Powder Calcination Temperature Research Articles

Fabrication of multifilament Bi-2223/Ag tapes by varying the lead content and calcination temperature of precursor powders

A set of multifilament Bi-2223/Ag tapes were fabricated by varying the lead content and calcination temperature of starting precursors. The influence of precursor conditions on the phase formation, microstructure and Jc property of Bi-2223/Ag tapes were explored with XRD, DTA, SEM-EDS and transport current measurements. The results showed that the Pb content of 0.20 in the nominal composition of Bi1.8PbxSr2.0Ca2.2Cu3.0Oz is too low to lead to a fully formation of Bi-2223 phase in tapes compared with Pb content of 0.25 and 0.30. In addition, despite the Pb variations, the powders calcined at 820 °C resulted in the highest Jc in final tapes against the powders calcined at 810 and 830 °C. The correlation between the transport property and the varied phase assemblages of precursors induced by lead and calcination temperature variations was discussed.

The effect of processing parameters on the phase assemblage and critical current density in Bi(Pb)-2223 tapes

In this work, the phase assemblage of the precursor powder, especially the Ca 2PbO 4 phase, was changed by adjusting the powder calcination temperature and the correlation between the properties of precursor powder and the heat treatment process of tapes, as well as the critical current has been analyzed. It was found that the tape heat treatment temperature has close relations with the content of the Ca 2PbO 4 phase in the precursor powders. The optimum heat treatment temperature of the tape increases dramatically and the tape sintering processing window is enhanced when the relative content of Ca 2PbO 4 phase decreasing in the precursor powders.

Sintering behavior and electrical conductivity of Ce 0.9Gd 0.1O 1.95 powder prepared by the gel-casting process

Nanoscale Ce 0.9Gd 0.1O 1.95 (gadolinia doped ceria, GDC) powders were prepared by a gel-casting process. Differential thermal analysis, thermogravimetry and X-ray diffraction results showed that the single-phase fluorite structure forms at a relatively low calcination temperature of 600 °C. X-ray patterns of the GDC powders revealed that the crystallite size of the powders increases with increasing calcination temperature, which is consistent with transmission electron microscopy observations. The sintering behavior and the ionic conductivity of the cast tapes prepared from GDC powders calcined at 600–1000 °C were also studied. At sintering temperatures ≥1450 °C, more than 96% of the relative density is obtained for tapes prepared from powders calcined at three different temperatures. The average grain size increases with decreasing powder calcination temperature. The alternating-current impedance spectroscopy results showed that the GDC sample sintered at 1450 °C has ionic conductivity of 0.046 S cm −1 at 700 °C in air. The present work results have indicated that the gel-casting route is a relatively low-temperature preparation technique to synthesize GDC powders with a high sinterability and a good ionic conductivity.

Study of (Bi 4−x La x ) Ti 3 O 12 Powders and Ceramics Prepared by Sol-Gel Method

La-modified (Bi4−xLax)Ti3O12 (abbreviated as BLT) powders were prepared by sol-gel processing methods. The powders were characterized by differential thermal analysis (DTA) and laser-diffraction particle-size analysis. The (Bi4−xLax)Ti3O12 ceramics were prepared from the powders and characterized by X-ray diffraction (XRD). The results indicate that the sol-gel method can be used to prepare nanometer powder for the new types of BLT ferroelectric ceramics. The solid reaction of BLT powders occurs at 730°C approximately resulting in the growth of BLT grain. The average grain size may be varied in the range 60–500 nm, depending on the calcination temperature of the powders. The (Bi4−xLax)Ti3O12 ceramics prepared from the powders were polycrystalline materials with completely monoclinic (Bi4−xLax)Ti3O12 phase.

Combustion synthesis of zirconia-based cermet powders

Zirconia-based cermet powders have been synthesised by combustion synthesis, using nitrates as metal precursors and urea as fuel component. Two families of cermet were prepared : Ni-YSZ (commonly used as anode material in Solid Oxide Fuel Cells) and Ni-Co-YSZ cermets. Fine homogeneous powders have been obtained at low temperature. SEM observations have shown well-crystallized grains, confirmed by X-Ray diffraction. Crystalline size and specific surface area were measured as functions of the amount of urea used for the synthesis, cermet compositions and calcination temperature of as-prepared powders.

Influence of the powder calcination temperature on the microstructure in Bi(Pb)-2223 tapes

One goal of our research is to be able to manufacture high temperature superconducting cables for power transmission. The key elements is the production of superconducting tapes using the oxide powder in tube process. If quality and critical current density of the tapes can be improved, the quality and capacity of the final cable will also be improved. In this work we have calcinated the powder used in the powder in tube process at different temperatures and the microstructure of ceramic phase has been studied after rolling and after two annealings. It is observed that the powder calcination temperature has a strong influence on the microstructure, that is the arrangement and growth of superconducting phases as well as the secondary phases. It is found that the amount of big secondary particles is lowest for calcination temperatures of 820-830/spl deg/. Better crystal growth and grain sintering during first and second annealing are also observed for these calcination temperatures.

Microstructure‐Property Relations of Solid Oxide Fuel Cell Cathodes and Current Collectors: Cathodic Polarization and Ohmic Resistance

Microstructure, cathodic polarization, and ohmic resistance on the cathode side of ‐based solid oxide fuel cells have been studied for the intermediate temperature operation range between 700 and 900°C. Starting powder characteristics, powder calcination temperature, and sintering temperature strongly influence the final microstructure of cathodes. Electrochemical performance depends on these processing parameters as well as on the cathode thickness and the contact spacing of current collectors. A decrease in effective electrode area occurs both on the microscopic level with coarse and inhomogeneous cathode microstructure and on the macroscopic level with a wide contact spacing of the current collectors. The smaller effective electrode area causes inhomogeneous current density distribution and results consequently in higher ohmic losses originating from the electrolyte and higher cathodic polarization. These losses are evaluated using cathodes with different microstructures and on the mole percent electrolyte. The influence of current path constrictions on the ohmic and nonohmic losses is demonstrated using Pt current collectors of different geometric spacings.