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  • 1. Biendicho, J. J.
    et al.
    Shafeie, S.
    Frenck, L.
    Gavrilova, D.
    Boehme, S.
    Bettanini, A. M.
    Svedlindh, P.
    Hull, S.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Istomin, S. Ya.
    Grins, J.
    Svensson, G.
    Synthesis and characterization of perovskite-type Sr(x)Y1-xFeO(3-delta) (0.63 <= x < 1.0) and Sr0.75Y0.25Fe1-yMyO3-delta (M=Cr, Mn, Ni), (y=0.2, 0.33, 0.5)2013In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 200, p. 30-38Article in journal (Refereed)
    Abstract [en]

    Oxygen-deficient ferrates with the cubic perovskite structure SrxY1-xFeO3-delta were prepared in air (0.71 <= x <= 0.91) as well as in N-2 (x=0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-delta=2.79(2) for x=0.75 to 3-delta=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.25Y0.25FeO2.29 using TOP neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and highresolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along (1 0 0)(p) with G +/- similar to 0.4(1 0 0)(p) indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5-390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25Fe02.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm/K in air at 298-673 K. At 773-1173 K TEC increases up to 17.2 ppm/K due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1-yMyO3-delta (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25Fe02.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25Fe02.79.

  • 2.
    Bu, Junfu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Preparation of 30 mol.% Y-doped hafnia (Hf0.7Y0.3O2-delta) using a modified solid-state reaction method2015In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 41, no 2, p. 2611-2615Article in journal (Refereed)
    Abstract [en]

    A pure and well-crystallized Hf0.7Y0.3O2-delta (YSH) powder was synthesized using a modified solid-state reaction method. Water-based milling and freeze drying process were implemented to facilitate powder synthesis and final densification process. The improved powder performance, in aspects of phase development and sintering behaviour, was investigated by systematic comparison between different powder processing procedures. Dense YSH ceramic material with a relative density of 0.975 was successfully obtained using conventional sintering at 1650 degrees C for 10 h. XRD, SEM and EDS were employed to characterize the synthesized powder and dense YSH ceramics. Dense YSH ceramic possesses a fluorite cubic structure with an a value of 5.1406 angstrom, and the ionic radius of Y3+ in YSH was determined to be 0.1006 nm.

  • 3.
    Cheng, Yajuan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wang, Jing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Optimization of high-quality vertically aligned ZnO rod arrays by the response surface methodology2015In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 626, p. 180-188Article in journal (Refereed)
    Abstract [en]

    Optimization of the deposition parameters was conducted by the response surface methodology to synthesize high-quality ZnO rod arrays with a high texture coefficient, a large aspect ratio and a narrow bandgap. In addition, mathematical models based on statistical analysis were also developed to predict the texture coefficient, aspect ratio and bandgap of the ZnO rod arrays. With the optimized parameters, all of the three involved responses obtained the desired optimum values. The results show that the texture coefficient can be elevated up to a value of 0.998, which represents an almost perfect value. Moreover, wide range of aspect ratios was obtained for various applications and the obtained maximum value of 21.3 is relatively high value by wet chemical method, especially when no capping agent and no refreshing growth solution in a nearly neutral solution is used.

  • 4.
    Eliasson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Interaction behaviour between solid inclusions and solidification front and inclusion behaviour in iron base alloys during teeming and at deoxidation by the Kirkendall Effect2006Report (Other academic)
  • 5.
    Eliasson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Liquid phase sintering of W-Ni-Fe composites: liquid penetration, agglomerate separation and tungsten particle growth2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The initial stage of liquid phase sintering, involving liquid penetration, agglomerate separation, particle spreading and growth has been investigated in experiments using tungsten heavy alloys. The particle composites used were produced by hot isostatic pressing (HIP) of pure powder mixtures of W-Ni-Fe-(Co). By using different HIP temperatures, volume fractions of tungsten, alloying elements like Cobalt and Sulphur or excluding Iron from the matrix, liquid penetration, agglomerate separation and particle growth conditions were affected. The investigations were performed mainly under microgravity (sounding rockets or parabolic trajectories by airplanes) but at high tungsten particle fractions, short sintering times or at infiltration of solid pure tungsten, they were performed at normal gravity. The liquid penetration of the tungsten agglomerates is explained by initial wetting under non-equilibrium conditions, due to the reaction between the liquid matrix and the particles, and a decrease of interfacial energy. The dissolving of tungsten gives a pressure drop in the penetrating liquid and a driving force for the liquid movement by a suggested parabolic penetration model. For cold worked tungsten, a penetration theory was proposed, where an internal stress release in the penetrated tungsten grains creates space for the advancing liquid.

    The spreading of the tungsten agglomerates is explained by an interagglomerate melt swelling due to a Kirkendall effect. The liquid matrix undergoes a volume increase since the diffusion rates of Ni-Fe are higher than for W and initial concentration gradients of W and Ni, Fe exists. The suggested model by Kirkendall are also used for an analysis of the interaction behaviour between solid particles and a solidification front and inclusion behaviour in iron base alloys during teeming and deoxidation.

    The average tungsten particles size decrease initially since part of the tungsten particles is dissolved when the non-equilibrium matrix phase is melting. When equilibrium is reached, the tungsten particles grow in accordance with the Ostwald ripening process by an approximately 1/3 power law. Larger particle fraction of particles showed a higher growth rate, due to shorter diffusion distances between the particles. Cobalt, Sulphur and absence of iron in the matrix were found to increase the growth rate of the tungsten particles due to a higher surface tension between the solid tungsten particles and the matrix melt.

  • 6.
    Eliasson, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Ekbom, L.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Tungsten grain separation during initial stage of liquid phase sintering2008In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 51, no 4, p. 343-349Article in journal (Refereed)
    Abstract [en]

    The initial stage, the first few seconds of liquid phase sintering has been investigated in experiments using a tungsten heavy alloy with low tungsten content. The heavy alloy has been melted in a temperature gradient for short periods, similar to 9 s in an ellipsoid mirror furnace. During the liquid phase sintering at about 1470 degrees C, a penetration followed by a remarkably rapid separation and dispersion of the tungsten grains by the molten matrix occur. The suggested explanation for this grain separation and dispersion is based on the effect of composition gradients in the liquid matrix and a theory based on interagglomerate melt swelling due to a Kirkendall effect.

  • 7.
    Eliasson, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Ekbom, Lars B
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Fredriksson, Hasse
    Liquid Penetration and Particle Separation during the Initial Stage of Liquid Phase Sintering2006In: Metallurgical transactions. A, ISSN 0360-2133Article in journal (Refereed)
  • 8. Formenti, A.
    et al.
    Eliasson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Mitchell, A.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Solidification sequence and carbide precipitation in Ni-base superalloys IN718, IN625 AND IN9392005In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 24, no 4, p. 239-258Article in journal (Refereed)
    Abstract [en]

    Differential Thermal Analysis (DTA) and Directional Solidification and Quenching (DSQ) were used to evaluate the solidification and precipitation sequence for the Ni-base superalloys IN718, IN625 and IN939. They all showed a similar precipitation sequence, with an initial precipitation of gamma dendrites, followed by an intermediate non-invariant divorced eutectic reaction of type L -> gamma + MC, and a final eutectic precipitation of Laves phase for alloy IN718 and IN625 and of eta-phase for alloy IN939. The reaction temperatures and the amounts of carbides and of final precipitates were evaluated. Precipitated nitrides were found to act as nucleation sites for the precipitation of blocky carbides/carbonitrides, at low interdendritic supersaturation, while in interdendritic regions with high supersaturation, a 'script-like' carbide formation was found instead.

  • 9.
    Formenti, Angelo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Eliasson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On the dendritic growth and microsegregation in Ni-base superalloys IN718, IN625 and IN9392005In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 24, no 4, p. 221-238Article in journal (Refereed)
    Abstract [en]

    Directional Solidification and Quenching (DSQ) has been used to analyse the solidification, segregation and precipitation behaviour of the Ni-base alloys IN718, IN625 and IN939. The microsegregation in the primary solidified gamma-phase was analysed by Energy Dispersive Spectroscopy (EDS) and were mainly found to be Nb for alloy IN718 and Ti for alloy IN939. The microsegregation behaviour were analysed by numerical back diffusion models and it was found that the diffusion rate in the samples was higher than expected from the theory. A suggested explanation was that this was an effect of the formation of lattice defects during the solidification process. The coarsening process that occurs during the further cooling of the samples is proved to be by the mechanism of back diffusion i.e. the smaller secondary dendrite arms grow together with the thicker ones into a plate.

  • 10.
    Gao, Zhan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Liu, Xingmin
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Comparative study of Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) electrolyte synthesized by different routes2011In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, no 35, p. 8720-8727Article in journal (Refereed)
    Abstract [en]

    In this work, four different methods, including polyvinyl alcohol (PVA)-assisted sol-gel process, polyethylene glycol (PEG)-assisted sol-gel process, citrate sol-gel process and oxalate coprecipitation process (OCP) are employed to synthesize the Sm and Nd co-doped ceria electrolyte with the composition of Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) (SNDC). The phase structure of the powders can be well indexed with the fluorite-type CeO(2) structure. The morphology of sintered samples indicates that the ceramics can be highly densified. The relative density and the average grain size vary with the synthesis processes and the sintering temperatures. The bulk conductivities are quite close and the OCP-SNDC yields highest grain-boundary conductivities and total conductivities. The results indicate that the OCP process for the powder synthesis results in higher relative density and conductivities, lower grain-boundary resistance and activation energy. Grain-boundary space charge potentials for different specimens are calculated based on the Mott-Schottky model. The synthesis process and sintering temperature have significant effect on the space charge potential and the specific grain-boundary conductivity. (C) 2011 Elsevier B.V. All rights reserved.

  • 11.
    Gao, Zhan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Liu, Xingmin
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Electrical properties of ceria co-doped with Sm3+ and Lu3+electrolyte materialsArticle in journal (Other academic)
    Abstract [en]

    Sm and Lu co-doped ceria with compositions of Ce1-x(Sm3Lu2)x/5O2-δ (SLDC, x=0.05, 0.1, 0.15, 0.2) are investigated to validate the concept of critical dopant ionic radius ( rc ), where the number-average dopant ionic radius is designed tomatch the critical dopant ionic radius ( c r ). A variety of techniques including X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to characterize the SLDC powders and the sintered pellets. Electrical properties of different specimens are investigated by using the impedance spectroscopy. The result sdemonstrated that the critical dopant ionic radius concept is not totally valid for Sm-Lu co-doping strategy, even that the co-doping with appropriate chemicalcomposition, Ce0.85(Sm3Lu2)0.03O2-δ, yields higher total conductivity than either Smor Lu-doped ceria. More co-doping strategies need to be studied to test the critical dopant ionic radius concept.

  • 12.
    Gao, Zhan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Liu, Xingmin
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Enhanced ionic conductivity of Ce0.8Sm0.2O2-delta by Sr addition2012In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 208, p. 225-231Article in journal (Refereed)
    Abstract [en]

    Sm and Sr co-doped ceria-based electrolyte with compositions of Ce-0.8(Sm1-xSrx)(0.2)O2-delta (x = 0, 0.3, 0.5, 0.7) are synthesized and investigated with the aim of improving the electrical properties of Ce0.8Sm0.2O2-delta. X-ray diffraction (XRD) and electron microscope (SEM and TEM) techniques are employed to characterize the microstructure of powders and sintered pellets. The ionic conductivity has been examined by the A.C. impedance spectroscopy in air. The Ce-0.8(Sm0.7Sr0.3)(0.2)O2-delta exhibits the highest bulk conductivity among the series, which can be mainly ascribed to the increase of oxygen vacancy concentration. The specific grain-boundary conductivities are observed to increase with the Sr doping content up to x = 0.5. Further increase in Sr concentration will lead to reduced specific grain-boundary conductivities. The total conductivities of all Sm and Sr co-doped ceria are higher than that of Ce0.8Sm0.2O1.9. The results indicate that Sr co-doping opens a new avenue to improve ionic conductivity in Ce0.8Sm0.2O1.9.

  • 13.
    Gao, Zhan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Liu, Xingmin
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Mao, Zongqiang
    Novel BaZr0.1Ce0.7Y0.2O3-δ (BZCYO)-Ce0.8Y0.2O2-δ (YDC) composite ceramic electrolyte for low-temperature SOFCsArticle in journal (Other academic)
    Abstract [en]

    Novel BaZr0.1Ce0.7Y0.2O3-δ (BZCYO)-Ce0.8Y0.2O2-δ (YDC) composite ceramic electrolyte possessing both proton and oxygen ion vacancies conduction was first reported. There are no chemical reactions between the two compositions. The composite ceramic electrolyte shows excellent chemical stability to reduction. BZCYO2-YDC8 exhibits the highest bulk ionic conductivities in the temperature range of 450 oC to 650 oC and total ionic conductivities when the temperatures are higher than 550 oC. The conductivity enhancement mechanism has been discussed. BZCYO-YDC composite ceramics may be promising electrolytes in low-temperature solid oxide fuel cells.a)

  • 14. Kese, K. O.
    et al.
    Li, Z. C.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Contact residual stress relaxation in soda-lime glass Part II. Aspects relating to strength recovery2006In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 26, no 6, p. 1013-1022Article in journal (Refereed)
    Abstract [en]

    Strength recovery of Vickers indented soda lime glass was measured and compared after annealing at two temperatures: one below and one above T, The atomic force microscope was used to study the cracks. At 540 degrees C, no changes were observed in crack morphology either below the surface or on the surface relative to the pre-anneal state. At 630 degrees C, both sub-surface and surface crack morphology changes were observed. The trends in strength recovery were compared with residual stress relaxation as measured by a new method of stress estimation based on nanoindentation elastic response. At short hold times at 630 degrees C, and regardless of the length of hold time at 540 degrees C, strength recovery of only similar to 30% was measured while at moderately long hold times at 630 similar to C, strong recovery of fracture strength, similar to 132% was measured. Trends in strength recovery above T. are shown to match those of crack tip radius instead of trends in stress relaxation across the residual stress field.

  • 15. Kese, K. O.
    et al.
    Li, Z. C.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Effect of ageing on the electrical resistivities of (Ba0.69Pb0.31)Ti-3 PTCR ceramic thermistors2005In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 31, no 3, p. 375-378Article in journal (Refereed)
    Abstract [en]

    The electrical resistivity of (Ba0.69Pb0.31)TiO3 PTCR ceramic thermistors aged at temperatures of 175, 200, 250 and 300 degrees C, respectively, were measured. When the samples were aged at temperatures of 175 and 200 degrees C, room-temperature resistivity decreased at the initial ageing stage, and then increased with the ageing time. The samples displayed a monotonous rise of the room-temperature resistivity when the ageing treatments were performed at 250 and 300 degrees C. PTCR effects showed different characteristics after different ageing treatments. These ageing characteristics were analyzed by considering interior oxidation and reduction reactions.

  • 16. Kese, K.
    et al.
    Tehler, M.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Contact residual stress relaxation in soda-lime glass Part I. Measurement using nanoindentation2006In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 26, no 6, p. 1003-1011Article in journal (Refereed)
    Abstract [en]

    The contact residual stress field created by a Vickers indentation is a micro-size region of high and varying stresses. Stress relaxation studies in such a micro-region may not be accessible to the conventional methods of investigation. In this paper the elastic response during nanoindentation has been used to study the isothermal stress relaxation of a Vickers residual stress field in soda-lime glass at 540 and 630 degrees C. At each temperature, the stress relaxation profile varied from one location of the stress field to the other suggesting non-linear response to stress. Also, the relaxation profiles at identical positions were different for the two temperatures suggesting that the Vickers residual stress field is not a thermorheologically simple region of material.

  • 17.
    Kese, Kwadwo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Li, Zhi-Cheng
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Method to account for true contact area in soda-lime glass during nanoindentation with the Berkovich tip2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 404, no 1-2, p. 1-8Article in journal (Refereed)
    Abstract [en]

    An. empirical relationship for estimating the pile-up contact area from the contact stiffness, S and the contact depth, h(c) has been developed. This was achieved first by using the atomic force microscope to image nanoindents made with the Berkovich indenter in soda-lime glass and approximating the pile-up contact perimeter as a semi-ellipse. Then, by determining the pile-up contact area for several peak indentation loads, a correlation was found between the pile-up contact area and the load used to generate it. The importance of this new method of determining the pile-up contact area is that the need for indent imaging is made completely redundant, since the contact stiffness is a quantity that is routinely obtained during nanoindentation data analysis. Elastic modulus of soda-lime glass of 70 +/- 1.5 GPa is measured with loads ranging from 20 to 500 mN. The hardness measured also falls within the range of values, 5.2-5.9 GPa, normally quoted in the literature for the glass.

  • 18.
    Lapina, Alberto
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Li, Shuai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 powder by gel combustion route with two-step doping strategy2012In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, no 10, p. 2325-2331Article in journal (Refereed)
    Abstract [en]

    A two-step doping strategy was applied to the synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 (LSGM1020) powder by a gel combustion method. The Mg-doped LaGaO 3 powder was prepared in the first step, and Sr incorporation in the Mg-doped LaGaO 3 powder was done in the second step to obtain the final LSGM1020 powder. The two-step procedure is effective in preparing higher purity powders than the traditional one-step procedure. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that incorporation of Mg in LaGaO 3 in the first step enlarges the LaGaO 3 lattice: this facilitates the incorporation of Sr in the second doping step and thus high purity powder is obtained. Relatively phase pure LSGM1020 powder with only 3.1% of LaSrGaO 4 was obtained after calcination at 1300°C for 5h. Therefore, the two-step doping strategy is an effective procedure for the preparation of LSGM powders with high Sr- and Mg-doping levels.

  • 19.
    Li, Shuai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Preparation and characterization of perovskite structure lanthanum gallate and lanthanum aluminate based oxides2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present work was initiated to study the synthesis and properties of lanthanum gallate based oxides as intermediate temperature electrolyte for solid oxide fuel cells. The wet chemical method, polymer complexing route, was used to prepare the precursor powders. To further investigate the polymer complexing method, it was also applied to the preparation of lanthanum aluminate based oxides.

     

    Single perovskite phase La0.8Sr0.2Ga0.83Mg0.17O2.815 can be prepared by the polymer complexing method using PVA as complexing agent. The thermal decomposition of the precursor powder undergoes three stages. While complete decomposition of the precursor is obtained at 1000°C. Further investigation of LaGaO3 doped with various amounts Sr or/and Mg was conducted. Three secondary phases were identified by X-ray diffraction, e.g. LaSrGaO4, LaSrGa3O7 and La4Ga2O9. The relative amount of these secondary phases depends on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased activation energy of conductivity.

     

    Preliminary study showed that the lanthanum gallate and ceria composite electrolyte is mainly fluorite CeO2 phase after sintering. The minority secondary phase, Sm3Ga5O12, was also detected by XRD. The composite electrolyte showed superior electrical performance. It exhibited the highest conductivity in the temperature range of 250–600°C, compared with lanthanum gallate and ceria specimens.

     

    The phase pure perovskite La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 powders can easily be obtained by the polymer method using PVA as complexing agent. No secondary phase was detected after calcination at various temperatures (500–1100°C). The fully crystallized LaAlO3 phase was prepared after calcination at 900°C. Meanwhile the secondary phases were difficult to eliminate in the Sr- and Mg- doped LaGaO3 powder prepared by the same polymer method. It is thus concluded that the polymer, PVA in this work, provides more homogeneous mixing for cations of lanthanum aluminate based oxides, compared with the one for doped lanthanum gallate.

     

    The influence of different complexing agents, e.g. PVA and PEG, was investigated in the synthesis of lanthanum aluminate powders. Minority impurity La2O3 existed in the PEG powder, but it could be eliminated after sintering at high temperatures. Although the pure phase LaAlO3 can be easily obtained in PVA powders calcined at 950°C, more seriously aggregated particles existed. PEG showed advantages over PVA in terms of better densification and microstructure control in the sintered products. To select proper polymers in complex oxide synthesis, the agglomeration and morphology of the powder are the most important factors to be considered.

     

  • 20.
    Li, Shuai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Doping effect on secondary phases, microstructure and electrical conductivities of LaGaO3 based perovskites2009In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 29, no 6, p. 1139-1146Article in journal (Refereed)
    Abstract [en]

    The intermediate temperature electrolytes La1-xSrxGa1-yMgyO3-delta (LSGM, where delta=(x+y)/2) with perovskite structure were prepared using a poly(vinyl alcohol) (PVA) solution polymerization method. Three secondary phases were identified by X-ray diffraction, LaSrGaO4, LaSrGa3O7 and La4Ga2O9. The relative amount of these secondary phases depended on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. LaSrGaO4 could not be detected by SEM for the sintered pellets. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased conductivity activation energy. La0.8Sr0.2Ga0.9Mg0.1O2.85 had the highest ionic conductivity sigma = 0.128 S/cm at 800 degrees C in this work.

  • 21.
    Li, Shuai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Zhao, Zhe
    A Polymer Complexing Route for Low Temperature Synthesis of Perovskite Lanthanum Aluminate Powder2010In: HIGH-PERFORMANCE CERAMICS VI  / [ed] Pan W; Gong J, 2010, Vol. 434-435, p. 863-867Conference paper (Refereed)
    Abstract [en]

    Lanthanum aluminate powders were prepared via a polymer complexing method by using PEG as complexing agent. The LaAlO3 powder was characterized by XRD and SEM. The influence of processing parameters such as molar ratio of PEG monomers to metal cations (PEG:Men+) and aging process on the phase purity and powder morphology were investigated. The calcined powder with the PEG:Me ratio larger than 2:1 may contain the secondary phase, namely La2O3. The formation of phase pure LaAlO3 powder occurs when the PEG:Men+ ratio is 1:1 or enough gelation time is involved. Although the phase pure powder is obtained by this PEG method, all the single phase LaAlO3 powders are found to have seriously aggregated particles. The weakly agglomerated powder morphology is only found in the powders which contain La2O3.

  • 22.
    Li, Shuai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhao, Zhe
    Preparation and characterisation of perovskite La0.8Sr0.2Ga0.83Mg0.17O2.815 electrolyte using a poly(vinyl alcohol) polymeric methodIn: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689Article in journal (Other academic)
  • 23.
    Li, Shuai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Synthesis and characterization of lanthanum aluminate powders via a polymer complexing plus combustion route2012In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 132, no 2-3, p. 309-315Article in journal (Refereed)
    Abstract [en]

    Lanthanum aluminate powders were prepared by a simple polymer complexing plus combustion method using PVA or PEG as complexing agent and fuel. The influence of different polymers on phase purity, powder morphology and sintering performance were investigated. Trace amount impurity La 23 exists in the PEG powder, but it could be eliminated after high temperature sintering. The pure phase LaAlO 3 can be easily obtained in PVA powders calcined at 950 °C even severe aggregation always exists. PEG shows advantages over PVA in terms of the densification and microstructure control during sintering process. The high relative density of 97.0% and homogeneous fine microstructure with grain size < 3 μm can be obtained in the PEG-derived sample sintered at 1600 °C for 5 h. To obtain better quality LaAlO 3 powders through combustion route, PEG is preferred over PVA.

  • 24.
    Li, Shuai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhao, Zhe
    Synthesis of La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 using a polymeric method2009In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, ISSN 0955-2219, Vol. 29, no 6, p. 1133-1138Article in journal (Refereed)
    Abstract [en]

    Nanocrystalline La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 (LSAMC) powders were synthesized via a polymeric method using poly(vinyl alcohol) (PVA). The effect of PVA content on the synthesized powders was studied. When the ratio of positively charged valences (Mn+) to hydroxyl groups (-OH) is 1.5:1, crystalline LaAlO3 could be obtained at such a low calcination temperature as 700 degrees C. While at 900 degrees C the ratio is of less importance, since pure LaAlO3 perovskite could be formed for all powders after calcination at 900 degrees C. Thermal analysis (TG/DTA) was utilized to characterize the thermal decomposition behaviour of precursor powders. The chemical structure of the calcined powder was studied by Fourier transform infrared (FTIR) spectroscopy. The powder morphology and microstructure were examined by SEM. Dense pellets with well-developed submicron microstructures could be formed after sintering at 1450 degrees C for 5 h. Compared with the solid-state reaction method, the sintering temperature is substantially lower for powder prepared by the PVA method. This is due to the ultrafine and highly reactive powder produced.

  • 25.
    Li, Shuai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Li, Zhicheng
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lanthanum gallate and ceria composite as electrolyte for solid oxide fuel cells2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, ISSN 0925-8388, Vol. 492, no 1-2, p. 392-395Article in journal (Refereed)
    Abstract [en]

    The composite of doped lanthanum gallate (La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(2.85), LSGM) and doped ceria (Ce(0.8)Sm(0.2)O(1.9), CSO) was investigated as an electrolyte for solid oxide fuel cell (SOFC). The LSGM-CSO composite was examined by X-ray diffraction (XRD) and impedance spectroscopy. It was found that the sintered LSGM-CSO composite contains mainly fluorite CeO(2) phase and a minority impurity phase, Sm(3)Ga(5)O(12). The LSGM-CSO composite electrolyte shows a small grain boundary response in the impedance spectroscopy as compared to LSGM and CSO pellets. The composite electrolyte exhibits the highest conductivity in the temperature range of 250-600 degrees C, compared to LSGM and CSO. The LSGM-CSO composite can be expected to be an attractive intermediate temperature electrolyte material for solid oxide fuel cells.

  • 26. Li, Z. C.
    et al.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Electrical properties and ageing characteristics of BaTiO3 ceramics doped by single dopants2005In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 25, no 4, p. 441-445Article in journal (Refereed)
    Abstract [en]

    BaTiO3 ceramics doped by single dopants Of SM2O3, Ho2O3, Bi2O3, La2O3, CeO2 and Ta2O5, respectively, were prepared and aged in air. The room-temperature resistivity was measured and the relationship between resistivity change versus ageing time was determined. The electrical resistivity of Bi- and Ta-doped samples decreases at the early ageing stage, and then increases with the ageing time; the other doped ceramics display a monotonous increase of the resistivity with ageing time. The electrical properties and ageing characteristics are analyzed by considering interior oxidation and reduction reactions and the electronegativity of the doping elements.

  • 27. Li, Z. C.
    et al.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Thermal cycle characteristics of PTCR ceramic thermistors2005In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 118, no 1, p. 92-97Article in journal (Refereed)
    Abstract [en]

    Thermal cycle treatment was performed in BaTiO3 and (Ba, Pb)TiO3 PTCR ceramic thermistors. When the treatment temperatures were higher than the Curie points, the room-temperature resistivities decreased at the initial thermal cycle stage, and then increased further with the thermal cycles. When the treatment temperatures were lower than Curie points, the room-temperature resistivities increased monotonously with the number of thermal cycle. The PTCR effects were also affected by the thermal cycle treatment. The oxygen absorption and oxidation were proposed for the monotonously increasing resistivity. Domain alternation and defect mechanisms were suggested to be the major cause for the resistivity decrease at the initial thermal cycle stage.

  • 28. Li, Z. C.
    et al.
    Zhang, H.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Synthesis and characterization of nanostructured Bi2O3-doped cerium oxides fabricated by PVA polymerization process2008In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 34, no 8, p. 1949-1953Article in journal (Refereed)
    Abstract [en]

    Bi2O3-doped ceria oxygen-ion conductors were prepared by a wet chemical synthesis method, which is per-formed by polymerization of polyvinyl-alcohol (PVA). The experiments showed that Bi2O3-CeO2 solid solution with 9.2 nm grains and pure fluorite type phase can be synthesized at a calcination temperature of 500 degrees C by PVA polymerization process. X-ray analysis revealed that high density narrostructured bulks could be prepared at a sintering temperature of 900 degrees C, and these bulk samples with an average grain size less than 70 nm could effectively be obtained at various heating rates during sintering. Oxygen-ion conductivity increased with the increase of dopant concentrations between 5 mol% and 15 mol% in present study.

  • 29. Li, Z. C.
    et al.
    Zhang, H.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Zou, X.
    Synthesis and characterization of La0.85Sr0.15Ga0.85Mg0.15O3-delta electrolyte by steric entrapment synthesis method2006In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 26, no 12, p. 2357-2364Article in journal (Refereed)
    Abstract [en]

    Strontium and magnesium doped lanthanum gallate La0.85Sr0.15Ga0.85Mg0.15O3-delta (LSGM) oxygen ionic conducting ceramics were prepared by a steric entrapment synthesis (SES) method, which is a polymeric precursor synthesis method by using polyvinyl alcohol in aqueous solution. The perovskite LSGM phase formed essentially at a calcination temperature of 900 degrees C. Pure and single perovskite LSGM phase with high relative density of 97.1% was obtained after sintering at 1450 degrees C, while the relative density of the LSGM sample sintered at the same temperature by solid state reaction (SSR) method was 80.6% in present experiment. Comparing with SSR synthesis method, the sintering temperature by SES can be reduced at least 100 degrees C. Impedance spectra revealed that the grain-boundary resistivity of LSGM synthesized by SES was smaller than that by SSR method. and the conductivities of the samples by SES were higher than those by SSR method at all measuring temperatures.

  • 30. Li, Z. C.
    et al.
    Zhang, H.
    Zou, X. D.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Synthesis of Sm-doped BaTiO3 ceramics and characterization of a secondary phase2005In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 116, no 1, p. 34-39Article in journal (Refereed)
    Abstract [en]

    Sm2O3-doped barium titanate ceramics with a positive temperature coefficient of resistivity (PTCR) were synthesized by solid-state reaction sintering. The electrical properties are related to the dopant content. The grain size decreases with increasing dopant content. Electron diffraction analysis revealed that a secondary phase with a space group of P6(3)22 and lattice parameters a = 10.6 Angstrom and c = 20.2 Angstrom formed in the ceramics.

  • 31.
    Luberry, Claire
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Morphological control of Ceria particles by precipitation method2011Independent thesis Advanced level (degree of Master (One Year)), 30 credits / 45 HE creditsStudent thesis
  • 32.
    Munoz, Romain
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Co-precipitation of Y2O3 powder2011Independent thesis Advanced level (degree of Master (One Year)), 30 credits / 45 HE creditsStudent thesis
  • 33. Murugesan, S.
    et al.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Direct evidence for purely silver ion conduction in Cul-doped silver oxysalt superionic systems: Combined electrolysis and EDS studies2007In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 52, no 28, p. 8064-8068Article in journal (Refereed)
    Abstract [en]

    Maiden attempt has been made for the direct estimation of the contributions of silver and copper ions to the ionic conductivity in superionic solids obtained in CuI-doped silver oxysalt systems. The application of the combined electrolysis and EDS techniques towards qualitative and quantitative analyses of the mobile ionic species in solid electrolyte systems having more than one possible mobile ion is reported. These studies confirmed that these electrolyte materials are purely Ag+ conducting up to 50 mol% CuI in xCuI-(100-x)[2Ag(2)O-0.7V(2)O(5)-0.3B(2)O(3)] and xCuI-(100 - x)[Ag2O-0.7MoO(3)-0.3WO(3)] systems and small fraction of t(Cu+) exists above 60 mol% CuI. These solid electrolyte materials exhibited a high ionic transport numbers (t(i)) of >0.985 and the t(i) increases when two glass formers are used.

  • 34. Murugesan, S.
    et al.
    Wijayasinghe, A.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Ion transport studies in CuI-doped silver borovanadate glassy system2008In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 354, no 10-11, p. 1066-1073Article in journal (Refereed)
    Abstract [en]

    In the present report, ionic transport properties and microstructural investigations of superionic materials in a cost-effective glassy system xCuI-(100 - x)[2Ag(2)O-0.7V(2)O(5)-0.3B(2)O(3)], where x = 30, 40, 45, 50 and 60, have been described. The temperature dependent electrical conductivity studies were carried out by ac impedance analysis. The microstructure of the materials studied by SEM indicated the presence of dispersed CuO and AgI micro-crystals in the silver oxysalt glass matrix. High room temperature electrical conductivity of 3.58 x 10(-3) S cm(-1) and low activation energy of 0.24 eV were obtained for the best conducting composition. The ac impedance data were analyzed using impedance and modulus formalisms. These materials show extremely high t(i) value of 0.999 and the ionic conductivity is apparently due to Ag+ ions only. The use of two glass formers helped to form materials with higher T-g, higher thermal stability and better ionic transport properties.

  • 35. Murugesan, S.
    et al.
    Wijayasinghe, A.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Preparation and characterization of CuI-doped silver borovanadate superionic system2007In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 178, no 11-12, p. 779-783Article in journal (Refereed)
    Abstract [en]

    A new cost effective glassy/crystalline superionic system xCul-(100-x)[2Ag(2)O-0.7V(2)O(5)-0.3B(2)O(3)], where x=30, 40, 45, 50 and 60, has been prepared by melt quenching technique and the ionic transport properties were studied. The phase analysis and thermal properties of the samples carried out using XRD, FTIR and DSC techniques confirmed the glassy-crystalline composite nature of the prepared materials. DSC analyses indicated the crystallization of some phases between 130 and 170 degrees C and the subsequent melting of these crystallized phases in the temperature range of 200-250 degrees C. The room temperature electrical conductivity studies were carried out by a.c. impedance analysis. High room temperature electrical conductivity of 3.58 x 10(-3) S cm(-1) was obtained for the best conducting composition. These materials show high t(Ag+) value of 0.997. The use of two glass formers helped to form materials with higher T, higher thermal stability and better ionic transport properties.

  • 36.
    Qadeer, Muhammad Ifran
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Azhdar, Bruska
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Hedenqvist, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Savage, Steven J.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Improved oxidation resistance of SmCo magnetic alloy powders by silanization2013In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 76, no 1, p. 94-100Article, review/survey (Refereed)
    Abstract [en]

    The thermal stability of Sm2Co17 powders coated with four different silanes was studied between 25 degrees C and 500 degrees C and isothermally at 400 degrees C. Thermogravimetry data indicated that the silane-based coatings provided improved oxidation resistance. The microstructural analysis of uncoated powders oxidized for 10 h at 400 degrees C revealed the formation of a featureless ca. 10 mu m thick shell, surrounding the unreacted core. The development of this shell was attributed to the inward diffusion of oxygen, decomposition of intermetallic phases and redistribution of alloying elements. The EDS elemental maps revealed that the shell was rich in O, Fe and Co, and depleted in Sm, Zr and Cu. In the presence of the silane-based coatings the thickness of the shell was reduced by more than 80% (to less than 2 mu m) and the redistribution of alloying elements was insignificant. Based on the thermogravimetric analysis at or above ca. 400 degrees C and the nnicrostructural analysis it was possible to assess the relative effectivity of the different silanes in preventing the oxidation of the SmCo powder. Methyltrimethoxysilane (MTMS), which also formed the thinnest coating, was the best silane. (3-Glycidyloxypropyl)trimethoxysilane, forming a thicker coating, was less effective than MTMS, but superior to the two amine-functionalized silanes ((3-aminopropyl)triethoxysilane and (3-aminopropyl)trimethoxysilane).

  • 37.
    Qadeer, Muhammad Ifran
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Azhdar, Bruska
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Savage, Steven J.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    The Effect of Silanisation on Microstructural Stability and Magnetic Properties of the Intermetallic Sm2(Co, Fe, Cu, Zr)172011In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 1295, p. 443-448Article in journal (Refereed)
    Abstract [en]

    The effects of silanising using the coupling agent γ-glycidoxpropyltrimethoxysilane on microstructural stability and magnetic properties of Sm-Co powder particles have been investigated. The silanisation provides structural stability by improving the oxidation resistance at 400oC for 10 hours. The untreated particles undergo microchemical changes by redistribution of alloying elements which mainly accumulate in parallel black and grey streaks in the interior of the particles. The silanised particles after heat treatment show coercivity of 836 Oe and the untreated particles show a much lower coercivity of 376 Oe. The difference in magnetic properties of uncoated particles is caused by diffusion of oxygen and microstructural instability.

  • 38.
    Qadeer, Muhammad Ifran
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Savage, Steven J.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Hedenqvist, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    High temperature magnetic properties of Sm-Co and Sm-Co/polyamide-12 materials: effects of temperature, particle size, and silanization2013In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, no 23, p. 8163-8170Article in journal (Refereed)
    Abstract [en]

    There is an increasing demand for polymer-bonded magnets (PBM) in high temperature applications. While most research deals with high temperature properties of NdFeB-PBM, only a few studies consider Sm-Co PBM. Therefore, this study, on the thermal and magnetic properties of Sm-Co alloy powders and blends of these with polyamide-12 (PA12), was undertaken. Since the Sm-Co powders were the product of ball milling, they contained a variety of shapes and sizes. Studies on size fractions of these showed that the thermal stability and magnetic properties were improved as the particle size increased. It was suggested that higher residual strains and smaller crystallite sizes in the small particles were responsible for a decrease in the thermal stability and magnetic properties. In addition, energy dispersive X-ray spectroscopy revealed that the oxygen content increased with decreasing particle size (larger specific surface area) and higher oxygen content was possibly also responsible for a decrease in the magnetic properties. It was shown that, in general, the surface modification by silanization, using (3-aminopropyl)trimethoxsilane, increased the saturation magnetization and remanence of both the particles and the Sm-Co/PA12 composite. The silanization also improved the thermal stability of the particles.

  • 39.
    Qadeer, Muhammad Irfan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    SmCo for polymer bonded magnets: Corrosion, silanization, rheological, mechanical and magnetic properties2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents the study of organofunctional alkoxysilane coatings to prevent high temperature oxidation of Sm-Co powders. Sm-Co are important permanent magnetic alloys, owing to their high Curie temperature and large values of magnetocrystalline anisotropy. They possess stable magnetic properties in the temperature range -40 to 120 °C which makes them very attractive candidates for automobile’s electric motors. However, the environmental conditions for such applications are a sum of high temperatures, humidity, fuels and salts which provide perfect breeding ground for corrosion.

    In this study we report the high temperature oxidation resistance of Sm2Co17 powders coated with four common commercially available organofunctional silanes; (3-aminopropyl)trimethoxysilane (APTMS), (3-aminopropyl)triethoxysilane (APTES), methyltrimethoxysilane (MTMS) and (3-glycidyloxypropyl)trimethoxysilane (GPTMS).

    The as received powder was a multimodal mixture of many sizes and shapes which represented a typical ball milling product. The thermal analyses of the powders suggested that the powders without surface coatings had profound affinity towards oxidation. The thermal properties of sieved uncoated powders revealed that the small powders were more susceptible to oxidation than the large powders due to their large specific surface area.

    The isothermal properties of coated powders revealed that the powders coated with silanes had at least 10 times higher resistance to oxidation as compared to uncoated powders heated at 400 °C for 10 h. The non-isothermal tests conducted from room temperature to 500 °C also revealed that the uncoated powders gained 6 times more mass as compared to the powders coated with an ideal (MTMS) silane.

    The microstructural analysis of the uncoated powders heated from 400 °C to 550 °C revealed diffusion of oxygen, instable intermetallic phases which resulted in a redistribution of alloying elements, precipitation of alloying elements and formation of a featureless shell (approximately 20 µm in thickness) that surrounded the unreacted core. The coated powders on the other hand showed homogenous distribution of alloying elements, stable intermetallic phases and limited the shell thickness (1 µm).

    The thermo-magnetic properties of Sm-Co powders showed that the thermal instability also affected the magnetic properties adversely. It was found that the magnetic properties were deteriorated with a decrease in powder size. The energy dispersive spectroscopic (EDS) analyses showed that the small powders contained higher oxygen content than the large powders. Moreover XRD analysis also revealed that the small powders contain higher residual strains and smaller crystallite size which can play their role in deteriorating magnetic properties.

    It was found that surface modification by silanization improve the thermo-magnetic properties by effectively shielding the powder surfaces from surface oxidation.

    The rheological properties Sm-Co/PA12 composites revealed that the viscosity of the composites was increased with decreasing powder size due to the presence of rough surfaces and sharp corners in small powders. The rheological properties of the melts containing coated powders revealed that the silane layer acted as a lubricant and decreased the melt viscosity. It was found that coating the powders with silanes not only improve the rheological properties but also improve the other physical properties such as glass transition temperature the loss modulus by modifying the interfacial layer between the polymer matrix (PA12) and the powder. It results in a decrease in viscosity, a broadening of the glass transition temperature and a change in the damping properties of the composites.

    The dynamic mechanical properties of Sm-Co/PA12 composites showed that the storage modulus was increased with decreasing powder size. The results were expected as the rough surfaces act as local welding points between the powder and the polymer matrix. It was found that the surface modification improve the storage modulus. It is assumed that the silanes modify the interfacial properties which not only resulted in increasing the storage modulus but also broadened the glass transition temperature, Tg and damping, tanδ peaks.

    From the thermogravimetric, microstructural, rheological and magnetic analyses it can be concluded that the silanes are the effective coatings in preventing high temperature oxidation, stabilizing microstructure, enhancing mechanical properties, and improving rheological and magnetic properties.

  • 40.
    Ragnarsson, Lars
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Ek, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Eliasson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Flow pattern in ingot during mould filling and its impact on inclusion removal2010In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 37, no 5, p. 347-352Article in journal (Refereed)
    Abstract [en]

    A two-dimensional non-steady state computational fluid dynamic model was employed to gain a basic understanding of the flow in the ingot during casting. The surface velocity was found to be affected by the inlet angle and was found to vary with the casting level. The information of surface velocity was related to the probability of the inclusion removal. Water model experiments were also conducted to help the understanding. The model calculation revealed the same trends as the results of water model experiments. Both computational fluid dynamic data and the physical modelling showed that the inlet angle of 5 degrees currently used in the industry was a good alternative regarding inclusion removal. The present work suggests strongly that the melting shop should try to obtain a liquid or semiliquid film at as early stage as possible in ingot casting.

  • 41. Smuk, O.
    et al.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    The effect of copper on secondary phase precipitation in duplex stainless steel - a thermodynamic calculations approach2005In: Zeitschrift für Metallkunde, ISSN 0044-3093, Vol. 96, no 8, p. 918-923Article in journal (Refereed)
    Abstract [en]

    Thermodynamic calculations with Thermo-Calc software and the steel database TCFE3 was applied to investigate the precipitation behavior of industrial grades of duplex stainless steels with high copper content, 1.6 and 2.3 wt.%, Duplok 27 and DUP 27, respectively. Well-documented super duplex stainless grade SAF 2507 with copper content of 0.20 wt.% was used as the reference steel. The results of the calculations are compared with the experimental results obtained previously for these steels. It is shown that copper decreases the high-temperature limit of precipitation of sigma and chi phases and reduces the equilibrium amount of precipitated chi phase. Copper addition to a duplex stainless steel facilitates precipitation of chromium nitride phase and stabilizes it at elevated temperatures. The ferrite-austenite balance at high temperatures is also affected in these steels by the copper addition.

  • 42. Stuer, M.
    et al.
    Carry, C. P.
    Bowen, P.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Comparison of apparent activation energies for densification of alumina powders by pulsed electric current sintering (spark plasma sintering) and conventional sintering - Toward applications for transparent polycrystalline alumina2017In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 32, no 17, p. 3309-3318Article in journal (Refereed)
    Abstract [en]

    In the quest for high real in-line transmittances for transparent polycrystalline alumina (PCA), we need defect free processing. One of the biggest advances in producing high density defect free ceramics over recent years has been the advent of spark plasma sintering (SPS) or pulsed electric current sintering. The production of PCA with high transmittances >60% has been demonstrated, but the mechanisms behind this fast, pressure aided sintering method are still much debated. Here, we investigate the sintering of doped α-alumina powders using traditional and pulsed electric current dilatometry. We demonstrate that at the final sintering stage, there is no major difference in the sintering mechanisms between conventional sintering and SPS sintering. High densification rates occurring in SPS are shown to be related to powder reorientation at the very early sintering stage and viscous-flow dominated densification in the intermediate sintering cycle. This paper clarifies what parameters in the processing-sintering domain have to be improved for even higher real in-line transmittances for PCA.

  • 43. Stuer, Michael
    et al.
    Bowen, Paul
    Cantoni, Marco
    Pecharroman, Carlos
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Nanopore Characterization and Optical Modeling of Transparent Polycrystalline Alumina2012In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 22, no 11, p. 2303-2309Article in journal (Refereed)
    Abstract [en]

    Production of transparent ceramics has become a topic of resurgent interest in recent years, with its promise of near-net shaping appealing to applications ranging from biomedicine to solar energy. However, the mechanisms governing ceramic transparency, translucency, and opaqueness are not entirely understood. Models of both grain boundary and pore scattering have been proposed, but too often without sufficient experimental corroboration. An extensive experimental analysis of transparent alumina samples is presented, establishing a first direct link between the observed transparency, defect size, and porosity. Given the unprecedented experimental detail from the full 3D pore reconstruction from the FIB tomography, how to correctly interpret the experimentally observed transparency is additionally shown. The unprecedented experimental and theoretical agreement for the first time identifies the relative contributions of different scattering mechanisms, thereby paving the way forward for microstructural tuning of transparent polycrystalline alumina.

  • 44. Stuer, Michael
    et al.
    Carry, Claude Paul
    Bowen, Paul
    Zhao, Zhe
    KTH, School of Chemical Science and Engineering (CHE), Chemistry. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Comparison of apparent activation energies for densification of alumina powders by pulsed electric current sintering (spark plasma sintering) and conventional sintering-toward applications for transparent polycrystalline alumina2017In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 32, no 17, p. 3309-3318Article in journal (Refereed)
    Abstract [en]

    In the quest for high real in-line transmittances for transparent polycrystalline alumina (PCA), we need defect free processing. One of the biggest advances in producing high density defect free ceramics over recent years has been the advent of spark plasma sintering (SPS) or pulsed electric current sintering. The production of PCA with high transmittances >60% has been demonstrated, but the mechanisms behind this fast, pressure aided sintering method are still much debated. Here, we investigate the sintering of doped a-alumina powders using traditional and pulsed electric current dilatometry. We demonstrate that at the final sintering stage, there is no major difference in the sintering mechanisms between conventional sintering and SPS sintering. High densification rates occurring in SPS are shown to be related to powder reorientation at the very early sintering stage and viscous-flow dominated densification in the intermediate sintering cycle. This paper clarifies what parameters in the processing-sintering domain have to be improved for even higher real in-line transmittances for PCA.

  • 45.
    Wang, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Guo, Peng
    Guo, Qiangsheng
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Zhao, Zhe
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Fabrication of novel g-C3N4/nanocage ZnS composites with enhanced photocatalytic activities under visible light irradiation2014In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 16, no 21, p. 4485-4492Article in journal (Refereed)
    Abstract [en]

    In order to develop efficient visible light-driven photocatalysts for environmental applications, novel g-C3N4/nanocage ZnS composites have been successfully fabricated via an anion exchange route using ZIF-8 as a self-sacrificing template. The as-prepared g-C3N4/ZnS composites were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy and photoluminescence. In addition, the photocatalytic oxidation of organic contaminants in aqueous solution was investigated with the g-C3N4/ZnS composite system under visible light irradiation by using rhodamine B as a model compound. The results indicate that the g-C3N4/ZnS composite photocatalysts show higher photocatalytic activity than the single component (pure g-C3N4 or ZnS). More specifically, the optimum photocatalytic activity of the g-C3N4/ZnS composite was achieved with a weight ratio of 6 : 1, which is as high as 37.8 and 2.8 times those of individual ZnS and g-C3N4 under visible light irradiation. The enhanced photocatalytic activity of g-C3N4/ZnS is mainly attributed to an efficient electron-hole separation at the interface of the two semiconductors, as determined by photoluminescence spectroscopy. Moreover, it is observed that. O-2 is the main active species in the photocatalytic oxidation of RhB solution using a g-C3N4/nanocage ZnS composite.

  • 46. Wijayasinghe, A.
    et al.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Lagergren, Carina
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    LiFeO2-LiCoO2-NiO materials for Molten Carbonate Fuel Cell cathodes. Part I: Powder synthesis and material characterization2006In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 177, no 1-2, p. 165-173Article in journal (Refereed)
    Abstract [en]

    Ternary compositions of LiFeO2LiCoO2 and NiO are expected to posses desirable characteristics for the Molten Carbonate Fuel Cell (MCFC) cathode application. This paper presents a detailed description of the synthesis of LiFeO2-LiCoO2-NiO powders as well as dense sintered materials together with a brief discussion on the common aspects and trends observed in the characterization of these materials for MCFC cathode application. Feasibility of two wet-chemical powder preparation techniques, the Pechini method and the glycine-nitrate method, was investigated to obtain powders with characteristics appropriate for cathode fabrication. Materials in the LiFeO2-NiO binary system and five ternary subsystems, each with a constant molar ratio of LiFeO2/NiO while varying LiCoO2 content, were studied. Powders with characteristics appropriate for MCFC cathode fabrication could be obtained by the Pechini method. The particle size of LiFeO2-LiCoO2-NiO powders considerably depends on the calcination temperature and the material composition. The electrical conductivity study reveals the ability of preparing LiFeO2-LiCoO2-NiO materials with adequate electrical conductivity for MCFC cathode application.

  • 47. Wijayasinghe, A.
    et al.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Lagergren, Carina
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    LiFeO2-LiCoO2-NiO materials for Molten Carbonate Fuel Cell cathodes. Part II. Fabrication and characterization of porous gas diffusion cathodes2006In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 177, no 1-2, p. 175-184Article in journal (Refereed)
    Abstract [en]

    LiFeO2-LiCoO2-NiO ternary materials are considered as more viable alternatives to lithiated NiO2 in solving the cathode dissolution problem of the Molten Carbonate Fuel Cell (MCFC). This paper presents a detailed description of fabrication and characterization of LiFeO2-LiCoO2-NiO porous gas diffusion cathodes for MCFC, together with a brief discussion on the limitations and trends observed in cathode optimization. Several LiFeO2-LiCoO2-NiO ternary compositions and a LiFeO2-NiO binary composition, were fabricated into porous cathodes by tape casting and sintering. The sintered cathodes were subjected to phase analysis, electrical conductivity and pore structural characterization. A bimodal pore structure, appropriate for the MCFC cathode, could be achieved in sintered cathodes prepared using poreformers and sub-micron size powders. The amount of poreformers significantly influences the pore structure and the electrical conductivity of sintered cathodes. Furthermore, this study indicates the nature of the compromise to be made between the electrical conductivity, phase purity, pore structure and porosity in optimization cathodes for the MCFC application.

  • 48.
    Wijayasinghe, Athula
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Lagergren, Carina
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    LiFeO2-LiCoO2-NiO cathodes for molten carbonate fuel cells2005In: / [ed] Pierre Taxil, Catherine Bessada, Michel Cassir, Marcelle Gaune-Escard, 2005, p. 425-429Conference paper (Other academic)
  • 49. Zhang, H.
    et al.
    Li, Z. C.
    Bergman, Bill
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Zou, X. D.
    Investigation of La9.33Si6O26 oxygen ionic conductor2007In: Journal of Materials Science & Technology, ISSN 1005-0302, Vol. 23, no 5, p. 629-632Article in journal (Refereed)
    Abstract [en]

    La9.33Si6O26 oxygen ionic conductor was synthesized by solid state reaction method. Its structure was determined by single-crystal X-ray diffraction analysis at room temperature. The results showed that La9.33Si6O26 oxide has the apatite structure with space group P6(3)/m. AC impedance measurements indicated that the oxides sintered in nitrogen have much higher conductivity than those sintered in air. The effects of grain boundaries on the conductivity were discussed.

1 - 49 of 49
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