Formation of closed pore structure in CaO-MgO-Al2O3-SiO2 (CMAS) porous glass-ceramics via Fe2O3 modified foaming for thermal insulation

Due to the low density, low thermal conductivity and low water absorption, porous glass-ceramics have demonstrated excellent performance for thermal insulation. Closed pore structure can greatly reduce the thermal conductivity and convection as well as achieve high mechanical strength. However, yet it is difficult to realize closed pore structure due to the critical preparation condition. Here we use Fe2O3, which is the by-product of copper tailings, to optimize the pores structures of the porous glass-ceramics and facilitate the formation of uniform closed pore structure. The porous glass-ceramics were prepared by melting-quenching method, followed by sufficiently foaming through powder sintering route with SiC powders as foaming agent. The foaming process, micro structure, pore structure and thermal insulation performance were directly observed by heating micro-scope, scanning electron microscope (SEM), X-ray computed tomography and infrared thermal imager. The re-sults show that the addition of Fe2O3 modified the depolymerization degree of the glass network and increased the numbers of non-bridged oxygen, decreasing the foaming temperature. The resultant closed pore structure showed a better thermal insulating performance than open pore structure. Accordingly, we achieved a low thermal conductivity of 0.19 W center dot m-1 center dot K-1 with the highest specific strength of 19.55 MPa center dot g- 1 center dot cm-3 based on closed pore structure.