Life Time of Tungsten Heater for Kinescope Evaporation

Generally, tungsten heater, also known as wolfram twisted spiral, which is used as a heating element for kinescope evaporation. Heating the metal in vacuum, and the metal would be evaporated by tungsten heater to the sub-surface of the workpiece which is going to be evaporated, and finally form a thin film, this process is evaporation coating. This process requires heating elements should have a good thermostability and corrosion resistance. Currently, users as home and abroad commonly choose spiral coil which is twisted by tungsten wire into various shapes as tungsten heater.

But in the deposition process, the life time of tungsten heater cannot be sustained for a long time, it is unable to meet the requirements for a stable life time, which would severely reduce automation efficiency of kinescope evaporation. The main reasons of their life time are recrystallized structure of tungsten, and the amount of insertion of aluminum.

The test showed that the more the grain boundary on surface of wire, in other words, the smaller grains, the easier diffusion of aluminum, which will lead to tungsten twisted spiral begin to deform even break and eventually end of its life time. Another primary reason is the amount of insertion of aluminum and its fluidity. During kinescope deposition process, in general, manufacturers would like to inset more aluminum than theory insertion of evaporation, which will produce residual aluminum and these residues will continue to react with the tungsten after each evaporation, and the it would finally generate W-Al compounds that can contaminate the tungsten wire, and it would significantly shorten the life time of the heater element. Practice has proved that, compared to the situation of aluminum residues, the evaporation which have no aluminum residue will increase the life time of heater element. In short, with the increase of the amount of insertion of aluminum, the life time of tungsten element will be shortened.

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