The evolution of particle structure in the formation of submicron single-crystal spherical palladium particles by spray pyrolysis was investigated by observing the change of the morphology and internal structure of the particles during heat treatment. Below 700°C oxide particles with solid and homogeneous structure were formed. Decomposition of PdO took place within a particle above 700°C and an oxide layer was left on the surface of palladium particles until the decomposition is completed. The yielded palladium clusters sintered immediately and the particles shrank uniformly and dramatically as the decomposition reaction took place. The shrinkage of particles was completed almost simultaneously as the decomposition of PdO was completed, however, a little expansion was observed which is attributed to the decomposition of entrapped oxide in the particles. High temperature lead to rapid grain growth within a particle and allowed the formation of single-crystal palladium particles in the spray pyrolysis process. Particles prepared by ultrasonic spray pyrolysis at above 1200°C were single crystals and had clean surface without any amorphous or oxide layer.
