Abstract: 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. Einstein diffusion was observed in a 250～300 ps simulation. The diffusion coefficient for the O2 range 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, that for the Na2SO4 vapor range 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 C/SiC composite will be increased via the B2O3 preventing the diffusion of O2 and Na2SO4 vapor into the pyrolytic interphase and carbon fibers.

Key words: Molecular dynamics, Diffusion coefficient, C/SiC composite, Environment properties