THE ELECTROCHEMICAL-BEHAVIOR OF 9CR-LMO STEEL IN CONCENTRATED ACID-SOLUTION MIXTURES

The electrochemical polarization behaviour of 9Cr-1Mo steel has been i nvestigated in binary and ternary mixtures of concentrated phosphoric acid, acetic acid, sulphuric acid, and formic acid at 20 +/- 1 degrees C. The steel showed active-passive and transpassive behaviour in all solutions. The alloy surface exhibited a tendency to undergo electropo lishing in acetic acid-based phosphoric acid electrolytes. In the tran spassive region, a current plateau was always observed but electropoli shing occurred only in a few selected mixtures (10-20 volume percent a cetic acid + balance phosphoric acid). The experimental results reveal that electropolishing is under mass transport control and the existen ce of a current plateau is not a sufficient condition. A low content o f water is beneficial for electropolishing. (C) 1998 Published by Else vier Science Ltd. All rights reserved.