Influence of F-Doped 612 Impregnants on the Emission Properties of Dispenser Cathodes

The 612-type barium–calcium aluminates (BaO:CaO:Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>3</roman></sub> = 6:1:2) is the most practical impregnant in Ba–W dispenser cathode. However, the high impregnation temperature of the 612 impregnant is unconducive to building dispenser cathodes with high-emission properties. In this work, a new F-doped 612 impregnant using BaF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sub> as an additive was developed, and the composition of impregnant and the cathode performance were tested. With the increase of fluorine content, the current emission density of the F-doped cathode tends to increase and get the highest at 0.3-mol F-doped. At 1100 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∘</sup><roman xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</roman><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>b</roman></sub>, the direct current (dc) density and pulse current (PC) density of optimal F-doped cathode are 7.76 and 13.66 A/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sup>, respectively, which were 1.1–1.3 times higher than those of the 612 impregnated cathode. Ba<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>3</roman></sub>CaAl<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>7</roman></sub> and Ba<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>5</roman></sub>CaAl<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>4</roman></sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>12</roman></sub> in the optimal F-doped impregnant contribute to the improved emission performance. The emission enhancement by F doping is attributed to the decreased work function and structural defects formed inside the aluminates favorable for production of active barium atoms during cathode operation. The lifetime of F-doped cathodes has been prolonged by 10% due to the lower evaporation rate.