Corrosion Behaviour of Mild Steel in a Glacial Acetic-Formic Acid System

The corrosion behaviour of mild steel (MS) has been investigated at, 25, 35 and 45 degrees C in different media containing either pure glacial acetic acid (AA) or mixed with different amounts of formic acid (FA). The results of weight loss (WL) experiments yielded the largest value of corrosion rate (CR) in pure glacial AA. The effect of addition of FA to GAA shows contrasting trends-the CR decreases while increasing FA content from 2 to 10%, whereas a slight increase in CR is observed when FA is varied from 10 to 20%. MS corrodes considerably faster in glacial acetic acid (GAA) at each studied temperature (T). It is inhibited by FA containing some water in it. This behaviour has been compared with that obtained earlier by electrochemical method. The decrease in CR may be attributed to the formation of a protective layer due to the presence of water in FA. The increase in T leads to an increase in CR. It is seen that the compositions of solutions and experimental T have a marked influence on the CR. The surfaces of the specimens prior to and after being subjected to corrosion have been analysed by visual inspection and Scanning Electron Microscopy (SEM). Conclusions drawn from the surface study support the results of WL experiments.