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The effect of a galia (Ga2O3) addition on the crystallographic phase evolution and the crystal growth behavior of zirconia (ZrO2) rich powder were investigated. Binary compositions of galia-zirconia powder (on the zirconia-rich side of the quasi-binary phase diagram) were obtained by the sol-gel method and calcined at different temperatures for 2 h. Rietveld refinement (FullProf program) was used to determine the crystallographic phase composition. Crystal size was approximated based on X-ray diffractions analysis combined with estimates of average crystal size obtained by processing high-resolution scanning electron microscopy images. The surface area of the powders obtained was measured via the Brunauer-Emmett-Teller method. Zirconia-galia sol-gel powders were found to form tetragonal or mixed tetragonal-monoclinic solid solution phases depending on both composition and calcination temperature. It was shown that galia suppressed crystal growth process in zirconia, producing finer nano-powders with higher surface area compared to pure zirconia. [ABSTRACT FROM AUTHOR]

The effect of a galia (Ga2O3) addition on the crystallographic phase evolution and the crystal growth behavior of zirconia (ZrO2) rich powder were investigated. Binary compositions of galia-zirconia powder (on the zirconia-rich side of the quasi-binary phase diagram) were obtained by the sol-gel method and calcined at different temperatures for 2 h. Rietveld refinement (FullProf program) was used to determine the crystallographic phase composition. Crystal size was approximated based on X-ray diffractions analysis combined with estimates of average crystal size obtained by processing high-resolution scanning electron microscopy images. The surface area of the powders obtained was measured via the Brunauer-Emmett-Teller method. Zirconia-galia sol-gel powders were found to form tetragonal or mixed tetragonal-monoclinic solid solution phases depending on both composition and calcination temperature. It was shown that galia suppressed crystal growth process in zirconia, producing finer nano-powders with higher surface area compared to pure zirconia. [ABSTRACT FROM AUTHOR]

Zirconia (ZrO2) and yttria-stabilized-zirconia (YSZ) are known as advanced oxides, widely applied in gas-turbine engines, fuel cells and other applications, requiring controlled thermal conductivity values. In the current research hot-pressed ZrO2–8YSZ composites, were synthesized. The effect of the three apparent phases, 8YSZ, ZrO2 and the pores on the thermal conductivity was analyzed using the general effective media (GEM) approach, while considering their relative amounts and morphology. [ABSTRACT FROM AUTHOR]

Rare-earth (RE) oxides are important in myriad fields, including metallurgy, catalysis, and ceramics. However, the phase diagram of RE oxides in the nanoscale might differ from the phase diagrams for bulk, thus attracting attention nowadays. We suggest that grain size in the nanoscale also determines the obtained crystallographic phase along with temperature and pressure. For this purpose, nanoparticles of Sm 2 O 3 and Eu 2 O 3 were mixed in an inert MgO matrix via the sol-gel method. This preparation method allowed better isolation of the oxide particles, thus hindering the grain growth process associated with increasing the temperature. The mixed oxides were compared to pure oxides, which were heat-treated using two methods: gradual heating versus direct heating to the phase transition temperature. The cubic phase in pure oxides was preserved to a higher extent in the gradual heating treatment compared to the direct heating treatment. Additionally, in MgO, even a higher extent of the cubic phase was preserved at higher temperatures compared to the pure oxide, which transformed into the monoclinic phase at the same temperature in accordance with the phase diagram for bulk. This indicates that the cubic phase is the equilibrium phase for nanosized particles and is determined also by size.

Zirconia (ZrO2) and yttria-stabilized-zirconia (YSZ) are known as advanced oxides, widely applied in gas-turbine engines, fuel cells and other applications, requiring controlled thermal conductivity values. In the current research hot-pressed ZrO2-8YSZ composites, were synthesized. The effect of the three apparent phases, 8YSZ, ZrO2 and the pores on the thermal conductivity was analyzed using the general effective media (GEM) approach, while considering their relative amounts and morphology.