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  • 1. Aastrup, T.
    et al.
    Wadsak, M.
    Leygraf, Christofer
    KTH, Superseded Departments, Materials Science and Engineering.
    Schreiner, M.
    In situ studies of the initial atmospheric corrosion of copper influence of humidity, sulfur dioxide, ozone, and nitrogen dioxide2000In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 147, no 7, p. 2543-2551Article in journal (Refereed)
    Abstract [en]

    Infrared reflection absorption spectroscopy and quartz crystal microbalance, integrated into a one-surface analytical system, and complemented with tapping mode atomic force microscopy, has been used to explore the metal/atmosphere interfacial region under atmospheric pressure conditions. This unique combination of ill situ techniques, all possessing submonolayer sensitivity, has revealed information on the different accelerating roles of ozone (O-3) and nitrogen dioxide (NO2) on the SO2-induced atmospheric corrosion of copper. The formation of reaction products could be followed quantitatively with respect to chemical identity and kinetics. Exposure in SO2-containing humidified air resulted in CuSO3. xH(2)O-like species, formed atop a cuprous oxide, designated Cu2O, all over the copper surface. O-3 introduction resulted in an accelerated mass gain with an increased formation rate of both Cu2O and of CuSO4. xH(2)O all over the surface. NO2 introduction resulted in less mass gain than observed under SO2 and O-3, with no formation of new Cu2O, an initial oxidation of CuSO3. xH(2)O to CuSO4. xH(2)O, and with sulfite oxidation gradually replaced by copper nitrate formation, possibly as CuNO3(OH)(3) The formation rates of the dominating end products, CuSO4. xH(2)O in SO2/O-3 and Cu2NO3(OH)(3) in SO2/NO2 seemed to be limited by the supply of the gaseous constituents.

  • 2. Aastrup, T.
    et al.
    Wadsak, M.
    Schreiner, M.
    Leygraf, Christofer
    KTH, Superseded Departments, Materials Science and Engineering.
    Experimental in situ studies of copper exposed to humidified air2000In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 42, no 6, p. 957-967Article in journal (Refereed)
    Abstract [en]

    Three complementary experimental techniques for in situ surface analysis have been combined for the first time in order to explore the chemistry and physics of a copper surface exposed to humidified air. Infrared reflection absorption spectroscopy, quartz crystal microbalance and atomic force microscopy provide a congruent picture of the processes occurring at the surface. At a given relative humidity, cuprous oxide forms according to an approximately logarithmic rate law. In addition, an aqueous adlayer of constant mass physisorbs on the surface. Increased relative humidity stimulates the physisorption of water and enhances the nucleation rate of oxide grains, thereby increasing the formation rate of cuprous oxide.

  • 3.
    Aastrup, Teodor
    KTH, Superseded Departments, Materials Science and Engineering.
    In situ investigations of the metal/atmophere interface1999Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis presents a new experimental setup for surfaceanalysis studies, incorporating chemical information frominfrared reflection absorption spectroscopy (IRAS) andquantitative information from quartz crystal microbalance(QCM). The integrated IRAS/QCM surface analysis system enablesin situstudies to be conducted of the metal/atmosphereinteraction on a sub-monolayer level. In combination withtopographical information from tapping mode atomic forcemicroscopy (TM-AFM), it was possible to follow the formation ofcorrosion products providing information about chemicalidentity, quantity and lateral distribution. The newlydeveloped system was used to study the influence of relativehumidity (RH) and levels of sulfur dioxide (SO2), ozone (O3)and nitrogen dioxide (NO2) down to concentrations of subparts-per-million (ppm), on the initial stages of atmosphericcorrosion of copper.

    Exposure to RH led to the formation of small grains ofcuprous oxide (Cu2O), with an average diameter of approximately40 nm. The grain nucleation rate increased with increasing RHdue to the increasing amount of physisorbed water on thesurface.

    Exposure to RH and SO2 led to the formation of coppersulfite (CuSO3•xH2O) species as well as reduction in therate of Cu2O formation. The formation of CuSO3•xH2Ooccurred through the dissolution and consecutive precipitationof surface-bound copper sulfite complexes.

    The roles of O3 and NO2 in the SO2-induced atmosphericcorrosion of copper was also investigated. O3 was found to havea two-fold effect, resulting in the oxidation of the coppersulfite species to copper sulfate and the enhancement of Cu2Oformation. NO2 promoted the oxidation of copper sulfitespecies, though less efficiently than O3, and reduced Cu2Oformation. In addition, copper nitrate formation wasobserved.

    IRAS was also used to investigate the interaction betweenSO2 and surfaces made of platinum and palladium. Sulfuric acidformation was observed on both metals, showing the importanceof the surface on the formation of the metal/atmospherereaction products.

    Keywords:Atmospheric corrosion, IR-spectroscopy, IRAS,QCM, AFM, SO2, O3, NO2, Cu.

  • 4. Abe, T.
    et al.
    Sundman, Bo
    KTH, Superseded Departments, Materials Science and Engineering.
    A description of the effect of short range ordering in the compound energy formalism2003In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 27, no 4, p. 403-408Article in journal (Refereed)
    Abstract [en]

    The current state of the compound energy formalism (CEF) to model ordering and the technique to handle short range ordering (SRO) were discussed. Although there are some methods which allow better treatment for SRO, such as the cluster variation method (CVM) or the Monte Carlo method (MC), these methods are difficult to handle in multi-component systems because of their complexity. In the compound energy formalism, SRO is not explicitly described. However it is possible to take the contribution of SRO to the Gibbs free energy into account through the reciprocal parameter, which has the same concentration dependency as DeltaG(m)(SRO). Introducing the reciprocal parameter of the form, L-i,L-j:i,L-j for the two sublattice model and L-i,L-j:i,L-j:*:* for the four sublattice model, one can satisfactorily describe the contribution of SRO to the Gibbs free energy in the CEF.

  • 5. Abrikosov, I. A.
    et al.
    Olovsson, W.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Valence-band hybridization and core level shifts in random Ag-Pd alloys2001In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 8717, no 17Article in journal (Refereed)
  • 6.
    Adamopoulos, Othon
    KTH, Superseded Departments, Materials Science and Engineering.
    A study on nanosized certium oxides systems for environmental catalysis2003Licentiate thesis, comprehensive summary (Other scientific)
  • 7.
    Agde Tjernlund, Jessica
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gamstedt, Kristofer
    KTH, Superseded Departments, Solid Mechanics.
    Xu, Zhi-Hui
    KTH, Superseded Departments, Materials Science and Engineering.
    Influence of molecular weight on strain-gradient yielding in polystyrene2004In: Polymer Engineering and Science, ISSN 0032-3888, E-ISSN 1548-2634, Vol. 44, no 10, p. 1987-1997Article in journal (Refereed)
    Abstract [en]

    Experimental observations have indicated that the presence of strain gradients has an influence on the inelastic behavior of polymers as well as in other materials such as ceramics and metals. The present study has experimentally quantified length-scale effects in inelastic deformations of the polymer material polystyrene (PS) with respect to the molecular length. The experimental technique that has been used is nano-indentation to various depths with a Berkovich indenter. The hardness has been calculated with the method by Oliver and Pharr, and also by direct measurements of the area from atomic force microscopy. The experiments showed that the length-scale effects in inelastic deformations exist in polystyrene at ambient conditions. The direct method gave a smaller hardness than the Oliver-Pharr method. It was also shown that the length-scale parameter according to Nix and Gao increases with increasing molecular weight. For high molecular weights above a critical value of entanglement, there was no pertinent increase in the length-scale parameter. The length-scale parameter for strain-gradient plasticity has a size of around 0.1 μm for polystyrene.

  • 8.
    Ahlberg Tidblad, Annika
    KTH, Superseded Departments, Materials Science and Engineering.
    Surface characterization of the chromium hydroxide and basic calcic deposition layers formed on the steel cathode in the chlorate production process1999Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    During technical service, the surface of the steel cathodein the chlorate production process changes with respect tochemical composition and morphology. Deposition of insolublespecies from the electrolyte and corrosion products from thebase metal accumulate and form surface layers that influencethe cathode activity with regards to hydrogen evolution, theprimary reaction, as well as to various parasitic reactions.Improving the activity on the cathode side could reduce theproduction cost of chlorate significantly. Surface analysis hasbeen performed on the thin film formed by reduction of chromateand the layer consisting of basic calcium and magnesiumspecies.

    Small amounts of sodium chromate are added to the chloratebrine in order to improve the current efficiency of theprocess. Chromate is reduced and forms a thin film withselective permeability that hinders parasitic reduction ofhypochlorite and chlorate ions.Ex situsurface analysis with ESCA and GD-OES were usedin combination within situspectroscopic ellipsometry. Several experimentaldifficulties had to be overcome in order to performellipsometric measurements. The surface film was identified asa hydrated chromium(III) hydroxide, Cr(OH)3*x H2O. The film grows homogeneously on the substrateand attains a maximum thickness of 1-10 nm, depending onchromate concentration, cathodic polarization and substratematerial. The thickness of a monolayer is approximately 0.5 nm.The chemical composition and structural arrangement areconstant during growth and dissolution of the surface productsignificant.

    Industrial brine contains ppm levels of calcium andmagnesium impurities and carbonate and sulfate ions,<1 g l-1Na2CO3and 10-20 g l-1Na2SO4. Hydrogen gas evolution produces hydroxide ionsand a steep gradient with elevated pH forms in the vicinity ofthe cathode, where various calcium and magnesium saltsprecipitate and form a thick surface layer, 1-1000 µm. Thecalcic deposit is nonconductive and causes cathodicoverpoteniallosses. Characterization using SEM/EDS shows thatthe layer consists of a mixture of calcium hydroxide/carbonate,magnesium hydroxide and sodium sulfate species, which wasconfirmed by an independent kinetic model. The model treatscomplex chemical processes in great detail and employsliterature data for model parameters. To the author'sknowledge, this is the first published attempt at modeling thechemical aspects of the formation of the calcic layer. Thecalcium/magnesium ratio is 3-5, which is higher than predictedby the model, due to the superior ability of calcium to formsoluble complexes and precipitate close enough to beincorporated in the surface layer. High calcium concentrationspromote distinct crystals and dense deposits. Magnesium reducesparticle size and increases the insulating properties of thelayer. Carbonate and sulfate ions contribute to increasingstructural disorder. Precipitation of sodium sulfate onlyoccurs above a critical concentration of sulfate, estimated to25 g l-1Na2SO4. Sodium sulfate precipitates as Na2SO4or as NaClO3*3Na2SO4at high chlorate concentrations.

    Key words: chlorate cathode processes,chromium(III)hydroxide film, calcic deposit, ESCA, GD-OES,SEM/EDS, spectroscopic ellipsometry, kinetic modeling

  • 9. Ahlen, N.
    et al.
    Johnsson, M.
    Larsson, A. K.
    Sundman, Bo
    KTH, Superseded Departments, Materials Science and Engineering.
    On the carbothermal vapour-liquid-solid (VLS) mechanism for TaC, TiC, and TaxTi1-xC whisker growth2000In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 20, no 14-15, p. 2607-2618Article in journal (Refereed)
    Abstract [en]

    The growth of TaC, TiC and TaxTi1-xC whiskers has been studied in some detail. The whiskers were synthesised via a vapour-liquid-solid (VLS) growth mechanism in the temperature range 1220-1400 degreesC. The starting materials were Ta2O5, TiO2, C, NaCl, and a catalyst metal (Ni, Co, Fe, and Cu were tested). The main reaction during synthesis was a carbothermal reduction of Ta2O5 and TiO2, and NaCl was added to form the oxochlorides and chlorides of Ta and Ti that account for the transport to the catalyst metal. The syntheses were made in a protecting Ar atmosphere. From experiments interrupted after different times at the synthesis temperature it is clear that sodium tantalates form as intermediate products, whereas sodium titanates cannot be identified. Only metals that are able to dissolve the elements building up the whiskers work as catalysts. Whisker growth starts either from a catalyst droplet in contact with carbon or from an oxide particle in contact with both catalyst metal and carbon. For TaC and TaxTi1-xC the only growth direction observed is [100], while TiC may grow either along [100] or along [111].

  • 10. Ahuja, R.
    et al.
    Dubrovinsky, L.
    Dubrovinskaia, N.
    Guillen, J. M. O.
    Mattesini, M.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Le Bihan, T.
    Titanium metal at high pressure: Synchrotron experiments and ab initio calculations2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 18Article in journal (Refereed)
  • 11. Ahuja, R.
    et al.
    Eriksson, O.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Electronic and optical properties of BaTiO3 and SrTiO32001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 4, p. 1854-1859Article in journal (Refereed)
  • 12. Ahuja, R.
    et al.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Theoretical prediction of the Cmca phase in Ge under high pressure2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 89, no 5, p. 2547-2549Article in journal (Refereed)
  • 13. Ahuja, R.
    et al.
    Rekhi, S.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Theoretical prediction of a phase transition in gold2001In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 6321, no 21Article in journal (Refereed)
  • 14.
    Ahuja, Rajeev
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Osorio-Guillen, J. M.
    de Almeida, J. S.
    Holm, B.
    Ching, W. Y.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Electronic and optical properties of gamma-Al2O3 from ab initio theory2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 16, p. 2891-2900Article in journal (Refereed)
    Abstract [en]

    We report on a density functional theory calculation of the electronic structure and optical properties of gamma-Al2O3. We have made a comparison between the optical and electronic properties of the alpha and gamma phases of alumina. The calculated bulk modulus of the gamma phase is slightly lower than that of the a phase. The calculated static dielectric function and the optical constant of the gamma phase are very close to those of the alpha phase.

  • 15.
    Ahuja, Rajeev
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Persson, Clas
    da Silva, A. F.
    de Almeida, J. S.
    Araujo, C. M.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Optical properties of SiGe alloys2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 7, p. 3832-3836Article in journal (Refereed)
    Abstract [en]

    The optical properties of Si1-xGex have been investigated theoretically using a full-potential linear muffin-tin-orbital method. We present the density-of-states as well as the real and imaginary parts of the dielectric function. The calculated dielectric function was found to be in good agreement with the spectroscopic ellipsometry measurements by J. Bahng , J. Phys.: Condens. Matter 13, 777 (2001), and we obtained a static dielectric constant of epsilon(0)=12.19+2.45x in the Si rich regime (xless than or equal to0.5).

  • 16. Akerman, J. J.
    et al.
    Venturini, E. L.
    Siegal, M. P.
    Yun, S. H.
    Karlsson, U. O.
    Rao, K. V.
    KTH, Superseded Departments, Materials Science and Engineering.
    Two-stage crossover from thermal to quantum flux creep of dilute vortex ensembles in various high-T-c superconducting thin films2001In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 64, no 9Article in journal (Refereed)
    Abstract [en]

    The thermal-to-quantum flux creep crossover at low vortex densities has been studied in YBa2Cu3O7, TlBa2CaCu2O7-delta, and HgBa2CaCu2O6+delta thin films using ac susceptibility. The crossover temperatures T-cr are 10-11, 17, and 30 K, respectively. Both thermal and quantum flux creep is suppressed as the vortex density is decreased. We observe a two-stage nature in the crossover behavior which appears to be a general property of all the three materials studied.

  • 17. Akerman, J. J.
    et al.
    Yun, S. H.
    Karlsson, U. O.
    Rao, K. V.
    KTH, Superseded Departments, Materials Science and Engineering.
    Dislocation-mediated creep of highly separated vortices in a-axis-oriented HgBa2CaCu2O6+delta thin films2001In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 64, no 2Article in journal (Refereed)
    Abstract [en]

    Using ac susceptibility, we determine the critical current density J(c) and the flux creep activation energy U of an a-axis-oriented HgBa2CaCu2O6+delta thin film. The critical current density at helium temperatures is found to be 4.6 x 10(4) A/cm(2), i.e., about two orders of magnitude smaller than for corresponding films with c-axis orientation. The temperature and ac field dependent activation energy is consistent with dislocation-mediated flux creep and well described by U(T,H-ac)=U-o(1-t(4))H-ac(-1/2) with t=T/T-c, T-c=120K, and U-o = 0.77 eV Oe(1/2) for temperatures T>45 K and in the field range studied. The activation energy is of the same order as that found in c-axis-oriented films. Below T = 45 K the activation energy is observed to decrease as thermally assisted quantum creep becomes increasingly important.

  • 18. Alexis, J.
    et al.
    Ramirez, M.
    Trapaga, G.
    Jönsson, Pär
    KTH, Superseded Departments, Materials Science and Engineering.
    Modeling of a DC electric arc furnace - Heat transfer from the arc2000In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 40, no 11, p. 1089-1097Article in journal (Refereed)
    Abstract [en]

    A mathematical model describing heat and fluid flow in an electric are has been developed and used to predict heat transfer from the are to the steel bath in a DC Electric Are Furnace. The are model takes he separate contributions to the heat transfer from each involved mechanism into account, i.e. radiation, convection, condensation and energy transported by electrons. The model predicts heat transfer for different currents and are lengths. Model predictions show that are efficiency is higher for lower power input. The model also predicts shear stresses and current density distribution at the steel surface. This information can be used as boundary condition input to simulate the effect of heating with electrodes in a DC EAF on the heat and fluid flow in the steel bath.

  • 19.
    Alexis, Jonas
    KTH, Superseded Departments, Materials Science and Engineering.
    Modeling of the ladle furnace with emphasis on electromagnetic phenomena2000Doctoral thesis, comprehensive summary (Other scientific)
  • 20. Allen, P. D.
    et al.
    St Pierre, T. G.
    Chua-anusorn, W.
    Ström, Valter
    KTH, Superseded Departments, Materials Science and Engineering.
    Rao, K. V.
    Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin2000In: Biochimica et Biophysica Acta - Molecular Basis of Disease, ISSN 0925-4439, E-ISSN 1879-260X, Vol. 1500, no 2, p. 186-196Article in journal (Refereed)
    Abstract [en]

    Low-frequency low-field magnetic susceptibility measurements were made on four samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (') dugong liver hemosiderin; (3) thalassemic human spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. These samples were chosen because Mossbauer spectroscopic measurements on the samples indicated that they exemplified the variation in magnetic and mineral structure found in mammalian tissue iron oxide deposits. The AC-magnetic susceptometry yielded information on the magnetization kinetics of the four samples indicating samples 1, 2, and 3 to be superparamagnetic with values of around 10(11) s(-1) for the preexponential frequency factor in the Neel-Arrhenius equation and values for characteristic magnetic anisotropy energy barriers in the range 250-400 K. Sample 4 was indicated to he paramagnetic at all temperatures above 1.3 K. The AC-magnetic susceptometry data also indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Mossbauer spectroscopic data on these samples. At temperatures below 200 K, samples 1-3 exhibited Curie-Weiss law behavior, indicating weak particle-particle interactions tending to favor antiparallel alignment of the particle magnetic moments. These interactions were strongest for the dugong liver hemosiderin. possibly reflecting the smaller separation between mineral particles in this sample. This is the first magnetic susceptometry study of hemosiderin iron deposits and demonstrates that the AC-magnetic susceptometry technique is a fast and informative method of studying such tissue iron oxide deposits.

  • 21. Andersson, A. J.
    et al.
    Andersson, Margareta A.T.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, P. G.
    Use of an optimisation model for the burden calculation for the blast furnace process2004In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 33, no 3, p. 172-182Article in journal (Refereed)
    Abstract [en]

    The aim of a burden calculation in the blast furnace process is to compute the amounts of burden materials to be charged for obtaining desired hot-metal and slag composition. Burden calculations are normally based on trial-and-error instead of optimisation. In this study, the use of an optimisation model for a typical blast furnace operation is presented. The yield factors of some components, such as Mn, Si, S, P and V, used in the model have been determined. The more common distribution coefficients have also been studied. Both the yield factor and distribution coefficient values were generally good and showed stable behaviour for repeated periods under similar operational conditions. In this study, the model was found to be an excellent tool for determining burden material amounts and hot-metal and slag compositions for a blast furnace under steady and normal operation conditions. Using an optimising burden calculation model is time efficient, because it demands only 1 calculation procedure instead of a couple calculations as in the case with a trial-and-error method.

  • 22. Andersson, A. M. T.
    et al.
    Jonsson, Lage T. I.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, P. G.
    A model of reoxidation from the top slag and the effect on sulphur refining during vacuum degassing2003In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 32, no 3, p. 123-136Article in journal (Refereed)
    Abstract [en]

    A 2-dimensional fluid-flow model covering 3 phases (steel, slag and gas) has been augmented to include thermodynamic equations to study simultaneous reoxidation and desulphurization, including macro kinetic behaviour. The numerical simulations were isothermal. Predicted steel and slag component concentrations were compared with plant data from vacuum degassing and the agreement was found to be quite good. When the initial FeO content in the slag was increased, the predicted desulphurization rate decreased, the final sulphur content in the steel increased, and aluminium loss increased. When the temperature was increased, the predicted aluminium loss decreased somewhat. The effect of changes in temperature on the predicted final sulphur content was influenced by the initial FeO content in the top slag. The results show that the model can be used for future work on the dynamic modelling of slag/metal reactions if the initial FeO content is less than 3-4% (by weight).

  • 23.
    Andersson, Annika
    KTH, Superseded Departments, Materials Science and Engineering.
    A Study on Selected Hot-Metal and Slag Components for Improved Blast Furnace Control2003Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The main objective of this work was to gain an increasedunderstanding of selected blast furnace phenomena which couldbe utilized for an improved blast furnace process control. Thisthesis contributes with both a model study and an experimentalstudy on blast furnace tapping, and results from these findingscan be used to enhance the control of the blast furnace.

    The work was divided in two parts. The first part dealt witha model study for optimisation of the blast furnace burdencalculation. During the second part the frequency of thehot-metal and slag sampling was increased compared to routinesampling throughout the taps of a commercial blast furnace.Thereafter, composition variation and correlation betweendistribution coefficients were examined.

    With an optimisation of the burden calculation the firststep towards controlled hot-metal production is taken, sincethe optimal material mixture for a desired hot-metalcomposition could easily be found. Due to the fact that theoptimisation model uses yield factors, which are easy tocalculate from material and hot-metal compositions, thesevalues have to be accurate for a controlled process control ofthe furnace. The study of hot-metal and slag compositionsduring tapping concluded that variations exist. The largevariations for C, Si, S, Mn and V in hot metal during tappinglead to the conclusion, that one single sampling ofhot metalwas not enough to get a representative value for thecomposition. The solution was to use a double-samplingpractise, were the hot metal was sampled first after tap startand secondly short after slag start, and subsequently anaverage composition value was calculated. The following studywas on the elemental distribution between hot metal and slagfrom a thermodynamic point of view. The major conclusion fromthis study was that the distribution coefficients behaved asexpected when looking at the equilibrium reactions. The studiedslag-metal distributions were also showing strong, trend-likerelationships, which was not affected by the operational statusof the blast furnace during the studied sampling period.

    The overall conclusion is that with a more reliablecomposition of hot metal and slag from the taps, thedistribution coefficients could be calculated with betterprecision and hence, the yield factors for the optimisationmodel would be more accurate. This procedure would probablylead to a more reliable burden optimisation and a thereforebetter and more stable blast furnace control.

  • 24. Andersson, Annika J.
    et al.
    Andersson, Margareta A. T.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jönsson, Pär G.
    KTH, Superseded Departments, Materials Science and Engineering.
    Variation in hot metal and stag composition during tapping of blast furnace2004In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 31, no 3, p. 216-226Article in journal (Refereed)
    Abstract [en]

    To determine the quality of the hot metal and the thermal conditions inside the blast furnace, the composition of the hot metal and slag must be known. Obtaining representative metal and slag samples during tapping is thus highly important to blast furnace operation. The study covered in the present report focused on hot metal and slag composition variation during tapping from a commercial blast furnace. From the results, optimal sampling time points for obtaining elemental concentrations that can be taken as representative for the whole tapping sequence were identified. It was furthermore concluded, that the reliability of hot metal composition data is significantly improved by averaging elemental concentrations determined from two samples, each taken at a particular time point. One sampling, however, was found to be adequate for slag. Results from the study also showed a fairly strong correlation between amounts of silicon and carbon, sulphur and carbon, and silicon and sulphur in the hot metal, while a weaker correlation between hot metal temperature and each of these elements was observed.

  • 25.
    Andersson, David
    KTH, Superseded Departments, Materials Science and Engineering.
    Modeling of Point Defects in Metals and Metal-Oxygen Compounds from First Principles Calculations2004Licentiate thesis, comprehensive summary (Other scientific)
  • 26.
    Andersson, David A.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Simak, S. I.
    Monovacancy and divacancy formation and migration in copper: a first-principles theory2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 11, p. 115108-Article in journal (Refereed)
    Abstract [en]

    The formation and migration of monovacancies and divacancies in copper have been studied from first-principles in order to resolve the discrepancies between previously published experimental and theoretical data. The monovacancy and divacancy formation, migration and binding enthalpies as well as the formation volumes have been calculated in the framework of a plane-wave pseudopotential implementation of the density functional theory, with full structural relaxations included. The monovacancy and divacancy formation entropies have been estimated from experimental data by performing a least-squares analysis. We show that the complete set of first-principles data, taking into account the presence of both vacancies and divacancies as well as the temperature dependence of the formation enthalpies and entropies allow one to reproduce the Arrhenius plot of the total vacancy concentration and the diffusion coefficient, both in good agreement with the most accurate experiments.

  • 27.
    Andersson, Henrik C. M.
    KTH, Superseded Departments, Materials Science and Engineering.
    Influence of weld microstructures on creep crack growth2003Licentiate thesis, comprehensive summary (Other scientific)
  • 28. Andersson, Henrik C. M.
    et al.
    Sandström, Rolf
    KTH, Superseded Departments, Materials Science and Engineering.
    Creep crack growth in service-exposed weld metal of 2.25Cr1Mo2001In: International Journal of Pressure Vessels and Piping, ISSN 0308-0161, E-ISSN 1879-3541, Vol. 78, no 11-12, p. 749-755Article in journal (Refereed)
    Abstract [en]

    Creep crack growth (CCG) has been studied for ex-service weld metal of 2.25Cr1Mo (P22). The testing was conducted at a temperature of 550degreesC and prior to testing, the material had been exposed to high temperature service for 110 000 h at 530 C. The results show a marked effect of the service exposure on the CCG properties of the material when compared to similar testing performed on a new material. The CCG rate was higher by a factor 3.1 in the service-exposed material, which should be compared to the model value of 3.2 based on the relations between the elongation values. The consumed deformation capacity was also estimated with the omega model for tertiary creep. In this case, an enhanced growth rate of 2.4 was obtained. Within a distance of about 10 mm in front of the propagating cracks, the number of creep cavities was significantly higher than in the surrounding material. The variation of the density of cavities as a function of distance from the crack tip was successfully modelled. (C) 2002 Published by Elsevier Science Ltd.

  • 29. Andersson, Henrik C. M.
    et al.
    Seitisleam, Facredin
    Sandstrom, Rolf
    KTH, Superseded Departments, Materials Science and Engineering.
    Creep testing of thick-wall copper electron beam and friction stir welds2004In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 824, p. 51-56Article in journal (Refereed)
    Abstract [en]

    Thick section copper canisters are planned to be used as a corrosion protection of nuclear waste disposal containers for long term underground deposal in Sweden. The copper canisters will have the top and possibly the bottom lid welded to the canister walls using electron beam or friction stir welding. Due to the high external hydrostatic pressure and the relatively high temperature of the waste during the first one hundred years the copper will creep. The creep process will close the manufacturing gap between the cast iron container and the copper canister. The creep ductility must be sufficient to avoid cracking of the weld. Specimens cut from the friction stir welds and the electron beam welds have been creep tested at temperatures ranging from 75 to 175 degreesC. Cross-weld specimens were used for both friction stir and electron beam welds. Weld metal, heat affected zone and base metal were also studied for friction stir welds. The results for the electron beam welds show that the main creep deformation is concentrated to the weld metal where the failure takes place. Weld metal and most cross-weld tests of friction stir weld material show similar creep lives and ductility as base metal tests. Ductility at rupture was found to exceed 30% for friction stir weld specimens, and the Norton power law exponent was determined to be between 30 and 50.

  • 30.
    Andersson, Karin
    KTH, Superseded Departments, Materials Science and Engineering.
    Aqueous Processing of WC-Co Powders Aqueous processing of WC-Co powders2001Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The object of this work is toobtain a fundamental understanding of the principal issuesconcerning the handling of WC-Co powders, in an aqueousmedium.

    The oxidation and dissolution oftungsten carbide powder dispersed in water was investigatedusing X-ray Photoelectron Spectroscopy (XPS) and leachingstudies. The WO3surface layer on the oxidised tungsten carbidepowder dissolves at pH>3 with the tungsten concentrationincreasing linearly with time. Adding cobalt powder to thetungsten carbide suspension resulted in a significant reductionof the dissolution rate at pH<10. Electrokinetic studiesindicate that the reduced dissolution rate may be related tothe formation of surface complexes; experiments showed that Cospecies in solution adsorb on the oxidised tungsten carbidepowder. The experimental data are discussed in relation totheoretical modelling of the WO3solution chemistry and the Co2+adsorption at oxide/water interfaces.

    The DLVO surface forces ofoxidised tungsten and cobalt surfaces were investigated usingthe atomic force microscope (AFM) colloidal probe technique.The colloidal probe consisted of an oxidised tungstenmicro-sphere and the flat surface was either oxidised tungstenor cobalt. The surfaces are representative as model systems forindustrial WC and Co powders. The surface chemistry andcomposition of the surfaces were analysed with XPS, X-rayDiffraction (XRD),and electrokinetic measurements. The effects of ionicstrength and pH, in the systems, were studied. The measuredinteractions are well described by theoretical Hamakerconstants, calculated from optical data for two WO3surfaces and one WO3and one CoOOH surface interacting over water,respectively.

    The effects on the surfaceforces of adsorption cobalt ions to tungsten oxide surfaces,and adsorption of polyethyleneimine (PEI) in both the symmetricand asymmetric systems, were investigated. Low concentrationsof cobalt ions to a WO3system resulted in an additional short-range forceand lower absolute value of the surface potential. It was shownthat PEI adsorbs to the WO3surfaces and induces an electrosteric repulsion,in both systems. The possible complexation of cobalt ions withPEI does not significantly influence the thickness of theadsorbed layer.

    Key words:Hard metal, cemented carbide, WC-Co, tungstencarbide, cobalt, oxidation, dissolution, surface complexation,XPS, AFM, colloidal probe, force curve, Hamaker constant,Cauchy, WO3, CoOOH, Co3O4, CoO, ESCA, zeta-potential, surface potential,polyethyleneimine, PEI, suspension, disperse, van der Waals,steric

  • 31.
    Andersson, Magnus
    KTH, Superseded Departments, Materials Science and Engineering.
    Enthalphy change of the ε→γ transformation in Fe-Mn-Si alloys1997Report (Other academic)
  • 32.
    Andersson, Magnus
    KTH, Superseded Departments, Materials Science and Engineering.
    Thermal and stress induced gamma to epsilon martensitic transformations in Fe-Mn-Si shape memory alloys1997Doctoral thesis, comprehensive summary (Other scientific)
  • 33.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Forsberg, Annika
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    KTH, Superseded Departments, Materials Science and Engineering.
    Martensitic and magnetic transformations in Fe-Mn-Si shape memory alloys1993In: Transactions of the materials research society of Japan, 1993, p. 973-976Conference paper (Other academic)
  • 34.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Stalmans, Rudy
    Ågren, John
    KTH, Superseded Departments, Materials Science and Engineering.
    The Influence of External Stresses on the Transformation Behaviour in a Fe-Mn-Si Alloy1997In: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 7, no C5, p. 411-416Article in journal (Refereed)
    Abstract [en]

    The influence of external stresses on the transformation behaviour has been studied for a polycrystalline Fe-3 IMn-SSi alloy exhibiting the y-+& martensitic transformation. Samples have been loaded at temperatures above the M, temperature, cooled with a constant external load to a temperature below the M, temperature and subsequently heated without load to a temperature above the A, temperature of the alloy. Stress, strain and temperature have been continuously measured and transformation temperatures and strains have been determined from the change in strain during the transformation. It has been found that the M, temperature during cooling with load is not influenced by 0.3-2 % plastic pre-deformation of the austenite whereas there is a substantial increase in the transformation strain, i.e. variants with a favourable orientation are enhanced by pre-strain of austenite.

  • 35.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Stalmans, Rudy
    Ågren, John
    KTH, Superseded Departments, Materials Science and Engineering.
    Unified thermodynamic analysis of the stress-assisted γ→ε martensitic transformation in Fe–Mn–Si alloys1998In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 46, no 11, p. 3883-3891Article in journal (Refereed)
    Abstract [en]

    A unified thermodynamic analysis has been developed which allows the combined complex effects of applied stresses and alloy composition on the martensite start temperature, Ms(σ), to be explained and predicted. In this unified analysis, a thermodynamic analysis of the effect of applied stress on the relative stability of the high and low temperature phase is combined with existing thermodynamic descriptions of the alloy system. The calculated results are compared with experimental results for the γ martensitic transformation in Fe–Mn–Si shape memory alloys. For single crystals, the comparison shows that the influence of applied stresses can be directly predicted with a reasonable accuracy for a wide composition range. By integrating a polycrystallinity parameter in the analysis it is shown that the calculations are also valid for polycrystalline alloys. Application of this analysis to experimental values of Ms(σ) can also generate useful data for future optimizations of the thermodynamic description of several alloy systems.

  • 36.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Van Humbeeck, Jan
    Ågren, John
    KTH, Superseded Departments, Materials Science and Engineering.
    Effects of recrystallization and grain size on the martensitic transformation in Fe-31% Mn-5% Si alloy1996In: Materials transactions, JIM, ISSN 0916-1821, Vol. 37, no 7, p. 1363-1370Article in journal (Refereed)
    Abstract [en]

    The effects of recrystallization and grain size have been studied in an Fe-31%Mn-5%Si shape memory alloy. The amount of martensite formed in samples which have been hot rolled at 1373 K and subsequently homogenized for 24 h at 1273 K followed by a final 30 min anneal at 1323 K is twice as large as in samples which have been hot rolled and homogenized in the same way as the former followed by a compression and a subsequent recrystallization at 1323 K for 30 min. The only difference between the samples is the plastic deformation induced by the compression. We thus conclude that some effect of the compressive deformation remains despite the recrystallization and suppresses the subsequent martensite formation. However, we have not yet been able to identify this effect. This matter will be subject to further investigations.

    No significant change is found in the M(S) and A(S) temperatures for the gamma <----> epsilon transformations determined by DSC. When the grain size varies between 40 and 160 mu m in completely recrystallized samples the variation in transformation temperatures is small, less than 10 K.

  • 37.
    Andersson, Magnus
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    KTH, Superseded Departments, Materials Science and Engineering.
    Effect of Prestraining and Training on the γ→ε Transformation in Fe-Mn-Si Alloys1995In: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 5, no C8, p. 457-462Article in journal (Refereed)
    Abstract [en]

    The effect of training and predeformation on the martensitic transformation is investigated. It is concluded that MS as a function of predeformation strain must have a maximum at around 3% strain. Prestrains less than 5% will enhance the martensitic transformation whereas larger prestrains depress it due to strain hardening of the γ phase.

  • 38.
    Andersson, Margareta
    KTH, Superseded Departments, Materials Science and Engineering.
    Some aspects of oxygen and sulphur reactions towards clean steel production2000Doctoral thesis, comprehensive summary (Other scientific)
  • 39.
    Andersson, Margareta A. T.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, Lage T. I.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, P. G.
    A thermodynamic and kinetic model of reoxidation and desulphurisation in the ladle furnace2000In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 40, no 11, p. 1080-1088Article in journal (Refereed)
    Abstract [en]

    A thermodynamic and kinetic model of reoxidation and desulphurisation in the ladle furnace has been developed by using a two-dimensional fluid-flow model combined with equations expressing the thermodynamics of reoxidation and desulphurisation. More specifically ladle vacuum treatment of a gas-stirred ladle has been simulated. In order to describe the activities of the oxide components of the slag, expressions by Ohta and Suito(1)) were adopted. The thermodynamic model describes the slag/metal equilibria between Al, Si, O, Mn and S in the molten steel and Al2O3, SiO2, FeO, MnO and S in the slag. A fluid dynamic model that considers the slag, steel and argon phases derives the kinetics. Results from an isothermal calculation have been heuristically compared with industrial plant data and they show good agreement. The model results have also revealed that the reduction of silica plays a part in aluminium loss during ladle treatment.

  • 40.
    Andersson, Margareta A. T.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, P. G.
    Hallberg, M.
    Optimisation of ladle slag composition by application of sulphide capacity model2000In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 27, no 4, p. 286-293Article in journal (Refereed)
    Abstract [en]

    The sulphur distribution ratio for ladle slags at Ovako Steel AB has been determined by calculating the sulphide capacity using the Royal Institute of Technology (KTH) model and the alumina activity via an empirical expression suggested by Ohta and Suite, and by using the well established theories for sulphur refining. A parameter study was carried out based on plant data from a previous study on desulphurisation, The effect of carbon and aluminium in the steel, the temperature of the steel, and alumina and lime in the slag on the sulphur distribution ratio was investigated, it was shown that the Al2O3/CaO ratio had the largest influence on the conditions studied, and that when it increased the sulphur distribution ratio decreased. Based on these results, new plant trials were carried out, in which the alumina content in the slag was changed. The calculated sulphur distribution ratios for these trials were found to be in good agreement with experimentally determined sulphur distribution ratios. It is concluded that the present approach can be used to optimise multicomponent ladle slags with respect to sulphur refining. I&S/1493.

  • 41.
    Andersson, Margareta A.T.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Berlin, D.
    Jönsson, Pär
    KTH, Superseded Departments, Materials Science and Engineering.
    Lownertz, M.
    The influence of different calcium-based additions on desulphurisation and inclusion characteristics2001In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 30, no 3, p. 127-135Article in journal (Refereed)
    Abstract [en]

    The size, distribution, and composition of inclusions during the desulphurisation and deoxidation steps were studied in laboratory experiments. 3 different calcium-based desulphurisation mixtures were used. The number of inclusions and composition of inclusions were then determined using optical microscopy and scanning electron microscopy, respectively. The results show that 2 of the 3 proposed desulphurisation mixtures managed to render lower and roughly equivalent inclusion counts. The results also show that the composition of the inclusions in all 3 samples varied from the beginning to the end of the desulphurisation process. A desulphurisation mixture consisting of Al, CaO, CaCO3 and CaSi produced the overall best results with respect to desulphurisation and inclusion characteristics.

  • 42.
    Andersson, Margareta A.T.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Hallberg, Malin
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Slag-metal reactions during ladle treatment with focus on desulphurisation2002In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 29, no 3, p. 224-232Article in journal (Refereed)
    Abstract [en]

    Within several cooperative projects, KTH (Royal Institute of Technology), Ovako Steel AB, and MEFOS have investigated the desulphurisation of bearing steel during vacuum degassing. The work includes thermodynamic calculations of the slag-metal equilibrium, CFD modelling of slag-metal reactions, and plant trials. Results from the various studies are presented and discussed in this paper. Models for predicting slag properties (sulphide capacity, viscosity, and oxide activities) in liquid slags as functions of slag composition and temperature have been used for the calculation of data which have been employed in static and dynamic modelling of sulphur refining. The results from static modelling show that the method allows fast and easy evaluation of the theoretical desulphurisation conditions during degassing at Ovako Steel AB, as well as theoretical determination of the parameters that have the greatest influence on the equilibrium sulphur distribution. The conclusion from dynamic modelling is that the vacuum degassing operation can be described dynamically with the present knowledge of sulphide capacity, sulphur distribution, viscosity, and oxide activities of ladle slags if this knowledge is combined with fluid flow modelling to derive the overall kinetics. The presented model approaches have been found useful in understanding the sulphur refining process at Ovako Steel AB. The dynamic modelling concept is also believed to have potential for dynamic descriptions of other slag-metal reactions in steelmaking.

  • 43.
    Andersson, Tomas
    KTH, Superseded Departments, Materials Science and Engineering.
    Thermal shock and thermal fatigue in ceramic materials1997Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis concerns thermal stress fracture in ceramicmaterials. The work describes a new technique for determiningthe thermal shock resistance of brittle materials as well asexperimental results and thermal stress simulations.

    A new indentation-quench method to the determine theresistance of ceramics to thermal shock and thermal cycling isdescribed. The method defines a critical temperaturedifference, ΔTc, from the amount of extension and propagation ofsmall Vickers cracks. Statistically significant data areobtained by studying a large number of cracks in each specimen.Few test specimens are thus required. Another advantage withthe method is that no specific specimen shape is required. Themethod can therefore be used directly on complex shapedcomponents. This is important since the thermal shockresistance of a material is highly dependent on its size andshape.

    The new method is used to determine the thermal shockresistance for several materials. The materials are rankedaccording to their value of ΔTc. The ranking from quenches into water at roomtemperature is compared with that from quenches into boilingwater. The results show that the thermal conductivity of thematerials becomes of large importance when the materials aresubjected to slower quenching rates in boiling water, while thevalues of ΔTcis more dependent on the mechanical properties forquenches into water at room temperature. The resistance to tenthermal cycles close to the ΔTcof the materials is investigated. Thesecomparisons show that milder quenching conditions gives alarger crack extension. Milder quenches give longer durationtimes of the thermal stresses. The cracks will thus have longertimes to find weak paths in the microstructure. Furthermore itis shown that a finely distributed toughening phase ispreferable in thermal cycling conditions.

    Thermal stresses are simulated in flat plates subjected tosymmetric cooling in order to estimate the effect of severalimportant thermal shock variables. The simulated conditions aresimilar to those met by alumina in quench tests. A thermaldiffusivity, with negative temperature dependence is found toincrease the thermal stresses significantly for thinner platesizes, whereas the effects for thicker plates are small. Theeffect of the statistical distribution of fracture strengths isshown to give a larger scatter in thermal shock resistance forthin specimens than for thick ones.

    Keywords:Thermal shock, thermal stress, thermalfatigue, indentation, SiC-whisker-reinforced alumina, waterquench, cooling rate, thermal diffusivity.

  • 44.
    Anghel, Clara
    KTH, Superseded Departments, Materials Science and Engineering.
    Studies of transport in oxides on Zr-based materials2004Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Zr-based materials have found their main application in the nuclear field having high corrosion resistance and low neutron absorption cross-section. The oxide layer that is formed on the surface of these alloys is meant to be the barrier between the metal and the corrosive environment. The deterioration of this protective layer limits the lifetime of these alloys. A better understanding of the transport phenomena, which take place in the oxide layer during oxidation, could be beneficial for the development of more resistant alloys.

    In the present study, oxygen and hydrogen transport through the zirconia layer during oxidation of Zr-based materials at temperatures around 400C have been investigated using the isotope-monitoring techniques Gas Phase Analysis and Secondary Ion Mass Spectrometry. The processes, which take place at oxide/gas and oxide/metal interface, in the bulk oxide and metal, have to be considered in the investigation of the mechanism of hydration and oxidation. Inward transport of oxygen and hydrogen species can be influenced by modification of the surface properties. We found that CO molecules adsorbed on Zr surface can block the surface reaction centers for H2 dissociation, and as a result, hydrogen uptake in Zr is reduced. On the other hand, coating the Zr surface with Pt, resulted in increased oxygen dissociation rate at the oxide/gas interface. This generated enhanced oxygen transport towards the oxide/metal interface and formation of thicker oxides. Our results show that at temperatures relevant for the nuclear industry, oxygen dissociation efficiency decreases in the order: Pt > Zr2Fe > Zr2Ni > ZrCr2 ≥ Zircaloy-2.

    Porosity development in the oxide scales generates easy diffusion pathways for molecules across the oxide layer during oxidation. A novel method for evaluation of the gas diffusion, gas concentration and effective pore size of oxide scales is presented in this study. Effective pore sizes in the nanometer range were found for pretransition oxides on Zircaloy-2.

    A mechanism for densification of oxide scales by obtaining a better balance between inward oxygen and outward metal transport is suggested. Outward Zr transport can be influenced by the presence of hydrogen in the oxide/metal substrate. Inward oxygen transport can be promoted by oxygen dissociating elements such as Fe-containing second phase particles. The results suggest furthermore that a proper choice of the second-phase particle composition and size distribution can lead to the formation of dense oxides, which are characterized by low oxygen and hydrogen uptake rates during oxidation.

  • 45.
    Anghel, Clara
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Hörnlund, Erik
    KTH, Superseded Departments, Materials Science and Engineering.
    Hultquist, Gunnar
    KTH, Superseded Departments, Materials Science and Engineering.
    Limbäck, Magnus
    Gas phase analysis of CO interactions with solid surfaces at high temperatures2004In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 233, no 1-4, p. 392-401Article in journal (Refereed)
    Abstract [en]

    An in situ method including mass spectrometry and labeled gases is presented and used to gain information on adsorption of molecules at high temperatures (>300 degreesC). Isotopic exchange rate in H-2 upon exposure to an oxidized zicaloy-2 sample and exchange rate in CO upon exposure to various materials have been measured. From these measurements, molecular dissociation rates in respective system have been calculated. The influence of CO and N-2 on the uptake rate of H-2 in zirconium and oxidized zicaloy-2 is discussed in terms of tendency for adsorption at high temperatures. In the case of oxidized Cr exposed to CO gas With C-12, C-13, O-16 and O-18, the influence of H2O is investigated with respect to dissociation of CO molecules. The presented data supports a view of different tendencies for molecular adsorption of H2O, CO, N-2, and H-2 molecules on surfaces at high temperatures.

  • 46. Ansara, I.
    et al.
    Sundman, Bo
    KTH, Superseded Departments, Materials Science and Engineering.
    Calculation of the magnetic contribution for intermetallic compounds2000In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 24, no 2, p. 181-182Article in journal (Refereed)
  • 47.
    Apazidis, Nicholas
    et al.
    KTH, Superseded Departments, Mechanics.
    Lesser, M. B.
    Tillmark, Nils
    KTH, Superseded Departments, Mechanics.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    An experimental and theoretical study of converging polygonal shock waves2002In: Shock Waves, ISSN 0938-1287, E-ISSN 1432-2153, Vol. 12, no 1, p. 39-58Article in journal (Refereed)
    Abstract [en]

    An experimental investigation was carried out to explore the possibility of producing converging polygonal shocks in an essentially two-dimensional cavity. Previous calculations by Apazidis and Lesser (1996) suggested that such configurations could be produced by reflecting a cylindrical outgoing shock from a smoothly altered circular boundary, the alteration having n-gonal symmetry. In the experiments the outgoing shock was produced by a spark discharge which yielded shocks in the Mach number range from 1.1 to 1.7 at a radius just prior to the reflection. Polygonal shocks were observed as predicted by using a modified form of geometrical shock dynamics, derived in the above paper. In addition, the modified theory was used to calculate the results of an experiment carried out by Sturtevant and Kulkarny (1976). The results of the numerical calculations were found to be in substantial agreement with both experiments, suggesting that the modifications in geometrical shock dynamics for non-uniform flow ahead of an advancing shock are useful in the case of shock focusing. The experiment. also showed that the polygonal shapes were stable in the examined range of shock Mach numbers. a result that may be of importance for a number of practical situations in which shock focusing is present.

  • 48. Arapan, S. C.
    et al.
    Korepov, S. V.
    Liberman, M. A.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Conductance of a disordered double quantum wire in a magnetic field: Boundary roughness scattering2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 11Article in journal (Refereed)
  • 49. Arapan, S. C.
    et al.
    Korepov, S. V.
    Liberman, M. A.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Effect of the boundary roughness on the conductance of double quantum wire in a magnetic field2003In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 64, no 2, p. 239-245Article in journal (Refereed)
  • 50. Arvanitidis, I.
    et al.
    Kapilashrami, A.
    Du, S. C.
    Seetharaman, Seshadri
    KTH, Superseded Departments, Materials Science and Engineering.
    Intrinsic reduction kinetics of cobalt- and nickel-titanates by hydrogen2000In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 15, no 2, p. 338-346Article in journal (Refereed)
    Abstract [en]

    The isothermal reduction of synthetic CoTiO3 and NiTiO3 in hydrogen (1 atm) was investigated using thermogravimetric analysis technique in the temperature range, 928-1287 K (CoTiO3) and 884-1387 K (NiTiO3). Shallow beds of fine titanate powders were reduced by hydrogen at a high flow rate. Quenched samples were analyzed by scanning electron microscopy. The rates of the reaction of the titanates with H-2 were very fast during the reduction of Co2+, Ni2+, or Fe2+ ions into metals. The reduction of the remaining titanium oxide was very slow. The activation energy for the reduction of CoTiO3 by hydrogen to Co and TiO2 was evaluated to be 151 +/- 1 kJ/mol, and the activation energy for the reduction of NiTiO3 by hydrogen to Ni and TiO2 was evaluated to be 153 +/- 1 kJ/mol. The study was complemented by hydrogen reduction of synthetic TiO2 (rutile). The results were also compared with the hydrogen reduction of FeTiO3.

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