Emitter tri-layer technology

The emitter tri-layer technology combines the best aspects of the single cell and multi-cell thermionic fuel element designs. The emitter tri-layer technology places strict requirements on materials especially the insulator. Emitter tri-layers consisting of scandium oxide and single crystal and polycrystalline tungsten were fabricated, machined into test samples, and tested. Scandium oxide has met the requirements of thermal stability and mechanical strength by surviving 20 thermal cycles between 300 and 1900 K (27 k/min heating and cooling rates). Electrical resistance lifetime tests currently under way at 1900 K and a 2.6 volt applied potential show that the electrical resistivity of the scandium oxide in the emitter trilayer, 1.03x10(2) ohms-cm, is acceptable for a conductively coupled multi-cell thermionic fuel element with a designed current density of 10A/cm(2).