Effect of La₂O₃ on the oxidation resistance of SiC ceramic at 1973 K: Experimental and theoretical study

Abstract

The effect of La2O3 on the oxidation resistance of SiC ceramic at 1973 K was investigated using isothermal oxidation test and first‐principles calculations. The SiC ceramic with La2O3 shows a better oxidation resistance compared with that without La2O3 due to the in situ formed La2Si2O7 in SiO2 glass layer after oxidation at 1973 K. First‐principles calculations based on density functional theory were applied to analyze the solution behaviors of La atom in the surface of SiO2 and La2Si2O7. The solution energy of La atom in SiO2 (0 1 1) is −19.05 eV, which is far less than −4.19 eV in La2Si2O7 (2 0 1) with a La vacancy, thus resulting in that La atom in La2Si2O7 (2 0 1) diffuses into SiO2 (0 1 1). The SiO2 lattice with an interstitial La atom is more stable than that with a substitutional La atom and the interstitial La breaks the nearest Si–O bond to form La–O and La–Si bonds, which is beneficial to improving the high‐temperature stability of SiO2. Experimental and theoretical results indicate that the formation of refractory La2Si2O7 phase enhances the stability of SiO2 glass layer, so as to protect SiC ceramic from further oxidation at 1973 K.

Oxidation Resistance and Evolution of Multi-layered Oxide Scale During Isothermal and Cyclic Exposure of ZrB2–SiC–LaB6 Composites at 1300 °C to 1500 °C

“…It has been also shown that the presence of interstitial La breaks the bonding between Si and O atoms to form La-O and La-Si bonds, which improves the stability of glassy SiO 2 at high temperature. [48] c. Evolution of ZrO 2 + BSG layers The fraction (as percentage of total thickness) of coarse ZrO 2 + BSG layer has been found to increase at the expense of fine ZrO 2 + BSG layer with the increase in the LaB 6 content of the composites on exposure at a given temperature (1400 °C or 1500 °C). The increase in the diffusivity of the BSG caused by the viscosity reduction through the formation of higher amount of B 2 O 3 (l) in the oxide scales of the composites with higher LaB 6 content may be considered to have promoted the coarsening of ZrO 2 grains by Oswald ripening-type mechanism.…”

First-principles study of the effect of oxygen vacancy and iridium doping on formaldehyde adsorption on the La2O3(001) surface

“…Exploring and developing various potential photocatalysts with high efficiency are important research areas. 9,10 The photocatalysts reported thus far involve sblock elements such as sodium (Na), potassium (K), and strontium (Sr), p-block elements such as gallium (Ga), indium (In), germanium (Ge), and bismuth (Bi), d-block elements such as titanium (Ti), nickel (Ni), cobalt (Co), and zinc (Zn), and Laseries elements such as lanthanum (La), cerium (Ce), and samarium (Sm). The photocatalytic degradation of formaldehyde begins from its adsorption and activation on the photocatalyst surface.…”