Although inhibitor adsorption and inhibition mechanisms have been studied extensively using various electrochemical techniques, these electrochemical techniques only provide an indirect estimate of inhibitor adsorption. In the present study, a QCM with dissipation monitoring (QCM-D) was used to investigate the adsorption on gold coated quartz crystal resonator (QCR) of a model corrosion inhibitor (CI) compound at different bulk inhibitor concentrations. In a first step, the classical Sauerbrey's equation was used to analyze the normalized frequency change data for estimation of adsorbed mass. Normalized frequency change was also analyzed in conjunction with dissipation change using small load approximation (SLA) model to establish the nature of adsorbed layer and to qualify the validity of Sauerbrey's equation. In context of the bulk inhibitor concentrations tested (50 ppm(w) and 100 ppm(w) of CI in 1wt.% NaCl solution) in this study, the adsorbed layer behaves as a rigid mass. A conscious effort is made to state and validate the assumptions for the analysis of experimental results.
Oil and gas transportation pipelines are often prone to internal corrosion in service environments. Two main strategies used to combat the problem of internal corrosion in pipelines involve the use of corrosion inhibitors (CIs) and more corrosion resistant alloys. Corrosion mitigation using inhibitors is a favorable choice because of better economic feasibility.1–4 Among all the types of corrosion inhibitors, organic corrosion inhibitors are most widely used in the industry.
Organic corrosion inhibitors are typically surfactant-type organic molecules with a hydrophilic head group and a hydrophobic alkyl tail. Corrosion inhibition using organic CIs relies on the mechanisms related to the adsorption of inhibitor molecules on a metal surface.2,4 However, the exact adsorption mechanisms are not yet clearly understood. So, in designing CIs with improved efficiency and to have a better understanding of underlying inhibition mechanisms, it becomes extremely important to study and quantify adsorption mechanisms. Various studies focusing on electrochemical experiments have been performed in the past but due to the intrinsic limitations of traditional electrochemical techniques, there is a lack of molecular level understanding of electrode/electrolyte interfacial properties such as adsorbed layer thickness, orientation of adsorbed inhibitor molecules etc. in the presence of corrosion inhibitor.5–7
