Characterisation of high temperature oxidation of Nd-Fe-B magnets
Characterisation of high temperature oxidation of Nd-Fe-B magnets
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DOI：
10.1016/s0304-8853(97)00189-3
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发表时间：
1997-09-01
影响因子：
2.7
通讯作者：
Teillet, J
中科院分区：
文献类型：
--
作者：
Edgley, DS;LeBreton, JM;Teillet, J
研究了Nd16.4Fe75.7B7.9商用烧结磁体在500 ℃以下纯氧气氛和350 ~ 600 ℃空气中的长期高温氧化性能。在纯氧气氛中，发生三个放热反应，对应于富Nd晶粒间区域的氧化，Nd 2Fe 14 B基体相，和在Nd 2Fe 14 B氧化过程中形成的α-Fe相。在空气中，进一步研究了Nd_2Fe_（14）B的氧化行为。代替沿着晶界进行的氧化，Nd 2Fe 14 B基质解离以形成粘附的灰色表面层，该灰色表面层穿晶地生长到磁体中。这可能是由于在富Nd区域中发生的反应，该反应阻止了氧沿晶界沿着的快速路径扩散。主要反应是Nd 2Fe 14 B基体分解成α-Fe纳米晶体，其中含有Nd的氧化物的小沉淀。该反应的产物形成粘附的灰色层，该灰色层穿晶生长到磁体中。该反应的活化能为114 kJ·mol ~（-1），扩散系数为0.7mm ~（2）·s ~（-1）。在解离的灰色层的进一步氧化之后，α-Fe被氧化以形成α-Fe 2 O3，并且最后，从约600 ℃开始，一些α-Fe 2 O3与Nd的氧化物的小沉淀物反应以形成FeNdO 3。
The long term high temperature oxidation properties of a Nd16.4Fe75.7B7.9 commercial sintered magnet were investigated in pure oxygen atmosphere up to 500 degrees C and in air between 350 and 600 degrees C. In pure oxygen atmosphere, three exothermic reactions occur, corresponding to the oxidation of the Nd-rich intergranular regions, the Nd2Fe14B matrix phase, and the alpha-Fe phase that forms during the oxidation of Nd2Fe14B. In air, the oxidation of Nd2Fe14B was investigated further. Instead of the oxidation proceeding along the grain boundaries, the Nd2Fe14B matrix dissociates to form an adherent grey surface layer which grows transgranularly into the magnet. This is probably due to a reaction occurring in the Nd-rich regions which prevents fast path oxygen diffusion along the grain boundaries. The main reaction is the dissociation of the Nd2Fe14B matrix into alpha-Fe nanocrystals which contain small precipitates of oxides of Nd. The products of this reaction form the adherent grey layer which grows transgranularly into the magnet. The activation energy and the diffusivity pre-exponential factor for this reaction were found to be 114 kJ mol(-1) and 0.7 mm(2) s(-1) respectively. After further oxidation of the dissociated grey layer, alpha-Fe is oxidised to form alpha-Fe2O3 and finally, from about 600 degrees C, some of the alpha-Fe2O3 reacts with the small precipitates of oxides of Nd to form FeNdO3.