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2021-05-09
In order to increase the luminous efficiency of an incandescent lamp, it is necessary to increase the temperature of the filament; and the higher the temperature of the filament, the faster the evaporation of tungsten, and the tungsten filament will be quickly blown off. At the same time, due to the evaporation of tungsten, the blister on the blister becomes black, which reduces the luminous efficiency of the incandescent lamp. Therefore, in order to manufacture tungsten filaments with high luminous efficiency, it is necessary to further solve the problem of increasing filament temperature and reducing tungsten evaporation. If you can try to return the evaporated tungsten back to the filament, it will prevent the blackening of the tube wall and extend the life of the filament. Filling the bulb with pure iodine returns the evaporated tungsten back to the filament. Since iodine and tungsten are synthesized into tungsten iodide at a temperature ranging from 250 ° C to 1200 ° C, tungsten iodide is unstable and decomposes into tungsten and iodine at 1400 ° C or higher.
Therefore, if the bulb is filled with iodine and then the temperature of the bulb wall is maintained between 250 ° C and 1200 ° C, the tungsten evaporated from the filament forms tungsten iodide molecules with iodine at the bubble wall and diffuses toward the filament; The temperature near the filament is above 1400 ° C. The tungsten iodide is decomposed into iodine and tungsten near the filament, and the tungsten atom returns to the filament. The free iodine concentrates near the filament and spreads outward, thus forming a iodine-tungsten cycle. However, since the combined temperature of iodine and tungsten is between 250 ° C and 1200 ° C, the bulb wall must be maintained at this temperature range. Ordinary glass that works for a long time at this temperature will crystallize and become opaque. Also, due to some problems in the manufacturing process, ordinary glass cannot be used as the bulb. Quartz glass has a small thermal expansion coefficient, a high melting point, and good transparency at high temperatures, and is suitable as a blister for iodine-tungsten lamps. The iodine tungsten lamp has two types of vertical circular and tubular shapes. The structure of the tubular iodine tungsten lamp. Its outer casing is made of high temperature resistant quartz glass. The inside of the tungsten wire is wound into a single spiral shape with a number of tungsten wire loops in the middle to prevent the filament from sagging. The tube is evacuated and filled with argon and an appropriate amount of pure iodine. When the tubular iodine-tungsten lamp is used, the inclination should not exceed 4 degrees, otherwise the filament will be burnt due to the uneven circulation of iodine-tungsten due to convection.
Due to the application of the principle of iodine-tungsten cycle, the iodine-tungsten lamp greatly reduces the evaporation of tungsten, so its operating temperature can be increased to 3000 ° C, and the luminous efficiency is also improved a lot. Compared with ordinary incandescent lamps, iodine-tungsten lamps for illumination also have the advantages of small size, good light color and long life. For example, an ordinary 220 volt 1000 watt incandescent lamp has a luminous efficiency of about 16 streams/watt and an average life of 1000 hours. The 220 volt 1000 watt iodine tungsten lamp for lighting has a luminous efficiency of about 21 streams/watt and an average life of 1500. hour.
