title: Synthesis and thermal stability of zirconia and yttria-stabilized zirconia microspheres.
abstract: OBJECTIVE
  Zirconia microparticles produced by sol-gel synthesis have great potential for photonic applications. To this end, identifying synthetic methods that yield reproducible control over size uniformity is important. Phase transformations during thermal cycling can disintegrate the particles. Therefore, understanding the parameters driving these transformations is essential for enabling high-temperature applications. Particle morphology is expected to influence particle processability and stability. Yttria-doping should improve the thermal stability of the particles, as it does in bulk zirconia.
  
  
  METHODS
  Zirconia and YSZ particles were synthesized by improved sol-gel approaches using fatty acid stabilizers. The particles were heated to 1500 °C, and structural and morphological changes were monitored by SEM, ex situ XRD and high-energy in situ XRD.
  
  
  RESULTS
  Zirconia particles (0.4-4.3 μm in diameter, 5-10% standard deviation) synthesized according to the modified sol-gel approaches yielded significantly improved monodispersities. As-synthesized amorphous particles transformed to the tetragonal phase at ∼450 °C with a volume decrease of up to ∼75% and then to monoclinic after heating from ∼650 to 850 °C. Submicron particles disintegrated at ∼850 °C and microparticles at ∼1200 °C due to grain growth. In situ XRD revealed that the transition from the amorphous to tetragonal phase was accompanied by relief in microstrain and the transition from tetragonal to monoclinic was correlated with the tetragonal grain size. Early crystallization and smaller initial grain sizes, which depend on the precursors used for particle synthesis, coincided with higher stability. Yttria-doping reduced grain growth, stabilized the tetragonal phase, and significantly improved the thermal stability of the particles.
authors: Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany.
authors: Elisabeth W
authors: EW
authors: Leib
authors: Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, 21502 Geesthacht, Germany.
authors: Ulla
authors: U
authors: Vainio
authors: Institute of Advanced Ceramics, Hamburg University of Technology (TUHH), Denickestraße 15, 21073 Hamburg, Germany.
authors: Robert M
authors: RM
authors: Pasquarelli
authors: Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany.
authors: Jonas
authors: J
authors: Kus
authors: Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany.
authors: Christian
authors: C
authors: Czaschke
authors: Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany.
authors: Nils
authors: N
authors: Walter
authors: Institute of Advanced Ceramics, Hamburg University of Technology (TUHH), Denickestraße 15, 21073 Hamburg, Germany.
authors: Rolf
authors: R
authors: Janssen
authors: Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, 21502 Geesthacht, Germany.
authors: Martin
authors: M
authors: Müller
authors: Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, 21502 Geesthacht, Germany.
authors: Andreas
authors: A
authors: Schreyer
authors: Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany; The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany; Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia.
authors: Horst
authors: H
authors: Weller
authors: Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany. Electronic address: tobias.vossmeyer@chemie.uni-hamburg.de.
authors: Tobias
authors: T
authors: Vossmeyer
keywords: Ceramic; Microspheres; Phase transformation; Thermal barrier coating; YSZ; Zirconia