Zircon compatible glasses for down draw
A glass that is down-drawable and ion exchangeable. The glass has a temperature T 35kp which the viscosity is 35 kilopoise. T 35kp is less than the breakdown temperature T breakdown of zircon.
1. A glass comprising SiO 2 , Al 2 O 3 , and alkali oxides selected from the group consisting of Na 2 O and K 2 O, wherein SiO 2 +B 2 O 3 ≧66 mol %, 15 mol %≧Al 2 O 3 ≧7 mol %, B 2 O 3 ≦7 mol %, Na 2 O≧9 mol %, K 2 O≦2.37 mol %, B 2 O 3 + Na 2 O+K 2 O+MgO+CaO≧18 mol %, and CaO≦2 mol %, wherein 610.6 mol %−41.0[Al 2 O 3 ]+9.9[B 2 O 3 ]−3.5[Na 2 O]−20.2[K 2 O]−25.6[MgO]+34.2[CaO]≧0, where concentrations [Al 2 O 3 ], [B 2 O 3 ], [Na 2 O], [K 2 O], [MgO], and [CaO] are expressed in mol %.
2. The glass of claim 1 , wherein the glass comprises: 61 mol %≦SiO 2 ≦75 mol %; 7 mol %≦Al 2 O 3 ≦15 mol %; 0 mol %≦B 2 O 3 ≦7 mol %; 9 mol %≦Na 2 O≦21 mol %; 0 mol %≦K 2 O≦2.37 mol %; 0 mol %≦MgO≦7 mol %; and 0 mol %≦CaO≦2 mol %.
3. The glass of claim 1 , wherein the glass is down-drawable.
4. The glass of claim 1 , wherein the glass is fusion drawn into a glass sheet.
5. The glass of claim 4 , wherein the glass sheet has less than one inclusion of solid ZrO 2 per pound of glass sheet.
6. The glass of claim 1 , wherein B 2 O 3 +Na 2 O+K 2 O−Al 2 O 3≧ 0 mol %.
7. The glass of claim 1 , wherein the glass has a liquidus viscosity of greater than about 100 kpoise.
8. The glass of claim 1 , wherein the glass has a 350 poise temperature T 350 of less than or equal to 1650° C.
9. The glass of claim 1 , wherein the glass is formed into one of a cover plate, a window, a casing, a display screen, and a touch panel of an electronic device.
10. The glass of claim 1 , wherein the glass has a temperature T 35kp at which the glass has a viscosity of 35 kpoise and a zircon breakdown temperature T breakdown at which zircon breaks down to form ZrO 2 and SiO 2 , wherein T breakdown is greater than T 35kp .
11. The glass of claim 1 , wherein the glass is ion exchanged to form a compressive layer on at least one surface of the glass.
12. The glass of claim 11 , wherein the ion exchanged glass has a compressive stress of at least 350 MPa and a compressive depth of layer of at least 20 microns.
13. A glass comprising SiO 2 , Al 2 O 3 , and alkali oxides selected from the group consisting of Na 2 O and K 2 O, wherein 15 mol %≧Al 2 O 3 ≧7 mol %, B 2 O 3 ≦7 mol %, Na 2 O≧9 mol %, K 2 O≦2.37 mol %, CaO≦2 mol %, SiO 2 +B 2 O 3 ≧66 mol %, and B 2 O 3 +Na 2 O+K 2 O+MgO+CaO≧18 mol %, wherein the glass has a temperature T 35kp at which the glass has a viscosity of 35 kpoise, and a zircon breakdown temperature T breakdown at which zircon breaks down to form ZrO 2 and SiO 2 , wherein T breakdown is greater than T 35kp , and wherein T margin =T breakdown −T 35kp , where T margin =610.6 mol %−41.0[Al 2 O 3 ]+9.9[B 2 O 3 ]−3.5[Na 2 O]−20.2[K 2 O]−25.6[MgO]+34.2[CaO] where concentrations [Al 2 O 3 ], [B 2 O 3 ], [Na 2 O], [K 2 O], [MgO], and [CaO] are expressed in mol %, and wherein T margin ≧0.
14. The glass of claim 13 , wherein the glass comprises: 61 mol %≦SiO 2 ≦75 mol %; 7 mol %≦Al 2 O 3 ≦15 mol %; 0 mol %≦B 2 O 3 ≦7 mol %; 9 mol %≦Na 2 O≦21 mol %; 0 mol %≦K 2 O≦2.37 mol %; 0 mol %≦MgO≦7 mol %; and 0 mol %≦CaO≦2 mol %.
15. The glass of claim 13 , wherein the glass is down-drawable.
16. The glass of claim 13 , wherein the glass is fusion drawn into a glass sheet.
17. The glass of claim 16 , wherein the glass sheet has less than one inclusion of solid ZrO 2 per pound of glass sheet.
18. The glass of claim 13 , wherein B 2 O 3 +Na 2 O+K 2 O−Al 2 O 3 ≧0 mol %.
19. The glass of claim 13 , wherein the glass has a liquidus viscosity of greater than about 100 kpoise.
20. The glass of claim 13 , wherein the glass has a 350 poise temperature T 350 of less than or equal to 1650° C.
21. The glass of claim 13 , wherein the glass is formed into one of a cover plate, a window, a casing, a display screen, and a touch panel of an electronic device.
22. The glass of claim 13 , wherein the glass is ion exchanged to form a compressive layer on at least one surface of the glass.
23. The glass of claim 22 , wherein the ion exchanged glass has a compressive stress of at least 350 MPa and a compressive depth of layer of at least 20 microns.