Formation of a stationary polarization state of the surface of anode-oxidefilms of various structures at the surface of aluminum during water adsorption

The formation of a polarization state at the surface of anode-oxide films ( AOFs) of various structures on the surface of aluminum was studied. Changes in the electron work function caused by the adsorption of water in the ran ge of relative pressures 0.55-0.65 (typical atmospheric humidity) were dete cted through changes in the contact potential difference measured with the use of a capacitor composed of a reference and a test sample and whose air gap was irradiated with a constant-intensity alpha-radiation. Water adsorpt ion isotherms were measured at room temperature with a vacuum beam microbal ance. The topography of the AOFs was determined by scanning electron micros copy; the thickness of the AOFs was measured gravitometrically. It was demo nstrated that, depending on the film thickness (up to 2 mu m), AOFs on the aluminum surface under conditions of atmospheric humidity may exist in vari ous states of stationary polarization, which arise due to a decrease in the electron work function caused by the adsorption of various amounts of wate r. The results obtained led us to conclude that the main cause of the forma tion of the polarization state at the surface of the AOF coating aluminum u nder atmospheric conditions is the formation of a system molecular associat es (clusters) linked by hydrogen bonds (this system forms a dipole jump in the potential, with the negative charges being located more closely to the surface) rather than the dissociation of water.