碳钢和铁-铬-镍基合金在相变储能材料用熔融共晶氯化钠和氯化镁中的腐蚀行为

研究了3种铁-铬-镍基合金(Fe-Cr-Ni)和一种碳钢试样在520℃熔融共晶NaCl-MgCl2盐中的腐蚀行为。结果表明,碳钢试样晶界处Fe原子优先变为亚铁离子(Fe2+)和铁离子(Fe3+),发生了严重的沿晶腐蚀,但表面形成了厚而致密的MgO壳,对试样起到了一定的保护作用。3种Fe-Cr-Ni基试样表面也形成了MgO壳,但因铬元素优先被腐蚀,试样表面形成了疏松的富Ni骨架状微观组织结构,MgO壳或颗粒极易剥落,未能起到有效的保护作用;Cr含量越高,腐蚀越严重。对于太阳能储能技术,在廉价的铁基合金中添加镍元素作为熔融氯化盐相变储热介质的容器或者管道材料,具有良好发展前景。

Corrosion Behavior of a Carbon Steel and Iron-Chromium-Nickel Alloys in Molten Eutectic Sodium Chloride and Magnesium Chloride as Phase Change Material

As a phase change material for solar energy storage at moderate-high temperatures,the molten eutectic chloride salt of sodium chloride and magnesium chloride(NaCl-52 wt% MgCl2) is strongly corrosive to metal containers and pipes.The corrosion behavior of three kinds of iron-chromium-nickel(Fe-Cr-Ni) alloys and carbon steels in the molten eutectic salt at 520℃ was studied.Results show that the carbon steel is corroded along grain boundaries,and iron atoms become ferrous ions(Fe2+) and ferric ions(Fe3+).A thick and compact magnesium oxide(MgO) shell is formed on the surface of carbon steel,which protects the specimen from corrosion.The MgO shell is also formed on the surface of three kinds of iron-chromium-nickel alloys,but the magnesium oxide shell cannot protect them from corrosion in the molten salt.A loose skeletal Ni-rich microstructure is formed on the specimen surface because the chromium element is preferentially corroded.The magnesium oxide(MgO) shell or particles peel off easily.In addition,the higher the content of the chromium,the more severe the corrosion.As a vessel or pipe material for solar energy storage by molten chloride salt,cheap iron-based alloys with alloying element nickel have greater development prospects.