Estimating standard adsorption Gibbs energy from corrosion inhibition efficiencies: A case of multilayer adsorption
Year: 2025
Type: article
Abstract: In corrosion inhibition studies, the standard adsorption Gibbs energy is often estimated from c/θ versus c plots, where c is the inhibitor concentration and θ is the surface coverage. In doing so, inhibition efficiency (η) is assumed to be a good approximation of surface coverage, i.e., θ ≈ η. Consequently, adsorption is effectively treated as monolayer adsorption, since inhibition efficiency is, by definition, confined to values below one. However, there is no fundamental physical reason why adsorption on flat surfaces should be limited to a monolayer. For this reason, a model that maps inhibition efficiency to multilayer surface coverage is developed based on a few reasonable physical assumptions. It is shown that multilayer adsorption reduces the slope of the c/η versus c curve—widely interpreted as the c/θ curve due to the θ ≈ η approximation—and leads to a more pronounced curvature compared to the monolayer case. While the bending at low concentrations resembles that caused by repulsive lateral interactions, the overall curvature remains a distinct feature of multilayer adsorption. However, it is argued that in experiments—where only a limited number of data points are typically obtained—these features are often not distinctive enough to allow multilayer identification. This helps explain why the θ ≈ η approximation, which implicitly assumes monolayer adsorption, has been so widely accepted and used.
Source: Corrosion Science
Author: Anton Kokalj
Institution: Jožef Stefan Institute
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,070
OpenAlex ID: W4414620088