Ultralow expansion glass

Abstract

Silica-titania glasses with small temperature variations in coefficient of thermal expansion over a wide range of zero-crossover temperatures and methods for making the glasses. The method includes a cooling protocol with controlled anneals over two different temperature regimes. A higher temperature controlled anneal may occur over a temperature interval from 750-950° C. or a sub-interval thereof. A lower temperature controlled anneal may occur over a temperature interval from 650-875° C. or a sub-interval thereof. The controlled anneals permit independent control over CTE slope and Tzc of silica-titania glasses. The independent control provides CTE slope and Tzc values for silica-titania glasses of fixed composition over ranges heretofore possible only through variations in composition.

What is claimed is: 
     
         1 . A silica-titania glass having a titania content between 7.45 wt % and less than 8.39 wt %, said glass having Tzc in the range from 15° C. to 45° C. and a CTE slope at 20° C. below 1.30 ppb/K 2 . 
     
     
         2 . The silica-titania glass of  claim 1 , wherein said Tzc is in the range from 25° C. to 45° C., said CTE slope at 20° C. is below 1.25 ppb/K 2 , and said titania content is between 7.56 wt % and [8.07 wt %+(Tzc−25° C.)*(0.016 wt %/° C.)]. 
     
     
         3 . The silica-titania glass of  claim 1 , wherein said Tzc is in the range from 25° C. to 35° C. and said titania content is between 7.62 wt % and [7.95 wt %+(Tzc−25° C.)*(0.018 wt %/° C.)]. 
     
     
         4 . The silica-titania glass of  claim 1 , wherein said Tzc is in the range from 25° C. to 35° C., said CTE slope at 20° C. is below 1.25 ppb/K 2 , and said titania content is between 7.72 wt % and [8.07 wt %+(Tzc−25° C.)*(0.016 wt %/° C.)]. 
     
     
         5 . The silica-titania glass of  claim 1 , wherein said glass includes an OH concentration in the range from 700 ppm to 1000 ppm. 
     
     
         6 . A silica-titania glass having a titania content between 7.45 wt % and less than 8.23 wt %, said glass having Tzc in the range from 25° C. to 35° C. and a CTE slope at 20° C. below 1.30 ppb/K 2 . 
     
     
         7 . The silica-titania glass of  claim 6 , wherein said titania content is between 7.62 wt % and 8.13 wt %. 
     
     
         8 . The silica-titania glass of  claim 6 , wherein said titania content is between 7.72 wt % and 8.23 wt %. 
     
     
         9 . The silica-titania glass of  claim 6 , wherein said titania content is between 7.56 wt % and 8.07 wt % and said CTE slope at 20° C. is below 1.25 ppb/K 2 . 
     
     
         10 . The silica-titania glass of  claim 6 , wherein said titania content is between 7.72 wt % and 8.23 wt % and said CTE slope at 20° C. is below 1.25 ppb/K 2 . 
     
     
         11 . The silica-titania glass of  claim 6 , wherein said glass includes an OH concentration in the range from 700 ppm to 1000 ppm. 
     
     
         12 . A silica-titania glass having a titania content in the range from 7.72 wt % to less than 8.03 wt %, said glass having Tzc in the range from 25° C. to 35° C. and a CTE slope at 20° C. of less than 1.30 ppb/K 2 . 
     
     
         13 . The silica-titania glass of  claim 12 , wherein said glass includes an OH concentration in the range from 700 ppm to 1000 ppm.