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Halogen-free ionic liquids in lubrication
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.ORCID iD: 0000-0001-5149-378X
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.ORCID iD: 0000-0003-3652-7798
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.ORCID iD: 0000-0002-6810-1882
Machine Design, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
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2014 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

The use of wear-resistant non-ferrous and lightweight materials calls for novel types of lubricants including neat Ionic Liquids (ILs) and ILs as additives to base oils [1-4]. ILs are non-flammable low temperature molten salts, which have negligible volatility and a high thermal stability. However, most of previously studied ILs as promising lubricants contain BF4- or PF6- anions, which are prone to hydrolysis producing corrosive and toxic species. Here we report on the synthesis, physic-chemical and tribological characterisation of halogen-free ILs with cations belonging to different families (phosphonium, pyrrolidinium, imidazolium), combined with different orthoborate anions (bis(mandelato)borate [BMB], bis(salicylato)borate, bis(oxalato)borate, etc). It was found that these types of hf-BILs (both as neat liquids and as additives) outperform a fully formulated engine oil and a neat PEG oil as antiwear and friction reducing lubricants at steel-steel and steel-aluminium contacts.To reveal mechanisms of formation of tribofilms, the mechanochemically induced boundary films on surfaces of Al2O3, MgO and SiO2 in contact with orthoborate-based ILs were characterised using solid-state multinuclear (11B, 31P and 29Si) MAS NMR, FTIR and Raman spectroscopy. It was found that some of these ILs interact with the oxides, in particular, at elevated temperatures. We suggest that the boundary film formation between hf-BILs and -Al2O3, MgO and SiO2 surfaces is a complex process involving various chemical reactions at the solid-liquid interfaces. Self-diffusion of ionic species in orthoborate based ILs and in IL/PEG mixtures as a function of temperature was studied using pulse-field-gradient (PFG) 1H and 31P NMR [5]. It was found that [P66614][BMB] can exist in one or two different liquid “phases” with ionic species having dramatically different (by two orders of magnitude) self-diffusion coefficients: Slowly diffusing phosphonium cations with long and bulky alkyl chains form domains stabilised by hydrophobic interactions in these ILs in the temperature range 20-50 oC, while small orthoborate anions are fast diffusing species at these temperatures [5]. These domains are, however, disrupted by developed molecular motion with the cation-anion complexes having one and the same diffusion coefficient when the IL system is heated above 50oC. A similar phenomenon was also found in some other [BMB] based ILs with pyrrolidinium and imidazolium cations.

Place, publisher, year, edition, pages
2014.
National Category
Physical Chemistry
Research subject
Chemistry of Interfaces
Identifiers
URN: urn:nbn:se:ltu:diva-31359Local ID: 584c01d6-ef9e-4ef9-ab75-03ec40f44752OAI: oai:DiVA.org:ltu-31359DiVA, id: diva2:1004593
Conference
Conference on Molten Salts and Ionic Liquids : 06/06/2014 - 11/06/2014
Note
Godkänd; 2014; 20150101 (faisha)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-05-31Bibliographically approved

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Taher, MamounShah, Faiz UllahFilippov, AndreiAntzutkin, Oleg

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