SURFACE-COMPOSITION OF MACHINED LEADED BRASS

ESCA and RBS were used to obtain quantitative information on the thick ness and nature of the surface layers formed on machined brasses conta ining 1-3% lead. The results show that the brass surface is strongly e nriched in lead. The amount of this element accumulated on the surface increases with increasing bulk concentration. Lead appears to be pres ent as islands partially covering the brass surface and having variabl e thicknesses up to several hundred angstrom. The outermost layer of t he islands is mainly a Pb hydroxycarbonate, under which PbO and Pb met al can be detected. Between the islands, the brass surface is covered by a layer of zinc oxide covering the Cu-Zn metallic phase. The accumu lation of Pb at the surface is attributable to a smearing effect cause d by the machining tool.