Tungsten cathode production and sintering with powder metallurgy method

Vacuum tube technology is based on the interaction of electrical and magnetic fields with the electron flow. Cathodes are designed as electron sources for vacuum devices. The energy in electron beam is converted to electromagnetic radiation by the RF sources from a few hundred kilohertz to more than terahertz for applications in the area of communication, industrial heating, radar, spectroscopy, medical treatments and scientific research. Tungsten cathode are prepared by compressing the tungsten powder into cylindrical pelet, then these consolidated pelet typically is sintered at a temperature over 2000°C in a hydrogen atmosphere for some definite of time to obtain a 80% dense porous tungsten matrix. This porous matrix acts as a reservoir for the impregnation of the emitting material that is a compound consisting of barium oxide (BaO), calcium oxide (CaO), aluminum oxide (Al2O3). Typical barium-calcium-aluminate impregnate compositions used in thermionic cathodes have BaO:CaO:Al2O3 molar ratios of 5:3:2, 4:1:1 and 3:1:1, respectively. The thermionic cathode is heated to the temperature range from 1000°C to 1100°C in operation, this causes the emitting material barium diffuses to the surface for obtaining an active layer providing a low work function surface for the thermionic emission of the electrons. For better performance of the tungsten based dispenser cathodes, uniform and controlled porosity is critical. Therefore, the porosity distribution is the most significant parameter for its performance. The thermionic cathodes main part of the vacuum electronics devices used for application of the defense and security, space communication, medical treatments and scientific research will be performed by way of purposing this project. In this study, eighty percent density are obtained homogenously distributed in the cathode pores. In the heating test has proved successful integration process of heating up to 1050oC.