Thermal Study of Ferromagnetic Nanoparticles Coated with Silicon Oxide

In this work, a simple methodology to synthesize Fe₃O₄@SiO₂ nanocomposites, using the precipitation method for Fe₃O₄ nanoparticles (NPs) and the modified Stöber method to incorporate a SiO₂ shell into the NPs has been developed. By incorporating a shell or coating layer of SiO₂, the properties of silicon fused to Fe₃O₄, reduce Fe₃O₄ toxicity for drugs encapsulation or markers within the SiO₂ 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 Fe₃O₄@SiO₂ concentration. The thermal wave resonant cavity (TWRC) characterization technique was used to measure the thermal diffusivity and effusivity of the Fe₃O₄@SiO₂ nanofluids. For concentrations of 0.00171 vol % to 0.01718 vol % the values of thermal diffusivity were between 1.3 × 10^–7 m²·s⁻¹ and 5.5 × 10^–7 m²·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 Fe₃O₄@SiO₂ are a promising option for applications in biomedicine, as well as in hyperthermia therapies, drug delivery and imaging, among others.