Crystallization and Chemical Strengthening of Stuffed β‐Quartz Glass‐Ceramics

Abstract

Metastable solid solutions with the β‐quartz structure can be crystallized from most glasses in the system SiO 2 ‐Mg(AlO 2 ) 2 ‐LiAlO 2 as well as from many containing the additional components Zn(AlO 2 ) 2 Al(AlO 2 ) 3 , Li 2 ZnO 2 , and Li 2 BeO 2 . Internal nucleation is afforded by additions of ZrO 2 or TiO 2 . Either transparent or opaque crystalline materials can be formed from glasses containing about 70% SiO 2 . The transparency is due to a combination of low birefringence in the major stuffed β‐quartz phase and minute crystal size. Thermal expansions vary from ‐20 to +50 × 10 −7 /°C. Thermal stability is highly variable. Breakdown products include spinel, cordierite, β‐spodumene, willemite, mullite, and cristobalite. Magnesian compositions can be strengthened by a 2Li + ⇌ Mg 2+ ionexchange reaction. Abraded flexural strengths range from 30,000 to 160,000 psi.