Phase and surface area studies of maghemite nanoparticles dispersed in silica gel

First, the superparamagnetic maghemite nanoparticles were synthesised using Massart's procedure. Then, the nanocomposites of the synthesised maghemite nanoparticles and silica were produced by dispersing the as-synthesised maghemite nanoparticles into the silica xerogel prepared by sol-gel technique. The system was then heated for 3 days at 140°C. The phase analysis performed using X-ray diffraction confirmed that the as-synthesised nanoparticles and the nanoparticles within the silica gel were maghemite. Surface characteristic of the nanocomposite was evaluated by N2 adsorption. The 'pure' silica gel and maghemite nanoparticles showed high values of surface area (150-160 m2 g1), while the surface area of nanocomposite was less than 40 m2 g1. This was probably due to the formation of dense structures caused by incorporation of maghemite nanoparticles within the pores of silica gel. The pore width increased with increasing content of maghemite nanoparticles

Thermal conductivity of water based magnetite ferrofluids at different temperature for heat transfer applications

Magnetic magnetite, Fe3O4 nanoparticles produced by Massart’s procedure were used to prepare water based magnetite, Fe3O4 ferrofluids without addition of any stabilizing agent or surfactant. The thermal properties and suspension stabilization of the ferrofluids were investigated by varying the magnetite, Fe3O4 nanoparticles concentration in the ferrofluids prepared. The thermal conductivity of water based ferrofluids prepared using five different volume fraction of magnetite, Fe3O4 suspension (0.1, 0.05, 0.02, 0.01 and 0.005) were measured at five different temperature, 25°C, 30°C, 40°C, 50°C and 60°C in order to evaluate its potential application as heat transfer fluid. The results shows that the thermal conductivity of the ferrofluids are higher than the base fluid, and the thermal conductivity of the ferrofluids increased as the magnetite concentration in the ferrofluids decreased however reached its optimum for ferrofluids prepared using 0.01 volume fraction of magnetite suspension over 0.99 volume fraction of water. Accordingly, the thermal conductivity of the ferrofluids significantly increased as the temperature increased where 49.4% enhancement with respect to water were observed at temperature 60°C