Boehmite and Yttrium Oxide Coatings on Silicon Nitride From Aqueous Sols

Abstract

To improve the processing of silicon nitride, boehmite and yttrium oxide were coated on silicon nitride particles by an aqueous sol-gel method. It is shown that boehmite and Y2O3 can be coated on Si3N4 particles from aqueous solutions. However, the Y2O3 coating is not as complete as boehmite coating. The coating of a yttria coating followed by a boehmite coating was attempted and the TEM showed a coating twice as thick as the Y2O3 or AlOOH coating. Hydrothermal treatment of yttrium nitrate hydrous hydroxide results in the formation and growth of Y(OH)3 fibers which can be calcined and transformed into Y2O3 fibers at 500°C.

Effect of Acid on the Coating of Boehmite onto Silicon Carbide Particles in Aqueous Suspensions

“…The earlier study focused on a much higher amount of boehmite, 15% 7 and 6%. 17 It would be desirable to reduce the amount of boehmite so that the amount of processing aid can be minimized. However, when the amount of boehmite is too low, the coating may not be successful.…”