| 摘要 |
<p>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% Na2O, 7-13% K2O, 30-36% Al2O3, 35-43% SiO2, and 6-10% RO2, wherein RO2 consists of 6-10% TiO2 and 0-4% ZrO2, wherein the molar ratio Al2O3:SiO2 is >0.5 but <0.6 and the molar ratio K2O:Na2O is >1:3 but <1 and contains nepheline solid solution crystals corresponding to the formula Na8-xKxAl8Si8O32, 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+ ions replace at least part of the Na+ ions in the nepheline solid solution crystals to convert those crystals to kalsilite.</p> |
