Method for producing opaque quartz glass, and blank made from the opaque quartz glass
In one method for producing opaque quartz glass, a green body is produced from a slip containing fine, amorphous SiO 2 particles and coarse SiO 2 reinforcement bodies and the green body is sintered by way of a sintering treatment into a blank made from the opaque quartz glass. The reinforcement bodies with a specific density D K1 are here embedded in a SiO 2 matrix with a specific glass density D M . Starting from this, in order to provide a blank of opaque quartz glass that is less susceptible to cracking and illustrates homogeneous transmission even in the case of small wall thicknesses, in one aspect sinterable reinforcement bodies are used, the specific density D K0 of which prior to the sintering treatment is lower than the specific glass density D M , and which due to the sintering treatment reach the specific density D K1 which differs from the specific glass density D M by less than 10%.
1. A method for producing an opaque quartz glass in that a green body is produced from a slip containing fine, amorphous SiO 2 particles and coarse, porous and sinterable SiO 2 reinforcement bodies and the green body is sintered by way of a sintering treatment into a blank made from the opaque quartz glass, in which reinforcement bodies with a specific density D K1 are embedded n a SiO 2 matrix with a specific glass density D M , characterized in that prior to the sintering treatment, the coarse, porous and sinterable SiO 2 reinforcement bodies embedded in the green body have a mean particle size (D 50 value) of at least 500 μm, and a specific density D K0 , which is lower than the specific glass density D M , and wherein the coarse, porous and sinterable SiO 2 reinforced bodies due to the sintering treatment reach a specific density D K1 , which differs from the specific glass density D M by less than 10%.
2. The method according to claim 1 , characterized in that the coarse, porous sinterable SiO 2 reinforcement bodies due to the sintering treatment reach a specific density D K1 that differs from the specific glass density D M by less than 5%.
3. The method according to claim 1 , characterized in that opaque quartz glass is produced that at a measurement wavelength of 1700 nm and 3200 nm has a direct spectral transmission T G , and that due to the sintering treatment the coarse, porous and sinterable SiO 2 reinforcement bodies at a measurement wavelengths reach a direct spectral transmission T K that differs from T G by less than 0.05 percentage points.
4. The method according to claim 1 , characterized in that opaque quartz glass is produced that at a measurement wavelength of 1700 nm and 3200 nm has a direct spectral transmission T G , and that due to the sintering treatment the coarse, porous and sinterable SiO 2 reinforcement bodies at a measurement wavelengths reach a direct spectral transmission T K that differs from T G by less than 0.02 percentage points.
5. The method according to claim 1 , characterized in that a nominal specific glass density has a value between 2.10 and 2.18 g/cm 3 , and that the specific density of the coarse, porous and sinterable SiO 2 reinforcement bodies prior to the sintering treatment is between 85% to 95% of said value.
6. The method according to claim 1 , characterized in that a nominal specific glass density has a value between 2.15 and 2.18 g/cm 3 , and that the specific density of the coarse, porous and sinterable SiO 2 reinforcement bodies prior to the sintering treatment is between 85% to 95% of said value.
7. The method according to claim 1 , characterized in that the reinforcement bodies are produced by a process comprising the following steps: (a) providing fine, amorphous SiO 2 particles; (b) pre-compaction of the fine, amorphous SiO 2 particles into a porous molding, and (c) comminuting the porous molding into the coarse, porous and sinterable SiO 2 reinforcement bodies.
8. The method according to claim 7 , characterized in that pre-compaction comprises a pre-sintering treatment in which a maximum pre-sintering temperature is set, which in the range of 20-100° C. is lower than a maximum sintering temperature in the sintering treatment.
9. The method according to claim 1 , characterized in that the coarse, porous and sinterable SiO 2 reinforcement bodies have a mean particle size (D 50 value) of at least 1000 μm.
10. The method according to claim 9 , characterized in that the size ratio of the mean particle size of the coarse, porous and sinterable SiO 2 reinforcement bodies and the mean particle size (D 50 value) of the fine, amorphous SiO 2 particles is between 1:5 and 1:500.
11. The method according to claim 1 , characterized in that the coarse, porous and sinterable SiO 2 reinforcement bodies have a mean particle size (D 50 value) of at least 1500 μm.
12. The method according to claim 1 , characterized in that the coarse, porous and sinterable SiO 2 reinforcement bodies have a mean particle size (D 50 value) of at least 5000 μm.
13. The method according to claim 1 , characterized in that the volume ratio of the coarse, porous and sinterable SiO 2 reinforcement bodies and the fine, amorphous SiO 2 particles in the slip is between 1:3 and 3:1.