Fabrication of high performance MgB2 wires by an internal Mg diffusion process

We succeeded in the fabrication of high-Jc MgB2/Fe wires applying the internal Mg diffusion (IMD) process with pure Mg core and SiC addition. A pure Mg rod with 2 mm diameter was placed at the center of a Fe tube, and the space between Mg and Fe tube was filled with B powder or the powder mixture of B-(5mol%)SiC. The composite was cold worked into 1.2mm diameter wire and finally heat treated at temperatures above the melting point of Mg(~650oC). During the heat treatment liquid Mg infiltrated into B layer and reacted with B to form MgB2. X-ray diffraction analysis indicated that the major phase in the reacted layer is MgB2. SEM analysis shows that the density of MgB2 layer is higher than that of usual powder-in-tube(PIT) processed wires. The wires with 5mol% SiC addition heat treated at 670oC showed Jc values higher than 105A/cm2 in 8T and 41,000A/cm2 in 10T at 4.2K. These values are much higher than those of usual PIT processed wires even compared to the ones with SiC addition. Higher density of MgB2 layer obtained by the diffusion reaction is the major cause of this excellent Jc values.Comment: 7page, 6figure

Strain Effect in MgB2/Stainless Steel Superconducting Tape

The influence of mechanical strain on the critical current (Ic) is investigated for MgB2/stainless steel (SUS316) superconducting tapes. The tapes are fabricated by using 'powder in tube' method and deformation process without any heat treatment. The tensile axial strain along tape length is successfully induced to the sample by using a U-shape holder made of stainless steel (SUS304). Two samples are examined at 4.2 K in 5 T (B is applied perpendicular to the tape surface). While the initial Ic at zero external strain state (Ic0) varies (30.4 and 33.3 A), normalized Ic (Ic/Ic0) vs. external strain relations fall on the same curve. Linear increase of Ic is observed from zero external strain state to 0.5% strain (107% of Ic0). Rapid and large degradation occurs at the strain exceeding 0.4-0.5%. High durability against stress can be expected for MgB2/stainless steel superconducting tapes.Comment: 3 pages including 2 figures, submitted to Physica

Superconducting Properties of MgB2 Bulk Materials Prepared by High Pressure Sintering

High-density bulk materials of a newly discovered 40K intermetallic MgB2 superconductor were prepared by high pressure sintering. Superconducting transition with the onset temperature of 39K was confirmed by both magnetic and resistive measurements. Magnetization versus field (M-H) curve shows the behavior of a typical Type II superconductor and the lower critical field Hc1(0) estimated from M-H curve is 0.032T. The bulk sample shows good connection between grains and critical current density Jc estimated from the magnetization hysteresis using sample size was 2x104A/cm2 at 20K and 1T. Upper critical field Hc2(0) determined by extrapolating the onset of resistive transition and assuming a dirty limit is 18T.Comment: 3Pages PD

High transport critical current density obtained for Powder-In-Tube-processed MgB2 tapes and wires using stainless steel and Cu-Ni tubes

MgB2 tapes and wires were fabricated by the Powder-In-Tube method. Stainless steel and Cu-Ni tubes were used as sheath materials, and no heat treatment was applied. The tapes made of stainless steel showed transport critical current density Jc of about 10,000A/cm2 at 4.2K and 5T. A high Jc of about 300,000A/cm2 was obtained by extrapolating the Jc-B curves to zero field. Multifilamentary(7-core) MgB2 wire was successfully fabricated using Cu-Ni tubes. For both tapes and wires the grain connectivity of MgB2 was as good as a high-pressure sintered bulk sample. However, the Jc of the Cu-Ni sheathed wire was lower than the stainless steel sheathed tape due to the lower packing density of MgB2.Comment: 4 pages, 3 figure

Spatial reasoning skills about 2D representations of 3D geometrical shapes in grades 4 to 9

This is the final version. Available on open access from the Mathematics Education Research Group of Australasia via the DOI in this recordGiven the important role played by students’ spatial reasoning skills, in this paper we analyse how students use these skills to solve problems involving 2D representations of 3D geometrical shapes. Using data from in total 1357 grades 4 to 9 students, we examine how they visualise shapes in the given diagrams and make use of properties of shapes to reason. We found that using either spatial visualisation or property-based spatial analytic reasoning is not enough for the problems that required more than one step of reasoning, but also that these two skills have to be harmonised by domain-specific knowledge in order to overcome the perceptual appearance (or “look”) of the given diagram. We argue that more opportunities might be given to both primary and secondary school students in which they can exercise not only their spatial reasoning skills but also consolidate and use their existing domain-specific knowledge of geometry for productive reasoning in geometry