Cathode materials for high pressure discharge lamps
High-pressure mercury lamps, high-pressure sodium lamps and metal halide lamps are generally called high-intensity discharge lamps. They all work under high pressure and high current density. At this time, due to the bombardment of charged particles on the cathode, the cathode operating temperature is very high, the hot spot temperature can reach more than 1700℃, and the sputtering of the emission material is relatively serious. Therefore, high-pressure discharge lamps cannot use the spiral filament structure used in low-pressure discharge lamps to store electron emission materials, but must use a double-layer spiral structure wound with thick tungsten wire to prevent the sputtering of electron emission materials under positive ion bombardment.
High-pressure mercury lamps, high-pressure sodium lamps and metal halide lamps all use this electrode structure, but the filling emission materials are not exactly the same, and alkaline earth metal oxides cannot be used. The electron emission material of high-pressure mercury lamps is barium zirconate (BaZrO3) in China, and tungstate is also used abroad. High-pressure sodium lamps use tungstate. Metal halide lamps use rare earth metal oxides as their electron emission materials.