Wood bark oils of Cassia siamea-gonrai (CS), Cassia auriculata (CA), Crataeva religiosa (CR) and Strychnos nux-vomica (SNV) were extracted from the dry bark. These highly volatile oils are used as a vapour phase corrosion inhibitors (VPI) for mild steel and copper in sodium chloride and sulphur dioxide environments. The inhibition efficiency of these wood bark oils has been examined by using weight loss, potentiodynamic polarization and A.C. impedance spectroscopic methods. It has been found that the inhibition capability of these oils increases with increase in concentration from 0.4 to 4%. The results indicate that the bark oils have significant inhibitive effect. This is due to adsorption of inhibitor molecule on the metal surface. At higher concentration (8%) of the inhibitor, there is decrease in inhibition efficiency. It may be due to the formation of soluble metal-inhibitor complex in the salt environments. It has also been found that 4% concentration of these inhibitors offered, above 90% inhibition efficiency for both mild steel and copper.
N. Poongothai, Rajendran, P., Natesan, M., and Palaniswamy, N., “Wood bark oils as vapour phase corrosion inhibitors for metals in NaCl and SO2 environments”, Indian journal of chemical technology, vol. 12, pp. 641-647, 2005.