The corrosion of tin and tinned copper in dilute neutral solutions

Abstract

AbstractLocal corrosion of tin by dilute chloride solutions is not prevented indefinitely by special physical or chemical preparation of the metal surface, or by alloying additions to the metal. The time elapsing before local corrosion begins is affected by surface condition and, with increase in the severity of attack, by contact of the metal with another solid surface to form a crevice, reduction of pH of the solution and electrical contact with a more noble metal.The intermetallic compounds formed in hot‐dipped or wiped coatings of tin on copper are resistant to corrosion and may be slightly cathodic to copper, but tin remained anodic to copper even when ennobled by oxide films. Wiped coatings on copper are more susceptible to local corrosion than electrodeposited or hot‐dipped coatings because the attack on the free tin remaining on the surface is stimulated by contact with exposed areas of tin–copper compound.Addition of sodium bicarbonate, carbonate, benzoate, chromate, phosphate or silicate to chloride solutions prevents local corrosion and cathodic protection can be obtained with aluminium anodes.