35 research outputs found
Effect of Pressure on Synthesis of Pr-Doped Zirconia Powders Produced by Microwave-Driven Hydrothermal Reaction
A high-pressure microwave reactor was used to study the hydrothermal synthesis of
zirconia powders doped with 1 mol % Pr. The synthesis was performed in the pressure range
from 2 to 8 MPa corresponding to a temperature range from 215C∘ to 305C∘. This technology
permits a synthesis of nanopowders in short time not limited by thermal inertia of the vessel.
Microwave heating permits to avoid contact of the reactants with heating elements, and is thus
particularly well suited for synthesis of doped nanopowders in high purity conditions.
A mixture of ZrO2 particles with tetragonal and monoclinic crystalline phases, about 15 nm in size, was obtained.
The p/T threshold of about 5-6 MPa/265–280C∘ was necessary to obtain good quality of
zirconia powder. A new method for quantitative description of grain-size distribution was applied, which is
based on analysis of the fine structure of the X-ray diffraction line profiles. It permitted to
follow separately the effect of synthesis conditions on the grain-size distribution of the
monoclinic and tetragonal phases
Effect of pressure on synthesis of Pr-doped zirconia powders produced by microwave-driven hydrothermal reaction
A high-pressure microwave reactor was used to study the hydrothermal synthesis of zirconia powders doped with 1 mol % Pr.The synthesis was performed in the pressure range from 2 to 8MPa corresponding to a temperature range from 215◦C to 305◦C.This technology permits a synthesis of nanopowders in short time not limited by thermal inertia of the vessel. Microwave heatingpermits to avoid contact of the reactants with heating elements, and is thus particularly well suited for synthesis of dopednanopowders in high purity conditions. A mixture of ZrO2 particles with tetragonal and monoclinic crystalline phases, about15nm in size, was obtained. The p/T threshold of about 5-6MPa/265–280◦C was necessary to obtain good quality of zirconiapowder. A new method for quantitative description of grain-size distribution was applied, which is based on analysis of the finestructure of the X-ray diffraction line profiles. It permitted to follow separately the effect of synthesis conditions on the grain-size distribution of the monoclinic and tetragonal phases
International Symposium on Air Pollution Abatement Catalysis APAC 2005, 21-24 September 2005, Cracow, Poland : book of extended abstracts
Grain size and grain size distibution of zro<>2<>:Pr ceramics nanopowders determined by different methods
A range of characterization methods were used to measure size and distribution of sizes of the ZrO2 nanocrystals synthesized hydrothermally in a microwave heated high pressure reactor [1-4]. The aim of the work is to compare size readings of the same ceramics nanopowders as reported by different characterization methods. We describe briefly capabilities of TEM, XRD and BET characterization techniques, such as size vs. size distribution output, crystalline phase resolution, ability of error estimation of the size as well as dispersion of sizes readings (error bars: yes/no)
Generation and Relaxation of Microstrains in GaN Nanocrystals under Extreme Pressures
Nanocrystalline powders of GaN with grain sizes ranging from 2 to 30 nm were examined under high external pressures by in situ diffraction techniques in a diamond anvil cell at DESY (HASYLAB, Station F3). The experiments on densification of pure powders under high pressure were performed without a pressure medium. The mechanism of generation and relaxation of internal strains and their distribution in nanoparticles was deduced from the Bragg reflections recorded in situ under high pressures at room temperature. The microstrain was calculated from the full-width at half-maximum (FWHM) values of the Bragg lines. It was found that microstrains in GaN crystallites are generated and subsequently relaxed by two mechanisms: generation of stacking faults and change of the size and shape of the grains occurring under external stress
Generation and Relaxation of Microstrains in GaN Nanocrystals under Extreme Pressures
Nanocrystalline powders of GaN with grain sizes ranging from 2 to 30 nm were examined under high external pressures by in situ diffraction techniques in a diamond anvil cell at DESY (HASYLAB, Station F3). The experiments on densification of pure powders under high pressure were performed without a pressure medium. The mechanism of generation and relaxation of internal strains and their distribution in nanoparticles was deduced from the Bragg reflections recorded in situ under high pressures at room temperature. The microstrain was calculated from the full-width at half-maximum (FWHM) values of the Bragg lines. It was found that microstrains in GaN crystallites are generated and subsequently relaxed by two mechanisms: generation of stacking faults and change of the size and shape of the grains occurring under external stress