Abstract: Sol-gel process for the production of large glass monoliths, whereby tetraalkoxysilane is added to a dispersion of pyrogenically produced silica and the ratio of SiO2:TEOS is 2.6 to 5.5:1.

Abstract: Process for the production of monoliths by means of the sol-gel process, comprising the following steps: a. hydrolysis of an alkoxide in aqueous solution to form a hydrolysate and optionally evaporation to optimum concentration of the same, b. addition of an oxide prepared by the pyrogenic route, c. mixing of the hydrolysate of the alkoxide with the oxide prepared by the pyrogenic route to form a colloidal sol, d. optional removal of coarse contents from the colloidal sol, e. gelling of the colloidal sol in a mould, f. optional replacement of the water contained in the resulting aerogel by an organic solvent, g. drying of the aerogel, h. heat treatment of the dried aerogel, the coarse content being removed from the colloidal sol.

Abstract: It has been discovered that aquagels, formed from acid catalized composite sols, survive to conditions of high-tension when they are prepared by a process that hydrolyzes the silicon alkoxides in presence of fumed silica. The aquagel can be used for the production of monoliths of glass.

Abstract: Process for the production of monoliths of glass by means of the sol-gel process, comprising the following steps: a) dispersion in water of an oxide prepared by the pyrogenic route, b) hydrolysis of an alkoxide in aqueous solution to form a hydrolysate, c) mixing of the hydrolysate of the alkoxide with the oxide prepared by the pyrogenic route to form a colloidal sol, d) optional removal of coarse contents from the colloidal sol, e) gelling of the colloidal sol in a mould, f) replacement of the water contained in the resulting aerogel by an organic solvent, g) drying of the aerogel, h) heat treatment of the dried aerogel.

Abstract: Glassy articles are prepared by subjecting to hydrolysis and policondensation a solution or suspension of a suitable precursor, mainly comprising a silicon alkoxide, and by drying the obtained gel in a pressure chamber, the gel solvent having been substituted by a non-protic solvent, mainly acetone, under nitrogen flowing, at temperature and pressure conditions lower than the gel solvent critical values. The dried gel is then densified by a thermal treatment.

Abstract: Particularly shaped articles constituted by silicon oxide, as such or with suitable additives, prepared by room temperature molding according to a process comprising: preparation of a sol starting from a silicon alcoxide, or from a silicon alcoxide and at least a precursor of at least one of the additional elements; hydrolysis of the sol obtained thereby; addition of colloidal silica; pouring the resulting mixture into the desired mould; sol gelling and fast removal of the solid product; gel drying; gel densification by means of a thermal treatment at temperature ranging from 900 ° C to 1500 ° C. The articles can be used as preforms for the optic fiber spinning.

Abstract: Glassy articles are prepared by subjecting to hydrolysis and policondensation a solution or suspension of a suitable precursor, mainly comprising a silicon alkoxide, and by drying the obtained gel in a pressure chamber, the gel solvent having been substituted by a non-protic solvent, mainly acetone, under nitrogen flowing, at temperature and pressure conditions lower than the gel solvent critical values. The dried gel is then densified by a thermal treatment.

Abstract: A method for preparing inorganic oxide-based materials of spherical form with substantially monomodal distribution, consisting of forming a sol of at least one of the inorganic oxides of interest, adding to said sol a solvent immiscible with the sol, finely dispersing the obtained two-phase mixture into a dispersion of particles of equal diameter, growing said particles by limited coalescence to the desired diameter, gelling said mixture by adding a second solvent containing a gelling agent, and removing the solvent.

Abstract: A method for preparing inorganic oxide-based materials of spherical form with substantially monomodal distribution, consisting of forming a sol of at least one of the inorganic oxides of interest, adding to said sol a solvent immiscible with the sol, finely dispersing the obtained two-phase mixture into a dispersion of particles of equal diameter, growing said particles by limited coalescence to the desired diameter, gelling said mixture by adding a second solvent containing a gelling agent, and removing the solvent.