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Test methods influence the superlubricity of glycerol and nanodiamonds

Thursday (23.02.2017)
10:55 - 11:20 Rohrersaal
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Rotary and reciprocation type test methods are often used in friction and wear testing of lubricants. Here, we have compared the rotary (ball-on-disk) and reciprocation (high frequency reciprocation rig) tests operating under the same pressure, velocity, temperature and humidity to determine the friction and wear behavior of aqueous glycerol and aqueous glycerol with 0.1 % w nanodiamonds. Results indicate that the aqueous glycerol solution shows superlubricity effect as its friction coefficient is lower than 0.01 during the rotary test. This effect was attributed to the protective matrix comprised of a hydrogen bonded water layer that provide load bearing stability and above it a layer of free water molecules that produce low shear. However, this protective matrix was damaged due to the repetitive compressive stress from reciprocation. As a result there is no superlubricity behavior as observed during the rotary motion. Moreover the lubrication behavior of nanodiamond additives also depends on the test method. In the rotary test method the nanodiamond additives (dispersed in glycerol) and wear debris accumulates at the contact zone that grows to become a large abrasive particle mix. Whereas during the reciprocation there are few smaller nanodiamond and wear debris particles at the contact zone that polishes and smoothens the surface. Abrasive nature of nanodiamonds increases the wear and micro polishing effect decreased the friction, significantly. We conclude that the prevalence of superlubricity behavior of glycerol depends on the type of friction testing method used in the study. And, aqueous glycerol with nanodiamonds has potential to become green lubricants.


Additional Authors:
  • Angela Maria Tortora
    Ducom Instruments