Plasma arc Synthesis of Nano-Boron Towards the Synthesis of MgB2 Superconductors

Since the discovery of superconductivity in the tempting binary intermetallic compound MgB2, the solid-state synthesis technique is highly dominated by the usage of amorphous boron as one of the precursor powders. The formation of MgB2 phase proceeds through the diffusion of Mg into B powder mainly driven by the low melting point of Mg as compared to B. Once the nucleation is achieved, the progress of polycrystalline MgB2 phase occurs due to the out diffusion of boron through the MgB2 layer and by the inward diffusion of Mg. This growth is impeded due to the presence of certain oxide phases or formation of Mg deficient phases. It is speculated that the probability for the inclusion of Mg(B)–O phases is higher for crystalline boron precursor as compared to the amorphous B. Thus, the use of nanosized amorphous boron may lead to larger nucleation centers, smaller grain size and consequently higher packing density in the polycrystalline MgB2, which will in turn provide optimum superconducting properties. Hence an attempt to synthesize amorphous nano-boron powders is presented. Plasma arc discharge technique was successfully employed to produce nano-boron powder. The XPS analysis was carried out to inveterate the formation of boron. The as-synthesized powder had a uniform average particle size distribution of around 20 nm as confirmed by TEM measurements. The selected area electron diffraction pattern composed of diffused ring clearly depicts the amorphous nature of boron powder.