| abstract |
A method for preparing a silica sol having an elongated shape comprising a step (a) where an aqueous solution containing a water-soluble calcium salt or a water-soluble magnesium salt or a mixture of the water-soluble calcium salt or the water-soluble magnesium salt is mixed with an aqueous colloidal solution of an active silicic acid; a step (b) where an alkaline substance is mixed with the aqueous liquid obtained in the step (a); a step (c) where a part or the whole of the mixture obtained in the step (b) is heated at 60° C. or higher to obtain a heel solution and a feed solution is prepared by a part of the mixture obtained in the step (b) or a mixture separately prepared by the step (b) and the feed solution is added to the heel solution; and a step where water is evaporated during said addition step so that SiO 2 concentration is concentrated to 6 to 30% by weight. |