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  • 51.
    Ahmed, Hesham M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Investigations of the Kinetics of Reduction and Reduction/Carburization of NiO-WO3 Precursors.2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Kinetic studies of reduction of the mixtures of NiO and WO3 having different Ni/(Ni+W) molar ratios in flowing hydrogen gas were investigated by means of Thermo Gravimetric Analysis (TGA), Fluidized Bed (FB) technique as well as Thermal diffusivity measurements under isothermal conditions. In the case of TGA, the reaction progress was monitored by mass loss, while evolved gas analysis by a gas chromatograph was the indicator of the reaction progress in the case of FB. The results indicate that the reduction reaction proceeds through three consecutive steps, viz.

    NiO-WO3 Ni-WO3 Ni-WO2 Ni-W

    The present results show that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

    During the investigations, it was found that there was a delay in the reaction during the hydrogen reduction of NiO-WO3 mixed oxides in a fluidized bed reactor. In order to understand the same, a theoretical model was developed to estimate the apparent reaction rate constant for the reduction reaction from the intrinsic chemical reaction rate constant. Appropriate differential mass balance equations based on intrinsic chemical reaction rate constants and thermodynamic equilibria were developed. The proposed model was successfully applied in predicting the overall reaction kinetics of a fluidized bed reactor. This model is also suitable for scale-up calculations.

    SEM images showed that the particle size of the final product was dependent on the Ni/(Ni+W) molar ratio; smaller particles were formed at higher nickel contents. X-ray diffractions of the reduced precursors exhibited slight shift of Ni peaks from the standard one indicating the dissolution of W into Ni.

    A new method for studying kinetics of the hydrogen reduction of NiO-WO3 precursors was developed in which the reaction progress was monitored by following the change of thermal diffusivity of the precursors. Activation energies of reduction as well as sintering were calculated. This method is considered unique as it provides information regarding the physical changes like sintering, change of porosity and agglomeration along with the chemical changes occurring during the gas/solid reaction.

    As a continuation of the kinetic studies, Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of Ni-W-O system using H2-CH4 gas mixtures by TGA. The results showed that the reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. The above-mentioned experiments were conducted in such a way to ensure that the reaction was controlled by the chemical reaction. The activation energies of the reduction as well as carburization processes at different stages were calculated accordingly.

    The present dissertation demonstrates the potential of the investigations of gas/solid reactions towards tailoring the process towards materials with optimized properties as for example introduction of interstitials. The present process design is extremely environment-friendly with reduced number of unit processes and the product being H2O.

  • 52.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    El-Geassy, A. H. A.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Kinetics of Reduction of NiO-WO3 Mixtures by Hydrogen2010In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 1, p. 161-172Article in journal (Refereed)
    Abstract [en]

    The kinetics of reduction of the oxide mixtures of Ni-W with different Ni/(Ni-W) molar ratios within the range of 923 K to 1173 K in flowing hydrogen gas was investigated by means of thermogravimetric analysis under isothermal conditions. The products were examined by X-ray diffraction, scanning electron microscope (SEM), and electron dispersion spectroscopy (EDS) analyses. Five different oxide mixtures apart from the pure oxides were studied in the present work. The results indicate that the reduction reaction proceeds through three consecutive steps that are as follows: NiO-WO3 -> Ni-WO3 -> Ni-WO2 -> Ni-W From the experimental results, the Arrhenius activation energies of the three steps were evaluated for all of the studied compositions. The activation energy for the first step was calculated to be approximately 18 kJ/mol. For the second and third stages, the activation energy values varied from 62 to 38 kJ/mol for the second stage and 51 to 34 kJ/mol for the third stage depending on the Ni/(Ni + W) molar ratio in the precursors; the activation energy increased with increasing ratios. SEM images showed that the grain size of the final product was dependent on the Ni/(Ni + W) molar ratio; smaller grains were formed at higher nickel contents.

  • 53.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    El-Geassy, Abdel-Hady A.
    Viswanathan, Nurni Neelakantan
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO-WO(3) Precursors in Fluidized Bed Reactor2011In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, no 9, p. 1383-1391Article in journal (Refereed)
    Abstract [en]

    In the present work, Fluidized bed reduction of NiO-WO(3) precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H(2)O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

  • 54.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Isothermal dynamic thermal diffusivity studies of the reduction of NiO and NiWO(4) precursors by hydrogen2011In: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 102, no 11, p. 1336-1344Article in journal (Refereed)
    Abstract [en]

    Thermal diffusivity measurements of uniaxially cold pressed NiO and NiWO(4) were carried out in a dynamic mode in order to monitor the kinetics of hydrogen reduction of the above-mentioned materials using a laser flash unit. The calculated activation energy was found to be higher than that for chemically-controlled reaction obtained earlier by thermogravimetry. The difference has been attributed to physical changes occurring along with the chemical reaction. The activation energy of sintering of the products was evaluated to be 33 and 36 kJ.mol(-1) for NiO and NiWO(4), respectively. Thermal conductivities were calculated taking into consideration the change in heat capacity considering the compositional and the structural changes with the progress of the reaction. The potentiality of the laser-flash method as a complementary technique to thermogravimetry in understanding the mechanism of gas solid reactions is discussed.

  • 55.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture2010In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 1, p. 173-181Article in journal (Refereed)
    Abstract [en]

    Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of NiO-WO3 oxide precursors using H2-CH4 gas mixtures in the temperature range of 973 to 1273 K. The kinetics of the gas–solid reaction were followed closely by monitoring the mass changes using the thermogravimetric method (TGA). As a thin bed of the precursors were used, each particle was in direct contact with the gas mixture. The results showed that the hydrogen reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. Consequently, the reaction rate could be conceived as being controlled by the chemical reaction. From the reaction rate, Arrhenius activation energies for reduction and carburization were evaluated. Characterization of the carbides produced was carried out using X-ray diffraction and a scanning electron microscope (SEM) combined with electron dispersion spectroscopy (SEM-EDS) analyses. The grain sizes also were determined. The process parameters, such as the temperature of the reduction–carburization reaction and the composition of the gas mixture, had a strong impact on the carbide composition as well as on the grain size. The results are discussed in light of the reduction kinetics of the oxides and the thermodynamic constraints.

  • 56.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Viswanathan, N. N.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    On The Kinetics of Hydrogen Reduction of NiO-WO3 Precursors in Fluidized Bed- A Modeling Approach2011In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, no 9, p. 1383-1391Article in journal (Refereed)
    Abstract [en]

    In the present work, Fluidized bed reduction of NiO-WO3 precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H2O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

  • 57.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Viswanathan, Nurini N.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dynamic Thermal Diffusivity Measurements - A Tool for Studying Gas-Solid Reactions2011In: DIFFUSION IN SOLIDS AND LIQUIDS VI, PTS 1 AND 2, 2011, p. 217-222Conference paper (Refereed)
    Abstract [en]

    In the present work, the thermal diffusivity measurements of uniaxially cold pressed NiWO(4) has been carried out. The measurements were performed isothermally at temperatures between 973 and 1273 K under H(2) gas using the laser flash technique. The experimental thermal diffusivity values were found to increase with the reduction progress as well as with increasing temperature. The calculated activation energy was found to be higher than that for chemically controlled reaction. The difference has been attributed to factors like agglomeration of the product as well as sintering of the precursor along with the chemical reaction. In order to sort out the sintering effect on the thermal diffusivity values, complementary experiments have been done on pressed NiWO(4) and Ni-W, produced by the reduction of NiWO(4) at 1123K, under Argon gas. The porosity change and its effect on thermal diffusivity values have been studied.

  • 58.
    Ahmed, Hesham
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mis, Michal
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    El-Geassy, Abdel-Hady
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Seethararnan, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Reduction-Carburization of the Oxides of Ni and W Towards the Synthesis of Ni-W-C Carbides2010In: ADVANCED MATERIALS FORUM V, PT 1 AND 2  / [ed] Rosa LG; Margarido F, 2010, Vol. 636-637, p. 952-962Conference paper (Refereed)
    Abstract [en]

    Ternary Ni-W-C cemented carbides were synthesized directly from mixture powder of NiO-WO3 by simultaneous reduction-carburization in mixed H-2-CH4 gas environment in a thin bed reactor in the temperature range 973-1273K. The kinetics of the reaction was closely followed by monitoring the mass change using thermogravimetric method (TGA). The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. The gas mixture ratio was adjusted in such a way that the Ni-W-C formed was close to the two phase tie line. In view of the fact that each particle was in direct contact with the gas mixture, the reaction rate could be conceived as being controlled by the combined reduction-carburization reaction. From the reaction rate, the Arrhenius activation energies were evaluated. Characterization of the carbides produced was carried out by using X-ray diffraction, SEM-EDS as well as high resolution electron microscope (HREM). The grain sizes were also determined. Correlations were found between the carbide composition as well as grain size and the process parameters such as temperature of the reduction-carburization reaction as well as the composition of the gas mixture. The results are discussed in the light of the kinetics of the reduction of oxides and the thermodynamic constraints.

  • 59. Ahmed, Hesham
    et al.
    Morales-Estrella, R.
    Viswanathan, Nurin
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gas-Solid Reaction Route toward the Production of Intermetallics from Their Corresponding Oxide Mixtures2016In: METALS, ISSN 2075-4701, Vol. 6, no 8, article id 190Article in journal (Refereed)
    Abstract [en]

    Near-net shape forming of metallic components from metallic powders produced in situ from reduction of corresponding pure metal oxides has not been explored to a large extent. Such a process can be probably termed in short as the "Reduction-Sintering" process. This methodology can be especially effective in producing components containing refractory metals. Additionally, in situ production of metallic powder from complex oxides containing more than one metallic element may result in in situ alloying during reduction, possibly at lower temperatures. With this motivation, in situ reduction of complex oxides mixtures containing more than one metallic element has been investigated intensively over a period of years in the department of materials science, KTH, Sweden. This review highlights the most important features of that investigation. The investigation includes not only synthesis of intermetallics and refractory metals using the gas solid reaction route but also study the reaction kinetics and mechanism. Environmentally friendly gases like H-2, CH4 and N-2 were used for simultaneous reduction, carburization and nitridation, respectively. Different techniques have been utilized. A thermogravimetric analyzer was used to accurately control the process conditions and obtain reaction kinetics. The fluidized bed technique has been utilized to study the possibility of bulk production of intermetallics compared to milligrams in TGA. Carburization and nitridation of nascent formed intermetallics were successfully carried out. A novel method based on material thermal property was explored to track the reaction progress and estimate the reaction kinetics. This method implies the dynamic measure of thermal diffusivity using laser flash method. These efforts end up with a successful preparation of nanograined intermetallics like Fe-Mo and Ni-W. In addition, it ends up with simultaneous reduction and synthesis of Ni-WN and Ni-WC from their oxide mixtures in single step.

  • 60.
    Ahuja, Rajeev
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Sa
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje Örje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    High pressure structural transitions in Cm metal2006In: Mater Res Soc Symp Proc, 2006, p. 247-254Conference paper (Refereed)
    Abstract [en]

    The high pressure behaviour of Cm metal is investigated theoretically using ab initio electronic structure methods. Our calculations reproduce the structural phase transitions which are obsereved in recent experiment performed by Heatman et al. [Science 309, 110 (2005)]. Calculated transition pressures are in reasonable agreement with the experimental values. Calculations performed for an antiferromagnetic state is essential to reproduce the stability of Cm-III phase. Thus, the stability of the Cm-III phase is related to the spin polarization of its 5f electrons.

  • 61. Aimable, Anne
    et al.
    Doubi, Herve Goure
    Stuer, Michael
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Bowen, Paul
    Synthesis and Sintering of ZnO Nanopowders2017In: TECHNOLOGIES, ISSN 2227-7080, Vol. 5, no 2, article id 28Article in journal (Refereed)
    Abstract [en]

    Nanopowders are continuously under investigation as they open new perspectives in numerous fields. There are two main challenges to stimulating their development: sufficient low-cost, high throughput synthesis methods which lead to a production with well-defined and reproducible properties; and for ceramics specifically, the conservation of the powders' nanostructure after sintering. In this context, this paper presents the synthesis of a pure nanosized powder of ZnO (dv(50)similar to 60 nm, easily redispersable) by using a continuous Segmented Flow Tubular Reactor (SFTR), which has previously shown its versatility and its robustness, ensuring a high powder quality and reproducibility over time. A higher scale of production can be achieved based on a "scale-out" concept by replicating the tubular reactors. The sinterability of ZnO nanopowders synthesized by the SFTR was studied, by natural sintering at 900 degrees C and 1100 degrees C, and Spark Plasma Sintering (SPS) at 900 degrees C. The performance of the synthesized nanopowder was compared to a commercial ZnO nanopowder of high quality. The samples obtained from the synthesized nanopowder could not be densified at low temperature by traditional sintering, whereas SPS led to a fully dense material after only 5 min at 900 degrees C, while also limiting the grain growth, thus leading to a nanostructured material.

  • 62. Airiskallio, E.
    et al.
    Nurmi, E.
    Vayrynen, I. J.
    Kokko, K.
    Ropo, M.
    Punkkinen, M. P. J.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Magnetic origin of the chemical balance in alloyed Fe-Cr stainless steels: First-principles and Ising model study2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 92, p. 135-140Article in journal (Refereed)
    Abstract [en]

    Iron-chromium is the base material for most of the stainless steel grades. Recently, new insights into the origins of fundamental physical and chemical characteristics of Fe-Cr based alloys have been achieved. Some of the new results are quite unexpected and call for further investigations. The present study focuses on the magnetic contribution in the atomic driving forces related to the chemical composition in Fe-Cr when alloyed with Al, Ti, V, Mn, Co, Ni, and Mo. Using the ab initio exact muffin-tin orbitals method combined with an Ising-type spin model, we demonstrate that the magnetic moment of the solute atoms with the induced changes in the magnetic moments of the host atoms form the main factor in determining the mixing energy and chemical potentials of low-Cr Fe-Cr based alloys. The results obtained in the present work are related to the designing and tuning of the microstructure and corrosion protection of low-Cr steels.

  • 63. Akbar, F.
    et al.
    Kolahdouz, M.
    Larimian, Sh.
    Radfar, B.
    Radamson, Henry
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Graphene synthesis, characterization and its applications in nanophotonics, nanoelectronics, and nanosensing2015In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 26, no 7, p. 4347-4379Article in journal (Refereed)
    Abstract [en]

    In the last decade, as semiconductor industry was approaching the end of the exponential Moore's roadmap for device downscaling, the necessity of finding new candidate materials has forced many research groups to explore many different types of non-conventional materials. Among them, graphene, CNTs and organic conductors are the most successful alternatives. Finding a material with metallic properties combined with field effect characteristics on nanoscale level has been always a dream to continue the ever-shrinking road of the nanoelectronics. Due to its fantastic features such as high mobility, optical transparency, room temperature quantum Hall effect, mechanical stiffness, etc. the atomically thin carbon layer, graphene, has attracted the industry's attention not only in the micro-, nano-, and opto-electronics but also in biotechnology. This paper reviews the basics and previous works on graphene technology and its developments. Compatibility of this material with Si processing technology is its crucial characteristic for mass production. This study also reviews the physical and electrical properties of graphene as a building block for other carbon allotropes. Different growth methods and a wide range of graphene's applications will be discussed and compared. A brief comparison on the performance result of different types of devices has also been presented. Until now, the main focus of research has been on the background physics and its application in electronic devices. But, according to the recent works on its applications in photonics and optoelectronics, where it benefits from the combination of its unique optical and electronic properties, even without a bandgap, this material enables ultrawide-band tunability. Here in this article we review different applications and graphene's advantages and drawbacks will be mentioned to conclude at the end.

  • 64.
    Akbarnejad, Shahin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Experimental and Mathematical Study of Incompressible Fluid Flow through Ceramic Foam Filters2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ceramic Foam Filters (CFFs) are widely used to filter solid particles and inclusions from molten metal in metal production, particularly in the aluminum industry. In general, the molten metal is poured on the top of a ceramic foam filter until it reaches a certain height, also known as metal head or gravity head. This is done to build the required pressure to prime the filter media and to initiate filtration. To predict the required metal head, it is necessary to obtain the Darcy and non-Darcy permeability coefficients of the filter. The coefficients vary upon filter type. Here, it is common to classify CFFs based on grades or pore per inches (PPI). These CFFs range from10 to100 PPI and their properties vary in everything from cell and window size to strut size. The 80-100 PPI CFFs are generally not practical for use by industry, since the priming of the filters by a gravitational force requires an excessive metal head. However, recently a new method has been developed to prime such filters by using electromagnetic Lorentz forces. This allows the filters to be primed at a low metal head.

    To continue the research work, it was deemed necessary to measure the pressure gradients of single and stack of commercial alumina ceramic foam filters and to obtain the permeability characteristics. Therefore, efforts have been made to validate the previously obtained results, to improve the permeametry experimental setup, and to obtain Darcy and non-Darcy permeability coefficients of single 30, 50, and 80 PPI filters and stacks of filters. Furthermore, the experimentally obtained pressure gradients were analyzed and compered to the mathematically and analytically estimated pressure gradients.

    The studies showed that, in permeametry experiments, the sample sealing procedure plays an important role for an accurate estimation of the permeability constants. An inadequate sealing or an un-sealed sample results in an underestimation of the pressure drop, which causes a considerable error in the obtained Darcy and non-Darcy permeability coefficients. Meanwhile, the results from the single filter experiments showed that the permeability values of the similar PPI filters are not identical. However, the stacks of three identical filters gave substantially the same measured pressure drop values and roughly the same Darcy and non-Darcy coefficients as for the single filters.

    The permeability coefficients of the filters are believed to be best defined and calculated by using the Forchheimer equation. The well-known and widely used Ergun and Dietrich equations cannot correctly predict the pressure drop unless a correction factor is introduced. The accuracy of the mathematically estimated pressure drop, using COMSOL Multiphysics® 5.1, found to be dependent on the drag term used in the Brinkman-Forchheimer equation.  Unacceptable error, as high as 84 to 89 percent for the 30, 50 and 80 PPI single filters, compared to the experimentally obtained pressure gradient values were observed when the literature defined Brinkman-Forchheimer drag term was used. However, when the same second order drag term (containing the non-Darcy coefficient) as defined in the Forchheimer equation was used, the predicted pressure gradient profiles satisfactorily agreed with the experiment data with as little as 0.3 to 5.5 percent deviations for the 30, 50 and 80 PPI single filters.

  • 65.
    Akbarnejad, Shahin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Investigation on static strength of welded joints2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Although high strength steels represent yield strength up to 1300 MPa, welded structures reveal lowerstrength values. The strongest commercially available electrode provides the yield strength of about900 MPa. Therefore, in welded steels with strength above this type of filler metal, achieving anacceptable global strength is a crucial issue.

    In this master thesis, affects of different welding procedures on static strength of welded jointsof Weldox 960 and Weldox 1100 steels, were studied. These steels are produced by SSAB inOxelösund. Meanwhile, finite element method analyses were applied in order to investigatethe static strength behavior of such weldments under uniaxial tension.

    The welding parameters which were selected as variables are:

    •  Heat input
    • Weld joint geometry
    • Filler metal

    When weld metal is undermatching in strength levels than the base material, by applyingtension the soft weld metal begins to deform before parent metal. At that point thedeformation of resulted soft zone, including the weld metal and the heat affected zone, ishindered by high strength parent metal. Thus, uniaxial stress caused by uniaxial load isconverted to multiaxial stress. This conversion in tension results in increase in the staticstrength of weldment. The increase in strength is emphasized by increase in the width of thewelded joint while the thickness of the plate is kept as constant.

    After experiments and performing FEM studies, it was revealed that the static strength ofWeldox 960 welded joints approaches towards the tensile strength of parent metal by increasein the width of the weldment. In Weldox 1100 joints; a slight increase in tensile properties ofthe weldments, when the width of the sample increases, was observed.

  • 66.
    Akbarnejad, Shahin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jonsson, Lage Tord Ingemar
    Kennedy, Mark William
    Aune, Ragnhild Elizabeth
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Analysis on Experimental Investigation and Mathematical Modeling of Incompressible Flow Through Ceramic Foam Filters2016In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, no 4, p. 2229-2243Article in journal (Refereed)
    Abstract [en]

    This paper presents experimental results of pressure drop measurements on 30, 50, and 80 pores per inch (PPI) commercial alumina ceramic foam filters (CFF) and compares the obtained pressure drop profiles to numerically modeled values. In addition, it is aimed at investigating the adequacy of the mathematical correlations used in the analytical and the computational fluid dynamics (CFD) simulations. It is shown that the widely used correlations for predicting pressure drop in porous media continuously under-predict the experimentally obtained pressure drop profiles. For analytical predictions, the negative deviations from the experimentally obtained pressure drop using the unmodified Ergun and Dietrich equations could be as high as 95 and 74 pct, respectively. For the CFD predictions, the deviation to experimental results is in the range of 84.3 to 88.5 pct depending on filter PPI. Better results can be achieved by applying the Forchheimer second-order drag term instead of the Brinkman-Forchheimer drag term. Thus, the final deviation of the CFD model estimates lie in the range of 0.3 to 5.5 pct compared to the measured values.

  • 67.
    Akbarnejad, Shahin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Saffari Pour, Mohsen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jonsson, Lage Tord Ingemar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pӓr Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effect of Fluid Bypassing on the Experimentally Obtained Darcy and Non-Darcy Permeability Parameters of Ceramic Foam Filters2017In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 1, p. 197-207Article in journal (Refereed)
    Abstract [en]

    Ceramic foam filters (CFFs) are used to remove solid particles and inclusions from molten metal. In general, molten metal which is poured on the top of a CFF needs to reach a certain height to build the required pressure (metal head) to prime the filter. To estimate the required metal head, it is necessary to obtain permeability coefficients using permeametry experiments. It has been mentioned in the literature that to avoid fluid bypassing, during permeametry, samples need to be sealed. However, the effect of fluid bypassing on the experimentally obtained pressure gradients seems not to be explored. Therefore, in this research, the focus was on studying the effect of fluid bypassing on the experimentally obtained pressure gradients as well as the empirically obtained Darcy and non-Darcy permeability coefficients. Specifically, the aim of the research was to investigate the effect of fluid bypassing on the liquid permeability of 30, 50, and 80 pores per inch (PPI) commercial alumina CFFs. In addition, the experimental data were compared to the numerically modeled findings. Both studies showed that no sealing results in extremely poor estimates of the pressure gradients and Darcy and non-Darcy permeability coefficients for all studied filters. The average deviations between the pressure gradients of the sealed and unsealed 30, 50, and 80 PPI samples were calculated to be 57.2, 56.8, and 61.3 pct. The deviations between the Darcy coefficients of the sealed and unsealed 30, 50, and 80 PPI samples found to be 9, 20, and 31 pct. The deviations between the non-Darcy coefficients of the sealed and unsealed 30, 50, and 80 PPI samples were calculated to be 59, 58, and 63 pct.

  • 68.
    Akbarpour, Sahar
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Reinforcement around holes in composite materials by use of patched metal inserts2019In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 225, article id 111084Article in journal (Refereed)
    Abstract [en]

    Metal inserts are sometimes used to improve the load carrying capacity of bolted joints in composite materials. In this paper a new concept is introduced where inserts are built during composite manufacturing by integrating stacked metal patches at locations where holes are to be made after consolidation. Initial tests and a parameter study enable more informed design, and specimens with improved stacked inserts are then produced and tested. The specimens with inserts show up to 60% strength improvement in pin-loaded tests. In addition to the experimental work, finite element analysis is performed to investigate the stress fields and the failure mechanisms. The model indicates that the singular stresses at the multi-material corner points are governing for the strength and give indications of the failure mechanisms. Some basic analytical estimates are also presented.

  • 69.
    Akhtar, Suleman
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Material Factors Influencing Crack Initiation and Propagation During Seamless Tube Rolling of Low Carbon Steel Grades2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Lower hot ductility can lead to cracks in steels. Hot ductility is affected by grain boundary sliding at temperatures higher than A3 and by the presence of thin films of ferrite at grain boundaries at temperatures lower than A3. Grain boundary sliding might occur because of the segregation of harmful elements like sulphur, etc. While thin films of ferrite at grain boundaries lead to easy interlinking of MnS precipitates at grain boundaries and ultimately may cause cracks in the material. Also, stress concentration is higher at thin ferrite films at grain boundaries which for being softer as compared to austenite matrix lead to cracks in the material. Elongated  (Fe, Mn)S sulphides are more detrimental for the hot ductility as compared to round ones. Higher aspect ratio of the precipitates is also dependent on sulphur content. The higher the sulphur content, the higher would be the hot ductility. Silicon, being a ferrite stabilizer, causes the volume fraction of ferrite to increase which improves the hot ductility of the steels. Hot ductility can be improved by adding Boron that segregates to grain boundaries instead of sulphur improving the strength of grain boundaries. Increasing silicon content can lead to higher volume fraction of ferrite thus improving ductility because stress would uniformly be distributed across the grain and not merely on the grain boundaries. Apart from that, decreasing the solution treatment temperature and increasing holding time on solution treatment temperature can lead to lower dissolved content of sulphur and coarser MnS precipitates hence improving hot ductility. 

  • 70. Alam, M. M.
    et al.
    Kaplan, A. F. H.
    Tuominen, J.
    Vuoristo, P.
    Miettinen, J.
    Poutala, J.
    Näkki, J.
    Junkala, J.
    Peltola, T.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Analysis of the stress raising action of flaws in laser clad deposits2013In: Materials and Design, ISSN 0261-3069, Vol. 46, p. 328-337Article in journal (Refereed)
    Abstract [en]

    Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generated as well as stress raisers created by laser cladding defects for four different fatigue load conditions. As important as the defect types are their locations and orientations, categorized into zero-, one- and two-dimensional defects. Pores and inclusions become critical close to surfaces. The performance of as-clad surfaces can be governed by the sharpness of surface notches and planar defects like hot cracks or lack-of-fusion (LOF) are most critical if oriented vertically, transverse to the bar axis. The combination of the macro stress field with the defect type and its position and orientation determines whether it is the most critical stress raiser. Based on calculated cases, quantitative and qualitative charts were developed as guidelines to visualize the trends of different combinations.

  • 71. Alam, Minhaj M
    et al.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Häggblad, Hans Åke
    Jonsén, Pär
    Kaplan, Alexander
    The Effects of Surface Topography and Lack of Fusion on The Fatigue Strength of Laser Hybrid Welds2009In: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics, 2009, p. 38-46Conference paper (Refereed)
    Abstract [en]

    The geometrical aspects of laser hybrid welds (before, during and after the process) differ from autonomous laser welding and from arc welding. When studying the fatigue behaviour of laser hybrid welded fillet joints we identified that the micro-topography (i.e. the surface ripples) can be more important than the macrogeometry of the weld surface or lack of fusion (LOF), which frequently was detected. The plastic replica method was applied to measure the toe radii at the weld edges while the micro-topography was identified by interferometric profilometry. From metallurgical analysis of the joint interface, the tendency to LOF can be explained. Stress analysis was carried out by Finite element analysis (FEA) for the complex joint geometry and a bending load situation, showing maximum stress on the weld toes, even when including LOF. It was shown that the position and value of the maximum stress depends on a non-trivial combination of the weld geometry, including possible LOF, and the surface micro-topography. Thus it can be explained that at compressive stress conditions LOF does not contribute significantly to the fatigue strength of laser hybrid welds while the surface topography does. Recommendations for defining and in turn avoiding critical geometrical aspects during the welding process are discussed.

  • 72.
    Alander, B.
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials.
    Capezza, A.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials. Department of Plant Breeding, The Swedish University of Agricultural Sciences, Box 101, Alnarp, Sweden.
    Wu, Q.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Johansson, E.
    Olsson, Richard T.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Hedenqvist, Mikael
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    A facile way of making inexpensive rigid and soft protein biofoams with rapid liquid absorption2018In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 119, p. 41-48Article in journal (Refereed)
    Abstract [en]

    A novel and facile method to produce inexpensive protein biofoams suitable for sponge applications is presented. The protein used in the study was wheat gluten (WG), readily available as a by/co-product, but the method is expected to work for other cross-linkable proteins. The foams were obtained by high-speed stirring of pristine WG powder in water at room temperature followed by drying. Glutaraldehyde was used to crosslink the foam material in order to stabilize the dispersion, reduce its tackiness and improve the strength of the final foam. The foams were of medium to high density and absorbed readily both hydrophobic and hydrophilic liquids. The foam structure, consisting primarily of an open pore/channel system, led to a remarkably fast capillary-driven (pore-filling only) uptake of a hydrophobic liquid (limonene). Essentially all uptake occurred within the first second (to ca. 90% of the dry weight). In a polar liquid (water), the rapid pore-filling occurred in parallel with a more time-dependent swelling of the foam matrix material. Further improvement in the foam strength was achieved by making a denser foam or adding TEMPO-oxidized cellulose nanofibres. Soft foams were obtained by adding glycerol.

  • 73.
    Alberth, Lena
    KTH, School of Chemical Science and Engineering (CHE).
    Experimentell studie av kinetiken vid peroxidblekning av pappersmassa2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    During TCF-bleaching of pulp, hydrogen peroxide is one of the main chemicals. Today it is difficult to control the bleaching stages. The process operators must consider the production rate, changes in the bleach ability of the pulp and delays of trends in the control system. The PO-bleaching stage at Södra Cell Värö has approximately a retention time of four(4) hours and it is first after that, a result of a change in the process can be seen. Overbleaching is expensive due to high chemical need and therefore it is requested to find a way to control and optimize the peroxide bleaching stage. One way to do this was too simulate the stage experimentally and from those kinetic data accomplish a mathematical model that predicts the brightness increase of the pulp.

    Pulp from the mill was bleached at the laboratory under controlled conditions and with charges similar to what are used in the plant. The parameters that were studied at lab were temperature, hydrogen peroxide charge and alkali charge as they affect the brightness mostly. A model for brightness increase was adjusted to the achieved bleaching data. Equations for consumption of hydrogen peroxide and hydroxide anions were also developed from analyses of the bleaching filtrates. 

    From the start parameters, as concentration of the chemicals, temperature and pulp concentration, the model predicts the brightness well according to verification of data from mill and verification bleaching at laboratory. The value from the model is somewhat higher compared to that of the plant but that was expected due to the fact that the conditions at lab give a cleaner system. For those parameters that were studied, the model did adjust well to changes made and according to the verification at lab it was seen that the model also worked for changes in pulp concentration and different brightness at the beginning of the stage.

  • 74.
    Albertsson, Galina
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Abatement of Chromium Emissions from Steelmaking Slags - Cr Stabilization by Phase Separation2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Chromium is an important alloying element in stainless steel but also environmentally harmful element. A number of mineralogical phases present in the slag matrix can contain chromium and lead to chromium leaching. Chromium in slag if not stabilized, could oxidize to the cancerogenic hexavalent state, and leach out if exposed to acidic and oxygen rich environment. Other environmental concerns are slag dusting and chromium escape to the atmosphere. Despite the fact that there is a certain risk of Cr-emission from slags at operating conditions, still very little is known regarding the emission of the oxides of chromium during the slag tapping. Spinel phase is known to be important for controlling the leaching properties of chromium from the slag. The objective of the present study was to get an understanding of the phase relationships and chromium partition in the chromium-containing industrial slags and synthetic slags with a view to control the chromium stabilization in spinel phase. The impact of slag basicity, heat treatment, oxygen partial pressure and Al2O3 addition, on the phase relationships and chromium partition has been determined. The experimental results were compared with the phase equilibrium calculations. It was found that the oxygen partial pressure in the gas phase had a strong impact on chromium partition. The experimental results show that the impact of the slag basicity on chromium partition at lower oxygen partial pressures was negligible in contrast to that in air. The amount of spinel phase was found to increase with increased Al2O3 content. Slow cooling of slag and soaking at low oxygen partial pressure would improve the spinel phase precipitation. This treatment will also lead to less Cr dissolved in the unstable matrix phases. Chromium oxide was found to be emitted when chromium containing slags were exposed to oxidizing atmosphere. The results indicate that chromium oxide evaporation increases with increase in temperature and oxygen partial pressure, but decreases with slag basicity and sample thickness.

  • 75.
    Albertsson, Galina
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Effect of the presence of a dispersed phase (solid particles, gas bubbles) on the viscosity of slag2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The viscosities of a set of silicone oils containing different size ranges of charcoal or paraffin particles as well as the viscosities of silicone oil foams were measured at room temperature in order to determine the effect of dispersed phase on the viscosity of a liquid and its effect on foaming ability. The effective viscosity of the samples increased with volume fraction of the second phase. The foaming ability was improved by the presence of the particles. The improved foaming effect was for the most part not a result of the increased viscosity. No connection between the particle size and the effective viscosity could be determined. On the other hand particle morphology and the particle size distribution had effect on the effective viscosity. The viscosity data were compared with a number of existing equations for the estimation of effective viscosity. Einstein-Roscoe equation is suitable for two-phase mixtures containing globular particles with narrow particle size distribution and low interfacial tension. New mathematical models are required for effective viscosity prediction, where the suspending phase viscosity, effect of the interfacial tension, as well as the particle morphology should be taken in consideration.

  • 76.
    Albertsson, Galina
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Teng, Lidong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Björkman, Bo
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Engström, Fredrik
    Effect of Low Oxygen Partial Pressure on the Chromium Partition in CaO-MgO-SiO2-Cr2O3-Al2O3 Synthetic Slag at Elevated Temperatures2013In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 7, p. 670-679Article in journal (Refereed)
    Abstract [en]

    The objective of the present work is to get an understanding of the impact of Al2O3 addition on the phase relationships in the CaO-MgO-Al2O3-SiO2-Cr2O3 slags at low oxygen partial pressures (P-O2 = 10(-4) Pa), with a view to control the precipitation of Cr-spinel in the slag. The equilibrium phases in CaO-MgO-Al2O3-SiO2-Cr2O3 slag system in the range on 1673-1873 K have been investigated. The compositions close to the industrial slag systems were chosen. The Cr2O3 content was fixed at 6 wt% and MgO at 8 wt%. Al2O3 contents in the slag were varied in the range of 3-12 wt%. The basicity (CaO/SiO2) of slag was set to 1.6. Gas/slag equilibrium technique was adopted. The samples were heated to 1873 K and soaked at this temperature for 24 h. The samples were then slow cooled to 1673 K and equilibrated for an additional 24 h. The oxygen partial pressure was kept at 10(-4) Pa. A gas mixture of CO/CO2 was used to control the oxygen partial pressure. After the equilibration, the samples were quenched in water. The chromium distribution and phase compositions in the quenched slags were studied using SEM-WDS and XRD techniques. The results were compared with the phase equilibrium calculations obtained from FACTSAGE software and the samples equilibrated in air. The size of spinel crystals increased drastically after slow cooling followed by annealing compared to samples being quenched after soaking at 1873 K. It was also found that low oxygen partial pressure had a strong impact on chromium partition. The amount of spinel phase increases with increased Al2O3 content.

  • 77.
    Aldén, Rickard
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Metallurgical investigation in weldability of Aluminium Silicon coated boron steel with different coating thickness.2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Hot-pressed aluminium and silicon coated boron steel is used in the car industry where high tensile strength is of great importance, such as in the safety cage of a car where deformation has to be kept to a minimum in case of a collision. After hot-pressing the AlSi-boron steel shows excellent properties with high tensile strength, minimal spring back and also shows good protection against corrosion. A thickness of the AlSi coating of 150 [g/m2] for AlSi coated boron steel is typically used by the car industry today. However the coating thickness would be desirable to be minimized to 80 [g/m2]. Welding of this boron steel with 80 [g/m2]have shown difficulties; and it’s not clear why this occurs.

    In this report the metallurgical properties of the different coating layers will be investigated, simulations with Thermocalc module Dictra will be used, SEM/EDS will be used to characterize phases in coating layers and correlate to weldability. Resistance spot welding tests will also be performed where the welding parameters of pre-pulse, pulse time, time in between pulses and current will be varied to achieve desirable weld plug diameter without expulsion. Hardness testing in form of micro Vickers will executed. The Materials used will be USIBOR® 1500, AS80 with four different annealing times and one sample of AS150.

  • 78. Alemani, Mattia
    et al.
    Gialanella, S.
    Straffelini, G.
    Ciudin, R.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Perricone, G.
    Metinoz, I.
    Dry sliding of a low steel friction material against cast iron at different loads: Characterization of the friction layer and wear debris2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, p. 1450-1459Article in journal (Refereed)
    Abstract [en]

    Pin-on-disc testing was used to investigate the sliding behavior and the wear products of a low-steel friction material against a cast iron disc at different applied loads, to investigate the effect of the temperature rise induced by frictional heating. The testing rig was operated in a clean chamber with a purified incoming air flux. The outgoing flux carries the wear particles to an impactor that counted and sorted them by average diameter and weight. At increasing applied loads, corresponding to a proportional increase of the pin-disc contact temperature, the coverage of both the pin and disc surface by a friction layer was found to increase too. The relevant X-Ray diffraction patterns revealed the presence of a large amount of graphite and different compounds originating from the friction material and from the counterface disc, mainly iron oxides, as concerns this latter. After the test at the lowest investigated load, i.e., 1 kg, the disc worn surface exhibited abrasive grooves and a discontinuous friction layer mainly made of compacted iron oxide particles. After the test at higher loads, i.e., 5 and 7 kg, the disc surface was covered by a compact friction layer. As concerns the friction layer on the pins, most of the ingredients from the friction material were detected, in association with the iron oxides from the disc. These results can be interpreted in terms of the temperature stability range of the phenolic resin used as a binder of the friction material. The characterization of the collected airborne wear debris showed that the particles produced by the low temperature (i.e., low load) test were mostly equiaxed; whereas those produced by the high temperature (i.e., high loads) tests, predominantly displayed a plate-like morphology. The mechanisms of their formation in relation to the characteristics of the friction layers are illustrated and discussed.

  • 79.
    Alemrajabi, Mahmood
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Korkmaz, Kivanc
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Forsberg, Kerstin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Resource recovery.
    Recovery of rare earth elements from nitrophosphoric acid solutions2017In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 169, p. 253-262Article in journal (Refereed)
    Abstract [en]

    In the present study, the recovery of rare earth elements (REEs) from an apatite concentrate in the nitrophosphate process of fertilizer production has been studied. The apatite concentrate has been recovered from iron ore tailings in Sweden by flotation. In the first step, the apatite is digested in concentrated nitric acid, after which Ca(NO3)2.4H2O is separated by cooling crystallization. The solution is then neutralized using ammonia whereby the REEs precipitate mainly as phosphates (REEPO4.nH2O) and together with calcium as REEn Cam (PO4)(3n + 2m) / 3. In this work, the degree of rare earth coprecipitation during seeded cooling crystallization of Ca(NO3)2.4H2O has been studied. The solubility of calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) in acidic nitrophosphoric acid solutions in the temperature range of − 2 °C to 20 °C has been determined. For the neutralization step, it is shown that the calcium concentration and the final pH play an important role in determining the concentration of REEs in the precipitate. It is found that reaching maximum recovery of REE with minimum simultaneous precipitation of calcium requires careful control of the final pH to about 1.8. It is further observed that the precipitation yield of REEs and iron is favored by a longer residence time and higher temperature. Finally, the effect of seeding with synthesized REE phosphate crystals as well as a mixture of REE and Ca phosphates on the precipitation rate and the composition of the precipitate was studied.

  • 80.
    Alevanau, A. Y.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kuznechik, O. P.
    Vyhoniailo, O. I.
    Prospective Engineering Applications of Dynamic Transfer Processes Possessing the Self-Organized Fractal Interfaces2013In: Journal of Engineering, ISSN 2314-4904, E-ISSN 2314-4912, Vol. 2013, article id 310748Article in journal (Refereed)
    Abstract [en]

    General formulation of practically applicable fundamental approach for development of engineering applications in systems with dynamically appearing and disappearing fractal structures is proposed. The approach is illustrated on the low-temperature pyrolysis of butane/propane mixture being pumped via the liquid tin and bismuth alloy preserved at the temperature 200 ± 20°C in the U-shaped test glass. Other prospective engineering applications of the approach are proposed on the base of analysis of selected experiments described in literature.

  • 81.
    Alevanau, Aliaksandr
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Study of pyrolysis and gasification of biomass from the self-organization perspective2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on the analysis of kinetics of i) low-temperature pyrolysis of gaseous hydrocarbons, ii) high-temperature steam gasification of char of wood pellets (>700oC), iii) high temperature pyrolysis of straw pellets in an atmosphere of argon and steam, and iv) high temperature pyrolysis of slices of transversally cut wooden sticks. The results of the kinetic measurements in the high-temperature cases are approximated using a least-square based optimization software, which was specially developed to analyse kinetics prone for deviation from the Arrhenius law.In the thesis a general analysis of the researched materials and kinetics of their pyrolysis and gasification is presented from the self-organization perspective. The energy transfer phenomena in both the pyrolysis and gasification processes of biomass are discussed with an emphasis on an analysis of basic phenomena involving the self-organized dynamics on fractal structures in the chosen biomass samples.

  • 82.
    Alexis, Jonas
    et al.
    Swerea-Mefos.
    Jonsson, Lage
    KTH, Superseded Departments, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, Superseded Departments, Applied Process Metallurgy.
    Heat and fluid-flow models for stirring conditionsin ladle furnaces and their practical implications in secondary refiningoperations1997In: Clean Steel 5, Vol 1,  2-4 June 1997, Balatonszeplak,Hungary, Balatonszeplak, 1997, p. 49-58Conference paper (Refereed)
  • 83.
    Alexis, Jonas
    et al.
    Swerea-Mefos.
    Jönsson, Pär
    KTH, Superseded Departments, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, Superseded Departments, Applied Process Metallurgy.
    A model of an induction-stirred ladle accounting for slag and surface deformation1999In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 39, no 8, p. 772-778Article in journal (Refereed)
  • 84.
    Alexis, Jonas
    et al.
    Swerea-Mefos.
    Jönsson, Pär
    KTH, Superseded Departments, Metallurgy.
    Jonsson, Lage
    Heating and electromagnetic stirring in a ladle furnace – a simulationmodel2000In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 40, no 11, p. 1098-1104Article in journal (Refereed)
    Abstract [en]

    A three-dimensional simulation model coupling heating and induction stirring in an ASEA-SKF ladle furnace was developed. Data of the heat transfer from the area to the steel bath were predicted in a separate model and included as boundary conditions in a ladle model. The are model considers the contributions of heat transferred by of each of the following mechanisms: radiation, convection, condensation and energy transported by electrons. Predictions were made to simulate the change of temperature distribution in the ladle during simultaneous heating with electrodes and stirring by induction. A first attempt was made to compare the predictions with measured temperatures from a 100 t ASEA-SKF ladle. The agreement was found to be fairly good when heat-flux data for a 25 cm are length were used as input to the ladle model. This indicates that the model can be used for more in-depth studies of the effects of heating for ladles that are inductively stirred.

  • 85. Alfieri, G
    et al.
    Monakhov, EV
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Svensson, BG
    Capacitance spectroscopy study of high energy electron irradiated and annealed 4H-SIC2005In: SILICON CARBIDE AND RELATED MATERIALS 2004 / [ed] Nipoti, R; Poggi, A; Scorzoni, A, ZURICH-UETIKON: TRANS TECH PUBLICATIONS LTD , 2005, Vol. 483, p. 365-368Conference paper (Refereed)
    Abstract [en]

    Deep level transient spectroscopy (DLTS) was employed to investigate the annealing behaviour and thermal stability of radiation induced defects in nitrogen doped 4H-SiC epitaxial layers, grown by chemical vapor deposition (CVD). The epilayers have been irradiated with 15 MeV electrons and an isochronal annealing series has been carried out. The measurements have been performed after each annealing step and six electron traps located in the energy band gap range of 0.42-1.6 eV below the conduction band edge (E-c) have been detected.

  • 86.
    Alfredsson, Bo
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Linares Arregui, Irene
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Hazar, Selcuk
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Numerical analysis of plasticity effects on fatigue growth of a short crack in a bainitic high strength bearing steel2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, p. 36-51Article in journal (Refereed)
    Abstract [en]

    Plasticity effects on fatigue growth were simulated for a physically short crack. The material description comprised the Drucker-Prager yield surface, non-associated flow rule and non-linear combined hardening. The simulated development of the growth limiting parameter agreed with the experimental crack behaviour with early rapid propagation followed by a transition to slow R-controlled growth. The crack was open to the tip without any crack face closure throughout all load cycles. Instead compressive residual stresses developed at the unloaded tip which supplied an explanation to the slow rate of the propagated short crack in this bainitic high strength bearing steel. The material's strength differential effect was the key difference explaining why compressive residual stresses instead of crack face closure was responsible for the short crack effect in this material.

  • 87.
    Alfredsson, Bo
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Olsson, Mårten
    KTH, Superseded Departments, Solid Mechanics.
    Standing Contact Fatigue Testing of a Ductile Material: Surface and Sub-Surface Cracks2000In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 23, no 3, p. 229-240Article in journal (Refereed)
    Abstract [en]

    During standing contact fatigue testing of case hardened steel plates, four different fatigue crack types are found: ring/cone; lateral; radial; and median cracks. Fatigue results are presented as load versus cycle number, with endurance limits and initiation laws for the ring/cone and lateral cracks. The behaviour of the radial surface strain outside the contact is altered by the presence of cracks. In particular this makes in situ crack detection possible for the lateral crack.

    The ductility of the tested material is found to be important for fatigue crack initiation. Numerical elastoplastic computations are used to derive the stress cycles responsible for each crack type. Stress cycles at different locations and in different directions are compared in order to explain why a particular crack type initiates. It is noted that cracks are produced normal to principal stresses of sufficient range, which are tensile sometime during the load cycle. Implications for spalling are discussed.

  • 88.
    Alfthan, Johan
    KTH, Superseded Departments, Solid Mechanics.
    Micro-mechanically based modeling of mechano-sorptive creep in paper2004Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The creep of paper is accelerated by moisture content changes. This acceleration is known as mechano-sorptive creep, which is also found in wood and some other materials. Mechano-sorptive creep has been known for several decades but it is still not well understood, and there is no generally accepted model explaining the effect.

    In this thesis, it is assumed that mechano-sorptive creep is the result of transient redistributions of stresses during moisture content changes in combination with non-linear creep behaviour of the material. The stress redistributions are caused by the anisotropic hygroexpansion of the fibres, which will give a mismatch of hygroexpansive strains at the bonds and hence large stresses each time the moisture content changes. This redistribution will lead to an uneven stress state. If the creep of the material depends non-linearly on stresses this will give an increase in creep rate where the stresses are high, that is larger than the decrease of creep rate where stresses are low, so in average there will be an increase in creep rate. The stress distribution evens out as the stresses relax during creep, and the moisture content has to change again to create a new uneven stress state and maintain the accelerated creep.

    Two different network models based on this mechanism are developed in this thesis. Numerical simulations show that the models produce results similar to the mechano-sorptive creep found in paper. In the first model it is assumed that creep takes place in the fibre-fibre interfaces at the bonds, in the second the creep of the fibres themselves is accelerated. The second model is further developed. Experiments verify model predictions of the dependence of the amplitude of moisture changes.

    The second model shows a linear relationship between mechanical load and deformation, although creep of the fibres depends non-linearly on stresses. This linear behaviour is also found in applications. Further analysis shows that the mechanical load can be treated as a small perturbation of the internal stress state caused by moisture content changes. This can be used to develop a linearized model, from which a continuum model can be derived. This leads to a reduction of the necessary number of variables, and a significant increase in speed of calculations. Hence, this linearized continuum model can be used as a constitutive law of paper in problems with complicated geometries, for example a corrugated board box in varying humidity.

  • 89.
    Alfthan, Johan
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    A micromechanical model for mechanosorptive creep in paper2002In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, no 3, p. 98-104Article in journal (Refereed)
    Abstract [en]

    The creep of paper is accelerated by moisture cycling, a phenomenon known as mechanosorptive creep or accelerated creep. In this paper stress created at bonds due to anisotropic swelling during absorption and desorption of moisture, in combination with nonlinear creep, are proposed to be the cause for mechanosorptive creep. Two simplifled models are first discussed in order to demonstrate the suggested mechanism. A three-dimensional fibre network model composed of elastic fibres and inelastic bonds is then studied by finite element calculations. The relative sliding in the bonds is described by a nonlinear creep model which, in combination with anisotropic hygroexpansion of the fibres results in accelerated creep of the network.

  • 90. Al-Hamdi, Abdullah M.
    et al.
    Sillanpaa, Mika
    Dutta, Joydeep
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Gadolinium doped tin dioxide nanoparticles: an efficient visible light active photocatalyst2015In: Journal of Rare Earths, ISSN 1002-0721, Vol. 33, no 12, p. 1275-1283Article in journal (Refereed)
    Abstract [en]

    Photocatalytic degradation of phenol with sol-gel prepared rare earth doped tin dioxide (SnO2) nanoparticles was reported. Gadolinium doped tin dioxide (SnO2:Gd) nanoparticles were found to absorb higher visible light compared to lanthanum, neodymium and cerium doped materials that were studied in detail. Photocatalytic degradation of phenol under artificial white light and sunlight in the presence of SnO2: Gd nanoparticles was studied with high performance liquid chromatography (HPLC), capillary electrophoresis (CE), total organic carbon (TOC) measurements and the determination of chemical oxygen demand (COD). Clear correlations between the results obtained from these multiple measurements were found, and a kinetic pathway for the degradation process was proposed. Within 150 min of solar irradiation, the TOC of a 10 ppm phenol solution in water was reduced by 95%-99%, thus demonstrating that SnO2: Gd nanoparticles are efficient visible light photocatalysts.

  • 91.
    Ali, Amjad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan.;Univ Okara, Dept Phys, Okara 56300, Pakistan.
    Raza, Rizwan
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan.;Royal Inst Technol KTH, Dept Energy Technol, S-10044 Stockholm, Sweden..
    Khalil, R. M. Arif
    Bahauddin Zakariya Univ, Dept Phys, Multan 60800, Pakistan..
    Ahmad, M. Ashfaq
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan..
    Rafique, Asia
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan..
    Ullah, M. Kaleem
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan..
    Rehman, Amin Ur
    Lahore Univ, Dept Phys, Lahore 54000, Pakistan..
    Mushtaq, M. Naveed
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan..
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A potential electrolyte (Ce1-x CaxO2-delta) for fuel cells:Theoretical andexperimental study2018In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 44, no 11, p. 12676-12683Article in journal (Refereed)
    Abstract [en]

    First-principles calculations are performed using density function theory to explore the effects of dopant Ca in ceria (Ce1-x CaxO2-delta). The impact of oxygen vacancy on band gap and density of states is examined in doped ceria using generalized gradient approximations. Vacancy association and vacancy formation energies of the doped ceria are calculated to reveal the effect of dopant on ion conduction. The experimental study of the sample Ce0.875Ca0.125O2-delta) was performed to compare with the theoretical results. The obtained results from theoretical calculation and experimental techniques show that oxygen vacancy increases the volume, lattice constant (5.47315 angstrom) but decrease the band gap (1.72 eV) and bulk modulus. The dopant radius (1.173 angstrom) and lattice constant (5.4718 angstrom) are also calculated by equations which is close to the DFT lattice parameter. The result shows that oxygen vacancy shifts the density of states to lower energy region. Band gap is decreased due to shifting of valence states to conduction band. Vacancy formation shows a significance increase in density of states near the Fermi level. Density of states at Fermi level is proportional to the conductivity, so an increase in density of states near the Fermi level increases the conductivity. The experimental measured ionic conductivity is found to 0.095 S cm(-1) at 600 degrees C. The microstructural studies is also reported in this work.

  • 92.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A Visualization Study During Flow Boiling of R134a In A Horizontal Microchannel2010In: ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting, ICNMM2010, 2010, p. 85-94Conference paper (Refereed)
    Abstract [en]

    In this paper, the experimental flow boiling visualization results of a microchannel are presented and discussed. A series of visualization experiments have been conducted in a horizontal, circular, uniformly heated microchannel, to record the two-phase flow patterns evolved during the boiling process and to study the ebullition process. A high speed camera (REDLAKE HG50LE) with a maximum of 100000 fps together with tungsten lights was used to capture the images along the test section. Microchannel was made of circular fused silica tube having an internal diameter of 0.781 mm and a uniformly heated length of 191 mm. Outside of the test tube was coated with a thin, electrically conductive layer of Indium Tin Oxide (ITO) for direct heating of the test section. Refrigerant R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 25 degrees C and 30 degrees C. Mass flux was varied from 100 kg/m(2)s to 400 kg/m(2)s and heat flux ranged from 5 kW/m(2) to 45 kW/m(2). Visualization results show that the bubble growth is restricted by the tube diameter which results in very short existence of isolated bubbly flow regime except essentially restricted to a very short length of test tube. Flow patterns observed along the length were: Isolated bubble, elongated bubble, slug flow, semi annular and annular flow. Rigorous boiling and increased coalescence rates were observed with increase in heat flux. Bubble frequency was observed to increase with both heat and mass flux. A comparison with our previous flow boiling visualization studies, carried out for a test tube of 1.33 mm internal diameter, shows that the number of active nucleation sites is less while the bubble frequency is higher for the current study. Mean bubble length and bubble velocity during elongated bubble flow pattern have also been calculated from the images obtained during the tests.

  • 93.
    Ali, Silvia
    et al.
    STFI-Packforsk, Stockholm, Sweden .
    Salmén, Lennart
    From wood shavings to mechanical pulp - a new raw material?2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, ISSN 0283-2631, Vol. 20, no 4, p. 418-422Article in journal (Refereed)
    Abstract [en]

    Wood chips used in the thermomechanical pulping (TMP) process were originally designed to suit the chemical pulping process. The production of small wood pieces more suitable for the TMP process could lead to an energy saving in this energy-intensive process. This paper discusses the potential benefits of using wood shavings instead of chips as the raw material for TMP production. In some exploratory trials, wood shavings with a thickness of about 2 mm and wood chips were refined in two steps under normal TMP process conditions in a pilot refiner. The first-stage refining was performed under pressurized conditions at 130°C. The second-stage refining was performed at atmospheric pressure at approximately 100°C at four different energy levels. The quality of the pulp produced from wood shavings was found to be better than that of the pulp produced from wood chips, with respect to both strength properties (except tear index) and optical properties at comparable energy levels. The potential for energy savings at a given tensile index using wood shavings instead of the traditional chips is estimated to be about 25%.

  • 94. Alimadadi, H.
    et al.
    Ahmadi, M.
    Aliofkhazraei, M.
    Younesi, Seyed Reza
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Corrosion properties of electrodeposited nanocrystalline and amorphous patterned Ni-W alloy2009In: MATERIALS & DESIGN, ISSN 0261-3069, Vol. 30, no 4, p. 1356-1361Article in journal (Refereed)
    Abstract [en]

    Nickel-tungsten with satisfactory corrosion properties is a promising alloy to replace hard chromium. Relatively high adhesion between copper substrate and electrodeposited Ni-W alloy results in patterned morphology due to crack formation. In this work, corrosion resistance of patterned Ni-W alloys comprising 0-26 at.%.W were studied by potentiodynamic polarization and EIS in a medium containing Cl-. It is shown that corrosion resistance of single phase Ni-W is superior to amorphous and dual phase coated layers. It is also found that crack density is the dominant affecting factor on corrosion resistance of amorphous Ni-W alloys.

  • 95.
    Alipour, Yousef
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Machining of CoCr28Mo62011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The machining process of Cobait-Chromium medical ailoys become a veryessential topic for research due to widening range of application. They aregeneraily used because of their high wear resistance, low corrosioncharacteristics and high fatigue strength. This project describes an investigationof chip formation during the machining of Cobalt-Chromium-Molybdenum highcarbon alloy. A quick stop device has been employed to investigate mechanismof chip formation through analyzing of shear zone and shear plane. Thicknessmeasurement of segments, surface conditions after finishing, lowest valley andhighest peak with three different cutting tool inserts were studied as weil.Moreover cutting force measurement at different cutting speeds, feeds and radialnoses were performed. Microstructure and hardness of work material before andafter machining has been studied. Tool life of inserts was evaluated bymeasuring flank wear.

    The consequences obtained from the study illuminated:

    1. For the constant cutting speed and nose radius flank wear increased whenthe feed increased.
    2. For the constant feed and nose radius, increase in the cutting speedlowered flank and crater wear.
    3. Cutting force increased with the increase in feed.
    4. Increase in cutting speed to 40 m/min raised cutting force. However afterthat cutting force decreased.
    5. Insert CNMG 120408-MF1 TS2000 with cutting data v~=70 m/min, ap= 3mm and f=0.1 mm seemed fit the best in base of lower flank and craterwear, almost lower cutting force and smoother finish roughness.
  • 96.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. Vattenfall Res & Dev AB, Sweden.
    Szakalos, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Effect of temperature on corrosion of furnace walls in a waste wood fired boiler2015In: Materials at High Temperature, ISSN 0960-3409, E-ISSN 1878-6413, Vol. 32, no 1-2, p. 188-196Article in journal (Refereed)
    Abstract [en]

    One way of reducing the furnace wall corrosion is to lower the temperature of the wall by reducing the boiler pressure. To test this, four coupons of 16Mo3 were exposed in the furnace wall of a waste wood fired boiler for 1075 h. The temperatures of the samples were individually controlled in the range 280-410 degrees C. The corrosion rates and corrosion mechanism were investigated. The deposits were analysed by XRD and SEM/EDS. The corrosion fronts were studied by focused ion beam milling (FIB)/EDS. The environment was modelled by Thermo-Calc. The amount of potassium and chlorine in the deposit decreased with decreasing temperature. The FIB sections showed a distinctive iron chloride layer at the corrosion front, with an outer layer of iron oxide. The corrosion rate decreased with decreasing metal temperature, but the boiler pressure needs to be reduced to a low level to achieve this, which is not beneficial for the electrical efficiency and therefore not a viable way of reducing corrosion.

  • 97.
    Alipour, Yousef
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Viklund, Peter
    Henderson, Pamela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    The analysis of furnace wall deposits in a low-NOx waste wood-fired bubbling fluidised bed boiler2012In: VGB PowerTech Journal, ISSN 1435-3199, Vol. 92, no 12, p. 96-100Article in journal (Other academic)
    Abstract [en]

    Increasing use is being made of biomass as fuel for electricity production as the price of natural wood continues to rise. Therefore, more use is being made of waste wood (recycled wood). However, waste wood contains more chlorine, zinc and lead, which are believed to increase corrosion rates. Corrosion problems have occurred on the furnace walls of a fluidised bed boiler firing 100 % waste wood under low-NOx conditions. The deposits have been collected and analysed in order to understand the impact of the fuel.

  • 98. Alirezaei, Mohammadamin
    et al.
    Doostmohammadi, Hamid
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Microstructure evolution in cast and equilibrium heat-treated CuZn30-(Si) alloys2016In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 29, no 4, p. 222-227Article in journal (Refereed)
    Abstract [en]

    The main object of this work was to investigate the effect of Si addition and heat treatment on the microstructure of CuZn30 alloy. The alloys were prepared by casting and then the chemical composition, microstructure and phases were determined by optical and scanning electron microscope and XRD analysis. The resulting microstructures contained two phases, alpha and beta', with volume fraction depending on silicon content. Increments of Si content led to the formation of a Widmanstatten structure. It was also found that the silicon dissolved completely in alpha + beta phases and the lattice parameters of both alpha- and beta'-phases increased as the Si content increased. Hardness tests showed that hardness of both the as-cast and heat-treated samples increased as the Si content increased, and a significant increment of hardness in heat-treated alloy was due to the formation of a martensite phase.

  • 99. Allen, S. L.
    et al.
    Wampler, W. R.
    McLean, A. G.
    Whyte, D. G.
    West, W. P.
    Stangeby, P. C.
    Brooks, N. H.
    Rudakov, D. L.
    Phillips, V.
    Rubel, Marek J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Matthews, G. F.
    Nagy, A.
    Ellis, R.
    Bozek, A. S.
    C-13 transport studies in L-mode divertor plasmas on DIII-D2005In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 337-39, no 03-jan, p. 30-34Article in journal (Refereed)
    Abstract [en]

    (CH4)-C-13 was injected with a toroidally-symmetric gas system into 22 identical lower-single-null L-mode discharges on DIII-D. The injection level was adjusted so that it did not significantly perturb the core or divertor plasmas, with a duration of similar to 3 s on each shot, for a total of similar to 300 T L of injected particles. The plasma shape remained very constant; the divertor strike points were controlled to similar to 1 cm at the divertor plate. At the beginning of the subsequent machine vent, 29 carbon tiles were removed for nuclear reaction analysis of C-13 content to determine regions of carbon deposition. It was found that only the tiles inboard of the inner strike point had appreciable 1 3 C above background. Visible spectroscopy measurements of the carbon injection and comparisons with modeling are consistent with carbon transport by means of scrape-off layer flow.

  • 100.
    Allertz, Carl
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Sulfur and nitrogen in ladle slag2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present work deals with some aspects of slags related to secondary metallurgy in the steelmaking process. More specifically the focus is given to sulfur and nitrogen in ladle slags. Even though slags have been fairly well-researched in the past, the available data for these elements in typical ladle slag compositions is rather scarce. In some cases the available data is in discordance. There are also inconsistencies between the literature data and what is commonly observed in the industrial processes.

    Sulfide capacities were measured at steelmaking temperatures, 1823–1873 K, in ladle slags. The data was found to be in reasonable agreement with the industrial process norms. The sulfide capacity was found to increase with the basic oxides CaO and MgO; and decrease with the acidic components Al2O3 and SiO2. The sulfide capacity was also found to increase with temperature.

    The dependence of sulfide capacity on the oxygen partial pressure, for slags containing multivalent elements, was investigated experimentally at 1873 K with a slag containing vanadium oxide. A strong dependence of oxygen partial pressure was observed. The sulfide capacity increase by more than two orders of magnitude when the oxygen partial pressure was increased from 4.6×10-16 atm to 9.7×10-10 atm.

    The nitrogen solubility and the effect of carbon was investigated in typical ladle slags and the CaO–MgO–SiO2 system at 1873 K. Carbon increases the nitrogen solubility substantially. In the absence of carbon, the nitrogen solubility is extremely low. Low concentrations of cyanide was detected in the carbon saturated slag. This was much lower than the total nitrogen content and formation of cyanide cannot explain the large increase.

    The possibility of removing sulfur with oxidation from used ladle slag was investigated experimentally at 1373–1673 K. The sulfur removal of mostly solid slag was found to be a slow process, and would not suitable for industrial practice. At 1673 K the slag was mostly liquid and more than 85% of the sulfur was removed after 60 min of oxidation in pure oxygen atmosphere.

     

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