Uniform oxide microspheres and a process for their manufacture

Claim 1

A process for forming uniform-sized inorganic microspheres comprising the steps of: a. forming an aqueous sol containing uniform-sized inorganic- refractory colloidal particles which have hydroxylated surfaces and which are dispersible in said aqueous sol, said colloidal particles being isodimensional or rod-shaped particles with at least two dimensions in the range of 5 to 500 millimicrons and a third dimension in the range of 5 to 1,000 millimicrons; b. forming a homogeneous solution of said aqueous sol with a polymerizable material comprising formaldehyde and a second organic material selected from the group consisting of urea and melamine; c. reducing the pH of said solution to a level at which polymerization of said polymerizable materials occurs to cause coacervation of said organic material and said colloidal particles into substantially spherical microspheres having a diameter of about 0.5 to about 20.0 microns and to initiate copolymerization of said organic materials, said colloidal particles being insoluble in the acid medium at the selected pH; d. solidifying the microspheres so formed; e. collecting, washing and drying said microspheres; and f. oxidizing said microspheres at elevated temperatures to burn off the organic material without melting said colloidal particles, whereby forming uniform-sized porous inorganic microspheres.