Preparation and Characterization of Fluoride-Incorporated Plasma Electrolytic Oxidation Coatings on the AZ31 Magnesium Alloy
Round 1
Reviewer 1 Report
- All the comments are listed in the paper.
- The 3.4. Corrosion Resistance is quite superficially done, especially 3.4.1. Electrochemical Measurements. Can you complement / enhance Electrochemical Measurements and explain these results in more detail?
- Impedance data mast be fitted by a suitable electrical equivalent circuit (EEC) model, employing the complex non-linear least squares (CNLS) fit analysis
- "This result suggested that fluorine-containing coatings significantly improved the corrosion resistance of the AZ31, and C-15 exhibited the best corrosion resistance." for this suggestion the Nyquist plot for alloy samples and corresponding values for the parameters of the EEC obtained from the best fit to the impedance data are missing.
- On the page 9, table 4, the authors give values of the corrosion current density from the Tafel polarization plots. The authors might wish to compare these estimated values with those that can be calculated from the polarization resistance values obtained from EIS data.
- Many citations are incorrect formatted.
Comments for author File: 
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Author Response
On behalf of all the contributing authors, I would like to express our sincere appreciations for your letter and reviewers’ constructive comments.Please see the attachment for details.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors are requested to study carefully the attached annotated manuscript and comply with the reviwer's suggestions when revising their contribution.
Comments for author File: Comments.pdf
Author Response
Responses to Reviewer :
Thank you very much for your advice. We are very sorry for our carelessness. All the writing mistakes have been modified in the manuscript. The following responses are the answers for the specific problems.
Materials and Methods:line 104 “ What is the difference between test (?) and grazing angles ? Did you use GIXRD? Current and voltage data? ”
Response: Thanks for your careful checks.
(1) Test angle represents the range of diffraction peaks in the coating.
(2) Grazing angle is also called glancing angle. When dealing with a beam that is nearly parallel to a surface, it is sometimes more useful to refer to the angle between the beam and the surface, rather than that between the beam and the surface normal, in other words 90° minus the angle of incidence. This small angle is called a glancing angle or grazing angle. Incidence at grazing angles is called "grazing incidence". Grazing incidence diffraction is used in X-ray spectroscopy and atom optics, where significant reflection can be achieved only at small values of the grazing angle.
(3) we used GIXRD to avoid interference of strong signals on the substrate to the film layer.
(4)Some parameters are as follows: Cu target, tube voltage 40kV, tube current 60mA.
Materials and Methods: line 143 “ The solution was changed every 2 d, and the time of corrosion was recorded.”
Response: We are very sorry for our unclear expression and we have made corrections. “ The solution was changed every 2 d, and the time of corrosion point appeared was recorded using a digital camera.”
Result: line 196 “ In addition, some microcracks were evident on the surfaces of the coatings prepared from both solutions ”.
Response: We are very sorry for our unclear expression and we have made corrections. Here, “ both solutions ” means fluorine-free and fluorine-containing solutions. “ In addition, some microcracks were evident on the surface of the coatings prepared from different fluorine content solutions” has been used in the manuscript.
Result: Figure 2. “ Sample designation shon in red are barely visible. Please change.”
Response: Thanks for your careful checks. According to your suggestion, we have been made changes.
Result: Table 3. “ How reliable are this data? Standard deviations are missing. EDS is a poor tool to determine accurately the composition! Hence, giving composition with two decimals is ridiculous. ”
Response: Thanks for your help. According to your suggestion , we have made corrections in the manuscript.
Result: line 274 “ In addition, the degradation rate gradually decreased after 7 d for the bare AZ31, which was attributed to a protective layer on the AZ31 alloy.” This is just a statistical effect without any kinetic relevance!
Thanks for your careful checks.
(1) Test angle represents the range of diffraction peaks in the coating.
(2) Grazing angle is also called glancing angle. When dealing with a beam that is nearly parallel to a surface, it is sometimes more useful to refer to the angle between the beam and the surface, rather than that between the beam and the surface normal, in other words 90° minus the angle of incidence. This small angle is called a glancing angle or grazing angle. Incidence at grazing angles is called "grazing incidence". Grazing incidence diffraction is used in X-ray spectroscopy and atom optics, where significant reflection can be achieved only at small values of the grazing angle.
(3) we used GIXRD to avoid interference of strong signals on the substrate to the film layer.
(4)Some parameters are as follows: Cu target, tube voltage 40kV, tube current 60mA.
Materials and Methods: line 143 “ The solution was changed every 2 d, and the time of corrosion was recorded.”
Response: We are very sorry for our unclear expression and we have made corrections. “ The solution was changed every 2 d, and the time of corrosion point appeared was recorded using a digital camera.”
Result: line 196 “ In addition, some microcracks were evident on the surfaces of the coatings prepared from both solutions ”.
Response: We are very sorry for our unclear expression and we have made corrections. Here, “ both solutions ” means fluorine-free and fluorine-containing solutions. “ In addition, some microcracks were evident on the surface of the coatings prepared from different fluorine content solutions” has been used in the manuscript.
Result: Figure 2. “ Sample designation shon in red are barely visible. Please change.”
Response: Thanks for your careful checks. According to your suggestion, we have been made changes.
Result: Table 3. “ How reliable are this data? Standard deviations are missing. EDS is a poor tool to determine accurately the composition! Hence, giving composition with two decimals is ridiculous. ”
Response: Thanks for your help. According to your suggestion , we have made corrections in the manuscript.
Result: line 274 “ In addition, the degradation rate gradually decreased after 7 d for the bare AZ31, which was attributed to a protective layer on the AZ31 alloy.” This is just a statistical effect without any kinetic relevance!
Response: We are very sorry for our unclear expression and we have made corrections. We read some articles [1-3] that reported the AZ31 alloy had a relatively high corrosion rate at the early stage of soaking, and the corrosion rate decreased as the immersion time increased, and that the formation of the corrosion product layer would help to reduce the corrosion rate of the substrate. This conclusion coincides with our research results.
Result: line 288 “The corrosion occurred in the C-0 sample after 432 h and after 696 h for the C-5 and C-10 samples. ”
Response: We are very sorry for our unclear expression and we have made corrections. “ Figure 8 shows that the C-0 suffered localized corrosion damage after immersion for 432h, however, the C-5 and C-10 ,the corroded area appeared after immersion for 696h in SBF.”
Result: Figure 8 “ Is this figures of any deeper relevance? Omit.”
Response: Thanks for your comments, I'm very sorry, because I don't quite understand whether you mean deleting Figure 8 or one of the small pictures. The following is an explanation according to my understanding.
The long-term immersion test with simulated body fluid (SBF) was conducted to observe the corrosion behavior of AZ31 and coated samples from a macroscopic perspective, which was more useful to know the service time of AZ31 and coated samples in SBF and more conducive to guide clinical application.
Result: line 321 “As shown in Figure 11”
Response: Thanks for your help, we feel really sorry for our carelessness and we have made corrections.
Result: Figure 11 “Images show poor resolution and lack of contrast .”
Response: Thanks for your careful checks. According to your suggestion, we have been made changes.
References
Tian, P., F. Peng, D. Wang, and X. Liu. Corrosion behavior and cytocompatibility of fluoride-incorporated plasma electrolytic oxidation coating on biodegradable AZ31 alloy. Regen Biomater. 2017, 4, 1-10. Shi, P., B. Niu, S. E, Y. Chen, and Q. Li. Preparation and characterization of PLA coating and PLA/MAO composite coatings on AZ31 magnesium alloy for improvement of corrosion resistance. Surf. Coat. Technol. 2015, 262, 26-32.
Rojaee, R., M. Fathi, and K. Raeissi. Controlling the degradation rate of AZ91 magnesium alloy via sol–gel derived nanostructured hydroxyapatite coating. Mater. Sci. Eng: C 2013, 33, 3817-3825.
Result: Figure 11 “Images show poor resolution and lack of contrast .”
Response: Thanks for your careful checks. According to your suggestion, we have been made changes.
References
Tian, P., F. Peng, D. Wang, and X. Liu. Corrosion behavior and cytocompatibility of fluoride-incorporated plasma electrolytic oxidation coating on biodegradable AZ31 alloy. Regen Biomater. 2017, 4, 1-10. Shi, P., B. Niu, S. E, Y. Chen, and Q. Li. Preparation and characterization of PLA coating and PLA/MAO composite coatings on AZ31 magnesium alloy for improvement of corrosion resistance. Surf. Coat. Technol. 2015, 262, 26-32.
Rojaee, R., M. Fathi, and K. Raeissi. Controlling the degradation rate of AZ91 magnesium alloy via sol–gel derived nanostructured hydroxyapatite coating. Mater. Sci. Eng: C 2013, 33, 3817-3825.
Author Response File: Author Response.docx
Reviewer 3 Report
This work describes the PEO treatment for human body applications. The author characterized their PEO layer on Mg alloy with various techniques. Then, various tests were employed to claim their novelty of KF addition in PEO solution.
Their novelty of KF addition is already reported in many publications for Mg PEO. Thus characterizing MgF2 phase and its effects are not new. The author should highlight their novelty comparing previous works. English is not standard style, thus it is hard to read whole manuscript. I strongly recommend to proofread by native speaker. Please make the manuscript with consistent format. For example, please see line 73~79. There are too many errors in inferior letters. For example, magnesium fluoride should be expressed MgF2 not MgF2. In same manner, Icorr is wrong. Icorr is right. Why PEO is low cost process? It consumes huge electricity. What is 3C-0 and 3C-5 (line 203)? No label in Figure 2. In EDS, P was detected. However, there are no XRD peak related with P or phospate. In Figure 3, the thickness of oxide film is not uniform. However, in Table 2, the standard deviations are only less than 2 micrometer. I cannot believe the number. Why standard deviation was not used in Table 3? In line 127, EIS measurement does not includes potential scan. In Figure 6, the length of X and Y axis should be same in Nyquist Plot to see the phase angle. Generally, there are no significant discussions.
Author Response
Responses to Reviewer :
Thank you very much for your advice. We are very sorry for our carelessness. All the writing mistakes have been modified in the manuscript. The following responses are the answers for the specific problems.
Their novelty of KF addition is already reported in many publications for Mg PEO. Thus characterizing MgF2 phase and its effects are not new. The author should highlight their novelty comparing previous works.
Responses: Although many previous studies [1-3] have reported the quality of the coatings about KF addition, there are few studies on cytotoxicity of its content. In this study, plasma electrolytic oxidation was used to prepare different fluorine-containing coatings on the surface of the AZ31 magnesium alloy to enhance its corrosion resistance and cytocompatibility and to quantify the optimum fluorine content. Thus, this study provides knowledge for the application of magnesium alloys in the field of biomedicine.
English is not standard style, thus it is hard to read whole manuscript. I strongly recommend to proofread by native speaker.
Responses: Thanks for your careful checks. We feel sorry for our poor writings. However, we invited a native English speaker from USA to polish our article. Due to his help, the article had been edited extensively. And we hope the revised manuscript could be acceptable.
Please make the manuscript with consistent format. For example, please see line 73~79. There are too many errors in inferior letters. For example, magnesi`um fluoride should be expressed MgF2 not MgF2. In same manner, Icorr is wrong. Icorr is right.
Responses: Thanks for your help, we feel really sorry for our carelessness. Based on your comments, we have made corrections.
Why PEO is low cost process? It consumes huge electricity.
Responses: Thanks for your comment. According to articles [4, 5], we recognized PEO is a inexpensive method.
What is 3C-0 and 3C-5 (line 203)?
Responses: Thanks for your careful checks. We are very sorry for our unclear expressing , here, 3c-0 and 3c-5 refer to c-0 and c-5 in figure 3 respectively, and we have made corrections.
No label in Figure 2.
Responses: Thanks for your careful checks , and the sample designations are summarized in Table 1.
In EDS, P was detected. However, there are no XRD peak related with P orphospate.
Responses: Thanks for your suggestion. we read the relevant literature [1,6] and carefully analyzed the result. The X-ray diffraction (XRD) characterizes substance with crystalline phase structure. In this study, P is an amorphous phase substance, so there is no diffraction peak of P in XRD detection.
In Figure 3, the thickness of oxide film is not uniform. However, in Table 2, the s tandard deviations are only less than 2 micrometer. I cannot believe the number.
Responses: Thanks for your careful checks. We are sorry for our carelessness. A digital eddy-current thickness gauge (1100, Elcktrophysic, Cologne, Germany) was used to measure the film thickness after the plasma electrolytic oxidation treatment. However, because the number of tests points is not enough and the range of points taken is too small, the result is not quite accurate. Therefore, we expand the range and the number of tests points to modify the data, and the results are shown in table 2 of the manuscript.
Why standard deviation was not used in Table 3?
Responses: Thanks for your comments. According to your suggestion, this experiment has been done three times to ensure the accuracy of the results, and the details are shown in table 3 of the manuscript.
In line 127, EIS measurement does not includes potential scan.
Responses: Thanks for your careful checks. We feel sorry for our carelessness, and we have made changes in the manuscript.
In Figure 6, the length of X and Y axis should be same in Nyquist Plot to see the phase angle. Generally, there are no significant discussions.
Responses: Thank you very much for your advice! According to your suggestion, Figure 6 has been modified. Meanwhile, we read relevant literature[7-9] and have made supplementary explanations and modifications about this part.
Special thanks to you for your good comments!
References
Jia, Z.J., M. Li, Q. Liu, X.C. Xu, Y. Cheng, Y.F. Zheng, T.F. Xi, and S.C. Wei. Micro-arc oxidization of a novel Mg–1Ca alloy in three alkaline KF electrolytes: Corrosion resistance and cytotoxicity. Appl. Surf. Sci. 2014, 292, 1030-1039. Jiang, H.B., G. Wu, S.-B. Lee, and K.-M. Kim. Achieving controllable degradation of a biomedical magnesium alloy by anodizing in molten ammonium bifluoride. Surf. Coat. Technol. 2017, 313, 282-287. Wang, L., L. Chen, Z. Yan, H. Wang, and J. Peng. Effect of potassium fluoride on structure and corrosion resistance of plasma electrolytic oxidation films formed on AZ31 magnesium alloy. J. Alloys Compd. 2009, 480, 469-474. Rehman, Z.U. and B.H. Koo. Combined Effect of Long Processing Time and Na2SiF6 on the Properties of PEO Coatings Formed on AZ91D. J. Mater. Eng. Perform. 2016, 25, 3531-3537. Rehman, Z.U., S.H. Shin, I. Hussain, and B.H. Koo. Investigation of hybrid PEO coatings on AZ31B magnesium alloy in alkaline K2ZrF6–Na2SiO3 electrolyte solution. Protection of Metals and Physical Chemistry of Surfaces 2017, 53, 495-502. Gan, J.J., L.L. Tan, K. Yang, Z.Q. Hu, Q. Zhang, X.M. Fan, Y.D. Li, and W.R. Li. Bioactive Ca-P coating with self-sealing structure on pure magnesium. Shi, P., B. Niu, S. E, Y. Chen, and Q. Li. Preparation and characterization of PLA coating and PLA/MAO composite coatings on AZ31 magnesium alloy for improvement of corrosion resistance. Surf. Coat. Technol. 2015, 262, 26-32. Wang, L., J. Zhou, J. Liang, and J. Chen. Corrosion Mechanism of Plasma Electrolytic Oxidation Coated Magnesium Alloy with Laser Surface Melting Pretreatment. J. Electrochem. Soc. 2013, 161, C20-C24. Zuo, Y., T. Li, P. Yu, Z. Zhao, X. Chen, Y. Zhang, and F. Chen. Effect of graphene oxide additive on tribocorrosion behavior of MAO coatings prepared on Ti6Al4V alloy. Appl. Surf. Sci. 2019, 480, 26-34.
Author Response File: Author Response.docx
