Preparation and thermal performance of nano-copper/paraffin phase change composites for actuation

The nano-copper/paraffin composites were prepared by high energy ball milling. The microstructure, phase and thermophysical properties such as phase change temperature and latent heat enthalpy were characterized by means of TEM, SEM, XRD and DSC, and the impact of nano-copper particles on the thermal expansion, thermal sensitivity and thermal stability was also investigated. The results show that paraffin enwraps copper particles to form near-spherical composite particles with a mean size of 100 nm, which improves the antioxidant ability of nano-copper particles effectively. Those nano-composite particles tend to agglomerate to form micron-sized clumps of particles. Nano-copper particles do not exert noticeable effect on the phase change temperature, but the latent heat enthalpy of the nano-copper/paraffin composites decreases linearly with an increase of copper content. The thermal sensitivity of the composites improves effectively with the increasing of the copper content, while the thermal expansion decreases with the loading increasing. It is clear that the composites containing 60% mass fraction of copper is a desirable material for microactuator, with short heating time, a small decrease in volume expansibility and excellent thermal stability after being heated for many times.