Natural thyme as volatile corrosion inhibitor for mild steel in HCl environment

Thyme extract of Thymus vulgar L plant was evaluated as volatile corrosion inhibitor for mild steel in hydrochloric acid environment with 100% Relative Humidity. The corrosion behaviour of thyme powder was studied by gravimetric method. Thyme impregnated craft paper was evaluated by gravimetric and electrochemical methods such as potentiodynamic polarization and AC impedance measurements. It was found that both powder and impregnated craft paper have significant inhibitive effect on mild steel in hydrochloric acid environment. The inhibition efficiency increased with increase in concentration from 250 to 750 mg/l vapour space for the powder and 250 to 1000 mg/sq.ft for impregnated craft paper. At higher concentrations decrease in inhibition efficiency was observed. It may be due to the formation of soluble metal inhibitor complex in HCl environment. The adsorption behavior of thyme obeys Temkin's adsorption isotherm. It has also found that thyme powder of concentration 750 mg/l vapour space and impregnated craft paper of concentration 1000 mg/sq. ft. offered the maximum inhibition efficiency.