QC 20101020

<p>The main objective of this industrially important work was to gain an increasing understanding of the properties of materials such as CMSX-4 nickel base super alloy, mould powder used in continuous casting of steel and coke used in blast furnace, with special reference to the thermal diffusivities. The measurements were carried out in a wide temperature range, solid, liquid, glassy and crystalline states.</p><p>For CMSX-4 alloy, the thermal conductivities were calculated from the experimental thermal diffusivities. Both the diffusivities and conductivities were found to increase with increasing temperature. Microscopic analysis showed the presence of intermetallic phases such as NiTi and NiTi2 below 1253 K. In this region, the mean free path of the phonons is likely to be limited by scattering against lattice defects. Between 1253 K and solidus temperature, these phases dissolved in the alloy adding to the impurities in the matrix, which, in turn, caused a decrease in the thermal diffusivity. This effect was confirmed by annealing the samples at 1573 K. The thermal diffusivities of the annealed samples measured at 1277, 1403 and 1531 K were found to be lower than the thermal diffusivities of non-annealed samples and the values did not show any noticeable change with time. It could be related to the attainment of equilibrium with the completion of the dissolution of γ and γ´ phases during the annealing process.</p><p>Liquid CMSX-4 does not show any change of thermal diffusivity with temperature. It may be attributed to the decreasing the mean free path being shorter than characteristic distance between two neighbouring atoms.</p><p>On the other hand thermal diffusivities of mould powder having glassy and crystalline states decrease with increasing temperature at lower temperature and are constant at higher temperature except for one glassy sample.</p><p>Analogously, the thermal diffusivity measurements of mould powder did not show any significant change with temperature in liquid state. It is likely to be due to the silicate network being largely broken down.</p><p>The thermal diffusivity is increased with increasing crystallisation degree of mould powder, which is expected from theoretical considerations.</p><p>The coke sample, taken from deeper level of the blast furnace, is found to have larger thermal diffusivity. This could be correlated to the average crystallite size along the structural <i>c</i>-axis, L_c, which is indicative of the higher degree of graphitisation. This was also confirmed by XRD measurements of the different coke samples. The degree of graphitisation was found to increase with increasing temperature. Further, XRD measurements of coke samples taken from different levels in the shaft of the blast furnace show that the graphitisation of coke was instantaneous between room temperature and 1473 K.</p>

No description available.

<p>The understanding of the hardenability is important in steel development with respect to weldability of steels as well as to the design of quenched and tempered steels.The common way to judge if steel is suitability to welding is the use of a carbon equivalent, which reflects the alloy content to the hardenability of the heat affected zone (HAZ). Most common of these equivalent is the IIW carbon equivalent wich has been in use for decades.</p><p>However, this is an empirical equivalent, developed for CMn steels, and it doesn't say anything about the mechanical properties obtained in the HAZ. As a guideline a maximum HAZ hardness of 350 HV is normally put to avoid cold cracking in the HAZ. Numerous carbon equivalents have been published during the years, but few have been accepted and used. A drawnback of all these equivalents is that they have been evaluated for a set of chemical compositions which may be quite narrow, or that they have been evaluated on steels produced having other cleanliness, residual element levels etc. as is common in modern steelmarketing. </p><p>The hardenability of steel designated to quenching and tempering is normally evaluated using either Jominy testing or using a calculation using the Grossmann formalism. As the hardenability described in the carbon equivalents used in welding and the hardenability of quenched and tempered steels using the Grossmann formalism are two different descriptions of the same phenomenon the aim of this thesis is to link these two formalisms together and use the knowledge from the HAZ hardenability to design quenched and tempered steels. The goal is to produce such steel grades having a much better weldability as compared with standard grades available at the market. </p><p>In this work the hardenability in the heat affected zone (HAZ) in weldments in high strength low alloyed steels (HSLA steels) having a yield strength of 350 MPa. This part microalloying elements on the phase transformations which take place during cooling from the peak temperature of the welding cycle. These results have been linked to the mechanical properties of the HAZs. </p><p>In the second part of this thesis the development of tool steel grades with respect to optimise both hardenability with respect to; </p><p>- matrix hardenability (i.e the Grossmann approach) </p><p>- an enhanced weldability of such new steels due to a lower alloying content than is usual in such grades</p>

Experiments of directional solidification in a Hele-Shaw cell, 240 mm x 245 mm x 1 mm, were carried out to study the effects of convective flows and the evolution of structure in the "mushy layer", consisting of fluid and crystallites. Three different concentrations of ammonium chloride (NH₄Cl) solution, 26%, 27% and 28%, with a constant bottom cooling temperature ranging from 5°C to -20°C were used as an analogue model for metallic alloy systems. The experimental design included techniques using Peltier heat pumps along with PID feedback control for temperature regulation. A shadowgraphic visualization method made possible the simultaneous observation of the evolution of convection in the liquid region and the phenomena of chimney formation within the mushy layer. More than one hundred runs were carried out. Temperature information and simultaneously acquired digital images were recorded automatically. The time evolution of the solidification process was traced by image processing technique from the digital images. Results show that the phenomenon of intermittent plumes frequently occurs. The number of plumes near the liquid-mush interface decreases from a larger number in the beginning to about the same number of high plumes in the liquid region or chimneys in the mush. The number of chimneys is more static than that of plumes due to the relatively low speed of solidification or dissolution. The mush consists of three different layers. A thin layer of generally upward oriented crystal forms rapidly in the beginning, followed by a second layer aggregate gradually covering it. Finally a third layer of dendritic crystals dominates the top of the growing mush. Preliminary experiments in a Hele-Shaw cell inclined at 21 degrees caused the mush structures to develop differently than in the normal geometry. The significant differences include the dendritic crystal form, the lacunae of the mush, the shape of the chimneys, and the porosity changes of the structures. Directions for future research are suggested.

The assembly of nanoparticles at the interface of immiscible fluids holds promise for the preparation of new materials that benefit from both the physical properties of the nanoparticles and the chemistry associated with the ligands. Shaking nanoparticle solutions in organic solvents with water, results in the formation of nanoparticle-coated droplets that range in size from 10 µm to 200 µm. A strategy to control the size of these emulsions is described, by passing the droplets through commercial track-etch membranes with known pore sizes. Extrusion reduces the droplet size by breaking the droplets while passing theough the membrane pores, and reforming in the presence of excess nanoparticles in solution to form droplets as small as 1-5 µm. Crosslinking of nanoparticles at a liquid interface lends greater stability to the interfacial assembly, leading to ultrathin nanoparticle-based capsules, which possess mechanical integrity even after removal of the interface. Two approaches towards crosslinking are used in this thesis. Norbornene-functionalized CdSe/ZnS are used to afford facile capsule visualization by fluorescence confocal microscopy, as well as ease of crosslinking in mild conditions by means of ring-opening metathesis polymerization (ROMP). The crosslinked capsules can be used to encapsulate materials, and display size-selective retention capability, governed by the interstitial spaces between the nanoparticles. In a second approach to making hybrid capsules and sheets, horse spleen ferritin bionanoparticles and aldehyde-functionalized CdSe quantum dots are co-assembled at an oil-water interface. The cross-linked materials formed by reaction of the aldehyde functionality on the quantum dots with the surface-available amines on the ferritin bionanoparticles can be disrupted by addition of acid, thus leading to pH-degradable capsules and sheets. The driving force for assembly of nanoparticles at liquid interfaces is the reduction of the interfacial energy between the two liquids. The factors governing the amount of interfacial stabilization provided by the nanoparticles, namely the size and ligand coverage of the nanoparticles, are examined using the example of mixed assemblies of two different types of nanoparticles. Assemblies of 10 nm cobalt nanoparticles are disrupted upon the addition of 2.5 nm CdSe nanoparticles. The studies in this thesis demonstrate that the lower density of ligand coverage on CdSe quantum dots can overcome the large difference in size between the two nanoparticles, thus displacing the cobalt nanoparticles from the interface. Finally, preliminary results using amphiphilic graft copolymers instead of nanoparticles for interfacial stabilization of liquids are discussed. The resulting capsules are used for encapsulation and release of nanoparticles. In a technique termed repair-and-go, these nanoparticle-filled capsules are used for repairing cracked surfaces by passing the capsules over hydrophilic substrates containing hydrophobic cracks.

The improvement of electrical energy storage (EES) devices such as batteries and electrochemical capacitors (ECs) is crucial to the widespread adoption of electric drive vehicles and the increased mobility of portable electronics. This research takes a unique approach to the improvement of EES devices through the investigation of a novel nanocomposite system to improve the performance of particle based electrodes. The majority of commercially available batteries and ECs have electrodes fabricated from a powder of fine particles (typically with particle sizes on the order of several µms). There is a severe lack of options for transforming these powders into usable electrodes. The traditional electrode fabrication method is to mix the active material powder with a polymer binder to form a sheet or film, which can then be implemented into the device. However, reliance on and incorporation of the polymer binder introduces several disadvantages and performance limitations. In this research, porous networks of carbon nanotubes (CNTs) are investigated to replace the polymer binder in the fabrication of particle based electrodes for electrochemical devices. The multifunctional CNT networks provide the supporting structure and electron conduction pathways to create freestanding and flexible composite electrodes with high electrical conductivities (50 - 100+ S/cm). Two case studies were carried out to explore the properties and performance of the new electrode structure: 1) Activated carbon (aC) particle based electrodes for electrochemical capacitors and 2) Silicon (Si) particle based electrodes for lithium-ion batteries. Samples were fabricated and characterized with an emphasis on obtaining processing-structure-property relationships to guide further development of these unique nanocomposite materials. The aC-CNT electrodes showed specific capacitances of ~50 F/g (in 6M KOH) with less than 10% capacitance loss after 30,000 cycles; demonstrating the ability of the CNT networks to maintain structural integrity during operational conditions. Si-CNT electrodes had high coulombic efficiencies (> 90%) and initial reversible capacities of over 2000 mAh/g. Additionally, fundamental issues are addressed such as possible electrode failure mechanisms and the limits of particle weight fractions that are achievable. Knowledge of the maximum weight fraction of particles obtainable within the CNT networks is important to determine the feasibility of the electrodes for commercial use. A volume-fraction-limited phenomenon is proposed for the mechanism of the particle loading limit and discussed with supporting evidence. / A Thesis submitted to the The Graduate School in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2010. / November 12, 2010. / carbon nanotube, binder-free, nanocomposite, electrode, battery / Includes bibliographical references. / Zhiyong Liang, Professor Directing Thesis; Tao Liu, Committee Member; Hsu-Pin Wang, Committee Member; Jianping Zheng, Committee Member.

No description available.

<p>Continuous hot-dip galvanizing is a common industrial process in which a steel sheet is immersed in a molten zinc alloy bath. After solidification, a thin zinc-rich layer is formed on the steel surface which protects the substrate in corrosive environments. Small amounts of antimony are sometimes added to the galvanizing bath to reduce zinc viscosity and ease the gas jet wiping operation. One of the side effects of antimony addition to the zinc alloy bath is the formation of very large zinc grains. One of the problems associated with coatings containing large zinc grains are relatively poor paint adhesion and detrimental mechanical properties. In this study, a galvanizing simulator was used to investigate the influence of important process variables such as bath composition, steel surface roughness and cooling conditions on the solidification of zinc coatings. The coating surface and cross-sectional microstructures were characterized via optical microscopy and Scanning Electron Microscopy (SEM). In addition, the zinc grain orientation distribution was investigated using Electron Backscattered Diffraction (EBSD). Furthermore, Scanning Auger Microscopy (SAM) was carried out on the coating surface to study the distribution of alloying elements and bath impurities in intermetallic phases. The results showed that the presence of small amounts of antimony in the zinc alloy bath enhanced the grain growth in preferred crystallographic orientations on both substrates. It was also found that the substrate surface roughness had a strong influence on the coating crystallographic texture such that zinc grains had a strong basal preferred orientation on smooth substrates while exhibiting prismatic or pyramidal orientations onrough substrates. Finally, zinc crystals were smaller for the slow-cooled coatings while zinc grains had almost the same diameter for the intermediate and fast-cooled coatings on both the smooth and rough substrates. Factors affecting the solidified microstructure, crystallographic orientation of zinc grains and phase assemblage will be discussed.</p> / Master of Applied Science (MASc)

<p>New electrochemical deposition methods have been developed for the fabrication of advanced composite coatings for organic solar cells and hybrid organic solar cells. The methods are based on electrodeposition of conjugated polymers and composites. In this work, poly[3-(3-N,N-diethylaminopropoxy)thiophene] (PDAOT) and poly(9,9-bis(diethylaminopropyl)fluorine- co-phenylene) (PDAFP) were used as electron donors. Single walled carbon nanotubes (SWNTs), ZnO and Ti0₂ were used as electron acceptors. Also co-deposition of PDAOT and PDAFP has been developed in order to broaden the absorption range.</p> <p>An electrophoretic deposition (EPD) method has been developed for the deposition of nanostructured ZnO and Ti0₂ films. The stabilization and charging of the nanoparticles in suspensions was achieved using organic molecules, such as dopamine and alizarin yellow (AY) dye, which were adsorbed on the oxide nanoparticles. The adsorption mechanism is based on the complexation of metal ions at the surfaces of oxide nanoparticles. Cationic dopamine additive was used for the formation of deposits by cathodic EPD. The adsorption of anionic AY on the oxide nanoparticles resulted in charge reversal and enabled the formation of anodic deposits. The method enabled the co-deposition of ZnO and Ti0₂ and the formation of composite films.</p> <p>Electrophoretic deposition (EPD) method has been developed for the fabrication of Ti0₂ films. Benzoic acid and phenolic molecules, such as 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, gallic acid, salicylic acid and salicylic acid sodium salt were investigated as charging additives for the EPD of Ti0₂ particles. The deposition yield has been studied as a function of the additive concentration and deposition time for cathodic deposits obtained from the suspensions, containing benzoic acid, 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid and anodic deposits prepared from the suspensions, containing gallic acid and salicylic acid sodium salt. The results obtained for the phenolic molecules with different number of OH groups were analyzed and compared with corresponding experimental data for benzoic acid without OH groups. The adjacent OH groups, as well as adjacent OH and COOH groups bonded to the aromatic ring of the phenolic molecules were beneficial for adsorption of the molecules on oxide particles. The adsorption mechanisms involved the interaction of COOH groups and OH groups of the organic molecules with metal ions on the particle surfaces and complexation.</p> <p>The functional dispersants investigated in this work can be utilized for dispersion and functionalization of the nanoparticles and fabrication of hybrid large area organic solar cells. The new deposition method can be applied for the fabrication of dye-sensitized solar cells.</p> / Master of Applied Science (MASc)