## 3 Results and Discussion
### The Effects of EPS Immersion in Fire Extinguishing Solution  
The modeling of the SIE data for these systems was conducted in optimal conditions with the equivalent circuits from Figure 13. The equivalent circuit in Figure 13a describes a two-layer model in which corrosion was only controlled kinetically. This circuit was used for the 1 h and 36 day immersed samples, respectively. The circuit in Figure 13b also describes a two-layer model, but in which there is a mixed control of corrosion: kinetic and diffusional. This was used for the sample immersed for 78 days in FES. Figure 11: Elemental mapping in zone A on the ZnPS sample immersed in FES for 78 days. Figure 12: Elemental mapping in zone B on the ZnPS sample immersed in FES for 78 days. Figure 10: The compositions of the surface of the ZnPS sample after 78 days of immersion in FES. It is surprising that for such a complex alloy/FES interface (electric double layer phosphating layer/paint layer/reaction products) such a simple circuit can be used (an electric double layer and an outer layer, most likely porous). This could be because the paint layer is practically compact and almost impermeable, although it could also contain a series of pores and form a screen on which the reaction products that managed to pass through the pores are deposited. The values of the equivalent circuit parameters for the three immersion periods are presented in Table 5. The Nyquist (a) and Bode (b) diagram for EPS is presented in Figures S7-S9. From the analysis of this data, the following can be highlighted:  
* The resistance of the electrolyte (R\({}_{\text{s}}\)) varies appreciably with the immersion time, this being explained by the fact that the actual resistance of the FES layer between the sample and the reference electrode (4.6 \(\Omega\cdot\)cm\({}^{2}\) see the CS/FES system) added fractions of the strength of the paint layer and the resistance of the porous phosphating layer, and while maintained in solution, added fractions of the resistance of the corrosion products that clogged the pores and deposited on or under the paint layer. * The resistance of the outer layer (R\({}_{\text{ext}}\equiv\) R\({}_{\text{por}}\) in Figure 13) increased with the immersion time while the electrical capacity of this layer was replaced by the constant phase element (CPE1), which is physically an imperfect capacitor. The degree of imperfection of this element decreased accordingly with the immersion time as a consequence of the increase of the roughness and the chemical inhomogeneity of this layer. * The presence of superimposed layers over the active surface of carbon steel resulted in a high charge transfer resistance (R\({}_{\text{ct}}\)), which increased over time. * The electric double layer must be regarded as a non-ideal capacitor, represented in the equivalent circuit by the constant phase element CPE2. In this case, the fitting degree increased appreciably with the immersion time (from an almost pure capacitor to a diffusion element). * In the EPS sample immersed for 78 days in FES, the corrosion process was also influenced by the diffusion of the charges through the clogged pores and the layer of iron oxides that accumulated under and above the paint layer. * Due to the high value of the electric double layer resistance and the diffusion process, the corrosion rate decreased during the EPS contact with the FES. Figure 13: Equivalent circuits used for modeling the EIS data of EPS samples immersed in FES for (**a**) 1 h/36 days and (**b**) 78 days.