PERALUMINA-NEPHELINE/KALCILITE GLASS-CERAMIC AND MANUFACTURE THEREOF

摘要

The present invention is concerned with glass-ceramic articles which are extremely resistant to impact and spontaneous delayed breakage, are capable of being sawn with a diamond wheel to a depth of over one- third the cross section thereof without breakage, and exhibit modulus of rupture values of at least 150,000 psi. The articles consist of a body portion and an integral surface compression layer having a depth of at least 0.005". The body portion consists essentially, in weight percent, of about 8-13% Na.sub.2 O, 7-13% K.sub.2 O, 30-36% Al.sub.2 O.sub.3, 35- 43% SiO.sub.2, and 6-10% RO.sub.2, wherein RO.sub.2 consists of 6-10% TiO. sub.2 and 0-4% ZrO.sub.2, wherein the molar ratio Al.sub.2 O.sub.3 :SiO. sub.2 is 0.5 but 0.6 and the molar ratio K.sub.2 O:Na.sub.2 O is 1:3 but 1 and contains nepheline solid solution crystals corresponding to the formula Na.sub.8-x K.sub.x Al.sub. 8 Si.sub.8 O.sub. 32, with x varying from 0.25-4.73, as the predominant crystal phase. The surface layer contains kalsilite as the predominant crystal phase and is produced by subjecting the base glass-ceramic article to an ion exchange reaction wherein K.sup.+ ions replace at least part of the Na.sup.+ ions in the nepheline solid solution crystals to convert those crystals to kalsilite.