Elsevier

Journal of Alloys and Compounds

Volume 787, 30 May 2019, Pages 390-396
Journal of Alloys and Compounds

Magnetic and microwave absorption properties of FeNi3/NiFe2O4 composites synthesized by solution combustion method

https://doi.org/10.1016/j.jallcom.2019.02.039Get rights and content

Highlights

  • FeNi3/NiFe2O4 composites were in-situ synthesized by solution combustion method.

  • The saturation magnetization strongly increased with the appearance of FeNi3 phase.

  • The composites showed the strong absorption performance for their high permittivity and permeability.

Abstract

FeNi3/NiFe2O4 composites were prepared by solution combustion synthesis method. The solution combustion process was conducted in a closed system by use of conventional and microwave heating. Phase evolution, microstructure, magnetic and microwave absorption properties were studied by X-ray diffraction, electron microscopy, vibrating sample magnetometry and vector network analyzer techniques. The amount of FeNi3 phase was tuned by heating mode and amount of nickel precursor. The composites with higher amounts of FeNi3 phase and larger sintered particles (0.4–0.8 μm) were synthesized by microwave heating. The highest value of saturation magnetization (81 emu/g) was attained in the NiFe2O4-45 wt % FeNi3 composite. The FeNi3/NiFe2O4 composites had the high permeability due to the high saturation magnetization. The composites synthesized by conventional heating showed the maximum reflection loss of −15 dB in Ku band (12–18 GHz) with the band width of 3.8 GHz.

Introduction

Microwave absorbing materials are gaining a great attention for many potential applications in wireless devices, industrial protection, and military fields [[1], [2], [3]]. The absorbing materials including dielectric and magnetic materials convert electromagnetic (EM) waves into thermal energy [4]. The lightness, strong absorption, broad bandwidth, and good thermal and chemical stability are crucial properties for microwave absorbing materials [5,6]. Among the microwave absorbing materials, soft magnetic materials with high saturation magnetization (Ms), high permeability (μ) and low energy losses are attractive candidates [[7], [8], [9]]. Soft magnetic alloys such as FeNi3, FeCo, Finemet, etc. have limited applications in the high frequency range due to the large eddy-current loss, in spite of their very high Ms. The isolation of metallic particles in the insulating matrices such as SiO2, Al2O3, carbon, etc. decreases eddy-current losses [10]. For example, Liu et al. [11] decorated CoNi/SiO2 core-shells on reduced graphene oxide via liquid-phase reduction reactions combined with a sol-gel route. The composites show the maximum reflection loss of −46.3 dB at 6.2 GHz with a matching thickness of 4.2 mm. Kim et al. [2] used graphene as dielectric material for improving microwave absorption performance of FeNiCo particles. Lim et al. [12] synthesized Fe/MgO powders by ultrasonic spray pyrolysis and following H2 reduction. The composites show remarkable reflection loss of −65.6 dB (at 12 GHz; 1.5 mm), due to the synergetic effect of magnetic loss of Fe and dielectric loss of MgO. However, the demagnetization effects of the magnetic particles in nonmagnetic matrices suppress the permeability at microwave frequencies [13,14]. Therefore, the magnetic insulator matrices such as soft magnetic ferrites improve the absorption properties due to the decrease of demagnetization fields [15]. Wu et al. [16] synthesized wideband microwave absorber by loading ZnFe2O4 nanoparticles on carbonyl iron (Fe) flakes. The suppression of inverse electromagnetic radiation and eddy effect together with moderate magnetic loss ability by ZnFe2O4 led to the significantly microwave absorption.

Fe-Ni alloys, especially FeNi3, are commonly used as soft magnetic materials on account of their high permeability [17,18]. Many composites such as FeNi3/Al2O3 [10], FeNi3/C [14], FeNi3/NiZnFe2O4 [19,20], etc. have been explored for microwave absorption. Feng et al. [21] reported the microwave absorption performances of FeNi3/graphene composites. The minimum reflection loss of −57.2 dB was obtained at a matching thickness of only 1.45 mm. Nickel ferrite (NiFe2O4) has not only high resistivity to limit eddy current loss, but also good magnetic properties, permeability and permittivity values for microwave absorption [[22], [23], [24], [25]]. The FeNi3/NiFe2O4 composites were prepared by various physical and chemical synthesis routes such as mechanosynthesis, coprecipitation, hydrothermal, etc. [19,26,27]. Recently, solution combustion synthesis (SCS) method has also been used for preparation of nanostructured metals, oxides, sulfides, etc. for its simplicity, versatility, efficiency, and low cost [28,29]. SCS is based on the exothermic reaction between oxidants (e. g. nitrates, acetates, and carbonates) and organic fuels (e. g. citric acid, glycine, and urea), facilitating the formation of final products at low temperatures. The reactive gases released by burning of fuels modify the product composition via oxidation, reduction, sulfuration, etc. [[30], [31], [32]]. Manukyan et al. [33] prepared the metallic nickel powders by SCS method. The liberated gases such as H2, NH3, CO, etc. reduce NiO to Ni particles during combustion reaction.

In this work, FeNi3/NiFe2O4 composites were prepared in-situ by SCS method in a closed system. The FeNi3 phase contents were mainly controlled by various heating modes including of conventional and microwave ignition. The effects of the amount of FeNi3 phase on structure, microstructure, magnetic and microwave absorption properties were investigated.

Section snippets

Experimental procedures

2 mmol of ferric nitrate (Fe(NO3)3·9H2O) and x mmol of nickel nitrate (Ni(NO3)2·6H2O) as oxidants (x = 0.5, 1 and 1.5) were dissolved in distilled water. Then, glycine (C2H5NO2) as fuel was also added in which the fuel to oxidant molar ratio was fixed as 1.5. The dark brown homogeneous solution was dried at 80 °C. A part of the dried gel was poured into a round bottom flask and ignited by further heating up to 250 °C. The liberated gases were entrapped into a large beaker of water [34]. Another

Results and discussion

XRD patterns of the as-combusted powders by conventional and microwave heating are shown in Fig. 1, Fig. 2, respectively. The indexed peaks as (220), (222), (311), (400), (422), (511) and (440) are related to the nickel ferrite (JCDPS Card No. 01-074-1913), while the indexed peaks as (111), (200) and (220) are corresponded to FeNi3 phase (JCDPS Card No. 00-038-0419). The crystallite size of NiFe2O4 and phase constituent of powders are summarized in Table 1. With the increase of nickel

Conclusions

Solution combustion synthesis method was used for preparation of FeNi3/NiFe2O4 composites. The intermetallic FeNi3 phase was formed via reduction of metallic oxides during combustion. The higher amounts of FeNi3 phase were formed by using higher amounts of nickel precursor together with microwave ignition. The saturation magnetization increased from 42 up to 81 emu/g and the coercivity decreased from 157 to 78 Oe due to the presence of FeNi3 phase. The composites showed the weak absorption in

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