No abstract

Solid oxide fuel cells (SOFCs) have serious problems under heating cycle. As a solution for this problem, use of micro- tubular SOFCs is considered for robustness under rapid changes of operating temperature. We fabricated cube-shaped SOFC bundles with following method; Micro-tubular Gd-CeO2(GDC)-NiO anode was fabricated by extrusion, and then was co-fired with GDC electrolyte coated on the surface of the anode tube. La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) cathode matrices with grooves were also prepared by extruding of a mass with LSCF powder and pore-former. Then, the tubes were arranged in the grooves of LSCF cathode matrices, where the tubes and the matrices were jointed with LSCF pastes. Optimization of the micro tubular cell configuration in cube-shaped SOFC bundles and microstructure of cathode is important to achieve our target power density (2W/cm3). In this study, we considered the configuration of cube-shaped SOFC bundles and investigated the character of single tubular cell and cathode porous matrices.

NGK Spark Plug Co., Ltd. has been developing various silicon nitride materials, and the technology for fabricating components for ceramic gas turbines (CGT) using theses materials. We are supplying silicon nitride material components for the project to develop 300 kW class CGT for co-generation in Japan. EC-152 was developed for components that require high strength at high temperature, such as turbine blades and turbine nozzles. In order to adapt the increasing of the turbine inlet temperature (TIT) up to 1350 °C in accordance with the project goals, we developed two silicon nitride materials with further improved properties: ST-1 and ST-2. ST-1 has a higher strength than EC-152 and is suitable for first stage turbine blades and power turbine blades. ST-2 has higher oxidation resistance than EC-152 and is suitable for power turbine nozzles. On applying these silicon nitride ceramics to CGT engine, we evaluated various properties of silicon nitride materials considering the environment in CGT engine. Particle impact testing is one of those evaluations. Materials used in CGT engine are exposed in high speed gas flow, and impact damage of these materials is considered to be a concern. We tested ST-1 in the particle impact test. In this test, we observed fracture modes, and estimated the critical impact velocity. This paper summarizes the development of silicon nitride components, and the result of evaluations of these silicon nitride materials.

A new high quality turbine system using monolithic silicon-nitride ceramic is under development. In this study particle impact tests of the silicon-nitride have been tried at room and elevated temperatures with and without tensile load, which simulates centrifugal force of blade rotation. In the experiment 1 mm diameter particle is impacted at velocities up to 900 m s−1. In this paper, critical velocities for bending fracture and Hertzian cracks are examined. Moreover, strength degradation at elevated temperature and spall fracture of the blade are discussed. The main results are: 1) The bending fracture mode critical impact velocity for soft particles is higher than that for hard particles. 2)The impact parameter ϕ for initiation of Hertzian cracks ranges 1.08×10−5 – 1.56×10−5 for the materials tested. 3)Strength degradation at elevated temperature was clearly observed. 4) In the impact tests on blades spall fracture, which was caused by interaction of stress waves, appeared.

Microtubular solid oxide fuel cells (SOFCs) are shown to be robust under rapid temperature changes and have large electrode area per volume (high volumetric power density). Such features are believed to increase a variety of application. Our study aims to establish a fabrication technique for microtubular SOFC bundles with the volumetric power density of 2 W cm−3 at 0.7 V. So far, we have succeeded to develop a fabrication technology for microtubular SOFC bundles using anode supported tubular SOFCs and cathode matrices with well-controlled microstructures. A key to improve the performance of the microtubular SOFC bundles is to optimize the microstructure of the cathode matrices because it influences a pressure loss for air and electric current collection. In this paper, a simulation study of an air flow, temperature, and potential distributions in the microtubular SOFC bundle was conducted in order to understand the characteristics of the present bundle design. In addition, operating conditions of the microtubular SOFC bundles was discussed for realizing the target power density of 2 W cm−3.