为分析不锈钢在熔融NaCl中的腐蚀机制，通过850℃熔融NaCl完全浸没实验，测量了168 h内3种不锈钢的腐蚀动力学曲线，借助SEM、EPMA、EDS等设备表征了试样横截面形貌、元素分布等特征，研究了Ti元素对合金耐蚀性影响机制，采用X射线衍射仪检测了腐蚀24 h后熔融盐成分和168 h后试样表面成分，建立了电化学－化学－稀释联合作用腐蚀模型。结果表明：在熔融NaCl腐蚀介质中，金属材料作为阳极被溶解，吸附氧得到电子变成O2－作为阴极；金属阳离子与O2－在熔融NaCl中发生化学反应，生成易挥发性氯化物逃逸系统；熔融盐作为传质媒介，稀释腐蚀层区域的腐蚀产物浓度，提高腐蚀速度。合金中电极电位最负的微量组元优先溶解后形成微小孔隙，增大了微阳极表面积，加速腐蚀反应过程。
To analyze the corrosion mechanism of stainless steel in molten NaCl, corrosion kinetic curves of three kinds of stainless steel specimens were measured, the specimens were submerged in 850℃ molten NaCl for 168 h. Elements mass fraction and cross?section morphology were detected by scanning electron microscopy ( SEM) , X?ray energy dispersive spectrometry ( EDS ) and electron probe micro?analyzer ( EPMA ) . The composition of residual salt after being corroded for 24 h and the corrosion products on specimen surfaces for 168 h were detected by X?ray diffraction ( XRD) . Corrosion behavior was analyzed, and the effects of Ti on corrosion resistance were presented. Finally, a new coactions corrosion model of electrochemical?chemical?dilution was built. The result showed that, in molten NaCl, adsorbed oxygen changes into O2-and acts as cathode, alloy dissolves and acts as anode. Volatile metal chloride produces during the reaction between metal cations and O2-in molten NaCl and then escapes from corrosion system. What′s more, corrosion products are diluted by the medium of molten salt in corrosion layer, therefore, corrosion rate increases. Moreover, in the alloy, after the preferentially dissolution of very tiny amounts of Ti into molten salt, many small pores form and the micro?anode surface area is increased, which speeds up the corrosion rate.
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