A Comparative Study of YSZ Suspensions and Coatings
Round 1
Reviewer 1 Report
Please see line 71, 78, 128, 184- an error in the formatting of references is present in the document.
In Section 2.1 Suspension and feed material - Are the authors able to comment the source of the fine powder that was used for the home-made suspensions (HM1 and HM2)? And what its initial particle size distribution was?
Line 89 – information on Anton Paar is missing
Line 92 – mentions manual hand shaking of the commercial suspensions. Is it not recommended by the manufacturers a form of machine mixing for the suspensions? Is it possible that this influenced the measurement of particle size distribution?
For surface tension calculations, the authors state that 0.95 g/mm3 were used for all suspension densities. However, it is discussed in Section 2.2 that suspension densities were different for the suspensions and that they fluctuated during the coating process. Could the authors comment if this variation between suspensions would cause a noticeable variation in calculated surface tension?
For plasma spray conditions, the torches used here are of different technical generation (the 3MB being much older) and of differing size and envisaged end use. The power output level for both torches for the parameters selected would be of interest to the Reader for comparison purposes.
In Section 3.1.2 Particle size distributions – Table 4 gives information on original powder size. Was this measured by the authors or is it information from the powder/suspension manufacturer? Could the authors comment on how well the measurement of powder particle size correlates to the dried powder particles seen in Figure 3? It seems that especially in the case of C1, the measurement does not match well with the size of the particles observed in the image.
In Section 3.1.4 Viscosity - the authors state that the addition of surfactant to the commercial suspension (C3) and the measured increase in viscosity may be due to underdosing of the surfactant. Could it also be that the added surfactant reacts with surfactants already present in the commercial suspension, influencing the viscosity?
In the results section on Axial III microstructures; the standoff distance utilized for spraying is quite short for an Axial III torch. For spray systems operating with high gas flows like the 100HE or Axial III, it would seem the typical standoff distance would be roughly 3 inches or 70-75 mm from other reported works (e.g., Zhou et al., doi:10.3390/coatings7080120). Could the authors comment on the possible influence of the standoff distance on the coating structures (Figure 8) produced? Given the difference in powder particle size, is it possible that larger particles or droplets would show higher momentum at short stand-off distances and therefore columnar coatings would be less likely to form in this case?
Ganvir et al. (https://doi.org/10.1016/j.jeurceramsoc.2018.09.023) recently published a paper studying similar suspension influences on SPS coating formation using the same commercial suspensions and Axial III torch. The article also discusses atomization, droplet size, momentum and flight path that are relevant to the deposition of coatings performed in the work presented here. It would be of value to the article to reference and compare to this work as many of the same suspension analysis methods were undertaken.
Author Response
Dear editor (s) and Reviewers,
We thank you for your valuable feedback and comments to improve the quality of the presented work. Your comments are well received and applied to the manuscript. The questions are also responded here. We hope that the present version can satisfy the reviewers.
The reviewer’s comments in the attached file are in black and the corresponding responses in red.
Best Regards,
Fariba Tarasi
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article, entitled “A Comparative Study of YSZ Suspensions and Coatings”, has been carefully reviewed. As the needs are increasing in many fields, the plasma spraying technique become important, and the author’s approach investigating the microstructural changes by the suspensions is also great. However, some inconsistent parts make it hard to provide a clear message to readers. Until those parts are amended, I don’t think the article can be published at this journal.
1. Although the author intended to show the suspension based on fine powder forms somewhat agglomeration after the solvent drying, this observation is not connected to the main results of this work, microstructure of the deposited film. I cannot find any reason why figure 2 is needed.
2. Experimental part should contain information of the characterization method. In particular, the method to measure surface tension of the suspensions is not clearly seen.
3. I cannot agree with the authors’ explanation about the relationship between particle size and microstructure shown on page 9 to 10. Basically, reducing particle sizes are more beneficial to form dense structure. It is because that smaller sizes of particles are easier to fill up the space between particles on the deposited surface.
As the authors mentioned, there are possibly deviated particles from the mainstream in some amounts, but major film deposition should happen by the particles in the mainstream and the effect of the deviated particles should be very limited. And, the shadowing effect mentioned in the explanation is not understandable, either. For better understanding, it is required to add conceptual images briefly showing your suggestion.
I recommend for the authors to provide more general and acceptable mechanism for the reasons of the consequent microstructures. Kinetic energy and size of the injected droplets, which are considered keys in determining the microstructure of the deposited films.
Minor comments: The author should carefully revise the use of spaces and superscript/subscript, especially for units. I found many of such errors that deteriorates completeness of the document.
Author Response
Dear editor (s) and Reviewers,
We thank you for your valuable feedback and comments to improve the quality of the presented work. Your comments are well received and applied to the manuscript. The questions are also responded here. We hope that the present version can satisfy the reviewers.
The reviewer’s comments in the attached file are in black and the corresponding responses in red.
Best Regards,
Fariba Tarasi
Author Response File: Author Response.pdf
Reviewer 3 Report
In the work, the authors study the influence of the suspension preparation method and aging on the microstructure of suspension plasma sprayed coatings with two suspension injection configurations: radial and axial. In the case of radial injection the major influence of viscosity of the suspension is observed. In the case of axial injection the author show that another parameter is of higher influence, they speculate the effect of the particles geometry.
Even if the study is not a systematic study but rather based on the comparison of some specific suspensions, it is however convincing and the authors well define the limits of the conclusions they draw. Some information is missing (PVP, D50 in volume or in number). The discrepancy between the low values of D50 for HM1 and the large agglomerates observed by SEM needs to be discussed.
1) l.76 Please provide precise information on PVP raw material : mol wt, supplier, …
2) l.90 Please provide Anton-Paar company’s info (and remove the sentence in the text “provide Anton-Paar company’s info”..)
3) Figure 1 is not necessary, the set-up is rather simple and is detailed in the text.
4) Table 2 and Table 3:
"Suspension name" instead of “supplier”
"Injector diameter" instead of “injector dia.”
"Number of passes" instead of “# of Passes”
5) Table 4 : Please precise whether the particle size distribution is related to the volume or to the number of particles? Probably in volume as usual and as stated in the conclusion?
6) There is a discrepancy between the particle sizes observed by SEM in figure 2, with small particle around 0.4µm but also agglomerates up to 50µm (as stated in l. 130); and the value of D50 of 0.4 µm given for this suspension in table 4. Please discuss on this point. The graph of the particle size distribution would be useful in this case.
Missing links “Error! Reference source not found”
Author Response
Dear editor (s) and Reviewers,
We thank you for your valuable feedback and comments to improve the quality of the presented work. Your comments are well received and applied to the manuscript. The questions are also responded here. We hope that the present version can satisfy the reviewers.
The reviewer’s comments in the attached file are in black and the corresponding responses in red.
Best Regards,
Fariba Tarasi
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Dear Authors,
Thank you for taking time to elaborate on the earlier questions and points in the article.
There are two remaining points for clarfication,
The reviewer is familar with both of the industrial suspensions used in this study. Both companies are recommending machine rolling or tumbling for redispersion of the as delivered material.
Regarding the use of surfactants or other organics; Innovnano publically states that no stabilising agents are added to their suspension. This is not true in the case of Treibacher suspension.
The datasheet with the suspension shipment is not an indication of the presence of a surfactant (or absence of it), any addtion would likely not need to be declared unless it were dangerous or made up a significant portion of the composition. The same is true of polishing suspensions for metallography.
Author Response
Dear Editor(s) and Reviewers,
Thank you very much for taking your time in re-evaluation of the submitted manuscript. Please find here the responses to the latest comments.
The corrections beside track change, are highlighted in yellow in the article text.
Hope the corrections can be satisfactory.
Best Regards,
Fariba Tarasi
Author Response File: Author Response.pdf
Reviewer 2 Report
It is seen that the authors tried to sincerely respond to my comments. I recommend the manuscript to be published in this journal after minor corrections: font size in plots (too small), functional error messages, and typo/blanks.
Author Response
Dear Editor(s) and Reviewers,
Thank you very much for taking your time in re-evaluation of the submitted manuscript. Please find here the responses to the latest comments.
The corrections beside track change, are highlighted in yellow in the article text.
Hope the corrections can be satisfactory.
Best Regards,
Fariba Tarasi
Author Response File: Author Response.pdf
