The Interaction of Simple Gases with Hot Metal Filaments

  • Melvyn R. Painter

Student thesis: Doctoral ThesisDoctor of Philosophy


The interaction of iodine, methyl bromide, methyl cyanide
and methyl iodide with tantalum, tungsten, molybdenum and
platinum filaments has been studied in a magnetron system.
The interaction of two of these compounds, iodine and methyl
iodide, with tantalum filaments has also been studied in an
ultra high vacuum system.

The study of the surface ionisation of iodine and the
methyl compounds in the magnetron revealed the mechanisms of
ion formation for the bromide, cyanide and iodide negative
ions from these compounds. Adsorption and dissociation on
the filament surface were found to be important in the ion
formation reaction.

The study in the ultra high vacuum system consisted of
observing the thermal desorption of neutral species from the
surface and the effects of gas adsorption on the electron work
function of this surface. The study of the thermal desorption of
iodine and methyl iodide revealed the presence of adsorbed moleculariodine
and from a quantitative analysis of this reaction the
surface coverage of the desorbing species, the order of reaction
and the enthalpy and entropy of activation for the desorption
reaction were ascertained.

The effect of the vapours of all the compounds mentioned above
on the various surfaces employed was observed using both thermionic
emission and contact potential measurements and the most important
factor determining the emission properties was found to be the
formation of carbides by reaction of the metal with the methyl
group. The physical and thermionic emission properties of tantalum
carbide have been studied in detail.
Date of Award1973
Original languageEnglish


  • simple gases
  • hot metal filaments

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