The aim of this research was mainly to investigate desulfurization behaviour of ladle furnace slags of a low-sulfur steel. First, the change of the amount of unstable oxides (FetO and MnO) in slags was studied from the converter till the end of ladle furnace treatment for different steel quality groups. It was found that the change in the amount of unstable oxides could be examined best with low-C steel qualities. Then, the change of activity of iron oxide was investigated for a member of low-C steel quality group, namely 4937K, a low-S steel. The relation between the degree of desulfurization at the ladle furnace, % DeS (measured), and the change in activity of iron oxide, % Decrease in aFetO, was examined first using an empirical expression obtained from literature. Then, this relationship was studied using steel oxygen activity measurements conducted at the ladle furnace. With this method, a regression formula was proposed for 4937K slags relating activity coefficient of iron oxide, gama(FetO), with the major slag components. The results obtained from steel oxygen activities were found to be representative for 4937K steel-slag system showing similar behaviour with the ones from the empirical expression obtained from literature. Similar results were found using Temkin equation and the polymeric anion model. In relation to formation of less harmful inclusions to suppress adverse effects of sulfur, morphological studies of some steels produced in ERDEMiR plant were performed. D-type globular inclusions with severity values of 1-2 were observed.

In this study ferroboron (Fe - 14 at %B) was synthesized in crystalline form (Fe + Fe2B) via electrodeoxidation. For this purpose, Fe2O3 and H3BO3 were mixed in suitable proportions via spex mill. The powder was cold pressed and sintered at 900 &deg / C yielding a two phase structure Fe3BO6 and Fe2O3. The sintered pellets were electro-deoxidized in CaCl2 by applying 3.1 Volts at 850&deg / C for 12 hours. This yielded Fe and Fe2B in proportions slightly deviating from the target composition. The chemical pathway of reduction is inspected by the help of the available thermodynamic data and the x-ray characterization of partially reduced samples. CaO and the formation of Ca3B2O6 were found to be effective in the mid-steps of this electrodeoxidation process.

Electrochemical reductions of porous SiO2 pellets and bulk SiO2 plate were investigated in molten CaCl2 and/or CaCl2-NaCl salt mixture. The study focused on effects of temperature, particle size of the starting material, electrolyte composition and cathode design on the reduction rate. The behavior of the cathode contacting materials was also examined. Moreover, cyclic voltammetry study was conducted to investigate the mechanism of the electrochemical reaction. Mainly, XRD analysis and SEM examinations were used for characterizations. The rates of electrochemical reduction were interpreted from the variations of current and accumulative electrical charge that passed through the cell as a function of time under different conditions. The results showed that reduction rate of SiO2 increased slightly with increasing temperature or decreasing the particle size of SiO2 powder. Higher reduction rate was obtained when porous pellet was replaced by bulk SiO2 plate. Use of Kanthal wire mesh around the SiO2 cathode increased but addition of NaCl to the electrolyte decreased the reduction rate. X-ray diffraction results confirmed the reduction of SiO2 to Si in both CaCl2 salt and CaCl2-NaCl salt mixture. However, silicon produced at the cathode was contaminated by the nickel and stainless steel plates which were used as the cathode contacting materials. Microstructures and compositions of the reduced pellets were used to infer that electrochemical reduction of SiO2 in molten salts may become a method to produce solar grade silicon (SOG-Si). In addition, overall reduction potential of SiO2 pellet against the graphite anode and the potential of the cathode reaction at 750&deg / C in molten CaCl2-NaCl salt mixture were determined as 2.3 V (at 1.19 A current) and 0.47 V, respectively by cyclic voltammetry.

The purpose of this study was to synthesize calcium phosphates doped with titanium and fluoride ions in different combinations. Pure and doped calcium phosphates were synthesized by a precipitation method. The synthesized materials were sintered at 1100&ordm / C and 1300&ordm / C for 1h. The ceramics were characterized by density measurements to determine the effect of sintering temperature. Presence of phases and bonds were characterized by XRD diffraction and FTIR spectroscopy. Grain sizes of the samples were obtained by SEM. Microhardness test was applied on the samples to determine the mechanical properties of the samples. It was observed that Ti4+ addition decreased the density of samples significantly at 1100&deg / C, whereas increasing the sintering temperature to 1300&deg / C caused an increase. Increasing the F- ion amount increased the densification at 1100&deg / C when molar ratios were 1.0, 1.25, 1.50 and decreased the density at 1300&deg / C when Ca /P molar ratios were 1.0, 1.25, 1.67 and 2.0. Ti4+ and F- co-doped samples showed variety in their density behaviour after the sintering at 1100&ordm / C and 1300&ordm / C. The XRD analyses demonstrated that for Ca to P ratio 1 at 1100&deg / C, &beta / -CPP phase, when sintering temperature was raised to 1300&deg / C, as a second phase of &beta / -CPP and &alpha / -TCP observed. Increasing the molar ratio to 1.25 and 1.50 demonstrated &beta / -TCP and/or &beta / -CPP and &beta / -TCP/ HA at 1100&deg / C and &beta / -TCP and/or &beta / -CPP, &alpha / -TCP, TiO2 and HA, &alpha / -TCP, TiO2 phases at 1300&deg / C, respectively. In higher Ca/P molar ratios of 1.67 and 2.0, HA, &beta / -TCP, &alpha / -TCP, CaO, TiO2, CaTiO3 and HA, CaO, &alpha / -TCP, CaTiO3 phases were determined. Increasing the sintering temperature to 1300&deg / C resulted in transformation to &alpha / -TCP. In FTIR spectroscopy analysis, when the samples with molar ratio of 1, 1.25, 1.50, 1.67 and 2.0, sintered at 1100&deg / C, the characteristic bands of &beta / -CPP, OCP/&beta / -TCP, &beta / -TCP/HA, HA and HA were observed, respectively. With increasing the sintering temperature to 1300&deg / C, samples with molar ratio of 1.0 and 1.25 revealed additional secondary characteristic peaks of HA and &beta / -TCP. SEM images revealed that sintering temperature and ion amounts of dopants had significant effect on grain sizes of the samples. The grain sizes were generally increased when sintering temperature rose from 1100&deg / C to 1300&deg / C. The &mu / -hardness test demonstrated that Ti4+ and F- ions in large amounts had positive effect on the mechanical properties at the sintering temperatures of 1100&deg / C and 1300&deg / C

This study proposes a polarization-independent liquid-crystal Fresnel lens using the twisted nematic liquid crystal (TN-LC). At the high voltage state, the TN-LC behaves as an optically anisotropic material which makes the proposed LC Fresnel lens possess a polarization-insensitive characteristic. Two kinds of LC Fresnel lens, photoresist type and patterned electrodes type, are prepared in our experiment. Experimental results reveal that the photoresist type has a high diffraction efficiency and a good polarization-independent characteristic. However, its diffraction efficiency cannot be switched off. Contrarily, the patterned electrode type has the characteristics of the switch-off and good polarization-independent with a moderate diffraction efficiency

No description available.

The research outlined in this thesis is concerned with the environmental aspects of groundwater re-establishment as a consequence of surface mining. No principal effects which have been identified as being detrimental to the restored land area are as follows; i). The vertical and horizontal displacements of backfill materials following restoration, and ii). The pollution of groundwater from contact with weathered rockfill materials. The research into settlement has attempted to classify the types of movement which may occur within a backfill mass, in particular the differential movements which are of great importance to the stability of proposed structures or surface drainage. The field results from 10 opencast mine sites are presented, 3 of which were instrumented for detailed field investigations. It has been shown that backfill movements do not necessarily show similar trends under similar conditions, and reasons for this are proposed. A variety of instrumentation schemes have been devised to examine backfill displacements, both vertically and horizontally. Permeability testing has been conducted at different horizons the backfill mass in order to locate the zones of collapse settlement due to groundwater recovery. A critical review of the instrumentation utilised in the investigations is presented, with suggestions for improvement. Investigations into groundwater pollution have been devoted to examining the qualities of groundwater flowing into British surface mines and evaluating its likely reactions with fill materials. An insight into general groundwater pollution and treatment techniques is presented together with a critical analysis of their applicability, to British conditions. An investigation into water qualities in each of the six geographical regions of the opencast mining industry of Great Britain is detailed. Finally some suggestions for future research areas are indicated.

MgH2 is considered to be one of the most promising options for a solid state hydrogen storage material. For practical use it is still imperative to find a convenient means of overcoming its slow kinetics and high stability. In this investigation, a range of binary and ternary metal oxides of aluminium, silicon, titanium, and zirconium, as well as Pd-modified Ti02 samples, were prepared and characterised. The prepared oxides were ball milled with MgH2, and the hydrogen sorption behaviour of the ball milled mixtures was investigated using DSC-TGA-MSS, Sieverts and IGA. Thermodynamic parameters including enthalpies and entropies of hydrogen desorption were determined from experimental data, and activation energy calculations along with modelling of the kinetics were used to understand the mechanism and rate-limiting step of dehydrogenation. Oxide components, calcination temperature, and surface area were found to have a significant impact on the hydrogen sorption behaviour of MgH2 in the ball milled mixtures. Of the prepared binary and ternary oxides, Ti02 and mixed oxides with a Ti02 component were found to lower the dehydrogenation onset temperature by as much as 100°C, while additions of Pd-modified Ti02 resulted in the lowest dehydrogenation onset temperature of 205°C, compared to 360°C for ball milled MgH2. In addition, rates of hydrogen desorption and absorption were significantly increased as a result of the Ti02 and Ti02 - Pd additives. Dehydrogenation of 90 % of the full H2 capacity took 6 min at 300°C, compared to 230 min for milled MgH2 at 350°C. It was found that a reduction of the Ti02 oxide resulted in the active species responsible for the enhanced dehydrogenation behaviour. Through analysis of the reaction kinetics, the mechanism of dehydrogenation was found to change from a surface controlled, contracting volume model for ball milled MgH2 to one of a Johnson-Mehl-Avrami model of two - dimensional nucleation and growth upon addition of Ti02 and Ti02 - Pd.

The development of electronic surveying instruments, such as electronic theodolites, and concurrent advances in computer technology, has revolutionised engineering surveying; one of the more recent examples being the introduction of Electronic Theodolite Intersection Systems (ETISs). An ETIS consists of two or more electronic theodolites and a computer, with peripheral hardware and suitable software. The theoretical principles on which they are based have been known for a long time, but intersection has seldom been used as a method of measurement. The main reasons for its re-evaluation were the introduction of one-second electronic theodolites and the ability to interface these on-line to a computer. The last decade has seen the development of several commercially available systems and probably even more in-house developed systems. Such systems are capable of performing real-time, non-contact, three-dimensional coordinate determination to a high accuracy, enabling their use in a wide variety of applications. This thesis details all aspects of ETISs. Initially, the theoretical principles on which the systems are based are developed. The components of a system are then detailed and a review of current commercially available systems and their applications is given. The thesis then concentrates on the development of an ETIS by the author and details its' application in both industrial measurement and deformation monitoring. Finally, the thesis concludes with a discussion on the factors affecting the accuracies attainable with ETISs.

No description available.