magnesium Oxide Particles in the Water Vapor and the Properties of the Products

Abstract

In order to study the influence of the atmosphere on the sintering of magnesium oxide particles, the particles prepared by rapid decpmposition of magnesium oxalate in vacmo were sintered in water vapor of 20 mmHg at the temperatures from 500 to 900eC for various times ranging from one to ten hours. The features of this sintering system were described by measurements of the crystallite size, specific surface area, and lattice constant of the products,
Eaeh crystallite of the sintered magnesium oxide particles showed a cubic form (Fig. 1), aqd the degree of secondary agglomeration between them was relatively srilight(Fig. 6). The decrease of the specific surface area observed with the increase of the sintering time was an immediate consequence of the crystallite growth, andboth the phenomena could be treated in one kinetic equation (Equation (5)). The values of the apparent activation energy for the sintering were found to be 33.3.v36.lkcal/mol. It seems likely that the sintering in water vapor is acceleratedby increase of anion mobility due to repetition of the adsorption-desorption cycle of water molecules.
Aging of the sintered magnesium oxide particles upon exposure to the air was observed for 8 minutes to 2 years (Fig. 8, 9, and Table 1). lt was found that both lattice constants, and crystallite sizes were kept constant over the whole period, but the decrease qf the spe-cific suMrface area was already observed within 3 hours after exposure to the air. Through these measurements on aging, it is suggested that degrees of interaction of magnesium exide particles with water vapor vary during the lbng period of exposure, but the lattice constants of magnesium oxide particles are not affeeted by the degrees of interaction.