Comparative Study of Cold Sintering Process and Autoclave Thermo-Vapor Treatment on a ZnO Sample

Round 1

Reviewer 1 Report

Please check the followings:

1. line #64 - 67: please check the paragraph.
2. line #297: in the study of the mechanism ~  → In the study of ~
3. line #301:  in "When the velocities of these stages approach", What are the velocities?

Author Response

Comments and Suggestions for Authors

Please check the followings:

1. line #64 - 67: please check the paragraph.

Answer to the comment. Thank you, we checked the paragraph and found the absence of the verb. We suggest the following variant of the paragraph (line #63 – 66 after revising): «In this work, was study the effect of two activating additives – zinc acetate Zn (CH₃COO)2·2H₂O and ammonium chloride NH₄Cl on the recrystallization of ZnO during autoclave treatment in water vapor under free powder filling conditions and under CSP in a similar environment, but with the application of mechanical pressure».

2. line #297: in the study of the mechanism ~ → In the study of ~

Answer to the comment. Thank you, we’ve revised this mistake (line #300).

3. line #301: in "When the velocities of these stages approach", What are the velocities?

Answer to the comment. Thank you for your important comment. We offer the following explanation (line #303 – 305): «When the velocities of hydroxylation and dihydroxylation processes become approximately equal, a quasi-equilibrium of the particle with the medium is established».

For your convenience, we have attached the answer in a separate Word file.

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors investigated the crystal growth behavior under CSP and TVT treatment with different solvents and pressure. As most recent studies on CSP have focused on the densification of the ZnO-acetic acid (or Zn-acetate) system, this manuscript would provide another aspect of the crystal (or grain) growth of ZnO by the mass transport via pressure-solutions. The discussion part also includes detailed insights while contrasting to the reported result in the literature.
The reviewer would suggest the following points for the publication in Crystals;

- Figure 7 needs to be improved in terms of the resolution and the caption. It would be helpful for readers to add what corresponds to the black, green and blue peaks in the caption. If XRD data of CSP1-4 and TVT1-4 are available, it may be informative to show if the trend in FWHM of the peak consistent with the trend in the crystal size determined by SEM.
- Density measurement by the Archimedean method is sometimes difficult for the samples with open-pores. The reviewer suggests checking the densities of CSP 1-4 again by the geometric method and seeing if the reported values by Archimedean are reasonable.
- Authors reported some impurity phases in CSP-4. Do authors use the theoretical density of pure-ZnO when calculating the relative density of the specimen? As the impurity phases seem not to be minor, it could affect the reported density values. Ideally, the pycnometric method is useful to estimate the theoretical density for such mixed-phase specimens. At least, the estimated error values should be given in table 4.
- There are typos using C instead of °C. These points need to be fixed before publication.

- In line 169, "CS4" should be "CSP4"

Author Response

Comments and Suggestions for Authors

The authors investigated the crystal growth behavior under CSP and TVT treatment with different solvents and pressure. As most recent studies on CSP have focused on the densification of the ZnO-acetic acid (or Zn-acetate) system, this manuscript would provide another aspect of the crystal (or grain) growth of ZnO by the mass transport via pressure-solutions. The discussion part also includes detailed insights while contrasting to the reported result in the literature.

The reviewer would suggest the following points for the publication in Crystals:

1. Figure 7 needs to be improved in terms of the resolution and the caption. It would be helpful for readers to add what corresponds to the black, green and blue peaks in the caption. If XRD data of CSP1-4 and TVT1-4 are available, it may be informative to show if the trend in FWHM of the peak consistent with the trend in the crystal size determined by SEM.

Answer to the comment. Thank you, we have improved the resolution and added appropriate descriptions in the caption: « Figure 7. X-ray patterns of samples: (a) CSP1; (b) CSP4; (c) TVT4: black – full spectrum; green - the spectrum is shown with increased sensitivity for the low-intensity reflexes detection; green dots – reflexes of unidentified phase».

Unfortunately, we have not made XRD for all samples. Also, the size of the coherent scattering region (about 90 nm) is significantly smaller than the size of grains and crystals. A change in the size of the coherent scattering regions may indicate an ordering of the structure. These data for TVT can be found in the article on ZnO recrystallization (reference [19]). In this paper, we investigated only mass transfer, and grain size change-ordering of the structure is a separate study topic.

2. Density measurement by the Archimedean method is sometimes difficult for the samples with open-pores. The reviewer suggests checking the densities of CSP 1-4 again by the geometric method and seeing if the reported values by Archimedean are reasonable.

Answer to the comment. Thank you for your valuable comment. Unfortunately, we do not have the whole samples of СSP1-4, as we fractured them for SEM.

3. Authors reported some impurity phases in CSP-4. Do authors use the theoretical density of pure-ZnO when calculating the relative density of the specimen? As the impurity phases seem not to be minor, it could affect the reported density values. Ideally, the pycnometric method is useful to estimate the theoretical density for such mixed-phase specimens. At least, the estimated error values should be given in table 4.

Answer to the comment. Thank you for a significant comment. In future studies, we plan to use the pycnometric method. We believe that there are trace amounts of impurity phases, and these phases can be neglected to estimate the density. We added the density measurement estimated error and the crystal and grain size calculation error to table 4.

4. There are typos using C instead of °C. These points need to be fixed before publication.

Answer to the comment. Thank you, we’ve fixed it (252, 263, 265, 275, 351).

5. In line 169, "CS4" should be "CSP4".

Answer to the comment. Thank you, we’ve fixed it (line #219).

We carefully checked all the text, figures, and tables and found many inaccuracies and errors. We tried to fix everything. All revisions are highlighted using the "Track Changes" function in Microsoft Word.

For your convenience, we have attached all the answers in a separate Word file.

Please see the attachment.

Author Response File: Author Response.docx