CaO MgO Al2O3 Research Articles

Solubility of Gold in FeO–SiO2–CaO–Al2O3–MgO Slag for Smelting of Gold-Containing Secondary Resources

Solubility of Gold in FeO–SiO2–CaO–Al2O3–MgO Slag for Smelting of Gold-Containing Secondary Resources

Investigation of the Dissolution Behavior of AlN in CaO–Al2O3–MgO Refining Slag and CaO–Al2O3–F–Li2O–BaO Mold Flux

Low‐density steels have garnered widespread attention as novel lightweight materials. Owing to its high Mn and Al content, brittle AlN inclusions, detrimental to both steelmaking and steel properties, can precipitate directly from the molten steel. Employing slag absorption effectively removes these floating AlN inclusions from the molten steel. Herein, a series of analytical methods are utilized to investigate the dissolution behavior of AlN in CaO–Al2O3–MgO refining slag and CaO–Al2O3–F–Li2O–BaO mold flux. The results indicate that the initial dissolution temperatures of AlN in the slag and mold flux are 1361 and 1080 °C, respectively. The dissolution in the refining slag is attributed to the high‐temperature self‐decomposition of AlN, producing N2(g). In the mold flux, the dissolution reaction involves both the high‐temperature self‐decomposition of AlN and its reaction with Li2O in mold flux, generating N2(g) and Li(g). No reaction interface is observed at the AlN‐slag/mold flux boundary. As the dissolution mass of AlN in the slag/mold flux increases, the Al2O3 content in the slag/mold flux rises. The main phases in slag transition from Ca9(Al6O18) to Ca12Al14O33 and Ca3Al2O6. In the mold flux, the LiBaF3 phase disappears, and the 11CaO·7Al2O3·CaF2 phase, which can degrade the flux's physicochemical properties, becomes the dominant phase.

Viscosity of titanium slag in separating electric melting of a metallized mixture of perovskite and ilmenite concentrates

To assess the possibility of joint processing of ilmenite (FeTiO3) and perovskite (CaTiO3) concentrates using a duplex process involving solid-phase reduction of iron (metallization) and subsequent separating melting into pig iron and titanium slag, the properties of slag melts were studied. The crystallization beginning point (liquidus temperature) and the corresponding viscosity of titanium slag depend on its chemical composition. The increase in titanium oxides content results in increase of these properties, while the presence of iron and calcium oxides leads to their decrease. During the joint processing of ilmenite (IC) and perovskite (PC) concentrates, the CaO content in the slag can be adjusted by changing their PC/IC ratio, and the FeO fraction is determined by the degree of iron metallization during the preliminary reduction roasting of a concentrate mixture with a carbon reducing agent. To select the optimal PC/IC ratio the temperature dependences of the viscosity of model oxide melts of the TiO2–FeO–CaO–Al2O3–MgO system, similar in composition to the slags formed as a result of melting mixtures of perovskite and ilmenite concentrates within the range of PC/IC ratios equaling to 0.6÷1.4, and the metallization degree from 75 to 95% were determined. According to the results obtained, within the entire range of studied compositions and temperatures, the viscosity of slag melts does not exceed 0.8 Pa·s. That is to say, such slags will be sufficiently fluid at the tapping point if the melt temperature is higher than liquidus temperature — the crystallization beginning point. Increasing the PC/IC ratios when decreasing the metallization from 95 to 75%, results in a monotonous decrease in liquidus temperature and its corresponding viscosity from 1490 оC and 0.79 Pa·s up to 1270 оC and 0.17 Pa·s, respectively. It is recommended to use a charge containing equal mass fractions of concentrates (PC/IC equal to 1) at the consumption of carbon reducing agent based on metallization of 85% iron. In this case, slags with a relatively low iron oxide content (3.1%) will be fluid (0.38 Pa·s), and have liquidus temperature of 1400 оC which will allow carrying out top and bottom melt at operating temperatures of 1500–1550 оC.

Characterization and 3D Reconstruction of the Crushing Behavior of SiO2–CaO–Al2O3–MgO Complex Inclusions in Spring Steel with High Basicity Slag Treatment

This article mainly studies the element content, phase composition, and fragmentation mechanism of SiO2–CaO–Al2O3–MgO composite inclusions that cause fatigue fracture of spring steel. The study found that the SiO2–CaO–Al2O3–MgO composite inclusions in the wire rod are not a homogeneous phase. According to the electron microscopy energy spectrum analysis results, although the SiO2–CaO–Al2O3–MgO composite inclusion is in the low‐melting‐point area of the phase diagram according to the component content ratio. However, field‐emission transmission electron microscopy analysis reveals that this type of composite inclusions includes MgAl2O4, CaAl2Si2O8, CaSiO3, MgSiO3, and a small amount of CaS. The Zeiss Crossbeam 550 electron microscope is used to conduct a three‐dimensional reconstruction analysis of this type of composite inclusions, which once again verified that the composition of this type of inclusions includes calcium silicate, MgAl2O4, MgO, and other phases. It is also found that there is a certain gap between the inclusions and the matrix, and the gap between the inclusions with high‐melting‐points such as MgAl2O4 and MgO and the matrix is more obvious. During the rolling process of SiO2–CaO–Al2O3–MgO composite inclusions, due to differences in hardness and deformation rate between different phases, the rolling process is deformed and fragmented for extended periods.

Effect of MgO Content and CaO/Al2O3 Ratio of CaF2–CaO–Al2O3–MgO Slag on the Oxidation Behavior of Mg in Mg-Containing GH3128 Alloy

Effect of MgO Content and CaO/Al2O3 Ratio of CaF2–CaO–Al2O3–MgO Slag on the Oxidation Behavior of Mg in Mg-Containing GH3128 Alloy

Molten CMAS resistance strategy for PS-PVD TBCs based on laser textured and Al-modified bionic structure

Plasma spray-physical vapor deposition (PS-PVD) is a promising third-generation thermal barrier coatings (TBCs) technique. Feather-like columnar TBCs with excellent strain tolerance and low thermal conductivity can be achieved using PS-PVD. However, molten CMAS (CaO–MgO–Al2O3–SiO2) can penetrate coatings and accelerate PS-PVD TBCs failure due to the feather-like columnar structure. Hence, a strategy is proposed to alleviate molten CMAS corrosion. The super-hydrophobicity structure is fabricated via laser texturing on the surface of PS-PVD TBCs to repel molten CMAS wetting and spreading. Then, a thin layer of the Al-film is deposited on the laser-textured surface. Next, the Al-modified layer is in situ synthesized after vacuum heat treatment, preventing the infiltration of molten CMAS into the TBCs and reducing the coating damage. The results show that the contact angle of laser textured and Al-modified PS-PVD TBCs (LT-Al) at room temperature increased from 12.3° to 168.8°. The wetting and spreading behavior of molten CMAS of as-sprayed (AS), laser textured (LT), and LT-Al coatings is observed in situ at 1230 °C for 1800 s. The LT-Al coatings exhibited excellent CMAS corrosion resistance, attributed to the laser-textured micro-nano structures and Al-modified layer protection. The findings may be an effective approach for solving the disadvantage of PS-PVD feather-like columnar structure TBCs.

Phase equilibria in the low-TiO2 part of the CaO–MgO–SiO2–Al2O3–TiO2 system at a fixed MgO/CaO mass ratio of 0.2 and Al2O3/SiO2 mass ratio of 0.4

Adding titanium oxide has become a common practice in modern blast furnace operating procedures. The blast furnace slag is based on the CaO–MgO–Al2O3–SiO2–TiO2 low titanium slag system rather than CaO–MgO–Al2O3–SiO2 system. Phase equilibria in the CaO–SiO2–Al2O3–MgO–TiO2 system in the low-TiO2 part have been experimentally determined by means of high temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Introducing a small quantity of titanium-bearing materials can lower the liquidus temperature. The TiO2 content in the slag should be controlled below 4.6 wt%, otherwise it will enter the perovskite phase region where the liquidus temperatures increases rapidly. The compositions of the solid solutions corresponding to the liquidus have been precisely measured and should be utilized for developing the thermodynamic database.

Effect of B2O3 on the viscosity, structure and crystalline phase of CaO–MgO–Al2O3–SiO2–MnO-based high alumina slags

The effects of B2O3 on viscosities, structures and phase transitions of CaO–MgO–Al2O3–SiO2–MnO-(0-8.0 wt%)B2O3 slags were investigated in this work. From the viscosity experimental results, the slag viscosities declined and the Eη decreased from 205.19 to 175.95 kJ/mol with the addition of B2O3 in slags from 0 to 8.0 wt%. From the structure analysis by using FTIR and XPS, B2O3 entered into the silicate network to increase the slag polymerization degree, while the formation of simple two-dimensional BO3 trihedral units could significantly decline the symmetry and stability of the structure. The effects of decreasing the network stability and forming low-melting eutectics were more dominated than the effects of increasing the structure polymerization degree, which could reduce the slag viscosity. Furthermore, adding B2O3 could decrease the slag initial precipitation temperature and change the primary crystal phase of the slag from melilite to spinel. The comprehensive effects of reducing the slag structure stability and decreasing the influence of solid phase on viscosity eventually resulted in the improvement of the slag fluidity.

Effect of MgO content and CaO/Al2O3 ratio on melting temperature and viscosity of CaF2–CaO–Al2O3–MgO slag for electroslag remelting

During electroslag remelting (ESR), high MgO contents are typically added to CaF2–CaO–Al2O3 slag to control magnesium content in iron- and nickel-based alloys. The melting temperature and viscosity of ESR slag are pivotal for energy consumption, production efficiency, smooth operation, and ingot quality. However, there is currently a notable scarcity of research on the melting temperature and viscosity of CaF2–CaO–Al2O3–MgO slag with high MgO levels. Thus, the melting temperatures and viscosity of CaF2–CaO–Al2O3–MgO slags with varying MgO contents and CaO/Al2O3 (C/A) ratios were investigated. The results show that as the MgO content increases from 7.83 % to 13.18 %, the final precipitation content of the MgO phase significantly increases, resulting in an increase in the melting temperature from 1306 °C to 1319 °C. With the increase in the C/A ratio from 0.86 to 1.16, the precipitation completion temperatures of the Ca12Al14F2O32 and MgO phases significantly decrease and the MgAl2O4 phase transforms into the CaO phase. Hence, the melting temperature decreases from 1329 °C to 1314 °C. Further increasing the C/A ratio to 1.40, the final precipitation content of the CaO phase increases, resulting in a decrease in the melting temperature from 1314 °C to 1282 °C. Moreover, as the MgO content and C/A ratio increase, the slag viscosity exhibits different change trends within various temperature ranges. This depends on which of the depolymerization of the slag structure and the precipitation and clustering of the MgO phase has a greater effect on the slag viscosity.

Thermodynamics of Palladium Dissolution Behavior in FetO–SiO2–CaO–Al2O3–MgO Slag at 1873 K

Thermodynamics of Palladium Dissolution Behavior in FetO–SiO2–CaO–Al2O3–MgO Slag at 1873 K

Structural Interaction between BaO and Al2O3 in Aluminosilicate Slags

The effect of BaO and Al2O3 on the viscosity of SiO2–CaO–MgO–Al2O3–BaO slag from 1673 to 1873 K is studied by the rotating cylinder method. The structure of slag is examined by Raman spectroscopy and molecular dynamics simulation. In this study of viscosity, Al2O3 shows amphoteric oxide characteristics and BaO shows characteristics different from the basic oxide. The viscosity increases as the BaO increases from 2 to 4 wt% in the slag with CaO/SiO2 = 1.07. However, the viscosity decreases when the BaO content increases from 6 to 8 wt%. From molecular dynamics simulations and Raman analysis, the increase in BaO content leads to a greater aggregation of Al around Ba atoms and increases the number of Al–O bonds. This indicates that higher BaO content promotes the polymerization of the [AlO4] tetrahedral structure. Furthermore, a good quantitative relationship between viscosity and the ratio of Q3/Q2 of the Raman spectrum of the slag is observed.

CaO–MgO–Al2O3–SiO2 corrosion resistance of multi-rare-earth-oxide-doped zirconia thermal barrier coating

As a thermal barrier coating (TBC) material, 8 wt% yttria-stabilized zirconia (8YSZ) exhibits poor resistance against calcium–magnesium–aluminosilicate (CMAS) corrosion. This is caused by the penetration of molten CMAS glass and the depletion of Y3+, which limits the lifetime of 8YSZ. In this study, a multi-rare-earth-oxide-doped zirconia (15 wt% (Lu0.2Yb0.2Dy0.2Gd0.2Y0.2)–ZrO2, denoted as 15LYDGY–SZ) ceramic was prepared to examine its interaction with CMAS. The sluggish diffusion effect and the competition between various dopant elements toward reaction with CMAS effectively slow down the atomic diffusion and limit the transformation of tetragonal phase into monoclinic phase in 15LYDGY–SZ ceramic. Compared with the currently used 8YSZ ceramic, the corrosion resistance of 15LYDGY–SZ to CMAS and its retention rate of fracture toughness after CMAS corrosion are improved. The results show that the multi-rare-earth-oxide-doped zirconia ceramic prepared in this study is a promising candidate material for the development of future TBCs.

Bioinspired directional structures for inhibiting wetting on super-melt-philic surfaces above 1200 °C

Over the past two decades, superhydrophobic surfaces that are easily created have aroused considerable attention for their superior performances in various applications at room temperature. Nowadays, there is a growing demand in special fields for the development of surfaces that can resist wetting by high-temperature molten droplets (>1200 °C) using facile design and fabrication strategies. Herein, bioinspired directional structures (BDSs) were prepared on Y2O3-stabilized ZrO2 (YSZ) surfaces using femtosecond laser ablation. Benefiting from the anisotropic energy barriers, the BDSs featured with no additional modifiers showed a remarkable increase from 9.2° to 60° in the contact angle of CaO–MgO–Al2O3–SiO2 (CMAS) melt and a 70.1% reduction in the spreading area of CMAS at 1250 °C, compared with polished super-CMAS-melt-philic YSZ surfaces. Moreover, the BDSs demonstrated exceptional wetting inhibition even at 1 400 °C, with an increase from 3.3° to 31.3° in contact angle and a 67.9% decrease in spreading area. This work provides valuable insight and a facile preparation strategy for effectively inhibiting the wetting of molten droplets on super-melt-philic surfaces at extremely high temperatures.

The structure of CaO–MgO–Al2O3–SiO2 melts and glasses doped with FeOX–NiO

AbstractNeutron and x‐ray diffraction measurements have been performed on CaO–MgO–Al2O3–SiO2 (CMAS) glasses doped with NiO–FeXO at room temperature, along with x‐ray measurements on aerodynamically levitated liquids at ≥2000 K. The disordered structures have been modeled using empirical potential structure refinement to investigate the relation between the aluminosilicate network and the modifying cations. The SiO4 and AlO4 tetrahedra are found to have wider Si–O and Al–O bond distance distributions in the glass, and the first Ca–On coordination shell is highly distorted, redistributing different populations of long and short bonds between the liquid and the glass. The addition of Fe and Ni at low aluminosilicate content increases the number of free oxygens not bonded to AlO4 or SiO4. Mg–O and Fe–O are both found to be predominantly fourfold and fivefold in the liquid and glassy states. Despite these low coordination numbers, their bond angle distributions indicate that they are predominantly in nontetrahedral‐type geometries, with ferrous and ferric iron possessing similar coordination environments. The Ca–O and Mg–O average coordination numbers and enthalpies of solution are consistent with their higher reactivity within relatively acidic aluminosilicate melts.

Effects of CaO/SiO2 ratio and CaCl2 content on the densification, microstructure, and properties of sintered CaO–MgO–Al2O3–SiO2–CaCl2 glass-ceramic

The effects of CaO/SiO2 ratio (basicity) and CaCl2 addition amount on the properties of CaO–MgO–Al2O3–SiO2–CaCl2 glass-ceramics (GC) were investigated. When sintered at 825 °C, the increase in basicity from 0.35 to 0.75 reduced the porosity of GCs from 1.1 to 0.8 vol%, but the increase of CaCl2 addition amount from 5 to 10 wt% increased the porosity from 0.8 to 7.0 vol%. The main crystalline phase of GC changed from augite (Ca(Mg0·7Al0.3) (Si1·7Al0.3)O6) to Ca10Al12Cl2Si5O37 by increasing the CaCl2 addition amount to 7.5 wt%. The increase in CaCl2 addition had adverse effects on the bending strength and Vickers hardness, while the rise in basicity deteriorated the bending strength but had little impact on the Vickers hardness. This study may have a guiding significance for preparing slag-based GCs and treating CaCl2-containing wastes.

Epitaxial growth of gehlenite in CaO–MgO–Al2O3–SiO2 based glass ceramic induced by Nb2O5 addition

In this study, the crystallization behavior of a CaO–MgO–Al2O3–SiO2 based glass ceramics with Nb2O5 addition was investigated by using DSC, XRD and TEM techniques. It was found that three crystalline phases, namely, CaNb2O6, diopside and Gehlenite (Ca2Al2SiO7), were formed from the glass matrix during the crystallization heat treatment. The CaNb2O6 phase was the first to precipitate from the glass matrix at around 850 °C, acting as a nucleating agent that facilitated the formation of Gehlenite (Ca2Al2SiO7) at 900–950 °C. The TEM observation revealed a consistent orientation relationship between the CaNb2O6 and the Gehlenite (Ca2Al2SiO7) phases, indicating that CaNb2O6 could induce the epitaxial growth of Gehlenite (Ca2Al2SiO7). This result provides a new insight into the preparation of Gehlenite epitaxial films and glass ceramics.

Effect of Calcium Content on Characteristics of Inclusions in an Al‐Killed Steel

Laboratory experiments are performed to study the effect of T.Ca content in the molten steel on the composition, size, and quantity of inclusions. Different amounts of SiCa alloys are added into the molten steel to obtain samples with varied T.Ca contents. Samples are taken at 1, 5, 10, 15, and 20 min after the calcium addition to study the transformation of inclusions with time. After the addition of calcium into the molten steel, the size of pure liquid inclusions is small which are more difficult to be removed from the molten steel than solid ones, while partially liquid inclusions are easily removed from the molten steel so that the total oxygen content of the molten steel is lower. The size of solid inclusions is large due to their large coagulation coefficient value. The number density and area fraction of liquid inclusions are larger than solid inclusions due to the higher adhesion work required for the removal of liquid inclusions. The corrosion of MgO crucible easily occurs by the dissolved calcium in the molten steel. Then, the reaction between the reduced magnesium and inclusions in the molten can occur, leading to the generation of MgO–Al2O3 and CaO–MgO–Al2O3 inclusions.

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.

Effect of ladle-lining materials on inclusion evolution in Al-killed steel during LF refining

Abstract The effect of lining materials (Al2O3 and Al2O3–MgO·Al2O3) of ladle on evolution of non-metallic inclusions in aluminum-killed (Al-killed) steel during ladle furnace refining without Ca treatment was investigated through industrial experiments. The results showed that non-metallic inclusions experienced the changes from Al2O3 → MgO–Al2O3 → CaO–Al2O3. During the refining process using either of the two ladle lining materials, for all non-metallic inclusions, the vast majority are distributed in the high Al2O3 area of the CaO–Al2O3–MgO phase diagram, with very little or none in the low melting point zone. Non-metallic inclusions are mainly smaller than 3 μm, while those larger than 3 μm consisted primarily of MgO·Al2O3 and CaO–Al2O3 inclusions. The use of an Al2O3–MgO·Al2O3-lining ladle is more effective in reducing the number density of inclusions in the steel. However, during the refining process, the Al2O3-lining ladle does not have a significant impact on the presence of MgO–Al2O3 and CaO–Al2O3 inclusions in the molten steel. The Al2O3–MgO·Al2O3-lining ladle does not have a significant effect on MgO–Al2O3 inclusions, but it does promote the formation of CaO–Al2O3 and CaS inclusions in the molten steel.

The Effect of Ca Pretreatment on the Characteristics of Rare‐Earth Nonmetallic Inclusions in Super‐Duplex Stainless Steel

Rare‐earth treatment enhances steel properties. Nevertheless, this beneficial effect can be counterbalanced by the formation of large‐sized rare‐earth inclusions. To refine and spheroidize these inclusions, Ca pretreatment is employed between Al deoxidation and Ce treatment stages for super‐duplex stainless steel 2507 at 1580 °C, using a vertical tube furnace. A systematic analysis is performed to compare the characteristics of nonmetallic inclusions between the Ca‐untreated and Ca‐treated tests. Prior to Ce addition, Ca pretreatment transforms irregular and clustered MgO–Al2O3 spinel inclusions into spherical CaO–MgO–Al2O3 inclusions. Additionally, Ca pretreatment significantly reduces mean diameter of the inclusions from 2.36 ± 0.54 to 1.27 ± 0.47 μm. After Ce addition, rare‐earth inclusions appear near‐spherical with few clustered inclusions in Ca pretreatment case. Conversely, the absence of Ca treatment results in numerous clustered inclusions, thereby yielding significantly larger rare‐earth inclusions, measuring 2.75 ± 1.66 μm compared to 1.99 ± 1.09 μm. CaO component in CaO–MgO–Al2O3 inclusions is largely reduced by Ce. Consequently, Ca pretreatment only yields slight alterations in chemical composition of rare‐earth inclusions. Ce in situ reduces parent inclusions, initiating from the periphery and progressing toward the center. Therefore, the size and morphology of final rare‐earth inclusions are largely inherited from parent inclusions.