Surface analysis of copper, brass, and steel foils exposed to fluorine containing atmospheres

Abstract

The composition and thickness of fluoride films that form upon exposure of various metals to F2/N2 at room temperature were studied using x-ray photoelectron and Auger electron spectroscopy (AES). Depth profiles were obtained using AES with argon ion sputtering. The metals studied included low carbon steel, 302 stainless steel, copper, and brass (70% Cu/30% Zn). Samples treated in 0.12% F2/N2 display small amounts of surface fluorine, primarily in the form of fluorinated hydrocarbons rather than metal fluorides. In contrast, exposure to 25% F2 produces thicker films, consisting mainly of metal fluorides with some metal oxides. Fluorine does not seem to penetrate beyond the native oxide initially present on the metal foil surface. Iron fluorides form on low carbon steel, and copper fluorides form on copper. Surprisingly, iron fluorides preferentially form on stainless steel, and zinc fluorides preferentially form on brass. These results provide new insight about the passivation of metals by F2 and raise new questions.