Hybrid Zinc Coatings with Chitosan/Alginate Encapsulated CuO-Nanoparticles for Anticorrosion and Antifouling Protection of Mild Steel

Round 1

Reviewer 1 Report

The presented manuscript “Hybrid Zinc Coatings with Chitosan/Alginate encapsulated CuO-nanoparticles for Anticorrosion and Antifouling Protection of Mild Steel” contains good findings. I think that this manuscript requires some changes in following areas:

·         Abstract is generic. Need to address a) need of this work, b) novelty, c) methodology suggested, d) results obtained (numerical).

·         Introduction: Add more recent literature work to justify the novelty of your work and selected conditions of the study.

·         Add chemical composition of the materials used in the present study.

·         Avoid Bulk citations.

·         Add table for chemical composition of the used material.

·         What is the basis of the selection of mentioned input conditions? Specify them in detail.

·         Line 328-330: Justify the sentence with proper technical reason and relevant literature source.

·         Figure 6 and 7: Improve the quality.

·         Mention the limitations and further scope of improvement in last section.

·         Mention conclusions in bullet points

Author Response

The presented manuscript “Hybrid Zinc Coatings with Chitosan/Alginate encapsulated CuO-nanoparticles for Anticorrosion and Antifouling Protection of Mild Steel” contains good findings. I think that this manuscript requires some changes in following areas:

• Abstract is generic. Need to address a) need of this work, b) novelty, c) methodology suggested, d) results obtained (numerical).

The recommendation is taken into account. The Abstract was corrected to express more clearly the aim (and novelty) of the presented work as follows: “Construction of anticorrosion coatings containing antifouling agents is an effective way to ensure long-term durability of marine steel infrastructures. In this work, an innovative hybrid coating was prepared by introducing of biocide CuO nanoparticles in ordinary zinc coating to improve its protective ability in aggressive salt water environments. The CuO nanoparticles were embedded inside the matrix of chitosan/alginate complexes to prevent spontaneous copper leaching during corrosive attacks. Two procedures were applied for electrodeposition of hybrid zinc coatings on mild steel substrates (DC current): 1-st - co-electrodeposition of encapsulated CuO nanoparticles with zinc on cathode (steel) electrode from a slightly acidic sulfate electrolyte (pH 4.5-5.0) and 2-nd – the encapsulated CuO nanoparticles were electrodeposited from aqueous solution as an intermediate layer between two zinc deposites. Particles size and stability of suspensions were evaluated using dynamic light scattering. Both hybrid coatings were compared in terms of surface morphology and hydrophilicity (SEM and AFM analysis, contact angle measurement) and corrosion resistance (potentiodynamic polarization curves, polarization resistance). Protective characteristics of the coatings were compared in a 3.5% NaCl solution and artificial sea water. The hybrid coating showed 2-4 times higher polarization resistance than the bare zinc coating during 30 days’ immersion in artificial sea water, indicating that this coating have a potential for application in marine environment.” 

 

• Introduction: Add more recent literature work to justify the novelty of your work and selected conditions of the study.

 

Recent literature was added to the Introduction (Refs. 6-9) and some citations were extracted in order not to make difficulties during the reading of the manuscript.

 

 

• Add chemical composition of the materials used in the present study.

 

           The recommendation is taken into account and the composition of the low-carbon steel is added.

• Avoid Bulk citations.

 

    The recommendation is taken into account.

 

• Add table for chemical composition of the used material.

 

           The recommendation is taken into account and the composition of the low-carbon steel is added in separate rows.

• What is the basis of the selection of mentioned input conditions? Specify them in detail.

 

           The authors doubt what the reviewer means - if it is about obtaining оf the coatings, the process and conditions are described in detail in Point 2.3. If the corrosion tests are taken into account, we have used known methods for corrosion characterization of materials, which are described in Points 2.4. - 2.7.

 

• Line 328-330: Justify the sentence with proper technical reason and relevant literature source.

 

           The recommendation is taken into account and the text is justified.

 

• Figure 6 and 7: Improve the quality.

 

    The recommendation is taken into account and the figures are updated.

 

• Mention the limitations and further scope of improvement in last section.

 

    The recommendation is taken into account and the needed text is added.

 

• Mention conclusions in bullet points

 

     The recommendation is taken into account.

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

This work reports on the corrosion inhibition of carbon steel by Chitosan/Alginate coated CuO nanocomposite zinc coatings through electrochemical techniques and micro-morphological characterisation. In my opinion, this work is interesting. However, there are some serious problems and errors in the manuscript and it cannot be published in the journal. Some comments on the careless work or careless presentation are summarised below:

1. Does this research contribute anything new to the field of corrosion inhibitors. Also the latest research developments in this field need to be covered in the introduction section.

2. The manuscript needs a lot of revision in terms of language and grammar. For example, lines 81 to 84, the sentences are too long and cannot be understood quickly by the reader. In addition, there are many errors in the manuscript and therefore the whole manuscript needs some editing in English.

3. Was a repeat experiment carried out? The author forgot to present the measurement error.

4. Sub-section 2.5 of the manuscript, Corrosion properties and CVA studies needs a lot of revision. In the reviewer's opinion, it is not scientific to control the polarisation curve by observing the morphology of carbon steel with the naked eye.

5. The manuscript does not provide a separate analysis of the inhibition mechanism.

6. Many of the test curves are very poorly illustrated.

 Moderate editing of English language

Author Response

Reviewer 2

This work reports on the corrosion inhibition of carbon steel by Chitosan/Alginate coated CuO nanocomposite zinc coatings through electrochemical techniques and micro-morphological characterisation. In my opinion, this work is interesting. However, there are some serious problems and errors in the manuscript and it cannot be published in the journal. Some comments on the careless work or careless presentation are summarised below:

1. Does this research contribute anything new to the field of corrosion inhibitors. Also the latest research developments in this field need to be covered in the introduction section.

As noted in the Introduction, “incorporation of metal oxide particles has been found to enhance the protective characteristics of ordinary zinc coating due to formation of mixed barrier layers that simultaneously contain corrosion products and incorporated particles [5-10]”. Incorporation of CuO nanoparticles in ordinary zinc coating has recently been shown to improve the anticorrosion properties of mild steel in salt solutions (Refs. 5, 7, 10]. The new element in our work consists of CuO nanoparticles encapsulation with biopolymers in order not only to stabilize the suspension against aggregation (before electrodeposition), but also to prevent the spontaneous leaching of copper ions from the coating during the corrosion attack. In addition, it is really surprising to us that a rather detailed literature review is apparently not sufficient for the reviewer.

2. The manuscript needs a lot of revision in terms of language and grammar. For example, lines 81 to 84, the sentences are too long and cannot be understood quickly by the reader. In addition, there are many errors in the manuscript and therefore the whole manuscript needs some editing in English.

The sentence in lines 81 to 84 is rewritten to express more clearly the aim of the work: “The proposed innovative hybrid coatings are expected to combine the biocide effect of CuO nanoparticles with well-known ability of the ordinary zinc coating to protect steel from corrosion in salt containing media – 3.5% NaCl and ASW solutions. In addition to the role of the biopolymer shell for slowing down the copper release during a corrosion attack, positive effect of both polymers is also expected based on their antifouling and anticorrosion properties.” 

3. Was a repeat experiment carried out? The author forgot to present the measurement error.

Аpparently the reviewer missed what was written in Point 2.8., where reproducibility data is demonstrated. In terms of error - it's really not presented, but it's within 10%.

4. Sub-section 2.5 of the manuscript, Corrosion properties and CVA studies needs a lot of revision. In the reviewer's opinion, it is not scientific to control the polarisation curve by observing the morphology of carbon steel with the naked eye.

Аpparently this seems to be a misunderstanding, as nowhere is it mentioned by the authors that changes in morphology of the coatings are tracked by “naked eye”. It is about the fact that during the anodic dissolution of the coating some changes can be registered on the surface, which indicate the process, and this was established by the authors. In all cases if the polarization is not stopped at an appropriate moment the experiment is obviously meaningless.

5. The manuscript does not provide a separate analysis of the inhibition mechanism.

Аccording to the authors, it is not necessary to present such a mechanism, since the action of the components involved in the investigation is described in the cited literature and principally is well known to most of the contemporary researchers. However, to bring some clarity the following may be added. As mentioned in Introduction, the main factor for “enhancing the protective ability of metal coatings with incorporation of nanoparticles in their matrix is the formation of barrier layers that simultaneously contain corrosive products and incorporated particles”. The barrier layers prevent the direct contact of the metal surface with corrosive medium, thus retarding the corrosion rate. Most probably, zinc hydroxyde chloride is the main corrosive product in our case due to the great content of Cl- ions in both testing media.

6. Many of the test curves are very poorly illustrated.

Тhe authors will not answer on this remark as it lacks specificity. If selected curves with corresponding deficiencies are pointed out, they will be corrected, of course.

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors of this paper study hybrid zinc coatings with chitosan/alginate encapsulated CuO-nanoparticles for anticorrosion and antifouling protection of mild steel. The idea of chitosan/alginate encapsulated CuO-nanoparticles is very novel, and the obtained results are also interesting and useful for anticorrosion and antifouling protection of mild steel. However, there are some major problems in this article. I believe that this paper should be major revised for publication in this journal. Listed below are detailed comments on the author's manuscript.

*  Language and grammar must be improved.

*  Introduction: Scholars have studied the chitosan and alginate accouterment effects of the anticorrosion properties of steel in HCl solution. Please indicate the innovations of this manuscript.

*  Experimentation: Please provide the results of the anticorrosion and antifouling test of composite zinc coatings(contain CuO) as control group.

*  Experimentation: The highlights of this work is encapsulated CuO nanoparticles. Please provide the experimental data(SEM, EDS and XRD) of encapsulated CuO nanoparticle.

*  Experimentation: I recommend author increase schematic illustration of coatings preparation process. It include encapsulated CuO nanoparticles preparation process.

*  Results and discussion: Please further illuminate anticorrosion and antifouling protection mechanism of coatings with chitosan/alginate encapsulated CuO-nanoparticles.

Comments for author File: Comments.docx

Author Response

Reviewer 3

The authors of this paper study hybrid zinc coatings with chitosan/alginate encapsulated CuO-nanoparticles for anticorrosion and antifouling protection of mild steel. The idea of chitosan/alginate encapsulated CuO-nanoparticles is very novel, and the obtained results are also interesting and useful for anticorrosion and antifouling protection of mild steel. However, there are some major problems in this article. I believe that this paper should be major revised for publication in this journal. Listed below are detailed comments on the author's manuscript.

*  Language and grammar must be improved.

The recommendation is taken into account.

*  Introduction: Scholars have studied the chitosan and alginate accouterment effects of the anticorrosion properties of steel in HCl solution. Please indicate the innovations of this manuscript.

Chitosan and alginate polymers have been found to improve the corrosion protection of steel when polymers were directly added to a corrosive solution (HCl or NaCl). In such case, the polymer molecules play a role of corrosion inhibitor (having barrier effect) adsorbing on the metal surface. The anticorrosion properties of our hybrid coating is based mainly on the sacrificial protective role of electrodeposited zinc coating, while incorporation of CuO nanoparticles (encapsulated with chitosan and alginate) in the zinc coating have only reinforcing effect.

*  Experimentation: Please provide the results of the anticorrosion and antifouling test of composite zinc coatings (contain CuO) as control group.

Тhe authors have some research on the impact of CuO on biofouling which they will publish on a later stage. For the reviewer, we show the effect of the hybrid coating on some microorganisms below

CLSM images showing the colonization of Phaeodactylum tricornutum adhering to samples after 3 days incubation: (a) low-carbon steel substrate, (b) ordinary zinc coating, (c) hybrid zinc coating with incorporated CuO nanoparticles.

*  Experimentation: The highlights of this work is encapsulated CuO nanoparticles. Please provide the experimental data(SEM, EDS and XRD) of encapsulated CuO nanoparticle.

Encapsulation of CuO nanoparticles have been performed according to procedure applied by Leonardi et al. (Ref. 16 in the revised manuscript) where the desired experimental data are presented in detail (SEM Fig. 3b, EDS Fig. 4a, TEM Fig. 5). That was why we decided to present only results from DLS measurements for comparison.

*  Experimentation: I recommend author increase schematic illustration of coatings preparation process. It include encapsulated CuO nanoparticles preparation process.

The recommendation is taken into account and schematic illustration of CuO nanoparticles encapsulation and coatings preparation process was added in the revised manuscript.

*  Results and discussion: Please further illuminate anticorrosion and antifouling protection mechanism of coatings with chitosan/alginate encapsulated CuO-nanoparticles.

We suppose that the main factor for improvement the protective ability of the zinc coatings with incorporation of CuO nanoparticles into the zinc matrix is the formation of barrier layers (of corrosive products with low solubility and incorporated particles) that prevent direct contact of the metal surface with the corrosive media. Most probably, zinc hydroxyde chloride was the main corrosive product in our case due to the high Cl- concentration in both testing media.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Review of manuscript

Hybrid Zinc Coatings with Chitosan/Alginate Encapsulated CuO-nanoparticles for Anticorrosion and Antifouling Protection of Mild Steel

The development of antifouling corrosion protection coatings is very important to ensure the long-term durability of marine steel infrastructures. So, the paper topic is actual. The authors clearly show that the hybrid zinc coatings provided corrosion protection of mild steel in the model medium of 3.5% NaCl and artificial seawater solution. The descriptions are short and clear. So, I recommend the manuscript for publication with minor corrections.

Some comments are below.

Lines 33-34: English in the sentence “…To date, surface modification of the base metal by applying protective coatings remains as the most effective approach to attain anticorrosion performances” is not proper (underlined)

Lines 38-39: English in the sentence “…Nowadays, the bare zinc coatings are often replaced from composite zinc coatings [5]” is difficult to understand. Please, correct this.

Line 208: The surface morphology images do not prove the authors’ statements (lines 210-224) because of low magnification. The differences in CuO particle sizes need to be demonstrated more clearly.

 Line 335: The chapter “Atomic Force Microscopy (AFM) and Contact Angle Investigations” needs to be analyzed in more detail. For example, the author’s statement, “…The surface topography of the samples is generally close but, however, differs to a certain degree,” is not clear. The AFM results need to be analyzed together with SEM results.

 

Line 347: Authors have to correct Figure 7.” AFM topography of ZnS(left) and ZnH(right) samples: 3D images and contact angle of the  water drop”.  The resolution of images of contact angle is not good.   

English looks good with some corrections

Author Response

Reviewer 4

Review of manuscript

Hybrid Zinc Coatings with Chitosan/Alginate Encapsulated CuO-nanoparticles for Anticorrosion and Antifouling Protection of Mild Steel

The development of antifouling corrosion protection coatings is very important to ensure the long-term durability of marine steel infrastructures. So, the paper topic is actual. The authors clearly show that the hybrid zinc coatings provided corrosion protection of mild steel in the model medium of 3.5% NaCl and artificial seawater solution. The descriptions are short and clear. So, I recommend the manuscript for publication with minor corrections.

Some comments are below.

Lines 33-34: English in the sentence “…To date, surface modification of the base metal by applying protective coatings remains as the most effective approach to attain anticorrosion performances” is not proper (underlined)

The recommendation is taken into account and the text is rewritten. Lines 33-34: “Applycation of protective coatings on the metal surfaces plays a significant role in the fight against corrosion. Coatings offer protective barrier between the corrosive environment and the substrate.”

Lines 38-39: English in the sentence “…Nowadays, the bare zinc coatings are often replaced from composite zinc coatings [5]” is difficult to understand. Please, correct this.

The recommendation is taken into account and the text is rewritten. Lines 38-39: “One way to improve their properties and prolong their service life is by embedding different types of nanoparticles in the metallic matrix during preparation of protective coatings.”

 

Line 208: The surface morphology images do not prove the authors’ statements (lines 210-224) because of low magnification. The differences in CuO particle sizes need to be demonstrated more clearly.

The recommendation is taken into account. Lines 210-224: In order to better demonstrate the difference in the CuO particles size, Figure 2 was changed to present surface morphology at higher magnification (x5000 instead of x1000). It was difficult to evaluate the particles size in the coating with top zinc layer. So, in the text of the revised manuscript remained only a statement: “Smaller (vague) CuO nanoparticles are seen on the surface of the second coating type, most likely under a thin top zinc layer.”

 

Line 335: The chapter “Atomic Force Microscopy (AFM) and Contact Angle Investigations” needs to be analyzed in more detail. For example, the author’s statement, “…The surface topography of the samples is generally close but, however, differs to a certain degree,” is not clear. The AFM results need to be analyzed together with SEM results.

The recommendation is taken into account and the text is rewritten. “From the AFM measurements, it was found that for both types of samples, the roughness values ​​are close, and the topography of the surface of the two samples is different, which is due to the inclusion of CuO in the system”.

Line 347: Authors have to correct Figure 7.” AFM topography of ZnS(left) and ZnH(right) samples: 3D images and contact angle of the  water drop”.  The resolution of images of contact angle is not good.   

The recommendation is taken into account and the figure is updated.

 

Author Response File: Author Response.pdf

Reviewer 5 Report

The main comments are given below (major revision):

1. The lines 231-235. I agree that biofouling of Fe-bearing steel will lead finally to degradation of steel materials in aqueous environments in the presence of microorganism. In order to prevent biofouling the introducing of Copper or Nickel particles in the upper surface layer of steel may solve this issue. In turn, chlorine is a strong enough oxidizing agent for copper. Therefore, the release of Cu2+ ions is intensive in seawater. One can expect that anodic oxidation and subsequent release of copper ions will deteriorate the quality (adhesion) of coatings that may result in delamination of Zn/CuO/Zn coating form the steel substrate. So, you will not observe any biocide effect even after short period of time. My suggestion is confirmed by polarization curves shown in Fig. 4 (the complete dissolution of the coating takes place). In this regard, I do not understand the motivation and design of the research. Why do you deposit Cu-bearing particles onto steel and study their corrosion behavior in the aggressive seawater if all types of hybrid coating completely dissolve?  

2. Also, the corrosion current (Table 1) is practically the same and varies between (1.1-2.9)^10-5 A/cm2. I suppose that the authors do not show SEM images of the corroded surface because no coating is left. It means that for the practical point of view the proposed multilayer poor-adhesive coatings are not so good.

3. The common drawback of the paper is unclear description of the electrochemical experiments. For example, in Sec. 2.5 the authors write that «Cyclic Voltammetry (CVA) studies were applied in potential interval between -1.4 V and 0 V with a scan rate of 10 mV/sec.», however no information about the solution (electrolyte) is given. Then, in Sec. 2.8 the authors described that electrochemical tests were carried out in 3.5 wt. % NaCl and artificial sea water. Later, the Fig. 3 does not contain any information about the used solution, while in the text (238–239 lines) one can find that the CV tests are realized in the starting electrolytes for electrodeposition. This information contradicts with Methodology section. In the Fig. 3 the authors should add an appropriate legend to black, red and blue curves, because It’s impossible to understand whether you study the steel with CuO, separate CuO particles or steel with pure Zn coating or something else. The sweep direction is advisable to be added.

4. Moreover, in lines 242-243 the electrodeposition process of the ordinary Zn, according to the text, occurs at more negative potential value than that of hybrid coating. What figure should I look at? In Fig. 3 the anodic peak for Zn and ZnH are near close to -0.75 V, and how is the anodic dissolution associated with electrodeposition process? I don’t understand.

5. To my knowledge, polarization resistance could be measured via Electrochemical Impedance Spectroscopy or using Stern-Geary equation. What approach did the authors use? Please, add a description of the method for Rp evaluation in the methodology section.

6. Regarding the conclusion that «the hybrid zinc coatings provided corrosion protection of mild steel in model medium of 3.5% NaCl and artificial sea water solution for a prolonged period of 30 days», I would like to pay authors attention that this observation is confirmed only by Rp measurement in seawater (Fig. 5). In general, both ZnH and ZnS-type coatings behave themselves as pure Zn-coating near the corrosion potential and on the anodic branches. If the authors could show the surface morphology after 30 days of immersion, we may conclude about the practicability of the developed coating.

Author Response

Reviewer 5

The main comments are given below (major revision):

1. The lines 231-235. I agree that biofouling of Fe-bearing steel will lead finally to degradation of steel materials in aqueous environments in the presence of microorganism. In order to prevent biofouling the introducing of Copper or Nickel particles in the upper surface layer of steel may solve this issue. In turn, chlorine is a strong enough oxidizing agent for copper. Therefore, the release of Cu2+ ions is intensive in seawater. One can expect that anodic oxidation and subsequent release of copper ions will deteriorate the quality (adhesion) of coatings that may result in delamination of Zn/CuO/Zn coating form the steel substrate. So, you will not observe any biocide effect even after short period of time. My suggestion is confirmed by polarization curves shown in Fig. 4 (the complete dissolution of the coating takes place). In this regard, I do not understand the motivation and design of the research. Why do you deposit Cu-bearing particles onto steel and study their corrosion behavior in the aggressive seawater if all types of hybrid coating completely dissolve?

Introduction of copper oxide particles in antifouling coatings has been earlier proposed as an alternative to more toxic agents with antifouling activity against marine microorganisms (Refs. 16-19 in the manuscript). Copper is usually harmful to microorganisms at high concentrations in water (M. Grosell et al. Physiology is pivotal for interactions between salinity and acute copper toxicity to fish and invertebrates. Aquat. Toxicol. 84 (2007) 162) and this is the reason for us to incorporate small amount of CuO particles into the hybrid coating (0.025 g/L) and to encapsulate the particles with natural polymers in order to prevent (slow down) the spontaneous release of Cu²⁺ ions during the corrosion attack as well. On the other hand, CuO particles have been found to enhance the anticorrosion ability of zinc coatings (Refs. 5 and 10 in this manuscript). This is our motivation to combine both characteristics of CuO in fabrication of a new hybrid zinc coating.  We agree that the results of electrochemical studies in a 3,5% NaCl solution are close to pure zinc coating, probably because of the low CuO particle concentration. However, the results in artificial sea water are better and in line with our expectation.

2. Also, the corrosion current (Table 1) is practically the same and varies between (1.1-2.9)^10-5 A/cm2. I suppose that the authors do not show SEM images of the corroded surface because no coating is left. It means that for the practical point of view the proposed multilayer poor-adhesive coatings are not so good.

SEM images of corroded surfaces of zinc and hybrid zinc coating (containing polymer-coated CuO nanoparticles) were presented in Ref. 10. One could see that the coatings were not dissolved during 35 days’ immersion in 5% NaCl and ASW, which confirmed the results of polarization resistance measurements. Higher polarization resistance of the coatings was also found in ASW compared to NaCl solution, although the positive anticorrosive effect of the CuO particles was better expressed in both media (CuO concentration was 0.1 g/L). 

3. The common drawback of the paper is unclear description of the electrochemical experiments. For example, in Sec. 2.5 the authors write that «Cyclic Voltammetry (CVA) studies were applied in potential interval between -1.4 V and 0 V with a scan rate of 10 mV/sec.», however no information about the solution (electrolyte) is given. Then, in Sec. 2.8 the authors described that electrochemical tests were carried out in 3.5 wt. % NaCl and artificial sea water. Later, the Fig. 3 does not contain any information about the used solution, while in the text (238–239 lines) one can find that the CV tests are realized in the starting electrolytes for electrodeposition. This information contradicts with Methodology section. In the Fig. 3 the authors should add an appropriate legend to black, red and blue curves, because It’s impossible to understand whether you study the steel with CuO, separate CuO particles or steel with pure Zn coating or something else. The sweep direction is advisable to be added.

The recommendation is taken into account and the text and figure are partially rewritten and corrected for more clarity in the places mentioned by the reviewer.

4. Moreover, in lines 242-243 the electrodeposition process of the ordinary Zn, according to the text, occurs at more negative potential value than that of hybrid coating. What figure should I look at? In Fig. 3 the anodic peak for Zn and ZnH are near close to -0.75 V, and how is the anodic dissolution associated with electrodeposition process? I don’t understand.

Тhe electrodeposition process of ordinary zinc takes place at more negative potential values compared to the hybrid coating, most likely due to the fact that the CuO particles are larger in size and cover greater space on the substrate together with the zinc ions from the solution for the hybrid coating. In the anodic part a dissolution process occurs during which the mass of the coatings (already deposited during the cathodic polarization) is dissolved. The peak of ordinary zinc is higher because the deposited mass of this coating is greater compared to the hybrid one at these conditions. In corrosion tests, however, the thickness (mass) of both types of coatings is practically the same, which is achieved by selecting of appropriate deposition conditions.

5. To my knowledge, polarization resistance could be measured via Electrochemical Impedance Spectroscopy or using Stern-Geary equation. What approach did the authors use? Please, add a description of the method for Rp evaluation in the methodology section.

The approach used by the authors is the principle of Stern-Gery equation and the application of a special device for this purpose. The text in Part 2.5. has been additionally modified.

6. Regarding the conclusion that «the hybrid zinc coatings provided corrosion protection of mild steel in model medium of 3.5% NaCl and artificial sea water solution for a prolonged period of 30 days», I would like to pay authors attention that this observation is confirmed only by Rp measurement in seawater (Fig. 5). In general, both ZnH and ZnS-type coatings behave themselves as pure Zn-coating near the corrosion potential and on the anodic branches. If the authors could show the surface morphology after 30 days of immersion, we may conclude about the practicability of the developed coating.

SEM images of corroded surfaces of zinc and hybrid zinc coating (containing polymer-coated CuO nanoparticles) were presented in Ref. 10. One could see that the coatings were not dissolved during 35 days’ immersion in 5% NaCl and ASW, which confirmed the results of polarization resistance measurements. Higher polarization resistance of the coatings was also found in ASW compared to NaCl solution, although the positive anticorrosive effect of the CuO particles was better expressed in both media (CuO concentration was 0.1 g/L). 

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Manuscript can now be accepted for publication.

Reviewer 2 Report

Despite the author's revisions, the manuscript still does not meet the quality standards required for publication in Coatings.

Minor editing of English language required

Reviewer 3 Report

Thank you for taking into account the suggestion of this reviewer. Most of the changes have been done, and the rest have been justified clearly.The revised article can be received.

Reviewer 4 Report

I have no comments

Reviewer 5 Report

The revised manuscript "Hybrid Zinc Coatings with Chitosan/Alginate encapsulated CuO-nanoparticles for Anticorrosion and Antifouling Protection of Mild Steel" looks much better than previous one. However, I have some questions left after the Author’s response. I may advise to check one more time the English grammar and outline the development of your research as well as the future perspectives in comparison with your previous results [Ref. 10]. The scientific paper should be compressed and self-sufficient. My recommendations on displaying some SEM images of the corroded surface or additional (and informative) legend to Fig. 3 were ignored. Anyway, I accept this manuscript for publication.