Corrosion Behavior of Hybrid Zinc Coatings Based on Chitosan and Corrosion Inhibitor BTA: Effect of the Molecular Weight and ζ-Potential

Round 1

Reviewer 1 Report

This study investigates the corrosion resistance of composite coatings composed of zinc with or without loaded benzotriazole (BTA) and two types of particles (LMC or HMC), and explores the particle size and water suspension stability of the coated particles. The experiment demonstrates that the hybrid zinc coatings with loaded BTA corrosion inhibitors exhibit better corrosion resistance compared to pure zinc coatings. Additionally, it is shown that the radius of loaded BTA particles in solution is independent of the molecular weight of chitosan. However, there are some spaces to be improved. The reviewer suggests make minor revisions to ensure that it meets the demand of Coatings.

1.         The content in the abstract should focus more on quantitative analysis rather than qualitative analysis.

2.         The synthesis schematic in Figure 1 needs improvement; BTA appears to be mixed rather than loaded.

3.         There is a significant difference between the nanoparticle sizes provided in Table 1 and those indicated by the TEM scale in Table 2. Moreover, the size of CS190-TPP-BTA in Table 2 is larger than CS190-TPP, contradicting the conclusion in Table 1.

4.         Characterization of corrosion products should be added to verify whether the types of corrosion products mentioned in the discussion are consistent with those in the literature cited, thus confirming the accuracy of stating that corrosion products provide a physical barrier to enhance corrosion resistance.

5.         When discussing the experimental results, diagrams illustrating corrosion mechanisms can be added to help readers understand.

6.         The sizes of the water contact angle photos in Figure 11 are inconsistent. Additionally, the author needs to adjust the formatting of other images to maintain consistency.

7.         The reference formatting is disorderly, with the following issues: inconsistent page number placement; some journals include the month while others do not; some article titles are enclosed in quotation marks while others are not; and there is inconsistency in capitalization of article titles, with some having only the first letter capitalized while others have all words capitalized.

English can be further improved

Author Response

This study investigates the corrosion resistance of composite coatings composed of zinc with or without loaded benzotriazole (BTA) and two types of particles (LMC or HMC), and explores the particle size and water suspension stability of the coated particles. The experiment demonstrates that the hybrid zinc coatings with loaded BTA corrosion inhibitors exhibit better corrosion resistance compared to pure zinc coatings. Additionally, it is shown that the radius of loaded BTA particles in solution is independent of the molecular weight of chitosan. However, there are some spaces to be improved. The reviewer suggests make minor revisions to ensure that it meets the demand of Coatings.

1. The content in the abstract should focus more on quantitative analysis rather than qualitative analysis.

       The recommendation is taken into account and additional information has been added in the Abstract.

2. The synthesis schematic in Figure 1 needs improvement; BTA appears to be mixed rather than loaded.

        The explanation of Figure 1 is added to the text and the correction is done.

3. There is a significant difference between the nanoparticle sizes provided in Table 1 and those indicated by the TEM scale in Table 2. Moreover, the size of CS190-TPP-BTA in Table 2 is larger than CS190-TPP, contradicting the conclusion in Table 1.

According to the presented results, the size of BTA-loaded particles is smaller compared to the unloaded ones. The polydispersity of the sample from CS190-TPP-BTA (PDI ~ 0.12) is significantly higher compared to the CS190-TPP (PDI ~ 0.31). Moreover, the dimensions presented in Table 1 correspond to the hydrodynamic diameter of the produced particles, which is almost two times higher compared to the real size (Varoqui, R., Dejardin, Ph., J. Chem .Phys., 1977, 66, 4395)

4. Characterization of corrosion products should be added to verify whether the types of corrosion products mentioned in the discussion are consistent with those in the literature cited, thus confirming the accuracy of stating that corrosion products provide a physical barrier to enhance corrosion resistance.

       The recommendation is taken into account. Аll previous studies of the authors on zinc coatings (including hybrid ones) show that in the case of corrosion treatment in a chlorine environment the main corrosion product with low solubility is zinc hydroxide chloride – ZHC. We have not cited many our articles (except No.26) in order to avoid self-citation. However, after this remark we have expanded the Referee list with more articles of our research on this topic. In all cases, a surface protective film with barrier properties is formed, which consists of mainly of ZHC and various polymer particles included in it.

5. When discussing the experimental results, diagrams illustrating corrosion mechanisms can be added to help readers understand.

       Тhe authors generally agree with the reviewer that diagrams illustrating the corrosion processes would provide additional clarity and present such a diagram below. However, similar type of diagram exists in other author's articles and could cause copyright issues for a journal whose consent request would take a long time.

Otherwise, on the figure below is demonstrated the local corrosion process in chloride containing medium, for example (dissolution of the zinc coating – brown zones) in some areas, which gradually develops in depth and after a certain time will reach the steel substrate. Zinc hydroxide chloride (ZHC) - Zn₅(OH)₈Cl₂.H₂O - also forms, covering some areas of the surface (green zones).

In the cases when polymer particles present in the metal matrix, the corrosion process will localize in the metal zones around the particles. As a result, accelerated dissolution of zinc will begin and a “mixed” film consisting of ZHC and the particles will occur. In this case, the corrosion process will take place around the particles and the probability of obtaining local deep penetrations of the coating is reduced.

Therefore, such a development of the process will increase the probability that local corrosion will partially transform into general one, which in turn will reduce the possibility of destruction deeply inside. When general corrosion occurs, surface damages are well visible, which means that the prevention can be realized in time.

6. The sizes of the water contact angle photos in Figure 11 are inconsistent. Additionally, the author needs to adjust the formatting of other images to maintain consistency.

According to the Referee comment respective corrections in Figure 11 were made. Additional formatting of the other images has also been done.

7. The reference formatting is disorderly, with the following issues: inconsistent page number placement; some journals include the month while others do not; some article titles are enclosed in quotation marks while others are not; and there is inconsistency in capitalization of article titles, with some having only the first letter capitalized while others have all words capitalized.

The recommendation is taken into account and the needed corrections were done.

Author Response File: Author Response.pdf

Reviewer 2 Report

The research, which I received for assessment, focuses on developing corrosion-resistant hybrid zinc coatings that include chitosan particles with either low (LMC) or high (HMC) molecular weight. This approach aims to guarantee the secure and long-lasting functioning of different steel constructions. Within this framework, it is asserted that hybrid coatings comprising zinc and two varieties of chitosan particles (LMC or HMC), with or without the corrosion inhibitor benzotriazole (BTA), are electro-precipitated on low carbon steel substrates to mitigate corrosion in environments abundant in chloride. Chitosan particles are acquired and subsequently electro-precipitated as hybrid coatings on mild steel substrates. The electrokinetic charge and hydrodynmic size of the encapsulated particles, as well as the stability of their aqueous suspensions, were assessed in the use of dynamic light scattering throughout a thorough research. The authors employ SEM, AFM and other techniques analysis to compare the surface morphology, topography, and hydrophilicity of the hybrid coatings. They also measure the water contact angle and assess the corrosion and electrochemical behavior using potentiodynamic polarization curves, polarization resistance, and cyclic voltammetry.
The research demonstrated the impact of particle molecular weight and potential on the effectiveness of hybrid coatings in inhibiting corrosion, in comparison to standard zinc coatings.

Nevertheless, it is my contention that the following pivotal segments need assessment.

·     The introduction paragraph of the research is straightforward and demonstrates simplicity. Nevertheless, it is crucial to examine the important components using quantitative data in this part. Nevertheless, this part lacks any quantitative data. Emphasising the importance of the study and processing it with some numerical data is considered to be quite appropriate.

·         Although Fig. 1 shows how the study was carried out, it was determined that it was not meaningful and understandable. It would be appropriate to reconsider this section and expand it with its writings.

·         Fig. 10 displays AFM topography pictures. While this finding has significant importance, it is worth noting that no information on phase or amplitude is provided. If deemed required, it would be better suitable to include this section as a supplementary file.

·         The statements mentioned in 367-376 and given as findings should be expanded with references and definitive judgements should be avoided.

·        The whole article should be reread and some spelling mistakes and figure numbers should be checked. For example, fig. 6 is written instead of fig. 9. And so on.

In the light of these explanations, it is the predominant opinion that it would be appropriate to re-evaluate after some major changes are made due to the reasons I have stated above.

Author Response

The research, which I received for assessment, focuses on developing corrosion-resistant hybrid zinc coatings that include chitosan particles with either low (LMC) or high (HMC) molecular weight. This approach aims to guarantee the secure and long-lasting functioning of different steel constructions. Within this framework, it is asserted that hybrid coatings comprising zinc and two varieties of chitosan particles (LMC or HMC), with or without the corrosion inhibitor benzotriazole (BTA), are electro-precipitated on low carbon steel substrates to mitigate corrosion in environments abundant in chloride. Chitosan particles are acquired and subsequently electro-precipitated as hybrid coatings on mild steel substrates. The electrokinetic charge and hydrodynmic size of the encapsulated particles, as well as the stability of their aqueous suspensions, were assessed in the use of dynamic light scattering throughout a thorough research. The authors employ SEM, AFM and other techniques analysis to compare the surface morphology, topography, and hydrophilicity of the hybrid coatings. They also measure the water contact angle and assess the corrosion and electrochemical behavior using potentiodynamic polarization curves, polarization resistance, and cyclic voltammetry.
The research demonstrated the impact of particle molecular weight and potential on the effectiveness of hybrid coatings in inhibiting corrosion, in comparison to standard zinc coatings.

Nevertheless, it is my contention that the following pivotal segments need assessment.

•     The introduction paragraph of the research is straightforward and demonstrates simplicity. Nevertheless, it is crucial to examine the important components using quantitative data in this part. Nevertheless, this part lacks any quantitative data. Emphasising the importance of the study and processing it with some numerical data is considered to be quite appropriate.

      The comment is taken into consideration and some additional information is added to the Introduction part.

• Although Fig. 1 shows how the study was carried out, it was determined that it was not meaningful and understandable. It would be appropriate to reconsider this section and expand it with its writings.

      The explanation of Figure 1 is added to the text and the correction is done.

• Fig. 10 displays AFM topography pictures. While this finding has significant importance, it is worth noting that no information on phase or amplitude is provided. If deemed required, it would be better suitable to include this section as a supplementary file.

      The authors thank the reviewer for this recommendation. The new Figure 11 showing AFM phase images of the hybrid coatings has been introduced and more detailed explanations of AFM analysis have been included in the main text of the manuscript.

• The statements mentioned in 367-376 and given as findings should be expanded with references and definitive judgements should be avoided.

The comment is taken into consideration and the needed information is added.

•        The whole article should be reread and some spelling mistakes and figure numbers should be checked. For example, fig. 6 is written instead of fig. 9. And so on.

The comment is taken into consideration and the correction is done.

In the light of these explanations, it is the predominant opinion that it would be appropriate to re-evaluate after some major changes are made due to the reasons I have stated above.

The comment is taken into consideration and the correction is done.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The present revised paper is acceptable for the journal.