Oxidation Kinetics of Mn[sub 1.5]Co[sub 1.5]O[sub 4]-Coated Haynes 230 and Crofer 22 APU for Solid Oxide Fuel Cell Interconnects

Abstract

The oxidation behavior of Mn1.5Co1.5normalO4 (MCO)-coated Haynes 230 (H230) and Crofer 22 APU was investigated between 700 and 900°C . The oxidation kinetics of the coated alloys was compared with that of base alloys at 800°C . An apparent two-stage kinetics behavior of the MCO-coated Crofer 22 APU was observed. The coating effectively reduced the oxidation rate constants of Crofer 22 APU by 5.5 times, whereas it did not seem to affect the oxidation kinetics of H230. The oxidation activation energies of the coated alloys suggest distinctly different oxidation mechanisms between the coated H230 and Crofer 22 APU. A Cr-modified spinel was observed in the interface region between the metal oxide scale and the spinel coating after long-term oxidation for both alloys. A semiquantitative model of oxidation kinetics was developed to explain the different behaviors observed. Apparently, the Cr-modified spinel may play a more important role on H230 during long-term oxidation. The heat-treatment of H230 in the reducing environment used for the MCO coating application processes appeared to debit oxidation resistance of the base alloy. The optimization of the MCO application process is expected to benefit oxidation resistance as well as chromia containment on H230.

Fabrication of Mn–Co Spinel Coatings on Crofer 22 APU Stainless Steel by Electrophoretic Deposition for Interconnect Applications in Solid Oxide Fuel Cells

“…In both cases, the square of the weight gain per unit area (DW/A) 2 increases linearly with the increase in the isothermal oxidation time. This confirms that (DW/A) 2 as a function of oxidation time satisfies the parabolic kinetics law described by the following equation 24 :…”

“…It also minimizes the interfacial contact area-specific resistance (ASR) between cathode and interconnect by limiting the growth of the Cr-based oxide scale, which has relatively low conductivity. 7 Efforts have been made by various groups [20][21][22][23][24][25][26][27][28] to demonstrate that a (Mn,Co) 3 O 4 spinel could be a promising barrier for interconnect applications in SOFCs. For example, Yang et al 25 found that Mn 1.5 Co 1.5 O 4 spinel coatings (prepared by a slurry screen-printing method) were effective in reducing the contact resistance and providing high electrical conductivity.…”

Efficient dual layer interconnect coating for high temperature electrochemical devices

“…These effects of the coating will be discussed in the following paragraphs. Parabolic rate constants from the present study may be compared to oxidation constants of spinel-coated steels from previous investigations [39,44,45]. The data are presented in Table 3.…”

“…In a recent study of Chen et al [39], the authors investigated the oxidation of a spinel coated and uncoated Crofer 22 APU at different temperatures. They found that the activation energy of coated and uncoated steel was similar and equal to w290 kJ mol À1 [39]. This value is comparable to the reported activation energy of Cr 3þ diffusion in Cr 2 O 3 (280 kJ mol À1 [34]).…”

Influence of grain orientation on the incipient oxidation behavior of Haynes 230 at 900 °C

“…It was demonstrated that inter-granular oxidation and internal oxidation occurred at 982°C and 1093°C after 300 h exposure, respectively. Further, many researcher tried to improve the oxidation behavior of Haynes 230 by several methods, using alloying [22,23], electrical discharge alloying (EDA) [24,25], MOCVD [26] or various surface modification [27,28].…”