Lubrication under low-temperature environments is a core challenge in aerospace, polar exploration, and liquefied gas storage and transportation. Traditional lubricating oils thicken rapidly and even solidify below -40°C, leading to equipment startup difficulties and sudden increases in friction resistance. Molybdenum disulfide (MoS2), as a layered-structure solid lubricant, maintains low friction coefficient operation even in cryogenic environments at -180°C, as its lubrication performance does not depend on viscosity changes. Experimental data show that the friction coefficient of MoS2 at room temperature ranges from 0.02 to 0.06, and when tested at liquid nitrogen temperature (-196°C), the friction coefficient rises slightly but still remains below 0.08, far superior to the performance of conventional greases at that temperature.

The physical mechanism of low-temperature lubrication failure lies in the suppression of lubricating oil molecular motion. Mineral oils can increase kinematic viscosity tens of times at -30°C, and synthetic ester oils also undergo glass transition around -60°C. The lubrication mechanism of MoS2 is based on interlayer sliding of its S-Mo-S structure, where interlayer bonding forces are only at the van der Waals level, with an interlayer dissociation energy of approximately 0.15 J/m². This means that temperature changes have limited impact on its lubrication performance, and interlayer shear slip can occur normally even when molecular thermal motion is greatly reduced.

In aerospace engineering, low-temperature lubrication demands are concentrated on satellite deployment mechanisms and rocket valve components. Certain components of geosynchronous orbit satellites operate at temperatures as low as -170°C. NASA test reports show that sputtered MoS2 films, after 5,000 cycles of operation in a -180°C vacuum environment, exhibited wear rates below 10⁻⁹ mm³/Nm. The solar array drive mechanism of the International Space Station also employs MoS2-based solid lubrication solutions to meet the 15-year on-orbit lifetime requirement. These data are from publicly available NASA technical reports (NASA/TM-2003-212440 series).

Liquefied Natural Gas (LNG) storage and transportation equipment represents another typical low-temperature lubrication scenario. LNG storage tank pumps and transport valves operate in -162°C environments, where conventional lubricating greases completely lose fluidity. Maintenance records from an LNG receiving terminal show that valves with MoS2 coatings experienced no sticking failures after 3 years of operation, whereas previously, when using cryogenic greases, re-lubrication was needed every 6 months on average. The temperature range of -162°C to -180°C is precisely the high-value application area for MoS2 solid lubrication as a replacement for grease.

Polar expedition vehicles and equipment also face low-temperature lubrication difficulties. Winter temperatures in Antarctica can reach -80°C, and vehicle transmission systems and hydraulic devices experience enormous resistance during startup. After applying MoS2 dry film coatings to drive shafts and hinges, cold-start friction torque can be reduced by approximately 35%-50%, according to comparative test results from the equipment maintenance report of China's 35th Antarctic expedition.

It should be noted that MoS2 has a positive effect of reduced oxidation rate at low temperatures, but its moisture resistance is poor in humid environments. When used in environments with alternating humidity, sealing and protective measures are recommended. For applications below -180°C, the thermal expansion coefficient match between the coating and substrate also needs evaluation to prevent coating delamination during temperature cycling. Sputtered MoS2 films on titanium alloy and stainless steel substrates exhibit good adhesion during deep cryogenic thermal cycling.

low-temperature lubrication, 低温润滑, MoS2, 二硫化钼, -180°C, extreme environment, 极端环境, solid lubricant, 固体润滑剂, aerospace, 航空航天, layered structure, 层状结构