Synthetic Corundum

(via Wahroongai News, Volume 23, Number 2, February 1989)

The natural growth angle (angle to the c-axis on which the atoms of Al2O3 will stack) of the Verneuil corundum boule is 60°.

Boules grown on seeds cut at 90° to the c-axis have square cross sections.

Boules grown on seeds cut at 0° to the c-axis fracture readily…..both during growth, and during cooling or subsequent cutting.

It is not possible to cut or shape any Verneuil corundum boules until they have been adequately annealed to remove stresses induced during their growth.

Impurities of materials, bubbles, included unmelted powder particles, poor dissemination of the chromophore, and an unclean vertical blowtorch—all contribute to the production of poor quality boules.