Role of alcohols on dissolution of 70/30 brass in HNO3-H2SO4 bath

Effects of some alcohols, namely, methyl, ethyl, iso-propyl and butyl alcohols at their different concentrations have been studied for the dissolution of 70/30 brass in sulphuric and nitric acid mixtures. It is noted that the addition of methanol in the acid mixture strongly reduce the corrosion rate as well as gas evolution. At and above the concentration of 2.0% of the additive, inhibition of the order of 90% is achieved. Additions of ethanol, iso-propanol and butanol, however, accelerate the corrosion rate as well as gas evolution when compared to the blank solution. The reaction rate is found to increase with the increase in chain length of the alcohols. The possible mechanism for this behaviour has been described. Solution analysis indicates that in the absence of methanol, de-zincification of the brass takes place. This, however, decreases with increase in the efficiency of the inhibitor.