氧化鋯種類對碳化矽/氧化鋯/莫來石之複合材料氧化行為的影響

Abstract

本研究使用熱壓法製備碳化矽/氧化鋯/莫來石之複合材料(氧化鋯內的安定劑分別為3 mol﹪Y2O3、8 mol﹪Y2O3、9 mol﹪MgO或12 mol﹪CeO2)，並將之暴露在950、1000、1050以及1200℃的空氣中進行2至500小時的氧化實驗。實驗的主要目的是探討氧化鋯種類及含量對碳化矽/氧化鋯/莫來石之複合材料氧化行為的影響，並以x-ray、SEM和TEM分析試片的顯微結構。在950-1200℃時，複合材料之氧化速率皆遵循拋物線定律，氧化鋯含量為15 vol% 的複合材料，以含12 mol﹪CeO2-ZrO2的複合材料氧化速率最快，其餘試片的氧化速率差異不大。氧化鋯含量為50 vol%的複合材料，其氧化速率由快到慢依序如下：含12 mol﹪CeO2-ZrO2的試片>含3 mol﹪Y2O3-ZrO2的試片>含8 mol﹪Y2O3-ZrO2的試片>含9 mol﹪MgO-ZrO2的試片。氧化鋯含量為15 vol% 的複合材料的活化能為78.5~120kJ/mol；氧化鋯含量為50 vol% 的複合材料的活化能為141~209 kJ/mol。複合材料經溫度1050℃/500小時氧化後，氧化產物產生結晶相cristobalite，而在氧化1200℃/500小時後，產生zircon相為ZrO2和氧化產物 silica的反應物。藉由氧化層厚度與氧化深度的關係，探討不同成分複合材料的氧化模式。不同安定劑種類的氧化鋯含量為50 vol﹪之複合材料，具有一較深的氧化深度和較平緩的氧化層厚度變化梯度，氧化模式為Mode II，而氧化鋯含量為15vol﹪之複合材料，具有一較淺的氧化深度和較陡的氧化層厚度變化梯度，氧化模式為Mode I。

SiC/zirconia/mullite composites with various zirconia(stabilizer with 3 mol﹪Y2O3、8 mol﹪Y2O3、9 mol﹪MgO or 12 mol﹪CeO2), fabricated by hot pressing, were exposed to air isothermally between 950-1200℃ for up to 500 h. This study aims at the effect of various zirconia and content on the oxidation behavior. The microstructures of the oxidation samples as well as as-hot pressed samples were characterized by XRD, SEM and TEM. The oxidation followed a parabolic laws. Oxidation rate of the composites containing 15 vol% zirconia can be described as followed：mullite-(12 mol﹪CeO2 partially stabilized ZrO2-SiC) >mullite -(9 mol﹪MgO partially stabilized ZrO2-SiC) 3 mullite-(8 mol﹪Y2O3 fully stabilized ZrO2-SiC) 3 mullite-(3 mol﹪Y2O3 partially stabilized ZrO2-SiC), while the composites containing 50 vol% zirconia can be described as followed：mullite-(12 mol﹪CeO2 partially stabilized ZrO2-SiC) > mullite-(3 mol﹪Y2O3 partially stabilized ZrO2-SiC) >mullite-(8 mol﹪Y2O3 fully stabilized ZrO2-SiC) >mullite-(9 mol﹪MgO partially stabilized ZrO2-SiC). Activation engery were 78.5 ~ 120kJ/mol for the composites containing 15 vol% zirconia and 141~209 kJ/mol for the composites containing 50 vol% zirconia. It was found crysatllization product of the cristobalite from the composites after exposed at 1050℃/500 h and the formation of zircon (ZrSiO4), as a result of the reaction between ZrO2 and the oxidation product (i.e., SiO2) after exposed at 1200℃/500 h. Plotting the silica layer thickness vs depth, the oxidation modes of various composites material were determined. When composites containing 50 vol﹪various zirconia, the oxidation behavior exhibited the behavior of Mode II, were followed a large oxidation depth as well as a relatively small gradient. In contrast to the composites containing 15 vol﹪various zirconia demonstrate the oxidation behavior of Mode I.