Effect of B4C Content on the Oxidation Resistance of a B4C-SiO2–Albite/Al2O3 Coating at 900 °C

B4C is beneficial for forming a glassy film that is effective at impeding oxygen diffusion and improving the oxidation resistance of coatings at high temperature. The effect of B4C content on the oxidation resistance of a B4C-SiO2–Albite/Al2O3 (BSA/AO) double-layer coating by the slurry brushing method at 900 °C was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), and differential scanning calorimetry (DSC) with thermogravimetric analysis (TGA) in this work. It is indicated that the composite coating with 20 wt% B4C exhibits excellent oxidation resistance at high temperature, which shows a mass loss of only 0.11% for the coated carbon block after being exposed to 900 °C for 196 h. This is attributed to the in situ formation of a thin, dense glass layer with good self-healing ability at the interface of the B4C-SiO2–Albite/Al2O3 composite coating within 1 h and the persistence and stability of the dense glass layer during exposure. The mechanism is discussed in detail.