Continuous sol-gel process for producing silicate-containing glasses or glass ceramics

Abstract

A continuous sol-gel process for producing silicate-containing glasses and glass ceramics is proposed, comprising the following steps: (a) continuously feeding a silicon tetraalkoxide, a silicon alkoxide with at least one non-alcoholic functional group and an alcohol into a first reactor (R1), and at least partially hydrolyzing by the addition of a mineral acid to obtain a first product stream (A); (b) continuously providing a second product stream (B) in a second reactor (R2) by feeding a metal alkoxide component or continuously mixing an alcohol and a metal alkoxide component; (c) continuously mixing product streams (A) and (B) in a third reactor (R3) for producing a presol to obtain a third product stream (C); (d) continuously adding water or a diluted acid to the product stream (C) to obtain a sol (gelation); (e) continuously filling the emerging sol into molds to obtain an aquagel; (f) drying the aquagels to obtain xerogels; (g) sintering the xerogels to obtain silicate-containing glasses and glass ceramics.

It is claimed: 
     
         1 . A continuous sol-gel method for the production of silicate-containing glasses and glass-ceramics comprising the steps of:
 (a) continuously feeding a mixture of tetraethyl orthosilicate and methyltriethoxysilane and alcohol into a first reactor R1, and at least partially hydrolyzing by adding a mineral acid to obtain a first product stream A;
 the weight ratio of tetraethyl ortho-silicate to the methyltriethoxysilane is 5:1 to 15:1; 
   (b) continuously providing a second product stream B in a second reactor R2 by adding a metal alkoxide component or continuously mixing the alcohol and metal alkoxide components;   (c) continuous mixing of product streams A and B in a third reactor R3 to produce a pre-sol to obtain a third product stream C;   (d) continuously adding water or dilute acid to product stream C to obtain sol gelation;   (e) continuously filling the obtained sol into a mould to obtain a hydrogel;   (f) drying the hydrogel to obtain a xerogel;   (g) sintering the xerogel at 850 to 1200° C. to obtain a silicate-containing glass and glass-ceramic; wherein the metal oxide component is present in the silicate-containing glass or silicate-containing glass-ceramic in an amount of 20 wt.% to 55 wt.%.   
     
     
         2 . The method of  claim 1 , wherein nitric acid is used as the mineral acid in the step (a). 
     
     
         3 . The method according to  claim 1 , characterized in that in the step (a), 1 to 60% of the inorganic acid by weight of the silicon alkoxide is used. 
     
     
         4 . The method according to  claim 1 , wherein the at least partial hydrolyzing of the silicon alkoxide in the step (a) is carried out at a temperature of 1-100° C. 
     
     
         5 . The method of  claim 1 , wherein in the step (b), an alkyl orthotitanate is used as the metal alkoxide component. 
     
     
         6 . The method according to  claim 1 , wherein in the step (b), zirconium (IV) alkoxide is used as the metal alkoxide component. 
     
     
         7 . The method of  claim 1 , wherein the product streams (A) and (B) are mixed in a volume ratio of metal alkoxide to silica of 10:1 to 1:10. 
     
     
         8 . The method of  claim 1 , wherein the product streams (A) and (B) are mixed in a temperature range of 0-80° C. 
     
     
         9 . The method of  claim 1 , wherein at least one of steps (a), (b) or (c) is carried out in a continuous reactor, which may have an upper agitator element. 
     
     
         10 . The method of  claim 9 , wherein the continuous reactor has a length of 1 cm to 1000 m and/or a cross-sectional width of 1 to 10 mm. 
     
     
         11 . The method of  claim 1 , wherein the gelation is carried out in a temperature range of 0 to 100° C. 
     
     
         12 . The method of  claim 1 , wherein the drying is carried out in a temperature range of 0-150° C. 
     
     
         13 . A silicate-containing glass or a silicate-containing glass-ceramic obtainable by a continuous sol-gel method comprising the steps of:
 (a) continuously feeding a mixture of tetraethyl orthosilicate and methyltriethoxysilane and alcohol into the first reactor R1, and at least partially hydrolyzing by adding a mineral acid to obtain a first product stream A; the ortho-silicon The weight ratio of tetraethyl acid to the methyltriethoxysilane is 5:1 to 15:1;   (b) continuously providing a second product stream B in the second reactor R2 by adding the metal alkoxide component or continuously mixing the alcohol and metal alkoxide components;   (c) continuous mixing of product streams A and B in a third reactor R3 to produce a pre-sol to obtain a third product stream C;   (d) continuously adding water or dilute acid to product stream C to obtain sol gelation;   (e) continuously filling the obtained sol into a mould to obtain a hydrogel;   (f) drying the hydrogel to obtain a xerogel;   (g) sintering the xerogel at 850 to 1200° C. to obtain a silicate-containing glass and glass-ceramic; wherein the metal oxide component is present in the silicate-containing glass or silicate-containing glass-ceramic in an amount of 20 wt.% to 55 wt.%.   
     
     
         14 . The silicate-containing glass or silicate-containing glass-ceramic according to  claim 13 , wherein a refractive index nd of the silicate-containing glass or silicate-containing glass-ceramic is 1.45-1.8. 
     
     
         15 . The silicate-containing glass or silicate-containing glass-ceramic according to  claim 14 , wherein the refractive index nd of the silicate-containing glass or silicate-containing glass-ceramic is 1.48-1.75. 
     
     
         16 . The silicate-containing glass or silicate-containing glass-ceramic according to  claim 15 , wherein the refractive index nd of the silicate-containing glass or silicate-containing glass-ceramic is 1.5 to 1.7. 
     
     
         17 . The silicate-containing glass or the silicate-containing glass-ceramic according to  claim 13 , wherein the silicate-containing glass or the silicate-containing glass-ceramic is resistant to light with a wavelength of 300 to 900 nm is transparent. 
     
     
         18 . The silicate-containing glass or the silicate-containing glass-ceramic according to  claim 17 , wherein the silicate-containing glass or the silicate-containing glass-ceramic is resistant to light with a wavelength of 350 to 850 nm is transparent. 
     
     
         19 . The silicate-containing glass or the silicate-containing glass-ceramic according to  claim 18 , wherein the silicate-containing glass or the silicate-containing glass-ceramic is resistant to light with a wavelength of 380 to 780 nm is transparent. 
     
     
         20 . The silicate-containing glass or silicate-containing glass-ceramic according to  claim 13 , wherein the silicate-containing glass or silicate-containing glass-ceramic has a light transmittance in the visible light range, andthe difference in light transmittance with quartz glass in the visible light range is not more than 30%.