Abstract
Electrochemical behavior of brass and inhibitory effect of L‐cysteine in HCl solution are investigated using electrochemical techniques in addition to SEM‐EDS analysis. Results show that inhibition efficiency depends on inhibitor concentration and immersion time of brass electrode in inhibitor solution. Electrochemical test results point to formation of Cu(I)‐cysteine complex on the brass surface in chloride solutions with addition of different amounts of cysteine. The formed complex has an important role in inhibition of the corrosion process in the examined media because Cu(I)‐cysteine significantly reduces dissolution of brass. Curves obtained in acidic solution in the presence of cysteine after pretreatment in sodium dodecyl sulfate (SDS) by cyclic measurements and potentiodynamic polarization measurements indicate intense inhibition of corrosion processes. Efficient inhibition of brass dissolution is result of formation of a stable protective layer on the brass surface after pretreatment of the electrode in SDS solution. The brass surface is modified in sodium dodecyl sulfate solution in order to increase cysteine adsorption on the electrode surface and to improve inhibition efficiency. Inhibition mechanism of cysteine includes adsorption on active sites on the electrode surface, which is confirmed by SEM‐EDS analysis of brass. Adsorption of cysteine in hydrochloric acid solution obeys the Langmuir adsorption isotherm. Also, Gibbs free energy of adsorption has a value of −31.5 kJ/mol and indicates strong adsorption of cysteine on the electrode surface.
Highlights
Brass is widely used in various industries due to its stability in aggressive environments. e environment in which chloride ions are present is one of these [1, 2], and corrosion processes in these environments are a major problem [3]
Open circuit potential obtained in HCl solution with an addition of cysteine generally has more negative values in regard to open circuit potential (OCP) values obtained in bare HCl solution. is trend of shift of OCP values indicates adsorption of cysteine molecules on active sites on the electrode surface
Change of OCP values indicates that cysteine acts like cathodic type of inhibitor in acidic chloride solutions
Summary
Brass is widely used in various industries due to its stability in aggressive environments. e environment in which chloride ions are present is one of these [1, 2], and corrosion processes in these environments are a major problem [3]. During the years of examinations of dissolution of metals and alloys in chloride solutions, different ways were revealed to slow down the oxidative processes in such media. Most compounds that can be used as copper and brass corrosion inhibitors are toxic and nonbiodegradable and pose a threat to environmental protection. In addition to amino acids, compounds such as purine and adenine showed good results as nontoxic corrosion inhibitors in different aggressive media [19,20,21,22,23]. Nontoxic compounds which can be used as potent inhibitors should contain heteroatoms which have strong affinity to specific metals or a ring with delocalized electrons. Cysteine (Cys) is a very interesting amino acid due to the amino group in its structure and –SH group that has strong affinity to copper (Figure 1)
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