Insulators and Materials for Close-Spaced Thermoelectric Modules

70316 In close-spaced thermoelectric modules that use PbTe/TAGS as the N- and P-legs, cross contamination of elements occurs from one leg into the other, resulting in degraded power output as the compositions of the legs shift. Mica, typically used as a separator because of its low thermal and electrical conductivities and its stability, appears to allow Te and other elements from the high vapor pressure TAGS to diffuse through. This project will investigate two different types of separators: (1) ceramic, injection-molded eggcrate structures, and (2) modified separators that include a diffusion barrier composed of a thin layer of tungsten sandwiched between two layers of mica. In addition, the use of segmented thermoelectric legs, which would reduce the hot-side temperature of the TAGS in the P leg will be evaluated. In Phase I, mica separators with an intermediate tungsten layer will be fabricated, and their efficacy in preventing interdiffusion between PbTe and TAGS will be determined. Techniques will be developed for ceramic injection molding of thin layers of ZrO2 for use as separators, initially in sheet form and subsequently as eggcrate structures. Use of segmented legs to reduce the operating temperatures of volatile leg materials (such as TAGS) will be evaluated. Commercial Applications and Other Benefits as described by the awardee: The new separators should provide enhanced performance (higher efficiency) of Radioisotope Thermoelectric Generators used in spacecraft. Other applications include generators powered by other heat sources in the commercial sector, especially those with high grade waste heat sources.