Adsorption on evaporated tungsten films I. Oxygen and carbon monoxide chemisorption and the determination of film surface areas
The chemisorption of oxygen and of carbon monoxide by evaporated tungsten films has been studied between 20 and - 195° C and at pressures up to 10 -2 mm., with the primary aim of measuring the surface areas of the films. The two methods give results which agree, and the film areas have been determined to an accuracy of about 5 %. Chemisorption of oxygen is followed by a second process, probably an oxidation, which slows very rapidly as gas is taken up, and for which an activation energy of 7000 cal. has been evaluated. The heat of carbon monoxide chemisorption is so low in densely packed layers that measurable equilibrium gas pressures are required even at liquid-air temperatures for completion of chemisorption. Values for the fraction of the surface atoms covered at various temperatures and pressures have been obtained, together with isothermal heats at various coverages. At the lowest temperatures onset of second-layer formation has been observed; first- and second-layer formations do not form a stepwise process.