TY - JOUR
T1 - Micro/nanostructure observation of microwave-heated Fe3O 4
AU - Yoshikawa, Noboru
AU - Cao, Ziping
AU - Louzguin, Dmitri
AU - Xie, Guoqiang
AU - Taniguchi, Shoji
N1 - Funding Information:
We are grateful for the financial support provided by a Grant-in-Aid from Ministry of Education, Sports, Culture, Science and Technology, Japan, Priority Area on Science and Technology of Microwave-Induced, thermally Non-Equilibrium Reaction Field, and by a Grant-in-Aid from Exploratory Research by JSPS. The precious discussions with Prof. Nobuyuki Nishi at National Institute for Molecular Science and with Prof. Sato at National Institute for Fusion Science on the nanostructure formation in Fe3O4 are greatly acknowledged, the discussion was made on their original high-resolution TEM observation.
PY - 2009/5
Y1 - 2009/5
N2 - To investigate the microwave (MW) processing of Fe3O 4, 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 °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 Fe304 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-0 phase diagram.
AB - To investigate the microwave (MW) processing of Fe3O 4, 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 °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 Fe304 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-0 phase diagram.
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U2 - 10.1557/jmr.2009.0192
DO - 10.1557/jmr.2009.0192
M3 - Article
AN - SCOPUS:67649545072
VL - 24
SP - 1741
EP - 1747
JO - Journal of Materials Research
JF - Journal of Materials Research
SN - 0884-2914
IS - 5
ER -