Tribological and Thermophysical Properties of Environmentally-Friendly Lubricants Based on Trimethylolpropane Trioleate with Hexagonal Boron Nitride Nanoparticles as an Additive

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 rheological measurements. Density and viscosity were measured from 278.15 to 373.15 K, while rheological behavior was analyzed at shear rates from 1 to 1000 s−1 at 283.15 K. Newtonian behavior was exhibited by all nanolubricants at the explored conditions, with the exception of the highest concentration at the lowest shear rates, where possible non-Newtonian behavior was observed. Tribological tests were performed under a normal load of 2.5 N. Wear was evaluated by means of a 3D profiler, scanning electron microscopy and confocal Raman microscopy. The best tribological performance was achieved by the 0.75 wt.% nanolubricant, with reductions of 25% in the friction coefficient, 9% in the scar width, 14% in the scar depth, and 22% of the transversal area, all with respect to the neat oil. It was observed that physical protective tribofilms are created between rubbing surfaces.This work was supported by the Spanish Ministry of Economy and Competitiveness and the ERDF programme through the ENE2014-55489-C2-1/2-R and ENE2017-86425-C2-1/2-R projects. Moreover, this work was funded by the Xunta de Galicia (ED431E 2018/08, GRC ED431C 2016/001 and GRC ED431C 2016-034). These three funders also financed the acquisition of the 3D Optical Profile Sensofar S Neox (UNST15-DE-3156)S

Improving the tribological performance of a biodegradable lubricant adding graphene nanoplatelets as additives

This research is based on the investigation of the tribological properties of a biodegradable polymeric ester lubricant (BIOE) additivated with two different pristine graphene nanoplatelets (GnPs), named as GnP7 and GnP40. These GnPs have lateral sizes of 7 and 40 μm, and thickness of 3 and 10 nm, respectively. Four different nanoadditive loadings: 0.015, 0.035, 0.055 and 0.075 wt% have been used. Stability of nanolubricants has been investigated using the visual control and the refractive index evolution during time, revealing a slightly better stability for the nanolubricants formulated with the largest lateral size graphene nanoplatelets (GnP40). The influence of the thickness and lateral size of these carbon-based nanoadditives on the antifriction and antiwear capabilities of BIOE is analysed. For this purpose, rotational friction tests were taken with the eight nanolubricants under a 20 N working load and 340 m sliding distance. All nanolubricants showed friction coefficients and worn area lower than those previously reported for the unadditivated BIOE. As regards friction, the ideal loading for both GnPs was 0.055 wt% GnP, being the best anti-friction behaviour obtained using GnP40 as additive (up to 26% reduction), whereas the 0.055 wt% GnP7/BIOE nanolubricant leads to the best anti-wear capability with wear reductions up to 56%. Finally, from Raman microscopy and roughness assessments on the worn surfaces, it can be determined that the good tribological performance of nanolubricants is owing to the protective film formation and surface repairing mechanismThis research was supported by the “Ministerio de Ciencia, Innovación y Universidades” (Spain) and the FEDER program through the ENE2017-86425-C2-1/2-R project and by Xunta de Galicia (ED431C 2020/10). Authors would like to thank Verkol Lubricantes and Avanzare Innovacion Tecnologica S.L. for providing the BIOE base oil and pristine graphene nanoplatelets, respectively. Authors would like also to thank the help of RIAIDT-USC analytical facilities. M.J.G.G. and J.I.P. are grateful for the support of the Xunta de Galicia for the postdoctoral (reference ED481B-2019-015) and predoctoral fellowship grantsS

Lubricant properties of trimethylolpropane trioleate biodegradable oil: High pressure density and viscosity, film thickness, Stribeck curves and influence of nanoadditives

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 vibrating tube densimeter, respectively. Film thickness and friction properties were determined with a ball-on-disc apparatus from temperatures of 303.15 to 353.15 K, from slide-roll ratios from 5 to 50% at 50 N (applied load). Finally, it has also been evaluated if the use of nanoparticles as additives could involve changes on film thickness and Stribeck curves of TMPTO base oil. For this aim, hexagonal-boron nitride nanoparticles (h-BN) and graphene nanoplatelets (GnPs) were used at mass concentrations of 0.25, 0.5 and 1.0 wt%. The viscosity of TMPTO increases from 15 mPa s (at 10 MPa and 353.15 K) to 525 mPa s (at 150 MPa and 303.15 K). The Stribeck curves for TMPTO are placed between elastohydrodynamic and mixed lubrication. All nanolubricants show very similar Stribeck curves, being the lowest friction coefficient obtained for 0.25 wt% of GnP. It has been found that for most of the experimental conditions the addition of the GnP promotes an increase of the film thicknessSpanish Ministry of Economy and Competitiveness, the European Regional Development Fund programme and the Xunta de Galicia have supported this manuscript through ENE2017-86425-C2-2-R, GRC ED431C 2020/10 and ED431E 2018/08 projects. Dr. María J. G. Guimarey acknowledges a postdoctoral fellowship from the Xunta de Galicia (Spain) and the financial support from IACOBUS programmeS

Unha enxeñeira ou científica en cada cole

Póster presentado na V XORNADA UNIVERSITARIA GALEGA EN XÉNERO. TRANSFORMANDO DENDE A UNIVERSIDADE. Vigo, 7 Xullo 2017Nesta comunicación, presentamos o proxecto Unha enxeñeira ou científica en cada cole organizado pola Oficina de Igualdade de Xénero da Universidade de Santiago de Compostela (USC) en colaboración co Concello de Santiago de Compostela. Esta iniciativa pretende incentivar a presenza de rapazas en carreiras relacionadas coas disciplinas STEM (ciencia, enxeñería, tecnoloxía e matemáticas), mediante actividades didácticas nos centros educativos que rachen cos estereotipos sexistas da nosa sociedade. A actividade didáctica consistiu na realización de dezanove obradoiros, dirixidos a nenas e nenos de 5º ou 6º de primaria e realizados nos meses de setembro e outubro de 2016. Os obradoiros foron impartidos por profesoras ou investigadoras da USC e do Centro de Supercomputación de Galicia (CESGA) para crear referentes femininos e incentivar a presenza de rapazas no ámbito científico tecnolóxico. Ademais, estes obradoiros amosaron a relación da ciencia e da tecnoloxía coa nosa vida cotiá e serviron para achegar ao alumnado a estas disciplinas dun xeito lúdicoConcello de Santiago de Compostel

PEG 400-based phase change materials nano-enhanced with functionalized graphene nanoplatelets

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 nanomaterial and/or the poly(ethylene glycol) were characterized. Design parameters of NePCMs were defined on the basis of a temporal stability study of nanoplatelet dispersions using dynamic light scattering. Influence of graphene loading on solid-liquid phase change transition temperature, latent heat of fusion, isobaric heat capacity, thermal conductivity, density, isobaric thermal expansivity, thermal diffusivity and dynamic viscosity were also investigated for designed dispersions. Graphene nanoplatelet loading leads to thermal conductivity enhancements up to 23% while the crystallization temperature reduces up to in 4 K. Finally, the heat storage capacities of base fluid and new designed NePCMs were examined by means of the thermophysical properties through Stefan and Rayleigh numbers. Functionalized graphene nanoplatelets leads to a slight increase in the Stefan number.Xunta de Galicia | Ref. GRC ED431C 2016-034Xunta de Galicia | Ref. GRC ED431C 2016/001Xunta de Galicia | Ref. AGRUP2015/11Ministerio de Economía y Competitividad (España) | Ref. Ref. ENE2014-55489-C2-2-RMinisterio de Economía y Competitividad (España) | Ref. Ref. ENE2014-55489-C2-1-

Tribological Performance of a Paraffinic Base Oil Additive with Coated and Uncoated SiO2 Nanoparticles

Electric vehicles (EVs) have emerged as a technology that can replace internal combustion vehicles and reduce greenhouse gas emissions. Therefore, it is necessary to develop novel low-viscosity lubricants that can serve as potential transmission fluids for electric vehicles. Thus, this work analyzes the influence of both SiO2 and SiO2-SA (coated with stearic acid) nanomaterials on the tribological behavior of a paraffinic base oil with an ISO VG viscosity grade of 32 and a 133 viscosity index. A traditional two-step process through ultrasonic agitation was utilized to formulate eight nanolubricants of paraffinic oil + SiO2 and paraffinic base oil + SiO2-SA with nanopowder mass concentrations ranging from 0.15 wt% to 0.60 wt%. Visual control was utilized to investigate the stability of the nanolubricants. An experimental study of different properties (viscosity, viscosity index, density, friction coefficient, and wear) was performed. Friction analyses were carried out in pure sliding contacts at 393.15 K, and a 3D optical profilometer was used to quantify the wear. The friction results showed that, for the SiO2-SA nanolubricants, the friction coefficients were much lower than those obtained with the neat paraffinic base oil. The optimal nanoparticle mass concentration was 0.60 wt% SiO2-SA, with which the friction coefficient decreased by around 43%. Regarding wear, the greatest decreases in width, depth, and area were also found with the addition of 0.60 wt% SiO2-SA; thus, reductions of 21, 22, and 54% were obtained, respectively, compared with the neat paraffinic base oil.This research is supported by Xunta de Galicia (ED431C 2020/10), by the State Research Agency (AEI) of Spain, and by the European Regional Development Fund (ERDF, FEDER in Spanish) through the PID2020-112846RB-C22 project. J.M.L.d.R. acknowledges the grant of the Margarita Salas program, funded by MCIN/AEI/10.13039/501100011033 and “NextGenerationEU/PRTR”. M.J.G.G. also acknowledges the Xunta de Galicia (Spain) for the postdoctoral fellowship (reference ED481D 2023/016)

Una física en cada cole

Comunicación presentada en la XXXVI Reunión Bienal de la Real Sociedad Española de Física, Santiago de Compostela, 17 - 21 de julio de 2017En esta comunicación presentamos los talleres que formaron parte de la actividad "Unha enxeñeira ou científica en cada cole", y que están relacionados con la Física y la Óptica. Estos talleres sirven por un lado para visibilizar a científicas dentro de estas disciplinas, y por otro lado contribuyen a fomentar el aprendizaje a través de actividades manipulativas, mediante la experimentación directa con materiales y objetos cotidianos. La buena acogida que ha tenido esta actividad nos lleva a animar a más científicas a acercar la ciencia al alumnado no universitarioConvenio OIX y Ayuntamiento de Santiago de Compostel