Preparation of MgAl2O4-Coated Al2O3np and Migration of Ceramic Nanoparticles during Ultrasonic Processing of Aluminum Matrix Composites
Round 1
Reviewer 1 Report
The presented paper contains the results of the investigation of polycrystalline layer of nano-MgAl2O4 spinel was in-situ coated on the surface of nano-sized alumina particles by electroless plating and calcination process, and the aluminum matrix composites reinforced with hybrid of MgAl2O4-coated Al2O3np and MgAl2O4 particles were prepared by high intensity ultrasonic assisted casting method. In this study detailed the production of MgAl2O4-coated Al2O3np. Although the study is not novel and many works have been previously done in similar topics, some parts of the manuscript and the way authors have looked at the data are novel and interesting for publication. I think that this paper need a strong enhancement during the revision step since many parts are really difficult to be understood. The paper requires some major improvements like a few below comments that the authors may wish to consider when submitting the revised manuscript. For all these reasons I suggest a major revision hoping that the quality of the paper in the revised version may be higher.
- No clearly indicated aim of work, the description in the introduction is too long.
- Line 176-178, Authors mentioned ” The exogenous Mg phase can affect the measurement of crystallinity of Al2O3np by XRD, which indirectly indicates that Mg is uniformly dispersed on the surface of the carrier.” On what basis were such conclusions made? The diffraction beam scans the entire indicated surface (slits, masks on the incident beam), so the resulting diffractogram does not distinguish whether we are dealing with clusters or scattered reinforcing particles. The above sentence is incorrect and should be corrected.
- Line 178-180, Authors mentioned ”… the acidic substances in the sensitizing and activation solutions possibly destroyed the crystal structure of the Al2O3np surface, accordingly resulting in the reduced diffraction intensity”. Really, there is a documented knowledge in the literature of what kind of changes take place on the surface when different solutions are used. The authors should refer to this issue and cite the corresponding literature. It should also be mentioned that structural changes are not deep and do not strongly affect the intensity of diffraction reflections from the matrix.
- Line 180-182. Authors mentioned ”… t can be found that the diffraction peaks of MgAl2O4-coated Al2O3np are slightly shifted…” On what basis was it found that the lines are shifted? Is it as a result of observations or measurements of network parameters, e.g. using the Rietveld method? How are they shifted, are they the result of unit cell expansion or unit cell contraction? The work lacks information on how the atomic radii have reinforcing particles and the matrix. Changes in position may indeed result from volumetric changes of crystallites, but they may also result from incorrect position in the goniometer's axis as well as from high roughness which causes the Brag-Brentano measurement conditions not to be met. It is recommended to use GIXD (Grazing Incidence X-ray Diffraction) method to effectively measure structural changes in coatings and transition zone.
- Line 183-184. Authors mentioned ”… the X-ray diffraction characteristics of Mg and MgAl2O4 are not obvious, which means that the amount of formed Mg and MgAl2O4 is very small”. The reviewer does not understand this sentence, please explain it more deeply and accurately and cite the relevant literature.
- In conclusion of points 2-5, the diffraction measurements should be repeated because the shown diffractograms have low counts, which leads to incomplete analysis due to the low intensities of the diffraction lines, especially from reinforcing particles. The Rietveld method should be used to investigate structural changes.
- Line 194. Authors noticed “….coating, the surface of alumina becomes very rough, and the coating thickness is in the range of 10 to 50 nm.” On what basis do the authors claim this? What was examined, please indicate on the figures. Was the measurement made in several places or in one, because the distribution is significant.
- Figure 11. Chemical decomposition of the elements on the tested surface should be performed. This will show the distribution of the elements in the material. It is also recommended to take EDS BSE measurements.
- The conclusions should be improved as they are to correspond to the assumed title of the paper. Conclusions should be compacted and not repeat parts of the discussion of results.
- The work has numerous editorial errors and typos, e.g., line 34 "beacuse", line 47 "uniforn", line 86 "competely", line 104 and 105 "sulfate", line 150 "providing favorable conditions", line 194 "rangle", line 28 "wetting behavior between", line 245 "increase ofand below", line 349 repetitions "which can be expressed", 362 "absense", line 421 "nano-seed".
In my opinion this manuscript is should be strongly improved and then sent for reassessment before publication in Coatings.
Author Response
Dear Reviewer
The revisions suggested by the reviewer are very professional and detailed. We benefit much from these. It is important for us to improve the ability of research. We had revised conscientiously the paper. The responses to all comments by the referee are provided as below:
1. No clearly indicated aim of work, the description in the introduction is too long.
The aim of work was indicated,and the relevant explanations were given in the last paragraph in the “Introduction” section. The description in the introduction was simplified.
2. Line 176-178, Authors mentioned” The exogenous Mg phase can affect the measurement of crystallinity of Al2O3np by XRD, which indirectly indicates that Mg is uniformly dispersed on the surface of the carrier.” On what basis were such conclusions made? The diffraction beam scans the entire indicated surface (slits, masks on the incident beam), so the resulting diffractogram does not distinguish whether we are dealing with clusters or scattered reinforcing particles. The above sentence is incorrect and should be corrected.
The reviewer is very professional. We've removed this expression of uncertainty.
3. Line 178-180, Authors mentioned ”… the acidic substances in the sensitizing and activation solutions possibly destroyed the crystal structure of the Al2O3np surface, accordingly resulting in the reduced diffraction intensity”. Really, there is a documented knowledge in the literature of what kind of changes take place on the surface when different solutions are used. The authors should refer to this issue and cite the corresponding literature. It should also be mentioned that structural changes are not deep and do not strongly affect the intensity of diffraction reflections from the matrix.
The corresponding literature about the effect of PH values on the structure change of alumina were listed in the Page 5, Line 170. The relevant explanations were given in the Page 5 , Line 170 to 175.
4. Line 180-182. Authors mentioned ”… t can be found that the diffraction peaks of MgAl2O4-coated Al2O3np are slightly shifted…” On what basis was it found that the lines are shifted? Is it as a result of observations or measurements of network parameters, e.g. using the Rietveld method? How are they shifted, are they the result of unit cell expansion or unit cell contraction? The work lacks information on how the atomic radii have reinforcing particles and the matrix. Changes in position may indeed result from volumetric changes of crystallites, but they may also result from incorrect position in the goniometer's axis as well as from high roughness which causes the Brag-Brentano measurement conditions not to be met. It is recommended to use GIXD (Grazing Incidence X-ray Diffraction) method to effectively measure structural changes in coatings and transition zone.
The reviewer has very theoretical knowledge and practical experience in XRD testing. The opinions propose by the reviewer have a good guiding significance for our future research. The slight shift of diffraction peaks observed in the XRD patterns may be induced by multiple reasons, such as measurement method, measurement condition, unit cell change, volumetric changes of crystallites, as proposed by the reviewer. In the our tests, under the same test conditions, the slight shift of diffraction peaks may be induced by the slight change of test conditions during the test. Thus, the expression of uncertainty was deleted and the line of dashes in the figure 2 were deleted.
5. Line 183-184. Authors mentioned ”… the X-ray diffraction characteristics of Mg and MgAl2O4 are not obvious, which means that the amount of formed Mg and MgAl2O4 is very small”. The reviewer does not understand this sentence, please explain it more deeply and accurately and cite the relevant literature.
The sentence was revised and was listed in the Page 5, Line 175 to 176. The relevant literature was listed in the Page 5, Line 176.
6. In conclusion of points 2-5, the diffraction measurements should be repeated because the shown diffractograms have low counts, which leads to incomplete analysis due to the low intensities of the diffraction lines, especially from reinforcing particles. The Rietveld method should be used to investigate structural changes.
In our experiment, Mg and MgAlO4 phases need to be determined on the surface of alumina particle. We successively carried out XRD, SEM, EDS and TEM detection to confirm whether these phases were produced. We again carried out the GIXD detection, but the difference of diffraction peak characteristics was still not obvious. Maybe the content of formed Mg or MgAl2O4 was too low. And, the subsequent SEM, EDS and TEM detection can be used to further confirm the presence of these phases. Also, the presence of these phases indirectly proved the structural changes on the surface of alumina.
7. Line 194. Authors noticed “….coating, the surface of alumina becomes very rough, and the coating thickness is in the range of 10 to 50 nm.” On what basis do the authors claim this? What was examined, please indicate on the figures. Was the measurement made in several places or in one, because the distribution is significant.
We measured the coating thickness at different positions. We found that the minimum thickness was about 10 nm and the maximum thickness was about 50 nm. The revised figures were given in the figure 3.
8. Figure 11. Chemical decomposition of the elements on the tested surface should be performed. This will show the distribution of the elements in the material. It is also recommended to take EDS BSE measurements.
The chemical decomposition of the particles on the tested surface were performed by EDS measurement. The revised figures were given in figure 11.
9. The conclusions should be improved as they are to correspond to the assumed title of the paper. Conclusions should be compacted and not repeat parts of the discussion of results.
The conclusions were improved and the relevant contents were given in the “Conclusions” section.
10. The work has numerous editorial errors and typos, e.g., line 34 "beacuse", line 47 "uniforn", line 86 "competely", line 104 and 105 "sulfate", line 150 "providing favorable conditions", line 194 "rangle", line 28 "wetting behavior between", line 245 "increase ofand below", line 349 repetitions "which can be expressed", 362 "absense", line 421 "nano-seed".
Thank the review very much for pointing out these mistakes. We checked the spelling and grammar throughout the paper and revised earnestly.
Yours faithfully
Xiao-Hui Chen
18-October-2020
Author Response File: 
Author Response.doc
Reviewer 2 Report
An interesting piece of work with fairly high industrial interest for effective strengthened composites. The paper is well written with extensive discussions of results.
1) More thorough referencing at the beginning of the introduction is necessary regarding ceramic powder-strengthened aluminium. The references for modelling are sufficient.
2) Please ask an English-speaker to read and correct the manuscript - There are too many syntactic and grammatical errors and in many places it's not possible to obtain clear meaning.
3) in page 12, the calculated pressure Pc of 5GPa is the maximum theoretical pressure and cannot of course be generated within these materials. You should make this clear. I suggest a wording such as "...thereby giving a maximum theoretical value for Pc of about 5GPa, which is more than sufficient to ...". Also please avoid so many decimal places in such rough, approximate calculations. The same corrections must be carried out in the conclusions.
Author Response
Dear Reviewer
The revisions suggested by the reviewer are very professional and detailed. We benefit much from these. It is important for us to improve the ability of research. We had revised conscientiously the paper. The responses to all comments by the referee are provided as below:
1. More thorough referencing at the beginning of the introduction is necessary regarding ceramic powder-strengthened aluminium. The references for modelling are sufficient.
All the references at the beginning of the introduction were regarding ceramic powder-strengthened aluminium. The references 2 and 4 were replaced.
2. Please ask an English-speaker to read and correct the manuscript. There are too many syntactic and grammatical errors and in many places it's not possible to obtain clear meaning.
The language of the paper was improved, and the English writing of the paper was carefully edited by a native English speaker. Possibly, there are still some problems within the paper. I'd like to hear your advice.
3. in page 12, the calculated pressure Pc of 5GPa is the maximum theoretical pressure and cannot of course be generated within these materials. You should make this clear. I suggest a wording such as "...thereby giving a maximum theoretical value for Pc of about 5GPa, which is more than sufficient to ...". Also please avoid so many decimal places in such rough, approximate calculations. The same corrections must be carried out in the conclusions.
The revised contents were given in the Page 12, Line 322 to 323. The approximate calculations was carried out in the conclusions.
Yours faithfully
Xiao-Hui Chen
18-October-2020
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report
Dear Authors,
The authors clearly focused on the points i raised in the previous review stage addressing all the stated points.
For this reason i suggest this work for publication in Coatings journal.
Best regards,
