Master thesis deals with highly filled particulate composite materials for dental applications. In the practical part, the dimetacrylate matrix was filled with a mixture of particles of different types and different sizes to achieve the maximum possible packing. Moreover, filler content and the influence of filler on composite material was studied. Hydrolytic stability was also tested on composite materials. The methods used to characterize composite materials were bending test, thermogravimetric analysis (TGA), differential scanning photocalorimetry (DPC), dynamic-mechanical analysis (DMA) and scanning electron microscopy (SEM). Curing of the matrix was characterized by the degree of conversion, the heat of polymerization and the polymerization rate. Furthermore the polymerization shrinkage was measured. The glass transition temperature, the dynamic modulus at 40 °C and 100 °C, the modulus of elasticity, the strength, the critical value of the stress factor and the critical energy release rate were found in the tested samples.

Numerical models were developed to simulate the propagation of elastic and electromagnetic waves in an arbitrary, dense dispersion of spherical particles. The scattering interactions were modeled with vector multipole fields using pure-orbital vector spherical harmonics, and solved using the full vector form of the boundary conditions. Multiple scattering was simulated by translating the scattered wave fields from one particle to another with the use of translational addition theorems, summing the multiple-scattering contributions, and recalculating the scattering in an iterative fashion to a convergent solution. The addition theorems were rederived in this work using an integral method, and were shown to be numerically equivalent to previously published theorems. Both ordered and disordered collections of up to 5,000 spherical particles were used to demonstrate the ability of the scattering models to predict the spatial and frequency distributions of the transmitted waves. The results of the models show they are qualitatively correct for many particle configurations and material properties, displaying predictable phenomena such as refractive focusing, mode conversion, and photonic band gaps. However, the elastic wave models failed to converge for specific frequency regions, possibly due to resonance effects. Additionally, comparison of the multiple-scattering simulations with those using only single-particle scattering showed the multiple-scattering computations are quantitatively inaccurate. The inaccuracies arise from nonconvergence of the translational addition theorems, introducing errors into the translated fields, which minimize the multiple-scattering contributions and bias the field amplitudes towards single-scattering contributions. The addition theorems are shown to converge very slowly, and to exhibit plateaus in convergence behavior that can lead to false indications of convergence. The theory and algorithms developed for the models are broad-based, and can accommodate a variety of structures, compositions, and wave modes. The generality of the approach also lends itself to the modeling of static fields and currents. Suggestions are presented for improving and implementing the models, including extension to nonspherical particles, efficiency improvements for the algorithms, and specific applications in a variety of fields.

Air pollution is highly variable in both space and time, which presents many challenges to researchers when they wish to model concentrations. The modelling of air pollution is necessary for a number of reasons, which include the determination of human health effects, providing warning of health risks, and to understand general ecosystem health. In this thesis, modelling of air pollution through both space and time has been explored, with a focus on improving models that can be used to assign air pollution exposure. The techniques presented in this thesis have leveraged the ability of mobile monitoring units to collect air pollution concentration data multiple locations throughout a study period. First, we explore the use of combining mobile air pollution monitoring data with traditional fixed location monitoring. We find that the mobile data is able to provide insight into changes in spatial pattern between two temporal periods that could not be identified solely with the fixed location monitors, which demonstrates value in this monitoring approach that can be built upon with refinement of techniques. Second, we present a method to determine the amount of classical error that will be introduced when a long-term mean concentration is calculated from a discontinuous time-series dataset, which are the type of datasets collected by mobile air pollution monitoring. Third, we merge mobile and stationary air pollution monitoring data, along with meteorological, transportation, and land use information to model the hourly air pollution field using neural network models. The models developed allowed for the assignment of air pollution exposure incorporating human activity patterns. Also, they can be used to provide a spatially refined air quality health index. Lastly, we demonstrate exposure assignment that incorporates human activity patterns to calculate the dose exposure for students during their trips to school. This work commences with a demonstration of the basic utility of mobile air pollution monitoring data, which is to increase the number of monitored locations. Building on that utility of mobile technology, a technique was developed to estimate the error when mobile units are used for long-term estimates, similar to stationary monitoring units; and we were able to provide guiding principles for mobile monitoring data collection. Furthering our objective, to better understand the value of mobile data in a fully integrated monitoring network, we utilized both mobile and stationary data collection techniques together, in a single model, to produce accurate estimates of an air pollution field on an hourly basis. Finally, the research culminates with the demonstration of how mobile monitoring can be used for activity based air pollution exposure estimates, which was shown with a case-study of students’ trips between home and school. Overall, the chapters in this thesis work toward a better understanding of how to incorporate mobile monitoring data into air pollution assessment studies. / Thesis / Doctor of Philosophy (PhD)

<p> Ambient air pollution and pollution emitted from point sources, contribute to the total suspended particulate loadings measured at various monitoring stations, in any given area. Studies have shown that various meteorological variables may influence the concentration of particulates measured at these stations. 1989 data, from monitoring stations throughout Hamilton, Ontario, in conjunction with meteorological data from the Mount Hope airport, have been used to reveal, and to explain the aforementioned relationships. Results from graphical analysis, supports past findinqs from Stewart and Matheson (1967), Rouse and McCutcheon (1970), Dobroff (1990) and others, by showing that winds derived from a northern sector increase mean particulate loadings, and that wind speeds tend to be inversely related to measured particulate concentrations. In contrast to supporting findings from the graphical analysis, statistical ordinary least squares regression showed that for more stations than not, most parameter coefficients were not statistically significant. Results from the coefficient of determination show that none of regressions employed (linear, linear-log and log-log) could explain the relationship between the independent meteorological variables and the dependent variable (particulate concentration at a given monitoring site) with great precision. It follows that a non-linear correlation may well explain the dependence of particulate loading on wind speed, wind direction, mean temperature and total precipitation, and that source, (point and fugitive emissions), and other factors play important roles in this complex relationship.</p> / Thesis / Candidate in Philosophy

There are a number of inherent problems associated with the analysis of polycyclic aromatic compounds (PAC) in airborne particulate matter. The compounds of interest constitute a very small fraction of the total sample, but consist of hundreds of different components. Therefore, analytical techniques with very high resolving power are required. To try to address these problems, methods have been developed and improved to isolate, and subsequently profile, and identify the PAC present in typical airborne particulate samples. Since no single chromatographic technique can provide the desired resolution, a multi-stage clean-up scheme was required prior to analysis. Two methods were investigated in this study. Both methods used a Soxhlet extraction followed by fractionation using an adsorption chromatography step (silica or alumina) and Sephadex LH-20 to isolate the PAC fraction from the other organic constituents. Another problem associated with the analysis of PAC in airborne particulate matter was because of the method of sample collection. It was believed that there were changes in the chemical composition of the particulate and hence the PAC, during sample collection using a Hi-Vol sampler. Artifacts were being formed by reaction of gaseous pollutants with the particulate collected on the filter. An experiment was established to show that the addition of a denuder bundle to a Hi-Vol sampler could reduce this artifact formation during sampling by removing the reactive gases prior to the surface of the filter. The value of the denuder bundle was evaluated by comparison of the PAC from the denuder Hi-Vol with a standard Hi-Vol. Normal-phase HPLC coupled with mass spectrometry was shown to be a good method to compare the PAC in these samples. Some differences between standard and denuder Hi-Vol samples were observed in laboratory experiments, while the results from field sampling were inconclusive. The use of a parallel column gas chromatography-mass spectrometry (GC-MS) (also called third order chromatography) technique was investigated to determine its viability for the identification of the diverse range of PAC present in environmental samples. The PAC . in the NBS urban dust sample (SRM 1649) was analyzed to evaluate the method. To aid in data processing, a semi-automated peak detection routine has been developed. This routine used programs to aid in the data processing by simplifying peak detection and allow calculation of the retention indices of the components. Using the information supplied by the retention indices and the mass spectra, a data base was developed that was applied to a typical airborne particulate sample. / Thesis / Doctor of Philosophy (PhD)

Intermetallic composites of molybdenum disilicide reinforced with various amounts of silicon carbide particulate were produced by combustion synthesis from their elemental powders. Elemental powders were mixed stoichiometrically then ball-milled. The coldpressed mixture was then chemically ignited at one end under vacuum at approximately 700°C. The combustion temperature of the process was approximately 1600°C which was lower than the melting point of molybdenum disilicide. This processing technique allowed the fabrication of the composites at 700°C within a few seconds, instead of sintering at temperatures greater than 1200°C for many hours. The end product was a porous composite, which was densified to >97% ofthe theoretical density by hot pressing. The grains ofthe matrix were 8-14 μm in size surrounded by SiC reinforcement of 1-5 μm. The morphology and structure of the products were studied by x-ray diffraction and scanning electron microscopy (SEM). Samples were prepared for hardness, fracture strength, and toughness testing at room temperature. There were improvements in the mechanical properties of the composites with increasing SiC reinforcement. The hardness of the materials increased from 10.1 ± 0.1 GPa (959 ± 13 kg/mm2) to 11.7 ± 0.6 GPa (1102 ± 52 kg/mm2) to 12.7 ± 0.4 GPa (1199 ± 36 kg/mm2) with the 10 vol% and 20 vol% SiC reinforcement, respectively. The strength increased from 195±39 MPa to 237±39 MPa with 10 vol% and to 299 ± 43.2 MPa with a 20 vol% SiC reinforcement. The fracture toughness increased from 2.79 ± 0.36 MPa.m1/2 to 3.31± 0.41 MPa.m1/2 with 10 vol% SiC and to 4.08± 0.30 MPa.m1/2 with 20 vol% SiC. The increase in hardness and flexural strength is due to the effective load transfer across the strong interface in the composites. The main toughening mechanism is crack deflection by the residual stress in the materials, induced by the differences in the thermal expansion coefficients and the elastic moduli ofthe matrix and reinforcement. / Thesis / Master of Engineering (ME)

Automotive brake systems are source of particulate matter (PM) emissions, particularly in the urban areas. Several human ill-health are related with this kind of pollution. Along tire wear, road wear and dust from resuspension, the brake wear comprises the most relevant non-exhaust source of road traffic related emissions. Aiming at studying the PM brake emissions, this thesis is composed of an introductory part containing the main concepts and the state of art of the main subjects; and the experimental part, which comprehends three investigations. Chapters 2, 3, 4 and 5 are dedicated to the introduction part. Chapter 2 provides a brief description of the friction and wear, as well as the fundamental principles of braking by contact. Chapter 3 discuss the disc braking system, with particular attention to the pad friction materials. Chapter 4 is dedicated to friction layer: the layer usually developing at the disc/pad interface, affecting the performances of the tribological system. Finally, Chapter 5 provides an extensive discussion of the issues related to the particulate matter originated from disc brake systems. The experimental part is presented in the Chapters 6, 7, 8 and 9. Chapter 6 describes the methodology applied in all the investigations. Chapter 7 investigates the PM emissions behavior and its interaction with the friction and wear, aiming to identify the mechanism of generation the PM emissions. A copper-containing and a copper-free commercial friction materials were used, with particular emphasis on the effect of the scorching treatment. The Chapter 8 is dedicated at investigating the tribological behavior and the corresponding PM emissions in two Cu-free commercial friction materials, aiming to a better understanding the effect of abrasive ingredients on the emissions generation. Finally, the Chapter 9 investigated the addition of natural ingredient rice husk in a new eco-friendly Cu-free brake friction material composition, focusing the attention on the tribological and emissions behavior. All tests were carried out using a pin-on-disc tribometer equipped with an enclosure, especially designed for investigating the tribological properties, as well as the airborne particles generated by contact. Low-metallic friction materials, both commercial and laboratory-produced, were tested against cast iron discs. The tests parameters used correspond to mild sliding conditions resembling those faced in real braking. Such conditions are characteristic of driving in urban areas, where the expose to traffic PM is concentrated. A specific methodology of analysis was developed, based on SEM/EDXS techniques. Using this methodology, comparative investigations between the elemental composition of the virgin friction materials, the worn surfaces of the friction materials and the airborne particles collected during the tribological tests were carried out. The results point out the triboxidative wear as the main mechanism of the PM brake emissions generation. Moreover, particles produced by abrasive wear can be also directly emitted to the environment.

With the possession of extremely broad unique properties, particulate reinforced aluminum composites are very attractive in diverse applications. Aluminum matrix particulate composites are challenging to work with. A single pressing and sintering process was used to fabricate the reinforced aluminum composites in this study. The key advantage of this method is its comparative low expense. However, abrasive reinforcement powders can lead to shorter tool life. To study the fundamental wear mechanisms during the die compaction process, a new method was developed and combined with experiments to quantify tool wear. Automatic die compaction experiments and tribological experiments are employed in this study. The tribologcial experiments consist of a modified pin-onlat test and a modified loop test. Mass loss of tools was recorded during all the experiments. A new tool wear model was used in this study to investigate effect of different hard phase and different lubricant level on die compaction process.

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