PRODUCTION OF SILICA POWDER OF HIGH OIL ABSORPTION

摘要

PURPOSE:To enable inexpensive production of the title silica, by acid-treating tobermorite type calcium silicate which has been prepared by reaction between an acidic volcanic rock and calcium hydroxide in an aqueous slurry. CONSTITUTION:(A) An acidic volcanic rock of more than 80wt.% of SiO2, mainly consisting of alpha-cristobalite, crushed into particles of less than 5mum median diameter, is allowed to react with (B) calcium hydroxide at 1.0-3.0 SiO2/CaO molar ratio, in the presence of water of 4.5-30ml/g of the solid, so that alpha- cristobalite disappears over 60% according to the equation [Is is the peak height of (101) face of the alpha-cristobalite in the component A; It is the peak height of (101) face of the alpha-cristobalite in the product, to give (C) the subject tobermorite type calcium silicate. Then, the product C is neutralized with an acid whose calcium salt is soluble in water such as hydrochloric acid to give a powdery silica of more than 200ml/100g oil absorption.