3.2.4. Comparison Studies

Finally, Figure 16 compares the results of the three methods used in the present study to assess the corrosion protection efficiency. It was found that the CCIn had a superior corrosion resistance to the local clay in all of these procedures. The corrosion resistance value of the 1% PCN of the commercial Indian clay is about three times higher than the value of the 1% PCN of the local Khulays clay, as illustrated in Figure 16. Furthermore, the corrosion resistance of these polymer clay nanocomposites decreased gradually from 1–5% PCN. When comparing the corrosion resistance (Rct) obtained from the EIS results (Figure 16), it was found that they coincide with the corrosion current density (ICorr) values derived from the EFM and Tafel methods (Figure 17a,b). This main conclusion may be attributed to the chemical composition of the commercial Indian clay and the high percentage of montmorillonite content compared with the local Khulays clay. The high percentage of montmorillonite content (64.9%) [25] increased the ability of this clay to swell more than the local Khulays clay, which contains 35.22% montmorillonite. This resulted in the improved CPC intercalation and greater dispersion of the commercial Indian clay layers inside the polystyrene chains, which increased the tortuous course of the corrosive ions and resulted in a higher coating efficiency. Fully exfoliated organoclay layers within the PS matrix improve the protective qualities of the PS coating more than partially exfoliated nanocomposite and pure PS coatings. Thus, the permeating molecules are forced to take a wiggling path and diffuse via the convoluted channels around them, especially at low OC content, which increases the tortuosity of the oxygen, water, and chloride ion diffusion pathways and increases the coating efficiency compared with using a pure PS coating [4,9,17].

**Figure 16.** Comparison of electrochemical results from EIS method of PCN coating of present study for both clay types.

**Figure 17.** (**<sup>a</sup>**,**b**) Comparison of electrochemical results from (**a**) EFM and (**b**) Tafel for PCN coating of present study for both clay types.

A comparison with other studies is shown in Table 4 using current density values. It is noticed that the current density values of our study are much better than those of the best study, which is Chen-Yang et al. [42] using polyurethan. The current density value of PCN (CCIn) 7.23 × 10−<sup>8</sup> A/cm<sup>2</sup> is better than any other formulation, as shown in Table 4. However, it is hard to make such a comparison with other studies, as there are many parameters that need to be taken into consideration, such as the adhesion of the polymer and PCN on the metal, the coating thickness, the metal, the temperature of the study, and the exfoliation of the organoclay layers within the polymer matrix.


**Table 4.** A comparison of our results with previous ones.
