1,3-Diketone Fluids and Their Complexes with Iron

Tribological experiments with 1,3-diketone fluids in contact with iron surfaces show ultralow friction, which was suggested to be connected to the formation of iron complexes. In order to support this assumption, we calculate infrared and optical spectra of various substituted 1,3-diketones and their iron complexes using gradient-corrected density functional theory (DFT). The description of the complexes requires the application of the DFT+U scheme for a correct prediction of the high spin state on the central iron atom. With this approach, we obtain excellent agreement between experiment and simulation in infrared and optical spectra, allowing for the determination of 1,3-diketone tautomeric forms. The match in the spectra of the complex strongly supports the assumption of iron complex formation by these lubricants

Ultralow Friction Induced by Tribochemical Reactions: A Novel Mechanism of Lubrication on Steel Surfaces

The tribological properties of two steel surfaces rubbing against each other are measured while they are in contact with 1,3-diketones of varying structure. Such systems show after a short running-in period ultralow friction properties with a coefficient of friction of as low as μ = 0.005. It is suggested that the extremely favorable friction properties are caused by a tribochemical reaction between the 1,3-diketones and the steel surfaces, leading to formation of a chelated iron–diketo complex. The influence of temperature and the molecular structure of the 1,3 diketo-lubricants onto the friction properties of the system is elucidated under both static and dynamic conditions. With progression of the tribochemical reaction, the sliding surfaces become very conformal and smooth, so that the pressure is greatly reduced and further wear is strongly reduced. All iron particles potentially generated by wear during the initial running-in period are completely dissolved through complex formation. It is proposed that the tribochemical polishing reaction causes a transition from boundary lubrication to fluid lubrication

Macroscopic Superlow Friction of Steel and Diamond-Like Carbon Lubricated with a Formanisotropic 1,3-Diketone

Energy dissipation due to friction and wear is reducing the energy efficiency and reliability of mechanical systems. Thus, great efforts are being made to minimize friction for technical applications. In our present work, we investigate the tribological behavior of stainless steel 100Cr6 with a-C:H and a-C:H:Si coating lubricated with a surface-active formanisotropic 1,3-diketone. The results show that superlow friction can be achieved on the macroscale using a steel 100Cr6 self pairing (COF ∼ 0.005) and with 100Cr6 in combination with a-C:H coating (COF ∼ 0.008). Furthermore, the replacement of steel with a-C:H coating leads to a considerable decrease of wear. The reduced COF arises from the chemical interaction of the lubricant with the surface and nascent iron ions. It was found that interfacial parameters correlate with tribological results. In addition, the alignment of the formanisotropic molecules in the tribological contact at thin-film lubrication leads to an anisotropic viscosity with a minimum shear resistance in sliding direction. Atomistic simulation of tribochemical interactions was conducted to derive a friction model based on the thin-film lubrication theory. This investigation indicates the potential to substantially reduce friction and wear using this fluid in real technical applications