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Bermudez M.D.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica | Carrion F.J.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica | Espejo C.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica | Martinez-Lopez E.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica | Sanes J.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica
Applied Surface Science | Year: 2011

Single-walled carbon nanotubes (NTs) and single-walled carbon nanotubes modified (NTms) by the room-temperature ionic liquid (IL) 1-octyl, 3-methylimidazolium tetrafluoroborate ([OMIM]BF 4) were added in a 1 wt.% to polystyrene (PS) and processed by compression or injection moulding to obtain PS + NT and PS + NTm, respectively. Friction coefficients and abrasive wear from penetration depth, residual depth and viscoelastic recovery were determined under multiple scratching. The effect of the moulding process, the additives and the sliding direction was studied. Compression moulded PS shows a transition to more severe damage after a critical number of successive passes. Addition of NTs or NTms to compression moulded PS induces a strain hardening effect and reduces friction, residual depth and viscoelastic recovery. Strain hardening is also observed in injection moulded PS with sliding in the longitudinal and random directions, but not in the transverse direction. The scratch resistance of PS + NTm depends on sliding direction. The lowest friction coefficient and residual depth values, and the highest viscoelastic recovery were found for injection moulded PS + NTm, in the sliding direction parallel to injection flow. Mechanisms of surface damage are discussed upon scanning electron microscopy (SEM), focused ion beam-field emission scanning electron microscopy (FIB-FESEM), 3D surface topography, surface roughness and profilometry observations. © 2011 Elsevier B.V. All rights reserved.

Jimenez A.E.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica | Bermudez M.D.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica
Tribology Letters | Year: 2010

The tribological behaviour and surface interactions of Ti6Al4V sliding against AISI 52100 steel have been studied in the presence of three commercial methylimidazolium (mim) room-temperature ionic liquids (ILs) containing the same anion, bis(trifluoromethylsulfonyl)amide, [(CF 3SO 2) 2N] (Tf 2N), and cations with increasing alkyl chain length, 1-ethyl-3-methylimidazolium [C 2mim], 1-butyl-3- methylimidazolium [C 4mim] and 1-octyl-3-methylimidazolium [C 8mim]. Increasing alkyl chain length increases viscosity whilst reducing the onset temperature for thermal degradation in air, the surface tension and the molecular polarity of the ILs. At room temperature, the tribological performance of the three ILs has been compared with that of a mineral oil (MO). The results show the reduction of the running-in period for the ILs with respect to the MO. In contrast with previously described results for IL lubrication, wear rates for Ti6Al4V at room temperature increase as the alkyl chain length of the ILs increases. The maximum wear reduction, of a 39%, with respect to MO is obtained for the [C 2mim] cation, with only two carbon atoms on the lateral chain. This was the IL selected for the tests at 100 °C. At this temperature, the reduction of the mean friction coefficient with respect to the MO is higher than 50%, whilst the wear rate of Ti6Al4V is reduced by 78%. The friction-sliding distance records for the IL at 100 °C show sharp transitions, related to formation of wear debris and surface interactions between the Tf 2N anion and the aluminium present in the Ti6Al4V alloy. Surface tribolayers and wear debris have been studied by SEM-EDX observations and XPS analysis. © 2010 Springer Science+Business Media, LLC.

Espinosa T.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica | Sanes J.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica | Jimenez A.-E.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica | Bermudez M.-D.,Grupo de Ciencia de Materiales e Ingenieria Metalurgica
Applied Surface Science | Year: 2013

In order to select possible candidates for use as lubricants or as precursors of surface coatings, the corrosion and surface interactions of oxygen-free high conductivity (OFHC) copper with two new protic (PIL) and four aprotic (APIL) room-temperature ionic liquids have been studied. The PILs, with no heteroatoms in their composition, are the triprotic di[(2-hydroxyethyl) ammonium] succinate (MSu) and the diprotic di[bis-(2-hydroxyethyl)ammonium] adipate (DAd). The four APILs contain imidazolium cations with short or long alkyl chain substituents and reactive anions: 1-ethyl-3-methylimidazolium phosphonate ([EMIM]EtPO3H); 1-ethyl-3-methylimidazolium octylsulfate ([EMIM]C8H17SO4); 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM]BF4) and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6). Contact angles between the ionic liquids and OFHC copper surface were measured. Mass and roughness changes of OFHC copper after 168 h in contact with the ionic liquids have been determined. Copper surfaces were studied by XRD, SEM-EDX and XPS surface analysis. FTIR spectra of the liquid phases recovered after being in contact with the copper surface were compared with that of the neat ionic liquids. The lowest corrosion rate is observed for the diprotic ammonium adipate PIL (DAd), which gives low mass and surface roughness changes and forms adsorbed layers on copper, while the triprotic ammonium succinate salt (MSu) produces a severe corrosive attack by reaction with copper to form a blue crystalline solid, which has been characterized by FTIR and thermal analysis (TGA). All imidazolium APILs react with copper, with different results as a function of the anion. As expected, [EMIM]C8H17SO4 reacts with copper to form the corresponding copper sulphate salt. [EMIM]EtPO3H produces severe corrosion to form a phosphonate-copper soluble phase. [HMIM]BF4 gives rise to the highest roughness increase of the copper surface. [HMIM]PF 6 shows the lowest mass and roughness changes of the four imidazolium ionic liquids due to the formation of a solid layer containing phosphorus and fluorine. The results described in the present study are in agreement with the outstanding good tribological performance of the diprotic ammonium adipate (DAd) ionic liquid for the copper-copper contact, in pin-on-disc tests, preventing wear and giving a very low friction coefficient of 0.01. Under the same conditions, [HMIM]PF6 gives a friction value of 0.03, while the reactivity of MSu towards copper produces maximum friction peaks of 0.05. In contrast with the absence of surface damage on copper, an abrasive wear mechanism is observed for MSu and [HMIM]PF6. The results confirm a better lubricating performance for a lower corrosion rate. © 2013 Elsevier B.V. All rights reserved.

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