Annelies Malfliet

Synthesis and Characterization of Composite Coatings for Thermal Actuation

The synthesis and thermal expansion of metal coatings containing phase change material (PCM) prepared by electrolytic deposition were investigated. Such a composite combines the thermomechanical properties of the PCM with the high thermal conductivity of the metal, and can be used as a thermal actuator material. This study used paraffin as the PCM and copper as the metal matrix. The paraffin was first microencapsulated by emulsion polymerization to obtain microcapsules with a diameter of 1-5 μm containing 90 vol% paraffin to facilitate the incorporation of paraffin in copper by electrocodeposition. The microcapsules were added to a copper sulfate bath up to a concentration of 500 g/L. The electrocodeposition was performed at room temperature with a current density between 2 and 5 A dm -2 . These composites were examined by scanning electron microscopy, differential scanning calorimetry, and vertical dilatometry. Coatings with 40 vol % of microcapsules and a heat capacity of 12 kJ kg -1 during phase transformation were obtained. The thermal expansion of the composite showed a sharp increase in a small temperature range above the melting point. Although this behavior is ideal for thermal actuators, the effect decreased by thermal cycling. This remarkable thermomechanical behavior is explained by a thermoelastoplastic model for two-phase composites.

Electrochemical Extraction of Rare Earth Metals in Molten Fluorides: Conversion of Rare Earth Oxides into Rare Earth Fluorides Using Fluoride Additives

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.

(Fe, Cr)6Nb6Ox phase of the filled Ti2Ni type with × ± 0.75 in the quaternary Cr–Fe–Nb–O system

Abstract 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.

Aluminum Deoxidation Equilibrium of Fe-Ni Alloy at 1773 K and 1873 K

The aluminum deoxidation equilibrium in molten Fe-36 mass pct Ni and Fe-46 mass pct Ni alloys was experimentally determined at 1773 K and 1873 K to obtain the thermodynamic parameters around the liquidus temperature, which is required to predict the deoxidation reaction for the ingot-casting process. Automatic SEM-EDS inclusion analysis was performed to estimate the undissolved oxygen content. Thermodynamic analysis on Al deoxidation was carried out using Miki and Hino’s formula, which is based on Darken’s quadratic formalism and the Redlich–Kister polynomial. From the composition dependence of the apparent equilibrium constant in Fe-Ni alloy, the necessity of the third-order interaction parameter of Ni-Al was found. Then, the interaction parameters of Fe-Al, Al-O and Ni-Al were evaluated.

Preface to the 5th International Slag Valorisation Symposium: From Fundamentals to Applications

From April 3 to 5, 2017, the 5th International Slag Valorisation Symposium took place in Leuven, Belgium. Since the first Symposium in 2009, actors from both academia and industry have gathered in these Symposia to disseminate knowledge and to discuss the latest advances in the field of slag valorization. The subtheme for this Symposium was From Fundamentals to Applications. It covered the themes of clean slag production, metal recovery, slag solidification, and energy recuperation, next to slag-incorporating processes and products, such as new cements, aggregates, inorganic polymers, and alkali-activated binders. As sustainable materials management was a common thread in the past four Slag Valorisation Symposia, a specific session was dedicated to the principle of industrial ecology for high-temperature (metallurgical) residues as part of a circular economy. Selected contributions from this Symposium were invited in this thematic section of the Journal of Sustainable Metallurgy, as an extended and peer-reviewed version of the Symposium paper. A first illustration of the development of fundamental knowledge related to slag valorization can be found in the work by Müller et al. [1] on modeling the viscosity of oxide slags. As changes in the viscosity of the slag can affect the mass transfer and flow in a metallurgical process, knowledge about and the ability to predict this property is important to simulate high-temperature processes. The group of Müller developed a new viscosity model to predict the viscosity of fully molten slags, which uses the same structural units as used in the thermodynamic description of the melt, thereby reflecting the relation between the viscosity and the structure of the slag. This is presented in their paper, together with the extension of the model taking into consideration the effect of crystallization on both the change from a liquid to a dispersion and the change on the liquid composition. The second example of fundamental research is shown in the paper by Bellemans et al. [2] who studied a particular case of metal losses in liquid slag. They considered that the adherence of metal droplets to solid particles can cause inadequate sedimentation behavior, which was experimentally studied by evaluating the Cu droplets and their attachment to spinel particles in a Fe–Si–Al–O-based system. Supported by other works of the group using phase field modeling, this study draws conclusions on the origin of the attachment, which is the basis for understanding and eventually avoiding this mechanism and the associated production losses. In the work of Nedeljkovic et al. [3], the carbonation of alkali-activated slag (AAS) pastes exposed to natural and accelerated conditions for up to 1 year was studied. Two aspects of carbonation mechanism were evaluated. The first was the potential carbonation of the main binding phases in finely powdered AAS pastes. The second was the reactivity and diffusivity of CO2 within the bulk AAS paste. It was found that powdered AAS was largely carbonated within 28 days, the main carbonation products being calcium carbonates. On the contrary, the bulk paste samples were highly resistant to carbonation, and the initial pH value and strength of the samples did not decrease under accelerated carbonation, nor was the mineralogy influenced by the two carbonation regimes studied. The authors conclude that the gel pores (in the range of 2–15 nm) were dominant in the pastes, and that this dense microstructure was the main barrier for CO2 diffusion. Mercado-Borrayo et al. [4] summarized and discussed the studies dealing with the use of metallurgical slag to remove inorganic, organic, and biological contaminants from water, originating from industrial activities or natural wells. The strategy of these studies, the suggested mechanisms of removal and the general trends in effectiveness of steel, iron, or copper slag as removing agent or catalyst are addressed. The authors come to the conclusion that most of & Annelies Malfliet annelies.malfliet@kuleuven.be

In-Situ Observation of Rare Earth Containing Precipitated Phase Crystallization and Solidification of CaO-SiO2-Nd2O3 and CaO-SiO2-Nd2O3-P2O5 Melts

In order to optimize the recycling process, fundamental understanding of the rare earths distribution in the slag and the precipitation behavior of the REE containing compounds during slag solidification are of significant importance. In this work, “in-situ” observations of rare earth containing phase precipitation, and solidification behavior of the CaO-SiO2-Nd2O3 and CaO-SiO2-Nd2O3-P2O5 melts were performed using a confocal scanning laser microscope (CSLM) combined with an infrared imaging furnace heating (IIF). The compositions of the precipitates formed during cooling of those slags were examined using EPMA method. The addition of P2O5 was found to influence the precipitation behavior and to decrease the liquidus as well as the solidus temperatures of the slags.

Fundamental Study of the Rare Earths Recycling Through the Pyrotetallurgical Route —Phase Relations and Crystallization Behavior of the CaO-SiO 2 -Nd 2 O 3 System

This study aims to investigate phase relations of the CaO-SiO2-Nd2O3 ternary system for high temperature recycling of Neodymium. The slag samples were equilibrated at 1500°C and 1600°C for 24h in Ar, and quenched in water. From the phase analysis of the samples, the isothermal sections were partially constructed and the liquid stability regions were assessed. Based on the identified phase relations, a solidification process with different cooling paths was studied in-situ using a confocal scanning laser microscope within the interesting slag phase regions for recycling. The phases needed for optimizing recycling can be produced accordingly.

Freeze‐Lining Formation from Fayalite‐Based Slags

Formation of freeze-linings from aggressive process slags is used in industrial pyrometallurgical processes to protect the furnace wall. In this laboratory study, the formation of freeze-linings from fayalite-based (FeO-SiO2-Al2O3-CaO) slags was investigated. This was performed with a gas-cooled probe at 1200 °C under protective atmosphere. The microstructure of the freeze-linings formed on the samples was characterized using scanning electron microscopy (SEM). The influence of cooling rate, slag agitation and slag composition on the freeze-lining formation was studied by varying the gas-flow rate, rotating the crucible and changing the CaO and Al2O3 contents in the fayalite-based slag, respectively. The results indicate that fayalite (Fe2SiO4) precipitated from the slag and grew into large columnar crystals along the heat gradient from the cooled probe to the bath slag. The thickness of the freeze-lining increased with increasing cooling rate, while an increase in the slag agitation and the CaO and Al2O3 contents in the slag decreased the thickness of the freeze-lining. These macroscopical observations are discussed with respect to the microstructural evolution in the formed freeze-lining samples.

Rheological behavior of fayalite based secondary copper smelter slag in iron saturation

A fayalite based slag is formed during the smelting process of secondary copper containing resources. Of particular importance is the slag viscosity which quantifies the flow properties of the slag and affects the reaction kinetics, the refractory corrosion in the smelter and operational practice. In the present work, a high temperature rheometer system has been employed to study the rheological behavior of the industrial slag system FeO-ZnO-SiO2-Al2O3-CaO (FeO/SiO2 = 1–1.5, ZnO = 6–8 wt %, CaO = 1.5 wt % and Al2O3= 4.5 wt %) at 1150 °C with iron saturation. The slag behaves as a shear thinning fluid. The degree of shear thinning was quantified by fitting the flow curve with the Oswald-De Waele power law model. The relation between the slag composition and the flow behavior index has been discussed.

Slag Valorisation as a Contribution to Zero-Waste Metallurgy

Zero waste is a challenging, though vital, strategy for the 21st century. This philosophy profoundly reshapes our thinking about resources and production, where waste is no longer waste but a secondary resource, a crucial part of a sustainable material’s life cycle. It encourages industry, government, and the society as a whole to redesign our practices to avoid waste being landfilled or incinerated. The 4th edition of the International Slag Valorisation Symposium (15–17 April 2015, Leuven, Belgium)—with Zero Waste as a subtheme—was organized by the Department of Materials Engineering and the Centre for High Temperature Processes and Sustainable Materials Management of the KU Leuven to contribute toward near zero waste processing and closed material loops in the field of high-temperature (metallurgical) residues. The content of this symposium offered a rich overview of the contemporary trends in the worldwide research and innovation strategies as regards the valorization of ferrous and nonferrous slag, fly ash, bottom ash, and other metallurgical residues. The contributions from the participants were encompassed in four thematic categories, thereby covering the whole slag production and treatment chain, from the high-temperature molten state to solidification and finally to metal extraction and end-products: • Hot stage slag engineering for higher value-added applications and energy recuperation, • Base and critical metal recovery, • Innovative/low-carbon building applications, and • Non-traditional slag valorization processes and products.