Oxygen diffusivities in mullite/zirconia composites measured by O-18/O-16 isotope exchange and secondary ion mass spectrometry

Abstract

Oxygen diffusivities in mullite/zirconia composites were measured by O-18/O-16 isotope exchange and secondary ion mass spectrometry. They exhibited a wide range of values from 10(-21) to 10(-10) m(2)/S at temperatures between 1000 and 1350 C in the composites with 0 to 80 vol% zirconia. At a fixed temperature, oxygen diffusivities m high-zirconia composites were larger by at least eight orders of magnitude than those in low-zirconia composites. The percolation threshold occurred between 30 and 40 vol% zirconia, where oxygen diffusivities dramatically changed. There was a clear tendency of the activation energies of oxygen diffusion in composites to decrease with increasing zirconia contents. The large oxygen diffusivities in the high-zirconia composites were attributed to the interconnected channels of zirconia from the microstructural aspect.