## 3 Results and Discussion
### In Vitro Electrochemical Study Using Electrochemical Impedance Spectroscopy  
To determine the mechanism and kinetics of electrochemical corrosion occurring on the surface of the CoCrMo electrode in the environment of artificial saliva before and after modification, and comparatively in a saline, a complementary electrochemical impedance spectroscopy (EIS) method was used. Figure 4 shows the CPE1 model, consisting of electrolyte resistance (R\({}_{\text{s}}\)) and a parallel system of a constant-phase element (CPE) combined with charge transfer resistance (R\({}_{\text{ct}}\)). The best fitting of experimental EIS data with the software-generated model curve for the real and imaginary part of the circuit impedance was obtained depending on the frequency of changes in the measurement signal for all the corrosive environments used (Figures 5-7). The CPE1 equivalent electrical circuit with a one-time constant is characteristic of an electrode material with an undifferentiated surface morphology, with shallow pits on the surface. For the purposes of CNLS fitting, CPE was used instead of a capacitor, which was treated in the considerations as a \"leaky\" capacitor with non-zero real and imaginary components. The CPE impedance (\(\hat{Z}_{\text{CPE}}\)) is given via Equation (1) [31]:  
\[\hat{Z}_{\text{CPE}}=\frac{1}{\text{T}(\text{j}\omega)^{\varphi}} \tag{1}\]  
where T [F cm\({}^{-2}\) s\({}^{\Phi-1}\)] is a capacitive parameter, which is a function of the electrode potential, and the dimensionless parameter \(\phi\) is the angle of rotation of the purely capacitive line on the Nyquist plot (\(\alpha\) = 90\({}^{\circ}\) (1 \(-\) \(\phi\))). Figure 4: CPE1 model for the equivalent electrical circuit (used for the pitting corrosion of the CoCrMo electrode in the biological environment). Figure 5: Experimental (symbols) and simulated (lines) Nyquist diagrams in the form \(-Z^{\prime\prime}=\mathrm{f}(Z^{\prime})\) for the CoCrMo electrode in the applied corrosion environments at a temperature of 37 \({}^{\circ}\)C. The inset shows the high-frequency (HF) part. Figure 6: Experimental (symbols) and simulated (lines) Bode diagrams in the form of \(\Phi=\mathrm{f}(\log\mathrm{f})\) for the CoCrMo electrode in the applied corrosion environments at a temperature of 37 \({}^{\circ}\)C.  
In the Nyquist spectral spectrum for the CoCrMo electrode in all the tested corrosion environments, only one semicircle was observed in the entire range of tested frequencies, the radius of which depended on the type of corrosion environment (Figure 5). As a result of adding modifiers, in the form of NaF (3) (4) and mouthwashes (5) (6), to the artificial saliva environment (1) (2), there was a tendency for the recorded semicircle in the spectrum to become increasingly blurred. This means that the electrochemical corrosion process occurs more easily in the environment of unmodified artificial saliva. The Bode diagrams presented in Figures 6 and 7 confirm a very good fit of the experimental data in relation to the software-generated model curve. The phase angle shift value provides important information about the mechanism and kinetics of the ongoing corrosion processes. Obtaining the shape of Bode diagrams in the form \(\Phi=\) f(logf), as shown in Figure 6, is characteristic of pitting corrosion that occurs on the passivated material [5; 8; 13; 30]. An increase in the phase angle shift value is proportional to the increase in the corrosion resistance of the material. Moreover, as shown in Figure 6, there was only one time constant for the samples tested in all environments, which means that the electrochemical corrosion process took place in one stage. The \(\Phi=\) f (logf) graphs were characterized by a wide plateau range visible for the middle frequencies and one maximum, which demonstrates the high corrosion resistance of the passivated material. The high resistance of the tested alloy can be attributed to the elements Cr and Mo, which are characterized by excellent resistance in extremely aggressive corrosive environments.