Corrosion of Grey Cast Iron in Concentrated Sulphuric Acid

The Pauling process of regenerating spent sulphuric acid is an example of industrial application of the corrosion resistance of grey cast iron in boiling strong sulphuric acid. The corrosion behaviour of cast iron in boiling sulphuric acid depends on the corrosion potential. At a high corrosion potential, the material shows a stable passive state. In a study on the influence of the alloy components Si, Cu and Sn on the corrosion resistance of grey cast iron, the following results were derived. In the active area state, cast iron containing more than 1.4-1.5% Si exhibits a corrosion maximum in 97% boiling sulphuric acid, whereas alloyed grey cast iron with low Si content displays in the active state better corrosion behaviour over the whole concentration range from 93-98% H sub 2 SO sub 4 . When the alloyed cast iron is in the passive state, corrosion resistance increases as the silicon content is reduced and the sulphuric acid concentration is raised. 13 ref.--AA