Patent ID: 6405563
Filing Date: 2002-06-18
Classification: C03B,C03C,Y10S,Y10T

Abstract:
A process for producing an opaque silica glass article comprising a transparent portion and an opaque portion, wherein the glass of the opaque portion has an apparent density of 1.70 to 2.15 g/cm3 and contains 5Ã—104 to 5Ã—106 bubbles per cm3 of the glass, said bubbles having an average bubble diameter of 10 to 100 &mgr;m; and the glass of the transparent portion has an apparent density of 2.19 to 2.21 g/cm3 and the amount of bubbles having a diameter of at least 100 &mgr;m in the transparent portion is not more than 1Ã—103 of the glass, which process comprises the steps of:charging a heat-resistant mold with a raw material for forming the opaque portion of the silica glass article, which is a uniform mixture comprising a finely divided silica powder having an average particle diameter of 10 to 500 &mgr;m with 0.001 to 0.05 parts by weight, based on 100 parts by weight of the silica powder, of a finely divided silicon nitride powder, and a raw material for forming the transparent portion of the silica glass article so that the two raw materials are located in the positions corresponding to the opaque portion and the transparent portion, respectively, of the silica glass article to be produced; and heating the raw materials in vacuo at a temperature in the range of the melting temperature of the raw materials and 1,900Â° C., whereby the raw materials are vitrified.