| 摘要 |
PROBLEM TO BE SOLVED: To obtain a glass excellent in breaking strength and chemical resistance and useful as a glass substrate for hard disks, by subjecting a glass of a specified composition to a specific chemical reinforcement treatment. SOLUTION: This glass is obtained by subjecting a glass with the composition described below to such chemical reinforcement treatment as to be 0.5-20h in immersion time at 350-550 deg.C in an ion exchange bath containing >90wt.% of a potassium salt (e.g. KNO3 ). The composition is as follows (on an oxide basis): SiO2 : 63.0-67.5mol%, Al2 O3 : 9.5-12.0mol%, Na2 O: 8.5-15.5mol%, K2 O: 2.5-4.0mol%, MgO: 3.0-9.0mol%,ΣCaO+SrO+BaO+ZnO: 0-2.5mol%, TiO2 : 0.5-1.5mol%, CeO2 : 0.02-0.5mol%, As2 O3 : 0-0.35mol%, SnO2 : 0-1.0mol%, F2 : 0.05-2.6mol%, under the following conditions: SiO2 /Al2 O3 =5.3-6.85, Na2 O/K2 O =3.0-5.6, Al2 O3 /K2 O=2.8-3.6, Al2 O3 /(TiO2 +CeO2 )=7.6-18.5.
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