Glass substrates and methods of annealing the same
A method for forming a glass substrate comprises the steps of forming a glass blank with opposing substantially planar surfaces and at least one edge, coating the glass blank in silica-alumina nanoparticles, the silica-alumina nanoparticles comprising an inner core of silica with an outer shell of alumina, annealing the coated glass blank to form a conformal coating of silica-alumina around the glass blank, and polishing the coated glass blank to remove the conformal coating of silica-alumina from the opposing substantially planar surfaces thereof.
1. A method for forming a glass substrate, comprising the steps of:
forming a glass blank with opposing substantially planar surfaces and at least one edge;
coating the glass blank in silica-alumina nanoparticles, the silica-alumina nanoparticles comprising an inner core of silica with an outer shell of alumina;
annealing the coated glass blank to form a conformal coating of silica-alumina around the glass blank; and
polishing the coated glass blank to remove the conformal coating of silica-alumina from the opposing substantially planar surfaces thereof and to remove a portion of the glass substrate from each of the opposing substantially planar surfaces.
2. The method according to claim 1 , wherein the step of coating the glass blank in the silica-alumina nanoparticles comprises soaking the glass blank in a colloidal suspension comprising the silica-alumina nanoparticles.
3. The method according to claim 2 , wherein the colloidal suspension has a concentration of between about 0.01 weight percent and 0.30 weight percent silica-alumina nanoparticles.
4. The method according to claim 2 , wherein the colloidal suspension has a concentration of between about 0.08 weight percent and 0.10 weight percent silica-alumina nanoparticles.
5. The method according to claim 1 , wherein the silica-alumina nanoparticles adhere to the glass blank due to a charge difference between the silica-alumina nanoparticles and the glass blank.
6. The method according to claim 1 , wherein the step of coating the glass blank in the silica-alumina nanoparticles comprises forming a conformal layer of the silica-alumina nanoparticles less than about 1 micron around the glass blank.
7. The method according to claim 1 , wherein the silica-alumina nanoparticles have an average diameter of less than about 50 nm.
8. The method according to claim 1 , wherein the silica-alumina nanoparticles have an average diameter of less than about 20 nm.
9. The method according to claim 1 , wherein the step of annealing the coated glass blank comprises heating the coated glass blank to a temperature at or above a glass transition temperature of the coated glass blank.
10. The method according to claim 9 , wherein the step of annealing the coated glass blank further comprises maintaining the coated glass blank at a temperature at or above a glass transition temperature of the coated glass blank for between about 0.5 and 10 hours.
11. The method according to claim 1 , wherein the step of annealing the coated glass blank comprises stacking a second coated glass blank directly upon the coated glass blank, and wherein the silica-alumina nanoparticles prevent the coated glass blank from fusing to the second coated glass blank.
12. The method according to claim 11 , wherein pressure exerted by the second coated glass blank upon the coated glass blank helps to flatten one of the opposing substantially planar surfaces of the coated glass blank.
13. The method according to claim 1 , wherein the step of annealing the coated glass blank comprises stacking a weight upon the coated glass blank to flatten one of the opposing substantially planar surfaces of the coated glass blank.
14. The method according to claim 1 , wherein the portion removed from each of the opposing substantially planar surfaces is between about 5 and 50 microns thick.
15. The method according to claim 1 , wherein after the step of polishing the opposing substantially planar surfaces, the conformal coating of silica-alumina remains along the at least one edge of the glass blank.
16. The method according to claim 15 , wherein the at least one edge of the glass blank comprises one or more cracks, and wherein the conformal coating of silica-alumina along the at least one edge of the glass blank penetrates the one or more cracks.
17. The method according to claim 1 , wherein the glass blank comprises an annulus, and wherein the at least one edge comprises an inner edge of the annulus and an outer edge of the annulus.
18. A method for forming a plurality of glass substrates, comprising the steps of:
forming a plurality of glass blanks, each glass blank having opposing substantially planar surfaces and at least one edge;
coating the plurality of glass blanks in silica-alumina nanoparticles, the silica-alumina nanoparticles comprising an inner core of silica with an outer shell of alumina;
stacking the plurality of coated glass blanks directly upon one another;
annealing the stacked plurality of coated glass blanks to form a conformal coating of silica-alumina around each glass blank; and
polishing each glass blank to remove the conformal coating of silica-alumina from the opposing substantially planar surfaces thereof and to remove a portion of the glass substrate from each of the opposing substantially planar surfaces.