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  • 1.
    Altzar, Oskar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Surface Characteristics and Their Impact on Press Joint Strength2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Press fitting is a commonly used method in the assembly of shafts and gearwheels in gearboxes andare using the friction created between them to hold them together. To increase productivity Scania CVAB in Södertälje, Sweden, are going to replace the current hard machining method for layshafts. Whiletesting the new methods in rig it occurred that the gearwheel slipped in tangential direction towardsthe layshaft at a lower torque then with the current method even through all requirements on thelayshafts surface was meet. The purpose and aim with this study is to investigate differences betweenthe methods and to find new requirements for the layshaft. The torque of slip, (Ms) established in atorque test rig and analysis of surface roughness, hardness and microstructure conducted of both thelayshafts and gearwheels. The characteristics of the layshaft surface was also analysed and comparedbetween the different hard machining methods. The study concludes that no correlation between thesurface parameters and the Ms occurred and no major differences in the material between themethods. The study also concluded that the Ms between the layshaft and gearwheel is lower if thelayshaft surface is harder and smoother than the gearwheel surface.

  • 2. Beyhaghi, Maryam
    et al.
    Kiani-Rashid, Ali-Reza
    Kashefi, Mehrdad
    Khaki, Jalil Vandati
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Effect of powder reactivity on fabrication and properties of NiAl/Al2O3 composite coated on cast iron using spark plasma sintering2015In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 344, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Powder mixtures of Ni, NiO and Al are ball milled for 1 and 10 h. X-ray diffractometry and differential thermal analysis show that while ball milling for 1 h produced mechanically activated powder; 10 h ball milling produced NiAl and Al2O3 phases. Dense NiAl/Al2O3 composite coatings are formed on gray cast iron substrate by spark plasma sintering (SPS) technique. The effect of powder reactivity on microstructure, hardness and scratch hardness of NiAl/Al2O3 coatings after SPS is discussed. Results show that in the coating sample made of mechanically activated powder in situ synthesis of NiAl/Al2O3 composite coating is fulfilled and a thicker well-formed diffusion bond layer at the interface between coating and substrate is observed. The diffusion of elements across the bond layers and phase evolution in the bond layers were investigated. No pores or cracks were observed at the interface between coating layer and substrate in any of samples. Higher Vickers hardness and scratch hardness values in coating made of 10 h ball milled powder than in coating fabricated from 1 h ball milled powder are attributed to better dispersion of Al2O3 reinforcement particles in NiAl matrix and nano-crystalline structure of NiAl matrix. Scratched surface of coatings did not reveal any cracking or spallation at coating-substrate interface indicating their good adherence at test conditions.

  • 3. Dalborg, M.
    et al.
    Jacobson, K.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Methods for determining the spatial distribution of oxidation in ultra-high molecular-weight polyethylene prostheses2007In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 92, no 3, p. 437-447Article in journal (Refereed)
    Abstract [en]

    Oxidative degradation is a well-known problem for UHMWPE used in prostheses. The aim of the present study has been to find suitable techniques to study the spatial distribution of this oxidation in 8 retrieved acetabular cups. The techniques used were visual examination using an optical microscope and computer scanner, FTIR mapping, imaging chemiluminescence, and staining with SO2 and HCl. The staining technique is based on a previous study which showed that by treating oxidized UHMWPE with SO2 followed by heat treatment, the hydroperoxides present in the sample react with the SO2 and discolor the sample. The intensity of this discoloring is, at low levels of oxidation, proportional to the amount of hydroperoxides and accordingly to the level of the oxidation. The same study also showed that staining a sample with hot HCl resulted in a brown discoloration which was proportional to the amount of carbonyls. It was found that the staining techniques do not give as much information about the chemical and physical changes in the material as FTIR mapping but have a great advantage in better spatial resolution of the oxidation and are also much quicker and easier to use. Imaging chemiluminescence turned out not to be a suitable method to use, compared to the other two, since it gives less information and is more difficult to interpret. When interpreting the results from the different techniques used, it was found that all cups showed the typical oxidation behavior of gamma sterilized UHMWPE. All cups but one showed substantial wear of the articulating surface but very little backside wear. Examination of the oxidation and whitening profile suggests that at least some of the oxidation must have occurred in vivo.

  • 4.
    Ekström, Madeleine
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Development of a ferritic ductile cast iron for improved life in exhaust applications2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Due to coming emission legislations, the temperature is expected to increase in heavy-duty diesel engines, specifically in the hot-end of the exhaust system affecting components, such as exhaust- and turbo manifolds. Since the current material in the turbo manifold, a ductile cast iron named SiMo51, is operating close to its limits there is a need for material development in order to maintain a high durability of these components. When designing for increased life, many material properties need to be considered, for example, creep-, corrosion- and fatigue resistance. Among these, the present work focuses on the latter two up to 800°C improving the current material by additions of Cr, for corrosion resistance, and Ni, for mechanical properties. The results show improved high-temperature corrosion resistance in air from 0.5 and 1wt% Cr additions resulting in improved barrier layer at the oxide/metal interface. However, during oxidation in exhaust-gases, which is a much more demanding environment compared to air, such improvement could not be observed. Addition of 1wt% Ni was found to increase the fatigue life up to 250°C, resulting from solution strengthening of the ferritic matrix. However, Ni was also found to increase the oxidation rates, as no continuous SiO2-barrier layers were formed in the presence of Ni. Since none of the tested alloys showed improved material properties in exhaust gases at high temperature, it is suggested that the way of improving performance of exhaust manifolds is to move towards austenitic ductile cast irons or cast stainless steels. One alloy showing good high-temperature oxidation properties in exhaust atmospheres is an austenitic cast stainless steel named HK30. This alloy formed adherent oxide scales during oxidation at 900°C in gas mixtures of 5%O2-10%H2O-85%N2 and 5%CO2-10%H2O-85%N2 and in air. In the two latter atmospheres, compact scales of (Cr, Mn)-spinel and Cr2O3 were formed whereas in the atmosphere containing 5%O2 and 10%H2O, the scales were more porous due to increased Fe-oxide formation. Despite the formation of a protective, i.e. compact and adherent, oxide scale on HK30, exposure to exhaust-gas condensate showed a detrimental effect in form of oxide spallation and metal release. Thus, proving the importance of taking exhaust-gas condensation, which may occur during cold-start or upon cooling of the engine, into account when selecting a new material for exhaust manifolds. 

  • 5.
    Ekström, Madeleine
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Oxidation and corrosion fatigue aspects of cast exhaust manifolds2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Emission regulations for heavy-duty diesel engines are becoming increasingly restrictive to limit the environmental impacts of exhaust gases and particles. Increasing the specific power output of diesel engines would improve fuel efficiency and greatly reduce emissions, but these changes could lead to increased exhaust gas temperature, increasing demands on the exhaust manifold material. This is currently the ferritic ductile cast iron alloy SiMo51, containing about 4 wt% Si and ~1 wt% Mo, which operates close to its fatigue and oxidation resistance limits at peak temperature (750C). To ensure high durability at higher temperatures, three different approaches to improving the life of exhaust manifolds were developed in this thesis.

    The first approach was to modify SiMo51 by adding different combinations of Cr and Ni to improve its high-temperature strength and oxidation resistance, or by applying a thermal barrier coating (TBC) to reduce the material temperature and thereby improve fatigue life. In the second approach, new materials for engine components, e.g. austenitic ductile iron and cast stainless steel, were investigated for their high-temperature fatigue and oxidation properties. In order to identify the most suitable alloys for this application, in the third the environmental effects of the corrosive diesel exhaust gas on the fatigue life of SiMo51 were investigated.

    The high-temperature oxidation resistance of SiMo51 at 700 and 800C in air was found to be improved by adding Cr, whereas Ni showed adverse effects. The effects of solid-solution hardening from Ni and precipitation hardening from Cr were low at 700C, with improvements only at lower temperatures. Applying a TBC system, providing thermal protection from a ceramic topcoat and oxidation protection from a metallic bond coat, resulted in only small reductions in material temperature, but according to finite element calculations still effectively improved the fatigue life of a turbo manifold. Possible alternative materials to SiMo51 identified were austenitic cast ductile iron Ni-resistant D5S and austenitic cast stainless steel HK30, which provided high durability of exhaust manifolds up to 800 and 900C, respectively. Corrosion fatigue testing of SiMo51 at 700C in diesel exhaust gas demonstrated that the corrosive gas reduced fatigue life by 30-50% compared with air and by 60-75% compared with an inert environment. The reduced fatigue life was associated with a mechanism whereby the crack tip oxidized, followed by crack growth. Thus another potential benefit of TBC systems is that the bond coat may reduce oxidation interactions and further improve fatigue life.

    These results can be used for selecting materials for exhaust applications. They also reveal many new research questions for future studies. Combining the different approaches of alloy modification, new material testing and improving the performance using coatings widened the scope of how component life in exhaust manifolds can be improved. Moreover, the findings on environmental interactions on SiMo51 fatigue provide a completely new understanding of these processes in ductile irons, important knowledge when designing components exposed to corrosive environments. The novel facility developed for high-temperature corrosion fatigue testing can be useful to other researchers working in this field. 

  • 6.
    Ekström, Madeleine
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    High-temperature corrosion fatigue of a ferritic ductile cast iron in inert and corrosive environments at 700˚C2015In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336Article in journal (Refereed)
    Abstract [en]

    In the present work, low-cycle fatigue testing of a ferritic ductile cast iron named SiMo51 has been carried out in three atmospheres: argon, air and a synthetic diesel exhaust-gas at 700°C. The fatigue life was reduced up to 80% in the worst case. Two crack growth mechanisms were observed and directly linked to oxidation. At weak oxidation, a nodule-to- nodule crack growth occurred. At strong oxidation, crack growth occurred through oxidized material in front of the crack tip. 

  • 7.
    Ekström, Madeleine
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    High-temperature mechanical- and fatigue properties of cast alloys intended for use in exhaust manifolds2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 616, p. 78-87Article in journal (Refereed)
    Abstract [en]

    In the present work materials for use in exhaust manifolds of heavy-duty diesel engines were tested in air from 20 to 1000 degrees C with respect to mechanical properties. Two cast irons, SiMo51 and Ni-resist D5S, four austenitic cast steels, HF, A3N, HK30 and HK-Nb, and one ferritic cast steel, 1.4509 were studied. The experimental work included thermal conductivity, thermal expansion, uniaxial stress-strain testing, low-cycle fatigue testing up to 30,000 cycles and fractography. Below 500 degrees C, SiMo51 is superior. At higher temperatures, a transition from elastic to plastic strain dominance was observed for the cast irons, reducing their performance. Carbide-forming elements increase heat conductivity and result in a dendrite-like fracture surfaces during fatigue testing. The austenitic steels are superior only at higher temperatures.

  • 8.
    Ekström, Madeleine
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    The influence of Cr and Ni on the high-temperature low-cycle fatigue behavior of a ferritic cast ductile iron2012In: Conference proceeding for 7th International Conference on Low Cycle Fatigue, 2012Conference paper (Refereed)
    Abstract [en]

     The current material in exhaust manifolds for heavy-duty diesel engines: a Si- and Mo-alloyed, ferritic ductile cast iron, named SiMo51, is operating close to its limits and improvements are needed. Thus, in the present study, the effects on mechanical properties of adding Cr and Ni to SiMo51 has been investigated with focus on low-cycle fatigue behavior in air, at temperatures up to 700°C. Both additions improve fatigue life but reduce elongation. Adding 1wt% Ni improves fatigue life up to 250°C whereas adding 0.5wt% Cr improves fatigue life at room temperature, only.

  • 9.
    Ekström, Madeleine
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Szakalos, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Influence of Cr and Ni on High-Temperature Corrosion Behavior of Ferritic Ductile Cast Iron in Air and Exhaust Gases2013In: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 80, no 5-6, p. 455-466Article in journal (Refereed)
    Abstract [en]

    Due to an expected temperature increase of the exhaust gases in heavy-duty engines in order to meet future emission regulations, there is a need to develop materials that can operate at higher temperatures. The exhaust manifold in the hot end of the exhaust system is specifically affected since the most common material today, SiMo51, is already operating close to its limits. Accordingly, the effects of Cr and Ni-additions on the high-temperature corrosion resistance of this material in air and exhaust gases were examined. It was found that the addition of 0.5 and 1 wt% Cr improved the oxidation resistance in air at 700 and 800 A degrees C by the formation of an SiO2 barrier layer as well as a Cr-oxide at the oxide/metal interface. However, no Cr-oxide was detected after exposure to exhaust gases, probably due to a water vapor-assisted evaporation of Cr from the oxide. The addition of 1 wt% Ni resulted in a deteriorated SiO2 barrier layer and reduced oxidation resistance.

  • 10.
    Ekström, Madeleine
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Thibblin, A.
    Tjernberg, A.
    Blomqvist, C.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Evaluation of internal thermal barrier coatings for exhaust manifolds2015In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 272, p. 198-212Article in journal (Refereed)
    Abstract [en]

    Seven different thermal barrier coatings (TBC) intended for coating the inside of an exhaust manifold to reduce its material temperature were studied. They comprised five plasma-sprayed (mullite, forsterite, La2Zr2O7, 8YSZ, and nanostructured 8YSZ) and two sol-gel composite (one sprayed and one dipped) coatings, which were examined for their thermal insulation properties and oxidation and spallation resistance. Thermal cyclic tests in air and in exhaust gas in a diesel test engine showed that thermal expansion mismatch between substrate and TBC was most crucial for TBC lifetime. Moreover, thermal modeling indicated that it is possible to reduce the material temperature by 50 °C, which is important for improving the fatigue life of exhaust manifolds. This reduction can be obtained with a 0.2 mm thick TBC with thermal conductivity close to 0.1 W/m K, or a 3–6 mm thick TBC with thermal conductivity 1.5–3 W/m K. 

  • 11.
    Ekström, Madeleine
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Zhu, B.
    Szakalos, P.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    High-temperature corrosion of materials for cast exhaust components2014In: 7th European Corrosion Congress, 2014Conference paper (Other academic)
  • 12.
    Ekström, Madeleine
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Zhu, B.
    Scania.
    Szakalos, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Jonsson, Stefan
    An electrochemical impedance spectroscopy study on the effect of condensate on oxides formed on a 25Cr/20Ni cast stainless steel in exhaust environmentsManuscript (preprint) (Other academic)
    Abstract [en]

     Condensation of diesel exhaust gases inside an exhaust- or turbo manifold may occur during cold-start and cooling of an engine, resulting in acidic liquid covering the oxide surfaces inside the manifolds. In the present study, the interaction between a chloride-containing exhaust-gas condensate of pH 2.4 and oxide scales formed on a 25Cr/20Ni cast stainless steel in air and in two different exhaust environments, 10%H2O-5%O2-85%N2 and 10%H2O-5%CO2-85%N2, at 900°C has been examined by means of electrochemical impedance spectroscopy, EIS. Interpretation of impedance spectra was coupled to oxide scale structures, revealed by SEM, EDX, XRD and GDOES, and to metal release studies using ICP. It was observed that the acidic condensate caused oxide spallation, followed by corrosion of the underlying metal surface for all test samples. The metal release rate of the oxide scale and underlying alloy was found to decrease at longer immersion times (>1h), most likely due to precipitation of corrosion products on the surfaces. EIS combined with equivalent circuit fitting showed to be a useful technique in describing the electric properties of the oxide scales, suggesting oxidation in H2O/O2 to result in formation of oxide scales being more resistive compared to the other environments. This was coupled to higher thickness and higher defect density, which correlated well with oxide scale analysis.

  • 13.
    Granbom, Ylva
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Structure and mechanical properties of dual phase steels: An experimental and theoretical analysis2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The key to the understanding of the mechanical behavior of dual phase (DP) steels is to a large extent to be found in the microstructure. The microstructure is in its turn a result of the chemical composition and the process parameters during its production. In this thesis the connection between microstructure and mechanical properties is studied, with focus on the microstructure development during annealing in a continuous annealing line. In-line trials as well as the lab simulations have been carried out in order to investigate the impact of alloying elements and process parameters on the microstructure. Further, a dislocation model has been developed in order to analyze the work hardening behavior of DP steels during plastic deformation.

    From the in-line trials it was concluded that there is an inheritance from the hot rolling process both on the microstructure and properties of the cold rolled and annealed product. Despite large cold rolling reductions, recrystallization and phase transformations, the final dual phase steel is still effected by process parameters far back in the production chain, such as the coiling temperature following the hot rolling.

    Lab simulations showed that the microstructure and consequently the mechanical properties are impacted not only by the chemical composition of the steel but also by a large number of process parameters such as soaking temperature, cooling rate prior to quenching, quench and temper annealing temperature.

     

  • 14.
    Hoseini, Mohammed
    et al.
    SP Swedish National Testing and Research Institute, Transport and Vehicle Technology, Building Technology and Mechanics, Borås.
    Jedenmalm, Anneli
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Boldizar, Antal
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Göteborg.
    Tribological investigation of coatings for artificial joints2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 958-966Article in journal (Refereed)
    Abstract [en]

    A modified pin-on-disc machine was used for the tribological investigation of ultrahigh molecular weight polyethylene (UHMWPE) sliding on stainless steel or stainless steel coated with diamond-like carbon, titanium nitride or Micronite. Micronite is a new type of coating applied by a physical vapour deposition technique combined with a very low friction coating material giving improved tribological properties. The tribological parameters used were chosen to mimic the conditions prevailing in the human body. The wear debris and the counter-surfaces were analysed. The surface analysis showed that the coating changed the roughness of the counter-surfaces. The diamond-like carbon and Micronite coatings had a much higher surface roughness than the titanium nitride coating. The results indicated that the enhanced tribological behaviour of the Micronite/UHMWPE sliding pair might be used as a material combination in artificial joints. Further studies are however required in order to support this.

  • 15.
    Janis, Jesper
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Inoue, Ryo
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Effects of Primary Oxide and Oxide-Nitride Particles on the Solidification Structure in a Fe-20 mass%Cr Alloy Deoxidised with Ti and M (M = Zr or Ce)2013In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 53, no 2, p. 221-229Article in journal (Refereed)
    Abstract [en]

    The ratio of equiaxed grains on a cross section and the size of equiaxed grains in a Fe-20 mass% Cr alloy deoxidised with Ti/M (M = Zr or Ce) were studied as function of nitrogen content and particle characteristics such as size distribution, morphology and composition. Fe-20 mass% Cr alloys were melted at 1 600 degrees C, deoxidised, and cooled to 1 400 degrees C followed by water quenching. Thereafter, the particles were separated from the matrix using electrolytic extraction using a 10%AA electrolyte and collected on a film-filter surface. The inclusion characteristics were determined using SEM. It was found that the number of particles increases with an increased N content. Furthermore, that the solidification structure was clearly affected by the number of primary oxide and oxide-nitride particles in the Ti/Zr deoxidation experiments. However, a similar effect could not be detected in the Ti/Ce deoxidation experiments.

  • 16.
    Kasedde, Hillary
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Characterization of Raw Materials for Salt Extraction from Lake Katwe, Uganda2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Uganda is well endowed with economic quantities of salt evident in the interstitial brines and evaporite deposits of Lake Katwe, a closed saline lake located in the western branch of the great East African rift valley. Currently, rudimentally methods of salt mining based on solar evaporation of brine continue to be used for salt extraction at the lake. These have proved to be hazardous and unsustainable to the salt miners and the environment. In this work, literature concerning the occurrence of salt and the most common available technologies for salt extraction is documented. Field studies were undertaken to characterize the salt lake deposit and to devise strategies of improving salt mining and extraction from the salt lake raw materials. The mineral salt raw materials (brines and evaporites) were characterized to determine their physical, chemical, mineralogical, and morphological composition through field and laboratory analyses. In addition, laboratory extraction techniques were undertaken to evaluate possibilities of future sustainable salt extraction from the lake deposit. Also, PHREEQC simulations using Pitzer models were carried out to determine the present saturation state of the lake brine and to estimate which salts and the order in which they precipitate from the brine upon concentration by evaporation.

    Results reveal that the raw materials from the salt lake contain substantial amounts of salt which can be commercialized for optimum production. The brines are highly alkaline and rich in Na+, K+, Cl-, SO42-, CO32-, and HCO3-. Moreover, they contain trace amounts of Mg2+, Ca2+, Br-, and F-. The lake is hydro-chemically of a carbonate type with the brines showing an intermediate transition between Na-Cl and Na-HCO3 water types. The evaporites are composed of halite mixed with other salts such as hanksite, burkeite, trona etc, with their composition varying considerably within the same grades. The laboratory extraction experiments indicate that various types of economic salts such as thenardite, anhydrite, mirabilite, burkeite, hanksite, gypsum, trona, halite, nahcolite, soda ash, and thermonatrite precipitate from the brine of Lake Katwe. The salts crystallize in the order following the sequence starting with sulfates, followed by chlorides and carbonates, respectively. Moreover, thermodynamic modeling in PHREEQC accurately predicted the solubility and sequence of the salt precipitation from the lake brine. Understanding the sequence of salt precipitation from the brine helps to control its evolution during concentration and hence, will lead to an improved operating design scheme of the current extraction processes. The work providesinformation towards future mineral salt exploitation from the salt lake.

     

  • 17.
    Kasedde, Hillary
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Towards the Improvement of Salt Extraction from Lake Katwe Raw Materials in Uganda2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Uganda is well endowed with economic quantities of mineral salts present in the interstitial brines and evaporite deposits of Lake Katwe, a closed (endorheic) saline lake located in the western branch of the great East African rift valley. Currently, rudimentally and artisanal methods continue to be used for salt extraction from the lake raw materials. These have proved to be risky and unsustainable to the salt miners and the environment and they have a low productivity and poor product quality. This work involves the investigation of the salt raw materials that naturally occur in the brines and evaporites of Lake Katwe. The purpose is to propose strategies for the extraction of improved salt products for the domestic and commercial industry in Uganda.

    The literature concerning the occurrence of salt and the most common available technologies for salt extraction was documented. Also, field investigations were undertaken to characterize the salt lake deposits and to assess the salt processing methods and practices. The mineral salt raw materials (brines and evaporites) were characterized to assess their quality in terms of the physical, chemical, mineralogical, and morphological composition through field and laboratory analyses. An evaluation of the potential of future sustainable salt extraction from the lake deposits was done through field, experimental, and modeling methods. Moreover, the mineral solubilities in the lake brine systems and dissolution kinetics aspects were investigated.

    The results reveal that the salt lake raw materials contain substantial amounts of salt, which can be commercialized to enable an optimum production. The brines are highly alkaline and rich in Na+, K+, Cl-, SO42-, CO32-, and HCO3-. Moreover, they contain trace amounts of Mg2+, Ca2+, Br-, and F-. The lake is hydro-chemically of a carbonate type with the brines showing an intermediate transition between Na-Cl and Na-HCO3 water types. Also, the evaporation-crystallization is the main mechanism controlling the lake brine chemistry. These evaporites are composed of halite mixed with other salts such as hanksite, burkeite, trona etc, but with a composition that varies considerably within the same grades. The laboratory isothermal extraction experiments indicate that various types of economic salts such as thenardite, anhydrite, mirabilite, burkeite, hanksite, gypsum, trona, halite, nahcolite, soda ash, and thermonatrite exist in the brine of Lake Katwe. In addition, the salts were found to crystallize in the following the sequence: sulfates, chlorides, and carbonates.

    A combination of results from the Pitzer’s ion-interaction model in PHREEQC and experimental data provided a valuable insight into the thermodynamic conditions of the brine and the sequence of salt precipitation during an isothermal evaporation. A good agreement between the theoretical and experimental results of the mineral solubilities in the lake brine systems was observed with an average deviation ranging between 8-28%. The understanding of the mineral solubility and sequence of salt precipitation from the brine helps to control its evolution during concentration. Hence, it will lead to an improved operating design scheme of the current extraction processes. The dissolution rate of the salt raw materials was found to increase with an increased temperature, agitation speed and to decrease with an increased particle size and solid-to-liquid ratio. Moreover, the Avrami model provided the best agreement with the obtained experimental data (R2 = 0.9127-0.9731). In addition, the dissolution process was found to be controlled by a diffusion mechanism, with an activation energy of 33.3 kJ/mol.

    Under natural field conditions, the evaporative-crystallization process at Lake Katwe is influenced by in-situ weather conditions. Especially, the depth of the brine layer in the salt pans and the temperature play a significant role on the brine evaporation rates. With the optimal use of solar energy, it was established that the brine evaporation flux can be speeded up in the salt pans, which could increase the production rates. Moreover, recrystallization can be a viable technique to improve the salt product purity. Overall, it is believed that the current work provides useful information on how to exploit the mineral salts from the salt lake resources in the future.

     

  • 18.
    Kasedde, Hillary
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Bäbler, Matthäus
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Kirabira, John Baptist
    Makerere University, Kampala, Uganda.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Mineral recovery from Lake Katwe brines using isothermal evaporation2013In: International Mine Water Association Annual Conference 2013: Reliable Mine Water Technology / [ed] Adrian Brown, Linda Figueroa, Christian Wolkersdorfer, IMWA International Mine Water Association , 2013, p. 855-860Conference paper (Refereed)
    Abstract [en]

    Lake Katwe is a saline lake within the East African Rift system in Western Uganda, with a rich source of mineral salts. The present work aims at evaluating possibilities of future salt extraction from the lake deposit. An isothermal evaporation experiment was conducted on the lake brines. The precipitated salts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. Various economic salts such as thenardite, gypsum, mirabilite, burkeite, hanksite, anhydrite, trona, halite, nahcolite, thermonatrite, and soda ash precipitate from the lake brines. The experiments also reveal the sequence of mineral salt precipitation in the order sulfates→chlorides→carbonates.

  • 19.
    Kasedde, Hillary
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. Makerere University, Kampala, Uganda.
    Kirabira, John Baptist
    Bäbler, Matthäus
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Phase developments during natural evaporation simulation of Lake Katwe brine based on Pitzer's model2014Conference paper (Refereed)
  • 20.
    Kasedde, Hillary
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy. Makerere University.
    Kirabira, John Baptist
    Makerere University.
    Bäbler, Mätthäus
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Characterization of brines and evaporites of Lake Katwe, Uganda2014In: Journal of African Earth Sciences, ISSN 0899-5362, Vol. 91, p. 55-65Article in journal (Refereed)
    Abstract [en]

    Lake Katwe brines and evaporites were investigated to determine their chemical, mineralogical and morphological composition. 30 brine samples and 3 solid salt samples (evaporites) were collected from different locations of the lake deposit. Several analytical techniques were used to determine the chemical composition of the samples including Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), Inductively Coupled Plasma-Sector Field Mass Spectrometry (ICP-SFMS), ion chromatography, and potentiometric titration. The mineralogical composition and morphology of the evaporites was determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Physical parameters of the lake brines such as density, electrical conductivity, pH, and salinity were also studied. The results show that the lake brines are highly alkaline and rich in Na+, Cl-, CO32-, SO42-, and HCO3- with lesser amounts of K+, Mg2+, Ca2+, Br-, and F- ions. The brines show an intermediate transition between Na-Cl and Na-HCO3 water types. Among the trace metals, the lake brines were found to be enriched in B, I, Sr, Fe, Mo, Ba, and Mn. The solid salts are composed of halite mixed with other salts such as hanksite, burkeite and trona. It was also observed that the composition of the salts varies considerably even within the same grades.

  • 21.
    Kasedde, Hillary
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Kirabira, John
    Mechanical Engineering, Makerere University, Uganda.
    Bäbler, Matthäus
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    A State of the Art Paper on Improving Salt Extraction from Lake Katwe Raw Materials In Uganda2012Report (Other academic)
    Abstract [en]

    The characteristics of Katwe salt lake are briefly discussed. The lake is the largest of the eight saline lakes in the Katwe-Kikorongo volcanic field and is a major source of salt production in Uganda. Today, salt production at the lake is carried out using traditional and artisanal mining methods. Attempts to mechanize the production of domestic and commercial grade salt at the lake were unsuccessful due to the use of a wrong technology. In this paper, the most common available technologies for salt extraction from brine are described. These are divided into four broad categories, namely thermal, membrane, chemical and hybrid processes. A review of the state of the art, previous research and developments in these technologies is presented. A detailed analysis of the processes used was done based on studies reported in the literature. From the analysis, it was observed that thermal salt production processes, especially distillation and solar evaporation have the highest share in installed capacities worldwide. Membrane technologies such as Electro-dialysis, Reverse Osmosis and chemical technologies have not found wide application in the commercial salt industry. Electro-dialysis and Reverse Osmosis have been used mainly as pre-concentration processes for subsequent thermal processes. Prospects for application of hybrid systems for salt production through integration of thermal desalting processes should be investigated for better performance efficiencies and recoveries at the salt lake.

  • 22. Kirabira, J. B.
    et al.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Drotz, M.
    Karathanasis, M.
    Norman, B.
    Properties of super-calendered (SC) paper filled with Mutaka kaolin, Uganda2009In: Paper Technology, ISSN 0306-252X, Vol. 50, no 1, p. 11-16Article in journal (Refereed)
    Abstract [en]

    The experts from Makerere University (Mak) and the Royal Institute of Technology (KTH) evaluated three mineral deposits for the production of fireclay refractories in Uganda and found that the Mutaka kaolin deposit in Uganda is of extraordinary quality. Ten tons of raw kaolin was mined at the Mutaka deposit and shipped in a container to STFI-Packforsk, Sweden. The kaolin was first dry sieved in a shaker to remove sand, mica and large particles. The sieved material was mixed with fresh water to a dry content of 15% and hydrocycloned to separate and remove coarse particles. The paper machine trials were carried out at STFI-Packforsk on the EuroFEX paper machine. The results indicate that the potential of exploiting the Mutaka kaolin deposit for paper filling is high. Paper filled with Mutaka clay resulted in a slightly lower opacity, however, with an optimized particles size distribution, this could be improved.

  • 23.
    Kirabira, John Baptist
    et al.
    Makerere University.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Byaruhanga, Joseph Kadoma
    Makerere University.
    Powder characterization of high temperature ceramic raw materials in the Lake Victoria Region.2005In: Silicates industriels, ISSN 0037-5225, Vol. 70, no 10-sep, p. 127-134Article in journal (Refereed)
    Abstract [en]

    Two main deposits of kaolin and one of fireclay, located in the Lake Victoria Region, Uganda, were investigated to assess their potential in the manufacture of refractory bricks. Raw- and processed sample powders were investigated by means of x-ray diffraction (XRD), thermal analysis (DTA-TG) and Scanning Electron Microscopy (SEM). In addition, the chemical composition, particle size distribution, density, and surface area of the powders were determined.

  • 24.
    Kirabira, John Baptist
    et al.
    Makerere University.
    Kasedde, Hillary
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy. Makerere University.
    Ssemukuuttu, Dominic
    Makerere University.
    Towards the improvement of salt extraction at Lake Katwe, Uganda2013In: International Journal of Scientific and Technology Research, ISSN 2277-8616, Vol. 2, no 1, p. 76-81Article in journal (Refereed)
    Abstract [en]

    The occurrence of Lake Katwe salt deposit in Western Uganda is well-known through the East African region. Production of salt from this saline lake has been practiced for decades following traditional methods; however the quality and yield of the products are poor. There are also risks of burns, as the workers get into direct contact with the brine. Detail assessment and evaluation of the mine has been done through field studies, raw sample materials analysis. Results indicate that the raw brine from the lake is rich in sodium, chloride, potassium, carbonates, sulphate ions with traces of calcium, magnesium, and bicarbonate ions. This motivates the aspiration to properly extract salts from such a rich source. The lake brines contain impurities such as organic matter and suspended solids. With increasing demand for usage of sustainable technologies for saltextraction, the present study calls for the improvement of salt extraction at Lake Katwe through optimizing the use of the current solar evaporation technique while integrating it with a mechanized chemical separation process. This would ensure better recovery and process efficiencies, low costs and simple brine pre-treatment procedures.

  • 25.
    Kirabira, John Baptist
    et al.
    Makerere University, Kampala, Uganda .
    Wijk, Gunnar
    Höganäs Bjuf AB.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Byaruhanga, Joseph Kadoma
    Makerere University.
    Fireclay refractories from Ugandan kaolinitic minerals2006In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, ISSN 1611-3683, Vol. 77, no 8, p. 531-536Article in journal (Refereed)
    Abstract [en]

    In the present work, two deposits, one of kaolin and the other of ball clay, located in Uganda were investigated for the possibility of manufacturing fireclay refractories. Kaolin from the Mutaka deposit was used as the main source of alumina while ball clay from Mukono was the main plasticizer and binder material. The formulated green body was consolidated by wet pressing and fired at 1350 degrees C in a tunnel kiln. Characterization of the sintered articles was done by X-ray diffraction, scanning electron microscopy, and chemical composition (ICP-AES). In addition, technological properties related to thermal conductivity, thermal shock, alkali resistance, water absorption, porosity, shrinkage, permanent linear change, linear thermal expansion, refractoriness under load, and cold crushing strength were determined. The properties of the articles manufactured from these naturally occurring raw minerals reveal that they compare favorably with those of parallel types. Thus, the raw materials can be exploited for industrial production.

  • 26. Lundberg, J.
    et al.
    Stone-Elander, S.
    Zhang, X. -M
    Korsgren, O.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Holmin, S.
    Endovascular Method for Transplantation of Insulin-Producing Cells to the Pancreas Parenchyma in Swine2014In: American Journal of Transplantation, ISSN 1600-6135, E-ISSN 1600-6143, Vol. 14, no 3, p. 694-700Article in journal (Refereed)
    Abstract [en]

    Insulin-producing cells are transplanted by portal vein injection as an alternative to pancreas transplantation in both clinical and preclinical trials. Two of the main limitations of portal vein transplantation are the prompt activation of the innate immunity and concomitant loss of islets and a small but significant risk of portal vein thrombosis. Furthermore, to mimic physiological release, the insulin-producing cells should instead be located in the pancreas. The trans-vessel wall approach is an endovascular method for penetrating the vessel wall from the inside. In essence, a working channel is established to the parenchyma of organs that are difficult to access by percutaneous technique. In this experiment, we accessed the extra-vascular pancreatic parenchyma in swine by microendovascular technique and injected methylene blue, contrast fluids and insulin-producing cells without acute adverse events. Further, we evaluated the procedure itself by a 1-year angiographical follow-up, without adverse events. This study shows that the novel approach utilizing endovascular minimal invasiveness coupled to accurate trans-vessel wall placement of an injection in the pancreatic parenchyma with insulin-producing cells is possible. In clinical practice, the potential benefits compared to portal vein cell transplantation should significantly improve endocrine function of the graft and potentially reduce adverse events. This study presents one-year follow-up safety data on the microendovascular trans-vessel wall technique and shows that the technique can be used to transplant insulin-producing cells to the swine pancreas parenchyma.

  • 27. Lundberg, Johan
    et al.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Holmin, Staffan
    Long Term Follow-Up of the Endovascular Trans-Vessel Wall Technique for Parenchymal Access in Rabbit with Full Clinical Integration2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 8, p. e23328-Article in journal (Refereed)
    Abstract [en]

    Objective: Endovascular techniques are providing options to surgical/percutaneous cell transplantation methods. Some cells, e. g. insulin producing cells, are not suitable for intra-luminal transplantation and for such cells, other options must be found. We have constructed a "nanocatheter'' with a penetrating tip for vessel perforation, thereby creating a working channel for parenchymal access by endovascular technique. To finish the procedure safely, the distal tip is detached to provide a securing plug in the vessel wall defect. Materials and Methods: We have performed interventions with full clinical integration in the superior mesenteric artery (SMA), the subclavian artery and the external carotid artery in rabbits. No hemorrhagic-or thromboembolic events occurred during the procedure. Stenosis formation and distal embolisation were analyzed by angiography and macroscopic inspection during autopsy at five, 30 and 80 days. All animals and implanted devices were also evaluated by micro-dissections and histochemical analysis. Results: In this study we show safety data on the trans-vessel wall technique by behavioral, angiographical and histological analysis. No stenosis formation was observed at any of the follow-up time points. No animals or organs have shown any signs of distress due to the intervention. Histological examination showed no signs of hemorrhage, excellent biocompatibility with no inflammation and a very limited fibrous capsule formation around the device, comparable to titanium implants. Further, no histological changes were detected in the endothelia of the vessels subject to intervention. Conclusions: The trans-vessel wall technique can be applied for e. g. cell transplantations, local substance administration and tissue sampling with low risk for complications during the procedure and low risk for hemorrhage, stenosis development or adverse tissue reactions with an 80 days follow-up time. The benefit should be greatest in organs that are difficult or risky to reach with surgical techniques, such as the pancreas, the CNS and the heart.

  • 28. Lundberg, Johan
    et al.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Holmin, Staffan
    New Endovascular Method for Transvascular Exit of Arteries and Veins: Developed in Simulator, in Rat and in Rabbit with Full Clinical Integration2010In: PLOS ONE, ISSN 1932-6203, Vol. 5, no 5, p. e10449-Article in journal (Refereed)
    Abstract [en]

    Background: Endovascular technique has benefits vis-a-vis surgical access to organs with less accessible anatomical locations. To minimize surgical risk we propose a novel endovascular technique, to create parenchymal access through endovascular methods. Methodology/Principal Findings: We have developed, manufactured and tested an endovascular catheter with a depth limiting collar and a penetrating tip that is used to perforate vessels, thereby creating a working channel to the extravascular space. Computer simulations and subsequent interventions have been performed ex vivo and in vivo in both small and large animals by testing different prototypes. All tests were designed for testing extravascular hemostasis and absence of thrombo-embolic complications when exiting the vessels from the inside to the extra vascular space. We have deposited prototypes after intervention in vascular walls over a period of 14 days in rat with no impairment on blood flow and no signs of thrombo-embolic complications upon re-exploration (n = 7). We have also incorporated the catheter system with clinically available systems both in an ex vivo simulator setting and in a full scale clinical angiographical setting in rabbit were no bleeding (0%) in any of the interventions performed (n = 40). To prevent hemorrhage during termination of the procedure, a hollow electrolysis detachment-zone leaves the distal tip in the vessel-wall after the intervention. This has also been tested with absolute hemostasis in large animals (n = 6). Conclusions/Significance: We have developed and tested a new system for transvascular tissue access in simulations, ex vivo and in vivo in small and large animals, integrating it with standard clinical catheters and angiographical environment, with absolute hemostasis and without thromboembolic complications. In a clinical setting for stem cell transplantation, local substance administration or tissue sampling, the benefit should be greatest in organs that are difficult or high-risk to access with other techniques, such as the pancreas, the central nervous system (CNS) and the heart.

  • 29.
    Nordén, Kristina
    et al.
    Högskolan Dalarna.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    A study of surface deformation during wire-rod rolling of high speed steels using experimental and computational techniques2007In: Steel Research International, ISSN 1611-3683, Vol. 78, no 12, p. 876-883Article in journal (Refereed)
    Abstract [en]

    The evolution of surface defects during shape rolling of high-speed steel billets is studied using longitudinal surface defects prepared by machining and welding. The reduction of the defects during rolling in a production mill is compared to the total area reduction of the billets. Samples are collected after pass 4, 6, 8, 14, 19 and the final pass, 28, representing the finished 5.5mm wire. By inspecting the cross sections, the rotation of the billets from pass to pass is evaluated. Results from FE simulations on solid billets are compared to the experimental results. Generally, simulations predict less reduction than observed experimentally. In most cases cracks reduce most effectively followed by carbon steel welds and stainless steel welds.

  • 30.
    Olofsson, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM).
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Hardening Distortions of Serial Produced Crown Wheels2017In: Materialwissenschaft und Werkstofftechnik, ISSN 0933-5137, E-ISSN 1521-4052Article in journal (Other academic)
    Abstract [en]

    The hardening distortions of serial produced crown wheels are studied with respect to gear runout, inner diameter and back-face tilt. The data analysed originates from a production data base from ordinary production as well as from directed experiments carried out in production, resulting in a large set of data. Strong influences are found for steel plants, position of material in ingots and stacking levels on hardening trays. It could be concluded that rectangular strands have a detrimental effect on gear runout, which, however, can be strongly decreased by disabling the magnetic stirring during casting. Furthermore, the inner diameter after quenching is influenced by the stacking level on the hardening tray when free-hardening or when using a segmented central expander during press quenching. This influence is attributed to variations in hardening temperature. When press quenching using a fixed mandrel, the effect of stacking level disappears. Moreover, it is found that the back-face tilt strongly depends on the position in the ingot as well as on the stacking level on the hardening tray.

  • 31.
    Olofsson, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy. Scania CV, Södertälje, Sweden.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy. Scania CV, Södertälje, Sweden.
    Brash, Benjamin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy. Scania CV, Södertälje, Sweden.
    Hardening distortions related to segregations in crown wheels2016In: HTM - Journal of Heat Treatment and Materials, ISSN 1867-2493, Vol. 71, no 2, p. 68-74Article in journal (Refereed)
    Abstract [en]

    The back-face tilt of press-hardened crown wheels is investigated for continuous and ingot cast material. Two different geometries are studied, one with a flat back-face and one with a step. For two ingots, the original material position is tracked and coupled to back-face tilt, cross section hardness and chemical segregation. The chemical gradients are shifted from top to bottom of the ingot and are strongly coupled to the back-face tilt.

  • 32. Olupot, P. W.
    et al.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Byaruhanga, J. K.
    Development of electrical porcelain insulators from ceramic minerals in Uganda2014In: Ceramic Engineering and Science Proceedings, 2014, no 2, p. 115-125Conference paper (Refereed)
    Abstract [en]

    Characterisation studies on ceramic minerals in Uganda have revealed their possibility for application in ceramic insulator production. Sand, feldspar and clay were used to formulate porcelain bodies based on established theories for ensuring high dielectric and mechanical strength. Sintering profiles and their effects on strength, crystalline phase content and morphology were investigated using dilatometiy, 4-point bending strength, XRD and FEG-SEM. Optimum properties of insulators from these minerals were attained with heating/cooling rates of 6°C/min to peak temperature of 1250°C with dwell time of 2h. The quartz content of the sintered body decreased as peak temperature was increased beyond 1250°C along with a decline in strength of the bodies. Neither increasing dwell time at 1250°C nor reducing the heating/cooling rate to less than 6°C/min for a peak temperature of 1250°C were shown to result in improvement of strength. The morphology of mullite crystals did not change with change in either heating/cooling rate or dwell time at peak temperature of 1250°C. The industrial sized specimens produced exhibited dry and wet flashover voltages of 22.8kV and 11.4kV respectively, transverse load capacity of 12.5kN and bulk density of 2.27g/cm3. These are satisfactory for low voltage insulation applications.

  • 33.
    Olupot, Peter W.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Byaruhanga, J. K.
    Effects of mixing proportions and firing temperature on properties of electric porcelain from Ugandan minerals2008In: Industrial ceramics, ISSN 1121-7588, Vol. 28, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Five sample mixtures of Ugandan kaolin, ball clay, feldspar and flint were formulated and porcelain samples fabricated by extrusion through a vacuum pugmill. Samples were evaluated for formability. The degree of densification of sintered specimens fired at 1200 to 1350 degrees C was evaluated by measuring the firing shrinkage, bulk density, water absorption and bending strength. Crystalline phases and mullite morphology were studied using XRD and SEM respectively. Dielectric strength measurements were carried out on disc specimens. Dielectric and bending strength properties deteriorated at high temperatures because of pore formation and decreasing amount of undissolved quartz in the crystalline phase. An optimum composition of 30% kaolin, 15% ball clay, 30% feldspar and 25% quartz yielded an unglazed body with highest bending strength of 72MPa and dielectric strength of 19MVm(-1) after firing at 1250 degrees C. The body consisted of small, closely packed mullite needles and undissolved quartz crystals embedded in a glass matrix.

  • 34.
    Olupot, Peter Wilberforce
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Characterization of Ceramic Raw Minerals in Uganda for Production of Electrical Porcelain Insulators2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this work an extended literature survey on ceramics and porcelains in particular, has been documented. Samples from two Ugandan deposits of each feldspar and quartz were characterised by means of X-ray diffraction, thermal analysis, chemical analysis and scanning electron microscopy and found to possess requisite properties for making electro porcelain insulators. Five porcelain bodies were formulated and samples were fabricated from materials collected from selected deposits in Uganda using different mixing proportions of clay, feldspar and quartz. The properties of the formulated bodies were studied in relation to workability, firing temperature, dielectric and bending strengths. The strengths (both mechanical and dielectric) were found to decrease as the firing temperature was increased above 1250°C. Additionally, ten formulations with components in the range of 30-60% clay, 20-45% feldspar and 20-25% sand were prepared. Specimens for mechanical and physical characterisation were made using the plastic extrusion method. The samples were characterised in terms of constituent oxide composition, flexural strength, fracture toughness, dielectric strength along with microstructural and phase properties using ICP-AES analyses, 4-point load bending strength test, Vicker’s indentation method, SEM and XRD analyses respectively. XRD studies revealed that the crystalline phases formed were mullite and quartz and their intensity was almost identical for all samples fired at 1250°C but there was a decrease inquartz content as temperature was increased above 1250°C. Samples with 20% sandcontent resulted in higher density, MOR and fracture toughness compared to thosecontaining 25% sand. Mullite content on the other hand did not change at temperatures above 1200°C but there were significant differences in the morphologies of the mullite crystals in the samples. Optimum mechanical and electrical properties were found at maximum vitrification and a microstructure showing small closely packed mullite needles. This occurred at a firing temperature of 1250°C.

    Three promising porcelain formulations from the above investigations were chosen and five glazes formulated to fit on biscuit fired specimens. The best-fitting glaze was adopted. The formulated specimens were investigated using dilatometry, Steger test, FEG-SEM, XRD, 4-point bending, dielectric strength and fracture toughness tests. A porcelain specimen consisting of 68% SiO2, 19% Al2O3, 4.7% K2O and a glaze of Seger formula RO:0.57Al2O3:4.86SiO2 exhibited MOR of 105MPa with Weibull modulus of 5.6 and a dielectric strength of 18kV/mm upon firing at a heating rate of 6ºC/min to 1250ºC, soaking for 2h at the top temperature and cooling down to 500°C at a rate of 6°C/min, followed by furnace cooling. The microstructure of the high strength specimen exhibited round mullite needles, quartz and glass. Holding samples for 2h at peak temperature resulted in a 22% increase in MOR compared to 1h holding. Glazing further improved strength by 67% for the best sample. Compressive stresses in glaze contributed to the strengthening effect. The dielectric and mechanical strengths obtained make the ormulated sample suitable for application in low voltage electrical insulation.

  • 35.
    Olupot, Peter Wilberforce
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Byaruhanga, Joseph K.
    Characterization of feldspar and quartz raw materials in Uganda for manufacture of electrical porcelains2006In: Journal of the Australasian Ceramic Society, ISSN 1018-6689, Vol. 42, no 1, p. 29-35Article in journal (Refereed)
    Abstract [en]

    Electric porcelains are widely used for insulation purposes. The aim of this study is to characterize feldspar and quartz raw materials in Uganda for use in manufacture of electric porcelains. Samples from two deposits of each feldspar and silica are investigated to assess their potential as raw materials in the manufacture of electric porcelains. Raw samples ground to powder form are investigated by means of X-ray diffraction, thermal analysis, and scanning electron microscopy. In addition, the chemical composition, particle size distribution and density of the powders are determined. The study reveals one of the feldspar deposits to consist of purely ordered microcline, while the other has ordered microcline, quartz and albite. The silica deposits are purely of quartz mineral. The materials investigated, are suitable for use in porcelain production.

  • 36.
    Olupot, Peter Wilberforce
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Byaruhanga, Joseph K.
    Development and characterisation of triaxial electrical porcelains from Ugandan ceramic minerals2010In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 36, no 4, p. 1455-1461Article in journal (Refereed)
    Abstract [en]

    Ten formulations of triaxial porcelain composed from 30-60% clay, 20-45% feldspar and 20-25% sand, were prepared from raw materials sourced from Ugandan deposits. Specimens were made using the plastic extrusion method and characterized in terms of constituent oxide composition, flexural strength, fracture toughness, dielectric strength, microstructure and phase properties using ICP-AES analyses, 4-point load strength test, Vicker's indentation, FEG-SEM and powder-XRD analyses, respectively. XRD studies revealed that the crystalline phases are mullite and quartz and their intensity is almost identical for all samples fired at 1250 degrees C but there is a decrease in quartz content as temperature is increased. Samples with 20% sand content resulted in higher density, modulus of rupture and fracture toughness compared to those containing 25% sand. The major factor influencing bending strength was found lobe porosity in samples as opposed to crystallinity. A sample with 67.3% SiO2, 20.2% Al2O3, 3.4% K2O and 6.3% others exhibited best properties. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

  • 37.
    Olupot, Peter Wilberforce
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Byaruhanga, Joseph K.
    State of the art paper on development of electric porcelain insulators from Ugandan raw materialsManuscript (preprint) (Other academic)
  • 38.
    Olupot, Peter Wilberforce
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Byaruhanga, Joseph K.
    Study of Glazes and Their Effects on Properties of Triaxial Electrical Porcelains from Ugandan Minerals2010In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 19, no 8, p. 1133-1142Article in journal (Refereed)
    Abstract [en]

    Kaolin, ball clay, feldspar, and sand were collected from deposits in Uganda, milled and sieved to particle sizes of 45, 45, 53, and 25 μm, respectively. Three porcelain bodies and five glazes were formulated from them. The glazes were applied on porcelain specimens and subsequently evaluated for their effects on properties of porcelain samples. The formulated specimens were investigated using dilatometry, Steger test, FEG-SEM, XRD, 4-point bending, dielectric strength, and fracture toughness tests. A porcelain specimen consisting of 68% SiO2, 19% Al2O3, 4.7% K2O, and a glaze RO:0.57Al2O3:4.86SiO2 exhibited MOR of 105 MPa with Weibull modulus of 5.6 and a dielectric strength of 18 kV/mm upon firing at a heating rate of 6 °C/min to 1250 °C and holding for 2 h. The microstructure of the high-strength specimen exhibited round mullite needles, quartz, and glass. Holding samples for 2 h at peak temperature resulted in a 22% increase in MOR compared to 1 h holding. Glazing further improved strength by 67% for the best sample. Compressive stresses in glaze contributed to the strengthening effect. The dielectric and mechanical strength values obtained qualify the formulated sample for application in electrical insulation.

  • 39.
    Thibblin, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Scania CV AB.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Influence of microstructure on thermal cycling lifetime, thermal insulation, and mechanical properties of yttria-stabilized zirconia thermal barrier coatingsIn: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) may improve the fuel efficiency of heavy-duty diesel engines by reducing heat losses. A combination of durability, low thermal conductivity, and high reflectance is required for a TBC in the combustion chamber. These properties are evaluated for yttria-stabilized zirconia coatings, produced using atmospheric plasma spraying (APS) and plasma spray–physical vapour deposition (PS-PVD). The influences of different types of microstructure and reflective metallic coatings on the surface are studied. APS coatings with segmentation cracks and PS-PVD coatings with columnar microstructure have the best thermal cycling lifetime, while nanostructured and conventional APS coatings have the lowest thermal conductivities. The nanostructured APS coating has the highest reflectance at low temperatures, while the columnar PS-PVD coating has the highest reflectance at elevated temperatures. It is further demonstrated that a thin silver layer improves the reflectance of a dense, segmented APS YSZ coating.

  • 40.
    Thibblin, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Scania CV AB.
    Kianzad, Siamak
    Scania CV AB.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Running-in Behaviour of Thermal Barrier Coatings in the Combustion Chamber of a Diesel EngineIn: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) have the potential to improve the fuel efficiency of heavy-duty diesel engines by reducing heat losses. A method for in-situ measurement of heat flux from the combustion chamber of a heavy-duty diesel engine has been developed and was used to study the running-in behaviour of different TBC materials and types of microstructures. The in situ measurements show that the initial heat flux was reduced by up to 4.7 % for all investigated TBCs compared to a steel reference, except for an yttria-stabilized zirconia (YSZ) coating with sealed pores that had an increase of 12.0 % in heat flux. Gd2Zr2O7 had the lowest initial value for heat flux. However, running-in shows the lowest values for YSZ after 2–3 h. Potential spallation problems were observed for Gd2Zr2O7 and La2Zr2O7.

  • 41.
    Zeng, Zhipeng
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Deformation Behaviour, Microstructure and Texture Evolution of CP Ti Deformed at Elevated Temperatures2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the present work, deformation behavior, texture and microstructure evolution of commercially pure titanium (CP Ti) are investigated by electron backscattered diffraction (EBSD) after compression tests at elevated temperatures. By analysing work hardening rate vs. flow stress, the deformation behaviour can be divided into three groups, viz. three-stage work hardening, two-stage work hardening and flow softening. A new deformation condition map is presented, dividing the deformation behavior of CP Ti into three distinct zones which can be separated by two distinct values of the Zener-Hollomon parameter. The deformed microstructures reveal that dynamic recovery is the dominant deformation mechanism for CP Ti during hot working. It is the first time that the Schmid factor and pole figures are used to analyse how the individual slip systems activate and how their activities evolve under various deformation conditions. Two constitutive equations are proposed in this work, one is for single peak dynamic recrystallization (DRX), the other is specially for CP Ti deformed during hot working. After the hot compression tests, some stress-strain curves show a single peak, leading to the motivation of setting up a DRX model. However, the examinations of EBSD maps and metallography evidently show that the deformation mechanism is dynamic recovery rather than DRX. Then, the second model is set up. The influence of the deformation conditions on grain size, texture and deformation twinning is systematically investigated. The results show that {10-12} twinning only occurs at the early stage of deformation. As the strain increases, the {10-12} twinning is suppressed while {10- 11} twinning appears. Three peaks are found in the misorientation frequency-distribution corresponding to basal fiber texture, {10-11} and {10-12} twinning, respectively. A logZ-value of 13 is found to be critical for both the onset of {10-11} compressive twinning and the break point for the subgrain size. The presence of {10-11} twinning is the key factor for effectively reducing the deformed grain size. The percentage of low angle grain boundaries decreases with increasing Z-parameter, falling into a region separated by two parallel lines with a common slope and 10% displacement. After deformation, three texture components can be found, one close to the compression direction, CD, one 10~30° to CD and another 45° to CD.

  • 42.
    Zeng, Zhipeng
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Roven, Hans J.
    Zhang, Yanshu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Modeling the flow stress for single peak dynamic recrystallization2009In: MATERIALS & DESIGN, ISSN 0264-1275, Vol. 30, no 6, p. 1939-1943Article in journal (Refereed)
    Abstract [en]

    A model is developed to predict the flow stress for single peak dynamic recrystallization during hot working based on the analysis of the mechanism of the process. The model reveals the dependence of flow stress on strain, strain rate, temperature and microstructure. The flow stress in the recrystallized zone is derived by an integral with the recrystallized volume fraction as the variable. The correlation between the microscopic variable and flow stress is investigated with the model. The performance of the model is evaluated through application on magnesium alloy AZ31D. The mean error of flow stress between the experimental and predicted results is examined. Good agreement between the predicted and experimental data is achieved. All mean errors are between −5.9% and 6.7%.

  • 43.
    Zeng, Zhipeng
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Zhang, Yanshu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Constitutive equations for pure titanium at elevated temperatures2009In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 505, no 1-2, p. 116-119Article in journal (Refereed)
    Abstract [en]

    Isothermal compression tests were conducted on pure titanium using a Gleeble 1500 thermal simulator under constant strain rates of 0.001, 0.01, 0.1 and 1.0/s and at deformation temperatures ranging from 673 to 973 K up to a 60% height reduction of the sample. The high temperature deformation behaviour of pure titanium was characterized based on an analysis of the stress–strain curves. A set of constitutive equations for pure titanium were proposed by employing an Arrhenius-type equation. Material constants, A, β and activation energy Q, were found to be functions of strain. The equations revealed the dependence of flow stress on strain, strain rate and temperature. In order to evaluate the accuracy of the deformation constitutive equations, the mean errors of flow stress between the experimental data and predicted results were plotted. The results show that there is a close agreement between the predicted and experimental stress–strain curves.

  • 44.
    Zeng, Zhipeng
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Zhang, Yanshu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Deformation behaviour of commercially pure titanium during simple hot compression2009In: Materials and Design, ISSN 0261-3069, Vol. 30, no 8, p. 3105-3111Article in journal (Refereed)
    Abstract [en]

    Commercially pure titanium (CP Ti), grade II, is subjected to hot compression at temperatures ranging from 673 to 973 K with 50 K intervals and strain rates of 0.001, 0.01, 0.1 and 1/s up to 60% height reduction. By analysing work hardening rate vs. flow stress, the deformation behaviour can be divided into three groups, viz. three-stage work hardening, two-stage work hardening and flow softening. By plotting the data in a T vs. log(strain rate) diagram, the present and previous data fall into three distinct domains which can be separated by two distinct values of the Zener–Hollomon parameter. The microstructure after deformation is characterized by optical microscopy and electron back scattered diffraction. The formation of {10-11} twins is related to the Zener–Hollomon parameter. Geometric dynamic recrystallization seems most appropriate when describing the grain refinement process of CP Ti during hot compression.

  • 45.
    Zeng, Zhipeng
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Zhang, Yanshu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Microstructure and texture evolution of commercial pure titanium deformed at elevated temperatures2009In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 513, p. 83-90Article in journal (Refereed)
    Abstract [en]

    Microstructure and texture evolution of commercial pure titanium were investigated by electron backscattered diffraction (EBSD) after compression tests at elevated temperatures. The basal planes of both the fine and coarse grains in the deformed samples tend to rotate from the initial orientations, perpendicular to the compression axis, to an inclination of 45°. The Schmid factor is used to analyse how the individual slip systems activate and how their activities evolve under various deformation conditions. After deformation, the distribution frequency of the misorientation angles shows that the low angle grain boundaries increased dramatically while the high angle grain boundaries decreased. In particular, after deformation at 723 K and 0.1/s, a peak around 50–60° in the misorientation frequency-distribution is found, which is due to {10-11} twinning. The analysis of the deformed microstructure indicates that dynamic recovery is the dominant deformation mechanism for commercial pure titanium when subjected to the investigated deformation conditions.

1 - 45 of 45
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