Strengthened glass and related systems and methods

Abstract

A strengthened glass or glass-ceramic sheet or article as well as processes and systems for making the strengthened glass or glass-ceramic sheet or article is provided. The process comprises cooling the glass sheet by non-contact thermal conduction for sufficiently long to fix a surface compression and central tension of the sheet. The process results in thermally strengthened glass sheets.

What is claimed is: 
     
         1 . A process for thermally strengthening a glass material comprising:
 heating an article of a glass material above a glass transition temperature of the glass material;   supporting the heated article with a flow of pressurized gas; and   cooling the heated article in a cooling station, the cooling station including a heat sink having a heat sink surface facing the heated article and a gas gap separating the heat sink surface from the heated article, wherein the heated article is supported in the gas gap by the flow of pressurized gas such that the heat sink surface does not touch the heated article;   wherein the heated article is cooled within the cooling station to a temperature below the glass transition temperature such that surface compressive stresses are created within the article;   wherein the flow of pressurized gas is delivered to the gas gap at a flow rate between 50 slpm and 50,000 slpm per square meter of surface area of the heated article.   
     
     
         2 . The process of  claim 1 , wherein the flow rate of the pressurized gas is low such that the heated article is cooled by transferring thermal energy from the heated article to the heat sink by conduction across the gas gap such that more than 20% of the thermal energy leaving the heated article crosses the gas gap and is received by the heat sink. 
     
     
         3 . The process of  claim 1 , wherein the flow rate of the pressurized gas is low such that the heated article is cooled by transferring thermal energy from the heated article to the heat sink by conduction across the gas gap such that more than 50% of the thermal energy leaving the heated article crosses the gas gap and is received by the heat sink. 
     
     
         4 . The process of  claim 1 , wherein the gas gap has an average length between an outer surface of the heated article and the heat sink surface that is small such that the article is cooled by transferring thermal energy from the heated article to the heat sink by conduction across the gas gap such that more than 20% of the thermal energy leaving the heated article crosses the gas gap and is received by the heat sink, wherein the average length of the gas gap is greater than or equal to 10 μm and is less than or equal to 500 μm. 
     
     
         5 . The process of  claim 4 , wherein the average length of the gas gap is greater than or equal to 25 μm and is less than or equal to 300 μm. 
     
     
         6 . The process of  claim 1 , wherein the pressurized gas is air and the flow rate of the pressurized air is greater than or equal to 100 slpm and less than 30,000 slpm per square meter of surface area of the heated article. 
     
     
         7 . The process of  claim 1 , wherein the pressurized gas is helium and the flow rate of the pressurized helium is greater than or equal to 100 slpm and less than 10,000 slpm per square meter of surface area of the heated article. 
     
     
         8 . The process of  claim 1 , wherein the article of glass material is a glass ribbon that is supplied to the cooling station from a first reel and the article of glass material is stored on a second reel following cooling. 
     
     
         9 . The process of  claim 1 , wherein the article of glass material is at least one of melted and formed in-line with the cooling station. 
     
     
         10 . The process of  claim 1 , wherein the glass material is one of an annealed glass and a glass ceramic. 
     
     
         11 . A system for thermally strengthening a glass sheet having a surface area, the system comprising:
 a heating station including a heating element delivering heat to the glass sheet;   a cooling station including opposing first and second heat sink surfaces defining a channel therebetween such that during cooling the glass sheet is located within the channel; and   a gas bearing delivering pressurized gas to the channel such that the glass sheet is supported within the channel;   wherein the gas bearing delivers the pressurized gas to the channel at a flow rate between 50 slpm and 50,000 slpm per square meter of the surface area of the glass sheet.   
     
     
         12 . The system of  claim 11 , wherein the gas bearing delivers the pressurized gas through apertures formed in the first and second heat sink surfaces, wherein the apertures have a total aperture area, wherein the total aperture area is less than 10% of a total surface area of the first and second heat sink surfaces. 
     
     
         13 . The system of  claim 11 , wherein the gas bearing delivers the pressurized gas through apertures formed in the first and second heat sink surfaces, wherein the apertures have a total aperture area, wherein the total aperture area is less than 5% of a total surface area of the first and second heat sink surfaces. 
     
     
         14 . The system of  claim 11 , wherein the gas bearing delivers the pressurized gas through apertures formed in the first and second heat sink surfaces, wherein the apertures have a total aperture area, wherein the total aperture area is less than 1% of a total surface area of the first and second heat sink surfaces. 
     
     
         15 . The system of  claim 11 , wherein the heating station defines a heating channel and further comprising a heating station gas bearing delivering pressurized gas to the heating channel such that the glass sheet is supported within the heating channel, wherein heating station gas bearing delivers pressurized gas to the heating channel at a flow rate between 50 slpm and 50,000 slpm per square meter of the surface area of the glass sheet. 
     
     
         16 . The system of  claim 15 , wherein the heating channel has an average length between an outer surface of the glass sheet and the heating station gas bearing that is greater than or equal to 50 μm and is less than or equal to 1000 μm. 
     
     
         17 . The system of  claim 15 , wherein the heating station includes at least one heating element that generates heat that is delivered to the channel of the heating station. 
     
     
         18 . A strengthened glass article comprising:
 a first major surface;   a second major surface opposite the first major surface;   an interior region located between the first and second major surfaces; and   wherein at least one of the first or second surfaces has a relatively large surface area, that being at least 2500 mm 2 ;   wherein at least one of the first major surface and the second major surfaces are under compressive stress and the interior region is under tensile stress;   wherein the compressive stress comprises a thermally tempered stress of at least 100 MPa and a chemically tempered stress that is less than 20% of the thermally tempered stress.   
     
     
         19 . The strengthened glass article of  claim 18 , wherein the compressive stress comprises a thermally tempered stress of at least 500 MPa and a chemically tempered stress that is less than 10% of the thermally tempered stress. 
     
     
         20 . The strengthened glass article of  claim 18 , wherein a composition of the strengthened glass article located in at least a part of the portions of the strengthened glass article exterior to and adjoining the interior region, under the compressive stress, is the same in terms of ion content and chemical constituency as a composition located in at least a part of the interior region, under the tensile stress, such that at least some of the compressive stress is independent of a change in the composition of the strengthened glass article, wherein a composition of the strengthened glass article at at least one of the first and second major surfaces is different in terms of ion content and chemical constituency from the composition located in at least a part of the interior region, under the tensile stress, such that at least some of the compressive stress is dependent on a change in the composition of the strengthened glass article.