Journal of Power Sources 195 (2010) 3631–3635 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Creep properties of solid oxide fuel cell glass–ceramic seal G18 Jacqueline Milhans a,∗ , Mohammed Khaleel b , Xin Sun b , Mehran Tehrani c , Marwan Al-Haik c , H. Garmestani a a Georgia Institute of Technology, School of Material Science and Engineering, United States b Pacific Northwest National Lab, United States c University of New Mexico, Department of Mechanical Engineering, United States article info Article history: Received 27 October 2009 Received in revised form 10 December 2009 Accepted 10 December 2009 Available online 16 December 2009 Keywords: SOFC Elastic properties Creep Glass–ceramic Seal Nanoindentation abstract This study utilizes nanoindentation to investigate and measure creep properties of a barium calcium alumino-silicate glass–ceramic used for solid oxide fuel cell seals (SOFCs). Samples of the glass–ceramic seal material were aged for 5, 50, and 100 h to obtain different degrees of crystallinity. Instrumented nanoindentation was performed on the samples with different aging times at different temperatures to investigate the strain rate sensitivity during inelastic deformation. The temperature dependent behavior is important since SOFCs operate at high temperatures (800–1000 ◦ C). Results show that the samples with higher crystallinity were more resistant to creep, and the creep compliance tended to decrease with increasing temperature, especially with further aged samples. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Solid oxide fuel cell (SOFC) technology has been demonstrated as a promising and efficient alternative energy source. In planar SOFCs, a hermetic seal is required to separate fuel and air sides of the electrodes. The seal also is often used to bond components of the fuel cell together. This seal must be able to withstand the thermal cycling caused by powering up and powering down the fuel cell, which operates at approximately 800 ◦ C. Also, it is impor- tant that the joining temperature of the seal is above the operating temperature of the fuel cell it is intended for. Glass–ceramic materi- als are currently being investigated as candidates for SOFC sealant materials. This is due to their ability in maintaining mechanical properties at high temperatures, manufacturability and low cost. The seal is bonded to several components of the seal (e.g. intercon- nect, electrodes, frame, etc.), therefore making it costly to replace. Seal materials must have long life spans due to their difficulty to repair [1–5]. Furthermore, a SOFC seal must not display significant creep at high temperatures to maintain the stack level geometric sta- ∗ Corresponding author at: Georgia Institute of Technology, 771 Ferst Dr., Love Bldg, Rm 353, Atlanta, GA 30332, United States. Tel.: +1 978 870 7944; fax: +1 404 894 9140. E-mail address: jackie.milhans@gmail.com (J. Milhans). bility. By understanding the creep properties, the life of the seal may be predicted in terms of creep deformation. In the case of glass–ceramics, changing the degree of crystallinity of the mate- rial can alter the properties. The desired level of crystallinity can be produced by a combination of aging time and temperature. The creep properties can be changed to an extent by “designing” the microstructure in this sense of crystalline volume fraction. In this study, nanoindentation is performed on G18 (a glass–ceramic seal developed by Pacific Northwest National Lab- oratory [3–8] to determine its temperature- and time-dependent viscoplastic properties. Nanoindentation has been used in other studies, for glasses at high temperatures and more especially for polymers, in finding creep properties [9–14]. Because G18 is a glass–ceramic designed for high-temperature operation, it displays similar viscoplastic characteristics as polymers at high temperatures. Nanoindentation is an effective technique to study mechanical properties high-temperature SOFC materials. High-temperature nanoindentation is used establish mechanical behavior–microstructure relationships in the SOFC seal material. Glass–ceramic seals are multi-phase materials, with the ability to tailor the mechanical behavior through controlling the amount of crystallinity. With better mechanical property–microstructure relationships, development of glass–ceramic seals could be more rapid and progressive. Nanoindentation can also reveal periodicity in mechanical properties, which may be due to phase clustering or other morphologies in the microstructure. Nanoindentation of 0378-7753/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2009.12.038