Molded body made of opaque quartz glass and method for producing same
Producing a molded body made of opaque quartz glass includes providing SiO 2 grains obtained by comminuting quartz glass having a purity of at least 99.9 wt % SiO 2 , forming a slurry containing a suspension liquid and the SiO 2 grains and which has a total solids content, wet grinding the SiO 2 grains in the slurry so as to form ground SiO 2 grain particles, forming a porous green body from the slurry, and sintering the porous green body. To provide a low cost quartz glass, the wet grinding of the SiO 2 grains takes place at least temporarily in the presence of SiO 2 nanoparticles, the proportion of which in the total solids content of the slurry is in the range of 0.1 wt % to 10 wt %, and the slurry has a solids content in the range of 76 to 80 wt % after addition of the SiO 2 nanoparticles and after the wet grinding.
1 . A method for producing a molded body made of opaque quartz glass, comprising:
(a) providing SiO 2 grains obtained by comminuting quartz glass having a purity of at least 99.9 wt % SiO 2 ,
(b) forming a slurry which contains a suspension liquid and the SiO 2 grains and which has a total solids content,
(c) wet grinding the SiO 2 grains in the slurry so as to form ground SiO 2 grain particles,
(d) forming a porous green body from the slurry comprising a process step in which the slurry is poured into a dewatering mold, and
(e) sintering the porous green body so as to form the molded body of opaque quartz glass,
wherein the wet grinding of the SiO 2 grains according to (c) takes place, at least part of the time or during the entire step of wet grinding, in the presence of SiO 2 nanoparticles, the proportion of which in the total solids content of the slurry is in the range of 0.1 wt % to 10 wt %, and in that the slurry has a solids content in the range of 76 to 79.5 wt % after addition of the SiO 2 nanoparticles and after the wet grinding, and wherein at least a portion of the SiO 2 nanoparticles of the slurry are added in colloidal form into a dispersion with a specific surface area (BET) of at least 20 m 2 /g, and wherein the molded body has a homogeneity defined by a difference in density between a maximum density and a minimum density of less than 0.026 g/cm 3 .
2 . The method according to claim 1 , wherein the proportion of SiO 2 nanoparticles in the total solids content is in the range of 1 wt %-5 wt %.
3 . The method according to claim 1 , wherein the wet grinding of the SiO 2 grains according to (c) in the presence of SiO 2 nanoparticles is at least 1 hour.
4 . The method according to claim 1 , wherein the wet grinding of the SiO 2 grains according to (c) in the presence of SiO 2 nanoparticles is at least 120 hours.
5 . The method according to claim 1 , wherein the slurry is cooled, after the wet grinding, under movement, for at least 1 hour.
6 . The method according to claim 1 , wherein the slurry is cooled, after the wet grinding, under movement for at least 30 hours.
7 . The method according to claim 1 , wherein, after the wet grinding, the slurry has SiO 2 particles having a particle size distribution which is defined by a D 90 of less than 50 μm and a D 50 value of less than 15 μm.
8 . The method according to claim 1 , wherein, after addition of the SiO 2 nanoparticles and after wet grinding, the slurry has a pH in the range of 3 to 5 and a solids content in the range of 77 to 79.5 wt %.
9 . The method according to claim 1 , wherein the slurry has a sedimentation behavior which is characterized in that a column of the slurry having a height of 145 mm has formed a sediment with a sediment height of less than 20 mm after a standing time of 24 hours.
10 . The method according to claim 1 , wherein the SiO 2 grains are obtained by comminuting synthetically produced transparent quartz glass, wherein the comminuting comprises electrodynamic and/or electrohydraulic fragmentation of the transparent quartz glass.
11 . The method according to claim 1 , wherein the green body is dried before sintering, wherein the drying is carried out at above room temperature and comprises a drying duration of at least 24 hours.
12 . The method according to claim 1 , wherein a surface region of the green body is removed before sintering by mechanical machining, by sanding, wherein a machining tool is used that has machining surfaces made of plastic-bonded grains.
13 . The method according to claim 1 , wherein the sintering in accordance with method step (e) takes place at a sintering temperature in the range between 1325° C. and 1600° C.
14 . The method according to claim 1 , wherein the sintering in accordance with (e) takes place at a sintering temperature at 1450° C.