Abstract: In a process for manufacture of dense, amorphous quartz glass granulate by production of a porous granulate from amorphous SiO2 powder and vitrification of the granulate, a porous SiO2 granulate is exposed to a fuel gas flame and is finely dispersed, heated and vitrified therein. The fuel gas flame is more flexible as concerns adjustment of the temperature than in known processes. It is in particular possible to set higher temperatures. The granulate can be exposed to very high sintering temperatures in the fuel gas flame without sintering into agglomerates. At the same time, heat resistance problems of sintering containers such as furnaces and melting pots are avoided. In addition, contamination of the SiO2 granulate by contact with the walls of sintering or vitrifying containers is eliminated. The process makes it possible to economically produce a highly pure and dense quartz glass granulate.

Abstract: A rotating cylindrical quartz glass tube is partitioned into at least 3 chambers comprising a pre-heating chamber, a reaction chamber, and a gas desorption chamber. The process comprises pre-heating the starting quartz powder by continuously supplying it into the pre-heating chamber, refining the powder by transferring it into the reaction chamber in which the powder is brought into contact with a chlorine-containing gas atmosphere, and transferring the powder into the gas desorption chamber; the chambers may be partitioned using a sectioning plate having an opening. Alkali metal elements such as sodium and potassium, as well as transition metal elements such as iron, copper, chromium, and nickel are removed from a powder of naturally occurring quartz. The process also removes alkaline earth metal elements such as magnesium and calcium. Furthermore, it is of high productivity because it can be operated continuously to yield high purity quartz powder at a low cost.