Micro/nanostructure observation of microwave-heated Fe3O4
Micro/nanostructure observation of microwave-heated Fe3O4
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DOI：
10.1557/jmr.2009.0192
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发表时间：
2009-05-01
影响因子：
2.7
通讯作者：
Taniguchi, Shoji
中科院分区：
文献类型：
--
作者：
Yoshikawa, Noboru;Cao, Ziping;Taniguchi, Shoji
为了研究微波处理Fe3O4（已有报道）的脱晶现象，本研究对微波加热Fe3O4粉末的微纳米结构进行了观察。在TE10单模辐照器中，在磁场(H)场最大位置用2.45 GHz MW辐照样品。试样在h场中加热至远高于居里温度。在1000℃以上加热后，试样表面呈玻璃状，x射线衍射峰强度减弱。它们类似于宾夕法尼亚州立大学早期工作中报道的脱晶特征。根据微波加热试样的XRD谱图，可以观察到FeO的形成，Fe3O4的峰随着宽度的加宽向低角度移动。为了解释这些发现，提出了一个模型，即由于氧含量的增加，FeO和Fe3O4的相分离导致晶格参数的增加。这种活性是由纳米尺度的局部氧运输引起的。考虑到XRD中Fe3O4主峰带肩的形状和纳米束衍射（NBD）中晕的存在，存在非晶相区。透射电镜观察结果表明，它们处于纳米尺度的局部区域，而非完全无定形的类玻璃形态（或脱晶形态）尚未得到证实。结合Fe-O相图，讨论了所观察到的微纳结构和非晶相形成机理。
To investigate the microwave (MW) processing of Fe3O4, for which occurrence of decrystallization has been reported, the micro/nanostructures of MW-heated Fe3O4 powder were observed in this study. The specimens were irradiated by 2.45 GHz MW at the position of magnetic (H)-field maximum in a TE10 single mode applicator. The specimen was heated well above the Curie temperature in H-field. The heated specimen above 1000 degrees C revealed the glass-like surface with the diminished x-ray diffraction (XRD) peak intensities. They resemble the reported features of decrystallization in an earlier work performed at Penn State University. According to the XRD profiles of the MW-heated specimens, formation of FeO and shift of Fe3O4 peaks to the lower angle with the broadened width were observed. To account for the findings, a model is presented that phase separation occurred into FeO and Fe3O4 resulting in an increased lattice parameter due to the increased oxygen content. This activity is caused by local transport of oxygen in nanoscale. Considering the shape of the main XRD Fe3O4 peak with a shoulder and the existence of halo in nanobeam diffraction (NBD), amorphous phase areas exist. As a result of transmission electron microscopy observation, it was shown that they were in nanoscaled localized regions, and it was not confirmed that the glass-like morphologies (or decrystallized morphologies) are totally amorphous. The observed micro/nanostructures and mechanism of the amorphous phase formation were discussed considering the Fe-O phase diagram.