PROCESS FOR PRODUCING FINELY-DIVIDED PRECIPITATED SILICA

• Main Authors: PETER NAUROTH, HELMUT REINHARDT
• Format: Patent
• Language: English
• Published: 18.03.1969
• Subjects: CHEMISTRY; COMPOUNDS THEREOF; INORGANIC CHEMISTRY; METALLURGY; NON-METALLIC ELEMENTS

Finely divided silica with low iron content and high surface area is prepared by precipitation from water glass and a mineral acid at a pH less than 5 (preferably 1.5-2.5) and a temperature between 85 DEG and 95 DEG C. in the presence of substances which form a soluble complex with iron. The complex formers are preferably an inorganic fluorine compound and a monovalent or polyvalent organic acid or an alcohol, amide or amine; sodium fluoride and oxalic acid being preferred. The precipitated product is filtered, washed, dried and pulverized in a gas or steam jet mill. Precipitation is preferably carried out by running the water glass solution and sulphuric acid into a stirred volume of water at the required temperature during 90 minutes, stirring for 30 minutes and then filtering.ALSO:Photographic and photocopying papers used for reproduction purposes are coated with a finely divided silica having a low iron content (for preparation see Division C1). The silica is applied to the paper in an aqueous suspension containing binders such as starch, casein and plastics dispersions, the suspensions having a low viscosity.