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STUDY ON DURABILITY FOR THERMAL CYCLE OF PLANAR SOFC Motoo Ando, Kei-ichi Nakata, Shin-ichiWakayama, Yoshiyuki Someya, Toshihiko Yoshida Corporate Research & Development Laboratory TONEN CORPORATION 1-3-1, Nishi-Tsurugaoka, Ohi-Machi, Iruma-Gun, Saitama, 356, JAPAN Introduction

TONEN CORPORATION has developed planar type SOFC since 1986. We demonstrated the output of 1.3kW in 19910>and5.1kWin 1995p). Simultaneously wehavestudied how to raise electric efficiency and reliability utilizing hydrogen and propane as fuel(3X4).

Durability for thermal cycle is one of the most important problems of planarSOFC to make it more practical. The planar type SOFC is madeup of separator, zirconia electrolyte and glass sealant. The thermal expansion of these components areexpected to be the same value, however, they still possess small differences. In this situation, athermal cyclecausesa thermalstress dueto the difference of the cell components and is often followed by a rupture in cell components, therefore, the analysis of the thermal stress should give us much useful information.

The thermal cycle process consists ofa heatingup and cooling down procedure. Zirconia electrolyte is not bonded to the separator under the condition of the initial heating up procedure, and glass sealant becomes soft or melts and glass seals spaces between the zirconia and separator. The glass sealant becomes harder with the cooling down procedure. Moreover, zirconia is tightly bonded with separator below a temperature which is defined as a constraint temperature and thermal stress also occurs. This indicates that the heating up process relaxes the thermal stress and the cooling down increases it.

In this paper, we simulated dependenceof the stress on the sealing configuration, thermal expansion of sealant and constraint temperatjire of sealant glass. Furthermore, we presented SOFC electrical properties after a thermal cycle. Calculation

In order to investigate the stress in cell components, we simulated the thermal cycle condition by the Finite Element Method(FEM). As a model we assumed three types of models as shown in figure 1. The cell is made up from LaSrCiCo03(LSCC) separator, 8mol% Y203 doped ZiOi(8YSZ) electrolyte and glass sealant. 8YSZ and LSCC are size of 200mm square. The thickness of the LSCC is 5mm, and 8YSZ is 0.2mm. LSCC separator has several gas channels.

In MODEL 1 simulated 8YSZ and LSCC are tightly bonded at two sides and strained below a constraint temperature. InMODEL 1, thermal expansion of 8YSZandLSCC caused a thermal stress.

<Modeling>

Separator Electrolyte Separator

Separator Electrolyte Separator

(a)MODEL 1

Sealant

(b)MODEL 2 Fig.1 Calculation Model of planer SOFC

(c)MODEL 3

(a)MODEL 1

Sealant

(b)MODEL 2 Fig.1 Calculation Model of planer SOFC

(c)MODEL 3

In MODEL 2 and MODEL 3, sealant was put at two or four sides of the cell as shown in figure 1(b) (c). We analyzed the cooling down procedure from 1000*0 to room temperature and it is assumed that the thermal stress occurred below a constraint temperature.

Table 1. Conditions of calculation

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