Maintaining a low vacuum during the activation of the barium tungsten cathode and the installation of the lamp can make the lamp have better performance and more stable quality.
The activation process can be divided into two steps. The first step is to remove impurities and oxides from the electrode; the second step is the activation of the salt, which needs to be completed by diffusion under high temperature, long time and high vacuum environment. Both steps are very important. When there is residual water vapor in the lamp tube, the tungsten matrix will react with H2O to generate WO3 and deposit on the inner wall of the glass in the form of black spots. Insufficient activation will affect the life of the lamp tube.
1) Heat the lamp tube and electrode to 700-850℃. Heating and vacuuming need to be continued. This process is to remove moisture and other impurities in the electrode and lamp tube. When the vacuum no longer decreases and is lower than 10-5Pa, start the next step of activation.
2) Slowly increase the temperature to 1200℃ and maintain for 1-2h. During this process, the vacuum should only increase slightly. If the vacuum increases greatly, it may be caused by the large amount of volatilization of barium salts. The temperature needs to be lowered appropriately. When the activation step is almost completed, the pressure in the lamp tube should be between 10-6-10-7Pa, so that the cathode is fully activated.
3) The electrodes can be activated one by one during the installation of the lamp, or multiple electrodes can be installed in a quartz tube for unified activation before use. After activation, argon gas is flushed into the tube. After a short period of storage, it can be used immediately.
Due to the different heating equipment, temperature measurement method, and vacuum system of the equipment, the above information is for reference only. Calibrate the temperature measurement system before activation, and determine the optimal activation temperature and time after multiple tests to increase the vacuum degree of the lamp making process as much as possible: temperature, time and vacuum degree need to be adjusted according to the size of the electrode or lamp tube. Large lamp tubes or electrodes require higher temperatures, longer times, and higher vacuum degrees.
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