Guided by the aforementioned experiments, a powder-metallurgy process for fabricating skutterudite was modified to provide for covering the outer surfaces of the segments with titanium foils. In the unmodified process, the thermoelectric material, in powder form, is hot-pressed in a graphite die, then removed, then further processed. The combination of high temperature and pressure in the die acts to promote bonding between particles, and as such, is ideal as a means of adding an adherent sublimation- suppressing outer layer. Hence, the process is modified by simply lining the inner wall of the die with a foil of the barrier material before filling the die with the thermoelectric powder (see figure).
In preparation for further experiments, the modified process was used to fabricate specimens of n- and p-type skutterudites covered with adherent 25- μm-thick foils of titanium. In the experiments, these specimens were heated in a vacuum under the same conditions as in the experiments described above, then sectioned and examined. Like the niobium foils in those experiments, the titanium foil outer layers in these experiments were found to have suppressed sublimation of Sb.
This work was done by Jeffrey Sakamoto, Thierry Caillat, Jean-Pierre Fleurial, and G. Jeffrey Snyder of Caltech for NASA's Jet Propulsion Laboratory.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, NASA Management Office–JPL. Refer to NPO-40040.