Gel-silica science

Sol-gel techniques can be used to produce two new types of optical silicas, termed Type V for the full density material and Type VI for the optically transparent porous material. This paper summarizes the processing differences between these six types of commercial silicas. The primary emphasis of this paper is to discuss the scientific basis for the processing of Types V and VI optical silica. First, however, the use of sol-gel processing of other systems will be briefly reviewed. The controlled hydrolysis of alkoxides has also been used to produce submicrometer TiO2, doped TiO2 (17), ZrO2 (18), doped ZrO2 (18), doped SiO2 (19), SrTiO3 (20), and corderite (20) powders. Emulsions have been employed to produce spherical powders of mixed cation oxides, such as yttrium aluminum garnets (YAG) and many other systems (20). Sol-gel powder processes have also been applied to fissile elements (21) where spray form sols UO2, and rigid gel spheres of UO-PuO2 are formed during passage through a column of heated liquid. Both crystalline and vitreous ceramic fibers have been prepared using the sol-gel method. Compositions include TiO2-SiO2 and ZrO2-SiO2 glass fibers (22), high purity SiO2 waveguide fibers (23), Al2O3, ZrO2, ThO2, MgO, TiO2, ZrSiO4, 3AlO3-2SiO2 fibers (24). Sol-gel derived alumina grains are important commercial products (25)