Effect of Heat Treatment on Thermal Sprayed Protective Oxides for SOFC Metallic Interconnects

Tuesday, 7 October 2014: 11:20
Sunrise, 2nd Floor, Galactic Ballroom 5 (Moon Palace Resort)
K. Z. Fung (Research Center for Energy Technology and Strategy, Dept. of Materials Science and Engineering, National Cheng Kung University, Taiwan), S. Y. Tsai (Dept. of Materials Science and Engineering, National Cheng Kung University, Taiwan), C. T. Ni (Dept. of Materials Science and Engineering, National Cheng Kung University), and H. C. Ho (National Cheng Kung University)
For the stack design of solid oxide fuel cells (SOFC), metallic interconnects such as Crofer 22H is widely used to replace ceramic interconnects. Most metallic interconnects use chromium-containing alloy that form chromia scales to suppress further oxidation at high temperatures. Since chromia may react with cathode and cause degradation, a protective oxide may be used to suppress the growth of chromia. Although several techniques have been adopted to deposit oxides on metallic interconnects, the thermal spray is found to be an appropriate technique. Thermal spray coating process has been widely used to produce a high quality coating by a combination of high temperature, high energy heat source, a spraying gas medium, such as argon, and high particle velocities. This process allows the spraying of various types of metallic or ceramic coatings on to a wide range of substrate materials. As a result, uniform coating layer with excellent bond strength to substrate is obtained without noticeable distortion.

For metallic interconnects used for SOFC applications, several oxides such as LaMnO3 and LaCrO3-based perovskite oxides and (Mn,Co)3O4, (MCO), with spinel structure have been used to form protective layer for metallic interconnects. However, the temperature during thermal spraying may be high enough to change the crystal structure and conductivity of protective oxides. The  heat treatment is believed to be an appropriate method to obtain adequate properties for protective oxide. Thus, the after-spray treatment will play an important role for metallic interconnects to obtain desired electrical properties. In this study, the high-temperature ferritic stainless steel Crofer 22H and nickel-chromium alloy Inconel 625 were first thermally sprayed with oxides with perovskite and spinel structures.

The objective of this work is to investigate the effect of after-spray treatment on the crystal structure and conductivity of the sprayed oxide. The crystal structure, morphology and electrical conduction of interconnect with sprayed oxide films will be examined by using XRD, FESEM and resistance measurement.