Preparation of large particle silica sols

A process of preparing large particle aqueous silica sols suitable for use as abrasive materials in mechanically polishing semi-conductor wafers which comprises heating an alkaline aqueous silica sol containing smaller silica particles having an average diameter not more than approximately 40 millimicrons mixed with larger silica particles having an average diameter of at least approximately 60 millimicrons while maintaining a predetermined ratio of the total surface area of the smaller silica particles to the total surface area of the larger silica particles and conditions of pH, temperature, and pressure such that the smaller silica particles dissolve and redeposit on the larger silica particles to produce in a single step an aqueous silica sol in which the majority of the silica particles have a size substantially larger than the larger silica particles in the starting mixed sol.