Effect of calcium modification on the microstructure and oxidation property of submicron spherical palladium powders

Ca-modified spherical palladium particles were prepared from the mixed solution of Pd(NO3)(2) and Ca(NO3)(2) by ultrasonic spray pyrolysis. Pure palladium powder and that modified with less than 55 ppm Ca were composed of single crystal particles. However, Ca addition of more than 500 ppm resulted in polycrystalline particles. Crystallite size of the particles decreased with the increase of Ca addition and changed dramatically at the addition of some hundred ppm. Ca additive did not form solid solution with palladium but formed CaPd3O4 on the surface and grain boundary of the particles. 50 ppm-1% of Ca addition significantly reduced the oxidation of palladium powder. More addition of Ca resulted in excess oxidation due to the reaction between palladium and calcium oxide.