Metal Dusting of Nickel–Aluminium Alloys

Abstract

Alloys of c-Ni(Al), c-c 0 Ni(Al)-Ni 3 Al, c 0 -Ni 3 Al and b-NiAl were exposed in 1 h cycles to a carbon-supersaturated CO-H 2 -H 2 O gas mixture (a C = 36.7, p O 2 = 2.83 9 10 -26 atm) at 650°C and an overall pressure of 1 atm. It was found that all alloys except b-NiAl had been attacked by metal dusting, leaving a layered structure of nickel particles, graphite and catalytically grown nano-sized carbon filaments as the corrosion product. Carbon uptake and metal wastage rates were slowed with increasing aluminium content for the single-phase alloys. However, the c-c 0 two phase alloy had the overall highest metal loss rate. Surface morphologies reflected uniform attack for the c and c-c 0 alloys, whereas on c 0 a pitting type of attack was observed. Amorphous alumina formation was identified on the surface of the c 0 and b alloys, and is thought to be the major factor providing protection against dusting attack.

First-principles investigations of Ni3Al(111) and NiAl(110) surfaces at metal dusting conditions

“…Again, we interpret this result such that there must be other driving forces for Ni to segregate to the surface, as observed experimentally [23]. One possibility is that steps and defects are required to allow alteration of the surface stoichiometry.…”

“…This shows that the oxide may fall off during operation, which is also reported in experiments [23,29]. -NiAl is also used as bi-metallic catalyst [30], and the present study therefore also may have relevance to the field of catalysis.…”

“…However, we note that for defects such as phase boundaries, segregation energies may be lower so that stoichiometry variations can be expected there. Here, a mixed --Ni 3 Al phase has been observed [23].…”

“…A disadvantage of gas additives in steam reforming plants is the need for continuous feed and subsequent cleaning of the process gas. A different strategy is to alloy Ni with metals that may form protective oxide coatings, for instance Ti or Al [19,20,21,22,23,24].…”

“…As pointed out by Young [23] there are only few studies of the metallic Ni-Al alloys [20,22,25,26] in a metal dusting environment. The Fe 3 Al and Ni 3 Al alloys have been investigated by Grabke and co-workers [20] in short term metal dusting experiments followed by characterisation.…”