<p>The increasing use of aluminium in automotive and transport applications is primarily driven by its high strength to weight ratio, enabling substantially improved fuel economy and reduced CO₂ emissions when substituted for heavier materials. However, the change of material presents new challenges with respect to design and methods of joining. Structural adhesive bonding offers several advantages compared with welding, but a major limitation is concern about the durability of joints in wet and corrosive environments. The pre-treatment of the aluminium surface prior to bonding is the key to long service life. Pre-treatments successfully employed by the aerospace industry cannot be used in automotive production, where cheaper and more environmentally friendly pre-treatments are required. Specifically, the use of chromates is unacceptable. Hence, there is a need to develop chromate-free pre-treatments that will consistently provide the required level of performance, while being acceptable both in terms of general engineering practice and economy. To accomplish this task, basic knowledge of the processes occurring on the aluminium surface during pre-treatment, properties of the modified surface, and mechanisms of joint degradation are necessary.</p><p>The purpose of the present work has therefore been to contribute to a better understanding of how the aluminium substrate affects the formation and properties of conversion coatings for adhesive bonding. In particular, a commercial chromate-free fluorotitanate/zirconate based process has been investigated and compared with conventional chromate treatment. The materials chosen for this work were commercially extruded AA6060-T6 aluminium and a structural single-part epoxy adhesive. To complement the studies of the commercial alloy, model analogues of the AA6060 aluminium matrix and α-Al(Fe,Mn)Si phase particles present in the commercial alloy were also investigated.</p><p>It was observed that the α-Al(Fe,Mn)Si particles played an essential role in the formation and properties of Ti-Zr oxide conversion coatings on AA6060 aluminium. The particles were significantly nobler than the aluminium matrix in the pre-treatment solution. An alkaline diffusion layer therefore developed around the particles during pre-treatment due to oxygen reduction and hydrogen evolution reactions. As Ti-Zr oxide precipitation was favoured at high pH, the conversion layers normally deposited at and in the vicinity of the cathodic particles. The conversion layers formed consequently exhibited considerable lateral variations in thickness. In addition to substrate microstructure, bulk pH and agitation of the conversion bath were important factors controlling the extent of Ti-Zr oxide deposition and its distribution on the surface. On areas well away from the cathodic particles coverage was generally very poor, although a high density of small (<50 nm) oxide particles was deposited, presumably with a composition similar to the continuous conversion layer close to the α-Al(Fe,Mn)Si particles. The cathodic activity of the particles was only slightly reduced by formation of the Ti-Zr oxide conversion coating. In combination with poor coverage of the aluminium matrix, these conversion coatings are therefore not expected to improve the corrosion resistance of aluminium significantly.</p><p>In contrast to the above mechanism, the chromate conversion coating (CCC) formed by a <i>redox reaction</i> between chromate ions and aluminium. A relatively thick, porous chromium oxide layer developed over the aluminium matrix of AA6060, while a significantly thinner film was formed on the α-Al(Fe,Mn)Si particles. The morphology of the CCC covering the matrix was influenced by the hardening Mg₂Si phase, primarily by promoting nucleation of the CCC. Despite the thin film (<50 nm) formed on the α-Al(Fe,Mn)Si particles by chromating, the cathodic activity was significantly reduced. Inhibition of the cathodic reactivity at these particles is suggested as an important factor contributing to the high performance of chromate pretreatments on aluminium.</p><p>Testing of epoxy-bonded AA6060 aluminium joints in humid environment showed that Ti-Zr based pre-treatment provided improved adhesion relative to alkaline etching and deoxidation only. However, Ti-Zr based pre-treatment was inferior to chromating. Rapid, interfacial crack growth during wedge testing was particularly observed for adherends with a relatively thick Ti-Zr oxide deposit, suggesting that excessive Ti-Zr oxide deposition should be avoided. Furthermore, as the substrate microstructure (i.e. type, area fraction and distribution of cathodic sites) strongly affected the Ti-Zr oxide deposition, the pre-treatment conditions should be adapted to the specific alloy in order to achieve optimum performance.</p><p>In the presence of chlorides, degradation of adhesive-bonded joints may be accelerated by a filiform corrosion (FFC) type of mechanism. The α-Al(Fe,Mn)Si particles in AA6060 played a crucial role in promoting FFC, as demonstrated by complete FFC immunity of the iron-free AA6060 model analogue alloy. Ti-Zr based pre-treatment provided less protection against FFC relative to chromate pre-treatment. The good FFC resistance of CCCs was partly attributed to a better inhibition of the cathodic activity at the α-Al(Fe,Mn)Si particles.</p><p>The cathodic α-Al(Fe,Mn)Si particles present on the surface of AA6060 aluminium could be effectively removed by different etch treatments. However, selective removal of surface intermetallics did not prevent FFC because filament growth was supported by cathodic activity on particles that become exposed in the filament tail as a result of the corrosion process.</p><p>Based on lap shear testing, hot AC anodising in sulphuric acid to a film thickness of about 0.2 µm showed promise as another chromate-free pretreatment for durable adhesive bonding. The performance was better than a conventional chromic-sulphuric acid based etch treatment. While hot AC anodising did not significantly inhibit the cathodic activity on the α-Al(Fe,Mn)Si particles, good resistance against FFC was still obtained due to the oxide film covering the whole aluminium matrix. Based also on separate durability data recently available, hot AC anodising is considered as a robust alternative to chromating for adhesive bonding of aluminium in certain industrial applications.</p>

<p>The topic of this thesis is investigation of a small-scale stand-alone power system, based on both experimental work and computer simulations. The power system in this study uses solar energy as energy input, lead-acid batteries as short-term energy storage, and hydrogen as long-term energy storage. The main focus is upon operation and control of the hydrogen subsystem, as a robust controller is needed in order to prevent excessive use of the components in this subsystem. The laboratory power system comprises of: Hydrogen subsystem (PEM electrolyser, metal hydride, and PEM fuel cell), a lead-acid battery, programmable power supply for emulation of PV arrays, wind turbines, and controlled characterisation of the individual system components, and a programmable electronic load. </p><p>The intention was to build the laboratory power system as simple and energy efficient as possible. The components were connected directly in parallel on a common 48 V DC bus bar, no power electronics were applied between the components. Furthermore, the metal hydride and the fuel cell were air-cooled, avoiding auxiliaries required for water- cooling. The electrolyser, however, needed water-cooling. But with the electrolyser delivering hydrogen at 16 bars to a low pressure metal hydride, no use of compressor was required. On the other hand, metal hydrides needs purified hydrogen gas, > 99.999 %, in order to maintain its capacity as specified by the manufacturer. </p><p>The actual work in this thesis is divided in three main parts: </p><p>1. Design, construction, and operation of a laboratory hydrogen power system </p><p>2. Establishment of a computer model of the laboratory hydrogen power system, which interpolates and extrapolates its outputs based on experimental data collected from the laboratory system </p><p>3. Establishment of control algorithms for high-level energy management of the laboratory hydrogen power system based on the developed computer model. It is a goal to make the implementation and maintenance of these control algorithms as simple as possible. Furthermore, the control algorithms must enable efficient usage of the system components and secure energy supply to the end user </p><p>The results of this thesis are divided in two main parts: </p><p>The first part of the main results relates to the proposal and development of two types of control algorithms for high-level energy management, which will be denoted as the Control Matrix and the Fuzzy controller in the thesis. These control algorithms are suggested as opposed to the more traditional battery five-step charge controller. Identification of important system parameters and choosing proper settings for control parameters must be implemented into the control algorithms in order to finalise a complete control strategy. It will be shown that the electrolyser annual runtime decreases while the electrolyser annual hydrogen production remains the same by using the proposed control strategies, thus running the electrolyser more efficient.</p><p>Furthermore, with a reduction in the total number of electrolyser start-ups, a more stable system operation is achieved. </p><p>The second part of the main results relates to the operational experience of the small-scale laboratory hydrogen power system. Due to the amount of power required by the local control system integrated into the fuel cell and the electrolyser, the energy efficiency of the fuel cell and the electrolyser is lower at partial loads. Thus, with the additional energy needed for hydrogen purification, the round-trip efficiency of the hydrogen subsystem is found to be rather low (< 30 %), when the fuel cell and the electrolyser runs at low partial loads. However, it is encouraging that the hydrogen subsystem can reach 35 – 40 % when the fuel cell and the electrolyser are allowed to run at nominal power levels, in addition to optimal arrangement of the hydrogen purification unit. These energy efficiencies are higher than efficiencies achieved with diesel-fuelled generators. Besides, stand-alone power systems often resides in remote areas where transportation of diesel is costly, thus local production of the fuel by means of electrolyser and excess renewable energy can be profitable. </p><p>Regarding the difficulty of measuring the true amount of hydrogen present in the metal hydride, and because this system parameter is important in the control strategy, a pressurised vessel is recommended instead of the air-cooled metal hydride. Furthermore, it is recommended to use DC/DC converters in the hydrogen power system in order to ensure power quality within specifications and robust operation. </p>

The increasing use of aluminium in automotive and transport applications is primarily driven by its high strength to weight ratio, enabling substantially improved fuel economy and reduced CO2 emissions when substituted for heavier materials. However, the change of material presents new challenges with respect to design and methods of joining. Structural adhesive bonding offers several advantages compared with welding, but a major limitation is concern about the durability of joints in wet and corrosive environments. The pre-treatment of the aluminium surface prior to bonding is the key to long service life. Pre-treatments successfully employed by the aerospace industry cannot be used in automotive production, where cheaper and more environmentally friendly pre-treatments are required. Specifically, the use of chromates is unacceptable. Hence, there is a need to develop chromate-free pre-treatments that will consistently provide the required level of performance, while being acceptable both in terms of general engineering practice and economy. To accomplish this task, basic knowledge of the processes occurring on the aluminium surface during pre-treatment, properties of the modified surface, and mechanisms of joint degradation are necessary. The purpose of the present work has therefore been to contribute to a better understanding of how the aluminium substrate affects the formation and properties of conversion coatings for adhesive bonding. In particular, a commercial chromate-free fluorotitanate/zirconate based process has been investigated and compared with conventional chromate treatment. The materials chosen for this work were commercially extruded AA6060-T6 aluminium and a structural single-part epoxy adhesive. To complement the studies of the commercial alloy, model analogues of the AA6060 aluminium matrix and α-Al(Fe,Mn)Si phase particles present in the commercial alloy were also investigated. It was observed that the α-Al(Fe,Mn)Si particles played an essential role in the formation and properties of Ti-Zr oxide conversion coatings on AA6060 aluminium. The particles were significantly nobler than the aluminium matrix in the pre-treatment solution. An alkaline diffusion layer therefore developed around the particles during pre-treatment due to oxygen reduction and hydrogen evolution reactions. As Ti-Zr oxide precipitation was favoured at high pH, the conversion layers normally deposited at and in the vicinity of the cathodic particles. The conversion layers formed consequently exhibited considerable lateral variations in thickness. In addition to substrate microstructure, bulk pH and agitation of the conversion bath were important factors controlling the extent of Ti-Zr oxide deposition and its distribution on the surface. On areas well away from the cathodic particles coverage was generally very poor, although a high density of small (&lt;50 nm) oxide particles was deposited, presumably with a composition similar to the continuous conversion layer close to the α-Al(Fe,Mn)Si particles. The cathodic activity of the particles was only slightly reduced by formation of the Ti-Zr oxide conversion coating. In combination with poor coverage of the aluminium matrix, these conversion coatings are therefore not expected to improve the corrosion resistance of aluminium significantly. In contrast to the above mechanism, the chromate conversion coating (CCC) formed by a redox reaction between chromate ions and aluminium. A relatively thick, porous chromium oxide layer developed over the aluminium matrix of AA6060, while a significantly thinner film was formed on the α-Al(Fe,Mn)Si particles. The morphology of the CCC covering the matrix was influenced by the hardening Mg2Si phase, primarily by promoting nucleation of the CCC. Despite the thin film (&lt;50 nm) formed on the α-Al(Fe,Mn)Si particles by chromating, the cathodic activity was significantly reduced. Inhibition of the cathodic reactivity at these particles is suggested as an important factor contributing to the high performance of chromate pretreatments on aluminium. Testing of epoxy-bonded AA6060 aluminium joints in humid environment showed that Ti-Zr based pre-treatment provided improved adhesion relative to alkaline etching and deoxidation only. However, Ti-Zr based pre-treatment was inferior to chromating. Rapid, interfacial crack growth during wedge testing was particularly observed for adherends with a relatively thick Ti-Zr oxide deposit, suggesting that excessive Ti-Zr oxide deposition should be avoided. Furthermore, as the substrate microstructure (i.e. type, area fraction and distribution of cathodic sites) strongly affected the Ti-Zr oxide deposition, the pre-treatment conditions should be adapted to the specific alloy in order to achieve optimum performance. In the presence of chlorides, degradation of adhesive-bonded joints may be accelerated by a filiform corrosion (FFC) type of mechanism. The α-Al(Fe,Mn)Si particles in AA6060 played a crucial role in promoting FFC, as demonstrated by complete FFC immunity of the iron-free AA6060 model analogue alloy. Ti-Zr based pre-treatment provided less protection against FFC relative to chromate pre-treatment. The good FFC resistance of CCCs was partly attributed to a better inhibition of the cathodic activity at the α-Al(Fe,Mn)Si particles. The cathodic α-Al(Fe,Mn)Si particles present on the surface of AA6060 aluminium could be effectively removed by different etch treatments. However, selective removal of surface intermetallics did not prevent FFC because filament growth was supported by cathodic activity on particles that become exposed in the filament tail as a result of the corrosion process. Based on lap shear testing, hot AC anodising in sulphuric acid to a film thickness of about 0.2 µm showed promise as another chromate-free pretreatment for durable adhesive bonding. The performance was better than a conventional chromic-sulphuric acid based etch treatment. While hot AC anodising did not significantly inhibit the cathodic activity on the α-Al(Fe,Mn)Si particles, good resistance against FFC was still obtained due to the oxide film covering the whole aluminium matrix. Based also on separate durability data recently available, hot AC anodising is considered as a robust alternative to chromating for adhesive bonding of aluminium in certain industrial applications.

The topic of this thesis is investigation of a small-scale stand-alone power system, based on both experimental work and computer simulations. The power system in this study uses solar energy as energy input, lead-acid batteries as short-term energy storage, and hydrogen as long-term energy storage. The main focus is upon operation and control of the hydrogen subsystem, as a robust controller is needed in order to prevent excessive use of the components in this subsystem. The laboratory power system comprises of: Hydrogen subsystem (PEM electrolyser, metal hydride, and PEM fuel cell), a lead-acid battery, programmable power supply for emulation of PV arrays, wind turbines, and controlled characterisation of the individual system components, and a programmable electronic load. The intention was to build the laboratory power system as simple and energy efficient as possible. The components were connected directly in parallel on a common 48 V DC bus bar, no power electronics were applied between the components. Furthermore, the metal hydride and the fuel cell were air-cooled, avoiding auxiliaries required for water- cooling. The electrolyser, however, needed water-cooling. But with the electrolyser delivering hydrogen at 16 bars to a low pressure metal hydride, no use of compressor was required. On the other hand, metal hydrides needs purified hydrogen gas, &gt; 99.999 %, in order to maintain its capacity as specified by the manufacturer. The actual work in this thesis is divided in three main parts: 1. Design, construction, and operation of a laboratory hydrogen power system 2. Establishment of a computer model of the laboratory hydrogen power system, which interpolates and extrapolates its outputs based on experimental data collected from the laboratory system 3. Establishment of control algorithms for high-level energy management of the laboratory hydrogen power system based on the developed computer model. It is a goal to make the implementation and maintenance of these control algorithms as simple as possible. Furthermore, the control algorithms must enable efficient usage of the system components and secure energy supply to the end user The results of this thesis are divided in two main parts: The first part of the main results relates to the proposal and development of two types of control algorithms for high-level energy management, which will be denoted as the Control Matrix and the Fuzzy controller in the thesis. These control algorithms are suggested as opposed to the more traditional battery five-step charge controller. Identification of important system parameters and choosing proper settings for control parameters must be implemented into the control algorithms in order to finalise a complete control strategy. It will be shown that the electrolyser annual runtime decreases while the electrolyser annual hydrogen production remains the same by using the proposed control strategies, thus running the electrolyser more efficient. Furthermore, with a reduction in the total number of electrolyser start-ups, a more stable system operation is achieved. The second part of the main results relates to the operational experience of the small-scale laboratory hydrogen power system. Due to the amount of power required by the local control system integrated into the fuel cell and the electrolyser, the energy efficiency of the fuel cell and the electrolyser is lower at partial loads. Thus, with the additional energy needed for hydrogen purification, the round-trip efficiency of the hydrogen subsystem is found to be rather low (&lt; 30 %), when the fuel cell and the electrolyser runs at low partial loads. However, it is encouraging that the hydrogen subsystem can reach 35 – 40 % when the fuel cell and the electrolyser are allowed to run at nominal power levels, in addition to optimal arrangement of the hydrogen purification unit. These energy efficiencies are higher than efficiencies achieved with diesel-fuelled generators. Besides, stand-alone power systems often resides in remote areas where transportation of diesel is costly, thus local production of the fuel by means of electrolyser and excess renewable energy can be profitable. Regarding the difficulty of measuring the true amount of hydrogen present in the metal hydride, and because this system parameter is important in the control strategy, a pressurised vessel is recommended instead of the air-cooled metal hydride. Furthermore, it is recommended to use DC/DC converters in the hydrogen power system in order to ensure power quality within specifications and robust operation.

<p>Rapid dissolution of alumina upon addition to the cryolitic melt is crucial for the modern Hall-Heroult process for aluminium production. The formation of slow - dissolving alumina agglomerates may be detrimental, and irregular dissolution kinetics may cause the loss of process control. So-called anode effects may subsequently ignite, which are a major source of green-house gases from the primary aluminium industry.</p><p>A literature review and the study of the theory of sintering provides the background for discussing the present work. The most probable mass transport mechanism in the transition alumina-fluoride-moisture system studied here is surface diffusion. Surface diffusion is a non-densifying mass transport mechanism that will result in coarsening (alumina grain growth) but only weak interparticle bonding since no macroscopic shrinkage is involved. Rapid mass transport is known to result when there is a simultaneous phase transformation, and this is the case when transition alumina transforms to α-alumina, catalyzed by the presence of fluorides.</p><p>The main experimental techniques used in the present work were powder X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Supporting techniques used have been speciffc area determination by the BET method and simple thermo-gravimetric techniques. An optical furnace was designed and built in order to study the dissolution of tablet alumina agglomerates.</p><p>A preliminary agglomeration study of preformed cylindrical alumina samples served to map some of the most important mechanisms involved when alumina powder interacts with alumina-saturated cryolitic melt. The conditions at the alumina-melt interface were studied, but it is concluded that the experimental method could not provide the necessary parameter control in order to study the agglomeration mechanism in further detail.</p><p>The tablet agglomerate study is the major experimental contribution of the present work. The experimental method provided good control of the sample chemistry and well defined temperature and time variables. It is concluded that liquid cryolitic melt (NaAlF₄) provides an effective mass transport route for the transformation assisted growth of α-alumina platelets. The platelets that initially form will provide the limited mechanical strength necessary for agglomerate formation and their persistence in a cryolitic melt. Alumina agglomeration may therefore take place with only partial, initial phase transformation. It is concluded that differences in the agglomeration behavior of various qualities of alumina may be the rate determining property for alumina dissolution kinetics in cryolitic melts. Differences in the agglomeration behavior may be due to a number of physical properties of alumina. It is argued here that the fundamental, but difficult to measure, alumina nano-structure may be most important.</p><p>The alumina nano-structure is correlated to secondary alumina properties such as the α-alumina content, specific surface area (BET) and moisture content (MOI, LOI). In this study an X-ray diffraction line profile analysis using the Warren-Averbach method shows that there is a significant difference in the nano-structure of the two smelter grade alumina qualities under study. This may explain the different agglomeration behavior that is observed.</p><p>An optical study of tablet agglomerate dissolution in cryolitic melt proved to be largely unsuccessful due to severe corrosion of the quartz crucibles used. However, a proposed mechanism for the tendency for disintegration of alumina agglomerates, thus dissolving as \snow-flakes" is supported. </p><p>The temperature response time in the tablet alumina samples was studied in order to determine the experimental limit of the shortest time period possible in the experiments. The exothermal γ -> α transformation is observed for secondary alumina samples containing adsorbed fluorides. An interesting effect of the carbon content in secondary alumina is also shown.</p><p>The moisture content of smelter grade alumina is a function of the alumina quality, in particular the technology used for the calcination of the aluminium trihydrate precursor. In the current study the moisture content is shown to be a dynamic function of the ambient temperature and relative humidity. The moisture content is an important variable for the study of alumina agglomeration, and for the fluoride emission from the Hall-Heroult process. The kinetics of moisture desorption and absorption for various alumina qualities is studied. The desorption kinetics is concluded to be signifcantly different, while it is also shown that practical absorption kinetics is a function of the sample size and available surface area. </p>

<p>The overall objective of this work has been to develop aluminium alloys, which after hot and cold deformation are able to withstand high temperatures without recrystallising. This has been done by investigating aluminium alloys with various additions of hafnium, scandium and zirconium, with a main focus on Hf and to which extent it may partly substitute or replace Zr and/or Sc as a dispersoid forming elements in these alloys.</p><p><i>What is the effect of hafnium, alone and in combination with Zr and/or Sc and how do hafnium containing alloys perform?</i></p><p>It is shown that hafnium may alter or modify the casting structure, though, not to the better as it can form TCGs in combinations with Zr and/or Sc. This is not advantageous neither as far as it concerns grain refining nor precipitation of dispersoids.</p><p>When precipitation of binary Al-Hf is compared to Al-(Hf)-(Zr) alloys, hafnium shows even slower precipitation than in Al-(Hf)-(Zr) alloys and also much slower and with a poorer spatial distribution of dispersoids than in Al-Sc or Al-Hf-Sc alloys. As a consequence, it may be concluded that binary aluminium-hafnium alloys are of limited interest as they display a poor recrystallisation resistance when no other alloying elements are added.</p><p>However, when hafnium is added together with scandium and/or zirconium, precipitation may actually improve both in Al-Hf-Zr alloys and in scandium containing alloys like Al-Hf-Sc and Al-Hf-Sc-Zr. Hafnium can still not completely replace neither Zr nor Sc due to its poor precipitation properties. However, Al-Hf-Sc-Zr alloys show a better dispersoid distribution (number density and volume fraction) than what was observed in Al-Sc-Zr alloys after extrusion. The Al-Hf-Sc-Zr alloys also show extreme high temperature properties, by withstanding recrystallisation at high temperatures and long annealing times. After severe cold deformation, the extruded profiles of both the Al-Sc-Zr alloy and the Al-Hf-Sc-Zr alloy displayed a remarkable recrystallisation resistance.</p><p>The reason why the Al-Zr-Sc- and the Al-Hf-Zr-Sc alloys behave so well has been investigated by detailed 3D Atom Probe investigations. Due to the homogeneous precipitation of Al3Sc dispersoids and the retarding effect from Hf and/or Zr containing shells, thus limiting the coarsening of these dispersoids, these combinations have been shown successful.</p><p>As we have seen when Hf and Zr are added in combination equal or improved recrystallisation properties can be obtained. This is specially the case when both these elements are added together with scandium. Since Hf and Zr are extremely difficult (and thus costly) to separate, Al-Zr master alloys used in industry today can in the future probably contain more Hf, lowering the cost of master alloys.</p><p>The work presented in this thesis have hopefully added some new insight and a better understanding of the effects of adding various dispersoid forming elements to aluminium, alone and in various combinations, which may be useful for industry today and a basis for further alloy development.</p>

Rapid dissolution of alumina upon addition to the cryolitic melt is crucial for the modern Hall-Heroult process for aluminium production. The formation of slow - dissolving alumina agglomerates may be detrimental, and irregular dissolution kinetics may cause the loss of process control. So-called anode effects may subsequently ignite, which are a major source of green-house gases from the primary aluminium industry. A literature review and the study of the theory of sintering provides the background for discussing the present work. The most probable mass transport mechanism in the transition alumina-fluoride-moisture system studied here is surface diffusion. Surface diffusion is a non-densifying mass transport mechanism that will result in coarsening (alumina grain growth) but only weak interparticle bonding since no macroscopic shrinkage is involved. Rapid mass transport is known to result when there is a simultaneous phase transformation, and this is the case when transition alumina transforms to α-alumina, catalyzed by the presence of fluorides. The main experimental techniques used in the present work were powder X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Supporting techniques used have been speciffc area determination by the BET method and simple thermo-gravimetric techniques. An optical furnace was designed and built in order to study the dissolution of tablet alumina agglomerates. A preliminary agglomeration study of preformed cylindrical alumina samples served to map some of the most important mechanisms involved when alumina powder interacts with alumina-saturated cryolitic melt. The conditions at the alumina-melt interface were studied, but it is concluded that the experimental method could not provide the necessary parameter control in order to study the agglomeration mechanism in further detail. The tablet agglomerate study is the major experimental contribution of the present work. The experimental method provided good control of the sample chemistry and well defined temperature and time variables. It is concluded that liquid cryolitic melt (NaAlF4) provides an effective mass transport route for the transformation assisted growth of α-alumina platelets. The platelets that initially form will provide the limited mechanical strength necessary for agglomerate formation and their persistence in a cryolitic melt. Alumina agglomeration may therefore take place with only partial, initial phase transformation. It is concluded that differences in the agglomeration behavior of various qualities of alumina may be the rate determining property for alumina dissolution kinetics in cryolitic melts. Differences in the agglomeration behavior may be due to a number of physical properties of alumina. It is argued here that the fundamental, but difficult to measure, alumina nano-structure may be most important. The alumina nano-structure is correlated to secondary alumina properties such as the α-alumina content, specific surface area (BET) and moisture content (MOI, LOI). In this study an X-ray diffraction line profile analysis using the Warren-Averbach method shows that there is a significant difference in the nano-structure of the two smelter grade alumina qualities under study. This may explain the different agglomeration behavior that is observed. An optical study of tablet agglomerate dissolution in cryolitic melt proved to be largely unsuccessful due to severe corrosion of the quartz crucibles used. However, a proposed mechanism for the tendency for disintegration of alumina agglomerates, thus dissolving as \snow-flakes" is supported. The temperature response time in the tablet alumina samples was studied in order to determine the experimental limit of the shortest time period possible in the experiments. The exothermal γ -&gt; α transformation is observed for secondary alumina samples containing adsorbed fluorides. An interesting effect of the carbon content in secondary alumina is also shown. The moisture content of smelter grade alumina is a function of the alumina quality, in particular the technology used for the calcination of the aluminium trihydrate precursor. In the current study the moisture content is shown to be a dynamic function of the ambient temperature and relative humidity. The moisture content is an important variable for the study of alumina agglomeration, and for the fluoride emission from the Hall-Heroult process. The kinetics of moisture desorption and absorption for various alumina qualities is studied. The desorption kinetics is concluded to be signifcantly different, while it is also shown that practical absorption kinetics is a function of the sample size and available surface area.

The overall objective of this work has been to develop aluminium alloys, which after hot and cold deformation are able to withstand high temperatures without recrystallising. This has been done by investigating aluminium alloys with various additions of hafnium, scandium and zirconium, with a main focus on Hf and to which extent it may partly substitute or replace Zr and/or Sc as a dispersoid forming elements in these alloys. What is the effect of hafnium, alone and in combination with Zr and/or Sc and how do hafnium containing alloys perform? It is shown that hafnium may alter or modify the casting structure, though, not to the better as it can form TCGs in combinations with Zr and/or Sc. This is not advantageous neither as far as it concerns grain refining nor precipitation of dispersoids. When precipitation of binary Al-Hf is compared to Al-(Hf)-(Zr) alloys, hafnium shows even slower precipitation than in Al-(Hf)-(Zr) alloys and also much slower and with a poorer spatial distribution of dispersoids than in Al-Sc or Al-Hf-Sc alloys. As a consequence, it may be concluded that binary aluminium-hafnium alloys are of limited interest as they display a poor recrystallisation resistance when no other alloying elements are added. However, when hafnium is added together with scandium and/or zirconium, precipitation may actually improve both in Al-Hf-Zr alloys and in scandium containing alloys like Al-Hf-Sc and Al-Hf-Sc-Zr. Hafnium can still not completely replace neither Zr nor Sc due to its poor precipitation properties. However, Al-Hf-Sc-Zr alloys show a better dispersoid distribution (number density and volume fraction) than what was observed in Al-Sc-Zr alloys after extrusion. The Al-Hf-Sc-Zr alloys also show extreme high temperature properties, by withstanding recrystallisation at high temperatures and long annealing times. After severe cold deformation, the extruded profiles of both the Al-Sc-Zr alloy and the Al-Hf-Sc-Zr alloy displayed a remarkable recrystallisation resistance. The reason why the Al-Zr-Sc- and the Al-Hf-Zr-Sc alloys behave so well has been investigated by detailed 3D Atom Probe investigations. Due to the homogeneous precipitation of Al3Sc dispersoids and the retarding effect from Hf and/or Zr containing shells, thus limiting the coarsening of these dispersoids, these combinations have been shown successful. As we have seen when Hf and Zr are added in combination equal or improved recrystallisation properties can be obtained. This is specially the case when both these elements are added together with scandium. Since Hf and Zr are extremely difficult (and thus costly) to separate, Al-Zr master alloys used in industry today can in the future probably contain more Hf, lowering the cost of master alloys. The work presented in this thesis have hopefully added some new insight and a better understanding of the effects of adding various dispersoid forming elements to aluminium, alone and in various combinations, which may be useful for industry today and a basis for further alloy development.

De seneste årene er det oppdaget slitasjeskade på offshorevindturbinenes fortøyningsplass, hvor båter kommer inntil for på og avlastning av drift og vedlikeholdspersonell. Hensikten med denne oppgaven er å se på beleggenes egenskaper i forhold til slitasje og å få en forståelse av hvorfor slitasjeskade oppstår ved fortøyning mellom båt og vindturbin. Beleggene som er valgt ut til testing, er beleggsystemer som i dag brukes på offshorerelaterte strukturer, som oljeplattformer og vindturbiner De mekaniske egenskapene til beleggene ble undersøkt ved hjelp av vickers mikrohardhetsmåler, ruhetsmåler, slitasjeapparat og strekkapparat. • Polyester inneholder glasspartikler og fikk påvist høyest massetap, glasspartiklene kan ha falt av under slitasje og bidratt til skade på beleggoverflaten. • I slitasjetesten ble det funnet at gummi heftet på beleggenes overflate. Den avsatte gummien kan derfor ha virket som et beskyttende lag. • Det ble funnet at lang herdetid øker slitasjeegenskapene til belegget. • For epoksybeleggene og varmforsinket stål var slagfastheten bedre enn for de andre beleggene, dette skyldes god heft mellom lagene. Testene i denne oppgaven viser at det er ulike årsaker til at skade oppstår i belegg på grunn av fender. Det er funnet at glasspartikler, høy ruhet, dårlig heft mellom strøkene og kort herdetid kan ha vært årsaken til skade på belegg på grunn av fender. Et Epoksy belegg er funnet til å være det som vil være best egnet til å brukes på fender- rør.

In this master thesis experiments were conducted to determine the abrasion-corrosion properties of a steel designed for TBM tunnelling. This was done by three different tests, reciprocal ball-on-plate, rubber wheel and hyperbaric soil abrasion test. The reciprocal tests were done by rubbing steel balls onto rock obtained from a tunnel boring site in the Faroe Islands. The test were performed in dry conditions, in water from the same site as rock and a mixture of the water and a foam designed for use in hard rock tunnel boring. During these tests no measurable weight loss was produced, but the water and the foam caused some pitting to occur on the steel surface. The water and foam also provided some lubrication, where the foam clearly was the best lubricant by producing elastohydrodynamic lubrication (EHL). The rubber wheel tests were performed in different combinations of water, sand, oil and a foam specially designed for soft ground tunnel boring. The sands used were sand used for making casting moulds and sand obtained from a soft ground tunnel boring site in Israel. The two different water samples used were obtained from the site in the Faroe Islands mentioned above and the previous mentioned Israel site. The tests showed that adding foam to the sand and water mixture significantly reduced the measured weight loss. However, as for the reciprocal ball-on-plate test, the foam caused pitting to occur. The same corrosion effect was observed for the oil additive, but the oil did not provide enough lubrication to avoid abrasive wear. Consequently, the test with the oil additive produced the biggest weight loss of all the rubber wheel tests. The hyperbaric soil abrasion tests were performed in the sand obtained at the site in Israel. The sand was tested both dry and saturated with water from Israel. Tests showed that the measured weight loss from these two tests was similar. However, SEM pictures revealed that in the test with sand saturated with water, both abrasion and corrosion had occurred. While in the dry sand, only abrasion had occurred. This indicates that in this test the hardness of the steel and abrasiveness of the sand is more decisive for the weight loss than the corrosivity of the solution.