News

Electrodes are important materials used in discharge lamps.

The discharge lamp introduces electrical energy through the electrode and emits a large number of electrons through the electrode to maintain the discharge. Since the life of the discharge lamp is mainly determined by the performance of the electrode, the design of the electrode and the selection of the electrode material are important links in the production of the discharge lamp. The electrode material must be a good thermal electron emitter and must be able to work at a high temperature of 1000℃~1800℃, so as to obtain the necessary electron emission density. The electrode evaporation rate is required to be low to prevent excessive pollution of the gas in the lamp and to maintain the life of the electrode itself. In addition, the electrode material must be able to withstand ion bombardment and have sufficient mechanical strength and sputtering resistance at high temperatures. There are very few pure metals that can meet these requirements, only tungsten, followed by tantalum, which have practical value in the light bulb industry.

Tungsten can emit a large number of electrons above 2000℃, but such a high temperature is not conducive to the design of the electrode and affects the life of the electrode. Coating one or more alkaline earth metal oxides on the electrode can greatly improve the electron emission ability of the electrode. This electron emission layer can generate a large number of free electrons when heated, so that the electrode can work at a not very high temperature, thereby improving the performance of the lamp and increasing its life.

The electrodes of hot cathode fluorescent lamps use double helix, triple helix or braided filaments. Like incandescent lamps, they are generally made of doped tungsten filaments that do not sag. Under working conditions where the electrodes are susceptible to vibration, tungsten filaments doped with 3% to 5% rhenium are sometimes used to make electrodes.

In short arc mercury lamps and Xenon Lamps, tungsten electrodes containing 0.5% to 3.0% thorium oxide are sometimes used, especially in high-power lamps where sputtering of the emission layer may occur. This thoriated tungsten electrode is often used. Metal halide lamps must also use thoriated tungsten electrodes because the reaction of earth metal oxides with halogens will form a non-volatile solid. In contrast, the reaction of thorium and tungsten with halogens can produce a migration cycle of metal halides, causing the metal vapor of thoriated tungsten to be deposited again on the incandescent electrode.

PREVIOUS：Glass to metal sealing NEXT：Electromagnetic radiation excitation