The Formation and Nature of Fluoride Film on Aluminium

Abstract

The fluorination film was prepared on the aluminium surface by the anodic polarization in the liquid hydrogen fluoride and by the direct fluorination with the elemental fluorine and their natures were studied by means of X-ray diffractometry and X-ray photoelectron spectroscopy. The fluoride film, made by anodic polarization at 30 V, 1 h in liquid hydrogen fluoride, had the F/C ratio of 3.5. ESCA study suggested that fluoride hydroxide was formed on the surface of the film prepared in the liquid hydrogen fluoride containing more than 0.5 wt%H₂0. On the other hand, the F/0 ratio of the film prepared by direct fluorination (50 0°C, 24 h, F₂: 1 atm) was 9.5. Fluorinated film with high fluorine content showed the good corrosion resistance against moisture in air and aqueous solution. It was found that the diffusion coefficient of fluorine through aluminium fluoride film depended on the fluorine content in the fluoride film and that the order was from 10^-15 to 10^-14 cm²/s in the temperature range of 150-500°C. It was estimated that the activation energy for diffusion of fluorine was 43.1k T /mol from Arrhenius Dlot.