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A 2 B 2 O 7 oxides with pyrochlore or defected fluorite structure are among the most promising candidates for insulation layer material in thermal barrier coatings. The present paper presents the procedure of synthesis of holmium zirconate Ho 2 Zr 2 O 7 and praseodymium zirconate Pr 2 Zr 2 O 7 via Polymerized-Complex Method (PCM). Thermal analysis of precursor revealed that after calcination at relatively low temperature (700°C) fine-crystalline, single-phase material is obtained. Thermal diffusivity was measured in temperature range 25-200°C, Ho 2 Zr 2 O 7 exhibits lower thermal diffusivity than Pr 2 Zr 2 O 7 . Additionally, PrHoZr 2 O 7 was synthesized. The powder in as-calcined condition is single-phase, but during the sintering decomposition of solid solution took place and Ho-rich phase precipitated. This material exhibited the best insulating properties among the tested ones.

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“…As the samples contained micropores, the measured values were adjusted using following equation [12]:…”

Section: Characterizationmentioning

confidence: 99%

Synthesis, Characterization and Thermal Diffusivity of Holmium and Praseodymium Zirconates

Stopyra¹,

Niemiec²,

Moskal³

2016

Archives of Metallurgy and Materials

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“…7 The oxygen vacancies in YSZ are believed to have a major effect on thermal transport, but their interactions with phonons are not understood.…”

Section: Introductionmentioning

confidence: 99%

Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia

Smith

Lan

et al. 2015

Phys. Rev. B

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Inelastic neutron scattering measurements on monoclinic zirconia (ZrO2) and 8 mol% yttriumstabilized zirconia were performed at temperatures from 300 to 1373 K. Temperature-dependent phonon densities of states (DOS) are reported, as are Raman spectra obtained at elevated temperatures. First-principles lattice dynamics calculations with density functional theory gave total and partial phonon DOS curves, and mode Grüneisen parameters. These mode Grüneisen parameters were used to predict the experimental temperature dependence of the phonon DOS, with partial success. However, substantial anharmonicity was found at elevated temperatures, especially for phonon modes dominated by the motions of oxygen atoms. Yttrium-stabilized zirconia (YSZ) was somewhat more anharmonic, and had a broader phonon spectrum at low temperatures, owing in part to defects in its structure. YSZ also has a larger vibrational entropy than monoclinic zirconia.

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“…This value was several times smaller than when using a quartz sand support [29,34]. The thermal conductivity of YSZ materials was about 3 W m À1 K À1 at 25 C [35], smaller than that of silica quartz (~7 W m À1 K À1 at 27 C) [36]. However, the great fluidity and narrow particle size distribution of YSZ spheres resulted in a close packing of the catalytic bed, without cracks that were usually seen in packed beds made with impregnated materials [34,37].…”

mentioning

confidence: 80%

“…Advantages of these YSZ spheres were their narrow particle size distribution, good fluidity, and mechanical/chemical inertness, which allowed for a randomly packed catalytic bed inside the LTCC micro-reactor with minor risks for cracking or large void formation. Their low heat conductivity (~2 W m À1 K À1 at 500 C [35]) may be a disadvantage to the packed-bed from a heat transfer point of view, though. The catalyst pellets were prepared as follows in weight: 15% of catalyst nanoparticles and 85% of calcined, washed and dried YSZ spheres were mixed via a dry milling process without additional milling media for 4 h. The surface area of as-prepared catalyst pellets were evaluated by BrunauereEmmetteTeller (BET) measurements (AutoChem II 2920, Micromeritics Instrument Corp., USA).…”

Section: Catalyst Loadingmentioning

confidence: 99%