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Cathode materials for high-pressure discharge lamps

High-pressure mercury lamps, high-pressure sodium lamps, and metal halide lamps are collectively known as high-intensity discharge lamps. They all operate at high pressure and high current density. During this operation, the cathode's operating temperature is extremely high due to the bombardment of charged particles, with hot spots reaching over 1700°C, resulting in significant sputtering of the emissive material. Therefore, high-pressure discharge lamps cannot utilize the spiral filament structure used in low-pressure discharge lamps to store the electron-emitting material. Instead, they utilize a double-layer spiral structure wound with thick tungsten wire to prevent sputtering of the electron-emitting material under positive ion bombardment.

High-pressure mercury lamps, high-pressure sodium lamps, and metal halide lamps all utilize this electrode structure, but the emissive materials used are not identical, and alkaline earth metal oxides are not suitable. In China, barium zirconate (BaZrOs) is used as the electron-emitting material for high-pressure mercury lamps. High-pressure sodium lamps use tungstates. Metal halide lamps, on the other hand, utilize rare earth metal oxides as their electron-emitting materials.

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