In the present work we investigated effect of selective sources of carbon (C) addition on bulk MgB₂ produced by in-situ solid-state reaction in Ar atmosphere. The superconducting performance of MgB₂ bulk with nano-scale charcoal and diamond additions were investigated and compared. Activated charcoal which was natural sourced from mahogany and pre-treated obtaining ~60 nm size and diamond particles of 10 nm size were employed with different doping levels (0 to 0.8 wt%). X-Ray diffraction results indicated that the C doped samples showed slight decrease in the a- lattice parameters. Microstructural observation by FE-SEM and EPMA indicated the presence of precipitated particles in the bulk matrix along with the grain boundary as a consequence of C doping which was also observed in the slight degradation of critical temperatures, T_c. The critical current density, J_c at self-field and 20 K of 0.8 wt% doped charcoal is ~455 kA/cm² and 0.8 wt% doped nano-diamond particles are ~480kA/cm².  The enhancement of the J_c was observed in all doped samples as compared to the undoped sample at 20 K. Nano-diamond doping was observed to be most affective due to the effective nano inclusions in the bulk material. Flux pinning force density supports the effective enhancement in the J_c performance compared to the pure MgB₂ sample with doped ones. Our work clarified that the presence of C-related impurity in the matrix is a useful inter-grain inclusion for effective flux pinning, hence responsible for the improvement in the J_c.

Keywords: Activated charcoal, Nanodiamond, Critical current density, Scanning electron microscopy