The effect of Al₂O₃ on the high‐temperature oxidation resistance of Si‐B‐C ceramic under air atmosphere

Abstract

Si‐B‐C ceramics were prepared through reaction sintering, and the influence of Al2O3 addition on the high‐temperature (1100‐1300°C) oxidation behavior of the material under air atmosphere was studied. The erosion behavior and mechanism are determined from the measurement of weigh changes, microstructure observations, and characterization of the generated oxides on postexposure specimens. Results show that Al2O3 is enriched in the oxidized layer, inhibiting the volatilization of B2O3 and impeding the crystallization ability of oxide (cristobalite). Narrower erosion layer and less weigh change are observed with Al2O3. Low‐frequency Raman results reveals that with the increase in Al2O3, the bending vibrations of the BO4 units and B‐O‐B stretching of the metaborate ring relative intensity are enhanced. Furthermore, high‐frequency Raman results shows that the relative proportion of high‐dimensional vibration modes Q3 and Q4 which result in a higher viscosity of melt and a greater resistance of oxygen diffusion are positively correlated with Al2O3.

Silica‐based ceramic core for aviation applications: Facile pore filling and flexural strength improvement

“…The presence of viscous flow has an effect on filling the cracks and increasing the bonding strength between particles . Shao et al demonstrated that liquid phase Y 3 Si 2 C 2 could fill the pores in a SiC‐based ceramic during sintering, which promoted neck formation and grain growth.…”

More effective crack self‐healing capability of SiCf/SiC‐B4C with Al2O3 modified under wet environment

“…However, the phase of B 12 (B, C, Si) 3 was also not obviously shown in X-ray results ( Figure 6). In our previous study, 17 we found that B and C were the main elements of this black phase in addition of small amount of Al and Si. Figure 2 presents the microstructure of composites.…”

“…Fortunately, Al 2 O 3 can be dissolved in glass phase in cracks (Figure 5I). It can increase the viscosity of glass phase and inhibit the oxidizing medium from diffusing along the crack into internal material 17,21 . Table 1 summarizes the cracks healing property of typical boron‐containing self‐healing composites under different test condition.…”

“…It can increase the viscosity of glass phase and inhibit the oxidizing medium from diffusing along the crack into internal material. 17,21 Table 1 summarizes the cracks healing property of typical boron-containing self-healing composites under different test condition. It can be clearly seen that the cracks in the interior of composites are relatively easy to be healed whether in air or wet environment compared to cracks in the surface.…”

“…15,16 It was found that the oxidation product Al 2 O 3 could limit the volatilization of B 2 O 3 in air environment, which was testified in our previous research. 17 Research by Cheng 18 showed that the content of [BO 4 ] unit would increase in Al 2 O 3 -B 2 O 3 -SiO 2 system because of the formation of Al-O-B bridging bond. The same phenomenon could also be observed in BaO-Al 2 O 3 -B 2 O 3 -SiO 2 SOFC sealing glass system.…”