Effects of La₂O₃ content and particle size on the long-term stability and thermal cycling property of La₂O₃-dispersed SUS430 alloys for SOFC interconnect materials

We developed oxide-dispersed alloys as interconnect materials for a solid oxide fuel cell by adding La₂O₃ to SUS430 ferritic steels. For this purpose, we prepared two types of La₂O₃ with different particle sizes and added different amounts of La₂O₃ to SUS430 powder. Then, we mixed the powders using a high energy ball mill, so that nano-sized as well as micro-sized oxide particles were able to mix uniformly with the SUS430 powders. After preparing hexahedral green samples using uni-axial and cold isostatic presses, we were finally able to obtain oxide-dispersed alloys having high relative densities after firing at 1,400 °C under hydrogen atmosphere. The nano-sized La₂O₃ dispersed alloys showed properties superior to those of micro-sized dispersed alloys in terms of long-term stability and thermal cycling. Moreover, we determined the optimum amounts of added La₂O₃. Finally we were able to develop a new oxide-dispersed alloy showing excellent properties of low area specific resistance (16.23 mΩ cm²) after 1000 h at 800 °C, and no degradation after 10 iterations of thermal cycling under oxidizing atmosphere.