Lightweight MgB₂ wires with a high temperature aluminum sheath made of variable purity Al powder and Al₂O₃ content

Abstract

The properties of high temperature aluminum (HITEMAL, hereinafter HIT) composites made of powders with different particle sizes ranging from 0.8-3 μm and purities of 99.9%-99.996% were tested. The thermal, electrical, and mechanical properties of these materials were examined and compared with pure Al. Three different HIT materials were used for the outer sheath of single-core MgB 2 wires with a Ti barrier manufactured by internal magnesium diffusion into a boron process. The critical currents, thermal stability, and strain tolerances of the MgB 2 /Ti/HIT wires were measured at liquid He temperature. It was found that the Al powder purity and particle size used for HIT affect the performance of MgB 2 wires. A sheath made of high purity Al powder allows better thermal stability of MgB 2 wire, but the strain tolerance is lower in comparison to the wire with HIT made of less pure powder and higher Al 2 O 3 content. The presented wire configurations are promising for lightweight, thermally stabile, and strain tolerant superconducting MgB 2 wires.

MgB2 cables made of thin wires manufactured by IMD process

“…The set of single-core MgB 2 wires has been made by identical IMD process. The metallic tubes with purity 99.9% of diameter 9.0/6.2 mm were used for outer sheath: from Cu (named Cu-A) and from Al with 1.5 vol % Al 2 O 3 metal matrix composite (named Al-B) and Al with 3.1 vol % Al 2 O 3 (named Al-C) prepared by powder metallurgy [14][15][16] are described by table 1. HV0.05 is the micro-hardness measured for these sheath materials in as-deformed state.…”

Thermal conductivities and thermal runaways of superconducting MgB2 wires stabilized by an Al + Al2O3 sheath

“…Different Al+Al 2 O 3 metal matrix composites (called HITEMAL) have been used for the outer sheath of single-core MgB 2 /Ti/Al+Al 2 O 3 wires fabricated by the internal magnesium diffusion (IMD) process [9]. Three Al+Al 2 O 3 sheaths were made from aluminium powders of different purities 99.9%-99.999% and averaged particle size d av between 0.8 μm and 3.0 μm, which are referred to as H1, H2 and H3 (see table 1).…”

“…Studies of the correlation between the thermal properties and composite wire design allow optimization of the thermal stability of MgB 2 conductors [7]. Recently, extralight MgB 2 wires with a Ti barrier and Al+Al 2 O 3 thermal stabilization have been made and tested at low temperatures [8][9][10]. Aluminium-based materials present an outstanding balance of cost, properties and low density and they are used principally in transport industry.…”

“…The light metal components are essential for the reduction of fuel consumption in transport applications. The mechanical and electrical properties of Al+Al 2 O 3 wires have already been studied [11], and their thermal conductivities κ only at zero field have been compared with pure Al [9]. Al+Al 2 O 3 is an interesting sheath material for extra-light superconducting MgB 2 wires, for which, in particular, electrical and thermal conductivity is very important.…”

Multi-core MgB2 wire with a Ti barrier and a reinforced Al+Al2O3 sheath

“…Figure 3(a) shows the critical currents (I c ) and n-exponents of a six-core rolled wire with cross-sectional dimensions of 1.16×1.16 mm, compared to a single-core one 1.02× 1.02 mm 2 in dimensions [12] which is shown in figure 4. The lower I c and n-exponents of the multi-core wire are attributed to a smaller cross-sectional area of the MgB 2 filaments, and also to current redistribution among the non-uniformly reacted filaments.…”