The Microstructure Stability of Atmospheric Plasma-Sprayed MnCo 2 O 4 Coating Under Dual-Atmosphere (H 2 /Air) Exposure
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Ying-Zhen Hu, Cheng-Xin Li, Shan-Lin Zhang, Guan-Jun Yang, Xiao-Tao Luo, and Chang-Jiu Li (Submitted May 6, 2015; in revised form October 21, 2015) Based on the specific structure of tubular solid oxide fuel cells, good chemical, microstructural, and phase stabilities for the protective coating are required in both the oxidizing and reducing environments. In this work, MnCo2O4 coatings were deposited onto porous Ni50Cr50-Al2O3 substrate by atmospheric plasma spray. The coated samples were tested at 800 °C with the coating exposed in air environment and the substrate in H2 environment. Reducing and pre-oxidizing treatments were performed prior to the stability test. The microstructural stability, phase composition, and electrical properties of the tested coatings were investigated. The surface morphology exhibited an excellent surface stability, and no obvious crystal coarsening was observed. With enhancement of the testing duration, the area-specific resistance presented a decreasing trend attributed to increase in the contact interface and densification of the upper layer. The cross-section views presented a dense upper layer and a relatively porous bottom layer. The x-ray diffraction results also indicated a single MnCo2O4 phase in the upper layer exposed to air environment and a reduced phase structure in the bottom layer from the substrate side. The evolution mechanism between the oxidation frontier and the reduction interface was then discussed.
Keywords
APS, dual atmosphere, FSS MnCo2O4 spinel coating, SOFC
interconnect,
1. Introduction The breakthrough on the preparation of thinner electrolyte layers (Ref 1, 2) and the research on cathode enable the reduction of solid oxide fuel cell (SOFC) operating temperature. This made it possible for some high temperature oxidation resistant alloys such as ironbased alloys to substitute the traditional LaCrO3 ceramic which had a high cost and high sintering temperature. Due to its suitable coefficient of thermal expansion (12 9 106/ K), high electron conductivity, high mechanical strength, relatively low cost, and easiness to mold, iron-based alloy such as ferritic stainless steel (FSS) has attracted interest of most researchers. In recent years, there has been wide research on Cr-containing FSS such as Crofer22 APU, T441, and AISI430 (Ref 3-7). However, during SOFC This article is an invited paper selected from presentations at the 2015 International Thermal Spray Conference, held May 11-14, 2015, in Long Beach, California, USA, and has been expanded from the original presentation. Ying-Zhen Hu, Cheng-Xin Li, Shan-Lin Zhang, Guan-Jun Yang, Xiao-Tao Luo, and Chang-Jiu Li, State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xian Jiaotong University, Xian 710049, Shaanxi Province, Peoples Republic of China. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
operation, the outward transport of Cr and inward transport of oxygen brought about the excessive growth of chromium oxide layer. More
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