Microstructure and Properties in Simulated Seawater of Copper-Doped Micro-arc Coatings on TC4 Alloy

Round 1

Reviewer 1 Report

 

In the paper, PEO coatings were deposited on Ti substrate from electrolyte with various concentrations of copper (II) sulphate. Authors aimed improvement of the coating characteristics, however, corrosion resistance was decreased and inhibition of bacteria proliferation was found to be about 50%, which is rather low (usually it is at least 95 or 99%). Authors also erroneously assigned some changes in the coating properties and morphology to presence of Cu, but they did not exclude effect of sulphate anion, which could be done by blank experiment with e.g. sodium sulphate.

 

1.     Experimental. Concentrations are missing for electrolyte composition. Authors must provide this information for publication.

2.     Line 73. “... test temperature...” – what is that?

3.     Fig.3. XPS says that coating contains both Cu(I) and Cu(II) species. However, only Cu(II) sulphate was loaded into electrolyte solution. Authors used anodic pulsed regime, therefore mechanism of reduction of Cu(I) to Cu(II) should be discussed. What did serve as reducing agent?

4.     Line 158 “flattened and smoother”, Line 161 “filled the coating micropores” – those statements require cross sectional analysis of the wear scar and general coating morphology, which were not shown in the paper. Irrelevant discussion.

5.     Fig.5. (a-f) – were not assigned to concentrations.

6.     Line 179. “as shown in Fig. 6. MAO prepared with different CuSO4 concentrations had negative corrosion potentials compared with” – Fig.6 does not show any potentials.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The paper ”Microstructure and properties in simulated seawater of copper-doped micro arc coatings on TC4 alloy” can be published in Coatings Journal after some minor corrections:

- the introduction needs updates regarding specific research with values of mechanical and corrosion resistance.

- at materials and methods extra information regarding SEM parameters are needed

- add extra explanation of the degradation rate of these coatings.

In rest is ok.

Author Response

The specific response comments are in the attachment, please check.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I am not satisfied with authors replies #1 and #4.

1. About the role of sulphate. It is necessary to show blank experiment with sodium sulphate.

2. Chemical "equations" are completely wrong.

(1) if Cu has charge 2+ the n must be strongly equal to n=2.

(2) if n = 2, Cu(OH)2 cannot be dehydrated to Cu2O, but only to CuO. Formation of Cu2O requires change of charged state from Cu(II) to Cu(I). The copper must receive 1 electron per ion. What is the source of that electron?

This discussion must be added to the text.

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf