Preparation of Nd–Fe–B by nitrate–citrate auto-combustion followed by the reduction–diffusion process

Abstract

The Nd₂Fe₁₄B alloy has been successfully synthesized by nitrate–citrate auto-combustion followed by the reduction and diffusion process with low energy consumption. H₃BO₃, Fe(NO₃)₃·9H₂O, and Nd(NO₃)₃·6H₂O were used as precursors and citric acid was used as the chelating ligand of metal ions. Ammonia water was used to adjust pH to 7. CaH₂ was used as a reducing agent for the reduction and diffusion process. NdFeO₃ and Fe₂O₃ were produced during auto-combustion of gel. The combustion process of the gel was investigated by TGA/DTA curve measurements. The phase compositions were studied by XRD measurements. The differences of the overall morphology and magnetic properties were measured by SEM, TEM and vibrating sample magnetometry (VSM) at 300 K. The comparison of the magnetic properties of the reduced samples between the pellet type and the random powder type was done with VSM and it showed better magnetic properties of the pellet type Nd₂Fe₁₄B. Making a compact pellet type sample for reduction is more efficient for solid reduction and phase transition for higher coercivity.