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Molybdenum Disulfide

Molybdenum disulfide, MoS2, forms a gray-black mass which is similar to graphite, both in appearance and to the touch. Like graphite MoS2 is widely used as solid lubricant. Molybdenum disulfide occurs in nature as molybdenite (crystalline) and as jordisite (amorphous). Metallic molybdenum is produced from molybdenite.

The lubrication properties are due to a layered structure of MoS2, where the molybdenum atoms are located between layers of sulfur atoms. The sheets of sulfur atoms exhibit only weak van der Waals interaction forces, resulting in a low coefficient of friction.

MoS2 is diamagnetic and a semiconductor.

Chemical Reactions

Molybdenum disulfide is stable in air or oxygen at normal conditions, but reacts with oxygen upon heating forming molybdenum trioxide:

\[2 MoS_2 + 9 O_2 \rightarrow 2 MoO_3 + 4 SO_3\]

Chlorine attacks molybdenum disulfide at elevated temperatures to form molybdenum pentachloride:

\[2 MoS_2 + 7 Cl_2 \rightarrow 2 MoCl_5 + 2 S_2Cl_2\]

Usage

MoS2 with particle sizes in the range of 0.1-40 µm is a common dry lubricant, offering high lubricity and stability up to 350°C. MoS2 is also used in ski glide wax.

Molybdenum disulfide was also used in the first rechargeable lithium batteries which have been introduced in the mid-1980s. The cell used lithium metal as the anode and MoS2 on an aluminum foil as the cathode with LiAsF6 as electrolyte. Due to the safety problems the batteries have been withdrawn from the market.

MoS2 is used as a catalyst for desulfurization in petroleum refineries. The catalytic surface is generated in situ by applying H2S to molybdate/cobalt or nickel-impregnated alumina.

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