In the present research, the shape- and size-controlled synthesis

In the present research, the shape- and size-controlled synthesis of iron-cobalt alloy nanoparticles was carried out in reverse micelles of water in hexanol,

and the magnetic properties of synthesized nanoparticles were studied. Then, the magnetic fluids of each series of nanoparticles were prepared, and the stability and inductive properties of FeCo nanofluids were studied. Finally, the mechanisms of heat generation were discussed based on experimental results and theoretical models. Methods Iron(III) chloride hexahydrate (FeCl3 · 6H2O (%99+)), cobalt(II) sulfate heptahydrate (Co(SO4) · 7H2O (%99+)), 1-hexanol, sodium borohydride (NaBH4 (%99+)), and cetyltrimethylammonium bromide (CTAB) were purchased from MERCK chemicals (Saadat Abad, Tehran, Iran) and used as received with no further purification. High-purity nitrogen gas (%99.99+) was used to provide an NVP-AUY922 oxygen-free environment during the synthesis procedure. Microemulsion 1 (ME1) and microemulsion 2 (ME2) were prepared on the basis of ternary phase diagram of water/CTAB/hexanol which is described elsewhere [25]. Fe0.7Co0.3 alloy nanoparticles were prepared by mixing equal volumes of ME1 and ME2

containing metal salts and precipitating agent, respectively. The [NaBH4]/[metal salts] molar ratio was kept at 2 with metal salt concentration of 0.1 M. First, ME1 was transferred into a three-necked round-bottomed flask and then ME2 was added drop by drop with vigorous stirring of ME1 under N2 atmosphere. Black precipitates of FeCo alloy nanoparticles appeared immediately after mixing of the two microemulsions. After 5 min of reaction, the synthesized nanoparticles were magnetically separated using a strong neodymium magnet, and the supernatant was decanted. Then, the nanoparticles were washed with acetone, ethanol, and chloroform several times to remove all residual elements and compounds.

Some of the as-synthesized powders were annealed in a tube furnace at 623 and 823 K for 10 min under H2 atmosphere. To maintain Methane monooxygenase a magnetic fluid with stable dispersion, FeCo nanoparticles were dispersed in a vigorously stirring solution of CTAB (2 gr)/1-butanol (2 ml) in deionized water for 1 h under an inert atmosphere. Characterization of samples was done using X-ray diffraction (XRD) (PANalytical X’Pert Pro MPD (PANalytical B.V., Almelo, The Netherlands) with Cu kα radiation), transmission electron microscopy (TEM) (ZEISS EM10-C (Carl Zeiss AG, Oberkochen, Germany) at 100 kV), and high-resolution transmission electron microscopy (HRTEM) (JEOL JEM-2100 (JEOL Ltd., Tokyo, Japan) at 200 kV). Elemental analysis was done using an energy-dispersive spectroscopy (EDS) detector attached to the HRTEM. The magnetic properties of samples were analyzed using a vibrating sample magnetometer (VSM). The stability of the magnetic fluids was investigated using a Gouy magnetic susceptibility balance instrument (MSB-MK1) at various nanoparticle sizes and concentrations.

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