This thesis reveals the tribological mechanisms behind the intrinsic low friction potential of the Co-based family of alloys called Stellites. Although being an established and important group of materials, a satisfactory explanation to why they exhibit low-friction properties under severe sliding conditions has not previously been found in the literature. The main part of this thesis is dedicated to the clarification of the tribological performance of Stellites in highly loaded sliding contact. The results should assist the development of Co-free alternatives, suitable for replacing Stellites in nuclear applications. Owing to their beneficial properties they are today the most commonly used material in the sealing surfaces on gate valves in the primary circuits of boiling water reactors (BWR). The underlying reason for the replacement in the nuclear applications is an undesired contribution to the background radiation level, originating from the Co in the Stellite surfaces. The Stellites mainly consist of Cr-rich carbides in a solid solution dominated by Co. The commonly used Stellite 6 and Stellite 21 were chosen as primary test materials and applied by laser cladding, providing a metallically bonded clad layer with a fine dendritic microstructure. By combining information from a series of dedicated tribological tests and modern high-resolution analysis instruments (e.g. SEM, XRD and TEM) available at the Ångström Laboratory at Uppsala University, the following conclusions can be made regarding the tribological performance of Stellites under high load sliding. Mechanisms. The (tested) Stellites form a thick deformation hardened layer, topped with a superficial easily sheared layer of hcp basal planes aligned parallel to the worn surface. The easy-shear layer is continually regenerated, replacing worn off material. Technical benefits. The Stellites offer low-friction properties thanks to their easily sheared surface layers. The risk of severe galling is also avoided by restricting shear and adhesive transfer to very thin superficial layers. In closed sliding contacts, self-generated protective layers formed by re-deposition of wear fragments are also offered.

Above true strain rates of $10^4$ s$^{-1}$ FCC metals exhibit a rapid increase in strength. Understanding of the physical mechanisms behind this strength transition is hindered by the number and interdependence of candidate mechanisms. Broadly, contributions to strength can be split into `instantaneous' effects and the more permanent `structural' ones. In this thesis a series of experiments are presented which are designed to separate the two types of contribution. Chapter 2 outlines the basics of dislocation plasticity, based on the seminal works of Taylor and Orowan. It then progresses on to discuss recent experimental and theoretical work on the understanding of slip as avalanche behaviour. Chapter 3 summarises traditional modelling approaches for instantaneous strength contributions which are routinely applied below $10^4$ s$^{-1}$. It then continues on to outline a number of different approaches which have been adopted to attempt to explain and model the strength transition. Chapter 4 outlines the methods used in the earliest stages of the study: Instron and split Hopkinson pressure bar methods. Both methods are well established, and cover the majority of the range of rates under study. Emphasis is made on minimising experimental sources of error, and subsequently accounting for those which are unavoidable. Finally, the specimen material is introduced and is shown to be fit for purpose. Chapter 5 presents a set of mechanical tests of specimens at strain rates between $10^4-10^5$~s$^{-1}$. The softening of the specimens with increased temperature is observed to increase with strain rate, both in absolute terms and when normalised to the 300 K measurement for each strain rate. The observations are most easily explained if the strength transition is due to an increase in early stage work hardening, however, some anomalous behaviours remain. Chapter 6 introduces a new experimental technique; direct impact Hopkinson pressure bars, required to perform experiments shown to be necessary by the results of Chapter 5. Photon Doppler velocimetry is applied to the projectiles used in experiments, removing one of the most significant flaws of the technique, and creating a more confident basis with which to perform further experimental work. Chapter 7 presents a series of `jump tests' at ambient temperatures. Specimens are deformed at strain rates ranging from $10^{-2}$ to $10^5$~s$^{-1}$ to a fixed strain of 0.1, then reloaded to yield at a strain rate of $10^{-1}$. The yield point at reload is shown to have the same rapid upturn as seen when the specimens were deforming at high rates, providing strong evidence that the increase in strength is due to changes in the underlying dislocation structure, rather than a dynamic effect, as it remains even when the high strain rate is removed. Chapter 8 continues on from the conclusions of Chapter 7. Jump tests are expanded to a variety of temperatures and strains, to provide a more complete characterisation of metal behaviour. No dramatic change in the saturation of work hardening is observed to coincide with the increase in early stage work hardening. Chapter 9 discusses discrepancies between contemporary high rate models and recent developments in the understanding of plasticity being an avalanche process. Potential consequences of incorporating avalanche plasticity into high rate models are explored. Particular attention is paid to Brown's observation that based on quasi static observations of avalanche behaviour, the formation of dislocation avalanches will begin to fail at strain rates of approximately $10^4$ s$^{-1}$. Consequences of the progressive breakdown of avalanche behaviour are discussed with respect to the experimental observations presented in earlier chapters. In Chapter 10, we will discuss the key conclusions of the work. Finally, a number of avenues are proposed for building upon the current work both theoretically and experimentally.

Orientador: Marco Aurelio Cremasco / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-09T06:13:25Z (GMT). No. of bitstreams: 1 Castilho_GuilhermeJosede_M.pdf: 55720465 bytes, checksum: ff5e31cd4371ec0283beb9eec7df3f35 (MD5) Previous issue date: 2007 / Resumo: Regimes gás-sólido têm inúmeras aplicações industriais, sendo empregados, por exemplo, em sistemas de transporte pneumático das partículas e em leito fluidizado. Nas últimas duas décadas notou-se a aplicação crescente do leito fluidizado circulante, principalmente para facilidades de geração de energia, como caldeira e reações catalíticas. No processo de craqueamento catalítico fluidizado (FCC), dentre os vários equipamentos que compõem uma unidade conversora, é no riser onde praticamente ocorrem todas as reações de craqueamento. Medidas de grandezas como concentração de sólidos são fundamentais para a compreensão da fluidodinâmica nestes reatores e é pré-requisito para o projeto técnico bem sucedido de sistemas de transporte pneumático. Dentre as várias técnicas utilizadas para medidas de grandezas básicas em sistemas particulados, a sonda de fibra óptica é relativamente simples, de alta precisão e utilizada em várias situações que envolvem o sistema fluido-partícula. Nesta Dissertação, a oncentração volumétrica dos sólidos é medida por meio de uma sonda de fibra óptica. A concentração volumétrica dos sólidos é tomada radialmente e em diversas posições axiais ao longo do riser sob diferentes condições de operação, na Unidade Multipropósito do Laboratório de Processos em Meios Porosos da Faculdade de Engenharia Química da Universidade Estadual de Campinas. Resultados mostram que a concentração volumétrica de sólidos é maior na parede em comparação ao centro do riser, para todas posições axiais, exceto para o ponto mais alto do reator, onde há a influência da região de saída do escoamento. Sobre a distribuição axial de de concentração, verificou-se que o escoamento é mais concentrado na parte inferior do equipamento e tende a ficar menos concentrado ao longo do reator. Através dos espectros de sinais obtidos pela sonda, pôde-se analisar as flutuações através da distribuição de probabilidade dos sinais e da distribuição do desvio padrão do sinal médio. Distribuições de probabilidade permitem identificar a presença de clusters em determinados pontos radiais, revelando que para as condições de mais concentradas, as flutuações são as maiores. As distribuições de desvio padrão apresentam picos, onde sugere maior interação entre as partículas / Abstract: Gas-solid systems have innumerable industrial applications, being used, for example, in the pneumatic conveying of particles and in fluidized bed. In the last two decades it was noticed increasing application of the circulating fluidized bed, mainly for easinesses of energy generation, as boilers and catalytic reactions. In the process of fluidized catalytic cracking (FCC), amongst some equipment that composes a converting unit, it is in riser where the cracking reactions practically occur at all. Measures as solid concentration are basic for the understanding of the fluidodynamic in these reactors and are prerequisite for the successful design of pneumatic transport systems. Amongst the several techniques used for measures in particulates systems, the optical-fiber probe is relatively simple, of high precision and used in some situations that involve fluid-particle system. In this Dissertation, the volumetric concentration of solids is measured by means of an optical-fiber probe. The volumetric concentration of solids is taken radially and in diverse axial positions throughout riser under different operation conditions, in the Multipurpose Unit of the Laboratory of Processes in Porous Means of the College of Chemical Engineering of the State University of Campinas. Results show that the volumetric solid concentration is bigger in the wall in comparison to the center of the riser, for all axial positions, except forthe highest point of the reactor, where it has the influence of the exit region of the flow. On the axial distribution of concentration, it was verified that the flow is more concentrated in the inferior part of the equipment. Through the electrical signs specters gotten by the probe, it could be analyzed the fluctuations through the distribution of probability of the signals and the distribution of the standard deviation of the average signal. The distribution of probability allows identifying the presence of clusters in determined radial points, disclosing that for the most concentrated conditions, the fluctuations are the greater. The distributions of the standard deviation present peaks, where it suggests greater interaction between particles / Mestrado / Engenharia de Processos / Mestre em Engenharia Química

Heavy Neutral Leptons (HNLs) are the heavier counterparts of the light neutrinos of the Standard Model of particle physics. HNLs can simultaneously solve several of the problems the Standard Model cannot yet resolve, one example being that they provide a candidate for Dark Matter. This thesis work aims to shed light on the nature of HNLs and study the displaced signature the particle gives rise to at colliders. The collider of interest is the Future Circular Collider that will be colliding electrons and positrons and the signal studied is the production of an HNL and a light neutrino from an intermediate Z boson, produced from the collision of an electron and a positron. The event generation was set up through MadGraph and PYTHIA and for the detector simulations DELPHES was used. Validation of three HNL samples were carried out in a standalone framework and in the FCC framework. The samples were validated by comparing theoretically calculated lifetimes with the lifetimes attained by simulation. Kinematic studies of the transverse momentum of the HNL and its decay particles showed correlation to the mass of the HNL. Reconstruction of the number of tracks created by the HNL decay was possible and the results of two track dominance were found to correlate with theory. For the vertexing study, the reconstruction of the production vertex of the decay particles was possible where displaced vertices were observed, hence proving the possibility of implementing displaced signatures in the FCC framework for the very first time. The next step in this trajectory of the study would be to investigate vertex fitting of the reconstructed vertices in order to carry out tracking studies of the HNL. This work hence sets the foundation for further exploration of HNLs and provides stepping stones for the possibility of discovery of HNLs in the FCC-ee.

Indiana University-Purdue University Indianapolis (IUPUI) / Nanoscale materials have become an active area of research due to the enhanced mechanical properties of the nanomaterials in comparison to their respective bulk materials. The effect that the size and shape of a nanomaterial has on its mechanical properties is important to understand if these materials are to be used in engineering applications. This thesis presents the results of molecular dynamics (MD) simulations on copper, gold, nickel, palladium, platinum, and silver nanowires of three cross-sectional shapes and four diameters. The cross-sectional shapes investigated were square, circular, and octagonal while the diameters varied from one to eight nanometers. Due to a high surface area to volume ratio, nanowires do not have the same atomic spacing as bulk materials. To account for this difference, prior to tensile loading, a minimization procedure was applied to find the equilibrium strain for each structure size and shape. Through visualization of the atomic energy before and after minimization, it was found that there are more than two energetically distinct areas within the nanowires. In addition, a correlation between the anisotropy of a material and its equilibrium strain was found. The wires were then subjected to a uniaxial tensile load in the [100] direction at a strain rate of 108 s-1 with a simulation temperature of 300 K. The embedded-atom method (EAM) was employed using the Foiles potential to simulate the stretching of the wires. The wires were stretched to failure, and the corresponding stress-strain curves were produced. From these curves, mechanical properties including the elastic modulus, yield stress and strain, and ultimate strain were calculated. In addition to the MD approach, an energy method was applied to calculate the elastic modulus of each nanowire through exponential fitting of an energy function. Both methods used to calculate Young’s modulus qualitatively gave similar results indicating that as diameter decreases, Young’s modulus decreases. The MD simulations were also visualized to investigate the deformation and yield behavior of each nanowire. Through the visualization, most nanowires were found to yield and fail through partial dislocation nucleation and propagation leading to {111} slip. However, the 5 nm diameter octagonal platinum nanowire was found to yield through reconstruction of the {011} surfaces into the more energetically favorable {021} surfaces.

A method is presented for adapting the classical Bishop-Hill model to the requirements of elastic/yield-limited design in metals of arbitrary crystallographic texture. The proposed Hybrid Bishop-Hill (HBH) model, which will be applied to ductile FCC metals, retains the `stress corners' of the polyhedral Bishop-Hill yield surface. However, it replaces the `maximum work criterion' with a criterion that minimizes the Euclidean distance between the applicable local corner stress state and the macroscopic stress state. This compromise leads to a model that is much more accessible to yield-limited design problems. Demonstration of performance for the HBH model is presented for an extensive database for oxygen free electronic (OFE) copper. The study also implements the HBH model to the polycrystalline yield surface via standard finite element analysis (FEA) tools to carry out microstructure-sensitive design. Anisotropic elastic properties are incorporated into the FEA software, as defined by the sample texture. The derived local stress tensor is assessed using the HBH approach to determine a safety factor relating to the distance from the yield surface, and thereby highlighting vulnerable spots in the component and obtaining a quantitative ranking for suitability of the given design. By following standard inverse design techniques, an ideal microstructure (meaning texture in this context) may be arrived at. The design problems considered is a hole-in-plate configuration of sheets loaded in uniaxial tension and simple compliant mechanisms. The further improvement of HBH model is discussed by introducing geometrically necessary dislocation (GND) densities in addition to the crystal orientations procedure in standard microstructure-based method. The correlations between crystal orientations and GND densities are studied. The shape of the yield surface most influenced by the texture of the material, while the volume of the envelope scales in accordance with the GND density. However, correlations between crystal orientation and GND content modify the yield surface shape and size. While correlations between GND density and crystal orientation are not strong for most copper samples, there are sufficient dependencies to demonstrate the benefits of the detailed four-parameter model. The four-parameter approach has potential for improving estimates of elastic-yield limit in all polycrystalline FCC materials.

No description available.

Catalytic pyrolysis technology is one of the thermochemical platforms used to produce high quality bio-oil and chemicals from biomass feedstocks. In the catalytic pyrolysis process, the biomass is rapidly heated under inert atmosphere in the presence of an acid catalyst or zeolite to promote deoxygenation and cracking of the primary vapors into hydrocarbons and small oxygenates. This dissertation examines the utilization of conventional fluid catalytic cracking (FCC) catalyst in the fractional catalytic pyrolysis of hybrid poplar wood. The influence of Y-zeolite content, steam treatment, addition of ZSM-5 additive, process conditions (temperature, weight hourly space velocity (WHSV) and vapor residence time) and recycling of the non-condensable gases (NCG) on the product distribution and the quality of the bio-oil were investigated. The first part of the study demonstrates the influence of catalytic property of FCC catalyst on the product distribution and quality of the bio-oil. It was found that FCC catalyst with higher Y-zeolite content produces higher coke yield and lower organic liquid fraction (OLF). Conversely, FCC catalyst with lower Y-zeolite content results in lower coke yield and higher OLF. The results showed that higher Y-zeolite content extensively cracks dehydrated products from cellulose decomposition and demethoxylates phenolic compounds from lignin degradation. The Y-zeolite promoted both deoxygenation and coke forming reactions due to its high catalytic activity and large pore size. Higher Y-zeolite content increased the quality of the bio-oil with respect to higher heating value (HHV), pH, density, and viscosity. The steam treatment at 732 oC and 788 oC decreased the total BET surface area of the FCC catalyst. The findings suggest that steam treatment reduces the coking tendency of the FCC catalyst and enhances the yield of the OLF. Analysis of the bio-oils showed that the steamed FCC catalyst produces bio-oil with lower viscosity and density. Gas chromatography and 13C-NMR spectrometry suggest that steam treatment affect the catalyst selectivity in the formation of CO, CO2, H2, CH4, C2-C5 hydrocarbons and aromatic hydrocarbons. The addition of ZSM-5 additive to the FCC catalyst was found to alter the characteristic/functionality of the catalytic medium. The product slate showed decrease in coke yield and increase in OLF with increase in ZSM-5 additive. The FCC/ZSM-5 additive hybrid catalysts produced bio-oils with relatively lower viscosity and higher pH value. The formation of CO2, CH4, and H2 decreased whilst C5 and aromatic hydrocarbons increased with increase in ZSM-5 additive level. The second part of the work assesses the effect of operating conditions on the catalytic pyrolysis process. The response surface methodology study showed reaction temperature to be the most influential statistically significant independent variable on char/coke yield, concentration of non-condensable gases, carbon content, oxygen content, pH and viscosity of the bio-oils. The WHSV was the most important statistically significant independent variable that affects the yield of organic liquid and water. Adequate and statistically significant models were generated for the prediction of the responses with the exception of viscosity. Recycling of the NCG in the process was found to potentially increase the liquid yield and decrease char/coke yield. The experiments with the model fluidizing gases showed that CO/N2, CO2/N2, CO/CO2/N2 and H2/N2 increase the liquid yield and CO2/N2 decrease char/coke yield. The results showed that recycling of NCG increases the higher heating value and the pH of the bio-oil as well as decreases the viscosity and density. The concept of recycling the NCG in the catalytic cracking of biomass vapors with FCC catalyst improved the overall process. The evaluation of the reactivity of conventional FCC catalyst towards bio-based molecules provide essential direction for FCC catalyst formulation and design for the production of high quality bio-oils from catalytic pyrolysis of biomass. / Ph. D.

The Fluidized Catalytic Cracking (FCC) is known for its ability to convert refinery wastes into useful fuels such as gasoline, diesel and some lighter products such as ethylene and propylene, which are major building blocks for the polyethylene and polypropylene production. It is the most important unit of the refinery. However, changes in quality, nature of crude oil blends feedstock, environmental changes and the desire to obtain higher profitability, lead to many alternative operating conditions of the FCC riser. There are two major reactors in the FCC unit: the riser and the regenerator. The production objective of the riser is the maximisation of gasoline and diesel, but it can also be used to maximise products like propylene, butylene etc. For the regenerator, it is for regeneration of spent or deactivated catalyst. To realise these objectives, mathematical models of the riser, disengage-stripping section, cyclones and regenerator were adopted from the literature and modified, and then used on the gPROMS model builder platform to make a virtual form of the FCC unit. A new parameter estimation technique was developed in this research and used to estimate new kinetic parameters for a new six lumps kinetic model based on an industrial unit. Research outputs have resulted in the following major products’ yields: gasoline (plant; 47.31 wt% and simulation; 48.63 wt%) and diesel (plant; 18.57 wt% and simulation; 18.42 wt%) and this readily validates the new estimation methodology as well as the kinetic parameters estimated. The same methodology was used to estimate kinetic parameters for a new kinetic reaction scheme that considered propylene as a single lump. The yield of propylene was found to be 4.59 wt%, which is consistent with published data. For the first time, a Z-factor correlation analysis was used in the riser simulation to improve the hydrodynamics. It was found that different Z factor correlations predicted different riser operating pressures (90 – 279 kPa) and temperatures as well as the riser products. The Z factor correlation of Heidaryan et al. (2010a) was found to represent the condition of the riser, and depending on the catalyst-to-oil ratio, this ranges from 1.06 at the inlet of the riser to 0.92 at the exit. Optimisation was carried out to maximise gasoline, propylene in the riser and minimise CO2 in the regenerator. An increase of 4.51% gasoline, 8.93 wt.% increase in propylene as a single lump and 5.24 % reduction of carbon dioxide emission were achieved. Finally, varying the riser diameter was found to have very little effect on the yields of the riser products.

In 1996, Congress passed the Telecommunications Act which increased the proportion of the national television audience a media company could reach to 35%. Seven years later, the FCC further deregulated ownership, increasing the proportion of audience a media company could reach to 45%. This change also allowed crossownership of media outlets in larger local markets. This paper will research how media ownership groups have changed by documenting the acquisitions and sales of four of the largest media companies in comparison to four smaller ownership groups. It will also discuss what effects those changes have had on ownership diversity. This thesis will answer the following question: has media ownership become less diverse since the 2003 Biennial Review of the 1996 Telecommunications Act?