Transparent glass-ceramic articles

Claim 1

A thermally crystallizable glass exhibiting a liquidus viscosity greater than 700 Pa.s which can be thermally crystallized in situ to a transparent glass-ceramic article demonstrating a linear coefficient of thermal expansion (20°-700° C.) of 0±3×10 -7 /°C., containing β-quartz solid solution as the predominant crystal phase, and capable of being crystallized in situ to a plate form exhibiting a distortion of less than 0.1% of its diagonal dimension when subjected to a very short thermal crystallization treatment, said glass consisting essentially, expressed in terms of weight percent on the oxide basis, of ______________________________________ SiO.sub.2 65-70 MgO + BaO + SrO 1.1-2.3 Al.sub.2 O.sub.3 18-19.8 ZrO.sub.2 1.0-2.5 Li.sub.2 O 2.5-3.8 As.sub.2 O.sub.3 0-1.5 MgO 0.55-1.5 Sb.sub.2 O.sub.3 0-1.5 ZnO 1.2-2.8 As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0.5-1.5 TiO.sub.2 1.8-3.2 Na.sub.2 O 0-<1.0 BaO 0-1.4 K.sub.2 O 0-<1.0 SrO 0-1.4 Na.sub.2 O + K.sub.2 O 0-<1.0 BaO + SrO 0.4-1.4 2.8Li.sub.2 O + 1.2ZnO/ >1.8 5.2MgO ______________________________________

Claim 24

A method for making a transparent glass-ceramic article demonstrating a linear coefficient of thermal expansion (20°-700° C.) of 0±3×10 -7 /°C., containing β-quartz solid solution as the predominant crystal phase, and, when in plate form, exhibiting a distortion less than 0.1% of its diagonal dimension consisting essentially of the steps: (a) melting a batch for a glass consisting essentially, expressed in terms of weight percent on the oxide basis, of ______________________________________ SiO.sub.2 65-70 MgO + BaO + SrO 1.1-2.3 Al.sub.2 O.sub.3 18-19.8 ZrO.sub.2 1.0-2.5 Li.sub.2 O 2.5-3.8 As.sub.2 O.sub.3 0-1.5 MgO 0.55-1.5 Sb.sub.2 O.sub.3 0-1.5 ZnO 1.2-2.8 As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0.5-1.5 TiO.sub.2 1.8-3.2 Na.sub.2 O 0-<1.0 BaO 0-1.4 K.sub.2 O 0-<1.0 SrO 0-1.4 Na.sub.2 O + K.sub.2 O 0-<1.0 BaO + SrO 0.4-1.4 2.8Li.sub.2 O + 1.2ZnO/ >1.8 5.2MgO ______________________________________ (b) cooling said melt to a temperature below the transformation range thereof and simultaneously forming a glass article of a desired configuration therefrom; (c) raising the temperature of said glass article at a rate of about 50°-80° C./minute to the temperature range of about 670°-800° C.; (d) retaining said glass article within the temperature range of about 670°-800° C. for about 15-25 minutes to develop nuclei therein; (e) raising the temperature of said nucleated glass article at a rate sufficient to bring said glass article within the temperature range of about 900°-960° C. in about 15-30 minutes; (f) retaining said nucleated glass article within the temperature range of about 900°-960° C. or about 10-25 minutes to grow β-quartz solid solution crystals on said nuclei; and thereafter (g) rapidly cooling said crystallized article to room temperature.

Claim 25

A method for making a transparent glass-ceramic article demonstrating a linear coefficient of thermal expansion (20°-700° C.) of 0±3×10 -7 /°C., containing β-quartz solid solution as the predominant crystal phase, and, when in plate form, exhibiting a distortion less than 0.1% of its diagonal dimension consisting essentially of the steps: (a) melting a batch for a glass consisting essentially, expressed in terms of weight percent on the oxide basis, of ______________________________________ SiO.sub.2 65-70 MgO + BaO + SrO 1.1-2.3 Al.sub.2 O.sub.3 18-19.8 ZrO.sub.2 1.0-2.5 Li.sub.2 O 2.5-3.8 As.sub.2 O.sub.3 0-1.5 MgO 0.55-1.5 Sb.sub.2 O.sub.3 0-1.5 ZnO 1.2-2.8 As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0.5-1.5 TiO.sub.2 1.8-3.2 Na.sub.2 O 0-<1.0 BaO 0-1.4 K.sub.2 O 0-<1.0 SrO 0-1.4 Na.sub.2 O + K.sub.2 O 0-<1.0 BaO + SrO 0.4-1.4 2.8Li.sub.2 O + 1.2ZnO/ >1.8 5.2MgO ______________________________________ (b) cooling said melt to a temperature below the transformation range thereof and simultaneously forming a glass article of a desired configuration therefrom; (c) raising the temperature of said glass article at a rate of about 50°-80° C./minute to the temperature range of about 670°-800° C.; (d) retaining said glass article within the temperature range of about 670°-800° C. for about 15-25 minutes to develop nuclei therein; (e) raising the temperature of said nucleated glass article at a rate sufficient to bring said glass article within the temperature range of about 900°-960° C. in about 15-30 minutes; (f) retaining said nucleated glass article within the temperature range of about 900°-960° C. or about 10-25 minutes to grow β-quartz solid solution crystals on said nuclei; and thereafter (g) rapidly cooling said crystallized article to room temperature.