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US 8,157,912 B2Granted
Method of converting PCA to sapphire and converted article
AssigneeOsram Sylvania Inc.
InventorGeorge C. Wei
Life of this patent
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Abstract
Polycrystalline alumina (PCA) that has been doped with magnesium oxide is converted to sapphire by additionally doping the PCA with boron oxide and sintering to induce abnormal grain growth. The boron oxide may be added to an already formed green PCA ceramic shape by applying an aqueous boric acid solution to the green ceramic and heating the green ceramic in air to convert the boric acid to boron oxide.
Claims14
A method for converting polycrystalline alumina to sapphire, the method comprising:
- doping a ceramic article comprised of MgO-doped polycrystalline alumina with from about 80 ppm to about 8000 ppm by weight boron oxide to form a boron-oxide doped ceramic article;
- and
- sintering the boron-oxide doped ceramic article at a temperature and for a time sufficient to induce grain growth and convert the polycrystalline alumina to sapphire.
A method for converting polycrystalline alumina to sapphire, the method comprising:
- doping a ceramic article comprised of MgO-doped polycrystalline alumina with from about 80 ppm to about 8000 ppm by weight boron oxide to form a boron-oxide doped ceramic article, the ceramic article containing from about 100 ppm to about 2000 ppm by weight MgO;
- and
- sintering the boron-oxide doped ceramic article at a temperature from about 1800° C. to about 1975° C. for about 1 hour to about 40 hours to convert the polycrystalline alumina to sapphire.
Dependencies are inferred from the claim text.