Mechanism and control of carbon deposition on high temperature alloys

In solid oxide fuel cells, the preferred anode electrode is a cermet of Ni-yttria-stabilized zirconia. When high carbon activity (ac >1) and low oxygen partial pressure (p O2) environments are encountered in the anode compartment, carbon deposition occurs in concert with a corrosion reaction known as metal dusting. Thus high temperature alloys that could resist the carbon deposition/metal dusting reaction are needed. The present work has led to a carbon deposition-resistant alloy in which the initial rapid formation of a surface MnO layer blocks carbon transfer. Subsequently, a Mn-rich spinel layer (Mn Cr2 O4) develops beneath the MnO layer providing long-term resistance to carbon transfer and corrosion. In the alloy, 20Fe-40Ni-10Mn-30Cr, a layer of MnO forms almost instantaneously when exposed to high carbon activity environments over the temperature range 650-950°C. In the above environment, MnO is an n-type conductor and allows rapid Mn transport via Mn vacancies. Beneath this MnO layer, a diffusion resistant, adherent Mn Cr2 O4 film develops.