Superlubricity and tribochemistry of polyhydric alcohols

Abstract

The anomalous low friction of diamondlike carbon coated surfaces lubricated by pure glycerol was observed at 80°C. Steel surfaces were coated with an ultrahard 1 µm thick hydrogen-free tetrahedral coordinated carbon ͑ta-C͒ layer produced by physical vapor deposition. In the presence of glycerol, the friction coefficient is below 0.01 at steady state, corresponding to the so-called superlubricity regime ͑when sliding is then approaching pure rolling͒. This new mechanism of superlow friction is attributed to easy glide on triboformed OHterminated surfaces. In addition to the formation of OH-terminated surfaces but at a lower temperature, we show here some evidence, by coupling experimental and computer simulations, that superlow friction of polyhydric alcohols could also be associated with triboinduced degradation of glycerol, producing a nanometer-thick film containing organic acids and water. Second, we show outstanding superlubricity of steel surfaces directly lubricated by a solution of myo-inositol ͑also called vitamin Bh͒ in glycerol at ambient temperature ͑25°C͒. For the first time, under boundary lubrication at high contact pressure, friction of steel is below 0.01 in the absence of any long chain polar molecules. The mechanism is still unknown but could be associated with friction-induced dissociation of glycerol and interaction of waterlike species with steel surface.

Low Friction Property of Diamond-Like Carbon Coating Films and Oxygen Transmission Ratio of Amorphous Carbon Films Deposited by Advanced Coating Processes

“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Martin et al proposed the possible mechanism of the super low friction was the forming water layer by the tribochemical reaction between ta-C and glycerol. [28][29][30][31][32][33] In this paper, the formation of water and acid was indicated as one possible chemical reaction for glycerol, as shown in (a) (a) (b) (b) For the oleic acid test, the water can be supplied from the ambient air. Therefore, the super low friction obtained by the ta-C(T) lubricated with oleic acid seemed to form the similar low share strength tribofilm at the sliding interface.…”

Modelling Tribochemical Reactions of Lubricants in the UHV Analytical Tribometer

“…This specific experiment has contributed to identify that superlow friction obtained for hard carbon coatings in presence of glycerol is related to the presence of a water-containing nanometer-thick tribofilm existing in the contact area, possibly by changing viscosity pressure properties of the mixture. Computer simulations have confirmed evidence of the tribodegradation of glycerol molecules under the combined effects of pressure and shear, generating aldehydes or organic acids and water molecules were given elsewhere [13]. …”

Physicochemistry aspects on frictional interfaces

“…In 2008, Matta et al observed a new superlubricity macrosystem of pure glycerol [1]. They found that the use of steel surfaces and/or ta-C coated surfaces, lubricated by selected polyhydric alcohol molecules, could give unsurpassed low friction values, below 0.01.…”

“…Because of the limits in measurement precision, in practical terms, the lubrication state can be considered as superlubricity when the friction coefficient is lower than 0.01 in a sliding system [1]. At present, superlubricity materials include solid lubricants (diamond like carbon (DLC), molybdenum disulfide (MoS 2 ), etc.)…”

“…Friction consumes a large amount of energy, which along with wear-related energy and material losses, costs about 5%-7% of the gross national product in most industrialized nations [1]. Thus, a reduction in friction will benefit the economic well-being of all nations.…”