GB1265550A - - Google Patents

Abstract

1,265,550. Alumina-coated silica sol. E.I. DU PONT DE NEMOURS & CO. 16 July, 1969 [18 July, 1968; 9 June, 1969], No. 35918/69. Heading C1A. A positively charged alumina-coated silica sol is made by mixing a negatively-charged aquasol of colloidal silica particles (e.g. 7-30 mÁ. in size) with an aqueous solution of a basic aluminium chloride, aging the sol and then raising the pH of the aged sol to 4À5-6À5 by adding NH 4 OH, an alkali or alkaline earth metal base, e.g. NaOH, KOH, LiOH, Ca(OH) 2 or Mg(OH) 2 , or a water soluble organic base, e.g. methylamine or monoethanolamine or two or more of these. When the aged sol contains 10% or less by wt. of solids, the pH may be raised to 4À5- 7À0. The molar ratio of aluminium to surface SiO a in the product may be 1 : 2 to 2 : 1. The basic aluminium chloride may be of the formula Al(OH) 2 Cl to Al 3 (OH) 8 Cl, e.g. Al 2 (OH) 5 Cl. Aging may be carried out by allowing the mixture to stand at room temperature, or by heating it at temperatures up to 100‹ C. or, under pressure, above 100‹ C., and is preferably continued till the lowered pH remains constant, generally at 4 or less. Specified aging conditions are about 2 hrs. at 60‹ C., about 30 mins. at 80‹ C. and about 15 mins. at 90‹ C.