β-spodumene glass-ceramic materials and process for making the same

A process for making a glass-ceramic article, comprising the following steps:

• (i) mixing raw materials in amounts such that upon melting thereof a glass is produced of a composition by weight of the total glass composition, comprising 55-66% SiO2;
• 18-22% Al2O3;
• 3.5-4.1% Li2O;
• 1.8-3.2% ZnO;
• 1.5-3.0% MgO;
• 2-5% TiO2;
• 0-2% ZrO2;
• 0-4% B2O3;
• 0-8% P2O5;
• 0-2% Na2O, 0-2% K2O, 0-0.1% As2O3, 0-0.1 Sb2O3;
• and at least one fining agent;
• wherein:
• the total of B2O3 and P2O5 is at least 1.5% by weight, the total of MgO and ZnO is at least about 3.5% by weight, the total of Na2O and K2O is less than about 3.0% by weight, the total of P2O5, B2O3, Na2O and K2O is less than about 11% by weight, the weight ratio of the sum total of Na2O+K2O to the sum total of P2O5+B2O3
• (
• Na
• 2
• ⁢
• O
• +
• K
• 2
• ⁢
• O
• B
• 2
• ⁢
• O
• 3
• +
• P
• 2
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• O
• 5
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• is less than about 0.5;
• (ii) melting the mixture of raw materials of step (i) at a temperature below about 1600° C. into melted glass followed by fining and homogenization thereof;
• (iii) forming the melted glass of step (ii) into glass article;
• (iv) heating the glass article to a nucleating temperature range between 600 and 850° C. for at least 15 minutes;
• (v) heating the article to a ceramming temperature Tc between 900 and 1050° C.;
• (vi) maintaining the glass article at the ceramming temperature for a period of time over 10 minutes;
• and
• (vii) cooling the article to room temperature;
• whereby a glass-ceramic article comprising β-spodumene solid solution as the predominant crystalline phase and having a CTE from about 25 to about 700° C. of about 10-30×10−7/°C. is produced.