Presentation Information
[P1-75]The influence of phosphorization treatment on the high-temperature oxidation resistance of Nd-Fe-B magnetic powder
* Jingwu Zheng1, Xinqi Zhang1, Dongsheng Shi1, Wei Cai1, Liang Qiao1, Yao Ying1, Shenglei Che 1 (1. Research Center of Magnetic and Electronic Materials, College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China (China))
Keywords:
Nd-Fe-B powders,Anti-oxidation,phosphorylation,Methylene diphosphonic acid (MDPA)
The commonly employed industrial approach for enhancing the high-temperature oxidation resistance of rare earth magnetic powder involves conducting surface phosphating treatment to generate a phosphate conversion coating. In response to the environmental concerns associated with the utilization of high-concentration inorganic phosphoric acid as a surface modifier, this article introduces a sustainable alternative in the form of a green organic phosphonic acid modifier (Methylene diphosphonic acid, MDPA). Furthermore, the impact of treatment with inorganic phosphoric acid and MDPA on the magnetic properties and antioxidant performance is investigated. The results indicate that, compared to the untreated powder, the coercivity and maximum magnetic energy product of the magnetic powder exhibit a slight decrease after treatment with inorganic phosphoric acid and MDPA at room temperature. However, there is a significant improvement in the high-temperature oxidation resistance of the magnetic powder. Moreover, MDPA demonstrates a superior modification effect compared to inorganic phosphoric acid. The enhanced magnetic performance at elevated temperatures following phosphating treatment can be attributed to the formation of a conversion coating characterized by uniformity and density, primarily composed of metal phosphates. After treatment with inorganic phosphoric acid, the conversion film exhibits a relatively higher Nd content. This phenomenon can be attributed to the preferential corrosion of the intergranular Nd-rich phase of magnetic powder by inorganic phosphoric acid, while the conversion film formed through MDPA treatment primarily consists of iron phosphate, resulting in a comparatively lower Nd content. This observation may provide an explanation for the lesser impact on magnetic performance with MDPA treatment.
