In-situ Observation of Initial Reaction Stages of Hot-Corrosion

在燃油锅炉和燃气轮机系统中，高温热腐蚀因其腐蚀性日益受到关注。热腐蚀的机理已有电化学和熔盐化学等方面的研究，但对热腐蚀的初始阶段研究甚少。在本研究项目中，开发了扫描电子显微镜来观察不同腐蚀环境下的熔化过程。所得结果总结如下：(1)在扫描电镜上安装差分抽真空系统，使样品室在各种腐蚀环境下保持稳定。(2)安装热台，可加热至500ºC。(3)在低压条件下，观察了熔点为90 C的合金、200 C m.p的ZnCl_2-KCl混合盐和231 C m.p的纯金属锡的熔点和凝固过程。然而，由于状态的快速变化，没有观察到熔化过程的细节。为了克服这个困难。应该需要视频监控系统。(4)研究了Fe-Cr合金在低硫压力下的硫化过程，以阐明晶界攻击的机理。(5)对与硫化有关的气体腐蚀进行了总结和评述。

In oil fired boiler and gas turbine systems high-temperature hot corrosion is increasing concerns, because of its aggressiveness. Mechanisms of the hot corrosion have been studied by using electrochemistry and fused salt chemistry, whereas there is little information on the initial stage of the hot corrosion.In this research project the scanning electron microscope was developed to observe the melting process in various corrosion environments.The results obtained are summarized as follows.(1) Differential evacuation system was installed to SEM in order to keep sample chamber in various corrosion environments. (2) Hot stage was installed, heating up to 500ﾟC. (3) Several samples, alloy with low melting temperature of 90ﾟC, mixed salt of ZnCl_2-KCl with 200ﾟC m.p., and pure tin metal with 231ﾟC m.p., were observed in the low air pressure and the melting and solidifing processes were observed clearly. However, details of the melting process was not observed because of rapid change in states. In order to overcome this difficulty. the video-monitoring system should be needed. (4) Sulfidation process of Fe-Cr alloys was investigated in low sulfur pressures in order to elucidate the mechanism of grain boundary attack. (5) Gaseous corrosion associated with sulfidation was summarized and critically reviewed.