Thermo-shock resistant sapphire for IR windows and domes and processes for its manufacture

摘要

A sapphire article is strengthened by a process comprising: (i) exposing at least a portion of the article to magnesium vapour to diffuse magnesium into the article, (ii) heating the article at 1800-2000[deg]C for 2-24 hours in the absence of magnesium vapour to homogeneously distribute the magnesium throughout the article, (iii) quenching the article to 1200-1450[deg]C at a cooling rate of at least 10[deg]C/min., and (iv) annealing the article for 0.1-60 hours to precipitate magnesium aluminate spinel particulates having the spinel structure to precipitation-harden the article. Also claimed is the above process wherein the sapphire consists of Al2O3 having a corundum crystal structure and (i) the magnesium is produced from magnesia in a hydrogen atmosphere at 1750[deg]C for 5 minutes so as to convert a portion of the sapphire adjacent to the outer layer to magnesium aluminate spinel, (ii) the article is heated at 1900[deg]C for 6 hours to distribute the magnesium, (iii) the article is quenched to 1450[deg]C, and (iv) the article is annealed for 1 hour.