Rapid Conversion of Perhydropolysilazane into Thin Silica Coating at Low Temperature

The conversion of perhydropolysilazane (PHPS) to silica at low temperature is beneficial for its application on thermally vulnerable substrates. In this work, it is demonstrated that (3-aminopropyl)triethoxysilane (APTES) has high catalytic efficiency for the low temperature conversion of PHPS and the catalytic mechanism of APTES was suggested. The influence of temperature and humidity on the catalytic conversion process was investigated, and it was found that PHPS can be rapidly converted to silica in 10 min at 80 degrees C with relative humidity of 90%. The achieved silica is mainly composed of SiNO3/SiO3OH and SiO4 structure with O/Si of 1.74 and N content of 1%. As an approach to prepare inorganic coating, the low-temperature conversion method achieves a silica coating with low volume shrinkage of 0.86%, low roughness of R-a=0.293 nm, high nanoindentation hardness of 3.62 GPa and modulus of 30.06 GPa, which exhibits high potentials as protective coating for various materials even those vulnerable to high temperature.