Xierong Zeng

Y2Si2O7 Whisker Reinforced MoSi2 Multi-composition Coating for SiC Pre-coated Carbon/Carbon Composites

Y2Si2O7–MoSi2/SiC multi-composition coatings were deposited on the surface of SiC pre-coated carbon/carbon (C/C) composites using a hydrothermal electrophoretic process. The prepared coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Influences of Y2Si2O7 whisker on the morphologies and anti-oxidation properties of coatings were particularly investigated. Results show that Y2Si2O7 whisker has a strong influence on the microstructure and oxidation resistant performance of the coated composites. Compared with MoSi2/SiC coating, Y2Si2O7–MoSi2/SiC coating exhibits dense, uniform, and homogeneous morphologies without any microcracks. Y2Si2O7 whisker can effectively decrease the thermal expansion coefficient of MoSi2 and prevent coatings from cracking, which results in improved oxidation resistant performance of the coated composites. The as-prepared multi-layer coating can protect C/C composites from oxidation for 100 h at 1773 K with a weight loss of 1.22×10–3g/cm2.

Direct Preparation of Y2SiO5 Nanocrystallites by a Microwave Hydrothermal Process

A novel fabrication technique of yttrium silicate (Y2SiO5) nanocrystallites has been investigated by a microwave hydrothermal process with a later heat treatment. The prepared powders were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal analysis, and field emission scanning electron microscopy (FESEM). Results show that high-purity yttrium silicate (Y2SiO5) powders can be synthesized by the microwave hydrothermal process with a later heat treatment at 700°C for 2 h. The Y2SiO5 precursor powders prepared by microwave hydrothermal process without heat treatment are weak crystallization, which shows an irregular and cotton-fiber-like morphology. After the heat treatment at 700°C for 2 h, well crystallized phase-pure Y2SiO5 powders with 400–600 nm grainy morphology are achieved. Further heat treatment at higher temperature will result in the sintering and serious agglomeration of the powders. The formation process of Y2SiO5 nanocrystallites was explained based on the photographs of SEM.