Except for a small amount of tungsten wire used as heating materials for high-temperature furnaces, heaters for electron tubes, and reinforcement ribs for composite materials, most of it is used to make various incandescent lamps and halogen tungsten lamp filaments and electrodes for gas discharge lamps. For tungsten wires or tungsten rods used as cathodes of gas discharge lamps, 0.5-3% thorium must be added to reduce its electron work function, which is called tungsten thorium wire. Since thorium is a radioactive element that pollutes the environment, cerium is used to replace thorium to make tungsten-cerium wire or tungsten-cerium rod. However, the evaporation rate of cerium is high, so tungsten-cerium wire or tungsten-cerium rod can only be used for low-power gas discharge lamps.
Once the tungsten filament is used at high temperature and recrystallized, it becomes very brittle and is very easy to break under impact or vibration. In some electric light source products that require high reliability, in order to prevent the filament from breaking, 3-5% rhenium is often added to the doped tungsten filament, called tungsten-rhenium filament, which can reduce the ductile-brittle transition temperature of tungsten to room temperature or below. This is a very peculiar rhenium effect, and no element has been found to replace rhenium and produce the same effect in tungsten.
Tungsten has good acid and alkali resistance at room temperature, but it is easily oxidized in humid air, so thin tungsten filament cannot be stored in a humid environment for too long. In addition, tungsten begins to react with carbon at around 1200℃ to form tungsten carbide, so this issue should be paid attention to during the hydrogen burning treatment of the filament, otherwise the tungsten will react with the graphite lubricant on its surface, and the filament will become brittle and break.