Oxygen Diffusion in Mullite/Zirconia Composites

• Main Authors: Hung-Da Ko, 柯宏達
• Other Authors: Chien-Cheng Lin
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/22980230679635562141

碩士 === 國立交通大學 === 材料科學與工程系 === 90 === Mullite/Zirconia composites with various zirconia contents, fabricated by hot pressing, were exposed in 18O/Ar atmosphere at 1000℃/5Hr, 1200℃/3Hr and 1350℃/2Hr. This study aims at the effect of zirconia content on the oxygen diffusion in mullite/zirconia composites. The oxygen diffusion coefficient has been measured by the 16O/18O isotope exchange technique using second ion mass spectroscopy (SIMS) depth profiling. The result of this study is as follows：Oxygen diffusivities and surface exchange coefficient of mullite/zirconia composites are increased with the increase of zirconia content. The activation energies are decreased with the increase of zirconia content. Activation energy of composites containing 5 vol%∼80 vol% zirconia are 269∼148 kJ/mol. Oxygen diffusivities of composites containing 5 vol% and 15 vol% zirconia are less than mullite, duo to the formation of zircon. The volume diffusivity and grain boundary diffusivity of mullite is expressed as Dv, mullite=1.12×10-8 exp [-(313±23)kJ/RT] m2s-1 and Dgb, mullitew=8.86×10-15 exp[-(256±11)kJ/RT] m3s-1(at 1000℃∼1350℃), respectively. After calculating, diffusion of oxygen in grain boundary is faster than that in the bulk by about 5 orders of magnitude.