Segregation And Oxidation Studies Of Aluminum-lithium And Aluminum-magnesium Alloys

Auger electron spectroscopy, work function measurements, low energy electron diffraction, nuclear reaction analysis, dynamic/static secondary ion mass spectrometry, thermal desorption spectroscopy, and synchrotron radiation-photoemission spectroscopy have been used to investigate the segregation and oxidation of (111) oriented Al-6.5(at.%)Li and (110) oriented Al-1.45(at%)Mg single crystal binary alloys. The resulting Li and Mg equilibrium surface concentrations are found to be 0.16 and 0.47 respectively. For both alloys, the increase in surface concentration was associated with a decrease in {dollar}\Delta\phi{dollar}. {dollar}\surd 3\rm x\surd 3R30\sp\circ{dollar} and c(2x2) superlattices were observed at the equilibrium surface concentrations for the Al-Li and Al-Mg alloys respectively. This is the first observation of ordered surface alloy phases accompanying surface segregation with Al-Li and Al-Mg single crystal alloys.;Oxidation measurements clearly indicate that the reactivities of the two alloy surfaces are substantially increased at the equilibrium Li and Mg surface concentrations. Oxidation of the Li-segregated surface occurs immediately, forming a mixed oxide composed of Al, Li, and O. The oxidation of the Mg-segregated occurs immediately also, and leads to the formation of a combination oxide (Al{dollar}\sb2{dollar}O{dollar}\sb3{dollar} + MgO) at higher exposures