Temperature measurements at thoriated tungsten electrodes in a model lamp and their interpretation by numerical simulation

Bergner, Andreas; Westermeier, M; Ruhrmann, C; Awakowicz, Peter; Mentel, J.

doi:10.1088/0022-3727/44/50/505203

Cited by 49 publications

(44 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, in practical applications, a number of alloys and compounds, such as thoriated tungsten 10,11,12,13 and lanthanum hexaboride 14,15 , are used because they offer relatively low work functions (≈ 2.5 eV) in combination with much better chemical and thermal stabilities. It has also been known since the 1930s 16,17 that it is possible to create surfaces with work functions lower than those of any elemental, bulk materials by using coatings with thicknesses on the order of a monolayer.…”

Section: Introductionmentioning

confidence: 99%

An orbital-overlap model for minimal work functions of cesiated metal surfaces

Chou

Voss

Bargatin

et al. 2012

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

We introduce a model for the effect of cesium adsorbates on the work function of transition metal surfaces. The model builds on the classical point-dipole equation by adding exponential terms that characterize the degree of orbital overlap between the 6s states of neighboring cesium adsorbates and its effect on the strength and orientation of electric dipoles along the adsorbate-substrate interface. The new model improves upon earlier models in terms of agreement with the work function-coverage curves obtained via first-principles calculations based on density functional theory (DFT). All the cesiated metal surfaces have optimal coverages between 0.6 to 0.8 monolayers (ML), in accordance with experimental data. All the cesiated tungsten surfaces we have considered are shown to have minimum work functions (MWF) lower than most cesiated metals, also in accordance with experiments.

show abstract

Section: Introductionmentioning

confidence: 99%

An orbital-overlap model for minimal work functions of cesiated metal surfaces

Chou

Voss

Bargatin

et al. 2012

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

show abstract

“…15. Instead, it is an indication that an emitter effect is generated by a thorium ion current towards the cathode, also in case of thoriated tungsten electrodes for HID lamps [35]. A publication of detailed investigations of the emitter effect at thoriated tungsten electrodes for HID lamps is under way.…”

Section: Interpretation Of the Measuring Resultsmentioning

confidence: 99%

Investigating the influence of the operating frequency on the gas phase emitter effect of dysprosium in ceramic metal halide lamps

Reinelt¹,

Westermeier²,

Ruhrmann³

et al. 2011

J. Phys. D: Appl. Phys.

Self Cite

View full text Add to dashboard Cite

To cite this version:J Reinelt, M Westermeier, C Ruhrmann, A Bergner, G M J F Luijks, et al.. Investigating the influence of the operating frequency on the gas phase emitter effect of dysprosium in ceramic metal halide lamps. Journal of Physics D: Applied Physics, IOP Publishing, 2011, 44 (22) Abstract. The dependence of the gas phase emitter effect of Dy on a variation of the operating frequency between some Hz and 2 kHz is investigated in a HID lamp. The buffer gas of the lamp consisting of Ar, Kr and predominantly Hg is seeded with DyI 3 , its burner vessel is formed from transparent YAG material. Phase and spatial resolved emission spectroscopy in front of the lamp electrode and pyrometric temperature measurements along the tungsten electrode are performed with a spectroscopic set up. Dy atom and ion densities in front of the electrode are deduced from absolute intensities of optically thin Dy lines and a plasma temperature, derived from the absolute intensity of mercury lines. Phase resolved values of the electrode tip temperature T tip and input power P in are obtained from temperature distributions along the electrode. Distinctly higher Dy ion and atom densities are measured in front of the electrode within the cathodic phase. With increasing operating frequency a reduction of both, atoms and ions, is observed in front of the cathode. In contrast, an increase of the ion density in front of the anode is seen. Moreover, the Dy ion density is drastically reduced by an additional seeding of the lamp with T lI. It is found that an up rating of the Dy ion density is correlated with a decline of T tip and P in . At higher frequencies this effect takes place not only within the cathodic phase but also within the anodic phase. The reduction of the average electrode tip temperature on the order of several hundred Kelvin compared to a YAG lamp with a pure mercury filling is explained by a Dy monolayer on the electrode surface which is sustained by a Dy ion current.Submitted to: J. Phys. D: Appl. Phys.Investigating the influence of the operating frequency on the gas phase emitter effect of Dy2

show abstract

“…The electrode temperature is determined using Planck's law modified by the emission coefficient of tungsten ðk; TÞ. 8,11 The emission coefficient is given in the literature for a smooth tungsten surface. 25 But at the electrode tip, the tungsten is roughened by the attachment of the arc and with it the emission coefficient is unpredictably varied so that the evaluated electrode tip temperatures are doubtful.…”

Section: A 2d Pyrometry and Imagingmentioning

confidence: 99%

“…It may be an indication that the heating of the electrode is intensified within the anodic phase by the inverse emitter effect as it was found at thoriated anodes when only small emitting sites are present on the anode surface. 11,12,38 …”

Section: B Influence Of Na On the Gas Phase Emitter Effect Of Lamentioning

confidence: 99%

“…10 On the other hand, with thoriated tungsten anodes an inverse emitter effect was observed by which the electrode is heated up compared to a pure tungsten anode. 11,12 Comparing the electrode temperature in dependence on the operating frequency within a YAG-lamp seeded either with cerium iodide (CeI 3 ) or caesium iodide (CsI) has shown that not only a reduced work function but also an elevated adsorption-energy of the emitter atoms favours the emitter effect especially at higher operating frequencies. 13 In Refs.…”

mentioning

confidence: 99%

See 1 more Smart Citation

The gas phase emitter effect of lanthanum within ceramic metal halide lamps and its dependence on the La vapor pressure and operating frequency

Ruhrmann

Hoebing

Bergner

et al. 2015

Journal of Applied Physics

View full text Add to dashboard Cite

The gas phase emitter effect increases the lamp lifetime by lowering the work function and, with it, the temperature of the tungsten electrodes of metal halide lamps especially for lamps in ceramic vessels due to their high rare earth pressures. It is generated by a monolayer on the electrode surface of electropositive atoms of certain emitter elements, which are inserted into the lamp bulb by metal iodide salts. They are vaporized, dissociated, ionized, and deposited by an emitter ion current onto the electrode surface within the cathodic phase of lamp operation with a switched-dc or ac-current. The gas phase emitter effect of La and the influence of Na on the emitter effect of La are studied by spatially and phase-resolved pyrometric measurements of the electrode tip temperature, La atom, and ion densities by optical emission spectroscopy as well as optical broadband absorption spectroscopy and arc attachment images by short time photography. An addition of Na to the lamp filling increases the La vapor pressure within the lamp considerably, resulting in an improved gas phase emitter effect of La. Furthermore, the La vapor pressure is raised by a heating of the cold spot. In this way, conditions depending on the La vapor pressure and operating frequency are identified, at which the temperature of the electrodes becomes a minimum.

show abstract

Temperature measurements at thoriated tungsten electrodes in a model lamp and their interpretation by numerical simulation

Cited by 49 publications

References 41 publications

An orbital-overlap model for minimal work functions of cesiated metal surfaces

An orbital-overlap model for minimal work functions of cesiated metal surfaces

Investigating the influence of the operating frequency on the gas phase emitter effect of dysprosium in ceramic metal halide lamps

The gas phase emitter effect of lanthanum within ceramic metal halide lamps and its dependence on the La vapor pressure and operating frequency

Contact Info

Product

Resources

About