**4. Conclusions**

Strontium zirconate SrZrO3 was sprayed by a high feed-rate water-stabilized plasma torch, WSP, with a spray rate over 10 kg per hour to form a thick film. The as-sprayed coatings exhibited a lamellar microstructure and a relatively high porosity of over 23%. This thick film, considered as a thermal barrier coating (TBC), was now studied in interaction with natural silicate dust, so called CMAS, at 1250 ◦C. The crystalline as-sprayed coating was amorphized, whereas the resting crystalline proportion transformed to different phases than SrZrO3, namely monoclinic ZrO2 and SrSiO3. The proportion of these predominant phases varied with time of annealing (i.e., CMAS attack), whereas the general trend to crystallization of the amorphous content with longer dwell time was shown by XRD. The whole thickness of the influenced layer was as large as up to 333 μm. This is a typical thickness of the whole TBC coating in many industrial applications. SEM and EDX observation of the cross sections showed, also, an Al-rich component. The cracks' formation selectively in the Sr-rich component and absence in the Al-rich component were observed as one of the results of CMAS attack, whereas the most dangerous through-thickness cracks were absent. A sintered mixture of powders (CMAS plus SrZrO3 spray feedstock) demonstrated the appearance of the most "exotic" phase-Na4Ca4(Si6O18) combeite. This component is luminescent, as was shown in our work, whereas contribution of SrSiO3 to the luminescence of the sintered mixture is also highly probable. Due to SrSiO3 presence, the coatings after interaction with CMAS are also partly luminescent. We sugges<sup>t</sup> using the luminescence as a fast and cheap diagnostic technique of CMAS presence/absence in the structure of a potential SrZrO3-based TBC.

**Author Contributions:** Conceptualization, P.C.; methodology, P.C.; writing—original draft preparation, P.C.; writing—review and editing, P.C.; XRD and SEM analyses were arranged externally as barter services or paid services; other processing and analyses, P.C. All authors and collaborators have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The author would like to thank to XRD (Petr Bezdiˇcka) and SEM (Petr Veselý) operators.

**Conflicts of Interest:** The author declares no conflict of interest.
