An examination of oxide films on tin and tinplate

Rates of growth of oxide films were studied by the estimation of combined oxygen by controlled cathodic reduction in a buffered solution and by separation of films from the metal by dissolution of the metal in Hg. Oxide films were produced both by heating in air and by a variety of passivation treatments. Using tinplate, the O content of the films was determined by cathodic reduction and by wt.-gain measurements after heating at 200°, 210° and 220°C; good agreement was found. X-ray examination of the film proved it to be SnO. Sn specimens were heated in dry air at 30°-210°C and it was shown that the amount of oxide formed was alpha log (time) at 30°C and alpha (time) 1/2 at temp.> 180°C. Films formed at> 170°C are SnO; < 170°C they are probably amorphous. The addition of 0.1% In or P considerably reduces, and the presence of moisture increases, the oxidation rate. Films formed from chromate solution contain Cr. 12 ref. -- AATA