Study On Fabrication Process And Reaction Mechanism Of Nd-Fe-B Magnetic Powder Prepared By Novel Chemical Method

Nd-Fe-B permanent magnet materials have been widely used in electric vehicles,wind turbines,information storage and many other fields because of their excellent magnetic properties.At present,the physical methods were main preparation ways of Nd-Fe-B magnetic powder,but those techniques had many disadvantages,such as complex process,high production cost,wide distribution of particle size and so on.A new process for preparing Nd-Fe-B magnetic powder by chemical method was presented in this paper in order to overcome the above shortcomings.The mechanism of preparing magnetic powder by this method and effect of preparation technology on properties and microstructure of magnetic powder were mainly studied.Finally,the reasonable process parameters were obtained and Nd-Fe-B nano-sized powders with good magnetic properties were prepared successfully.This study hope to find a new way to replace the existing powder-making process and provided a theoretical basis for the preparation of high-quality Nd-Fe-B magnetic powder accumulation by exploring preparation of Nd-Fe-B Powder by Chemical method,therefore,it has theoretical and practical significance.A new chemical method for the preparation of Nd-Fe-B magnetic powder has been studied in this paper.It was found that the method can be divided into three key steps:?1?Preparation of Nd-Fe-B intermediates,which were mainly composed of Fe₃O₄ particles,?Nd-Fe?organic compounds,M_x?BO₂?_y compounds.?2?The intermediate was annealed and the organic matter was decomposed and eliminated at high temperature to form three phases of NdFeO₃,NdBO₃,?-Fe.?3?The oxide powder was ground with CaH₂ which has strong reducibility,and then,this mixture was pressed in to a pellet and reduced to form three phases of H₅Nd₂,B and Fe by reducing and diffusing process,and the Nd-Fe-B magnetic powder was formed by continuous heated preservation and full diffusion between the phases.?C₂H₅?₃NBH₃ was not only the B source in this method,but also had the effect of reduction and capping after thermal decomposition,therefore,the effect of the?C₂H₅?₃NBH₃content on the phase,morphology and magnetic properties of the power produced at each stages was studied in this paper.It was found that the grain size of Nd-Fe-B intermediate decreased and the dispersity increased with the increase of?C₂H₅?₃NBH₃ content.After annealing,it was found that the agglomeration of oxide particles increased with the increase of?C₂H₅?₃NBH₃ content.This phenomenon eventually leads to the increase of the particle size of the magnetic powder with the aggravation of the agglomeration.The Fe₂B and Fe₃B phases appeared in the magnetic powder when the content of?C₂H₅?₃NBH₃ was excessive.The optimal?C₂H₅?₃NBH₃ content was 3.5 mmol by observing the influence of its content on magnetic properties,the coercive force and magnetic energy product was 5.09 kOe and2.862 MGOe,respectively.The results showed that annealing temperature,annealing time and reduction diffusion temperature had important effects on the preparation of Nd-Fe-B magnetic powder by this method.The organic matter could be effectively removed at 600-800°C,and the best intermediate phase was formed at 750°C,which was NdFeO₃,NdBO₃,?-Fe phase.Under the condition of 750°C,the optimum annealing time was 300 min,and the percentage content of NdFeO₃,NdBO₃ and?-Fe were 55 wt%,26 wt%and 19 wt%respectively.The oxide power was reduced and diffused for different time,it was found that the intensity of diffraction peak of Nd₂Fe₁₄B increased gradually with the prolongation of time.The Nd-rich amorphous phase can be observed at the grain boundary around the Nd₂Fe₁₄B grain when the time?180 min.The magnetic properties of the powder reach the maximum at 180 min,the coercive force was 4.85 kOe,the saturation magnetization was 81.68 emu/g,and the maximum magnetic energy product was 2.435 MGOe.