## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Inhibitor** & \(C_{\rm inh}\)**, mM** & \(E_{\rm corr}\)**, V** & \(R_{p}\)**, k\(\Omega\)**+cm\({}^{2}\)** & \(i_{\rm corr}\)**\(\mu\)**A**-cm\({}^{-2}\)** & \(Z_{\rm\mu}\) \% \\ \hline - & - & 0.172 & \(41.9\pm 4.6\) & \(1.2\pm 0.3\) & - \\ \hline \multirow{4}{*}{A} & 0.01 & 0.198 & \(20.8\pm 4.8\) & \(0.7\pm 0.2\) & 41.7 \\  & 0.10 & 0.140 & \(25.9\pm 1.7\) & \(0.6\pm 0.2\) & 50.0 \\  & 1.00 & 0.128 & \(107.2\pm 17.7\) & \(0.30\pm 0.10\) & 75.0 \\ \hline \multirow{4}{*}{B} & 0.01 & 0.162 & \(34.8\pm 5.3\) & \(0.9\pm 0.3\) & 25.0 \\  & 0.10 & 0.226 & \(62.6\pm 8.4\) & \(0.31\pm 0.10\) & 74.2 \\  & 1.00 & 0.295 & \(115.8\pm 18.3\) & \(0.20\pm 0.10\) & 83.3 \\ \hline \multirow{4}{*}{C} & 0.01 & 0.174 & \(42.4\pm 7.3\) & \(0.89\pm 0.11\) & 25.8 \\  & 0.10 & 0.179 & \(140\pm 19\) & \(0.24\pm 0.08\) & 80.0 \\  & 1.00 & 0.160 & \(172\pm 13\) & \(0.15\pm 0.02\) & 57.5 \\ \hline \multirow{4}{*}{D} & 0.01 & 0.159 & \(223\pm 33\) & \(0.28\pm 0.08\) & 76.6 \\  & 0.10 & 0.136 & \(208\pm 23\) & \(0.10\pm 0.02\) & 91.7 \\ \cline{1-1}  & 1.00 & 0.210 & \(195\pm 17\) & \(0.14\pm 0.04\) & 88.3 \\ \hline \end{tabular}
\end{table} 
Table 2: Open circuit potential \(E_{\rm corr}\), polarisation resistance \(R_{p}\), corrosion current density \(i_{\rm corr}\), and degree of protection of copper \(Z_{i}\), in 10 mM NaCl solutions with various derivatives of 5-amino-1\(H\)-1,2,4-triazole. The difference between cathodic curves of copper in solutions with and without A-C becomes noticeable only when \(C_{\text{inh}}\geq 0.10\) mM. The higher the concentration of the inhibitor, the lower the current density (Figure 1a-c, curves 3\({}^{\prime}\)-4\({}^{\prime}\)). This means that the cathodic process is slowing down. The region of the rapid growth of the cathodic current density is shifted towards negative values by at least 0.1 V for inhibitor A and at least 0.25 V for inhibitors B and C, as compared to that of the chloride solution without inhibitors. For inhibitor D, the shift is observed at any of the studied concentrations. The analysis of the polarisation resistance \(R_{\text{p}}\), the rate of corrosion, and the protection level determined by the potentiodynamic polarisation method (Table 2) demonstrated that the inhibition effect of all the studied 3-sulphvinylalkyl derivatives of 5-amino-1\(H\)-1,2,4-triazole depends on their concentration. The maximum protection level is observed when \(C_{\text{inh}}\geq 0.10\) mM (for inhibitor A at \(C_{\text{inh}}\geq 1.00\) mM). In this case \(R_{\text{p}}\) increases by 2-4 times and the corrosion rate decreases by 4-10 times. When the concentration of a compound is 0.01 mM, the inhibition effect for inhibitors A-C is weaker (below 40% of the effect observed during the test experiment). The exception is inhibitor D. At \(C_{\text{inh}}\geq 0.01\) mM the rate of corrosion is 4 times slower. Generally, the inhibition effect on copper in neutral chloride solutions increases with the growth of the sulphinylalkyl chain. Comparison of the results obtained for compounds with the similar structure, e.g., for 2-amino-5-(ethylthio)-1,3,4-thiadiazole [1] suggests an increase in the degree of protection during the transition of mercapto-derivatives to sulfinyl-derivatives. The electrochemical impedance spectroscopy also proves that a protective film forms on copper in neutral chloride solutions with 3-sulphinyalkyl-5-amino-1\(H\)-1,2,4-triazole. Figure 2 presents Nyquist diagrams obtained for the chloride-borate solution without (Figure 2a-d, _1_) and with the A, B, C, and D inhibitors with concentrations of \(C_{\text{inh}}=0.01\)-1.00 mM (Figure 2a-d, 2-4). The Nyquist plots are presented as an imperfect semicircle, the imperfection being usually accounted for by the impedance frequency dispersion and the geometric and/or energetic inhomogeneity of the electrode's surface.