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- Järlskog, Ida, 1991
(författare)
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Occurrence of Traffic-Derived Microplastics in Different Matrices in the Road Environment
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The prevalence of microplastic contamination has raised concerns about the potential risk and impact on the global environment. Traffic-derived microplastics, i.e., tire wear particles (TWP), polymer-modified bitumen, and road markings contribute to the emissions, and TWP are assumed to be one of the largest sources of microplastic emissions. Due to analytical difficulties, there is still a knowledge gap regarding transport routes, environmental concentrations, and toxicity. This thesis aims to investigate the occurrence of traffic-derived microplastics in several traffic environments and thereby increase the understanding of the particles. Samples were collected on the road surface (Paper I‒IV), in the stormwater (Paper I, II, and IV), in the air (Paper IV), and in material collected by a street sweeper (Paper I‒II). In addition to environmental samples, a road-simulator was used to generate TWP in a controlled environment enabling comparison between tire types and brands resulting in a deeper understanding of the characteristics and physicochemical properties of TWP (Paper V). Different sample preparation steps such as optimised density separation, solvent cleaning, and size fractionation have been assessed, and several analytical methods light microscopy, SEM/EDX, FTIR, and pyr-GC/MS have been evaluated and used for the analysis of traffic-derived particles. Further, a novel method, automated SEM/EDX single particle analysis coupled to a machine learning classifier, has been developed for the analysis of TWP and other traffic-derived particles (Paper III, implemented in Paper IV). The automated SEM/EDX determined the size, shape, surface texture, and elemental composition of the different particles, and was able to categorize the particles into several subclasses: TWP, bitumen, road markings, metals, organics, and minerals. The estimated absolute masses showed that the fine fraction (2‒20 µm) corresponds to more than 50w% of the TWP and bitumen wear particles independently of the sample matrix indicating that TWP can both affect the PM10 concentrations and be transported long distances through water and air (Paper IV). Further, it was concluded that the stormwater system is an important transport route for traffic-derived particles, especially since the road runoff in Sweden is not commonly treated prior to release to recipients. Street sweeping as a potential measure to prevent the spreading of TWP was evaluated in Paper I‒II. Even though the street sweeper collects considerable amounts of material containing high concentrations of TWP, metals, and organic pollutants, no clear reduction was detected neither on the road surface nor in the stormwater. Besides traffic-derived microplastics, Paper II analysed metals and organic pollutants. The results showed concentrations of metals, PAH, phthalates, and aliphatic hydrocarbons exceeding the national guidelines. The result from this thesis contributes to an increased knowledge about the properties and composition of TWP as well as the occurrence of traffic-derived microplastics in different environments. The results can be used as validation against theoretical emissions and transport models. The results have also highlighted the importance of including fine particles (<20 µm) in forthcoming works.
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| 2. |
- Nigro, Claudio F., Dr.
(författare)
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Phase-field modeling of stress-induced precipitation and kinetics in engineering metals
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The formation of brittle compounds in metals operating in corrosive environments can be a tremendous source of embrittlement for industrial structures and such phenomenon is commonly enhanced in presence of stresses. To study this type of microstructural change modeling is preferred to experiment to reduce costs and prevent undesirable environmental impacts. This thesis aims at developing an engineering approach to model stress-induced precipitation, especially near stress concentrators, e.g. crack tips, for multi-phase and polycrystalline metals, with numerical efficiency.In this thesis, four phase-field models are developed and applied on stress-induced hydride precipitation in zirconium and titanium alloys. The energy of the system is minimized through the time-dependent Ginzburg-Landau equation, which provides insights to the kinetics of the phenomenon. In these models, the driving force for precipitation is the coupling between the applied stress and the phase transformation-induced dilatation of the system. Models 1-3 implicitly incorporate near crack-tip stress fields by using linear elastic fracture mechanics so that only the phase-field equation is solved numerically with the finite volume method, reducing the computational costs. Phase transformation is investigated for intragranular, intergranular and interphase cracks in single- and two-phase materials by considering isotropy and some degrees of anisotropy, grain/phase boundary energy, different transition orders and solid solubility limit. Model 4 allows representing anisotropy connected to lattice mismatch and the orientation of the precipitates influenced by the applied stress. The model is employed through the finite element program Abaqus, where the fully coupled thermo-mechanical solving method is applied to the coupled mechanical/phase-field problem. Hydride growth is observed to follow the near-crack tip hydrostatic stress contours and can reach a steady state for specific conditions. The relation between hydride formation kinetics and material properties, and stress relaxation are well-reflected in the results.With the presented approaches, precipitation kinetics including different kinds of defects, multi-phase microstructures, phase/grain boundaries, order transitions and loading modes can be successfully captured with low computational costs. They could therefore contribute to the numerical efficiency of multi-scale environment-assisted embrittlement prediction schemes within commercial software serving engineering projects.
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| 3. |
- Nilsson, Viktor, 1985-
(författare)
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Highly Concentrated Electrolytes for Rechargeable Lithium Batteries
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electrolyte is a crucial part of any lithium battery, strongly affecting longevity and safety. It has to survive rather severe conditions, not the least at the electrode/electrolyte interfaces. Current commercial electrolytes are almost all based on 1 M LiPF6 in a mixture of organic solvents and while these balance the many requirements of the cells, they are volatile and degrade at temperatures above ca. 70°C. The salt could potentially be replaced with e.g. LiTFSI, but dissolution of the Al current collector would be an issue. Replacing the graphite electrode by Li metal, for large gains in energy density, challenges the electrolyte further by exposing it to freshly deposited Li, leading to poor coulombic efficiency and consumption of both Li and electrolyte. Highly concentrated electrolytes (HCEs) have emerged as a possible remedy to all of the above, by a changed solvation structure where all solvent molecules are coordinated to cations – leading to a lowered volatility, a reduced Al dissolution, and higher electrochemical stability, at the expense of higher viscosity and lower ionic conductivity.In this thesis both the fundamentals and various approaches to application of HCEs to lithium batteries are studied. First, LiTFSI–acetonitrile electrolytes of different salt concentrations were studied with respect to electrochemical stability, including chemical analysis of the passivating solid electrolyte interphases (SEIs) on the graphite electrodes. However, some problems with solvent reduction remained, why second, LiTFSI–ethylene carbonate (EC) HCEs were employed vs. Li metal electrodes. Safety was improved by avoiding volatile solvents and compatibility with polymer separators was proven, making the HCE practically useful. Third, the transport properties of HCEs were studied with respect to salt solvation, viscosity and conductivity, and related to the rate performance of battery cells. Finally, LiTFSI–EC based electrolytes were tested vs. high voltage NMC622 electrodes.The overall impressive electrochemical stability improvements shown by HCEs do not generally overcome the inherent properties of the constituent parts, and parasitic reactions ultimately leads to cell failure. Furthermore, improvements in ionic transport can not be expected in most HCEs; on the contrary, the reduced conductivity leads to a lower rate capability. Based on this knowledge, turning to a concept of electrolyte compositions where the inherent drawbacks of HCEs are circumvented leads to surprisingly good electrolytes even for Li metal battery cells, and with additives, Al dissolution can be prevented also when using NMC622 electrodes.
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