Change search
Refine search result
1257125812591260126112621263 62951 - 63000 of 78308
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 62951.
    Sedghiniya, Sima
    et al.
    School of Chemistry, College of Science, University of Tehran, Tehran, Iran.
    Soleimannejad, Janet
    School of Chemistry, College of Science, University of Tehran, Tehran, Iran.
    Foroutan, Masumeh
    School of Chemistry, College of Science, University of Tehran, Tehran, Iran.
    Ebrahimi, Mina
    School of Chemistry, College of Science, University of Tehran, Tehran, Iran.
    Naeini, Vahid Fadaei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A V(iii)-induced metallogel with solvent stimuli-responsive properties: structural proof-of-concept with MD simulations2021In: RSC Advances, E-ISSN 2046-2069, Vol. 11, no 58, p. 36801-36813Article in journal (Refereed)
    Abstract [en]

    A new solvent stimuli-responsive metallogel (VGel) was synthesized through the introduction of vanadium ions into an adenine (Ade) and 1,3,5-benzene tricarboxylic acid (BTC) organogel, and its supramolecular self-assembly was investigated from a computational viewpoint. A relationship between the synthesized VGel integrity and the self-assembly of its components is demonstrated by a broad range of molecular dynamics (MD) simulations, an aspect that has not yet been explored for such a complex metallogel in particular. MD simulations and Voronoi tessellation assessments, both in agreement with experimental data, confirm the gel formation. Based on excellent water stability and the ethanol/methanol stimuli-responsive feature of the VGel an easy-to-use visualization assay for the detection of counterfeit liquor with a 6% (v/v) methanol limit of detection in 40% (v/v) ethanol is reported. These observations provide a cheap and technically simple method and are a step towards the immersible screening of similar molecules in methanol-spiked beverages.

  • 62952. Sedhain Mainali, Laya
    Relationship between women and knowledge in Lessing's The Summer Before the Dark, Martha Quest and A Proper Marriage2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Download full text (pdf)
    FULLTEXT01
  • 62953.
    Sedig, Emmelie
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences.
    ”Jag hade kunnat fortsätta jobba dygnet runt och jag hade säkert inte blivit färdig i alla fall”: En studie om enhetschefers arbetsmiljö i kvinnodominerad kommunal verksamhet2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    During the recent decades, managers’ working conditions in the Swedish women dominated public sector have undergone important changes. For example, managers’ responsibilities have been expanded to contain more responsibilities of costs and efficiency. Later, it has been found that managers in professions dominated by women have a lack of sustainable working environment, caused by high job demands and a high degree of work strains. In consultation with a dominated municipal function in northern Sweden, I have been commissioned to investigate how first line managers experience their organizational and social work environment (psychosocial work environment) in this study, based on job demands, job control and social support. This study also investigates the work environment out of a gender perspective. The study has an abductive approach and the empiricism have been collected with qualitative semi structured interviews, where the number of interviews was seven. Thematic analysis has been devoted and the results have been analyzed by using Karasek and Theorell’s (1999) job demand-control-support model, Connell and Pearse’s (2015) idea of gender as socially constructed, and Ackers (1990) idea that gender is created in organizations through gender creating processes. The result shows that the first line managers are working in a municipal function that are boundless, which means that the work tasks never run out. Within the frames of the managers’ work there are variations in the experiences of the work environment. The result shows that the ability and possibility of setting boundaries in their work are important. The imagination of differences between male and female behavior are important for how the first line managers experience their work environment. The results also show that the first line managers experience that women are not as god as men to set boundaries in their work, and that women are not respected by the employer equally as men when it comes to set boundaries.

    Download full text (pdf)
    fulltext
  • 62954.
    Sedin, Peter
    Luleå University of Technology.
    Expression and filtration of highly compressible materials1999Licentiate thesis, monograph (Other academic)
  • 62955.
    Sedin, Peter
    Luleå University of Technology.
    On the determination and application of local filtration properties2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Filtration is a mechanical unit-operation used for the separation of liquid and solid. In this work, the three sub-operations cake build-up, expression and washing have been studied. One difficulty often encountered in the design of filtration equipment is that the materials being filtered form more or less compressible filter cakes. The use of local filtration properties is necessary in order to predict the behaviour of compressible filter cakes. Consequently, it is of great importance that more knowledge of local filtration properties is gained in order to design filtration equipment more accurately and to increase the efficiency of the filtration unit-operation. In the experimental part of this thesis, a number of different filtration test equipment and materials have been used. Piston presses were used to determine local filtration properties of calcium silicate, green liquor sludge, kaolin, lignin sludges and titanium dioxide. A piston press, with pressure transducers and a solidosity measurement system using gamma-rays, was constructed to simultaneously measure the local solidosity and local static pressure. From these simultaneous measurements, it was possible to obtain a good fit for constitutive relationships such as solidosity-solid compressive pressure, and specific filtration resistance-solid compressive pressure. The materials were found to form more or less compressible filter cakes. Values of the average specific filtration resistance, obtained from the classical filtration equation, were found to differ from the corresponding values calculated from local filtration properties. The use of constitutive relationships, based on local experimental measurements, improves accuracy in the design of filtration equipment. Various models were used in the evaluation of the expression phase. The classical expression models, i.e. the Terzaghi and Terzaghi-Voigt models, assume that the parameters in the models are constants. They also assume that the pressure profile at the transition between the cake build-up and expression phase follows a sine-relationship; this pressure profile was determined using kaolin and lignin sludges from the experiments. It was found that the sinusoidal relationship was a reasonable approximation for kaolin whereas large deviations occurred for lignin sludges. The classical Terzaghi model did not fit the experimental data for green liquor sludge, kaolin and lignin sludge; a better fit was obtained if the experimentally- determined pressure profile was used in the Terzaghi model. The Terzaghi- Voigt model was found to fit the experimental data, however, it was noted that the often used simplification of the Terzaghi-Voigt model does not always hold, especially for highly compressible filter cakes. Additionally, an extension of the Terzaghi model, which takes into account the fact that compressible filter cakes have non-constant filtration properties, was developed. The new models for the expression phase make it possible to use local filtration data and increase the knowledge of the expression phase. The use of these models makes the expression models more reliable when applied to the design and control of equipment. The influence of torsion shear on the dewatering of magnetite was studied. The pH was adjusted to investigate the effect of the double layer forces. The experimental results showed that the magnetic forces between the particles had the same magnitude as the double layer forces; this result was confirmed by a simple model. The magnetic forces do thus, determine the filtration process to a large extent. It was observed that sedimentation was present in the experiments. A model for the cake build-up phase which takes sedimentation into account was developed and described the experiments successfully. From the expression phase, it was found that the Terzaghi model could explain the experiments adequately. In sulphate pulp mills, green liquor sludge is to be found in the recovery cycle. Non-process elements may be removed from these pulp mills via green liquor sludge. The separation of green liquor sludge is known to be difficult. A study of four different green liquor sludges was carried out in which the filtration properties of green liquor sludge were determined. It was found that the filtration properties varied greatly between the sludges. Furthermore, it was found, and demonstrated, that the addition of lime mud to an unfiltered green liquor suspension made the separation and washing of green liquor sludge easier to perform.

  • 62956.
    Sedin, Peter
    et al.
    Luleå University of Technology.
    Johansson, C.
    Chalmers University of Technology, Department of Chemical Engineering and Environmental Science.
    Theliander, Hans
    Chalmers University of Technology, Department of Chemical Engineering and Environmental Science.
    On the measurement and evaluation of pressure and solidosity in filtration2003In: Chemical engineering research & design, ISSN 0263-8762, E-ISSN 1744-3563, Vol. 81, no 10, p. 1393-1405Article in journal (Refereed)
    Abstract [en]

    New test filtration equipment has been constructed that makes simultaneous measurement of local solid compressive pressure and local solidosity possible. Four materials were used to evaluate the new equipment. In this equipment the solidosity was measured with resolution of 1 mm in height (i.e. in the direction of the liquid flow). The experimental error was estimated to be 0.005-0.04 m3 m-3, depending on the properties of the slurry. Constitutive relationships for solidosity, permeability and specific filtration resistance were estimated and an overall good fit was obtained. Furthermore, it was found that the average specific filtration resistance based on the classical filtration equation could differ by as much as 20% compared to corresponding values based on local measurements.

  • 62957.
    Sedin, Peter
    et al.
    Luleå University of Technology.
    Theliander, Hans
    Chalmers University of Technology, Department of Forest Products and Chemical Engineering.
    Filtration properties of green liquor sludge2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 1, p. 67-74Article in journal (Refereed)
    Abstract [en]

    The filtration properties of green liquor sludge were investigated. Three different experimental set-ups were used: one for low pressure (up to 3 bars), one for high pressure (up to 100 bars) and one for washing and lime mud addition experiments (1 bar). Green liquor sludge from four different pulp mills was investigated in the low pressure tests. The influence of pressure and the addition of calcium, magnesium and aluminium ions were investigated. The low pressure filtration tests showed that green liquor sludge is relatively compressible (the compressibility coefficient is approximately 0.6), and that the average specific filtration resistance could differ by one order of magnitude between different mills (1012-1013 m/kg). It was found that the addition of both aluminium and calcium ions improved the filtration properties, whilst the addition of magnesium has the opposite effect. The high pressure tests showed that a considerable amount of water could be squeezed out of the filter cakes at high pressures. The addition of lime mud to the green liquor decreased the average specific filtration resistance to a large extent. In the washing experiments, breakthrough curves were calculated. These curves showed considerable deviations from ideal displacement washing. The dispersion model was fitted to the experiments and a fair fit was obtained.

  • 62958. Sedin, Stefan
    Återtagning av glödskalsslam till smältande process1999Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 62959.
    Sedlacek, Gerhard
    et al.
    RWTH Aachen.
    Collin, Peter
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Composite bridge design for small and medium spans2003Report (Refereed)
  • 62960.
    Sedlacek, Gerhard
    et al.
    RWTH, Aachen, Germany.
    Kammel, Christian
    RWTH, Aachen, Germany.
    Kühn, Bertram
    RWTH, Aachen, Germany.
    Hensen, W
    RTWH, Aachen, Germany.
    Condition assessment and inspection of steel railwaybridges, including stress measurements in riveted, bolted and welded structures: Sustainable Bridges Background document SB3.42007Report (Refereed)
    Abstract [en]

    Condition assessmentand inspection for steel railway bridges according to the current European state-ofthe-art considering the usefulness for practical application. It makes available essential extracts from several recent documents, guidelines and standards, describes novel methods based on recent research results, contains all necessary details to apply the condition assessment and inspection in practice, to chose the adequate inspection tools and to solve maintenance problems, and consequently is a valuable contribution towards the overall objectives of the Sustainable Bridges Project.

    Download full text (pdf)
    SB 3.4
  • 62961.
    Sedlmayer, Irene
    et al.
    BIOENERGY 2020+ GmbH.
    Arshadi, Mehrdad
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology.
    Haslinger, Walter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. BIOENERGY 2020+.
    Hofbauer, Hermann
    Technische Universität Wien, Environmental and Bioscience Engineering.
    Larsson, Ida
    RISE Research Institutes of Sweden, Safety, Fire Research.
    Lönnermark, Anders
    RISE Research Institutes of Sweden, Safety, Fire Research.
    Nilsson, Calle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Pollex, Annett
    DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH.
    Schmidl, Christoph
    BIOENERGY 2020+ GmbH.
    Stelte, Wolfgang
    Technical University of Denmark, Center for Bachelor of Engineering Studies.
    Wopienka, Elisabeth
    BIOENERGY 2020+ GmbH.
    Bauer-Emhofer, Waltraud
    BIOENERGY 2020+ GmbH.
    Determination of off-gassing and self-heating potential of wood pellets: Method comparison and correlation analysis2018In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 234, p. 894-903Article in journal (Refereed)
    Abstract [en]

    Several methods for identifying the phenomena of self-heating and off-gassing during production, transportation and storage of wood pellets have been developed in recent years. Research focused on the exploration of the underlying mechanisms, influencing factors or the quantification of self-heating or off-gassing tendencies. The present study aims at identifying a clear correlation between self-heating and off-gassing. Thus, different methods for determining self-heating and off-gassing potentials of wood pellets are compared. Therefore, eleven wood pellet batches from the European market were analyzed. For this investigation, three methods for the determination of self-heating, like isothermal calorimetry, oxi-press and thermogravimetric analysis, and four methods for off-gassing, like volatile organic compound (VOC) emissions measurements, gas phase analysis of stored pellets in a closed container by offline and by glass flask method and determination of fatty and resin acids content, were performed. Results were ranked according to the self-heating and off-gassing tendency providing a common overview of the analyzed pellets batches. Relations between different methods were investigated by Spearman’s correlation coefficient. Evaluation of the results revealed an equal suitability of offline and glass flask methods to predict off-gassing tendency and indicated a very significant correlation with isothermal calorimetry for the identification of self-heating tendency. The thermogravimetric analysis as well as the fatty and resin acids determination proved to be insufficient for the exclusive assessment of self-heating and off-gassing tendency, respectively.

  • 62962.
    Sedlmayer, Irene
    et al.
    BEST – Bioenergy and Sustainable Technologies GmbH, Graz, Austria; Technische Universität Wien, Institute of Chemical, Environmental and Bioscience Engineering, Vienna, Austria.
    Bauer-Emhofer, Waltraud
    BEST – Bioenergy and Sustainable Technologies GmbH, Graz, Austria.
    Haslinger, Walter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. BEST – Bioenergy and Sustainable Technologies GmbH, Graz, Austria.
    Hofbauer, Hermann
    Technische Universität Wien, Institute of Chemical, Environmental and Bioscience Engineering, Vienna, Austria.
    Schmidl, Christoph
    BEST – Bioenergy and Sustainable Technologies GmbH, Graz, Austria.
    Wopienka, Elisabeth
    BEST – Bioenergy and Sustainable Technologies GmbH, Graz, Austria.
    Off-gassing reduction of stored wood pellets by adding acetylsalicylic acid2020In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 198, article id 106218Article in journal (Refereed)
    Abstract [en]

    During transportation and storage of wood pellets various gases are formed leading to toxic atmosphere. Various influencing factors and measures reducing off-gassing have already been investigated. The present study aims at applying an antioxidant, acetylsalicylic acid (ASA), to reduce off-gassing from wood pellets by lowering wood extractives oxidation. Therefore, acetylsalicylic acid was applied in industrial and laboratory pelletizing processes. Pine and spruce sawdust (ratio 1:1) were pelletized with adding 0-0.8% (m/m) ASA. Glass flasks measurements confirmed off-gassing reduction by adding ASA for all wood pellets investigated.The biggest effect was achieved by adding 0.8% (m/m) ASA in the industrial pelletizing experiments where the emission of volatile organic compounds (VOCtot) was reduced by 82% and a reduction of carbon monoxide (CO) and carbon dioxide (CO2) emissions by 70% and 51%, respectively, could be achieved. Even an addition of 0.05% (m/m) ASA led to off-gassing reduction by >10%. A six week storage experiment to investigate the long-term effectivity of ASA addition revealed, that antioxidant addition was effective in reducing CO-, CO2- and VOCtot-release, especially during the first four weeks of the storage experiment, after which time the relative reduction effect was significantly decreased.

  • 62963.
    Seedorf, Jan
    et al.
    NEC Laboratories Europe.
    Ewald, Thilo
    NEC Laboratories Europe.
    Schmidt, Mischa
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science. NEC Laboratories Europe.
    Jahanpanah, Armin
    NEC Laboratories Europe.
    Stiemerling, Martin
    NEC Laboratories Europe.
    Bąk, Andrzej
    Warsaw University of Technology.
    Pilarski, Marcin
    Warsaw University of Technology.
    Kopertowski, Zbigniew
    Orange Labs Warsaw.
    Towards Operator-managed P2P Content Delivery with Application Layer Traffic Optimization2010Conference paper (Refereed)
    Abstract [en]

    P2P technology provides a flexible and very popular way of content delivery for various services, including networked media applications. However, P2P-based content delivery generates large amount of backbone traffic. Recently, several approaches have been proposed for guiding P2P services based on operator preferences, in order to reduce the amount of costly backbone traffic generated by P2P applications. Application Layer Traffic Optimization (ALTO) is a one key approach for such managed P2P applications. In short, ALTO is a dedicated service, operated by a network operator or ISP, which can provide useful network layer information to application layer clients for improved peer selection and corresponding content delivery. This paper provides an overview of standardisation and research activities for improving P2P content delivery with ALTO which are carried out within the EU FP7 project NAPA-WINE. In particular, we give an overview on standardisation efforts, present simulation results, explain our prototypical implementation of the ALTO concept, and highlight ongoing large-scale operational trials we are currently conducting within the network of Polish Telecom and among NAPA-WINE partners

    Download full text (pdf)
    fulltext
  • 62964.
    Seefried, Kim
    Luleå University of Technology, Department of Arts, Communication and Education.
    Visualizing effects: In stereoscopic images2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis explores and includes research on different impressions given in stereo rendering when creating a fire in three different manners.As technology progresses, stereoscopic rendering becomes increasingly more popular. Both movies and games are shown through VR to give users a more satisfying and lifelike interaction with a virtual environment.Three different versions of a fire were created in a game engine and then viewed with HTC Vive. Comparing mono and stereo rendering gave insights on how the different method looks when using stereoscopic rendering, and what impression the different methods gave the user.The different fires were tested with several users. Finally, this thesis concludes with an interview to one of the users and his different impressions of the fires.

    Download full text (pdf)
    fulltext
  • 62965. Seers, Dudley
    et al.
    Öström, KjellLuleå University of Technology, Department of Business Administration, Technology and Social Sciences, Industrial Organisation.
    The crises of the European regions1983Collection (editor) (Refereed)
    Abstract [en]

    The book consists of papers presented at a conference of the European Periphery Group of the European Association of Development Institutes, held in Sweden in 1981. In most countries of Europe the world recession has hit peripheral regions hardest and has also often resulted in cutbacks in regional aid, thus increasing centre-periphery tensions and demanding a new approach to regional policies. The book includes three general papers and chapters on experience in Finland, Sweden, Yugoslavia, Portugal and Spain. These last four are followed by brief comments by discussants. Individual chapters are abstracted separately.-

  • 62966.
    Seery, Christoffer
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Geotechnical properties of tailings from the Boliden mining area2018Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Tailings are the most fine grained mine waste generated due to mining and consists of crushed rock in the size ranges of sands, silts and clays depending on the ore processed. Due to the risk of high contents of metals, acids and soluble salts in the tailing a environmentally safe approach of disposal becomes imperative. Failures to retain tailings can and has in many cases led to both mechanical and chemical destruction in the sense of environmental pollution, destruction of infrastructure, health issues and loss of life.

    Therefore, a better understanding of the geotechnical properties of the different tailings are needed in order to better plan and manage the tailings and their storage facilities. This report focuses on some of the mine waste from the Boliden mining area contained in the Hötjärn tailings facility. Specifically the hydraulic conductivity and compressibility characteristics of the tailings from the Kristineberg mine and the furnace slag from the Rönnskär smelters. The coarser sand fractions of the Kristineberg tailings are at times used as backfill material in the mines and the sample has therefore been separated in to three different Kristineberg based samples and one slag based sample.

    In order to get an overview of the materials some basic geotechnical investigations (particle size distribution and particle density tests), constant head tests for hydraulic conductivity and oedometer tests to determine compressibility were carried out.

    Results showed a clear difference in particle size distribution with a fines content spanning between approximately 25 and 50 percent. Furthermore hydraulic conductivity was shown to be dependent on dry density and material, decreasing with increasing density. Finally the unaltered Kristineberg tailings showed the largest strains whereas the Rönnskär slag showed smallest strains.

    The results presented within this report constitute a god basis for further consolidation and seepage analyzes within the Hötjärn tailings facility.

  • 62967.
    Sefer, Birhan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Environment Related Surface Phenomena and their Influence on Properties of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo: Oxidation at Elevated Temperature and Corrosion During Chemical Treatment2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This doctoral thesis covers investigation of the surface phenomena of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys related with oxidation at elevated temperature and corrosion duringchemical treatment in hydrofluoric-nitric acid (HF/HNO3) solutions. The explored phenomenaare related to manufacturing and service conditions of aero-engine components. Duringmanufacturing and operation, the alloys are running at elevated temperatures in oxygencontaining environment. Under these conditions there are formations of an oxide on the surfaceand an oxygen enriched layer below the oxide, commonly referred as alpha-case. The alpha-caseis a hard and brittle layer that is detrimental to the mechanical properties and must therefore beminimized or completely eliminated. A conventional method for elimination of alpha-case ischemical processing in HF/HNO3 solutions, known as chemical milling.Isothermal oxidation treatments in air at 500, 593 and 700 ºC for up to 500 hours were carriedout in this study. Both alloys developed rutile type of oxide structure and Ti-6Al-2Sn-4Zr-2Moexhibited stronger oxidation resistance than Ti-6Al-4V. Transition from parabolic to linearoxidation rate was observed at 700 ºC and ≥ 200 hours for both alloys. The difference in theoxidation kinetics of the two alloys is suggested to be related with the chemical composition ofthe alloys. The oxygen enriched layer, i.e. alpha-case layer, was characterised and its thicknesswas measured using conventional metallographic and microscopic techniques. Parabolicrelationship of the alpha-case layer growth rate with time was observed for both alloys. Theoxygen diffusion parameters and activation energies were estimated in the temperature range of500-700 ºC. Additionally, the oxidation at 700 ºC for 500 hours resulted in microstructuralchanges and element re-distribution. The bulk and alpha-case layer hardness at micro- and nanoscalewere measured using microhardness and nanoindentation techniques. The alpha-case layerhad higher hardness due to the solid solution strengthening effect of the diffused oxygen.The effect of chemical milling in 1:11 HF/HNO3 solution on the surface integrity, and theinfluence on low cycle fatigue (LCF) strength of cast Ti-6Al-2Sn-4Zr-2Mo alloy wasinvestigated. Short and long chemical processing times (5 and 60 minutes) and three imposedtotal strain ranges in fatigue tests were evaluated. Significant drop in fatigue life was observedfor the samples etched before LCF testing, as compared to the non-etched samples. The influencefrom etching was found to be most detrimental for fatigue samples tested at the lowest strainranges. The fatigue life reduction was correlated with the number of crack initiation sites.Multiple crack initiation sites were observed for the etched samples, whereas only one crackinitiation site was discerned in the non-etched samples. Inspection of the surface of the etchedsamples revealed selective and severely etched prior β grain boundaries and pit formation at thetriple joints of the prior β grain boundaries. These surface defects were considered as stressraisers promoting an earlier fatigue crack initiation.The influence of two different molar concentration ratios (1:3 and 1:11) of HF and HNO3acids on the corrosion behaviour of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo were investigatedusing electrochemical and atomic force microscopy (AFM) techniques. The corrosion of the twoalloys was a function of the HF/HNO3 concentration ratio and also of the alloys’ chemicalcompositions. The AFM measurements revealed selective and faster dissolution rate of the α-phase than the β-phase in the Widmanstätten microstructure. It was considered that the reason forselective dissolution was the formation of local micro-galvanic cells between the α-phase and theβ-phase. Moreover, the Volta-potential was measured using scanning Kelvin probe forcemicroscopy (SKPFM) and the obtained maps revealed difference in the Volta-potential betweenvithe α-laths and the β-laths in both alloys. This observation strengthened the likelihood forformation and operation of micro-galvanic cells between the α-phase and the β-phase when thealloys were in contact with HF/HNO3 solution.Keywords: Titanium alloys, oxidation, oxide, alpha-case, chemical milling, corrosion.

    Download full text (pdf)
    fulltext
  • 62968.
    Sefer, Birhan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oxidation and Alpha–Case Phenomena in Titanium Alloys used in Aerospace Industry: Ti–6Al–2Sn–4Zr–2Mo and Ti–6Al–4V2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Titanium and its alloys are attractive engineering materials in aerospace industry because of their outstanding mechanical properties such as high specific strength and excellent corrosion resistance. Ti–6Al–2Sn–4Zr–2Mo (Ti–6242) and Ti–6Al–4V (Ti–64) are two alloys commonly used for manufacturing components in jet engines, such as fan blades, disks, wheels and sections of the compressor where the maximum temperature is in the range of 300–450 °C. At temperatures above 500 °C and in oxygen containing environments, these alloys are oxidizing rapidly. Oxidation normally involves formation of an oxide scale on top of the metal and a hard and brittle oxygen enriched layer beneath the scale which is known as “alpha–case”. The alpha–case layer has a detrimental effect on important mechanical properties such as ductility, fracture toughness and especially the fatigue life when an engine component is subjected to dynamic loading. In order to increase the understanding of the oxidation and alpha–case phenomena, the behaviour of these two alloys after long time exposure in air at elevated temperature has been investigated. Heat treatments were performed on Ti–6242 and Ti–64 alloys in ambient air at 500, 593 and 700 °C for times up to 500 hours. The oxide scale and the alpha–case layer were analysed, characterized and compared for both alloys. It was found that the oxide scale and alpha–case thickness are functions of temperature and time. Faster and more complex oxidation kinetics was noted in Ti–64, whereas in Ti–6242 the oxidation kinetics was found moderate at all tested temperatures and times. Discrepancies in the oxidation kinetics are believed to be because of the differences in the chemical composition and the microstructure of the two alloys. In addition, different morphology of the oxide scales was observed after 500 hours exposure time at 700 °C. The thickness of the alpha–case layer was measured using conventional metallographic and microscopic techniques. It was found that in both alloys the alpha–case growth obeys parabolic law with respect to time at all three tested temperatures. In addition, the diffusion coefficients and the activation energy of oxygen diffusion were estimated in the temperature range of 500–700 °C for the two alloys. Electron probe micro analyser (EPMA) was used to measure the oxygen concentration along the thickness of the alpha–case layer. It was found that the oxygen concentration decreases along the alpha–case layer. The oxygen concentration profiles were used to estimate the alpha–case thicknesses and it was found good agreement with the optically measured values for almost all investigated temperatures and times. Only at 700 °C in the time interval 300–500 hours in Ti–6242 a difference between the results from the two methods was found. Moreover, the EPMA concentration profiles of the main α and β alloying elements, before and after heat treatment at 700 °C for 500 hours, revealed microstructural changes and an increase of the α–phase volume fraction in the two investigated alloys.

    Download full text (pdf)
    FULLTEXT01
  • 62969.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Science and Metallurgical Engineering, Universitat Politècnica de Catalunya.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Division of Surface and Corrosion Science, KTH Royal Institute of Technology.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Research and Technology Centre, GKN Aerospace Engine Systems.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemical Milling of Cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo Alloys in Hydrofluoric-Nitric Acid Solutions2017In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 73, no 4, p. 394-407Article in journal (Refereed)
    Abstract [en]

    The behavior of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo during chemical milling in hydrofluoric-nitric (HF-HNO3) acid solutions with 1:3 and 1:11 molar ratios was investigated using electrochemical and atomic force microscopy (AFM) techniques. Faster corrosion rate in 1:3 solutions was measured for Ti-6Al-4V than for Ti-6Al-2Sn-4Zr-2Mo, whereas in 1:11 solution Ti-6Al-2Sn-4Zr-2Mo exhibited higher corrosion rate. Scanning Kelvin probe force microscopy measurements revealed difference in the Volta potential between the α-laths and the β-layers in the Widmansttäten microstructure indicating operation of microgalvanic cells between the microconstituents when in contact with HF-HNO3 solution. The AFM topography measurements demonstrated faster corrosion of the α-laths compared to the β-layers, in both alloys. In 1:3 solutions, higher α/β height difference was measured in Ti-6Al-4V, whereas in 1:11 solution, the difference was higher in Ti-6Al-2Sn-4Zr-2Mo. The results revealed that the chemical milling behavior of the two investigated alloys is controlled by the microscopic corrosion behavior of the individual microconstituents.

  • 62970.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gaddam, Raghuveer
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. GKN Aerospace Engine Systems Sweden.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Study of the Alpha-Case Layer in Ti–6Al–2Sn–4Zr–2Mo and Ti–6Al–4V by Electron Probe Micro Analysis2014Conference paper (Refereed)
    Abstract [en]

    Titanium and its alloys are susceptible to oxidation when exposed to elevated temperatures and oxygen containing environments for long exposure times, e.g. in jet engines [1–3]. In such conditions oxygen rapidly reacts with titanium, stabilizing α–titanium and forming solid solution due to the high solubility of oxygen in titanium (14.5 wt.%) [4]. The oxidation results in simultaneous formation of oxide scale on top of the metal and a brittle oxygen enriched layer beneath the scale, commonly referred as alpha–case. Alpha–case layer reduces important mechanical properties such as ductility, fracture toughness, and most severe reduces the fatigue life of jet engine components when subjected to dynamical loadings [5]. Therefore, the alpha-case layer in aerospace applications is usually removed by chemical milling [1–3] or prevented by using vacuum environments and high temperature coatings [1–3,6–9]. In the present study alpha–case in Ti–6Al–2Sn–4Zr–2Mo and Ti–6Al–4V alloys was developed by performing isothermal heat treatments at 700 °C in ambient air for 500 hours. The developed alpha–case layer was evaluated metallographically and by using instrumental techniques. It was found that the alpha–case development is a function of alloy composition and microstructure. The oxygen and the main alloying elements concentration profiles were measured using Electron Probe Micro Analyzer (EPMA) in both alloys. Based on the analysis of the concentration profiles an increase of the amount of alpha phase in the two alloys was found as a result of beta to alpha phase transformation.

    Download full text (pdf)
    FULLTEXT01
  • 62971.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gaddam, Raghuveer
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Sandvik Materials Technology, Sandviken, S-81181, Sweden.
    Roa, Joan Josep
    Department of Materials Science, Universitat Politècnica de Catalunya, Av. Diagonal 647, Barcelona, Spain.
    Mateo, Antonio
    Department of Materials Science, Universitat Politècnica de Catalunya, Av. Diagonal 647, Barcelona, Spain.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemical milling effect on the low cycle fatigue properties of cast Ti-6Al-2Sn-4Zr-2Mo alloy2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 92, no 1, p. 193-202Article in journal (Refereed)
    Abstract [en]

    The current research work presents the chemical milling effect on the low cycle fatigue properties of cast Ti-6Al-2Sn-4Zr-2Mo alloy. Chemical milling treatment is one of the final steps in manufacturing titanium alloy components that removes the brittle alpha-case layer formed during various thermal processes. The treatment includes immersion of the components in solutions containing hydrofluoric (HF) and nitric (HNO3) acids in relevant molar ratios. Although this treatment demonstrates advantages in handling components with complex net geometries, it may have detrimental effects on the surface, by introducing pitting and/or intergranular corrosion and thereby adversely affecting in particular the fatigue strength. The first series of specimens were tested in as-machined condition. Two more series were, prior to fatigue testing, subjected to 5 and 60 minutes chemical milling treatment. It was found that the fatigue lives were substantially decreased for the chemically treated specimens. The fractographic investigation of all mechanically tested samples revealed multiple fatigue crack initiation sites in the chemically milled samples. These cracks were located either at the prior beta grain boundary or the prior beta grain boundary triple joints. The prior beta grain boundaries were found to have deep ditch-like appearance which depth increased with increasing milling time. These ditch-like grain boundaries acts as stress raisers and thereby promote early fatigue crack initiation and thus lower fatigue life.

  • 62972.
    Sefer, Birhan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rovira, Joan Josep Roa
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Mateo, Antonio
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona.
    Pederson, Robert
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Evaluation of the bulk and alpha-case properties in Ti-6Al-4V at micro- and nano-metric length scale2016In: 13th World Conference on Titanium: August 16-20, 2015 * Manchester Grand Hyatt * San Diego, California / [ed] V. Venkatesh; A.L. Pilchak; J.E. Allison; S. Ankem; R. Boyer; J. Christodoulou; H.L. Fraser; M.A. Imam; J. Kosaka; H.J. Rack; A. Chaterjee; A. Woodfield, John Wiley and Sons , 2016, p. 1619-1624, article id 271Conference paper (Refereed)
    Abstract [en]

    In the present study the hardness of individual alpha (α)-Ti grains in Ti-6Al-4V was measured by nanoindentation using Berkovich tip indenter. Additionally, alpha-case layer was induced by performing isothermal heat treatment at 700°C in air for 500 hours. The average hardness of the α-Ti grains found in the bulk material and in the alpha-case layer were 6.7 ± 0.7 GPa and 9.4 ± 1.4 GPa, respectively. The high hardness of the α-Ti grains in the alpha-case layer is due to solid solution strengthening caused by interstitial oxygen diffusion. The thickness of the developed alpha-case layer was estimated metallographically and compared with that measured from a hardness profile performed along the layer. Moreover, electron back-scattered diffraction was used to determine the local crystallographic orientation, the texture of the alloy microstructure, as well as phase fraction changes, where the nanoindentation measurements were performed.

  • 62973.
    Seferinoğlu, Meryem
    et al.
    Luleå University of Technology. MTA, Mineral Research and Exploration Directorate, Balgat, Ankara, Turkey.
    Paul, Mehtap
    Luleå University of Technology.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Köker, Agah
    MTA, Mineral Research and Exploration Directorate, Balgat, Ankara, Turkey.
    Toprak, Selami
    MTA, Mineral Research and Exploration Directorate, Balgat, Ankara, Turkey.
    Paul, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Acid leaching of coal and coal-ashes2003In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 82, no 4, p. 1721-1734Article in journal (Refereed)
    Abstract [en]

    Twelve Turkish lignites and the corresponding ashes were leached in sulfuric acid (pH 1.0, 25 oC) for 14 days. Asphaltite from Silopi amended the coals. The conditions mimic treatment in the effluent from bioleaching of sulfidic mineral concentrates, but the results are equally valid for an isolated leaching process. The extended time meant that we approached equilibrium and maximum extraction.The coals have limited neutralizing capacity. H2SO4 (1.0-2.0 l, 1 M) was needed to stabilize 1 kg coal at pH 1.0 (liquid:solid ratio 10:1), but the coal-ashes required 18.0-24.0 l/kg dry solid, which is the neutralizing equivalent to CaO.Leaching of dominant inorganic phases consume acid, but our interest is merely to remove trace elements present as dopants. We removed large fractions of Mg and Mn, but Al, K and Na extractions were limited by the presence of stable minerals and bimetallic oxides. The formation of the latter is driven by combustion at high temperatures. Alumina, normally not stable at pH 1.0, was protected from the effluent by the organic phase in coal. Fe leaching varied and appeared to be a marker for different chemical occurrences in the solids.Cd, V, Zn, U and Th were leached to near 80% from the ashes, but considerably less from the coals. Co and Ni extractions were near 60%, but not always higher from the ashes compared with the coals. Cu yields increase following ashing and reached ca. 60%. Ti, Ba, and Cs were not leached.We suggest that direct acid leaching is of interest to limit the deleterious impact of ash deposits and to recirculate metals from the ash. Ash may partly replace limestone in hydrometallurgical processing, but, more importantly, metal ions extracted from ash may be fed into the metal recovery stages of such processes. It is particularly interesting to leach Co, Cu, Ni and Zn, besides Mn, V and the environmentally hazardous Cd, U and Th. Leaching of whole coals is well motivated for domestic use-lump sizes around 18-50 mm, or slightly smaller, 10 mm, if mandated by practical residence times-where generally no other measures are taken to protect the local environment.

  • 62974.
    Sefidari, Hamid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Mechanisms of Deposit formation in the Grate-kiln Process2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fly ash particles from the combustion of coal together with disintegrated particles arising from iron-ore pellets result in accumulation of deposits on the refractory linings of the grate-kiln induration machine during the iron-ore pelletizing process. Deposit formation gives rise to decreased production efficiency, unscheduled shutdowns, high cleaning costs, and equipment failures. The deposits amass in the high-temperature regions of the induration furnace thus disturbing the flow of gas and pellets. Therefore, to tackle the above-mentioned issues, an understanding of deposit formation mechanism is of crucial importance. In contrast to pulverized-fuel-fired boilers, a grate-kiln process is characterized by a longer residence time, a highly oxidizing atmosphere, the presence of recirculating alkalis and disintegrated iron-ore pellet dust in the process gas. Given the foregoing, ash deposition phenomena in the grate-kiln process are much more complex compared to ordinary pulverized-fuel-fired boilers. This study was conducted with the objective of addressing the effect of disintegrated iron-ore pellet dust on deposit formation and the mechanisms behind deposition (slagging) in the grate-kiln process.Because of climate change and other pollution concerns, there is a desire to reduce on the combustion of carbon-intensive fuels. Moreover, as previously mentioned, the ash material from coal together with the disintegrated pellet dust cause deposition and slagging in rotary grate kilns, which can inflict severe production losses. For these reasons, it is of interest to study the potentials of co-firing coal with alternate fuels such as woody biomass. While the combustion of such woody biomass can be carbon-neutral, their effects upon deposition and slagging during co-firing with coal in a grate-kiln is unknown. Therefore, co-firing coal and woody biomass (softwood bark) was also thermodynamically investigated with particular emphasis on the effect of alkali recirculation upon deposition (slagging).To initiate elucidation of deposit formation during the iron-ore palletization process, a comprehensive set of experiments was conducted in a 0.4 MW pilot-scale pulverized-coal-fired furnace (ECF) where three different scenarios were considered as follows; Case1 (reference case): a high-rank bituminous coal was combusted without the presence of disintegrated iron-ore pellet dust. Case2: Natural gas was combusted together with simultaneous addition of hematite dust to the gas stream. Case 3: Coal was combusted together with the addition of hematite dust simulating the situation in the large-scale setup. Particles and short-term deposits were sampled from 3 positions of different temperature via a water-cooled rapid dilution sampling probe. Several characterization methods coupled with thermochemical equilibrium calculations (TECs) and viscosity estimations were employed to shed light on deposit formation and the mechanisms behind it in rotary kilns of iron-ore pelletizing plants. The most extensive interaction between hematite dust and coal-ash particles was observed in the coarse mode where a significant number of coal ash globules were abundantly found attached to the surface of the hematite particles. The morphology of the sharp-edged hematite dust particles was changed to smooth-edged round particles suggesting that hematite dust particles must have interacted with the surrounding aluminosilicate glassy phase. Consequently, the Fe content of the aforementioned glassy phase experienced a considerable increase. The short-term deposits during coal combustion (Case1) were highly porous in contrast to the high degree of sintering observed in the experiments with hematite addition (Case3). The incorporation of Fe into the aluminosilicate glassy phase (liquid fraction) decreased the viscosity and resulted in the formation of stronger (heavily sintered) deposits. The results suggested that hematite dust slagging tendency was independent of temperature, within the studied temperature-range (approximately 1100-1500 ºC), and required an auxiliary phase-provided by coal-ash- to form tenacious particles and cause slagging. In light of the experimental observations and TECs, a scheme of slag formation during the iron-ore pelletizing process was proposed.The TECs carried out for the woody biomass/coal blends indicated that that woody biomass is likely to increase the fraction of molten slag and exacerbate slagging when the molar ratio of Si/Ca > 2ii(equivalent to addition of more than 30 wt.% woody biomass, i.e. bark). However, when the abovementioned molar ratio is less than 2 (equivalent to addition of less than 10 wt.% bark), the fraction of molten slag increases by about 10 wt.% which does not seem to promote slagging extensively and can serve as a reasonable experimental blend.Overall, this work forms part of a wider study which aims at deepening the understanding of ash transformation phenomena during the large-scale pelletizing process. The findings from the current work are necessary to pave the path towards achieving the aforementioned goal.

    Download full text (pdf)
    fulltext
  • 62975.
    Sefidari, Hamid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. RISE ETC (Energy Technology Centre) AB, Box 726, S-941 28 Piteå, Sweden.
    Lindblom, Bo
    Luossavaara-Kiirunavaara Aktiebolag (LKAB), S-971 28 Luleå, Sweden.
    Nordin, Lars-Olof
    Luossavaara-Kiirunavaara Aktiebolag (LKAB), S-971 28 Luleå, Sweden.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. RISE ETC (Energy Technology Centre) AB, Box 726, S-941 28 Piteå, Sweden.
    The Feasibility of Replacing Coal with Biomass in Iron-Ore Pelletizing Plants with Respect to Melt-Induced Slagging2020In: Energies, E-ISSN 1996-1073, Vol. 13, no 20, article id 5386Article in journal (Refereed)
    Abstract [en]

    Combustion-generated fly ash particles in combination with the particles arising from the disintegration of iron-ore pellets, could give rise to the build-up of deposits on the refractory linings of the induration facility. Due to climate change and other environmental issues, there is a desire to cut down on use of fossil fuels. Therefore, it is of interest to investigate the feasibility of replacing coal with less carbon-intensive alternatives such as upgraded biomass, e.g., biochar and pyrolysis bio-oil. While the combustion of biomass can be carbon-neutral, the effects of biomass ash upon slagging during the iron-ore pelletizing process in a grate-kiln setup is unknown. In the present study, the effect of the interaction between the pellet dust and biomass-ash upon melt formation and the viscosity of the resulting melt, which can collectively affect melt-induced slagging, was theoretically assessed. The slagging potential of 15 different biomass fuels, suitable for the pelletizing process, was quantified and compared with one another and a reference high-rank coal using a thermodynamically derived slagging index. The replacement of coal with biomass in the pelletizing process is a cumbersome and challenging task which requires extensive and costly field measurements. Therefore, given the wide-ranging nature of the biomasses investigated in this study, a prescreening theoretical approach, such as the one employed in the present work, could narrow down the list, facilitate the choice of fuel/s, and help reduce the costs of the subsequent experimental investigations.

  • 62976.
    Sefidari, Hamid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lindblom, Bo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Luossavaara-Kiirunavaara Aktiebolag (LKAB).
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. RISE ETC (Energy Technology Centre) AB.
    Nordin, Lars Olof
    Loussavaara-Kiirunavaara Limited, Luleå.
    Lennartsson, Andreas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Bhuiyan, Iftekhar Uddin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The effect of disintegrated iron-ore pellet dust on deposit formation in a pilot-scale pulverized coal combustion furnace: Part II: Thermochemical equilibrium calculations and viscosity estimations2018In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 180, p. 189-206Article in journal (Refereed)
    Abstract [en]

    Fly ash particles from the combustion of solid-fuels together with disintegrated particles arising from iron-ore pellets result in accumulation of deposits on the refractory linings of the grate-kiln induration machine during the iron-ore pelletizing process. The deposits amass in the high-temperature regions of the induration furnace thus disturbing the flow of gas and pellets. Therefore, to tackle the above-mentioned issues, an understanding of deposit formation mechanism is of crucial importance. This study was conducted with the objective of addressing the effect of disintegrated iron-ore pellet dust on deposit formation and the mechanisms behind deposition (slagging) in the grate-kiln process. A comprehensive set of experiments was conducted in a 0.4 MW pilot-scale pulverized-coal- fired furnace where three different scenarios were considered as follows; Case 1 (reference case): Coal was combusted without the presence of pellet dust. Case 2: Natural gas was combusted together with simultaneous addition of pellet dust to the gas stream. Case 3: Coal was combusted together with the addition of pellet dust simulating the situation in the large-scale setup. Fly ash particles and short-term deposits were characterized and deposition was addressed in Part I of this study. In light of the experimental observations (Part I) and the thermochemical equilibrium calculations (Part II), a scheme of ash transformation during the iron-ore pelletizing process was proposed. The dissolution of hematite particles into the Ca-rich-aluminosilicate melt (from the coal-ash constituents) decreased the viscosity and resulted in the formation of stronger (heavily sintered) deposits. Overall, this pilot-scale work forms part of a wider study which aims at deepening the understanding of ash transformation phenomena during the large-scale pelletizing process.

  • 62977.
    Sefidari, Hamid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lindholm, Bo
    Luossavaara-Kiirunavaara Aktiebolag (LKAB).
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. RISE ETC (Energy Technology Centre) AB.
    Nordin, Lars Olof
    Loussavaara-Kiirunavaara Limited, Luleå.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Bhuiyan, Iftekhar Uddin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The effect of disintegrated iron-ore pellet dust on deposit formation in a pilot-scale pulverized coal combustion furnace: Part I: Characterization of process gas particles and deposits2018In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 177, p. 283-298Article in journal (Refereed)
    Abstract [en]

    o initiate the elucidation of deposit formation during the iron-ore pelletization process, a comprehensive set of experiments was conducted in a 0.4 MW pilot-scale pulverized-coal-fired furnace where three different scenarios were considered as follows; Case 1 (reference case): Coal was combusted without the presence of pellet dust. Case 2: Natural gas was combusted together with simultaneous addition of pellet dust to the gas stream. Case 3: Coal was combusted together with the addition of pellet dust simulating the situation in the large-scale grate-kiln setup. Particles and deposits were sampled from 3 positions of different temperature via a water-cooled sampling probe. Three distinct fragmentation modes were identified based on the aerodynamic particle diameter (Dp). The fine mode: Particles with 0.03 < Dp < 0.06 μm. The first fragmentation mode: Particles with 1 < Dp < 10 μm. The second fragmentation mode: Coarse particles (cyclone particles, Dp > 10 μm). A transition from a bimodal PSD (particle size distribution) to a trimodal PSD was observed when pellet dust was added (Case 3) and consequently the elemental bulk composition of the abovementioned modes was changed. The most extensive interaction between pellet dust and coal-ash particles was observed in the coarse mode where a significant number of coal ash globules were found attached to the surface of the hematite particles. The morphology of the sharp-edged hematite particles was changed to smooth-edged round particles which proved that hematite particles must have interacted with the surrounding aluminosilicate glassy phase originating from the coal ash. The short-term deposits collected during coal combustion (Case 1) were highly porous in contrast to the high degree of sintering observed in the experiments with pellet dust addition (Case 3) which is attributed to the dissolution of hematite particles in the aluminosilicate glassy phase. The results suggest that pellet dust itself (Case 2) has low slagging tendency, independent of temperature. However, when coal-ash is present (Case 3), auxiliary phases are added such that tenacious particles are formed and slagging occurs.

  • 62978.
    Sefidari, Hamid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Luossavaara-Kiirunavaara Aktiebolag (LKAB), Luleå, Sweden.
    Ma, C.
    Department of Applied Physics and Electronics, Thermochemical Energy Conversion Laboratory, Umeå University, Umeå, Sweden.
    Fredriksson, C.
    Luossavaara-Kiirunavaara Aktiebolag (LKAB), Luleå, Sweden.
    Lindblom, Bo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Luossavaara-Kiirunavaara Aktiebolag (LKAB), Luleå, Sweden.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. RISE ETC (Energy Technology Centre) AB, Piteå, Sweden.
    Nordin, L.O
    Luossavaara-Kiirunavaara Aktiebolag (LKAB), Luleå, Sweden.
    Wu, G.
    GTT Technologies, Herzogenrath,Germany. Institute of Energy and Climate Research, Microstructure and Properties of Materials (IEK-2), Forschungszentrum Jülich GmbH, Germany.
    Yazhenskikh, E.
    Institute of Energy and Climate Research, Microstructure and Properties of Materials (IEK-2), Forschungszentrum Jülich GmbH, Germany.
    Müller, M.
    Institute of Energy and Climate Research, Microstructure and Properties of Materials (IEK-2), Forschungszentrum Jülich GmbH, Germany.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The effect of co-firing coal and woody biomass upon the slagging/deposition tendency in iron-ore pelletizing grate-kiln plants2020In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 199, article id 106254Article in journal (Refereed)
    Abstract [en]

    Woody biomass is being considered a potential co-firing fuel to reduce coal consumption in iron-ore pelletizing rotary kilns. An important consideration is the slagging inside the kiln caused by ash deposition that can lead to process disturbances or shutdowns. In terms of ash chemistry, co-firing woody biomass implies the addition of mainly Ca and K to the Si- and Al-dominated coal-ash (characteristic of high-rank coals) and Fe from the iron-ore that are both inherent to the process. An alkali-laden gaseous atmosphere is also present due to the accumulation of alkali via the recirculation of flue gas in the system. The slagging propensity of blending woody biomass with coal in the grate-kiln process was studied based on the viscosity of the molten phases predicted by global thermochemical equilibrium modeling. This was carried out for variations in temperature, gaseous KOH atmosphere, and fuel blending levels. Results were evaluated and compared using a qualitative slagging indicator previously proposed by the authors where an inverse relationship between deposition tendency and the viscosity of the molten fraction of the ash was established. The results were also compared with a set of co-firing experiments performed in a pilot-scale (0.4 MW) experimental combustion furnace. In general, the co-firing of woody biomass would likely increase the slagging tendency via the increased formation of low-viscosity melts. The fluxing behavior of biomass-ash potentially reduces the viscosity of the Fe-rich aluminosilicate melt and intensifies deposition. However, the results also revealed that there are certain conditions where deposition tendency may decrease via the formation of high-melting-point alkali-containing solid phases (e.g., leucite).© 2019 Elsevier

  • 62979.
    Sefidari, Hamid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Razmjoo, Narges
    Richards, Tobias
    Kinetic Analysis of Isothermal and Non-isothermal Gasification of Undigested Organic Solid Waste with CO2 from Thermogravimetric Analysis2011Conference paper (Refereed)
  • 62980.
    Sefidari, Hamid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Department of Bioenergy Technology, Linnaeus University, SE-351 95 Växjö, Sweden.
    Razmjoo, Narges
    Department of Bioenergy Technology, Linnaeus University, SE-351 95 Växjö, Sweden.
    Strand, Michael
    Department of Bioenergy Technology, Linnaeus University, SE-351 95 Växjö, Sweden.
    An experimental study of combustion and emissions of two types of woody biomass in a 12-MW reciprocating-grate boiler2014In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 135, p. 120-129Article in journal (Refereed)
    Abstract [en]

    The gaseous emissions of primary concern from biomass combustion are nitrogen oxides (NOX), carbon monoxide, and various unburned gaseous components. Detailed characterization of the gas in the hot reaction zones is necessary to study the release, formation, and evolution of the gas components. In the present study, gas temperature and concentration were measured in a 12-MWth biomass-fired reciprocating-grate boiler operated with over-fire air and flue-gas recirculation. Temperature measurement was combined with flue gas quenching and sample gas extraction using two water-cooled stainless-steel suction pyrometers. The concentration profiles of O2, NO, and CO were experimentally determined throughout the furnace, and the profile gas temperature was measured in several positions inside the furnace for the two types of woody biomass studied. For both fuels, the gas temperature varied between approximately 450 °C (average primary chamber temperature) and 1200 °C (average secondary chamber temperature). The concentration profiles of CO and O2 suggested no conclusive difference between the two types of biomass. However, the local mean concentrations of NO and NOX emission factors (measured in the stack) were higher for Greenery fuel due to its higher nitrogen content than that of Standard fuel.

  • 62981.
    Sefidari, Hamid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Luossavaara-Kiirunavaara Aktiebolag (LKAB), Luleå, Sweden.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. RISE ETC (Energy Technology Centre) AB, Piteå, Sweden.
    Lindblom, Bo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Luossavaara-Kiirunavaara Aktiebolag (LKAB), Luleå, Sweden.
    Nordin, Lars Olof
    Luossavaara-Kiirunavaara Aktiebolag (LKAB), Luleå, Sweden.
    Wu, G
    GTT Technologies, Herzogenrath, Germany.
    Yazhenskikh, E
    Institute of Energy and Climate Research, Microstructure and Properties of Materials (IEK-2), Forschungszentrum Jülich GmbH, Jülich, Germany.
    Müller, M
    Institute of Energy and Climate Research, Microstructure and Properties of Materials (IEK-2), Forschungszentrum Jülich GmbH, Jülich, Germany.
    Ma, C
    Department of Applied Physics and Electronics, Thermochemical Energy Conversion Laboratory, Umeå University, Umeå, Sweden.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Comparison of high-rank coals with respect to slagging/deposition tendency at the transfer-chute of iron-ore pelletizing grate-kiln plants: A pilot-scale experimental study accompanied by thermochemical equilibrium modeling and viscosity estimations2019In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 193, p. 244-262Article in journal (Refereed)
    Abstract [en]

    Iron-ore pelletizing plants use high-rank coals to supply the heat necessary to process ores. Ash material from coal, in combination with iron-ore dust originating from the disintegration of the pellets, can cause deposition/slagging which often leads to severe production losses and damage. Deposition/slagging is most prominent in the hot areas of the grate-kiln setup and is more severe at the inlet of the rotary-kiln, i.e., the transfer-chute. Following on from our previous work, high-rank bituminous coals with potential for use in the pelletizing process were combusted in a pilot-scale (0.4 MW) pulverized-coal fired experimental combustion furnace (ECF). The fly-ash particles and short-term deposits were characterized to shed light on the observed difference in slagging/deposition tendencies of the coals. Global thermodynamic equilibrium modeling, in combination with viscosity estimates, was used to interpret the experimental findings and investigate the effect of the coal-ash composition upon deposition/slagging. This approach was carried out with and without the presence of Fe2O3-rich pellet-dust under oxidizing conditions within the temperature range at the transfer-chute of iron-ore pelletizing rotary-kilns. Based on the findings, a Qualitative Slagging Indicator (QSI) was proposed that can help pre-screen new solid fuels for potential slagging issues. The proposed QSI highlights the following: (1) an inverse relationship between viscosity and slagging/deposition tendency of the coals was observed (2) as viscosity decreases (either with increasing temperature or due to the change in the coal-ash composition), stronger deposits will form that will complicate the mechanical removal of the deposited layer. It was therefore inferred that low viscosity molten phases facilitate deposition/slagging, which is exacerbated by the presence of fluxing agents (e.g., CaO, MgO, K2O, Na2O, and Fe2O3) in the deposits. The low viscosity coal-ash-induced molten phases are also more likely to interact with the Fe2O3-rich pellet-dust that results in further decreases in viscosity, thereby intensifying depositions. The results from this work complement the on-going research by our group to elucidate and alleviate ash-related problems in industrial grate kilns.

  • 62982. Segarra, Roger
    Development of Iron Oxide Based Sorbents for Arsenic Stabilization in Contaminated Soil2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    High arsenic level in natural waters, and in the ground, is nowadays a worldwide problem. Soil stabilization is a low-cost technology aiming to reduce the arsenic mobility in soil preventing the migration of the contaminant into the environment.Addition of iron oxides to arsenic contaminated soils has been proposed as an effective remediation technique. The aim of the present work was to re-use iron ore broken pellets, i.e. a waste from mining industry, to immobilize arsenic within soil. A treatment was developed to increase the surface area of the iron ore broken pellets and therefore increasing its adsorption efficiency. Four different iron oxides were evaluates: metallic iron grid, fine magnetite powder, iron ore broken pellets and broken pellets modified by the developed treatment. Spherical nanoparticle aggregates covering the surface of the broken pellets were observed upon the application of the developed treatment.The immobilization performance of the iron oxide materials was evaluates for soil with and without plants. Soil pore water samples were collected and analysed after 11, 30 and 54 days. At the end of the experiment, the trace-element content of the plant shoots was analysed and a sequential extraction was performed for bulk and rhizosphere samples.While the zerovalent iron significantly reduced the mobility of arsenic in the contaminates soil, both in the presence and absence of plants, the other three iron oxide amendments did not significantly reduced the mobility of arsenic in the soil.

    Download full text (pdf)
    FULLTEXT02
  • 62983. Segawa, Samuel
    Managing Technical and Administrative Metadata in the Preservation of Digital Information2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A case study of the national library of Netherlands, E-depot

    Download full text (pdf)
    FULLTEXT02
  • 62984.
    Segelstad, Johan
    Luleå University of Technology, Department of Arts, Communication and Education.
    Layering animation principles on motion capture data: Surpass the limitations of motion capture2019Independent thesis Basic level (degree of Bachelor of Fine Arts), 180 HE creditsStudent thesis
    Abstract [en]

    This thesis deals with the use of Disney's twelve animation principles in relation to Motion Capture. The purpose of the work was to investigate whether animation principles can be applied to finished motion capture animations to surpass the limitations of motion capture  by using animation layers, where each added layer is a new principle. To investigate this, motion capture data was retrieved with various movements from Mixamo, which was then imported into Maya where various animation principles were applied with the help of Maya animation layers. The result of this research will answer the following…

    • Is it possible to surpass the limitations of motion capture by layering disney's animation principles on motion captured animations in Maya with the use of animation layers?

    Download full text (pdf)
    fulltext
  • 62985.
    Seger, Elvira
    Luleå University of Technology, Department of Arts, Communication and Education.
    "Att skriva musik, det kan väl inte vara så svårt?" En beskrivning av kompositionsprocesser och hur låtarna påverkas nar de spelas med musiker2017Independent thesis Basic level (degree of Bachelor of Fine Arts), 10 credits / 15 HE creditsStudent thesis
    Download full text (pdf)
    fulltext
  • 62986.
    Seger, Mikael
    Luleå University of Technology.
    TPM : total productive maintenance: Möjligheter och begränsningar1994Licentiate thesis, monograph (Other academic)
  • 62987. Segerberg, Simon
    Energioptimering av Boden Arena2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Download full text (pdf)
    FULLTEXT02
  • 62988. Segerlund, Anna
    et al.
    Wäppling, Magdalena
    Effekter på godstransporttillväxten orsakade av Ikea: s etablering i Haparanda2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Download full text (pdf)
    FULLTEXT01
  • 62989. Segerlund, Catrin
    Rekrytering som process: Luleå kommuns strategiska och operativa arbete med rekrytering2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Download full text (pdf)
    FULLTEXT02
  • 62990. Segerlund, David
    Parametriserad konstruktion av virkestorkar2000Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
  • 62991. Segerlund, Eva
    et al.
    Wikström, Hanna
    Economic Value Added: ett nytt perspektiv på värde2000Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 62992.
    Segerlund, Filip
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences.
    Gerdin, Emil
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences.
    Excel i redovisningsutbildningar: En studie om svenska lärosäten2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The primary goal of accounting havealways been the same, to create and provide information to internal and external decision makers. The accounting profession have undergone change due to digitalization. Therefore it is of utmost importance to follow thedevelopmentof technological tools.Studies have shown that the most demanded qualities in an employee is Excel knowledge after experience. Previous studies have shown that newly graduated students donot meet the employers demand. The purpose of this study is to map what swedish universities do to cater for the Swedish labour market regarding digitalization in general and Excel specifically. In order to achieve the purpose 72 syllabuses in accounting courses were examined at 22 different universities. This was followed by interviews with 10 course coordinators at 10 different universities with questions formulated from Technology Acceptance Model 2. This essay had a qualitative approach in general with quantitative elements. Results show that Excel was mentioned in 1 of the 72 syllabuses examined but used in 6 of the 10 interviewed universities. Further resultspointed that labour markets demands, job relevance and output quality werethe main variables affecting Excel involvement at target universities. This essay contributes with knowledgeon what is decisive for universities when it comes to adopting technological tools or not.

    Download full text (pdf)
    fulltext
  • 62993. Segerlund, Håkan
    et al.
    Sundqvist, Anneli
    Lokomotivföretag i Norrbotten: en studie om två ledande företag2007Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Download full text (pdf)
    FULLTEXT01
  • 62994. Segerlund, Jenny
    Industriplanering och layouter inför 2000-talet: elva fallstudier inom svensk tillverkningsindustri2001Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 62995. Segerlund, Johan
    Produktionssimulering sänker ledtiderna1999Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
  • 62996. Segerlund, Kajsa
    Dold samäganderätt till fast egendom: en redogörelse av förutsättningarna ur ett familjerättsligt perspektiv2009Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Download full text (pdf)
    FULLTEXT01
  • 62997. Segerlund, Magdalena
    Aktuell behandling vid Multipel skleros2009Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Download full text (pdf)
    FULLTEXT01
  • 62998.
    Segerlund, Manne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Estimating progenitor mass and distance to Galactic Core-Collapse Supernova using neutrino observatory IceCube2021Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Galactic core-collapse supernovae is a once-in-a-lifetime event which could carry with it information about new physics. In this work a method for estimating the progenitor mass and distance using the IceCube Neutrino Observatory is presented. The mass is expressed through an intermediate parameter called compactness. For a supernova with a progenitor mass less than 10 solar masses all stars with a mass over 15 solar masses in the galaxy can be excluded using the method developed in this work. At 10 kpc the distance to the supernova can be estimated to within 8.5% taken into account the strength of the neutrino signal and the uncertainty in the method used. This shows promising results of estimating parameters such as distance andmass using neutrinos.

    Download full text (pdf)
    fulltext
  • 62999. Segerlund, Maria
    et al.
    Sundquist, Jessica
    Revisorers syn på sin roll sedan avskaffandet av revisionsplikten2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Download full text (pdf)
    FULLTEXT02
  • 63000. Segerstedt, Anders
    A capacity-constrained multi-level inventory and production control problem1996In: International Journal of Production Economics, ISSN 0925-5273, E-ISSN 1873-7579, Vol. 45, no 1-3, p. 449-461Article in journal (Refereed)
    Abstract [en]

    This paper presents a mathematical formulation of a capacity constrained multistage inventory and production control problem. It argues that most practical multistage inventory and production control problems can be summarised in the formulation. The model has a strong connection to the model of Billington, McClain and Thomas (1983) and is also inspired of a paper from Bard and Golany (1991). The revised Billington/McClain/Thomas model is formulated in a dynamic programming recursion. A numerical solution to a simple problem is presented. A scheduling problem concerning capacity constrained models are enlightened. Further, the paper points to differences and relationships between this capacity constrained model, MRP, Kanban and Cover-Time Planning.

1257125812591260126112621263 62951 - 63000 of 78308
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf