Output Characteristics and Work Function Measurement of LaB<sub>6</sub> Thermionic Converter

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  • LaB<sub>6</sub>熱電子コンバータの出力特性と仕事関数の測定
  • LaB6熱電子コンバータの出力特性と仕事関数の測定
  • LaB6 ネツ デンシ コンバータ ノ シュツリョク トクセイ ト シゴト カ

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This paper reports on design and test fabrication of a poly-crystalline lanthanum hexa-boride (LaB6) thermionic converter, and experimental results of the output power generation characteristics both in unignited and ignited mode operation, and the measurement of the LaB6 emitter and the LaB6 collector work function in cesium (Cs) vapor based on the data in unignited mode V-I characteristics.<br> Poly-crystalline LaB6 emitter work function øE was obtained from the forward saturation current Jfor in unignited mode V-I curves. The bare work function of the LaB6 emitter øEbare is 3.4 eV, and øE in Cs vapor is, for example, 2.68 eV at TE/TR=3.0, here TE is the emitter temperature, TR is the cesium reservoir temperature.<br> Poly-crystalline LaB6 collector work function øc in Cs vapor was measured from the reverse saturation current Jrev in unignited mode V-I curves. Although øc depends on the emitter and/or the collector temperature, the minimum øc is 1.35 eV when Tc=720K, Tc/TR=1.53, here Tc is the collector temperature.<br> The value of øcmin=1.35 eV is far less than the value of øcmin=1.6_??_1.7 eV of refractory metal collectors. Therefore the LaB6 thermionic converter has possibility to greatly improve power generation efficiency of a thermionic converter.<br> The maximum power density of the LaB6 thermionic converter in ignited mode operation was 0.39W/cm2, when output voltage V=0.5V, output current density J=0.78A/cm2, TE=1, 746K, Tc=1, 018 K, TR=454 K, and the interelectrode spacing d=1.1mm. The value of the barrier index was VB=2.5eV.

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