Calcination Studies of Magnesium Oxides

Magnesium carbonate, basic carbonate, and hydroxide were calcined at temperatures of 300° to 2000°C. for periods ranging from 120 hours at the low temperatures to a few minutes at the higher ones. The resulting magnesium oxides were studied by means of X‐ray powder diffraction and electron and petrographic microscopy. Only the cubic, periclase, crystal structure for MgO was observed. A small increase in the size of the unit cell was noted, however, for oxides obtained by low‐temperature calcination. Calcination of magnesium compounds was observed to take place in two distinct steps: (1) loss of gases at temperatures of 300° to 500°C. and (2) recrystallization or sintering at temperatures above 900°C. At the lower temperatures the loss of gases leaves a very porous structure with a large internal surface area and great reactivity (adsorptive power). Lattice dilation and imperfection is considered to account in part for the observed properties.