High expansion glass-ceramic articles

Abstract

The present invention relates to the production of photothermally crystallizable, chemically-machinable glass-ceramic articles exhibiting coefficients of thermal expansion over the temperature interval of 20.degree.-400.degree. C. between 120-160.times.10.sup.-7 /.degree. C. Base glass articles having compositions consisting essentially, in weight percent, of 5.5-15% Li.sub.2 O, 2-25% Al.sub.2 O.sub.3, the weight ratio Al.sub.2 O.sub.3 :Li.sub.2 O being less than 1.7:1, 60-85% SiO.sub.2, and at least one photosensitive metal in the indicated proportion selected from the group of 0.001-0.03% gold, computed as Au, 0.001-0.3% silver, computed as AgCl, and 0.001-1% copper, computed as Cu.sub.2 O, are first exposed to ultraviolet radiations to develop a latent image therein, then heated to a temperature between the annealing and softening points thereof to generate metallic nuclei therein and the growth of lithium metasilicate particles thereon, and, finally, heated to a temperature in excess of 700.degree. C., but less than 800.degree. C., to effect an essentially crystalline article, including the conversion of a portion of the lithium metasilicate crystals to lithium disilicate. Quartz and/or cristobalite will also be formed.

Dependencies are inferred from the claim text.