Yasuo Hikichi

Electrical and elastic properties of conductor-polymer composites

Several series of conductor-polymer composites were prepared from metal, graphite and conducting ceramics as filler materials, and epoxy, silicone rubber, polyethylene and polypropylene as polymer matrix. Their percolation curves, pressure dependence of resistivity, and Youngs modulus were examined for applications such as a pressure sensor.

Porous ceramics prepared by mimicking silicified wood

Abstract Porous titania, alumina and zirconia ceramic woods with wood-like microstructures, analogous to that of silicified wood, were prepared from natural woods as templates. The production of these ceramic woods was performed by the following process: (1) infiltration of metal alkoxide into wood specimens, (2) hydrolysis of the alkoxide in the cell structure to form titania, alumina or zirconia gels, (3) firing in air to form titania, alumina or zirconia ceramic woods. The resulting titania, alumina and zirconia ceramic woods were studied by means of an X-ray diffractometer, a mercury porosimeter and a scanning electron microscope. The microstructure of these ceramic woods retained the same structure as that of the raw wood: with the pore sizes corresponding to those of the original wood, and the major pores being unidirectionally connected.

HTS conductors for magnets

We have successfully improved the J/sub c/ value of Bi-2212 round wire to 500 kA/cm/sup 2/ at 4.2 K in self-field. The J/sub c/ value strongly depended on the filament size, aspect ratio, and geometry. Adjusting the filament size made it possible to obtain wires with J/sub c/ values higher than 450 kA/cm/sup 2/ in a range of wire diameters from 0.8 to 1.3 mm. The J/sub c/ value remained constant up to an applied tensile strength of 150 MPa. A 1 + 6 stranded cable fabricated using 1.02 mm diameter wires carried an I/sub c/ value of 4.5 kA at 4.2 K in self-field. A 16-strand Rutherford cable could also be fabricated using this wire.

Thermal and mechanical properties of sintered LaPO4-Al2O3 composites

Abstract Mixtures of (1 − x)LaPO 4 and xAl 2 O 3 (x = 0 to 1 mass) were dry-pressed to disks or bars. Relative densities larger than 94% and apparent porosities less the 6% were achieved when the specimens were sintered at 1600°C for 5 hours in air. The sintered ceramics (x = 0 to 0.7) were found to be machinable — they could be drilled easily using conventional metallic WC drills. The thermal and mechanical properties of the sintered (1 − x)LaPO 4 - xAl 2 O 3 composites had the following ranges: 10 × 10 −6 /°C (x = 0) to 9.0 × 10 −6 /°C(x = 1) (linear thermal expansion coefficient at 200°–1000°C); 5.0 (x = 0) to 43 W/(m·K)(x = 1) (thermal conductivity at 25°C); 140±19 (x=0) to 352±23 MPa (x = 1)(bending strength at room temperature); 5.7 (x = 0) to 16.5 GPa (x = 1) (Vickers hardness); and 155 (x = 0) to 400 GPa (x = 1) (Young’s modulus).

12 kA HTS Rutherford cable

One of the advantages of Bi-2212 is that a high J/sub c/ value can be obtained in wires with various shapes and filament configurations. Realization of a high J/sub c/ round wire made it possible to fabricate many kinds of cable developed for applications of low temperature superconductors (LTC). We successfully fabricated a 30-strand Rutherford cable using 0.8 mm/sup d/ round wire. Optimization of cabling factor enables to reduce the I/sub c/ degradation at the cable edge. I/sub c/ values were about 650-750 A at 65 K in a noninductive winding condition, which corresponds to 11-13 kA at 4.2 K in self-field.

Bi-2212 phase formation process in multifilamentary Bi-2212/Ag wires and tapes

We investigated phase formations of multifilamentary Bi-2212/Ag wires during the heat-treatment. We carried out systematic quenching experiments. In the partial-melting process in pure O/sub 2/, when heating rate was 10/spl deg/C/h, melting of filaments was started from central filaments and spread to the edge-located filaments. However, when heating rate was 5/spl deg/C/h, melting of filaments was caused uniformly. In the partial-melting process in 8% O/sub 2/ also, melting of filaments occurred caused uniformly. Phase identification indicates that the existing alkaline earth cuprate was 2:1 alkaline earth cuprate in 8% O/sub 2/ while alkaline earth cuprate was 14:24 alkaline earth cuprate in pure O/sub 2/. These results showed effect of O/sub 2/ partial pressure in filaments. In the slow solidification process, the Bi-2212 phase grew up greatly and broke through the silver matrix in pure O/sub 2/, but the grain growth was suppressed in 8% O/sub 2/, resulting in the suppressing of bridging of Bi-2212 filaments.

Synthesis and thermal reactions of rhabdophane-(Yb or Lu)

Abstract Poorly crystalline rhabdophane-(Yb or Lu) was synthesized by precipitation from mixed aqueous solutions of Ln(NO 3 ) 3 (Ln = Yb or Lu), (NH 4 ) 2 HPO 4 , and citric acid with the mixing mole ratios of (NH 4 ) 2 HPO 4 /Ln(NO 3 ) 3 = 4 and citric acid/Ln(NO 3 ) 3 = 5 to 30, at pH 7 and 90°C for 7 to 30 days. However, unknown XRD peaks and C–O bond FTIR absorption peaks were observed for the precipitates. These peaks disappeared with increasing heating temperature up to 400°C in air, and single phase rhabdophane-(Yb or Lu) was obtained when heated at 400 to 800°C in air. Chemical formulas of the single phase rhabdophane were YbPO 4 ·0.4H 2 O and LuPO 4 ·0.5H 2 O, respectively. The water corresponding to 0.4H 2 O (or 0.5H 2 O) was zeolitic water. The lattice constants are a = 0.676 and c = 0.626 nm for Yb, and a = 0.674 and c = 0.630 nm for Lu. Rhabdophane-(Yb or Lu) changed into the xenotime structure above 860°C, which was stable even at 1800°C in air.

Mechanochemical changes in hydrated rare earth orthophosphate minerals by grinding

Abstract By mechanochemical reactions at 20 °C in air, rhabdophane-type (r-) RPO 4 ·0.5H 2 O (R  La, Ce, Pr, Nd, Sm or Gd) gradually changed into monazite-type (m-) RPO 4 , weinschenkite-type (w-) RPO 4 ·2H 2 O (R  Dy, Y or Er) into r-RPO 4 · n H 2 O (R  Dy, n = 0.7; R  Y, n = 0.8; R  Er, n = 0.9) and w-YbPO 4 ·2H 2 O into xenotime-type (x-) YbPO 4 . The r-RPO 4 · n H 2 O (R  Y or Er) obtained by grinding w-RPO 4 ·2H 2 O at 20 °C are new compounds. The r-RPO 4 · n H 2 O changed into m-RPO 4 (above 500 °C (R  La-Gd) and at 800 °C (R  Dy)) and x-RPO 4 (above 900 °C (R  Dy or Y) and 700 °C (R  Er)) in air. The m-DyPO 4 is a new compound.

Property and Structure of YBa2Cu3O7-x-Nb2O5 Composite

Nb2O5-doped YBa2Cu3O7-x superconductors were prepared by heating at 950°C for 24 h in air and cooling to room temperature at a rate of 5°C/min in air. The bulk density and critical current density (Jc, 77 K and H=0 T) increased with increasing amount of Nb2O50.5 wt%; up to 5.80 g/cm3 and 437 A/cm2 (sample thickness 1 mm), respectively. The critical temperature (Tc (zero)) was about 92 K. Experimentally we have succeeded in improving the superconducting properties, microstructure and degradation in moisture with addition of Nb2O50.5 wt%.

Performance test of a refrigerator cooled magnet fabricated using Bi-2212 multilayer superconducting tapes

A stacked pancake coil was fabricated by Ag-alloy sheathed Bi-2212 multilayer tapes and tested using a refrigerator. The magnet consisted of ten double pancakes wound with 100 m class tapes. The I/sub c/ values of the tapes varied from 80 A to 150 A at 4.2 K and 10 T because of the scattering of the thickness in the superconducting layers. The magnet carried a critical current of 57 A at 12 K and generated B/sub max/ of 1.4 T in a 60 mm bore. At 12 K, the magnet could operate with an operating current of 45 A which corresponded to about 80% of I/sub c/. Thermal runaway was not observed even with a ramp rate of 10 T/min.