Study Of Si-Coated Carbon Nanotube And Silicon Carbide Whisker And Properties Of Coating

Carbon nanotubes (CNTs) and silicon carbide whiskers (SiCw) are promising reinforcement materials for manufacturing metal or ceramic based composites. However, they are prone to interact with the matrix in a reactive atmosphere that often alters the structure and properties of CNTs and SiCw and depresses their reinforcing effect. To overcome this problem, a protective silicon layer has been successfully deposited on CNTs and SiCw using quasi-atomic layer deposition by in-situ decomposition of gaseous SiH4. The coating thickness can be adjusted at nanometric scale by changing the gas flux into the reactor per cycle and the cycling times.The phase structure and thermal property of the Si-coated CNTs and SiCw were characterized using Transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman scattering spectroscopy (RS), differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA). To evaluate the protective effect of the silicon film, comparison were made between Si-coated samples and uncoated samples.The silicon coating is well-covered and continuous with a cubic-phase structure. It effectively improves the thermal stability of CNTs and SiCw by acting as a protective film, which inhibits and delays the onset of oxidation. TGA reveals that the oxidation of Si-coated CNTs occures at a temperature of 676.3°C, which is 105.1°C higher than that of uncoated CNTs, and the weight loss decreases with the increasing thickness of silicon coating.The weight loss of uncoated SiCw is about 25%, while that of Si-coated SiCw is almost zero.The samples (CNT and SiCw) before and after coating reinforced borosilicate glass-alumina composites were prepared by hot pressing at 850°C for 15 minutes. Three point-bending strength of composites were measured with DKZ-5000 bending strength test instrument.The value of bending strength achieved for the Si-coated CNTs and SiCw reinforced samples are respectively 17.65% and 23.86% higher than that of uncoated samples. For Al-based composite, the bending strength values achieved for the Si-coated CNTs and SiCw reinforced sample were alsoimproved compared with that of uncoated samples. The presence of silicon film improved the mechanical properties of the alumina matrix.All these results further verified that the silicon film could effectively protect CNTs and SiCw from oxidization and damage. Therefore coating silicon film over CNTs and SiCw could improve the composits'bending strength.