Abstract
This research deals with the tribological behavior and corrosion performance of three novel fatty acid anion-based ionic liquids (FAILs): methyltrioctylammonium hexanoate ([N8,8,8,1][C6:0]), methyltrioctylammonium octadecanoate ([N8,8,8,1][C18:0]) and methyltrioctylammonium octadec-9-enoate ([N8,8,8,1][C18:1]), employed for the first time as neat lubricant with five different material pairs: steel–steel, steel–aluminum alloy, steel–bronze, steel–cast iron and steel–tungsten carbide. These novel substances were previously obtained from fatty acids via metathesis reactions, identified structurally via NMR (nuclear magnetic resonance) and FTIR (Fourier-transform infrared spectroscopy) techniques, and then characterized from a physicochemical (density, water solubility, viscosity, viscosity index and refractive index) and environmental (bacterial toxicity and biodegradability) points of view. The corrosion behavior of the three FAILs was studied by exposure at room temperature, while friction and wear tests were performed with a reciprocating ball-on-disc configuration. The main results and conclusions obtained were: (1) Corrosion in the presence of the three FAILs is observed only on the bronze surface; (2) All FAILs presented similar tribological behavior as lubricants for each tested material pair; (3) XPS (X-ray photoelectron spectroscopy) analysis indicated that the surface behavior of the three FAILs in each material pair was similar, with low chemical interaction with the surfaces.
Highlights
In 1914, Peter Walden synthesized, for the first time, the ethylammonium nitrate, an event that nowadays can be considered as the birth of ionic liquids (ILs) [1]
Otero et al [54] studied the tribological performance of two phosphonium cation-based ionic liquids: [P6,6,6,14][(C2F5)3PF3] and [P4,4,4,2][C2C2PO4] as neat or lubricants’ additives in steel–steel contact, with XPS analysis revealing the formation of tribofilms on the worn surface of both ILs, mainly composed of iron phosphides and oxides
TwheereEDoSbsreervveeadledfoarhibgrhonozxeyg(eFnigcuornete4n)t odnabyrsonezxepsouserfdacetoex[pNo8s,8e,8d,1][tCo 1t8h:0e] tawnod a[Nbo8,v8,e8,1m][eCn1t8i:1o].nTedheFAEIDLSs, rwevheicahleids iandhiicgahtivoxeyogfeonxicdoantitoenntp(hTeanbolem3e)nao.n bronze surface exposed to the two abovementioned fatty acid anion-based ionic liquids (FAILs), which is indicative of oxidation phenomena
Summary
In 1914, Peter Walden synthesized, for the first time, the ethylammonium nitrate, an event that nowadays can be considered as the birth of ionic liquids (ILs) [1]. Otero et al [54] studied the tribological performance of two phosphonium cation-based ionic liquids: [P6,6,6,14][(C2F5)3PF3] and [P4,4,4,2][C2C2PO4] as neat or lubricants’ additives in steel–steel contact, with XPS analysis revealing the formation of tribofilms on the worn surface of both ILs, mainly composed of iron phosphides and oxides. Other materials used in engineering applications, such as aluminum, silicon, titanium, copper, sialon ceramics, and different coatings, have been tested when lubricated with ILs [38,39,66–77]. The possibility of creating tailored ILs through the combination of existing ions via synthesis is leading to new IL families with improvements in terms of toxicity and biodegradability [80–83] Among these new ILs are fatty acid anion-based ionic liquids (FAILs), reported for the first time in 2013 [84], and whose use in lubrication studies has greatly increased [85–105]. Aaddediintioonrdalelry,towdeaertescctasrus rofanctehaeltdeirsacstuiornfascaens dwedreetesrtumdiineedtbhye Xp-rreadyopmhiontaoneltewcteroanr mspeecchtraonsicsomp.yA(XdPdSit)iotoneavllayl,uwateeatrhsecsaursrfoacne-tIhLe idnitsecrasuctrifoanc.esAwpehroetsoteuldecietrdonbyspXe-cratryompheotetore(lSePcEtrConS)swpeitchtraoshceompyis(pXhPeSri)ctaol eevnaelrugayteanthaelyszuerr(fPahceo-iIbLosinttyeprea)ctwioans. eAmpphlooyteode.lectron spectrometer (SPECS) with a hemispherical energy analyzer (Phoibos type) was employed
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