氧在莫來石/氧化鋯複合材料之擴散研究

Abstract

本研究使用熱壓法製備莫來石/氧化鋯(mullite/ZrO2)複合材料，並且將之暴露在18O/Ar氣氛中進行1000℃/5小時、1200℃/3小時及1350℃/2小時之擴散實驗。研究主要目的是探討氧化鋯含量對此複合材料之氧擴散的影響，氧擴散係數的計算是經由16O-18O交換反應，並利用二次離子質譜儀(SIMS)測量18O的縱深分布。研究結果顯示，莫來石/氧化鋯複合材料的氧擴散係數(Dv)及表面交換係數(α)會隨著氧化鋯含量的增加而增加，而擴散活化能則隨著氧化鋯含量增加而減少。氧化鋯含量5 vol%∼80 vol%之複合材料的擴散活化能為269∼148 kJ/mol。氧化鋯含量為5 vol%及15 vol%之複合材料，因有zircon相的產生，使其氧擴散係數低於純mullite。氧在純mullite中之體擴散Arrhenius關係式為Dv, mullite=1.12×10-8 exp[-(313±23)kJ/RT] m2s-1 (at 1000℃~1350℃)；晶界擴散Arrhenius關係式為Dgb, mullitew=8.86×10-15exp[-(256±11)kJ/RT] m3s-1 (at 1000℃~1350℃)。經計算後，氧在晶界擴散係數遠大於體擴散係數，相差約有105左右。

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.