Influence of NaAlO2 Concentration on the Characteristics of Micro-Arc Oxidation Coating Fabricated on a ZK60 Magnesium Alloy
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors The manuscript investigates the effect of NaAlO2 concentration on the mechanical and corrosion properties of a Micro-Arc Oxidation (MAO) coating. Please address the following major revisions: 1. Lines 14 and 15: The sentence in these lines is redundant and should be removed. 2. Lines 35, 54, 58, 91, 99, 108, 359, etc.: There is a missing space. Please check the entire text for editing and proofreading.3. Line 150: SiC should be corrected.
4. The names of the companies producing the raw materials should be mentioned in the Materials and Methods section.
5. The test conditions for the impedance analysis, including the device used, frequency range, and scan rate, should be fully described at the end of the Materials and Methods section.
6. Please explain how the conductivity of the solution can have a desirable or undesirable effect on the final coating properties.
7. There are extra spaces in Table 4.
8. Please explain the obtained results from Figure 3 in more detail. All images should be fully explained.
9. Please recheck lines 507 and 508.
10. Line 557: Celsius degree?
11. Please report the reference card numbers for the XRD results to verify the matching accuracy.
12. Why is the Peak Sum of the deconvoluted peaks not consistent with the experimental raw peaks in the XPS spectra? The deconvolution process was not properly performed for these spectra.
13. EDS analysis is a semi-quantitative test and the reported percentages in Table 9 have a high error. Why were the element percentages not extracted from XPS analysis?
14. The impedance test results have several issues. Firstly, the frequency range and scan rate are not the same for different samples. Secondly, there is an inductive loop at low frequencies in the Bode plots, but the loops have been removed from the Nyquist plots. Thirdly, fitting parameters should be plotted on experimental data to evaluate fitting accuracy. Fourthly, all electrochemical parameters should be reported in Table 10. Finally, according to the Bode plots, sample 6 g/L has one of the lowest solution resistances among all samples, but according to Table 10, it has the highest solution resistance. Therefore, all reported results in Table 10 are unreliable. So, the EIS section needs to be rewritten.
15. What is the mechanism behind the improvement in antibacterial properties and contact angle reduction at 6 g/L NaAlO2 concentration? Please provide an explanation. Comments on the Quality of English Language
Minor editing of English language required
Author Response
Response to Reviewer 1 Comments
The manuscript investigates the effect of NaAlO2 concentration on the mechanical and corrosion properties of a Micro-Arc Oxidation (MAO) coating. Please address the following major revisions:
Point1. Lines 14 and 15: The sentence in these lines is redundant and should be removed.
Response: thank you for your review, this mistake is corrected in the revised manuscript.
Point2. Lines 35, 54, 58, 91, 99, 108, 359, etc.: There is a missing space. Please check the entire text for editing and proofreading.
Response: The errors are corrected, and other parts of manuscript are rechecked.
Point 3. Line 150: SiC should be corrected.
Response: This error is corrected in the revised manuscript.
Point 4. The names of the companies producing the raw materials should be mentioned in the Materials and Methods section.
Response: All medicines and ingredients used in this paper are presented with manufacturers’ names and purity in Table 4.
Point 5. The test conditions for the impedance analysis, including the device used, frequency range, and scan rate, should be fully described at the end of the Materials and Methods section.
Response: The missing description of devices, parameters, conditions, and procedures are added in the revised manuscript., at lines of 275-285.
Point 6. Please explain how the conductivity of the solution can have a desirable or undesirable effect on the final coating properties.
Response: The conductivity of the electrolyte solution affects evidently the current during constant-voltage stage, the first 5 mins of MAO preparation. With a much more significant current, the thickness of MAO coating increases rapidly during this period. This would result in a higher resistance during the later constant-current stage, which lasts 10 mins. A higher voltage in this period with violent arc discharging phenomena causes poorer superficial properties of coating.
Point7. There are extra spaces in Table 4.
Response: This error is corrected in the revised manuscript.
Point 8. Please explain the obtained results from Figure 3 in more detail. All images should be fully explained.
Response: A more detailed explanation of macro morphology corresponds to Figure 3 is added in the revised manuscript at lines of 367-372.
Point 9. Please recheck lines 507 and 508.
Response: The sentence is corrected in the revised manuscript.
Point 10. Line 557: Celsius degree?
Response：This error is corrected in the revised manuscript.
Point 11. Please report the reference card numbers for the XRD results to verify the matching accuracy.
Response: I’m truly sorry that I cannot provide the numbers, because the XRD patterns were realized years ago by my graduated senior. I can re-conduct the XRD analysis in next week to ameliorate this manuscript, my apologies.
Point12. Why is the Peak Sum of the deconvoluted peaks not consistent with the experimental raw peaks in the XPS spectra? The deconvolution process was not properly performed for these spectra.
Response: The XPS analyses are re-conducted, and new results are presented in Figure 13, with little shift of peaks.
Point 13. EDS analysis is a semi-quantitative test and the reported percentages in Table 9 have a high error. Why were the element percentages not extracted from XPS analysis?
Response: the XPS sample, which is not larger than 5×5×3 mm, can only represent a small portion of the entire sample. Due to the size of the MAO sample is 15×15×5 mm. the XPS sample is cut from the flank of it. Thus, the XPS elements analysis may have significant error due to the uneven distribution and uneven microstructure of coating. However, the EDS is obtained from the whole top or under surface (the bigger surface). Thus, the EDS results is considered.
Point 14. The impedance test results have several issues. Firstly, the frequency range and scan rate are not the same for different samples. Secondly, there is an inductive loop at low frequencies in the Bode plots, but the loops have been removed from the Nyquist plots. Thirdly, fitting parameters should be plotted on experimental data to evaluate fitting accuracy. Fourthly, all electrochemical parameters should be reported in Table 10. Finally, according to the Bode plots, sample 6 g/L has one of the the lowest solution resistances among all samples, but according to Table 10, it has the highest solution resistance. Therefore, all reported results in Table 10 are unreliable. So, the EIS section needs to be rewritten.
Response: The impedance test is also re-conducted to acquire more reliable results; all values are presented in the revised manuscript. And the explanation in this section is also adjusted.
Point 15. What is the mechanism behind the improvement in antibacterial properties and contact angle reduction at 6 g/L NaAlO2 concentration? Please provide an explanation.
Response: For most studies which contains antibacterial activity of MAO coating, the coating concerned often possesses antibacterial elements such as Ag, Cu, and Ti. In this paper, these elements are not contained in the coating. The antibacterial ability relies mostly on the elevation of PH value in the solution during the tests. Yet, this cannot fully explain the phenomenon, it requires more delicate and advanced cell biology experiments, which are for now unable to perform in the institute. it is planned to cooperate with hospitals to perform cytotoxicity test etc. to acquire more complete and detailed results on the mechnism of antibacterial ability.
And I'm TRULY SORRY that I mistakenly upload a wrong edition of manuscript in the position of reply cover letter, PLAESE IGNORE IT! Thank you for your wisedom and revision!
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript focuses on a ZK60 magnesium alloy and a treatment (micro-arc oxidation coatings) to improve the properties of this alloy for biomedical applications. Since a potential biomaterial should have optimal properties such as corrosion resistance, biocompatibility, mechanical elasticity, hardness..., this is not an easy task in practise. Therefore, the investigation of materials that could be considered as biomaterials is a constant challenge for scientists.
Although the manuscript has potential, the main drawback is the lack of results for the bare Mg alloy. In order to qualitatively and quantitatively evaluate the influence of the coatings on the properties of the alloy, the behaviour of the alloy must be investigated. The coated surface of the Mg alloy was characterised in detail using various techniques, but the surface of the bare alloy was not investigated.
A list of specific comments can be found below.
- Section 2, line 150: Please correct: Sic (SiC) abrasive paper
- lines 151-152: Please explain. Why were the alloy sheets immersed in ethanol? For how long?
- line 177: Please explain and add details. Ethanol dipping step for oxidative treatment?
- Table 2: Electrical parameters of the MAO preparation. Did you test any other electrical parameters of the coating preparation?
- lines 240-247: Water contact angle measurements. Firstly, there is a missing value for the water contact angle recorded for the bare Mg alloy. The first sentence is not entirely correct. Wetting properties can be an indirect indication of biocompatibility and are correlated with anti-corrosion properties. These properties are a direct indication of the successful formation of the analysed coatings. Volume of the drop of water used, temperature at which the measurements were taken?
- lines 255-256: "In the human body, the equilibrium electrode potential for Mg is -2.37 V." Potential value according to which reference electrode? Please provide a suitable reference for this data.
- corrosion resistance - general remark: A coating provides protection for the underlying Mg alloy. It would therefore be more correct to say: corrosion resistance of the coated Mg alloy.
- lines 260-263: "Preparatory steps include cutting the Mg alloy substrate into 15 mm × 15 mm × 5 mm specimens before coating application. These samples undergo meticulous degreasing and cleaning." Why was the same treatment of the electrodes not used as described in section 2, lines 148-152?
- Hank's solution, Table 3: Please give the reference for the composition of the solution.
- Impedance measurements (EIS), lines 275-277: The electrochemical cell and the electrodes (reference and counter electrode) used for the impedance measurements must be described. Also the experimental conditions (frequency range, ac voltage amplitude, stabilisation period or pre-treatment, if any).
- Bode and Nyquist diagrams are ways of visualising measured raw data. So if raw data is fitted, it is also displayed together with the raw data.
- The data of the electrical equivalent circuit (EEC), which can be seen in Figure 16, is missing. Which software, which model was used?
- lines 551-553: „...with Mg2SiO4 representing the high-temperature phase found in the Earth's mantle at depths ranging from 350 to 1,000 km [59]." Please explain why this information is so important for the investigation.- lines 557: „...of the secondary peak at 52 °C(?) for MgSiO4." Please correct.
- XRD results. Figure 12 and its labelling are unclear. What coating is shown?
- Figure 12, blue line, What do the 3 peaks between 20 and 25° (not visible in the red line) represent?
It would be useful to show XRD patterns for all coatings analysed, for coatings without NaAlO2 and for the bare Mg alloy. Then a complete phase analysis can be performed.
- XPS deconvolution spectra are suspect. What are the most intense peaks in the entire spectrum? The whole spectrum is complex. Please explain that.
-lines 593-597: Please add and cite appropriate references related to the Ca/P ratio in human bone and other osseoconductive coatings such as hydroxyapatite.
- section 3.5, Corrosion data: Corrosion data for the bare Mg alloy measured under the same conditions as the coated Mg alloy are missing.
- Figure 15 caption. The title should be more detailed. This applies to all figure captions in the manuscript!
- lines 610-625: In order to evaluate the protective effect of the prepared coatings during the immersion period, a corrosion rate of the bare alloy examined during the same period is missing.
- Perhaps the lowest corrosion rate of the coating 6 g/L is the same or very similar to that of the bare coating? Is it possible that coatings desorb/detach the surface of the alloy after 20 days of immersion?
- Results of the electrochemical impedance (EIS). Most likely, these measurements were also carried out to assess the corrosion rate (resistance) of the samples analysed, but their explanation is not entirely correct. The same remark as for the determination of the corrosion rate: In order to evaluate the protective effect of the prepared coatings during the immersion period, an EIS measurement of the bare alloy during the same period is missing.
Firstly, the EIS data can be shown in the form of Bode and Nyquist diagrams. The Nyquist diagram shows Zimag versus Zreal, while the Bode diagram shows IZI versus log f and phase angle (q) versus log f. The labelling in Figure 16 is therefore not entirely correct. As can be seen from Figure 16, the EIS data was adjusted according to the electrical equivalent circuit (EEC). Then Bode and Nyquist plots should represent the raw data and the modelled data together. Figure 16b is not a Bode diagram. Figure 16b and c together represent the Bode diagram.
The phase angle values are most likely negative and it seems that Figure 16b shows the phase angle values and Figure 16c shows the IZI values. Please check this carefully. All data should be measured (displayed) in the same frequency range! The experimental conditions and the fitting model of the EIS measurements are missing in section 2.
The response of the EIS data is complex for all coatings and contains at least two time constants. The explanation of the elements in the EEC needs to be reconsidered and reviewed. Why are the values of other elements (capacitance) not listed in Table 10? The capacitance is directly related to the coating thickness, so these results can be correlated with the results of other techniques used.
To interpret the corrosion from EIS measurements, a polarisation resistance (Rp) can be determined, which is a direct measure of the corrosion rate. The values of the polarisation resistance can therefore be directly correlated with the corrosion rate (Fig. 15).
Please check the EIS data carefully and correct it. Then a correlation of the results obtained with different techniques can be made.
- Water contact angle measurements: The coating produced with 6 g/L NaAlO2 showed the best corrosion results and this coating also has the lowest water contact angle. The statement that hidrophilicity has a positive influence on osseoconductivity is correct, but it is known that hidrophilicity has a negative influence on corrosion protection. The value of approx. 90° obtained for the coating with 12 g/L NaAlO2 indicates hidrophobicity, which has a positive effect on corrosion. Please explain.
- Conclusion. It would be advantageous to better correlate the results after the necessary correction.
Author Response
Response to Reviewer 2 Comments
Point1: Section 2, line 150: Please correct: Sic (SiC) abrasive paper.
Response: Thank you very much for your revision. This issue has been corrected in the revised manuscript.
Point 2: lines 151-152: Please explain. Why were the alloy sheets immersed in ethanol? For how long?
Response: I’m very sorry that I didn’t notice this problem of writing redundancy. My apologies, I have now corrected it in the revised manuscript.
-Point 3: line 177: Please explain and add details. Ethanol dipping step for oxidative treatment?
Response: The samples are soaked in the ethanol in a beaker, which is placed in the sink of Ultrasonic cleaner with water inside. The sample is cleansed by ultrasonic wave for 45 seconds at least.
-Point 4: Table 2: Electrical parameters of the MAO preparation. Did you test any other electrical parameters of the coating preparation?
Response: The pioneers of our group have studied the optimization of electrical parameters of MAO preparation for several years. The parameters concerned in this paper come from their optimized results.
-Pont 5: lines 240-247: Water contact angle measurements. Firstly, there is a missing value for the water contact angle recorded for the bare Mg alloy. The first sentence is not entirely correct. Wetting properties can be an indirect indication of biocompatibility and are correlated with anti-corrosion properties. These properties are a direct indication of the successful formation of the analyzed coatings. Volume of the drop of water used, temperature at which the measurements were taken?
Response: The device for measuring water contact angle is temporarily unavailable, I plan to measure it later. The writing is reconsidered and ameliorated in the manuscript and the volume of water drop is 0.4 μL and the measuring temperature is 20 ℃.
-Point 6: lines 255-256: "In the human body, the equilibrium electrode potential for Mg is -2.37 V." Potential value according to which reference electrode? Please provide a suitable reference for this data.- corrosion resistance - general remark: A coating provides protection for the underlying Mg alloy. It would therefore be more correct to say: corrosion resistance of the coated Mg alloy.
Response: A reference to support this value is added to the revised manuscript.
-Point 7: lines 260-263: "Preparatory steps include cutting the Mg alloy substrate into 15 mm × 15 mm × 5 mm specimens before coating application. These samples undergo meticulous degreasing and cleaning." Why was the same treatment of the electrodes not used as described in section 2, lines 148-152?
Response: The sample plays the role of the anode in the MAO preparation, the cathode, as a matter of fact is the reaction sink connected to the MAO power supply. Thus, before the preparation begins, the sink is washed with deionized water and then used for the preparation.
-Point 8: Hank's solution, Table 3: Please give the reference for the composition of the solution.
Response: The table of all medicines and ingredients with their manufacturers’ names are added to the paper as Table 4 in revised manuscript.
-Point 9: Impedance measurements (EIS), lines 275-277: The electrochemical cell and the electrodes (reference and counter electrode) used for the impedance measurements must be described. Also the experimental conditions (frequency range, ac voltage amplitude, stabilisation period or pre-treatment, if any).
Response: The description of all parameters and test process are added in the revised manuscript for completing the description in lines of 274-279.
-Point 10: Bode and Nyquist diagrams are ways of visualising measured raw data. So if raw data is fitted, it is also displayed together with the raw data.
Response: Due to the loss of old data, the impedance test is re-conducted, and new results are presented in Figure 16 of the revised manuscript.
- Point 11: The data of the electrical equivalent circuit (EEC), which can be seen in Figure 16, is missing. Which software, which model was used?
Response: The data processing and the software with which the fitting process is performed are now introduced in the revised manuscript at lines of 280-284.
-Point 12: lines 551-553: „...with Mg2SiO4 representing the high-temperature phase found in the Earth's mantle at depths ranging from 350 to 1,000 km [59]." Please explain why this information is so important for the investigation.
Response: It is aimed to explain that Mg2SiO4 is stable in high temperature and provides mechanical properties for the coating.
Point 13: lines 557: „...of the secondary peak at 52 °C(?) for MgSiO4." Please correct.
Response: This mistake is corrected in the revised manuscript.
Point 14: XRD results. Figure 12 and its labeling are unclear. What coating is shown?
Response: this figure shows the XRD patterns of MAO coating in 6 g/L NaAlO2 concentration group and the non-NaAlO2 MAO coating.
-Point 14: Figure 12, blue line, What do the 3 peaks between 20 and 25° (not visible in the red line) represent?
It would be useful to show XRD patterns for all coatings analyzed, for coatings without NaAlO2 and for the bare Mg alloy. Then a complete phase analysis can be performed.
Response: A peak among them indicates the existence of MgSiO4. The XRD patterns are corrected by presenting a new figure 12in the revised manuscript.
-Point 15:XPS deconvolution spectra are suspect. What are the most intense peaks in the entire spectrum? The whole spectrum is complex. Please explain that.
Response: The XPS analyses are re-conducted for revision, and new fitting results with little shift is represented with figure 13 in the revised manuscript.
-Point 16:lines 593-597: Please add and cite appropriate references related to the Ca/P ratio in human bone and other osseoconductive coatings such as hydroxyapatite.
Response: More references and citations about HA and Ca/P ratio are added in the revised manuscript.
-Point 17:section 3.5, Corrosion data: Corrosion data for the bare Mg alloy measured under the same conditions as the coated Mg alloy are missing.
Response: In section 3.5, the corrosion resistance of coating is characterized by both immersion test and impedance test. For the fact that the immersion test requires at least 3 weeks to obtain a systematic result, and our semester nearly approaches its end. Thus the test can be performed after the Chinese traditional new year vacation. I’m sorry that for now I can’t provide the immersion result of bare Mg alloy. On the other hand, the impedance of bare Mg alloy is at level of hundreds Ω·cm2, this result is obtained from my colleague who focus on the Mg alloy substrate. Thus it would be nearly impossible to see the Mg alloy curve in the same figure with other coating curves. I would like to know whether you, respectable reviewer, would agree that I cite this value in the context or I make another figure of bare Mg alloy.
- Point 18: Figure 15 caption. The title should be more detailed. This applies to all figure captions in the manuscript!
Response: Thank you for the advice, the captions of figures in the manuscript is rechecked and adjusted in the revised manuscript.
-Point 19: lines 610-625: In order to evaluate the protective effect of the prepared coatings during the immersion period, a corrosion rate of the bare alloy examined during the same period is missing.
Response: I now completely agree that it is necessary to show the immersion results and impedance results etc. of bare Mg alloy to complete the comparison. However, as I mentioned previously, my institute for now approaches the national vacation and it is going to shot down for 3-4 weeks. Thus it is not feasible for me to accomplish this mission, I’m truly sorry.
-Point 20: Perhaps the lowest corrosion rate of the coating 6 g/L is the same or very similar to that of the bare coating? Is it possible that coatings desorb/detach the surface of the alloy after 20 days of immersion?
Response: I now do not possess the carrion rate of bare Mg alloy. But since it is commonly trusted that the MAO coating, although porous, can provide certain protections against corrosive medium. In our immersion test, even after more than 20 days immersion, MAO coating with better superficial quality stays in one piece although damaged. Thus it should have a disparity of corrosion rate between the coating and the bare Mg alloy.
-Point 21: Results of the electrochemical impedance (EIS). Most likely, these measurements were also carried out to assess the corrosion rate (resistance) of the samples analysed, but their explanation is not entirely correct. The same remark as for the determination of the corrosion rate: In order to evaluate the protective effect of the prepared coatings during the immersion period, an EIS measurement of the bare alloy during the same period is missing.Firstly, the EIS data can be shown in the form of Bode and Nyquist diagrams. The Nyquist diagram shows Zimag versus Zreal, while the Bode diagram shows IZI versus log f and phase angle (q) versus log f. The labelling in Figure 16 is therefore not entirely correct. As can be seen from Figure 16, the EIS data was adjusted according to the electrical equivalent circuit (EEC). Then Bode and Nyquist plots should represent the raw data and the modelled data together. Figure 16b is not a Bode diagram. Figure 16b and c together represent the Bode diagram. The phase angle values are most likely negative and it seems that Figure 16b shows the phase angle values and Figure 16c shows the IZI values. Please check this carefully. All data should be measured (displayed) in the same frequency range! The experimental conditions and the fitting model of the EIS measurements are missing in section 2.
Response: The whole electrochemical tests are re-conducted, and the figures are re-drawn to present now both raw data and fitted data in figure 16 of the revised manuscript.
Point 21: The response of the EIS data is complex for all coatings and contains at least two time constants. The explanation of the elements in the EEC needs to be reconsidered and reviewed. Why are the values of other elements (capacitance) not listed in Table 10? The capacitance is directly related to the coating thickness, so these results can be correlated with the results of other techniques used.
Response: All values of elements including CPE are now presented in Table 10 in the revised manuscript.
Pont 22: To interpret the corrosion from EIS measurements, a polarisation resistance (Rp) can be determined, which is a direct measure of the corrosion rate. The values of the polarisation resistance can therefore be directly correlated with the corrosion rate (Fig. 15). Please check the EIS data carefully and correct it. Then a correlation of the results obtained with different techniques can be made.
Response: I completely agree with your revision that Potentiodynamic Polarization is an excellent technique to measure the corrosion resistance of coating. And it would help to complete my electrochemical tests section. However, more time to perform the tests is really needed. Our institute and Labs will open until the 26 Jan.2024, I shall perform the test in that work week to accomplish this section.
-Point 23: Water contact angle measurements: The coating produced with 6 g/L NaAlO2 showed the best corrosion results and this coating also has the lowest water contact angle. The statement that hidrophilicity has a positive influence on osseoconductivity is correct, but it is known that hidrophilicity has a negative influence on corrosion protection. The value of approx. 90° obtained for the coating with 12 g/L NaAlO2 indicates hidrophobicity, which has a positive effect on corrosion. Please explain.
Response:
I completely agree that hydrophilicity damages the corrosion resistance for it allows corrosive medium contact and even enters the defects of MAO coating, which may result in the contact between corrosive medium and Mg alloy substrate, even cause the premature failure of coating. Still, the coating in 6 g/L group possesses best superficial quality, least defects, as microstructure analyses show in the paper. Thus, for determine this issue, it may require a perform of orthogonal tests to balance the hydrophilicity and corrosion resistance.
-Point 24: Conclusion. It would be advantageous to better correlate the results after the necessary correction.
Response: The conclusion is adjusted for the correction of other sections.
And I'm TRULY SORRY that I mistakenly upload a wrong edition of manuscript in the position of reply cover letter, PLAESE IGNORE IT! Thank you for your wisedom and revision!
Reviewer 3 Report
Comments and Suggestions for AuthorsThe article examines the properties of micro arc oxidation coating depending on the concentration of NaAlO2. A large amount of research has been carried out. Unfortunately, I cannot recommend the article for publication in its current form; it must be radically changed. Key notes:
1. The article is essentially a report on the research conducted. The information is poorly systematized, a number of Figs are redundant. It is necessary to remove all unnecessary things, concentrating on the most significant results.
2. The language of the article requires significant correction. Not so much the English language, but the writing style itself is more suitable for fiction than for a scientific article. I recommend that authors use superlatives like “superior properties” as little as possible, but indicate specific data.
3. The rest - see below:
I recommend not introducing abbreviations in the Abstract unless they are reused (in the Abstract).
The abstract is too long - it would be more correct to focus not on the research methods, but on the results.
The introduction is too long and contains information that is not essential to justify the goals and objectives of the study. I recommend shortening fragments like “For instance, Gao [19] employed...” or “For instance, Chen et al. [30] conducted...” or “For instance, ... Chang et al. [31] delved ..." or "For instance, Laleh [33] examined" and the like. The introduction should not contain background information or list previously conducted research. The introduction should be focused on justifying the scientific novelty and relevance of the research being carried out, justifying the goals and objectives of the work.
The last paragraph of the Introduction rather refers to the Materials and Methods section.
It is useful to conclude the Introduction with a focused statement of goals and objectives.
“...play an indispensable role in experimental procedures...” and “It is pertinent to note...” are a bit strange formulations for a scientific article.
Why were these particular reagents chosen?
“Considering the available laboratory equipment and instruments, established methodologies for preparation, and the collective knowledge of previous researchers within the research group...” is also a strange formulation. It is especially unclear what “available laboratory equipment and instruments” means - is this what is necessary for correct planning of an experiment? or just what was available? "collective knowledge of previous researchers" - is this published somewhere? (need references) - or is this some kind of “secret knowledge”?
"...is a deliberate choice..." - what does "deliberate" mean? could there be a "non deliberate" choice?
"to achieve MAO coatings with superior corrosion resistance and biocompatibility" - "superior" in relation to what?
In Table 1, it is rational to designate each of the sample groups by indicating the NaAlO2 concentration for each group, instead of designating “Differences in each group”.
In general, the Materials and Methods section is overly detailed and long. If standard methods are used, it is enough to provide a brief description of them and relevant references. Only information necessary to understand the research process is needed.
Lines 302 - 305. The meaning of this “Introduction” to the section is not very clear.
In principle, electrical conductance should be constant for identical conditions. What does the spread of values of this parameter mean (Figure 1)?
If NaAlO2 is a conductor, then electrical conductivity will increase with increasing concentration of NaAlO2. It is obvious. What is the purpose of this study?
What does "unmistakably reveals" mean?
Figure 3 - photographs of poor quality and low resolution. It is impossible to draw correct conclusions from these images.
"different colors representing different thickness of coating" - how is this confirmed? On what basis was this conclusion made?
"possess better macro morphology" - why?
It is better to remove this section altogether. Leave only section 3.2.1.
"In this segment, we delve into an in-depth analysis..." “An intriguing phenomenon” - is this the language of a scientific article?
How was porosity measured?
"Notably, a discernible negative correlation exists between porosity and the corrosion resistance of the coating" - but this is obvious!!! What's "Notably" about this statement?
In my opinion, all the coatings discussed in Figure 4 are of low quality. It seems doubtful that they can provide improved corrosion resistance based on the presence of a large number of pores and cracks. This is also confirmed in Figure 5.
Figure 8 - what's on the y (vertical) axis? Load? You must label the axis and specify the values.
Figure 11 should be moved to the Materials and Methods section.
Figure 14 - what is the meaning of these images?
Figure 16 - should also be moved to the Materials and Methods section.
Conclusions: “...exhibits superior properties...” - compared to what? Quite low hardness, low quality (porosity, cracks), etc.
"satisfactory thickness" - what is "satisfactory"? For what?
“characterized by ... uniformity” – but this is not visible in Figs 4 and 5!
"These defects are crucial as conductive channels when exposed to external corrosive environments." - but this has not been studied!
Comments on the Quality of English LanguageThe language of the article requires significant correction. Not so much the English language, but the writing style itself is more suitable for fiction than for a scientific article.
Author Response
Dear respectful reviewer, thank you for your revision which has pointed out lots of problems which I could barely notice, and the manuscript has been through an entire recheck upon the language usage etc. Yet still, I would like to explain that the Micro-arc Oxidation coating is porous, ceramic, and, with Ca/P containing electrolyte, biocompatible. However, the porosity and defects of the MAO coating make it unable to possess enough corrosion resistance to protect the magnesium alloy substrate by itself. Thus, the MAO coating is often used to preparer a composite coating such as MAO/ Layered Double Hydroxide coating, MAO/sol-gel coating. The new outer layer of coating can often seal the pores and cracks of the inner MAO coating. Thus, they can together provide satisfying corrosion resistance. In this manuscript, the study mainly focuses on the electrolyte, and the corrosion resistance is indeed not enough to endure a physiological environment with large amount of pores and cracks. The optimized MAO coating is actually used to prepare a MAO/LDH composite coating which possesses much better corrosion resistance.
Point1. The article is essentially a report on the research conducted. The information is poorly systematized, a number of Figs are redundant. It is necessary to remove all unnecessary things, concentrating on the most significant results.
Response: The manuscript has been revised according to your points.
Point 2. The language of the article requires significant correction. Not so much the English language, but the writing style itself is more suitable for fiction than for a scientific article. I recommend that authors use superlatives like “superior properties” as little as possible but indicate specific data.
Response: The language of this manuscript is rechecked, those unproper words have been deleted.
- The rest - see below:
I recommend not introducing abbreviations in the Abstract unless they are reused (in the Abstract).
Point 3: The abstract is too long - it would be more correct to focus not on the research methods, but on the results.
Response: The abstract is shortened and refined and focuses now on the results. Some methods are mentioned but not detailedly.
Point 4: The introduction is too long and contains information that is not essential to justify the goals and objectives of the study. I recommend shortening fragments like “For instance, Gao [19] employed...” or “For instance, Chen et al. [30] conducted...” or “For instance, ... Chang et al. [31] delved ..." or "For instance, Laleh [33] examined" and the like. The introduction should not contain background information or list previously conducted research. The introduction should be focused on justifying the scientific novelty and relevance of the research being carried out, justifying the goals and objectives of the work.
Point 5: The last paragraph of the Introduction rather refers to the Materials and Methods section.
Point 6: It is useful to conclude the Introduction with a focused statement of goals and objectives.
Response: The introduction is shortened, the unnecessary references are removed, the last paragraph of this section is rewritten.
Point 7: “...play an indispensable role in experimental procedures...” and “It is pertinent to note...” are a bit strange formulations for a scientific article.
Response: This sentence is rewritten to make it clearer for understanding and proper for an article.
Point 8: Why were these particular reagents chosen?
Response: The ingredients of the electrolyte is a legacy of previous studies in our group, they mainly serve for the formation of the MAO coating with smoother and gentler spark discharge in the preparation, because the discharge can damage gravely the coating surface, the Ca and P elements are meant for have an osseous inductivity for the MAO coating.
Point 9: “Considering the available laboratory equipment and instruments, established methodologies for preparation, and the collective knowledge of previous researchers within the research group...” is also a strange formulation. It is especially unclear what “available laboratory equipment and instruments” means - is this what is necessary for correct planning of an experiment? or just what was available? "collective knowledge of previous researchers" - is this published somewhere? (need references) - or is this some kind of “secret knowledge”?
Response: Thank you for pointing out the problems, respectful reviewer. I must confess that this is some ‘writing advice’ that I’ve received and taken from writing AI. This part is now rewritten to make it proper and neat.
Point 10: "...is a deliberate choice..." - what does "deliberate" mean? could there be a "non deliberate" choice?
Response: The sentence is rewritten.
Point 10:"to achieve MAO coatings with superior corrosion resistance and biocompatibility" - "superior" in relation to what?
Response: The phrase was saying to have better properties than non-NaAlO2 MAO coating. Because we have tested properties of MAO coating with the electrolyte, but NaAlO2 excluded. However, this part is not concerned in the manuscript for it having been already too long.
Point 11:In Table 1, it is rational to designate each of the sample groups by indicating the NaAlO2 concentration for each group, instead of designating “Differences in each group”.
Response: The table 1 is corrected according to you. The NaAlO2 concentration is now marked as 3, 6, 9, 12 g/L.
Point 12: In general, the Materials and Methods section is overly detailed and long. If standard methods are used, it is enough to provide a brief description of them and relevant references. Only information necessary to understand the research process is needed.
Response: Dear reviewer, as you know, the manuscript has been through some previous reviewers and editors. In the case of this Material and Methods section, it is demanded by some of them that the details and parameters are lacked and needed completion. I, as a fresh new beginner of scientific article writing, have unfortunately not enough capacity to judge where the ‘enough details’ gauge lies. Thus, I plead that you could, if it pleases you, teach me how to refine this part without making it ‘not enough detailed’. Thank you!
Point 13: Lines 302 - 305. The meaning of this “Introduction” to the section is not very clear.
Response: The word ‘introduction’ is now corrected into ‘addition’ to make a clearer phrase.
Point14: In principle, electrical conductance should be constant for identical conditions. What does the spread of values of this parameter mean (Figure 1)?
Response: Figure1(Fig. 2 in the revised manuscript) tells the evolution of electrical conductance of electrolyte when the NaAlO2 concentration rise from 3 to 12 g/L. Actually, the addition of NaAlO2, though it doesn’t work like adding NaAlO2 into a 3 g/L electrolyte to make a 6 g/L, but all electrolyte solution are prepared separately. Yet the appearance of 4 kinds of electrolyte are different, the amount of not solved suspension in solution are different, and the electrical conductance are not same.
Point 15: If NaAlO2 is a conductor, then electrical conductivity will increase with increasing concentration of NaAlO2. It is obvious. What is the purpose of this study?
Response: The point of this section is to state the fact of this conductance difference and to link the conductance, the voltage values of preparation to the microstructure properties and other properties. Because, the only variable in this study is the NaAlO2 concentration, and the most direct and instinctive influence is the conductance, which would lead to the difference of voltage values and affect coating surface.
Point 16: What does "unmistakably reveals" mean?
Response: this expression has been deleted.
Point 17: Figure 3 - photographs of poor quality and low resolution. It is impossible to draw correct conclusions from these images.
"different colors representing different thickness of coating" - how is this confirmed? On what basis was this conclusion made?
"possess better macro morphology" - why?
It is better to remove this section altogether. Leave only section 3.2.1.
Response: this part has been deleted as your review.
Point 18: "In this segment, we delve into an in-depth analysis..." “An intriguing phenomenon” - is this the language of a scientific article?
Response: This expression has been deleted as previous ones.
Point 19: How was porosity measured?
Response: The porosity of coating is obtained with SEM image of the coating, the image undergoes a calculation performed by a software called ImageJ, which can identify the pores from other surface areas, and it performs a division of pores’ area upon the whole area.
Point 20:"Notably, a discernible negative correlation exists between porosity and the corrosion resistance of the coating" - but this is obvious!!! What's "Notably" about this statement?
Response：this expression is deleted to make a proper phrase.
Point 21: In my opinion, all the coatings discussed in Figure 4 are of low quality. It seems doubtful that they can provide improved corrosion resistance based on the presence of a large number of pores and cracks. This is also confirmed in Figure 5.
Response: As I explained at the beginning of the reply, the MAO coating alone cannot provide enough corrosion resistance against physiological environment. But its optimization can still affect the properties after being made into a MAO/LDH composite coating. Thus, this study is a prepositive part of the study on the composite coating. The composite coating is actually the ultimate goal of the whole aspect.
Point 22: Figure 8 - what's on the y (vertical) axis? Load? You must label the axis and specify the values.
Response: The yellow curve represents the Mg element content when indenter advances. Because when the coating is punctured, the Mg alloys substrate is exposed, and the Mg content should rise considerably. The blue line is not the Y axis but a mark of position where the coating is punctured.
Point 23: Figure 11 should be moved to the Materials and Methods section.
Response: this figure has been moved to Material and Methods section.
Point 24: Figure 14 - what is the meaning of these images?
Response: this figure is the EDS results. It indicates the elemental distribution of Mg, Al, and Ca. it can confirm that Ca and Al are consumed and enter the coating. Or rather, it is confirmed by the figure that the coating contains Ca and Al elements. Because the formation of MAO coating is extremely complicated, that sometimes for example, with an Ag added electrolyte, the obtained MAO coating cannot have a XRD result which shows the existence of Ag containing phase. Thus, tests such as EDS and FT-IR are often adopted to confirm the elements of the coating.
Point 25: Figure 16 - should also be moved to the Materials and Methods section.
Response: In fact, this part has been through times of revision, it is suggested by an editor that this section including the EEC should learn from the article called ‘Developing super-hydrophobic and corrosion-resistant coating on magnesium-lithium alloy via one-step hydrothermal processing’
Developing super-hydrophobic and corrosion-resistant coating on magnesium-lithium alloy via one-step hydrothermal processing - ScienceDirect
And in that article, the fig of EEC is placed closed to other results (Fig. 5). So it is for this reason that I also place it closed to other results.
Point 26: Conclusions: “...exhibits superior properties...” - compared to what? Quite low hardness, low quality (porosity, cracks), etc.
"satisfactory thickness" - what is "satisfactory"? For what?
“characterized by ... uniformity” – but this is not visible in Figs 4 and 5!
"These defects are crucial as conductive channels when exposed to external corrosive environments." - but this has not been studied!
Response: The conclusion is also rewritten to make it clear and neat.
Reviewer 4 Report
Comments and Suggestions for AuthorsThe authors have nicely presented the paper, and it requires no revision.
Author Response
Dear respectful reviewer, thank you!
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript can be published in the present form.
Author Response
Thanks for your revision, respeactable reviewer!
Reviewer 2 Report
Comments and Suggestions for AuthorsI kindly asked the authors to check and correct their results according to the Report 1.
For example, the Experimental section with the missing data should be corrected so that someone can easily repeat the experiment.
If the authors have data on bare Mg, please provide the appropriate reference.
Table 4 contains chemicals (better than medicine and ingredients).
The section on electrochemical impedance has not been corrected according to Report 1. The meaning of the electrical equivalent circuit diagram, the units of the elements in Table 11 are missing... The mathematical representation of the data in Table 11 should be improved. What is the physical meaning of the elements of the electrical equivalent circuit diagram? In Figure 16 b and c, both figures should be shown together as one figure. Please see the Report 1 (point 21) for meaning of the Bode diagram.
Author Response
Thank you for your review, respectable reviewer. In the second revision, the experimrntal parameters of XRD, details on mechanical tests and immersion tests are added to better describe the tests. An impedance of bare ZK60 alloy citation is added to form a comparison with coating impedance of this paper. The Bode diagram is reworked according to your review, and certain errors are corrected.
Reviewer 3 Report
Comments and Suggestions for AuthorsSince the authors took into account most of the reviewer’s recommendations or gave a reasonable answer to the recommendations, I believe that the article can be recommended for publication, but additional comments must be taken into account:
The Abstract has improved, but I still recommend additional changes - the Abstract now talks more about the research methods rather than the results. I recommend changing this - for example, not “are quantified and analyzed” or “investigate chemical bonding and phase composition”, but what results were obtained.
In the final part of the Introduction, I recommend presenting a clear and focused goal of the research - not “foundation for further study”, but why this is needed, what is the meaning of this research.
Figure 8. "The yellow line indicates the change of Mg element content" - this is understandable, but what units? at% wt%?
Figure 13 - I meant that in their current form these images are not very informative and their quality does not allow us to draw any significant conclusions.
It is better to structure the conclusion according to points 1. 2. 3. ....
Comments on the Quality of English LanguageEnglish as it stands is quite understandable
Author Response
Dear respectful reviewer, thank you for your kindhearted understanding,
Since the authors took into account most of the reviewer’s recommendations or gave a reasonable answer to the recommendations, I believe that the article can be recommended for publication, but additional comments must be taken into account:
Point 1: The Abstract has improved, but I still recommend additional changes - the Abstract now talks more about the research methods rather than the results. I recommend changing this - for example, not “are quantified and analyzed” or “investigate chemical bonding and phase composition”, but what results were obtained.
Response: the abstract is adjusted to show more testing results.
Point 2: In the final part of the Introduction, I recommend presenting a clear and focused goal of the research - not “foundation for further study”, but why this is needed, what is the meaning of this research.
Response: the last paragraph of the introduction is adjusted to show more goals and objectives.
Point 3: Figure 8. "The yellow line indicates the change of Mg element content" - this is understandable, but what units? at% wt%?
Response: the curves represent actually the atomic fraction of Mg element in EDS linear scanning, and their units should be A.U., about this I’ve consulted Professor Liang-Yu Chen, an author of this paper and also a teacher in our group. According to him, the evolution of this value shows the change of Mg content in the single test. Its relative values are taken into account, while absolute values of curves are not able to be compared.
Point 4: Figure 13 - I meant that in their current form these images are not very informative and their quality does not allow us to draw any significant conclusions.
Response: the color saturation of the Fig. 13 is adjusted to 400% (the highest value) to make the blue and green colors more distinguished. Due to the fact that this fig is obtained by a senior of my who has already graduated for years, it is indeed not a perfect experiment presentation. Or we can reconduct the EDS linear scanning and remake a new Fig if you wish. But surly, it would take us several days to accomplish.
Point 5: It is better to structure the conclusion according to points 1. 2. 3. ….
Response: the form of the abstract is adjusted. Some data values are added into it.
Round 3
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript has not been improved according to the Report s 1 and 2 and still contains a crucial errors. I will focus only on the impedance results.
As you can see from Figure 16, in the Nyquist plot the X and Y axes are in units (Ohm cm2), and in the Bode plot the Y1 axis (log IZ "I) is wrong. The Y1 axis is IZI and not IZ "I and it must have the unit (Ohm cm2) as it contains the values of Z` and Z". The authors must check and correct their results. There are numerous books on EIS and a very useful and easy to read book is "Electrochemical Impedance Spectroscopy" by Mark E. Orazem and B. Tribollet.
The phase angle must have negative values!
Something is wrong with the raw data and the modelled data. It seems that the electrical equivalent circuit used is probably not suitable to describe the electrode/ electrolyte interface. Also, the authors have used simbol and lines to represent the results and the modelled data, so the representation of the results is unclear.
The description of the EEC does not seem to be correct. According to the EEC, the time constant (CPE1 R2) refers to the high/medium frequency range and the time constant (CPE2 R3) to the low frequency range. Thus, (CPE1 R2) can be correlated with the coating and (CPE2 R3) with defects in the coating (as seen in the results of other techniques). If EEC describes the coating and the substrate, then the high frequency time constant refers to the coating and the low frequency refers to the substrate. Please check carefully!!
The selected EEC must be assigned the references.
The authors have mentioned defects/pores in the prepared coatings, so the EIS results must also show these pores!
Table 11: Which units apply for resistance values, Ohm or Ohm cm2? The samples have an area of 15 mm x 15 mm!
What does the CPE stand for? Why was it used? The CPE element has Q and n values? The n- values are not included in Table 11. The trend of the EIS parameters should be correlated with other techniques.
The data on Mg cannot be correlated with the results in this manuscript because the Mg alloy was measured in a different medium (saliva, not Hank solution) and the time is questionable. If some data come from other studies/papers, the corresponding reference must be cited.
Author Response
Thank you for your review, respectable reviewer, the issues and problems are studied and corrected as followed answers.
Point1: As you can see from Figure 16, in the Nyquist plot the X and Y axes are in units (Ohm cm2), and in the Bode plot the Y1 axis (log IZ "I) is wrong. The Y1 axis is IZI and not IZ "I and it must have the unit (Ohm cm2) as it contains the values of Z` and Z". The authors must check and correct their results. There are numerous books on EIS and a very useful and easy to read book is "Electrochemical Impedance Spectroscopy" by Mark E. Orazem and B. Tribollet.
Response: The Bode diagram and the EIS diagram are rework due to the axe issue and the equivalent circuit problem.
Point 2:The phase angle must have negative values!
Response: The phase angle are negative, when I was drawing the figure, I used the absolute values of phase angles, but I forgot to make it clear in the figure.
Pont3: Something is wrong with the raw data and the modelled data. It seems that the electrical equivalent circuit used is probably not suitable to describe the electrode/ electrolyte interface. Also, the authors have used simbol and lines to represent the results and the modelled data, so the representation of the results is unclear.
Response: The figures are rework, though the experiment cannot be due to the vacation. They are now much better clearly presented.
Point 4: The description of the EEC does not seem to be correct. According to the EEC, the time constant (CPE1 R2) refers to the high/medium frequency range and the time constant (CPE2 R3) to the low frequency range. Thus, (CPE1 R2) can be correlated with the coating and (CPE2 R3) with defects in the coating (as seen in the results of other techniques). If EEC describes the coating and the substrate, then the high frequency time constant refers to the coating and the low frequency refers to the substrate. Please check carefully!!
Response: The EEC is changed after consulting on several thesis and articles, it is now more suitable for the condition of barrier layer-inner porous layer- outer porous layer, a triplex model.
Point5: The selected EEC must be assigned the references.
Response: A reference corresponding to the EEC is added to support the idea of this paper.
Point6: The authors have mentioned defects/pores in the prepared coatings, so the EIS results must also show these pores!
Response: The new EEC is strongly related to pores and defects.
Point 7: Table 11: Which units apply for resistance values, Ohm or Ohm cm2? The samples have an area of 15 mm x 15 mm!
Response: Table 11 is also reworked and units of values are checked.
Point 8: What does the CPE stand for? Why was it used? The CPE element has Q and n values? The n- values are not included in Table 11. The trend of the EIS parameters should be correlated with other techniques.
Response: CPE is constant phase element, which is related to shift of fitting results from pure resistance or capacitance behavior. The Q and n values are added into Table 11.
Point 9: The data on Mg cannot be correlated with the results in this manuscript because the Mg alloy was measured in a different medium (saliva, not Hank solution) and the time is questionable. If some data come from other studies/papers, the corresponding reference must be cited.
Response: New reference is found, the impedance of ZK60 in Hank’s solution is reliable, though the testing temperature has difference. It can provide a rough range of bare ZK60 impedance.
Round 4
Reviewer 2 Report
Comments and Suggestions for AuthorsAlthough the manuscript, i.e. the part on EIS, is now improved, it still contains particular weaknesses. As can be clearly seen in Figure 16 (the figure is now clearer), the fitted lines do not follow the experimental raw data, especially at low frequencies (below 102 Hz). This means that the electrical equivalent circuit does not describe the electrolyte/electrode interface very well. The Χ2 values (Table 11) are a little too high. The authors should therefore re-examine the EEC and adjustment results.
The authors should be careful as this EEC is used for the titanium substrate (according to the reference 73), whose electrochemical behaviour is completely different from that of the ZK60 magnesium alloy.
Perhaps the possible solution lies in diffusion through the pores and then the Warburg elements could better describe the electrolyte/electrode interface. Diffusion is normally visible at low frequencies.
Now the CPE element is described and each CPE element has Q and n values. So if the selected EEC has 3 CPE elements, 3Q and 3n values should be visible. This is not evident from Table 11. The value of the exponent n can indicate the diffusion process.
The authors discuss the corrosion resistance of the coatings formed, but it is not clear how they calculated/determined this value. Is this a sum of all three resistance values (according to the EEC used) or ?
Furthermore, the authors have not corrected the values for the resistance of the coatings in the summary and conclusions.
Author Response
Dear reviewer,
the Section of EIS test is completely rework under the suggestion of yours and editors, the EEC applied is suitable in the case of this work accoding to the editor. The fitting curves are redrawn and the fitting results are updated in the table.
