Effect of hexamethylpararosaniline chloride (crystal violet) on mild steel corrosion in acidic media

The corrosion inhibition of mild steel in 0.5 M H2SO4 and 1 M HCl by hexamethylpararosaniline chloride (HMPC) was investigated using the gravimetric technique in the temperature range 303–333 K. The results indicate that HPMC inhibited the corrosion reaction in both acid media at all temperatures and inhibition efficiency increased with HMPC concentration. The inhibiting action is attributed to general adsorption of protonated and molecular HPMC species on the corroding metal surface. Adsorption followed a modified Langmuir isotherm and the Temkin isotherm, with very high negative values of the free energy of adsorption (ΔGads0). An increase in temperature reduced the inhibition efficiency of HPMC in 0.5 M H2SO4 but increased efficiency in 1 M HCl. Activation parameters such as activation energy (Ea), activation enthalpy (ΔH∗) and activation entropy (ΔS∗) as well as the adsorption heat (Qads) were evaluated from the effect of temperature on corrosion and inhibition processes.