Corrosion of cast iron in concentrated sulphuric acid under potentiostatic conditions

Abstract

Polarisation curves and corrosion rates have been determined for grey cast iron in 96 wt.-% sulphuric acid at temperatures varying from room temperature to the boiling point. For boiling acid, the polarisation curves have been determined in the concentration range from 90 to 100 wt.-% acid and in 96 wt.-% acid after addition of organic impurities. The polarisation curves show that grey cast iron corrodes in an active manner at the lower temperatures, but at temperatures higher than about 220° the cast iron will behave as a passive metal in the pure 96wt.-%acid. Dilution of the acid to about 93 wt.-% or the presence of reducing impurities results in an active corrosion potential. The corrosion rate in boiling acid has been measured under potentiostatic conditions, and the corrosion rate is shown to vary by a factor of 1000 by variation of the corrosion potential in a range of 300 mV.