Wear of Iron and Nickel in Corrosive Liquid Environments

An investigation was conducted to examine the friction and wear behavior of iron and nickel sliding on aluminum oxide in aerated sulfuric acid and hydrochloric acid. The results indicate that the concentration of acid is an important factor in controlling the metal loss caused by wear-corrosion processes in the acids. At very dilute acid concentration (10⁻⁴ N), iron behaves differently than nickel. Iron develops a soft, friable deposit, while nickel develops no corrosion layer. The formation and removal of the corrosion deposit on iron resulted in high metal loss and coefficient of friction, as compared to the relatively low metal loss and coefficient of friction observed for nickel. At slightly higher acid concentration (10⁻³ and 10⁻² N), no corrosion products were produced on either iron or nickel. Wear of iron and nickel was generally at a minimum. At higher acid concentration (10⁻¹ N and above), loss of iron and nickel increased as the acid concentration increased. In sulfuric acid the maximum loss of both iron and nickel was at 7.5 N (30 percent) concentration, and the metal losses of both iron and nickel dropped markedly at 15 N (50 percent) and above. In hydrochloric acid, however, the iron loss continued to increase with the increase of acid concentration, and the maximum iron loss occurred in the most concentrated acid (12.1 N, 37 percent). There were variations in loss with nickel from specimen to specimen examined in concentrated hydrochloric acids (10⁻¹ N and above). The coefficient of friction for iron decreased with increasing concentration of both acids. The coefficient of friction for nickel increased slightly with an increase in acid concentration up to 10⁻² N. When corrosion started to dominate in the wear-corrosion process, the coefficient of friction decreased in both sulfuric and hydrochloric acids at 10⁻¹N and above.