Formation Process of the Integrated Core(Fe-6.5wt.%Si)@Shell(SiO₂) Structure Obtained via Fluidized Bed Chemical Vapor Deposition

Round 1

Reviewer 1 Report

Line 46: name a couple of various insulating oxides along with the sentence. Also, Fan et al. is the first author for one of the cited references. Others have different first authors, so restructure the sentence correctly.

Line 96: Instead of formation, Synthesis sounds better.

Please mention how the micro-strains calculated along with relevant formulas in the main text. Authors fail to mention how wrinkle and pit affect the surface stress and strain distribution. Justify it with some references.

Providing a precise schematic art of the core-shell diagram would have made the reader much more interested. 

First of all, the XPS figure 4 is not visible. I would suggest authors can move a,b,c, and d comprehensive scan figures in supplementary. Make other spectra's more noticeable. For XPS, is the charge reference for binding energy calibration is C1s? Mention that binding energy? Why no explanation of C1s spectra provided? The authors also need to mention the resolution, pass energy, and scan time for XPS in the materials and method section. The authors also need to provide a discussion about Fe3p spectra (can be in supplementary). Even from the comprehensive scan figures, Fe2p peak gone for b,c, and d. Why is it so? Also, the authors failed to mention the reason behind the occurrence of Fe2p peak in the case of the 480s. Now, let us come to reference 26, which never says anything about Si2p. Instead, it talks about Si2s. The peaks are at 150.5eV attributed to elemental Si. Then 155.3 assigned to SiO₂. I do not think they have said anything about Si2p. So citing this reference for Si2p peaks assignment is unacceptable. Now for reference number 27, Do not have any XPS data in that paper. So again, citing that paper about XPS is wrong. Please cite relevant articles.

For O1s spectra, why no reference provided?

I failed to understand about Figure 4, and groups said inline 93. Where are the carbons? It is adding confusion. The authors should clear it up. For Figure 4, there is no legend for the color code of the atoms provided.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript describes the coating of Fe-6.5wt.%Si with SiO2 using fluidized bed chemical vapor deposition. The authors have more particularly studied the transition from Fe-6.5wt.%Si/SiO2 composite to  Fe-6.5wt.%Si/SiO2 core-shell structure. The paper is well written and the study is interesting. The study fits with the scopes of Metals journal and is timely relevant. However, the manuscript needs to be improved before a possible acceptance for publication. See comment:

 

• The authors should complete the introduction and should cite the previous works of Ferguson et al. (doi.org/10.1016/S0040-6090(00)00973-1), King et al. (doi.org/10.1016/j.powtec.2011.12.020, doi.org/10.1016/j.surfcoat.2007.05.002) and more recently Rauwel et al. (doi: 10.1002/cvde.201207005, doi: 10.1149/2.086204jes). The last set of references refers to the coating of nanoporous alumina particles of similar diameter than Fe-6.5wt.%Si the authors coated with SiO2.
• The authors should add a low magnification SEM image of Fe-6.5wt.%Si before coating. The image should show a particle of 70μm of diameter.
• Line 158, the authors wrote:” The diffraction patterns are shown in Figure 3(a-f)”, I guess the authors means SEM images.
• The image in figure 3 are too small.
• The XPS spectra in figure 4 are too small.
• XPS depth of analysis is usually 10nm in the case of SiO2 film. This should mean that after 960s the SiO2 coating is thicker than 10nm. The authors should check and confirm this hypothesis with references.
• For Ms value, the authors should state if emu/g correspond to the Fe in the sample (6.5wt.%) or the weight of the whole sample. How do they estimate the quantity of Fe after SiO2 coating? This is not clear.
• All values in table 1 are very similar, the authors should comment these numbers and add error bars.
• The authors should add a scheme to illustrate equation 1 (θ and θ*).
• Line 191 the autho0rs wrote:”degrees of polymerization”, I guess they mean oxidation state (Si+, Si2+, Si3+ and Si4+.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript metals-756315 deals with the preparation of Core@shell particles. The (Fe-6.5wt.%Si)@SiO2 samples were prepared by fluidized-bed chemical vapor deposition using TEOS as precursors of SiO2 and Fe-6.5wt.%Si particles of 70µm of diameter. The Fe-6.5wt.%Si particles are heated at 920 K and fluidized thanks to the introduction of 80mL/min of Ar. Then the TEOS precursor pre-heated at 423K is introduced into the fluidized bed reactor using Ar as a carrier gas. The authors studied the influence of deposition time (ranging from 60 to 3,840 s) on the ferromagnetic@SiO2 structural evolution during the fluidized bed CVD process. The different samples obtained have been characterized by XRD, FE-SEM, XPS, and magnetic properties have been analyzed. Even if the results are well presented and seem to support the conclusions, some points have to and some others can be improved. That for these reasons that I recommend MAJOR REVISION for this manuscript. 

 

My comments and suggestions are reported below. I hope that they could help the authors.

 

1. Fig. 1: add the signals from the International Center for Diffraction Data powder diffraction file 09-065-9130 as bare diagram 
2. The authors discussed the evolution of the microstructures of the samples (Table 1 and lines 107-112). However, we do not know how they get this information. Moreover, there is no error bare for the different parameters of Table 1. I think that a Rietveld refinement could help the authors to give a more accurate description of it. (e.g., FullProf suite software)
3. Fig. 2: could the authors provide lower magnification images for the comparison of larger areas? Moreover, could the authors give more details about the localization of the deposit? In the present form, I am not sure that the images support their conclusions.  
4. The authors discussed heterogeneous nucleation, but what's about the effect of gas-phase nucleation?
5. Fig. 3: EDS could be used to show the increase of Si content between the inner and outer parts of the particle. 
6. Lines 185-187: “The Fe…960 s.” The authors should develop this part. Why did they write “this indicated that the formation of the Fe-6.5wt.%Si/SiO2 C-S was complete after 960 s”? (i.e., just more details are needed)
7. Static magnetic properties: even if it is mentioned in lines 226-227, the authors should add in the experimental part that the saturated magnetizations are expressed in emu/g of sample. The evaluation of iron content in each sample could also be a plus for the manuscript. 
8.  (viii)Conclusion: why “184.5 nm” here (line 271) and “ranging from 107 nm to 262 nm” in the text (lines 165-166)
9. Line 274: the authors wrote 4,000 s I thought that it was 3,840 s?

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

The paper is secondary in the light of the recently published paper:

'Temperature-controlled conversion from Fe–Si particles to integrated Fe–Si/ SiO2 core–shell structure particles during fluidised bed chemical vapour deposition'

L. Liu, X.W. Liao, J.X. Jia, H. Konga, X.A. Fan, Z.Y. Wu, X.S. Wang, Ceramics International 2020, 46, 3059-3065

 

hence, it lacks scientific novelty and cannot be published.

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Issues I have with reference in XPS section:

[32]: The line it is sited does not reflect the same thing in the reference. They talked about the XRD patterns of MCM-41. The reference does not speak about XPS. Should site proper reference instead of this reference or remove it. It is a nature paper. It never mentions anything about this Q1, Q2, Q3, and Q4 group related to the text.

[33] It is not a nature paper. It was published in JACS. It is discussed only based on XRD, NMR, and adsorption isotherm. How can it be like XPS?  The material mentioned in the reference is compositionally different than the author's content.

[34] Do not at all talked about the same thing which authors are stating in the text. It has XPS data, which has only N1 spectra. So, it does not go anything close mentioned in the article.

[35] It is based on NMR. Here Q1, Q2, Q3, and Q4 group is categorized based on NMR. How authors can relate it with XPS. They are two different tools of analysis.

[36] FTIR based. Somewhat related with Q1, Q2, Q3, and Q4 group but do not have any XPS data. Can be kept

[37] has nothing mentioned regarding XPS.

[38] It do not mark as anything regarding those O1 spectra which authors cited for.

For  XPS authors need to cite proper references at least related to the same bond groups closely related to Authors' work. It seems to me authors have read the references they are citing. They are citing references randomly without properly looking into it. This is callous and unacceptable.

Line 49: Reference 17 and 18 do not have the same first author, so how could you start with et al. with only one in the first sentence. Change it.

Reference 14 to 16 do not have anybody named as first author Yan. It is wrongly mentioned. You can say, Yan and coworkers.

Line 201: Do not have any reference to support Si2p peaks. Why?

Figure 2 (a) The marked regions in Inset is not visible. The reader can barely see what the authors have written to the corresponding highlighted section.

In the Supplementary regarding Fe2p peak, authors mention they assigned the Fe2p spectra according to this article “Materials Science and Engineering of Powder Metallurgy, 2018, 23(1): 63-69.” What is the title of the article? Need to provide the whole citation with authors and article name. Such a way of citation is not acceptable.

 

 

Author Response

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Reviewer 2 Report

This paper describes the coating of Fe-6.5wt.%Si with SiO2 using fluidized bed chemical vapor deposition. I have had a careful look at the authors’ responses and at the modifications performed in the manuscript. I am satisfied of the changes made, and in my opinion the paper can be accepted for publication in MDPI Metals.

 

Author Response

Dear Reviewer:

 

Point 1: This paper describes the coating of Fe-6.5wt.%Si with SiO2 using fluidized bed chemical vapor deposition. I have had a careful look at the authors’ responses and at the modifications performed in the manuscript. I am satisfied of the changes made, and in my opinion the paper can be accepted for publication in MDPI Metals. 


 

Response 1: Thanks for the anonymous Reviewer’s careful work and thoughtful suggestions that have helped improve this paper substantially.

Reviewer 3 Report

As an answer to the authors about iron content determination, ICP-AES would be a method of choice to get value the closest to the real iron content.

Author Response

Dear Reviewer:

 

Point 1: As an answer to the authors about iron content determination, ICP-AES would be a method of choice to get value the closest to the real iron content. 


 

Response 1: It is really true that ICP-AES is an efficient way to obtain the iron content in the Fe-6.5wt.%Si/SiO₂ C-S particles, and we will also pay more attention to the use of ICP-AES characterization in the future work. Thanks for the anonymous Reviewer’s careful work and thoughtful suggestions that have helped improve this paper substantially.