This thesis deals with the preparation, optical characterization and analyses of experimental work and theoretical modeling on selective solar absorbers used in solar thermal collectors. The overall goal has been to obtain efficient absorbers by optimizing the optical properties, and to improve their durability using cost-effective techniques. A Ni-Al2O3 absorber was pyrolytically coated with SnO2 to improve its coating quality. Undesirable increase of solar reflectance obtained as a result of the SnO2 was reduced by applying a silica antireflection layer produced by a dipping technique from colloidal silica sol. Annealing of Ni particles in an Al2O3 matrix was also carried out and compared to particles heated without the matrix. Due to the Al2O3 matrix, a much slower oxidation rate was found for the embedded particles. In addition, the optical performance of commercial Ni-Al2O3 and Ni-NiOx absorbers were experimentally compared at oblique incidence. A better solar-absorptance of the Ni-Al2O3 at higher angles of incidence was found. This is due to enhanced optical interference in the double-layer structure of Ni-Al2O3, which could not be achieved in the graded index film of Ni-NiOx. The optical properties of Si-Al2O3 films of different thicknesses have been investigated by preparing the films using an integral coloration method. The solar-absorptance and thermal-emittance were found to increase with increasing film thickness. Due to high thermal-emittance, the Si-Al2O3 coating shows non-selective absorbing properties. Its feasibility for a selective solar absorber was studied by modeling the coating as a function of coating thickness for different particle size and volume fraction using four-flux theory. The results indicated that the Si-Al2O3 coating is not a suitable candidate for selective solar absorbers. Scattering and absorption cross-sections of FeMnCuOx and black carbon pigments have been obtained from reflectance and transmittance measurements in the solar wavelength range. The cross-sections were determined by using pellets consisting of low pigment volume fractions dispersed in KBr matrix. The cross-sections exhibit linear dependence of the volume fraction, indicating that single scattering dominates. The cross-sections were used to model the optical properties of solar selective paints using four-flux model resulting in good agreement between calculations and experiments.

An angle-resolved scatterometer and an integrating sphere for reflectance measurements at oblique angles of incidence have been designed and evaluated. The integrating sphere has a centre-mounted sample holder and the detector sits at the end of the sample holder and therefore always faces the same sphere wall area. The sphere geometry plays an important role for the modelling of detected signals and the reflected intensity has to be divided into a specular and a diffuse component. These components must be treated separately in the modelling. These two instruments, as well as traditional spectrophotometers, have been used for the evaluation of solar energy materials. Scattering as well as non-scattering surfaces have been studied, requiring different measurement techniques. By using angle-resolved scatterometry it has been demonstrated that a solar reflector does not need to be perfectly specular provided the concentration factor is low. Thus it is possible to use inexpensive aluminium foil as the reflector material. The possibility of increasing the reflectance of aluminium with thin dielectric films of silicon and titanium oxides for pv-cell and solar thermal collector application has been investigated. Particular attention has been paid to the angular optical properties since thin films strongly affect them owing to interference effects. In an under-glazing application for pv-cells, the use of aluminium coated with titania and silica is recommended. The long-term stability of several reflector materials has been studied and anodised aluminium protected by a UV-stabilised polymer coating is recommended for solar collector reflectors. Antireflective films consisting of porous silicon oxide for solar collector cover glazings have been studied. The films were prepared by a dip-coating process using a suspension of nano-sized silicon oxide particles. This treatment increased the solar transmittance by 5.5 percentage points. It has also been shown that it is possible to temper antireflection treated glazings without seriously affecting the optical performance. The tempering also strongly improves the mechanical stability of the film.Some of the measurements presented in this thesis were used as input data to simulation programs, which calculate the collected annual energy as a function of the optical properties of the different components. It was found that spectrophotometric laboratory measurements agree well with outdoor collector testings.

During recent decades, huge amount of radioactive waste has been dumped into the earth's surface environments. 129I (T1/2 = 15.6 My) is one of the radioactive products that has been produced through a variety of processes, including atomic weapon testing, reprocessing of nuclear fuel and nuclear accidents. This thesis describes development of the Accelerator Mass Spectrometry (AMS) ultra-sensitive atom counting technique at Uppsala Tandem Laboratory to measure 129I and discusses investigations of its distribution in the hydrosphere (marine and fresh water) and precipitation. The AMS technique provides a method for measuring long-lived radioactive isotopes in small samples, relative to other conventional techniques, and thus opens a new line of research. The optimization of the AMS system at Uppsala included testing a time of flight detector, evaluation of the most appropriate charge-state, reduction of molecular interference and imporvement of the detection limit. Furthermore, development of a chemical procedure for separation of iodine from natural water samples has been accomplished. The second part of the thesis reports investigations of 129I in natural waters and indicates that high concentrations of 129I (3-4 orders of magnitude higher than in the pre-nuclear era) are found in most of the considered natural waters. Inventory calculations and results of measurements suggest that the major sources of radioactive iodine are the two main European nuclear reprocessing facilities at Sellafield (U.K.) and La Hague (France). This information provides estimates of the transit time and vertical mixing of water masses in the central Arctic Ocean. Results from precipitation, lakes and runoff are used to elucidate mechanisms of transport of 129I from the point sources and its pathways in the hydrological environment. This study also shows the need for continuous monitoring of the 129I level in the hydrosphere and of its future variability.

By the introduction of machine elements made of light metals, e.g. Al or Mg alloys, which are coated with a material providing high wear resistance and low friction coefficient, both economical and environmental benefits can be gained. A high resistance against wear results in increased lifetime and lower costs for spare parts and maintenance. This also means fewer production stops and less machine downtime. Moreover, a vehicle of lower weight and with reduced friction losses will consume less fuel. The light metal alloys display low hardness and elastic modulus and in addition they have a high tendency to stick to the countersurface in sliding contact. Hence, to be used in tribologically demanding applications, they must be coated with a material providing low friction and wear. Due to the thin and brittle nature of the available coatings an intermediate load-carrying layer has to be introduced to protect the base material from large deformations and the brittle surface coating from cracking. In this thesis both experiments and theoretical simulations has shown that the load-carrying layer between the soft and compliant base material and the thin brittle coating should have high elastic modulus and hardness as well as a for the contact situation sufficient thickness. A number of vapour deposited coatings have been investigated regarding their tribological behaviour with special emphasis on the mechanisms providing low friction. When sliding against steel, it was found that carbon-rich coatings show much lower friction and wear of the countersurface than nitrogen-rich coatings. The explanation is that steel has a tendency to stick to nitrogen-rich coatings, leading to steel against steel contact, but not to carbon-rich coatings. Another explanation is that material is transferred from a carbon-rich coating to the steel and this gives an easily sheared contact with low friction coefficient.

This thesis deals with studies of thin films using soft x-ray emission spectroscopy. Thin films are frequently used in optical, semiconductor and magnetic applications, and along with the development of thin film deposition techniques, there is a growing need for thin film characterisation and production control. Soft x-ray spectroscopy provides elemental as well as chemical bonding information and has the advantage of being relatively insensitive to electric and magnetic fields. It may thus be used in-situ during deposition for monitoring sputtering deposition. Thin films of TiVN were reactively co-sputtered using two targets, and soft x-ray spectroscopy and optical emission spectroscopy were used to determine the film composition in-situ. These measurements were compared with ex-situ elemental analysis as well as with computer simulations. The results agree qualitatively and indicate that soft x-ray spectroscopy can be used for in-situ determination of film composition. In another study, the composition of chromium nitride was studied in-situ under varying deposition conditions. The fraction of different stoichiometric phases in the deposited films as a function of nitrogen flow was determined in-situ. The thesis also deals with the angular dependence of soft x-ray emission spectroscopy. The angular dependence of the emission was measured and compared to simulations for layered samples consisting of different transition metals, one sample consisting of Fe(50Å)/Cu(100Å)/V(100Å)/Si and another set of samples consisting of Fe(XÅ)/V(100Å)/MgO, where X = 25, 50 and 100 Å. The measured angular variation can be described qualitatively by calculations including refractive effects. For measurements below the critical angle of reflection, only the top layer corresponding to the evanescent wave region of 20-50 Å is probed, whereas for larger grazing angles the probe depth reaches thousands of Å. This demonstrates the feasibility of using the angular dependence as a way of studying composition and layer thickness of thin films.

This thesis treats angle-resolved optical properties and the energy efficiency of windows. A theoretical evaluation of optical and thermal properties of windows is briefly surveyed and the energy performance of a large selection of windows, under different conditions, is examined. In particular, angle dependent optical properties are analysed. A new model assessing angle dependence of the total solar energy transmittance, g, of windows is presented. A comparison of simple models for angle-dependence prediction has been performed, including both fictitious and measured real window glazings. The new proposed model illustrates low errors for both the real and the fictitious glazings. The impact of inaccuracy in the angle dependence of the g-factor has been assessed and found to be clearly noticeable but not necessarily critical. A simple model for comparing the energy efficiency of different windows in different types of buildings and different climates has been further developed and analysed for several conditions. The energy performance of a large number of windows has been analysed using this model, and also by using other building and window simulation models. Typical savings when changing from a standard double glazed window to the optimal window for the investigated case is in the order of 100-150 kWh/m2yr. The annual energy balance of modern low emittance windows illustrates that they can be annual energy savers rather than energy losers, unlike traditional windows. However, it is shown that it is not important to argue about small changes (~0.01) of the thermal emittance value. Furthermore, advance solar control glazings effectively reduce solar transmittance with maintained high light transmittance. AR-coatings and low-iron glazings can increase the transmittance of glazings considerably. In fact, a "super" low emittance window with a U-value below 1 W/m2K can have higher light transmittance than a common double-glazed unit. Windows with variable transmittance, switchable windows, are compared with high-performing solar control windows, illustrating some degree of potential energy savings compared to high performing static solar control windows, depending on the type of control that is used. This is accompanied by the potential for automatic thermal comfort- and glare control. Different models for energy rating of windows have been evaluated, demonstrating that a simple linear rating depending on the U and g-factor of the window may be sufficient with certain restrictions. Division into climate zones is essential. In all, the results demonstrate that energy-efficient windows provide huge energy-saving potentials on a large (regional, national, global) scale.

This doctoral thesis is concerned with rapid solidification of AB5 materials suitable for electrochemical hydrogen storage. The primary objective of the work has been to characterise the microstructure and crystal structure of the produced AB5 materials as a function of the process parameters, e.g. the cooling rate during rapid solidification, the determination of which has been paid special attention to. The thesis is divided in to 6 parts, of which Part I is a literature review, starting with a short presentation of energy storage alternatives. Then a general review of metal hydrides and their utilisation as energy carriers is presented. This part also includes more detailed descriptions of the crystal structure, the chemical composition and the hydrogen storage properties of AB5 materials. Furthermore, a description of the chill-block melt spinning process and the gas atomisation process is given. In Part II of the thesis a digital photocalorimetric technique has been developed and applied for obtaining in situ temperature measurements during chill-block melt spinning of a Mm(NiCoMnAl)5 hydride forming alloy (Mm = Mischmetal of rare earths). Compared with conventional colour transmission temperature measurements, this technique offers a special advantage in terms of a high temperature resolutional and positional accuracy, which under the prevailing experimental conditions were found to be +/- 29 K and +/- 0.1 mm, respectively. Moreover, it is shown that the cooling rate in solid state is approximately 2.5 times higher than that observed during solidification, indicating that the solid ribbon stayed in intimate contact with the wheel surface down to very low metal temperatures before the bond was broken. During this contact period the cooling regime shifted from near ideal in the melt puddle to near Newtonian towards the end, when the heat transfer from the solid ribbon to the wheel became the rate controlling step. In Part III of the thesis the changes of the crystal structure and the grain structure of La0.60Ce0.29Pr0.04Nd0.07Ni3.37Co0.79Mn0.25Al0.74 with increasing cooling rate during chill-block melt spinning are described. Totally, the material was rapidly solidified at 9 different cooling rates. The grain structure, crystallographic texture and the lattice parameters were studied by means of electron microscopy and powder X-ray diffraction. Additionally, the density of the rapidly solidified materials was measured by a gas pycnometer. All these properties were found to change with increasing cooling rate. The grain size decreased continuously with increasing cooling rate and was in the range of 1-5 μm. The strength of the crystallographic texture first increased and then decreased with increasing cooling rate. Transmission electron microscopy studies revealed that the grains contained a large amount of crystallographic twins and that the solidification morphology changed from cellular to plane front at a cooling rate during solidification of approximately 6·104 Ks-1. The unit cell volume and the density followed the same pattern with increasing cooling rate and decreased within each solidification morphology, but at the cooling rate from which the morphology changed, both these parameters suddenly increased. The identical variations in the unit cell volume and the density is explained by formation of excess lattice vacancies during rapid solidification. In Part IV of the thesis rapid solidification of the materials La0.60Ce0.27Pr0.04Nd0.09Ni4.76Sn0.24 and LaNi4.76Sn0.24 at 7 different cooling rates are described. The materials were analysed by means of electron microscopy and powder X-ray diffraction. The grain structures of both alloys were found to be in the nanometer range, and the grain sizes were almost invariant with increasing cooling rate. Furthermore, the lattice parameters of these materials were almost unaffected by increasing cooling rate. However, elemental line scans showed that the tin containing materials were not chemically homogeneous after chill-block melt spinning. The tin and nickel level fluctuated in an opposite manner, and the origin of these fluctuations is possibly due to inhomogeneities in the master alloys produced prior to rapid solidification. Part V of the thesis deals with the effect of heat treatment of the rapidly solidified materials presented in Part III and IV. The first material was heat treated at 400°C and the latter two at 1000°C and 900°C respectively. Electron microscopy investigations showed that the grain structure of the first material remained unchanged during the heat treatment while the latter two were subject to sincere grain growth. The inhomogeneities were removed during the heat treatment, and X-ray powder diffraction showed that the lattice constants were changing towards equilibrium values during the heat treatment. Furthermore, the density variations in the rapidly solidified material in Part III were removed by the heat treatment. This change and the change of the lattice parameters were probably due to annihilation of excess lattice vacancies during the heat treatment. Finally, in Part VI of the thesis the measured variations in the lattice parameters with increasing cooling rate are compared with the electrochemical hydrogen storage properties of the materials, which has been studied in a parallel work. It is shown that the hydrogen storage capacity and the absorption pressure of the material in Part III are controlled by the unit cell volume and hence the cooling rate during solidification.

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 -> 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.

Steam explosions are possible during granulation of Si and FeSi75. These explosions are a great hazard, and must be avoided. Norwegian ferroalloy producers have initiated a research program to learn more about such violent melt-water interactions, in a joint effort with NTNU and SINTEF. The focus has primarily been on important parameters that can be controlled industrially, such as water temperature and metal composition. This thesis-work has focused on the effect of small additions of Al and Ca in Si-metal and FeSi75. However, within the same project, experiments on the effect of water temperature have also been carried out. The work has primarily been of experimental character. Two experimental apparatuses have been used. The first apparatus allows us to rapidly melt a sample of metal in an inert atmosphere to a desired temperature, expose the surface of the melt to an oxidizing agent (i.e. water) and then rapidly cool the sample to room temperature. The oxide that forms at the surface is examined with a microprobe. Thus, information regarding the composition and substance of the oxide layer is available. The second apparatus is suitable for releasing single drops of melt into a water tank, where they can be triggered and explode. A variety of techniques have been used in order to monitor the experiment: regular video, high-speed film, high-speed video, open-shutter imaging and pressure transducer measurements. Both Si and FeSi75 must be triggered in order to explode. Trigger pressures range from 0.3 MPa (FeSi75) to 2 MPa (Si-metal). We have established at which depths the molten drops can be triggered. Molten drops of FeSi75 can be triggered at depths twice of those of molten drops of Si. The latter can be triggered even if they are partially solidified. The explosion itself is strong enough to trigger neighbor drops as far away as 400 mm. Thus, we cannot rule out the possibility of large-scale steam explosions during granulation of molten Si or FeSi75, which is in accordance with industrial practice. By the use of high-speed imaging techniques and pressure measurements, we have been able to describe qualitatively what happens when a molten drop of Si/FeSi75 fragments rapidly in water. As the melt fragments, the rapid heat transfer generates vapor as bubbles, which expand and collapse in a cyclic manner. Large pressure pulses are generated upon collapse of the steam bubble, that is, when water jets impact in the center of the collapsing bubble. The first step in the oxidation of liquid silicon is the formation of gaseous SiO. The fate of this gas now depends on the flow conditions at the surface of the melt. In the case of a molten drop descending in water, most of the gas is flushed away from the surface. Thus, there are only minor traces of oxygencontaining material (i.e. silica) at the surface of the solidified drop. The addition of small amounts of Al and/or Ca dramatically changes the behavior of the molten drop. A strange effect is the two-fold increase in the fall velocity for molten drops of silicon. A similar effect was detected for molten drops of FeSi75. Alloying elements such as Al and Ca greatly reduce the risk for a steam explosion of molten Si. The significance of these elements is related to the oxidation reactions at the surface of the molten drop of metal. As silicon reacts with water vapor and oxidizes, hydrogen gas is formed. If Al and Ca are present in the melt, these elements will speed up the hydrogen generation considerably. This gas is strongly influencing on the probability for a steam explosion to occur. H2 stabilizes the vapor film around the drop, that is, much stronger trigger pressures are needed to collapse the film. Even if the trigger pressure is strong enough to collapse the vapor film, violent interactions are almost completely absent. A fragmentation of the melt is observed, but the heat transfer is apparently not rapid enough to generate steam bubbles, i.e. the generation of steam is below the critical limit.

Magnetic properties of nanoparticle systems and spin glasses have been investigated theoretically, and experimentally by squid magnetometry. Two model three-dimensional spin glasses have been studied: a long-range Ag(11 at% Mn) Heisenberg spin glass and a short-range Fe0.5Mn0.5TiO3 Ising spin glass. Experimental protocols revealing ageing, memory and rejuvenation phenomena are used. Quantitative analyses of the glassy dynamics within the droplet model give evidences of significantly different exponents describing the nonequilibrium dynamics of the two samples. In particular, non-accumulative ageing related to temperature-chaos is much stronger in Ag(11 at% Mn) than in Fe0.5Mn0.5TiO3. The physical properties of magnetic nanoparticles have been investigated with focus on the influence of dipolar interparticle interaction. For weakly coupled nanoparticles, thermodynamic perturbation theory is employed to derive analytical expressions for the linear equilibrium susceptibility, the zero-field specific heat and averages of the local dipolar fields. By introducing the averages of the dipolar fields in an expression for the relaxation rate of a single particle, a non trivial dependence of the superparamagnetic blocking on the damping coefficient is evidenced. This damping dependence is interpreted in terms of the nonaxially symmetric potential created by the transverse component of the dipolar field. Strongly interacting nanoparticle systems are investigated experimentally in terms of spin-glass behaviour. Disorder and frustration arise in samples consisting of frozen ferrofluids from the randomness in particle position and anisotropy axes orientation. A strongly interacting system is shown to exhibit critical dynamics characteristic of a spin-glass phase transition. Ageing, memory and rejuvenation phenomena similar to those of conventional spin glasses are observed, albeit with weak temperature-chaos effects.