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

A silicate-containing glass ceramic made by a continuous sol-gel process, 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;
• and
• (g) sintering the xerogels at a temperature of 950 to 1100° C. to obtain silicate-containing glass ceramic;
• wherein the silicon alkoxide with at least one non-alcoholic functional group is selected from the group consisting of methyltriethylsilane, dimethyldiethylsilane, trimethylsilane, methyltriethoxysilane (MTES), triethoxyoctylsilane, octylmethyldichlorosilane, triethoxyvinylsilane and vinyltrimethoxysilane;
• and wherein the weight ratio of silicon tetraalkoxide and the silicon alkoxide with at least one non-alcoholic functional group is in the range of 30:1 to 1:5 and
• wherein zirconium (IV) alkoxides are employed as the metal alkoxide components in step b) and the obtained glass ceramics comprise the metal oxide component in an amount of 20 to 55 wt. %;
• and
• wherein the difference in the value of transmission of the silicate-containing glass ceramic in the range of visible light from the value of transmission of silica glass in the range of visible light is no more than 20%.