Nanodiamond-Fe3O4 nanofluids: Preparation and measurement of viscosity, electrical and thermal conductivities

Nanodiamond (ND) attached with magnetite (Fe3O4) nanoparticles have been synthesized successfully by in-situ and chemical reduction of Fe3 + and Fe2 + cations on the acid treated-ND surface by using sodium hydroxide as a reducing agent. The synthesized magnetic ND-Fe3O4 nanocomposite was characterized by XRD and TEM. The results indicate that Fe3O4 nanoparticles were homogeneously dispersed on the outer surface of the ND particles. The stability of ND-soot, acid treated-ND and ND-Fe3O4 dispersed in distilled water were investigated by zeta potential and optical images. The electrical conductivity was measured by using four probe technique by considering dry ND-Fe3O4 powder make it into 1 cm circular pellet. The stable magnetic nanofluids were prepared by dispersing ND-Fe3O4 nanocomposite in water and ethylene glycol/water mixtures and then measured both thermal conductivity and viscosity with effects of particle loadings and temperatures experimentally. Results indicate that thermal conductivity enhancements are 17.8%, 13.4%, 13.6%, 14.6% and viscosity enhancements are 1.72-times, 2.19-times, 1.50-times, 1.79-times for water, 20:80%, 40:60% and 60:40% EG/W-based nanofluids at 0.2% volume concentration at a temperature of 60 °C, respectively. Correlations for the thermal conductivity and viscosity of nanocomposite nanofluids have been proposed based on the experimental data.