Ultrafine aerosol generation from free falling nanopowders : experiments and numerical modelling (original) (raw)
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A System to Create Stable Nanoparticle Aerosols from Nanopowders
Journal of visualized experiments : JoVE, 2016
Nanoparticle aerosols released from nanopowders in workplaces are associated with human exposure and health risks. We developed a novel system, requiring minimal amounts of test materials (min. 200 mg), for studying powder aerosolization behavior and aerosol properties. The aerosolization procedure follows the concept of the fluidized-bed process, but occurs in the modified volume of a V-shaped aerosol generator. The airborne particle number concentration is adjustable by controlling the air flow rate. The system supplied stable aerosol generation rates and particle size distributions over long periods (0.5-2 hr and possibly longer), which are important, for example, to study aerosol behavior, but also for toxicological studies. Strict adherence to the operating procedures during the aerosolization experiments ensures the generation of reproducible test results. The critical steps in the standard protocol are the preparation of the material and setup, and the aerosolization operatio...
A system to assess the stability of airborne nanoparticle agglomerates under aerodynamic shear
Stability of airborne nanoparticle agglomerates is important for occupational exposure and risk assessment in determining particle size distribution of nanomaterials. In this study, we developed an integrated method to test the stability of aerosols created using different types of nanomaterials. An aerosolization method, that resembles an industrial fluidized bed process, was used to aerosolize dry nanopowders. We produced aerosols with stable particle number concentrations and size distributions, which was important for the characterization of the aerosols' properties. Next, in order to test their potential for deagglomeration, a critical orifice was used to apply a range of shear forces to them. The mean particle size of tested aerosols became smaller, whereas the total number of particles generated grew. The fraction of particles in the lower size range increased, and the fraction in the upper size range decreased. The reproducibility and repeatability of the results were good. Transmission electron microscopy imaging showed that most of the nanoparticles were still agglomerated after passing through the orifice. However, primary particle geometry was very different. These results are encouraging for the use of our system for routine tests of the deagglomeration potential of nanomaterials. Furthermore, the particle concentrations and small quantities of raw materials used suggested that our system might also be able to serve as an alternative method to test dustiness in existing processes.
Nanoparticle aerosol science and technology: an overview
China Particuology, 2005
As a new scientific discipline, nanoparticle aerosol science and technology (NAST) deals with the formation, properties and behavior of nanoparticles in gases. Driven by its practical applications in many different fields, NAST has been undergoing rapid development. A conceptual framework of the discipline, with its own basic principles, experimental methods and computational techniques, is now taking shape. This paper presents an overview of the current status and research needs of the new discipline. The presentation begins with a discourse on the relationship among various particle systems, which occur frequently in nature and industry. The properties and behavior of nanoparticle aerosols are then discussed, with emphasis on the key roles played by particle size and morphology. Similar to fluid dynamics, NAST is an enabling discipline in the sense that it has provided the concepts and methodology needed for the development of many other fields. Applications of nanoparticle aerosol science and technology are highlighted in three important areas: (1) aerosol processes for synthesis of nanoparticles, (2) atmospheric nanoparticles and global climate, and (3) dosimetry of inhaled nanoparticles. These fields have features in common insofar as nanoparticle aerosols follow the same basic laws of physics and chemistry.
Relevance of aerosol dynamics and dustiness for personal exposure to manufactured nanoparticles
Journal of Nanoparticle Research, 2009
Production and handling of manufactured nanoparticles (MNP) may result in unwanted worker exposure. The size distribution and structure of MNP in the breathing zone of workers will differ from the primary MNP produced. Homogeneous coagulation, scavenging by background aerosols, and surface deposition losses are determinants of this change during transport from source to the breathing zone, and to a degree depending on the relative time scale of these processes. Modeling and experimental studies suggest that in MNP production scenarios, workers are most likely exposed to MNP agglomerates or MNP attached to other particles. Surfaces can become contaminated by MNP, which constitute potential secondary sources of airborne MNP-containing particles. Dustiness testing can provide insight into the state of agglomeration of particles released during handling of bulk MNP powder. Test results, supported by field data, suggest that the particles released from powder handling occur in distinct size modes and that the smallest mode can be expected to have a geometric mean diameter [100 nm. The dominating presence of MNP agglomerates or MNP attached to background particles in the air during production and use of MNP implies that size alone cannot, in general, be used to demonstrate presence or absence of MNP in the breathing zone of workers. The entire respirable size fraction should be assessed for risk from inhalation exposure to MNP.
Aerosol Science and Technology, 2016
Occupational exposure to nanomaterial aerosols poses potential health risks to workers at nanotechnology workplaces. Understanding the mechanical stability of airborne nanoparticle agglomerates under varied mechanical forces and environmental conditions is important for estimating their emission potential and the released particle size distributions, which in consequence alters their transport and human uptake probability. In this study, two aerosolization and deagglomeration systems were used to investigate the potential for deagglomeration of nanopowder aerosols with different surface hydrophilicity under a range of shear forces and relative humidity conditions. Critical orifices were employed to subject airborne agglomerates to the shear forces induced by a pressure drop. Increasing applied pressure drop was found to be associated with decreased mean particle size and increased particle number concentrations. Rising humidity decreased the deagglomeration tendency as expressed by larger modal particle sizes and lower number concentrations compared to dry conditions. Hydrophilic aerosols exhibited higher sensitivities to changes in humidity than hydrophobic particles. However, the test systems themselves also differed in generated particle number concentrations and size distributions, which in turn altered the responses of created aerosols to humidity changes. The results of the present study clearly demonstrate that (a) humidity control is essential for dustiness and deagglomeration testing, (b) that (industrial) deagglomeration, for example, for preparation of aerosol suspensions, can be manipulated by subjecting airborne particles to external energies, and (c) that the humidity of workplace air may be relevant when assessing occupational exposure to nanomaterial aerosols.
2014
This paper focuses on presenting the forefront of the interdisciplinary studies conceived towards the generation of the wear particles aerosol when materials are subjected to mechanical stresses. Various wear mechanisms and instrumentation involved during stress application and aerosolization of wear particles, as well as particles characterization, measurement, and modeling techniques are presented through the investigation of a series of contextual works which are emphasized on the identification of these aspects. The review is motivated from the fact that understanding mechanisms involved in wear-induced particle generation, both at nanoand at microscale, is important for many applications that involve surfaces sliding over each other due to various potential health aspects. An attempt has been made to explain how the information based on this broad spectrum of subjects discovered in this contribution can be used and improved in order to produce a more resilient, rational, and versatile knowledge base which has been found lacking in the present literature during its survey. The area of study is highly multidisciplinary since it involves aerosol, particle, and material sciences.
Assessment of Explosion Hazards Associated With Nano-Powders
SPE Kingdom of Saudi Arabia Annual Technical Symposium and Exhibition
Nano-powders are composed of particles in size range from about 1 to 100 nano-metres (nm). The growing demand for nano-powders arises from the change in physical, chemical and electrical properties exhibited by such particles when their size falls below 100 nm. Along with the increasing production and use of Nano scale particles, there has been a growing concern over the impact of this new technology on health, safety and environment. This has almost exclusively concentrated on the potential health hazards of nano-powders. One potential hazard that appears to have received little attention to date is their explosivity. Explosive dust clouds can be generated from most organic materials, many metals and even some non-metallic inorganic materials. Dust explosions involving particle sizes ranging from a few microns to hundreds of microns, there is a need for these particles to be extensively studied. This work involves computationally modelling the explosion, and investigation of critical parameters that can enhance the severity of the explosion. These parameters include but are not limited to effect of particle size, dust concentration and composition, ignition strength, degree of dust dispersion, explosion characteristics of nano-particles, operating conditions. Further, the work involved in this paper looks at the impact onto the environment by explosion of such nano-powders. The possibility of dust generation accumulation and explosion in various areas of the facility are investigated. A checklist for adequacy of existing safety measures is prepared, and requirement for additional safeguards is studied, in order to avoid catastrophic effects.
Investigating airborne stability of nanomaterials - aerosol generations and characterizations
Annals of Occupational Hygiene, 2015
background: Working in a canteen will involve more than one activity e.g. cutting, grinding, washing. These activities may lead to stress and muscle fatigue. objective: To analyse health effects in canteen staff working at the university. Methods: A cross-sectional study was conducted in canteen staff. A questionnaire was used to compare the level of feeling e.g. strength, force, interest before and after work between canteen staff using a subjective judgment scale from 1-10, together with assessing muscles; extensor of the wrist, biceps, triceps at different times by using surface electromyography (EMG). A paired t-test was used to analyse data. results: 23 canteen staff participated the project (100%). Canteen staff did not report any significant difference in feeling e.g. freshness, keenness, force or strength that differentiated before work and after work. Extensor of the wrist seems to be the most muscle using part in a canteen activity. Conclusions: Stress levels related to working in a university canteen are low as is muscle fatigue measured by EMG. However, performing repetitive work in a canteen could lead to muscle fatigue or stress so break interval time may be important for preventing muscle fatigue and reducing stress.
Journal of Nanoparticle Research, 2012
In this study, nanoalumina and nanoclay particles were compounded separately with ethylene vinyl acetate (EVA) polymer to produce nanocomposites using a twin-screw extruder to investigate exposure and effective controls. Nanoparticle exposures from compounding processes were elevated under some circumstances and were affected by many factors including inadequate ventilation, surrounding air flow, feeder type, feeding method, and nanoparticle type. Engineering controls such as improved ventilation and enclosure of releasing sources were applied to the process equipment to evaluate the effectiveness of control. The nanoparticle loading device was modified by installing a ventilated enclosure surrounding the loading chamber. Exposures were studied using designed controls for comparison which include three scenarios: (1) no isolation; (2) enclosed sources; and (3) enclosed sources and improved ventilation. Particle number concentrations for diameters from 5 to 20,000 nm measured by the Fast Mobility Particle Sizer and aerodynamic particle sizer were studied. Aerosol particles were sampled on transmission electron microscope grids to characterize particle composition and morphology. Measurements and samples were taken at the near-and far-field areas relative to releasing sources. Airborne particle concentrations were reduced significantly when using the feeder enclosure, and the concentrations were below the baseline when two sources were enclosed, and the ventilation was improved when using either nanoalumina or nanoclay as fillers.
Whole-Body Nanoparticle Aerosol Inhalation Exposures
Journal of Visualized Experiments, 2013
Inhalation is the most likely exposure route for individuals working with aerosolizable engineered nano-materials (ENM). To properly perform nanoparticle inhalation toxicology studies, the aerosols in a chamber housing the experimental animals must have: 1) a steady concentration maintained at a desired level for the entire exposure period; 2) a homogenous composition free of contaminants; and 3) a stable size distribution with a geometric mean diameter < 200 nm and a geometric standard deviation σ g < 2.5 5 . The generation of aerosols containing nanoparticles is quite challenging because nanoparticles easily agglomerate. This is largely due to very strong inter-particle forces and the formation of large fractal structures in tens or hundreds of microns in size 6 , which are difficult to be broken up. Several common aerosol generators, including nebulizers, fluidized beds, Venturi aspirators and the Wright dust feed, were tested; however, none were able to produce nanoparticle aerosols which satisfy all criteria 5 .