TW200833606A - Process for producing silica sol having elongated shape - Google Patents

Abstract

This invention provides a process for producing silica sol having elongated shapes, which includes the steps of: (a) adding a solution containing water soluble calcium salts or magnesium salts or their mixtures into a gel solution of active silicic acid, which comprises 1 to 6 mass% SiO2 and has the pH value of 2 to 5. Wherein, the ratio of CaO, MgO or both of CaO and MgO to SiO2 of the active silicic acid is 1500 to 15000ppm; (b) By the conversion of molecular ratio of SiO2/M2O =20 to 200, (SiO2 represents the total amount of the silica components from the active silicic acid and from the water soluble silicic acid; M represents the alkali metal atom or organic base molecule), the equivalent amount of alkali metal hydroxides or water soluble organic bases or their water soluble silicic acids added into the solution obtained in the step (a), and mixed well; (c), heating the mixture obtained in the step (b) at a temperature of 85-200 degree Celcius for 0.5 to 20 hours to produce a gel solution; (d) removing a part of water in the gel solution obtained from the step (c), and removing at least a part of anions in aforementioned solution containing the water soluble calcium salts, magnesium salts or their mixtures; and (e) heating the gel solution obtained in the step (d) at a temperature of 80 to 195 degree Celcius, which is lower than the heating temperature in the step (c), for 0.5 to 20 hours.