Lomonosov Institute of Fine Chemical Technologies, MIREA – Russian Technological University, Moscow, Russia

N. V. Grechishnikov, Postgraduate Student at the Department of Chemistry and Technology of Rare Elements, e-mail: nklgrchshnkv@yandex.ru
E. E. Nikishina, Associate Professor at the Department of Chemistry and Technology of Rare Elements, Candidate of Chemical Sciences, e-mail: nikishina@mirea.ru

Baykov Metallurgy and Materials Institute at the Russian Academy of Sciences, Moscow, Russia
A. A. Ilyicheva, Senior Researcher at the Laboratory for Physicochemistry of Barothermal Processes, e-mail: ailyicheva@imet.ac.ru
L. I. Podzorova, Lead Researcher at the Laboratory for Physicochemistry of Barothermal Processes, Candidate of Chemical Sciences, e-mail: lpodzorova@imet.ac.ru

Zirconates of rare elements are of particular value in the production of thermal barrier coatings for nuclear, aviation and aerospace units and power plants. The problem of developing new and optimizing the existing techniques for obtaining zirconates of rare elements is of relevance today. This paper considers a dilution method for obtaining europium zirconate from dry zirconium hydroxide and europium acetate while applying microwaves at the drying stage. The authors looked at the effect produced by the state of dry zirconium hydroxide (in the form of powder and gel) and microwave drying on the phase composition of the final product. With the help of X-ray phase analysis, the authors established that, in the air drying process, the use of dry hydroxide in the gel form does not lead to any noticeable increase in the concentration of the target pyrochlore phase when compared with the use of dry zirconium hydroxide powder. Microwave treatment does not lead to any significant increase in the amount of pyrochlore phase in the final product when using dry zirconium hydroxide powder. At the same time, the concentration of the pyrochlore phase rises to 26% when using dry zirconium hydroxide gel. However, an infrared spectroscopy study showed no difference between the middlings before baking that were produced from dry zirconium hydroxide powder and gel and that were air dried and microwave treated. On the basis of these outcomes, a conclusion was drawn that due to the use of dry zirconium hydroxide gel followed by microwave treatment of the reaction mixture, one can save time and energy required for drying, as well as raise the concentration of the target pyrochlore phase in the final product.

1. Chen H. F., Zhang C., Liu Y. C., Song P. et al. Recent progress in thermal/environmental barrier coatings and their corrosion resistance. Rare Metals. 2020. Vol. 39, No. 5. pp. 498–512.
2. Wu S., Zhao Y., Li W., Liu W. et al. Research progresses on ceramic materials of thermal barrier coatings on gas turbine. Coatings. 2021. Vol. 11, No. 1. 79.
3. Zhang J., Guo X., Jung Y. G., Li L., Knapp J. Lanthanum zirconate based thermal barrier coatings: A review. Surface and Coatings Technology. 2017. Vol. 323. pp. 18–29.
4. Subramanian M. A., Aravamudan G., Subba Rao G. V. Oxide pyrochlores – A review. Progress in Solid State Chemistry. 1983. Vol. 15, Iss. 2. pp. 55–143.
5. Fuentes A. F., Montemayor S. M., Maczka M., Lang M. et al. A critical review of existing criteria for the prediction of pyrochlore formation and stability. Inorganic Chemistry. 2018. Vol. 57. pp. 12093–12105.
6. Liu Q., Huang S., He A. Composite ceramics thermal barrier coatings of yttria stabilized zirconia for aero-engines. Journal of Materials Science and Technology. 2019. Vol. 35, No. 12. pp. 2814–2823.
7. Li Y., Kowalski P. M., Beridze G., Birnie A. R. et al. Defect formation energies in A₂B₂O₇ pyrochlores. Scripta Materialia. 2015. Vol. 107. pp. 18–21.
8. Wang S., Li W., Wang S., Chen Z. Synthesis of nanostructured La₂Zr₂O₇ by a non-alkoxide sol-gel method: From gel to crystalline powders. Journal of the European Ceramic Society. 2015. Vol. 35, Iss. 1. pp. 105–112.
9. Gao L., Zhu H., Wang L., Ou G. Hydrothermal synthesis and photoluminescence properties of Gd₂Zr₂O₇:Tb³⁺ phosphors. Materials Letters. 2011. Vol. 65, Iss. 9. pp. 1360–1362.
10. Srinivasulu K., Manisha Vidyavathy S. Effect of different calcination techniques on the morphology and powder flowability characteristics of rare-earth zirconates (Re₂Zr₂O₇; Re = La, Gd, Nd, Y) synthesized by solid-state highenergy milling process. Journal of Ceramic Processing Research. 2019. Vol. 20, No. 1. pp. 8–17.
11. Brykała U., Tomaszewski H., Diduszko R., Węglarz H. et al. A new material in the nuclear technology: gadolinium zirconate pyrochlore prepared by reactive sintering. Journal of Radioanalytical and Nuclear Chemistry. 2014. Vol. 299. pp. 637–641.
12. Lu X., Chen M., Dong F., Wang X., Wu Y. et al. Leaching stability of simulated waste forms for immobilizing An3+ by Gd2Zr2O7 with Nd³⁺. Journal of Wuhan University of Technology, Materials Science Edition. 2014. Vol. 29, No. 5. pp. 885–890.
13. Liu C., Zou B., Rondinone A. J., Zhang Z. J. Sol-gel synthesis of freestan ding ferroelectric lead zirconate titanate nanoparticles. Journal of the American Chemical Society. 2001. Vol. 123, Iss. 18. pp. 4344, 4345.
14. Kong L., Karatchevtseva I., Gregg D. J., Blackford M. G. et al. A novel chemical route to prepare La2Zr2O7 pyrochlore. Journal of the American Ceramic Society. 2013. Vol. 96, No. 3. pp. 935–941.
15. Kong L., Karatchevtseva I., Gregg D. J., Blackford M. G. et al. A novel chemical route to prepare La2Zr2O7 pyrochlore. Journal of the American Ceramic Society. 2013. Vol. 96, Iss. 3. pp. 935–941.
16. Zhukov A. V., Chizhevskaya S. V., Pjo P., Panov V. A. Heterophase synthesis of zirconium hydroxide from zirconium oxychloride. Neorganicheskie materialy. 2019. Vol. 55, No. 10. pp. 1051–1058.
17. Colomer M. T. Straightforward synthesis of Ti-doped YSZ gels by chemical modification of the precursors alkoxides. Journal of Sol-Gel Science and Technology. 2013. Vol. 67, No. 1. pp. 135–144.
18. Imran M., Singh V. V., Garg P., Mazumder A. et al. In-situ detoxification of schedule-I chemical warfare agents utilizing Zr(OH)₄@W-ACF functional material for the development of next generation NBC protective gears. Scientific Reports. 2021. Vol. 11, No. 1. pp. 1–21.
19. Kalinkin A. M., Vinogradov V. Yu., Kalinkina E. V. Solid-phase synthesis of nanocrystalline gadolinium zirconate using mechanical activation. Neorganicheskie materialy. 2021. Vol. 57, No. 2. pp. 189–196.
20. Aghazadeh M., Barmi A. A. M., Hosseinifard M. Nanoparticulates Zr(OH)4 and ZrO2 prepared by low-temperature cathodic electrodeposition. Materials Letters. 2012. Vol. 73. pp. 28–31.