Method for producing a pore-containing opaque quartz glass
A method for producing a pore-containing opaque quartz glass includes: (a) producing porous SiO 2 granulate particles from synthetically produced SiO 2 , (b) thermally densifying the SiO 2 granulate particles to form partly densified SiO 2 granulate particles, (c) forming a dispersion from the partly densified SiO 2 granulate particles, (d) comminuting the partly densified SiO 2 granulate particles to form a slip containing comminuted SiO 2 granulate particles, (e) shaping the slip into a shaped body and forming a porous SiO 2 green body with a green density rG, and (f) sintering the SiO 2 green body into opaque quartz glass. To produce opaque quartz glass that is also suited for the use of spray granulate, during step (b), partly densified SiO 2 granulate particles are produced with a specific surface BET-(A) between 0.025 and 2.5 m 2 /g, and during step (d), comminuted SiO 2 granulate particles are produced with a specific surface BET-(B) between 4 and 10 m 2 /g.
1. Method for producing a pore-containing opaque quartz glass, the method comprising the steps of:
(a) producing porous SiO 2 granulate particles by agglomeration of amorphous, synthetically produced SiO 2 primary particles,
(b) thermally densifying the porous SiO 2 granulate particles to form partly densified SiO 2 granulate particles,
(c) forming a dispersion containing a dispersion liquid and the partly densified SiO 2 granulate particles dispersed therein,
(d) comminuting at least a part of the partly densified SiO 2 granulate particles in the dispersion to form a slip which contains comminuted SiO 2 granulate particles,
(e) shaping the slip into a shaped body and removing the dispersion liquid to form a porous SiO 2 green body with a green density ρG, and
(f) sintering the porous SiO 2 green body into the pore-containing opaque quartz glass,
(i) wherein during the thermal densification of step (b), the partly densified SiO 2 granulate particles are produced with a specific surface BET-(A) in the range of 0.025 to 2.5 m 2 /g determined by BET sorption measurement, and
(ii) wherein during the comminution of step (d), the comminuted SiO 2 granulate particles are produced with a specific surface BET-(B) in the range of 4 to 10 m 2 /g determined by BET sorption measurement.
2. Method according to claim 1 , wherein during the thermal densification, the partly densified SiO 2 granulate particles are produced with a specific surface BET-(A) of less than 0.8 m 2 /g determined by BET sorption measurement.
3. Method according to claim 1 , wherein the porous SiO 2 granulate particles prior to the comminution according to step (d) are partly densified at a temperature in the range of 800° C. to 1300° C., such that the partly densified SiO 2 granulate particles have a specific micropore surface of ≤0.25 m 2 /g, which is determined by BET sorption measurement.
4. Method according to claim 1 , wherein the porous SiO 2 granulate particles prior to the comminution according to step (d) are partly densified at a temperature in the range of 800° C. to 1300° C., such that the partly densified SiO 2 granulate particles have a specific micropore surface of ≤0.1, which is determined by BET sorption measurement.
5. Method according to claim 1 , wherein the comminuted SiO 2 granulate particles have a final particle size distribution defined by a D 10 value D 10 (B) <5 μm and a D 90 value D 90 (B)<50 μm.
6. Method according to claim 5 , wherein the comminuted SiO 2 granulate particles are dispersed in the dispersion with an initial particle size distribution defined by a D 10 value D 10 (A) >15 μm and a D 90 value D 90 (A) >105 μm.
7. Method according to claim 1 , wherein at least 80% of the comminuted SiO 2 particles with a particle size of more than 5 μm have a splintery morphology.
8. Method according to claim 7 , wherein at least 90% of the comminuted SiO 2 particles with a particle size of more than 5 μm have a splintery morphology.
9. Method according to claim 1 , wherein the slip while being shaped into the shaped body contains SiO 2 particles at a weight percentage of at least 70%.
10. Method according to claim 1 , wherein the slip while being shaped into the shaped body contains SiO 2 particles at a weight percentage of at least 75%.
11. Method according to claim 1 , wherein the slip while being shaped into the shaped body has a multimodal particle size distribution, with a first maximum at a particle size of less than 5 μm and a second maximum at a particle size of more than 20 μm.
12. Method according to claim 1 , wherein the porous SiO 2 granulate particles are produced with a bulk density in the range of 0.7 to 1 g/cm 3 .
13. Method according to claim 1 , wherein partial densification is carried out in a chlorine-containing atmosphere.
14. Method according to claim 1 , wherein the slip prior to shaping into the shaped body according to method step (e) is exposed to a vacuum.
15. Method according to claim 1 , wherein the green density of the porous SiO 2 green body is set to a value ρG in the range of 1.6<ρG<1.9 g/cm 3 .
16. Method according to claim 1 , wherein the production of the porous SiO 2 granulate particles according to method step (a) is carried out by way of spray granulation.