X-ray induced fluorescence measurement of segregation in a DyI₃–Hg metal-halide lamp

Abstract

Segregation of elemental Dy in a DyI 3-Hg metal-halide high-intensity discharge lamp has been observed with x-ray induced fluorescence. Significant radial and axial Dy segregation are seen, with the axial segregation characterized by a Fischer parameter value of λ = 0.215 ± 0.002 mm −1. This is within 7% of the value (λ = 0.20 ± 0.01 mm −1) obtained by Flikweert et al (2005 J. Appl. Phys. 98 073301) based on laser absorption by neutral Dy atoms. Elemental I is seen to exhibit considerably less axial and radial segregation. Some aspects of the observed radial segregation are compatible with a simplified fluid picture describing two main transition regions in the radial coordinate. The first transition occurs in the region where DyI 3 molecules are in equilibrium with neutral Dy atoms. The second transition occurs where neutral Dy atoms are in equilibrium with ionized Dy. These measurements are part of a larger study on segregation in metal-halide lamps under a variety of conditions.

Metal-halide lamps in micro-gravity: experiment and model

“…In order to also study the effect of convection, experiments have also been done at hyper-gravity [11] and normal gravity [10], the future plan is to compare numerical results of the model to these experiments.…”

Competition between convection and diffusion in a metal halide lamp, investigated by numerical simulations and imaging laser absorption spectroscopy

“…The model was run with lamp fillings ranging from 3 to 20 mg Hg. To fix the boundary conditions for the elemental pressure we assume the existence of a cold spot at the bottom corner of the lamp, where the elemental pressure is derived from the x-ray induced fluorescence measurements at 1g of the elemental density of Dy and I at the cold spot [20]. Everywhere else the flux through the wall is zero.…”

“…Increase in the temperature by 10 K is enough to raise the vapour pressure to 30%. Using a vapour pressure of 150 Pa rather than the value of 517 Pa measured by x-ray fluorescence (XRF) by Nimalasuriya et al [20] on similar lamps yields a better quantitative match between model and experiment.…”

“…Direct measurements of the elemental pressure at the walls are not possible for the lamps in the centrifuge, therefore we assume a Dy elemental pressure at the wall of 517 Pa and an I elemental pressure of 4268 Pa. These vapour pressures were determined with x-ray induced fluorescence measurements at 1g [20]. These are assumed to give a good estimation of the vapour pressure at the walls and are used to fix the boundary conditions.…”

The Metal-Halide Lamp Under Varying Gravity Conditions Measured by Emission and Laser Absorption Spectroscopy

“…Previous efforts to observe the arc and its characteristics in micro-gravity include emission spectroscopy in the space shuttle Bellows et al 1984Bellows et al , 1985. Besides lab experiments (1g) Nimalasuriya et al 2005Nimalasuriya 2007) we investigated the lamp during parabolic flights. Here the lamp was measured during periods of about 20 s of micro-gravity (0g) and hyper-gravity (∼ 1.8g) .…”