Process for production of chemically prestressed glass
AssigneeSchott Glaswerke
InventorBurkhard Speit
Life of this patent
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Abstract
The process for producing a chemically prestressed glass of very high surface quality includes subjecting an Li.sub.2 O-free starting glass from the SiO.sub.2 -Al.sub.2 O.sub.3 -M.sub.2 O-MO system which also contains TiO.sub.2, CeO.sub.2 and F.sub.2 to chemical ion exchange by immersing it in a potassium salt bath at a temperature between 350.degree. C. and 550.degree. C. and at a residence time of between 0.5 and 20 hours to form the chemically prestressed glass. In a preferred embodiment of the process, the potassium salt bath contains a potassium nitrate melt and the glass is polished after prestressing. The chemically prestressed glass is particularly useful for making hard disks.
Claims8
A process for producing a chemically prestressed glass of high breaking strength and high chemical resistance, said process comprising chemically prestressing a starting glass having the composition (in mol %, based on oxides):
- SiO.sub.2 from 63.0 to 67.5 mol %,
- Al.sub.2 O.sub.3 from 9.5 to 12.0 mol %,
- Na.sub.2 O from 8.5 to 15.5 mol %,
- K.sub.2 O from 2.5 to 4.0 mol %,
- MgO from 3.0 to 9.0 mol %,
- .SIGMA. CaO+SrO+BaO+ZnO from 0 to 2.5 mol %,
- TiO.sub.2 from 0.5 to 1.5 mol %,
- CeO.sub.2 from 0.02 to 0.5 mol %,
- As.sub.2 O.sub.3 from 0 to 0.35 mol %,
- SnO.sub.2 from 0 to 1.0 mol %, and
- F.sub.2 from 0.05 to 2.6 mol %,
- wherein a molar ratio of said SiO.sub.2 to said Al.sub.2 O.sub.3 in said starting glass is between 5.3 and 6.85, a molar ratio of said Na.sub.2 O to said K.sub.2 O in said starting glass is between 3.0 and 5.6, a molar ratio of said Al.sub.2 O.sub.3 to said K.sub.2 O in said starting glass is between 2.8 and 3.6 and a molar ratio of said Al.sub.2 O.sub.3 to at total amount of said TiO.sub.2 and said CeO.sub.2 is from 7.6 to 18.5;
- in an ion exchange bath comprising more than 90% by weight of at least one potassium salt at a temperature between 350.degree. C. and 550.degree. C. and at a residence time of between 0.5 and 20 hours to form the chemically prestressed glass.
Dependencies are inferred from the claim text.