On the use of the Langmuir and other adsorption isotherms in corrosion inhibition

• Published in: Corrosion science Vol. 217; p. 111112
• Main Author: Kokalj, Anton
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2023
• Subjects: Corrosion inhibition; Flory–Huggins isotherm; Frumkin isotherm; Langmuir isotherm; Standard adsorption free energy; Temkin isotherm; Flory–Huggins isotherm; Temkin isotherm; Corrosion inhibition; Standard adsorption free energy; Frumkin isotherm; Langmuir isotherm
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2023.111112

In corrosion inhibition studies, the standard adsorption Gibbs energy is often estimated via the linear regression of the Langmuir isotherm in the c/θ=1/K+c form, where both the intercept and the slope are estimated, although the Langmuir isotherm requires the slope of 1. Hence, c/θ=1/K+mc is actually used, where m is the slope. Herein, a theoretical basis for this equation is established. It is demonstrated to be an effective equation that can decently describe various adsorption models and provide relatively accurate estimates of the standard adsorption Gibbs energy, provided surface coverages are reliably determined experimentally. However, any significant deviation from the slope of 1 signals non-Langmuir adsorption due to inter-adsorbate interactions, multi-site adsorption, or surface heterogeneity. Among these three causes, only attractive inter-adsorbate interactions lead to a slope of less than 1. [Display omitted] •▪ is often estimated via the c/θ=1/K+mc equation, where m is the slope.•A theoretical basis for this equation is established.•It is an effective equation that can well describe various adsorption models.•Attractive interactions between adsorbates result in a slope of less than 1.•Repulsive interactions, multi-site adsorption, or surface heterogeneity result in a slope greater than 1.