To produce a high quality synthetic silica glass having a high transmittance, sufficient mechanical strength, adequate thermal shock resistance and a high corrosion resistance by constituting the oven wall with a refractory material containing at least a specific proportion of Al2O3 and having porosity within a specific range.
The oven wall of this production unit is constituted of a refractory material 12 with the Al2O3 content at ≥99wt.% and a porosity of 40-70%. Synthetic silica glass is produced by flame hydrolysis technique using this unit equipped with the synthetic oven 10. Specifically, high-purity silicon tetrachloride as feedstock is diluted with a carrier gas and injected through a burner 14 into the oven. The feedstock thus injected from the burner 14 is converted to silica glass powder which is then accumulated on a target 16 and melted to produce the aimed synthetic silica glass; in this case, the target 16 is pulled down to the accumulation rate so as to always keep the central position of the synthesis surface 18a of the ingot 18 at a given distance apart from the burner.
NAKAGAWA KAZUHIRO
JINBO HIROKI
