RUTHERFORD BACKSCATTERING SPECTROMETRY INVESTIGATION OF THE EFFECTS OF OXYGEN AND HYDROGEN PRETREATMENT OF PYROLYTICALLY COATED GRAPHITE ONPB ATOMIZATION

A delay in the vaporization of Pb from an oxygenated, pyrolytically co ated graphite substrate was observed under atmospheric pressure using Rutherford backscattering spectrometry. When the same experiment was r epeated under vacuum, this delay was no longer observed. The concentra tion of oxygen on the graphite surface was quantified by use of the 3. 04 MeV resonance in the O-16-(alpha,alpha)O-16 elastic scattering reac tion. The amount of adsorbed oxygen was found to increase with the tem perature of the pretreatment step and to correspond to the amount of l ead present on the graphite flat prior to vaporization. While Pb remai ned on the surface of the hydrogen-pretreated graphite surface, the mi gration of Pb into the bulk of the pyrolytically coated graphite subst rate was observed with the oxygen-pretreated and the nontreated flats.