GB968202A - Improvements in or relating to metal oxide sols and silica sols - Google Patents

Abstract

Aqueous sols of polyvalent metals may have a particle size of 0.1-100mm and aqueous silica sols may have a particle size of 0.1-3 mm . Such aqueous sols may be prepared by contacting an aqueous solution of a metal salt or of an alkali metal silicate with a solution of an alkylamine or of an alkyl-phosphoric, -sulphuric or -carboxylic acid respectively in a water-immiscible organic solvent, allowing the phases to separate and removing the aqueous layer containing the sol. The formation of sols of SiO2, Cr2O3 and ThO2 respectively from sodium silicate, CrCl3 or Cr(NO2)3 and Th(NO2)4 solutions employing di-(2-ethyl-hexyl) phosphoric acid, di-tridecylamine and C18-C20 mixed primary amines or di-tridecylamine are exemplified. In each case 5 vol. per cent iso-decanol is present in the organic phase to avoid formation of third phases, and the organic solvent is kerosene. The metals Ni, Fe, Al, Ba, Ca, Cu, Mg and U are also mentioned; they may be present as nitrates, sulphates, phosphates, chlorides or other halides. Organic acids specified contain as alkyl groups, 2-ethyl hexyl, n-octyl, 3,5,5-trimethylhexyl, heptadecyl and 4 - ethyl - 1 - isobutyloctyl. Sulphuric or phosphoric acid may be used to regenerate these acids after sol formation. Bases which may be used may be primary, secondary and tertiary amines and quaternary ammonium compounds, trioctylmonomethylammonium hydroxide, trioctylamine, ditridecylamine and mixed isomers of primary amines of t.-C18H37NH2 to t.-C21H43NH2. After sol-formation the basic material may be regenerated with sodium carbonate. In addition to i-decanol, the alcohols 2-ethyl hexanol, 4-ethyl octanol, capryl alcohol, undecanol, diisobutyl carbonol, tetradecanol and trimethyl nonanol may be used to prevent the formation of a third phase. Organic solvents mentioned are hexane, kerosene, carbon tetrachloride, chloroform, benzene and polar solvents; solvents may be first scrubbed with sodium carbonate solution to avoid contamination. If so desired the sol formation may be carried out at above room temperature, up to 100 DEG C., this resulting in an increase in size of the particles. In a preferred embodiment, the aqueous salt solution and the organic solution are fed into a reaction zone containing a previously prepared seed sol. The aqueous phase may be fed at a constant or a logarithmic rate and the organic phase fed at a constant rate; a quiescent zone in the reaction zone provides for settling out of the phases and the organic phase may be recirculated after regeneration (e.g. by two-stage counter-current contact with sodium carbonate) and washing with water. The size of the particles may thus be built up, and sol thus produced made the seed material in further similar processes. In examples, single-stage processes produce Cr2O3 sols of particle diameter 6.2 and 9 mm and a ThO2 sol of 9.5 mm diameter and in successive stages a ThO2 sol had particle diameter of 9.5, 19.7, 35 and 56 mm . The sols of Specification 924,999 are disclaimed.