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Production of microspheres having a very high silica content produced from a starting glass whose silica content is less than 80% by weight, with the remainder being essentially made up of boron oxide and one or more alkaline oxide(s). This starting glass is reduced into fine particles by grinding,

Production of microspheres having a very high silica content produced from a starting glass whose silica content is less than 80% by weight, with the remainder being essentially made up of boron oxide and one or more alkaline oxide(s). This starting glass is reduced into fine particles by grinding, optionally mixed with a fluidizing agent, and then passed through the flame of a burner at a temperature at least equal to 1500°C. to form molten hollow microspheres which are suddenly cooled to form solid hollow microspheres. The microspheres produced thereby are recovered and contacted with a dealkalization agent to increase the silica content thereof to at least 92%. ..CL: A process for the production of hollow microspheres with a high silica content from a starting glass whose silica content is less than 80% by weight, with the balance being essentially boron oxide and one or more alkaline oxides, which process comprises: grinding the starting glass into fine particles; passing these fine particles through the flame of a burner at a temperature of at least about 1500°C. but less than about 1750°C. to form molten hollow microspheres; suddenly cooling the molten hollow microspheres to solid hollow microspheres; recovering the microspheres; and contacting the recovered microspheres with a gaseous dealkalization agent of a temperature greater than 200°C. but below that which would alter the structure of the microspheres to increase the silica content of the microspheres to at least 92%.

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