Microstructure Of Slag Research Articles

Presidential Address: Metallurgical slags: A drive to circularity and search for new research agenda

Poor phase separation and fine dissemination of the desired components within congruous slag phases are key challenges limiting the recoverability of values from slags by conventional beneficiation methods. Slag microstructure conditioning is a pragmatic approach to increasing the value-in-use of discard slags, especially when integrated with the broader smelter infrastructure. Although not yet tested on oxide slag systems, this paper explores the potential application of magnetohydrodynamic principles to the crystallization behaviour of bulk slags. Integrating the slag microstructure conditioning infrastructure to the existing smelter infrastructure is key to unlocking the economic value of slags because it is most economic to condition the properties of molten slag directly after tapping. A new business model that integrates smelting units to transversal economic activities, such as cement production and suppliers of construction aggregates, can significantly increase the circularity of metallurgical slags.

Process Optimization and Mechanism Study for Sulfur Recovery from High-Silica Phosphogypsum via Carbothermal Reduction Smelting.

Phosphogypsum produced from wet-processed phosphoric acid mainly consists of calcium sulfate dihydrate, which is an important sulfur resource. The traditional sulfuric acid and cement process based on phosphogypsum suffers from unstable cement quality owing to impurities such as phosphorus and fluorine and kiln ringing caused by the low-melting phase. This study investigated sulfur recovery and value-added utilization of liquid slag from high-silica phosphogypsum via carbothermal reduction smelting. A phosphogypsum ingredient (PGI) system was constructed by adding appropriate amounts of silica, alumina, magnesium oxides, and iron oxides to meet the production requirements of slag wool. Carbothermal reduction smelting experiments suggested that the temperature and C/S molar ratio significantly affected the desulfurization rate and phase structure of the slag. More than 97.44 wt % of sulfur could be recovered with a C/S molar ratio of 0.5-0.8 at 1300 °C or above in the molten state, and the molten slag was an amorphous magnesium-calcium-aluminosilicate. The PGI desulfurization mechanism is discussed based on the phase transformation and slag microstructure evolution.

Chemical Composition, Crystal Structure, and Microstructure of Slags on the Korean Peninsula from the First Copper Production Remains of the 9th Century

The scarcity of excavated early-stage smelting sites related to copper production presents significant challenges in gaining a comprehensive understanding of the copper production process. However, the archaeological site discovered in 2018 in Daeryang-ri, Jinan-gun, Jeollabuk-do, boasts a substantial number of copper smelting remains and related slags, marking it as the first copper manufacturing production site identified on the Korean Peninsula. Consequently, this study selected 10 slag samples, chosen based on surface color and characteristics indicative of a connection to copper smelting, for scientific analysis to accurately ascertain the site’s nature. The primary component analysis of the slags indicated that CuO content ranged from 0.30 to 3.29 wt%, which, although not high, reveals significant quantities of FeO and SiO2. X-ray diffraction analysis revealed the presence of minerals such as cristobalite, along with fayalite and wüstite, commonly found in slags, varying by sample. Furthermore, microstructural observation revealed circular copper particles containing sulfur and iron, indicating the presence of copper particles in a matte state that have not been refined. This analysis suggests that the slags recovered from Jinan Daeryang-ri bear evidence of iron smelting at the site, with the slag being produced as an intermediate by-product during copper production.

Internal superhydrophobic marine concrete: Interface modification based on slag microstructure regulation

Structures in coastal environments are susceptible to damage from the combined effects of loading, scouring, corrosion, rust-frost-crystallization expansion forces, etc. Superhydrophobic materials can effectively alleviate these problems due to their excellent water rejection properties. However, in practical applications, superhydrophobic performance failure occurs after the surface is subjected to various stresses. To further explore this point, this article prepared an integrated superhydrophobic protective material using solid waste material slag to achieve the resource utilization of solid waste materials. Superhydrophobic particles covered with paraffin wax (SPP) reduce the direct damage of external forces on hydrophobic particles, extend their service life, and achieve self-healing of superhydrophobicity. Its comprehensive performance indices, including all-round wettability, water repellences, carbonisation resistance and electrochemical corrosion performance, were investigated. The results show that the contact angles of the superhydrophobic mortar inside and outside the contact angle are more than 150°, indicating three-dimensional superhydrophilicity. The 30% SPP dosage of superhydrophobic mortar in 48 h water absorption compared to ordinary mortar reduced by 78%, 120 h water permeability up to 0.72%; and carbonized 28 days after no traces of carbonisation; in the electrochemical corrosion experiments to prevent corrosive liquids from entering the reinforcing bars in the concrete has good anti-corrosion properties. In the electrochemical corrosion experiment, the corrosive agent effectively prevents the corrosive liquid from entering contact with the steel reinforcement in the concrete, and the resulting material has good anti-corrosion performance. These key characteristics can provide unique advantages for a wide range of applications in coastal environments, such as construction, bridging, decoration, transportation and power transmission.

Overview of the role of fluorine in the mold fluxes

Fluoride is one of components of the traditional mold flux, but it causes environmental pollution. With the increasing requirement of environmental protection on the metallurgical industry, it is a trend to develop low fluorine or fluorine-free mold fluxes in the future. In recent years, many scholars have researched some low fluorine or fluorine-free mold fluxes. However, because the action mechanism of fluorine in mold flux is not completely clear, the performance of mold fluxes composed of fluorine-substituting components has not reached the effect of fluorine-containing mold fluxes. In view of this, this paper summarizes the effects of fluorine in protective slag from macro and micro aspects: in the study of the macro properties of mold flux, it is generally believed that a certain amount of fluorine plays an important role in adjusting the melting temperature, viscosity and surface tension of mold flux, but its adjusting mechanism is not clear; in terms of microstructure, the structural behavior of fluorine in mold flux is very complicated due to the influence of alkalinity, other components and fluorine content. The microstructure of slag determines the properties of slag. Therefore, the complexity of the structural behavior of fluorine leads to the complexity of the transformation mechanism of the physical properties of mold flux, which makes it impossible to control the properties of mold flux fundamentally and increases the difficulty in selecting the alternative component of fluorine in the process of developing low fluorine or fluorine-free mold flux. Therefore, it is necessary to further study the influence mechanism of fluorine on the structure of mold flux.

Understanding the mechanism of ash deposition on boiler heating surface: The lattice Boltzmann and molecular dynamics simulations

Severe ash deposition can cause a decrease of the heat transfer ability on the heating surface for the furnace and the release of more pollutants. In order to get the widespread use of Zhundong coal, the temperature distribution characteristics of ash deposition for Zhundong coal was studied by lattice Boltzmann method in this paper. Furthermore, the microstructure of slag was further revealed by molecular dynamics. The results indicated that the temperature of ash deposition improves with the increase of time. The temperature of the particles in the outer and middle layers for Zhundong coal is significantly smaller than that of lignite and bituminous coal. Compared with other coal types, it is difficult to transfer heat for the deposited layer of Zhundong coal, which can not achieve better energy saving effect. Additionally, calcium and sulfur in Zhundong coal ash can easily react to form calcium sulfate, aggravating ash deposition on the heating surface of the boiler. These results provide a theoretical support to solve the problem of ash deposition burning Zhundong coal.

Influence of MgO on the alkali fusion behavior and mechanism of titanium-containing melting slag

The influence of MgO on the alkali fusion behavior and mechanism of titanium-containing melting slag is unclear. To clarify this, the phase transformation and microstructure of titanium-containing melting slag and alkali fusion slag were compared and analyzed by X-ray diffraction, scanning electron microscopy, and crystal structure analysis. The conversion rate of titanium-containing melting slag with different MgO contents was calculated. The results indicated that titanium-containing phases and other phases transformed into their corresponding sodium salts after the alkali fusion reaction. Upon increasing the MgO content, the phase transformation was complete, and the transformation from Na2TiO3 to NaMO2 (M = Mg, Ti) was more common. MgO greatly influenced the microstructure of slag samples and increased the conversion rate of titanium.

Study on Compressive Strength and Microstructure of Slag–Calcium Carbide Residue Solidified Mud Under Wetting–Drying Cycles

Study on Compressive Strength and Microstructure of Slag–Calcium Carbide Residue Solidified Mud Under Wetting–Drying Cycles

Correlation study between microstructure and fluidity of molten slag during co-gasification of coal and indirect coal liquefaction residue: Molecular dynamics simulation

Co-gasification of indirect coal liquefaction residues (ICLR) and coal is an effective way to achieve harmless and sustainable treatment of hazardous wastes. The long-term and stable operation of a co-gasification largely depends on the flow behavior of coal-ash slag. Herein, classical molecular dynamics simulation (MD) and Raman spectroscopy were used to study the microstructure of slag and its relationship with viscosity during the co-gasification of ICLR and coal. The results showed that with the addition of ICLR, the viscosity of slag decreased continuously. This reduction in viscosity was attributed to the increase of FeO content in the system with the addition of ICLR. As a network modifier, FeO could easily provide O2− at high temperatures, thereby destroying bridge oxygen and converting more tricluster oxygen and bridge oxygen into non-bridge oxygen. This significantly reduced the structure complexity and polymerization degree of slag, thereby reducing its viscosity. Finally, the correlation between the microstructural and viscosity was further analyzed. It was found that there was a quadratic function relationship between Q4 proportion and viscosity, and the formula was μ = 0.025(Q4)2-Q4 + 12.03. The purpose of this work was to provide theoretical support for slag flow mechanisms during the gasifier slagging-tapping process and the resource treatment of hazardous wastes.

Effect of electropulsing on the solidification of mould flux

The effect of electropulsing on the microstructure formation in solidification of mould flux has been investigated. Experimental characterization and image analysis reveals that the electropulsing treatment reduces 46% porosity and increases the interfacial perimeter to area ratio by 100%. The latter provides strong evidence that electric current influences interfacial energy. Dendrite arm spacing is reduced considerable. Electropulsing promotes the anisotropic crystal growth and retards the formation of interconnected crystal network. The latter is favourable to the current flow, liquid refilling and lubrication. The work demonstrates that electropulsing can be used to modify the microstructure of slag and hence to control the horizontal heat transfer rate in the mould, which is desirable in continuous casting of advanced high strength steels.

The Microstructure Formation in Slag Solidification at Continuous Casting Mold

The microstructure of slag film solidified on the inner wall of mold in continuous casting of low carbon steel has been examined experimentally and analyzed theoretically. A puzzle for the crystallization sequence has been solved by this work, which is useful to guide the modification of slag microstructure in efficient casting of advanced steels. The experiments observed three crystalline bands, each containing an initial block-shaped crystal sub-band and late-developed dendrite sub-band. The grain size and morphology change monotonically across the crystalline layers to form a gradient structure. The reason for this is that the solute segregation causes considerable surging of viscosity and constitutional undercooling in the liquid phase. This is rarely seen in the casting of alloys and have not been pointed out previously in the casting of oxide mixtures.

Effects of waterborne epoxy resin on the mechanical properties and microstructure of slag cementing slurries

The enhancement mechanism of epoxy resin on the physical properties of a slag solidified body with poor mechanical properties and susceptibility to cracking was investigated. Furthermore, the mechanical properties of an epoxy resin/slag cured body with varying resin contents and temperatures were studied experimentally. SEM, XRD, FTIR, and TG-DTG were used to test the structure and morphology of the epoxy resin/slag cured body. The results are as follows: (1) When the ratio of epoxy resin to curing agent is 10:3, the cured slag’s 7 days (7d) compressive and tensile strength at 50 °C are 65% and 52% higher, respectively, than the blank sample when the epoxy resin content is 15%. The compressive and tensile strength at 90 °C for seven days increased by 101% and 102%, respectively, compared to the blank sample. When epoxy resin content is 25%, the solidified slag's 7d compressive and tensile strength at 70 °C is 191% and 134% higher, respectively, than the blank sample. (2) Calcium silicate aluminate hydrate (C-A-S-H) is still the main hydration product of the composite, but there is less silica-magnesium hydrotalcite structure, which is different from the slag solidified body; (3) In the composite material, the three-dimensional network structure formed by epoxy resin curing is combined with the hydration products, and the polymer film fills the pores and cracks of the slag, improving the microstructure and mechanical properties of the slag. The results have theoretical significance for enhancing the physical properties of solidified slag and broadening its potential applications.

Mechanical properties and microstructure of slag and fly ash alkali-activated lightweight concrete containing miscanthus particles

To improve the early age strength of miscanthus-based composites, alkali-activated binders (ground granulated blast furnace slag and fly ash: AASF) were investigated against Portland cement. The impact of miscanthus content on strength development was assessed at three levels of aggregate to precursor binder mass ratio (0.27, 0.43 and 0.76). For the same aggregate to binder ratio, AASF mixes developed compressive strengths exceeding 1.3 MPa at 5% strain, seven times higher than those obtained with Portland cement, with the bulk density values measured in the range of 910–1070 kg/m3. However, these values for vegetal concretes remain lower than non-vegetal concretes of similar apparent densities such as those made with polystyrene aggregates. The analysis of the microstructure of AASF composites indicates a strong interfacial transition zone, showing microstructural features that suggest the achievement of a complete reaction.

Effect of Al2O3 on the molten slag microstructure information by molecular dynamics simulation and experimental analysis

The metallurgical properties of blast furnace slag changed when high alumina iron ore was used extensively due to the resulting changes of the molten slag microstructure. In the study, based on typical CaO–MgO–SiO2–Al2O3 slag systems with different w(Al2O3) content, molecular dynamics simulation was used to calculate the microstructural properties of particles in the high-temperature slag system, such as bond length, partial radial distribution function, coordination numbers, and diffusion coefficient. In addition, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and 27Al solid-state magic angle spinning nuclear magnetic resonance (27Al SS MAS NMR) were used to detect and analyze the samples. The comprehensive calculations and experimental results show that increasing w(Al2O3) can enhance the structural stability of each ion pair, and the strength of the structural stability is such that Si–O > Al–O > Mg–O > Ca–O. The self-diffusion coefficients are as follows: Mg2+ > Ca2+ > Al3+ > Si4+, which leads to the transformation of the [SiO4]4−(Q0), [Si2O7]6−(Q1) and [Si2O6]4−(Q2) structural units to [Si2O5]2−(Q3). The degree of polymerization of slag increased as well as the stability of the structural units. Moreover, the coordination of Al will change from the [AlO6]9−octahedral structure of six-coordinated Al to the [AlO5]7−pentahedral structure of five-coordinated Al and the [AlO4]5−tetrahedral structure of four-coordinated Al. It was also found that the content of non-bridge oxygen in the whole slag system decreased continuously, leading to the increasing degree of polymerization of slag, and the experimental results were consistent with the molecular dynamics calculation.

Effects of Cr2O3 content on viscosity and microstructure of copper converter slag

The influences of Cr2O3 on the viscosity of copper converter slag were investigated employing the rotating method in air atmosphere. The free running temperature was determined according to the viscosity-temperature curve and the activation energy was calculated based on Arrhenius-type relationship. The molten slag microstructure evolution was researched by Raman spectroscopy and Fourier Transform Infrared spectroscopy (FTIR). The results showed that the viscosity, free running temperature as well as activation energy increased significantly after the addition of Cr2O3. The viscosity of the original slag was 0.464 Pa·s at 1573K, exceeded 8.000 Pa·s after 5 wt% Cr2O3 being incorporated. Meanwhile, the Raman spectrums demonstrated that silicate network structure components of the molten slag samples converted from Q0 ([SiO4]4−, monomer) / Q1 ([Si2O7]6−, dimer) to Q2 ([SiO3]4−, chains) / Q3 ([Si2O5]2−, sheets), which indicated the formation of more complex structures and finally contributed to the increase of the viscosity. The influence mechanism of Cr2O3 on the copper converter slag viscosity and microstructures were uncovered to give reference for understanding the excellent slag resistance property of Cr2O3 containing refractories used in copper smelting furnaces.

Research Progress of Slag Structure and Hydration Activity

Slag is widely used as mineral admixtures in cement-based materials by its potential hydration activity. It has the advantage of saving resources and energy, reducing carbon emission, improving the performance of concrete, and plays an increasingly important role in the building materials industry. But the early strength of slag is low, and the industrialization of useful hydration products also need to be activated, so the utilization rate of slag in high grade cement is restricted. The hydration activity of slag depends not only on the content of vitreous in slag, but also on the structure of vitreous slag. To explore slag glass micro composition and structure of its active role, The slag micro-structure was analyzed from the structure levels, and then the factors affecting the activity of slag was evaluated. The potential advantages and disadvantages of some different methods to active slag were discussed such as physical ways, chemical activation method and compound activation way. The existing problems and development direction of improving the activity of slag were summarized , which could provide a valuable reference for the efficient use of slag.

Micromechanical and multi-scale modeling of manganese containing slag comminution in the design of energy efficient secondary raw material beneficiation processes

Efficient separation of valuable metals from various slags is of great interest for the industry to effectively utilize valuable raw materials. Present work focuses on modeling the deformation and damage behavior of manganese containing slag materials at the microstructural level, which dictates the macroscopic material behavior and allows one to investigate possibilities to perform metal separation after comminution of the slags. The model includes finite element micromechanical description of the material behavior and slag microstructure. Computational micromodels are constructed based on direct input characterization data and statistically representative synthetic models. The damage model treats brittleness and ductility of the material together with phase specific material behavior, all relevant to comminution of the slag. Finally, a simplified jaw crusher simulation accounts for freeing materials, assisting the evaluation of empirical random breakage, all together with a microstructural particle study which is analyzed against micromechanical modeling. Crystal plasticity level simulations of surface deformation and hardening in jaw crusher are presented to couple macroscale crushing events with microscale deformation of wear parts. The work overall presents a workflow and proposes a methodology how digitalization and multi-scale material modeling can contribute to the development of efficient comminution means for hard to process secondary raw materials.

Mechanism of Phosphorus Enrichment in Dephosphorization Slag Produced Using the Technology of Integrating Dephosphorization and Decarburization

In order to better understand and develop the technology of integrating dephosphorization and decarburization in a single converter (abbreviated as IDDSC), the relevant thermodynamic issues were discussed by calculation. Based on the thermodynamic calculation, the bridges between the phosphorus distribution ratio, temperature, and slag composition were constructed. Besides, the connections between the dephosphorization behavior and the microstructure of slag were also established by investigating four heats of hot metal smelt using IDDSC technology. As a result, the mechanism of phosphorus enrichment in the dephosphorization slag was revealed. Also, the results show that the dephosphorization efficiency increases gradually with increasing slag basicity. While the dephosphorization efficiency increases first and then decreases with the increase of FeO content in slag. There is a competition relationship between P2O5 and FeO in reacting with CaO and SiO2. When CaO/FeO is relatively high, not enough FeO is provided. Thus P2O5 is in priority to react with CaO and SiO2 through [3n + 2](CaO) + 2SiO2 + n(P2O5) = n(3CaO·P2O5)-2CaO·SiO2(s), generating P2O5-rich nC2S-C3P solid solution which promotes the removal of [P] from the hot metal. When CaO/FeO is relatively low, FeO competes over P2O5 in reacting with CaO and SiO2 through a(CaO) + b(SiO2) + c(FeO) = aCaO·bSiO2·cFeO(s), generating CaFeSiO4 instead of P2O5-rich solid solution. As a consequence, the slag with low CaO/FeO shows a poor dephosphorization ability.

Structure and flow properties of coal ash slag using ring statistics and molecular dynamics simulation: Role of CaO/Na2O in SiO2–Al2O3–CaO–Na2O

Molecular dynamics simulation was applied to investigate the microstructure of slag in SiO2-Al2O3-CaO-Na2O system. A new structure model for slag was established through ring-statistics by MD simulation. The network structure was simplified into crosslinked rings divided into three types based on the ring size. The change of amorphous structure was well described by ring distribution. The destruction of slag structure by Ca2+ is more significant than Na+, and high CaO/Na2O resulted in low content of medium and large rings and low viscosity. The ring distribution coefficient (Rdc) was defined to establish the relationship between structure and viscosity: ŋ=26.7Rdc-10.2. When CaO/Na2O ratio increases, the ring distribution transforms from medium or high-order to low-order, leading to the decreasing of Rdc and slag viscosity. Moreover, CaO/Na2O ratio also changes the diffusivity of slag and thus the melting behavior. Finally, a linear relationship between the empirical liquidus temperature (Tliq) and atomic diffusivity from the MD simulations was obtained.

Effects of B2O3 on the structure and properties of blast furnace slag by molecular dynamics simulation

B2O3 has the advantages of reducing the liquidus temperature and enhancing the fluidity of slag, while its influence mechanism in atomic scale has not yet been fully understood. Molecular dynamics simulation was conducted to investigate the influence of B2O3 on the structure and properties of SiO2CaO-Al2O3-B2O3 blast furnace slag system at 1773 K. Results showed that a large number of [SiO4]4−-[BO3]3− structures are generated in the system after B2O3 added, Si4+ ions mainly exist in the form of [SiO4]4- tetrahedrons and B3+ ions mainly exist in the form of [BO3]3− planar triangular structures and [BO4]5− tetrahedrons. With the increase of B2O3 content, the proportion of [BO3]3− planar triangular structures increase. In addition, the content of bridge oxygen in the microstructure of slag increases obviously, the content of non-bridge oxygen decreases, and the polymerization degree of the system increases somewhat. Through the analysis of microscopic mechanism and the modified NPL viscosity model, combined with experimental data, the truth that the slag viscosity decreases with the increase of B2O3 contents were known in the simulated concentration range.