Synthesis of dense bulk MgB₂by an infiltration and growth process

Abstract

Abstract:We report the processing of dense, superconducting MgB 2 (ρ ≈ 2.4 g/cm 3 )by an infiltration and growth technique. The process, which involves infiltration of liquid magnesium at 750 ºC into a pre-defined boron precursor pellet, is relatively simple, results in the formation of a hard, dense structure and has the potential to fabricate large bulk samples of complex geometries. X-ray diffraction has been used to confirm the presence of the MgB 2 primary phase with only residual magnesium content in the fully processed samples. The samples exhibit sharp superconducting transitions at 38.4 K and have critical current densities of up to 260 kA/cm 2 in selffield at 5 K. Modest measured values of Hc 2 (0) of 17 T suggest that superconductivity in bulk MgB 2 fabricated by this technique is in the clean pairing limit.

Characterization of Bulk MgB₂ Synthesized by Infiltration and Growth

“…J c up to 400 kA · cm −2 at 5 K and 280 kA · cm −2 at 20 K was achieved. This value is significantly higher than that observed in our earlier studies where maximum critical current density of 260 kA · cm −2 was measured [8]. This is likely to be due to the very low fraction of MgO in the sample and to the presence of fine 20-50 nm particles that enhance flux pinning in the bulk material.…”

“…The technique involves the infiltration of liquid magnesium into predefined boron precursors. This is an ambient pressure technique that results in high density MgB 2 and potentially scalable to complex shaped bulks [8]. Also, the pores resulting from volume contraction are occupied by surrounding Mg, which manifests as very high normal state electrical connectivity and critical current density in the bulk.…”

Catalyzed synthesis of rhombohedral boron nitride in sodium chloride molten salt

“…As Alpha increased, the amount of MgB 7 decreased gradually, MgB 7 were unstable phases and the phase evolution in the system was closely related to the Alpha value, and finally achieved their minimum value when Alpha increased to 2. If excess Mg were added in the reactants, the dissolved B may react with Mg to form MgB X [37][38][39][40]. In Fig.…”

Microstructural evolution in infiltration‐growth processed MgB2 bulk superconductors

“…The resultant product is essentially a MgB 2 ‐Mg ceramic matrix composite, with Mg levels up to 15%. The relative density of IG processed MgB 2 is significantly higher (>90%) than samples fabricated using conventional sintering techniques, with process requiring no high‐pressure apparatus . Moreover, near‐net complex shapes can be fabricated with infiltration route that are not easily achievable by conventional sintering methods …”