Opaque hollow glass body prodn. for use in epitaxial tubes - by heating particulate hollow body in radial temp. gradient

Prodn. of opaque hollow bodies of quartz glass or high silica content glass involves forming a poured silica particulate body with an open cavity and heating the body with a graphite heating element to form a cylindrical melt front which advances away from the heating element. The novelty is that (a) the body is poured in the form of a hollow cylinder between an inner wall (3), associated with the cavity, and an outer wall (1), acting as the heating element; and (b) the body is heated, while maintaining a temp. gradient between the walls, so that the melt propagates towards the inner wall up to the central cavity within the body. The temp. gradient is maintained by thermal insulation (5,6), which shields the cavity, and/or by forced cooling of the cavity esp. with a heat sink (10). The body (11) is evacuated before heating and is inductively heated under inert gas, esp. Ar or N2. USE/ADVANTAGE - For prodn. of thick walled opaque hollow bodies which may be cut into, e.g., flanges for epitaxy tubes. The process allows simple and inexpensive mfr. of thick walled, homogeneous, finely porous, high purity, opaque hollow bodies of quartz glass or high silica content glass, with wide freedom of choice of prod. shape.