Synthesis and thermal stability of ZrO 2 @SiO 2 core-shell submicron particles

• Published in: RSC advances 2019-08, Vol.9 (46), p.26902-26914
• Main Authors: Finsel, Maik, Hemme, Maria, Döring, Sebastian, Rüter, Jil S V, Dahl, Gregor T, Krekeler, Tobias, Kornowski, Andreas, Ritter, Martin, Weller, Horst, Vossmeyer, Tobias
• Format: Article
• Language: English
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c9ra05078g

ZrO @SiO core-shell submicron particles are promising candidates for the development of advanced optical materials. Here, submicron zirconia particles were synthesized using a modified sol-gel method and pre-calcined at 400 °C. Silica shells were grown on these particles (average size: ∼270 nm) with well-defined thicknesses (26 to 61 nm) using a seeded-growth Stöber approach. To study the thermal stability of bare ZrO cores and ZrO @SiO core-shell particles they were calcined at 450 to 1200 °C. After heat treatments, the particles were characterized by SEM, TEM, STEM, cross-sectional EDX mapping, and XRD. The non-encapsulated, bare ZrO particles predominantly transitioned to the tetragonal phase after pre-calcination at 400 °C. Increasing the temperature to 600 °C transformed them to monoclinic. Finally, grain coarsening destroyed the spheroidal particle shape after heating to 800 °C. In striking contrast, SiO -encapsulation significantly inhibited grain growth and the → transition progressed considerably only after heating to 1000 °C, whereupon the particle shape, with a smooth silica shell, remained stable. Particle disintegration was observed after heating to 1200 °C. Thus, ZrO @SiO core-shell particles are suited for high-temperature applications up to ∼1000 °C. Different mechanisms are considered to explain the markedly enhanced stability of ZrO @SiO core-shell particles.