Super-hydrophobic hexamethyl-disilazane modified ZrO2–SiO2 aerogels with excellent thermal stability

Abstract

Hexamethyl disilazane modified ZrO₂–SiO₂ aerogels (HMDS/ZSAs) have been prepared by the addition of HMDS into ZrO₂–SiO₂ gels during the aging process in order to improve their thermal stability at high temperature. FTIR analysis shows that the methyl siloxy groups ((CH₃)₃Si–O–) could replace the superficial hydroxy groups (–OH) through the condensation between the (CH₃)₃Si–OH of HMDS and –OH on the initial ZSA surface. HMDS/ZSAs could maintain their three-dimensional network structure without collapse and exhibit a remarkable thermal stability with retention of most physical characteristics up to a temperature of 1000 °C, such as a high surface area (174.4 m² g⁻¹), high pore volume (0.7246 cm³ g⁻¹) and high elastic modulus (5.23 MPa). TGA and XRD analyses demonstrate that the phase transition of HMDS/ZSAs from amorphous to crystalline occurs up to 1000 °C, which is 100 °C higher than that of ZSAs. It was demonstrated that the modified inert methyl siloxy groups could form small silicon particles (3 to 5 Å in diameter) to restrict the migration of grain boundaries, which was favorable to suppress the ZrO₂ crystallization at elevated temperatures. Furthermore, HMDS/ZSAs exhibit super-hydrophobic properties with a contact angle of 154°. The high performance of HMDS/ZSAs paves the way for their applications in the field of thermal insulation, energy-absorbing services, environmental remediation, etc.