Bismuth nanoparticles synthesized by laser ablation in lubricant oils for tribological tests M. Flores-Castañeda a,b,⇑ , E. Camps b , M. Camacho-López a , S. Muhl c , E. García c,d , M. Figueroa c,d a Universidad Autónoma del Estado de México, Av. Instituto Literario No. 100, Oriente Col. Centro, Toluca, Estado de México C.P. 50000, México b Instituto Nacional de Investigaciones Nucleares, Carretera México-Toluca s/n, La Marquesa, Ocoyoacac, Edo. de México C.P. 52750, México c Instituto de Investigación en Materiales (UNAM), Circuito Exterior, Ciudad Universitaria, Coyoacán, 04510 México, D.F., México d Instituto Politécnico Nacional, Av. Luis Enrique Erro S/N, Unidad Profesional Adolfo López Mateos, Zacatenco, Delegación Gustavo A. Madero, C.P. 07738 México, D.F., México article info Article history: Available online 30 December 2014 Keywords: Bismuth nanoparticles Laser ablation Tribology Mineral base oils abstract The improvement of the tribological properties of mineral base oils through the addition of bismuth nanoparticles as an additive, together with the idea of obtaining lubricants free of heavy metals, was eval- uated. Bismuth nanoparticles were produced directly in the heavy and light viscosity mineral base oils (BS900 and BS6500) using the technique of laser ablation of solids immersed in liquids. Transmission electron microscopy measurements showed the presence of pure bismuth nanoparticles. Small Angle X-ray Scattering (SAXS) measurements showed that the average size of the nanoparticles was between 7 and 65 nm depending on the experimental conditions used. The tribological properties of the base oil with the bismuth nanoparticles additives were evaluated using a four-ball tester. Tests were per- formed using the base oil with and without Bi nanoparticles. It was observed that the coefficient of fric- tion of the oil decrease with an increasing concentration of the nanoparticles. The results also showed that the wear rate was reduced when the Bi nanoparticle additives were used. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction The majority of lubricant base oils are produced from refining of crude oil. The reasons for the predominance of refined petroleum base oils are because of their performance, availability and price. In general, large scale oil refining operations produce base oils with excellent characteristics in a variety of modern lubricant formula- tions at economic prices. Modern lubricants are produced from a range of the base oils with chemical additives. The base oil has several functions but it is primarily the lubricant which provides the fluid layer to separate moving surfaces. It also removes heat and wear debris whilst min- imizing friction. Many properties of the lubricant can be enhanced or created by the addition of special chemical additives to the base fluid. For example, stability to oxidation and degradation in engine oil is improved by the addition of antioxidants, whilst extreme pressure (EP) and anti-wear properties needed in gear lubrication are created by the addition of different additives. The base oil acts as the carrier for these additives and therefore must be able to maintain them in solution, or suspension, under all normal work- ing conditions [1]. In recent years, many of the studies of the use of nanomaterials additives in lubricating oils has drawn attention to how the phys- ico-chemical properties of the additives can directly contribute to the improvement of tribological properties of the lubricants, such as anti-wear, reducing friction, operation under extreme pressure and thermal stability [2–4]. Some of the lubricant additives that have been studied include nanoparticles of metals [5,6], metal oxides [7,8], metal sulfides [9,10], rare earth compounds [11], etc. In many of these cases sig- nificant improvements to the tribological properties of the lubri- cants have been obtained. However, some of these nanomaterials contain sulfur or phosphorus compounds, or even involve the incorporation of heavy metals that are potentially harmful to humans and the environment. In the present investigation the incorporation of nanoparticles of bismuth as an additive offers an ecological alternative, as this element is known to have low toxic- ity and is considered a good Green alternative. Nanoparticle additives to lubricants present several major advantages compared to the organic molecules that are currently used, for example their small size allows them to easily enter the contact area. They are often efficient at ambient temperature and http://dx.doi.org/10.1016/j.jallcom.2014.12.054 0925-8388/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Instituto Nacional de Investigaciones Nucleares, Carretera México-Toluca s/n, La Marquesa, Ocoyoacac, Edo. de México C.P. 52750, México. E-mail address: mar.floc@hotmail.com (M. Flores-Castañeda). Journal of Alloys and Compounds 643 (2015) S67–S70 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom