• PDF / 447,304 Bytes
• 6 Pages / 420.48 x 639 pts Page_size
• 57 Downloads / 237 Views

DOWNLOAD

REPORT

---

G. MAJKIC, L. WHEELER, K. SALAMA Materials Research Science and Engineering Center, University of Houston, Houston, TX 77204 ABSTRACT In order to achieve commercial utilization, oxygen separation membranes and solid oxide fuel cells must be able to maintain their mechanical integrity over acceptable life-time periods. This imposes a need for characterization of mechanical behavior of the materials used under operating conditions (high temperature and low stress), in order to identify mechanisms that lead to mechanical degradation during operation. In this study, a series of compressive creep tests on rectangular specimens of SrCosFeo.203-x of different grain sizes (2.4 to 6.8 microns) is performed in air, covering a temperature range of 850 to 975 °C and stress range of 10-20 and 40-50 MPa. In the high stress range the material has been found to render temperature dependent stress exponents (2.2 to 2.9) and high steady-state strain rates. In the low stress range the stress exponent has been found to be dose to unity (1.1 to 1.3) indicating diffusion controlled creep. The activation energy appears to assume two different values depending on operating temperature region, 457 kJ/mole below 925 OC and 268 kJ/mole above 925 OC. These values, being much higher than that for oxygen diffusion (