| 1. |
- Andersson, Joel, et al.
(author)
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Semi-deterministic chemo-mechanical model of boundary lubrication
- 2012
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In: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 156, s. 343-360
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Journal article (peer-reviewed)abstract
- A model for tribofilm growth is developed. The model is used in combination with numerical contact mechanics tools to enable evaluation of the combined effects of chemistry and contact mechanics. The model is tuned with experimental data and is thereafter applied to rough surfaces. The growth of the tribofilm is evaluated for 3 different contact cases and short-term tribofilm growth behaviour is analyzed. The results show how tribofilms grow in patches. The model is expected to be used as a tool for analysis of the interaction between rough surfaces.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
- Emadi, Maryam, et al.
(author)
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Does your lubrication system conform to the concept of green chemistry?
- 2016
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Conference paper (other academic/artistic)abstract
- We frequently find “EAL” (environmentally acceptable lubricant or relevant such as “environmentally friendly,” “environmentally adapted,” “environmental benign,” “biodegradable,” “ecological,” “green,” in the title and keywords of tribology papers. It intimates "something good for environment" and may catch the readers' attention. However, one might feel unease because the definition of these terms is unclear. These terms are too loosely used with the authors’ satisfaction in most cases. Of course, lubrication engineering contributes to protect global environment by improving energy efficiency and prolonging machine life through reducing friction and wear. In this regard, lubrication itself is definitely one of the “green” technologies. This led a simple question – why adjectives such as “environmental” are used with lubrication? The unrivalled reference book in tribology defines “environmentally friendly lubricants” as “readily biodegradable in nature” [1]. We agree with it, but shall ask "is biodegradability enough for protection of global environment?" This motivated us to propose unambiguous criteria for EAL.
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| 6. |
- Fatima, Nowshir, et al.
(author)
-
Adsorption of ATF additives on wet clutch friction interfaces under water contaminated lubricant conditions
- 2014
-
Conference paper (peer-reviewed)abstract
- Stable friction and positive slope of friction-speed is the typical criterion for a good clutch performance. Lubricated friction interfaces used for wet clutches produces different friction behavior depending on the lubricant conditions. Usually the lubricant conditions vary for different automatic transmission fluid (ATF) formulations implying e.g. water contamination and these conditions might influence the deterioration of the clutch plates. The aim of this paper is to verify additive adsorption on friction interfaces and ageing of the friction material in wet clutch system for a water contaminated commercial ATF (DEXRON® VI). Standard clutch plates are employed in an automated wet clutch test rig to evaluate the friction characteristics of the tested lubricant. For controlled test conditions (speed, contact pressure, oil temperature) and specific number of test cycles, the mean friction coefficient and the friction vs. speed relations are monitored during sliding test. The resultant tribofilms on the tested friction interface surfaces are characterized by means of Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM- EDS), Attenuated Total Reflectance -Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS analysis). The spectroscopic techniques were used to analyse adsorbed additives on friction interfaces and made it possible to correlate measured data to the specific friction behavior obtained after water contamination of the ATF.
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| 7. |
- Fatima, Nowshir, et al.
(author)
-
Degradation Mechanism of Automatic Transmission Fluid by Water as a Contaminant
- 2015
-
In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : SAGE Publications. - 1350-6501 .- 2041-305X. ; 229:1, s. 74-85
-
Journal article (peer-reviewed)abstract
- The degradation mechanism of water contaminated Automatic Transmission Fluids (ATF) was experimentally investigated. Water contaminated ATF was tribotested in a full-scale wet clutch test rig to monitor the friction durability during clutch ageing, and was also statically aged in oven to evaluate the interaction of ATF with water. The bulk properties and chemical nature of the ATF were analysed using viscosity measurements, Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). It was shown that water presence in the ATF can increase the mean friction coefficient over a short time period, though in the long term perspective there is a higher loss of mean friction. Phase separation of the water-in-oil emulsion by centrifugation at 20000 rpm made it possible to examine the water phase using infrared 2spectroscopy. The spectroscopic analysis revealed the hydrophilic nature of certain ATF constituents, although the impact of water on the bulk properties like lubricant viscosity and thermal stability was insignificant. The analysis of the tribotests showed that the friction increase for water contamination was a short-term effect and likely due to the interaction between polar surface active additives and water. Even though no significant change has been found for thermal degradation or in bulk properties of the lubricant, the initially changed action of the water soluble additives and generation of high friction resulted in a total deterioration of the clutch performance during long term use.
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| 8. |
- Fatima, Nowshir, et al.
(author)
-
Influence of water on the tribological properties of zinc dialkyl-dithiophosphate and over-based calcium sulfonate additives in wet clutch contacts
- 2015
-
In: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 87, s. 113-120
-
Journal article (peer-reviewed)abstract
- Usually the wet clutch lubricant properties vary with different formulations of base oil types and additives. The aim of this paper was to evaluate the effect of water on the performance of additives in ATF. Simplified lubricants, ZDDP and over-based Ca-sulfonates detergent additives in an API Group I mineral base oil, were employed to compare with the commercial fully-formulated automatic transmission fluid (DEXRON®VI) during water-contamination. A full-scale wet clutch test rig was used to evaluate the frictional response due to water contamination of the lubricants. Fourier Transform Infrared Spectroscopy was utilized to evaluate the variation in the solubility of these polar organic additives in the water phase and Karl-Fischer titration was utilized to evaluate the post-test water content for different formulations.
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| 9. |
- Fatima, Nowshir, et al.
(author)
-
Surface chemistry of wet clutch influenced by water contamination in automatic transmission fluids
- 2016
-
In: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 96, s. 395-401
-
Journal article (peer-reviewed)abstract
- Lubricated friction interfaces used for wet clutches produces different friction behaviour depending on the lubricant conditions. Usually the lubricant conditions vary for water contamination in automatic transmission fluid (ATF). The presence of water retards the ATF performance by increasing the friction and can influence the deterioration of the clutch plates. Water as a polar contaminant can change the absorbability of the surface active additives, which might cause the characteristic friction behaviour. The aim of this paper is to verify the surface chemistry of tribotested standard friction interfaces lubricated with water contaminated commercial ATF (DEXRON® VI). The evidences of the influence of water on ATF performances were shown by surface analyses
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| 10. |
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| 11. |
- Hansen, Jonny, et al.
(author)
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Performance and mechanisms of silicate tribofilm in heavily loaded rolling/sliding non-conformal contacts
- 2018
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In: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 123, s. 130-141
-
Journal article (peer-reviewed)abstract
- Lubricant performance is vital as heavy-duty gear manufacturers increase power density in their efforts towards increased efficiency. In this work, a recently developed ionic liquid is introduced as a multifunction additive for use in hydrocarbon base fluid. A ball-on-disc tribological test machine was used to evaluate friction and wear in heavily loaded mixed rolling/sliding conditions. The novel multifunctional additive is benchmarked against conventional axle-gear oil additives, and results shows excellent tribological performance in terms of friction and wear. Post-test surface analysis of the wear scars revealed a silicate based tribofilm derived from the novel ionic additive, contrary to conventional phosphorous and/or sulfur based. The silicate tribofilm is correlated to a significantly increased wear resistance and vastly improved running-in performance.
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| 12. |
- Kaur, Parminder, et al.
(author)
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Photoelectrocatalytic treatment of municipal wastewater with emerging concern pollutants using modified multi-layer catalytic anode
- 2023
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In: Chemosphere. - : Elsevier Ltd. - 0045-6535 .- 1879-1298. ; 339
-
Journal article (peer-reviewed)abstract
- Municipal wastewater contains emergent chemical and biological pollutants that are resistant to conventional wastewater treatments. Therefore, the focus of the current study was to address the challenge of removing emergent chemical and biological pollutants present in municipal wastewater. To achieve this, a photo electro-catalytic (PEC) treatment approach was employed, focusing on the removal of both micro and biological pollutants that are of emergent concern, as well as the reduction of Chemical Oxidation Demand (COD) and Total Organic Carbon (TOC). The treatment involved the use of a modified multi-layer catalytic anode photo-electroactive anode as an effective anode for PEC treatment of municipal wastewater. In the continuous mode of operation, %COD removal was optimized for the treatment of municipal wastewater under Ultra-Violet C (UVc), 280 nm, and Visible (Vis) radiation, 400 nm. Therefore, a comparative study was performed to investigate the effect of Vis radiation on %COD removal, micropollutants removal, and disinfection of municipal wastewater. Micropollutants present in municipal wastewater were effectively oxidized/degraded with the highest reduction rate between 100% and 80% under the influence of UVc and Vis radiation respectively by the PEC treatment process. Disinfection of various microorganisms present in the wastewater with the effect of UVc and Vis assisted PEC treatment was also monitored. Overall, 75–80% of the disinfection of municipal wastewater was contributed by the modified multi-layer catalytic anode. The UVc in the PEC system, contributes approximately 20–25% to the overall disinfection of municipal wastewater.
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| 13. |
- Minami, Ichiro, et al.
(author)
-
Coating-lubricant combination for improving tribo-system performance
- 2014
-
In: Lubrication Science. - : Wiley. - 0954-0075 .- 1557-6833. ; 26:5, s. 375-386
-
Journal article (peer-reviewed)abstract
- New tribo-systems composed of green chemicals have been investigated. Compatibility of friction modifiers with DLC was evaluated by using SRV test machine. A Zn-free lubricant formulation showed a steady-state friction coefficient of 0.15 for steel/steel contact. Hydrogenated DLC coating showed similar tribological properties when slid against steel. Interestingly, this lubricant showed low friction coefficient of 0.02 for hydrogen-free amorphous DLC when slid against steel. A model friction modifier improved the running-in performance and reduced wear for hydrogen-free DLC, while it marginally increased steady-state friction coefficient up to 0.04. The importance of material–lubricant combination and lubrication model has been highlighted
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| 14. |
- Minami, Ichiro
(author)
-
Ionic Liquid Lubricants
- 2013
-
In: Encyclopedia of Tribology. - Boston, MA : Springer-Verlag New York Inc.. - 9780387928968 - 9780387928975 ; , s. 1866-
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Book chapter (peer-reviewed)
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| 15. |
- Minami, Ichiro
(author)
-
Molecular science of lubricant additives
- 2017
-
In: Applied Sciences. - Basel : MDPI. - 2076-3417. ; 7:5
-
Journal article (peer-reviewed)abstract
- This review aims at introducing an engineering field of lubrication to researchers who are not familiar with tribology, thereby emphasizing the importance of lubricant chemistry in applied science. It provides initial guidance regarding additive chemistry in lubrication systems for researchers with different backgrounds. The readers will be introduced to molecular sciences underlying lubrication engineering. Currently, lubricant chemistry, especially "additive technology", looks like a very complicated field. It seems that scientific information is not always shared by researchers. The cause of this is that lubrication engineering is based on empirical methods and focuses on market requirements. In this regard, engineering knowhow is held by individuals and is not being disclosed to scientific communities. Under these circumstances, a bird's-eye view of lubricant chemistry in scientific words is necessary. The novelty of this review is to concisely explain the whole picture of additive technology in chemical terms. The roles and functions of additives as the leading actors in lubrication systems are highlighted within the scope of molecular science. First, I give an overview of the fundamental lubrication model and the role of lubricants in machine operations. The existing additives are categorized by the role and work mechanism in lubrication system. Examples of additives are shown with representative molecular structure. The second half of this review explains the scientific background of the lubrication engineering. It includes interactions of different components in lubrication systems. Finally, this review predicts the technical trends in lubricant chemistry and requirements in molecular science. This review does not aim to be a comprehensive chart or present manufacturing knowhow in lubrication engineering. References were carefully selected and cited to extract "the most common opinion" in lubricant chemistry and therefore many engineering articles were omitted for conciseness
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| 16. |
- Minami, Ichiro
(author)
-
Nuclear magnetic resonance (NMR) spectroscopy for lubricant chemistry
- 2012
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In: Society of Tribologists & Lubrication Engineers Annual Meeting and Exhibition 2012. - Red Hook, NY : Curran Associates, Inc.. - 9781622762484 ; , s. 152-154
-
Conference paper (peer-reviewed)abstract
- 31P-NMR is a useful tool for identifying and monitoring phosphorous-containing additives. 31P is an NMR active and 100% natural abundance isotope, implying that even a small amount of phosphorus-containing compounds can be detected by NMR. A discussion covers the application of NMR in particular for tribological purpose; and example, illustrating the use of 31P-NMR for tracing zinc bis(dialkyldithiophosphate) in lubricant maintenance. This is an abstract of a paper presented at the Society of Tribologists & Lubrication Engineers Annual Meeting and Exhibition 2012 (St. Louis, MO, 5/6-10/2012).
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| 17. |
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| 18. |
- Minami, Ichiro, et al.
(author)
-
Tribological properties of halogen-free ionic liquids
- 2012
-
In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : SAGE Publications. - 1350-6501 .- 2041-305X. ; 226:11, s. 891-902
-
Journal article (peer-reviewed)abstract
- The tribological properties of halogen-free ionic liquids, tricyanomethanide [C(CN)3−] salt, tetracyanoborate [B(CN)4−] salts, and N-alkylimidazole-trialkylborane complexes were evaluated by laboratory tribo-testing of steel–steel contact under boundary conditions. Tricyanomethanide salt is composed of hydrogen, carbon, and nitrogen. The other two types of liquids are composed of hydrogen, boron, carbon, and nitrogen. They are free of halogens and heavier elements that are components of common ionic liquids, such as fluorine, phosphorus, and sulphur. As expected, the halogen-free ionic liquids exhibited low corrosion properties to steel. When evaluated as neat liquid, these halogen-free ionic liquids provided less tribological properties in comparison with a reference, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. Tributylmethylphosphonium dimethylphosphate was examined as a prototype tribo-improving additive. It improved the wear-preventing properties and friction reducing properties of tetracyanoborate salts by 10–25% and 20–30% at a concentration of 10 mM (620 ppm of phosphorus), respectively. The additive performances for tricyanomethanide salt and the imidazole-trialkylborane complexes were not uniform under these conditions. Boron oxide and iron oxides were found by surface analysis of rubbed surfaces with tetracyanoborate salts.
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| 19. |
- Nyberg, Erik, 1986-, et al.
(author)
-
Additive Technology for Halogen-free Room Temperature Ionic Liquids
- 2016
-
In: STLE 2016 Annual Meeting and Exhibition, 2016. - Las Vegas, NV, USA.
-
Conference paper (peer-reviewed)abstract
- Room temperature ionic liquids (RTIL) are increasingly being studied as advanced lubricants due to inherent properties such as thermal stability, low volatility, and non-flammability. While traditional lubricants are being optimized by additive technology, researched RTILs have generally been additive-free due to a lack of miscible additives. Recently, new RTILs have been designed for improved solvency of synthetic lubricant additives. In this work, RTIL samples based on tetralkylphosphonium cations have been evaluated. They are halogen-free and hydrophobic to minimize corrosion. Five RTILs were evaluated in a steel-steel tribotest where the results showed excellent tribological performance for RTILs with friction modifying and anti-wear additives designed for synthetic lubricants. These novel RTILs combined with additives demonstrate high potential as advanced lubricants due to their persistent nature in combination with excellent tribological performance.
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| 20. |
- Nyberg, Erik, 1986-, et al.
(author)
-
Additives to Improve Tribological Properties of Ionic Liquid as Base Fluids
- 2017
-
Conference paper (peer-reviewed)abstract
- Room temperature ionic liquids (RTILs) have several properties which make them interesting candidates as base fluids for extreme conditions. However, a lack of compatibility with tribo-improving additives combined with an often overly aggressive nature is limiting their use as base fluids. To overcome these drawbacks, hydrocarbon-imitating RTIL base fluids have recently been developed. These lubricants aim for a more balanced interaction with metal surfaces while enabling compatibility with common additives, so that the reactivity with the lubricated surface can be tuned in a manner similar to hydrocarbon base oil–additive systems. In this work, the effects of several common additives in the novel RTIL were examined by laboratory tribotesting. Surface analysis was performed in order to study the lubrication mechanisms.
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| 21. |
- Nyberg, Erik, 1986-, et al.
(author)
-
Boundary Film Formation from Hydrocarbon-mimicking Ionic Liquids
- 2017
-
Conference paper (peer-reviewed)abstract
- Ionic liquids have properties that are very useful in high performance lubricants. However, they must be well tuned to the tribological system. Hydrocarbon-mimicking ionic liquids have been developed in an effort to overcome some of the compatibility problems that are holding back the use of ionic liquids in tribology. In this work, hydrocarbon-mimicking ionic liquids are evaluated as base fluids in steel-steel reciprocating tribotests. Wear and friction reducing boundary films are formed and found to be composed mainly of Si and O. An amine additive is found to stimulate the formation of this boundary film.
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| 22. |
- Nyberg, Erik, 1986-, et al.
(author)
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Boundary Film Formation of P-SiSO in Reduced Oxygen Atmosphere
- 2018
-
In: NORDTRIB 2018. - Uppsala.
-
Conference paper (peer-reviewed)abstract
- Modern space exploration missions, such as planetary exploration of Mars, have significantly different tribological concerns compared to conditions faced by mechanical devices in satellites. Space lubricants have traditionally implied extremely low vapor pressure, but limited performance in boundary lubrication. Mars devices on the other hand are subjected to heavier loads, while operating in an atmosphere composed of CO2 at <1 kPa. Ionic liquids are synthetic fluids with inherently low vapor pressure that are known to readily form boundary films under severe conditions. In an effort to improve the tribological performance of ILs, hydrocarbon-mimicking ionic liquids have recently been designed. This recent work has displayed significantly improved lubrication performance for steel – steel tribo-systems in air, compared to PFPEs or fluorine-based ILs. Also, as a consequence of the hydrocarbon-mimicking structure, compatibility with several conventional tribo-improving additives have been displayed. In this work, we evaluate these novel fluids in a reduced oxygen environment under boundary lubricated conditions to evaluate the effect of oxygen supply on boundary film formation.
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| 23. |
- Nyberg, Erik, 1986-, et al.
(author)
-
Formation of Boundary Film from Ionic Liquids Enhanced by Additives
- 2017
-
In: Applied Sciences. - Basel : MDPI. - 2076-3417. ; 7:5
-
Journal article (peer-reviewed)abstract
- Room temperature ionic liquids (RTILs) have several properties that make them interesting candidates as base fluids for extreme conditions. However, a lack of compatibility with tribo-improving additives combined with an often overly aggressive nature is limiting their use as base fluids. To overcome these drawbacks, hydrocarbon-imitating RTIL base fluids have recently been developed. In this study, the effects of several common additives in the novel RTIL (P-SiSO) were examined by laboratory tribotesting. A reciprocating steel-steel ball-on-flat setup in an air atmosphere was used, where the lubricant performance was evaluated over a range of loads and temperatures. Surface analyses after testing were carried out using optical profilometry, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Neat P-SiSO displayed high performance in the tribotests. At an elevated load and temperature, a shift in lubrication mode was observed with an accompanying increase in friction and wear. Surface analysis revealed a boundary film rich in Si and O in the primary lubrication mode, while P was detected after a shift to the secondary lubrication mode. An amine additive was effective in reducing wear and friction under harsh conditions. The amine was determined to increase formation of the protective Si–O film, presumably by enhancing the anion activity.
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| 24. |
- Nyberg, Erik, 1986-, et al.
(author)
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Improvement in the Tribological Performance of Room Temperature Ionic Liquids by Additive Technology
- 2016
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In: Nordic Symposium on Tribology - NORDTRIB 2016. - Hämeenlinna, Finland.
-
Conference paper (peer-reviewed)abstract
- Room temperature ionic liquids (RTILs) have interesting properties such as thermal stability, low volatility, and non-flammability. Most research on RTIL lubricants regard RTILs composed of fluorine-containing anions. In metal-metal contacts, these fluids form boundary films of iron fluoride which reduces friction and wear to some extent, but on the other hand cause corrosion under humid conditions. Additives are one way of improving RTIL performance, however; most additives are designed for conventional petroleum base oils, and are therefore hardly miscible with RTILs. In order to improve the performance of RTILs, halogen-free and additive compatible RTILs have recently been developed as potential base oils for advanced lubricants. In this work, RTILs based on phosphonium cations and silylalkyl-sulfonate anions have been evaluated. These fluids are halogen-free and hydrophobic, showing good results in Cu-corrosion testing. Five RTILs, prepared from different anion-cation combinations, were evaluated in steel-steel tribotest. Compared as neat fluids, the RTILs performed superior to perfluoropolyether (PFPE) -based reference lubricant in terms of wear and friction reduction. In the attached figure, it can be seen that the mean friction coefficient is significantly lower for the neat RTIL samples at both 100 and 150 N. Regarding wear volume; the results show that the investigated RTILs produce better protection against wear and are robust to increased load. The tribological performance of RTILs is further improved when adding friction modifying and anti-wear agents designed for synthetic lubricants. This excellent tribological performance, in combination with the inherently persistent nature of ionic liquids demonstrates the high potential as advanced lubricants for these novel RTILs.
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| 25. |
- Nyberg, Erik, 1986-, et al.
(author)
-
Influence of atmosphere on boundary film formation from ionic liquids
- 2018
-
Conference paper (peer-reviewed)abstract
- Modern space exploration missions, such as planetary exploration of Mars, have significantly different tribological concerns compared to conditions faced by mechanical devices in satellites. Space lubricants have traditionally implied extremely low vapor pressure, but limited performance in boundary lubrication. Mars devices on the other hand are subjected to heavier loads, while operating in an atmosphere composed of CO2 at <1 kPa. Ionic liquids are synthetic fluids with inherently low vapor pressure that are known to readily form boundary films under severe conditions. In our recent work, an ionic liquid designed as lubricant base fluid formed highly effective boundary films composed of silicate when evaluated in air. These boundary films include oxygen, which can possibly be supplied by the atmosphere or by the lubricant itself. In this work, we employ tribotesting in CO2, and N2, and perform surface analysis to evaluate the effect of oxygen supply on boundary film formation.
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| 26. |
- Nyberg, Erik, 1986-
(author)
-
Ionic Liquid Lubricants for Space Applications
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- Lubrication is critical to the efficient and reliable operation of machine elements such as gears, bearings, or any other moving mechanical assembly (MMA). On Earth, machine designers are accustomed to the access of a wide range of liquid lubricants that enable predictable and reliable long-term operations of high performance MMA. In space applications on the other hand, engineers are constrained to a comparatively limited choice of lubricant candidates that can meet the stringent demands of tribosystems operating in a space environment. At the same time, repair or maintenance are seldom options that are possible in space, and consequently lubricant failures are potentially critical. As international space agencies are converging on the goal of establishing a permanently crewed lunar Gateway for human presence on the Moon and eventually onwards to Mars, there is a need for radical improvements in many aspects of space exploration technology, including space tribology and space grade lubricants. Liquid lubricants are enablers of high performance. A thin fluid film – even in the submicron scale – is often sufficient to separate opposing surface boundaries from direct contact, and thereby prevent excessive friction and wear. Liquid lubricants are therefore attractive for use in space mechanisms. Unfortunately, liquid lubricants must overcome several issues in order to be effective in the space environment. Vacuum, microgravity, and low temperatures are all factors that oppose the effective supply of liquid lubricants into the tribological contact of MMA. If the tribological contact becomes starved of oil, the surfaces enter the boundary lubrication regime where seizure is an ever-present threat. There are very few types of fluids available that meet the stringent space grade lubricant requirements. Perfluoropolyalkylethers (PFPE), or multiply alkylated cyclopentanes (MAC) are two fluids with significant heritage in space applications. These fluids are currently employed as lubricants in a wide range of space applications, as they are rare examples of fluids that meet the high demands on resistance to vacuum outgassing. Unfortunately, these compounds are susceptible to degradation under boundary lubrication conditions, and unlike conventional lubricants employed on Earth, these fluids have poor compatibility with the boundary lubrication additives that are commonly employed in conventional oils. Ionic liquids (ILs) have emerged as potential liquid lubricant candidates in space. These synthetic fluids are composed of anions and cations. The resulting ionic interaction enables the substance to have low vapor pressure with relatively low molecular weight. For this reason, ILs have been advocated as one of the candidate lubricants for space applications. When employing ILs as lubricants, the ionic charge provides Coulombic interaction with surfaces to enable the formation of a boundary lubricating film. This is an important part of the IL lubricating mechanism, but successful lubricant performance requires integrating the lubricant candidate into the tribosystem, taking into account operating conditions and environment. Therefore, the boundary film formation should be tunable to the application at hand. Ionic liquids are designable fluids, with properties dependent on the combination of anion and cation as well as incorporated functional groups. Based on this background, this work focused on evaluating the feasibility of employing ionic liquid lubricants for space applications. In this thesis, the molecular design of an IL lubricant was described Paper [1], and the resulting hydrocarbon-mimicking ionic liquid (P-SiSO) was evaluated in tribological experiments in boundary lubricated conditions. Boundary film formation by neat P-SiSO was studied in Paper [2], and in Paper [3] we describe the use of P-SiSO as a multipurpose performance ingredient in MAC. A test methodology was devised in Paper [4] in order to evaluate the lubrication performance under component scale experiments in space relevant conditions. The designed ionic liquid lubricant was evaluated in Paper [5] by the specific methodology. Advanced surface analysis was employed to understand the tribo-mechanism of P-SiSO in both the model scale experiments as well as the component scale. The lubricated surfaces were analyzed in terms of surface topography- and chemistry, and mechanisms of lubrication are discussed. A highly effective boundary film based on ionic adsorption and formation of silicate was observed by these ionic liquids. This thesis demonstrates the feasibility of employing ionic liquids for lubrication of moving mechanical assemblies in space applications.
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| 27. |
- Nyberg, Erik, 1986-, et al.
(author)
-
Ionic Liquids as Performance Ingredients in Space Lubricants
- 2021
-
In: Molecules. - Switzerland : MDPI. - 1431-5157 .- 1420-3049. ; 26:4
-
Journal article (peer-reviewed)abstract
- Low vapor pressure and several other outstanding properties make room-temperature ionic liquids attractive candidates as lubricants for machine elements in space applications. Ensuring sufficient liquid lubricant supply under space conditions is challenging, and consequently, such tribological systems may operate in boundary lubrication conditions. Under such circumstances, effective lubrication requires the formation of adsorbed or chemically reacted boundary films to prevent excessive friction and wear. In this work, we evaluated hydrocarbon-mimicking ionic liquids, designated P-SiSO, as performance ingredients in multiply alkylated cyclopentane (MAC). The tribological properties under vacuum or various atmospheres (air, nitrogen, carbon dioxide) were measured and analyzed. Thermal vacuum outgassing and electric conductivity were meas- ured to evaluate ‘MAC & P-SiSO’ compatibility to the space environment, including the secondary effects of radiation. Heritage space lubricants—MAC and perfluoroalkyl polyethers (PFPE)—were employed as references. The results corroborate the beneficial lubricating performance of incorporating P-SiSO in MAC, under vacuum as well as under various atmospheres, and demonstrates the feasibility for use as a multifunctional additive in hydrocarbon base oils, for use in space exploration applications.
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| 28. |
- Nyberg, Erik, 1986-, et al.
(author)
-
Lubrication Concept Evaluated for Geared Actuators under Starved Conditions
- 2020
-
In: 45th Aerospace Mechanisms Symposium. - : National Aeronautics and Space Administration (NASA). ; , s. 255-260
-
Conference paper (peer-reviewed)abstract
- Lubricant starvation leads to the risk of a shift in the lubrication regime from (elasto)hydrodynamic towards boundary conditons. Effective tribofilm formation is essential to limit surface damages in these conditions, but additive technology for space-grade lubricants is lacking. This work evaluates the feasibility of a novel type of multifunctional ionic liquid lubricant, for use with multiply alkylated cyclopentane (MAC). Actuator gearboxes are operated under starved conditions in nitrogen atmosphere to evaluate the effectiveness of the tribofilm forming lubricant (designated P-SiSO). The effectiveness of P-SiSO was evaluated from macro to micro scale in both surface and sub-surface analysis by use of microscopy (optical, interferometric, SEM) and X-ray microtomography (XMT), and mechanisms of effective lubrication are discussed.
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| 29. |
- Nyberg, Erik, 1986-
(author)
-
Lubrication mechanism of hydrocarbon-mimicking ionic liquids
- 2017
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Licentiate thesis (other academic/artistic)abstract
- Lubrication is critical in order to achieve high efficiency and reliability of machine elements such as gears, bearings, and other moving mechanical assemblies (MMA). In space applications, tribological properties of lubricants are quickly growing more important. Traditional space systems such as satellites imply MMA such as gyroscopes, antenna pointing mechanisms, and solar array drives. These MMA operate in high vacuum (<10-5 Pa) under lightly loaded conditions. Modern space missions on the other hand, such as remotely operated vehicles used for in-situ Mars exploration relies on different types of MMA. In these robotic systems, electromechanical actuators are being used extensively to provide controlled motion. Gears and bearings in these actuators operate in an atmosphere mainly consisting of CO2 at ~10+3 Pa under heavily loaded contact conditions. In these conditions, the tribosystem is likely to operate in the boundary lubricated regime, with consequent risk of high friction and wear.High molecular weight fluids have significant heritage in space because of their low vapor pressure. They are currently employed as lubricants in a wide range of space applications, as they meet high demands on resistance to vacuum outgassing. Unfortunately, the large molecules are susceptible to degradation under heavy load.Ionic liquids (ILs) on the other hand, are synthetic fluids that consist entirely of ion pairs with opposing charge. The resulting ion bonds enable inherently low vapor pressure of the fluid without the need for a high molecular weight. For this reason ILs have been advocated as potential lubricants for space applications, but so far compatibility issues have hampered their use as lubricants. Countless IL variations are possible, and solutions are thus likely to exist. Constituent ions can be designed individually and combined in various configurations. However, the fundamental understanding of the lubricating mechanism of ionic liquids is still incomplete, and consequently the optimum molecular structure for IL lubricants remain unknown.In this thesis, a stepwise approach to molecular design of IL lubricants is described, and the resulting hydrocarbon-mimicking ionic liquids are evaluated in tribological experiments. In this thesis, the experiments focus on tribological performance, using steel-steel tribopairs in air environment under boundary lubrication (Paper I). Boundary film formation under a range of contact pressures and temperatures, is analyzed after tribotesting by optical profilometry, scanning electron microscopy (SEM), and energy dispersive X- iii ray spectroscopy (EDS) in Paper II. The analysis reveal formation of a highly effective boundary film based on silicate, that can be further enhanced by amine additives. This thesis demonstrates the feasibility of improving tribological performance of ionic liquids by molecular design.
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| 30. |
- Nyberg, Erik, 1986-, et al.
(author)
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Molecular design of advanced lubricant base fluids : hydrocarbon-mimicking ionic liquids
- 2017
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In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 7:11, s. 6364-6373
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Journal article (peer-reviewed)abstract
- This paper describes the molecular design and tribological evaluation of novel room-temperature ionic liquid (RTIL) lubricants{,} abbreviated as P-SiSOs. The RTILs are designed to mimic hydrocarbons{,} in order to ensure their compatibility with existing tribosystems as well as enable use of conventional additives. Steel-on-steel ball-on-flat reciprocating tribotests performed under atmospheric conditions show that the neat P-SiSOs exhibit favorable performances{,} resulting in friction and wear significantly lower than those in the case of the perfluoropolyether lubricants used as references. Tribotests performed at elevated loads and temperatures indicate the formation of friction-reducing boundary films of the neat P-SiSOs. The tribological performance of the P-SiSO is improved further by the incorporation of additives conventionally used in hydrocarbon oils. When used in a concentration of 5 wt%{,} the additives glycerol monooleate{,} dibenzyl disulfide{,} and oleylamine improve the tribological characteristics of P-SiSO. These results indicate that molecular-designed hydrocarbon-mimicking RTIL lubricants can exhibit suitable performances in the neat form and that their performances can be improved further by using conventional additives{,} as in the case of hydrocarbon base oil-additive systems.
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| 31. |
- Nyberg, Erik, 1986-, et al.
(author)
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Tribology in Space Robotic Actuators : Experimental Method for Evaluation and Analysis of Gearboxes
- 2021
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In: Aerospace. - : MDPI. - 2226-4310 .- 2226-4310. ; 8:3
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Journal article (peer-reviewed)abstract
- Liquid lubricants are critical to enable long-life operation of high-performance machinery, such as geared actuators employed in robotics. In space applications, actuator gearboxes must operate in low temperatures, where liquid lubricants face inherent problems related to low temperature rheology. Heaters are relied upon to provide acceptable gearbox temperatures. Unfortunately, heating is energy-intense and does not scale well with increasing mechanism mass and performance. Effective boundary lubrication (BL), on the other hand, can minimize problems of low temperature rheology. BL relies on tribofilm formation over conventional fluid film separation. Effective space grade boundary lubricants can potentially allow for drastically reduced amounts of oil and the accompanying rheological problems. In this work, we describe the design of a methodology to evaluate and analyze tribology of actuator gearboxes operated under cryogenic oil-starved conditions in N2 atmosphere. The devised methodology enables research pertinent to space actuator tribology by accelerated testing and advanced analysis, as demonstrated by a lubricant candidate case study. Complementary microscopy techniques are discussed, and a novel methodology devised for gear internal microstructure analysis by X-ray microtomography (XMT) is presented.
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| 32. |
- Pettersson, Anders, et al.
(author)
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Additives for environmentally adapted lubricants : tribo film formation
- 2008
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In: Tribology Online. - : Japanese Society of Tribologists. - 1881-2198. ; 3:3, s. 168-172
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Journal article (peer-reviewed)abstract
- Five different anti-wear additives, suitable to formulate environmentally adapted hydraulic fluids, were tested. The used base fluid was a saturated, environmentally adapted synthetic complex ester. The tested materials were steel-steel and bronze-steel. A modified Falex pin and a vee-block tester were used for the tribotests. XPS was used to characterize the surfaces. It was found that the new types of more polar additives work better than the traditional ones, though they can give selective transfer of cupper to the steel pin. To use this type of additives in fully formulated products more investigations have to be performed.
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| 33. |
- Pettersson, Anders, et al.
(author)
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Additives för environmentally adapted lubricants : friction and wear protection
- 2008
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In: Tribology Online. - : Japanese Society of Tribologists. - 1881-2198. ; 3:3, s. 163-167
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Journal article (peer-reviewed)abstract
- Five different anti-wear additives, suitable for the formulation of environmentally adapted hydraulic fluids were tested, both commercially available and newly developed. The used base fluid was a high performance saturated complex ester. The formulated fluids' performance was evaluated through the use of an assembled pin & vee block in a modified Falex wear tester according to wear and frictional behaviour. The combinations of tested materials were steel-steel and bronze-steel tribopairs. The friction, wear scar volume and visual appearance both inside and outside the wear scar were studied. Some of the tested combinations gave unwanted performance, such as high friction, large wear and etching damages, whereas others gave good performance. It was found that the new additives showed promising results for formulation of environmentally adapted lubricants based on saturated complex esters. Further investigations will look closer at the chemical composition of the formed tribofilms with the use of surface sensitive analysis technology.
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| 34. |
- Pirker, Franz, et al.
(author)
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Tribological Characterisation Services for Materials – i-TRIBOMAT
- 2020
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In: Tribologie und Schmierungstechnik. - : Expert Verlag. - 0724-3472. ; 67:5-6, s. 35-50
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Journal article (peer-reviewed)abstract
- Um den Entwicklungsprozess von neuen Komponenten zu beschleunigen, ist die Vorrausage der Eigenschaften der eingesetzten Werkstoffe im Betrieb der Komponenten von enormer Bedeutung. Um neue Werkstoffe hinsichtlich Ihrer Performance (in einer Komponente) bewerten zu können, ist deshalb die Entwicklung neuer innovativer Methoden notwendig. Diese Methoden können auch unter dem Begriff „lab-to-field“ oder „materials“ – up-scaling zusammengefasst werden. D. h. Werkstoffe werden im Labor charakterisiert, und deren Eigenschaften mittels z.B. Simulation auf die Komponentenperformance hochskaliert (upscaling). i-TRIBOMAT ist ein EU gefördertes Projekt (H2020, GA Nr. 814494) mit dem Ziel ein Open Innovation Test Bed für tribologische Werkstoffcharakterisierung aufzubauen und ent-sprechende Services von der tribologischen Charakterisierung neuer Werkstoffe bis hin zu Simulationsmodellen zur Vorrausage der Perfomance von Komponenten der Industrie anzubieten. Durch die Bündelung von Knowhow und Infrastruktur zu Charakterisierung sowie den Aufbau einer digitalen Plattform, wird i-TRIBOMAT das weltgrößte Open Innovation Test Bed für tribologische Werkstoffcharakterisierung.
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| 35. |
- Rodríguez Ripoll, Mane, et al.
(author)
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Diallyl disulphide as natural organosulphur friction modifier via the in-situ tribo-chemical formation of tungsten disulphide
- 2018
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In: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 428, s. 659-668
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Journal article (peer-reviewed)abstract
- The present work shows a novel method for generating in-situ low friction tribofilms containing tungsten disulphide in lubricated contacts using diallyl disulphide as sulphur precursor. The approach relies on the tribo-chemical interaction between the diallyl disulphide and a surface containing embedded sub-micrometer tungsten carbide particles. The results show that upon sliding contact between diallyl disulphide and the tungsten-containing surface, the coefficient of friction drops to values below 0.05 after an induction period. The reason for the reduction in friction is due to tribo-chemical reactions that leads to the in-situ formation of a complex tribofilm that contains iron and tungsten components. X-ray photoelectron spectroscopy analyses indicate the presence of tungsten disulphide at the contact interface, thus justifying the low coefficient of friction achieved during the sliding experiments. It was proven that the low friction tribofilms can only be formed by the coexistence of tungsten and sulphur species, thus highlighting the synergy between diallyl disulphide and the tungsten-containing surface. The concept of functionalizing surfaces to react with specific additives opens up a wide range of possibilities, which allows tuning on-site surfaces to target additive interactions.
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| 36. |
- Rodríguez Ripoll, Manel, et al.
(author)
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Methionine as a Friction Modifier for Tungsten Carbide-Functionalized Surfaces via in Situ Tribo-Chemical Reactions
- 2017
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In: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 5:8, s. 7030-7039
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Journal article (peer-reviewed)abstract
- This work presents a novel method for generating in-situ low friction tribofilms in lubricated contacts using α-amino acid L-methionine as additive. Methionine is an environmentally acceptable natural organosulphur compound that is typically used in food industry. Our approach relies in the use of steel surfaces functionalized with tungsten carbide particles that are tailored to interact with methionine via a tribo-chemical reaction. The results show that after an induction period, the friction drops dramatically by 60% down to values of 0.06 when methionine was used as additive in lubricated tungsten carbide functionalized surfaces. The low friction could only be achieved by the coexistence of tungsten from the functionalized surfaces and sulphur from methionine, which led to the presence of tribo-chemically generated tribofilms. Ab-initio simulations indicate that the tribo-chemical reaction for forming tungsten disulphide is energetically favourable, thus attributing the observed friction reduction mechanism to the in-situ formation of this compound during the sliding process. The concept of functionalizing surfaces to react with specific additives opens up a wide range of possibilities, which allows tuning surfaces to target specific additive interactions. This synergy can be exploited for using novel green additive technology, thus allowing more environmentally friendly formulations with outstanding tribological performance.
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| 37. |
- Schnabel, Stephan, et al.
(author)
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Monitoring of Running-in of an EHL contact using Contact Impedance
- 2016
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In: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 63:3
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Journal article (peer-reviewed)abstract
- Running-in is an important process for elasto-hydrodynamic lubricated contacts, which affect both service life and operating performance. However, the possibilities of monitoring running-in are still poor. Therefore, the properties of electrical contact impedance as a monitoring tool were studied by using an in-house made ball on disc apparatus. The contact impedance was monitored during run-in experiments with different initial surface roughness of the discs, different slide-to-roll ratios and with pure or additive containing paraffinic oil. The relationship between surface roughness parameters, contact resistance and contact capacitance was investigated. While the contact resistance seems to be affected by the parameter Rz, the contact capacitance seems more dependent on Rq. In addition, the experiments showed that surface active additives do not necessarily need to influence the contact impedance.
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| 38. |
- Serrano, Noelia Saurin, et al.
(author)
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Study of the effect of tribo-materials and surface finish on the lubricant performance of new halogen-free room temperature ionic liquids
- 2016
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 366, s. 464-474
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Journal article (peer-reviewed)abstract
- The present work evaluates different materials and surface finish in the presence of newly designed, hydrophobic halogen-free room temperature ionic liquids (RTILs) as lubricants. A reciprocating tribo-tester was employed with steel-ceramic and steel-thermosetting epoxy resin contacts under boundary lubrication conditions. Four different tetraalkylphosphonium organosilanesulfonate RTILs provided excellent lubricating performance, with friction coefficients as low as 0.057, and non-measurable wear for the higher roughness machine-finish stainless steel flat against sapphire balls, in the case of the lubricants containing the 2-trimethylsilylethanesulfonate anion. Higher friction coefficients of the order of 0.1 and wear volumes of the order of 10-4 mm3, were observed for the lower roughness fine-finished flat stainless steel surface. All RTILs prevent wear of epoxy resin against stainless steel balls, with friction coefficients in the range of 0.03-0.06. EDX analysis shows the presence of RTILs on the stainless steel surfaces after the tribological tests. Under the experimental conditions, no corrosive processes were observed.
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| 39. |
- Shi, Yijun, et al.
(author)
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Boundary and elastohydrodynamic lubrication studies of glycerol aqueous solutions as green lubricants
- 2014
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In: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 69, s. 39-45
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Journal article (peer-reviewed)abstract
- In this paper, the boundary and elastohydrodynamic lubricating behaviour of glycerol and its aqueous solutions are discussed in both rolling and sliding contacts with a view on assessing the use of glycerol as a green lubricant. To understand the lubricating mechanism, the film thickness of glycerol and its aqueous solutions were studied at different velocities. The results show that the viscosity of glycerol can be controlled for a wide range by adding different amounts of water. The lubricating behaviour of glycerol in all lubricating regimes can be improved by adding water. The results suggest that glycerol aqueous solutions have great potential to replace rapeseed oils as environmentally friendly base oils in several applications.
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| 40. |
- Terashima, Kyu, et al.
(author)
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Synthesis and synthetic applications of (4-hydroxyphenyl)perfluoroalkylmethanols
- 2022
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In: Tetrahedron. - : Elsevier. - 0040-4020 .- 1464-5416. ; 104
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Journal article (peer-reviewed)abstract
- Development of the convenient method for the synthesis of (hydroxyphenyl)perfluoro-alkylmethanols was achieved by the Meerwein-Ponndorf-Verley (MPV) type reduction of the in situ-generated perfluoroalkylated ketones as the key step. The benzylic OH group of the resultant alcohols was successfully converted to H or Rf(CH2)nO by way of the corresponding chlorides, this transformation being not easy by any other methods.
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| 41. |
- Totolin, Vladimir, et al.
(author)
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Lubrication Mechanism of Phosphonium Phosphate Ionic Liquid Additive in Alkylborane-Imidazole Complexes
- 2014
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In: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 53:2, s. 421-432
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Journal article (peer-reviewed)abstract
- The assessment of ionic liquids (ILs) as lubricants in several tribological systems has shown their ability to provide remarkable reduced friction and protection against wear, whether they are used as additives or in the neat form. However, their corrosion and limited solubility in non-polar hydrocarbon oils represent the bottleneck-limiting factors for the use of ILs as lubricants. Therefore, in order to tackle these problems, mixtures of alkylborane-imidazole complexes with one halogen-free IL as additive were used in this study. The knowledge of the additive-surface interactions and hence the understanding of tribological properties are an important issue for lubricant formulations and were also investigated in this work. Thus, combination effects between two ionic liquid additives, a halogenated and a halogen-free one, were evaluated by a ball-on-disc-type tribometer under boundary lubrication conditions. Effective friction reduction and anti-wear properties have been demonstrated in tribological investigations when adding between 0.7 and 3.4 wt% of the halogen-free IL into base fluid composed of alkylborane-imidazole complexes. X-ray photoelectron spectroscopy analyses of the steel specimens were conducted to study the correlation between tribological properties and chemical surface composition of the boundary films formed on the rubbing surface. This work suggests potential applications for using halogen-free ILs as additives for synthetic ionic liquid lubricants
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| 42. |
- Totolin, Vladimir, et al.
(author)
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Tribochemistry and thermo-oxidative stability of halogen-free ionic liquids
- 2017
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In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 7:77, s. 48766-48776
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Journal article (peer-reviewed)abstract
- Heat generation by friction during machine operation causes thermo-oxidative degradation and evaporation of lubricants which in turn generates volatiles. Therefore, having an excellent thermo-oxidative stability is one of the desired prerequisites for the applicability of lubricants in tribological systems. This study reports new insights regarding the thermo-oxidative stability of halogen-free room-temperature ionic liquids (RTILs) as well as fundamental changes in the tribofilm's composition that have a positive impact on their tribological performance at elevated temperatures. In this context, the formation of binary iron phosphates/phosphides based tribofilms from a phosphonium phosphate-based RTIL has been reported for the first time. This RTIL significantly enhances both thermo-oxidative stability and tribological performance of alkylborane–imidazole complexes. A beneficial effect between this RTIL and a conventional friction modifier led to enhanced anti-wear properties supported by the presence of iron phosphide/phosphate tribofilms on the disc surfaces, as detected by XPS.
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| 43. |
- Yazawa, Shuichiro, et al.
(author)
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Reducing Friction and Wear of Tribological Systems through Hybrid Tribofilm Consisting of Coating and Lubricants
- 2014
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In: Lubricants. - : MDPI AG. - 2075-4442. ; 2, s. 90-112
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Journal article (peer-reviewed)abstract
- The role of surface protective additives becomes vital when operating conditionsbecome severe and moving components operate in a boundary lubrication regime. Afterprotecting film is slowly removed by rubbing, it can regenerate through the tribochemicalreaction of the additives at the contact. However, there are limitations about theregeneration of the protecting film when additives are totally consumed. On the other hand,there are a lot of hard coatings to protect the steel surface from wear. These can enable thefunctioning of tribological systems, even in adverse lubrication conditions. However, hardcoatings usually make the friction coefficient higher, because of their high interfacial shearstrength. Amongst hard coatings, diamond-like carbon (DLC) is widely used, because of itsrelatively low friction and superior wear resistance. In practice, conventional lubricantsthat are essentially formulated for a steel/steel surface are still used for lubricating machinecomponent surfaces provided with protective coatings, such as DLCs, despite the fact thatthe surface properties of coatings are quite different from those of steel. It is thereforeimportant that the design of additive molecules and their interaction with coatingsshould be re-considered. The main aim of this paper is to discuss the DLC and theadditive combination that enable tribofilm formation and effective lubrication oftribological systems.
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