TUNING Tzc BY THE ANNEALING OF ULTRA LOW EXPANSION GLASS

Abstract

The disclosure describes a silica-titania glass having a selected titania content in the range of 5-20 wt % that has zero crossover temperature (Tzc) associated with the selected titania content withing this range, and the Tzc is adjustable by ±10° C. or less. The disclosure also describes a method by which the Tzc of a silica-titania glass article, for example, a mirror substrate, can be tuned to within a specification range by means of a selected final anneal that shifts Tzc of the article or substrate to the desired Tzc value. In addition, since different mirrors in a set can be specified at different values of Tzc, this process the method can be on used glass samples or pieces from a single glass boule to make parts with different Tzc values, thus reducing the number of separate boules required to fill an order.

1 .- 13 . (canceled) 
     
     
         14 . A silica-titania glass having a selected titania content in the range of 5-20 wt % and a Tzc associated with the selected titania content within this silica-titania range, said Tzc being adjustable by ±10° C. or less without any adjustment to the titania content. 
     
     
         15 . The silica-titania glass according to  claim 14 , wherein said Tzc is adjustable by ±5° C. or less without any adjustment to the titania content. 
     
     
         16 . A silica-titania glass having a selected titania content in the range of 5-12 wt % and an adjustable Tzc associated with a titania content within this range, said Tzc being adjustable by ±10° C. or less without any adjustment to the titania content. 
     
     
         17 . The silica-titania glass according to  claim 16 , wherein said Tzc is adjustable by ±5° C. or less without any adjustment to the titania content. 
     
     
         18 . A silica-titania glass containing 7.5±0.3 wt % titania and an adjustable Tzc centered at 20° C.±1° C., said Tzc being adjustable by ±10° C. or less. 
     
     
         19 . The silica-titania glass according to  claim 18 , wherein said Tzc is adjustable by ±5° C. or less. 
     
     
         20 . A silica-titania glass containing 8.1±0.3 wt % titania and an adjustable Tzc centered at 20° C.±1° C., said Tzc being adjustable by ±10° C. or less. 
     
     
         21 . The silica-titania according to  claim 20 , wherein said Tzc is adjustable by ±5° C. or less.