Extreme pressure behaviour of newly formulated oil-in-water emulsions

Oil-in-water (O/W) emulsions are broadly used in metal-machining processes, where combined lubrication and refrigeration are needed, such as in cutting, rolling, or grinding. These fluids consist of tiny oil droplets in water stabilised by small amounts of emulsifiers, namely surfactants. In an emulsion, oil is responsible for the lubricating properties, whereas water provides heat dissipation and fire resistance. Normally, emulsifiable metalworking oils are used in an oil concentration between 2 and 5 vol. %, depending on the application. Despite their wide use, the lubrication mechanisms of o/w emulsions have not been fully understood, mainly because of their complexity. Previous studies on oil-in-water emulsions showed that, in order to form thick lubricant films, oil droplets must wet the metal surfaces, displacing water. The ability of oil to wet is strongly dependent on the concentration of surfactant. Surfactant molecules tend to adsorb preferentially at the interface, modifying the nature of the layers adjacent to the metal surfaces and, thus, playing a key role in processes such as wettability, corrosion, or friction, as well as emulsion stability. The aim of this work is to study the influence of concentration of two different emulsifiers (anionic and non-inonic) on the wettability and extreme pressure properties of an oil-in-water emulsion. A mixture of a synthetic polyalphaolefin and a trimethylol propane ester was used as the base oil, and the concentrations of emulsifiers were below, equal to, and above their critical micellar concentrations (CMC). Extreme pressure tests (ASTM D 2783), which try to simulate the operating conditions of high speeds and pressures taking place in cutting processes, and contact angle measurements were carried out in order to establish a relationship between both properties and to evaluate the performance of these emulsions as lubricants

Ionic liquids as an additive in fully formulated wind turbine gearbox oils

This work presents the friction and wear behaviour of two fully formulated (polyalphaolefin- and mineral-based) wind turbine gearbox oils separately additivated with two ionic liquids ([Choline][NTf2] and [BMP][NTf2]) at 5wt% concentration. A tribometer using a ball-on-plate reciprocating configuration is adopted for friction and wear experiments. Friction is measured during tests and the worn surface is measured and analysed by confocal microscopy, SEM, EDS and XPS. The friction and wear results show that both ionic liquids used as an additive have a slight friction modifier character but a strong wear reducing performance, with [BMP][NTf2] performing better than [Choline][NTf2]. In addition, EDS and XPS analysis demonstrated the temperature-related chemical interactions and their influence on tribological behaviour

Wettability and corrosion of [NTf2] anion-based ionic liquids on steel and PVD (TiN, CrN, ZrN) coatings

Thewetting and corrosion behavior of three bis(trifluoromethylsulfonyl)imide-based ionic liquids: 1-Dodecyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide [C12MIM][NTf2], tributylmethylammonium bis(trifluoromethylsulfonyl)imide [N4441][NTf2] and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide [N1888][NTf2] are tested in this research. The surface tension was measured for temperatures of 293–353 K resulting in the expected linearly decreasing behavior with temperature increase. In addition, contact angle measurements were made on AISI 52100 steel and three coatings (TiN, CrN and ZrN) obtained by PVD technique, finding the regular behavior in hydrophobic (non-polar) systems: high contact angles led to high surface tensions. Complementary parameters like spreading parameter and polarity fraction were calculated to enhance the wetting evaluation of these ionic liquids. [N1888][NTf2]/TiN resulted as the best IL-surface combination for a good wettability, due to the higher dispersion of the charge on the large size cation in this IL and the higher values of total and polar component of the surface free energy for this coating. Finally, SEM-EDS analysis determined that [N1888][NTf2]/ZrN was the best option in order to avoid corrosion problems. The evaporation of water, present as impurity in the ionic liquids, was found the main reason because of corrosion did not occur in the tests carried out at 100 °C

Yeasts and bacterial biosurfactants as demulsifiers for petroleum derivative in seawater emulsions

Abstract Oil sludge or waste generated in transport, storage or refining forms highly stable mixtures due to the presence and additives with surfactant properties and water forming complex emulsions. Thus, demulsification is necessary to separate this residual oil from the aqueous phase for oil processing and water treatment/disposal. Most used chemical demulsifiers, although effective, are environmental contaminants and do not meet the desired levels of biodegradation. We investigated the application of microbial biosurfactants as potential natural demulsifiers of petroleum derivatives in water emulsions. Biosurfactants crude extracts, produced by yeasts (Candida guilliermondii, Candida lipolytica and Candida sphaerica) and bacteria (Pseudomonas aeruginosa, Pseudomonas cepacia and Bacillus sp.) grown in industrial residues, were tested for demulsification capacity in their crude and pure forms. The best results obtained were for bacterial biosurfactants, which were able to recover about 65% of the seawater emulsified with motor oil compared to 35–40% only for yeasts products. Biosurfactants were also tested with oil-in-water (O/W) and water-in-oil (W/O) kerosene model emulsions. No relationship between interfacial tension, cell hydrophobicity and demulsification ratios was observed with all the biosurfactants tested. Microscopic illustrations of the emulsions in the presence of the biosurfactants showed the aspects of the emulsion and demulsification process. The results obtained demonstrate the potential of these agents as demulsifiers in marine environments

Tribological performance of tributylmethylammonium bis(trifluoromethylsulfonyl)amide as neat lubricant and as an additive in a polar oil

The ionic liquid (IL) tributylmethylammonium bis(trifluoromethylsulfonyl)amide ([N4441][NTf2]) was used as neat lubricant and as an additive (1.5 wt%) in a polar oil to study its friction and wear reducing properties. Tribological tests were completed for 90 minutes at room temperature and 100 °C in a reciprocating configuration at loads of 30 and 70 N, 10 Hz-frequency, and 4 mm stroke length. Wear volume was measured by confocal microscopy and the surface-IL interaction determined by XPS. The main findings were that neat IL showed the best tribological behavior; the IL-containing mixture behaved similar to the base oil regarding friction, however outperformed the antiwear behavior of the base oil under higher temperature; surface-IL chemical interaction was found mainly at 100 °C

Two phosphonium cation-based ionic liquids as lubricant additive to a polyalphaolefin base oil

This paper studies the tribological performance of two phosphonium cation-based ionic liquids: trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate ([P6,6,6,14][(iC8)2PO2]) and trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate ([P6,6,6,14][BEHP]), as lubricant additive at 1 wt% to a polyalphaolefin. A comparison of their tribological behavior was made to that of one type of zinc dialkyldithiophosphate (ZDDP). Stribeck curve tests were made in a Mini Traction Machine (MTM) tribometer at entrainment speeds ranging from 2000 to 10 mm/s, 30 N-load, slide-to-roll ratio (SRR) of 50%, and temperatures of 40, 60, 80 and 100 °C. Tribofilm formation tests were also conducted in the MTM at 100 °C, load of 50 N, entrainment speed of 150 mm/s, SRR of 50%, and duration of 60 min. Additionally, reciprocating 60-min wear tests at 60 N-load, frequency of 15 Hz, stroke length of 4 mm and at room temperature were performed with IL-containing mixtures at 0.5 and 1 wt%. Coefficient of friction was recorded during the tests, and wear on the discs surface was measured using confocal microscopy. SEM-EDS and XPS were also used for studying the lubricant-surface interactions after these tests. Lubricants including [P6,6,6,14][(iC8)2PO2] exhibited better tribological performance than [P6,6,6,14][BEHP] ones and close to the ZDDP results. SEM images of worn surfaces exhibited evidence of plastic deformation and adhesive wear and EDS analysis showed that only active elements (P, S, Zn) were detected for mixtures containing ZDDP. XPS analysis indicated a different lubrication mechanism of the blends with ionic liquids compared with the ZDDP ones

Antifriction and Antiwear Properties of an Ionic Liquid with Fluorine-Containing Anion Used as Lubricant Additive.

Tribological behavior of trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide [P66614][NTf2] ionic liquid (IL) used as additive in a diester oil at concentrations of 0.25, 0.5 and 1 wt% was studied in this research. The IL solubility in the base oil was measured using the inductively coupled plasma mass spectrometry (ICP-MS) technique, and corrosion analysis was done at room temperature at relative humidity of 49–77%. Tribological tests were conducted for 30 min at room temperature, 15 Hz frequency, 4 mm of stroke length, a load of 80 N (corresponding to 2 GPa of maximum contact pressure) and relative humidity of 35–53%. Friction coefficient was recorded during tests, and the wear scar was measured by confocal microscopy. Worn surface was also analyzed by SEM, EDS and XPS. Results showed that a saturated solution of [P66614][NTf2] in the base oil contains about 30 wt% of IL and corrosion activity for the highest concentration of IL (1 wt%) was not found after a 20-day test. Although the base oil and the mixtures had similar friction behavior, only the 1 wt% sample exhibited slightly lower wear volume than the base oil. SEM images exhibited similar wear track width (707–796 µm) and wear mechanism (adhesive) for all samples tested. In addition, the EDS spectra only showed the elements present in the steel. Finally, the XPS measurements could not detect differences regarding iron chemical state among the samples, which is consistent with the tribological behavior obtained

The effect of emulsifier concentration on the lubricating properties of oil-in-water emulsions

Although the use of oil-in-water (O/W) emulsions as metalworking fluids is widespread, the mechanisms of emulsion lubrication are not yet well understood. Several theories have been proposed but there is not a clear agreement about the effect of different operating conditions and emulsion properties on the lubricating performance of O/W emulsions. In the present study, the film forming ability of O/W emulsions as a function of emulsifier concentration is studied. The emulsifier content exerts a strong influence on all the emulsion properties, such as stability, droplet size distribution, surface and interfacial tension, wetting ability, etc., as well as on the lubricating behaviour, so it has been used to ascertain the relationship between all the properties involved. Three different emulsifiers—anionic, nonionic and cationic—were used at different concentrations in the design of lubricant O/W emulsions. Experimental results show that the work of adhesion of oil droplets on the metal surface is a valuable parameter to predict the ability of emulsions to form thick films in elastohydrodynamic (EHD) contacts. The influence of pH value of O/W emulsions on their lubricating behaviour is also verified. The overall conclusion is that the interactions between metal and oil droplets rule the mechanism of lubrication and that this interaction is primarily controlled by emulsifier concentration