Abstract: Pure transparent quartz glass is provided by molding powdery amorphous silica into an article, converting the molded powdery amorphous silica into crystalline silica of high-temperature type cristobalite structure, and then fusing the crystalline silica, the quartz glass containing impurities respectively at a content of not higher than 1 ppm, and an OH group at a content of not higher than 20 ppm, and having a viscosity of 10.sup.12.0 poise or more at 1200.degree. C. The quartz glass is transparent and has high purity, and is excellent in high temperature viscosity characteristics. The quartz glass can be produced at a low cost.

Abstract: A process for preparing silica having a low silanol content which comprises heating amorphous silica in an atmosphere of a low partial pressure of water vapor to maintain the amorphous silica at a temperature in a range of from 600.degree. to 1000.degree. C. at a first heating step and then maintain at a temperature of 1200.degree. C. or more at a second heating step. The silica having a low silanol content obtained according to the present invention is advantageously used as a raw material for quartz glass, particularly as a raw material for preparing crucibles used to pull up silicon single crystals.

Abstract: A method for producing a nonsintered cristobalite particles comprising heating amorphous silica particles at a temperature of 1400.degree. to 1700.degree. C. in the presence of cristobalite particles (hereinafter referred to as cristobalite particles for addition and mixing) of at least 5 parts by weight based on 100 parts by weight of said amorphous silica particles to convert said amorphous silica particles to cristobalite particles with their particle form kept unchanged. According to the present invention, dense cristobalite having a low alkali content can be obtained in the form of particles. Such cristobalite is used as a filler, a dispersing agent, etc., and also as a material for high-quality artificial quartz, ceramics, etc., and particularly as a material for transparent quartz glass because of its generating no bubbles at the time of melt-molding.

Abstract: A method of manufacturing spherical silica particles comprising the steps of processing in an acid-containing solution and then washing with water the coagulant derived from an aqueous alkali metal silicate solution extruded through pores in a water-miscible organic medium or acid solution, wet-grinding the amorphous silica thus obtained in a liquid dispersion medium to obtain a fine particle silica suspension with a weight average particle size of 10 .mu.m or less, spray-drying this fine particle silica suspension with hot air and sintering the spherical granulated silica thus obtained. According to the present invention, the high-purity spherical silica particles can be obtained with high solidity and adjusted surface smoothness without any complicated operation or waste water treatment for use as a sealant filler for highly-integrated IC electronic parts.

Abstract: There is disclosed a process for producing unsintered cristobalite silica by heating an amorphous silica in the presence of an alkali component, which comprises heating an amorphous silica having a specific surface area (measured according to BET method) of 50 m.sup.2 /g or more at a temperature in the range of 1000.degree. to 1300.degree. C., in the presence of an alkali metal element in a concentration of 5 to 600 ppm to said silica to change it partially or completely into cristobalite and then heating at a temperature of exceeding 1300.degree. C. to eliminate alkali.

Abstract: This invention deals with a process for manufacturing high purity silica which comprises making an aqueous alkali silicate solution into fine fibrous gel in a coagulant, treating the fibrous gel obtained with an acid-containing solution, and then with water to extract and remove impurities; and optionallly heating a resulting silica at a temperature of 1,000.degree. C. or higher. Thus obtained silica is preferably used as a filler, especially, the one for resin compositions for encapsulating electronic parts; etc.