EVOLUTION OF PARTICLE STRUCTURE DURING THE FORMATION OF SINGLE-CRYSTAL SPHERICAL PALLADIUM PARTICLES BY SPRAY-PYROLYSIS

The evolution of particle structure in the formation of submicron sing le-crystal spherical palladium particles by spray pyrolysis was invest igated by observing the change of the morphology and internal structur e of the particles during heat treatment. Below 700 degrees C oxide pa rticles with solid and homogeneous structure were formed. Decompositio n of PdO took place within a particle above 700 degrees C and an oxide layer was left on the surface of palladium particles until the decomp osition is completed. The yielded palladium clusters sintered immediat ely and the particles shrank uniformly and dramatically as the decompo sition reaction took place. The shrinkage of particles was completed a lmost simultaneously as the decomposition of PdO was completed, howeve r, a little expansion was observed which is attributed to the decompos ition of entrapped oxide in the particles. High temperature lead to ra pid 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 degrees C were s ingle crystals and had clean surface without any amorphous or oxide la yer.