Influence of ferrite stabilizing elements and Co on structure and magnetic properties of carbon-encapsulated iron nanoparticles synthesized in thermal plasma jet

摘要

The encapsulation of Fe nanoparticles in protective carbon coatings always leads to formation of unde-sired paramagnetic austenite phase. Various ferrite stabilizing elements were included in the synthesis process to verify whether their inclusion may minimize the austenite content in carbon-encapsulated iron nanoparticles synthesized in thermal plasma jet. Eight ferrite stabilizing elements (Si, Al, Mo, Ti, Zr, Cr, W and V) and one austenite promoting additive (Co) were tested. Their influence on the synthesis yield, phase composition, morphology and magnetic properties of carbon-encapsulated iron nanoparticles was studied. It was found that the addition of ferrite stabilizers strongly influences the diameter distribution, graphitization degree, phase composition and magnetic properties. Contrary to the thermo-dynamic predictions the inclusion of ferrite stabilizing elements caused a substantial worsening of magnetic performance in carbon-encapsulated iron nanoparticles. It has been also shown that the subsequent heat treatment of carbon-encapsulated iron nanoparticles significantly improves their magnetic properties.