M. Baben - Academia.edu (original) (raw)

Papers by M. Baben

Journal of Sustainable Metallurgy

The first dynamic process model of a Top Submerged Lance (TSL) furnace based on a fundamental pha... more The first dynamic process model of a Top Submerged Lance (TSL) furnace based on a fundamental phase solution thermochemical basis is reported. This development is required to understand fully the role of TSL as an enabler of the circular economy, i.e., how well it brings materials back into the cycle. To achieve this understanding, the volume inside the furnace has been divided into six zones (bullion, bullion/slag interface, slag, bubble, splash, freeboard), gleaning from industrial experience and roughly guided by CFD studies by the authors. For each of these zones, local equilibrium is assumed. The model is implemented for lead smelting using SimuSage and has been benchmarked against reported production data. It is shown that the model can be used to optimize processing parameters: the process gas flow through the lance, to achieve a compromise between maximization of bullion production and process stability by avoiding the formation of matte phase. In a virtual experiment, a concentrate poorer in PbS is used and it is proposed how processing conditions should be modified to achieve a stable process and how the maximum achievable productivity changes. Finally, the model is applied to predict the partitioning of indium, as an important technology element from a typical recycling feed between the bullion, slag, and dust phases. It is observed that indium reports mainly to the slag phase during the smelting stage.

Polymer Degradation and Stability

Abstract The inhibition of the thermal degradation of molten polycarbonate at tool steel interfac... more Abstract The inhibition of the thermal degradation of molten polycarbonate at tool steel interfaces by magnetron sputtered TiAlN coatings was studied on fundamental level by means of in-situ and ex-situ spectroscopic and microscopic techniques. As reference systems, which enable the application of in-situ analytical techniques, oxide covered iron films were compared with atmosphere exposed Ti 0.52 Al 0.48 N 1.14 hard coatings. Moreover, SiO 2 terminated silicon and glass substrates as prototypical insulating and inert materials were studied. Interface and interphase analysis of the inorganic substrates and the polymer were performed using confocal fluorescence spectroscopy as well as FTIR, UV/VIS and X-ray photoelectron spectroscopy (XPS). The degradation of polycarbonate at the Fe-oxide interface as revealed by FTIR and UV/VIS spectroscopy indicated the formation of aromatic esters, cyclic anhydrides and discoloring products including char. Simultaneous cross-linking could be verified by strong broadening of the polycarbonates Young's modulus at the Fe-oxide interface as measured by AFM. XPS results indicate that the Fe(III)-states in the Fe-oxide were reduced to Fe(II) states which are likely to act as catalytic sites for PC degradation. In contrast, the surface oxidized Ti 0.52 Al 0.48 N 1.14 coatings effectively inhibited the thermal degradation but however induced slight restructuring of polycarbonate in comparison to the completely inert SiO 2 surface.

Calphad

Abstract Thermodynamic properties of the quasi binary Ca(NO3)2–NaNO3 system are of interest with ... more Abstract Thermodynamic properties of the quasi binary Ca(NO3)2–NaNO3 system are of interest with respect to thermal energy storage. In the present work the phase diagram as well as thermodynamic properties of the near eutectic mixture 45 mol% Ca(NO3)2 – 55 mol% (NaNO3)2 were determined experimentally and applied in the assessment of a new Gibbs energy dataset for thermochemical calculations. The enthalpy of fusion of the 45 mol% Ca(NO3)2 – 55 mol% (NaNO3)2 mixture is determined to be 24.7 ± 0.5 kJ/mol. The melting and crystallization enthalpy have good reproducibility, which makes it possible to use this mixture as a phase change material at temperature 225 °C. The assessed dataset describes liquid phase properties using a subregular solution model in the Redlich-Kister formalism with high accuracy. Therefore it can be used for the prediction of thermodynamic properties of different compositions in the whole Ca(NO3)2–NaNO3 system and be included in databases for calculation of multicomponent systems including other components.

The Journal of Chemical Thermodynamics

Abstract Thermodynamic properties of calcium nitrate are of interest for development of thermodyn... more Abstract Thermodynamic properties of calcium nitrate are of interest for development of thermodynamic databases, which can be applicable for thermal energy storage technologies. In the present work thermodynamic properties of Ca(NO3)2, i.e. heat capacity (Cp) and enthalpy of fusion, were determined experimentally. The enthalpy of fusion of Ca(NO3)2 (33.4 ± 1 kJ/mol) was measured in a closed Pt-crucible at the melting temperature 823 K for the first time. The heat capacity of Ca(NO3)2 was measured in the temperature range from 143 K to 723 K by three different differential scanning calorimeters. High temperature X-ray diffraction was used for determination of the temperature dependence of volume from 298 K to 723 K. Combination of heat capacity and volume allowed us to calculate the molar volume at 0 K and to obtain the thermal expansion. The Gruneisen parameter and bulk modulus were deduced from combination of the available ab initio values of Cv and the values of Cp as well as the thermal expansion obtained in this work. This methodology allowed us to perform a comprehensive analysis of experimental values and first principal calculations. A complete thermodynamic dataset for solid and liquid Ca(NO3)2 has been derived.

Materials Research Letters, 2016

The Journal of Chemical Physics, 2016

Self-healing materials allow for a design concept based on damage management where damage that is... more Self-healing materials allow for a design concept based on damage management where damage that is inflicted during operation can be healed autonomously. It has been shown that the Mn+1AXn phases Ti3AlC2, Ti2AlC and Cr2AlC exhibit autonomous self-healing behaviour. Cracks are filled and hence healed by oxidation products of the M and A elements in the MAX phase at high operating temperatures. After crack healing the fracture strength is recovered to the level of the virgin material. Cr2AlC MAX phase was shown to exhibit excellent erosion resistance and high damage tolerance. The oxide scale forming in the temperature range between 900- 1200°C after different oxidation times was studied. The influence of the addition of Y on the rate of oxidation of Cr2AlC films and on their self-healing behaviour was investigated. The aim of the ongoing research project is to assess the potential of Cr2AlC MAX phase coatings as autonomous self-healing material by understanding the basic physical and chemical principles governing multiple crack closure to heal erosion damage.

Journal of Applied Physics, 2015

ABSTRACT Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at.% we... more ABSTRACT Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at.% were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at.%) split segments in Ar/O2 atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at.% of Si was increased by more than 100 �C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the a-Al2O3 formation temperature, which increased by more than 120 �C. While for the latter retardation, the evidence for the presence of SiO2 at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotron X-ray diffraction experiments for amorphous Al2O3 with and without Si incorporation, we suggest that the experimentally identified enhanced thermal stability of amorphous alumina with addition of Si is due to the formation of shorter and stronger Si–O bonds as compared to Al–O bonds.

Journal of Applied Physics, 2014

Surface and Coatings Technology, 2011

Surface and Coatings Technology, 2011

The isothermal oxidation behavior of Cr2AlC coatings on alumina substrates was investigated in th... more The isothermal oxidation behavior of Cr2AlC coatings on alumina substrates was investigated in the temperature range of 1230 to 1410°C. The structure, surface morphology, microstructure evolution and chemistry of the reaction products have been investigated. In the investigated temperature range, the Cr2AlC films form a dense continuous oxide scale consisting of α-Al2O3 on Cr carbides. The oxidation rates determined by

Surface and Coatings Technology, 2010

An ∼5µm Cr2AlC coating was synthesized on near-α titanium alloy Ti6242 using an industrially size... more An ∼5µm Cr2AlC coating was synthesized on near-α titanium alloy Ti6242 using an industrially sized magnetron sputtering coater. Isothermal oxidation at 700°C and 800°C, and cyclic oxidation at 700°C of the bare alloys and coated specimens were investigated in air. The results indicated that the Ti6242 alloy faced serious oxidation problems at 700°C and 800°C. Repeated formation and spallation of

Journal of Physics: Condensed Matter, 2012

To identify the origin of the experimentally observed nitrogen over- and understoichiometry in Ti... more To identify the origin of the experimentally observed nitrogen over- and understoichiometry in TiAlN thin films, various point defect configurations were studied by ab initio calculations in terms of formation energies, equilibrium volume and elastic moduli. From formation energies and comparison to existing experimental equilibrium volume and elasticity data, it is shown that nitrogen vacancies and metal vacancies are responsible for nitrogen understoichiometry and overstoichiometry, respectively. Irrespective of the type of vacancies, the bulk modulus is decreased by approximately 7% as the nitrogen concentration is increased or decreased by 3 at.%.

Journal of Physics: Condensed Matter, 2013

Using density functional theory, the effect of Si on the stability and electronic structure of γ-... more Using density functional theory, the effect of Si on the stability and electronic structure of γ- and α-Al2O3 has been investigated. The concentration range from 0 to 5 at.% is probed and the additive is positioned at different substitutional sites in the γ-phase. The calculations for (Al,Si)2O3 predict a trend towards spontaneous decomposition into α-/γ-Al2O3 and SiO2. Therefore, the formation of the metastable γ-(Al,Si)2O3 phase can only be expected during non-equilibrium processing where the decomposition is kinetically hindered. The Si-induced changes in stability of this metastable solid solution may be understood based on the electronic structure. As the Si concentration is increased, stiff silicon-oxygen bonds are formed giving rise to the observed stabilization of the γ-phase.

Journal of Physics: Condensed Matter, 2013

In this work the electronic structure and mechanical properties of the phases X(2)BC with X =Ti, ... more In this work the electronic structure and mechanical properties of the phases X(2)BC with X =Ti, V, Zr, Nb, Mo, Hf, Ta, W (Mo(2)BC-prototype) were studied using ab initio calculations. As the valence electron concentration (VEC) per atom is increased by substitution of the transition metal X, the six very strong bonds between the transition metal and the carbon shift to lower energies relative to the Fermi level, thereby increasing the bulk modulus to values of up to 350 GPa, which corresponds to 93% of the value reported for c-BN. Systems with higher VEC appear to be ductile as inferred from both the more positive Cauchy pressure and the larger value of the bulk to shear modulus ratio (B/G). The more ductile behavior is a result of the more delocalized interatomic interactions due to larger orbital overlap in smaller unit cells. The calculated phase stabilities show an increasing trend as the VEC is decreased. This rather unusual combination of high stiffness and moderate ductility renders X(2)BC compounds with X = Ta, Mo and W as promising candidates for protection of cutting and forming tools.

Journal of Sustainable Metallurgy

The first dynamic process model of a Top Submerged Lance (TSL) furnace based on a fundamental pha... more The first dynamic process model of a Top Submerged Lance (TSL) furnace based on a fundamental phase solution thermochemical basis is reported. This development is required to understand fully the role of TSL as an enabler of the circular economy, i.e., how well it brings materials back into the cycle. To achieve this understanding, the volume inside the furnace has been divided into six zones (bullion, bullion/slag interface, slag, bubble, splash, freeboard), gleaning from industrial experience and roughly guided by CFD studies by the authors. For each of these zones, local equilibrium is assumed. The model is implemented for lead smelting using SimuSage and has been benchmarked against reported production data. It is shown that the model can be used to optimize processing parameters: the process gas flow through the lance, to achieve a compromise between maximization of bullion production and process stability by avoiding the formation of matte phase. In a virtual experiment, a concentrate poorer in PbS is used and it is proposed how processing conditions should be modified to achieve a stable process and how the maximum achievable productivity changes. Finally, the model is applied to predict the partitioning of indium, as an important technology element from a typical recycling feed between the bullion, slag, and dust phases. It is observed that indium reports mainly to the slag phase during the smelting stage.

Polymer Degradation and Stability

Abstract The inhibition of the thermal degradation of molten polycarbonate at tool steel interfac... more Abstract The inhibition of the thermal degradation of molten polycarbonate at tool steel interfaces by magnetron sputtered TiAlN coatings was studied on fundamental level by means of in-situ and ex-situ spectroscopic and microscopic techniques. As reference systems, which enable the application of in-situ analytical techniques, oxide covered iron films were compared with atmosphere exposed Ti 0.52 Al 0.48 N 1.14 hard coatings. Moreover, SiO 2 terminated silicon and glass substrates as prototypical insulating and inert materials were studied. Interface and interphase analysis of the inorganic substrates and the polymer were performed using confocal fluorescence spectroscopy as well as FTIR, UV/VIS and X-ray photoelectron spectroscopy (XPS). The degradation of polycarbonate at the Fe-oxide interface as revealed by FTIR and UV/VIS spectroscopy indicated the formation of aromatic esters, cyclic anhydrides and discoloring products including char. Simultaneous cross-linking could be verified by strong broadening of the polycarbonates Young's modulus at the Fe-oxide interface as measured by AFM. XPS results indicate that the Fe(III)-states in the Fe-oxide were reduced to Fe(II) states which are likely to act as catalytic sites for PC degradation. In contrast, the surface oxidized Ti 0.52 Al 0.48 N 1.14 coatings effectively inhibited the thermal degradation but however induced slight restructuring of polycarbonate in comparison to the completely inert SiO 2 surface.

Calphad

Abstract Thermodynamic properties of the quasi binary Ca(NO3)2–NaNO3 system are of interest with ... more Abstract Thermodynamic properties of the quasi binary Ca(NO3)2–NaNO3 system are of interest with respect to thermal energy storage. In the present work the phase diagram as well as thermodynamic properties of the near eutectic mixture 45 mol% Ca(NO3)2 – 55 mol% (NaNO3)2 were determined experimentally and applied in the assessment of a new Gibbs energy dataset for thermochemical calculations. The enthalpy of fusion of the 45 mol% Ca(NO3)2 – 55 mol% (NaNO3)2 mixture is determined to be 24.7 ± 0.5 kJ/mol. The melting and crystallization enthalpy have good reproducibility, which makes it possible to use this mixture as a phase change material at temperature 225 °C. The assessed dataset describes liquid phase properties using a subregular solution model in the Redlich-Kister formalism with high accuracy. Therefore it can be used for the prediction of thermodynamic properties of different compositions in the whole Ca(NO3)2–NaNO3 system and be included in databases for calculation of multicomponent systems including other components.

The Journal of Chemical Thermodynamics

Abstract Thermodynamic properties of calcium nitrate are of interest for development of thermodyn... more Abstract Thermodynamic properties of calcium nitrate are of interest for development of thermodynamic databases, which can be applicable for thermal energy storage technologies. In the present work thermodynamic properties of Ca(NO3)2, i.e. heat capacity (Cp) and enthalpy of fusion, were determined experimentally. The enthalpy of fusion of Ca(NO3)2 (33.4 ± 1 kJ/mol) was measured in a closed Pt-crucible at the melting temperature 823 K for the first time. The heat capacity of Ca(NO3)2 was measured in the temperature range from 143 K to 723 K by three different differential scanning calorimeters. High temperature X-ray diffraction was used for determination of the temperature dependence of volume from 298 K to 723 K. Combination of heat capacity and volume allowed us to calculate the molar volume at 0 K and to obtain the thermal expansion. The Gruneisen parameter and bulk modulus were deduced from combination of the available ab initio values of Cv and the values of Cp as well as the thermal expansion obtained in this work. This methodology allowed us to perform a comprehensive analysis of experimental values and first principal calculations. A complete thermodynamic dataset for solid and liquid Ca(NO3)2 has been derived.

Materials Research Letters, 2016

The Journal of Chemical Physics, 2016

Self-healing materials allow for a design concept based on damage management where damage that is... more Self-healing materials allow for a design concept based on damage management where damage that is inflicted during operation can be healed autonomously. It has been shown that the Mn+1AXn phases Ti3AlC2, Ti2AlC and Cr2AlC exhibit autonomous self-healing behaviour. Cracks are filled and hence healed by oxidation products of the M and A elements in the MAX phase at high operating temperatures. After crack healing the fracture strength is recovered to the level of the virgin material. Cr2AlC MAX phase was shown to exhibit excellent erosion resistance and high damage tolerance. The oxide scale forming in the temperature range between 900- 1200°C after different oxidation times was studied. The influence of the addition of Y on the rate of oxidation of Cr2AlC films and on their self-healing behaviour was investigated. The aim of the ongoing research project is to assess the potential of Cr2AlC MAX phase coatings as autonomous self-healing material by understanding the basic physical and chemical principles governing multiple crack closure to heal erosion damage.

Journal of Applied Physics, 2015

ABSTRACT Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at.% we... more ABSTRACT Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at.% were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at.%) split segments in Ar/O2 atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at.% of Si was increased by more than 100 �C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the a-Al2O3 formation temperature, which increased by more than 120 �C. While for the latter retardation, the evidence for the presence of SiO2 at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotron X-ray diffraction experiments for amorphous Al2O3 with and without Si incorporation, we suggest that the experimentally identified enhanced thermal stability of amorphous alumina with addition of Si is due to the formation of shorter and stronger Si–O bonds as compared to Al–O bonds.

Journal of Applied Physics, 2014

Surface and Coatings Technology, 2011

Surface and Coatings Technology, 2011

The isothermal oxidation behavior of Cr2AlC coatings on alumina substrates was investigated in th... more The isothermal oxidation behavior of Cr2AlC coatings on alumina substrates was investigated in the temperature range of 1230 to 1410°C. The structure, surface morphology, microstructure evolution and chemistry of the reaction products have been investigated. In the investigated temperature range, the Cr2AlC films form a dense continuous oxide scale consisting of α-Al2O3 on Cr carbides. The oxidation rates determined by

Surface and Coatings Technology, 2010

An ∼5µm Cr2AlC coating was synthesized on near-α titanium alloy Ti6242 using an industrially size... more An ∼5µm Cr2AlC coating was synthesized on near-α titanium alloy Ti6242 using an industrially sized magnetron sputtering coater. Isothermal oxidation at 700°C and 800°C, and cyclic oxidation at 700°C of the bare alloys and coated specimens were investigated in air. The results indicated that the Ti6242 alloy faced serious oxidation problems at 700°C and 800°C. Repeated formation and spallation of

Journal of Physics: Condensed Matter, 2012

To identify the origin of the experimentally observed nitrogen over- and understoichiometry in Ti... more To identify the origin of the experimentally observed nitrogen over- and understoichiometry in TiAlN thin films, various point defect configurations were studied by ab initio calculations in terms of formation energies, equilibrium volume and elastic moduli. From formation energies and comparison to existing experimental equilibrium volume and elasticity data, it is shown that nitrogen vacancies and metal vacancies are responsible for nitrogen understoichiometry and overstoichiometry, respectively. Irrespective of the type of vacancies, the bulk modulus is decreased by approximately 7% as the nitrogen concentration is increased or decreased by 3 at.%.

Journal of Physics: Condensed Matter, 2013

Using density functional theory, the effect of Si on the stability and electronic structure of γ-... more Using density functional theory, the effect of Si on the stability and electronic structure of γ- and α-Al2O3 has been investigated. The concentration range from 0 to 5 at.% is probed and the additive is positioned at different substitutional sites in the γ-phase. The calculations for (Al,Si)2O3 predict a trend towards spontaneous decomposition into α-/γ-Al2O3 and SiO2. Therefore, the formation of the metastable γ-(Al,Si)2O3 phase can only be expected during non-equilibrium processing where the decomposition is kinetically hindered. The Si-induced changes in stability of this metastable solid solution may be understood based on the electronic structure. As the Si concentration is increased, stiff silicon-oxygen bonds are formed giving rise to the observed stabilization of the γ-phase.

Journal of Physics: Condensed Matter, 2013

In this work the electronic structure and mechanical properties of the phases X(2)BC with X =Ti, ... more In this work the electronic structure and mechanical properties of the phases X(2)BC with X =Ti, V, Zr, Nb, Mo, Hf, Ta, W (Mo(2)BC-prototype) were studied using ab initio calculations. As the valence electron concentration (VEC) per atom is increased by substitution of the transition metal X, the six very strong bonds between the transition metal and the carbon shift to lower energies relative to the Fermi level, thereby increasing the bulk modulus to values of up to 350 GPa, which corresponds to 93% of the value reported for c-BN. Systems with higher VEC appear to be ductile as inferred from both the more positive Cauchy pressure and the larger value of the bulk to shear modulus ratio (B/G). The more ductile behavior is a result of the more delocalized interatomic interactions due to larger orbital overlap in smaller unit cells. The calculated phase stabilities show an increasing trend as the VEC is decreased. This rather unusual combination of high stiffness and moderate ductility renders X(2)BC compounds with X = Ta, Mo and W as promising candidates for protection of cutting and forming tools.