Process for producing silica glass product

Abstract

A process for producing a transparent or opaque silica glass product including mixing a silica fine powder and a cellulose derivative and injection molding the mixture, followed by degreasing treatment and baking treatment, which is characterized in that the cellulose derivative is a cellulose derivative which causes reversible thermal gelation in an aqueous solution of at least one member selected from methyl cellulose, hydroxypropylmethyl cellulose and hydroxyethylmethyl cellulose; in producing a transparent silica glass product, the cellulose derivative is added in water heated at a gelation temperature thereof or higher, and after cooling, the formed aqueous solution is kneaded with the silica fine powder; and in producing an opaque silica glass product, the cellulose derivative is added in a silica slurry containing a silica powder and heated at a gelation temperature of the cellulose derivative or higher.

1 . A process for producing an opaque silica glass product comprising the steps of:
 combining a silica fine powder and an aqueous mixture of a cellulose derivative that causes reversible thermal gelation in an aqueous solution to form a suspension, wherein the aqueous mixture is made by adding the cellulose derivative in water at or above a gelation temperature of the cellulose derivative followed by maintaining the mixture at not higher than 45° C. for from 1 to 120 minutes in order to adjust a particle size of the cellulose derivative powder;   kneading the resulting combination;   injection molding the kneaded combination in a molding die to form a molded silica article;   sequentially subjecting the molded silica article to a degreasing treatment, a purification treatment, and a baking treatment to obtain the transparent silica glass product.   
     
     
         2 . The process for producing a silica glass product according to  claim 1 , wherein the molding die is a resin-made or metal-made molding die and is at a temperature of from 70° to 120° C. 
     
     
         3 . The process for producing a silica glass product according to  claim 2 , wherein the degreasing treatment is carried out at a temperature rise rate of from 1° to 5° C./min, and when the temperature reaches 500° C., the molded article is kept at that temperature for from 3 to 6 hours. 
     
     
         4 . The process for producing a silica glass product according to  claim 1 , wherein the baking treatment is carried out at from 1,200° to 1,700° C. at reduced pressure. 
     
     
         5 . The process for producing a silica glass product according to  claim 1 , wherein a bubble-free silica glass layer of 0.1 mm or more is formed on a surface of the silica glass product. 
     
     
         6 . The process for producing a silica glass product according to  claim 2 , wherein a bubble-free silica glass layer of 0.1 mm or more is formed on a surface of the silica glass product. 
     
     
         7 . The process for producing a silica glass product according to  claim 3 , wherein a bubble-free silica glass layer of 0.1 mm or more is formed on a surface of the silica glass product. 
     
     
         8 . The process for producing a silica glass product according to  claim 4 , wherein a bubble-free silica glass layer of 0.1 mm or more is formed on a surface of the silica glass product.