How to Prepare Tungsten Diiodide by High-Temperature Chemical Method?

The high-temperature chemical method of tungsten diiodide is legally produced by the reaction of elemental tungsten and elemental iodine at temperatures between 600 and 800°C: W+I₂→WI₂. Generally, the temperature selected for the reaction is 800°C, and tungsten diiodide is produced using the reaction of tungsten powder with iodine.

Through the reaction conditions, we can find that the preparation of tungsten diiodide using elemental reactions is inherently difficult because most tungsten diiodide compounds are only stable at temperatures when the reaction rate is low. So in practice, the high-temperature chemical method exhibits the disadvantages of low yields, long reaction durations, and high iodine pressures in sealed silica tubes. Therefore, the high-temperature method is not a suitable method for producing tungsten diiodide in large quantities.

Although the pyrolysis method cannot be applied to the large-scale production of tungsten diiodide, this method can be expanded in the field of lighting. 1959, an American named Friedrich successfully explored the improvement of incandescent lamps, which utilizes the principle of the reaction and decomposition of tungsten diiodide at specific temperatures to optimize the service life and luminous efficiency of incandescent lamps.

Friedrich added a moderate amount of iodine to the lamp in addition to filling it with argon, a low-pressure inert gas, as a protective gas. Upon energization, the tungsten filament in the lamp sublimates even though it is heated, but due to the presence of iodine, the sublimated tungsten reacts with the iodine to form tungsten diiodide and establishes a chemical equilibrium between the iodine vapor, tungsten, and tungsten diiodide. When the vapor of tungsten diiodide in the lamp diffusion, meets the high temperature of the tungsten filament and decomposition, the tungsten is generated by the redeposition of tungsten on the tungsten filament. In this way, in the closed container of the lamp, due to the above chemical equilibrium, the tungsten filament is not easy to become thin, which prolongs the service life of the lamp and improves the luminous efficiency. Until now, tungsten iodine lamps can still be seen in large public spaces such as stadiums and airports.

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