Surface analysis of Ag-Pd ultrafine powders

Ag and Pd sub-micron powders and three different types of Ag-Pd ultrafine powders (MIX, COPPT and ALLOY) were prepared. MIX was the mechanical mixing powder of Ag and Pd powders obtained by precipitation from aqueous solution. COPPT powder was made by co-precipitation. ALLOY was prepared by heat treatment of COPPT powder in a vacuum. Ag3d_5/2 and Pd3d_5/2 photoelectron spectra and valence band spectra of fine powders were measured to characterize the surface. Since the surface of the Pd fine powder was partly oxidized and not completely covered with a dense oxide layer, it showed sufficient electroconductivity. No significant change of Pd valence band spectra was observed in powders where the average particle size ranged from 20 nm to 500 nm. Intensity ratios of Ag3d_5/2 to Pd3d_5/2 spectra of Ag-Pd fine powders were measured with Ar sputtering. It is suggested that Ag was enriched at the surface of the ALLOY powder.