Importance

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Abstract

The production of synthetic quartz glass granules by vitrifying a free-flowing SiO₂ granulate from porous granulate particles is time-consuming and expensive. The aim of the invention is to provide a method that allows a continuous and cost-effective production of dense synthetic quartz glass granules on the basis of porous SiO₂ granulate. According to the invention, this is achieved by the following method steps: (a) granulating pyrogenically produced silicic acid with the formation of the SiO₂ granulate made of porous granulate particles; (b) drying the SiO₂ granulate; (c) cleaning the SiO₂ granulate by heating in an atmosphere containing halogen in a cleaning furnace; and (d) vitrifying the cleaned SiO₂ granulate by sintering in a vitrifying furnace with the formation of quartz glass granules. The drying, cleaning, and vitrifying of the SiO₂ granulate are each carried out in a tary tube of a rotary tube furnace, said rotary tube rotating about a central axis. The rotary tube furnace used for vitrifying has a rotary tube, the inner wall of which consists of a ceramic material with a higher softening temperature than undoped quartz glass. Said rotary tube is flooded with a low-nitrogen treating gas or flushed with the treating gas, said gas containing at least 30 vol. % helium and/or hydrogen.

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First Claim