Highly porous silica synthesized by a microwave-assisted hydrothermal method derived from recycled silicon sludge for thermal insulation applications

Abstract

In this study, we synthesize a porous silica nanoparticles (SiO2) derived from recycled semi-conducting silica sludge via a conventional hydrothermal and microwave-assisted hydrothermal methods for flame-resistant applications. The corresponding thermal properties of as-synthesized SiO2 nanoparticles are investigated. The effects of reaction temperature and urea concentration are investigated in terms of surface morphology and thermal conductivity. The results of thermal conductivity tests indicate that 180 °C reaction temperature for both conventional hydrothermal reaction and microwave-assisted hydrothermal reaction demonstrated the best thermal insulator performance. The thermal conductivities are determined to be 0.0193 W/m·K and 0.0192 W/m·K, respectively. For flame penetration and combustion tests, microwave-assisted one exhibits much better performance, maintaining a temperature of 34 °C after 600 s of combustion under a butane torch at nearly 800 °C. Furthermore, there is no deformation occurred when direct contact with the flame at a high temperature, proving that microwave-assisted hydrothermal reaction-synthesized silica is a potential candidate for thermal barrier applications.