Under normal conditions, tungsten is a very stable metal. It does not react in air or oxygen at 20°C, but when it is heated in air, the color begins to turn dark gray black. When heated to 400°C, tungsten begins to oxidize, and the oxidation intensifies as the heating temperature increases. At higher temperatures, tungsten is gradually oxidized to yellow tungsten trioxide (WO3). But when the air humidity is high, even at room temperature, the tungsten powder will be gradually oxidized by the sheath, covering its surface with a blue-violet intermediate oxide film.

Tungsten trioxide is a lemon yellow crystalline powder with a density of 7.2~7.4g/cm3, a melting point of about 1470℃, and a boiling point of 1700~2000℃. It sublimates significantly above 800℃. Tungsten trioxide is easily reduced by various types. Agent reduction. At room temperature, even a small amount of organic matter can restore it and change its color. But the original color is restored when heated in the air. At 700~900℃, tungsten trioxide is easily reduced to metallic tungsten by hydrogen, carbon monoxide and carbon.

In a vacuum, tungsten wire can maintain the essence of tungsten even at high temperature. The melting point of tungsten itself is very high. The melting point is 3410 degrees. The melting time depends on the evaporation rate of tungsten, so it is not easy to break; and once exposed to air When in use, the high temperature tungsten wire will react with oxygen in the air to change its quality and produce tungsten oxide. The melting point of tungsten oxide, WO3, is 1400-1600 degrees. Once this temperature is exceeded, WO3 vaporizes rapidly at this temperature, so that the tungsten wire will quickly melt in the air.