Study Of Sc-Type Dispenser Cathode With Scandia Doped Tungsten Matrix

In this work, certain amounts of scandia or scandia with small amount of rhenium compound were added, in aqueous solution , to tungsten oxide. The matrix of Scandium dispenser cathode is made of scandia doped tungsten powder obtained from scandia aqueous doping tungsten oxide. The properties and particle fining mechanism of the doping powders, microstructure and the distribution of Scandia and surface behavior of the matrix have been investigated compared with that of with mechanical mixing scandia and tungsten matrix by using modern surface analysis techniques, such as Hitachi S-3500N SEM, Inca EDS and in "situ" AES . The Scandia doped tungsten body was applied in impregnated dispenser cathode and the effect of the improving matrix on the cathode characteristic was also studied.The mean particle size is much smaller , 80263 uniformly distributed and covered over tungsten grain existed like a film is showed in Scandia doped tungsten powder compared with that of mechanical mixing scandia and tungsten powder. During reduction of Sc-doped tungsten oxide when rhenium compound was added, the size of many particle is less than 100 nm that means a tremendously particle fining process took place .For cathodes with Sc2O3 doped tungsten bodies processed by the solid-aqueous solution doping method, homogeneous porous microstructure with film-like 80263 covering over tungsten grains but leaving porous areas for diffussion of barium to the suface,also the interface between Sc203 and W is great which results in the strong binding force between these two substance, which lead to high resistence to ion bombardment and high temperature.Emission properties of cathode with scandia doped tungsten matrix were tested by a homemade computer-control automatic emission-testing instrument. The effective workfunction of cathode is below 1.6 eV. Typical test results are over 15 A-cm-2 at 850℃ and over 50 A-cm-2 at 950℃. The results of surface behavior show that the activated layer of cathode exhibits fine recovery from ion bombardment and has the potential to work for long time. All mentioned above prove that cathode property reaches to the excellent study level in Sc-type dispenser cathode.