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This paper aims to investigate the influence of temperature and lignin concentration on the inhibition of carbon steel corrosion in 1 M HCl.

Weight loss corrosion tests were performed at different temperatures in the range of 30-70°C (303-343 K).

It was found that the corrosion inhibition efficiency (IE) of lignin on the carbon steel decreased when the temperature was increased from 60 to 70°C. However, at lower temperatures ranging from 30 to 50°C, the IE improved, due to occurrence of lignin adsorption on the surface of metal specimens. The IE was higher with increasing lignin concentration, thus reducing the weight loss of the carbon steel. The adsorption phenomenon involved exothermic processes because the value of enthalpy of adsorption (ΔH°_ads) < 0 and Gibbs free energy of adsorption (ΔG°_ads) were less negative with increase in temperature. The entropy of adsorption (ΔS°_ads) had negative values, representing the decrease in disorder of adsorption. The adsorption of lignin on the carbon steel surface in 1 M HCl was comprehensive, as deduced from kinetic and thermodynamic parameters. However, physisorption was the major contributor in the inhibition mechanism. The inhibitive features of carbon steel surfaces showed less damage once the steel was treated in lignin, as evident from macroscopy images.

The use of lignin as an acid corrosion inhibitor at high temperature is practical in metal surface treatment process.

The use of organic compounds gives an advantage to the environment, universal health and save cost, as the compounds can be found in nature.

Lignin can act as a flexible corrosion inhibitor within the temperature range of 30-70°C in 1 M HCl because it exhibits comprehensive adsorption (i.e. a combination of both physisorption and chemisorption) at specific concentrations.