Co-Adsorption of H2O, OH, and Cl on Aluminum and Intermetallic Surfaces and Its Effects on the Work Function Studied by DFT Calculations

Abstract

The energetics of adsorption of H2O layers and H2O layers partially replaced with OH or Cl on an Al(111) surface and on selected surfaces of intermetallic phases, Mg2Si and Al2Cu, was studied by first-principle calculations using the density function theory (DFT). The results show that H2O molecules tended to bind to all investigated surfaces with an adsorption energy in a relatively narrow range, between –0.8 eV and –0.5 eV, at increased water coverage. This can be explained by the dominant role of networks of hydrogen bonds at higher H2O coverage. On the basis of the work function, the calculated Volta potential data suggest that both intermetallic phases became less noble than Al(111); also, the Volta potential difference was larger than 1 V when the coverage of the Cl-containing ad-layer reached one monolayer. The energetics of H2O dissociation and substitution by Cl as well as the corresponding work function of each surface were also calculated. The increase in the work function of the Al(111) surface was attributed to the oxidation effect during H2O adsorption, whereas the decrease of the work function for the Mg2Si(111)–Si surface upon H2O adsorption was explained by atomic and electronic rearrangements in the presence of H2O and Cl.

Density Functional Theory Study of Influence of Oxide Thickness and Surface Alloying on Cl Migration within α-Al2O3

“…Influence of oxide thickness.-Localized corrosion of Al depends strongly on the stability of the oxide formed on the Al surface, while the oxide thickness 38 and the pH pzc of the oxide surface 6 have an influence on the corrosion resistance. Surface hydroxylation is also an important factor affecting its interaction with surrounding environments, and single hydroxyl groups on the surface could change the metal's work function 39 . Since the very first steps in the passive film formation are very important for the stability, 33,[40][41][42] our calculations include extremely thin oxide films, as thin as 4 Å.…”

Wire Tool Electrode Behavior and Wear under Discharge Pulses

“…A bias increase is followed by ionizing the space between two electrodes at the moment of their approach. Dielectric breakdown by spark provokes a discharge channel that creates the conditions of low-temperature plasma with 10,000 • C that can be observed in particular conditions (forming intermetallics of Al 2 Cu [14,15], ZnNi x [16], CeNi 2 [17], burning titanium at 1200 • C [18,19]) in the form of an instant growing gas bubble surrounded the discharge channel. Then, pulses interrupt to restore the breakdown conditions for the next pulse-the bias in the gap, erosion products' washing away from the working area.…”

Relation between Surface Composition and Electronic Properties of Native Oxide Films on an Aluminium-Copper Alloy Studied by DFT

“…[11][12][13][14][15] Some theoretical papers focused on work function calculation and comparison between different Al and Al 2 Cu surfaces, in order to better understand the effect of surface composition and termination on the work function value. 2,16,17 The work function is the minimum energy needed to emit an electron from the surface to vacuum, implying that a higher work function corresponds to a higher resistance against losing electrons, and vice versa. The work function is an appropriate measure of the electronegativity 18,19 and the work function value indeed leads to a reasonable estimated trend of charge transfer for molecular adsorbates.…”