| 主权项 |
1. A method for producing a synthetic amorphous silica powder, comprising, in the recited order: a granulating step for producing a siliceous gel, drying the siliceous gel into a dry powder, pulverizing particles of the dry powder, and then classifying the pulverized particles to obtain a silica powder; a spheroidizing step based on a thermal plasma for delivering, at a predetermined supplying rate, particles of the silica powder into a plasma torch in which argon is introduced therein with a predetermined flow rate and a plasma is generated by a predetermined high-frequency power, in a manner to heat the particles at a temperature from 2,000° C. to the boiling point of silicon dioxide, thereby melting the particles; a cleaning step for removing fine particles attached onto surfaces of the silica powder particles; and a drying step for drying the silica powder particles; wherein the spheroidizing step comprises adjusting the flow rate of the argon to 50 L/min or more and a value of A/B (Whr/kg) to 3.0×103 to less than 1.0×104, where A is the high-frequency power (W), and B is the supplying rate (kg/hr) of the silica powder particles, thereby obtaining a synthetic amorphous silica powder having: an average particle diameter D50 of 10 to 2,000 μm; a quotient of greater than 1.35 and not more than 1.75 obtained by dividing a BET specific surface area of the powder by a theoretical specific surface area calculated from the average particle diameter D50; a real density of 2.10 to 2.20 g/cm3; an intra-particulate porosity of 0 to 0.05; a circularity of 0.50 to 0.75; and an unmolten ratio of greater than 0.25 and not more than 0.60. |
