FINING AGENTS FOR SILICATE GLASSES

• US 20090215607A1
• Filed: 02/25/2009
• Published: 08/27/2009
• Est. Priority Date: 02/26/2008
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Dejneka, Matthew John, Gomez, Sinue
• Granted Patent: US 8,158,543 B2
• Time in Patent Office: Days
• US Class Current: 501/27
• CPC Class Codes: C03B 17/064 by the overflow downdraw fusion process; Isopipes therefor
• CPC Class Codes: C03B 5/225 Refining C03B5/18 takes precedence ; Refining agents C03C1/004
• CPC Class Codes: C03C 1/004 Refining agents refining C03B5/225
• CPC Class Codes: C03C 14/008 the non-glass component being in molecular form
• CPC Class Codes: C03C 21/002 to perform ion-exchange between alkali ions C03C21/005 takes precedence
• CPC Class Codes: C03C 3/083 containing aluminium oxide or an iron compound
• CPC Class Codes: C03C 3/085 containing an oxide of a divalent metal
• CPC Class Codes: C03C 3/087 containing calcium oxide, e.g. common sheet or container glass
• CPC Class Codes: C03C 3/091 containing aluminium
• CPC Class Codes: C03C 3/095 containing rare earths
• CPC Class Codes: Y02A 40/28 specially adapted for farming
• CPC Class Codes: Y10T 428/315 Surface modified glass [e.g., tempered, strengthened, etc.]

Abstract

A fining agent for reducing the concentration of seeds or bubbles in a silicate glass. The fining agent includes at least one inorganic compound, such as a hydrate or a hydroxide that acts as a source of water. In one embodiment, the fining agent further includes at least one multivalent metal oxide and, optionally, an oxidizer. A fusion formable and ion exchangeable silicate glass having a seed concentration of less than about 1 seed/cm³ is also provided. Methods of reducing the seed concentration of a silicate glass, and a method of making a silicate glass having a seed concentration of less than about 1 seed/cm³ are also described.

Claims

1. A silicate glass, the silicate glass having a seed concentration of less than about 1 seed/cm³, wherein the silicate glass is formed from a batch or raw materials that includes at least one fining agent, wherein the fining agent comprises at least one inorganic compound that acts as of a source of water at a temperature where a melt is formed, and wherein the silicate glass and the at least one fining agent are substantially free of antimony and arsenic.

2. The silicate glass according to claim 1, wherein the fining agent comprises at least one of a metal hydrate, a metal hydroxide, and combinations thereof.

3. The silicate glass according to claim 2, wherein the metal hydrate is one of a clay, a zeolite, a mica, and combinations thereof.

4. The silicate glass according to claim 2, wherein the metal hydroxide is one of aluminum hydroxide, an alkali metal hydroxide, an alkali earth metal hydroxide, zirconium hydroxide, and combinations thereof.

5. The silicate glass according to claim 1, wherein the fining agent further comprises at least one multivalent metal oxide that acts as a source of oxygen to the melt and, optionally, at least one oxidizer.

6. The silicate glass according to claim 5, wherein the at least one oxidizer is one of aluminum nitrate, an alkali metal nitrate, an alkali earth nitrate, zirconium nitrate, ammonium nitrate, and combinations thereof.

7. The silicate glass according to claim 1, wherein the silicate glass is one of a soda lime glass, a borosilicate glass, an aluminosilicate glass, and combinations thereof.

8. The silicate glass according to claim 7, wherein the silicate glass comprises:

60-70 mol % SiO₂;

6-14 mol % Al₂O₃;

0-15 mol % B₂O₃;

0-15 mol % Li₂O;

0-20 mol % Na₂O;

0-10 mol % K₂O;

0-8 mol % MgO;

0-10 mol % CaO;

0-5 mol % ZrO₂;

0-1 mol % SnO₂;

0-1 mol % CeO₂;

less than 50 ppm As₂O₃; and

less than 50 ppm Sb₂O₃;

wherein 12 mol %≦

Li₂O+Na₂O+K₂O≦

20 mol % and 0 mol %≦

MgO+CaO≦

10 mol %, and wherein the silicate glass is substantially free of lithium.

9. The silicate glass according to claim 1, wherein the silicate glass is down-drawable and ion exchangeable.

10. The silicate glass according to claim 9, wherein the silicate glass, when ion exchanged, has a surface compressive stress of at least about 200 MPa and a surface compressive layer having a depth of at least about 30 μ

m.

11. The silicate glass according to claim 1, wherein the silicate glass forms a cover plate for a mobile electronic device.

12. A fining agent for silicate glasses, the fining agent comprising an inorganic compound that acts as of a source of water at a temperature at which a melt is formed, wherein the water vaporizes and expands existing bubbles in the melt and allows the expanded bubbles to rise to the surface of the melt and escape the melt to reduce the seed concentration in the silicate glass to less than about 1 seed/cm³, and wherein the fining agent is substantially free of arsenic and antimony.

13. The fining agent according to claim 12, wherein the fining agent comprises at least one of:

a metal hydrate, a metal hydroxide; and

combinations thereof.

14. The fining agent according to claim 13, wherein the metal hydrate is one of a clay, a zeolite, a mica, and combinations thereof.

15. The fining agent according to claim 13, wherein the metal hydroxide is one of aluminum hydroxide, an alkali metal hydroxide, an alkali earth metal hydroxide, zirconium hydroxide, and combinations thereof.

16. The fining agent according to claim 15, wherein the fining agent further comprises at least one multivalent metal oxide that acts as a source of oxygen to the melt and, optionally, at least one oxidizer.

17. The fining agent according to claim 16, wherein the at least one oxidizer is one of aluminum nitrate, an alkali metal nitrate, an alkali earth nitrate, zirconium nitrate, ammonium nitrate, and combinations thereof.

18. The fining agent according to claim 13, wherein the fining agent acts as a flux that decreases the viscosity of the melt.

20. The method according to claim 18, wherein the at least one fining agent comprises at least one of:

a metal hydrate, a metal hydroxide; and

combinations thereof.

19. A method of reducing a concentration of seeds in a silicate glass, the method comprising the steps of:

a. providing a batch, the batch comprising raw materials for the silicate glass and at least one fining agent in an amount sufficient to generate one mole of water vapor per kilogram of glass, wherein the at least one fining agent is substantially free of arsenic and antimony and comprises at least one inorganic compound that acts as of a source of water at a temperature where a melt is formed;

b. melting the batch to form a melt, the melt having a surface;

c. vaporizing the water to form water vapor, wherein the water vapor expands existing bubbles in the melt;

d. allowing the expanded bubbles to rise to the surface of the melt and escape the melt to reduce the concentration of the plurality of seeds in the silicate glass melt to less than about 1 seed/cm³; and

e. removing at least a portion of the plurality of bubbles from the melt.

21. The method according to claim 19, wherein the at least one fining agent further comprises at least one multivalent metal oxide that acts as a source of oxygen to the melt and, optionally, at least one oxidizer.

22. A method of making a silicate glass having a seed concentration of less than about 1 seed/cm³, the method comprising the steps of:

a. providing a batch, the batch comprising raw materials for the silicate glass and at least one fining agent in an amount sufficient to generate one mole of water vapor per kilogram of glass, wherein the at least one fining agent is substantially free of arsenic and antimony and comprises at least one inorganic compound that acts as of a source of water at a temperature where a melt is formed;

b. melting the batch to form a silicate glass melt;

c. vaporizing the water to form water vapor, wherein the water vapor expands existing bubbles in the melt;

d. allowing the expanded bubbles to rise to the surface of the melt and escape the melt to reduce the seed concentration in the melt below a predetermined concentration;

e. removing at least a portion of the coalesced bubbles and seeds from the melt; and

f. solidifying the melt to form the silicate glass, wherein the glass has a seed concentration of less than about 1 seed/cm³.

23. The method according to claim 22, wherein the at least one fining agent comprises at least one of:

a metal hydrate, a metal hydroxide; and

combinations thereof.

24. The method according to claim 23, wherein the at least one fining agent further comprises at least one multivalent metal oxide that acts as a source of oxygen to the melt and, optionally, at least one oxidizer.