Improvement of the corrosion resistance of tinplate by a chemical treatment

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Abstract
The corrosion of tin by hot sodium hydroxide solutions is accelerated by small additions of sodium chromate but is retarded by larger additions. Tinplate immersed in solutions containing sufficient remains bright and acquires an improved resistance to some other forms of corrosion; the pores in the tin coating rust less readily in the atmosphere and the tin surface becomes much more resistant to staining by sulphur‐containing materials and to oxidation on heating in air.The best procedure and methods of test have been sought in order to provide a process for treatment of tinplate. Trials of canning soup in cans made from treated tinplate and in treated cans have shown the treatment to have practical value.A reliable procedure is to immerse tinplate in a solution containing 10 g. of sodium hydroxide, 3 g. of sodium chromate and a small quantity of a wetting agent in 1 litre, for a minimum of 3 seconds at 90–95°. A test of the correct working of the solution is to immerse treated samples in a hot solution containing 10 g. of potassium sulphide (liver of sulphur) and 10 g. of sodium hydroxide in 1 litre at 90–95° for 30 seconds.

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