Manufacture of low thermal conductivity anorthite ceramic foam using silica fume, aluminum slag, and limestone

Foamed ceramic based on stoichiometric anorthite (CaAl2Si2O8) composition was prepared from solid wastes and local raw materials (aluminum slag, silica fume, and limestone). Sintering of the green sample between 1000 and 1300 degrees C gave dicalcium silicate, wollastonite, hedenpergite, pseudowollastonite, and anorthite. The samples sintered at high temperatures, i.e., 1250 and 1300 degrees C, show swelling that is concomitant with low density. The microstructure displays that the pore spaces increase in size with increasing temperature and that the submicrometric and nanometric particles are disseminated in a glassy matrix, especially at 1300 degrees C. The bulk and specific density values vary in the range of 1.471-0.958 g/cc and 2.996-2.759 g/cm3, respectively. The thermal conductivity (0.6525 <= kappa <= 1.7668 W/(K.m)) is directly proportional to the bulk (apparent) density values (rho b, R2 = 0.966), which are in the range of 1.471-0.958 g/cm3, and inversely proportional to the porosity values (& empty;He, R2 = 0.954), which vary between 50.91 % and 81.56 %. Thermal conductivity is also directly proportional to the thermal diffusivity (0.3552 <= alpha <= 0.5255 mm2/s, R2 = 0.933) and heat capacitance (823.2 <= Cp <= 1122.3 J/(K.kg), R2 = 0.939). This lightweight prepared ceramic material can be used as a heat insulator up to 1000 degrees C.