Low-temperature high-strength lightweight refractory composites: Pore structures and insulating properties

Functional refractory remains critical due to its intrinsic properties such as: saving space, lightweight and excellent thermal stability to achieve the trade-off between insulating and overall performances. The present study deals with the production of low carbon footprint and lightweight refractory matrices, with controllable pores structures, thermally stable and having low thermal conductivities. The lightweight refractory products were obtained through the direct foaming of geopolymer pastes and sintered from 900 to 1200 degrees C. The mech-anism of pores formation, pores structures and the effect of both sintering temperature and foaming agent ratio on the thermal insulation, physical and microstructural characteristics were evaluated. The results showed that the produced matrices could be described as low thermal conductors, with thermal conductivity values between 0.49 and 0.18 W/mK. The 3D internal pore structures under laser microscopy observations confirms the mechanism of pore enlargement when high concentration of the foaming agent was added. Furthermore, the decomposition of kyanite particles within the matrices, at high temperature, favoured the extend reduction in porosity and the limitation of the liquid phase, by ensuring the formation of macro-porosities sized between 360 & mu;m and 2 mm. The formation of the refractory crystalline phases namely: cordierite, mullite, enstatite, leucite, as well as, kalsilite, acting as filler, ensure thermal stability of the matrices. The produced materials provide an energy-saving, lightweight ceramic foams with high-strength and low thermal conductivities, potential candi-dates for refractory applications.