Used as the cathode of gas discharge lamps tungsten filament or tungsten rod, in order to reduce its electron escape power, must be added to 0.5 ~ 3% of the thorium, known as tungsten thorium wire. As thorium is a radioactive element, polluting the environment, so there is cerium to replace thorium as cerium tungsten wire or cerium tungsten rod. But the evaporation rate of cerium is high, so cerium tungsten wire or cerium tungsten rod can only be used for small power gas discharge lamps.
Once the tungsten wire by high temperature recrystallisation occurs after the use of tungsten becomes very brittle, in the case of impact or vibration is very easy to break. In some of the requirements of high reliability of electric light source products, in order to prevent the filament from breaking, often in the doped tungsten filament to add 3 ~ 5% rhenium, called tungsten rhenium filament, which can make the tungsten brittle transition temperature down to room temperature or below room temperature. This is a very peculiar rhenium effect, so far has not found an element can replace rhenium, in tungsten to produce the same effect.
Tungsten at room temperature has a good resistance to acids and alkalis, but in the humid air is easy to be oxidised, so the fine tungsten wire can not be stored in a humid environment for too long. In addition, tungsten at 1200 ℃ up and down on the beginning of the reaction with carbon to generate tungsten carbide, so the filament of the burning hydrogen treatment should pay attention to this problem, otherwise tungsten and its surface graphite lubricant reaction, the filament will be brittle fracture.
