Polishing formulations for SiO2-based substrates

Abstract

Powders of particles comprising a ceramic core and a coating of ceria deposited thereon provide an economical and effective abrasive for glass polishing formulations.

We claim:  
     
         1 . Abrasive powder particles each comprising a core particle of a ceramic material with a shell of ceria deposited thereon such that the ceria represents from 2 to 40% of the particle weight.  
     
     
         2 . Abrasive powder according to  claim 1  in which the ceria represents from 3 to 20% of the particle weight.  
     
     
         3 . Abrasive powder according to  claim 1  in which the ceramic providing the core particles is selected from the group consisting of silica, alumina, zirconia, silicon carbide, calcium oxide, rare earth metal oxides and mixtures thereof.  
     
     
         4 . Abrasive powder according to  claim 4  in which the ceramic providing the core particles is fumed silica and colloidal silica.  
     
     
         5 . A glass polishing formulation comprising a dispersion medium and abrasive powder particles each comprising a core particle of a ceramic material with a shell of ceria deposited thereon such that the ceria represents from 2 to 40% of the particle weight, the powder being present in then formulation in an amount of from 2 to 20% by weight.  
     
     
         6 . A glass polishing formulation according to  claim 5  in which the pH is adjusted to at least pH 8.  
     
     
         7 . A process for the production of a glass polishing abrasive powder comprising ceramic core particles and a shell of ceria deposited thereon which comprises mixing a powder of the ceramic core particles with a solution of a soluble salt of cerium; adjusting the pH of the dispersion to at least a pH of 8; aging the dispersion at a temperature of from 60 to 95° C. until the pH has stabilized above 8; separating and drying the solids content of the dispersion; and firing the dried solids at a temperature of from 600 to 1000° C.