Evaluation of the base metal activity of oxide cathodes

Abstract

Activity of the base metal is evaluated by identifying reaction products with the oxide layer, measuring Ba vapor pressure from the oxide, measuring of emission current properties, and by analyzing the surface composition of the oxide. Reducing capabilities of Zr, W, and Mo activators in Ni base metal are determined. Their activators are alloyed to the Ni core metal up to the solubility limits. The experimental results are evaluated systematically from the standpoint of base metal activity, together with the thermochemical treatment for the various reactions and the emission mechanism of the oxide coated cathode.

Oxide cathodes for reliable electron sources

“…3.87 % tungsten (W) and 0.17 % magnesium (Mg) are contained as activators in nickel (Ni) base metal. The development of the new robust oxide cathodes is based on a novel idea of Gaertner et al [21] and old findings on the activity and the diffusivity of many activators in Ni base metal [22][23][24][25][26], as well as on our recent understandings of electron physics of oxide cathodes [27][28][29].…”

Analytical interfacial studies of double carbonate thermionic oxide cathodes over accelerated operational life

“…showing the temperature dependence of equilibriun1 Ba, Sr and Ca vapour pressures produced in the reaction of BaO, SrO and CaO with W [40]. L1GT fi•on1 equation 2 can simply be related to the Ba/Sr/Ca vapour pressure with the following equation:…”

“…as to whether Sr would be found in any reaction products and Eisenstein has even suggested that only a SrO emissive oxide layer could produce a Sr containing interfacial product [6,8]. Furthermore, the thermodynamic based work of Aida et al has also suggested that Ba containing products were likely to frmn rather than Sr based products [ 40]. However, Gaertner states that Sr does substitute Ba in the reaction products that it forms [ 19], which agrees with the results presented here.…”

“…40. Ion-induced secondary electron image from an oxide-cathode after 0 hours of life, a region where Pt has been deposited prior to ion etching.…”

Formation of a uniform intensity distribution in a cw CO2laser with a phase-stepped mirror

“…In particular, laser spectroscopy has delivered very important data on the Ba distribution over short periods, but it is less suitable for measurements extending over thousands of hours. Methods like mass spectroscopy [9] or the weighting of collected cathode material on a built-in quartz microbalance [10] always pertain to situations which strongly deviate from practical lamps. The use of radioactive mercury tracers ( 203 Hg) has proven to lead to very accurate methods for site-selective mercury quantification in Hg distribution studies of fluorescent lamps over long periods under all types of conditions [11].…”