Internal Stress in Crystallised Glasses in the System MgO-Al₂O₃-SiO₂-TiO₂

Abstract

The glass composition, MgO 11.5%, Al₂O₃ 21.4%, SiO₂ 60.5% and TiO₂ 6.4% (by weight), was crystallised, at different temperatures ranging from 825 to 1225° under controlled conditions. The crystal phases were detected by X-ray method and the modulus of rupture, thermal expansion and density of the crystallised samples were measured. All the three properties increased to a maximum with increasing crystallisation temperature. Higher density and thermal expansion of the crystal phases have been shown to produce compressive stress on glass and, as a result, the strength increases to a maximum of 5,500 kg/cm², compared to 1,700 kg/cm² for uncrystallised glass. The relations between stress, thermal expansion and density have been discussed quantitatively.