Dentifrice silica base prepn. - comprises silica deposition and neutralisation with set chloride or sulphuric acid ion addn. rates

摘要

SiO2 base for dentifrice has a refractive index of 1.42-1.45 and a specific surface area of 5-60 m2/g. as determined by the BET or 17ABmethod,thedifferenceinthevaluesdeterminedbythese methods being not more than 40 m2/g. In prepn. alkali metal silicate soln. is reacted with HCl or sulphuric acid in the presence of an electrolyte in a process comprising (i) SiO2 deposition with the reaction system pH at up to 10.0; and (ii) a neutralisation step in which the reaction system pH is 8.0-6.5 and the ratio of the Cl or sulphuric acid ion addn. rate to the addn. rate in SiO2 deposition is at least 5:3, and which is effected in 10-30 min.