Kinetic Study Of Zirconium‐Iodine Reaction By Modulated Molecular Beam Mass Spectrometry

Abstract

The reaction of molecular iodine with polycrystalline zirconium was studied by modulated molecular beam‐mass spectrometric methods. The reaction was investigated in the temperature range 400–1400 K and equivalent iodine pressures of was identified as the sole detectable reaction product at low temperatures (<850 K), achieving a maximum reaction probability at about 600 K. At high temperatures, molecular dissociation and atomic desorption of iodine play a predominant role in the gas‐surface reaction. The molecular beam data, in conjunction with Auger and ESCA analysis of the surface after the experiment, support a reaction model involving a thin scale of a lower iodide present on the surface at low temperatures during the reaction. The kinetics of the reaction are governed by the diffusional properties and the reactivity of this scale with respect to adsorbed iodine atoms. At high temperatures the reaction mechanism consists of adsorption and dissociation of on the metal partially covered with the iodide scale followed by desorption of atomic iodine.