Influence Of CaF2 Research Articles

Effect of CaF2 on the preparation and optical property of MgAl2O4 transparent ceramics

To achieve optimal light transparency in MgAl2O4 transparent ceramics, a higher sintering temperature is required to eliminate pores. However, inevitable rapid grain growth occurs, leading to lower mechanical properties. To address this problem, calcium fluoride (CaF2) is utilized as a sintering additive to enhance the transparency of MgAl2O4 ceramics. The influence of CaF2 on the densification process and microstructure evolution is investigated. CaF2 demonstrates notable abilities in facilitating densification and lowering the sintering temperature. Moreover, it inhibits grain growth during the final sintering stage. However, the sintering temperature must be controlled because the secondary phases (calcium aluminate) precipitate at a higher temperature, thereby affecting the homogeneity of the ceramic microstructure. After optimizing the sintering process, ceramics (with a thickness of 5 mm) containing 0.05 wt% CaF2 exhibited the highest in-line transmittance of 81 % and 87 % in the visible and near-infrared wavelengths, respectively, after pre-sintering at 1505 °C for 3 h and subsequent hot isostatic pressing (HIPing) at 1550 °C for 3 h.

Influence of CaF2 on the spectroscopic studies of Dy–Eu co-doped fluoroborate glass for lighting applications

To investigate novel glass materials applicable to W-LED, we designed and prepared a series of glasses with varying compositions. The compositions of the glasses were (64-x)B2O3–15Al2O3–10Na2O–10Bi2O3-xCaF2-0.5Dy2O3-0.5Eu2O3 (x = 0, 5, 10, 15, 20, 25). The glasses were synthesized using the melting quenching method. The effect of CaF2 on the structural feature of fluoroborate glass was studied by infrared spectroscopy analyses. Determination of fluorine content in glass by 19F NMR inversion spectroscopy. The absorbance of glass increased as the CaF2 content increased in the visible and ultraviolet light ranges. The optical band gap of the prepared glasses was obtained from the absorption spectrum, which confirmed the existence of nonbridging oxygen (NBO) in the glass network structure. The fluorescence lifetime of the glass increases with increasing CaF2 content, and the quantum yield of the glass first increases and then decreases. In addition, fluoroborate glass had a lower Urbach energy, indicating that its network structure was relatively uniform and stable. In contrast, the increase in Urbach energy is due to the substitution of CaF2, leading to more defects. By adjusting the excitation wavelength and CaF2 content, the color temperature (1598–3346 K) and color rendering index (36–63) of fluoroborate glass can be effectively adjusted. These results show that the prepared Dy/Eu co-doped fluoroborate glasses have a potential application in white lighting.

Study on physical properties of Al2O3-based slags used for the self-propagating high-temperature synthesis (SHS) – metallurgy method

Abstract The Al2O3-based slags are playing important roles in the preparation of Cu–Cr alloy through self-propagating high-temperature synthesis (SHS) – Metallurgy method. However, the current research on Al2O3-based slag is mainly concentrated on steel metallurgical slag and electroslag remelting slag, and the research on aluminum thermal reduction slag with high content of Al2O3 is still insufficient. Therefore, systematic studies of the physical properties of slag with high aluminum content were carried out in the present work, and the influence of CaF2, CaO, MgO, SiO2, and Na3AlF6 on viscosities, liquidus temperatures, densities, and surface tensions of high Al2O3 content slags was measured and analyzed. The results indicated that CaO and CaF2 have positive effects on the physical properties of Al2O3-based slags, MgO has positive effects when its content is not over 3%, and SiO2 and Na3AlF6 have negative impacts. CaO, CaF2, and MgO (not over 3%) could be used as additives to improve the metallurgical performance of Al2O3-based slags in aluminothermic reduction–slag refining method.

Effect of Al2O3 and CaF2 additives on the viscosity of conventional cryolite melts

The viscosity of cryolite melts of conventional composition NaF–AlF3–CaF2–Al2O3 was studied by rotational viscometry using the FRS 1600 high-temperature rheometer. The cryolite ratio of the NaF–AlF3 melt was 2.1, 2.3, and 2.5; the Al2O3 content varied from 2 to 6.6, and CaF2 – from 0 to 8 wt%. The measurements were carried out in the temperature range from liquidus to 1200 °C. The conditions for the laminar flow of the investigated melts were determined, based on the measurements of the cryolite melts viscosity as a function of the shear rate at a constant temperature. A shear rate of 12 ± 1 s–1 was chosen for studying the viscosity temperature dependence for all samples. The viscosity temperature dependence of cryolite melts is described by a linear equation. The temperature coefficient b in this equation has negative values and varies in the range of (–0.01)–(–0.06) mPa·s/deg. It was found that the viscosity of cryolite melts of conventional composition in the range of operating temperatures of aluminum electrolysis (950–970 °C) varies from 2.5 to 3.7 mPa·s (depending on the composition and temperature). The viscosity of cryolite-alumina melts increases with the rise of alumina content: 1 wt% Al2O3 increases the viscosity, on average, by 1%. However, the influence of CaF2 is more significant: the addition of 1 wt% CaF2 leads to an increase in viscosity by 3%. A decrease in the CR of the melt by 0.1 (in the range of 2.1–2.5) leads to a decrease in the viscosity of cryolite melts by 2.3%. A viscosity regression equation for the cryolite melts of conventional composition as a function of several independent parameters (temperature, CR, CaF2 and Al2O3 content) is obtained by the multivariable approximation of experimental data. The equation satisfactorily (within 1.5%) describes the viscosity of conventional industrial electrolytes and can be used for estimation of their viscosity.

Influence of CaF2 on spectroscopic studies of lead fluoro bismuth borate glasses doped with Cr3+ ions

An extensive study has been carried out to predict the physical and structural properties of CPBBCR: CaF2-PbF2-Bi2O3-B2O3Cr2O3 glasses. The changes in the density & molar volume due to the substitution of PbF2 by CaF2 have been discussed in terms of relative crystal densities of PbF2 & CaF2. The detailed UV–visible spectra for the CPBBCR samples have been done to study the variation of optical band, Urbach energy and Rachah parameters. The EPR spectrum of Cr3+ doped glass sample exhibited broad resonance signal with effective g = 4.12 and g = 1.97. Deconvoluted Raman spectra are used to attain hidden peaks in the Raman spectra. With the increase in CaF2, Raman spectra suggested that the there is a transfer of [BO4] to [BO3]. FTIR analysis of these samples confirmed the presence of metal cation vibrations, BiO3, BO3 & BO4 units. FTIR spectra also confirmed that the Bi2O3 will act as network modifier.

Influence of CaF2 on the preparation of ZnO via SHS method

A closing synthesis device with special structure was designed to effectively collect the ZnO synthesized via self-propagating high temperature synthesis (SHS) method. With this device, the influence of CaF2 on products was investigated. Products were characterized using scanning electron microscope (SEM) and X-ray diffraction (XRD). Results showed that with the increase of CaF2, there is a trend of first increase and following decrease in the yield of products and there appears increasing amount of one-dimensional ZnO nanostructures and there are no obvious changes on the structure of products. Possible mechanisms of the influence of CaF2 on products were discussed.

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.

Influence of CaF2 in calcium aluminate-based slag on the degradation of magnesia refractory

High temperature experiments were carried out using an induction furnace to simulate the refractory-slag-metal reactions in conjunction with thermodynamic computations using FactSage7.0 software. The Al-killed steel and the CaO-Al2O3–8SiO2–5MgO-xCaF2 (CaO/Al2O3 = 1.9, x = 0–15 wt%) slag were brought to equilibrium in a magnesia refractory at 1823 K. Moreover, the solubility of MgO in the slag was quantitatively measured using a resistance furnace as a function of CaF2 content and temperature to confirm the thermodynamic driving force of the dissolution of MgO. The penetration depth of a slag into the magnesia refractory increased with increasing CaF2 content, which originated from a decrease in slag viscosity. Also, it was confirmed that MgO grains were dynamically detached from the slag/refractory interface by increasing the content of CaF2.

Stable Wollastonite-Cuspidine Glass-Ceramic Using Inexpensive Raw Materials

Transparent glasses within the K2O-CaO-SiO2-F composition were prepared. The influence of CaF2, TiO2, Li2O, Li2O-TiO2 and CeO2 additions on the crystallization of the parent glass has been investigated. Crystallization process gave wollastonite and cuspidine as the major phases whereas; xontolite and traces of miserite were developed as subordinate ones. Wollastonite was developed alone in the temperature range of 800 °C-1100 °C in Li2O-containing the base glass. Wollastonite and cuspidine were stable in the 800-1100 °C range in Li2O+TiO2-containing samples and within the 900 °C-1100 °C range in CaF2 and CeO2 containing samples. The microstructure of the Li2O-containing glass-ceramic showed an interlocked needle in nano-scale wollastonite crystals, while fibrous textures were developed in all other crystallized samples at 1000 °C. The thermal expansion coefficient value of the crystallized samples was between 7.596 to 8.708 X10 −6 °C−1 (20-500 °C) and the higher values reflect the increase of crystallization content of cuspidine and even the traces of miserite. This glass-ceramic is thought to be important in dental laboratories.

Structure-Viscosity Relationship of Low-silica Calcium Aluminosilicate Melts

The structure-viscosity relationship of the low-silica (SiO2 ≤ 10 wt%) calcium aluminosilicate melts, which represent the secondary refining ladle slag systems, was investigated by employing the rotating-cylinder viscosity measurement in conjunction with the Raman spectroscopy measurement for linking the macroscopic thermophysical property and molecular (ionic) structural information. Furthermore, the influence of CaF2 on the structure-property relationship was explored. The viscosity of low-silica calcium aluminosilicate melts decreased with increasing both CaO/Al2O3 and CaO/SiO2 ratios. However, the effect of the former on the viscosity of low-silica calcium aluminosilicate melts was larger than that of the latter. By employing the Neuville’s structure model, in which the silicate structural units with various NBO, i.e. QnSi are located at the boundary of the AlO4 aluminate, and the Raman scattering data of the glass samples, it was demonstrated that the aluminate and silicate units are more effectively modified by increasing the CaO/Al2O3 ratio at fixed silica content. The addition of small amounts of CaF2 (~5 wt%) to the low-silica calcium aluminosilicate melts decreased the viscosity of the melts. From the analysis of Raman scattering data, the liberation of SiO44– (Q0Si) units from the AlO4 aluminate structure by addition of CaF2 was understood. However, the effect of CaF2 addition on the viscosity became less discernible at higher CaF2 content (≥ 10 wt%) region, where the F ions simply substitute for the non-bridging oxygen ions in AlO4 tetrahedra.

Innovative smelting of IIIX15CΓ-B electrosteel

A new smelting technology for IIIX15CΓ-B electrosteel is described. In this technology, the steel undergoes treatment in a ladle-furnace unit and a vacuum system. The output of bar batches of all five size groups is analyzed for the content of nonmetallic inclusions according to State Standard GOST 801-78 and the ASTM E-45 standard (method A). The phase-mineral composition of furnace slag on smelting steel in a DSP-60 arc furnace is studied by X-ray microstructural analysis. The change in chemical composition of oxide-fluoride slag when the steel passes through the ladle-furnace unit and the vacuum system is analyzed, along with the influence of CaF2 on the activity of FeO in oxide-fluoride slag and on the durability of the ladle lining. In conclusion, the need for environmental improvements is noted, in the light of the use of fluorspar; research into means of reducing fluorspar consumption must be activated.

Influence of CaF2 on the structure and dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics

Ag(Nb0.8Ta0.2)O3 ceramics were prepared by the traditional solid-state reaction method. The effect of CaF2 addition on the structure and dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics was investigated. The addition of CaF2 led the ceramics to a larger grain size and distortion of lattice. With the addition of 4.5 wt.% CaF2, the permittivity of the ceramics increased from 442 to 1028, the dielectric loss decreased sharply from 6.12 × 10−3 to 8.6 × 10−4, and the temperature coefficient of capacitance decreased from 1834 ppm/°C to −50 ppm/°C (at 1 MHz). These results indicated that the high permittivity was related with a large grain size, a low grain boundary density, and the weak Ta-O or Nb-O bond strength caused by the addition of CaF2.

Carbide Capacity of CaO-SiO2-CaF2(-Na2O) Slags at 1773 K

The influence of CaF2, Na2O, and basicity on the solubility of carbon in the CaO-SiO2-CaF2-Na2O slag at 1 773 K was investigated on the basis of carbide capacity concept. The carbide capacity of the CaOsatd-SiO2-CaF2 system increases with increasing CaF2 content up to about 40 mass%, followed by nearly constant value. The capacity of the slags saturated with Ca2SiO4 also increases with increasing the content of CaF2 and this trend can be explained from the depolymerization reaction of silicate network by F− ions. The carbide capacity of the slags increases by increasing the ratio of (%CaF2)/(%SiO2) up to about 0.8, followed by slight increase or nearly constant value at a fixed CaO content. The capacity also increases by increasing the ratio of (%CaO)/(%SiO2) at a fixed CaF2 content. The carbide capacity of the Na2O-containing slags linearly increases with increasing the basicity, B (≡{(%CaO)+(%Na2O)}/(%SiO2)) and the dependence of the capacity on the basicity decreases by increasing the CaF2 content. On the other hand, the capacity decreases with increasing CaF2 content at basicity, B of the slags greater than about 2.0 and vice versa in the composition of B≤2.0. The capacity of the slags containing CaF2 and Na2O could quantitatively be described by the activity of CaO rather than optical basicity.

Influence of CaF2 and AlF3 on the kinetics and mechanism of the Al electrode reaction in cryolite melts with various alumina contents

Electrochemical techniques were used to study the kinetics and mechanism of the aluminium electrode reaction in two cryolite-based melts containing cryolite with either 11 wt % AlF3 or 5 wt % CaF2 additions and variable alumina contents at 1000 °C. A three step electrode process was observed in both melts, comprising a preceding chemical reaction followed by two charge transfer steps. The exchange current density of the cathodic reaction was found to be dependent on the concentration of aluminium fluoride. By a combination of electrochemical impedance spectroscopy (EIS) and galvanostatic relaxation methods (GRM), the exchange current density of the first (slower) charge transfer step, the Warburg diffusion impedance, the double layer capacitance of the aluminium electrode and the rate of the preceding chemical step, were evaluated in the range of 2–8 wt % alumina. The role of the two additives, AlF3 and CaF2, was evaluated.

The Influence of CaF2 and AIF3 upon Mechanism and Kinetics of the Anodic Reaction in Cryolite-Alumina Melts

The Influence of CaF2 and AIF3 upon Mechanism and Kinetics of the Anodic Reaction in Cryolite-Alumina Melts

Adsorption of selected organic compounds onto calcium fluoride.

Selected organic compounds adsorb onto CaF2 and can be revealed by staining methods. The possible influence of CaF2 coated with organic compounds on the dissolution rate is discussed.