Obtaining and Corrosion Performance of Composite Zinc Coatings with Incorporated Carbon Spheres

Round 1

Reviewer 1 Report

The revised manuscript of N. Boshkov and coworkers is written fairly well, comprising the experimental material with interpretation. The references are close enough and are presented in the appropriate format for Coatings journal. The entire manuscript respects the journal's requirements.

However, there are some aspects that must be clarified by the authors, especially regarding the novelty of this study. This needs to be clarified taking into account that:

• the method used for the synthesis of carbon sphere is not new, but taken from the literature, from the reference [22];
• the electrodeposition method used for the coating of carbon spheres with zinc was also taken from the literature, from reference [2];
• the amphiphilic copolymer Pluronic F127 was also tested before by other authors for the modification of carbon nanotubes, graphene oxide and carbon black nanoparticles, respectively (see references [14], [15] and [19]).

What are the applications envisaged by the authors for the carbon nanospheres / polymer / zinc composite material obtained in the study?

Authors are asked to remove the abbreviations from the Abstract section of the manuscript.

Author Response

The revised manuscript of N. Boshkov and coworkers is written fairly well, comprising the experimental material with interpretation. The references are close enough and are presented in the appropriate format for Coatings journal. The entire manuscript respects the journal's requirements.

However, there are some aspects that must be clarified by the authors, especially regarding the novelty of this study. This needs to be clarified taking into account that:

• the method used for the synthesis of carbon sphere is not new, but taken from the literature, from the reference [22];
• the electrodeposition method used for the coating of carbon spheres with zinc was also taken from the literature, from reference [2];
• the amphiphilic copolymer Pluronic F127 was also tested before by other authors for the modification of carbon nanotubes, graphene oxide and carbon black nanoparticles, respectively (see references [14], [15] and [19]).

The novelty of our work consists in the design and fabrication of a new composite zinc coating with incorporated carbon spheres for improvement of the protective properties of the composite coating as compared to the bare zinc one. For this purpose, we used known objects and techniques for preparation and deposition of the main components of the composite coating, adapted to the needed conditions (pH, Pluronic F127- and carbon particles concentrations, preparation of carbon sphere particles). This is described in the Introduction and Experimental section of the work (Refs 22, 2, 14, 15, 19) as the reviewer correctly noted.

What are the applications envisaged by the authors for the carbon nanospheres / polymer / zinc composite material obtained in the study?

Generally, the incorporation of the carbon spheres increases the corrosion resistance and protective ability of the zinc-based coating. In that sense, the newly developed composite coating could be used to replace the ordinary zinc coating in some branches of the industry, in household, electronics etc.

Authors are asked to remove the abbreviations from the Abstract section of the manuscript.

The recommendation of the reviewer is taken into consideration. The abbreviations are removed from the Abstract.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors,

  Thanks for the chance to read and appreciate your work. This paper is interesting and in my opinion almost ready for publication. There are a few minor points that I ask you to address:

• English: I think the language is fairly good but please ask a fluent English speaker to correct the many small syntax mistake;
• The average size of the carbon spheres was measured by SEM. This is totally acceptable in this case, but you need to specify how many spheres were measured (alternatively: on how many SEM images at which magnification);
• I could not find the composition of the “low carbon steel”. There are more than 10,000 different steels that fit in this category and they have big differences in their chemical composition so please add the designation;
• How was the thickness of the zinc layer calculated?
• Figure 2: please add the data dispersion for each point;
• Figure 3: the image is clear but the small inset is hard to read;
• Figure 5: the claim about the “composite coating lasting longer” is a little stretched. The behavior is pretty similar. There is also a breakdown potential at about -0.95 V that should be discussed, it might be the electrolyte reaching steel;
• Can you please add the XRD of the standard zinc treatment too?

Author Response

Dear authors,

  Thanks for the chance to read and appreciate your work. This paper is interesting and in my opinion almost ready for publication. There are a few minor points that I ask you to address:

• English: I think the language is fairly good but please ask a fluent English speaker to correct the many small syntax mistake;

The recommendation of the reviewer is taken into consideration. Some adjustments in the text have been made accordingly.

• The average size of the carbon spheres was measured by SEM. This is totally acceptable in this case, but you need to specify how many spheres were measured (alternatively: on how many SEM images at which magnification);

During the SEM investigations the average size of the carbon spheres is measured from 10 individual samples at equal magnification.

• I could not find the composition of the “low carbon steel”. There are more than 10,000 different steels that fit in this category and they have big differences in their chemical composition so please add the designation;

The recommendation of the reviewer is taken into consideration. The composition of the steel is added in Part 2.4. and marked.

• How was the thickness of the zinc layer calculated?

The thickness of the zinc coating is calculated by using of a special formula as well as weight method – change of the sample mass before and after electrodeposition.

• Figure 2: please add the data dispersion for each point;

The recommendation of the reviewer is taken into consideration and the dispersion of the data is added in Fig. 2.

• Figure 3: the image is clear but the small inset is hard to read;

It is difficult to present clearer image for the carbon particles since most of them are covered by zinc coating. The reason for giving the small inset is only to demonstrate that the size of the incorporated particles is close to that of the initial carbon spheres. Nevertheless, we tried to improve the quality of the figure.

• Figure 5: the claim about the “composite coating lasting longer” is a little stretched. The behavior is pretty similar. There is also a breakdown potential at about -0.95 V that should be discussed, it might be the electrolyte reaching steel;

We agree with the reviewer that this point is debatable. However, it is obvious that there is some delay of the anodic rate of the composite zinc coating compared to the ordinary one in the potential zone between -1V up to -0.95V. In our opinion, one possible reason could be the appearing of a barrier effect due to the physical presence of the more carbon spheres on the surface as a result of the dissolution of the surrounding zinc. In all cases this phenomenon could be an object of our future investigations.

• Can you please add the XRD of the standard zinc treatment too?

The recommendation of the reviewer is taken into consideration. Figure 8 is partially changed and the XRD of the standard zinc treatment is added to it.

Author Response File: Author Response.pdf