Fining agents for silicate glasses

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/cm 3 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/cm 3 are also described.

1 . (canceled) 
     
     
         2 . (canceled) 
     
     
         3 . The method according to  claim 20 , wherein the metal hydrate is one of a clay, a zeolite, a mica, and combinations thereof. 
     
     
         4 . The method according to  claim 20 , wherein the metal hydroxide is one of aluminum hydroxide, an alkali metal hydroxide, an alkaline earth metal hydroxide, zirconium hydroxide, and combinations thereof. 
     
     
         5 . (canceled) 
     
     
         6 . method according to  claim 20 , wherein the at least one oxidizer is one of aluminum nitrate, an alkali metal nitrate, an alkaline earth nitrate, zirconium nitrate, ammonium nitrate, and combinations thereof. 
     
     
         7 . The fining agent according to  claim 12 , wherein the silicate glass is one of a soda lime glass, a borosilicate glass, an aluminosilicate glass, and combinations thereof. 
     
     
         8 . The fining agent according to  claim 12 , wherein the silicate glass comprises: 60-72 mol % SiO 2 ; 6-14 mol % Al 2 O 3 ; 0-15 mol % B 2 O 3 ; 0-1 mol % Li 2 O; 0-20 mol % Na 2 O; 0-10 mol % K 2 O; 0-8 mol % MgO; 0-10 mol % CaO; 0-5 mol % ZrO 2 ; 0-1 mol % SnO 2 ; 0-1 mol % CeO 2 ; less than 50 ppm As 2 O 3 ; and less than 50 ppm Sb 2 O 3 ; wherein 12 mol %≦Li 2 O +Na 2 O+K 2 O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %, and wherein the silicate glass is substantially free of antimony and arsenic. 
     
     
         9 . (canceled) 
     
     
         10 . (canceled) 
     
     
         11 . (canceled) 
     
     
         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/cm 3 , 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 alkaline 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 alkaline 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. 
     
     
         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/cm 3 ; and   e. removing at least a portion of the plurality of bubbles from 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. 
     
     
         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/cm 3 , 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/cm 3 , wherein the silicate glass comprises: 60-72 mol % SiO 2 ; 6-14 mol % Al 2 O 3 ; 0-15 mol % B 2 O 3 ; 0-1 mol % Li 2 O; 0-20 mol % Na 2 O; 0-10 mol % K 2 O; 0-8 mol % MgO; 0-10 mol % CaO; 0-5 mol % ZrO 2 ; 0-1 mol % SnO 2 ; 0-1 mol % CeO 2 ; less than 50 ppm As 2 O 3 ; and less than 50 ppm Sb 2 O 3 ; wherein 12 mol %≦Li 2 O+Na 2 O+K 2 O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %, and wherein the silicate glass is substantially free of antimony and arsenic.   
     
     
         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. 
     
     
         25 . The method according to  claim 23 , wherein the metal hydrate is one of a clay, a zeolite, a mica, and combinations thereof. 
     
     
         26 . The method according to  claim 23 , wherein the metal hydroxide is one of aluminum hydroxide, an alkali metal hydroxide, an alkaline earth metal hydroxide, zirconium hydroxide, and combinations thereof. 
     
     
         27 . The method according to  claim 23 , wherein the at least one oxidizer is one of aluminum nitrate, an alkali metal nitrate, an alkaline earth nitrate, zirconium nitrate, ammonium nitrate, and combinations thereof. 
     
     
         28 . The method according to  claim 19 , wherein the silicate glass is one of a soda lime glass, a borosilicate glass, an aluminosilicate glass, and combinations thereof. 
     
     
         29 . The method according to  claim 19 , wherein the silicate glass comprises: 60-72 mol % SiO 2 ; 6-14 mol % Al 2 O 3 ; 0-15 mol % B 2 O 3 ; 0-1 mol % Li 2 O; 0-20 mol % Na 2 O; 0-10 mol % K 2 O; 0-8 mol % MgO; 0-10 mol % CaO; 0-5 mol % ZrO 2 ; 0-1 mol % SnO 2 ; 0-1 mol % CeO 2 ; less than 50 ppm As 2 O 3 ; and less than 50 ppm Sb 2 O 3 ; wherein 12 mol %≦Li 2 O+Na 2 O+K 2 O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %, and wherein the silicate glass is substantially free of antimony and arsenic. 
     
     
         30 . The method according to  claim 22 , wherein solidifying the melt to form the silicate glass comprises down-drawing the melt. 
     
     
         31 . The method according to  claim 22 , further comprising ion exchanging the silicate glass, 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 μm.