The aluminum industry is in need of high-speed in-situ elemental identification technology for molten metals. wTe Corporation of Bedford, MA was granted funds to research this technology for aluminum through the Advanced Technology Program (ATP) of the National Institute of Standards and Technology (NIST). As a secondary metal scrap processor, wTe Corporation is interested in increasing the value of scrap and better identification technology is one way of doing this. With better identification technology, foundries and smelters will be more confident in the melt chemistry and more apt to use secondary aluminum which decreases the energy required for processing by approximately 85%. wTe Corporation is exploring two avenues for in-situ molten metal identification: Laser Induced Breakdown Spectroscopy (LIBS) and X-Ray Fluorescence (XRF). The objectives of this work were to contribute to developing XRF technology for in-situ identification of molten metal by establishing a method of data instrumentation and analysis for XRF to determine aluminum melt composition, investigate the major alloying elements in the Al380 alloy series and determine the relationship between intensity and concentration, and to determine the effect of temperature on XRF Spectra. The XRF instrumentation development and the technical challenges associated with high temperature measurements are presented. The relationship between intensity and concentration is presented for three alloys within the 380 alloy series, and lastly it is observed that there are significant differences between liquid and solid spectra and that a calibration curve for liquid data is necessary. Several hypotheses are given as to why this difference between liquid and solid state spectra may occur.

This thesis examines the flow of very viscous Newtonian fluids driven by gravity. It is written with concern for specific applications in the optics industry, with emphasis on the slumping of molten glass into a mould, as in the manufacture of optical components, which are in turn used to manufacture ophthalmic lenses. This process is known as thermal replication. However, the work has more general applicability, and disc viscometry, used to determine the viscosity of very viscous fluids, is also considered. In addition, one chapter of the thesis is devoted to the flow of dripping honey, as another example of a very viscous flow to which the model can be applied. The Stokes creeping-flow equations are used to model the very viscous flows of interest. The main solution method is finite elements, and a purpose-written computer program has been developed to solve the creeping-flow equations by this method. The present program is restricted to solving for either two-dimensional or axisymmetric flows but is extendible to three dimensions. In addition, semi-analytic series and asymptotic methods are used for some small portions of the work. The optical applications of this work demand consideration of the topic of computing surface curvature, and therefore second derivatives, from inexact and discrete numerical and experimental data. For this purpose, fitting of B-splines by a least-squares method to coordinate data defining the surface has been used. Much of the work assumes isothermal conditions, but in the context of the accuracy required in optical component manufacture it is also possible that non-isothermal effects will be important. Consequently, this restriction is eventually relaxed and some consideration given to non-isothermal conditions. In order to validate the creeping-flow model and finite-element program, comparisons of numerical simulations with experimental results are performed. A preliminary assessment of the importance of non-isothermal conditions to the thermal-replication process is also made by comparing isothermal and non-isothermal simulations with experimental results. The isothermal model is found to best match the experimental data. / Thesis (Ph.D.)--School of Applied Mathematics, 1998.

The transient two-dimensional thermocapillary convection and molten pool shape in melting or welding with a time-dependent and distributed incident flux are numerically predicted in this study. Determination of the molten pool shapes is crucial, because of its close relationships with the strength, microstructure, and mechanical properties of the fusion zone. In the work, the time-dependent incident flux is assumed to be a function of scanning speed and energy distribution parameter. Transport processes at the time corresponding to the maximum cross section can be identical to those under steady three-dimensional condition. The computed flow patterns and molten pool shapes under the flat free surface exhibits distinct regions for different Marangoni and Prandtl numbers. The effects of Peclet number and beam power on flow and temperature fields and fusion zone shapes are also presented. The computed results are confirmed by comparing the predicted peak speed on the free surface and molten pool width with those obtained from scale analysis provided in the literature.

No description available.

Microelectrodes have been found to be a valuable tool in a variety of analytical studies. Their advantages over macro-sized electrodes are well known, including their enhanced mass transport properties (due to their ubiquitous hemispherical diffusion) which lead to steady state responses without external convection. They also exhibit high signal-to-noise ratios (greater sensitivities), furthering their analytical application. Microelectrode arrays are analytical devices with multiple electrodes. There are suitable for practical sensing with all the benefits of microelectrodes but with greater currents, leading to greater ease of measurement. To produce a reliable electroanalytical device the microelectrode response must be reproducible, a fundamental property based on the quality control of their production. Square microelectrode and array fabrication techniques have been developed for this purpose. This research discusses the fabrication and development of closely spaced arrays of square microelectrodes. Simulated and measured responses are compared and used to characterize electrode and array responses by cyclic voltammetry, electrical impedance spectroscopy and current-time transients. Measurements on variably spaced arrays allow insight into overlap of hemispherical diffusion from individual electrodes and the subsequent effect including peak current output on the array device. By studying these devices key insights into the mass transport properties of single square microelectrodes and microelectrode arrays were gained. This study also prepares and develops microelectrodes from materials appropriate for use in the extreme environments of molten salts and concentrated nitric acid solutions. These robust electrodes were developed for use in hydro- and pyro-chemical techniques for nuclear fuel reprocessing. These results demonstrate the practical uses for microelectrode systems across a wide range of chemical systems and in extreme conditions.

Title page, summary and table of contents only. The complete thesis in print form is available from the University of Adelaide Library. / Ash deposition is a problem in power generation when coal with high ash and alkali contents are utilised. The problem is more severe in fluidised bed combustion where the ash deposition can causes agglomeration of the bed material, may lead to defluidisation of the unit. The successful operation of fluid bed combustion with coal high in ash and alkali content will depend on the ability to control ash deposition. The rheological properties of coal ash under furnace conditions are important in controlling the stickiness and mobility of the molten ash deposition. Therefore, a good knowledge of the rheological properties of coal will improve the understanding of the mechanisms associated with ash deposition, and may assist in controlling the deposition and agglomeration of fluid bed material. At present, a good deal of information about coal ash rheology under conditions similar to those found in fluidised bed combustion is not known, and greater understanding is required. This is primarily due to a lack of reliable instruments and measurement techniques. In this work, a new high temperature rheometer has been developed based on the principle concepts of visco metric flow. The developed rheometer allows fundamental rheological properties, such as shear stress and shear rate, to be obtained without relying on calibrations with materials of known properties. With this instrument the flow characteristics of the tested samples can be determined directly, without assuming a particular fluid model. The new rheometer has the capability to measure the rheological properties of materials at temperatures ranging from 500°C to 1300°C and under different processing conditions. Rheological characteristics and properties of a range of low rank Australian coal ashes have been carried out using the newly developed high temperature rheometer, equipped with a cone and plate measuring geometry. It has been found that coal ash samples exhibit thixotropic and visco plastic flow behaviours. SEM and XRD analyses have revealed that during high temperature rheological measurements the coal ash sample is basically a suspension of colloidal mineral solids in a molten eutectic liquid. The solid phase is mainly silica (SiO₂,), and the liquid phase is a mixture of alkali sulphates mainly CaS0₄, MgS0₄ and Na₂S0₄ compounds. The equilibrium visco metric data of coal ash samples is found to be satisfactorily described using the Herschel-Bulkley model. The equilibrium rheological properties are strongly affected by the concentration levels of CaS0₄, MgS0₄ and Na₂S0₄ . The operating temperature and chemical composition of the surrounding gas phase were also found to affect the rheological properties of the coal ash samples. In order to obtain a better understanding and to model the rheological properties of the coal ashes, a series of synthetic ash mixtures were examined. The synthetic mixtures contained the key chemical components that represent the solid and the liquid phases. The solid phase is represented by silica (SiO₂), while a mixture of CaS0₄, MgS0₄ and Na₂S0₄ compounds represented the liquid phase. In this work, the rheological characteristics of mixtures of synthetic ash were investigated using a factorial experimental design. Using the synthetic ash mixtures together with the statistical design experiment, the effect of key chemical compounds on the rheological properties could be systematically investigated. The rheological results showed that the synthetic mixtures exhibited thixotropic and viscoplastic behaviours. It was also found that mixtures predominantly high in CaS0₄and MgS0₄ had a high degree of thixotropy behaviour, while those mixtures predominantly high in Na₂S0₄ showed a lower degree of thixotropy behaviour. The statistical analysis also showed that Na₂S0₄ is the most significant chemical compound causes a high yield stress and high viscosity. In contrast, CaS0₄and MgS0₄ were found to decrease the value of the yield stress and the viscosity. The rheological behaviour of the synthetic ash mixtures can be used to describe rheological behaviour of the coal ash samples. Relationships between equilibrium flow properties and chemical compounds, and temperatures are developed using a linear regression method. The statistical analysis has shown that CaS0₄, MgS0₄ and Na₂S0₄ , and their interactions are all significant compounds that have effects on the yield stress and viscosity of the synthetic mixtures. It was also found that the yield stress and viscosity decreased with increasing concentration level of either CaS0₄or MgS0₄ . Yield stress and viscosity are increased with increases in the concentration of Na₂S0₄ . The statistical models can successfully predict rheological properties of ash with high concentrations of CaS0₄, MgS0₄ and Na₂S0₄ , but it fails to predict the rheological properties of ashes that also high concentrations of either Fe₂0₃ or Al₂0₃, or a combination of both. The relationship between ash rheology and fluidised bed agglomeration has been established. The yield stress of a coal ash may be used to describe the tendency of the molten ash to deposit on surface of the fluid bed particles. Yield stress also determines the tendency of stickiness of the molten ash deposit to adhere the fluid bed particles during fluidised bed combustion process. The viscosity of the molten ash describes the ability of the molten ash layer to adhere the fluid bed particles after a collision. High viscosity ash tend to hold the colliding particles together longer than a low viscosity ash. Shear thinning behaviour of the ash samples (decreasing viscosity with increasing shear rate) suggests that the operating conditions could be arranged so as to minimise the chance of agglomeration. For example, in order to avoid agglomeration a high viscosity coal ash would benefit from operating the fluidised bed combustion at a high velocity, this is because a high velocity means a higher shear rate and this causes a reduction in the viscosity of the molten ash. Thus, particles agglomerated by a low viscosity ash would be easily broken by the hydrodynamic forces present during the fluidised bed process. Finally, information about ash rheology has formed a basic knowledge for estimating tendency of fluid bed agglomeration when coal obtained from different source is being used. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1141958 / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2004

Title page, summary and table of contents only. The complete thesis in print form is available from the University of Adelaide Library. / Ash deposition is a problem in power generation when coal with high ash and alkali contents are utilised. The problem is more severe in fluidised bed combustion where the ash deposition can causes agglomeration of the bed material, may lead to defluidisation of the unit. The successful operation of fluid bed combustion with coal high in ash and alkali content will depend on the ability to control ash deposition. The rheological properties of coal ash under furnace conditions are important in controlling the stickiness and mobility of the molten ash deposition. Therefore, a good knowledge of the rheological properties of coal will improve the understanding of the mechanisms associated with ash deposition, and may assist in controlling the deposition and agglomeration of fluid bed material. At present, a good deal of information about coal ash rheology under conditions similar to those found in fluidised bed combustion is not known, and greater understanding is required. This is primarily due to a lack of reliable instruments and measurement techniques. In this work, a new high temperature rheometer has been developed based on the principle concepts of visco metric flow. The developed rheometer allows fundamental rheological properties, such as shear stress and shear rate, to be obtained without relying on calibrations with materials of known properties. With this instrument the flow characteristics of the tested samples can be determined directly, without assuming a particular fluid model. The new rheometer has the capability to measure the rheological properties of materials at temperatures ranging from 500°C to 1300°C and under different processing conditions. Rheological characteristics and properties of a range of low rank Australian coal ashes have been carried out using the newly developed high temperature rheometer, equipped with a cone and plate measuring geometry. It has been found that coal ash samples exhibit thixotropic and visco plastic flow behaviours. SEM and XRD analyses have revealed that during high temperature rheological measurements the coal ash sample is basically a suspension of colloidal mineral solids in a molten eutectic liquid. The solid phase is mainly silica (SiO₂,), and the liquid phase is a mixture of alkali sulphates mainly CaS0₄, MgS0₄ and Na₂S0₄ compounds. The equilibrium visco metric data of coal ash samples is found to be satisfactorily described using the Herschel-Bulkley model. The equilibrium rheological properties are strongly affected by the concentration levels of CaS0₄, MgS0₄ and Na₂S0₄ . The operating temperature and chemical composition of the surrounding gas phase were also found to affect the rheological properties of the coal ash samples. In order to obtain a better understanding and to model the rheological properties of the coal ashes, a series of synthetic ash mixtures were examined. The synthetic mixtures contained the key chemical components that represent the solid and the liquid phases. The solid phase is represented by silica (SiO₂), while a mixture of CaS0₄, MgS0₄ and Na₂S0₄ compounds represented the liquid phase. In this work, the rheological characteristics of mixtures of synthetic ash were investigated using a factorial experimental design. Using the synthetic ash mixtures together with the statistical design experiment, the effect of key chemical compounds on the rheological properties could be systematically investigated. The rheological results showed that the synthetic mixtures exhibited thixotropic and viscoplastic behaviours. It was also found that mixtures predominantly high in CaS0₄and MgS0₄ had a high degree of thixotropy behaviour, while those mixtures predominantly high in Na₂S0₄ showed a lower degree of thixotropy behaviour. The statistical analysis also showed that Na₂S0₄ is the most significant chemical compound causes a high yield stress and high viscosity. In contrast, CaS0₄and MgS0₄ were found to decrease the value of the yield stress and the viscosity. The rheological behaviour of the synthetic ash mixtures can be used to describe rheological behaviour of the coal ash samples. Relationships between equilibrium flow properties and chemical compounds, and temperatures are developed using a linear regression method. The statistical analysis has shown that CaS0₄, MgS0₄ and Na₂S0₄ , and their interactions are all significant compounds that have effects on the yield stress and viscosity of the synthetic mixtures. It was also found that the yield stress and viscosity decreased with increasing concentration level of either CaS0₄or MgS0₄ . Yield stress and viscosity are increased with increases in the concentration of Na₂S0₄ . The statistical models can successfully predict rheological properties of ash with high concentrations of CaS0₄, MgS0₄ and Na₂S0₄ , but it fails to predict the rheological properties of ashes that also high concentrations of either Fe₂0₃ or Al₂0₃, or a combination of both. The relationship between ash rheology and fluidised bed agglomeration has been established. The yield stress of a coal ash may be used to describe the tendency of the molten ash to deposit on surface of the fluid bed particles. Yield stress also determines the tendency of stickiness of the molten ash deposit to adhere the fluid bed particles during fluidised bed combustion process. The viscosity of the molten ash describes the ability of the molten ash layer to adhere the fluid bed particles after a collision. High viscosity ash tend to hold the colliding particles together longer than a low viscosity ash. Shear thinning behaviour of the ash samples (decreasing viscosity with increasing shear rate) suggests that the operating conditions could be arranged so as to minimise the chance of agglomeration. For example, in order to avoid agglomeration a high viscosity coal ash would benefit from operating the fluidised bed combustion at a high velocity, this is because a high velocity means a higher shear rate and this causes a reduction in the viscosity of the molten ash. Thus, particles agglomerated by a low viscosity ash would be easily broken by the hydrodynamic forces present during the fluidised bed process. Finally, information about ash rheology has formed a basic knowledge for estimating tendency of fluid bed agglomeration when coal obtained from different source is being used. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1141958 / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2004

This thesis examines the flow of very viscous Newtonian fluids driven by gravity. It is written with concern for specific applications in the optics industry, with emphasis on the slumping of molten glass into a mould, as in the manufacture of optical components, which are in turn used to manufacture ophthalmic lenses. This process is known as thermal replication. However, the work has more general applicability, and disc viscometry, used to determine the viscosity of very viscous fluids, is also considered. In addition, one chapter of the thesis is devoted to the flow of dripping honey, as another example of a very viscous flow to which the model can be applied. The Stokes creeping-flow equations are used to model the very viscous flows of interest. The main solution method is finite elements, and a purpose-written computer program has been developed to solve the creeping-flow equations by this method. The present program is restricted to solving for either two-dimensional or axisymmetric flows but is extendible to three dimensions. In addition, semi-analytic series and asymptotic methods are used for some small portions of the work. The optical applications of this work demand consideration of the topic of computing surface curvature, and therefore second derivatives, from inexact and discrete numerical and experimental data. For this purpose, fitting of B-splines by a least-squares method to coordinate data defining the surface has been used. Much of the work assumes isothermal conditions, but in the context of the accuracy required in optical component manufacture it is also possible that non-isothermal effects will be important. Consequently, this restriction is eventually relaxed and some consideration given to non-isothermal conditions. In order to validate the creeping-flow model and finite-element program, comparisons of numerical simulations with experimental results are performed. A preliminary assessment of the importance of non-isothermal conditions to the thermal-replication process is also made by comparing isothermal and non-isothermal simulations with experimental results. The isothermal model is found to best match the experimental data. / Thesis (Ph.D.)--School of Applied Mathematics, 1998.

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