GB1197377A - Silica - Google Patents

Abstract

1,197,377. Crystalline hydrated silica. ENTREPRISE MINIERE CHIMIQUE. 14 March, 1968 [17 March, 1967], No. 12480/68. Heading C1A. A crystalline hydrated silica, 2SiO 2 .H 2 O, has acid properties and a characteristic X-ray diffraction pattern. It may be prepared from potassium hydrogen disilicate KHSi 2 O 5 , by;treating with an acid, filtering off the precipitated silica, and drying. The reaction takes place rapidly at room temperature and 99% yields are possible if stoichiometric amounts of acid, relative to the potassium in the silicate, are used. Any aqueous acid can be used e.g. sulphuric, hydrochloric, nitric, phosphoric and acetic acids, and it should preferably be sufficiently dilute for the potassium salt product to be taken up into solution. The silica hydrate may be partially dried by standing in air or completely dried by standing in vacuo in the presence of phosphoric anhydride. In a preferred method the potassium hydrogen disilicate is prepared by the hydrothermal reaction of amorphous silica with potassium hydroxide in an autoclave at 150-400‹ C. The reaction mixture contains less than 1 mole of potassium hydroxide per mole of silica and the water to silica molar ratio is between 1 and 20.