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  • 1. Alander, E. M.
    et al.
    Uusi-Penttila, M. S.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Characterization of paracetamol agglomerates by image analysis and strength measurement2003In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 130, no 03-jan, p. 298-306Article in journal (Refereed)
    Abstract [en]

    Paracetamol is crystallized in different solvents and techniques are developed and used to characterize the product. The product particles from three different solvent compositions: ethylene glycol, acetone and an acetone-water mixture (30-70 wt.%) have been examined. Product properties visually observed are quantified by image analysis and evaluation of measured image descriptors with Principal Component Analysis (PCA). The agglomerate strength has been determined by crushing single agglomerates. Depending on the solvent, the content of single crystals and agglomerates differ. Agglomerates differ by the number and size of crystals grown together, as well as by the strength.

  • 2.
    Andersson, Daniel C.
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Cadario, Alessandro
    Lindskog, Per
    On the influence from punch geometry on the stress distribution at powder compaction2010In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 202, no 1-3, p. 78-88Article in journal (Refereed)
    Abstract [en]

    A numerical analysis, using the finite element method, of the mechanical behavior at powder compaction at higher densities was performed. In this investigation the material behavior is modeled using an advanced macroscopic constitutive description initially presented by Brandt and Nilsson [1]. This material model, like many other models describing powder compaction at higher densities, includes a large number of constitutive parameters and as a result, a complete material characterization is a difficult task to perform or at least requires a large number of different experiments. A remedy to this problem is to apply inverse modeling, i.e. optimization, for determination of relevant material properties from comparatively simple experiments. It is then of course important, in order to achieve high accuracy results from the optimization procedure, that the stress fields produced during the experiments involves high gradients of stress. Adhering to simple uniaxial die compaction experiments the main parameter that can be used in order to achieve such a feature is the geometry of the punch used for load application. In the present investigation a number of punch profiles are studied and it is found that a skewed punch geometry is the most appropriate one to be used for experimental die compaction aiming at a constitutive description of the powder material based on inverse modeling. The main efforts are devoted towards an analysis based on the previously mentioned material model by Brandt and Nilsson [1] but also relevant results for another type of constitutive model will be presented. (C) 2010 Elsevier B.V. All rights reserved.

  • 3. Beyhaghi, M.
    et al.
    Kiani-Rashid, A.
    Khaki, J. V.
    Kashefi, M.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Influences of mechanical activation and heating rate on reaction processes in combustion synthesis of NiAl-Al 2 O 3 composites2019In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 346, p. 237-247Article in journal (Refereed)
    Abstract [en]

    This paper investigates the combustion synthesis of NiAl-Al 2 O 3 composites by the heating of Ni, NiO and Al powder mixture from 20 °C to 1300 °C. The influence of mechanical activation (without and with 1 h) and heating rate (20 °C/min and 40 °C/min) on thermal events in combustion synthesis process are investigated. Thermal events are assessed by Differential Thermal Analysis (DTA), X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM). By heating the sample without mechanical activation, exothermic reaction of NiO reduction by Al and Ni-Al intermetallic phases (Al 3 Ni, Al 3 Ni 2 , AlNi and AlNi 3 ) production happened in the presence of molten Al at 870 °C as one DTA peak. Mechanical activation causes occurrence of these reactions more separately at lower temperatures (590 °C and 630 °C). By decrement in the heating rate, these reactions happened in a more dispersed way at lower temperatures (590 °C and 630 °C). The reaction temperature for nickel aluminides formation in the presence of eutectic melt of AlNi 3 -Al is constant regardless of heating rate in mechanically activated powder. A seven-stage mechanism for reactions in a mechanically activated sample at a heating rate of 40 °C/min is proposed. Initially, by heating of the powder, an exothermic reaction between nickel oxide and aluminum and also nickel and aluminum occurs at 590 °C in solid state. NiO is consumed totally and Al 2 O 3 is produced from the nickel oxide reduction by aluminum. Nickel aluminide phases are formed from reactions between aluminum and primary nickel and also from aluminum and nickel formed by aluminothermic reduction of nickel oxide. With continuation of heating process, Al-Al 3 Ni eutectic transition happens at 630 °C and results in the liquid phase formation. Presence of the molten phase accelerates the exothermic nickel aluminides formation reactions. Aluminum is consumed totally in this stage and more intermetallic phases are developed. By increasing the temperature, diffusion is enhanced. The remaining Al 3 Ni melts at 856 °C. This small amount of molten phase slightly enhances exothermic reactions between nickel aluminides and leads the system towards the equilibrium phase. After this event, reactions progresses gradually. The nickel core shrinks by the diffusion progressively and the whole nickel aluminides system undergoes a gradual evolution towards the NiAl equilibrium phase.

  • 4.
    Beyhaghi, Maryam
    et al.
    Islamic Azad Univ, Fac Engn, Dept Met & Ceram, Mashhad Branch, Mashhad, Iran..
    Khaki, Jalil Vandati
    Ferdowsi Univ Mashhad, Dept Met & Mat Engn, Mashhad 917751111, Iran..
    Manawan, Maykel
    Univ Indonesia, Dept Phys, Depok 16424, Indonesia.;Politekn Negeri Jakarta, Energy Engn, Depok 1624, Indonesia..
    Kiani-Rashid, Alireza
    Ferdowsi Univ Mashhad, Dept Met & Mat Engn, Mashhad 917751111, Iran..
    Kashefi, Mehrdad
    Ferdowsi Univ Mashhad, Dept Met & Mat Engn, Mashhad 917751111, Iran..
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    In-situ synthesis and characterization of nano-structured NiAl-Al2O3 composite during high energy ball milling2018In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 329, p. 95-106Article in journal (Refereed)
    Abstract [en]

    In this work, synthesis of NiAl-Al2O3 nanocomposite powders via the mechanosynthesis route and by using Ni, NiO and Al is investigated. Ignition of the reaction inside the ball-mill vial happens after 110 min; NiO is totally finished and NiAl and Al2O3 as product phases are formed. After 10 h of ball milling, raw materials are totally used in the reaction and only product phases exist in the vial. By continuing the ball milling process to 60 h, better mixing of the synthesized phases and decrement in their crystallite sizes plus partide size are observed. Crystallite sizes of the product phases are in the nanometer range in all ball milling times. Crystallite sizes of NiAl and Al2O3 after 10 h are around 11 nm and 19 nm respectively, and these are reduced to around 8 nm for both phases after 60 h of ball milling.

  • 5. Buscaglia, V.
    et al.
    Viviani, M.
    Buscaglia, M. T.
    Nanni, P.
    Mitoseriu, L.
    Testino, A.
    Stytsenko, E.
    Daglish, M.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Nygren, M.
    Nanostructured barium titanate ceramics2004In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 148, no 1, p. 24-27Article in journal (Refereed)
    Abstract [en]

    Dense nanocrystalline ceramics can be obtained starting from non-agglomerated nanopowders and using low-temperature sintering processes. The preparation and the properties of Barium Titanate (BaTiO3) ceramics and thick films are reported: ceramics were prepared by Spark Plasma Sintering (SPS) at 800 degreesC of nanopowders produced by a wet chemical process, while films were fabricated by airflow deposition (AD) of mixed fine and coarse powders at room temperature followed by isothermal firing. Ferroelectric ordering was found in both the ceramics and the sintered films by a.c. impedance. The transition from ferroelectric to paraelectric state was broadened over a wide temperature range with Curie-Weiss parameters strongly depressed in comparison to coarse-grained ceramics.

  • 6. Mangalaraja, R.V.
    et al.
    Mouzon, J.
    Hedström, Peter
    Division of Engineering Materials, Luleå University of Technology, Luleå, Sweden.
    Camurri, C.P.
    Ananthakumar, S.
    Odén, M.
    Microwave assisted combustion synthesis of nanocrystalline yttria and its powder characteristics2009In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 191, no 3, p. 309-314Article in journal (Refereed)
    Abstract [en]

    Microwave assisted combustion synthesis is used for fast and controlled processing of advanced ceramics. Single phase and sinter active nanocrystalline cubic yttria powders were successfully synthesized by microwave assisted combustion using the organic fuels urea, citric acid and glycine as reducing agents. The precursor powders were investigated by thermogravimetry (TG) and differential scanning colorimetry (DSC) analyses. The as-prepared precursors and the resulting oxide powders calcined at 1100 degrees C in oxygen atmosphere were characterized for their structure, particle size and morphology, The thermal analyses (TG/DSC). X-ray diffraction (XRD) and Fourier transform infra red (FT-IR) results demonstrate the effectiveness of the microwave assisted combustion synthesis. The scanning electron microscopy (SEM) observations show the different morphologies of as-prepared powders and transmission electron microscopy (TEM) shows the particle sizes in the range of 30-100 nm for calcined powders for different fuels. The results confirm that the homogeneous, nano scale yttria powders derived by microwave assisted combustion have high crystalline quality and the morphology of the as-prepared precursor powders depends on the nature of organic fuel used.

  • 7.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    A contact model for the normal force between viscoelastic particles in discrete element simulations2019In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 342, p. 985-991Article in journal (Refereed)
    Abstract [en]

    DEM modeling of granular materials composed of viscoelastic particles can provide valuable insights into the mechanical behavior of a wide range of engineering materials. In this paper, a new model for calculating the normal contact force between visoelastic spheres is presented based on contact mechanics that takes the mechanical behavior of the DEM particles into account. The model relies on an application of the viscoelastic correspondence principle to elastic Hertz contact. A viscoelastic relaxation function for the contact is defined and a generalized Maxwell material is used for describing this function. An analytical expression for the increment in contact force given an increment in overlap is derived leading to a computationally efficient model. The proposed model provides the analytical small deformation solution upon loading but provides an approximate solution at unloading. Comparisons are made with FEM simulations of contact between spheres of different sizes of equal and dissimilar materials. An excellent agreement is found between the model and the FEM simulations for almost all cases except at cyclic loading where the characteristic times of the viscoelastic behavior and the loading are similar.

  • 8.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    A numerical analysis of cold powder compaction based on micromechanical experiments2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 243, p. 71-78Article in journal (Refereed)
    Abstract [en]

    The discrete element method (DEM) is used for predicting the compaction behavior of two types of spray dried cemented carbide granules. The material model of the granules is determined by micromechanical experiments. First, compression tests are performed on single granules giving information of the deformation behavior at relatively small deformations. For larger deformations, nanoindentation tests are performed to give further information of the constitutive behavior indicating a strong hardening behavior at high strains. The material model is implemented in an FE model of two particles in contact and the relation between contact force and indentation depth is exported to a DEM program. The DEM program is used to simulate presently performed uniaxial die compaction experiments where the geometry of the die is taken into account. Excellent agreement is found between the experiments and the numerical predictions in the range where results from DEM simulations are valid.

  • 9.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Micromechanical Investigation of the Fracture Behavior of Powder Materials2015In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 286, p. 31article id 11185Article in journal (Refereed)
    Abstract [en]

    Fracture of compacted powder has been studied experimentally and numerically using a micromechanicalapproach. In the experimental investigation, the compacts are crushed in two dierent directions to accountfor general stress states and a microscopy study shows that fracture of the powder granules plays asignicant role in the fracture process. The numerical analysis is based on the Discrete Element Method(DEM) and a novel approach is presented to account for the fracture of the particles in the numericalmodel. The force-displacement relations for two particles in contact, which are needed in DEM, are derivedusing micomechanical experiments together with nite element analyses of the contact problem. The contactmodel accounts for plastic compression, elastic unloading and adhesive bonding together with frictionand tangential bonding. The model shows a very good agreement with the experimental data both for theelastic behavior during unloading and, if failure of the particles is accounted for, the fracture of the compacts.

  • 10.
    Shoaib, Muhammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Azhdar, Bruska
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Simulation of high-velocity compaction process with relaxation assists using the discrete element method2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 217, p. 394-400Article in journal (Refereed)
    Abstract [en]

    The discrete element method is used to investigate the high-velocity compaction process with additional piston supports known as relaxation assists. It is shown that by incorporating the relaxation assists in the piston-die assembly, particles can be better locked during the compaction process. The simulation results reveal that relaxation assists offer; smooth compaction during loading stage, prevention of the particle separation during unloading stage and conversion of higher kinetic energy of hammer into particle deformation. Finally, the influences of various loading elements on compaction process and effects of presence of adhesion during unloading stage are investigated. The results support the findings of experimental work.

  • 11.
    Strömgren, Tobias
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Modelling of turbulent gas-particle flows with focus on two-way coupling effects on turbophoresis2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 224, p. 36-45Article in journal (Refereed)
    Abstract [en]

    An Eulerian model was developed for turbulent gas-particle flow that takes into account the influence of particles on the gas-phase turbulence. For the description of the particle-phase stress the kinetic theory of granular flow and the simpler Hinze model were adopted. A K-ω model was used as the gas phase turbulence model. The difference between one- and two-way coupling was investigated for different particle volume fractions and particle diameters. It was found that particles with a much higher density than the fluid substantially affect the gas-phase in turbulent channel flow for particle volume fractions as low as 10 -4. The models with the particle-phase stress described by the kinetic theory of granular flow and the simpler Hinze model produce similar results for particles with small response times but deviate for larger response times. The study shows that two-way coupling and the turbophoretic effect must be taken into account in models even at relatively low particle volume fractions.

  • 12. Zhang, Z. Y.
    et al.
    Sandström, Rolf
    KTH, Superseded Departments, Materials Science and Engineering.
    Frisk, K.
    Salwen, A.
    Characterization of intermetallic Fe-Mn-Si powders produced by casting and mechanical ball milling2003In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 137, no 3, p. 139-147Article in journal (Refereed)
    Abstract [en]

    Mechanical milling is a common method used to produce different powders. Milling time is one of the most important factors in the process, which affects characteristics such as particle size distribution and morphology. Four compositions of mechanically milled Fe-Mn-Si master alloy powders were investigated in the present paper. Milling times from 10 to 120 min were used. Particle size distribution and milling kinetics of Fe-Mn-Si powders were studied, and the parameters in breakage function have been determined. The results show that powder characteristics vary with the contents of silicon and manganese. During milling, the particle size initially decreases. At longer milling times, however, small particles agglomerate to larger particles (overmilling). The optimum milling time to get powders with very fine particle sizes is alloy-dependent. Apart from the agglomeration, the milling process of Fe-Mn-Si powders can be described by a classic batch-grinding equation based on the population balance model.

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