预氧化及预氧化-还原处理改善NdFeB微晶磁粉的抗氧化性能

EFFECT OF PREOXIDATION AND PREOXIDATION-REDUCTION TREATMENT ON OXIDATION RESISTANCE OF NdFeB MINI-CRYSTAL MAGNETIC POWDER

以重铬酸钾为氧化剂及亚硫酸氢钠为还原剂，分别在强氧化条件下及氧化-还原条件下处理快淬ＮｄＦｅＢ微晶磁粉表面，研究了处理后磁粉的热氧化及抗氧化机理。结果表明，预氧化及预氧化-还原处理能使磁粉的抗氧化性能明显提高。

By using potassium dichromate as oxidizer and sodium bisulfite as reductor, the surface of rapidlychilled NdFeB mini-cystal magnetic powder was treated under the strong oxidation condition. The hotoxidation mechanism of the treated magnetic powders was studied. The resuits of weight gain duringdry and wet oxidation tests indicated that the above-mentioned preoxidation and preoxidation-reductiontreatment can considerably improve the oxidation resistance of the maguetic powder. For example, theweight gains reached 0.024% and 0.077% after oxidation at 430C and 500C for 1 hr, respectively, for thetreated powder, while 2.3% and 3.83% for the untreated powder. During the wet oxidation test (80C,RH90%, 100hr), the corresponding data were 0.067% and 7.30%. The treatments increased B, H, (BH)maxof the experimental cohesional magnet by 60%-100%. XPS of the magnetic powder before and after thetreatment were compared and the results showed that Nd, Fe on the surface of untreated powder were inoxidized states and the surface of the treated powder was covered by chromium oxide. The presence ofthe latter had the action of antioxidation and therefore enhanced the magnetic capability of the cohesionalmagnet.