Surface treatment of photothermally crystallizable, chemically-machinable glass-ceramic articles

Claim 1

A method for rendering a photothermally crystallizable, chemically-machinable, glass-ceramic article non-sticking with respect to the reaction products of moisture and organic materials, which comprises the steps of: (a) a batch is melted for a glass consisting essentially, expressed in weight percent on the oxide basis, of 5.5-15% Li 2 O, 2-25% Al 2 O 3 , the ratio Al 2 O 3 :Li 2 O being less than about 1.7:1, 60-85% SiO 2 , and a photosensitive metal in the indicated proportions 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 2 O, the sum of those components constituting at least 90% of the total composition; (b) the melt is simultaneously cooled to a glass and an article of desired geometry shaped therefrom; (c) the glass article is subjected to ultraviolet radiation to form a latent image in the glass; (d) the glass article is heated to a temperature between the annealing point and the softening point of the glass for a time sufficient to opacify the glass by forming siliceous crystallites therein, including lithium metasilicate, in an amount sufficient to provide a crystalline structure which is rigid enough to prevent distortion of the article upon heating to a softening point of the original glass; (e) the article is heated to a temperature above the softening point of the original glass and about 800° C., but not above 950° C., to cause further crystallization, including conversion of lithium metasilicate to a lithium-containing silicate having a lower weight percentage of lithium therein, thereby transforming the article to a glass-ceramic article; (f) exposing the glass-ceramic article to SO 2 vapors at a temperature between about 350°-600° C. for about 1-10 hours to cause a reaction to occur to a depth of at least 50 microns (˜0.002") in the surface of the article between Li + ions and SO 2 vapors to form a water soluble deposit of Li 2 SO 3 and/or Li 2 SO 4 thereon; and (g) removing the deposit of Li 2 SO 3 and/or Li 2 SO 4 from the surface of the glass-ceramic article.

Claim 2

A method for rendering a photothermally crystallizable, chemically-machinable, glass-ceramic article non-sticking with respect to the reaction products of moisture and organic materials, which comprises the steps of: (a) a batch is melted for a glass consisting essentially, expressed in weight percent on the oxide basis, of 5.5-15% Li 2 O, 2-25% Al 2 O 3 , the ratio Al 2 O 3 :Li 2 O being less than about 1.7:1, 60-85% SiO 2 , and a photosensitive metal in the indicated proportions 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 2 O, the sum of those components constituting at least 90% of the total composition; (b) the melt is simultaneously cooled to a glass and an article of desired geometry shaped therefrom; (c) the glass article is subjected to ultraviolet radiation to form a latent image in the glass; (d) the glass article is heated to a temperature between the annealing point and the softening point of the glass for a time sufficient to opacify the glass by forming siliceous crystallites therein, including lithium metasilicate, in an amount sufficient to provide a crystalline structure which is rigid enough to prevent distortion of the article upon heating to a softening point of the original glass; (e) the article is heated to a temperature above the softening point of the original glass and about 800° C., but not above 950° C., to cause further crystallization, including conversion of lithium metasilicate to a lithium-containing silicate having a lower weight percentage of lithium therein, thereby transforming the article to a glass-ceramic article; (f) exposing the glass-ceramic article to SO 2 vapors at a temperature between about 350°-600° C. for about 1-10 hours to cause a reaction to occur to a depth of at least 50 microns (˜0.002") in the surface of the article between Li + ions and SO 2 vapors to form a water soluble deposit of Li 2 SO 3 and/or Li 2 SO 4 thereon; and (g) removing the deposit of Li 2 SO 3 and/or Li 2 SO 4 from the surface of the glass-ceramic article.