合金元素Al对Ni-10 wt. % Fe基合金在熔融NaCl中腐蚀行为影响研究

Effect of alloy element Al on the corrosion behavior of Ni-10 wt. % Fe based alloy in molten NaCl

摘要:

NaCl及其混合盐作为太阳能中高温相变储热介质具有很多优点，但熔融氯化盐对金属储热容器材料具有强烈腐蚀性。研究了Al添加量分别为0 wt. %、5 wt. %和10 wt. %的三种Ni-10 wt. % Fe基试样（分别为1#、2#和3#）在850℃熔融NaCl中的腐蚀行为，分析了试样表面腐蚀产物和腐蚀残盐成分，对比了试样横截面腐蚀特征和元素变化趋势，探讨了腐蚀机制。结果表明，三种试样的腐蚀动力学曲线均满足线性腐蚀规律；添加Al的试样平均质量损失率大幅降低，2#和3#试样腐蚀速率分别为1#试样的12%和20%。原子量较小的Al优先于Fe、Ni被氧化和生成高温稳定性好的Al2O3，是腐蚀速率降低的两个主要原因。但Al含量较高（如本文中的10 wt. %）时，基体中Al原子向试样表面扩散较为容易，氧化膜较厚，且易于脱落，又导致腐蚀速率增大。本研究对研发耐熔融氯化盐腐蚀的新型合金奠定了基础。

Abstract:

NaCl and its mixed salt have many advantages as medium of solar energy phase change thermal storage at moderate and high temperature. But molten chloride has sharp corrosive action on metal thermal storage vessel. The corrosion behavior of three kinds of Ni-10 wt. % Fe based sample (1#, 2# and 3#) in 850℃ molten NaCl was studied. The content of Al in 1#, 2# and 3# sample is 0.0 wt. %、5.0 wt. % and 10.0 wt. %, respectively. The components of NaCl after corroding and corrosion products on samples surface were analyzed. Elements change trend and corrosion characteristic on cross section of the three samples were contrasted. Corrosion mechanisms were discussed finally. Results show that the kinetics curves of the three kinds of sample obey liner rule. The average mass loss rate reduce when Al is added in sample. The rate of 2# and 3# is only 12% and 20% of 1#, respectively. There are two reasons for the value reduction: first, Al will be oxidized prior to oxidization of Fe or Ni, and the atomic mass of Al is small. Second, Al2O3 is very stable at high temperature as corrosion products. However, when the content of Al is very high (for example 10 wt. % in here) in Ni-10 wt. % Fe based alloy, Al oxidized on sample surface provides convenient condition for Al atom transmission from sample matrix to surface.Al2O3 film becomes thick and exfoliates easily. The exfoliation led to the average mass loss rate increase in turn. The study establishes foundation for new corrosion resistance alloy research in molten salt.