Particle Size Of Precursor Powders Research Articles

Effects of precursor powder particle size on the powder-in-tube Ba1−xKxFe2As2 superconducting tapes

In this paper, we studied the effects of precursor powder particle size on Ag-sheathed powder-in-tube Ba1−xKxFe2As2 (Ba-122) superconducting tapes. Precursor powders with different particle sizes were prepared by changing the grinding time of calcined bulks. We systematically investigated the relationship between particle size of precursor powder, microstructure and superconducting properties of tapes. For short grinding time, the uneven particle size distribution damages the interface between Ba-122 core and Ag sheath, resulting in distinct sausage effect and decline of mass density of the Ba-122 core, causing severe fluctuation for the transport current density (J c). Then with the extension of grinding time, the transport J c becomes more uniform due to the improved homogeneity but lower with the reduction of average particle size from 21.5 to 9.5 μm. The J c of samples made with precursor powders by grinding 20 min reaches 5 × 104 A cm−2 at 4.2 K and 10 T. It has been shown that the coarse grains are easier to align along the rolling direction of tapes and lead to a higher degree of c-axis texture. Our results demonstrated the importance of controlling the homogeneity and particle size of precursor powders in achieving superior J c for iron-based superconducting tapes.

Electrical behavior of RuO2-glass composites: The effect of RuO2 particle size on the percolation threshold

Even small amounts of the fission byproduct ruthenium can increase the overall electrical conductivity of nuclear glasses by several orders of magnitude. In this context, the main goal of the present work is to evaluate the dependence of RuO2 particle size on the electrical behavior and percolation threshold of RuO2-glass composites. For this purpose, a set of sodium borosilicate glasses with different RuO2 content or distinct particle size is synthesized and characterized by X-ray diffraction and scanning electron microscopy. The electrical properties of these composites are assessed by impedance spectroscopy in a temperature range below the glass transition. The obtained results expose a transition in the electrical behavior of the RuO2-glass composites in the vicinity of the percolation threshold. The composites are mostly ionic conductors for low RuO2 content, but they become predominantly electronic conductors for RuO2 contents beyond the percolation threshold. The dependence of their electrical conductivity on temperature is also revealing. The composites showing ion-conducting behavior exhibit a strong and crescent dependence of the conductivity on temperature, while the electron-conducting composites show a metal-like conductivity. Even more noteworthy, the dependence of the electrical behavior on the RuO2 particle size unveils an extremely low percolation threshold (~1% vol.) and consequently higher conductivity for the glass composites synthesized with the nanometric RuO2 powder. These results bring new insights into the discussion of why these composites present such a low percolation threshold and suggest that the particle size of precursor powders play a crucial role in their final electrical properties.

Mechanochemical Activation of Precursor Powders for the Preparation of Dense Al2O3–ZrO2〈Y2O3〉 Nanoceramics

A process has been demonstrated for the preparation of precursor powders and nanocrystalline (60–90 nm) alumina-based ceramics in the Al2O3–ZrO2〈Y2O3〉 system. We have studied the influence of mechanochemical activation (MA) on the structure and particle size of precursor powders and found the most effective MA time. MA has been shown to lower the α-Al2O3 formation temperature and accelerate the powder sintering process. We have optimized powder consolidation conditions for the fabrication of dense nanoceramics and studied their physicochemical and mechanical properties.

Microstructure and Superconductivity of Bi-2223 Tape Prepared by Precursor Powders with Different Particle Sizes

The effects of particle size of precursor powders on microstructure and superconductivity of Bi-2223 tape were investigated. Three kinds of precursor powders with different particle sizes (8, 2, <1 μm) were prepared by a spray pyrolysis method via adjusting the concentration of metal nitrates solution and ball milling. All powders were composed of Bi-2212, (Sr, Ca)xCuyOδ (AEC) and CuO phase after heat treatment. Results show that AEC phase dimension and content increase with decreasing of particle size of the precursor powders. However, the powder with an average particle size of 2 μm has the minimal dimension and content of CuO phase. Among the 37-filaments Bi-2223 tapes fabricated from the three kinds of precursor powders, the one from the powder with average particle size of 2 μm achieves the highest critical current (Ic), which also has the most (Bi, Pb)3Sr2Ca2CuOx (Pb-3221) and least AEC phase compared to other tapes. The particle size of the precursor powders mainly affects dimension and content of AEC and CuO phase, which further causes difference of Ic and non-superconducting phases in Bi-2223 tape.

The influence of process variables of precursor powders on the microstructure evolution and transport current properties of Bi-2223/Ag tapes

The effect of Pb content and particle size of precursor powders has been studied to improve the grain growth and texture of Bi-2223/Ag tapes. The Pb content and particle size of precursor powders dominate the amount of liquid phases, and thus affect the value of J c with a variation of heat treatment condition. The best values of J c reached 53 kA/cm 2 at 77 K and 0 T, after 210 h heat treatment at 839 °C and two times intermediate pressing. It suggests that the improvement of J c characterized from high fraction of Bi-2223 with enlarged crystallites is attainable by optimizing the processing variables of precursor powders.

Effects of lead content and particle size of precursor powders on formation rate, grain growth and critical current density of BSCCO 2223 tapes

The influence of Pb content and particle size of precursor powders on the formation rate and grain growth of BSCCO 2223 has been studied to improve critical current density (J/sub c/). Our experimental results indicate that these variables have great influence on the partial melting temperature of the system, and it will affect the amounts of liquid phase and formation rate of BSCCO 2223 phase. Optimization of these variables will lead to enhanced critical current densities. The J/sub c/ in the fully reacted tapes with different Pb content and particle size of precursor powders varied from 24 kA/cm/sup 2/ to 52 kA/cm/sup 2/ at 77 K and 0 T. It suggests that a great improvement of J/sub c/ in certain tapes is characterized from the large textured BSCCO 2223 grains and fewer tracks of second phases in microstructure.

Microstructure of Ni/YSZ cermets according to particle size of precursor powders and their anodic performances in SOFC

Four different Ni/YSZ cermets were prepared by combining two sets of NiO and YSZ powders of different size. The microstructural change evolved during the course of electrode adhesion and cell operation was monitored using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The anodic activity was compared by analyzing the ∝ impedance spectra of four Ni/YSZ cermet (H2) / YSZ half cells at 1000 °C. Among the cermets, the one that prepared from the smaller NiO and larger YSZ powder showed the best anodic performances on aspects of the initial activity and long-term stability. This favorable performance is partly responsible to the presence of larger YSZ particles which provide a supporting matrix to suppress the microstructural change against Ni sintering and concomitant volume shrinkage, and partly to an easy formation of Ni channel for electronic conduction. Anodic performances of the other cermets were also discussed based on their microstructure.

Mechanical grinding of precursor powder and its effect on the microstructure and critical current density of Ag/Bi-2223 tapes

The effects of the particle size of precursor powder on the microstructure and critical current density, J c, of Ag-sheathed Bi-2223 tapes were investigated. The calcined powder with a nominal composition of Bi 1.89Pb 0.41Sr 2.01Ca 2.23Cu 3.03O y was milled for various times using a planetary ball mill. The transport property of the tapes was found to depend strongly on the particle size of the precursor powder. Enhanced reactivity of the milled powder facilitated the formation of 2223 phase and resulted in an increase of J c. Excessive milling, however, led to the amorphization of the powder. The heavily deformed powder was decomposed into 2201 and second phases during degassing treatment, which retarded the transformation of 2223 phase and hence significantly degraded the electrical property of the tapes.

The effect of mechanical deformation on silver - core interface and critical current density in Ag - Bi-2223 single- and multifilament tapes

Ag sheathed Bi-2223 tapes were prepared by the powder-in-tube method. A smooth Ag - oxide interface was obtained by decreasing the number of annealing steps, annealing temperature and time and wire size prior to flat rolling and by varying reduction per pass during flat rolling. For fabrication of multifilamentary tapes, the fill geometry and fill number are controlled to accord with deformation symmetry and homogeneity. The particle size of precursor powder was found to have more effect on `sausaging' in multifilamentary tape than monofilamentary tape. The difference in the deformation resistance between Ag sheath and oxide core was considered to explain and predict the `sausaging' effect. A higher degree of deformation is more beneficial for achieving higher in the tapes made by square rolled wire than the tapes made by the conventional drawing method. However, the square rolling method is not suitable for fabricating multifilamentary tape because strong inhomogeneity of deformation is introduced by this method. Tapes with a 0.07 mm thickness can be made using flat rolling without any `sausaging' effect. In the case of square rolled wire, the reaches with (1 T, plane)/ of about 20% at 77 K for the pressed tapes while values of and are achieved in rolled single- and 16-filament tapes respectively. More reproducible results with a in the range of for pressed tapes and for rolled tapes are achieved by conventional drawing approach in 19-filament tapes. Also, high (1 T, plane)/ values of 21 and 18% were obtained for pressed and rolled 19-filament tape, respectively.