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熔融NaCl作为相变储热介质对容器材料具有强烈腐蚀性。通过对Cr基、Ni基和Fe基合金在850℃熔融NaCl中192 h的腐蚀实验,绘制了其腐蚀动力学曲线;利用SEM、EPMA、EDS、XRD等方法分析了腐蚀后试样横截面特征、元素分布特点及试样表面的腐蚀产物,讨论了腐蚀行为。结果表明:3种合金均满足线性腐蚀规律;Cr元素与熔融NaCl等物质反应,是导致这3种合金质量损失率增大的主要原因。Cr基合金耐蚀性最差,明显表现出晶界腐蚀特征,并且晶界为熔融NaCl渗入合金基体提供通道,促进了反应进程。Ni基合金和Fe基合金试样表面均形成了较厚的腐蚀层,为Cr2O3提供附着基体,降低了Cr元素扩散驱动力,提高了合金耐蚀性。另外,Fe基合金表面形成了尖晶石结构的腐蚀产物,进一步抑制了腐蚀过程,其耐蚀性最好。
Melting NaCl as a phase change heat storage medium has a strong corrosive to the container material. The corrosion kinetics curves of Cr, Ni-based and Fe-based alloys during 192 h of molten NaCl at 850 ℃ were drawn. The cross-sectional characteristics of the samples after corrosion were analyzed by SEM, EPMA, EDS and XRD , The distribution of elements and the corrosion products on the surface of the sample, the corrosion behavior is discussed. The results show that all the three alloys satisfy the linear corrosion rule. The reaction of Cr with molten NaCl is the main reason for the increase of mass loss rate of the three alloys. The corrosion resistance of the Cr-based alloy is the worst, which shows the grain boundary corrosion obviously, and the grain boundary provides a channel for molten NaCl to infiltrate into the alloy matrix and promotes the reaction process. Thicker corrosion layers were formed on the surface of Ni-base alloy and Fe-based alloy samples, which provided an adhesion matrix for Cr2O3, reduced the driving force of Cr diffusion and improved the corrosion resistance of the alloy. In addition, the corrosion products of spinel structure were formed on the surface of Fe-based alloy, which further inhibited the corrosion process and had the best corrosion resistance.