Preparation of TaB2-SiC oxidation protective coating for carbon materials by liquid phase sintering

To control the microstructure and amounts of TaB2 phase in the TaB2-SiC coating, a novel liquid phase sintering method was developed on the basis of in-situ reaction method to prepare the TaB2-SiC coating, which includes synthesis of TaB2 powders and further preparation of TaB2-SiC coating. With Ta2O5, B2O3 and C employed as raw materials, hexagonal TaB2 powders were prepared by carbothermal reduction method at 1500 °C, whose mean particle size is 491 nm. The TaB2, SiC, C powders, and the low melting point phases Si and silica sol were used to prepare the TaB2-SiC coating by liquid phase sintering at 2373 K. The thickness of the coating is about 350 µm. Compared with the SiC coating, the weight loss of the samples modified by TaB2 decreased from 17.7% to 11.8%, and the average weight loss rate of the fastest weightloss zone reduced from −6 × 10−3 mg cm−2 s−1 to −5 × 10−3 mg cm−2 s−1. During oxidation, the Ta-oxides would gradually dissolve in the silicate glass to form Ta-Si-O glass ceramics with dendritic structure, which significantly improved the toughness and stability of the glass layer. The Ta-Si-O glass ceramics possesses the ability of sealing and arresting the microcracks, which can enhance the oxidation protective ability of the coating.