Preparation of a quartz glass body in a multi-chamber oven
One aspect relates to a process for the preparation of a quartz glass body, including providing a silicon dioxide granulate, wherein the silicon dioxide granulate was made from pyrogenic silicon dioxide powder and the silicon dioxide granulate has a BET surface area in a range from 20 to 40 m 2 /g, making a glass melt out of silicon dioxide granulate in an oven and making a quartz glass body out of at least part of the glass melt. The oven has at least a first and a further chamber connected to one another via a passage. The temperature in the first chamber is lower than the temperature in the further chambers. One aspect relates to a quartz glass body which is obtainable by this process. One aspect relates to a light guide, an illuminant and a formed body, which are each obtainable by further processing of the quartz glass body.
1. A process for the preparation of a quartz glass body comprising:
providing a silicon dioxide granulate,
wherein the silicon dioxide granulate was made from pyrogenic silicon dioxide powder and the silicon dioxide granulate comprises:
A BET surface area in a range from 20 to 40 m 2 /g;
making a glass melt out of the silicon dioxide granulate in an oven; and
making a quartz glass body out of at least part of the glass melt;
wherein the oven has at least a first and a further chamber connected to one another by a passage,
wherein the first and further chambers are at different temperatures;
wherein the temperature in the first chamber is lower than the temperature in the further chamber; and
wherein in the first chamber there is a pressure of less than 500 mbar.
2. The process according to claim 1 , wherein there is an additive in the first chamber selected from the group consisting of halogens, inert gas, base, oxygen or a combination of two or more of them.
3. The process according to claim 2 , wherein the halogen is selected from the group consisting of chlorine, fluorine, compounds containing chlorine, compounds containing fluorine and a combination of two or more thereof, and wherein the inert gas is selected from the group consisting of nitrogen, helium and a combination of the two.
4. The process according to claim 1 , wherein the silicon dioxide granulate comprises at least one of:
a mean particle size in a range from 50 to 500 μm
a bulk density in a range from 0.5 to 1.2 g/cm 3 ;
a carbon content of less than 10 ppm;
an aluminium content of less than 200 ppb;
a tamped density in a range from 0.7 to 1.2 g/cm 3 ;
a pore volume in a range from 0.1 to 2.5 mL/g;
an angle of repose in a range from 23 to 26°
a particle size distribution D 10 in a range from 50 to 150 μm;
a particle size distribution D 50 in a range from 150 to 300 μm; and
a particle size distribution D 90 in a range from 250 to 620 μm;
wherein the ppm and ppb are each based on the total weight of the silicon dioxide powder.
5. The process according to claim 1 , wherein the silicon dioxide is transported from the first to the further chamber as granulate.
6. The process according to claim 1 , wherein the first chamber comprises at least one element selected from the group consisting of quartz glass, a refractory metal, aluminium and a combination of two or more of them.
7. The process according to claim 1 , wherein the further chamber is a crucible of a metal sheet or a sinter material containing a sinter metal, wherein the metal sheet or the sinter metal is selected from the group consisting of molybdenum, tungsten and a combination of them.
8. The process according to claim 1 , wherein the BET surface area before making a glass melt out of the silicon dioxide granulate in an oven is not reduced to less than 5 m 2 /g.
9. The process according to claim 1 , wherein melt energy is transmitted to the silicon dioxide granulate via a solid surface.
10. The process according to claim 1 , wherein hydrogen, helium, nitrogen or a combination of two or more of them is present in the gas space of the oven.
11. The process according to claim 1 , wherein providing the silicon dioxide granulate comprises:
providing silicon dioxide powder comprising:
a BET surface area in a range from 20 to 60 m 2 /g; and
a bulk density in a range from 0.01 to 0.3 g/cm 3 ;
processing the silicon dioxide powder to obtain a silicon dioxide granulate;
wherein the silicon dioxide granulate has a larger particle size than the silicon dioxide powder.
12. The process according to claim 11 , wherein the provided silicon dioxide powder comprises at least one of:
a carbon content of less than 50 ppm
a chlorine content of less than 200 ppm;
an aluminium content of less than 200 ppb;
a total content of metals which are different from aluminium of less than 5 ppm;
at least 70 wt.-% of the powder particles have a primary particle size in a range from 10 to 100 nm;
a tamped density in a range from 0.001 to 1.3 g/cm 3 ;
a residual moisture content of less than 5 wt.-%;
a particle size distribution D 10 in the range from 1 to 7 μm;
a particle size distribution D 50 in the range from 6 to 15 μm; and
a particle size distribution D 90 in the range from 10 to 40 μm;
wherein the wt.-%, the ppm and the ppb are each based on the total weight of the silicon dioxide powder.
13. The process according to claim 1 , wherein the silicon dioxide powder is made from an element selected from the group consisting of siloxanes, silicon alkoxides and silicon halides.
14. The process according to claim 1 , further comprising forming a hollow body with at least one opening from the quartz glass body.