Effects of nano-CaCO3 and nano-iron phosphate on microstructure and properties of SiO2 porous ceramics prepared by direct foaming

SiO2 porous ceramics are often used in industrial kilns for thermal insulation. Burning loss method is the main method for preparing SiO2 porous ceramics at present, but there are problems of environmental pollution and uneven pore distribution. Meanwhile, SiO2 is prone to cracking due to crystal-to-crystal transformations. In order to overcome above problems, in this study, nano-CaCO3 and nano-iron phosphate with high activity have been used to stabilize the crystal-to-crystal transformations of SiO2, and SiO2 porous ceramics have been prepared by simple and environmental direct foaming method. Results show that the addition of nano-CaCO3 and nano-iron phosphate can promote the formation of tridymite and densification of SiO2 porous ceramics, which can also increase their pore wall thickness and improve compressive strength. In addition, the compressive strength of SiO2 porous ceramics is proportional to their relative density, which is consistent with the Ashby's theory. And their thermal conductivity is well matched with the universal model, indicating that SiO2 porous ceramics have complex pore structures. Comparing the effects of nano-CaCO3 and nano-iron phosphate on SiO2 porous ceramics, it is concluded that nano-CaCO3 as the mineralizer is better than nano-iron phosphate. This study enriches the fabrication technology of energy-saving and environmentally friendly SiO2 porous ceramics, which is of great significance to the practical production and application of SiO2 porous ceramics.