Electrodeless mercury lamp

Fig. 14.1 The electrodeless mercury lamp made by William F. Meggers. With permission from the National Institute of Standards and Technology,Technology Administration,...

One subcategory of low-pressure lamp that might become more important in the future is the electrodeless discharge lamp, which is energized by an external field. These lamps comprise a quartz tube that has been evacuated, leaving behind a small pressure of argon and mercury or other metal or metal halide. Emission is obtained by placing the lamp in a microwave field, for example. Whilst these lamps are available commercially, they may also be built in-house rather easily [5]. 

The energy sources of uv light cured coatings are typically medium-pressure mercury lamps, electrodeless vapor lamps, pulsed xenon lamps, or lasers. These generally emit... 

Cold vapor mercury detection limits were determined with a FIAS(ji )-100 or FIAS-400 flow-injection system with amalgamation accessory. The detection limit without an amalgamation accessory is 0.2/ig/L with a hollow cathode lamp, 0.05 /ig/L with a System 2 electrodeless discharge lamp. (The Fig detection limit with the dedicated FIMS(ji )-100 or FIMS-400 mercury analyzers is <0.010/ig/L without an amalgamation accessory and <0.001 /ig/L with an amalgamation accessory.) Flydride detection limits shown were determined using an MFlS-10 Mercury/Flydride system. 

Fig. 19.16. Experimental setup of a flowthrough quartz photoreactor used for photocatalytic decomposition in aqueous Ti02 dispersions using cylindrical electrodeless mercury discharge lamps. A, cylindrical EDL...

The electrodeless discharge lamp The electrodeless discharge lamp (EDL) is another atomic line source that allows one to produce a highly effective excitation source for elements that cannot be cast into hollow cathodes, such as mercury, arsenic, antimony, and some other elements. 

UV Curing. The UV lamps are usually medium-pressure mercury lamps or electrodeless gas-filled lamps. Cooling is necessary to avoid overheating of the lamp which would lead to decreased lifetime and changes in the spectral output. 

As the cold-vapor mercury sample is already in the atomic state, there is no need of an atomizer, per se. The vapor, transferred directly from the cell or desorbed as a plug from a heated amalgamation trap, is commonly swept into a moderately heated (resistance wound heating to 200°C) 10 cm quartz T-tube located within the optical beam of a conventional AA spectrometer. Attenuation of an intense electrodeless discharge lamp line source at 253.7nm is used as a measure of the absorption. Alternatively, dedicated continuum source AA-based spectrometers fitted with long path absorption cells (30 cm) are frequently used to increase sensitivity and detection limit. 

Sources that emit a few discrete lines find wide use in atomic absorption spectroscopy, atomic and molecular fluorescence spectroscopy, and Raman spectroscopy (refractometry and polarimetry also use line sources). The familiar mercury and sodium vapor lamps provide a relatively few sharp lines in the ultraviolet and visible regions and are used in several spectroscopic instruments, Hollow-cathode lamps and electrodeless discharge lamps are the most important line sources for atomic absorption and fluorescence methods. Discussion of such sources is deferred to Section 9B-1. 

Five basic lamp systems are available to produce UV radiation (1) medium-pressure mercury vapor lamps (2) electrodeless lamps (3) pulsed xenon lamps (4) hybrid xenon/mercury vapor lamps and (5) low-pressure germicidal lamps. Medium-pressure mercury lamps that emit a wide range of wavelengths are by far the most important radiation sources for curing of coatings. 

In general, the electrodeless lamp contains a small amount of mercury and a neutral starter gas. The mercury pressures during its operation are in the 5-20 bar range, which is higher than for arc lamps, with pressures only in the 1-2 bar range. The characteristics of fhe lamp can be modified by fhe addition of mefal halides in confrolled quanfifies to the gas. The frequently used D or V lamps contain iron or gallium salts, respectively. Some characteristics of microwave-powered lamps are in Table 3.1. 

In general, the electrodeless lamp contains a small amount of mercury and is filled with a neutral starter gas. The mercury pressures during its operation are in... 

A high-intensity, electrodeless ultraviolet source has recently been introduced. This UV source is distinguished from other conunercially available UV lamps by the fact that no electrodes are Inside the lamp. Electrical energy is supplied in the form of radio frequency power that is coupled into an evacuated quartz tube containing mercury and other additives. As compared to conventional medium-pressure mercury arcs with electrodes, the electrodeless system has several attributes that make it unique (17). These are summarized as follows (1) instant on-off (2) modular lamp design (3) increased lamp lifetime (4) variable spectrum (5) excellent energy conversion. 

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