Multi-walled Carbon Nanotubes Of Different Diameters And Types Of Octadecane Phase Transition Study Of The Performance Impact

Phase-change materials can absorb, store and release large amounts of latent heat over a defined temperature range while the material changes phase or state. n-Alkane is a kind of phase-change material with its advantages of high latent phase-change heat, no significant super-cooling, stable property, nontoxic and low price. Different types and various contents of Multi-walled Carbon Nanotubes (MWNTs) were added into n-octadecane. The effects of types and contents of MWNTs on the phase change properties of the mixtures were discussed.Different diameters and types of MWNTS were mixed with n-octadecane at 50℃. The mixture was ultrasonic vibrated for 1 h. Then the mixture was dried in a vacuum oven. The mixtures were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetry (TG), Transmission Electron Microscope (TEM) and Accelerated Surface Area and Porosimetry System, etc.Adding higher contents of carbon nanotubes can decrease the melting and crystallization temperature, the efficiency of enthalpy of the mixture, meanwhile, improve the thermal stability. The increase of the contents of MWNTs with the same diameter decreases the efficiency of enthalpy. The smaller the diameter of MWNTs with the same contents, the lower the efficiency of enthalpy. The addition of MWNTs also reduces the efficiency of enthalpy when the content of MWNTs is lower than 5 wt%.MWNTs, hydroxyl MWNTs and carboxyl MWNTs have effects on the melting temperature and crystallization temperature of the mixture. The efficiency of enthalpy of the mixture decreases. In addition, with the increase of the contents of MWNTs, the efficiency of enthalpy decreases quickly. The types of the functional group on MWNTs have no significant effect on the efficiency of enthalpy of the mixture. The presence of functional group on MWNTs has a significant impact on the efficiency of enthalpy of the mixture, however.The experimental results show that, n-octadecane is mainly attached on the surface of MWNTs. Probably only a small amount of MWNTs are inserted inside MWNTs.