Uniform oxide microspheres and a process for their manufacture

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.