Barium tungsten electrode (W-Ba electrode) is often used in discharge lamps, vacuum tubes and other devices in high temperature environment due to its excellent high temperature oxidation resistance. Its high temperature oxidation resistance mechanism is mainly closely related to the chemical properties of barium and its role in the tungsten matrix.
1. Low work function and electron emission ability of barium: Barium (Ba) is an alkaline earth metal with a low work function, which can significantly reduce the surface work function of the tungsten matrix, thereby enhancing the thermal electron emission ability of the electrode. At high temperature, barium atoms form an active film on the surface of tungsten, which improves the emission performance of the electrode. At the same time, this film protects the tungsten matrix to a certain extent and slows down oxidation.
2. Barium oxide protective layer: In a high temperature environment, barium easily reacts with oxygen to form barium oxide (BaO). BaO has high chemical stability and can form a dense oxide protective layer on the surface of tungsten. This protective layer can effectively isolate oxygen from direct contact with the tungsten matrix, slow down the oxidation rate of tungsten, and thus improve the electrode's resistance to high-temperature oxidation.
3. Diffusion and self-repair mechanism of barium: The doping or coating form of barium in the tungsten matrix enables it to continue to diffuse to the surface at high temperatures. When the barium oxide on the surface volatilizes or loses due to high temperature, the internal barium atoms will diffuse to the surface and re-form a protective layer. This "self-repair" mechanism enables the barium tungsten electrode to maintain good oxidation resistance during long-term high-temperature operation.
4. Stability of tungsten matrix: Tungsten (W) itself has an extremely high melting point (about 3422°C) and good oxidation resistance, making it an ideal matrix material for high-temperature electrodes. The addition of barium further enhances the chemical stability of the tungsten surface and inhibits the tendency of tungsten to react with oxygen at high temperatures.
5. Synergy: The synergy between barium and tungsten is the key to high-temperature oxidation resistance. The low work function and oxide protective layer of barium combined with the high melting point and mechanical strength of tungsten make the barium tungsten electrode show excellent stability in a high-temperature oxidation environment.
