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  • 1.
    Abas, Riad Abdul
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Property measurements towards understanding process phenomena2005Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The main objective of this industrially important work was to gain an increasing understanding of the properties of materials such as CMSX-4 nickel base super alloy, mould powder used in continuous casting of steel and coke used in blast furnace, with special reference to the thermal diffusivities. The measurements were carried out in a wide temperature range, solid, liquid, glassy and crystalline states.

    For CMSX-4 alloy, the thermal conductivities were calculated from the experimental thermal diffusivities. Both the diffusivities and conductivities were found to increase with increasing temperature. Microscopic analysis showed the presence of intermetallic phases such as NiTi and NiTi2 below 1253 K. In this region, the mean free path of the phonons is likely to be limited by scattering against lattice defects. Between 1253 K and solidus temperature, these phases dissolved in the alloy adding to the impurities in the matrix, which, in turn, caused a decrease in the thermal diffusivity. This effect was confirmed by annealing the samples at 1573 K. The thermal diffusivities of the annealed samples measured at 1277, 1403 and 1531 K were found to be lower than the thermal diffusivities of non-annealed samples and the values did not show any noticeable change with time. It could be related to the attainment of equilibrium with the completion of the dissolution of γ and γ´ phases during the annealing process.

    Liquid CMSX-4 does not show any change of thermal diffusivity with temperature. It may be attributed to the decreasing the mean free path being shorter than characteristic distance between two neighbouring atoms.

    On the other hand thermal diffusivities of mould powder having glassy and crystalline states decrease with increasing temperature at lower temperature and are constant at higher temperature except for one glassy sample.

    Analogously, the thermal diffusivity measurements of mould powder did not show any significant change with temperature in liquid state. It is likely to be due to the silicate network being largely broken down.

    The thermal diffusivity is increased with increasing crystallisation degree of mould powder, which is expected from theoretical considerations.

    The coke sample, taken from deeper level of the blast furnace, is found to have larger thermal diffusivity. This could be correlated to the average crystallite size along the structural c-axis, Lc, which is indicative of the higher degree of graphitisation. This was also confirmed by XRD measurements of the different coke samples. The degree of graphitisation was found to increase with increasing temperature. Further, XRD measurements of coke samples taken from different levels in the shaft of the blast furnace show that the graphitisation of coke was instantaneous between room temperature and 1473 K.

    Fulltekst (pdf)
    FULLTEXT01
  • 2. Abbasalizadeh, A.
    et al.
    Sridar, S.
    Chen, Z.
    Sluiter, M.
    Yang, Y.
    Sietsma, J.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hari Kumar, K. C.
    Experimental investigation and thermodynamic modelling of LiF-NdF3-DyF3 system2018Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 753, s. 388-394Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrolysis of molten fluorides is one of the promising methods for the recovery and recycling of rare earth metals from used magnets. Due to the dearth of phase equilibria data for molten fluoride systems, thermodynamic modelling of LiF-DyF3-NdF3 system using the CALPHAD approach was carried out. Gibbs energy modelling for LiF-NdF3 and LiF-DyF3 systems was performed using the constitutional data from literature. Ab initio calculations were used to obtain enthalpy of reaction of LiDyF4, an intermediate phase that is found to exist in the LiF-DyF3 system. Differential thermal analysis was carried out for selected compositions in the NdF3-DyF3 system, in order to determine liquidus and solidus temperatures. The Gibbs energy parameters for the limiting binaries determined in this work is used for modelling the Gibbs energy functions of equilibrium phases in the ternary system. Selected compositions of LiF-NdF3-DyF3 were subjected to DTA in order to validate the calculated phase temperatures involving melt.

  • 3. Abbasalizadeh, A.
    et al.
    Teng, Lidong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Sietsma, J.
    Yang, Y.
    Rare Earth Extraction from NdFeB Magnets and Rare Earth Oxides Using Aluminum Chloride/Fluoride Molten Salts2015Inngår i: Rare Earths Industry: Technological, Economic, and Environmental Implications, Elsevier, 2015, s. 357-373Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    In the current research, the feasibility of the recovery of neodymium and dysprosium from spent NdFeB magnets (about 6wt% Dy) was investigated using molten salt processes. The salt bath consisted of a eutectic composition of an NaCl-KCl-LiCl mixture. To enable the efficient dissolution of metal in the molten salt phase, AlCl3 was used as a chlorinating agent. Iron-free electrodeposition was carried out successfully. Energy-dispersive spectroscopic analysis of the electrodeposit revealed that co-deposition of the dysprosium occurs along with neodymium at the cathode. The process shows that this method is well suited for recovering rare earth metals from magnetic scrap containing these metals.Furthermore, the setup design for recovery of neodymium and dysprosium from their oxides was investigated with regard to previous studies on the neodymium magnets. The stability of different fluoride and chloride salts was studied by means of thermodynamic calculation. Aluminum fluoride-based molten salt systems were studied in detail as the electrolyte for electrochemical extraction of rare earth oxides into rare earth metal elements with Al.

  • 4. Abbasalizadeh, Aida
    et al.
    Malfliet, Annelies
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sietsma, Jilt
    Yang, Yongxiang
    Electrochemical Extraction of Rare Earth Metals in Molten Fluorides: Conversion of Rare Earth Oxides into Rare Earth Fluorides Using Fluoride Additives2017Inngår i: JOURNAL OF SUSTAINABLE METALLURGY, ISSN 2199-3823, Vol. 3, nr 3, s. 627-637Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present research on rare earth extraction from rare earth oxides (REOs), conversion of rare earth oxides into rare earth fluorides with fluoride fluxes is investigated in order to overcome the problem of low solubility of the rare earth oxides in molten fluoride salts as well as the formation of oxyfluorides in the fluorination process. Based on thermodynamic calculations, a series of experiments were performed for converting the rare earth oxides into rare earth fluorides using AlF3, ZnF2, FeF3, and Na3AlF6 as fluorinating agents in a LiF-Nd2O3 system. The formation of neodymium fluoride as a result of the reactions between these fluxes and neodymium oxide is confirmed. The rare earth fluoride thus formed can subsequently be processed through the electrolysis route in the same reactor, and rare earth metal can be produced as the cathodic deposit. In this concept, the REO dissolution in molten fluorides would become unnecessary due to the complete conversion of the oxide into the fluoride, REF3. The results of XRD and EPMA analysis of the reacted samples indicate that AlF3, ZnF2, and FeF3 can act as strong fluorinating agents for the neodymium oxide giving rise to a complete conversion of neodymium oxide into neodymium fluoride.

  • 5. Abbasalizadeh, Aida
    et al.
    Malfliet, Annelies
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sietsma, Jilt
    Yang, Yongxiang
    Electrochemical Recovery of Rare Earth Elements from Magnets: Conversion of Rare Earth Based Metals into Rare Earth Fluorides in Molten Salts2017Inngår i: Materials transactions, ISSN 1345-9678, E-ISSN 1347-5320, Vol. 58, nr 3, s. 400-405Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present work, selective extraction of rare earth (RE) metals from NdFeB magnets is investigated by studying the effects of various fluxes, viz. AlF3, ZnF2, FeF3 and Na3AlF6 in the LiF-NdFeB system. The aim is to convert RE from RE magnet into the fluoride salt melt. The results show the complete selective separation of neodymium (also dysprosium) from the magnet and formation of rare earth fluoride, leaving iron and boron unreacted. The formed rare earth fluoride can subsequently be processed in the same reactor through an electrolysis route so that RE can be deposited as a cathode product. The results of XRD and EPMA analysis of the reacted samples indicate that AlF3, ZnF2 and FeF3 can act as strong fluorinating agents for extraction of rare earth from NdFeB magnet, converting the RE to REF3. The results confirm the feasibility of the rare earth metals recovery from scrap NdFeB magnet as raw material. The fluoride conversion- electrolysis route suggested in the present work enables the extraction of rare earth metals in a single step using the above-mentioned fluxes.

  • 6.
    Abbasalizadeh, Aida
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Teng, Lidong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Sridhar, Seetharaman
    Grinder, Olle
    Izumi, Yukari
    Barati, Mansoor
    Highlights of the Salt Extraction Process2013Inngår i: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 65, nr 11, s. 1552-1558Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article presents the salient features of a new process for the recovery of metal values from secondary sources and waste materials such as slag and flue dusts. It is also feasible in extracting metals such as nickel and cobalt from ores that normally are difficult to enrich and process metallurgically. The salt extraction process is based on extraction of the metals from the raw materials by a molten salt bath consisting of NaCl, LiCl, and KCl corresponding to the eutectic composition with AlCl3 as the chlorinating agent. The process is operated in the temperature range 973 K (700 degrees C) to 1173 K (900 degrees C). The process was shown to be successful in extracting Cr and Fe from electric arc furnace (EAF) slag. Electrolytic copper could be produced from copper concentrate based on chalcopyrite in a single step. Conducting the process in oxygen-free atmosphere, sulfur could be captured in the elemental form. The method proved to be successful in extracting lead from spent cathode ray tubes. In order to prevent the loss of AlCl3 in the vapor form and also chlorine gas emission at the cathode during the electrolysis, liquid aluminum was used. The process was shown to be successful in extracting Nd and Dy from magnetic scrap. The method is a highly promising process route for the recovery of strategic metals. It also has the added advantage of being environmentally friendly.

  • 7. Abbasalizadeh, Aida
    et al.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Venkatesan, Prakash
    Sietsma, Jilt
    Yang, Yongxiang
    Novel Reactive Anode for Electrochemical Extraction of Rare Earth Metals from Rare Earth Oxides2017Inngår i: RARE METAL TECHNOLOGY 2017 / [ed] Kim, H Alam, S Neelameggham, NR Oosterhof, H Ouchi, T Guan, X, SPRINGER INTERNATIONAL PUBLISHING AG , 2017, s. 87-92Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Electrolytic production of metallic neodymium is carried out in fused fluoride salts containing neodymium oxide. Two major challenges pertaining to neodymium production are (a) low oxide solubility, (b) possibility of anodic fluorine gas evolution if the electrolysis rate exceeds feeding rate of neodymium oxide. In this study, a novel method is proposed in which iron fluoride (FeF3) is used as a fluorinating agent to convert neodymium oxide into neodymium fluoride. Electron Probe Micro Analysis (EPMA) results of as-converted salt show a complete conversion of neodymium oxide into neodymium fluoride. In the electrolysis process, iron is used as a reactive anode with electrochemical dissolution of iron into the melt, thus preventing fluorine gas evolution at the anode. Therefore, the fluorinating agent is constantly regenerated in situ which enables the continuous conversion of neodymium oxide feed. The cathodic product is a Nd-Fe alloy which can be directly used as a master alloy for the production of NdFeB permanent magnets.

  • 8.
    Abbasalizadeh, Aida
    et al.
    Delft Univ Technol TU Delft, Dept Mat Sci & Engn, Mekelweg 2, NL-2628 CD Delft, Netherlands..
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Venkatesan, Prakash
    Delft Univ Technol TU Delft, Dept Mat Sci & Engn, Mekelweg 2, NL-2628 CD Delft, Netherlands..
    Sietsma, Jilt
    Delft Univ Technol TU Delft, Dept Mat Sci & Engn, Mekelweg 2, NL-2628 CD Delft, Netherlands..
    Yang, Yongxiang
    Delft Univ Technol TU Delft, Dept Mat Sci & Engn, Mekelweg 2, NL-2628 CD Delft, Netherlands..
    Use of iron reactive anode in electrowinning of neodymium from neodymium oxide2019Inngår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 310, s. 146-152Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrolytic production of metallic neodymium is carried out in fused neodymium fluoride salts containing neodymium oxide. Two major challenges pertaining to neodymium production in fluoride salts are a) low solubility of neodymium oxide in fluoride melt, b) possibility of anodic gas evolution (CO, CO2, CF4, C2F6). In this study, iron is used as a reactive anode in the electrolysis process, promoting electrochemical dissolution of iron into the melt, preventing PFC (perfluorocarbon) gas evolution at the anode. Further, the rare earth oxide is converted to rare earth fluoride by the use of iron fluoride formed as the result of iron dissolution. Thus, the fluoridizing agent is constantly regenerated in-situ which enables the continuous conversion of neodymium oxide feed. The cathodic product is Nd-Fe alloy which can be used as a master alloy for the production of NdFeB magnets. 

  • 9.
    Abbasalizadeh, Aida
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Teng, Lidong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Seetharaman, S.
    Dysprosium extraction using molten salt process2014Inngår i: Rare metal technology 2014: proceedings of a symposium sponsored by The Minerals, Metals & Materials Society (TMS) held during TMS 2014, 143rd Annual Meeting & Exhibition, February 16-20, 2014, San Diego Convention Center, San Diego, California, USA, 2014, s. 207-208Konferansepaper (Fagfellevurdert)
  • 10.
    Abbasalizadeh, Aida
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Teng, Lidong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Sridhar, S.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Neodymium extraction using salt extraction process2015Inngår i: Mineral Processing and Extractive Metallurgy: Transactions of the Institutions of Mining and Metallurgy: Section C, ISSN 0371-9553, E-ISSN 1743-2855, Vol. 124, nr 4, s. 191-198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present paper deals with the feasibility of the neodymium recovery from spent Nd-Fe-B magnets using molten salt electrodeposition method. The salt bath consisted of a mixture of LiCl- KCl-NaCl corresponding to the eutectic composition. The experimental set-up with its salient features is presented. AlCl3 was used as flux and graphite rods dipped in the salt bath served as electrodes. The voltage for the electrolysis was chosen on the basis of the decomposition potential of NdCl3. The reaction sequence can be described as Iron-free neodymium deposition could be carried out successfully. In view of the proximity of the electrode potentials, the co-deposition of the aluminium and neodymium was observed to occur at the cathode, as revealed by SEM/EDS and XRD analyses of the electrodeposit.

  • 11.
    Abdoshahi, Neda
    et al.
    Univ Leoben, Dept Mat Sci, Franz Josef Str 18, A-8700 Leoben, Austria..
    Dehghani, Mohammad
    Mat Ctr Leoben Forsch GmbH, Roseggerstr 12, A-8700 Leoben, Austria..
    Hatzenbichler, Lukas
    Univ Leoben, Dept Mat Sci, Franz Josef Str 18, A-8700 Leoben, Austria..
    Spoerk-Erdely, Petra
    Univ Leoben, Dept Mat Sci, Franz Josef Str 18, A-8700 Leoben, Austria..
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Mat Ctr Leoben Forsch GmbH, Roseggerstr 12, A-8700 Leoben, Austria.
    Musi, Michael
    Univ Leoben, Dept Mat Sci, Franz Josef Str 18, A-8700 Leoben, Austria..
    Mayer, Svea
    Univ Leoben, Dept Mat Sci, Franz Josef Str 18, A-8700 Leoben, Austria..
    Spitaler, Juergen
    Mat Ctr Leoben Forsch GmbH, Roseggerstr 12, A-8700 Leoben, Austria..
    Holec, David
    Univ Leoben, Dept Mat Sci, Franz Josef Str 18, A-8700 Leoben, Austria..
    Structural stability and mechanical properties of TiAl plus Mo alloys: A comprehensive ab initio study2021Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 221, s. 117427-, artikkel-id 117427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Titanium aluminides are technologically important intermetallic alloys with also many curious properties interesting from a basic research point of view. When alloyed with Mo, several (meta)stable phases have been reported; their properties are, however, largely unknown due to the alloy processing (e.g. fast cooling) and/or non-existence as a single-phase material. Here we employ first principles calculations to study compositional trends in structural and mechanical properties. We could show that Mo increases the density of all studied phases, leads to their chemical destabilization with the exception of the ordered bcc /3o phase, increases their ductility, and enhances the elastic anisotropy. Discrepancies between two employed ab initio methods (special quasi-random structures vs. coherent potential approximation) in the case of the /3o and B19 phases are rationalized with significant local distortions which may eventually facilitate a spontaneous phase transformation. Predictions of ordering temperatures solely based on the configurational entropy do not yield values in the experimentally expected ranges.

  • 12.
    Abdoshahi, Neda
    et al.
    Univ Leoben, Dept Mat Sci, Franz Josef Str 18, A-8700 Leoben, Austria..
    Dehghani, Mohammad
    Mat Ctr Leoben Forsch GmbH, Roseggerstr 12, A-8700 Leoben, Austria..
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Strukturer. Mat Ctr Leoben Forsch GmbH, Roseggerstr 12, A-8700 Leoben, Austria..
    Friak, Martin
    Czech Acad Sci, Inst Phys Mat, Zizkova 22, CZ-61662 Brno, Czech Republic.;Brno Univ Technol, Fac Mech Engn, Inst Mat Sci & Engn, Tech 2896-2, CZ-61669 Brno, Czech Republic..
    Sob, Mojmir
    Czech Acad Sci, Inst Phys Mat, Zizkova 22, CZ-61662 Brno, Czech Republic.;Masaryk Univ, Fac Sci, Dept Chem, Kotlarska 2, CZ-61137 Brno, Czech Republic..
    Spitaler, Juergen
    Mat Ctr Leoben Forsch GmbH, Roseggerstr 12, A-8700 Leoben, Austria..
    Holec, David
    Univ Leoben, Dept Mat Sci, Franz Josef Str 18, A-8700 Leoben, Austria..
    On the energetics of the cubic-to-hexagonal transformations in TiAl plus Mo alloys2022Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 240, artikkel-id 118268Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Diffusionless transformations allow access to metastable phases and enrich the materials design portfolio. They are well suited for atomistic modeling; nonetheless, they are challenging when involving disordered systems or alloys with complex compositions. This work presents a comprehensive study of transforma-tion energetics between bcc and hcp ordered and disordered phases in the TiAl+Mo model alloy system. By employing two complementary techniques I. VASP-SQS, and II. EMTO-CPA, we can show that chemical disorder flattens the energy landscape but may introduce a small barrier. Unlike that, the energetics of ordered phases are barrier-less and hence would suggest a spontaneous transformation. Finally, we show that Mo stabilizes the bcc phases, leading to a barrier-less transformation hcp -+ bcc for both ordered and disordered states when Mo content exceeds ti 12 at.%.

  • 13.
    Abdul Abas, Riad
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Experimental Studies of Thermal Diffusivities concerning some Industrially Important Systems2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The main objective of this industrially important work was to gain an increasing understanding of the properties of some industrially important materials such as CMSX-4 nickel base super alloy, 90Ti.6Al.4V alloy, 25Cr:6Ni stainless steel, 0.7% carbon steel, AISI 304 stainless steel-alumina composites, mould powder used in continuous casting of steel as well as coke used in blast furnace with special reference to the thermal diffusivities. The measurements were carried out in a wide temperature range covering solid, liquid, glassy and crystalline states.

    For CMSX-4 alloy, the thermal conductivities were calculated from the experimental thermal diffusivities. Both the diffusivities and conductivities were found to increase with increasing temperature. Microscopic analysis showed the presence of intermetallic phases γ´ such as Ni3Al below 1253 K. In this region, the mean free path of the electrons and phonons is likely to be limited by scattering against lattice defects. Between 1253 K and solidus temperature, these phases dissolved in the alloy adding to the impurities in the matrix, which, in turn, caused a decrease in the thermal diffusivity. This effect was confirmed by annealing the samples at 1573 K. The thermal diffusivities of the annealed samples measured at 1277, 1403 and 1531 K were found to be lower than the thermal diffusivities of non-annealed samples and the values did not show any noticeable change with time. It could be related to the attainment of equilibrium with the completion of the dissolution of γ´ phase during the annealing process. Liquid CMSX-4 does not show any change of thermal diffusivity with temperature. It may be attributed to the decrease of the mean free path being shorter than characteristic distance between two neighbouring atoms.

    Same tendency could be observed in the case of 90Ti.6Al.4V alloy. Since the thermal diffusivity increases with increasing temperature below 1225 K and shows slight decrease or constancy at higher temperature. For 25Cr:6Ni stainless steel, the thermal diffusivity is nearly constant up to about 700 K. Beyond that, there is an increase with temperature both during heating as well as cooling cycle. On the other hand, the slope of the curve increases above 950 K, which can be due to the increase of bcc phase in the structure. 0.7% carbon steel shows a decrease in the thermal diffusivity at temperature below Curie point, where the structure contains bcc+ fcc phases. Above this point the thermal diffusivity increases, where the structure contains only fcc phase. The experimental thermal conductivity values of these alloys show good agreement with the calculated values using Mills model.

    Thermal diffusivity measurements as a function of temperature of sintered AISI 304 stainless steel-alumina composites having various composition, viz, 0.001, 0.01, 0.1, 1, 2, 3, 5, 7, 8 and 10 wt% Al2O3 were carried out in the present work. The thermal diffusivity as well as the thermal conductivity were found to increase with temperature for all composite specimens. The thermal diffusivity/conductivity decreases with increasing weight fraction of alumina in the composites. The experimental results are in good agreement with simple rule of mixture, Eucken equation and developed Ohm´s law model at weight fraction of alumina below 5 wt%. Beyond this, the thermal diffusivity/ conductivity exhibits a high discrepancy probably due to the agglomeration of alumina particles during cold pressing and sintering.

    On the other hand, thermal diffusivities of industrial mould flux having glassy and crystalline states decrease with increasing temperature at lower temperature and are constant at higher temperature except for one glassy sample. The thermal diffusivity is increased with increasing crystallisation degree of mould flux, which is expected from theoretical considerations.

    Analogously, the thermal diffusivity measurements of mould flux do not show any significant change with temperature in liquid state. It is likely to be due to the silicate network being largely broken down.

    In the case of coke, the sample taken from deeper level of the pilot blast furnace is found to have larger thermal diffusivity. This can be correlated to the average crystallite size along the structural c-axis, Lc, which is indicative of the higher degree of graphitisation. This was also confirmed by XRD measurements of the different coke samples. The degree of graphitisation was found to increase with increasing temperature. Further, XRD and heat capacity measurements of coke samples taken from different levels in the shaft of the pilot blast furnace show that the graphitisation of coke was instantaneous between 973 and 1473 K.

    Fulltekst (pdf)
    FULLTEXT01
  • 14.
    Abdul Abas, Riad
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Hayashi, M.iyuki
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Thermal Diffusivity measurement of CMSX-4 alloy by Laser flash method2007Inngår i: International journal of thermophysics, ISSN 0195-928X, E-ISSN 1572-9567, Vol. 28, nr 1, s. 109-122Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present work, thermal diffusivity measurements have been carried out on industrial samples of CMSX-4 nickel-base superalloy using the laser-flash method with emphasis on studying the effect of temperature and microstructure on the thermal diffusivity. The measurements were performed in the temperature range from 298 to 1623 K covering both solid as well as liquid ranges. Below 1253 K, the thermal-diffusivity values were found to increase with increasing temperature. Microstructural investigations of quenched samples revealed that below 1253 K, an ordered phase, usually referred to as the -phase was present together with the disordered fcc phase, often referred to as the γ phase. Between 1253 K and the solidus temperature, the phase was found to dissolve in the matrix alloy causing an increase in the disordering of the alloy, and thereby a small decrease in the thermal-diffusivity values. The thermal-diffusivity values of samples pre-annealed at 1573 K exhibited constancy in the temperature range from 1277 to 1513 K, which is attributed to the attainment of thermodynamic equilibrium. These equilibrium values were found to be lower than the results for samples not subjected to annealing. The thermal-diffusivity values of the alloy in the liquid state were found to be independent of temperature.

  • 15.
    Abdul Abas, Riad
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Hayashi, Miyuki
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Thermal Diffusivity Measurements of some Industrially Important Alloys by a Laser Flash Method2007Inngår i: International journal of materials reseach, ISSN 1862-5282, Vol. 98, nr 6, s. 535-540Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present work, thermal diffusivity measurements of three industrially significant alloys, viz. 90Ti.6Al.4V, stainless steel with 25Cr and 6Ni as well as plain carbon steel with 0.7 % carbon have been carried out as a function of temperature. The aim of this work is to study the effect of temperature and microstructure on the thermal diffusivities of these alloys. For the 90Ti.6Al.4V alloy, thermal diffusivity increases with temperature below 1225 K. Above this temperature, the values started decreasing probably due to the dissolution of Ti3Al intermediate phase in the matrix, which would result in an increase in the disorder of the structure. For 25Cr: 6Ni stainless steel, the thermal diffusivity is nearly constant up to about 700 K. Above this, there is an increase in the thermal diffusivities with temperature during the heating cycle, which was reproducible during thermal cycling. On the other hand, the slope of the curve increases above 950 K.

    In the case of the 0.7 % carbon steel, the thermal diffusivity shows a decreasing trend with temperature below the Curie point for the alloy, where the alloy consists of bcc + fcc phases. Above this point, only the fcc phase is prevalent and the thermal diffusivity was found to increase with temperature. Heat transfer is carried out by lattice vibration (phonons) as well as electrons. The contribution of electrons varies depending upon the type of alloy. In this study, the highest electron contribution was found in 0.7 % carbon steel, while the lowest was in stainless steel. The thermal conductivity values of these alloys are in good agreement with the calculated values using the model proposed by Mills.

  • 16.
    Abdul Abas, Riad
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jakobsson, Anders
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hayashi, Miyuki
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Studies on Graphitisation of Blast Furnace Coke by X-ray Diffraction Analysis and Thermal Diffusivity Measurements2005Inngår i: Steel research, ISSN 0177-4832, Vol. 77, nr 11, s. 763-769Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High temperature XRD and thermal diffusivity experiments were employed to investigate the degree of graphitisation in blast furnace coke. The experiments were conducted between room temperature and 1473 K. X-ray diffraction studies were carried out in order to monitor the degree of graphitisation in the coke samples from the same campaign. In these cases, the degree of graphitisation was followed by the changes in the vertical dimension. The degree of graphitisation was found to be dependent on temperature. On the other hand, the graphitisation at each temperature was instantaneous, even at as low a temperature as 973 K and no dependency on time could be noticed. The thermal diffusivities of the coke samples taken from deeper level of the experimental blast furnace were measured using the laser-flash technique. The results from these measurements showed that thermal diffusivities increased with the degree of graphitisation, which in turn, can be affected by the level in the blast furnace at which the coke sample was taken. The present results indicate that the degree of graphitisation as followed by X-ray diffraction analysis as well as thermal diffusivities can be used to trace the thermal history of coke. DSC measurements show that the heat capacity of the coke increases with temperature towards the heat capacity of graphite, which could be due to the increasing the graphitisation degree of the coke.

  • 17.
    Abdul Abas, Riad
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermal Diffusivity of Sintered Stainless steel-Alumina Composites2006Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, nr 4, s. 513-518Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermal diffusivity measurements were carried out as a function of temperature on sintered AISI 304 stainless steel-alumina composites having various compositions (0.001, 0.01, 0, 1, 1, 2, 3, 5, 7, 8, and 10 wt pct Al2O3). The measurements were carried out between room temperature and 1473 K. The thermal diffusivity and the thermal conductivity were found to increase with temperature in all the composite specimens. The thermal diffusivity was found to decrease with increasing weight fraction of alumina. This tendency can clearly be seen at temperatures above 755 K. The experimental results are in good agreement with the simple rule of mixture, the Eucken equation, and the Ohm’s law model developed by Hayashi et al. at weight fractions of alumina below 5 wt pct. Beyond this composition, the thermal diffusivity/conductivity shows a large discrepancy from the models. This could probably be attributed to the accumulation of alumina particles during cooled pressing and sintering.

  • 18. Abe, T.
    et al.
    Sundman, Bo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Termodynamisk modellering.
    Onodera, H.
    Thermodynamic assessment of the Cu-Pt system2006Inngår i: Journal of Phase Equilibria and Diffusion, ISSN 1547-7037, Vol. 27, nr 1, s. 5-13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A CALPHAD assessment of the Cu-Pt system has been carried out. Two and four sublattice models were applied to describe the Gibbs free energies of ordered phases where the contribution of SRO is taken explicitly into account through the reciprocal parameters. The disordered fcc A1 and liquid phases were treated as substitutional solutions. A consistent set of parameters for the phases in the Cu-Pt system as obtained, and those parameters can satisfactorily reproduce the experimental phase equilibria and thermodynamic properties, such as enthalpies, activity of Cu, and long-range order parameters.

  • 19.
    Abelin, Mathias
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Blomkvist, Håkan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Investigation of the scale factor between full scale ladle furnace process and water models2020Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    The ladle furnace process is an important process in the steel manufacturing industry. The purpose of this process is to optimize the composition of the elements in the melt as well as to homogenize the temperature in the liquid.

    It is common practice to model this process using smaller water models. In order to accurately scale these models a variety of criteria and scaling factors are needed. The central phenomenon which all else is derived from is the two-phase gas plume dominating the fluid flows. The plume, and its dependant parameters are difficult to define. Which ones ought to be used and how to use them has not been standardized. Concerns have been raised whether the most common method of scaling is even applicable in ladle metallurgy. This report gives an account for studies concerning these variables and their effect on the subject. The objective of this report is to highlight ways to improve these simulations with respect to debated parameters.

    The conclusion of this study points out the reasons for why these variables may be of importance for the modeling of the ladle furnace process. It also specifically mentions future work that should be conducted in order to provide deeper knowledge of thedifferent parameters affecting the method of modeling.

    Fulltekst (pdf)
    fulltext
  • 20. Aboulfadl, Hisham
    et al.
    Sopiha, Kostiantyn, V
    Keller, Jan
    Larsen, Jes K.
    Scragg, Jonathan J. S.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thuvander, Mattias
    Edoff, Marika
    Alkali Dispersion in (Ag,Cu)(In,Ga)Se-2 Thin Film Solar Cells-Insight from Theory and Experiment2021Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 13, nr 6, s. 7188-7199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silver alloying of Cu(In,Ga)Se-2 absorbers for thin film photovoltaics offers improvements in open-circuit voltage, especially when combined with optimal alkali-treatments and certain Ga concentrations. The relationship between alkali distribution in the absorber and Ag alloying is investigated here, combining experimental and theoretical studies. Atom probe tomography analysis is implemented to quantify the local composition in grain interiors and at grain boundaries. The Na concentration in the bulk increases up to similar to 60 ppm for [Ag]/([Ag] + [Cu]) = 0.2 compared to similar to 20 ppm for films without Ag and up to similar to 200 ppm for [Ag]/([Ag] + [Cu]) = 1.0. First-principles calculations were employed to evaluate the formation energies of alkali-on-group-I defects (where group-I refers to Ag and Cu) in (Ag,Cu)(In,Ga)Se-2 as a function of the Ag and Ga contents. The computational results demonstrate strong agreement with the nanoscale analysis results, revealing a clear trend of increased alkali bulk solubility with the Ag concentration. The present study, therefore, provides a more nuanced understanding of the role of Ag in the enhanced performance of the respective photovoltaic devices.

  • 21.
    Abouzari, Sara
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Solid solution strengthening effect on creep strength of austenitic stainless steel2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Sanicro 25 is a newly developed austenitic stainless steel, designed for the next generation of Ultrasupercritical coal-fired boilers in electrical power plants. This material is applicable in reheater and superheater tubes, where the material temperature is up to 700

    °C. One of the main strengthening mechanisms in high temperature materials is solid solution strengthening. A combination of this mechanism and precipitation hardening, promotes creep strength of heat resistance materials. The aim of this work was to characterize the effects of solid solution strengthening on creep strength of Sanicro 25.Previous works has been done for effects of phosphorous in copper and also for influence of laves phase on the creep properties of CrMo alloys. The results of these two works are used and the model is adapted to austenitic stainless steel. First a Zero starting state was defined which was Alloy 316H and then the calculation was made for Sanicro 25. Thermodynamic calculations were made using DICTRA and Thermo-Calc. Elastic misfit parameter was determined using ab initio calculations. The results from the simulation in this work indicate that solutes with larger size misfit compare to the parent atoms have better solid solution strengthening effect. A decrease in the creep strength by increasing temperature has been observed which could be attributed to growth of laves phase.

    Fulltekst (pdf)
    Solid solution strengthening effect on creep strength of austenitic stainless steel
  • 22. Abrikosov, I. A.
    et al.
    Kissavos, A. E.
    Liot, F.
    Alling, B.
    Simak, S. I.
    Peil, O.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Competition between magnetic structures in the Fe rich fcc FeNi alloys2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the results of a systematic ab initio study of the magnetic structure of Fe rich fcc FeNi binary alloys for Ni concentrations up to 50 at. %. Calculations are carried out within density-functional theory using two complementary techniques, one based on the exact muffin-tin orbital theory within the coherent potential approximation and another one based on the projector augmented-wave method. We observe that the evolution of the magnetic structure of the alloy with increasing Ni concentration is determined by a competition between a large number of magnetic states, collinear as well as noncollinear, all close in energy. We emphasize a series of transitions between these magnetic structures, in particular we have investigated a competition between disordered local moment configurations, spin spiral states, the double layer antiferromagnetic state, and the ferromagnetic phase, as well as the ferrimagnetic phase with a single spin flipped with respect to all others. We show that the latter should be particularly important for the understanding of the magnetic structure of the Invar alloys.

  • 23. Abrikosov, I. A.
    et al.
    Ponomareva, A. V.
    Barannikova, S. A.
    Hellman, O.
    Vekilova, O.Yu.
    Simak, S. I.
    Ruban, Andrei V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Multiscale approach to theoretical simulations of materials for nuclear energy applications: Fe-Cr and Zr-based alloys2013Inngår i: Advances in materials for nuclear energy: symposium held November 25-30, Boston, Massachusetts, U.S.A., Materials Research Society, 2013, s. 3-14Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We review basic ideas behind state-of-the-art techniques for first-principles theoretical simulations of the phase stabilities and properties of alloys. We concentrate on methods that allow for an efficient treatment of compositional and thermal disorder effects. In particular, we present novel approach to evaluate free energy for strongly anharmonic systems. Theoretical tools are then employed in studies of two materials systems relevant for nuclear energy applications: Fe-Cr and Zr-based alloys. In particular, we investigate the effect of hydrostatic pressure and multicomponent alloying on the mixing enthalpy of Fe-Cr alloys, and show that in the ferromagnetic state both of them reduce the alloy stability at low Cr concentration. For Zr-Nb alloys, we demonstrate how microscopic parameters calculated from first-principles can be used in higher-level models.

  • 24. Abu-Odeh, A.
    et al.
    Galvan, E.
    Kirk, T.
    Mao, Huahai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Chen, Q.
    Mason, P.
    Malak, R.
    Arróyave, R.
    Efficient exploration of the High Entropy Alloy composition-phase space2018Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 152, s. 41-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High Entropy Alloys (HEAs), Multi-principal Component Alloys (MCA), or Compositionally Complex Alloys (CCAs) are alloys that contain multiple principal alloying elements. While many HEAs have been shown to have unique properties, their discovery has been largely done through costly and time-consuming trial-and-error approaches, with only an infinitesimally small fraction of the entire possible composition space having been explored. In this work, the exploration of the HEA composition space is framed as a Continuous Constraint Satisfaction Problem (CCSP) and solved using a novel Constraint Satisfaction Algorithm (CSA) for the rapid and robust exploration of alloy thermodynamic spaces. The algorithm is used to discover regions in the HEA Composition-Temperature space that satisfy desired phase constitution requirements. The algorithm is demonstrated against a new (TCHEA1) CALPHAD HEA thermodynamic database. The database is first validated by comparing phase stability predictions against experiments and then the CSA is deployed and tested against design tasks consisting of identifying not only single phase solid solution regions in ternary, quaternary and quinary composition spaces but also the identification of regions that are likely to yield precipitation-strengthened HEAs.

  • 25.
    Adamopoulos, Othon
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Papadopoulos, Triantafillos
    Nanostructured bioceramics for maxillofacial applications2007Inngår i: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 18, nr 8, s. 1587-1597Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Biomaterials science and technology have been expanding tremendously the recent years. The results of this evolution are obvious in maxillofacial applications especially with the contemporary development of Nanotechnology. Among biomaterials, bioceramics possess a specific field due to various interactions with the biological tissues. The combination of bioceramics and nanotechnology has resulted in enhanced skeletal interactions in maxillofacial applications. Nanotechnology secures better mechanical properties and more effective biological interactions with jaws. The main production methods for the synthesis of nanostructured materials include plasma arcing. chemical vapour deposition, sol-gel and precipitation. The bioceramics in Dentistry comprise inert, bioactive, resorbable and composite systems. The purpose of the present article is to describe the available nanotechnology methods and how these could be addressed to synthesise maxillofacial bioceramics with advanced properties for better biological applications. Additionally, it describes specific clinical applications in maxillofacial surgery of these biomaterials-either by themselves or in combination with others-that can be promising candidates for bone tissue engineering. Such applications include replacement of lost teeth, filling of jaws defects or reconstruction of mandible and temporomandibular joint.

  • 26.
    Adineh, Morteza
    et al.
    Shahid Bahonar Univ Kerman, Coll Engn, Dept Mat Engn & Met, Kerman 7618868366, Iran..
    Doostmohammadi, Hamid
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Shahid Bahonar Univ Kerman, Coll Engn, Dept Mat Engn & Met, Kerman 7618868366, Iran..
    Microstructure, mechanical properties and machinability of Cu-Zn-Mg and Cu-Zn-Sb brass alloys2019Inngår i: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 35, nr 12, s. 1504-1514Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lead-free alloys have attracted great attentions recently due to the toxic nature of lead for the human body. In this study, low amounts of Mg and Sb were added to the Cu65-Zn35 brass and microstructure, mechanical properties and machinability of samples were compared to Cu65-Zn35 brass. Both Mg and Sb led to the promotion of beta ' phase as well as the formation of new ternary copper rich intermetallic particles. It was found that these particles had a significant role in the reduction of the ultimate tensile strength, toughness, work hardening and elongation while increasing the hardness of samples. Results of machinability evaluation of samples showed that the cutting forces were decreased significantly and morphology of chips were improved compared to Cu65-Zn35 brass sample.

  • 27. Adit Maark, T.
    et al.
    Hussain, T.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Structural, electronic and thermodynamic properties of Al- and Si-doped α-, γ-, and β-MgH2: Density functional and hybrid density functional calculations2012Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 37, nr 11, s. 9112-9122Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, we present a detailed study of Al- and Si-doped α-, γ-, and β-MgH 2 phases using the gradient corrected density functional GGA-PBE and the hybrid Hartree-Fock density functionals PBE0 and HSE06 within the framework of generalized Kohn-Sham density functional theory (DFT) using a plane-wave basis set. We investigate the structural, electronic, and thermodynamical properties of these compounds with regard to their hydrogen storage effectiveness. PBE0 and HSE06 predict cell parameters and bond lengths that are in good agreement with the GGA-PBE calculations and previously known experimental results. As expected smaller band gaps (E gs) are predicted by GGA-PBE for the pure magnesium hydride phases. PBE0 overcomes the deficiencies of DFT in treating these materials better than HSE06 and yields E gs that compare even better with previous GW calculations. Both the hybrid functionals increase the E gs of the Al-doped magnesium hydrides by much less magnitudes than of the Si-doped phases. This difference is interpreted in terms of charge density distributions. Best H 2 adsorption energies (ΔH ads) are computed by HSE06 while GGA-PBE significantly overestimates them. Si-doped α- and β-MgH 2 exhibited the least negative ΔH ads in close proximity to the H 2 binding energy range of -0.21 to -0.41 eV ideal for practical H 2 storage transportation applications.

  • 28.
    Adolfi, Sofia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Slag inclusion formation during solidification of steel alloys and in cast iron2007Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis explores the formation of segregation and inclusions during solidification of steel and cast iron. A better understanding of the formation mechanism should result in decreasing fraction of defects during solidification of ingot and strand material.

    Density driven macrosegregation was studied both experimentally and theoretically to see the effect of channel segregation on the total segregation. Formation of these pencil-like segregations is due to natural convection in the solidifying metal caused by liquid enrichment of elements with lower density compared to the bulk. It is suggested to change the composition to compensate for this density difference.

    Inclusion precipitation can be finite by limitations in segregation. Saturated liquid is found in the last solidified areas, often between dendrites. Here the enrichment of the liquid is possible due to microsegregation. Meanwhile crystals form and solidify the elements with low solubility in the solid is pushed out in the remaining liquid. Soon the liquid is saturated to the level where spontaneous formation of inclusions occurs. Microstructure studies by aid of SEM and micro-probe measurements are analysed to find at what point during solidification process the inclusions start to form. In steel making this formation has a detrimental effect on the mechanical properties in contrary to the production of nodular cast iron where the inclusions have a beneficial effect on the graphite formation.

    Inoculation of cast iron aims at reaching higher number density of graphite nodules, nodule morphology modification and control of nodule distribution during solidification. Late precipitation of nucleation sites has shown to have a positive impact on preventing chill. To find the most potent inoculation agent different additives were tested. Special effort has been made to analyse the effect of oxides and sulphides as nucleation sites.

    Fulltekst (pdf)
    FULLTEXT01
  • 29.
    Adolfi, Sofia
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mori, Kenji
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    MnS precipitation during solidification in presence of oxide nuclei2007Konferansepaper (Annet vitenskapelig)
  • 30. Affatato, S.
    et al.
    Leardini, W.
    Jedenmalm, Anneli
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ruggeri, O.
    Toni, A.
    Larger diameter bearings reduce wear in metal-on-metal hip implants2007Inngår i: Clinical Orthopaedics and Related Research, ISSN 0009-921X, E-ISSN 1528-1132, nr 456, s. 153-158Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Metal-on-metal hip arthroplasty has the longest clinical history of all total arthroplasties. We asked whether large diameter femoral heads would result in less wear than those with small diameters. We also asked if there is a threshold diameter that ensures good wear behavior. We tested three batches of cast high-carbon cobalt-chromium-molybdenum hip implants (28 mm, 36 min, and 54 min diameters) in a hip simulator for 5 million cycles. We used bovine serum as lubricant and weighed the samples at regular intervals during testing. The 28-mm configuration had almost twice the wear of the 54-mm configuration, but we observed no difference between the 36-mm and the 54-mm configurations. The similarity in the wear performances of the larger configurations supports the presence of a threshold diameter that ensures good wear behavior.

  • 31. Affatato, S.
    et al.
    Leardini, W.
    Jedenmalm, Anneli
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zavalloni, M.
    Ruggeri, O.
    Tarterini, F.
    Viceconti, M.
    Microstructural effects on the wear resistance of CO-CR implant alloys2006Inngår i: Proceedings of the 8th Biennial Conference on Engineering Systems Design and Analysis, 2006, s. -951Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Modem metal-on-metal articulation have been proposed to reduce the incidence of osteolysis due to polyethylene particles debris, as a late complication. The tribology of large metal-on-metal articulations allows theoretical advantages with respect to other configurations, especially for the lubrication regime. This study was aimed to compare the wear performances of different diameters of clinically available acetabular metallic components manufactured in a cast cobalt-chrome alloy. To evaluate the influence of the material properties of wear and microstructure, metal-on-metal components were tested in a hip joint simulator for five million cycles with bovine calf serum as lubricant. In particular, three different configurations of metal-on-metal components (28-mm, 36-mm, 54-mm) were tested. After the test all specimens were examined with optical and electronic scanning microscope. A statistical difference were observed among the three groups tested in the run-in and steady-state wear rates, favoring the larger femoral heads. The results of this study indicate that the 54-mm diameter femoral heads prove a better wear behavior than the smaller configurations.

  • 32.
    Afraz, Syed Ali
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mechanical, Microstructural and Corrosion performance for MIM materials based on coarse (-45µm) powders of ferritic stainless steel2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The purpose of this research is to investigate the mechanical, microstructural and corrosion performance of the ferritic stainless steel coarse powders, used in Metal Injection Molding (MIM) process. Three coarser powders made by Höganäs AB, were examined along with a commercially available fine MIM powder and samples from sheet metal. The studied powders were individually mixed with binders and then injection molded in the shape of dog bone shaped tensile bars. These green samples were then debinded and sintered to examine under different characterization methods. The methods used for examining the samples were tensile test, hardness test, metallography, SEM, chemical analysis, and salt spray test. After a comparative study of these different materials, it turns out that the chemical composition and the process parameters have more effect on materials properties compared to only particle size distribution in studied materials. After this study, 434 coarse powder was preferred upon the PolyMIM 430 fine powder, because of its lower price and same performance as that of PolyMIM 430.

    Fulltekst (pdf)
    Syed Ali Afraz's Masters Thesis
  • 33.
    Afzal, Muhammad
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Nanocomposite Materials for New Energy Conversion Device2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis gives an approach how to develop newperovskite and nanocomposite cathode material for low temperature solid oxidefuel cells on the basis of nanocomposite approach to lower the operatingtemperature of SOFC. BaxCa1-xCoyFe1-yO3-δ(BCCF) and BSCF perovskite or nanocomposite oxides have been synthesized andinvestigated as catalytically potential cathode materials for low temperaturesolid oxide fuel cells (LTSOFC). Some single component materials have been alsosynthesized for new energy conversion device or EFFC. These nanocomposite andperovskite electrical conductors were synthesized by wet chemical, sol gel,co-precipitation and solid state reaction methods. Comparison with that ofcommercial Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) cathode material, BCCF and locally prepared BSCF exhibit higher electricalconductivities as compared to that of commercial BSCF at same setup andconditions. In particular, novel Ba0.3Ca0.7Co0.8Fe0.2O3-δhas shown the maximum conductivity of 143 S/cm in air and local BSCF withconductivity of 313 S/cm in air at 550°C were measured by DC 4 probe method. Anadditional positive aspect of BCCF is that it is cost effective and works atroom temperature but with small output which will lead SOFC to operate atextremely low temperatures. XRD patterns of the samples reveal perovskite andnanocomposite structures of the said materials. Microstructure studies give thehomogeneous structure and morphology of the nanoparticles by using HighResolution Scanning Electron Microscopy (SEM). Cell resistance has beendetermined by Electrochemical Impedance Spectroscopy (EIS). Devised materialshave shown very good mechanical strength and stability proving their importancein advanced fuel cell technology. Power density of devices from 126 to 192 mWcm-2hasbeen achieved.

    Fulltekst (pdf)
    Afzal Muhammad-Master Thesis Final-Nanocomposite Materials for New Energy Conversion Device.pdf
  • 34.
    Agca, Can
    et al.
    Univ Calif Davis, Peter A Rock Thermochem Lab, Davis, CA 95616 USA.;Oak Ridge Natl Lab, POB 2009, Oak Ridge, TN 37831 USA..
    Lindwall, Greta
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    McMurray, Jake W.
    Oak Ridge Natl Lab, POB 2009, Oak Ridge, TN 37831 USA..
    Neuefeind, Jorg C.
    Oak Ridge Natl Lab, POB 2009, Oak Ridge, TN 37831 USA..
    Liu, Zi-Kui
    Penn State Univ, Dept Mat Sci & Engn, University Pk, PA 16802 USA..
    Navrotsky, Alexandra
    Univ Calif Davis, Peter A Rock Thermochem Lab, Davis, CA 95616 USA.;Arizona State Univ, Ctr Mat Universe, Sch Mol Sci, Tempe, AZ 85287 USA..
    Experimental and computational studies of melting of the spinel phase in the Fe-Al-O ternary system2020Inngår i: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 70, artikkel-id 101798Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The melting behavior of spinel in the Fe-Al-O system at high temperatures (1500-1800 degrees C) was studied by a combination of experimental and computational investigations. Differential thermal analysis (DTA) at ultra-high temperatures coupled with cooling traces on CO2 laser-heated levitated samples provided melting temperatures and the heats of fusion of (Fe,Al)(3)O-4 spinel phases. The experimental results are in fair agreement with the predictions using a published CALPHAD description and areas for modeling improvement are identified. New insights into the melting of defect spinel are provided.

  • 35.
    Aghasibeig, Maniya
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Laser cladding of a featureless iron-based alloy2012Inngår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 209, s. 32-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser cladding experiments with powder injection technique were carried out to create coatings of Fe-8.1Cr6.4Mn-5.3Si-6.9Mo-3.6C alloy on AISI 1018 steel substrates using a diode laser. Analysis of the clad layers showed that an almost featureless structure was formed at different dilutions between 1% and 4%. The featureless phase with a high hardness of 1155 HV was characterized as a metastable solid solution of e phase. However, the featureless structure appeared to be very brittle with numerous cracks. After heat-treatment, it decomposed into a bainitic structure with a high hardness of 884 HV.

  • 36.
    Ahlbäck, Anton
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. KTH.
    Study of the optimization of the electromagnetic field configuration for electromagnetic brakes for thin slab casting with different casting throughput using CFD simulations.2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In steelmaking, the quest for increased productivity without losing quality is never-ending, and new processes and changes to existing ones are constantly explored. In the 20th century, electromagnetic devices were introduced to the steel industry, in order to increase productivity in various parts of the steelmaking process. One of these devices is called an Electromagnetic Brake, or EMBR, and is applied at the mold of the continuous caster. The EMBR generates an electromagnetic field that affects the flow of the steel, and this paper has investigated how different electromagnetic fields affect the steel flow. The project has been performed in collaboration with ABB and the aim have been to investigateif it is possible to optimize the braking effect by altering the EMBR iron core of an existing EMBR, thus generating electromagnetic fields of new geometrical characters. This was done at a casting throughput of 4,5 metric ton/min. Furthermore, it was also investigated how the modified EMBRs affected a steel flow of a higher casting throughput of 8,0 metric ton/min. The investigations have been performed by conducting CFD simulations; however, no industrial experiments have been performed in order to validate the CFD results. It was found that it is possible to achieve more optimized braking by changing the geometry of the electromagnetic field and it was possible to brake the meniscus velocity below the critical value of 0,3 m/s. It was also found that with increased throughput an electromagnetic field of greater magnetic flux density was needed to have a braking effect. However, the meniscus velocity when casting with a throughput of 8,0 metric ton/min never reached below the critical value of 0,3 m/s. The electromagnetic field that had the most damping effect on the meniscus velocity of the lower throughput was also the field that had the highest damping effect on the higher throughput.

    Fulltekst tilgjengelig fra 2044-12-24 09:10
  • 37.
    Ahlin, Björn
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Gärdin, Marcus
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Automated Classification of Steel Samples: An investigation using Convolutional Neural Networks2017Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    Automated image recognition software has earlier been used for various analyses in the steel making industry. In this study, the possibility to apply such software to classify Scanning Electron Microscope (SEM) images of two steel samples was investigated. The two steel samples were of the same steel grade but with the difference that they had been treated with calcium for a different length of time. 

    To enable automated image recognition, a Convolutional Neural Network (CNN) was built. The construction of the software was performed with open source code provided by Keras Documentation, thus ensuring an easily reproducible program. The network was trained, validated and tested, first for non-binarized images and then with binarized images. Binarized images were used to ensure that the network's prediction only considers the inclusion information and not the substrate.

    The non-binarized images gave a classification accuracy of 99.99 %. For the binarized images, the classification accuracy obtained was 67.9%.  The results show that it is possible to classify steel samples using CNNs. One interesting aspect of the success in classifying steel samples is that further studies on CNNs could enable automated classification of inclusions. 

    Fulltekst (pdf)
    fulltext
  • 38.
    Ahlin, Björn T. I.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Nitrogen Removal in a Vacuum Tank Degasser: An Investigation on the Nitrogen Removal Performance2019Independent thesis Advanced level (degree of Master (Two Years)), 300 hpOppgave
    Abstract [en]

    The impending change of processes at SSAB Oxelösund due to the HYBRIT project, where the blast furnace and LD converter are to be replaced with an EAF will have a significant impact on the manufacturing of steel in Oxelösund. One issue that will arise is the nitrogen content in the steel. Sources claim that the nitrogen content in steel from an EAF route is substantially larger, 60-70 ppm, than in steel from a blast furnace and LD converter route, which have a nitrogen content of around 25 ppm. Therefore, the nitrogen removal capabilities of SSAB Oxelösund’s vacuum tank degasser were to be examined. Industrial trials were performed where the amount of slag during vacuum treatment was lowered. The intention was that half the amount of slag removed prior to vacuum treatment and later completely slag free. This was performed in an attempt to increase the effective reaction area, where nitrogen removal occurs. Due to some practical problems with the steel mill, the industrial trial were unfortunately cut short. Consequently, only trials with half the amount of slag were performed and compared to existing process data for standard praxis. Also, nitrogen removal calculations based on the industrial data were performed. A parameter representing the overall reaction rate, which is dependent on effective reaction area was obtained, validated and subsequently applied to a future case scenario. The results indicate that the reduction in slag amount does have the desired effect, increasing the said area and increasing the rate of nitrogen removal. However, the sample size is not nearly sufficient enough to determine this definitively. The conclusions reached were that the facility does have the possibility to decrease the increased nitrogen content down to reasonable levels, around 20-30 ppm. Albeit, an increase in vacuum treatment time is probably required. Another conclusion was that surface active elements, such as oxygen and sulphur greatly reduce the nitrogen removal. Therefore, efforts should be taken to remove these elements prior to vacuum treatment. In addition, it was established that the effective reaction area is of great importance for a successful nitrogen removal. Therefore, actions to maximise this area should be taken. Finally, it was stated that further research is necessary in order to fully understand nitrogen contamination prevention- and removal techniques

    Fulltekst (pdf)
    fulltext
  • 39.
    Ahmad, Yousef
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Oxidation of Graphite and Metallurgical Coke: A Numerical Study with an Experimental Approach2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    At the royal institute of technology (KTH) in the department of applied process metallurgy, a novel modelling approach has been developed which allows a dynamic coupling between the commercial thermodynamic software Thermo-Calc and the commercial computational fluid dynamic (CFD) software Ansys Fluent, only referred to as Fluent in the study. The dynamic coupling approach is used to provide numerical CFD-models with thermodynamic data for the thermo-physical properties and for the fluid-fluid chemical reactions occurring in metallurgical processes. The main assumption forthe dynamic coupling approach is the existence of local equilibrium in each computational cell. By assuming local equilibrium in each computational cell it is possible to use thermodynamic data from thermodynamic databases instead of kinetic data to numerically simulate chemical reactions. The dynamic coupling approach has been used by previous studies to numerically simulate chemical reactions in metallurgical processes with good results. In order to validate the dynamic coupling approach further, experimental data is required regarding surface reactions. In this study, a graphiteand metallurgical coke oxidation experimental setup was suggested in order to provide the needed experimental data. With the experimental data, the ability of the dynamic couplings approach to numerically predict the outcome of surface reactions can be tested.By reviewing the literature, the main experimental apparatus suggested for the oxidationexperiments was a thermo-gravimetric analyzer (TGA). The TGA can provide experimental data regarding the reaction rate, kinetic parameters and mass loss as a function of both temperature and time. An experimental setup and procedure were also suggested.In order to test the ability of Fluent to numerically predict the outcome of surface reactions, without any implementation of thermodynamic data from Thermo-Calc, a benchmarking has been conducted. Fluent is benchmarked against graphite oxidation experiments conducted by Kim and No from the Korean advanced institute of science and technology (KAIST). The experimental graphite oxidation rates were compared with the numerically calculated graphite oxidation rates obtained from Fluent. A good match between the experimental graphite oxidation rates and the numerically calculated graphite oxidation rates were obtained. A parameter study was also conducted in order to study the effect of mass diffusion, gas flow rate and the kinetic parameters on the numerically calculated graphite oxidation rate. The results of the parameter study were partially supported by previous graphite oxidation studies. Thus, Fluent proved to be a sufficient numerical tool for numerically predicting the outcome of surface reactions regarding graphite oxidation at zero burn-off degree.

    Fulltekst (pdf)
    fulltext
  • 40.
    Ahmed, Hesham M.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Investigations of the Kinetics of Reduction and Reduction/Carburization of NiO-WO3 Precursors.2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

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

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

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

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

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

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

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

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

  • 41.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    El-Geassy, A. H. A.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Kinetics of Reduction of NiO-WO3 Mixtures by Hydrogen2010Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, nr 1, s. 161-172Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 42.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    El-Geassy, Abdel-Hady A.
    Viswanathan, Nurni Neelakantan
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO-WO(3) Precursors in Fluidized Bed Reactor2011Inngår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, nr 9, s. 1383-1391Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 43.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    El-Geassy, Abdel-Hady
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Kinetic Studies of the Hydrogen Reduction of NiO-WO3 precursors in a Fluidized-bed reactorInngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Artikkel i tidsskrift (Annet vitenskapelig)
  • 44.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Isothermal dynamic thermal diffusivity studies of the reduction of NiO and NiWO(4) precursors by hydrogen2011Inngår i: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 102, nr 11, s. 1336-1344Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 45.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture2010Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, nr 1, s. 173-181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 46.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Viswanathan, N. N.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    On The Kinetics of Hydrogen Reduction of NiO-WO3 Precursors in Fluidized Bed- A Modeling Approach2011Inngår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, nr 9, s. 1383-1391Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 47.
    Ahmed, Hesham M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Viswanathan, Nurini N.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Dynamic Thermal Diffusivity Measurements - A Tool for Studying Gas-Solid Reactions2011Inngår i: DIFFUSION IN SOLIDS AND LIQUIDS VI, PTS 1 AND 2, 2011, s. 217-222Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 48.
    Ahmed, Hesham
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mis, Michal
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    El-Geassy, Abdel-Hady
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Seethararnan, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Reduction-Carburization of the Oxides of Ni and W Towards the Synthesis of Ni-W-C Carbides2010Inngår i: ADVANCED MATERIALS FORUM V, PT 1 AND 2  / [ed] Rosa LG; Margarido F, 2010, Vol. 636-637, s. 952-962Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 49. Ahmed, Hesham
    et al.
    Morales-Estrella, R.
    Viswanathan, Nurin
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Gas-Solid Reaction Route toward the Production of Intermetallics from Their Corresponding Oxide Mixtures2016Inngår i: Metals, ISSN 2075-4701, Vol. 6, nr 8, artikkel-id 190Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 50. Ahola-Tuomi, M.
    et al.
    Punkkinen, Marko Patrick John
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Laukkanen, P.
    Kuzmin, M.
    Lang, J.
    Schulte, K.
    Pietzsch, A.
    Perala, R. E.
    Rasanen, N.
    Vayrynen, I. J.
    Properties of self-assembled Bi nanolines on InAs(100) studied by core-level and valence-band photoemission, and first-principles calculations2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 24, s. 245401-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied self-assembled bismuth (Bi) nanolines on the Bi-terminated InAs(100) surface by core-level and valence-band photoelectron spectroscopy, and ab initio first-principles calculations. A structural model for this intriguing surface is suggested based on the comparison of the measured and calculated core-level shifts. Also, the atomic origins for the core-level shifts are proposed based on the calculations. A clear peak related to this surface was observed in the valence band 0.34 eV below the Fermi level, which can be used as a "fingerprint" of a well-ordered Bi/InAs(100) nanoline surface.

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