Results And Discussion

The relative density was determined by percentage of a sample density and a theoretical density. The relative densities of Cr metal and 25LC were 97 and 95 %, respectively. Thus the sintered sample is considered to satisfy a gas tightness condition in a cell stack. The ac electrical conductivity was measured at a frequency of 1 kHz by four probe method. The Cr metal and 25LC had ac conductivities of 3.63x10'' and 0.92xl04 S/cm at room temperature, respectively. Also the conductivity of Plansec's DUCROLLOY(Cr5Fel Y203) was estimated using the same method for comparison. Its ac conductivity was 1.06xl04 S/cm, which is lower than the reported dc conductivity of 3.4xl04 S/cm(5). This may be considered to be due to a difference of a measurement method and a contact resistance of the used probes. Nevertheless, the 25LC indicated high conductivity like DUCROLLOY. This means that the 25LC is able to be used as an interconnect material from the viewpoint of electrical conductivity.

Thermal expansion of composite body can be calculated by Turner's and Renter's models(6). Figure 2 shows the calculated thermal expansion coeflIcient(TEC) of Cr alloy at 1000 °C as a function of LaCr03 content A TEC of about 25 vol.% LaCr03 at 1000 °C is compatible with that of 8mol% yttria-stabilized zirconia(8YSZ) because, although an average TEC of 8YSZ in the range of room temperature and 1000 °C is 10.5x10"® m/m.K, 8YSZ at 1000 °C has a TEC of 12.5x10^ m/m. Figure 3 shows the measured thermal expansion curves of 25LC and 8YSZ between room temperature andlOOO °C. These seem to be reasonably in good agreement on the whole.

Figure 4 shows the oxidation behavior of the 25LC and the pure Cr metal. The 25LC is much more resistant to oxidation in air titan the pure Cr. The oxidation rate of the 25LC decreased slowly with increasing number of oxidation cycle, whereas that of the pure Cr increased with number of cycles and then decreased alter 4 cycles. From optical microscopy, a delamination of the oxide scale formed at the surface of the 25LC was not found and thus the decreased oxidation rate during oxidation test is considered to be due to an evaporation of the surface oxide. On the other hand, the oxide scale in the Cr metal was spalled, which is thought to be a main reason of the decreased oxidation rate after 4 cycles.

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