SOLID-STATE WETTING OF GRAPHITE BY PB AND PB-NI ALLOYS

Equilibrium segregation of Ni to the interface of solid Pb/graphite was studied using a solid-state wetting approach. Increasing amounts of Ni, ranging from 0 to 0.2 wt pct Ni, added to Pb were found to systematically lower the contact angle. No significant surface concentration of Ni was found at the Pb surface. The reduction of the contact angle was therefore attributed entirely to the lowering of the interfacial energy by interfacial adsorption of Ni. The amount of Ni at the interface was determined using the Gibbs adsorption isotherm. The presence of excess Ni at the interface was confirmed qualitatively by crater-edge profiling studies performed using a scanning Auger microprobe (SAM). All the experiments were performed under ultrahigh vacuum (UHV) to reduce the effects due to surface adsorption of impurities.