Tribological behaviour of copper oxide nanoparticle suspension

This work presents and discusses the tribological behaviour of nanoparticle suspensions in a polyalphaolefin (PAO6). CuO nanoparticles were separately dispersed at 0.5, 1.0 and 2.0% wt. in PAO6 using an ultrasonic probe for 2 minutes. AW properties were obtained using a TE53SLIM tribometer with a block-on-ring configuration and EP properties were obtained using a Four-Ball machine according to ASTM D2783. Wear surfaces were analyzed by SEM and EDS after tests. The study led to the following conclusions: nanoparticle suspensions exhibited reductions in friction and wear compared to the base oil; CuO suspensions showed the highest friction coefficient and lowest wear per nanoparticle content of 2%; all concentrations of nanoparticles improved the EP properties of PAO6; CuO showed better results at 0.5% wt. of nanoparticles; and the antiwear mechanism of nanoparticulate additive was produced by tribo-sintering

Viscosity and tribology of copper oxide nanofluids

Nanofluids, a term proposed by Choi in 1995 [1], are composites consisting of solid nanoparticles with sizes varying generally from 1 to 100 nm dispersed in a liquid. Numerous nanoparticles used as oil additives have been investigated in recent years [2-7]. Results show that they deposit on the rubbing surface and improve the tribological properties of the base oil, displaying good friction and wear reduction characteristics even at concentrations below 2%wt. Although the viscosity of the nanofluids is a property of crucial importance for film forming, and hence friction and wear reduction, which are characteristic of lubricants, only Hwang et al. [8] have studied thermal characteristics, kinematic viscosity and tribological properties of nanofluids simultaneously. In this paper, we present measurements of dynamic viscosity of nanofluids formed by copper oxide nanoparticles dispersed in a polyalphaolefin, for temperatures and concentrations varying from 20 to 60ºC and 0.5 to 2% wt., respectively. Dependence of the nanofluid viscosity to the solid fraction and temperature was compared with existing models and its influence on lubrication was also analysed

Elastic Reciprocity and Symmetry Constraints on the Stress Field Due to a Surface-Parallel Distribution of Dislocations

Elastic reciprocity and geometric symmetry are used to constrain the expressions for stresses due to introduction of line dislocations near a half-space surface. Specifically, a relationship is shown to exist between the changes induced by dislocations of orthogonal Burgers vectors (normal and parallel to the free surface). These results are used to address inconsistencies of solutions in the literature.Earth and Planetary SciencesEngineering and Applied Science

Lubrication of DLC Coatings with Two Tris(pentafluoroethyl)trifluorophosphate Anion-Based Ionic Liquids

The lubrication of a Cr-DLC coating with ethyl-dimethyl-2-methoxyethylammonium tris(pentafluoroethyl)trifluoropho-sphate [(NEMM)MOE][FAP] and 1-butyl-1-methylpyrro-lidinium tris(pentafluoroethyl)trifluorophosphate [BMP] [FAP] ionic liquids (ILs) as 1 wt% additives to a polyalphaolefin (PAO 6) was studied. Zinc dialkyldithiophosphate (ZDDP) was also used as reference in order to evaluate the effectiveness of the ILs. Reciprocating ball-on-plate tribological tests at loads of 20 and 40 N were performed. The results showed that both ILs exhibited a friction reduction, especially at the lowest load tested. Antiwear properties were also improved; the PAO 6 + 1% [BMP][FAP] mixture was slightly better, close to the values for PAO 6 + 1% ZDDP. Scanning electron microscopy (SEM) images and X-ray photoelectron spectroscopy (XPS) analysis indicated that the additive–surface interaction was responsible for the tribological improvement

El patrimonio gastronómico del municipio de Toluca: el caso del pulque y las pulquerías (1841-1920)

Se hace un esbozo de algunos elementos históricos del pulque y las pulquerías del municipio de Toluca en el periodo de 1841-1920, particularmente sobre la producción, comercialización y consumo. El método utilizado fue la microhistoria con información obtenida del Archivo Histórico del Municipio de Toluca y fuentes bibliohemerográficas. Los resultados muestran una producción significativa del pulque, la existencia de un gran número de establecimientos que lo expendían, la importancia del rol de la mujer en la comercialización y cómo el ferrocarril contribuyó a la distribución de la bebida. Se concluye que este patrimonio gastronómico fue importante para el municipio y que el consumo de la bebida era generalizado entre toda la población

La responsabilidad de los administradores sociales por no disolución de sociedades mercantiles en pérdidas agravadas en el Anteproyecto de Ley del Código Mercantil

Esta contribución examina la responsabilidad de los administradores sociales en el Anteproyecto de Ley de Código Mercantil y estudia, en concreto, los casos de no disolución de sociedades mercantiles en pérdidas agravadas. Para ello revisa la causa de disolución por pérdidas y los distintos presupuestos de la responsabilidad, con especial énfasis en la responsabilidad de los administradores. Se finaliza analizando la regulación de la prescripción

Off-Fault Plasticity and Earthquake Rupture Dynamics: 2. Effects of Fluid Saturation

We present an analysis of inelastic off-fault response in fluid-saturated material during earthquake shear rupture. The analysis is conducted for 2-D plane strain deformation using an explicit dynamic finite element formulation. Along the fault, linear slip-weakening behavior is specified, and the off-fault material is described using an elastic-plastic description of the Drucker-Prager form, which characterizes the brittle behavior of rocks under compressive stress when the primary mode of inelastic deformation is frictional sliding of fissure surfaces, microcracking and granular flow. In this part (part 1), pore pressure changes were neglected in materials bordering the fault. In part 2, we more fully address the effects of fluid saturation. During the rapid stressing by a propagating rupture, the associated undrained response of the surrounding fluid-saturated material may be either strengthened or weakened against inelastic deformation. We consider poroelastoplastic materials with and without plastic dilation. During nondilatant undrained response near a propagating rupture, large increases in pore pressure on the compressional side of the fault decrease the effective normal stress and weaken the material, and decreases in pore pressure on the extensional side strengthen the material. Positive plastic dilatancy reduces pore pressure, universally strengthening the material. Dilatantly strengthened undrained deformation has a diffusive instability on a long enough timescale when the underlying drained deformation is unstable. Neglecting this instability on the short timescale of plastic straining, we show that undrained deformation is notably more resistant to shear localization than predicted by neglect of pore pressure changes.Earth and Planetary SciencesEngineering and Applied Science

Ending a Touristic Destination in Four Decades: Cancun’s Creation, Peak and Agony

This article aims to explain how Cancun was born in the 1970’s, and how this beautiful natural site with a warm weather which had fostered a wide variety of marine and terrestrial fauna and flora was transformed. The article describes the way in which its touristic offer has evolved, the way in which the number of arriving tourists has developed throughout the years, as well as the problems faced by hotel owners due to the impact of various hurricanes and the influenza AH1N1 epidemic in 2009 amongst other facts.Cancun, similarly to other resorts created under similar circumstances, has received dramatic environmental and social impacts as a result of the substantial transformation of its natural habitat and to the application of policies which have only looked for short term economical benefits; some of these impacts are explained hereby. Finally, the consequences of the development scheme followed for decades in this Mexican resort facing serious survival problems are discussed