To enable the heat-treatment of a glass preform in high quality at a low cost by forming a TiC film on the inner surface of a base material of a furnace core tube for heat-treating a porous glass preform and specifying the relationship between the thermal expansion coefficients of the base material and the TiC.
A TiC film 12-2 is applied to the surface of a base material 12-1 of a furnace core tube 12 placed inside of a heater 20 for producing a glass preform or a glass material composed mainly of SiO2. The thermal expansion coefficient of the base material 12-1 is adjusted within ±10% relative to that of TiC. The abrasion of the base material caused by the moisture, etc., of the heating atmosphere can be suppressed by the TiC film applied to the surface of the furnace core tube 12. The generation of thermal strain caused by temperature difference can be suppressed to enable the stable use of the apparatus over a long period by using the base material of the furnace core tube 12 having a thermal expansion coefficient close to that of the TiC film to be applied to the surface.
OGA YUICHI
MATSUI MASAHIKO
NAKAMURA MOTONORI
ITO MASUMI
TANAKA SATOSHI
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