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Radiant heat transfer between the coated solid electrolyte surface and a condenser in an AMTEC cell can be reduced by the use of radiation shields. The shields do not deliver or remove any heat from the system, but only increase the “resistance” of the heat flow path. By reducing heat transfer, radiation shields serve not only to minimize parasitic heat loss, but also to reduce thermal stresses in the electrolyte below a critical level. A radiation shield also increases the impedance to atom flow and reduces power density. The pressure drops across gas flow impedances in the Knudsen regime are proportional to flow rate and since the effect on voltage of pressure is logarithmic through the Nernst equation, the loss of power by insertion of a shield may be acceptably small for some practical circumstances.

The fracture toughness and fracture strength of beta”-alumina are critical material properties for insuring reliable assembly, performance and lifetime of sodium-sulfur batteries in electric vehicle applications. The fracture toughness of the electrolyte is of major importance because it has been shown that the critical sodium ion current density for electrolyte degradation is proportional to the fracture toughness of the electrolyte to the fourth power. High fracture strength of the electrolyte is required for making and maintaining reliable seals to the insulating header. Greater fracture strength and toughness of beta”-alumina can be attained through transformation toughening while maintaining tolerable ionic resistivities.