Anisotropic surface energy reduction of Zr by chemisorption

Abstract

The anisotropy of the surface free energy reduction of Zr due to gas adsorption was studied by calculating the surface energies of crystal planes at solid-vapour interfaces. The Langmuir adsorption isotherm was adopted for the calculation, whereby the anisotropy was introduced from the nearest-bond energy approximation based on a pairwise interaction model. The (101̄0) plane was found to have the lowest relative surface energy in the unembrittled state, that of the (0001) plane being slightly higher. Gas adsorption, however, influences the energy state significantly, and the effective surface free energy after adsorption becomes lowest for the (0001) plane, followed by the ( 10 1 ̄ 1 ) plane family. This tendency became more pronounced as the coverage increased. Energy maxima occurred in the planes that were inclined about 30–50° and 70–75°, respectively, to the basal plane. The mode of spatial distribution of the surface energies at 350°C on stereographic triangles was sensitive to a coverage higher than 0.5; the effect of temperature in the range of 250–450°C, however, was relatively insignificant.