Preparation of quartz glass bodies from silicon dioxide granulate

Patent metadata

Field	Value
Publication number	US-11492285-B2
Application number	US-201616061558-A
Country	US
Kind code	B2
Filing date	Dec 16, 2016
Priority date	Dec 18, 2015
Publication date	Nov 8, 2022
Grant date	Nov 8, 2022

Abstract

One aspect relates to a process for the preparation of a quartz glass body including, providing a silicon dioxide granulate obtainable from a silicon dioxide powder, wherein the silicon dioxide granulate has a larger particle size than the silicon dioxide powder, making a 5 glass melt out of silicon dioxide granulate and making a quartz glass body out of at least part of the glass melt. The melting crucible has at least one inlet and at least one outlet. A least part of the glass melt is removed via the melting crucible outlet. One aspect further relates to a quartz glass body which is obtainable by this process. One aspect further relates to a light guide, an illuminant and a formed body, which are each obtainable by further processing 10 of the quartz glass body.

First claim

The invention claimed is:

1. A process for the preparation of a quartz glass body comprising:
providing a silicon dioxide granulate comprising:
providing a silicon dioxide powder; and
processing the silicon dioxide powder to obtain a silicon dioxide granulate, wherein the silicon dioxide granulate has a greater particle size than the silicon dioxide powder and such that the silicon dioxide granulate is open-pored;
wherein the silicon dioxide granulate has a particle size distribution D 50 of 160 μm or greater in order to avoid crust formation and has a particle size distribution D 50 of 290 μm or less in order to avoid gas bubble formation;

making a glass melt out of the silicon dioxide granulate in an oven, wherein the oven comprises a melting crucible; and
making a quartz glass body out of at least part of the glass melt;
wherein the melting crucible comprises at least one inlet and at least one outlet; and
wherein at least part of the glass melt is taken from the outlet of the melting crucible.

2. The process according to claim 1 , wherein processing the silicon dioxide powder to obtain a silicon dioxide granulate comprises:
providing a liquid;
mixing the silicon dioxide powder with the liquid to obtain a slurry; and
spray-drying the slurry.

3. The process according to claim 2 , whereby the spray-drying of the slurry is performed by spraying the slurry from through a nozzle into a spray tower comprising at least one of:
spray granulation in the spray tower;
presence of a pressure on the slurry at the nozzle in the range from 5 to 12 bar, wherein the pressure stated is absolute (relative to p=0 hPa);
a temperature of droplets as they enter the spray tower in a range from 18 to 25° C.;
a temperature of the side of the nozzle facing the spray tower in a range from 350 to 430° C.;
a throughput of slurry through the nozzle in a range from 0.25 to 0.4 m 3 /h;
a solids content of the slurry of at least 60 to 70 wt.-%, based on the total weight of the slurry;
a gas inflow into the spray tower in a range from 40 to 60 kg/min;
a temperature of a gas flow as it enters the spray tower in a range from 350 to 430° C.;
a temperature of a gas flow as it leaves the spray tower of less than 170° C.;
a gas is selected from the group which consists of air, nitrogen and helium or a combination of two or more thereof;
a residual moisture of the silicon dioxide granulate when taken from the spray tower in a range from 0.1 to 0.3 wt.-%, based on the total weight of the silicon dioxide granulate obtained from the spray drying;
at least 50 wt.-% of a spray granulate, based on the total weight of the silicon dioxide granulate obtained from the spray drying, completes a flight time in a range from 25 to 70 s;
at least 50 wt.-% of a spray granulate based on the total weight of the silicon dioxide granulate obtained from the spray drying, covers a flight path of a range of from 30 to 80 m;
the spray tower is of cylindrical geometry;
a height of the spray tower is in a range from 15 to 20 m;
screening out of particles less than 90 μm in size before the silicon dioxide granulate is removed from the spray tower;
sieving out of particles more than 500 μm in size after the silicon dioxide granulate is removed from the spray tower on a vibrating chute; and
slurry droplets exit from the nozzle at an angle of 45° to the vertical.

4. The process according to claim 2 , wherein the silicon dioxide granulate obtained from the spray-drying comprises:
a particle size distribution D 10 in a range from 50 to 150 μm, and
a particle size distribution D 90 in a range from 250 to 620 μm.

5. The process according to claim 2 , wherein the solids content of the slurry is 50-80 wt. %.

6. The process according to claim 1 , wherein processing the silicon dioxide powder to obtain a silicon dioxide granulate comprises:
providing a liquid;
mixing the silicon dioxide powder with the liquid to obtain a slurry; and
roll granulating the slurry.

7. The process according to claim 6 , wherein the roll granulation of the slurry comprises at least one of:
the roll granulation of the slurry is carried out in a rotating stirring vessel;
the roll granulation of the slurry is carried out at a gas flow from 10 to 150 kg gas per 1 kg slurry per hour;
an inlet gas temperature is 40 to 200° C.;
granules with a particle size of less than 100 μm and more than 500 μm are sieved out;
granules formed have a residual moisture content of 15-30 wt.-%; and
granules formed are dried at 80 to 250° C. in a continuous drying tube to a residual moisture content of less than 1 wt.-%.

8. The process according to claim 1 , wherein the silicon dioxide granulate comprises an angle of repose in a range from 23 to 26°.

9. The process according to claim 8 , wherein the silicon dioxide granulate also comprises at least one of:
a mean particle size in a range from 180-300 μm;
a bulk density in a range from 0.5 to 1.2 g/cm 3 ;
a carbon content of less than 50 ppm;
an aluminium content of less than 200 ppb;
a tamped density in a range from 0.7 to 1.3 g/cm 3 ;
a pore volume in a range from 0.1 to 2.5 mL/g;
a particle size distribution D 10 in a range from 50 to 150 μm;
and
a particle size distribution D 90 in a range from 250 to 620 μm,
wherein the ppm are based on the total weight of the silicon dioxide granulate.

10. The process according to claim 2 , wherein the spray drying comprises at least one of:
the slurry is conveyed in contact with a plastic surface;
the slurry is sheared;
the slurry is at a temperature of more than 0° C.;
the slurry has a zeta potential at a pH value of 7 in a range from −30 to −45 mA;
the slurry has a pH value in a range from 8.5 to 10;
the slurry has an isoelectric point in a range from 3 to 3.5;
the slurry has a solids content in a range from 60 to 70 wt.-%, based on the total weight of the slurry;
the slurry has a viscosity in accordance with DIN 53019-1 (5 rpm, 30 wt.-%) in a range from 700 to 800 mPas;
the slurry has a thixotropy in accordance with DIN SPEC 91143-2 (30 wt.-% in water, 23° C., 5 rpm/50 rpm) in the range from 4.0 to 4.5; and
in a 4 wt.-% slurry, the silicon dioxide particles in the slurry have an average particle size in suspension in accordance with DIN ISO 13320-1 in the range from 200 to 300 nm.

11. The process according to claim 1 , wherein the silicon dioxide powder is prepared from a compound selected from the group consisting of siloxanes, silicon alkoxides and silicon halides.

12. The process according to claim 1 , wherein the silicon dioxide powder comprises at least one of:
a BET surface area in a range from 20 to 60 m 2 /g;
a bulk density in a range from 0.01 to 0.3 g/cm 3 ;
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 different from aluminium of less than 5 ppm;
at least 70 wt.-% of the silicon dioxide powder have a primary particle size in a range from 10 to 100 nm;
a tamped density in a range from 0.001 to 0.3 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 ppm and ppb are each based on the total mass of the silicon dioxide powder.

13. The process according to claim 1 , further comprising making a hollow body with at least one opening out of the quartz glass body.

14. A process for the preparation of a light guide comprising

Assignees

• Heraeus Quarzglas

Inventors

• Otter Matthias
• Lehmann Walter
• Hünermann Michael
• Nielsen Nils Christian
• Wittrin Mirko
• Wilde Markus

Classifications

• C03C2201/32

  containing aluminium (C03C2201/36 takes precedence) · CPC title

• C03C2201/02

  Pure silica glass, e.g. pure fused quartz · CPC title

• C03B17/04

  Forming tubes or rods by drawing from stationary or rotating tools or from forming nozzles · CPC title

• C03C2201/23

  containing hydroxyl groups · CPC title

• C03C2201/11

  containing chlorine · CPC title