Investigation of the tantalum-fluorine reaction by modulated molecular beam mass spectrometry

Abstract

The reaction of molecular fluorine with polycrystalline tantalum was studied by modulated molecular beam-mass spectrometric methods. The reaction was investigated at temperatures of 690 and 930°K at equivalent fluorine pressures between 10 −5 and 10 −4 Torr. TaF 5 was identified as the sole reaction product. Lower fluorides of tantalum were not present in the product vapors. Fluorine atoms could not be detected, but on theoretical grounds were not expected. The molecular beam data support a reaction model involving a thin scale of a lower fluoride (probably TaF 3) present on the surface during reaction. The kinetics of the reaction are governed by the diffusional properties and the reactivity of the lower fluoride scale with respect to adsorbed F atoms. No independent evidence of a surface scale was obtained, however.