Stability and thermal conductivity of different nano-composite material prepared for thermal energy storage applications

•Addition of nano-TiO2, nano-MgO, and a mixture of the two types by 50% each to paraffin.•The addition of these nanoparticles by mass fractions caused the paraffin color to change to white in addition to the change of the absorptivity and transmittance properties of the products.•The studied products showed high stability after more than 65 cycles of melting-solidification.•Hybrid nano-TiO2 and MgO was found to give good and suitable results for adding it to the Iraqi paraffin, and its use in solar applications. The interest in solar energy applications doubles due to the necessities of the stage, and because of it, the interest in heat storage materials expands, the most important of which is paraffins. Paraffins suffer from low thermal conductivity, so many researchers have added nanomaterials that improve this property. In this study, nano-TiO2 and MgO and a 50% mixture of each were added to the Iraqi paraffin. The addition of nanoparticles caused the paraffin to change color from brown to white with the change of absorbance and transmittance properties. The density, viscosity, and heat capacity of the products increased slightly. The thermal conductivity of the products improved and the highest value obtained was 24.92%. The melting and solidification points decreased by one degree Celsius for the case of addition of nano-TiO2 and MgO and by 2 °C for the case of addition of the hybrid nanoparticles. Besides, the period of phase change of the products decreased. The nano-paraffin mixture showed high stability for more than 90 days and it is preferable to repeat the mixing process every 6 months to ensure this property. The study concludes that the addition of hybrid nano-TiO2 and MgO to Iraqi paraffin is suitable for solar energy applications.