Beta-spodumene glass-ceramics exhibiting excellent dimensional stability

Claim 1

A method for making an opaque a glass-ceramic article demonstrating an average coefficient of thermal expansion (0°-1000° C.) less than about 20 × 10 -7 /° C. and a change in length of less than about 750 PPM after an exposure of 1000 hours to temperatures up to 950° C. consisting essentially of fine-grained crystals of beta-spodumene solid solution, mullite and/or corundum, ZrTiO 4 solid solution, and, occasionally, ZrO 2 solid solution uniformly dispersed within a glassy matrix, said crystals constituting at least 75% by volume of the article which consists of the steps: a. melting a batch for a glass consisting essentially, in weight percent on the oxide basis, of 3.7-7.5% Li 2 O, 18.5-33% Al 2 O 3 , 55-75% SiO 2 , and 3.4-5.0% Ro 2 , wherein RO 2 consists of 1.5-2.5% TiO 2 and 1-2.7% ZrO 2 in a molar ratio TiO 2 :ZrO 2 between about 3:1-1:1; b. simultaneously cooling the melt to at least within the transformation range and shaping a glass article of a desired configuration therefrom; c. heating said glass article to a temperature between about 1150°-1350° C. to cause the crystallization in situ of fine-grained crystals of beta-spodumene solid solution, mullite and/or corundum, ZrTiO 4 solid solution, and, occasionally, ZrO 2 solid solution; and then d. cooling the crystallized article to room temperature.

Claim 2

A method for making an opaque a glass-ceramic article demonstrating an average coefficient of thermal expansion (0°-1000° C.) less than about 20 × 10 -7 /° C. and a change in length of less than about 750 PPM after an exposure of 1000 hours to temperatures up to 950° C. consisting essentially of fine-grained crystals of beta-spodumene solid solution, mullite and/or corundum, ZrTiO 4 solid solution, and, occasionally, ZrO 2 solid solution uniformly dispersed within a glassy matrix, said crystals constituting at least 75% by volume of the article which consists of the steps: a. melting a batch for a glass consisting essentially, in weight percent on the oxide basis, of 3.7-7.5% Li 2 O, 18.5-33% Al 2 O 3 , 55-75% SiO 2 , and 3.4-5.0% Ro 2 , wherein RO 2 consists of 1.5-2.5% TiO 2 and 1-2.7% ZrO 2 in a molar ratio TiO 2 :ZrO 2 between about 3:1-1:1; b. simultaneously cooling the melt to at least within the transformation range and shaping a glass article of a desired configuration therefrom; c. heating said glass article to a temperature between about 1150°-1350° C. to cause the crystallization in situ of fine-grained crystals of beta-spodumene solid solution, mullite and/or corundum, ZrTiO 4 solid solution, and, occasionally, ZrO 2 solid solution; and then d. cooling the crystallized article to room temperature.