Preparation of Thoria Microspheres by the External Gelation of Low Viscosity Sols

Abstract

Thoria microspheres have been prepared by the forced base hydrolysis of thorium nitrate, but without the aid of thickeners or high levels of neutralization commonly used in this process. Dried microspheres could be heated at a rate of 200 degrees C/min without cracking, and sintered to greater than 99% of the theoretical density within one minute at 1100 degrees C. The process can be used to prepare microspheres up to about 600 umin diameter. These and other aspects of the process, such as drop formation, the washing and drying of microspheres, and a simple modification which permits microspheres to be made up to 1 200 umin diameter are discussed.