Effect of Alloy Element Al on the Corrosion Behavior of Ni-10wt%Fe Based Alloy in Molten NaCl

NaCl and its mixed salt have many advantages as a 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 alloy (1#, 2# and 3#) in 850 °C molten NaCl was studied. The content of Al in 1#, 2# and 3# sample was 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 characteristics 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 a liner rule. The average mass loss rate declines when Al is added in the sample. The rate of 2# and 3# is only 12% and 20% of that of 1#, respectively. There are two reasons for the value reduction: firstly, Al will be oxidized prior to oxidization of Fe or Ni, and the atomic mass of Al is small; secondly, 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 a convenient condition for Al atom transmission from sample inside to surface. Al2O3 film becomes thick and exfoliates easily. The exfoliation increases the average mass loss rate in turn.