Abstract: The invention relates to a process for preparing highly disperse silicon dioxide by combustion of organochlorosilicon compounds, which comprises transporting a liquid which contains at least one hydrocarbon compound and at least one organochlorosilicon compound into a burner and burning the liquid there in the presence of an oxygen-containing gas and without supply of water.

Abstract: A process for continuously rendering finely divided, pyrogenic silica hydrophobic at low temperatures in the presence of a hydrophobicizing aid such as aliphatic alcohols having from 1 to 3 carbon atoms. The process of rendering silica hydrophobic is conducted at temperatures of from 60.degree. to 350.degree. C., and more preferably from 80.degree. to 150.degree. C., over a period of from 2 to 5 hours, and more preferably from 3 to 4 hours. The hydrophobicizing agents are known organohalosilanes and the preferred hydrophobicizing aid is methanol. The hydrophobicizing aid is used in amounts of from 2% to 15% by weight, and more preferably in amounts of from 2% to 10% by weight, based on the weight of silica used.

Abstract: The invention relates to a process for continuously hydrophobicizing pyrogenic, finely divided silica, in which the waste gases are fed back to a mixing chamber upstream of the SiO.sub.2 reaction flame.

Abstract: A process for the production of pyrogenic silicic acid having an increased thickening effect which comprises subjecting silicon-containing materials to a pyrolysis flame while introducing additional energy into the flame. The invention also relates to the product so obtained, particularly useful for articles of dental care.

Abstract: Waste gases resulting from the production of silicon in connection with the ormation or decomposition of chlorosilanes, which gases always contain hydrogen chloride, can be worked up without removal of the hydrogen chloride. For this purpose, the waste gases which, after separation from the chlorosilanes, only contain hydrogen and hydrogen chloride, are subjected to combustion with addition of air and, after addition of silicon tetrachloride, the result being highly dispersed SiO.sub.2. The hydrogen chloride then remaining in the gaseous phase is returned to the process stream for production of trichlorosilane.

Abstract: A process for the manufacture of highly dispersed silicon dioxide with improved thickening action by treatment of pyrogenically produced silicic acid comprising the following steps:A. preparing silicic acid by flame hydrolysis from silicon halides;B. separating the silicic acid from generated gases;C. reating the acid with 2 to 10 percent by weight of silicon tetrachloride calculated on silicic acid, while optionally/mechanically stirring;D. hydrolyzing the product by means of an air/water vapor mixture, and finally deacifying to obtain the silicon dioxide of improved thickening action.The invention also relates to the thickening agent, which is useful for a variety of purposes, among others as additive for preparations of dental hygiene.

Abstract: A process and device for the manufacture of highly disperse silicon dioxide by reacting gaseous organosilanes and other gases that burn with formation of water with oxygen-containing gases in a flame which comprises evaporating the organosilane in an evaporator in such a manner that the level of liquid organosilane is held constant at an organosilane evaporatinng vapor pressure of 0.2 to 1.2 atmospheres gage and, at most, at a temperature of 45.degree. C, preferably 20.degree. to 35.degree. C, above the boiling point of the particular organosilane, maintaining the temperature of the vapor until mixing with the other gases occurs, metering the gas mixture resulting from the mixing through a cone-shaped inlet into a combustion chamber, flushing oxygen-containing gases through an annular nozzle surrounding the inlet into the combustion chamber, and indirectly but positively, cooling the latter.