The interaction of hydrogen sulphide with films of nickel and tungsten has been studied over the temperature range -80" to 100°C. Rapid dissociative adsorption, followed by desorption of hydrogen occurred on both metals. The average composition of the surface phase was expressed as H,S and n decreased with increase of both surface coverage and temperature. Adsorption of hydrogen sulphide on silver films at -80°C caused sintering to occur ; a substantial fraction of the adsorption was reversible but some dissociation also took place.The completion of the surface layer on nickel at 0°C was followed by the formation of bulk sulphide. Activation energies for the incorporation process were determined as the thickness of the sulphide layer increased over the temperature range 0" to 90°C. No clear evidence for incorporation on tungsten was obtained at temperatures below 100°C but a slow process was observed on silver films between 150" and 260°C.Evidence for two kinds of adsorbed hydrogen atoms was found by exchange experiments with deuterium on films of nickel and tungsten partially covered with hydrogen sulphide.
A rapid method for the measurement of the critical surface tension γ c values of individual wool fibers is described. Using this method, a comprehensive study of the wettability of untreated wool fibers has been carried out, and subsequent changes in γ c after various chemical treatments have been monitored. It is shown that the value of γ c obtained depends on the liquid series used for the measurement; the use of aqueous alkanol solutions for such measurements is criticized. The value of γ c for Hcrcosset-57 has been measured, and the spreading coefficient S and work of adhesion WA for this polymer on wool have been re-evaluated.
The adsorption and subsequent decomposition of tetramethylsilane Si(CH3)4 on evaporated films of tungsten and iron have been investigated. The results are compared with results previously obtained with neopentane C(CH3)4. Si(CH3)4 is rapidly and irreversibly adsorbed on tungsten at 293 K, and gaseous hydrogen and methane are formed ; further H2 and CH4 are desorbed on heating the surface to temperatures up to 42OK. Additional information regarding the adsorbed phase has been obtained from deuterium exchange experiments. Similar experiments carried out with iron show that much less dissociation of the Si(CH3)4 occurs on adsorption and on heating the adsorbed layer; no gaseous products are observed blow 320K. Comparison of both sets of mults with those for C(CH3), indicates that Si(CH& is more extensively dissociated under all conditions ; this is attributed rnainly to the weaker C -S i bond. The results suggest that the rate determining step in hydrocracking reactions of hydrocarbons is likely to be hydrocarbon breakdown rather than desorption of products.
The interaction of methyl mercaptan with evaporated films of nickel and tungsten has been investigated in the temperature range -80" to about 140°C. Dissociative adsorption occurred on nickel at -80°C and hydrogen and some methane were desorbd. Sulphidation of the metal began at 0°C with the evolution of methane but above 40°C a second reaction involving the formation of dimethyl sulphide and hydrogen became important. The factor controlling the changeover in mechanism appeared to be tbe concentration of adsorbed hydrogen atoms on the surface which decreased with rise in temperature. Activation energies for the evolution of the various gases were determined ; substantial sulphidation took place by the second reaction with a value of 10 kcal/mole which was independent of the thickness of the sulphide layer.Dissociative adsorption together with some molecular adsorption occurred on tungsten at -80°C.Hydrogen, and with rise in temperature, methane, were evolved but no dimethyl sulphide was formed and no incorporation of sulphur took place below 100°C.
The formation of thin films by electron bombardment has been studied and some of the important factors controlling the nature and surface characteristics of the films have been identified. A number of experimental techniques have been developed in order to obtain information on both the species likely to be involved in film growth and also the nature of the film surfaces. The surface characteristics have been monitored by contact angle studies,The possible importance of negative ions in film formation is illustrated with Si(CH&, where over 20 different negative ions were detected, the major ones being H-, C2H-and Sic;. Such results also have an important bearing on electron affinity data obtained by the magnetron method.Thin films formed from perffuorobut-Zene have surface characteristics which vary with the monomer pressure, the substrate temperature, and electron and ion energies. Information on the relative importance of the role of negative ions compared with electron and adsorbed monomer reaction is obtained. Some suggestions are discussed regarding possible surface structures inferred from wetting characteristics.
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