Josefa Fernández

Verified

Josefa verified their affiliation via an institutional email.

Learn more

Verified

Josefa verified their affiliation via an institutional email.

Learn more

• Applied Physics Professor
• Professor at University of Santiago de Compostela

The aim of this research is to analyze the thermophysical, wettability, and tribological properties of some base oils of different nature (synthetic and mineral), as well as of formulated oils, to find potential transmission oils for electrical vehicles. Regarding the thermophysical properties, viscosity, density, and viscosity index were analyzed....

In this work, the thermophysical properties of four mineral (paraffinic and naphthenic) and four synthetic (polyalphaolefin and ester) base oils are measured. Knowledge of these properties is of vital importance for the correct and optimal formulation and design of lubricants, and for the development of equations of state and transport models that...

This work presents the antifriction and antiwear properties of TiO2 nanoparticles coated with oleic acid, TiO2-OA, as additives of a low viscosity polyalphaolefin base oil, PAO8. To find the optimal concentration of nanoadditives that minimize friction and wear, four PAO8 based nanodispersions were formulated: PAO8 + 0.10 wt% TiO2-OA, PAO8 + 0.25 w...

This research reports the antifriction and antiwear properties of Mn3O4-Graphene nanocomposites (Mn3O4-G) as additives of a paraffinic base oil commonly used in the formulation of electric vehicles transmission oils, G-III base oil. Four G-III base oil nanodispersions have been designed, G-III base oil + 0.025 wt% Mn3O4-G, G-III base oil + 0.050 wt...

Lubrication usage is one of the most effective method of controlling friction and wear in mechanical equipment, and in order to improve the performance of such lubricants additives are added into them leading these oils to be able to meet the requirements of modern industry. Lubricant additives that mainly work as a multifunctional enhancer such as...

Two new highly viscous biodegradable oils are investigated for use in wind turbine gearboxes (BIO-G00) and in mechanical transmissions of agricultural tractors (BIO-G02). Studies on their thermophysical and tribological properties were performed. High-pressure-viscosity measurements were obtained up to 250 MPa and 363.15 K using a falling-body appa...

In the present work, lubrication properties (friction and wear) of a synthetic ester oil, tris(2-ethylhexyl) trimellitate (TOTM) containing ferrite nanoparticles coated with oleic acid (F3O4-OA) were investigated for two different material pairs: steel ball-steel disc and silicon nitride ball-steel disc. Thus, four TOTM nanolubricants were formulat...

In this work, ZnO nanoparticles (NPs) were successfully synthesized and coated with oleic acid (OA). The mean diameter of these NPs (ZnO-OA) was around 10 nm, their core was characterized by XRD and their coating by FTIR and Raman. Homogeneous dispersions at different concentrations (0.10, 0.25, 0.50, 0.75 and 1.00 wt%) of ZnO-OA in polyalphaolefin...

Tribological performance of polyalphaolefin 32, PAO, is investigated by adding two nanomaterials (graphene nanoplatelets, GnP, and hexagonal boron nitride nanoparticles, h-BN) and an ionic liquid ([P6,6,6,14][DEHP], IL1, [P2,4,4,4][DEP], IL2, or [P6,6,6,14][(iC8)2PO2], IL3). Designed double hybrid nanodispersions are PAO/1 wt% ILX/0.05 wt% GnP/0.1...

In the present work, antifriction and antiwear synergies of two functionalized graphene oxides (reduced graphene oxide, rGO, and reduced graphene oxide modified with octadecylamine, [email protected]) with a phosphonium ionic liquid (IL) as additives of a biodegradable ester base oil, BIOE, were investigated. For this aim, four BIOE nanodispersions...

Thermophysical properties of lubricants are important to understand which ones are appropriated for the industrial conditions expected. Thermophysical properties of two different families of lubricants were analysed: polyalphaolefins (PAO6, PAO20, PAO32 and PAO40) and four ester-based lubricants. Specific heat capacity, density, surface tension, an...

Antifriction synergies between an ionic liquid (IL) and nanopowders as additives of an ester base oil were analysed at rolling conditions. For this aim, two nanodispersions based on hybrid combinations of hexagonal boron nitride nanoparticles (h‐BN) or graphene nanoplatelets (GnP) with tri(butyl) ethylphosphonium diethylphosphate ionic liquid as ad...

Lubricant properties of trimethylolpropane trioleate synthetic base oil (TMPTO) were experimentally determined under different temperatures, pressures and rolling-sliding conditions. With the aim to obtain the viscosity-pressure coefficient, density and viscosity measurements were performed up to 150 MPa with a falling-body viscometer and a vibrati...

Tribological performance of three ionic liquids (ILs), trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate (IL1), tributylethylphosphonium diethylphosphate (IL2) and trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate (IL3) combined with graphene nanoplatelets (GnP) as hybrid additives for a polyalphaolefin (PAO 32) base oil wa...

In this work, antifriction and antiwear capabilities of hexagonal boron nitride nanoparticles (h-BN) or graphene nanoplatelets (GnP) as additives of a polyalphaolefin neat oil (PAO 40) were studied at pure sliding conditions. For this purpose, eight PAO 40 nanodispersions were prepared: four nanodispersions with h-BN and four others based on GnP. T...

Solid lipid microparticles (SLMPs) are attractive carriers as delivery systems as they are stable, easy to manufacture and can provide controlled release of bioactive agents and increase their efficacy and/or safety. Particles from Gas-Saturated Solutions (PGSS®) technique is a solvent-free technology to produce SLMPs, which involves the use of sup...

Recently graphene and other 2D materials were suggested as nano additives to enhance the performance of nanolubricants and reducing friction and wear-related failures in moving mechanical parts. Nevertheless, up to our knowledge there are not previous studies on electrochemical exfoliated nanomaterials as lubricant additives. In this work, engine o...

Development of nano-lubricants by the dispersion of nano-particles in current lubricants has contributed to improving energy efficiency reducing wear and friction. During the last two decades, ionic liquids have evolved as novel lubricants or lubricant additives, especially for high vacuum and high temperature. Nevertheless, the number of experimen...

Hybrid nanostructure combinations of ionic liquids (ILs) and hexagonal boron nitride (h-BN) nanosheets are proposed as additives to lubricants to enhance their tribological performance and their temporal stability. Trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate (IL1), tributylethylphosphonium diethylphosphate (IL2) and trihexyltetradecylp...

The main task of this work is to study the tribological performance of nanolubricants formed by trimethylolpropane trioleate (TMPTO) base oil with magnetic nanoparticles coated with oleic acid: Fe3O4 of two sizes 6.3 nm and 10 nm, and Nd alloy compound of 19 nm. Coated nanoparticles (NPs) were synthesized via chemical co-precipitation or thermal de...

In this work, the synergy between an ionic liquid (IL) and nanoparticles as additives of lubricants was studied. For this purpose, four dispersions based on graphene nanoplatelets, GnPs, or nanoparticles of hexagonal boron nitride, h-BN, with or without the IL tri(butyl) ethylphosphonium diethylphosphate in an ester type base oil, triisotridecyltri...

Dispersions based on hexagonal boron nitride, h-BN, nanoparticles, at 0.50, 0.75 and 1.0 wt.% mass concentrations, in an ester base oil composed mainly of trimethylolpropane trioleate, were investigated as potential nanolubricants. The stability of the dispersions was assessed to determine the reliability of the tribological, thermophysical and rhe...

This article presents a study on the viscous behaviour at high pressure of a synthetic oil, tris(2-ethylhexyl) trimellitate (TOTM). This fluid is being recommended as potential industrial reference material for high viscosity-high pressure measurements. Here we report new experimental viscosity values for TOTM at temperatures from 278.15 K to 373.1...

This article presents an experimental investigation on the effects of concentration and morphology of nanoadditives on the thermophysical properties of nanolubricants (NLs) at different temperatures. A polyalphaolefin (PAO6) oil was used as base fluid. A two-step method was used to prepare the NLs. Zirconium oxide (ZrO2) and boron nitride (BN) nano...

Convection heat transfer coefficients and pressure drops of four functionalized graphene nanoplatelet nanofluids based on the commercial coolant Havoline® XLC Pre-mixed 50/50 were experimentally determined to assess its thermal performance. The potential heat transfer enhancement produced by nanofluids could play an important role in increasing the...

The overheating of mechanical and electrical components in generators of wind turbines considerably reduces their overall performance. Consequently, their cooling systems usually need to dissipate large amounts of heat, leading to high electrical energy consumptions. These systems habitually use commercial industrial coolants as working fluids in o...

Measurements of viscosity and density of three lubricating oils (two synthetic and one mineral) were performed. The density of these lubricants was measured at atmospheric pressure by means of a density measuring cell which works on the proven principle of the oscillating tube. Using the same device, the viscosity of these lubricants was measured a...

The main goal of this work is to study the tribological properties of nanolubricants formed by trimethylolpropane trioleate (TMPTO) or a polyalphaolefin (PAO 40) base oils with reduced graphene oxide sheets (rGO). This reduction was carried out in order to have a good stability of the nanoadditives in the fluids. For this aim, rGO nanopowders were...

This paper presents the results of an investigation into possible liquid viscosity standards to meet an industrial requirement for a liquid with a nominal viscosity of 20 mPa s at a temperature of 473 K and pressure of 200 MPa with a relative expanded uncertainty of less than 5%. There are no commercially available certified viscosity reference liq...

Solubility of individual light fullerenes (C60 and C70) in n-heptane was measured in the ranges of pressure from 0.1 up to 110 MPa and temperature from 298.3 to 358.3 K. At 0.1 MPa, the solubility diagrams of the C60 – n-heptane, C70 – n-heptane binary systems consist of only one branch corresponding to crystallization of mono-solvated fullerenes –...

The objective of this work is to study the tribological and thermophysical properties of nanolubricants composed by a trimethylolpropane trioleate (TMPTO) oil, and graphene nanoplatelets (GnP). For this aim, nanolubricants based on TMPTO with 0.05, 0.10, 0.25 and 0.50 wt% of graphene nanoplatelets were prepared. The dependence on temperature and co...

Isobaric molar heat capacity (Cp) of eight ionic liquids (ILs) was measured from 283.15 K to 338.15 K with a micro DSC III calorimeter with a heating rate of 0.25 K·min⁻¹ using batch cells. Cp values were determined with an expanded uncertainty about 2%. Four of the selected ILs are imidazolium based with the anions hexylsulfate, trifluoromethanesu...

This article presents an experimental study on some thermophysical properties (density, viscosity and adiabatic bulk modulus) of six nanolubricants based on synthetic oils and ZrO2 nanoparticles. Two-step method with ultrasonic disruptor was used to prepare the nanodispersions. The morphology, crystalline degree and elemental composition of nanopar...

Using a Beckman thermometer, the concentration dependence of water crystallization temperatures was investigated for C60(OH)22–24 – H2O, C70(OH)12 – H2O, C70[C(COOH)2]3 – H2O, С60(C5H9NO3)2 - H2O, С60(C6H14N2O2)2 – H2O binary systems. The semi-empirical Virial Decomposition Asymmetric Model of virial expansion of the excess Gibbs energy of the ligh...

Reliable equations of state (EoS) together with heat capacities at atmospheric pressure make possible to determine properties as the isobaric thermal expansivity, compressibility, both isothermal and isentropic, high pressure isobaric heat capacities or speed of sound. In this work, we have analysed the reliability of two density scaling based EoS,...

This study presents new Nano-enhanced Phase Change Materials, NePCMs, formulated as dispersions of functionalized graphene nanoplatelets in a poly(ethylene glycol) with a mass-average molecular mass of 400 g·mol-1 for possible use in Thermal Energy Storage. Morphology, functionalization, purity, molecular mass and thermal stability of the graphene...

In this article the volumetric behaviour of the nanostructured liquids, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, is reported. Density was measured in the temperature range (278.15–398.15) K up to 120 MPa with a high pressure densimeter based on the vibrating tube prin...

Thermal stability of three ionic liquids (ILs) and five base stock lubricants was analysed using a Perkin Elmer thermogravimetric device and compared with that of the 19 ILs previously studied. The ILs are 1-(2-methoxyethyl)-1-methyl-pyrrolidinium tris(pentafluoroethyl)trifluorophosphate, [1-(2-methoxyethyl)-1-methyl-pyrrolidinium bis(trifluorometh...

Characterization of Elastohydrodynamic Lubrication, EHL, contacts requires an appropriate EoS for the lubricant. Experimental viscosities and speeds of sound of six lubricants from 278.15 to 398.15 K at 0.1 MPa together with densities up to 120 MPa are reported. Tammann-Tait and the two EoSs based on the scaling concept describe the experimental de...

Ionic liquids have been broadly studied in the past decade for being used as lubricants or lubricant additives. The rheological characterization of these fluids is very important in this context because it determines to a great extent their performance for different lubricants applications, such as hydraulic or gear lubricants. Thus, in this work w...

Solubility of light fullerenes (C60 and C70) in n-nonane was investigated in the ranges of pressure form 0.1 MPa up to 100 MPa and temperature from 298.3 K to 353.3 K. Under isothermal conditions, the solubility, expressed as weight fraction of the fullerene in the solution, increases monotonously with increasing pressure. At ambient pressure, we h...

This paper presents a reference correlation for the viscosity of tris(2-ethylhexyl) trimellitate designed to serve in industrial applications for the calibration of viscometers at elevated temperatures and pressures such as those encountered in the exploration of oil reservoirs and in lubrication. Tris(2-ethylhexyl) trimellitate has been examined w...

Thermal stability is an essential property to select the most suitable compounds for applications as high temperature lubricants, thermal fluids and solvents for high-temperature organic reactions. The degradation processes were determined by dynamic thermogravimetric analysis under dry air atmosphere for four ionic liquids (ILs). The ILs are based...

This work analyzes the friction coefficients and the wear volumes obtained in probes made of AISI 420 stainless steel worn with AISI 52100 chrome steel balls under loads of 8, 18, and 30 N; the contact was lubricated with 1-ethyl-3-methylimidazolium ethyl sulfate or 1-ethyl-3-methylimidazolium hexyl sulfate. Under the two lowest loads, the results...

In this paper the results of volumetric, isobaric heat capacity, and thermal conductivity measurements in the liquid region of a round-robin sample of Krytox GPL102 oil are reported. The measurements presented here are part of a worldwide program for the determination of transport properties of this perfluoropolyether oil. Density was measured from...

The solubility of light fullerenes (C60 and C70) in 1-hexanol was investigated in the range of pressures of 0.1–100 MPa and in the range of temperatures of 298.15–363.15 K. In all of the studied temperatures, solubility increases monotonously with increasing pressure. At ambient pressure, we have found that the temperature dependence of solubility...

In this paper the volumetric behaviour of the ionic liquids 1-butyl-1-methylpyrrolidinium tetracyanoborate, 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate, 1,3-dimethylimidazolium dimethylphosphate, 1-ethyl-3-methylimidazolium hexylsulfate, and trihexyl(tetradecyl)phos...

In this work, we have evaluated the applicability of the so-called thermodynamic scaling and the isomorph frame to describe the shear viscosity of Mie n-6 fluids of varying repulsive exponents (n = 8, 12, 18, 24, and 36). Furthermore, the effectiveness of the thermodynamic scaling to deal with binary mixtures of Mie n-6 fluids has been explored as...

A new calibration procedure was used and four new temperature probes have been placed on a falling-body viscometer to improve its accuracy. The new configuration and calibration procedure allow measuring viscosities with an uncertainty of 3.5% at pressures up to 150 MPa. This device was employed to measure viscosities as a function of temperature a...

In this paper, a densimeter based on vibrating tube principle is used to determine experimentally the density of 1-butyl-2,3-dimethylimidazolium tris(pentafluoroethyl)trifluorophosphate and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide at temperatures between (278.15 and 398.15) K and at pressures up to 120 MPa. The apparatus wa...

Ionic liquids possess several remarkable properties that make them striking for their use as lubricants for different applications. Isothermal compressibility (or bulk modulus) is a fundamental parameter in the hydraulic fluids field. Therefore, an analysis of the compressibility of different ionic liquids, mineral, synthetic and vegetable oils, as...

The tribological performance of three ionic liquids (ILs) containing the same cation, 1-butyl-1-methylpyrrolidinium [C4C1Pyrr]+, and the anions tetracyanoborate [B(CN)4]−, trifluoromethanesulphonate [CF3SO3]− and tris(pentafluoroethyl)trifluorophosphate [(C2F5)3PF3]−were analyzed. A reciprocating ball-on-plate tribometer was used at room temperatur...

After doing several miscibility essays with eight ionic liquids (ILs) and four base oils, the ILs tri(butyl)ethylphosphonium diethylphosphate [P4,4,4,2][C2C2PO4] and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate [P6,6,6,14][(C2F5)3PF3] were selected to be studied as lubricant additives. The neat IL [P4,4,4,2][C2C2PO4], th...

A setup based on a static visual synthetic method for determining phase equilibria up to 100 MPa is presented. Solubilities of carbon dioxide (CO2) in a high-oleic sunflower oil (HOSO) and in an additivated vegetable lubricant (BIO-2T-05) were determined from 298 K to 363 K up to CO2 mass compositions of 0.42. The experimental device was verified c...

The ionic liquids 1-butyl-1-methylpyrrolidinium bis(tri-fluoromethylsulfonyl)imide, [C4C1Pyrr][Tf2N], and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, [C4C1C1Im][Tf2N], were evaluated as neat lubricants for steel–steel sliding contacts using a ball-on-plate reciprocating tribometer under loads of 8, 18, and 30 N at room temper...

The aim of this paper is to examine the application of a hard-sphere scheme to the correlation and prediction of the viscosity and thermal conductivity of ionic liquids. Ionic liquids present an excellent case, because of their high viscosity. It was found that, regardless of the fact that the scheme had to be extended by orders of magnitude, it wa...

Using quantum methods it was possible to build an atomistic force field for ionic liquids interacting with a graphene surface. Density functional calculations of 1-ethyl-3-methylimidazolium cation and thiocyanate anion interacting with a cluster of carbon atoms representing a graphene surface were performed, at a series of distances and orientation...

Nowadays, one of the primary choices of base oils for environmentally aware lubricants is vegetable oils. This is due to their good natural biodegradability and very low toxicity in combination with very good lubricity characteristics. The development of new vegetable-based lubricants requires the knowledge of their thermophysical properties such a...

Densities and viscosities were determined for binary mixtures of 2,2,2-trifluoroethanol (TFE) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) or 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([bmim][NTf2]) over the entire range of composition. The experi...

This paper presents new reference correlations for both the density and viscosity of squalane at high pressure. These correlations are based on critically evaluated experimental data taken from the literature. In the case of the density, the correlation, based on the Tait equation, is valid from 273 to 473 K at pressures to 200 MPa. At 0.1 MPa, it...

Squalane is being recommended as a secondary reference material for viscometry at moderate to high pressure and at moderate viscosity. As part of this work, a correlation has been developed for atmospheric pressure (Comuñas et al., 2013) [12]. Here we report new experimental high pressure viscosities for squalane (176 data points obtained for tempe...

Squalane is being recommended as a secondary reference material for viscometry at moderate to high pressure and at moderate viscosity. As part of this work, a correlation has been developed for atmospheric pressure (Comuñas et al., 2013) [12]. Here we report new experimental high pressure viscosities for squalane (176 data points obtained for tempe...

The tribological behaviour was evaluated for two ionic liquids (ILs) as neat lubricants for the sliding pair stainless steel AISI420 and 100Cr6 under four loads (14, 18, 22 and 26 N). The ILs contain the same anion, tris(pentafluoroethyl)trifluorophosphate [(C2F5)3PF3]− (also known as [FAP]−), combined with the cations 1-butyl-2,3-dimethylimidazoli...

Using molecular dynamics simulations we have studied the structure of three 1-butyl-1-methylpyrrolidinium ionic liquids whose anions are triflate, bis(trifluoromethanesulfonyl)imide and tris(pentafluoroethyl)trifluorophosphate The structure of the bulk phase of the three ionic liquids has been interpreted using radial and spatial distribution funct...

This chapter reviews recent advances in modelling and predicting some transport properties of dense fluids. We summarize the recent developments for transport in supercooled liquids, focussing on links between structural relaxation and viscosity and decoupling between viscosity and diffusion/mobility. Building on theoretical advances in the superco...

The paper presents a new reference correlation for the viscosity of squalane at 0.1 MPa. The correlation should be valuable as it is the first to cover a moderately high viscosity range, from 3 to 118 mPa s. It is based on new viscosity measurements carried out for this work, as well as other critically evaluated experimental viscosity data from th...

In this work solubility measurements of CO2 in three vegetable oils, a high oleic sunflower oil (HOSO), a castor oil and a rapeseed oil, for mole fractions ranging from 0.32 to 0.93 in the temperature range 298–363 K and up to 75 MPa were performed. Moreover, the densities and viscosities of these oils are reported from 278.15 to 373.15 K at atmosph...

New experimental viscosity values for three ionic liquids, 1-butyl-2,3-dimethylimidazolium tris(pentafluoroethyl)trifluorophosphate, 1-(2-methoxyethyl)-1-methyl-pyrrolidinium tris(pentafluoroethyl)trifluorophosphate and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, are reported in this work. The measurements were carried out us...

Viscosities at high pressures for 16 base oils (six polyolesters, three polyglycols, six ionic liquids and squalane) were used to analyze the influence of their chemical structure on the pressure-viscosity coefficient, α. Comparisons with literature α values for vegetable bases (canola, soybean and jojoba oils) are also performed. For the molecular...

Thermal stability of ionic liquids (ILs) is one of the key properties for industrial applications, such as lubrication. This property is usually determined by thermogravimetric (TG) analysis. Though in the last years, numerous studies have been carried out, the conditions to determine the temperature limits of an IL usefulness are not still clear....

Using molecular dynamics simulations we have studied the structure of alkylsulfate based ionic liquids: 1-ethyl-3-methylimidazolium n-alkylsulfate [C2C1im][CnSO4] (n = 2, 4, 6 and 8). The structure of the different ionic liquids have been interpreted taking into account radial and spatial distribution functions, and structure factors, that allowed...

A new falling-body viscometer has been implemented to measure viscosity of liquids in a temperature range from (313.15 to 363.15) K at pressures up to 150 MPa. The accuracy of the viscometer was verified after comparing experimental results of squalane with previous literature data finding an average absolute deviation lower than 1.5%. With this de...

Experimental densities of two ionic liquids (ILs), 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([C4C1Pyrr][NTf2]) and 1-(2-methoxyethyl)-1-methyl-pyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([C1OC2C1Pyrr][(C2F5)3PF3]), were measured over a broad temperature and pressure range, i.e. from (278.15 to 398.15) K and up t...

In this work, a general equation of state (EOS) recently derived by Grzybowski et al. [Phys. Rev. E 83, 041505 (2011)] is applied to 51 molecular and ionic liquids in order to perform density scaling of pVT data employing the scaling exponent γ(EOS). It is found that the scaling is excellent in most cases examined. γ(EOS) values range from 6.1 for...