Effect Of CaF2 Addition Research Articles

Preparation of oily sludge-derived glass-ceramics by low-temperature melting with addition of CaF2

Oily sludge (OS), a hazardous waste that generated in the process of petroleum exploration, utilized as raw material in this study for preparation of high value-added glass-ceramics. The effect of CaF2 addition and temperature on the melting behavior, crystallization mechanism, physical-chemical properties and heavy metals leaching of glass-ceramics was highlighted. The results indicated that the obtained parent glass demonstrated completely amorphous structure at 1200 °C when CaF2 content was 4 wt%. The addition of CaF2 improved crystallinity of glass-ceramics, which further improved the glass-ceramics properties. Comparing the properties of OC-1200-830 with OCF4-1030, it was observed that the density increased from 2.27 g/cm3 to 2.60 g/cm3, compressive strength increased from 56.43 MPa to 122.00 MPa, bending strength increased from 6.16 MPa to 11.41 MPa, acid resistance increased from 92.8% to 96.8%, alkali resistance increased from 94.6% to 98.2%, and water absorption reduced from 0.19% to 0.12%. The leaching concentrations of heavy metals in the glass-ceramics were below than the thresholds required in GB 5058.3–2007, China. The theoretical energy consumption of glass-ceramics melted at 1200 °C was 30.84%–41.37% lower than that melted at 1500 °C, which demonstrated that the glass-ceramics prepared in this study have cost advantages.

Chemical controls on niobium and zirconium mobility inferred from dissolution experiments on wöhlerite in alkaline silica-undersaturated melts

The solubility of wöhlerite, ideally Na2Ca4ZrNb(Si2O7)2O3F, in peralkaline SiO2-undersaturated melts (Na2O–CaO–Al2O3–SiO2 ± F ± H2O) was studied at the following temperature (T) and pressure (P) conditions: 750 °C, 200 MPa, 850 °C, 100 MPa, and 1000 °C, 200 MPa. Wöhlerite appeared to be stable up to high temperature, with increasing solubility, which is consistent with field observations of early wöhlerite crystallization in pegmatites in the Larvik Plutonic Complex. A lovozerite-group mineral (combeite–zirsinalite–lovozerite) was frequently observed to crystallize in the experiments at 750 °C, and, at very high Na/Al ratios, also at 850 °C. Fluorcalciopyrochlore formed at 1000 °C in experiments where water was added. The concentrations of Zr and Nb in the quenched glasses were generally very high and found to increase strongly with temperature. Moreover, they also increase with addition of water and with increasing peralkalinity. The effect of CaF2 addition was insignificant. Based on comparison with the limited information in the available literature, the solubilities of Ca-bearing Zr and Nb minerals (wöhlerite, lovozerite-group minerals, fluorcalciopyrochlore) in peralkaline silica-undersaturated melts may be lower than those of nominally Ca-free Zr and Nb minerals (zircon, baddeleyite, wadeite, columbite-(Mn)). The experimental data do not support the existence of significant ZrF or NbF complexation. The high concentrations of Nb and Zr in the reacted peralkaline melts can be explained by strongly enhanced formation of alkali-Nb/Zr-silicate complexes compared to that at peraluminous conditions. These complexes are the underlying chemical reason for characteristic high-field-strength-element (HFSE) enrichment in agpaitic and hyperagpaitic rocks.

Effect of CaF2 addition on the densification behavior and mechanical properties of resistant anorthite and its bioactivity

In the current study, anorthite ceramic (CaO, Al2O3, 2SiO2) was synthesized by a simple solid-state reaction method, using local Algerian raw materials. The effect of sintering temperature at 800, 850, 900, 950, 1000, and 1100 °C for 1h under atmosphere, and 0.5, 1.5, and 3 wt % calcium fluoride (CaF2) addition on the densification and mechanical properties of anorthite were studied. The correlation between these properties and the bioactivity of samples was investigated. The results showed that samples with 1.5 wt.% CaF2 sintered at 900 °C has the highest bulk density (2.7 g.cm-3 ), lowest apparent porosity (3%), outstanding micro-hardness (8.7 GPa), and high flexural strength (222 MPa) of anorthite. The in vitro bioactivity test was assessed by determining the changes in surface composition and morphology after immersion in a simulated body fluid (SBF) for 8 h to 21 days. The results of the bioactivity test determined the formation of hydroxyapatite (Ca5(PO4)3OH) on the sample surface after 3 days, suggesting it is a bioactive ceramic.

Effect of CaF2 on fluorocarbon plasma resistance and thermal properties of CaO-Al2O3-SiO2 glasses

ABSTRACT The effect of CaF2 addition on plasma resistance and thermal properties of CaO-Al2O3-SiO2 (CAS) glasses was investigated. The amount of SiO2 and Al2O3 was fixed to 42.9 and 9.1 (in mol%), respectively, while total amount of CaO and CaF2 was 48 mol% and the ratios of CaO:CaF2 were changed from 10:0 to 8:2. As the amount of CaF2 of CAS glass increased, CF4/O2/Ar plasma etch rate of glass decreased proportionally. In case of sample with CaO:CaF2 = 8:2, its etch rate had 5.04 ± 0.14 ㎚/min, which was about 20 times lower than that of quartz glass and was improved by more than 25% compared to the glass without CaF2. All glass samples maintained the initial surface and roughness even after plasma etching. In addition, the glass transition (Tg), crystallization (Tc), and the first melting temperature (Tf1) temperatures decreased with the amount of increased CaF2. F− ion in CAS glasses not only enhances the plasma resistance but also facilitates glass melting and forming operations.

Effect of CaF2 on Phosphorus Refining from Molten Steel by Electric Arc Furnace Slag using Direct Reduced Iron (DRI) as a Raw Material

The effect of CaF2 addition on dephosphorization reaction between molten steel and electric arc furnace (EAF) slag using direct reduced iron (DRI) at 1823 K (1550 °C) was investigated. Basicity, the thermodynamic parameter affecting the removal capacity of phosphorus (i.e., phosphate capacity), decreased using DRI due to an increased SiO2 concentration in the slag. To minimize slag volume and maximize dephosphorization efficiency, the CaF2 was added to the slag. As CaF2 content increased (0 to 10 mass pct), dephosphorization efficiency also increased. Thermodynamic analysis in conjunction with slag structural studies using Raman spectroscopy were conducted to explain the complicated phenomena. The results exhibited that even 5 to 6 mass pct CaF2 can improve the dephosphorization efficiency when DRI is used as raw material in an EAF process.

Crystallisation kinetics and structural stability of transparent CaF2 glass ceramics: Dependence of light transmittance on the amount of CaF2 added

The effect of CaF2 addition (15.4, 20.4, 27.4 and 35.4 wt%) on the crystallisation ability and preparation of transparent glass ceramics (TGCs) containing CaF2 nanocrystals was studied. It was found that samples with 15.4, 20.4, and 35.4 wt% CaF2 are crystallised with multiple crystal phases, making the TGCs opaque. Only when the amount of CaF2 added is increased to 27.4 wt%, TGCs with only CaF2 nanocrystals can be successfully prepared by heat treatment at 630 and 730 °C for 2 h. The crystallisation activation energy of the sample with 27.4 wt% CaF2 is 247.07 kJ mol−1, and the crystallisation energy barrier to be overcome corresponds to the formation of CaF2 nanocrystals rather than the formation of aluminosilicates, whose size and distribution easily make the glass opaque. Similarly, the FT-IR and XPS results indicate that as the amount of CaF2 added is increased to 27.4 wt%, the polymerisation degree of the sample is more suitable for the diffusion of calcium and fluorine atoms to form only CaF2 nanocrystals; therein, the corresponding mole fractions of the bridging oxygen (Oo), non-bridging oxygen (O−), and free oxygen (O2−) are approximately about 0.12, 0.77 and 0.11, respectively.

Sintered glass-ceramics and foams by metallurgical slag with addition of CaF2

The possibilities for the production of self-glazed sintered glass-ceramics or/and glass-ceramic foams using metallurgical slag are discussed. The effect of CaF2 addition on the glass melting, the densification and the foaming is also studied.The sintering and the bloating trends are evaluated by hot stage microscopy and the phase formation is estimated by X-ray diffraction spectroscopy. The structure of the obtained samples is studied with scanning electron microscopy and with computed tomography.The results demonstrate a good sinter ability of the used glass powders in the interval 800–950 °C and a subsequent intensive bloating behaviour of the sintered samples in the range 1050–1150 °C.The addition of a certain amount of CaF2 in the glass batches leads to a noticeable decrease of both the melting and the sintering temperatures as well as to some increase of the crystallinity. As a result, self-glazed glass-ceramics with high percentage of CaF2 and with an improved micro-hardness and crystallinity can be obtained using finer glass powders, moderate heating rates and holding temperatures of 950–1000 °C.At the same time, glass-ceramic foams with closed porosity of about 80 vol % can be synthesized using glass powders with a modest addition of CaF2 by applying higher heating rates and holding temperatures of 1100–1150 °C.

Effect of CaF2 addition on macro/microstructures and mechanical properties of wire and arc additive manufactured Ti-6Al-4V components

A titanium/CaF2 component was manufactured through the combination of wire and arc additive manufacturing systems as well as activating flux. The effects of CaF2 on macro/microstructures evolution and mechanical properties were investigated. The results showed that the addition of CaF2 to Ti-6Al-4V reduced the width of component and the aspect ratio of α-lath, increased β volume fraction, whereas the intermittent grain boundary-α structure was obtained. In addition, tensile strength of the components at room temperature was significantly improved. Consequently, these findings indicated that activating fluxes offered a possibility to produce the desired microstructures and improve mechanical properties of titanium alloys during additive manufacturing.

Novel oxyfluorophosphate glasses and glass-ceramics

Effect of CaF2 addition at the expense of CaO on the thermal, physical, optical and structural properties of glasses in the NaPO3–CaO system was studied. The glasses were prepared by the conventional melt quenching method. For each glass, the thermal properties were studied by differential thermal analysis (DTA) and the optical properties by UV–Vis-NIR spectroscopy. The changes in the glass structure induced by the progressive replacement of CaO by CaF2 were investigated using IR and Raman spectroscopies. The glasses were heat treated at 20°C above their respective glass transition temperature for 17h to form nuclei and then at their peak crystallization temperature for 1h to grow the nuclei into crystals. An increase in the CaF2 content increased the polymerization of the phosphate network leading to shift of the band gap to lower wavelength and reduced the crystallization tendency of the glasses. At least two crystalline phases precipitated in all the investigated glasses, the composition of which depended on the CaF2 content. Finally, bulk crystallization was suspected to occur in the oxyfluorophosphate glasses.

Effect of CaF2 Addition on the Silicothermic Reduction of MnO in Ferromanganese Slag

The effect of temperature and CaF2 (fluorspar) addition on the silicothermic reduction behavior of MnO in the CaO-40 pct MnO-SiO2 (C/S = 1.0) system, which is used to simulate high carbon ferromanganese (HCFeMn) slag, was investigated at 1773 K (1500 °C). The production of SiO2 was stoichiometrically balanced with the consumption of MnO in the slag phase in the CaF2-containing systems based on the reaction “[Si] + 2(MnO) = (SiO2) + 2[Mn],” whereas the SiO2 production was lower than the MnO consumption in the CaO-MnO-SiO2 ternary system, which may have originated from the production of SiO gas in the latter. From the temperature dependence of the mass transfer coefficient of SiO2, the activation energy of the silicothermic reduction process was determined to be about 217.9 kJ/mol, which was very close to the activation energy reported in the literature for mass transfer in the slag phase. The mass transfer coefficient of SiO2 exhibited a maximum value at 5 mass pct CaF2, which originated from an increase in the apparent viscosity of the slag due to the precipitation of solid cuspidine at CaF2 content greater than 5 pct. Consequently, the addition of fluxing additive CaF2 should be carefully determined, because an excess of CaF2 results in the formation of cuspidine during silicothermic reactions.

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.

溶銑の脱りん速度に及ぼすCaF<sub>2</sub>添加量，温度，塩基度，生石灰粒径の影響

溶銑の脱りん速度に及ぼすCaF<sub>2</sub>添加量，温度，塩基度，生石灰粒径の影響

Effect of CaF2 Addition on the Viscosity and Structure of CaO–SiO2–MnO Slags

Effect of CaF2 Addition on the Viscosity and Structure of CaO–SiO2–MnO Slags

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.