High modulus glass-ceramics containing fine grained spinel-type crystals

摘要

This invention is directed at glass-ceramic articles, and methods for producing such articles, exhibiting Young's modulus between about 14 to 24 x 10⁶ psi and a fracture toughness in excess of 1.0 MPa√in. The crystal phase assemblage is comprised predominately of generally uniformly-sized spinel-type crystals which are uniformly dispersed within a highly siliceous residual glass matrix phase. The composition of these glass-ceramic articles is consists essentially, expressed in terms of weight percent on the oxide basis, of 35-60% SiO₂, 20-35% Al₂O₃, 0-25% MgO, 0-25% ZnO, at least about 10% MgO+ZnO, 0-20% TiO₂, 0-10% ZrO₂, 0-2% Li₂O and 0-8% NiO. However, if the Al₂O₃ constituent is present in an amount less than about 25%, the TiO₂+ZrO₂+NiO amount should be at least 5%. The composition may also contain up to 5% of optional constituents selected from the group consisting of BaO, CaO, PbO, SrO, P₂O₅, B₂O₃, Ga₂O₃, 0-5% R₂O and 0-8% of a transition metal oxide; the R₂O selected from the group consisting of Na₂O, K₂O, Rb₂O and Cs₂O.