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Abstract

A process for producing opaque silica glass in which a quartz raw material grain having a particle size of 10 to 350 .mu.m is filled into a heat resistant mold, the quartz raw material grain is heated in a non-oxidizing atmosphere from a room temperature up to a temperature lower by 50.degree. to 150.degree. C. than a temperature at which the above raw material grain is melted at a temperature-increase speed not exceeding 50.degree. C./minute, then, slowly heated up to a temperature higher by 10.degree. to 80.degree. C. than the temperature at which the quartz raw material grain is melted at the speed of 10.degree. C./minute or less, and the heated quartz raw material grain is further maintained at the temperature higher by 10.degree. to 80.degree. C. than the temperature at which the quartz raw material grain is melted, followed by cooling down to the room temperature. Especially, in the case of producing a large scale opaque silica glass block, a quartz raw material grain filled into a heat-resistant mold is heated by a belt-like heating source located perpendicularly to a trunk of a filling layer of the quartz raw material grain so as to form a moving heating zone in the filling layer and the heating zone is successively moved either upwardly starting at the lower end portion of the filling layer or downwardly starting at the upper end portion thereof in a non-oxidizing atomosphere.

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First Claim