Emission mechanism of Mo-Y2O3cathode①
(School of Materials Science and Engineering, Beijing Polytechnic University,
Beijing 100022, P.R.China)
Beijing 100022, P.R.China)
Abstract: The valence of element yttrium of Y2O3-Mo cathode material was studied by thermal analysis, X-ray diffraction analysis, scanning electron microscopy and X-ray photoelectron spectra, and the emission mechanism of Mo-Y2O3 cathode was discussed. It was proved that reaction between powder Y2O3and Mo2C can happen at 1173K, and Y2O3 be reduced to metallic yttrium. After the powder mixture of Y2O3and Mo2C is heat treated at 1873K, yttrium exists in two kinds of state—yttrium of zero valence and yttrium of three valences. The formation of monoatomic layer of metallic yttrium at the surface of filament is the cause of emissivity of the cathode. Yttrium at the surface doesn’t provide emission current, but the momoatomic active surface layer has a lower work function than clean molybdenum.
Key words: emission mechanism; Mo-Y2O3cathode; valence; yttrium