Exposure and Emission Measurements During Production, Purification, and Functionalization of Arc-Discharge-Produced Multi-walled Carbon Nanotubes.

Background: The production and use of carbon nanotubes (CNTs) is rapidly growing. With increased production, there is potential that the number of occupational exposed workers will rapidly increase. Toxicological studies on rats have shown effects in the lungs, e.g. inflammation, granuloma formation, and fibrosis after repeated inhalation exposure to some forms of multi-walled CNTs (MWCNTs). Still, when it comes to health effects, it is unknown which dose metric is most relevant. Limited exposure data for CNTs exist today and no legally enforced occupational exposure limits are yet established. The aim of this work was to quantify the occupational exposures and emissions during arc discharge production, purification, and functionalization of MWCNTs. The CNT material handled typically had a mean length <5 μm. Since most of the collected airborne CNTs did not fulfil the World Health Organization fibre dimensions (79% of the counted CNT-containing particles) and since no microscopy-based method for counting of CNTs exists, we decided to count all particle that contained CNTs. To investigate correlations between the used exposure metrics, Pearson correlation coefficient was used

In-situ characterization of metal nanoparticles and their organic coatings using laser-vaporization aerosol mass spectrometry

The development of methods to produce nanoparticles with unique properties via the aerosol route is progressing rapidly. Typical characterization techniques extract particles from the synthesis process for subsequent offline analysis, which may alter the particle characteristics. In this work, we use laser-vaporization aerosol mass spectrometry (LV-AMS) with 70-eV electron ionization for real-time, in-situ nanoparticle characterization. The particle characteristics are examined for various aerosol synthesis methods, degrees of sintering, and for controlled condensation of organic material to simulate surface coating/functionalization. The LV-AMS is used to characterize several types of metal nanoparticles (Ag, Au, Pd, PdAg, Fe, Ni, and Cu). The degree of oxidation of the Fe and Ni nanoparticles is found to increase with increased sintering temperature, while the surface organic-impurity content of the metal particles decreases with increased sintering temperature. For aggregate metal particles, the organic-impurity content is found to be similar to that of a monolayer. By comparing different equivalent-diameter measurements, we demonstrate that the LV-AMS can be used in tandem with a differential mobility analyzer to determine the compactness of synthesized metal particles, both during sintering and during material addition for surface functionalization. Further, materials supplied to the particle production line downstream of the particle generators are found to reach the generators as contaminants. The capacity for such in-situ observations is important, as it facilitates rapid response to undesired behavior within the particle production process. This study demonstrates the utility of real-time, in-situ aerosol mass spectrometric measurements to characterize metal nanoparticles obtained directly from the synthesis process line, including their chemical composition, shape, and contamination, providing the potential for effective optimization of process operating parameters

Physical characterization of engineered aerosol particles

This thesis will explore parts of the life of engineered nanoparticles, from generation in research environments andprocess monitoring, to emissions in an industrial setting. The aim is to give insights into how the particles can becharacterized in different settings and how different characterization methods can be applied depending on need ordemand.Airborne nanoparticles have been around forever but the use of them in specialized materials has increaseddramatically during the past decades. The new materials bring improvements to old applications, and brand new usesas the world of nanotechnology expands. It is, however, not only one-sided positive effects from this increase in use;some of these materials have properties previously experienced as health hazards. The physical size and amounts ofmaterial handled during the production can be different from what has been experienced before and with that, newhazards might arise. In order to assess these hazards, careful characterization of the particle behavior can be utilized incontrolled environments to further the knowledge on how the particles might behave out in the real world during use andapplication. Particles can be characterized in many different ways and aspects. Finding out which path that suits acertain situation is a key to make a successful measurement campaign or experiment. The systems used to producethese particles also need to be well characterized. In addition to safe handling, well characterized generation systemswill also allow for new uses and exploration of materials previously not investigated.In this thesis, I have characterized the initial stages of particles generated with spark discharge discovering how theparticles evolve depending on process parameters milliseconds after generation. I further dive deeper into the sparkdischarge characterization and show how the emitted light from the discharge can be correlated with the particles beingproduced and show how the input power doesn’t linearly correlate with particles produced in this process. In the samesystem, I successfully generate particles of InSb. It is demonstrated how a reducing atmosphere during generation iscritical for the formation of pure particles of this material. Several different characterization techniques to determine theproperties of the generated particles are described.One of the most interesting properties of nanoparticles from a toxicological view point is surface area. Knowing thesurface area of complex particles is, however, not always straightforward and is often difficult to measure directly. Ipresent an overview of a set of models that can be used to estimate the surface area of agglomerated particlesgenerated from different particle sources. The input to the methods relies on online measurements of mobility diameter,mass, and offline characterization of morphology via microscopy samples.No matter how harmful particles with specific properties are to humans, there is no harm unless people get exposed tothe particles. I present results from an extensive workplace campaign in which we utilized online aerosol instruments tocharacterize the emissions. A new method for classifying carbon nanotube materials via electron microscopy from filtersamples, as well as from surface sampling with adhesive tape, is further introduced.From this campaign release of engineered nanoparticles at several occasions during the work day was found. It wasevident that online methods alone would not enable us to discern carbon nanotubes from other particles but with thecombination of online time resolved characterization of emissions and extensive microscopy analysis emission eventswere identified. It was also revealed that the surface contamination of engineered particles were extensive. Severalsampled surfaces showed contamination by not only carbon nanotubes but also of nanomaterial which were nothandled during the time of the measurements.From this thesis it is clear that measuring nanoparticles is as difficult as you make it. It is possible to measure withsimple means to yield results that are sufficient to give an indication that some things needs to improve. In this thesis Iwill also show that an extensive arsenal of equipment can yield results which complement and build upon each other.While it is possible to measure all kinds of data on the same aerosol given enough time and resources, it is clear thatthe optimization and tailoring of a study might be the real challenge

Nanoparticles: Characterization and exposure metrics

Exposure to aerosol nanoparticles has always been present in the evolution of humans, and thus has the human body developed ways of dealing with particles that enters the body. However with the emerging nanotech industry, new types of nanoparticles are being produced and used. Many of these particles have properties never seen before and this rise concern about how exposure to them might cause unwanted health effects. The research field of occupational health tends to move slower than the field of materials research. This is apparent when it comes to nanomaterials. The old exposure metrics based on mass is most likely not the best one to use for new materials such as carbon nanotubes (CNTs). In most applications only a few percent would be expected to be nanomaterials and the mass based methods often not that specific. Standards which rely on conventional optical microscopy have severe limits in resolution and won't be of any use when trying to detect, for example, release of single strands of CNTs. To get a better understanding of the possible adverse health effects of nanoparticle it is necessary to investigate a simpler system to isolate the importance of different factors, such as surface area. Understanding of the fundamental processes responsible of the outcome from aerosol processes generating these model particles need to be well understood to get the full picture of the model particles. In this thesis, work that aims to improve the understanding of exposure to nanomaterials is presented. Electron microscopy has been used in a systematic manner to detect nanomaterial, and a novel way of quantifying the detected material has been developed. Synergistic combinations of measurement methods from field measurements are shown, and methods for characterization of model particles are presented