Corrosion Behaviour of Pure Chromium in HCI Solutions

Cr is widely used as an essential alloying element for improvement of corrosion resistance. Metallic Cr has a poor workability in itself and therefore scarcely is used. Recently the high purity Cr sheets have been developed by the improved processing techniques and electrolytic techniques, so that various types of sheets and pipes can be fabricated. It is known that pure Cr and Cr base alloys have not so good corrosion resistance in non-oxidized acid. However, the corrosion behaviour of pure Cr has not yet been completely investigated.Corrosion behaviours of 99.83%Cr as well as Fe-Cr alloys and Ti were investigated by measuring the polarization curves and corrosion rates in the solutions of various HCI concentrations.Cr has a large value of active dissolution current in a HCI solution of less than 10% concentration, but the passive current density is very small. And the passivation ability of Cr is higher than the other materials. Cr has much better corrosion resistance in HCl solutions than Ti and the other Fe-Cr alloys. However, with increasing temperature or concentration of HCl, the accelerated active dissolution current and the passive current density increase. On the other hand, the active dissolution currents and passtve currents of the Fe-30Cr alloy and Ti are much larger than those of Cr. Therefore they do not show any passivation ability in all HCI solutions.