3 Fabrication Of Single Cell

A tubular flat plate was made by extrusion, and a single cell was made by fabricating the electrolyte, electrode, and interconnection layers onto that plate. Then, fuel electrode material was applied to the flat plate and electrolyte layer was plasma-sprayed onto it. Air electrode was made on the electrolyte layer by slurry-coating and sintering. The electrode plate, which acts as a cell support, must have good conductivity, porosity, and mechanical strength, so we studied ways to improve of the properties of the fuel electrode, before making cells for the stack.

(1) Properties of fuel electrode

Nickel-zirconia cermet powder was synthesized from nickel oxide and YSZ (Toso: TZ-8Y) by mixing the powders in a ball mill. The characteristics of nickel-zirconia cermets arc known to be influenced by the raw material, nickel oxide content and sintering conditions. In order to obtain a cermet with sufficient mechanical strength, we calcincd YSZ powder and applied it to the ccrmcts.

Conductivity was measured by the 4-probe method in a hydrogen atmosphere at 1000°C, and porosity was measured by mercury porosimetory and mechanical strength by the 3-point bending test (Japanese Industrial Standard). Gas permeability was measured at room temperature using helium gas.

Figure 2 shows the conductivity of the ccrmcts. Conductivity, which is influenced by the calcination temperature of YSZ, was improved by approximately 10 times. These new cermets show high conductivity evenwhen the nickel oxide content is low. Calcination temperature of YSZ also affects the strength; - „ . .. .. , ».-.vpt r ° Fig. 2 Conductivity of Ni/YSZ cermets the strength was lower for a sample synthesized a function of NiO content, from YSZ calcined at higher temperature.

-Ni> oontent(wt2 )

However, by choosing the appropriate calcination temperature, we obtained a cermet with high strength. Based on this study, we made the flat electrode plate. Several characteristics of the cermets used for the cell are shown in Table 1. As shown in Table I, the use of the calcined YSZ improved the bending strength by 20%, and also improve pore distribution, and gas-pcrmeability.

Table 1 Characteristics of the cermets

SanpK\

YSZ powdei

(a)

He gas pemteatbn mpffrfant <b)

Conductivity (S/tm)

(c)

M echani^L söEngth (Nyrttm2) (d:

material

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