Surface nitrided alkali-free glasses cross-reference to related applications

Abstract

Alkali-free glasses are disclosed having (in weight %) 50≦SiO 2 ≦80%, 2≦Al 2 O 3 ≦17%, 8≦B 2 O 3 ≦36%, and greater than or equal to 2% and less than or equal to 25% of at least one of CaO, MgO, BaO, SrO or ZnO. The alkali-free glasses can have a surface layer with greater than 0.2 weight % N. Such alkali-free glasses are achieved by nitriding processes and exhibit increased strength, scratch resistance and chemical durability.

1 - 30 . (canceled) 
     
     
         31 . A method of strengthening an alkali-free glass composition comprising:
 subjecting a glass article comprising the alkali-free glass composition to a heated gas mixture, wherein the gas mixture comprises at least one nitrogen-containing compound, for a time and at a temperature sufficient to create in at least one surface of the glass article a nitrogen-containing layer comprising greater than 0.2 weight % N, wherein the nitrogen-containing layer increases the Young's modulus of the article.   
     
     
         32 . The method according to  claim 31  wherein the gas mixture comprises NH3. 
     
     
         33 . The method according to  claim 31  wherein the time is from 24 to 240 hours and the temperature of the gas mixture is from 200° C. and 1200° C., and the gas pressure is between 0.2 to 20 atmospheres. 
     
     
         34 . An article comprising an alkali-free glass composition comprising a substrate comprising at least 99.9 wt % SiO2, the alkali-free glass composition comprising a surface layer comprising greater than 0.2 weight % N. 
     
     
         35 . The article according to  claim 34  wherein the surface layer comprises a thickness of greater than 1 nm. 
     
     
         36 . The article according to  claim 34  wherein the surface layer comprises greater than 1 weight % N. 
     
     
         37 . An article comprising an alkali-free glass composition comprising a molar volume greater than 26 cm3/mole, the composition comprising a surface layer comprising greater than 0.2 weight % N. 
     
     
         38 . The article according to  claim 37  wherein the molar volume is greater than 27 cm3/mole. 
     
     
         39 . The method according to  claim 31 , wherein the Young's modulus increases by at least about 17%. 
     
     
         40 . The method according to  claim 31 , wherein the Young's modulus is at least about 72.7 GPa. 
     
     
         41 . The method of according to  claim 40 , wherein the Young's modulus is in a range from about 72.7 GPa to about 137.7 GPa.