Mechanically Alloyed Nd-Fe-B Nanoparticles with Graphitic Carbon Shell: Synthesis, Characterization and Magnetic Properties
DOI:
https://doi.org/10.65834/jdsi.12.46Keywords:
Nd-Fe-B nanoparticles, mechanical alloying, graphitic carbon shell encapsulation, chemical vapor deposition, magnetic propertiesAbstract
In this study, Nd-Fe-B nanoparticles with permanent magnet properties were synthesized from elemental raw materials using the mechanical alloying (MA) method and subsequently encapsulated with graphitic carbon shell to enhance their thermal and chemical stability for potential electronic applications. Alloy composition Nd ≈ 23.3 wt.%, Fe ≈ 75.7 wt.%, B ≈ 1.0 wt.%, Nd₁₀Fe₈₄B₆ atomic composition, were milled for varying durations 8-10 and 12 h to evaluate the effects of milling duration on magnetic performance. Due to high-energy milling, powder yield remained between 41% and 53%, influenced by particle adhesion and partial melting. X-ray Diffraction (XRD) confirmed the formation of the tetragonal Nd₂Fe₁₄B phase in all MA-synthesized powders, while Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM) analyses verified nanoparticle size and agglomerated morphologies characteristic of welding-fracture-rewelding cycles in MA. Annealing at 900°C for 1 h improved crystallinity and promoted the formation of additional phases, as supported by XRD, SEM and Energy Dispersive Spectroscopy (EDS) results. A Graphitic Carbon Shell (GCS) was successfully deposited on the nanoparticle surfaces via Chemical Vapor Deposition (CVD) under a CH₄/H₂ atmosphere at 950°C; the presence of the carbonaceous coating was confirmed by XRD and elemental mapping. Transmission Electron Microscopy (TEM) analysis revealed the core-shell structure, the number of graphitic carbon shell layers, and the uniformity of the encapsulation surrounding the nanoparticles. Magnetic characterization using Vibrating Sample Magnetometer (VSM) showed variations in coercivity, saturation magnetization and remanence before and after encapsulation. Among all samples, the 10 h milled, annealed and graphitic carbon shell encapsulated sample (NFB2TG) exhibited the most favorable magnetic properties, reaching a coercivity of 185.71 Oe and saturation magnetization of 46.3 emu/g. These results demonstrate that MA followed by annealing and encapsulation GCS is a promising route for producing stable Nd-Fe-B nanoparticles.
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