Direct energy conversion of heat to electricity using AMTEC
Former renewable technologies, which did not prosper at that time due to engineering and material limitations, emerge once again, as in the case of the Alkali Metal Thermal to Electric Converter (AMTEC). This energy converter transforms heat to electricity through an electrochemical process at high temperature (700 - 1000 °C). At Karlsruhe Institute of Technology (KIT) an AMTEC test cell and an AMTEC TEst FAcility (ATEFA) have been designed and are under construction. The paper gives an overview of the history of AMTEC converter and its development; and presents the ATEFA facility included its latest progress in design and construction. In addition, a scoping study on the stability of PEEK polymer compound in liquid sodium environment was started and is reported.
A supersaturation model for the degradation of sodium β/β″-aluminas
A mechanism is proposed for the sodium degradation of β/β″ alumina electrolytes. It is based on the Na+ supersaturation of feeder grains peripheral to flaws in the liquid-sodium/ electrolyte interface. This supersaturation is brought about by the focusing of the current by the flaw and leads to local oxidation of oxygen ions in the aluminate structure. This process leads to the formation of colour-centres and sodium atoms in the grains. The latter coalesce to form sodium colloids, microcracking the microstructures. These microcracks join the originating flaw and promote its extension. A model is presented which demonstrates the feasibility of the proposed degradation mechanism and it is discussed in light of other associated physical phenomena.
Blocking defects in β″-alumina observed by high resolution electron microscopy
THE sodium-sulphur battery containing the solid electrolyte β″-alumina is one of the most scientifically intriguing and widely studied battery systems ever discovered. A major reason for this is its potential use in vehicular and energy storage applications. Practical Na–S batteries are constructed with ceramic tubes of Mg-stabilised β″-alumina as solid electrolyte (U.S.P. 3446677 or 3475225)1 and a considerable amount of research work on such batteries with β-alumina or β″-alumina has been done. The greatest area of uncertainty with β″-alumina is the effect on cell performance of certain changes in the electrolyte with time; serious changes are loss of sodium ions from the positive electrode side of the electrolyte and changes in structural characteristics. We report here, for the first time, an investigation to reveal the defect structure of the crystals of β″-alumina using high resolution electron microscopy.