Patent ID: 6312775
Filing Date: 2001-11-06
Classification: C03B,C03C,Y10S,Y10T

Abstract:
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/cm.sup.3 and contains 5.times.10.sup.4 to 5.times.10.sup.6 bubbles per cm.sup.3 of the glass, said bubbles having an average bubble diameter of 10 to 100 .mu.m; and the glass of the transparent portion consists essentially of silica, and has an apparent density of 2.19 to 2.21 g/cm.sup.3 and the amount of bubbles having a diameter of at least 100 .mu.m in the transparent portion is not more than 1.times.10.sup.3 per cm.sup.3 of the glass, said transparent portion being exposed on at least part of the surface of the opaque silica glass article and forming a surface layer of the opaque silica glass article which is firmly bonded to the opaque portion of the silica glass article as a substrate and said transparent portion of the opaque silica glass article having a surface smoothness sufficient to form a sealing surface between the opaque glass article and another object in contact with the opaque glass article.