Size Effect of Fe3O4 Nanoparticles on Magnetism and Dispersion Stability of Magnetic Nanofluid

Fang Chen,Shengnan Yan,Hao Fu,Xiaobing Liu,Nasir Ilyas,Zhenggui Li

doi:10.3389/fenrg.2021.780008

Abstract

It is well known that magnetic nanofluids are widely applied in various fields ranging from heat transfer to miniature cooling, and from damping to sealing, due to the mobility and magnetism under magnetic field. Herein, the PFPE-oil based magnetic nanofluids with superior magnetization and dispersion stability were obtained via regulating reaction temperature. The structures of particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The size effects of particles on the magnetism and coating effect of particles, and on the stability and saturation magnetization of the fluids were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM) and density instrument, respectively. The results indicate that the impurity phase FeOOH only appear in the sample prepared at 18°C and the average size of Fe3O4 nanoparticles reduces from 120 to 20 nm with raising reaction temperature. The saturation magnetization of Fe3O4 particles increases firstly and then reduces with increasing particle size, which is affected by the thickness of magnetic dead layer and impurity phase FeOOH. The Fe3O4 particles could be chemically coated by PFPE-acids, and the coated mass is a little affected by particle size. The stability of the nanofluids lowers while the saturation magnetization increases firstly and then decrease with increasing particle size. At reaction temperature of 60°C, Fe3O4 particles of 25 nm and the nanofluids with superior stability and saturation magnetization were obtained. Our results indicate that the control of nanoparticles size by regulating reaction temperature can be a useful strategy for preparing magnetic nanofluids with desirable properties for various potential applications.

Highlights

IntroductionThe nanofluids are colloidal suspensions composed of various nanoparticles (Al2O3, TiO2, ZnO, CuO, SiO2, Fe3O4, etc.) (Shahrul et al, 2016; Nayak et al, 2020; Aldabesh et al, 2021; Awan et al, 2021; Iskander, 2021; Khan et al, 2021; Tlili et al, 2021), and these particles have different characteristics, for example, ZnO has the highest thermal conductivity, SiO2 has lowest thermal conductivity, Fe3O4 has magnetism and enhancement of thermal conductivity (Lemes et al, 2017)
The Fe3O4 nanoparticles prepared at room temperature (RT), the dual-phase structure consisting of the Fe3O4 spinel phase seemed dominant (Yang et al, 2012) and an impurity phase as well
Fe3O4 nanoparticles dispersed into the magnetic nanofluids were prepared

Summary

Introduction

The nanofluids are colloidal suspensions composed of various nanoparticles (Al2O3, TiO2, ZnO, CuO, SiO2, Fe3O4, etc.) (Shahrul et al, 2016; Nayak et al, 2020; Aldabesh et al, 2021; Awan et al, 2021; Iskander, 2021; Khan et al, 2021; Tlili et al, 2021), and these particles have different characteristics, for example, ZnO has the highest thermal conductivity, SiO2 has lowest thermal conductivity, Fe3O4 has magnetism and enhancement of thermal conductivity (Lemes et al, 2017). The performance and applications of magnetic nanofluids depend on their stability, which is related to the proper dispersion of nanoparticles (Chen et al, 2016a; Colla et al, 2012; Aishwarya et al, 2013; Mabood and Akinshilo, 2021). The conventional ferrofluids possess low saturation magnetization due to their small average particle size (i.e., ∼10 nm) and the differences of particle morphology and types of magnetic component (López-López et al, 2012). Even though some magnetorheological fluids contain larger average particle size (i.e., ∼ 1 μm) with higher saturation magnetization (Tang, 2011), they exhibit unsatisfied dispersion stability compared to ferrofluids (Chen et al, 2021). The two critical parameters, saturation magnetization and stability, must be considered simultaneously for different nanofluids application occasions

Objectives

Methods

Results

Conclusion