Influence of He and N 2 plasma on in-situ surface passivated Fe nanopowders by plasma arc discharge

: DC transferred arc plasma method was employed for the synthesis of core (Fe)-shell (Fe oxide) nanopowders under N2 and He atmospheres. The phase and elemental compositions were studied by x-ray diffraction (XRD) and energy-dispersive x-ray spectroscopy (EDS) techniques. The structural and magnetic properties were investigated by high-resolution transmission electron microscopy (HRTEM), vibrating sample magnetometer (VSM) and Mossbauer spectroscopy. XRD and EDS results confirmed the presence of iron and iron oxide. From HRTEM, the average particle sizes of 32, 47 and 71 nm and 20, 26 and 37 nm were obtained against processing currents of 50, 100 and 150 A under N2 and He atmospheres respectively. The average particle size values were found to increase with increases in processing current. Spherical and hollow hexagonal nano-structures were obtained under N2 atmosphere whereas spherical and distorted cubes were formed under He atmosphere. The elemental mapping revealed the presence of oxygen on the surface and Fe in the core of the nanoparticles.