Spectroscopic study of cataphoresis in He-Cd mixtures : Cd source-anode region

• Published in: Journal of applied physics Vol. 72; no. 2; pp. 384 - 394
• Main Authors: MIZERACZYK, J, CARLSSON, C, HARD, S
• Format: Journal Article
• Language: English
• Published: Woodbury, NY American Institute of Physics 15.07.1992
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Study of interfaces; Transport phenomena; Cadmium; Binary mixture; Ion transfer; Gaseous state; Theoretical study; Electrode electrolyte interface; Cataphoresis; Experimental study; Helium
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.351866

The results of measurements of the axial distributions of the Cd 479.9 nm, Cd+ 441.6 nm, and He 447.2 nm line intensities as a result of cataphoresis in a He-Cd capillary positive column (3 mm diam) between the Cd source, placed at the cathode side, and the anode are presented. The measurements were carried out using optical scanning along the positive column. The measuring procedure also allowed the Cd atom density distributions along the positive column to be determined. It is found that the He-Cd positive column divides into three regions: the seemingly uniform, blue-colored cadmiumlike discharge region, the whitish transition region, and the orange heliumlike discharge region. The Cd atom density decreases linearly from the Cd source towards the anode in the cadmiumlike discharge region of the positive column. In the transition region the Cd atom density decreases quasiexponentially, extending its tail into the heliumlike discharge region. The very tail of the Cd atom density distribution found in the heliumlike region is perhaps not real. Instead it could be due to misinterpretation of scattered background light for fluorescence light. This ambiguity makes it impossible to draw any definite conclusion about the ability of cataphoresis to confine the Cd vapor at the cathode side of the positive column. It is found that particularly the linear but also the quasiexponential decrease of the Cd atom density, occurring in the He-Cd positive column, are in good agreement with Druyvesteyn’s theory [Physica 2, 255 (1935)]. The slope of the Cd atom density distribution curve in its linear part was found to be proportional to the product of the discharge current and He pressure, whereas in its quasiexponential part it first increases and then saturates with increasing discharge current and He pressure. The results obtained can be used for estimating the so-called cataphoretic confinement section length for the positive column and hollow-cathode discharge He-Cd+ lasers, as well as for other ion He–metal-vapor lasers. The features of cataphoresis in the He-Cd positive column found also seem to be characteristic of cataphoresis in other binary gas mixtures.