Effect of Al2O3-coated SiO2 on properties of Al2O3-coated SiO2/PI composite films

In this pa per, Al2O3-coated SiO2 particles were prepared using nano-SiO2 and Al2O3 sol. Al2O3 particles were also prepared by Al2O3 sol, and the obtained powders have been studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), and infrared spectroscopy (FTIR). The results indicated that the average diameters of Al2O3-coated SiO2 particles and Al2O3 particles were about 30 nm and 10 nm, respectively. For Al2O3-coated SiO2 particles, Al2O3 was successfully coated on the surface of SiO2 particles, and it has been demonstrated that the ingredient of Al2O3 particles is α-monohydrate Al2O3(AlOOH). Polyimide (PI)/SiO2 composite films, Al2O3-coated SiO2/PI composite films, and PI/Al2O3 composite films with the inorganic content of 16 % (by wt) were prepared by in situ polymerization. The mechanical properties, breakdown field strength, thermal properties, and corona-resistance time of the composite films were tested and analyzed. The test results showed that the mechanical properties of the Al2O3-coated SiO2/PI composite films were optimal. The tensile strength and elongation-at-break of the Al2O3-coated SiO2/PI composite films were found to be 123.73 MPa and 12.49 %, respectively, and increase by 6.1 and 34.4 % compared with the PI/SiO2 composite films. The breakdown field strength, initial decomposition temperature, and corona-resistance time of the Al2O3-coated SiO2/PI films were measured as 224.3 kV/mm, 594.72 °C, and 168 min, respectively. The thermal performance of the Al2O3-coated SiO2/PI films is superior to that of the PI/SiO2 films and PI/Al2O3 films. The breakdown field strength and corona-resistance time of the Al2O3-coated SiO2/PI films were similar to those of the PI/SiO2 films and superior to those of the PI/Al2O3 films.