A novel thin film anodized aluminum oxide templating process was developed and applied to make nanopatterns on crystalline silicon to enhance the optical properties of silicon. The thin film anodized aluminum oxide was created to improve the conventional thick aluminum templating method with the aim for potential large scale fabrication. A unique two-step anodizing method was introduced to create high quality nanopatterns and it was demonstrated that this process is superior over the original one-step approach. Optical characterization of the nanopatterned silicon showed up to 10% reduction in reflection in the short wavelength range. Scanning electron microscopy was also used to analyze the nanopatterned surface structure and it was found that interpore spacing and pore density can be tuned by changing the anodizing potential.

A novel thin film anodized aluminum oxide templating process was developed and applied to make nanopatterns on crystalline silicon to enhance the optical properties of silicon. The thin film anodized aluminum oxide was created to improve the conventional thick aluminum templating method with the aim for potential large scale fabrication. A unique two-step anodizing method was introduced to create high quality nanopatterns and it was demonstrated that this process is superior over the original one-step approach. Optical characterization of the nanopatterned silicon showed up to 10% reduction in reflection in the short wavelength range. Scanning electron microscopy was also used to analyze the nanopatterned surface structure and it was found that interpore spacing and pore density can be tuned by changing the anodizing potential.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Multilayered iron electrodeposits composed of alternating layers of coarse-grained iron (grain size: 1.87 μm; (110) texture; hardness: 177 VHN) and fine-grained iron (grain size: 132 nm; (211) texture; hardness: 502 VHN), with layer thicknesses ranging from ~0.2-7 μm were successfully synthesized. The average hardness of the multilayered electrodeposits increased from 234 VHN to 408 VHN with decreasing layer thickness, consistent with a Hall-Petch type behaviour. In three-point bending tests, they failed in a macroscopically brittle manner although local ductility was observed in certain layers. Fractography analysis has shown that strain incompatibility between alternating layers contributes to the brittle nature of these materials. This study has demonstrated the possibility of applying a multilayered structure design to tailor the microstructure and mechanical properties of electrodeposited iron.

Multilayered iron electrodeposits composed of alternating layers of coarse-grained iron (grain size: 1.87 μm; (110) texture; hardness: 177 VHN) and fine-grained iron (grain size: 132 nm; (211) texture; hardness: 502 VHN), with layer thicknesses ranging from ~0.2-7 μm were successfully synthesized. The average hardness of the multilayered electrodeposits increased from 234 VHN to 408 VHN with decreasing layer thickness, consistent with a Hall-Petch type behaviour. In three-point bending tests, they failed in a macroscopically brittle manner although local ductility was observed in certain layers. Fractography analysis has shown that strain incompatibility between alternating layers contributes to the brittle nature of these materials. This study has demonstrated the possibility of applying a multilayered structure design to tailor the microstructure and mechanical properties of electrodeposited iron.

The sulphation and sulphate decomposition occurring during the oxidation of nickel concentrates were studied by thermal analysis. Samples of industrial nickel concentrates were heated in inert gas to temperatures between 400°C and 850°C and oxidized isothermally in air or in a 4%O2-96%N2 mixture. During isothermal oxidation of the concentrates, SO2 evolved from the roasting reactions led to partial formation of metal sulphates. Following the oxidation and sulphation of the sample, the decomposition of the formed sulphates was studied. This was completed either by heating the sulphated sample to 950°C to thermally decompose the sulphates, or by lowering the partial pressure of oxygen while holding the sample at the isothermal oxidation temperature. The sulphation of the sample was found to follow the parabolic rate law, implying diffusion as the rate controlling-step. The thermal decomposition of the sulphates occurred at a near constant rate, implying zero-order kinetics.