Thermal Study of Ferromagnetic Nanoparticles Coated with Silicon Oxide

In this work, a simple methodology to synthesize Fe 3 O 4 @SiO 2 nanocomposites, using the precipitation method for Fe 3 O 4 nanoparticles (NPs) and the modified Stöber method to incorporate a SiO 2 shell into the NPs has been developed. By incorporating a shell or coating layer of SiO 2 , the properties of silicon fused to Fe 3 O 4 , reduce Fe 3 O 4 toxicity for drugs encapsulation or markers within the SiO 2 shell. For such applications, is of special interest to measure the thermal properties such as thermal diffusivity, thermal effusivity and to calculate the thermal conductivity as function of Fe 3 O 4 @SiO 2 concentration. The thermal wave resonant cavity (TWRC) characterization technique was used to measure the thermal diffusivity and effusivity of the Fe 3 O 4 @SiO 2 nanofluids. For concentrations of 0.00171 vol % to 0.01718 vol % the values of thermal diffusivity were between 1.3 × 10 –7 m 2 ·s −1 and 5.5 × 10 –7 m 2 ·s −1 . For the thermal effusivity the values were: 1450 ± 39 Ws 1/2 ·m −2 ·K −1 to 1646 ± 29 Ws 1/2 ·m −2 ·K −1 . From the relationship between the thermal diffusivity and the thermal effusivity, the values for thermal conductivity were between 0.52 W·m −1 ·K −1 and 1.25 W·m −1 ·K −1 . Therefore, these superparamagnetic systems of Fe 3 O 4 @SiO 2 are a promising option for applications in biomedicine, as well as in hyperthermia therapies, drug delivery and imaging, among others.