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| EFFECT OF PREOXIDATION AND PREOXIDATION-REDUCTION TREATMENT ON OXIDATION RESISTANCE OF NdFeB MINI-CRYSTAL MAGNETIC POWDER |
| Dijiang Wen; |
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Abstract By using potassium dichromate as oxidizer and sodium bisulfite as reductor,the surface of rapidly chilled NdFeb mini-crystal magnetic powder was treated under the strong oxidation condition.The hot oxidation mechanism of the treated magnetic powders was studied.The results of weight gain during dry and wet oxidation tests indicated that the above-mentioned preoxidation and preoxidation-reduction treatment can considerably inprove the oxidation resistance of the magnetic powder.For example,the weight gains reached 0.024% and 0.077% after oxidation at 430℃ and 500℃ for 1 hr,respectively,for the treated powder,while 2.3% and 3.83% for the untreated powder.During the wet oxidation test (80℃,RH90%,100hr),the corresponding data were 0.067% and 7.30%.The treatments increased B,H,(BH)max of the experimental cohesional magnet by 60%-100%.XPS of the magnetic powder before and after the treatment were compared and the results showed that Nd,Fe on the surface of untreated powder were in oxidized states and the surface of the treated power was covered by chromium oxide.The presence of the latter had the action of antioxidation and therefore enhanced the magnetic capability of the cohesional magnet.
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Received: 22 July 2005
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Corresponding Authors:
Dijiang Wen
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