Novel processing routes for oxide cathode emission materials
An investigation has been carried out into the production of the alkaline earth carbonate and oxide powders and coatings suitable as cathode emission materials by the ethylenediaminetetraacetic acid (EDT A) gel method for potential application as cathode emission materials. The emission performance of thermionic cathodes coated with these materials has been measured, and found to give encouraging results, comparable with conventionally prepared oxide emission materials, despite the former having not been optimised. Amorphous gels of composition Ca-EDTA, Sr-EDTA, Ba-EDTA, [SrO.5 Bao.5J-EDTA and [SrO.5 Bao.5 Cao.05J-EDTA were successfully prepared from aqueous solutions of alkaline earth nitrates and EDT A. Subsequently, the thermal decomposition of the gels and the effects of temperature and atmospheres on the decomposition have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The gels and the powders derived from calcination of these gels at different temperatures have been characterised by Fourier transform infrared spectroscopy (FTIR) , X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) with X-ray energy dispersive (EDX) spectroscopy. Coatings prepared by dip-coating, spraying and electrophoretic deposition (EPD) from the EDT A-sols have been characterised by FTIR, XRI> and SEM techniques. In addition, an attempt was made to study the coating of the colloidal particles in the suspension of methanolethanediol- EDTA sol by electrochemical impedance spectroscopy.