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 24×10.sup.6 psi and a fracture toughness in excess of 1. 0 MPa. sqroot. 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% SiO. sub.2, 20-35% Al.sub.2 O.sub.3, 0-25% MgO, 0-25% ZnO, at least about 10% MgO+ZnO, 0-20% TiO.sub.2, 0-10% ZrO.sub.2, 0-2% Li.sub.2 O and 0-8% NiO. However, if the Al.sub.2 O.sub.3 constituent is present in an amount less than about 25%, the TiO.sub.2 +ZrO.sub.2 +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, P.sub.2 O.sub.5, B.sub.2 O.sub.3, Ga.sub.2 O.sub.3, 0-5% R.sub.2 O and 0- 8% of a transition metal oxide; the R.sub.2 O selected from the group consisting of Na.sub.2 O, K.sub.2 O, Rb.sub.2 O and C.sub.2 O.