Ceramic electrolytes and secondary recovery

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Ceramic electrolyte work centers on two applications - electrochemical sensors and solid oxide fuel cells. During steelmaking, liquid steel picks up oxygen from the air. It is essential to measure it as it affects casting behaviour and mechanical properties. To overcome inaccuracy of commercially available probes based on stabilized zirconia especially at low oxygen contents (referred to as clean steel), the highly stable yttria-calcia and dysprosia-calcia systems are being studied, especially electrical properties. Thermal and redox cycling resistance, fuel impurities and long-term microstructural stability continue to plague commercial development of high temperature fuel cells. Non-hydrogen fuels, e.g., natural gas, syngas from coal, will only be possible if fuel electrode (anode) materials that resist sulphur poisoning and carbon deposition can be identified. Both thermal cycling and redox cycling (air enters the fuel chamber oxidizing and expanding the electrode) cause cracking and delamination. This can be avoided by fabricating a porous support (same material as the electrolyte) by slip casting to act as the main structural component. The ceramic powders used to prepare the slurry for casting (slip) must have been previously heated to 1300-1500C to create a fine pore network. However, anode impregnation (initially nickel) into the support must be feasible and will be studied. Tungsten carbide is under consideration as an anode material. It has a very stable microstructure (resists sintering), appears to tolerate a moderate amount of sulphur and does not nucleate carbon deposition. Regarding secondary recovery, to deal with industrial waste disposal problems and/or recover valuable metals, transformational roasting (heating in air at 500-1000C) has been considered whereby one or more solid reagents are added to the material prior to roasting to rapidly alter the minerals present to either sequester toxic metals or liberate valuable ones. It has been applied to oil sands fly ash and electric arc furnace steelmaking dust with mixed results, but successfully applied to zinc ferrite residue and nickel sulphide electrowinning concentrate. It may have wide applicability to industrial processes.