Improved thermal properties of paraffin wax by the addition of TiO2 nanoparticles

• TiO2 nanoparticles vary composite phase-change temperature and latent heat capacity.
• With <1% loading, phase-change temperature drops, latent heat capacity increases.
• With >2% loading, phase-change temperature increases, latent heat capacity drops.
• A significant increase in latent heat capacity is found around 0.7 wt% loading.
• Thermal conductivity of the composite increases monotonically with loading.

TiO2 nanoparticles about 20 nm in diameter in the form of anatase were prepared and characterized. The nanoparticles were successfully dispersed into a paraffin wax (PW) matrix without any surfactant. The differential scanning calorimetric instrument and the transient short hot-wire method were used to measure the thermal properties of the TiO2/PW composites. It is found that the phase-change temperature and latent heat capacity vary with TiO2 nanoparticles loading levels. When the loading is not over 1 wt%, the phase-change temperature drops, and the latent heat capacity increases. When the loading is over 2 wt%, the phase-change temperature increases, and the latent heat capacity drops. A significant increase in latent heat capacity is found around 0.7 wt% loading. The thermal conductivity of the composites increases monotonically with increasing TiO2 loading. But such a tendency tends to decrease when the loading is over 3 wt%.