Effect of the Fluoride Species and Content of the PEO Electrolyte on the Corrosion Properties of the Layers Obtained on AZ31 for Biomedical Purposes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript has great innovative significance in investigating effect of the fluoride species and content of the PEO electrolyte on the corrosion behavior of the coatings on AZ31 in biomedical area. The work can arouse wide interests of researchers in understanding the technique for preparation of corrosion resistant layers on AZ31. The manuscript is interesting. In my frank opinion, the manuscript should be deserved for its final publication in such high-level Journal. However, the main comments to be solved are as follows:

1. In Section 2, do the addition of KOH and Na2SiO3 together with pH of solution influence the resultant layer? Why choose these parameters?
2. If possible, please provide EIS in Section “2. Electrochemical behaviour”. Electrochemical measurement of AZ31 should also be included to compare with that of various layers and corrosion protection efficiency of these layers can be calculated according to the reference “H.J. Yang, Y.M. Dong, X.W. Li, Y.M. Gao, W.P. He, Y.H. Liu, X.L. Mu, Y.Z. Zhao, Anti-corrosion superhydrophobic micro-TiB2/nano-SiO2 based coating with “multi-scale hard particles-embedding-soft membrane” structure fabricated by spray deposition, J. Ind. Eng. Chem. 144 (2025) 496-511.”
3. Corrosion mechanism of these layers can be fully analyzed and described with a diagram.
4. Please line Figures2, 5 and 13 with axes at all sides.
5. Corrosion rate of these layers should be calculated according to Figure 13.
6. Please provide SEM images in Figure 14 with lower magnification and analyze the corrosion mode and type.

Comments on the Quality of English Language

English Language should be further improved.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article is devoted to the study of magnesium alloy coatings corrosion resistance and morphology. The coatings were characterized using various modern physical methods: SEM-EDS, XRD, and electrochemical impedance spectroscopy.

The studied coatings claim to be potential implants for bone surgery. Unfortunatelly, I didn't notice any in vivo experiments in the article. I wish authors to proceed to the next level and investigete the biological compatibility of materials in their future works.

The reviewed article is well written and can be published after few minor additions.

XRD method describtion lacks specifications. What device and settings have the authors used?

XRD patterns are too perfect. What was the exposition time per step?

Have the authors smoothed the obtained diffraction data? Was the background substracted?

All these details need to be added to the experimental part.

Please, describe the meaning of black lines at figure 5!

 

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Authors have examined the influence of different fluoride salts on the PEO coating morphology and corrosion resistance on AZ91 magnesium alloy. Paper is well written and proposed thesis about corrosion of magnesium coated with PEO protective layers are well explained by the obtained results.
Introduction
The introduction is well written, with occasional editorial mistakes (i.e. big letter “A” after the colon in line 28), which can be improved curing the editing
Some clarification is however needed:
1.
In line 29 authors claim, that screws used to secure bone implant can weaken the bone, but there is no reason given for this influence. Short explanation of the weakening mechanism should be added.
2.
In line 32 authors claim superiority of metallic implants instead of ceramic or polymeric ones, but its superiority is not clear in the light of aim to restore the bone with only one surgery, which is the context given by the first paragraph. Text should be rewritten to avoid confusion of less experienced readers.
Methodes:
Authors have well described the experiments, making it easy for other scientists who would like to repeat their experiments. However, some details are lacking:
1.
Authors have used Image-J software for average pore size characterization, but the programme version is missing + it require propper citing (https://imagej.net/contribute/citing and thus https://doi.org/10.1038/nmeth.2089)
2.
What apparatus was used for XRD characterization?
3.
What was the KCl concentration for the reference electrode? It has a strong influence on the reported potential
4.
Why did the authors decided to make the IES experiment to 100 mHz instead of more commonly used range from 105 to 0.01 mHz, which gives more info about the mechanism of corrosion reaction?
5.
Why wasn’t the OCP potential measured during the entire 2h of immersion, but instead for only 15 minutes?
Results and discussion
Authors have well shown obtained results with both text and graphics, however some further improvement is needed for following parts:
1.
Scale on the fig. 1 is hard to read
2.
Why are authors using the term “burnt surface” to explain the less porous surface obtained in LiF electrolyte? Some citation confirming this thesis is needed
3.
Table 2 – if the authors are showing the average values, they should also show the standard deviation from this average value
4.
Table 2; some mistake during the bale formatting occurred, it looks liek the WF (%) column should have the same editing style as the ret of “pore density” columns, and not like the “average pore size” columns
5.
Paragraph describing the different porosity (lines 151-158) needs rewriting due to the high amount of figure references and given values between the description (the text is not flowing and it’s hard to follow)
6.
Figure 2 is of low quality and thus hard to read, it should be improved
7.
Fig. 3 needs more readable scale
8.
More attention should be given to the fact, that for PEO coatings obtained during 30 min process in LiF electrolyte have had the lowest fluoride content in its outside layer, which is important from the biomedical application point of view.
9.
The authors should also discuss the role of sodium, since it is known to strongly influence the sparks intensity during the PEO process, and thus layer morphology and corrosion resistance
10.
Table 6 should be better formatted to make it more readable, i.e. if one of the values are given exponential notation all of them should be reported the same way, preferably with the same exponent, to make it easier to compare for the readers.
11.
Authors are claiming, that for the 4 minutes PEO process the inner layer resistance is higher for the fluoride containing samples due to the MgF2 formation, but its presence wasn’t proven with XRD studies even for 30 minutes samples. Such a claim should be supported by other experiment results or if that is impossible by proper citation.
12.
Why are authors claiming that 24h o immersion are guaranteeing easier access of corrosive species to the barrier layer? Such relation should be explained more clearly
13.
The EIS spectra for bare metal should also be shown for 2h of immersion
14.
Tab 7 – formatting issue the same as for tab 6
15.
Description of EIS in one medium should be written together for both PEO times, to make this paper part less chaotic
16.
Lack of (a) and (b) marks for fig.13 and 15
17.
Line 392; why is hydrogen molecule called “dihydrogen”?
18.
The text describing the figures 14 and 15 should be below graph 13
19.
Reported results should be also discussed in comparison to other papers about fluoride containing Peo coatings on magnesium reported in literature.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been carefully revised and can be accepted.