Alumina refractories and methods of treatment

Abstract

Methods for improving the strength of alumina refractory materials are disclosed. The method involves exposing the alumina material to a halogen gas. The treated materials can be used in furnaces for producing fused silica optical members.

What is claimed is:  
     
         1 . A method of improving the strength of an alumina refractory material comprising exposing the alumina refractory material to a halogen gas.  
     
     
         2 . The method of  claim 1 , wherein the step of exposing the alumina refractory to a halogen gas is performed at a temperature above 1000° C.  
     
     
         3 . The method of  claim 2 , wherein the temperature during the step of exposing the alumina refractory is performed at a temperature between 1000° C. and 1400° C.  
     
     
         4 . The method of  claim 3 , wherein the halogen gas is selected from the group consisting of fluorine, iodine, and chlorine.  
     
     
         5 . The method of  claim 4 , wherein the gas includes chlorine.  
     
     
         6 . The method of  claim 5 , wherein the gas includes a mixture of chlorine and a carrier gas.  
     
     
         7 . The method of  claim 6 , wherein the carrier gas includes helium.  
     
     
         8 . The method of  claim 3 , wherein the exposing step takes place for at least one hour and less than 10 hours.  
     
     
         9 . The method of  claim 3 , wherein the exposing step is performed in the presence of a reducing agent.  
     
     
         10 . The method of  claim 9 , wherein the reducing agent is a carbon-containing material.  
     
     
         11 . The method of  claim 2 , wherein the four point bend strength of the material is improved by at least 50% by the exposure to the halogen gas.  
     
     
         12 . A furnace for the production of fused silica optical members including an alumina refractory material treated in accordance with  claim 3 .  
     
     
         13 . A method of improving the strength of an alumina refractory material comprising exposing the refractory material to chlorine gas at a temperature exceeding 1000° C. and for a time exceeding one hour.  
     
     
         14 . The method of  claim 13 , wherein the step of exposing the refractory material to chlorine gas is performed in the presence of a carbon-containing material.  
     
     
         15 . A furnace for the production of fused silica optical members including a refractory treated in accordance with  claim 14.