Exploratory study into advanced thermal energy storage materials and thermal coatings for survival in the urban environment

Work presented in this research thesis provides a contribution to closing the knowledge gaps concerning thermal energy storage materials, particularly in the area of Miscibility Gap Alloys. The work herein has revealed that it is possible to create MGA modules for desired application temperatures. This was achieved by identifying suitable candidates in the required temperature ranges. It has shown that it is possible to make MGA thermal storage materials from C-Al, C-(Al-Si), C-Mg, C-Cu, AlN-Al, MgO-Al and Al2O3-Al. The newfound thermal energy storage (TES) materials present high thermal conductivity (~140W/mK for the C-Al and C-(Al-Si) systems) and energy densities in the region of 1 MJ/L for ΔT = 100 ℃. This work has presented the effects of extended thermal cycling over the intended use range to test its effect on integrity, phase composition and microstructure for both the CAl and C-(Al-Si) candidate materials. This research has thus proven that metastable immiscible materials may also be used as MGA. This is supported by the absence of X-ray diffraction peaks from the carbide Al4C3 in data from the cycled materials, along with their continued strong latent heat DTA signals after long thermal holds (120 h). The work finally presents newer Miscibility Gap Alloys with a ceramic matrix. These ceramic MGA, which include; AlN-Al, AlN-(Al-Si), Al2O3-Al and MgO-Al systems were designed with a view to create an oxidation resistant macroscopically solid, phase change enhanced, thermal energy storage module. These MGA displayed no signs of degradation after 24 h of oxidation testing. The Al2O3-Al and MgO-Al systems formed not only a viable ceramic matrix material after firing, but also showed no signs of oxidation of Al after 72 h in air at 700 ℃. These results open up a promising new series of thermal energy storage materials, some of which appear to have very good oxidation resistance under the test conditions. It is expected that the knowledge gained from this research will provide a critical step towards implementing MGA thermal storage materials into concentrating solar power plants.