Papers by Author: John Drennan

Abstract: This paper outlines the current state of research into laser welding of titanium and its alloys for medical applications. The differences that exist between the medical and other industries are described and a direction for advancing research in this field is proposed.

Abstract: A new nitriding method has been devised which requires only a simple vacuum furnace and enables direct nitridation of solid aluminium without any prior surface treatment. It can be used to produce thick aluminium nitride surface layers on aluminium, under nitrogen at atmospheric pressure. A critical element of the process is the use of a magnesium vapour source that reduces/disrupts the natural, protective oxide film on the aluminium surface and facilitates nitriding. The nitride surface layers form through two distinct modes, one growing outward from the aluminium plate surface and the other growing into the aluminium. Studies of the nitride layers utilizing optical microscopy, TEM, SEM, XRD and XPS have been conducted. Details of the composition, structure and growth as well as possible mechanisms for the nitride formation are presented. Understanding of the reaction may have important implications for the production of wear resistant coatings on bulk Al as well as for the production of Al/AlN composites.

Abstract: Rare earth doped ceria compounds are fluorite related oxides which show oxide ionic conductivity higher than yttria stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for ‘low (below 500°C)’ temperature operation of solid oxide fuel cells (SOFCs). In this study, the nano-sized powders of DyxCe1-xO2-x/2 (x=0.15 and 0.2) were prepared using ammonium carbonate co-precipitation method. To design the nano-structure in aforementioned materials, the round shape particles were prepared in nano-scale. The combined process of Spark Plasma Sintering (SPS) and Conventional Sintering (CS) was examined for fabrication of nano-structured doped CeO2 solid electrolytes. The nano-structural features in the (SPS+CS) specimen and CS specimen were observed using transmission electron microscopy (TEM). This micro-analysis suggested that the micro-domain with distorted pyrochlore structure exists in the grain of these materials. The conducting properties in the specimens were strongly influenced by the micro-domain size. It is found that the present combined process minimized the micro-domain size and maximized the conductivity in the specimens. Also nano-structured Dy doped CeO2 sintered bodies in the present study had wide ionic domain and high transport number of oxygen. This suggests that fabricated sintered bodies are suitable for the solid electrolyte in low temperature operated SOFCs. It is concluded that a control of micro-domain size is a key for development of high quality doped CeO2 electrolytes for fuel cell application. It is expected that advanced solid electrolytes for clean energy production will be produced by a design of nano-structure in rare earth doped CeO2 solid electrolyte.