Abstract:
A process for producing hydrophobic finely divided fume silica which comprises the following steps in the specified sequence: A. FORMING, IN A FIRST REACTION ZONE, PARTICLES OF A FUME SILICA HAVING A SIZE OF LESS THAN APPROXIMATELY 150 MILLIMICRONS BY THERMAL DECOMPOSITION AND HYDROLYSIS IN THE VAPOR PHASE OF A VOLATILE SILICON HALIDE, THE SAID FUME SILICA PARTICLES HAVING AN ACIDITY CORRESPONDING TO A PH of approximately 2.0, and including a hydrogen halide and water adsorbed on their surfaces, B. PASSING THE THUS-PRODUCED FUME SILICA PARTICLES OUT OF THE SAID FIRST REACTION ZONE AND SUBJECTING THEM TO A DEACIDIFICATION AND DEHYDRATION PRETREATMENT TO REDUCE THEIR ACIDITY TO A VALUE CORRESPONDING TO A PH of approximately 4.0 by removing substantially all of the adsorbed hydrogen halide and water therefrom, C. PASSING THE THUS-PRETREATED PARTICLES OF FUME SILICA TOGETHER WITH WATER VAPOR INTO A SECOND REACTION ZONE INTO CONTACT WITH A STREAM OF HOT GASES CONTAINING SUBSTANTIAL PROPORTIONS OF AN ORGANOHALOSILANE WHILE THE SECOND REACTION ZONE IS MAINTAINED AT A TEMPERATURE BETWEEN APPROXIMATELY 400* AND APPROXIMATELY 800* C and the particles therein are maintained in a fluidized state and maintained therein for a period sufficient to convert them to hydrophobic fume silica particles, THE FOREGOING STEP, (C) OF THE PROCESS BEING PERFORMED IN THE ABDENCE OF MOLECULAR OXYGEN, AND D. SEPARATING AND RECOVERING THE HYDROPHOBIC FUME SILICA PARTICLES THUS PRODUCED FROM THE HOT GASES AND HYDROGEN HALIDE FORMED FROM THE ORGANOHALOSILANE WHILE STILL CONTINUING TO EXCLUDE MOLECULAR OXYGEN FROM CONTACT WITH THE PARTICLES UNTIL THE PARTICLES HAVE COOLED TO A TEMPERATURE BELOW 400* C.
Abstract:
The silica, pref. in the form of a filter cake, is dispersed uniformly in water, adjusted to pH 1-6, pref. 2-4, with stirring, and stabilised by addn. of 0.001-1, pref. 0.005-0.1% thickener w.r.t. the total amt. of dispersion. The pref. thickener is alpha-methylcellulose strengthened with synthetic resin. The dispersions are useful, e.g. as antislip agent for cardboard. The process makes it possible to produce stable dispersions from isolated and opt. dried silicas, which are not alkaline.
Abstract:
A mixture of two or more metal or metalloid oxides, which have been produced by thermal decomposition from the mixture of halide vapours in the presence of hydrogen with or without added oxygen, is dispersed in a liquid medium with the aid of a minor amount of a phosphate and/or an alkali-metal silicate. Alumina/silica oxide dispersions may be more or less colloidal solutions of aluminium silicate. In examples, silicon or titanium tetra chloride or aluminium trichloride are decomposed to form aerogel oxides, to which water is added and also a small amount of sodium metaphosphate, or tri-metaphosphate. The mixture is then vigorously stirred with the addition of water glass.
Abstract:
Process for the production of a finely divided oxide of a metal or silicon by the hydrolytic conversion of a volatile corresponding metal halide or silicon halide in a flame, said process comprising feeding the volatile halide in a mixture with a combustible hydrogen-containing gas and air or oxygen to a burner provided with a mouth emitting a flame, burning the mixture in a fire tube to form a first portion of water vapor, said burner surrounded by an annular chamber forming a nozzle through which hydrogen is passed to keep the mouth of the burner free of attachments of solid substances, the quantity of oxygen or air being sufficient for the practically complete combustion of the combustible gas, and the quantities of oxygen or air and combustible gas being sufficient to produce the first portion of water vapor which will at least suffice for the hydrolysis of the volatile halides, and further wherein said flame is allowed to burn in an atmosphere consisting of gases containing a second portion of water vapor, to avoid the formation of halogen gas in waste gases and separating the resulting oxide from other reaction products. The finely divided oxides are useful as additives and fillers in the manufacture of coatings, adhesives and elastomers.
Abstract:
Process for the production of a finely divided oxide of a metal or silicon by the hydrolytic conversion of a volatile corresponding metal halide or silicon halide in a flame, said process comprising feeding the volatile halide in a mixture with a combustible hydrogen-containing gas and air or oxygen to a burner provided with a mouth emitting a flame, burning the mixture in a fire tube to form a first portion of water vapor, said burner surrounded by an annular chamber forming a nozzle through which hydrogen is passed to keep the mouth of the burner free of attachments of solid substances, the quantity of oxygen or air being sufficient for the practically complete combustion of the combustible gas, and the quantities of oxygen or air and combustible gas being sufficient to produce the first portion of water vapor which will at least suffice for the hydrolysis of the volatile halides, and further wherein said flame is allowed to burn in an atmosphere consisting of gases containing a second portion of water vapor, to avoid the formation of halogen gas in waste gases and separating the resulting oxide from other reaction products. The finely divided oxides are useful as additives and fillers in the manufacture of coatings, adhesives and elastomers.
Abstract:
Finely divided metal or silicon oxides are prepared by the vapour phase hydrolytic reaction of volatile metal or silicon halides in a flame into which the halide is introduced in admixture with oxygen and a gas whose combustion is accompanied by the formation of water, in such proportions that the mixture contains enough oxygen for the complete combustion of the flammable gas whilst the amount of water formed is at least sufficient to hydrolyse the volatile halide, said flame burning in an enclosed reaction zone and being surrounded by a gas inert to the reactions in the flame. In the diagram, the mixture of gases is fed to a burner 11 and the flame 12 burns in a flame tube 13 in an atmosphere of nitrogen supplied by a feed pipe 16 via a gauze 15. The air may be supplied to the burner in two streams, primary air supplied direct and supporting air bearing the metal halide.