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Traditional techniques of inclusion size determination are time consuming and cannot be implemented for on-line quality control. With the development of pulse discrimination analysis – optical emission spectroscopy (PDA-OES), the on-line determination of inclusions has become possible. However, PDA-OES measures only the number of inclusions present in the steel irrespective of size. In the present paper, the potential of PDA to determine the inclusion size is evaluated by employing two methodologies: (i) obtaining the average inclusion size by dividing the difference of total and soluble aluminium concentration by the number of Al based inclusions for 200 industrial ULC heats and (ii) measuring the Al concentration for individual peak intensity for specific heats, giving the inclusion size distribution. The methodologies of inclusion size measurement by PDA-OES as well as the possible causes of the discrepancies obtained after comparison with the inclusion extraction technique are explained in detail.

The effect of O on the phase equilibria in Nb–Fe–Cr alloys, more specifically on the formation of a Ti2Ni type phase, has been studied. Nb–xFe–yCr alloys with × = 37.4 – 41.4 at.%, y = 7.6 – 8.6 at.% were subjected to long term annealing experiments at 950 8C after oxygenation. The phases were identified and characterized using scanning electron microscopy, X-ray diffraction and wavelength dispersive spectroscopy. In the pure Nb-37Fe-8Cr and Nb-41Fe-9Cr alloys respectively a two phase equilibrium between (Nb) and l FeNb and a three phase equilibrium between (Nb), l FeNb and Fe2Nb are established. In the oxygenated alloys a Ti2Ni type phase with composition (Fe, Cr)6Nb6Ox appears mainly at the expense of the l FeNb phase. With respect to composition and crystallographic parameters the (Fe, Cr)6Nb6Ox phase has large similarities with the Fe2.4Nb3.6O and Fe6Nb6O phase. From wavelength dispersive spectroscopy measurements, it is concluded that × equals 0.75 when (Fe, Cr)6Nb6Ox is in equilibrium with (Nb), l FeNb and Fe2Nb. × is higher when this phase is in equilibrium with NbO. The structure of (Fe, Cr)6Nb6Ox is also analyzed with Rietveld refinement. This analysis reveals that Cr atoms partially replace Fe atoms only on the 16d site and not on the 32e site.

The formation of Al2O3 inclusions in liquid iron has been investigated in a resistance heated tube furnace to obtain deoxidation and reoxidation related data. The formation of inclusions during the early stages of deoxidation was simulated by bringing a piece of Al in contact for a short time with liquid Fe containing different dissolved oxygen levels. Reoxidation was studied by exposing Al containing Fe melts to a CO/CO2 atmosphere. Through modeling, an estimate of the local and time-dependent growth conditions for the inclusions can be made and linked to the inclusion characteristics.

Options to Prevent Dicalcium Silicate-Driven Disintegration of Stainless Steel SlagsIn this paper, a short overview is given on the strategy for high dicalcium silicate stainless steel slags stabilisation along with some results from work done and currently being performed at the K.U. Leuven.

Inside a silica tube, a piece of Al was brought in contact for a very short time (1-60 s) with liquid Fe containing different dissolved oxygen ((O) under bar) levels (170-1800 ppm) at 1600 degrees C. The purpose was to investigate the inclusion formation during the initial deoxidation period. Intermetallic compounds of the Fe-Al system appeared due to the interdiffusion of Fe and Al, and the reaction between (Al) under bar and (O) under bar at the interface gave rise to the formation of Al2O3 inclusions. These inclusions showed different characteristics according to the initial (O) under bar level in liquid Fe and the interaction time. With lower (O) under bar content, the amount of inclusions decreased and faceted particles were dominant among the morphologies. While increasing the (O) under bar content to 780 and 1800 ppm, the inclusion number increased drastically and numerous small spherical inclusions were observed. Further away from the reaction front, clusters of fine particles were formed through a collision-coagulation mechanism. The change in Al2O3 morphology with the initial (O) under bar content was interpreted as a consequence of different supersaturation degrees with respect to (Al) under bar and (O) under bar.

The dissolution of Ti additions in liquid steel during secondary steelmaking occurs in a two step process. In the first step, a steel shell solidifies around the initial cold addition, whereas in the second step, after this shell has remelted, the Ti dissolves directly in the steel bath. The initial presence of this steel shell modifies the position of dissolution and influences the local concentration and thus the inclusion formation. Further complications arise from the fact that part of the Ti will dissolve while enclosed by the steel shell, altering the alloy composition first released in the ladle and effectively shortening the subsequent free dissolution period. The duration of the steel shell period and the fraction of predissolved Ti have been investigated using a conservative one-dimensional sharp interface model solving the coupled heat and mass transfer in a cylindrical shell/addition composite. The influence of the convection conditions and the original Ti radius was evaluated in a pa...

Ferroalloys are added during secondary steelmaking to impart special properties to the steel. Depending upon the ferroalloy quality this may lead to the formation of inclusions. The present knowledge lacks in the exact content of the individual elements and the nature of inclusions dispersed in the ferroalloys. In order to broaden the knowledge concerning ferroalloy quality, eight different ferroalloys (i.e. FeMo, FeNb, HCFeMn, LCFeMn, FeTi70, FeTi35, FeSi75 and FeP) were characterised for their impurity content. The samples were investigated for chemical analysis (inductively coupled plasma atomic emission spectroscopy and Leco combustion technique) and microstructural analysis (SEM energy dispersive spectroscopy). These impurities are linked to the ferroalloy manufacturing route. The inclusions observed in the microstructure are in good agreement with the inclusions extracted by the dissolution technique. In the present manuscript, the possible influence of ferroalloy quality over steel cleanli...

Interfacial reaction between refractory materials such as zirconia, magnesia and doloma brick, and the metallurgical slags of the CaO-SiO2-MgO-CaF2 system with varying CaF2 content were investigated at high temperatures using various methodologies with static and dynamic modes. To figure out the corrosion mechanism due to interfacial reaction with the slag, the slag characteristics were examined in terms of flow temperature and viscosity and the corroded interface of zirconia, magnesia and doloma refractories were analyzed by SEM-EDS and EPMA. With an addition of CaF2, three different layers were formed at the interface between slag and zirconia refractory. Furthermore, the corrosion of zirconia refractory was found to be accelerated with an increase of CaF2 which facilitated the dissolution of intermediate compounds. The penetration of slag through the grain boundaries of MgO refractory is enhanced by increasing the content of CaF2 due to an increase in the fluidity of slag in the dynamic mode. On the other hand, in the static condition, a dense Ca2SiO4 layer is formed at the hot face of magnesia-doloma refractory due to a reaction between silica in slag and lime in doloma, resulting in the protection of direct corrosion of refractory brick. However, the thickness of C2S layer decreases with increasing content of CaF2 due to an increase in fluidity of slag.

For the first time, the pinning effect of small spheroid particles with aspect ratios 1, 2 and 3 on grain growth in polycrystalline structures was studied by three-dimensional phase-field simulations. This was possible by using an efficient parallel sparse bounding box algorithm. Simulation results for different volume fractions of the second-phase particles show that distributions of particles with higher aspect ratios have a stronger pinning effect, since grain boundaries have the tendency to align with the largest cross-section of the particles. The number of particles at triple, quadruple or higher order junctions increases with volume fraction, and with aspect ratio. Nevertheless, the final grain size has a volume fraction dependence of the form 1 / f V 0.93 , following theoretical predictions assuming random intersections between grain boundaries and particles. A generalised Zener relation with a prefactor depending on the aspect ratio is proposed.

The effect of O on the phase relations at 950 °C in Fe–15Cr–1Nb alloys is experimentally investigated. Fe–15Cr–1Nb alloys are oxygenated by subjecting high-purity Fe–15Cr–1Nb to an O atmosphere at 600 °C. Both the high-purity and the oxygenated Fe–15Cr–1Nb alloys are heat treated for up to 500 h at 950 °C, quenched and investigated by scanning electron microscopy, transmission electron microscopy and electron probe microanalysis. The results show that Fe2Nb is in equilibrium with α (Fe, Cr) with 0.29 at.% Nb in solid solution in the pure Fe–15Cr–1Nb alloy. The presence of a small amount of O induces the precipitation of a Fe6Nb6Ox phase with a cubic crystal structure and lattice parameter 1.13 nm, thereby decreasing the Nb in solid solution in α (Fe, Cr) with increasing O content.

To further boost the CMOS device performance, Ge has been successfully integrated on shallow trench isolated Si substrates for pMOSFET fabrication. However, the high threading dislocation densities (TDDs) in epitaxial Ge layers on Si cause mobility degradation and increase in junction leakage. In this work, we studied the fabrication of Ge virtual substrates with low TDDs by Ge selective growth and high temperature anneal followed by chemical mechanical polishing (CMP). With this approach, the TDDs in both submicron and wider trenches were simultaneously reduced below 1 × 107 cm− 2 for 300 nm thick Ge layers. The resulting surface root-mean-square (RMS) roughness is about 0.15 nm. This fabrication scheme provides high quality Ge virtual substrates for pMOSFET devices as well as for III–V selective epitaxial growth in nMOSFET areas. A confined dislocation network was observed at about 50 nm above the Ge/Si interface. This dislocation network was generated as a result of effective threading dislocation glide and annihilation. The separation between the confined threading dislocations was found in the order of 100 nm.

The phenomena taking place at the early stage of Al deoxidation were investigated with specific attention on the formation of Al2O3 inclusions. In a quartz tube, Al was exposed to liquid Fe containing different amounts of dissolved oxygen ((O) under bar) for 1, 5, 30 and 60s. In this paper, quenched microstructures of the diffusion couple were examined to identify the interactions and the nature of the phases at the experimental temperature. They revealed that the reaction zone was composed of successive layers of Fe-Al intermetallic compounds, as predicted by the phase diagram of the system, i.e. alpha Fe(Al), FeAl, FeAl2, Fe2Al5 and FeAl3. Based on the microstructure, the concentration profiles, diffusion processes in solid and liquid phases, and the behavior of Al2O3 inclusions in the reaction zone, it was demonstrated that the reaction zone was completely liquid and that the solid Fe shell melted for the samples with holding time of 30 and 60 s.

In order to identify the influence of MnO on the wear rate of MgO–C bricks for the production of high Mn stainless steel, MgO–C refractory samples were exposed to slags containing different MnO levels (up to 26 wt.%). Although the investigations of the worn brick microstructures revealed the presence of numerous Mn-rich metal particles and the formation of a (Mg,Mn)O solid solution at the slag/refractory interface, no clear evidence of wear rate enhancement was observed due to high MnO concentration in the slags. With respect to refractory wear, the MgO content in the slag is the dominant factor. The degradation processes are discussed by combining experimental results and thermodynamic calculations.

This article focuses on the CaO–CrOx–MgO–SiO2 system at low CaO contents, providing quantitative phase relation data, and improving the thermodynamic description. The observed liquidus data are compared with literature data and state-of-the-art thermodynamic calculations (FactSage 5.5). The experimental phase diagram measurements are performed under various conditions: (1) liquidus of CaO–CrOx–MgO–SiO2 at a basicity CaO/SiO2=0.5 (by weight), at 1500°C and at a partial oxygen pressure pO2=10−11.04 atm, (2) liquidus of CaO–CrOx–MgO–SiO2 at 1600°C and pO2=10−9.36 atm with constant molar ratio Mg/Cr of 1/2 and varying basicity, (3) phase equilibria of the CrO–Cr2O3–MgO–SiO2 system at 1600°C and pO2 ranging from air to equilibrium with metallic chromium. In the experiments, equilibrium samples of crystalline phases and melts are analyzed by electron probe microanalysis using wavelength dispersive spectroscopy to determine both solid and liquid compositions. Some discrepancies from previous literature data and calculations are found. In order to improve the thermodynamic calculations, a new thermodynamic model of the CrO–Cr2O3–MgO–SiO2 system is also developed using the Modified Quasichemical Model for the liquid and the compound energy formalism for the solid solution phases. The newly optimized model parameters can describe the present experimental data and literature data more accurately.

Recently, freeze linings have been selected more frequently to protect pyrometallurgical reactor walls, due to a number of advantages over conventional refractory lining such as a self-regenerating capability and the possibility of operating under high-intensity process conditions. A freeze lining is formed on a cooled reactor wall in a time-dependent temperature gradient. To model freeze-lining behavior, input data on several assumptions, such as the phase formation and the temperature at the bath–freeze-lining interface during freeze-lining formation, are needed. In order to provide experimental data, the freeze-lining formation of a synthetic lead slag system (PbO-FeO-Fe2O3-ZnO-CaO-SiO2) is investigated. A lab-scale freeze lining was produced by submerging an air-cooled probe into a liquid slag bath for 120 minutes. The temperature evolution during freeze-lining formation was estimated using the experimentally determined position and composition of the phases, the phase-temperature relations predicted with the thermodynamic computer package FactSage, and the results of reference experiments. For the studied slag system, it is concluded that heat transfer is much faster than mass transfer and crystallization. As a result, the liquid in front of the freeze lining undercools. The degree of undercooling depends on the solidification rate. It is concluded that the temperature at the bath–freeze-lining interface varies between the glass transition and liquidus temperatures of the slag bath during freeze-lining formation.

Freeze linings are frequently used to protect the reactor wall in pyrometallurgical processes. In order to minimize reactor wall corrosion, the stability of a freeze lining has to be guaranteed. To illustrate the importance of slag engineering in the optimization of freeze-lining behavior, the freeze-lining formation of six synthetic lead slags is studied. Lab-scale freeze linings are obtained using a cooled-probe technique and their microstructures are characterized using light optical microscopy (LOM) and microprobe analysis. The results show that slag engineering can have a major impact on the operative freeze-lining formation mechanisms. Some slag properties found to affect the freeze-lining formation are the viscosity, the temperature stability range of the relevant phases, the type of phases that form (interlocking or not), and the crystallization behavior of the slag. The operational demands of a protective freeze lining are defined by the authors as follows: (1) a rapid formation to limit the contact between the reactor wall and the corrosive bath material and (2) a sufficient stability during changes in heat input from the bath and in bath composition. From the comparison of the microstructural features of the freeze linings formed with the studied slags, it is concluded that these demands can be fulfilled with the growth of an initial layer dominated by the presence of interlocking crystals in combination with the subsequent formation of a high-melting crystalline layer at the bath–freeze-lining interface, which is in equilibrium with the slag bath and the composition of which differs sufficiently from the bath composition.

The degree of supersaturation is a factor that influences the Al2O3 inclusion characteristics in steel. The influence of the addition of a large amount of Al in the molten steel on the formation, growth and morphology of Al2O3 inclusions was investigated by laboratory scale experiments. Consecutive steel samples were taken during the deoxidation process and subjected to chemical analysis (ICP-AES), automated image analysis (AIA) and scanning electron microscopy (SEM) assessment with respect to the extracted inclusions. The characterisation and quantification of Al2O3 particles show different growth processes, leading to variations in particle size distribution as well as in the morphology.

The process of Al deoxidation and Ti alloying during RH degassing treatment was studied under an Ar atmosphere at secondary steelmaking temperature (1600—1650°C) in an induction furnace equipped with an oxygen probe and a steel sampler. The formation of inclusions during partial Al deoxidation and Ti addition, and the reduction of Ti–Al–O inclusions by second Al addition are discussed using thermodynamic calculations. Specific attention is given to inclusion size and the compositional relation between the inclusions and the steel. The combination of experimental and calculated results shows that, in order to prevent Ti oxidation in liquid steel, it is essential to control [Al] in liquid steel to a level of approximately 200 ppm prior to Ti addition to achieve around 500 ppm [Ti] with minimal Ti loss during the alloying process.

We present the lattice Boltzmann equation (LBE) with multiple relaxation times (MRT) to simulate pressure-driven gaseous flow in a long microchannel. We obtain analytic solutions of the MRT-LBE with various boundary conditions for the incompressible Poiseuille flow with its walls aligned with a lattice axis. The analytical solutions are used to realize the Dirichlet boundary conditions in the LBE. We use the first-order slip boundary conditions at the walls and consistent pressure boundary conditions at both ends of the long microchannel. We validate the LBE results using the compressible Navier-Stokes (NS) equations with a first-order slip velocity, the information-preservation direct simulation Monte Carlo (IP-DSMC) and DSMC methods. As expected, the LBE results agree very well with IP-DSMC and DSMC results in the slip velocity regime, but deviate significantly from IP-DSMC and DSMC results in the transition-flow regime in part due to the inadequacy of the slip velocity model, while still agreeing very well with the slip NS results. Possible extensions of the LBE for transition flows are discussed.

In Flanders, recycling of bottom ash is mainly inhibited by the high leaching of Cu. Although it has been proved that dissolved organic C plays a major role in the Cu leaching, the possible role of inorganic Cu mineral speciation has never been experimentally examined. In this study the speciation of Cu is investigated using a combination of optical microscopy and electron microprobe –WDX/EDX. Several Cu species were determined. Metallic Cu (with or without an oxide shell), CuO and Cu2O were the most abundant. These particles were most likely present in wire-like structures. Copper also occurred as alloy (brass, bronze, zamak), and was found frequently together with typical elements such as Ca, Cl and S. Finally, small metallic Cu particles seemed to be trapped in or precipitated on oxides and silicates. Based on this Cu speciation study, pure Cu minerals were selected and leached as a function of time. The solubility after equilibrium of all studied Cu minerals never exceeded 20 μg/L (which equals 10% of the total Cu leaching). The effect of heating (2 h at 400 °C) on the speciation of Cu was investigated using the same combination of techniques. Results show that metallic Cu seemed to be converted to Cu oxide (mostly CuO) and that the particles were more porous after heating. These conclusions were verified by XRD analysis of the heated pure Cu minerals. After heating, the Cu minerals were also leached as a function of time, to study the impact on Cu leaching. Results indicate that their leaching had slightly increased in comparison with the non-heated Cu minerals. However, the major decrease in Cu leaching in heated bottom ash, more than neutralizes this effect and thus can be attributed to the destruction of organic matter and not to the (small) change in Cu speciation.

During air-cooling, high temperature, reduced metallurgical slags are brought in contact with ambient air, resulting in a gradient in both temperature and oxygen partial pressure. In this article, the pO2 dependency of slags containing multivalent oxides is investigated. Computer simulations with an extended version of the Scheil solidification model indicate significant differences in both end mineralogy and solidification path depending on oxygen partial pressure and oxygen diffusion. It is shown that metallic particles can form inside the slag during cooling because of a lack of oxygen exchange with the surrounding atmosphere. This is confirmed by laboratory solidification experiments, which corroborate that the level of oxygen diffusion is indeed limited. The proposed solidification mechanisms are extrapolated to industrial practice, based on key features of a stainless-steel electric arc furnace slag. The possible implications for slag recycling are discussed.

Lab scale freeze layers of an industrial nonferrous slag with as main components Al2O3-CaO-FeO x -MgO-SiO2-ZnO were studied to explore the mass transport in an industrial freeze lining. The freeze layers were formed by submerging a water-cooled probe into a liquid slag bath. In previous research,[1] two distinct types of microstructures were observed in these freeze layers: one with only melilite columnar crystals and one with both melilite and olivine columnar crystals. In this article, the mass transport during the formation of these microstructures is investigated. The element distribution, the phase fraction, and the crystal morphology were examined using electron microscopy and electron probe microanalysis. In addition, thermodynamic software was used to calculate the solidification path of the slag. The impact of the mass transport on the growth of a freeze lining depends on the solidification rate. For high solidification rates, only short-range mass transport is observed and small crystals form. For lower solidification rates, long-range mass transport is observed, resulting in an exchange of components between the freeze layer and liquid slag bath and in the formation of large crystals. Different growth mechanisms are observed for melilite and olivine crystals. The broad large melilite crystals have to exchange components with the liquid slag bath to grow, because the amount of liquid slag between the crystals is limited, while the long thin olivine crystals can exchange components with a large amount of liquid slag in between the crystals. Furthermore, the mass transport of minor elements may be very important, because these elements can pile up at the crystal-liquid slag interface and hamper the crystal growth.

Dissolution of ZrO2 oxide in synthetic CaO - Al2O3 - SiO2 - Na2O - B2O3 mould fluxes was investigated in situ using a Confocal Scanning Laser Microscope (CSLM). Evolution of particle radius with time is obtained exhibiting strong dependence on temperature and basicity of the mould fluxes. The rate-limiting step of the dissolution process was discussed, and basicity was shown to significantly influence the rate-limiting step.

In this work, the liquidus of synthetic CaO–SiO2–MgO–Al2O3–CrOx slags is evaluated in the industrially relevant compositional domain. Equilibrium experiments are carried out at 1500°C and partial oxygen pressure (pO2) 10−11.04 atm, and at 1600°C and pO2=10−10.16 and 10−9.36 atm. The studied basicities (CaO/SiO2) are 1.2 and 0.5. Al2O3 levels range from 0 to 30 wt%. Oversaturated liquid is sampled and phase relations are measured with quantitative electron probe microanalysis–wavelength dispersive spectroscopy (EPMA–WDS). The results are compared with the commercially available FactSage thermodynamic databases. Qualitative agreement is always obtained. Also a good quantitative agreement is found at the higher basicity, especially for the spinel liquidus. A minor but systematic deviation can be observed for the eskolaite liquidus. At the lower basicity, the calculated phase diagram deviates strongly from the experimental results, probably due to missing ternary interactions in the database.

Indirect dissolution is modelled using a two-component lattice Boltzmann model. A boundary condition is developed to impose equilibrium concentrations on the interfaces. The interfaces are captured using a volume-tracking scheme. The model is applied to a one-dimensional diffusion couple and the expected behaviour is observed. A two-dimensional situation with and without convection is also simulated, and the behaviour under grid refinement is studied.

Disintegration of stainless-steel slag during cooling is caused by the β→γ transformation of dicalcium silicate (2CaO·SiO2 or C2S). It is well established that disintegration can be avoided by borate additions, which are commonly believed to stabilize the high-temperature polymorphs by forming a solid solution with C2S. In this study, the borate distributions in slowly cooled synthetic and industrial slag samples are determined. The slag microstructures are characterized using electron probe microanalysis (EPMA), quantitative X-ray diffraction (QXRD), and wavelength dispersive spectroscopy (WDS). The results show that only a limited fraction of the added borates forms a solid solution with the C2S phase, while the main fraction is found in a calcium borosilicate phase. In combination with literature data, this suggests that slag stabilization involves more than the chemical stabilization of the high-temperature C2S polymorphs.

TiB2 coatings were plasma sprayed in air and were studied by XPS. There are five elements in the top surface of the studied coatings, namely, B, C, N, O and Ti. Oxygen pick-up in the coatings results in formation of oxides of boron and titanium. Nitrogen was shown to exist in N-Ti and O-N-Ti in the coating. Depending on the spraying parameters, mono-boride as well as di-boride was also detected in the studied coatings. With careful peak fitting it was shown that oxygen may exist in the coating as dissolved atomic O in addition to as lattice oxygen in the oxide of boron and titanium.

The interfacial reactions between a solidified Fe shell and Ti were investigated within the framework of steel alloying. Ti cylinders were immersed into liquid Fe for various durations and subsequently water-quenched. An Fe shell solidifies around the Ti. At the interface between Fe and Ti a reaction zone is formed. Initially it consists of a liquid eutectic layer, though in later stages all stable phases at elevated temperature can be found in the quenched microstructure. The larger part of this reaction zone is fluid at high temperature and both Ti and Fe dissolve into it. Moreover, intermetallic compound formation and mixing of Fe and Ti generate extra heat, shortening the time required for shell melt-back. The reaction zone reaches thicknesses up to 40 % of the initial sample’s radius and when the shell has completely remolten, a discontinuity in the thickness-time profile is expected. The exact morphology of the reaction zone at high temperature remains to be determined: presence of a solid layer of Fe2Ti may impede mixing in the initial stages.

The Mn and Cr equilibria between a Mn rich stainless steelmaking slag (CaO–SiO2–MgOsat.–MnO–CrO1.5) and Fe–Cr–Mn stainless steel were investigated in a temperature range from 1823 to 1873 K under Ar atmosphere. The partition ratios LMn and LCr between liquid slag and steel were determined as a function of slag composition and temperature. By combining the experimental results with thermodynamic calculations, it was found that, as basicity increases, LMn decreases, while LCr increases. The elevated basicity leads to a high MnO activity coefficient. On the other hand, the CrO1.5 activity coefficient decreases with higher slag basicities. The influence of MnO and CrO1.5 contents on the activity coefficients was also considered. It is concluded that in order to maximize Mn recovery during high Mn stainless steel production, a basic slag with a high MnO activity coefficient must be employed whereas high temperatures should be avoided.

Labscale freeze layers of an industrial nonferrous slag with Al2O3-CaO-FeOx-MgO-SiO2-ZnO as main components are studied to explore the microstructure and the composition of an industrial freeze lining. The freeze layers were formed by submerging a watercooled probe into a liquid slag bath. The influence of submergence time, of heat input from the furnace, and of the rotational speed of the crucible is studied. The microstructures of the freeze layers are examined using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). Thermodynamic software is used to interpret the solidification microstructure. The results show that the freeze layer microstructure consists of different zones, depending on the local thermal history. These zones show different growth morphologies and different microstructure scales, from an amorphous matrix with small crystals to large columnar crystals. Furthermore, two microstructure types are observed, one with melilite columnar crystals and the other with olivine columnar crystals. These microstructure types appear for similar experimental conditions and are even observed within the same freeze layer. An increase in submergence time or in heat input from the slag bath does not seem to favor a particular microstructure type. A high rotational speed of the crucible resulting in a higher convection in the slag bath seems to favor the microstructure type with olivine columnar crystals.

A combined selective dissolution/quantitative X-ray diffraction (QXRD) approach is proposed for the quantitative mineralogical phase analysis of hydraulic limes. The proposed methodology is validated by the analysis of two model mixtures. Afterwards two commercial hydraulic binders and one self-burned hydraulic quicklime were analysed. Chemical, thermal and microprobe analyses were performed to check the results. It is shown that the proposed selective dissolution/QXRD approach yields reliable quantitative mineralogical information for hydraulic limes in spite of their complex phase composition and the presence of amorphous material.

A phase field model for simulating grain growth and thermal grooving in thin films is presented. Orientation dependence of the surface free energy and misorientation dependence of the grain boundary free energy are included in the model. Moreover, the model can treat different mechanisms for groove formation, namely through volume diffusion, surface diffusion, evaporation-condensation, or a combination of these mechanisms. The evolution of a groove between two grains has been simulated for different surface and grain boundary energies and different groove formation mechanisms.

Three-dimensional simulations of grain growth in thin films containing finely dispersed second-phase particles were performed using a phase field model. The simulations show that although the growth behavior of the columnar grain structures in thin films is essentially two-dimensional, the interaction between the particles and the grain boundaries is three-dimensional. Grain boundaries can therefore more easily break free from the particles than in purely two-dimensional systems, resulting in fewer grain boundary–particle intersections and a larger final grain size. For a given volume fraction fV and size of the particles r, the final grain size R ¯ lim increases with film thickness. Moreover, it was found that particles located in the middle of the film are most efficient in pinning grain boundaries. A classical Zener type relation R ¯ lim / r = K ( 1 / f V b ) cannot describe these effects.

In this paper, the Scheil–Gulliver approach on solidification modeling is applied to slag solidification. The Scheil–Gulliver model assumes no diffusion in the solid phases, infinitely rapid diffusion in the liquid phase, and local equilibrium at the solid/liquid interface. For two distinct CaO–MgO–SiO2 slags, solidification is simulated with the Scheil–Gulliver model and with the commonly used thermodynamic equilibrium model. The simulations show that in the Scheil–Gulliver model, as opposed to the equilibrium model, compositional gradients in the solid phases can exist and peritectic reactions do not occur. Solidification experiments are performed under laboratory conditions to validate the simulation results. The experimental results show a better correspondence with the Scheil–Gulliver model than with the equilibrium model. However, quantitative differences in mineralogy persist.

The disposal of zinc-containing residues is an important sustainability issue currently facing the metallurgical industry. These residues can be treated by using zinc slag-fuming processes in which heavy metals are chemically reduced and evaporated from a molten slag bath. Continuous operation of these processes requires high zinc-fuming rates while retaining vessel integrity. To meet these challenges, a new generation of technologies is being developed that depends on the formation of a freeze lining on the internal reactor walls. A general zinc-fuming process model that simultaneously describes the chemical reactions, phase equilibria, and thermal- and heat-transfer outcomes of these processes has been developed using the FactSage thermodynamic databank system and the ChemApp programmer’s library for thermochemical applications. This simultaneous description of these processes allows the model to be used as part of a new approach to the design of freeze linings, namely, the use of slag engineering and composition adjustment to obtain optimum process efficiency and freeze lining behavior.

The friction of diamond and diamond-like carbon (DLC) materials was evaluated in reciprocating sliding wear testing under controlled relative humidity. The testing conditions were a displacement stroke of 100 μm, an oscillatory frequency of 8 Hz and a normal load of 2 N. The coefficient of friction of diamond and hydrogen-free DLC (a-C) coatings against a corundum sphere in the steady regime decreased with an increase in relative humidity. A water layer physisorbed at the interface between the mating surfaces played two major roles: acting as a lubricant and increasing the true area of contact. However, it was noticed that the friction coefficient of the hydrogenated DLC (a-C:H) coatings first increased and then decreased with increasing relative humidity in the steady state. There appeared to be a critical relative humidity for the a-C:H coatings, at which the steady-state friction reached the maximum value. The frictional behaviour of the a-C:H coatings also showed dependence on the wear test duration. The interaction between hydrogen and oxygen at the interface between the a-C:H coating and water layer was mainly responsible for such behaviour.

A new high-temperature submerged plasma zinc-fuming process has been developed for the treatment of zinc leach residues, electric arc furnace (EAF) dusts, and other zinc-containing waste materials. Continuous operation of this process requires high zinc-fuming rates while retaining vessel integrity through the formation of a stable freeze lining. A zinc-fuming process model using the FactSage thermodynamic databases and ChemApp thermodynamic software has been developed, which simultaneously describes chemical, thermal, and heat-transfer outcomes of this process. The model has been used to systematically investigate the potential effects of operating parameters such as feed composition, fuel/oxygen ratio, electrical power and fluxing parameters on bath temperature, heat loss, Zn concentration and content in slag, Cu concentration, and content in matte.

The dissolution of magnesia particles in synthetic CaO–Al 2 O 3 –SiO 2 (CAS)-based slags with and without MgO addition was investigated in situ with a confocal scanning laser microscope (CSLM) at 1500 and 1600 °C. The dissolution process was recorded. The effects of slag composition and temperature on the dissolution process and the time dependency of the MgO particle size during dissolution were obtained. Increasing the temperature increases the dissolution rate. However, MgO addition to the slag retards the dissolution rate significantly. The rate limiting steps are discussed. It is shown that boundary layer diffusion is responsible for the dissolution. By combining in situ observations with post mortem analyses, thermodynamic calculations of local and global equilibrium, and kinetic considerations, the conditions under which MgAl 2 O 4 spinel can be formed at the particle–slag interface are clarified.

The confocal scanning laser microscopy (CSLM) technique has been successful in many metallurgical fields. This paper assesses its applicability to the in situ investigation of the high-temperature behaviour of complex ceramic materials. Magnesia–chromite refractory is selected as a ceramic test material. At room temperature, CSLM images correspond well to typical light optical microscopy (LOM) and backscattered electron (BSE) micrographs. In fact, because of the high axial resolution (short focal depth) and the confocal optics of the CSLM technique, the porosity level of the mirror polished ceramic specimens is more truthfully assessed by the CSLM (2-D) images than by the BSE micrographs (long focal depth). However, at high-temperatures (1550–1650 °C) the observed CSLM (2-D) image quality is slightly poorer. The principal explanation is the in situ roughening of the specimen surface during heating. The roughening has two causes: differential thermal expansion of the two primary phases in the ceramic test material and, to a lesser extent, thermal grooving. Nevertheless, it is shown that the CSLM image quality suffices for an in situ study of the high-temperature behaviour of ceramic materials. This is illustrated for the magnesia–chromite system by examining the dissolution mechanism of secondary (magnesiochromite) spinel into the periclase phase.

The penetration and corrosion resistance to copper and anode slag of six magnesia–chromite and six chrome-free refractory brick types were tested using static finger tests at a typical copper-refining temperature (1300 °C). The microstructures of the as-delivered and tested refractory types were investigated by means of electron-probe micro-analysis (EPMA) and scanning electron microscopy (SEM) techniques. The results showed that the overall wear rate of the fingers was very low, with the exception of the alumina-based brick made of fused corundum and magnesia–alumina spinel, and the magnesia-based brick made of sintered magnesia and zircon addition. In all refractory types new phases were formed as a result of slag-refractory interactions. Apart from the samples recovered from the copper zone of the latest generation of direct-bonded magnesia–chromite bricks, all the rest were completely infiltrated by copper and slag components (copper oxide, iron oxide, alumina and silica). However, the amount of infiltrated liquid in the chrome-free types was higher than in the magnesia–chromite bricks. Explanations are provided for the distinct infiltration behaviour. The results show that economically viable chrome-free refractory alternatives are still elusive for anode furnace linings.

For the purpose of controlling the size of non-metallic inclusions in steel, the effect of interfacial properties of alumina inclusions and molten iron on the characteristics and clustering of alumina inclusions was investigated. The interfacial properties were modified by adding different amounts of Te to molten iron at 1873 K before Al deoxidization. When the melt is not stirred after Al addition, Te was found to decrease the size of alumina inclusions and to narrow the size distribution by promoting nucleation. This effect, however, fades out with increasing holding time. When the melt is stirred for 30 s after Al addition, Te favors alumina clustering. The mean diameter of alumina inclusions, the clustering degree and the average number of particles per cluster increase with increasing Te addition from 0 to 250 ppm, thereafter decrease with further Te addition. The effect of Te addition on the clustering of alumina inclusions is discussed from the viewpoint that Te makes alumina inclusions more faceted and Te decreases the surface tension of molten iron. ispartof: ISIJ International vol:55 issue:9 pages:1891-1900 status: published

NdFeB magnets currently dominate the magnet market. Supply risks of certain rare earth metals (REMs), e.g., Nd and Dy, demand efficient recycling options that are applicable to different types and compositions with minimum use of chemicals and waste generation. In this study, a hydrometallurgical method is presented, which is adjustable to all NdFeB magnets, regardless of their composition. After completely transforming powdered samples into a sulfate mixture, a suitable selective roasting and water leaching treatment resulted in 95–100 % extraction efficiencies for Nd, Dy, Pr, Gd, Tb, and Eu, while Fe remained in the resultant residue forming a marketable hematitedominated by-product. Impurities other than Fe were also greatly separated from the leachate thereby enabling the production of a liquid with at least 98 % REM purity. Such a solution then can be directly treated with subsequent shortened downstream processes without pretreatments for impurity removal. Due to decomposition reactions of impurities, including Fe, during the selective roasting stage, the majority of consumed acid is recyclable resulting in an environment-friendly flow sheet. ispartof: Journal of Sustainable Metallurgy vol:1 issue:3 pages:199-215 status: published

Clustering of alumina inclusions in liquid steel commonly takes place during Al deoxidization process and the extent of clustering significantly influences steel cleanliness. The clustering is suggested to have a close relationship with the interfacial properties of alumina inclusions and liquid steel. In the present work, the effect of the interfacial properties on the clustering of alumina inclusions was investigated. Different amounts of Te were added to molten iron before Al deoxidization at 1873 K to modify the interfacial properties. A method was developed to analyze alumina clustering, such as the mean diameter, the clustering degree and the average number of particles per cluster. The values of these parameters were found to increase with increasing Te addition up to 200 ppm, thereafter to decrease with further Te addition. The effect of Te addition on the clustering of alumina inclusions is discussed with the theory of spontaneous cavitation between non-wetting surfaces. Te affects the clustering in two opposite ways. First, it decreases the surface tension of molten iron. This makes clustering less likely; Second, it makes alumina inclusions more faceted. This favors clustering. Due to the two opposite effects, the extent of alumina clustering reaches a maximum at 200 ppm Te addition. ispartof: pages:731-736 ispartof: Proceedings of The 6th International Congress on the Science and Technology of Steelmaking vol:6 pages:731-736 ispartof: The 6th International Congress on the Science and Technology of Steelmaking location:Beijing, China date:12 May - 14 May 2015 status: published

Static magnetic field processing of non-ferromagnetic materials has been of broad interest and been applied in such fields as drug delivery, colloid chemistry and engineering of materials containing particles. A ‘strong’ magnetic field refers to a ‘strong’ response from the manipulated material and can vary in definitions. The response is corresponding to a local interaction between the material and the local magnetic field, being influenced by the magnetic susceptibilities of the material and the surrounding/coated medium. By carefully designing the medium, a significantly ‘strong’ response from a weakly magnetic material can even be generated by a traditional magnet, i.e. magnetic flux density ∼0.01 T. Therefore, the ability to manipulate materials by using a magnetic field depends critically on the understanding of the principles of the magnetic properties of materials and their magnetic responses. This paper provides a critical discussion on the principles including magnetic field effect thermodynamics, magnetic energy, magnetic anisotropy and different magnetic forces during ’strong’ magnetic field processing of weakly magnetic materials (focusing on metallic materials). A series of case studies and the related magnetic field effect are subsequently integrated and discussed. Overall this review aims to provide a better understanding and efficient overview on the phenomenon principles in the field of magnetic field processing.

The supply risk for some critical rare-earth elements (REEs), which are instrumental in many cleantech applications, has sparked the development of innovative recycling schemes for End-of-Life fluorescent lamps, permanent magnets and nickel metal hydride batteries. These waste fractions represent relatively small volumes, albeit with relatively high rare-earth contents. Rare earths are also present in lower concentrations in a multitude of industrial process residues, such as phosphogypsum, bauxite residue (red mud), mine tailings, metallurgical slags, coal ash, incinerator ash and waste water streams. This review discusses the possibilities to recover rare earths from these “secondary resources”, which have in common that they contain only low concentrations of rare-earth elements, but are available in very large volumes and could provide significant amounts of rare earths. The success rate is set to increase if the rare-earth recovery from these industrial waste streams is part of a comprehensive, zero-waste, “product-centric” valorisation scheme, in which applications are found for the residual fractions that are obtained after removal of not only the rare earths but also other valuable (base) metals. ispartof: Journal of Cleaner Production vol:99 pages:17-38 status: published

In non-ferrous metallurgy the refractory life is application dependent, typically going from several months up to 2 years or more. Slag engineering is widely used to reduce the dissolution rate of a refractory lining by forming a solid protection layer at the slag-lining interface, thereby increasing the lining's lifetime. The non-ferrous slag in this paper is engineered to form a protective spinel layer. This phase, however, only forms near and at the slag-lining interface, while deeper inside the sample forsterite grains are detected, resulting in direct contact between the still unsaturated slag and the magnesia-chromite refractory phases. At this position the MgO dissolution increases with a factor 3–4 compared with the slag-refractory interface, attacking the bonding between grains and decreasing the brick's mechanical strength. As this happens deeper inside the sample, the spalling risk increases. Strategies to simultaneously reduce refractory dissolution and spalling are discussed. publisher: Elsevier articletitle: The influence of slag compositional changes on the chemical degradation of magnesia-chromite refractories exposed to PbO-based non-ferrous slag saturated in spinel journaltitle: Journal of the European Ceramic Society articlelink: http://dx.doi.org/10.1016/j.jeurceramsoc.2014.08.017 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved. ispartof: Journal of the European Ceramic Society vol:35 issue:1 pages:347-355 status: published