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This paper aims to investigate the tribological properties of two protic ionic liquids used as lubricity-improving additives in the water. Their concentration was optimized for different metal friction pairs including bearing steel, stainless steel and aluminum alloy.

In this study tribological properties were investigated by using a ball-on-plate reciprocating tribometer. Three different friction pairs were selected: bearing steel-bearing steel; bearing steel-stainless steel; bearing steel-aluminum alloy. To optimize the concentration of investigated protic ionic liquids four concentrations were selected. Wettability was investigated using the droplet method. The corrosiveness of additive-loaded water was investigated using the iron chip method.

The results show that by using protic ionic liquids the lubricity of water could be greatly improved. However, the friction pair material and additive concentration play a significant role. The positive tribological effect was attributed to the polarity of the additive molecule which tends to form an adsorption layer. The polarity of molecules also leads to better surface wettability. It was also found that both investigated protic ionic liquids can improve the anticorrosion properties of water.

To the best of the authors’ knowledge, this is the first study to present a complex investigation of tribological properties of two protic ionic liquids as additives in the water. In this case, three different metal friction pairs and four additive concentrations were investigated. The results could be interesting to those who are working in the field of water-based lubricants and luck for multipurpose lubricity-improving additives.

The purpose of this paper is to investigate the possibility of using the iron nanoparticles and iron nanoparticles coated with copper layer as additives to base oils.

Fe and Fe+Cu nanoparticles were synthesized by a reduction modification method and added to mineral oil. The size and structure of prepared nanoparticles were characterized by SEM, TEM, XRF, AAS and XRD analysis. Tribological properties of modified lubricants were evaluated on a four‐ball machine in a model of sliding friction pairs.

Spectral and microscopy analysis evidently displayed the formation of Fe and Fe+Cu nanoparticles in suspensions of colloidal solutions and oil. The size of formed nanoparticles was in 15‐50 nm range. Tribological experiments show good lubricating properties of oils modified with Fe and Fe+Cu nanoparticles: higher wear resistance (55 per cent and 46 per cent accordingly) and lower friction coefficient (30 per cent and 26 per cent accordingly). The tests show that nanoparticles provide decreasing tendency of friction torque during the operation of friction pair.

The paper demonstrates that iron nanoparticles and iron nanoparticles coated with copper layer, not only reduce the wear and friction decrease of friction pairs, but possibly also can create layer in oil which separates two friction surfaces and have some self‐organisation properties.

The purpose of this paper is to conduct research on the possibility of improving the tribological and utilization properties of lard and rapeseed oil bio-based greases by mixing it with ethanol and selection of thickener and modification with special biological additives.

Rapeseed oil- and lard-based greases with sodium and lithium soap thickeners were mixed with either water or ethanol and modified with a special biological anti-wear additive. Tribological properties of modified lubricants evaluated on a four-ball machine.

Rapeseed oil- and lard-based greases suspended in ethanol and modified with bio-additive have the same wear resistance as the industrial non-biological lubrication grease and much higher wear resistance as bio-based reference grease. The tribological efficiency of the additives is higher in greases of rapeseed oil and less efficient in lard-based greases. Oxidation and wear tests show that investigated bio-based greases have comparatively stable tribological properties also after their aging. Modified greases have sufficient consistence according penetration measurements and high thermal resistance according drop-point temperature measurements. All produced experimental greases pass within the category of the easily degradable materials.

The greases mixed with the ethanol make possible to form more homogeneous and stable grease mixture. Modified bio-based greases have significantly higher wear resistance as bio-based reference grease, their lubrication properties are stable also after the aging and are categorized as easily degradable materials.