The effect of organic lubricant on Nd-Fe-B powder and sintered magnet

In order to optimize the process of magnetic pressing for preparing Nd-Fe-B sintered magnet, the organic additives are generally mixed into Nd-Fe-B powder, acting as the lubricants. This paper aims to reveal the interactions between lubricant and powder. The additives of C38H76N2O2 (AⅠ), C17H35CONH2 (AⅡ), and C14H31N (AⅢ) were selected as lubricants, respectively, and their influence in Nd-Fe-B powder and magnet was investigated. Based on the distributions of EHOMO and ELUMO, representing the ability to donate and accept electrons, respectively, for the AⅠ, AⅡ and AⅢ molecules, the value of the ΔE (ELUMO - EHOMO) was calculated, indicating the higher adsorption activity of AⅠ than those of AⅡ and AⅢ. In order to explore the interactions between the lubricant and Nd2Fe14B powder, the molecular dynamic (MD) simulation and X-ray Photon-electron Spectroscopy (XPS) analysis were performed. The results indicated that the lubricant was covered on surface of Nd-Fe-B powder through chemical and physical adsorption. Furthermore, AⅠ exhibited the stronger adsorption capability on the (001) plane of Nd2Fe14B than those for AⅡ and AⅢ. However, the long carbon chain in AⅠ increased the interparticle friction among powder and the residual carbon content in sintered magnet. The AⅢ-magnet exhibited the highest grain orientation, magnetic properties and lowest residual carbon content under the combined effect of adsorption capability and carbon chain length. It provides a guidance for designing the organic lubricant on Nd-Fe-B powder of sintered magnet.