Oxidation behaviour of a (Mo, W)Si2-based composite in dry and wet oxygen atmospheres in the temperature range 350–950 °C
Oxidation behaviour of a (Mo, W)Si2-based composite in dry and wet oxygen atmospheres in the temperature range 350–950 °C
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DOI：
10.1016/j.jeurceramsoc.2008.12.009
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发表时间：
2009-07
影响因子：
5.7
通讯作者：
K. Hellström;Jun Tang;T. Jonsson;M. Halvarsson;R. Pompe;M. Sundberg;J. Svensson
中科院分区：
文献类型：
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作者：
K. Hellström;Jun Tang;T. Jonsson;M. Halvarsson;R. Pompe;M. Sundberg;J. Svensson
研究了(Mo，W)Si2基复合材料在350-950℃温度范围内的氧化行为。考察了温度和水蒸气对氧化的影响。用热天平研究了反应动力学，用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和能量色散X射线(EDX)分析了氧化物的形貌和组成。对一些氧化膜进行了聚焦离子束(FIB)球磨，使我们能够在横截面上观察到非机械扰动的氧化膜/氧化物。发现在550-750℃温度范围内发生快速氧化。O2中的质量增益显著大于O2+10%H2O中的质量增益。这是由于在O2+10%H2O中挥发性MoO_2(OH)_2和WO_2(OH)_2的蒸汽压高于(MoO_3)_3和(WO_3)_3在干O_2中的蒸汽压。在氧气中的温度约为750℃，在氧气+10%H2O中的温度约为650℃时，出现峰值质量增加。在850°C以上的温度下，特别是在存在水蒸气的情况下，从氧化膜中去除钼和钨的速度足够快，从而使二氧化硅部分愈合，导致氧化速率下降。在950℃的O2+10%H2O中，保护性的二氧化硅膜可以迅速重建并保持，导致氧化基本停止。
The oxidation of a (Mo, W)Si2-based composite was investigated in the temperature range (350–950°C). The influence of temperature and water vapour on the oxidation was examined. The kinetics was studied using a thermobalance whereas the morphology and composition of the oxides were examined using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive X-ray (EDX). Focused ion beam (FIB) milling was performed on some of the oxide scales which allowed us to look at a non-mechanically disturbed scale/oxide in cross-section. Rapid oxidation was found to occur in the 550–750°C temperature range. The mass gains were significantly larger in O2than in O2+10%H2O. The different mass changes in the two exposure atmospheres were attributed to the higher vapour pressure of the volatile MoO2(OH)2and WO2(OH)2species in O2+10%H2O than that of (MoO3)3and (WO3)3in dry O2. The peak mass gain was found to occur at a temperature of about 750°C in O2and 650°C in O2+10%H2O. At temperatures above 850°C, especially when water vapour is present, the removal of Mo and W from the oxide scales is rapid enough to allow partial healing of the silica, causing the oxidation rate to drop. At 950°C in O2+10%H2O, a protective SiO2scale could be re-established quickly and maintained, causing the oxidation to essentially cease.