1,809 research outputs found
General introduction to critical materials
No full textA growing world population and rising levels of prosperity are driving up the global demand for energy and materials and are increasing the negative impact on the environment. Challenges related to energy use, materials consumption, and climate change are closely intertwined. On the one hand, producing materials consumes about 21% of global energy use and is responsible for about the same percentage of carbon emitted to the atmosphere. On the other hand, the transition from a fossil to a non-fossil electricity mix — to mitigate climate change — would result in a much higher usage of metals. The increase in the usage of metals would range from a few percent to a factor of a thousand for certain metals. Concerns over the future security of the supply of raw materials has led to the identification of critical raw materials for the USA, Japan, and the EU.4–8 As part of the World Scientific Series on Current Energy Issues, this book is focused on ‘Critical Materials’.(OLD) MSE-
Substitution case study: Replacing niobium by vanadium in nano-steels
No full textThe substitution of critical alloying elements in metals is a strategy to reduce the criticality of materials. Nano-steels are a novel grade of advanced highstrength steels that are suited for application in the chassis and suspension of cars and as fire-resistant steel in high-rise buildings. The high strength and ductility per unit mass make the nano-steels resource-efficient and reduce vehicle weight while maintaining crash worthiness. The excellent mechanical properties of certain nano-steels rely on the addition of small amounts (up to 0.1 wt.%) of Niobium as alloying element to the steel. Niobium is considered to be a critical raw material by the European Union due to its high economic importance as an alloying element in advanced, high-strength steel grades and due to the high supply risk related to the high degree of monopolistic production within the supply chain. This chapter describes the fundamental materials science that is needed for the substitution of the critical alloying element Niobium by Vanadium as an alloying element in nano-steels.(OLD) MSE-
Microstructure Control of Fire-resistant, Low-alloy Steel; An in-situ 3D X-ray Diffraction and A Small-angle X-ray Scattering Study
No full textThe research presented in this thesis aims at deepening our understanding of the formation of the microstructure of steel during thermal processing in order to control the microstructure and thereby improve the fire-resistance of low-alloy steel. The strength of steel decreases during a fire mainly due to the following changes in the microstructure: 1) increased dislocation motion at elevated temperatures, facilitating plastic deformation, 2) coarsening of the microstructure by grain growth and coarsening of precipitates, which reduce the pinning effect on dislocations, 3) the phase transformation from ferrite to austenite can result in a coarser-grained single-phase structure, and 4) grain boundary sliding. Therefore it is very important to understand the kinetics for the formation of precipitates, dislocation structures, and grains and sub-grains during the austenite-to-ferrite phase transformation during thermal processing. In-situ characterization of these microstructural features is possible by using large-scale synchrotron radiation facilities. The precipitate size distribution evolution during thermal processing can be studied in-situ by small-angle x-ray scattering (SAXS). The nucleation and growth of grains during solid-state phase transformations can be studied in-situ by means of three-dimensional x-ray diffraction (3DXRD) microscopy. The evolution of the dislocation structure during thermal processing can be studied by combining SAXS and 3DXRD. Chapter 2 introduces the basic concepts of microstructures and mechanisms to strengthen low-alloy steel at elevated temperatures. Firstly, the different types of dislocations and slip mechanisms in steel are reviewed. Secondly, the main characteristics of low and high-angle grain boundaries are presented. Thirdly, the main mechanisms for the loss of strength of steel at high temperature are discussed briefly. Lastly, a review of the literature for improving the fire-resistance of steel is presented. Chapter 3 introduces the theory of small-angle X-ray scattering (SAXS) and 3 Dimensional X-ray diffraction (3DXRD) microscopy using synchrotron radiation for microstructural analysis. In the section related to SAXS, the experimental method and data analysis strategies which are used for measuring the characteristics of precipitates and dislocation walls are described in detail. In the section related to 3DXRD, the experimental method, the pre-processing steps for the data analysis, and the 3DXRD data analysis procedure applied for finding grain characteristics are described. Chapter 4 presents the evolution of the size distribution of the (Fe,Cr)-carbides and dislocation structures in steel during a heat treatment as investigated by in-situ SAXS using synchrotron radiation with a new data analysis strategy. The size distribution of the (Fe,Cr)-carbides during heat treatments is determined from the isotropic component of the SAXS patterns. Bright-field transmission electron microscopy (BF-TEM) and high-resolution transmission electron microscopy (HR-TEM) reveal the nearly spherical morphology of the precipitates. Additional measurements have been carried out on a single crystal of ferrite containing (Fe,Cr)-carbides by combining 3DXRD and SAXS during rotation of the specimen at room temperature in order to understand the origin of the streaks in the SAXS-pattern. From simulations based on the theory of SAXS from dislocations we derive that the measured streaks, in the 2D SAXS-patterns including the spottiness, correspond to a dislocation structure of symmetric low-angle tilt boundaries, which in turn corresponds to the crystallographic orientation gradient in the single crystal of ferrite as measured by 3DXRD. Chapter 5 presents the effect of niobium and the grain boundary density on the fire-resistance of Fe-C-Mn steel. Two steels are used: Fe-C-Mn steel and Fe-C-Mn-Nb steel with an atomic ratio Nb/C=1.3. Two different sets of heat treatments are carried out before the fire-test. The first set of heat-treatments consists of heating the steel to 1100°C to bring all niobium in solid solution and austenitizing before continuous cooling at three different cooling rates during the austenite-to-ferrite phase transformation. The second set of heat treatments consists of heating the steel to bring all niobium in solid solution and austenitizing, rapid cooling to room temperature, reheating to 600?C, and annealing for different times before rapid cooling to room temperature. The fire-tests are carried out on specimens by applying a force equal to 60% of the room temperature yield strength at elevated temperature using a Gleeble thermo-mechanical simulator. In this study two techniques are used for analysing the microstructure: 1) Electron Back Scattered Diffraction (EBSD) and, 2) Optical microscopy. In this chapter we show that the low-angle and high-angle grain-boundary densities increase with increasing cooling rate during the austenite to ferrite phase transformation for the niobium containing steel, whereas total grain boundary density decreases with increasing the annealing time at 600°C. We show that the addition of 0.10 wt.% niobium to Fe-C-Mn steel increases the failure temperature of steel by 92°C during a fire-resistance test. Moreover, we demonstrate that the failure temperature increases linearly up to an additional 45°C with increasing grain boundary density from 0.06 to 0.64 ?m-1 for the niobium-containing steel. In Chapter 6 the effect of niobium in solid solution and NbC-precipitates on the austenite-to-ferrite phase transformation kinetics is investigated. In order to separate the effects of NbC-precipitates and Nb in solid solution on the phase transformation kinetics, we use three high-purity Fe-C-Mn steels with different niobium concentrations and one without niobium. Three-dimensional x-ray diffraction (3DXRD) microscopy is used at a third-generation synchrotron radiation facility to study in-situ and simultaneously the nucleation and growth of individual ferrite grains in the bulk of steel during the austenite/ferrite phase transformation. The measured nucleation rate is compared to the classical nucleation theory (CNT) to determine the nucleation parameters. The effects of NbC-precipitates and the concentration of Nb in solid solution on the incubation time, frequency factor, and the activation energy for ferrite nucleation are quantified. The experimentally measured nucleation start temperature is 40-115°C lower than predicted by Thermo-calc for the four alloys under ortho-equilibrium conditions, depending on the concentration of niobium. The frequency factor for nucleation is found to decrease exponentially with increasing concentration of Nb in solid-solution. The ?-parameter, which contains information about the shape of the nucleus and the interfacial energies that are involved in the nucleation process, increases with increasing concentration of Nb in solid solution. The dependence of ?-parameter on the concentration of Nb in solid solution is best described by a pill-box type of geometry of the nucleus and a square root dependence of the ?/?-grain boundary energy with the Nb concentration in solid solution. The ratio of the density of ferrite grains to the density of austenite grains decreases by more than 25% due to the formation of NbC-precipitates, which can be interpreted as reduction of nucleation probability of potential nucleation sites for ferrite, i.e. grain corners, by NbC-precipitates. The ratio of the density of ferrite grains to the density of austenite grains does not depend significantly on the amount of niobium in solid solution. The delay in the start of the transformation as a function of the concentration of niobium in solid solution is found to depend on three factors: 1) the segregation of Nb to the ?/?-grain boundaries, which increases the activation energy for nucleation, 2) reduction of nucleation probability of potential nucleation sites by NbC-precipitates, and 3) diffusion of Nb-atoms from the ?/?-grain boundaries back into the matrix during the nucleation. The drag-effect of niobium in solid-solution on the growth of individual ferrite grains is quantified for different Nb-concentrations. In this work we follow the ‘dissipation’-approach initially developed by Hillert and Sundman et al. and further developed by Odqvist et al. By measuring the velocity of the interface and estimating the chemical driving force, the pressure due to curvature, and the pinning pressure, we determined the dissipation of Gibbs energy caused by the diffusion of the solute atoms being dragged along with the migrating interface, ?Gdiff (J/mol), as a function of the Nb-concentration in solid solution. The drag effect increases with increasing concentration of Nb. Chapter 7 presents an in-situ study in which the partial 3D microstructure of the austenite and ferrite phases before and after the transformation are characterized and in which the nucleation rate of ferrite is measured in an Fe-C-Mn alloy. Separating the experimentally observed ferrite nucleation rate in the bulk and in the surface region of the sample shows that the maximum nucleation rate is reached at lower temperature in the surface region than in the bulk. The activation energy for the nucleation of ferrite in the surface region is higher than in the bulk. An explanation for this could be the application of a thin nickel coating at the surface of specimen, which might result in interfaces between austenite and nickel grains that have lower energy than grain boundaries between austenite grains in the bulk. Future work could focus on deepening our understanding of the effect of low-angle grain boundaries on the fire-resistance of steel containing precipitates. Hitherto, it was assumed that low-angle grain boundaries do not contribute substantially to the strength of steel. However, this research demonstrates that low-angle grain boundaries do contribute substantially to the strength of steel at room temperature and they improve the fire-resistance. How does the interaction between a dislocation and a low-angle grain boundary lead to strengthening of the steel? How do the low-angle grain boundaries form during the austenite-to-ferrite phase transformation in niobium containing steel? What are the prerequisites for the formation of low-angle boundaries? Would the low-angle boundaries also form in steel containing different alloying elements than niobium? Which methods can be used to introduce an even higher density of grain boundaries? From a more application oriented point of view, future research could focus on testing the fire-resistant steel that is presented in chapter 5 under more realistic fire-conditions. Fire-tests could be performed in tensile-mode rather than compression-mode. Moreover, the creep-resistance of this alloy could be investigated to explore its potential applications in gas turbines for power generation and steel-pipes for the transport of hot-gasses from sea to land. An investigation into the low-temperature properties of the steel would also be very interesting in order to test the suitability of the steel for arctic conditions.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
Critical Materials: Underlying Causes and Sustainable Mitigation Strategies
No full textThis book covers a new frontier of research in Critical Materials that provides insight in terms of the possible sustainable mitigation strategies, the complexity, broadness and multi-disciplinarity of the subject. By exploring in both "systems view" and "in-depth materials view" in the light of circular economy, this book tackles the problem of sustainable usage of materials that is closely intertwined with the energy issue and climate change. Topics covered include: geopolitics of materials, the energy-materials nexus, definitions of the criticality of materials, circular product design, the development of alternative materials (substitution), sustainable mining and recycling.(OLD) MSE-
Evolving Microstructures in Carbon Steel: A Neutron and Synchrotron Radiation Study
No full textAerospace Engineerin
Applying a life cycle perspective to research on metal recovery from electronic waste using bioleaching
No full textThe Master’s programme Industrial Ecology is jointly organised by Leiden University and Delft University of Technology. Waste electronics and electrical equipment (WEEE) constitute a growing waste stream which is becoming more problematic in its management. Unsafe disposal contributes to environmental pollution and threatens human health as well as wasting secondary resources. A biologically mediated natural process, termed bioleaching, applied to the recovery metals from electronic waste, may become a promising emerging technology contributing to secondary resource recovery. Improved resource efficiency is highly relevant in the context of a transition to a more environmentally benign circular economy. Initial experimental bioleaching results using bacteria show efficient yields. Claims of benign environmental performance in the research literature are only based on process centric suppositions. Compared to metal recovery using smelting at high temperatures, the bioleaching micro organisms can work at close to ambient temperatures and directly generate few contaminants. This thesis reports on the environmental assessment of the novel bioleaching process. LCA methodology was applied at the early research stage to the process to embed it in a life cycle context, linking it to upstream and downstream flows. Then LCA was combined with an elaborate conjectural scenario to gauge its application in a potential future context and compare it to an established metal recovery process. The implications for LCA methodology were then discussed. Using primary data from the lab research, a product system was defined at laboratory scale to which LCA was applied. Data for elemental copper recovery was not available so this was estimated. After gathering ample contextual information on the direction of research, regulations, technological precedents and existing similar technologies a short term future scaling up scenario was defined. A second LCA was performed on this estimated scaled up product system. Environmental profiles were obtained for the lab product system, the scaled up system and optimised versions of the scaled up system. The latter were compared to the environmental performance of an existing technology, which aligned with the scaled up scenario in terms of scope and comparability. In the first two LCAs potential hotspots were identified in the energy and material inputs for the bioleaching process and solvents for copper recovery. However, the comparison with the existing technology returned a far inferior environmental profile, even after further optimisation. These results could not be considered robust given the precociousness of application, yet valuable information was generated. The uncertainties also prompted further enquiry about the system boundary and comparability of product systems. Despite the amount of uncertainty and conjecture involved, the whole exercise can nonetheless be considered a valid, informative mock-up of a plausible future. The tandem application of ex ante LCA and exploratory scenario brings a degree of systematic rigour and discipline to an ambiguous situation. It provides a medium for stimulating attitudes of critical examination and discovery in the very early in development can allow it to have a significant influence in broadening the research context. It is recommended that, for the bioleaching research, the LCA be built upon and refined in subsequent development stages with appropriate data gathering. In general, the approach should be applied again, possibly even earlier and for other technologies, to test it and establish its validity as an environmental screening tool in these anticipatory circumstances. As estimations are key for its application, this component should be targeted by dedicated simulation software and databases also adapted for this purpose. The promotion of the systems approach perspective of the methodology can also be disseminated by using it as an exercise as part of the training of designers, researchers and engineers. If it can be sufficiently validated after application to other research and concepts then it may be expanded to incorporate economic & social aspects.Industrial EcologyIndustrial EcologyDelft University of Technolog
The delamination process of the dross build-up structure on submerged hardware in Zn-Al and Zn-Mg-Al baths: An empirical study
No full textHot-dip galvanizing is a well-known process to increase the corrosion resistance of steel. As a by-product dross is formed in the Zn-bath. The dross particles are composed of Fe, Al and Zn in the form of Fe2Al5Znx and interact with the hardware that is submerged in the Zn-bath and eventually accumulate on the surface of the hardware. This accumulation of dross on the hardware is known as dross build-up.Dross is formed in the Zn-bath as a result of the dissolution of Fe from the steel strip. This Fe reacts with Al present in the liquid Zn forming the Fe2Al5Znx dross particles. Once the hardware is submerged in the liquid Zn a thin compact Fe2Al5-layer is formed on top of the surface of the hardware, known as the diffusion layer. This diffusion layer acts as a barrier for Fe towards the Zn-bath and Zn towards the hardware surface. Once the diffusion layer is formed dross particles precipitate on top of this diffusion layer followed by a slow growth of the intermetallic dross particles. The diffusion layer and accumulated intermetallic dross particles are known as the dross build-up. The thickness of this dross build-up depends on immersion time, bath temperature and bath chemistry and varies typically between 90 μm up to several millimetres.The dross build-up is thought to be a critical factor in the bath hardware lifetime. The surface quality of the bath hardware directly influences the quality of products produced on the galvanizing line. More dross in the Zn-bath could lead to more defects in the coating, which could lead to failure when the steel strips are processed further, or giving the coating on the steel strip a bad appearance. Because of the dross build-up on the hardware, the bath hardware is changed every 4-6 weeks. By controlling the dross in the Zn-bath, the service lifetime of the hardware could possibly be extended. When the service lifetime of the hardware is extended the maintenance downtime and costs of the galvanizing lines are reduced.Recently, Tata Steel introduced a new type of Zn-coating: MagiZinc (MZ). This type of Zn-coating differs from the conventional Zn-coating: Conventional Zn-coating (GI) consists of Zn with 0,30 wt% Al whereas MagiZinc consists of Zn with 1,60 wt% Al and 1,60 wt% Mg. This difference in composition has an influence on the dross build-up formed on the hardware. At Tata Steel, there is some evidence that the dross build-up layer on the bath hardware created in the conventional Zn-bath is diminishing when the hardware is submerged in the MagiZinc-bath.This thesis project aims to identify the characteristics of this cleaning behaviour in MagiZinc of the dross build-up that is formed on bath hardware when submerged in conventional Zn.Based on the results obtained from experiments in this study it can be concluded that the delamination process of the intermetallic dross particles is a combination of intergranular diffusion of Zn and crack formation as a result of thermal shock.By changing the baths from conventional Zn to MagiZinc the composition of the bath changes. As a result the thermodynamic stability of the intermetallic Fe2Al5Znx dross particles change with respect to the liquid Zn-phase in such a way that the intermetallic dross particles partly dissolve in the liquid MagiZinc. As a result, the intermetallic dross particle/liquid Zn interface changes from a faceted to a curved interface. As a consequence of this change in structure intergranular diffusion can take place between the intermetallic dross particles. By the intergranular diffusion of Zn the cohesion of the grain boundaries of the intermetallic dross particles is reduced. This reduction in cohesion is probably the start of the delamination of the intermetallic dross particles, breaking into smaller pieces at the grain boundaries when enriched with Zn.The diffusion layer remains largely unaffected in the delamination process due to the better adhesion to the hardware surface compared with the adhesion of the intermetallic dross particles to the diffusion layer. The better adhesion of the diffusion layer to the hardware surface is the result of diffusion of Cr and Ni from the 316L SS substrate into the liquid Zn at time of immersion. The area from where Cr and Ni are dissolved, Al is diffusing into the 316L SS substrate forming the diffusion layer. Simultaneously the intermetallic dross particles form at the hardware surface. This layer is mainly formed from Fe and Al from the bath, not from the 316L SS substrate.Due to this limited bonding between the intermetallic dross particles and the diffusion layer the intermetallic dross particles are more prone to crack formation due to thermal shock.By changing the Zn-bath from conventional Zn to MagiZinc and vice versa the hardware and thus also the dross build-up rapidly cools down to room temperature. This thermal shock creates stresses within the intermetallic dross particle-layer. Due to a difference in thermal expansion between the 316L stainless steel matrix and the intermetallic dross particle-layer large cracks form in the intermetallic dross particle-layer. When the hardware is immersed again in liquid Zn the cracks still exist and these cracks accelerate the delamination process of the dross build-up structure. This observed mechanism is independent from the type of Zn-bath that the hardware is immersed in. The process also takes place when the hardware is taken out a conventional Zn-bath and placed back into a conventional Zn-bath.Materials Science and Engineerin
Reconstruction of Three-Dimensional Microstructures from Non-Destructive 3DXRD Microscopy Measurements: Development of a computational methodology
No full textTechnische MateriaalwetenschappenMechanical, Maritime and Materials Engineerin
Theoretical and Experimental Development of Surface Tension Measurements under Arc Plasma Conditions
No full textMechanical, Maritime and Materials EngineeringTechnische Materiaalwetenschappe
CFD Modelling of HIsarna Off-gas System
No full textHIsarna is a new and breakthrough smelting reduction technology for producing liquid hot metal for steelmaking directly from iron ores. Compared to the conventional blast furnace route, HIsarna achieves a 20% reduction in CO2 emissions by eliminating coking and the need for iron ore agglomeration processes such as sintering and pelletizing and directly receiving fine coal and iron ore. The process is built on a pilot scale capable of producing 8 tons/hour of hot metal. The technology combines the Cyclone Converter Furnace (CCF) technology (developed by Hoogovens/Corus/Tata Steel) with the Smelting Reduction Vessel (SRV) from the HIsmelt technology (developed by RioTinto). Operational since 2010 at the IJmuiden Works of Tata Steel Nederland, it has been continually developed towards industrial demonstration. Fine iron ore and pure oxygen are injected into the CCF. The oxygen is needed as an oxidizer to partially combust the CO-H2 mixture of the off-gas from the SRV. The combustion process supplies heat to pre-reduced ore particles, melting them during their fly time in the CCF. Eventually, the molten ore particles accumulate on the furnace wall, forming a liquid film that drips along the wall and falls into the molten bath of the SRV. Coal is introduced into the slag layer of the bath via a carrier gas to fully reduce pre-reduced iron oxide (FeOx) droplets falling from the CCF above. CO gas is generated in the form of bubbles, rising to the top space of the SRV, where it undergoes partial combustion with oxygen injected through oxygen lances (OL), providing the necessary heat in the SRV.Through operational analysis of the pilot plant, it has been determined that replacing half of the primary raw material with galvanized steel scrap as a secondary source in the HIsarna process is feasible. This substitution would result in a significant reduction in the injection of fine iron ore. Another advantage is the continuous evaporation of zinc from the scrap surface, accumulating in the off-gas dust, which can later be separated and recovered. In contrast to the blast furnace route, the zinc element does not form a circulating loop inside the reactor but is converted to the oxidized/ferrite form, ultimately ending up in the dust bag and filters.However, plant measurements and laboratory analysis of the HIsarna dust reveal that the evaporated zinc primarily reacts with available oxygen and iron oxides to form zinc ferrite. This necessitates additional pre-processing steps before feeding into the zinc smelting unit, incurring extra costs. Consequently, the formation of ferrite is deemed undesirable.In a nutshell, this thesis focuses on developing a precise computational fluid dynamic (CFD) model to predict the behaviour of the HIsarna off-gas system. This model is crucial for predicting temperature and composition profiles within the off-gas system, particularly in zones where data are not measured at the pilot plant. The possibility of zinc ferrite formation reduction and off-gas system is investigated using plant measurements, CFD data analysis, and thermodynamic calculations. Furthermore, the developed CFD model is utilized to propose modification/optimization of the process, reducing iron ore dust escaping the system, reducing post-combustion oxygen consumption, optimizing post-combustion lance, and off-gas system scale-up.Chapter 1 of the thesis is dedicated to a brief history of ironmaking and introduces the HIsarna process in detail, as well as the research focus and thesis structure. Chapter 2 focuses on establishing and validating a CFD model and offers a detailed description. Chapter 3 provides an extensive discussion of the model selection and sensitivity analysis. This chapter primarily delves into critical insights regarding the reasons behind the choice of sub-models within the CFD model. Flow analysis of the off-gas system is presented in Chapter 4, and in Chapter 5, the behaviour of the escaped ore entering the off-gas system is investigated, and potential solutions to mitigate injected ore losses from the off-gas system are discussed. The modified geometry introduced in Chapter 5 is subjected to analysis using the same validated CFD model, ensuring its effective operation within the entire off-gas system. These findings are discussed in Chapter 6 of the thesis. In Chapter 7, the formation of zinc oxide and zinc ferrite are investigated in the original and modified geometry of the off-gas system, and possible solutions to reduce the ferrite formation are proposed. In Chapter 8, a modification to the oxygen lance is proposed to enhance the combustion of the CO-H2 mixture. This modification involves using a fluidic oscillator instead of injecting oxygen through a conventional nozzle. The results demonstrate an improvement in CO-H2 combustion in the reflux chamber. The proposed geometry is constructed and implemented in the reflux chamber for further evaluation and is discussed in detail.In Chapter 9 (Part 3), the CFD model developed for the pilot plant is employed to conduct a CFD-based scale-up of the off-gas system to the industrial scale. Within this chapter, the optimized geometry and recommended operating conditions are presented. Conclusions, remarks, and recommendations are presented in the final chapter of the thesis (Chapter 10).Team Yongxiang Yan
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