In addition to a small amount of tungsten filaments being used as heating materials for high-temperature furnaces, heaters for electron tubes, and reinforcing ribs for composite materials, most of them are used to make filaments for various incandescent lamps and tungsten halogen lamps and electrodes for gas discharge lamps. For the tungsten wire or tungsten rod used as the cathode of a gas discharge lamp, in order to reduce its electron work function, 0.5 to 3% thorium must be added, 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 in low-power gas discharge lamps.
Once tungsten wire recrystallizes after being used at high temperatures, it becomes very brittle and can easily break under impact or vibration. In some electric light source products that require high reliability, in order to prevent filament breakage, 3 to 5% rhenium is often added to the doped tungsten filament, called tungsten-rhenium filament, which can reduce the brittle transition temperature of tungsten to Room temperature or below. This is a very peculiar rhenium effect. So far, no element has been found that can replace rhenium and produce the same effect in tungsten.
Tungsten has good acid and alkali resistance at room temperature, but is easily oxidized in humid air, so fine tungsten wire cannot be stored in a humid environment for too long. In addition, tungsten begins to react with carbon at around 1200°C to form tungsten carbide, so attention should be paid to this issue when burning hydrogen in the filament. Otherwise, the tungsten will react with the graphite lubricant on its surface, and the filament will become brittle and break.
