Surface Area and Particle Size of Evaporated Lead Sulfide Films

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Abstract
Physical adsorption isotherms of lead sulfide films evaporated in vacuum and through oxygen were measured in order to determine their surface area and particle size. The surface areas of fresh and of annealed vacuum evaporated films were found to increase linearly with film thickness. Annealing the films in vacuum decreased the surface area considerably. The average specific surfaces of the fresh and annealed films were 63 m2/g and 6 m2/g, corresponding to particle sizes of 0.013μ and 0.13μ, respectively. The surface area of fresh films evaporated through oxygen depended upon the rate of evaporation. The average specific surface of the fresh slowly evaporated films was 66 m2/g; for those evaporated faster, it was 118 m2/g. The corresponding particle sizes were 0.012μ and 0.0068μ. When these films were annealed in a closed vacuum system, the specific surface became 12 m2/g and 14 m2/g, corresponding to particle sizes of 0.067μ and 0.056μ, respectively. For films evaporated through oxygen, the oxygen is chemisorbed on the surface of the film during evaporation. When such a film is annealed sulfur dioxide is evolved and sulfate is formed.

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