Browsing by Author "Saleh, J M"

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    Adsorption and Incorporation on Copper
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (8), 1972) Saleh, J M
    The interaction of H2S, H2Sc, AsH3, HC1, SO2, CS2 and N2O with evaporated films of copper has been studied in the temperature range -80 to 250 C. Weak reversible adsorption of CS> and SO2, and mainly dissociative chemisorption of H2S, H2Sc, AsH3 and HC1 took place at -80 C. The extent of N2O adsorption on a Cu film at this temperature was negligibly small. The completion of the surface layer on a Cu film by either H2S, H2Se or AsH3 at temperatures > - 80 C was followed by the formation of bulk compounds and the process was accompanied by H2 evolution ; the activation energies of the incorporation processes were estimated from the rates of adsorption at different temperatures but virtually the same surface coverage. Dissociative chemisorption of N2O on Cu film above 30°C was very slow and proceeded to only a limited extent. Cu did not chemisorb CS2, SO2 or HC1 at any temperature in the range 30 to 250 C. The latter four gases were circulated over a heated W filament before reaction with the Cu film. The rate of uptake of the gas was a function of its pressure and the temperature of both the Cu film and the W filament. Activation energies were determined from the rates of adsorption at different temperatures either of the Cu film or of the W filament. Extensive incorporation of the gas was then possible at as low film temperatures as — 80°C.
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    Interaction of Hydrogen Chloride with Evaporated Metal Films: Part 2.—Adsorption and Incorporation on Films of Pd, Ag and Pb, Deposited on Iron Substrates
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (8), 1972) Dadiza, Y M; Saleh, J M
    An attempt was made to deposit films of Pd, Ag and Pb on top of iron films and then to investigate the interaction of HCl with the resulting “two-metal” films of Pd/Fe, Ag/Fe and Pb/Fe in the temperature range –80 to about 200°C. The area of the Fe film increased by subsequent deposition of Pd and decreased on deposition of Ag or Pb. Adsorption of HCl at –80°C on these films occurred as on films of Pd, Ag and Pb respectively; no H2 was evolved in any case in contrast to the behaviour of an Fe film. At temperatures [gt-or-equal] 30°C, the Pb/Fe film preserved much of the properties of the Fe film. A solid solution or an alloy of Fe in Pb is assumed to be formed due to the diffusion of Fe atoms into the Pb phase; the ease with which the electron and the defect can migrate through Pb is thus disturbed by this process. The formation of such structures was probably less pronounced with an Ag/Fe film due to the smaller difference in the atomic diameter between Ag and Fe as compared with the difference between Pb and Fe and, also, because of the higher melting point of Ag than Pb; the Ag/Fe film was, therefore, slightly more active than Ag. With Pd/Fe film, where both metals have almost the same atomic diameter and melting point, there was no tendency to form a solid solution or an alloy and, therefore, the film behaved toward HCl at temperatures [gt-or-equal] 30°C exactly in the same way as Pd film. Extensive oxygen adsorption and incorporation occurred on Pd/Fe film, very much like that on Fe. The Fe atoms may have a considerable mobility for outward diffusion as a consequence of either a strong electric field on the oxidized surface or due to the lowering of the surface tension of the surface by oxygen.