Chemically strengthened lithium aluminosilicate glass having high strength effective to resist fracture upon flexing

Abstract

Chemically strengthened lithium aluminosilicate glass is characterized by a surface compression of at least 100,000 psi and a compression case depth of at least 600 microns. The glass also may be characterized by a compression at 50 microns below a surface of the glass that is at least 30,000 psi. A method of making this glass includes providing a lithium aluminosilicate glass having a composition comprising (in weight %): LiO in an amount ranging from 3 to 9%, NaO+KO in an amount not greater than 3%, and AlOin an amount ranging from 7 to 30%. The composition provides the glass with an annealing point temperature of at least 580° C. A mixed potassium and sodium salt bath is provided comprising predominantly potassium salt. A ratio of moles of sodium salt to moles of potassium salt in the mixed salt bath can range from 1:10 to 1:2. The temperature of the salt bath is maintained in a range of 450° C. up to an annealing point temperature of the glass. The glass is immersed in the salt bath for a period ranging from 2 to 96 hours. The inventive strengthened glass has high strength effective to resist fracture upon flexing and includes: bullet-resistant glass, blast-resistant glass, glass for armored defense vehicles, windows for government buildings, windows for monuments, windows for vehicles, train transparencies, aircraft transparencies, hurricane-resistant windows, earthquake-resistant windows, bank teller windows, display cases, and ATM touch panels.