Explore the vast range of titles available.

Calcium ferrite containing aluminum (CFA) is a precursor of the low-temperature bonding phase in the sintering process of iron ore fines for blast furnace ironmaking. Thus, improving the formation of CFA at lower temperature is very important for saving energy, improving efficiency and production. In this paper, the formation process of CFA was investigated at 1200 °C by reactions of alumina (Al2O3), respectively with a mixture of calcium oxide (CaO) and hematite (Fe2O3) and monocalcium ferrite (CF) as a recognized initial product, as well as reaction of Al-containing hematite (Hss) with CF. The result confirmed that CF is an intermediate product formed easily in the sintering process, and it may react with excessive Fe2O3 to generate an alpha-calcium iron oxide (Ca2Fe15.50O25) as a new phase. It was found that CFA can be formed directly by reactions of CF with Hss and Ca2Fe15.50O25 with Al2O3, while the reaction of CF with Al2O3 is more helpful in generating Ca2Fe15.5O25 rather than CFA, simultaneously forming a calcium aluminum oxide (CaAl2O4, CA; CaAl4O7, CA2). It was revealed that the appearance of CA and CA2 is a main reason to hinder CFA formation in the sintering process of iron ore fines.

Al 2 O 3 and SiO 2 greatly influence the formation of complex calcium ferrite, which is the main bonding phase in high basicity sinters. The effects of Al 2 O 3 /SiO 2 ratios on the morphology of complex calcium ferrite were studied. The main mineral phases in the samples with different Al 2 O 3 /SiO 2 ratios were CaFe 2 O 4 with a solid solution of Si or Al atoms and the silico-ferrite of calcium and aluminum. The results showed that the morphology of the complex calcium ferrite changed from lumpy to plate-like and acicular with increases in the SiO 2 content and the Al 2 O 3 /SiO 2 ratio. When the content of SiO 2 was 4 wt.%, the main calcium ferrite morphology was acicular, and the number of macropores in the samples increased with the Al 2 O 3 /SiO 2 ratio increasing. The first-principles analysis of the calcium ferrite crystal structure showed that adding SiO 2 and Al 2 O 3 changed the growth mechanism of the CaFe 2 O 4 crystal, promoting the formation of platy and acicular complex calcium ferrite. The size of calcium ferrite was significantly smaller due to the increase in CaO–Fe 2 O 3 –SiO 2 –Al 2 O 3 viscosity with increasing the Al 2 O 3 /SiO 2 ratio.

Al2O3 is a gangue component in iron ores, significantly influencing the formation and crystallization of calcium ferrite in the sintering process. But the mechanism of the Al2O3 effect on the crystallization of calcium ferrite is rarely reported. In this work, a crystallization device was designed to investigate the crystallization behavior of calcium ferrite in Fe2O3-CaO-SiO2-Al2O3 melt under non-isothermal conditions. XRD, SEM-EDS, and optical microscopy were used to identify the crystalline phase and the microstructure of samples. The result shows that the crystal morphology of SFCA changed in the order of strip, column, and needle as the Al2O3 content increased. The crystallization sequence of samples containing Al2O3 was observed as Ca4Fe14O25 (C4F14) → Fe2O3 → Ca3.18Fe15.48Al1.34O36 (SFCA-I) → CaFe2O4 (CF) → Ca5Si2(Fe, Al)18O36 (SFCA) → γ-Ca2SiO4 (C2S). The generation pathway of SFCA-I was found to be C4F14 + Si4+ + Al3+ → SFCA-I. Increasing the cooling rate can promote the formation of C4F14, SFCA-I, Fe2O3 and the amorphous phase. However, it prevented the crystallization of CF and SFCA while inhibiting the transformation of β-C2S to γ-C2S. When the Al2O3 content reached or exceeded 2.5 mass pct, the viscosity of Fe2O3-CaO-SiO2-Al2O3 melt increased sharply, resulting in the decrease in the crystal size of calcium ferrite.

To enhance the slagging efficiency of the lime-based slag system during the pre-treatment stage of hot metal, a composite calcium ferrite flux based on aluminum industry solid waste was developed in this study. The melting characteristics of the flux and its application in the pre-treatment of hot metal were investigated. The results indicated that the main phases of the composite calcium ferrite were CaFe2O4, Ca2Fe2O5, and Ca2(Fe,Al)2O4. It exhibited high oxidation, high alkalinity, and a low melting point, thereby achieving excellent melting performance. Simulations of various dephosphorization fluxes in the pre-treatment of high-phosphorus hot metal, ordinary hot metal, and kilogram-scale dephosphorization experiment processes were conducted. Under the same experimental conditions, the composite calcium ferrite flux was able to achieve a dephosphorization rate of over 90% and a final phosphorus content of less than 0.02 wt% under high carbon content ([%C] = 3.2 wt%). In the application of hot metal pre-dephosphorization, this flux was able to achieve efficient melting and rapid slagging of lime at a lower temperature, and its slagging time was 50% faster than that of calcium ferrite flux. In addition, this flux enhanced the utilization efficiency of lime during the steelmaking process, effectively prevented the agglomeration of slag, and achieved efficient slag–metal separation. These characteristics were significantly better than the application effect of calcium ferrite flux. This flux has significant implications for the industrial application of deep dephosphorization in the pre-treatment stage of hot metal or the early stage of converter steelmaking.

Japan started the national project “COURSE 50” for CO 2 reduction in the 2000s. This project aimed to establish novel technologies to reduce CO 2 emissions with partially utilization of hydrogen in blast furnace-based ironmaking by 30% by around 2030 and use it for practical applications by 2050. The idea is that instead of coke, hydrogen is used as the reducing agent, leading to lower fossil fuel consumption in the process. It has been reported that the reduction behavior of hematite, magnetite, calcium ferrite, and slag in the sinter is different, and it is also considerably influenced by the sinter morphology. This study aimed to investigate the reduction behavior of sinters in hydrogen enriched blast furnace with different mineral morphologies in CO—CO 2 —H 2 mixed gas. As an experimental sample, two sinter samples with significantly different hematite and magnetite ratios were prepared to compare their reduction behaviors. The reduction of wustite to iron was carried out at 1000, 900, and 800°C in a CO—CO 2 —H 2 atmosphere for the mineral morphology-controlled sinter, and the following findings were obtained. The reduction rate of smaller amount of FeO led to faster increase of the reduction rate curve at the initial stage of reduction. Macro-observations of reduced samples showed that the reaction proceeded from the outer periphery of the sample toward the inside, and a reaction interface was observed where reduced iron and wustite coexisted. Micro-observations revealed three layers, namely, wustite single phase in the center zone of the sample, iron single phase in the outer periphery zone of the sample, and iron oxide-derived wustite FeO and iron, or calcium ferrite-derived wustite ‘FeO’ and iron in the reaction interface zone. A two-interface unreacted core model was successfully applied for the kinetic analysis of the reduction reaction, and obtained temperature dependent expressions of the chemical reaction coefficients from each mineral phases.

High-temperature X-ray diffraction measurements of calcium ferrite (CF)-type MgAl 2 O 4 were performed in a temperature range of 300–673 K at atmospheric pressure. From temperature dependence of the unit cell volume, thermal expansivity ( α ) was determined to be α ( T ) = (2.46 ± 0.13) × 10 –5  + (1.2 ± 0.3) × 10 –8   T in 1/K. Thermoelastic parameters of isothermal bulk modulus at zero pressure ( K T 0 ), its pressure derivative ( K T ′) and temperature derivative [(∂ K T 0 /∂ T ) P ] of MgAl 2 O 4 CF were optimized by iteration calculation combining the least squares fitting of a third-order Birch–Murnaghan equation of state to previous P – V – T data with α calculation using the Grüneisen relation equation, α  =  γ th C V /( K T 0 V ) where γ th and C V are thermal Grüneisen parameter and isochoric heat capacity, respectively. γ th was constrained by the α measured in this study. When pressure data were rescaled by Au equations of state which are different from that adopted in the previous study and temperature data were corrected using pressure dependence of electromotive force of a W–Re thermocouple, K T 0 , K T ′ and (∂ K T 0 /∂ T ) P were assessed to be 216(4) GPa, 3.9(3) and − 0.027(3) GPa/K, respectively. It was suggested that the optimized α was about 17% lower than that determined by the previous study at 2000 K.

SiO 2 is the main component of gangue in sinters and a crucial constituent in the formation of the SiO 2 –Fe 2 O 3 –CaO (SFC) system. The non-isothermal crystallization kinetics of the SFC system were investigated using differential scanning calorimetry. The crystallization process of SFC was studied under different cooling rates (5, 10, 15, and 20 K/min), and the crystalline phases and microstructures of the SFC crystals were verified through X-ray diffraction and scanning electron microscopy. The results indicate that when the SiO 2 content is 2 wt.%, increasing the cooling rate promotes the precipitation of CaFe 2 O 4 (CF) in the SFC system, thereby inhibiting the precipitation of Ca 2 Fe 2 O 5 (C 2 F). In contrast to the CaO–Fe 2 O 3 (C–F) system, the addition of SiO 2 does not alter the precipitation mechanisms of C 2 F and CF. By further adding SiO 2 , the precipitation of Ca 2 SiO 4 (C 2 S) significantly increases. Simultaneously, the CaO content in the liquid phase decreases. This leads to the crystallization process of the CF 4 S (4 wt.% SiO 2 ) system bypassing the precipitation of C 2 F and directly forming CF and CaFe 4 O 7 (CF 2 ). In the case of the CF 8 S (8 wt.% SiO 2 ) system, the crystallization process skips the precipitation of C 2 F and CF, directly yielding CF 2 . The crystallization process of both CF 2 S (2 wt.% SiO 2 ) and CF is similar, comprising two reaction stages. The Ozawa method was used to calculate the activation energy for the crystallization of C 2 F and CF as − 329 and − 419 kJ/mol, respectively. Analysis using the Malek method reveals model functions for both stages.

Calcium ferrite (CF) is recognized as a potential green and efficient functional material because of its advantages of magnetism, electrochemistry, catalysis, and biocompatibility in the fields of materials chemistry, environmental engineering, and biomedicine. Therefore, the obtained research results need to be systematically summarized, and new perspectives on CF and its composite materials need to be analyzed. Based on the presented studies of CF and its composite materials, the types and structures of the crystal are summarized. In addition, the current application technologies and theoretical mechanisms with various properties in different fields are elucidated. Moreover, the various preparation methods of CF and its composite materials are elaborated in detail. Most importantly, the advantages and disadvantages of the synthesis methods of CF and its composite materials are discussed, and the existing problems and emerging challenges in practical production are identified. Furthermore, the key future research directions of CF and its composite materials have been prospected from the potential application technologies to provide references for its synthesis and efficient utilization.

In this research, we used a fast and simple method for synthesis of calcium titanate (CaTiO 3 ) and calcium ferrite (CaFe 2 O 4 ) nanostructures: microwave assisted co-precipitation method. The effect of time, microwave radiation power and type of solvent on the morphology of magnetic nanoparticles was studied. Calcium ferrite/calcium titanate (CaFe 2 O 4 /CaTiO 3 ) nanocomposite was prepared by the same method. The morphology and particles size of samples were studied by scanning electron microscopy. The porous nanostructure of CaTiO 3 and CaFe 2 O 4 /CaTiO 3 were ideal for photocatalytic behavior. The crystallographic properties of products were analyzed using X-ray diffraction technique. The purity of the samples confirmed by Fourier transform infrared spectroscopy. The magnetic property of CaFe 2 O 4 and CaFe 2 O 4 /CaTiO 3 nanoparticles was determined by vibrating sample magnetometry. Both products had ferromagnetic properties with nanocomposite being a hard ferromagnetic sample. The photocatalytic behavior of CaTiO 3 and prepared nanocomposite was studied by measuring degradation efficiency of three different acidic dyes irradiated under UV–Visible light in different initial conditions. The results confirmed that both products have photocatalytic properties, but the CaFe 2 O 4 /CaTiO 3 has a higher photocatalytic activity due to coupling of two semiconductors, which can be employed for effective charge separation and increase of lifetime in the charge carriers.

During the iron ore sintering process, its SiO2 content considerably affects the sinter quality. In this study, the effect of SiO2 content on iron ore sintering indexes was studied, with mineral composition and microstructure analyses. It was shown that the strength and reducibility of sintering products improved when SiO2 content increased. The sinter yield and tumbler index increased from 69.57% and 58.67% to 74.02% and 62.32%, respectively, with SiO2 content increasing from 3.92% to 5.12%. Moreover, the reduction disintegration index (RDI+3.15) increased from 66.50% to 68.28%. There was a quadratic function relationship between SiO2 content (x) and RDI+3.15 (y): y = −0.4841x2 + 5.8932x + 50.8189. Maintaining the SiO2 content in the range of 4.52% to 5.12% would promote the formation of compound calcium ferrite (SFCA) and silicate as the main binding phase which determined the quality of sintering products.