Increasing CaF2 Content Research Articles

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.

A Biodegradable Bioactive Glass-Based Hydration Sensor for Biomedical Applications.

Monitoring changes in edema-associated intracranial pressure that complicates trauma or surgery would lead to improved outcomes. Implantable pressure sensors have been explored, but these sensors require post-surgical removal, leading to the risk of injury to brain tissue. The use of biodegradable implantable sensors would help to eliminate this risk. Here, we demonstrate a bioactive glass (BaG)-based hydration sensor. Fluorine (CaF2) containing BaG (BaG-F) was produced by adding 5, 10 or 20 wt.% of CaF2 to a BaG matrix using a melting manufacturing technique. The structure, morphology and electrical properties of the resulting constructs were evaluated to understand the physical and electrical behaviors of this BaG-based sensor. Synthesis process for the production of the BaG-F-based sensor was validated by assessing the structural and electrical properties. The structure was observed to be amorphous and dense, the porosity decreased and grain size increased with increasing CaF2 content in the BaG matrix. We demonstrated that this BaG-F chemical composition is highly sensitive to hydration, and that the electrical sensitivity (resistive-capacitive) is induced by hydration and reversed by dehydration. These properties make BaG-F suitable for use as a humidity sensor to monitor brain edema and, consequently, provide an alert for increased intracranial pressure.

Unveiling the Effect of CaF2 on the Microstructure and Transport Properties of Phosphosilicate Systems.

As an effective flux, CaF2 is beneficial in improving the fluidity of slag in the steel-making process, which is crucial for dephosphorization. To reveal the existence form and functional mechanism of CaF2 in phosphosilicate systems, the microstructures and transport properties of CaO-SiO2-CaF2-P2O5 quaternary slag systems are investigated by molecular dynamics simulations (MD) combined with experiments. The results demonstrate that the Si-O coordination number does not vary significantly with the increasing CaF2 content, but the P-O coordination number dramatically decreases. CaF2 has a minor effect on the single [SiO4] but makes the structure of the silicate system simple. On the contrary, F- ions could reduce the stability of P-O bonds and promoted the transformation of [PO4] to [PO3F], which is beneficial for making the P element-enriched phosphate network structure more aggregated. However, the introduction of CaF2 does not alter the tetrahedral character of the original fundamental structural unit. In addition, the results of the investigation of the transport properties show that the self-diffusion coefficients of each ion are positively correlated with CaF2 content and arranged in the order of F- > Ca2+ > O2- ≈ P5+ > Si4+. Due to CaF2 reducing the degree of polymerization of the whole melts, the viscosity decreases from 0.39 to 0.13 Pa·s as the CaF2 content increases from 0% to 20%. Moreover, the viscosity of the melt shows an excellent linear dependence on the structural parameters.

Effect of CaF2/P2O5 ratios on physical and mechanical properties of novel CaO–Na2O–B2O3–SiO2 glasses

This paper outlines the fabrication of bioactive glass derived from waste eggshells as a source of calcium via the melt and water quenching method. The influence of the CaF2/P2O5 ratio on the physical, structural and mechanical properties of bioglass samples was investigated. XRD confirmed the amorphous structure, while the presence of Si–O–Si, P–O, and C–O indicated the formation of bioglass samples. It was found that increasing CaF2 content with appropriate P2O5 content could improve the mechanical properties of the bioglass. The increase in density can significantly impact the bioglass samples’ compressive strength and vickers microhardness. The bioglass with CaF2/P2O5 ratio of 6/4 possessed better properties, showing the optimal compressive strength (48.98 ± 0.11 MPa) and vickers microhardness (3.09 ± 0.07 GPa), which is compatible with the human enamel and commercial bioglass. Thus, the findings seem to contribute to a prospective cost-effective waste-derived bioglass system used in dental applications.

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.

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.

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.

Manganese Recovery by Silicothermic Reduction of MnO in BaO-MnO-MgO-CaF2 (-SiO2) Slags

The effects of reducing agent, CaF2 content, and reaction temperature upon the silicothermic reduction of MnO in the BaO-MnO-MgO-CaF2 (-SiO2) slags were investigated. Mn recovery was proportional to Si activity in the molten alloy. Moreover, 90 pct yield of Mn recovery was obtained under 5 mass pct CaF2 content and 1873 K (1600 °C) reaction temperature. Increasing CaF2 content above 5 pct yielded little or no further increase in Mn recovery, because it was accompanied by increased slag viscosity owing to the precipitation of high melting point compounds such as Ba2SiO4.

Influence of CaF2 on the Viscosity and Structure of Manganese Ferroalloys Smelting Slags

Addition of CaF2 to the CaO-SiO2-MnO (CaO/SiO2 = 0.5) system, which corresponds qualitatively to a silicomanganese ferroalloy smelting slag, affected not only the critical (crystallization) temperature (TCR) but also the viscosity at high temperatures, and its influence on slag properties was strongly dependent on the content of MnO in the slag. The viscosity of CaF2-free 10 mass pct MnO slag was relatively high, i.e., about 10 dPa s at 1773 K (1500 °C), but decreased continuously upon addition of CaF2 to the system. In contrast, the viscosity of the 40 pct MnO system was very low, i.e., 1 dPa s at 1773 K (1500 °C), and CaF2 did not have a large effect. This indicates that Mn2+ is a strong network modifier in manganese ferroalloy smelting slags. Nevertheless, CaF2 addition was very effective at decreasing the viscosity of low MnO slags at low temperatures. The activation energy for the viscous flow of silicate melts decreased linearly in response to CaF2 addition, but this tendency was less pronounced in the more basic composition of the slag. The effect of CaF2 on the viscosity and activation energy for viscous flow of melts was analyzed quantitatively using micro-Raman spectra of quenched glass samples and the silicate polymerization index, i.e., Q3/Q2 ratio. The polymerization index decreased continuously with increasing CaF2 content in less basic (10 pct MnO or C/S = 0.5) slags, whereas it was not affected by CaF2 content in highly basic (40 pct MnO and C/S = 1.0) slags. Bulk thermophysical properties of the CaO-SiO2-MnO-CaF2 slags were quantitatively correlated with the structural information of the slags.

Structure, properties and crystallization of non-stoichiometric lithium disilicate glasses containing CaF2

The role of CaF2 on the structure, crystallization behaviour and properties of a relatively simple non-stoichiometric lithium disilicate (Li2Si2O5) based glass composition was studied. Different x amounts (x=0, 1, 3 and 5mol%) of CaF2 were added to (100−x) of a parent glass (22.96Li2O–2.63K2O–2.63Al2O3–71.78SiO2) composition. The glasses were produced by conventional melt-quenching technique, whilst glass–ceramics were produced via crystallization of monolithic bulk glasses.A scanning electron microscopy (SEM) examination of as cast non-annealed monolithic glasses revealed precipitation of nanosize droplet phase in glassy matrices suggesting the occurrence of liquid phase separation in all investigated compositions. The extent of phase segregation, as judged from the mean droplet diameter and the packing density of droplets, decreased with increasing CaF2 content in the glasses. A slight depolymerisation of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for CaF2. The presence of CaF2 enhanced the crystallization at lower temperatures in comparison to CaF2-free glass.

Effect of Boron Mud and CaF2 on Surface Tension and Density of CaO-SiO2-B2O3 Ternary Slag Systems

The effect of boron mud and CaF2, which were used as fluxing agents, on surface tension and density of CaO-SiO2-B2O3 ternary slag systems was investigated. The surface tension and density were measured by using the ring detachment method and Archimedean method, respectively. The results indicated that surface tension and density of the slag systems decreased with increasing temperature in the range of 1380—1480 °C. When 5%—10% CaF2 was employed as fluxing agent, the surface tension and density of slag were decreased with increasing CaF2 content, and the surface tension changed from 0.3 to 0.6 N/m, while the density changed from 3.4 to 4.1 g/cm3. However, when using 5%—10% boron mud as fluxing agent, the surface tension was enhanced, whereas the density decreased with the increase of boron mud content, and the variation range was 0.4—0.6 N/m for surface tension and 3.2—3.9 g/cm3 for the density. As a conclusion, using boron mud as fluxing agent to substitute for CaF2 did not cause significant changes in slag surface tension and density.

The influence of CaF2 content on the physical properties and apatite formation of bioactive glass coatings for dental implants

This report details the physical properties, bioactivity and biocompatibility of manufactured glasses containing a range of calcium fluoride (CaF2) concentrations. Compositions were based on the following system: SiO2, CaO, Na2O, K2O, P2O5, ZnO and MgO, and in total seven glasses were synthesized using a melt–quench route. The ratio of the base compounds was kept constant, but had increasing CaF2 concentrations (0.00, 2.44, 4.77, 9.11, 10.33, 11.53 and 13.00mol%). Glasses were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dilatometery. Density was quantified according to Archimedes method and apatite formation tested following immersion in simulated body fluid (SBF) and Tris-buffer solution. Glass coatings were prepared by enamelling technique using 10mm in diameter pure titanium disks. XRD demonstrates that all glasses are amorphous and that the sintering window, glass transition and softening temperatures decrease with increasing CaF2 content. In contrast, thermal expansion coefficient and glass density increase with CaF2 content. After 1week immersion in SBF and Tris, XRD and Fourier transform infrared (FTIR) spectroscopy showed that the surfaces of all glasses underwent structural changes with evidence of surface apatite formation. Fluoride-electrode analysis indicates that the amount of fluoride released was proportional to the original CaF2 content. The survival and growth of osteoblasts on the surface of these glasses is consistent with biocompatible characteristics.

Study on Properties of Al<sub>2</sub>O<sub>3</sub> -CaO-SiO<sub>2</sub>-CaF<sub>2</sub> Slag System

Liquidus temperature, electrical conductivity and phase composition of Al2O3－CaO－SiO2－CaF2 System were studied. The results showed that the liquidus temperature of the slag decreased with increasing CaF2 content, and its electrical conductivity increased with increasing CaF2 content and temperature. When the content of CaF2 is 20%, the liquidus temperature is 1469°C. When the contents of CaF2 is 10%，its main phase compositions are composed of Ca5Al6O14、Al2Ca3(SiO4)3、Al2(SiF6)3 and Ca3Al10O18. Ca2AlF7、Ca2Al3O6F becomes more and more with increasing the content CaF2 because of F1- replacing O2- in molten slag.

Study on Properties of Al<sub>2</sub>O<sub>3</sub> -CaO-CaF<sub>2</sub> Slag System

Liquidus temperature, electrical conductivity and phase composition of Al2O3 -CaO-CaF2 slag system were studied. The results showed that the liquidus temperature of the slag decreased with increasing CaF2 content, and its electrical conductivity increased with increasing CaF2 content and temperature. The liquidus temperature is 1468°C when the content of CaF2 is 20%. Its phase composition are composed of CaAl2O4、Ca2Al3O6F、Ca2AlF7 andAlF3. When the content of CaF2 is 10%, there are lots of CaAl2O4. The content of CaAl2O4 decreased with increasing CaF2, but the content of Ca2Al3O6F and Ca2AlF7 increased.

Structure of fluoride-containing bioactive glasses

Fluoride prevents dental cavities, stimulates bone mineralisation and decreases the melting temperature of glasses and is therefore an interesting component of bioactive glasses for use as dental or orthopaedic biomaterials. However, when designing new glass compositions, the structural role of fluoride in the glass needs to be better understood. We have characterised a glass series in the system SiO2–P2O5–CaO–Na2O with increasing concentrations of CaF2. Network connectivity was fixed at 2.13 by adding CaF2 while the ratio of all other components was kept constant. 19F and 29Si MAS NMR spectra showed that addition of CaF2 does not cause disruption of the glass network by formation of Si–F bonds but forms mixed calcium sodium fluoride species. 31P MAS NMR showed phosphate being present as orthophosphate. Hence it does not form part of the actual glass network backbone and no Si–O–P bonds are present. 23Na MAS NMR showed the presence of multiple sodium sites with an increase in the mean coordination number of sodium with increasing CaF2 content. The glass transition temperature decreased with increasing amounts of CaF2. As no Si–F bonds were formed, this can be explained by formation of hypothetical CaF+ species. The results can be used for designing new fluoride-containing bioactive glass compositions for specific applications.

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.

The effect of CaF2 on the viscosities and structures of CaO-SiO2(-MgO)-CaF2 slags

The viscosities of CaO-SiO2(-MgO)-CaF2 slags were measured to clarify the effect of CaF2 on the viscous flow of molten slags at high temperatures and the solidification behavior of slags. Furthermore, the infrared (IR) spectra of the quenched slags were analyzed to understand the structural role of CaF2 in the modification of slag structure. The CaF2 affects the critical temperature (T CR) of the slags; that is, the higher the content of CaF2, the lower the T CR of the slags. It is suggested that some extent of undercooling as a driving force is needed for the precipitation of solid particles in the melt. In the composition of B (≡(mass pct CaO)/(mass pct SiO2)) = 1.0, the T CR was decreased about 150 to 200 K by addition of 10 mass pct MgO, while the T CR was increased about 100 K by MgO addition at B = 1.3. The effect of CaF2 on the viscous flow of molten slags can be understood based on a decrease in the degree of polymerization by F− as well as by O2− ions and this was confirmed by the IR spectra of the quenched slags. The relative intensity of the IR bands for [SiO4]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO4]-tetrahedra with high NBO/Si increased with increasing CaF2 content. The decrease in viscosity of the CaO-SiO2-MgO-CaF2 (B = 1.0) system by CaF2 addition was negligible, while the effect of CaF2 on the viscosity was significant in the more basic system (B = 1.3).

On the rhombohedral-cubic phase transition of solid solutions ROFCaF2 with RGd, Tb and Dy

The rhombohedral-cubic phase transition typical of stoichiometric rare earth oxide fluorides of the formula type ROF was investigated for the ROF-based solid solution systems R1−xCaxO1+x F1+x, with RGd, Tb, Dy, by differential scanning calorimetry and by X-ray powder diffraction. It was found that the solubility limit of CaF2 in these ROF is almost identical with x⪷ 0.09 and that the transition temperatures decrease with increasing CaF2 content. At x ≈ 0.9 this decrease is approximately 290 K, 250 K and 240 K for RGd, Tb temperatures decrease with increasing CaF2 content. At x ≈ 0.9 this decrease is approximately 290 K, 250 K and 240 K for RGd, Tb and Dy, respectively, as compared to the transition temperatures of pure ROF. The formula volumes of the rhombohedral as well as the cubic solid solutions were determined as a function of x, and the structural implications of the observed trend is discussed for the rhombohedral modification. A partial tentative phase diagram is exemplarily proposed for Gd1 −xCaxO1 −x F1 −x.

ChemInform Abstract: Formation and Properties of Calcia‐Calcium Fluoride‐Alumina Glasses.

AbstractThe glass transformation temp. in the CaO‐CaF2‐Al2O3 system is found to decrease with increasing CaF2 content.

Thermal and Mechanical Properties of High Thermal Expansion ZrO<sub>2</sub>-CaF<sub>2</sub> Composite Ceramics

Thermal and mechanical properties of two-phase composite sintered-materials consisting of ZrO2 with 3mol% Y2O3 and various volume fractions of CaF2 were measured. The composites were made by hot-pressing micronized powders at 1300°C under 30MPa pressure. No phase except ZrO2 and CaF2 was observed by the X-ray diffraction method in the composites, and no crack in sintering bodies was observed by scanning electron microscope. Thermal expansion coefficient increased with increasing CaF2 content, in agreement with the prediction obtained by the Turner's equation for thermal expansion coefficients of composites. Bending strength decreased with increasing CaF2 content. The composite containing 50vol% CaF2 showed a high thermal expansion coefficient of 15×10-6/°C and a bending strength was approximately 350MPa. These properties are similar to that of stainless steel and Al2O3, respectively.