Study of Gd₂O₃-Doped La₂(Zr_0.7Ce_0.3)₂O₇ Thermal Barriers for Coating Ceramic Materials for CMAS Resistance

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

The subject of the manuscript focused on a review study on Gd2O3 doping La2(Zr0.7 Ce0.3)2O7 thermal barrier coating ceramic materials CMAS-resistance is in good relevance with the scope of COATINGS.

 

After reviewing the content of the revised manuscript, I conclude that the authors made all the necessary corrections.  

 

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

The English could be improved to more clearly express the research.

The English level is really not good, will continue to improve in the future, if possible, according to the requirements of the journal English polishing and modification is also feasible.

Reviewer 2 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

This manuscript is the resubmitted version of the previous one submitted last month. Although this version appears somewhat improved, the authors did not pay adequate attention to revising the manuscript according to the previous comments.

Here are the comments that were ignored:

1. Most of the characterization results are not from surface-sensitive methods. Without surface-sensitive evidence, the results and discussions may not be valid. The XPS study is highly recommended for inclusion.
2. There is no explanation as to why LZCO is of interest over LCO, nor is there any rationale provided for selecting 30% Ce for this study. Please provide this information in the introduction section, including references.
3. Only a few references are cited in the results and discussion section.
4. The explanation for the Raman results must be more quantitative. The wavelength numbers must be stated, and the corresponding vibrational modes must be assigned, with a comparison to data in the literature. The effect of the dopant on the change in vibrational modes must also be explained.
5. The formula for the apatite phase must be given, and it is necessary to discuss in more detail how it is formed.
6. The scale bar for Figure 4 is missing.
7. The enthalpy changes related to the thermal processes shown in Figure 6 must be calculated and tabulated. Furthermore, the obtained data must be compared with literature values.
8. The XRF elemental composition data (Table 3.2) contain too many significant figures.
9. The authors must provide the corresponding EDS data for the points A, B, and C shown in Figure 8.
10. The experimental details are too vague. Additionally, the details regarding Raman and DSC measurements are missing. Please rewrite these sections and make them much more informative.
11. Most of the figures have poor resolution. Please improve them.

12. Why do the authors number their tables starting from 3.1 and 3.2 instead of 1 and 2?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

Although not all the comments have been fully addressed, the revised manuscript can be accepted for publication.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The focus of this manuscript is to study the CMAS resistance of a novel ceramic that may be used as a thermal barrier coating in turbine parts. However, TBCs are applied as coatings on the turbine parts with the use of HVOF or more commonly atmospheric plasma spray. In this manuscript the TBCs were produced by using sintering for the production of bulk samples. There are fundamental differences between coatings deposited with a process involving high thermal output and a solid state diffusion process to produce bulk alloys. The microstructures, the properties and the hot corrosion mechanisms are completely different. Is is thus concluded that the findings in this manuscript cannot be correlated with the equivalent coatings for turbine part protection.

Taking all the above into consideration, the manuscript cannot be accepted. If the authors can think of other potential applications that may benefit of this specific ceramic material in the form of bulk parts they may tailor the manuscript and resubmit.

Reviewer 2 Report

Comments and Suggestions for Authors

This work reports on the effect of Gd content in LGZC and its corrosion behavior. The concept is interesting and holds potential for providing valuable information in the field of aircraft engine development. However, the experimental design and characterization data presented are insufficient to support the authors' claims, and as such, this manuscript cannot be recommended for publication in its current form. The major issue with the manuscript is that the authors rely heavily on SEM-EDS for characterizing the corroded surfaces. This technique is not suitable for speciation of the corrosion products as the authors suggest. For example, how can the authors accurately determine the phase compositions of areas A, B, and C using only SEM-EDS? While XRD was conducted, it is not a surface-sensitive method. Without surface-sensitive evidence, the results and discussions may not be valid.

Further issues include:

1. There is no explanation as to why LZCO is of interest over LCO, nor is there any rationale provided for selecting 30% Ce for this study.
2. Only one reference is cited in the results and discussion section.
3. The formula for the apatite phase mentioned on page 7 is not provided. This should be included to clarify the phase discussed.
4. Numerical EDS elemental compositions are not given. The authors must provide these data and compare them with XRF results to strengthen their conclusions.
5. The scale bar for Figure 4 is missing.
6. The manuscript currently lacks SEM and EDS data for all experimental conditions. These data should be provided or supplemented to offer a comprehensive overview of the findings.
7. The number of results presented is relatively low compared to the standards of Coatings journal.

Reviewer 3 Report

Comments and Suggestions for Authors

The subject of the manuscript focused on study on Gd₂O₃ doping La₂(Zr_0.7 Ce_0.3)₂O₇ thermal barrier coating ceramic materials CMAS-resistance is in good relevance with the scope of COATINGS.

The presented work adds valuable information to the literature on the corrosion resistance of CMAS. However,  the manuscript requires the following corrections and additions:

1.    The innovative nature of the planned research should be more clearly defined in the introduction, as many studies have been devoted to this issue.

2.    Materials and methods are described, however, in order to enable replication of the research it is worth adding more details about the parameters used in the SEM and EDS analyses, e.g. the accelerating voltage in the SEM.

3.    3. In the "Results and Discussion" section it would be advisable to divide it into specific subsections, e.g. separately for XRD, SEM and EDS results, which would improve clarity.

4.    A more detailed discussion is recommended, e.g. by comparing the peak intensities before and after corrosion.

5.    In the analysis of results for different exposure times to high temperature (e.g. 5, 10, 20 h), a deeper discussion on the degradation mechanism would be useful.

6.    Scale information is missing in some SEM micrographs (Fig.4). Furthermore, the labels in Fig. 17 should be sorted out and provided only in English, which will improve the readability of this figure.

7.    Typos: "high-tempurature" → should be "high-temperature" (e.g. in the abstract), "depth depth" in the summary – repetition, "bearring" → should be "bearing" (in the introduction). In the title, the notation of chemical formulas should be corrected by inserting subscripts. Some sentences are very long and complicated. It is recommended to simplify them for better readability.

8.    In References, there is no consistency in the citation style, some items have shortened author names, others have full names. It is recommended to organize the literature according to MDPI guidelines, e.g. add DOI numbers where possible. Punctuation not in accordance with the editorial requirements.

In summary, the manuscript presents valuable results but requires substantive, linguistic, and organizational improvements to increase its readability and scientific value.

Comments on the Quality of English Language

 The English could be improved to more clearly express the research.