CaF2 Content Research Articles

Industrial Ladle Furnace Slag Composition Analysis with Optical Emissions from the Arc

With the strict standards for steel quality and high production rates, the demand for faster and more convenient slag composition analysis for both electric arc and ladle furnaces has become a major issue in industrial steel plants. To overcome the time-delay between slag sampling and results of the slag composition analysis, an on-line slag composition analysis is required. Such a method that can be used in on-line analysis and is also chemically sensitive to the slag composition is optical emission spectroscopy. In this work, the optical emissions from the arc have been measured in an industrial ladle furnace and used for slag composition analysis. This article focuses on CaF2 and MgO, since the CaF2 is a common additive material in the ladle treatment and high MgO content means that the ladle refractory lining is dissolving into the slag. The analysis has been carried out by comparing emission line ratios to the XRF analyzed ratios of CaF2/MgO and MnO/MgO, respectively. The results show that several atomic emissions lines of calcium, magnesium, and manganese can be used to evaluate the CaF2/MgO and MnO/MgO ratios in the slag. It was found out that the plasma temperature derived from Ca I emission lines has a non-linear relation with the CaF2 content of the slag. Additionally, the dissociation pathways of molecular slag components were determined and studied in different plasma temperatures with equilibrium composition computation in order to determine the relations between the slag and plasma compositions.

The Role of Gangue Mineralogy on Flowsheet Development in Fluorite Processing

Fluorite, CaF2, is considered a strategically important mineral as it is a raw material for many strategic industries. Froth flotation is reported to be the most efficient and economically viable process for the production of an acid-grade product with a CaF2 content of at least 97%. Selective flotation of fluorite from gangue minerals, e.g., calcite and barite, is challenging because these minerals have similar physicochemical properties. This study employed batch flotation tests coupled with mineralogical analysis to design suitable customised flowsheets and efficiently optimised reagent regimes for optimum production of acid-grade fluorite concentrate from two different fluorite ores by the froth flotation process. The effect of pulp temperature on fluorite flotation was investigated in this study with the objective of lowering pulp temperatures in fluorite flotation. The results showed that an acid-grade CaF2 concentrate could be obtained from the flotation of both ores at ambient pulp temperatures. This eliminates the requirement for high-temperature pulp treatment, which would result in a significant reduction in thermal energy costs. This study showed that an understanding of gangue mineralogy is key to process optimisation for acid-grade CaF2 production. Although an acid-grade CaF2 concentrate could be produced from both ores, the flowsheets and reagent regimes were markedly different. For instance, the production of an acid-grade CaF2 product from a high quartz and calcite ore was achieved by employing a simple rougher–multiple cleaner flotation circuit using tannin and sodium silicate as calcite and quartz depressants, respectively. On the other hand, the production of an acid-grade CaF2 product from the flotation of the pyritic ore required a pre-sulphide flotation stage for upfront sulphur removal and the use of a sulphide depressant. Multiple stages of cleaning were required for improved selectivity in the flotation of both ores.

Synthesis of blue‐emitting AlN:Eu2+ spherical phosphors by carbothermal reduction nitridation method

AbstractIn this study, blue‐emitting AlN:Eu2+ spherical phosphors were successfully synthesized for the first time by the carbothermal reduction nitridation (CRN) method, assisted with high nitrogen pressure, appropriate synthesis temperature, and the addition of CaF2. The influence of typical experimental parameters, such as N2 pressure, heating temperature, CaF2 content and Eu2+ concentration on the morphologies and luminescence properties of AlN phosphors were comprehensively investigated. The formation mechanism of spherical morphology were significantly proffered, indicating that sufficient liquid Ca‐aluminates during the AlN growth stage were essential for the spheroidization process under the action of surface tension. The synthesized AlN:Eu2+ spherical phosphors presented an intense blue emission band centered in the range of 427‐ 476 nm relative to the reaction temperature. The lifetime of AlN:Eu2+ phosphor was calculated to be around 1.89 μs. The temperature‐dependent PL spectra suggested that the emission band did not shift until 225°C. In addition, the spectral analysis strongly suggested that the luminescence property of AlN:Eu2+ phosphors was significantly enhanced by the large particle size, spherical morphology, reduced impurity content, and appropriate Eu2+ concentration.

Evaluation of the influence of the dispersion-sludge characteristics of the pulp on the beneficiation indicators of technogenic fluorite-containing tailings

The article provides an assessment of the technological features of mature tailings from the processing of finely disseminated fluoritecontaining raw materials of the Yaroslavkaya Mining Company. The prospects for their secondary processing are considered. It has been established that the waste stored in various sectors of the enterprise’s tailings contain from 13 to 23% fluorite, 12-14% calcite. The characteristic is given to the technological features of raw materials. The fluorite grains present in the technogenic tailings are characterized by the presence of thin inclusions and veins of silicate minerals. An obstacle to the selective separation of minerals by the flotation method is the shielding coatings of the surface zone of mineral particles, formed from contact with reagents at the stage of primary ore processing and in the process of interaction with the water-air environment in the tailing dump. The ways of increasing the contrast of the adsorption properties of minerals are proposed. Important factors influencing the process of mineral selection, allowing to influence the quality characteristics of flotation of refractory secondary raw materials is fine grinding of the material in combination with a high degree of dilution of the pulp. The possibility of extracting concentrates with a CaF2 content of 95.2-95.6% with the recovery of fluorite in them of 57-60.7% is shown. The introduction of inter-cycle regrind of foam products into the operation scheme allows to reduce the content of silicone dioxide in concentrates to 0.98%, which meets the requirements of consumers.

Effect of Slag Composition on the Deoxidation and Desulfurization of Inconel 718 Superalloy by ESR Type Slag Without Deoxidizer Addition

Effects of slag composition and alloy content as well as temperature on the deoxidation and desulfurization of Inconel 718 superalloy by CaF2-CaO-Al2O3-MgO-TiO2 ESR-type slag without the addition of a deoxidizer were systematically investigated by laboratory-scale experiments and the developed mass transfer model. The model predictions were verified through comparison with experimental results in a double-layer crucible. The results showed that the oxygen content decreased with an increase of CaO, MgO and CaF2 content in the slag at 1773 K, and CaO has a great influence on the deoxidation of Inconel 718 alloy compared with MgO and CaF2 in slag, which was responsible for the decrease in equilibrium content of sulfur in the Inconel 718 alloy. The total oxygen and sulfur content decreased from 33.2 and 20 ppm in master alloys to about 10 and 6 ppm in alloy ingots at 1773 K, respectively. Properly increasing the Al and Ti content only lowered the oxygen and sulfur content in the nickel-based alloy to a limited extent when satisfying the mechanical properties of the Inconel 718 alloy. The interfacial oxygen content increased with increasing temperature, giving rise to a decrease in the desulfurization ratio $$ \left( {{{[{\text{pct S}}]_{t = t} } \mathord{\left/ {\vphantom {{[{\text{pct S}}]_{t = t} } {[{\text{pct S}}]_{t = 0} }}} \right. \kern-0pt} {[{\text{pct S}}]_{t = 0} }}} \right) $$. These results show that the lower temperature favored desulfurization of the nickel-based alloy.

Effect of CaF2 on the Viscosity and Microstructure of CaO–SiO2–Al2O3 Based Continuous Casting Mold Flux

In this study, a CaO–SiO2–Al2O3-based continuous casting mold flux was designed using the FactSage thermodynamics software to determine the composition range of CaF2. The viscosity characteristics of the mold flux were determined using a rotating viscometer. The results show that the constant temperature viscosity at 1300 °C decreases gradually as CaF2 content is increased from 3% to 11% in the CaO–SiO2–Al2O3-based slag. Viscosity is reduced from 0.854 to 0.241 Pa·s, viscous the flow activation energy is reduced from 157.74 to 114.34 kJ·mol−1, and the break temperature is reduced from 1280 to 1180 °C. Furthermore, when the CaF2 content is increased from 3% to 11%, the number of nonbridging fluorine bonds (Al–F structure and Si–F structure) in the melt increases to 287, the number of bridging fluorine bonds (Al–F–Al structure, Si–F–Si structure, and Si–F–Si structure) is only 17, and the network rupture of fluorine ions in the system is larger than the network formation. Consequently, both the degree of polymerization and viscosity are reduced.

Influence of CaF2 on microstructural characteristics and mechanical properties of 304 stainless steel underwater wet welding using flux-cored wire

Underwater wet welding (UWW) of 304 stainless steel was performed using a set of wires with various calcium fluoride contents. The appearances, compositions, microstructural characteristics and mechanical properties of welding joints were analyzed. As the proportion of CaF2 rose, the welding appearances had been improved owing to the increasing coverage of slag. The depth-width ratio descended from 33.5% to 15.7% with an increase of CaF2 from 0% to 65% due to the reduction of the molten pool heat. Microstructural observations showed that the fully austenitic weld metal was consisted of four regions and the proportion of each region varied with the content of CaF2. The t8/5 cooling times of the heat affected zone were prolonged from 4.4 s to 6.1 s as the CaF2 content increased from 0% to 65%, which contributed to the microstructure variation. Besides, the uppermost element in the welds was Ni (at least 65%) whose content gradually went up with more and more CaF2 in the wire. Under the same conditions, the concentration of the solutes in the Ni-based welds lowered, encouraging the dislocation to be smaller and more dispersive. It was 20% CaF2 that the wire contained when the weld reached the best mechanical property with 522 MPa tensile strength and 132.74 J/cm2 impact toughness.

Effect of CaF2, B2O3 and the CaO/SiO2 mass ratio on the viscosity and structure of B2O3‐containing calcium‐silicate‐based melts

AbstractThe relationship between the viscosity and structure of B2O3‐containing calcium‐silicate‐based mold fluxes and the effects of fluidizers including CaF2, CaO, and B2O3 on the viscosity and their correlation with the structural aspects were studied using a rheometer with Fourier transformation infrared and Raman spectroscopy. The viscosity decreased with increasing CaF2 addition up to 28 wt% at a fixed CaO/SiO2 ratio of 0.3, which was related to depolymerization. Furthermore, CaF2 addition also affected the apparent activation energy for viscous flow, which decreased with increasing CaF2 content to 105.1 from 151.1 kJ/mol. At higher C/S ratios, the viscosity decreased in the presence of greater Ca2+ and O2− supplied from CaO, which subsequently increased the activation energy to 149.7 from 122.0 kJ/mol. With regard to the B2O3‐melt, polymerization of the network structure was observed by comparing the B2O3‐free to 4.4 wt% B2O3 content. However, the viscosity was relatively constant with increasing B2O3 addition. However, the viscosity decreased due to greater simplification of the network structure above 4.4 wt% B2O3. The break temperature decreased with greater B2O3 addition as the crystallization was inhibited. Furthermore, the apparent activation energy decreased as depolymerization of the network structures occurred above 4.4 wt% B2O3.

Effect of different process parameters on non-metallic inclusions during electro-slag remelting of a tempering steel

The remelting behavior of the tempering steel 50CrMo4, was investigated with several experimental melts on a lab-scale ESR-plant. The investigated parameters included a variation of the slag compositions and the use of a protective nitrogen atmosphere. Variations of the slag composition comprised slags with different contents of CaF2, CaO and Al2O3 as well as a variation of the SiO2-content. The remelted ingots were forged and analyzed regarding their chemical composition as well as their distribution and composition of the non-metallic inclusions (NMI) by automated SEM-EDX method. The chemical composition of the slag after remelting was analyzed as well. The results clearly show a relationship mainly of Si and Al in the steel with the process parameters. NMI changed in their total amount, type and size distribution. The protective atmosphere reduced the Si-losses during remelting. The majority of the NMI were of the Al2O3- & MnS-type. In general, remelting lead to an almost complete removal of sulfides, a reduction of oxisulfides and a shift towards more oxides. The total amount of NMI was most strongly reduced by the high CaF2-containing remelting slag.

Evaluation of Factors on Removing Boron from Silicon by Slag Refining Under Atmospheric Conditions

Upgraded metallurgical grade silicon (Si) is available for high-efficiency solar cells. In the present article, Si refining with CaO-SiO2-CaF2 slags is carried out under open atmosphere, and orthogonal analysis is applied to evaluate the influencing factors. The results show that the influence order of the objective factors is: (1) slag/Si ratio > (2) refining time > (3) original slag basicity > (4) CaF2 content and that the slag/Si ratio acts as the key factor in boron removal. It is observed that boron decreases effectively within 30 min refining period. Moreover, the slags are pulverized when the basicity is > 1.39 because of the β-γ phase transition of Ca2SiO4, and the pulverization is beneficial to the separation of Si from slag.

Application of Raman spectroscopy to the flotation process of fluorite

Exact knowledge of the content of the various components in a flotation system is critical in both product analysis and process control. In the present work, FT Raman spectroscopy was successfully applied to an industrial fluorite flotation system for quantification of calcium fluoride (CaF2). In a first step, an artificial model system consisting of CaF2, barium sulphate and silica was set up to test feasibility of FT Raman spectroscopy and to generate a calibration curve. An empirical model was developed, which incorporates effects of particle size on Raman shift and peak area, so that a CaF2 quantification is feasible independent of particle size. Conversely, the empirical model provides information about the approximate particle size in the analysed sample. A cross-validation using X-ray fluorescence spectroscopy showed excellent quantification of CaF2 in seven industrial fluorite samples with CaF2 weight fraction in a range from 7% to 98% with absolute differences of less than 5%. In a first laboratory batch-flotation experiment, the CaF2 content of the froth product could be quantified successfully providing additional information about the approximate median particle size of the concentrate, making FT Raman spectroscopy superior to commonly applied X-ray fluorescence spectroscopy.

Effects of Fluoride and Sulphate Mineralizers on the Properties of Reconstructed Steel Slag

Abstract Improving the cementitious activity and volume stability of steel slag by thermal reconstruction is an innovative method for efficient utilization of steel slag. In this study, different amounts of CaF2 and CaSO4 were added to steel slag as a mineralizer based on the determining admixtures needed for the reconstruction reaction, and the effects of CaF2 and CaSO4 on the cementitious activity and volume stability of the reconstructed steel slag were investigated. The results show that when the CaF2 content is increased to 5 wt%, the cementitious activity index of the reconstructed steel slag gradually increases to 92%, which is 12% higher than the first level technical requirement specified by the national standards, and the free CaO (f - CaO) and MgO (f-MgO) contents gradually decrease to 0.35 and 0.13 wt%, respectively. With increasing CaSO4 content, the cementitious activity index first increases and then decreases, while the contents of f -CaO and f-MgO show the opposite trend. When the CaSO4 content is 2 wt%, the activity index is 105%,which is 25%higher than the first level technical requirement specified by the national standards, and the f -CaO and f-MgO contents reach minima of 0.44 and 0.35 wt%, respectively.

Research on High Temperature Friction and Wear Characteristics of H13-Cr2C3-CaF2 Self-lubricating Materials

Based on the service environment and requirements of hot working die,we proposed a H13-Cr2C3-CaF2 self-lubricating material formula system and powder metallurgy process parameters, and prepared the high temperature composite materials. The phase composition and distribution of H13-Cr2C3-CaF2 samples were analyzed by energy dispersive spectrometer. The friction coefficient, wear rate, wear morphology and spectrum of samples with different contents of CaF2 were tested and compared by ball-on-disc high temperature tribometer under the conditions of test temperature 600 °C, disk rotation speed 200 r/min and friction for 15 min,and the mechanism of high temperature friction and wear was described. It will support the green manufacturing and sustainable development of forging industry.

Effects of basicity and CaF2 on the viscosity of CaF2–CaO–SiO2 slag for electroslag remelting process

Effects of the basicity and the CaF2 content on viscosity of CaF2–CaO–SiO2 slag with high CaF2 content for electroslag remelting process were investigated by the rotating cylinder method in the temperature ranging from 1773 to 1533 K. The relationship between the structure and the viscosity variation of the slag was also clarified by the Fourier transform infrared (FT-IR) spectroscopy of water-quenched slags. The results show that the viscosity gradually decreases with the increase in the basicity of the slag from 1 to 3 under the present experimental conditions. It is found that the CaO does not depolymerize all silicate complex anions for the slag with the basicity of 1 at 1773 K and there are still some bridging oxygens. With the increase in the basicity to 3, the silicate complex anions are almost completely depolymerized to simple ions. As the CaF2 content increases from 40 to 80 mass%, the viscosity of the slag decreases due to the dilution of CaF2 for the concentration of the silicate complex anions in unit volume of the slag. Moreover, the effect of the temperature on the viscosity is not remarkable. The activation energy of viscous flow exhibits the decrease from 40.4 to 26.7 kJ · mol−1 with the increase in the basicity from 1 to 3, and also the decrease from 66.6 to 31.0 kJ · mol−1 with the increase in the CaF2 content from 40 to 80 mass%.

Effect of Chemical Composition on the Properties of Reconstructed Steel Slag

The steel slag is not widely or extensively used because of its poor volume stability and low cementitious activity. In this paper, the solid waste fly ash, quicklime and slag discharged from iron and steel enterprises are used as conditioning components in the experiment. In order to improve the cementitious activity and volume stability of steel slag, the high temperature reconstruction experiment of steel slag was completed. The effects of C/S (2.50~3.14), S/A (4.5~17. 81) on the cementitious activity and volume stability of reconstructed steel slag were investigated by means of the tests of compressive strength, scanning electron microscope, X-ray diffraction, lithofacies test, stability test and so on. The results showed that the cementitious activity and volume stability of the reconstructed steel slag were improved in the higher C/S or lower S/A. The cementitious activity and volume stability of the reconstructed steel slag were improved with the increase of CaF2 content. By analyzing the cementitious activity and volume stability of the reconstructed steel slag, the optimum technological parameters are obtained as follows: C/S is 2.70 , S/A is 5.78, the content of CaF2 is 4%.

Removal of boron from metallurgical grade silicon by CaO-SiO2 based slags

Slag refining is one of the most effective methods to remove boron from metallurgical grade silicon (MG-Si). In this paper, the removal of boron from metallurgical grade silicon was proposed by adding CaF2, BaO or rare earth oxides (La2O3 and CeO2) to CaO-SiO2 based slags. The effects of the BaO content, the CaF2 content, the rare earth oxides content, the molar ratio of CaO to SiO2 and the mass ratio of slag to silicon on the partition coefficient of boron (LB) between slag and silicon are investigated. The results show that LB has a maximum value of 5.17 in 45% CaO-45% SiO2-10% BaO slags at 1550 °C after reacting for 6 h with a slag to silicon mass ratio of 2. Besides, it is found that the addition of La2O3 or CeO2 shows better de-boronization ability compared with the addition of BaO.

Band gap engineering of CaxSr1-xF2 and its application as filterless vacuum ultraviolet photodetectors with controllable spectral responses

We experimentally demonstrate that the band gap of mixed crystals of calcium fluoride and strontium fluoride (CaF2 – SrF2, CaxSr1-xF2) can be engineered by modulating the composition ratio of CaF2 and SrF2. By increasing the CaF2 content, the band gap increases and the absorption edge is blue-shifted. A range of band gap energies can be obtained between 9.73 eV for pure SrF2 and 10.24 eV for pure CaF2. The first order Raman frequency shift increases linearly from 285.2 cm−1 for pure SrF2 to 327.8 cm−1 for pure CaF2. The ability to manipulate the band gap is maintained even at very low temperatures. Vacuum ultraviolet (VUV) photoconductive detectors are fabricated to explore the effect of varying composition ratios on spectral sensitivity. The spectral response of the photodetectors shifts to shorter wavelengths as the band gap increases. This allows the spectral response to be controlled by appropriately choosing the CaF2 – SrF2 ratio. Using CaxSr1-xF2 sensors also eliminates the need for extra filters to cut off unwanted longer wavelengths as the onset of their absorption occur in the VUV region. The controllable spectral response and filterless feature of CaxSr1-xF2 photodetectors provide an advantage over currently available oxide-, nitride-, and diamond-based photodetectors.

Fluorine-ion-releasing injectable alginate nanocomposite hydrogel for enhanced bioactivity and antibacterial property

The creation of a moist environment and promotion of cell proliferation and migration together with antibacterial property are critical to the wound-healing process. Alginate (Alg) is an excellent candidate for injectable wound dressing materials because it can form a gel in a mild environment. Taking advantage of its gelation property, an injectable nano composite hydrogel containing nano-sized (about 90 nm) calcium fluoride (CaF2) particles was developed using in-situ precipitation process. The amount of released fluorine (F−) ion from the nanocomposite hydrogel increased with increasing CaF2 content inside the composite hydrogel and the ions stimulated both the proliferation and migration of fibroblast cells in vitro. The antibacterial property of the composite hydrogel against E. coli and S. aureus was confirmed through colony formation test where the number of bacterial colonies significantly decreased compared to Alg hydrogel. The in vivo results based on a full-thickness wound model showed that the nanocomposite hydrogel effectively enhanced the deposition of the extracellular matrix compared to that of the Alg hydrogel. This study demonstrates the potential of this nanocomposite hydrogel as a bioactive injectable wound-dressing material with the ability to inhibit bacterial growth and stimulate cell proliferation and migration for accelerated wound healing.

Investigation of fluoride vaporization from CaF2[sbnd]CaO[sbnd]Al2O3 slag for vacuum electroslag remelting

In this study, five types of CaF2CaOAl2O3 slags with varying CaO/Al2O3 mass ratio and CaF2 content were selected for investigating the vaporization behavior of slag bearing high CaF2 content by thermo gravimetry and ion and molecule coexistence theory. The results show that the volatile product of slag is the AlF3. The vaporization rate is affected by the vapor pressure of AlF3, mole number of complex molecules and the viscosity of slag. For all slags, the vaporization rate of slag bearing approximately 70 wt% CaF2 and 30 wt% Al2O3 is the fastest due to the ultra-high vapor pressure of AlF3. In the test of slags containing 70 wt% CaF2, vaporization rate firstly decreases, then increases with CaO/Al2O3 mass ratio increasing from 0.05 to 1.10 and 2.00. In the case of slags containing same CaO/Al2O3 mass ratio, vaporization rate firstly increases, then decreases with CaF2 content decreasing from 68.9 wt% to 48.1 wt% and 28.7 wt%. Slag T5 bearing approximately 30 wt% CaF2, 33.9 wt% CaO and 36.1 wt % Al2O3 has lower electrical conductivity, slower vaporization rate and larger sulfide capacity, which will be economical, environmentally friendly and suitable for vacuum electroslag remelting.

Effect of the Slag Composition and a Protective Atmosphere on Chemical Reactions and Non‐Metallic Inclusions during Electro‐Slag Remelting of a Hot‐Work Tool Steel

The remelting behavior of the hot‐work tool steel X37CrMoV5‐1 is investigated with several experimental melts on a lab‐scale ESR‐plant. The investigated parameters comprise a variation of the slag compositions and the use of a protective nitrogen atmosphere. Variations of the slag composition include slags with different contents of CaF2, CaO, and Al2O3 as well as a variation of the SiO2‐content in the slag. The remelted ingots are forged and analyzed regarding their chemical composition. The distribution and composition of the non‐metallic inclusions (NMI) is studied by an automated SEM‐EDX method. Additionally, the chemical composition of the slag after remelting is analyzed. The results show clearly an equilibrium reaction between Si and Al in the steel with SiO2 and Al2O3 in the slag as well as the effect of oxygen in open ESR operation. A protective atmosphere reduces the Si‐losses during remelting, but has no major effect on the number or composition of NMI compared to open remelting. The content of NMI, especially the larger ones, is reduced significantly in all remelting experiments. The majority of the NMI are MA‐spinel type except for the CaO‐free slag, where alumina inclusions prevail. In general, remelting leads to an almost complete removal of sulfides, a reduction of oxisulfides, and a slight increase of oxides.