New Approaches to Improve High Temperature Corrosion Resistance in Chlorine-Based Atmospheres

Abstract

Chlorine gas is widely encountered in chemical industries, as well as in waste incinerators and plastic/polymer decomposition mills. The presence of chlorine may significantly reduce the life-time of the components. Under chlorine-based atmospheres, the process of scale formation may be considerably affected and the presence of chlorine usually impedes the formation of a long term protective dense oxide scale. Based on thermodynamic calculations and previous investigations, NiAl and NiAlMo APS-coatings were produced to be used as protection for conventional steels against chlorine corrosion. Indeed, thermodynamic diagrams showed that molybdenum should have a positive behaviour in “reducing”-chloridizing atmospheres, whereas aluminium has a positive behaviour in “oxidizing”-chloridizing atmospheres. Coatings of approximatively 300 μm thickness were thermally sprayed on Armco Iron and on a commercial ferritic 18 Cr steel. This work presents the corrosion behaviour of NiAl and NiAlMo APS-coatings under chlorine-based atmospheres at 800°C. In addition, metallographic characterisation as well as EPMA investigations of the coating cross sections were carried out before and after the corrosion tests.

Refractory metals and nickel in high temperature chlorine‐containing environments ‐ thermodynamic prediction of volatile corrosion products and surface reaction mechanisms: a review

“…In reducing atmospheres the beneficial effect of molybdenum with regard to high temperature corrosion resistance in chloridizing atmospheres is even more pronounced. Investigations by Brill and Altpeter as well as Bender and Latreche indicated that in a range of materials corrosion attack decreased with increasing molybdenum content. Especially “alloy B2” , which is basically nickel with 30% molybdenum, was the most resistant material in the temperature range of 650 °C to 850 °C in H 2 with 10% HCl.…”

Corrosion Behavior of NiAl(1-x)Hfx (x=0...0.2) Alloys in Chlorine Based High Temperature Environments

“…However due to its high CTE it does not fit the whole range of those steels to be protected. Very recently, bulk materials as well as HVOF coatings based on NiAlMo alloys have been investigated in chlorine containing environments [8]. It was shown that molybdenum-based phases exhibit a rather good corrosion resistance even under reducing conditions.…”