Chitosan and Its Derivatives as a Barrier Anti-Corrosive Coating of 304 Stainless Steel against Corrosion in 3.5% Sodium Chloride Solution

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

This work studied the corrosion inhibition of chitosan-based coatings for 304 stainless steel in a 3.5% NaCl solution. The manuscript has many flaws and lacks a real scientific discussion of the results. This is the main reason for recommending the rejection of the present version of the manuscript.

 

1.     In the title the solution used and the steel tested must be reported.

2.     The chitosan-based coatings must be characterized with either FTIR-ATR and/or XPS techniques. The EDS alone is not sufficient.

3.     The part reported from lines 163 to 172 is unnecessary in a scientific manuscript. Here you must report the parameters used to perform the EIS analysis, which you reported in section 3.2.

4.     The morphological analysis must also be reported in the “materials and method” section.

5.     The cross-section analysis, “section 3.1.1” must be improved. You must report the figures about this analysis. This also shows the goodness of the coating. The sentence “s. However, this expectation contrasts with SEM observations, as Chi, despite being the thickest coating, exhibited noticeable surface irregularities that could compromise its effectiveness” without any images cannot be validated.

6.      The EIS and PDP tests, must be reported in one plot. It is unnecessary to have multiple figures. Plus, this helps to understand better the results. Moreover, the X and Y axis on the EIS plots must have the same value.

7.     The electrochemical analysis needs to be significantly improved. The authors only report the results without explaining the reason. Also, the results are not consistent with each other (EIS and PDP differ). For instance, the fitting does not seem to agree with the experimental result (X², should be reported in the table).  The coated chitosan sample showed an Rp more than 10 times lower than the bare substrate. The same goes for the other chitosan-based coatings, therefore, the sentence in line 352, “the system demonstrates intermediate protective capacity” is unjustified. Chi/PTA, showed minimal improvement (around 12%). Does the coating decrease the corrosion resistance of the substrate?

8.     Provide a Table and compare your results on anti-corrosion performance with other results reported in the literature and comment them on

9.     How did you calculate the corrosion rate?

10.  Figure 10 seems to be incomplete. It is missing the anodic branch. While in figure 12 is the opposite.

11.  Based, on the abovementioned questions, the conclusion and abstract also must be improved.

 

 

Author Response

As a general comment:

Although the reviewer's comment on our document is not very favorable, we believe that the suggestions provided helped to improve the content of the manuscript. Thank you for the review; we appreciate the thorough review of our work, and the constructive feedback provided. We have addressed each of the comments and suggestions as outlined below. The manuscript has been revised accordingly, with changes marked in blue.

 

1. In the title the solution used and the steel tested must be reported.

As requested, the title has been updated to include the specific solution used and the steel tested.

“Chitosan and its derivatives as a barrier anti-corrosive coating of 304 Stainless Steel against corrosion in 3.5 % NaCl solution”

 

2. The chitosan-based coatings must be characterized with either FTIR-ATR and/or XPS techniques. The EDS alone is not sufficient.

 In response to the reviewer's suggestion. We have conducted FTIR-ATR studies to characterize the chitosan-based coatings, addressing the concern that EDS alone was insufficient.  Results are now included in the document (lines 167-172 and 357-378, including Fig 6)

 

3. The part reported from lines 163 to 172 is unnecessary in a scientific manuscript. Here you must report the parameters used to perform the EIS analysis, which you reported in section 3.2.

The section from lines 163 to 172, considered unnecessary, has been revised. We have now reported the specific parameters used for the EIS analysis in Section 2.41, instead of the previous location (see lines 184-194).

 

4. The morphological analysis must also be reported in the “materials and method” section.

The morphological analysis has been added to the "Materials and Methods" section under Sections 2.3.1 Morphological characterization (see lines 153-165) and 2.3.2 FTIR characterization (see lines 167-172).

 

5. The cross-section analysis, “section 3.1.1” must be improved. You must report the figures about this analysis. This also shows the goodness of the coating. The sentence “s. However, this expectation contrasts with SEM observations, as Chi, despite being the thickest coating, exhibited noticeable surface irregularities that could compromise its effectiveness” without any images cannot be validated.

We have improved the cross-section analysis in Section 3.1 by including the requested figures. These images, now found in Figure 5, provide visual representation of the coating's quality (line 311). Section 3.1.3 was edited; changes can be seen on lines 306-307 and 327-354.

 

6. The EIS and PDP tests, must be reported in one plot. It is unnecessary to have multiple figures. Plus, this helps to understand better the results. Moreover, the X and Y axis on the EIS plots must have the same value.

The EIS and PDP test results have been combined into unified plots to enhance clarity and facilitate better understanding. Additionally, the X and Y axes on the EIS plots have been standardized. The updated figures are now presented as Figure 7 (line 431) and Figure 8 (line 513), and the corresponding section has been revised and modified. Sections 3.2 (from line 399) and 3.3 (from line 497) were edited, and the changes were marked in blue in the document.

 

7. The electrochemical analysis needs to be significantly improved. The authors only report the results without explaining the reason. Also, the results are not consistent with each other (EIS and PDP differ). For instance, the fitting does not seem to agree with the experimental result (X, should be reported in the table).

The coated chitosan sample showed an Rp more than 10 times lower than the bare substrate. The same goes for the other chitosan-based coatings, therefore, the sentence in line 352, “the system demonstrates intermediate protective capacity” is unjustified. Chi/PTA, showed minimal improvement (around 12%). Does the coating decrease the corrosion resistance of the substrate?

The electrochemical analysis section has been improved. We have provided more in-depth explanations for the results. The statement regarding the intermediate protective capacity of the coating has been reconsidered, and the impact of the coatings on the corrosion resistance of the substrate has been re-evaluated (lines 411-479).

 

8. Provide a Table and compare your results on anti-corrosion performance with other results reported in the literature and comment them on

A comparison table (table 4) has been added (line 613), where we discuss our findings with other studies on anti-corrosion performance. The table is followed by commentary contextualizing our results within the broader literature (lines 602-611).

 

9. How did you calculate the corrosion rate?

In the revised manuscript, we have clarified the method used to calculate the corrosion rate, specifying that the data were processed using Cview software (see lines 497-499).

 

10. Figure 10 seems to be incomplete. It is missing the anodic branch. While in figure 12 is the opposite.

We have revised Figures 10 and 12 to address the noted issues, ensuring that both figures accurately represent the data. However, to respond to question 6 figures 10 and 12 are now included in the new Figure 8.

 

 

11. Based, on the abovementioned questions, the conclusion and abstract also must be improved.

Following the revisions made throughout the manuscript, the abstract (lines 20-23) and conclusion (lines 625-629) have been rewritten to reflect the new insights and findings.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. It seems to me, the title should reflect the content of the work, hence the title is in need to mention of material in relation to which electrochemical corrosion resistance was studied. Stainless steel also should be present as keyword.

 

2. Designations by abbreviations should be used once (e.g., lines 99 and 114, 115 and 164, 137, 138, 139, 140, 208 and 164 and 176 and many others) when the expression or word are mentioned for the fist time. Some abbreviations are not used at all.

 

3. Introduction contains a lot of general considerations. There are many unnecessary speculations (discussions) that are far fr and soom the subject of the article, e.g., lines 38-41, 51-61 and so on.

 

4. There are too many very large sentences (up to 7 lines) that are atypical for the English language even not taking into account appearing difficulties in understanding the meaning.

 

5. All electrochemical protection methods based on the use any coatings, with the exception of protection using the potential of an external source, are barrier-type methods.

 

6. It is unclear from the Introduction what the novelty and the aim of this work is. Dear authors are recommended to emphasize the improvements of their research compared to the works of other researchers tho also used coatings based on chitosan and its derivatives. May be, it it is reasonable to move the lines 386-389 into the Introduction?

 

7. The absolute deviations (Table 1) are provided statistically incorrectly.

 

8. The statement in lines 284-285 is electrochemically incorrect. The statement in lines 288-290 are needed to be referenced.

 

9. What about the porosity of barrier coating?

Comments on the Quality of English Language

English can be improved

Author Response

Reviewer #2: Comment:

As a general comment:

Thank you for the general appreciation of our paper and for the suggestions to improve this paper. Taking the observations of the reviewer into consideration, point by point, my answers are detailed below. The manuscript has been revised with changes marked in blue.

1. It seems to me, the title should reflect the content of the work, hence the title is in need to mention of material in relation to which electrochemical corrosion resistance was studied. Stainless steel also should be present as keyword.

As requested, the title has been updated to include the specific solution used and the steel tested.

“Chitosan and its derivatives as a barrier anti-corrosive coating of 304 Stainless Steel against corrosion in 3.5 % NaCl solution”

2. Designations by abbreviations should be used once (e.g., lines 99 and 114, 115 and 164, 137, 138, 139, 140, 208 and 164 and176 and many others) when the expression or word are mentioned for the fist time. Some abbreviations are not used at all.

Thanks for the comment. The manuscript was revised, and some expressions were removed so that only the designated abbreviation remained.

 

3. Introduction contains a lot of general considerations. There are many unnecessary speculations (discussions) that are far fr and soon the subject of the article, e.g., lines 38-41, 51-61 and so on.

The introduction was edited, and changes were made to avoid confusion and unnecessary speculation, for example, we removed unnecessary EIS information, and added another one referring to the coating, the changes can be seen in the manuscript marked in blue (from line 56)

4. There are too many very large sentences (up to 7 lines) that are atypical for the English language even not taking into account appearing difficulties in understanding the meaning.

Thank you for your comment. All the English language in the manuscript was reviewed and changes were made as deemed necessary for better understanding.

5. All electrochemical protection methods based on the use any coatings, with the exception of protection using the potential of anexternal source, are barrier-type methods.

What you say is correct, the difference between barrier-type methods lies in the fact that there are different types of protection for metallic materials, and the application of these will depend directly on the properties of the material; as well as the use they will have. Protection methods, such as coatings, are classified as:

• Organic.
• Metallic.
• Conversion.

Buchheit, R. G. (2005). Corrosion resistant coatings and paints. In Handbook of environmental degradation of materials (pp. 367-385). William Andrew Publishing.

Shreir, L. L. (Ed.). (2013). Corrosion: metal/environment reactions.

 

Marcus, P., & Oudar, J. (Eds.). (2002). Corrosion mechanisms in theory and practice (pp. 243-286). New York: Marcel Dekker.

Revie, R. W. (2008). Corrosion and corrosion control: an introduction to corrosion science and engineering. John Wiley & Sons.

6. It is unclear from the Introduction what the novelty and the aim of this work is. Dear authors are recommended to emphasize the improvements of their research compared to the works of other researchers tho also used coatings based on chitosan and its derivatives. May be, it it is reasonable to move the lines 386-389 into the Introduction?

Thank you very much for the suggestion. Lines 386-389 were placed in the introduction in lines 106-110; the changes can be seen in the manuscript marked in blue.

7. The absolute deviations (Table 1) are provided statistically incorrectly.

Table 1 was revised and supplemented by adding Figure 5. "High-Resolution Metallographic Image of Coating Thickness Measurement Using Leica DM-IRM Microscope for a) Chi/PEG, b) Chi/PTA, c) Chi/PVP, and d) Chitosan." (line 312)

 

8. The statement in lines 284-285 is electrochemically incorrect. The statement in lines 288-290 are needed to be referenced.

Thank you for pointing that out. The statement in question has been reviewed and appropriately discussed and referenced in the document (lines 327-354).

 

9. What about the porosity of barrier coating

Thank you for your suggestion. A brief discussion on the general porosity of the coatings has been incorporated into the SEM section (lines 280-291). This addition considers the importance of this aspect and aims to enhance the overall discussion. However, further targeted studies would be necessary to obtain more specific results and a detailed understanding of the performance of these coatings.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Comments of coatings-3148889

 

The main weaknesses of the manuscript:

 

1.     The novelty of the work should be clearly described. What benefits could be achieved from this process? Please revise accordingly.

2.     The caption and the legend for the figures and tables should be described in more detail.

3.     Figs. 5-9: y-axis title should be corrected to -Z".

4.     The length of the x and y axis on a Nyquist plot should be identical, otherwise there is no way of knowing if the data is semi-circular.so how can it be interpreted by the reader (Figs. 5-9).

5.     The EIS and PDP should be integrated into one picture respectively, and detailed comparative analysis should be performed.

6.     No cross-sectional observation in this study.

7.     Can you provide the specific XPS patterns to facilitate a more detailed understanding of the element analysis? How do the different crystal structures formed during the treatment affect the properties of the coatings, such as hardness and corrosion resistance?

8.     The test of corrosion resistance in the manuscript is too simple. It is not enough to only test the electrochemical performance. The test of neutral salt spray test should be added.

9.     Can you explain how the changes in coating thickness, defect distribution, and diameter of defects influence the ability of the coating to block the passage of Cl ions?

10.  The conclusion should be more concise in a better way.

Comments for author File: Comments.pdf

Author Response

Reviewer #3: Comment:

As a general comment:

I appreciate your comments and support for our paper. Below are detailed responses to the reviewer's observations, addressed point by point. The revised manuscript includes changes highlighted in blue.

1. The novelty of the work should be clearly described. What benefits could be achieved from this process? Please revise accordingly.

Thanks for the suggestion. The introduction now includes a statement clarifying the novelty and objective of the work (see lines 106-110)

Introduction

2. The caption and the legend for the figures and tables should be described in more detail.

Thanks for the suggestion. All figure titles have been edited, and details have been added for clarity.

3. Figs. 5-9: y-axis title should be corrected to -Z".

The suggestion was considered. Figures 5 to 9 are now presented as Figure 7. Additionally, the X and Y axes on the EIS plots have been standardized.                          

4. The length of the x and y axis on a Nyquist plot should be identical, otherwise there is no way of knowing if the data is semi-circular. so how can it be interpreted by the reader (Figs.5-9).

The suggestion was considered. Figures 5 to 9 are now presented as Figure 7. Additionally, the X and Y axes on the EIS plots have been standardized (See Figure 7 in the previous answer).    

5. The EIS and PDP should be integrated into one picture respectively, and detailed comparative analysis should be performed.

The EIS and PDP test results have been combined into unified plots to enhance clarity and facilitate better understanding. Additionally, the X and Y axes on the EIS plots have been standardized. The updated figures are now presented as Figure 7 and Figure 8, and the corresponding section has been revised and modified. Sections 3.2 (from line 403) and 3.3 (from line 560) were edited, and the changes were marked in blue in the document.

 

6. No cross-sectional observation in this study.

Thank you for the comment. We have improved the cross-section analysis in Section 3.1 by including the requested figures. These images, now found in Figure 5, provide a visual representation of the coating's quality (line 311). Section 3.1.3 was edited; changes can be seen on lines 306-307 and 327-354.

7. Can you provide the specific XPS patterns to facilitate a more detailed understanding of the element analysis? How do the different crystal structures formed during the treatment affect the properties of the coatings, such as hardness and corrosion resistance?

This is an excellent observation, but we apologize in advance for not being able to add information on the XPS patterns analysis. Our institution does not have X-ray diffraction equipment, so to perform such studies, we would have to contact and schedule an appointment with collaborating institutions, which would take a lot of time. But we will consider doing it.

8. The test of corrosion resistance in the manuscript is too simple. It is not enough to only test the electrochemical performance. The test of neutral salt spray test should be added.

Good observation, but the salt spray test will not be possible to include. These analyses must be monitored at 15, 30, and 45 days. We do not have the equipment, and in addition to the analysis time, we must add the management time to carry out the tests. We will not be able to comply with this requirement. But we will consider doing it. Apologies.

9. Can you explain how the changes in coating thickness, defect distribution, and diameter of defects influence the ability of the coating to block the passage of Cl ions?

Thank you for your insightful observation. This has prompted us to enhance the morphological analysis section of our study (lines 327-354).

The findings align with existing literature, which indicates that while very thin films offer insufficient protection, intermediate thicknesses are optimal, and excessive thickness can introduce defects that compromise effectiveness. Therefore, achieving optimal corrosion resistance requires both an adequate coating thickness and a smooth, defect-free surface, underscoring the complex interplay between coating thickness, surface morphology, and chemical composition in determining corrosion resistance.

The ability of a coating to block Cl⁻ ions is significantly influenced by these factors. Thicker coatings generally provide a better barrier, but their effectiveness is reduced if they have significant surface irregularities or stress-induced defects. Uniform and smooth coatings, such as the Chi/PTA coating, present a more consistent barrier that effectively prevents the ingress of Cl⁻ ions, thus enhancing corrosion protection. Larger defects or uneven surfaces can create pathways for Cl⁻ ions leading to localized corrosion. Therefore, the interplay between coating thickness, surface morphology, and chemical composition is crucial in determining the coating's effectiveness.

 

10. The conclusion should be more concise in a better way.

The suggestion was considered. Conclusions have been rewritten to reflect the new insights and findings (see changes in lines 625-629).

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Comments of coatings-3148889

 

The manuscript is well revised and can be published in present form.

Comments for author File: Comments.pdf