In Part 1 of this two part paper, the critical micelle concentration (CMC) and corrosion inhibitor efficiency response curve was estimated for mixtures relating to the homologous series of alkyldimethylbenzylammonium chlorides with C12, C14 and C16 tail lengths. In the first paper, the uninhibited and inhibited corrosion rates were used to estimate corrosion inhibitor efficiency and were used to determine the optimum mixture ratio of the three surfactants based on their ability to minimize the steady state inhibited corrosion rate. In this second part, the transient data between the uninhibited and inhibited steady state corrosion rate were used to estimate the rate of change of surface coverage. This transient response in coverage was then analyzed using a mixed first and second order adsorption kinetic model, which enabled quantification of the adsorption and desorption rate constants. The adsorption rate constants were determined for the same 10-point three-component simplex mixture experimental design introduced in Part 1. Cubic response curves were calculated for the adsorption and desorption rate constants, and adsorption equilibrium constant. The adsorption rate constant and desorption rate constants were found to have very different interaction strengths, with the adsorption rate constant showing a stronger pairwise interaction, whilst the desorption rate constant displayed a stronger ternary interaction. The differences between the interaction strengths between pairwise and ternary interactions is reflected in the composite equilibrium constant.
In the first paper, a mixture design matrix of a homologous series of alkyldimethylbenzylammonium chlorides (BAC) was used to assess the performance and facilitate optimization of a mixed surfactant corrosion inhibitor system based on surface coverage and steady state inhibited corrosion rate.1 In this second paper, the approach is extended to include adsorption kinetic analysis, as demonstrated in Woollam and Betancourt for a first-order Langmuir kinetic model.2
The traditional laboratory-based approach when evaluating corrosion inhibitor performance is to track the corrosion rate of steel over time using in-situ electrochemical techniques, e.g. linear polarization resistance (LPR). In such instances, typically only the initial, uninhibited rate and the final steady state corrosion rate are extracted to determine an inhibitor efficiency.
