Enhanced Corrosion Protection of Epoxy/ZnO-NiO Nanocomposite Coatings on Steel

Round 1

Reviewer 1 Report

In this article, the authors presented nanocomposite coatings of epoxy and ZnO-NiO particles can improve the corrosion resistance of steel. However, extensive improvements of the manuscript may require to meet the publication standard in the journal of "Coatings".

(i) The introduction part may need to describe the correlation between the ZnO-NiO nanoparticles and their applications in corrosion protection, rather than keep talking about the conjugated polymers. Is there any pioneer research about the usage of ZnO or NiO nanoparticles for the corrosion protection of steel? How's the performance? What kind of improvement can be made by using the method proposed in this paper?

(ii) The experimental section should present more details, such as the grades and companies of chemicals, the coating process of the epoxy resin, and the electrochemical process used to measure the corrosion behaviors of the coated steel.

(iii) The author should provide more mathematical comparisons of the experimental results rather than simply describing the shape of graphs. For example, they can tell the reader how they calculate the particle sizes of ZnO and NiO from the XRD spectrum. They can also calculate the impedance of the coated materials to provide a direct comparison on the anti-corrosion performance of the coatings.  

Author Response

Reviewer 1

In this article, the authors presented nanocomposite coatings of epoxy and ZnO-NiO particles can improve the corrosion resistance of steel. However, extensive improvements of the manuscript may require to meet the publication standard in the journal of "Coatings".

• The introduction part may need to describe the correlation between the ZnO-NiO nanoparticles and their applications in corrosion protection, rather than keep talking about the conjugated polymers. Is there any pioneer research about the usage of ZnO or NiO nanoparticles for the corrosion protection of steel? How's the performance? What kind of improvement can be made by using the method proposed in this paper?

We have updated the introduction part based on the reviewer’s suggestion.

• The experimental section should present more details, such as the grades and companies of chemicals, the coating process of the epoxy resin, and the electrochemical process used to measure the corrosion behaviors of the coated steel.

We have updated the experimental section based on the reviewer’s suggestion.

• The author should provide more mathematical comparisons of the experimental results rather than simply describing the shape of graphs. For example, they can tell the reader how they calculate the particle sizes of ZnO and NiO from the XRD spectrum. They can also calculate the impedance of the coated materials to provide a direct comparison on the anti-corrosion performance of the coatings. 

We have calculated the crystallite size from Debye Scherrer formula and measured the electrochemical fitting parameters from the tafel. The explanation has been updated in the modified manuscript.

Reviewer 2 Report

Corrosion resistance of steel is of significant value for its commercial application. This manuscript addresses an interesting method and its evaluation to develop corrosion resistance of mild steel. To make it more interesting and emphasize its significance to the readers, the authors are suggested to improve on the following points:

1) Introduction: It definitely needs a stronger and more careful introduction

    a) The whole section is written in a single paragraph which needs to be split into at least 2

    b) There is no connection between several arguments. Authors just jump from one to another statement

    c) A significant amount of research has been reported on epoxy, ZnO and/or NiO coatings to impart abrasion resistance to steel. The authors fail to refer to that and directly jump to their approach

2) Experimental:

   a) Line 73: What was the rationale behind heating the gels at the hot plate first and then in the oven? What was the thickness of the gel? How did the authors ensure uniform heating on a hot plate?

   b) What is the purity of the chemicals used? Where was the epoxy resin and curing agent obtained from?

   c) What was the protocol used to coat the steel?

    d) What is the term 'phr' on line 80?

   e) Line 91-99: Is that a part of intro, experimental or result section? Authors explain their rationale, result and brief method in that paragraph and it seems out of place. More significantly, they have not mentioned the details of the test, instrument used and protocol followed

   f) Details of EDAX, XRD, potentiodynamic, EIS and SEM studies are not mentioned

3) Results:

  a) Fig 1: The authors are advised to include diffractograms of pure ZnO and NiO for clarity

  b) Line 115: The standard term used to describe SEM images is 'micrographs' not 'photographs'

 4) There are various formatting and grammar mistakes throughout the manuscript which need to be corrected

  5) Figure 4 b: It would be helpful to include the steel -only plot for a clear comparison

 

Author Response

Reviewer 2

Corrosion resistance of steel is of significant value for its commercial application. This manuscript addresses an interesting method and its evaluation to develop corrosion resistance of mild steel. To make it more interesting and emphasize its significance to the readers, the authors are suggested to improve on the following points:

1) Introduction: It definitely needs a stronger and more careful introduction

1. a) The whole section is written in a single paragraph which needs to be split into at least 2

            We have rewritten the introduction part.

1. b) There is no connection between several arguments. Authors just jump from one to another statement

            We have rewritten the introduction part.

1. c) A significant amount of research has been reported on epoxy, ZnO and/or NiO coatings to impart abrasion resistance to steel. The authors fail to refer to that and directly jump to their approach

            We have included the reported research related to epoxy, ZnO, NiO coatings in the manuscript.  

2) Experimental:

1. a) Line 73: What was the rationale behind heating the gels at the hot plate first and then in the oven? What was the thickness of the gel? How did the authors ensure uniform heating on a hot plate?

The traditional sol-gel method involved the preparation of metal oxide nanoparticles and composites by mixing metal oxides in an aqueous or organic phase, followed by ripening, gelation, drying, and finally removing organics from the resultant product by heat treatment

The thickness of the gel is in the range of µm.

After that the mixture was continuously stirred, maintaining the temperature at 150 °C, until the mixture converted into a black paste after 4 hrs. It is obvious that, the temperature of reaction played important role in producing nanoparticles, the optimal yield of nanoparticles were achieved at 150 °C. 

1. b) What is the purity of the chemicals used? Where was the epoxy resin and curing agent obtained from?

            We have added the purity of the used chemicals. Bisphenol-A epoxy resin (LAPOX*C-51), and hardener (LAPOX AH-428) were purchased from Atul Limited, India for coating purposes. Update in the manuscript accordingly.

1. c) What was the protocol used to coat the steel?

Single-layer smart coatings (SLSCs) were prepared from Epoxy and ZnO/NiO composites. Update in the manuscript accordingly.

1. d) What is the term 'phr' on line 80?

            We have rewritten the line no 80.

1. e) Line 91-99: Is that a part of intro, experimental or result section? Authors explain their rationale, result and brief method in that paragraph and it seems out of place. More significantly, they have not mentioned the details of the test, instrument used and protocol followed

            We have included the all details in the experimental section.

1. f) Details of EDAX, XRD, potentiodynamic, EIS and SEM studies are not mentioned

            We have added the characterization part in the manuscript.

3) Results:

1. a) Fig 1: The authors are advised to include diffractogram of pure ZnO and NiO for clarity

            We have included the XRD pattern of pure ZnO and NiO in the XRD section.

1. b) Line 115: The standard term used to describe SEM images is 'micrographs' not 'photographs'

            We have rewritten the line based on the reviewer’s suggestion.

 4) There are various formatting and grammar mistakes throughout the manuscript which need to be corrected

            We have corrected the grammatical mistakes throughout the manuscript.

  5) Figure 4 b: It would be helpful to include the steel -only plot for a clear comparison

            We have included the steel only plot for comparison in figure 4b.

Reviewer 3 Report

First of all, English needs to be considerably improved throughout the text (both grammar and style). Some words are misused, like "assorted well" (line 83), "lofty clarity" (line 110), "minute grains" (line 119) and many others. Sentences are not clear and sometimes it is very difficult to understand what the authors want to express.

The introduction must be improved by pointing out what is new about the coating proposed by the authors. There are already studies on epoxy/ZnO coatings. Is the method or the composition different? And why was NiO chosen to be added in their nanocomposite?

A paragraph with the description of the devices used for characterization of the samples must be mentioned.

Have the authors prepared and tested samples with different concentrations than the ones presented in this manuscript? Could other concentrations in the final nanocomposite give better results?

The SEM image must be better explained. The authors claim that the average grain size is of ~100 nm, but this is difficult to see from the image shown (at a scale bar of 5 μm). What are those large particles/pieces of at least 1 μm, in the centre of the image?

Please give the errors obtained when the chemical elements where identified by EDAX.

In Fig. 5b, the symbols used for steel are white instead of black and almost invisible. Please change the colour to black.

The conclusions should be improved. It is stated that "SEM morphological properties proved the agglomerated particles". This must be reformulated, because in this form it shows no significance.

Author Response

1) First of all, English needs to be considerably improved throughout the text (both grammar and style). Some words are misused, like "assorted well" (line 83), "lofty clarity" (line 110), "minute grains" (line 119) and many others. Sentences are not clear and sometimes it is very difficult to understand what the authors want to express.

            We have corrected the grammatical mistakes and also English improved in the manuscript.

2) The introduction must be improved by pointing out what is new about the coating proposed by the authors. There are already studies on epoxy/ZnO coatings. Is the method or the composition different? And why was NiO chosen to be added in their nanocomposite?

            We have updated the introduction part in the manuscript.

3) A paragraph with the description of the devices used for characterization of the samples must be mentioned.

            We have added the characterization part.

4) Have the authors prepared and tested samples with different concentrations than the ones presented in this manuscript? Could other concentrations in the final nanocomposite give better results?

            Yes, other concentrations of nanocomposite will give best results. In future work, we will do the other concentration for corrosion studies.

5) The SEM image must be better explained. The authors claim that the average grain size is of ~100 nm, but this is difficult to see from the image shown (at a scale bar of 5 μm). What are those large particles/pieces of at least 1 μm, in the centre of the image?

            Based on the reviewer suggestion, we have added the SEM with 1 μm magnification.

6)Please give the errors obtained when the chemical elements where identified by EDAX.

            We have included the error percentage in EDAX.

7)In Fig. 5b, the symbols used for steel are white instead of black and almost invisible. Please change the colour to black.

            We have changed the black colon in Fig. 5b.

8)The conclusions should be improved. It is stated that "SEM morphological properties proved the agglomerated particles". This must be reformulated, because in this form it shows no significance.

            We have rewritten the statement in the conclusion part.

Round 2

Reviewer 1 Report

  The authors have paid substantial effort to improve the manuscript. However, it would be better to provide a brief comparison of the corrosion performance between the epoxy/ZnO-NiO nanocomposite and the other materials previously reported, and highlights the significance of the new nanocomposite.

Author Response

The authors have paid substantial effort to improve the manuscript. However, it would be better to provide a brief comparison of the corrosion performance between the epoxy/ZnO-NiO nanocomposite and the other materials previously reported, and highlights the significance of the new nanocomposite.

We have added the comparison table for corrosion parameters of different nanomaterials coatings (previously reported) in a tabular form and highlighted the present nanocomposite significance in the revised manuscript.

Reviewer 2 Report

The authors have incorporated some of the suggested changes in the manuscript which have helped to improve the quality of the manuscript. However, they missed to follow some of the suggestions, e.g.,

1) It was expected that the response to my question related to heating of the sol at hot plate followed by the oven (experimental section) would be included in the manuscript to make it clearer to the reader.

2) The last paragraph of the introduction should be strong enough to convey the rationale for conducting the reported research.

3) In the Characterization section, the authors have still not included details of EDAX analysis while they mentioned in their response that they have included that. Even in the section related to SEM and XRD analysis, they failed to give related details of sample prep and parameters involved.

 

Author Response

The authors have incorporated some of the suggested changes in the manuscript which have helped to improve the quality of the manuscript. However, they missed to follow some of the suggestions, e.g.,

• It was expected that the response to my question related to heating of the sol at hot plate followed by the oven (experimental section) would be included in the manuscript to make it clearer to the reader.

We have added clear statement regarding the composite synthesis in the revised manuscript.

• The last paragraph of the introduction should be strong enough to convey the rationale for conducting the reported research.

We have added more points in the last paragraph of introduction section.

• In the Characterization section, the authors have still not included details of EDAX analysis while they mentioned in their response that they have included that. Even in the section related to SEM and XRD analysis, they failed to give related details of sample prep and parameters involved.

We have improved the XRD and SEM analysis section in the revised manuscript.

Reviewer 3 Report

The authors have not significantly improved their manuscript and failed in addressing most of my comments in a proper way.

• English was not revised (except for a few words).
• The introduction was not improved by pointing out what is new about the coating proposed by the authors.
• The SEM image was not explained and the reader will not know what exactly is in that image, when a very wide range of particle dimensions is present.
• The errors obtained for the chemical elements identified by EDAX are not correctly presented and I have I serious doubt that they are indeed so small (especially for O).
• The conclusions were not improved.
• Their answer that “other concentrations of nanocomposite will give best results”, but “in future, we will do the other concentration” denotes an incomplete study that is not reliable and should not be published.

Author Response

The authors have not significantly improved their manuscript and failed in addressing most of my comments in a proper way.

• English was not revised (except for a few words).

We have improved the English in the revised manuscript.

• The introduction was not improved by pointing out what is new about the coating proposed by the authors.

We have added the more points about polymeric (epoxy resin) coating in the introduction part.

• The SEM image was not explained, and the reader will not know what exactly is in that image, when a very wide range of particle dimensions is present.

We have added explanation of SEM images in the revised manuscript.

• The errors obtained for the chemical elements identified by EDAX are not correctly presented and I have I serious doubt that they are indeed so small (especially for O).

In EDAX percentage values in terms of wt% are Zn (8.96%), Ni (10.53%) and O (80.51%) respectively. EDAX percentage values in terms of at% are Zn (23.51% ± 0.05%), Ni (24.80% ± 0. 08%), and O (51.69% ± 0.02%).

• The conclusions were not improved.

We have improved the conclusion part in the revised manuscript.

• Their answer that “other concentrations of nanocomposite will give best results”, but “in future, we will do the other concentration” denotes an incomplete study that is not reliable and should not be published.

We were assumed better results for higher concentrations and expected good results but unfortunately after the experiments at higher concentration the filler not able mixed well and started coagulating and forming clusters. Filler-filler interaction is playing a major role to forming these clusters. Among the tested composite coatings, EP/1.8 ZnO-NiO nanocomposite coating exhibit superior anticorrosive properties due to the surface modification of ZnO-NiO composite to speed up the possible chemical interactions between composite and epoxy matrix.

Round 3

Reviewer 3 Report

The revised manuscript was improved and all comments and suggestions have been taken into consideration.

 

Author Response

Editor comments

The authors have revised their manuscript several times and they showed that they tried to address the comments of the reviewers. However, some more improvements of the manuscript are necessary.

The authors should read their manuscript carefully: some sentences should be improved and references should be cited appropriately. For example, in Lines 49-51: “For instance, a research group has used Nano alumina Encapsulated epoxy coated on mild steel which was confirmed by EIS and scanning electrochemical microscopy (SECM) with a 3.5% NaCl solution.” Which research group? – Please provide an appropriate reference. Why do you use
capital letters for “Nano” and “Encapsulated”?

We have added the reference for this statement “a research group has used nano alumina encapsulated epoxy coated on mild steel which was confirmed by EIS and scanning electrochemical microscopy (SECM) with a 3.5% NaCl solution”. we have modified the english mistakes accordingly.

We have changed as “nano-alumina encapsulated” in the revised manuscript.

As referee 2 suggests: “The last paragraph of the introduction should be strong enough to convey the rationale for conducting the reported research”. Indeed, the authors revised the corresponding paragraph – but still the novelty of the paper is not clear.

We have highlighted and improved the discussion on the novelty of the work in the revised manuscript.

Elemental analysis, carried out by SEM-EDX, is described in the Results and Discussion and in the Abstract and therefore it is considered as a major result: Zn (8.96 wt%), 15 Ni (10.53 wt%) and O (80.51 wt%). It seems that this result is based on a single measurement. Several measurements should be carried out (in different areas) and RSD values should be reported.

We have redone the experiments and added the RSD values for EDAX results in the revised manuscript. EDAX: Zn (8.96±0.11 wt %), Ni (10.53±0.19 wt %) and O (80.51±3.12 wt %).