A Study of Scandia-Doped-Impregnated Cathode Fabricated by Spray Drying Method

Abstract

Scandia-doped-impregnated (SDI) cathodes were fabricated with scandia-doped tungsten powders using spray drying (SD) combined with two-step reduction in hydrogen atmosphere. The temperature-programmed reduction results show that the addition of Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> leads to a decrease of the reduction temperature of scandia-doped tungsten oxide powders. Using the obtained scandia-doped tungsten powders with homogenous distribution of nanosized scandia, a submicrometer porous matrix cathode composed of tungsten grains with active substances distributing uniformly around these grains has been obtained. For cathodes with the above matrices and impregnated with 411 or 612 Ba, Ca aluminates (named SDI/SD-411 or SDI/SD612 cathodes, respectively) and space charge limited current densities of ~72.5 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> have been reliably reached at 900 °Cb. After proper activation, the cathode surface is covered by a Ba-Sc-O active substance layer with preferable atomic ratios, leading to its good emission property. The average evaporation rate of 8.45 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> gcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 1150 °Cb for SDI/SD-612 cathode is the lowest one among Ba-W, W/Re/Os-M, SG-411 (the scandia-doped cathode fabricated by sol-gel method with impregnating 411 aluminates), and SDI/SD-612 cathodes.