Transition metal disulfide compounds, especially molybdenum disulfide and tungsten disulfide, are two-dimensional layered materials due to the similarity of their structure and properties to graphene, and their multifunctional properties such as self-lubrication, high surface area, electrical resistivity, stability, good mechanical strength, ease of charge transfer, feasibility of synthesizing these nanoparticles, and customizable band gaps make them widely used in different applications such as catalysis, sensing, adsorbents, lubricants , lithium-ion batteries, supercapacitors, and solar light collectors, among other diverse fields. This paper briefly describes the differences in tribological properties of MoS2, WS2 and graphite.

01 Differences between MoS2, WS2 and graphene self-lubricating coatings #

At room temperature, WS2 self-lubricating coatings are not as good as MoS2 coatings for film formation on metal substrates; at high temperature, the friction performance of WS2 coatings is better than that of MoS2 solid lubrication coatings. Graphite is usually used in direct spraying, but it is not suitable for use in vacuum, and its coefficient of friction is twice as high as that in air, and the wear is even up to 100 times.

• 石墨：其自润滑性能取决于空气和水的存在。作为润滑材料，石墨制品，工作环境中水分的临界值为/m3。如果低于这个值，石墨制品的摩擦系数会增大。在室温300~400度的空气介质中，石墨被强烈氧化时摩擦系数会增大。但在中性或还原性介质中，300~1000度的温度也能保持良好的耐磨性。石墨的结晶程度越高，它就越能保护被润滑材料不受磨损。另外，杂质的含量必须控制在1%以下，否则就容易出现明显的磨粒磨损。
• Molybdenum disulfide: MoS2 is formed by geothermal action, it is chemically stable to withstand heat and pressure and therefore has good resistance to heavy pressure. In environments with harsh, heavily loaded gears and bearings, and components with shock loads, the use of molybdenum disulfide grease is more effective than the use of graphite grease.
• Tungsten disulfide: WS2 used to be 10 times more expensive than MOS2, and is only used as an alternative to MOS2 for applications requiring good oxidation resistance or low resistivity. The friction factor is slightly lower than that of MoS2, and the thermal stability is higher; for sliding friction parts under special working conditions, the application of WS2 can bring out its better effect than MoS2.

Molybdenum disulfide, tungsten disulfide coating and graphene performance differences #