Preferential diffusion of oxygen along grain boundaries in polycrystalline MgO

Self-diffusion coefficient of oxygen in polycrystalline MgO can be represented by D=4.5×10−5exp(−60200/RT)cm2/sec for 80–115 mesh particles and by D=1.3×10−5exp(−60200/RT)cm2/sec for 170–200 mesh particles. These two activation energies are exactly the same, but the magnitude of the diffusion coefficients varied from one sample to another. When D was recalculated by taking a as the grain radius instead of particle radius, all the data points fall on a single solid line expressed by D=4.5×10−7exp(−60200/RT) cm2/sec. It is important to note that this line approximately meets the Arrhenius plot for oxygen diffusion in single-crystal MgO. Therefore, we conclude that the diffusion of oxygen along the grain boundaries in polycrystalline MgO is considerably faster than diffusion through the bulk.