Molecular dynamics simulation of gas diffusion in B₂O₃ and SiC

Molecular dynamics simulation using a universal force field has been employed to determine the diffusion coefficients of O₂ and Na₂SO₄ vapor into B₂O₃ and SiC from 700 K to 1273 K, respectively. The Einstein diffusion was observed in a 250-300 ps simulation. The diffusion coefficient for O₂ ranges from about 9.279×10^-9 cm²/s for B₂O₃ to 2.275×10^-10/cm²/s for SiC at a loading of 32 molecules per simulation box, while that for the Na₂SO₄ vapor ranges from about 9.888×10^-7 cm²/s for B₂O₃ to 1.837×10^-10 cm²/s for SiC at a loading of 8 molecules per simulation box. Environment properties of the C/Si composite will be increased due to B₂O₃ preventing the diffusion of O₂ and Na₂SO₄ vapor into the pyrolytic interphase and carbon fibers.