Thermal Stability of Tungsten Disulfide in Gaseous Mediums

Thermal stability of tungsten disulfide varies in different gaseous mediums or gas states. Tungsten disulfide can be heated and react not only in air but also in vacuum. Usually, hydrogen, argon and nitrogen are needed in the preparation of tungsten disulfide.

Thermal stability, also known as heat resistance, refers to the deformation capacity of substance under the influence of temperature. The smaller the deformation, the higher the thermal stability. Generally, we can judge the thermal stability of a substance by observing the phenomena during the heating.

Thermal stability of tungsten disulfide is as follows:

1. In air (O₂)

When heated in air, tungsten disulfide reacts with oxygen to form sulfur dioxide and tungsten trioxide with low friction coefficient. The higher temperature and the smaller tungsten disulfide particles lead to the more active reaction.

2. In vacuum

When heated in vacuum, tungsten disulfide can release a small amount of gas. It can slowly decompose into sulfur and tungsten when heated to above 1100°C. And when heated to 1250°C, it is decomposed completely.

3. Hydrogen (H₂)

Tungsten disulfide produces tungsten and hydrogen sulfide when heated to about 80°C in hydrogen. The chemical reaction is as follows:

1/2 WS₂ (solid) +H₂ (gas) ←→H₂S (gas) +1/2 W (solid)

The relationship of the equilibrium constant K and reaction temperature T at low temperature is different from that at high temperature, which is caused by different crystalline states of tungsten disulfide.

4. Nitrogen (N₂)

Tungsten disulfide is stable in nitrogen.

5. Argon (Ar)

Tungsten disulfide loses a small amount of sulfur when heated to more than 1000°C in argon.