Preparation of carbon-doped silicon dioxide granulate as an intermediate in the preparation of quartz glass

A process for preparation of a quartz glass body comprising:

• providing a silicon dioxide granulate I, the step of providing including:
• providing pyrogenically produced silicon dioxide powder;
• processing the silicon dioxide powder to obtain a silicon dioxide granulate I, wherein the silicon dioxide granulate I has a carbon content wC(1) in a range from 1 to 200 ppm, based on a total weight of the silicon dioxide granulate I, such that the carbon content wC(1) reduces alkaline earth metal content of the silicon dioxide granulate I and
• wherein the silicon dioxide granulate I has a content of alkaline earth metal wM(1), the content of alkaline earth metal based on the total weight of the silicon dioxide granulate I;
• treating the silicon dioxide granulate I with a reactant comprising chlorine or HCL at a temperature in a range from 1000 to 1300° C. to obtain a silicon dioxide granulate II,
• wherein the silicon dioxide granulate II has a carbon content wC(2) and has a content of alkaline earth metal wM(2), the contents wC(2) and wM(2) in each case based on a total weight of the silicon dioxide granulate II;
• wherein the carbon content wC(2) is less than the carbon content wC(1),
• wherein the content of alkaline earth metal wM(2) is less than the alkaline earth metal content wM(1);
• making a glass melt out of the silicon dioxide granulate II;
• and
• making the quartz glass body out of at least part of the glass melt, wherein the quartz glass body has a chlorine content of less than 60 ppm;
• wherein the silicon dioxide granulate II is fed into an oven and the glass melt formed therein is continuously removed from the oven without interruption thereby forming a quartz glass body.