Synthesis of aqueous NiFe2O4-Fe3O4 hybrid magnetic nanofluids and investigation on electrical conducting behaviour

Highly stable aqueous magnetic mono nanofluids of nickel ferrite (NiFe2O4), magnetite (Fe3O4), and hybrid magnetic nanofluids of NiFe2O4-Fe3O4 are synthesized through a two-step method. The structural analysis of the NiFe2O4 and Fe3O4 nanoparticles made through X-ray diffraction identifies their spinel cubic structure. The magnetic studies indicate their superparamagnetic nature, which is further confirmed through the Langevin fitting of the experimental data. The monodomain nature of nanoparticles is verified using the coupling constant, and a spherical morphology is observed using a transmission electron microscope. The surface charge of the nanoparticles is studied through zeta potential analysis. The electrical conductivity of the aqueous mono and hybrid magnetic nanofluids is measured for various concentrations and temperatures. The hybrid magnetic nanofluids show higher electrical conductivity values than those of both the mono nanofluids. For instance, NiFe2O4-Fe3O4 (1.2 vol%) hybrid nanofluid is found to have a conductivity value of 18.91 mu S/cm that is 1.5 times enhanced than that of Fe3O4 mono nanofluid (12.87 mu S/cm) and three times enhanced than that of NiFe2O4 (6.43 mu S/cm) mono nanofluid of same volume percentage at 303 K. A Maximum enhancement of 136 % is obtained for 1.2 vol% hybrid nanofluid with respect to water at 303 K and this enhancement further increases to 196 % with the rise in temperature to 323 K. There is no theoretical model found in literature to explain the electrical conductivity of hybrid nanofluids. Maxwell, Bruggeman, Cruz, and Shen models are applied to explain the conductivity of hybrid magnetic nanofluids. Through a comparison of experimental values with theoretical values, it is found that the Shen model, if modified suitably, can explain the electrical conduction of hybrid magnetic nanofluids. Also, the electrical conduction mechanism in hybrid magnetic nanofluids is described in terms of electrophoretic charge transportation and the Brownian motion. In addition, the magneto-electrical conductivity study is performed by measuring the electrical conductivity by applying a magnetic field of various strengths. The electrical conductivity, magneto-electrical conductivity studies and an understanding of electrical conduction mechanism are highly significant for magnetically transportable electronic cooling and conducting applications of hybrid magnetic nanofluids.