Nano particles emissions during friction stir welding of aluminium alloys

The influence of very ultrafine particulate, lying in the nanoparticles range, on human health has been pointed to be of much concern as airborne nanoparticles are resulting both from nanotechnologies processes and also from macroscopic common industrial processes such as welding. In fact, nanotoxicological research is still in its infancy and the issuing and implementation of standards for appropriate safety control systems can still take several years. Yet, the advanced understanding of toxicological phenomena on the nanometre scale is largely dependent on technological innovations and scientific results stemming from enhanced R&D. Meanwhile, the industry has to adopt proactive risk management strategies in order to provide a safe working environment for their staff, clients and customers, and obtain products without posing health threats at any point of their lifecycle. Understanding the relationship of airborne nano sized particulate and human health, under different environmental conditions is of great importance for improving exposure estimates and for developing efficient control strategies to reduce human exposure and health risk and for establishing, evaluating and improving regulations and legislation both on air quality, airborne emissions and the incorporation of nano sized materials in other products and commodities [1]. In the process of friction stir welding (FSW), the knowledge about the emissions of nanoparticles is reduced. During a long time, this process was considered as a clean process, without fume emissions. However, recent studies have shown the existence of particles with dimensions inferior to 100 nm. The nanoparticles have a high deposition capacity in the alveoli causing a decrease in the respiratory capability of individuals. This study aims to determine of surface area of nanoparticles deposited in the alveolar region of the human lung, its emission levels, morphology, and chemical composition, resulting from various operational parameters, and assesses also the need of proposing ways to minimize the emissions of nanoparticles in the process. FSW was done in two different aluminum alloys, with two different rotation speeds, and measurements were made to determine the surface area of nanoparticles deposited in the alveolar region, size distribution. Particles were also sampled for microscopic analysis. The obtained results confirmed the existence of emissions of nanoparticles with alveolar deposition capability, and the existence of relations between the welding parameters and the deposited area in the lung. It was shown that its chemical composition is directly connected with the nature of materials used in the process [2]. In order to perform the toxicological assessment of welding processes a Nanoparticle Surface Area Monitor, TSI, Model 3550, based on diffusion charging (measuring the electrostatic charge on a sampled aerosol, mainly composed of nanoparticles) was used for monitoring the emission of nanoparticles resulting from several welding processes. This equipment indicates the human lung-deposited surface area of particles expressed as square micrometers per cubic centimeter of air (µm2/cm3) [3]. Although this instrument is very precise and its use has been validated for this purpose, the definite presence of nanoparticles in welding fume has to be complemented by microscopy techniques such as transmission electron microscopy (TEM), which has proved very helpful in order to establish the size, shape and aggregation habit of sampled aerosols, as well as energy dispersive X-ray spectroscopy (EDS) for performing the chemical analysis of collected nanoparticles.The obtained results clearly demonstrated the existence of airborne nanoparticles, as shown in figures 1 and 2, in the analyzed welding processes