CaO MgO Al2O3 SiO2 Research Articles

A thermodynamic model for predicting activity of CaO–SiO2–Al2O3–MgO–TiO2–V2O3–FeO slags during electric furnace smelting process

A thermodynamic model for predicting activity of CaO–SiO2–Al2O3–MgO–TiO2–V2O3–FeO slags during electric furnace smelting process

Mechanical and thermal properties for corrosion products of lutetium silicates against CMAS

AbstractRare earth silicates are promising environmental/thermal barrier coating (E/TBC) materials facing severe CMAS (CaO‐MgO‐Al2O3‐SiO2) corrosion. Previous studies mainly focused on the intrinsic properties of precorrosion coatings, but there were few studies on their CMAS corrosion products that play a crucial role in the performance of coatings in postservice stage. In this work, the mechanical and thermal properties of nine corrosion products between lutetium silicates and CMAS are studied using first‐principles calculations. Their differences of elastic stiffness are attributed to the different crystal structures and bonding strength. The T:O ratio is identified as a factor of the crystal structure for silicate products, and it has a good correlation with their elastic stiffness. Moreover, the divergences of thermal conductivity are dominated by three essential factors, that is, atomic vibration intensity, lattice vibrational anharmonicity, and complexity of crystal structure. Compared with rare earth silicates, six products, that is, the α‐CaSiO3, β‐CaSiO3, Ca2MgSi2O7, Ca2Al2SiO7, CaAl2Si2O8, and Ca2Lu8(SiO4)6O2, showing good damage tolerance and low thermal conductivities, are predicted to be advantageous to E/TBCs. These discoveries reveal the mechanical/thermal properties of corrosion products between lutetium silicates and CMAS and are expected to support the future researches on the performance of E/TBC in the postservice stage.

Holistic comparison of environmental barrier coating material candidates through design of a figure of merit

AbstractThe first figure of merit for environmental barrier coating (EBC) materials was designed through a ranking system for material properties pertaining to established EBC failure modes in service. Seven past, present, and novel EBC candidate materials were used in the figure of merit design: SiO2, Ba0.75Sr0.25Al2Si2O8 (BSAS), HfSiO4, Yb2Si2O7, Yb2SiO5, Yb2O3, and YbPO4. Utilizing compiled data from the literature, the presented figure of merit verified Yb2Si2O7 as the state‐of‐the‐art candidate with optimal EBC properties and inferred that YbPO4 should be considered as a potentially viable EBC material candidate. The figure of merit allows for a holistic comparison of EBC candidates and informs experimental and computational search efforts for next‐generation complex EBCs. Clear knowledge gaps found through this work include CaO–MgO–Al2O3–SiO2 (CMAS)‐resistant coatings, EBC lifetimes before delamination, and oxidant diffusion rates in relevant EBC microstructures. It was shown that while some materials show promise for solving a single key failure mode for EBCs (i.e., CMAS reactivity), a community‐wide goal should be placed on materials development to achieve acceptable resistance against all major failure modes, which are interconnected. Novel compositionally complex EBC materials, in addition to layered EBC architectures, show promise for the optimization of material properties for long‐lifetime EBCs in combustion environments.

Study on the Causes and Control Measures of Mg–Al Spinel Inclusions in U75V Heavy Rail Steel

U75V heavy rail steel production uses an aluminum-free deoxidation process; however, large particles of MgO–Al2O3 inclusions form in the steel, which has a great impact on product quality. In this paper, we try to explain how spinel inclusions, which affect the metallurgical quality of heavy rail steel, are produced by thermodynamic and experimental methods, and then determined measures for avoiding such inclusions. The formation mechanism of spinel inclusions in U75V heavy rail steel was determined through the analysis of nozzle clogging in the pouring process and typical inclusions in steel. The results show that there are two types of spinel inclusions in heavy rail steel: one is pure Mg–Al spinel inclusions and the other is Mg–Al spinel inclusions coated with calcium aluminate. The small, pure Mg–Al spinel inclusions were precipitated during the solidification of the molten steel, and the precipitation temperature was related to the composition of the molten steel. The large spinel inclusions were derived from clogging of the submersed nozzle. Mg–Al spinel inclusions coated with calcium aluminate were transformed from CaO–SiO2–Al2O3–MgO complex inclusions in the steel during cooling, and the formation temperature was related to the content of Al2O3 and MgO in the inclusions. The content of Al2O3 and MgO in the inclusions was the key to the formation of the Mg–Al spinel inclusions. Therefore, in order to control the production of spinel inclusions in steel, it is necessary to strictly control the content of impurity elements such as magnesium and aluminum in the alloy auxiliary materials, to reduce the secondary oxidation of liquid steel and to reduce the erosion of refractory materials.

Relationship between viscosity, foaming, and structure of CaO–SiO2–Al2O3–MgO–FeO slag with the addition of SiO2 and Al2O3

Optimizing the foaming characteristics of slag in electric arc furnaces (EAF) presents a challenging task, affecting electrode heating efficiency and increasing smelting cost. This study explores the impact of adding silicon dioxide (15–35 wt%) and a small quantity of alumina (5–10 wt%) on the viscosity and foaming properties of CaO–SiO2–Al2O3–MgO–FeO slag. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to investigate structural changes in the slag melt. The findings reveal that higher levels of silica or a slight increase in alumina content enhance slag polymerization and foaming efficiency. Specifically, a 10 wt% alumina content, in contrast to 5 wt%, leads to high silica content, leading to faster polymerization but relatively lower viscosity. Structural analysis confirms that increasing alumina content, particularly when silica content is high, results in a less stable Al–O–Si structure, causing a shift from Q0 and Q1 units to Q2 and Q3 units, which ultimately reduces viscosity. When the alumina content remains at 5 wt% and silica content increases from 15 wt% to 35 wt%, foaming efficiency improves from 13.06 cm min to 94.97 cm min, a remarkable 627% rise. Moreover, when silica content is 30 wt% and alumina is slightly increased by 5 wt%, there is a notable enhancement in foaming efficiency, rising from 47.11 cm min to 89.16 cm min, while the effect on viscosity is not prominent.

The Effect of the Chemical Composition on Mechanical Properties of CMAS Diopside Glass Ceramics

Molecular dynamics simulations were performed on CaO-MgO-Al2O3-SiO2 (CMAS) diopside glass ceramics (GCs) to study the effect of nanocrystal on glass and the effect of chemical composition on mechanical properties. Under tensile loading, the GCs demonstrated that the strength lay between its glass and ceramic counterparts and maintained considerable ductility. Moreover, high Mg/Ca ion ratios are conductive to both the strength and ductility of GCs. In addition, Al ions should be avoided as far as possible since they would promote fracture. After analyzing the shear strain and displacement vector map for ion structures, we found that the presence of nanocrystal in glass changes the original deformation pattern and led to the deformation concentration surrounding the nanocrystal. A high Mg/Ca ion ratio would make the deformation more homogeneous, while a high Ca/Mg ion ratio would aggregate the deformation in the glass region near the nanocrystal. The existence of Al ions near the interface between glass and crystal would promote the formation of voids.

Preparation of innovative glass-ceramic materials based on mica schist within the CaO–MgO–Al2O3–SiO2 system

The preparation of affordable glass-ceramic materials by induced crystallization of glass-based mica schists and other natural raw materials (dolomite & limestone), as well as magnesite as a mine waste, was investigated for the first time. Five glass batches were designed based on the eutectic composition of the diopside-anorthite ratio with increasing the enstatite content from 0–40 wt.% within the quaternary CaO–MgO–Al2O3–SiO2 system. After melting at 1400 to 1500 °C, casting into discs & rod shapes, and annealing process, the prepared glasses were subjected to careful heat treatment schedules. Several techniques were used to characterize the applied raw materials, glass, and glass-ceramic materials such as X-ray Fluorescence (XRF), Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Polarizing-light Microscopy. The produced glass-ceramic from the glass batch with 30 wt% enstatite that was nucleated at 750 °C /2h followed by crystallization at 950 °C /h, displayed the well-developed product on the level of volume crystallization and pore formation.

Enhanced performance of low-pressure sintered CaO–MgO–Al2O3–SiO2–CaCl2 glass-ceramic by using Cr2O3 as the nucleating agent

The sintered glass-ceramic always has an uneven microstructure due to the surface crystallization, which limits the enhancement of its mechanical properties. In the present work, Cr2O3 was added into CaO–MgO–Al2O3–SiO2–CaCl2 glass as the nucleating agent, and the low-pressure (14 kPa) sintering technology was utilized to promote the densification process of the glass frits (0.42–2 mm). It was found that by adding 1 wt% of Cr2O3, the bulk crystallization can be achieved inside the glass particle and the microstructure of the glass-ceramic became more homogeneous. Correspondingly, the bending strength was improved from 127 to 147 MPa, and the Vickers hardness was enhanced from 6.5 to 6.7 GPa, comparing with the Cr2O3-free glass-ceramic. The current study confirmed the positive impact of nucleating agent in the performance of sintered glass-ceramic, which also provided a route for the utilizations of CaCl2-and Cr2O3-bearing wastes.

Phase Equilibria and Thermodynamic Modelling of the PbO-ZnO-FeO-FeO1.5-SiO2 system and its subsystems in equilibrium with air/metallic lead/iron

The phase equilibria of the ZnO-“FeO1..5”, ZnO-“FeO1.5”-SiO2, PbO–ZnO-“FeO1.5” and PbO–ZnO-“FeO1.5”-SiO2 slag systems in equilibrium with air or metallic lead/iron were studied as part of the investigation of the 19-component PbO–ZnO–Cu2O–FeO–Fe2O3–CaO–SiO2–Al2O3–MgO–S-(As, Sn, Sb, Bi, Ag, Au, Ni, Cr, Co as minor elements) slag/matte/metal/speiss/gas system, supporting the operation/development of existing and emerging pyrometallurgical processes. In the experimental part of the study, samples underwent high temperature equilibration followed by quenching, and the direct measurement of the lead, zinc, iron and silicon concentrations in the liquid slag, solid oxide, and metal phases by electron probe microanalysis (EPMA). The a) massicot (PbO), b) spinel ((Zn, Fe)Fe2O4), c) zincite ((Zn,Fe)O1+x, 2 polymorphs), d) lead ferrite (Pb2+xFe2O5+x), e) plumboferrite (Pb4Fe22-xZnxO37), f) magnetoplumbite (Pb(Fe2O3,PbFeO2,PbZnO2)Fe10O16), and g) W-ferrite (PbZn2-xFe16+xO27) primary phase fields of the PbO–ZnO-“FeO1.5” system in equilibrium with air were studied between 780 and 1300 °C. The ZnO-“FeO1.5”, ZnO-“FeO1.5”-SiO2 and PbO–ZnO-“FeO1.5”-SiO2 systems in equilibrium with air were studied up to 1745 °C, significantly improving the availability of information on the composition range of the high- and low-Fe zincite ((Zn,Fe)O1+x) phases, and on the liquid slag composition at the boundaries of their primary phase fields. Lastly, the solubilities of iron in larsenite (Pb(Zn,Fe)SiO4) and melilite (Pb2(Zn,Fe)Si2O7) in equilibrium with air or metal were studied between 700 and 800 °C. The newly obtained and existing experimental data were used to develop a self-consistent set of thermodynamic parameters describing all phases in the system using the FactSage computer package.

Dissolution mechanism and computational model for controlling dissolution rate of alumina particles in CaO–SiO2–Al2O3–MgO slag

In present study, a high-efficiency CaO–SiO2–Al2O3–MgO slag was designed to dissolve alumina particles, and the in situ observation for alumina particles dissolution by CSLM instrument equipped with color fast CCD camera was conducted, which broke through the limitations of the original CSLM equipment. The dynamic measurements showed that the dissolution behavior of alumina particles was controlled by diffusion. Moreover, the mechanism of dissolution of alumina particles was illustrated by combining SEM-EDS detection and thermodynamic calculations. It was found that there was an about 3 μm distinct interface layer when alumina particles were dissolved in slag, and the formation order of products of the interface layer was closely related to its thermodynamics. In addition, the apparent activation energy of reaction between Al2O3 and CaO was used to calculate the reaction time of alumina particles with different particle size, and the viscosity values of the all slags obtained by the Factsage 8.2 thermodynamic software and Stocks-Einstein theory were used to calculate the time required for diffusion of alumina particles with different particle sizes. Compared the total time of chemical reaction and the diffusion mass transfer, it is found that when the radius of alumina particles is greater than 2.5 μm, the dissolutions of alumina particles in all CaO–SiO2–Al2O3–MgO slag composition points are controlled by diffusion.

Effect of La2O3–CeO2 codoping on the microstructure and mechanical properties of tailing glass–ceramics

The effect of the La2O3–CeO2 content on the microstructure and mechanical properties of CaO–MgO–Al2O3–SiO2 tailing glass–ceramics codoped with La2O3 and CeO2 was investigated to gain insight into the properties of glass–ceramics produced from solid wastes. The results showed that augite was the dominant crystalline phase in all of the samples. Augite formed a solid solution phase containing La and Ce as the La2O3–CeO2 content increased, and the shape of the augite phases changed from dendritic to island-shaped because La oxyapatite precipitated at the augite boundary. Among the glass–ceramics, the highest percentage of Si–O tetrahedrons with two nonbridging oxygen atoms (Q2) was observed for that containing 1 wt% La2O3–CeO2. In addition, this particular composition exhibited an optimal microstructure owing to its high crystallinity and interlocking dendrites. Consequently, this microstructure displayed superior mechanical properties, such as Vickers hardness, bending strength, and fracture toughness of 7.95 GPa, 250.13 MPa, and 1.97 MPa/m1/2, respectively.

Phase composition and liquidus temperatures of the CaO–SiO2–MgO-13 wt%Al2O3–TiO2 system in reduction conditions

Effects of TiO2, binary basicity and MgO content on the liquidus temperatures of TiO2–CaO–SiO2–MgO–Al2O3 slags were experimentally studied in equilibrium with carbon. The experimental techniques include high temperature equilibration, quenching and Electron Probe X-ray Microanalysis (EPMA). It was found that the major primary phase in the composition range investigated is M3O5 (M = Ti, Mg, Al). The liquidus temperatures increase with increasing TiO2 and MgO contents, whereas decrease with increasing CaO/SiO2 mass ratio. The experimentally determined liquidus temperatures are much higher than the predicted ones by FactSage and the primary phases between the experiment results and predictions are also different. The mole fractions of Al2TiO5 and Ti3O5 in the M3O5 phase decrease, but MgTi2O5 increases with increasing MgO content and CaO/SiO2 in the samples. Moreover, the proportions of Al2TiO5 and MgTi2O5 in the M3O5 phase decrease, while Ti3O5 proportion in the M3O5 phase increases with increasing the reaction time. The mole ratio of Ti3+/Ti4+ in the M3O5 phase decreases with MgO content and CaO/SiO2 mass ratio in the samples but increases with increasing reaction time.

Interaction laws of RE2O3 and CMAS and rare earth selection criterions for RE-containing thermal barrier coatings against CMAS attack

Thermal barrier coatings (TBCs) with higher rare earth (RE) contents are more resistant to CaO-MgO-Al2O3-SiO2 (CMAS) attack due to their reaction to form apatite protective products. In this study, the reaction behavior between RE2O3 and CMAS was investigated and their interaction laws were clarified, based on which three criterions for selecting RE dopants for RE-containing TBC materials are proposed: 1) favorable reaction product types and strong protective products formation kinetics, 2) low RE3+ solubility in molten CMAS, and 3) low wettability of residual mixture. Sm2O3 and Gd2O3 are demonstrated as the most attractive dopants for RE-containing TBCs against CMAS attack.

Alkali-based components as slag fluidizers in steelmaking processes: A thermodynamic assessment

Defining the optimized volume of dual saturated (CaO and MgO) slags is of utmost importance to secondary metallurgy, especially for the ladle furnace. To be effective, these slags may present high desulphurization capability, combining the ability to shield the electric arc flare, to avoid the skull formation in the ladle borders and bottom, and suitable viscosity to provide fast incorporation of additives and tapping. Some fluidizers are applied for attaining the purpose of taking CaO/MgO into solution, being fluorspar (calcium fluoride, CaF2) and silica sand (silicon oxide, SiO2) broadly used in Si-killed steelmaking plants. At the Al-killed plants, either bauxite (mainly aluminum hydroxide) or calcium-aluminates are recommended choices. Nevertheless, for various reasons, some steelmakers use alternative fluidizers containing a significant amount of Na2O and K2O, such as sodalite and nepheline. Based on thermodynamic calculations (CALPHAD method), the effects of such alkalis on the CaO/MgO solubility and the optical basicity of slags on the CaO–SiO2–MgO–Al2O3 system were explored in this paper. Moreover, the potential impact on the performance of MgO-based refractories in contact with these alkali-containing slags was also assessed by a thermodynamic approach. Although kinetic aspects must also be considered, it was seen that (Na2O)2·(K2O) additions into these systems must be carefully managed to make the most of their ability to improve desulphurization, while avoiding the earlier corrosion of the refractory lining.

Effects of surface roughness on CMAS wetting and corrosion behaviour of rare earth modified zirconia coatings

CaO–MgO–Al2O3–SiO2 (CMAS) poses a severe challenge to the thermal barrier coatings (TBCs) of aviation engines and has attracted much attention. In this study, nanostructured yttria-stabilized zirconia (NYSZ) and multi-component rare-earth oxides modified zirconia (MSZ) coatings were prepared using atmospheric plasma spraying (APS). The effects of different surface roughness on CMAS wetting and corrosion behaviour of the two types of coatings were investigated by adjusting the surface roughness and conducting CMAS corrosion experiments at 1250 °C. Results revealed that the contact angles between CMAS and the coatings increase with decreasing surface roughness, highlighting the important role of reducing the coating roughness for higher CMAS wettability resistance and corrosion resistance. In addition, MSZ coatings exhibit superior CMAS wettability resistance and corrosion resistance relative to NYSZ coatings due to the smaller specific surface area. These findings provide valuable design guidance for the optimization of the microstructure and composition of TBCs to enhance CMAS corrosion resistance.

Effect of CMAS penetration behavior on stress evolution in TBCs under three-dimensional temperature gradients

CaO–MgO–Al2O3–SiO2 (CMAS) penetration is the primary failure mode of thermal barrier coating (TBC) film cooling systems, and therefore, understanding the CMAS penetration behavior and its effect on the internal stress evolution of TBCs is necessary. In this study, the effect of nonuniform CMAS penetration on the stress profile of a top ceramic (TC) coating layer was investigated under a nonuniform temperature field with three different mainstream temperatures (1561, 1623, and 1673 K). Further, a conjugate heat transfer numerical model was established to determine the temperature distribution in the TBCs with a gas-film cooling system. A phase-field model was adopted to study the CMAS penetration behavior. Moreover, the effects of CMAS penetration on the temperature distribution, growth rate of the thermal growth oxide (TGO), and residual stress are discussed. The CMAS penetration continuously eroded the TC layer, following the temperature distribution trend. CMAS penetration achieved temperature increments of 26.1, 35.1, and 40.3 K at the TC/TGO interface and TGO thickness differences up to 0.12, 0.26, and 0.37 μm after 500 h oxidation at the three mainstream temperatures. A significant increase in the residual stresses of the TBCs caused by CMAS penetration was observed. The von Mises stress increased from 243.7, 295.7, and 339.9 MPa to 367.0, 391.5, and 414.9 MPa, respectively. Driving forces for Mode I and Mode II interfacial cracks at the trailing edge of the cooling hole increased with CMAS penetration, and the increase in the mainstream temperature enhanced the driving forces.

Thermodynamic evaluation of viscosity behavior for CaO–SiO2–Al2O3–MgO slag systems examined at the temperatures range from 1500 to 1700 °C

This work showed an application of computational tools to understand systematically the behavior of viscosity on CSAM systems relevant to industrial uses. Consequently in this study, the viscosity experimental data obtained from the literature were compared with the thermodynamic calculated results via the software FactSage v.7.3 for melts in CaO–SiO2–Al2O3–MgO slag system with the range of compositions slags cover 0–100 wt% CaO, 0–100 wt% SiO2, 0–100 wt% Al2O3 and 0–15 wt% MgO at temperature ranges of 1500–1700 °C. Using open-source software in Python, the results of viscosity, liquid, and solid fraction of the slag, as a function of composition and temperature, are represented by multiple color maps and by iso-viscosity contours. The results of the viscosity values indicated that the effect of all the oxides in the CSAM slag system follows the well-known behavior trend observed in the literature. Viscosities of the slag were found to increase with increasing SiO2 contents and decrease with increasing basicities (high CaO). The increase in Al2O3 content increases the viscosity values. An increase of 0–15% MgO depolymerized the slag melt and decreases the viscosity. However, above 5% MgO content occur a decrease in the liquid zone (single phase) and a liquid fraction (two-phase region) of the slag. For a constant MgO concentration, the increase in temperature generates an expansion of low-viscosity zones associated with an increase in the liquid phase of the slag. From the comparison between the calculated and experimental viscosities data keeps up within 30% average relative deviation (Δ), the predictions are considered acceptable for viscosity in the CSAM slag system at high temperatures.

CMAS Corrosion Behavior of Nanostructured YSZ and Gd-Yb-Y-Stabilized Zirconia Coatings

With the development of industry, the operating temperature of aero engines and gas turbines continues to increase; developing thermal barrier coatings (TBCs) with superior resistance to CaO-MgO-Al2O3-SiO2 (CMAS) corrosion has become a prominent research focus. In this study, atmospheric plasma spraying (APS) was used to prepare yttria-stabilized zirconia (YSZ), nanostructured yttria-stabilized zirconia (n-YSZ), and Gd-Yb-Y-stabilized zirconia (GYYSZ) coatings. The effects of CMAS exposure on the microstructure, chemical composition, phase transition, and microhardness of the coatings were investigated. Comparative analysis revealed that both phase transition and exfoliation occurred in corroded YSZ and n-YSZ coatings, with n-YSZ exhibiting more pronounced changes. In contrast, GYYSZ coatings remained stable without phase transition and exhibited a smaller increase in microhardness (270 HV0.3). Consequently, doping Gd/Yb/Y elements into ZrO2 can improve the performance of TBCs.

Strain tolerance evolution of EB-PVD TBCs after thermal exposure or CMAS attack

The microstructural evolution and Young’s modulus evolution of EB-PVD TBCs upon thermal exposure and separately after CaO-MgO-Al2O3-SiO2 (CMAS) attack have been compared and investigated. Moduli measured by four methods all show an increase due to sintering whereas their rates of increase are different. On finer scale (i.e. nano indentation), modulus increases from 87.3 GPa in as-deposited coatings to 198 GPa after sintering at 1400 °C for 100 h. While on global scale, the modulus increases from below 10 GPa to153 GPa after identical exposure. For the CMAS attacked TBCs at 1300 °C for 0.5 h, modulus values acquired by different methods are much closer. The effect of sintering and CMAS infiltration on coating’s structural integrity is discussed in terms of elastic strain energy available for driving edge delamination. The energy release rate of CMAS attacked TBCs at 1300 °C for 0.5 h is ∼1200 J/m2, which is equivalent to that of TBCs exposed at 1400 °C for 250 h (no CMAS).

Experimental study on flow properties of blast furnace slag with different alumina contents based on the image measurement method

This paper established a novel visualization method for measuring blast furnace slag(BFS) flow properties and investigated the effect of alumina content on the CaO–SiO2–Al2O3–MgO BFS system. The outcomes indicate that elevating Al2O3 concentration in the BFS mixture from 14% to 26% results in a rise of critical flow temperature Tc from 1332.5 °C to 1384.1 °C, leading to a deterioration of BFS flow properties. However, the critical flow velocity Vc of BFS rises from 1.82 mm/min to 2.91 mm/min, representing a 60% increment. BFS with high Al2O3 content was found to be more likely to form high melting point crystals, such as gehlenite, with better crystallization, which is one of the main reasons for the deterioration of BFS flow properties. Fourier Transform Infrared Spectrometer (FTIR) and Raman spectra analysis indicate that the proportional content of simple silicate structures denoted as QSi0([SiO4]4−),QSi1([Si2O7]6−) decreased with increasing Al2O3 content, while those of complex silicate structures, QSi2([Si3O10]8−),QSi3([Si3O9]6−) increased. Furthermore, the Si–O–Al structural unit concentration progressively increased, indicating that the escalation in bridging oxygen within the BFS system raised the polymerization degree of the BFS, leading to a more complex aluminosilicate structure. Notably, the [AlO4]5- tetrahedra content within the BFS has reached saturation at roughly 21%. Further increases in Al2O3 content induced an excess of [AlO6]9−octahedra formation, which generally acts as a network modifier to lower the polymerization degree of the BFS system. However, this effect was not noticeable in this study, which may be attributable to the low basicity (CaO/SiO2 = 0.99) and MgO content (MgO/Al2O3 = 0.21–0.34) of the BFS samples in this study.