Mechanical properties of azobé (Lophira alata)

The use of tropical hardwoods in structural applications requires knowledge of the mechanical properties. Even though long experience is available with the species azobé (Lophira alata), much of the current knowledge is based on tests performed on small clear specimens for bending, compression and shear. Since tropical hardwoods are used in structures with high economic value, a sound knowledge of the mechanical properties allows for better optimisation and for minimal use of raw material. Bending, compression and shear tests have been performed on material in structural sizes. Characteristic values show that in most loading cases the structural capacity of the material is distinctly higher than currently assumed in practice. The relationship between static modulus of elasticity and bending strength has been determined. The depth effect was shown to be less pronounced than for softwoods

Untersuchungen zur Getterung metallischer Spaltprodukte im Primärkühlkreislauf eines Hochtemperaturreaktors

Supplementary to the recommended method to retain fission products by ceramic coatings (e.g. pyrocarbon, silicon carbide) in small spherical fuel particles, a new concept of gettering silver 110m and cesium 134/137 in the primary circuit of a High Temperature Reactor (HTR) is presented. It is based upon the known fact that the vapor pressure of metallic fission products in solid or liquid solutions is lower compared with that of the pure fission products. Although metallic additives were found not to influence the silver release from oxide fuel kernels, the effective diffusion coefficient of silver 110m in graphite matrix is reduced by about two orders of magnitude by small amounts of the metallic Cu, Ge, Sn or Au additions. However, these reduced silver diffusion coefficients are not sufficiently low in order to retain silver 110m in the fuel-free zone of spherical HTR fuel elements. On the other hand, metallic additives were found to be very efficient in gettering silver 110m from the gaseous phase: During a contact time of only 0,15 seconds at 950°C more than 80 %,at 850°C even more than 99 % of the Ag 110m could be absorbed from the streaming gas by using a metal-containing graphite filter. The best results were obtained by using tin or gold additives. By optimizing the filter geometry further increase of the efficiency should be possible

Processing and quality control of planar SOFC components

The implementation of a PC-based quality control system for the manufacturing of anode-supported solid oxide fuel cells (SOFCs) is a prerequisite for achieving reproducibility and high quality of the cells. To reach that goal a broad database for each manufacturing step including materials and processes is needed. This database is generated on the basis of the well developed manufacturing route of the Julich planar SOFC. This paper focuses on first results obtained through the BREDA database system (Brennstoffzellen-Datenbank, Database for Fuel Cells)

Influence of alumina dopant on the properties of yttria-stabilised zirconia for SOFC applications

The most important component of the solid oxide fuel cell (SOFC) is the dense electrolyte. Besides gastightness it must fulfill the requirements of good ionic conductivity and stability in reducing and oxidizing atmospheres. For this application yttria-stabilized zirconia is widely used. In this paper the effect of calcination temperature and milling time for zirconia powder stabilized with 8 mol% yttria (8YSZ) on the gastightness of the electrolyte layer was investigated. The influence of the addition of 0.77, 2 and 4 wt% Al2O3 to 8YSZ powder on the tightness and the sinterability of the electrolyte layer was studied. The performance of the cell with the electrolyte doped with 0.77 wt% Al2O3 was also investigated. The experiments show that the electrolyte layer, which was fabricated from 8YSZ powder (calcined at 1200degreesC) with particle size distributions of 0.25 mum-<0.3 mum (d(50)), gives the lowest leak rate. The Al2O3 added to 8YSZ improved the electrolyte tightness by increasing the sinterability of the electrolyte layer and reducing the sintering time. The performance of a cell with Al2O3 added to the electrolyte is better than that of a cell with an electrolyte of pure 8YSZ, especially at operating temperatures between 800 and 900degreesC. (C) 2002 Kluwer Academic Publishers