Oxidation and Resulting Mechanical Properties of Ni/8Y 2 O 3 -stabilized Zirconia Anode Substrate for Solid-oxide Fuel C
- PDF / 548,159 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 16 Downloads / 129 Views
Dimitrios Simwonis and Frank Tietz Forschungszentrum Jülich, Institute for Materials and Processes in Energy Systems, IWV1, D-52425 Jülich, Germany
Antonia Moropoulou National Technical University of Athens, Department of Chemical Engineering, Materials Science and Engineering Section, 9, Iroon Polytechniou Str. Zografou 15780 Athens, Greece
Aristides Naoumides Forschungszentrum Jülich, Institute for Materials and Processes in Energy Systems, IWV1, D-52425 Jülich, Germany (Received 8 March 2001; accepted 3 January 2002)
Ni/8 mol% Y2O3-stabilized zirconia cermets are used in thin-film electrolyte solid-oxide fuel cells as support substrates. Rapid oxidation of the metallic Ni can cause failure of the substrate and of the whole system. The rate of Ni oxidation in air and in an inert atmosphere containing water vapor was determined as a function of temperature between 500 and 950 °C. A logarithmic rate law describes the oxidation kinetics in air, whereas a linear rate law fits the first branch of the curve of the experimental data in a humidified inert atmosphere. The substrate exhibits no significant mechanical degradation after uniform oxidation under moderate conditions. However, the observed bending of the samples after oxidation in humidified argon, due to the nonuniform oxidation, can cause damage to fuel cell.
I. INTRODUCTION
Solid oxide fuel cells (SOFCs) are devices that convert the chemical energy of a fuel (H2 or various hydrocarbons) directly to electricity without intermediate stages of thermal and mechanical energy. The conversion is achieved through an electrochemical combination of the fuel and the oxidant (O2 or air). In comparison to the traditional methods of converting chemical energy to electricity (i.e., gas turbines), the main advantages of SOFCs are high efficiency and the low pollution.1,2 Because the polarization losses are lowest at the anode component, several groups have pursued a so-called “anode-supported” SOFC configuration.2–7 Under typical operating conditions, in which the anode is exposed to reducing atmospheres, the mechanical properties of the anode are sufficient to support the fuel cell. However, in the case of accidental oxidation at high temperature during initiation or shut-down of fuel cell operation, mechanical failure can occur (Fig. 1). This is thought to be the result of rapid oxidation of the Ni particles and accompanying volume expansion. J. Mater. Res., Vol. 17, No. 5, May 2002
http://journals.cambridge.org
Downloaded: 18 Mar 2015
This paper describes the rate of oxidation of Ni in the Ni/8 mol% Y2O3-stabilized zirconia (8YSZ) cermet and the influence of oxidation on the mechanical properties to determine the regime under which oxidation occurs without failure of the substrate and of the whole fuel cell system. The oxidation mechanism and kinetics of pure nickel and nickel alloys are well known and follow a parabolic law at high temperatures and a logarithmic law at low temperatures.8–16 However, porous nickel composites, such as the Ni/8YSZ cermet, are not ex
Data Loading...
