Reaction of modulated-molecular-beam chlorine with polycrystalline iron

Abstract

The volatilization of polycrystalline iron by chlorine gas has been studied by modulated-molecular-beam–mass-spectrometric methods. The reaction was investigated in the temperature range 300–1250 K at equivalent chlorine pressures from 2 × 10^–5 to 3 × 10^–4 Torr. FeCl₂ was the only detectable volatile reaction product; its production rate increased rapidly with surface temperature and levelled off at ca. 1100 K. Studies of the composition of the reacting surface by laser-stimulated desorption and by ESCA indicated the presence of a thin scale of a sub-stoichiometric iron chloride at the spot struck by the molecular beam. A reaction model based on diffusion of chlorine in the scale and production of gaseous FeCl₂ from parallel Eley–Rideal and Langmuir–Hinshelwood processes was developed from the molecular-beam data.