Fabrication, characterization and measurement of thermal conductivity of Fe3O4 nanofluids

https://doi.org/10.1016/j.jmmm.2010.08.016Get rights and content

Abstract

Magnetite Fe3O4 nanoparticles were synthesized by a co-precipitation method at different pH values. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electronic microscopy. Their magnetic properties were evaluated on a vibrating sample magnetometer. The results show that the shape of the particles is cubic and they are superparamagnetic at room temperature. Magnetic nanofluids were prepared by dispersing the Fe3O4 nanoparticles in water as a base fluid in the presence of tetramethyl ammonium hydroxide as a dispersant. The thermal conductivity of the nanofluids was measured as a function of volume fraction and temperature. The results show that the thermal conductivity ratio of the nanofluids increases with increase in temperature and volume fraction. The highest enhancement of thermal conductivity was 11.5% in the nanofluid of 3 vol% of nanoparticles at 40 °C. The experimental results were also compared with the theoretical models.

Introduction

Magnetic nanofluids, also called ferrofluids, are stable colloidal solutions consisting of magnetic nanoparticles dispersed in a based fluid [1]. The magnetic nanofluid behaves as a smart or functional fluid due to some of its unique features. They have some applications in a variety of fields such as electronic packing, mechanical engineering, aerospace, and bioengineering. Since the control and manipulation of the flow and energy transport processes in the magnetic nanofluids are possible using an external magnetic field, the promising potential of magnetic fluids expanded into thermal engineering during the past decade besides the above applications [2].

Water-based magnetic nanofluids are a special category of polar magnetic nanofluids with particular features of particle interactions and agglomerate formation processes [3]. The interest in water-based magnetic nanofluids in the selected bioengineering and biomedical systems has been growing exponentially in the last decades [4]. Surface coating of nanoparticles and colloidal stability of biocompatible water-based magnetic nanofluids are particularly important for biomedical applications such as magnetic cell separation, drug delivery, hyperthermia, and contrast enhancement in magnetic resonance imaging [3], [5]. They have been extensively applied to audio voice coil-damping, intertia-damping apparatuses, bearings, stepping motors, and vacuum seals [6].

Thermal conductivity of traditional heat transfer fluids such as lubricants, engines coolants, and water is inherently low. Metals and metal oxides in solid form have orders-of-magnitude of higher thermal conductivities than those of fluids. The thermal conductivity of fluids that contain suspended solid metallic and metal oxides particles could be significantly higher than that of conventional heat transfer fluids [7]. The exact mechanism of thermal transport in nanofluids has not been known at this moment, even if several potential mechanisms have been suggested to describe the experimental results of thermal conductivity of nanofluids [8].

Although the magnetic properties of the magnetic nanofluids are the subject of intense studies [9], [10], [11], there are few data in the literature concerning their thermal properties [12], [13], [14], [15], [16], [17]. The investigation of heat transfer characteristics of magnetic nanofluids is very interesting and important from the viewpoint of fundamental study on their thermal behaviors and the development of practical thermal devices of magnetic nanofluids in a number of areas such as the new kind of heat exchangers, cooling loops, and energy conversion systems [2].

Hong et al. [12] prepared Fe nanofluids in ethylene glycol and showed that the thermal conductivity of nanofluids increases nonlinearly with the volume fraction of nanoparticles. Hong et al. [13] investigated the thermal conductivity of nanofluids containing different volume fractions of Fe nanoparticles in ethylene glycol. Zhu et al. [14] prepared Fe3O4 nanofluids in distilled water and investigated the effect of volume fraction on the thermal conductivity of nanofluids. Philip et al. [15] observed the enhancement in the thermal conductivity of ethylene glycol with increase in volume fraction of Fe3O4 nanoparticles. They also measured the thermal conductivity of nanofluids in the presence of external magnetic field. Philip et al. [16] prepared a stable colloidal suspension of magnetite nanoparticles of average diameter 6.7 nm, coated with oleic acid and dispersed in hexadecane, and measured their thermal conductivity. They indicated that the thermal conductivity of nanofluids increases with the volume fraction of nanoparticles. Yu et al. [17] applied phase transfer method for preparing stable kerosene based Fe3O4 nanofluids. Their results showed that the enhancement of the thermal conductivity increases linearly with the volume fraction of Fe3O4 nanoparticles and the value is up to 34.0% for 1.0 vol.% of nanofluid.

To the best of our knowledge, in spite of widespread applications of water-based Fe3O4 nanofluid, especially in biomedical and bioengineering, there is only two reports in the literature [14], [18] concerning the measurement of its thermal conductivity in different volume fractions. They did not try to investigate the temperature dependence of thermal conductivity of Fe3O4 water-based nanofluids. Hence, the main goal of the present study is to investigate the effect of both temperature and volume fraction on the thermal conductivity of Fe3O4-water nanofluids.

In this work, the magnetic Fe3O4 nanoparticles were synthesized by co-precipitation method at different pH values. The XRD, FTIR, and TEM techniques were used to characterize the structure, purity, and the size of the nanoparticles. The magnetic properties were evaluated by vibrating sample magnetometer. The Fe3O4 nanoparticles were dispersed into deionized water to obtain the desired nanofluids. Tetramethyl ammonium hydroxide was used as a dispersant. The thermal conductivity of Fe3O4 nanofluids was measured as the function of temperature and volume fraction. The experimental results were compared with some known theoretical models.

Section snippets

Materials

The starting materials used in this work were ferric chloride hexahydrate (FeCl3·6H2O), ferrous chloride tetrahydrate (FeCl2·4H2O), aqueous ammonia, and tetramethyl ammonium hydroxide (N(CH3)4OH). All chemicals were used as received without further purification.

Synthesis procedure

To synthesize Fe3O4 nanoparticles, FeCl3·6H2O (1 M) and FeCl2·4H2O (2 M) were prepared by dissolving iron salts in HCl (2 M) solution. Typically, 4 ml of FeCl3 and 1 ml of FeCl2 were mixed in a molar ratio of 2:1. Then, 50 ml of ammonia

Results and discussion

The phase and purity of the products were examined by XRD and the patterns of all samples prepared under different conditions are shown in Fig. 1. All the reflection peaks in the patterns can be indexed to the face center cubic phase of magnetite with lattice parameter of a=8.374 Å, which are in agreement with the standard values (JCPDS file no. 01–1111). The existence of any impurity compound other than magnetite is not observed. The characteristic peaks of magnetite are (2 2 0), (3 1 1), (4 0 0), (4 2

Conclusions

Superparamagnetic Fe3O4 nanoparticles were successfully synthesized by a simple and cost-effective co-precipitation method in different conditions. The XRD, TEM, FTIR, and VSM techniques were used to characterize the structure, size, purity, and magnetic properties of the nanoparticles. The best crystallinity was observed for MN4 sample (pH initial=1.5 and pH final=9.5). The results reveal that the Ms value increases with increase in the crystallinity and particle size.

Fe3O4 nanofluids were

References (32)

Cited by (284)

View all citing articles on Scopus
View full text