Development of a vacuum-compatible hydrodynamic spindle using an ionic liquid as a lubricant

The importance of beam machining and extreme ultraviolet lithography technologies in the area of precise and fine machining used for high-density optical discs, integrated circuits and patterned media of hard disc drives (HDDs) is rapidly increasing.In this paper, a very simple vacuum-compatible rotary spindle is proposed that uses an ionic liquid as a lubricant with a very low vapor pressure. The usefulness of the proposed spindle lubricated by an ionic liquid was experimentally confirmed by measuring the partial pressures of outgassed products during rotation of the spindle in the vacuum chamber, measuring the accuracy of movement of the rotary table and machining circular grooves by an electron beam in a scanning electron microscope (SEM). It was found that the proposed spindle could be used in vacuum, and the partial pressures of outgassed products were almost the same as those of a clean, empty vacuum chamber. In addition, it was confirmed that by using the proposed spindle, circular grooves with diameters of 200 and 400 μm, 450 nm width and 40 nm depth could be machined on a photoresist surface coated on a silicon wafer in vacuum of an SEM.     

Influence of ionic structure on tribological properties of poly(dimethylsiloxane–alkylene oxide) graft copolymers

Lubricants based on ionic liquid (IL) modified poly(dimethylsiloxane–alkylene oxide) graft co-polymers (GC) were synthesised by condensation of hydroxyalkyl groups linked to GC chains and to IL moieties. The tribological performances of neat and IL-modified co-polymers were investigated in reciprocating steel–steel and in rotating steel–PTFE contacts at 30 and 100 °C. A clear dependence of friction and wear on temperature was observed for both neat and IL-modified co-polymers. Generally, friction decreased at higher temperature, especially pronounced for neat co-polymers. Neat as well as IL-modified co-polymers tend to increase wear at elevated temperature. At 30 °C, the IL-modified co-polymers exhibited significantly improved anti-wear properties when compared to neat co-polymers with bis(trifluoromethylsulfonyl)amide anion being the crucial moiety involved in tribochemical reactions.     

Electrochemical determination of sulfite and phenol using a carbon paste electrode modified with ionic liquids and graphene nanosheets: Application to determination of sulfite and phenol in real samples

Benzoylferrocene was used to construct a modified-graphene paste electrode. Also, hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) was used as a binder to prepare the modified electrode. The electro-oxidation of sulfite at the surface of the modified electrode was studied using electrochemical approaches. This modified electrode offers a considerable improvement in voltammetric sensitivity toward sulfite, compared to the bare electrode. Square wave voltammetry (SWV) exhibits a linear dynamic range from 5.0 × 10⁻⁸ to 2.5 × 10⁻⁴ M and a detection limit of 20.0 nM for sulfite. The diffusion coefficient and kinetic parameters (such as electron transfer coefficient and the heterogeneous rate constant) for sulfite oxidation were also determined. The prepared modified electrode exhibits a very good resolution between the voltammetric peaks of sulfite and phenol that makes it suitable for the detection of sulfite in the presence of phenol in real samples.     

Potential step study of electrooxidation of methanol in 1-butyl-3-methylimidazolium tetrafluoroborate

A potential step method was used to characterize the electrooxidation of methanol on a chemically modified electrode in an ionic liquid solvent. Two major findings were reported from this study. Firstly, the oxidation was dominant 2.2 s after the potential step. Before that, the double layer charging and adsorption were dominant. Therefore, there should be a waiting time of a few seconds if a methanol sensor is developed with a potential step method. Secondly, the oxidation of methanol on the electrode was diffusion controlled. The concentration of methanol affected the diffusion. The diffusion constant D₀ was 8.37 × 10⁻¹⁷ m²/s when the concentration was lower than 0.5 M and was 2.66 × 10⁻¹³ m²/s when the concentration was higher than 1.0 M. This suggests that the methanol concentration should be kept higher than a threshold in an ionic liquid based fuel cell.     

Nanocomposite polymer electrolyte based on rice starch/ionic liquid/TiO2 nanoparticles for solar cell application

Nanocomposite polymer electrolyte (NCPE) was prepared using solution cast technique. Rice starch (RS), lithium iodide (LiI), 1-methyl-3-propylimidazolium iodide (MPII) as ionic liquid and TiO₂ nanopowder (RS:LiI:MPII:TiO₂) were introduced to prepare the sample. The conductivity of 3.63 × 10⁻⁴ S/cm was achieved by introducing 30 wt.% of 1-methyl-3-propylimidazolium iodide (MPII) as ionic liquid and 2 wt.% of TiO₂. Temperature-dependent conductivity and dielectric behavior were analyzed in this work. Dye sensitized solar cell was fabricated using the nanocomposite film for this sample and analyzed.     

Fabrication of ionic liquid thin film by nano-inkjet printing method using atomic force microscope cantilever tip

We demonstrate the fabrication of thin films of ionic liquid (IL), 1-butyl-3-methyl-imidazolium tetrafluoborate, by nano-inkjet printing method using an atomic force microscope (AFM) cantilever. The IL filled in a pyramidal hollow of the AFM cantilever tip was extracted from an aperture at the bottom of the hollow and deposited onto a Pt substrate when the bias voltage was applied between the cantilever and the substrate. We succeeded in fabricating IL thin films with a thickness of 4 nm. The areas and thicknesses of IL thin films were controlled by the fabrication conditions in this method, which is also useful for the investigations of nanometer-scale properties of ionic liquid.     

1-N-alkyl -3-methylimidazolium ionic liquids as neat lubricants and lubricant additives in steel–aluminium contacts

The influence of the alkyl chain length and of the anion on the lubricating ability has been studied for the room-temperature ionic liquids (IL) 1-n-alkyl-3-methylimidazolium X⁻ [X = PF₆; n = 6 (L-P106). X = BF₄; n = 2 (L102), 6 (L106), 8 (L108). X = CF₃SO₃; n = 2 (L-T102). X = (4-CH3C6H4SO3); n = 2 (L-To102)]. Neat IL have been used for AISI 52100 steel-ASTM 2011 aluminium contacts in pin-on-disk tests under variable sliding speed. While all IL give initial friction values lower than 0.15, real-time sharp friction increments related to tribochemical processes have been observed for L102 and L-P106, at room-temperature and at 100 °C. Electronic microscopy (SEM), energy dispersive (EDS) and X-ray photoelectron (XPS) spectroscopies show that wear scar surfaces are oxidized to Al₂O₃ and wear debris contain aluminium and iron (for L102) fluorides. For L-P106, the steel surface is covered with a P-containing tribolayer. A change of anion (L-T102; L-To102) reduces friction and wear, but the lowest values are obtained by increasing the alkyl chain length (L106; L108). When the more reactive L102 and L-P106 are used as 1 wt.% base oil additives at 25 °C, tribocorrosion processes are not observed and a friction reduction (69–75% for 1 wt.% L102) and a change from severe (10⁻³ mm³ m⁻¹) to mild wear (10⁻⁴ to 10⁻⁶ mm³ m⁻¹) is obtained with respect to the neat IL. 1 wt.% IL additives also show good lubricating performance at 100 °C.     

Nano composite solid polymer electrolytes based on biodegradable polymers starch and poly vinyl alcohol

An attempt has been made to prepare nano composite solid polymer electrolytes by adding nano fumed silica in different weight ratios in a polymer matrix composed of biodegradable polymers Starch and Poly Vinyl Alcohol (PVA) to get high ionic conductivity with good mechanical strength. Fourier Transform InfraRed spectroscopy (FTIR) was used to confirm the complexation and interaction of the nano filler with the polymer matrix. From the FTIR investigations it could be established that the formation of COSi bonds by nano fumed SiO₂ with Starch and PVA lead to the crucial structural modification that finally increase the conductivity of the sample. Dielectric and frequency dependent measurements substantiate the sharp increase in number of charge carriers as the major factor contributing to the enhancement of the conductivity for 3 wt% nano fumed silica. Electric modulus studies confirmed the ionic nature and indicate absence of electrode polarization in the system. Maximum ionic conductivity ∼10⁻³ S/cm could be realized for 3 wt% silica at ambient condition.     

Thermo-oxidative stability and corrosion properties of ammonium based ionic liquids

Ionic liquids (ILs) as a novel and potential type of lubricants possess partly superior properties over traditional classes of lubricants. Their extremely low vapor pressure, generally high thermal stability and non-flammability suggest them for high performance applications. However, their tendency towards corrosiveness is neglected in general. The selection of three ILs was based on the aim to achieve relevant lubricant properties, in particular high oxidation stability and low corrosiveness, as well as high environmental benignity. The cations were in all cases ammonium based with and without functionalization. Bis(trifluoromethylsulfonyl)imide (NTF₂) was chosen as anion and has been replaced for one IL by methanesulfonate. Artificial aging was carried out to obtain knowledge about the lubricant long-term performance under both oxidative and humid conditions while being in contact with CuSn8P and 100Cr6 commonly used in tribology. For the evaluation of IL corrosion potential, the metal content in the IL was monitored by ICP-OES, metal specimens were examined optically and by SEM-EDX analysis. To find out the IL suitability for the long-term applications the thermo-oxidative stability of the IL has been analyzed by several mass spectrometric techniques. In this study, NTF₂ based IL - regardless of the cationic moiety - showed superior performance over methanesulfonate based IL under all conditions. In the case of 100Cr6, dry conditions lead to the lowest corrosion whereas CuSn8P caused the lowest corrosion under humid conditions. The degradation process based on thermally induced transmethylation of the IL investigated occurred only at the cationic moiety of methanesulfonate based IL This is based on mass spectrometric investigations and indicates a contribution to the enhanced corrosiveness by means of the IL reduced stability.     

Mechanism of tribofilm formation with P and S containing ionic liquids

Mechanism of tribofilm formation with two ionic liquids (IL), choline bis(2-ethylhexyl)phosphate and choline dibutyldithiophosphate was studied. XANES analysis of tribofilms indicates that the underlying mechanism of tribofilm formation with ionic liquids is similar to that formed when ZDDP is used. The chain length of glassy polyphosphates with IL in base oil is longer in length in comparison to that formed with ZDDP under identical conditions indicating a higher level of networking. In fully formulated oils, Ca replaces Zn and Fe (in the case of ZDDP) or Fe (when IL׳s are used) as the primary cationic species present in the polyphosphate network. The sulfur is present in the form of sulfates of different cationic species including Fe and Ca.     

Ionic Liquids as Novel Lubricants and Additives for Diesel Engine Applications

The lubricating properties of two ionic liquids (ILs) with the same anion but different cations, one ammonium IL [C₈H₁₇]₃NH.Tf₂N and one imidazolium IL C₁₀mim.Tf₂N, were evaluated both in neat form and as oil additives. Experiments were conducted using a standardized reciprocating sliding test with a segment of a Cr-plated diesel engine piston ring against a gray cast iron flat specimen. The cast iron surface was prepared with simulated honing marks as on a typical internal combustion engine cylinder liner. The selected ILs were benchmarked against conventional hydrocarbon oils. Substantial friction and wear reductions, up to 55% and 34%, respectively, were achieved for the neat ILs compared to a fully formulated 15W40 engine oil. Adding 5 vol% ILs into mineral oil has demonstrated significant improvement in the lubricity. One blend even outperformed the 15W40 engine oil with 9% lower friction and 34% less wear. Lubrication regime modeling, worn surface morphology examination, and surface chemical analysis were conducted to help understand the lubricating mechanisms for ILs. Results suggest great potential for using ionic liquids as base lubricants or lubricant additives for diesel engine applications.     

Nano/Microtribological Properties of Ultrathin Functionalized Imidazolium Wear-Resistant Ionic Liquid Films on Single Crystal Silicon

Ionic liquids (ILs) are considered as a new kind of lubricant for micro/nanoelectromechanical system (M/NEMS) due to their excellent thermal and electrical conductivity. However, so far, only few reports have investigated the tribological behavior of molecular thin films of various ILs. Evaluating the nanoscale tribological performance of ILs when applied as a few nanometers-thick film on a substrate is a critical step for their application in MEMS/NEMS devices. To this end, four kinds of ionic liquid carrying methyl, hydroxyl, nitrile, and carboxyl group were synthesized and these molecular thin films were prepared on single crystal silicon wafer by dip-coating method. Film thickness was determined by ellipsometric method. The chemical composition and morphology were characterized by the means of multi-technique X-ray photoelectron spectrometric analysis, and atomic force microscopic (AFM) analysis, respectively. The nano- and microtribological properties of the ionic liquid films were investigated. The morphologies of wear tracks of IL films were examined using a 3D non-contact interferometric microscope. The influence of temperature on friction and adhesion behavior at nanoscale, and the effect of sliding frequency and load on friction coefficient, load bearing capacity, and anti-wear durability at microscale were studied. Corresponding tribological mechanisms of IL films were investigated by AFM and ball-on-plane microtribotester. Friction reduction, adhesion resistance, and durability of IL films were dependent on their cation chemical structures, wettability, and ambient environment.     

Development and performance of a magnetic ionic liquid for use in vacuum-compatible non-contact seals

For the electron-beam machining of optical media, a very low rotational speed is required to enable the precise fabrication of grooves of various depths and widths. In addition, a lubricant with a very low vapour pressure, such as an ionic liquid, and a vacuum chamber are needed to avoid contamination of workpieces. Accordingly, the development of a vacuum-compatible hydrostatic bearing using an ionic liquid is required to satisfy these rotational conditions and nanometre-order machining accuracy. To use a hydrostatic bearing in a vacuum environment, a non-contact vacuum seal is needed to avoid leakage of the ionic liquid used as the lubricant. Furthermore, making a non-contact seal using an ionic liquid requires the development of a new type of magnetic ionic liquid. Therefore, this paper describes the development of such a magnetic ionic liquid, which consists of magnetite (Fe₃O₄) particles, a newly synthesized dispersant, and a pyridinium-based ionic liquid. The outgassed products from this magnetic ionic liquid were measured when it was applied to a non-contact seal in a vacuum of about 10⁻⁶ Pa. In addition, its mechanical properties, such as viscosity and burst pressure as a non-contact seal, were measured. From these investigations, it was found that the developed magnetic ionic liquid would meet the requirements for non-contact seals to be used in vacuum-compatible hydrostatic bearings.     

Tribological performances of two ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate) as nanolubricants on polyether-ether-ketone surface

This paper seeks to address the potential of using ionic liquids as nanolubricants on Polyether-ether-ketone (PEEK) surface. We characterize the tribological properties of two ionic liquids, namely1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate. The tribological data are compared with those of perfluoropolyether (PFPE) and Multiply Alkylated Cyclopentanes (MAC) data obtained from previous study. Ionic liquids at lower concentration of 0.4wt% (in solution prior to deposition) showed lower wear lives as compared to those for PFPE and MAC. However, at higher concentration of 4wt%, these ionic liquids have the same wear lives as those of PFPE and MAC, but show considerably lower coefficients of friction. Mechanisms of nanolubrication for ionic lubricants vis-a-vis those of PFPE and MAC are explained.     

Ionic liquids as lubricants of polystyrene and polyamide 6-steel contacts. Preparation and properties of new polymer-ionic liquid dispersions

Room-temperature ionic liquids (ILs) have been used as external lubricants in polystyrene (PS) and polyamide 6 (PA6)-steel contacts and as internal lubricants in new polymer-IL dispersions. 1−C _n H_2n+1−3−CH₃-imidazolium X⁻ [X=BF₄; n=2 (IL1), 6 (IL2), 8 (IL3). X=PF₆; n=6 (IL4). X=CF₃SO₃; n=2 (IL5). X=(4−CH₃C₆H₄SO₃); n=2 (IL6)] ionic liquids give low friction and extremely mild wear in PS/AISI 316L stainless steel contacts, independently of IL composition. For AISI 52100 steel pins a tribocorrosion reaction produces FeF₂ and increases friction. PS+IL1 (1; 1.35; 3 wt.% IL1) dispersions show lower dry friction and wear against AISI 52100 as IL1 proportion increases, but the lowest friction, with a one order of magnitude reduction with respect to PS, is reached for PS+1%IL1 once the skin layer has been worn out. Increasing IL1 content to 10 wt.% produces an heterogeneous material with non-uniform IL distribution. IL4 reduces friction and wear in PA6+3%IL4 dispersions against AISI 316L, although the lowest values are obtained with IL4 as external lubricant. The cryofracture surfaces of the polymers have been examined and the thermal stability of the polymers in the presence of ILs has been determined.     

Tribological properties of ultra-thin ionic liquid films on single-crystal silicon wafers with functionalized surfaces

Two kinds of room temperature ionic liquid (RTIL) films carrying vinyl and hydroxyl functional groups were prepared on single-crystal Si wafers by spin coating. The tribological properties of the RTIL films sliding against AISI-52100 steel ball and Si₃N₄ ball in a ball-on-plate configuration were investigated on a dynamic–static friction coefficient measurement apparatus, using perfluoropolyether (PFPE) film as a comparison. The tribological behaviors of the ionic liquid films sliding against the same counterparts at extended test durations were also evaluated using a universal UMT-2MT test rig. The morphologies of the wear tracks of the RTIL films and the counterparts were examined using a scanning electron microscope equipped with an energy-dispersive X-ray analyzer attachment. It was found that the tribological performances of the ionic liquid films were closely related to the chemical structures of the RTILs and the chemical characteristics of the substrate surfaces. The films of vinyl group functionalized ionic liquids on hydroxylated substrate and vinyl group modified substrate exhibited very good friction-reduction and wear-resistant properties. It was assumed that there were enough strong forces between the films and substrate in these cases, and the ionic liquid molecules maintained good flexibility simultaneously. The films on hydrogen-terminated and methyl-terminated substrate showed poor tribological performance, which could be related to the relatively weak forces between the films and substrates. Moreover, the films on hydroxylated substrate showed lower friction at higher sliding velocities, which was assumed to be governed by the more rapid adsorption of the ionic liquid molecules on the steel ball at a higher sliding velocity. In addition, the ionic liquid films also had excellent tribological properties as they slid against silicon nitride ball. Therefore, it was supposed that the ionic liquid films could be used as a kind of universal lubricant for various combinations of the frictional pair.     

Ionic liquids as a neat lubricant applied to steel–steel contacts

This paper studies the use of 3 ionic liquids ([(NEMM)MOE][FAP], [BMP][FAP] and [BMP][NTf₂]) as neat lubricant within steel–steel contact conditions. Tribological tests (at 40 and 100 °C) were conducted in a HFRR tribometer and hence a complementary study was developed using a MTM tribometer. The wear surface on the discs was measured after the HFRR tests by confocal microscopy and also analyzed by SEM and XPS. The [BMP][NTf₂] showed the lowest friction coefficient in the MTM and HFRR tests at 40 °C but at 100 °C its tribological behavior worsened due to its lowest viscosity. Similar results were found for wear behavior. Both antifriction and antiwear results were related to the tribofilms formation from the ECR and XPS measurements.     

Effect of Graphene and Ionic Liquid Additives on the Tribological Performance of Epoxy Resin

In the present study, we have determined the effect of graphene (PG), the ionic liquid (IL) and PG modified by mechanical blend with the IL 1-octyl-3-methylimidazolium tetrafluorobotate (IL + PG) on the tribological performance of epoxy resin (ER). IL + PG stable suspensions have been added to an epoxy resin (ER) matrix to obtain the new nanocomposite (ER + IL + PG), and its tribological performance has been compared with that of neat epoxy resin and with the nanocomposites containing PG (ER + PG) or IL (ER + IL). While neat ER presents a high dynamic friction coefficient of up to 0.31 and a severe wear with a specific wear rate of 8.1 × 10^?4 mm³ N^?1m^?1, the new nanocomposites show negligible surface damage, as determined by surface roughness and profilometry. All nanocomposites show low friction coefficients and negligible wear. The maximum friction reduction, up to a 70 %, is obtained for ER + PG. Results are discussed upon the basis of TEM microscopy, SEM microscopy and EDX analysis, differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical analysis. Addition of IL or IL + PG has a plasticizing effect on ER, while addition of PG increases the thermal stability and stiffness of ER. PG shifts the storage modulus onset and in the loss modulus and tan δ maximum peaks to higher temperatures, while a shift to lower values is observed with addition of IL or IL + PG.     

An ultra high-pressure test rig for measurements of small flow rates with different viscosities

Within the framework of a research project regarding investigations on a high-pressure Coriolis mass flow meter (CMF) a portable flow test rig for traceable calibration measurements of the flow rate (mass - and volume flow) in a range of 5 g min⁻¹ to 500 g min⁻¹ and in a pressure range of 0.1 MPa to 85 MPa was developed. The measurement principle of the flow test rig is based on the gravimetrical measuring procedure with flying-start-and-stop operating mode. Particular attention has been paid to the challenges of temperature stability during the measurements since the temperature has a direct influence on the viscosity and flow rate of the test medium. For that reason the pipes on the high-pressure side are double-walled and insulated and the device under test (DUT) has an enclosure with a separate temperature control. From the analysis of the first measurement with tap water at a temperature of 20 °C and a pressure of 82.7 MPa an extensive uncertainty analysis has been carried out. It was found that the diverter (mainly due to its asymmetric behaviour) is the largest influence factor on the total uncertainty budget. After a number of improvements, especially concerning the diverter, the flow test rig has currently an expanded measurement uncertainty of around 1.0% in the lower flow rate range (25 g min⁻¹) and 0.25% in the higher flow rate range (400 g min⁻¹) for the measurement of mass flow. Additional calibration measurements with the new, redesigned flow test rig and highly viscous base oils also indicated a good agreement with the theoretical behaviour of the flow meter according to the manufacturers׳ specifications with water as test medium. Further improvements are envisaged in the future in order to focus also on other areas of interest.     

Tribological Properties of Phosphor Bronze and Nanocrystalline Nickel Coatings Under PAO + MoDTC and Ionic Liquid Lubricated Condition

The friction and wear properties of phosphor bronze and nanocrystalline nickel coatings were evaluated using a reciprocating ball-on-plates UMT-2MT sliding tester lubricated with ionic liquid and poly-alpha-olefin containing molybdenum dialkyl dithiocarbamate, respectively. The morphologies of the worn surfaces for the phosphor bronze and nanocrystalline nickel coatings were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy. Results show that the phosphor bronze and nanocrystalline nickel coatings exhibited quite different tribological behaviors under different lubricants. Phosphor bronze plate shows higher friction coefficient (0.14) and wear rate (3.2 × 10⁻⁵ mm³/Nm) than nanocrystalline nickel coatings (average friction coefficient is 0.097, wear rate is 1.75 × 10⁻⁶ mm³/Nm) under poly-alpha-olefin containing molybdenum dialkyl dithiocarbamate lubricated conditions. The excellent tribological performance of nanocrystalline nickel coatings under above lubricant can be attributed to the formation of MoS₂ and MoO₃ on the sliding surface. a quite a number of C, O and F products on worn surface of phosphor bronze than NC nickel coatings can improve anti-wear properties while using ionic liquid as lubricant.