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熔融共晶NaCl-MgCl_2作为太阳能中高温相变储热介质,运行状态下其温度常在熔点附近波动。但不同温度下该熔融盐对金属容器材料腐蚀行为不清楚。以Fe-14Cr-Mn合金为例,采用浸盐法研究了718、768和818 K共晶熔融NaCl-MgCl_2对该合金的腐蚀行为,探讨了腐蚀机理。结果表明:腐蚀速率随温度增加略微增加,3种温度下试样腐蚀动力学曲线服从线性规律(斜率k≈–4.806×10~(-4))。腐蚀初期,试样表面形成泡状腐蚀产物,腐蚀80 h后形成腐蚀坑洞,主要是Fe、Fe-Cr和MgO,也检测到含微量Fe和Ni的Mg-Fe-Ni的氧化物。腐蚀机理主要是MgCl_2吸潮后以H2O形式引入的氧原子和溶解在熔融盐中的微量氧作为阴极去极化剂,合金元素Cr和Mn与Cl-反应生成氯化物,氯化物吸附水分子,形成具有低熔点的含水氯化物(如CrCl3·6(H_2O)和MnCl_2·n(H_2O))逃逸腐蚀体系。另外,在熔盐表面形成了由MgCl_2·(H2O)6,NaCl和MgO组成的盐壳,而在熔融盐内部,NaCl与NaMgCl_3共存。本研究为研发耐熔融NaCl-MgCl_2腐蚀的新合金奠定了基础。
Melting eutectic NaCl-MgCl 2 as solar energy medium-temperature phase change heat storage medium, its operating temperature is often fluctuating near the melting point. However, the corrosion behavior of the molten salt on the metal container material is not clear at different temperatures. Taking Fe-14Cr-Mn alloy as an example, the corrosion behavior of 718, 768 and 818 K eutectic melted NaCl-MgCl 2 on the alloy was studied by salt immersion method and the corrosion mechanism was discussed. The results show that the corrosion rate increases slightly with the increase of temperature, and the corrosion kinetics curves of the three kinds of samples follow the linear rule (slope k≈-4.806 × 10 ~ (-4)). At the initial stage of corrosion, bubble corrosion products were formed on the surface of the sample. After etching for 80 h, corrosion pits were formed, mainly including Fe, Fe-Cr and MgO. Mg-Fe-Ni oxides containing trace amounts of Fe and Ni were also detected. The corrosion mechanism is mainly the oxygen atoms introduced by H2O after the moisture is absorbed by MgCl 2 and the trace oxygen dissolved in the molten salt as the cathode depolarizer. The alloying elements Cr and Mn react with Cl- to form chlorides. Chlorides adsorb water molecules, The formation of a low melting point chloride containing water (such as CrCl3 · 6 (H_2O) and MnCl_2 · n (H_2O)) escape corrosion system. In addition, a salt shell composed of MgCl 2 · (H 2 O) 6, NaCl and MgO was formed on the surface of the molten salt, while NaCl and NaMgCl 3 coexisted in the molten salt. This study laid the foundation for the development of new alloys resistant to molten NaCl-MgCl 2.