The inhibitive effect of hexamethylenetetramine on the acid corrosion of steel

The efficiency of hexamethylenetetramine (HMTA), as corrosion inhibitors for steel in de-aerated 0.3 M HCl, 0.1 M H2SO4 and 0.1 M H2SO4 + 1.0 × 10−3 M HCl solutions have been determined by electrochemical studies. It was found that the HMTA acts a good corrosion inhibitor for steel corrosion in acids solutions. Increase in inhibition efficiency with the increase of concentrations of HMTA shows that inhibition actions are due to adsorption on the steel surface and adsorption follows the Langmuir isotherm. From the adsorption isotherms values of equilibrium constant (Kads), values of free energies of adsorption ( Δ G ads ° ), were calculated. The effect of temperature on the corrosion behaviour in the presence of 1.0 × 10−1 M inhibitors was studied in the temperature range of 293–323 K. The inhibition efficiency of HMTA increased with increasing temperature up to 323 K. Activation energies ( E a * ) were calculated from the obtained corrosion rates at different temperatures. Results obtained from both potentiodynamic polarisation and AC impedance measurements reveal that the compound is an effective inhibitor for the corrosion of steel and behave better in HCl than in H2SO4. Surface analyses were also carried out to establish the mechanism of corrosion inhibition of steel in acidic media.