Flowerlike iron oxide nanostructures and their application in microwave absorption

doi:10.1016/j.jallcom.2015.01.087

Journal of Alloys and Compounds

Volume 631, 15 May 2015, Pages 183-191

https://doi.org/10.1016/j.jallcom.2015.01.087 Get rights and content

Highlights

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Self-assembled flowerlike α-Fe₂O₃, Fe₃O₄ and γ-Fe₂O₃ were fabricated by a simple calcination procedure.
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The dielectric and magnetic loss of Fe₃O₄ flower are higher than those of γ-Fe₂O₃ flower.
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An optimal reflection loss of −46.0 dB is found at 3.4 GHz for flowerlike Fe₃O₄.
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Microwave absorption mainly results from magnetic loss rather than dielectric loss.
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The magnetic loss mainly results from the nature resonance rather than exchange resonance.

Abstract

Self-assembled flowerlike α-Fe₂O₃, Fe₃O₄ and γ-Fe₂O₃ were fabricated by a simple calcination procedure. The structure characterization shows that the flowerlike morphology and the size of the nanostructures are perfectly maintained in the conversion of precursor to α-Fe₂O₃, Fe₃O₄, and γ-Fe₂O₃. The complex permittivity and permeability results indicate that the dielectric and magnetic loss of Fe₃O₄ flower are both higher than those of γ-Fe₂O₃ flower. In addition, Fe₃O₄ flower shows a good electromagnetic impedance match and its microwave absorption mainly originates from magnetic loss rather than dielectric loss. An optimal reflection loss of −46.0 dB is found at 3.4 GHz for flowerlike Fe₃O₄, which indicates that the sample can be used as a highly efficient microwave absorber.

Introduction

Microwave absorbing materials based on the magnetic materials with low reflection and high absorption properties are receiving extensive attention because of their promising application in electronic devices used in commerce, industry, and military affairs [1]. In recent years, carbonyl irons were widely investigated as one of typical magnetic microwave absorbing materials [2], [3], [4]. However, the low density and absorption properties of the commercial carbonyl iron restrict its use in the applications. Hollow iron particle with low density is also a new material to improve the microwave absorption properties [5], [6]. Besides, iron-based materials such as γ-Fe₂O₃, and Fe₃O₄ are recognized as promising materials for microwave applications because of their relative high magnetization and antioxidation properties in air. Various iron oxides or iron composites with different morphologies such as rods, wires, tubes, flakes, urchins and dendrites have been successfully reported with their application as electromagnetic wave absorber [7], [8], [9], [10], [11], [12].

However, the relationship among the structure, morphology and magnetic properties of iron-based nanomaterials has not been fully understood. As we known, large surface areas and high magnetization will improve the microwave absorption properties. Herein, we report the synthesis of novel three-dimensional (3D) flowerlike iron oxide nanostructures with large surface areas by an ethylene glycol (EG)-mediated self-assembly process. The as-synthesized iron oxide precursor was transformed into iron oxide. Moreover, the phase of the final product can be easily controlled to be α-Fe₂O₃, γ-Fe₂O₃, or Fe₃O₄, three of the most common iron oxides, by altering the calcination conditions. The microwave absorption properties of α-Fe₂O₃, γ-Fe₂O₃, and Fe₃O₄ flowerlike nanostructures with almost the same large surface areas are presented in this study.

Section snippets

Experimental

The thermal decomposition of metal alkoxide is a simple route to achieving a tailored metal oxide. In a typical procedure, 2.4 g of ferric chloride (FeCl₃⋅6H₂O), 5.4 g of urea, and 14.4 g of tetrabutylammonium bromide were dissolved in 360 mL of ethylene glycol. The red solution was refluxed at 195 °C for 30 min. After cooling, the as-synthesized iron oxide precursor was collected as a green precipitate after centrifugation and ethanol-washing cycles. The morphology of the precursor was studied by

Results and discussion

The diffraction peaks of the as-obtained red product well agreed with those for α-Fe₂O₃ powder (JCPDS card 80-2377) (Fig. 2c), when the precursor was calcined at 450 °C in air for 3 h. When the precursor was calcined at 450 °C under N₂ protection for 3 h, the positions of all diffraction peaks of the corresponding product (Fig. 2b), well matched those of Fe₃O₄ (JCPDS card 87-0245). The formation of Fe₃O₄ can be attributed to the reductive ability of the organic species (glycolates) in the

Conclusions

Self-assembled flowerlike α-Fe₂O₃, Fe₃O₄ and γ-Fe₂O₃ were fabricated by a simple calcination procedure. The complex permittivity and permeability results indicate that the dielectric loss and magnetic loss of Fe₃O₄ flower are both higher than those of γ-Fe₂O₃ flower. Compared with γ-Fe₂O₃, the microwave absorption property of Fe₃O₄ is enhanced as evidenced by its higher saturation magnetization, crystalline anisotropy and better EM impedance match. An optimal RL of −46.0 dB was found at 3.4 GHz

Acknowledgment

This work is supported by National Natural Science Foundation of China (Nos: 51101079 and 51171076).

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Flowerlike iron oxide nanostructures and their application in microwave absorption

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgment

J. Alloys Comp.

Appl. Surf. Sci.

J. Magn. Magn. Mater.

Appl. Surf. Sci.

Mater. Lett.

J. Alloys Comp.

J. Alloys Comp.

Appl. Surf. Sci.

Mater. Sci. Eng. B

J. Magn. Magn. Mater.

J. Alloys Comp.

Acta Mater.

J. Appl. Phys.