Chemical Strengthening of Glass-Ceramics in the System Li2O-Al2O3-SiO2

Fine-grained glass-ceramics containing a large proportion of β-spodumene solid-solution crystals were strengthened by immersion in molten sodium and potassium salt baths. An ion-exchange reaction placed sodium or potassium ions in lithium ion sites in the β-spodumene structure. The resultant "crowding" of the structure produced a surface compressive layer. In this system, strengths (modulus of rupture on abraded specimens) in excess of 100,000 psi were realized. In a similar manner, stuffed β-quartz solid-solution glass-ceramics derived from the crystallization of Li₂O-Al₂O₃-SiO₂ glasses containing an appropriate amount of nucleating agent were strengthened by K⁺-for-Li⁺ exchange. Stable β-quartz solid-solution glass-ceramics were strengthened by Na⁺-for-Li⁺ exchange, but no significant increase in strength was obtained in the metastable β-quartz materials.