CaF2 System Research Articles

The Story, Properties and Applications of Bioactive Glass “1d”: From Concept to Early Clinical Trials

Bioactive glasses in the CaO–MgO–Na2O–P2O5–SiO2–CaF2 system are highly promising materials for bone and dental restorative applications. Furthermore, if thermally treated, they can crystallize into diopside–fluorapatite–wollastonite glass-ceramics (GCs), which exhibit appealing properties in terms of mechanical behaviour and overall bone-regenerative potential. In this review, we describe and critically discuss the genesis, development, properties and applications of bioactive glass “1d” and its relevant GC derivative products, which can be considered a good example of success cases in this class of SiO2/CaO-based biocompatible materials. Bioactive glass 1d can be produced by melt-quenching in the form of powder or monolithic pieces, and was also used to prepare injectable pastes and three-dimensional porous scaffolds. Over the past 15 years, it was investigated by the authors of this article in a number of in vitro, in vivo (with animals) and clinical studies, proving to be a great option for hard tissue engineering applications.

A modified method for calculating the viscosity of multicomponent slags based on Kriging interpolation

Model prediction is an effective method to obtain the physicochemical properties data of molten slags, which is difficult to test experimentally due to their high melting points. Empirical models are prevalent at present; however, it needs large amount of experimental data to fit the empirical parameters with narrow application scope. In this paper, the Kriging interpolation method modified with oxide property weights, is firstly introduced into the viscosity prediction of multicomponent slags. The prediction results of CaO–Al2O3–SiO2, CaO–Al2O3–CaF2, CaO–Al2O3–SiO2–MgO and CaO–Al2O3–SiO2–MgO–CaF2 systems showed that the predicted errors by the Modified Kriging Interpolation (MKI) method are smaller than those by various empirical models. It is anticipated that the MKI method can be extended to predicting the continuous physicochemical properties of multicomponent slags.

Electron passivation in CaF2 on calcium metal anodes.

Current electrolytes in calcium-ion batteries suffer from a lack of stability and degradation caused by reduction from the anode. The solid-electrolyte interphase (SEI) that forms on the anodes during operation stems the flow of electrons from the anode to the electrolyte. CaF2 is a common inorganic compound found in the SEI, and is derived from electrolyte salts such as Ca(PF6)2. CaF2 can exist in crystalline, polycrystalline, and amorphous phases in the SEI, and as recent work has shown, different phases of the same compound can have vastly different electronic conductivities. Using the non-equilibrium Green's function technique with density functional theory (NEGF-DFT), we find that amorphous phase systems enhance electron tunneling in thin CaF2 films by 1-2 orders of magnitude when compared to crystalline and polycrystalline CaF2 systems. Transport through several amorphous structures was considered showing that, despite their random structures, their conductance properties are similar. Through analysis of the decay constant β and the low-bias conductance of each system, we show that crystalline and polycrystalline CaF2 offer greater protection of the electrolyte than amorphous CaF2.

Study on the Melting Temperature of CaF2-CaO-MgO-Al2O3-TiO2 Slag under the Condition of a Fixed Ratio of Titanium and Aluminum in the Steel during the Electroslag Remelting Process.

During the process of electroslag remelting (ESR) of steel containing titanium and aluminum, the activity ratio between titania and alumina in CaF2-CaO-MgO-Al2O3-TiO2 slag must be fixed in order to guarantee the titanium and aluminum contents in the ESR ingots. Under the condition of fixed activity ratio between titania and alumina in the slag, the melting temperature of slag should be investigated to improve the surface quality of ESR ingots. Therefore, this paper focuses on finding a kind of slag with low melting temperature that can be used for producing steel containing titanium. In the current study, the thermodynamic equilibrium of 3[Ti] + 2(Al2O3) = 4[Al] + 3(TiO2) between SUS321 steel and the two slag systems (CaF2:MgO:CaO:Al2O3:TiO2 = 46:4:25:(25 − x):x and CaF2:MgO:CaO:Al2O3:TiO2 = 46:4:(25 − 0.5 x):(25 − 0.5 x):x) are studied in an electrical resistance furnace based on Factsage software. After obtaining the equilibrium slag with fixed activity ratio between titania and alumina, the melting temperatures of the two slag systems are studied using slag melting experimental measurements and phase diagrams. The results show that the slag systems CaF2:MgO:CaO:Al2O3:TiO2 = 46:4:25:(25 − x):x, which consists of pre-melted slag S0 (CaF2:MgO:CaO:Al2O3 = 46:4:25:25) and pre-melted slag F1 (CaF2:MgO:CaO:TiO2 = 46:4:25:25), can not only control the aluminum and titanium contents in steel, but also have the desired low melting temperature property.

Structure and crystallization of glassy La2O3–CaO–SiO2–CaF2 system rare-earth slag with variable rare-earth content

Raman spectroscopy and differential scanning calorimetry were employed to investigate the structure, crystallization behavior and crystallization activation energy of the La2O3–CaO–SiO2–CaF2 (RE) slags with different RE contents. Raman spectroscopy analysis indicated that the RE oxide, La2O3, acted as a network modifier, with the increase in La2O3 content decreasing the degree of polymerization of the RE slag. As the La2O3 content increased, the number of highly polymerized Q2 and Q3 species gradually decreased, while the minimally polymerized Q0 and Q1 species increased, and depolymerizing the complex network structure in the slag. The slag mainly contained the following three crystal phases: (Ca, La)5(SiO4)6F, CaSiO3, and Ca4Si2O7F2. When the La2O3 content increased to 15%, an additional Ca2SiO2F2 crystalline phase appeared. Furthermore, an increase in the La2O3 content from 10 to 17% reduced the crystallization temperature of the RE phase in the slag from 1641 to 1599K. The crystallization behavior of the RE phase under different cooling rates revealed that the increase in La2O3 content reduced the effective crystallization activation energy of the RE phase, thus enhancing the crystallization of the RE phase. Thus, a correlation between the structure and crystallization of the RE slag was established.

Synergetic strengthening mechanism of ultrasound combined with calcium fluoride towards vanadium extraction from low-grade vanadium-bearing shale

The effect and mechanism of ultrasound and CaF2 on vanadium leaching from vanadium-bearing shale were investigated systematically. In consideration of the enhancement for vanadium recovery, the combination of ultrasound and CaF2 (66.28%) exerts more evident effects than ultrasound (26.97%) and CaF2 (60.35%) alone, demonstrating the synergetic effect of ultrasound and CaF2. Kinetic analysis manifests that the product layer diffusion controls vanadium leaching in ultrasound system without CaF2, however product layer diffusion and interfacial reaction is the rate-controlling step for vanadium leaching in other three leaching systems. The combination of ultrasound and CaF2 notably decreases the activation energy (Ea) from 62.03 to 27.61 kJ/mol, nevertheless individual CaF2 only reduces the Ea to 50.70 kJ/mol. X-ray diffraction and fourier transform infrared spectrometer analyses show that the decomposition degree of the vanadium-bearing mica structure is the most significant in ultrasound and CaF2 system, proving the highest release degree of vanadium. Specific surface area and pore distribution combined with scanning electron microscope analyses reveal that the action of ultrasound and CaF2 would provide higher specific surface area, more abundant pores structure and cracks for the particles, which further prompts the rapid diffusion of H+, F− and HF, and achieves the conspicuous improvement of vanadium leaching recovery.

Effect of Fluorine on Melt Structure for CaO–SiO<sub>2</sub>–CaF<sub>2</sub> and CaO–Al<sub>2</sub>O<sub>3</sub>–CaF<sub>2</sub> by Molecular Dynamics Simulations

The melt structure with fluorine addition has been investigated using molecular dynamics (MD) simulation for the CaO–SiO2–CaF2 and CaO–Al2O3–CaF2 ternary slag system. By analyzing the coordination number of the network framework, the results indicate that the structure of Si–O tetrahedron is more stable than the structure of Al–O tetrahedron. F− ions are dominantly coordinated with Ca2+, there is a dynamic equilibrium between Ca2+ and the coordination anions (O2− and F−) in both systems, and the total coordination number (CN) is maintained between 6 and 7. The analysis of the distribution of oxygen types demonstrates the degree of polymerization (DOP) of network structure in CaO–SiO2–CaF2 system is lower than that in CaO–Al2O3–CaF2 system. Although the addition of CaF2 can lower the viscosity of both slag systems, the microscopic reasons for that are completely different: in CaO–SiO2–CaF2 system, CaF2 actually acts as network diluent, and creates the space where particles can move longer. But in CaO–Al2O3–CaF2 system, CaF2 can depolymerize the network structure of the melt.

Phase chemistry of Submerged Arc Welding (SAW) fluoride based slags

Phase chemical analysis of post-weld slags from Submerged Arc Welding (SAW) is applied to explain the chemical function of flux constituent compounds in the welding process. FactSage 6.4 calculations were used to aid in the interpretation of the phase chemical analyses. Five commercial agglomerated fluxes from two suppliers were used. These fluxes cover three types of fluoride based flux classes: Fluoride Basic flux, Aluminate Basic flux and Aluminate Rulile flux. Basic fluxes are based in the SiO2–Al2O3–MgO CaF2 system. The slag liquidus lowering effect of CaF2 is 19 °C/%CaF2 in the Fluoride Basic fluxes, and 4 °C/%CaF2 in the Aluminate Basic fluxes. The Aluminate Rutile flux is based in the SiO2–Al2O3–MgO–TiO2–MnO–CaF2 system. Little CaF2 addition is used in this flux since TiO2 addition lowers its liquidus temperature sufficiently. The level of CaF2 addition sets the quantity and chemistry of fluoride gas compounds formed. The main gas fluoride gas species expected to form in welding with the five fluxes are CaF2, MgF2, NaF, KF, NaAlF4, and AlF3. In addition, TiF3 is expected to form in welding with the Aluminate Rutile flux, indicating the importance of titanium oxidation state in fluoride gas formation.

Fluorite deposits in the Zhejiang Province, southeast China: The possible role of extension during the late stages in the subduction of the Paleo-Pacific oceanic plate, as indicated by the Gudongkeng fluorite deposit

Southeast China with its widespread occurrences of Mesozoic igneous rocks, is one of the largest magmatic provinces worldwide, containing a large variety of mineral types, including hypothermal W-Sn, porphyry Cu, epithermal Au deposits. The Gudongkeng deposit is an example consisting of fluorite mineralisation trending SE over a distance of about 6 km. The major minerals in the deposit include fluorite and calcite of a hydrothermal origin and interpreted as a vein-type deposit associated with the Linghou Granite that yields a zircon U–Pb date of 100 ± 1 Ma, but intriguingly the fluorite yields an Sm–Nd isochron age of 73 ± 3 Ma, placing the genesis of the fluorite as a post-magmatic event. Fluid inclusions in the fluorite have low homogenisation temperatures of 104–195° C, salinities of 0.5 to 2.24 wt% NaCl eqv., and densities of 0.67–0.94 g/cm3. The inclusions contain NaCl–H2O–CaF2 with δDV-SMOW values between −64.3 and-50.1‰ and δ18OV-SMOW values between −7.6 and −2‰. The initial 87Sr/86Sr ratios of the fluorite range from 0.709816 to 0.710165 are characteristic of a crustal contribution. The ore-forming fluids can be mainly attributed to a NaCl–H2O–CaF2 system of moderate to low temperature, low salinity, and low density. The ore-forming fluid has a meteoric water source, with the reaction between the fluid and wallrocks being the main mechanism for fluorite precipitation at relatively low temperatures. Gudongkeng is a low temperature epithermal deposit which was formed in an extensional setting within the Cathaysia Block during the Late Cretaceous.

Analysis of the influence of the solid and liquid phases on steel desulfurization with slags from the CaO–Al2O3 systems using computational thermodynamics

Normally, CaO is used in steel desulfurization in slags from the systems: CaO–CaF2, CaO–Al2O3, and CaO–SiO2. Among these, the CaO–CaF2 slags are more efficient. This paper uses computational thermodynamics to study the influence of solid and liquid phases in the efficiency of desulfurizing slags in the CaO–Al2O3 system. Desulfurizing slags were prepared to produce steels with sulfur levels below 20ppm. Simulations using computational thermodynamics were made to determine the properties of the slags at 1600°C. The experimental tests were carried out in an induction furnace at 1600°C. The experimental results showed that slags from CaO–Al2O3 system can be as efficient as slags from CaO–CaF2 system, reaching final sulfur contents lower than 10ppm. The conclusion was that slags containing higher quantities of liquid phase are more efficient. However, the presence of some amount of solid CaO is necessary to keep the liquid phase of slag always saturated in CaO and its activity equal to unity. A Steel Desulfurization Factor was proposed as an easy way to estimate the desulfurization efficiency.

Geometrical modelling of the physicochemical properties of CaO–Al2O3–CaF2 slag at 1873K

CaO–Al2O3–CaF2 system is the most basic slag system for electroslag remelting (ESR). Its physicochemical properties, such as viscosity, electrical conductivity and sulfide capacity are all critical to the control and optimization of ESR process. However, it is difficult to obtain all these data through experiment. In this article, an extended geometrical model is introduced for the prediction of these three properties, while three empirical models for various properties are also used for comparison. The present model shows better agreements with the experimental data than the other three empirical models with the mean deviations being 11.0%, 11.2% and 1.7% for viscosity, electrical conductivity and sulfide capacity respectively. The contour lines of various properties are also calculated by the present model. It is anticipated that the introduction of the present model will simplify the calculation of physicochemical properties of metallurgical slags and promote the optimization of ESR process greatly.

Sol–gel-derived mineral scaffolds within SiO2–P2O5–CaO–MgO–ZnO–CaF2 system

Ceramic scaffolds were prepared starting from a sol–gel powder, which was mixed with glucose as a pore-generating substance and subsequently thermally treated at different temperatures and for different periods in order to ensure the formation of a resistance structure. The final materials were characterized in terms of structure, morphology, and biological properties by employing X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, immersion in simulated body fluid, and specific cellular tests on mesenchymal stem cells (optical microscopy, MTT, and GSH assays). The results showed the occurrence of akermanite as the main crystalline phase in all scaffolds. The porosity and compression strength of these 3D architectures can be adjusted through the thermal treatment parameters. Moreover, the biological evaluation indicated an excellent bioactivity and a good biocompatibility at short term for all samples.

Akermanite-based coatings grown by pulsed laser deposition for metallic implants employed in orthopaedics

The aim of the present paper is to develop ceramic thin films by laser ablation in order to improve the biological behaviour of metallic implants dedicated to hard tissue restoration. The composition of the coatings was selected within SiO2–P2O5–CaO–MgO–ZnO–CaF2 system, while their processing has gone through two stages: target preparation via a wet chemistry approach and films deposition through a physical deposition method, on titanium substrates. The characteristics of the final layered structures were evaluated by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy and selected area electron diffraction. In vitro investigation techniques were employed for the bioactivity and biocompatibility assessment. The results indicated the growth of nanostructured akermanite-based thin films with an excellent bioactivity and a good effect on stem-type cells, which validates the suitability of such structures for medical implant applications.

Preparation and Characterization of Eu3+-Doped Transparent Oxyfluoride Glasses

A process has been proposed for the preparation of oxyfluoride glasses based on the SiO2–B2O3–Bi2O3–ZnO–CaF2 system at various ratios of batch components, and transparent glasses have been obtained at a temperature below 1000°C. According to X-ray diffraction data, all of the glasses are X-ray amorphous. The surface morphology of the glasses has been examined and their glass transition temperatures have been determined. Their local structure has been studied by IR spectroscopy and it has been shown that, independent of composition, the glasses contain complex polyborate anions formed by [BO3] and [BO4] groups. Bismuth is incorporated into the glass network to form Bi–O–Si bonds and [BiO6] network-formers.

Photoluminescence properties of Mn2+/Yb3+ co-doped oxyfluoride glasses for solar cells application

Mn2+/Yb3+ co-doped oxyfluoride glasses were facilely synthesized in the SiO2–Al2O3–Na2O–CaF2 system. Partial crystallization processed during the preparation of the glasses, by which small amounts of CaF2 nano-crystals were formed. Under ultraviolet and blue (370–500 nm) light excitation, an efficient down-conversion involving the emission of near-infrared is realized in the Mn2+/Yb3+ co-doped oxyfluoride glasses. The near-infrared emission peaks mainly at 976 nm and secondarily at 1020 nm, which is a comfortable match with the band gap of c-Si. The variation in visible and near-infrared spectra and the decay curves of Mn2+:4T1 → 6A1 emission have been investigated to verify the possible energy transfer from Mn2+ ions to Yb3+ ions. On analyzing the energy transfer processes theoretically and experimentally, we propose that quantum cutting and down-shifting processes may occur simultaneously in the samples. We suggest that the Mn2+-Yb3+ co-doped materials can provide a novel direction to realize UV–Vis to NIR down-conversion for Si solar cells.

The Properties of the New Composite Antifriction Parts for Printing Equipment’s Friction Units

The paper summarizes the formation of new materials’ structure and properties after using a new hot isostatic-pressing technology. It shows the efficiency of the developed technology of production and the following heat treatment for the new high speed bearings, which is confirmed by the results of complex experimental and industrial tests. Such technology is able to ensure the high and stable level of the functional properties.The experimental results of the new composite bearing material’s properties in a comparison with the already known nickel composite have been presented. The article shows that the dense friction films were formed on the contact surfaces during tribological tests. All the friction surfaces are covered by the dense antiscoring films, the so-called as secondary structures. They consist of the chemical elements of bearing and counterface, and solid lubricant СаF2. During the friction process, the different chemical reactions took place between O2 of the air and elements of researched specimen and steel R18 counterface at high rotation speeds and loads. Such chemical processes result in formation of friction films, which protect contact pairs against intensive wear and stabilize a work of friction unit in printing machine.So, we have developed a new effective bearing materials, based on Ni alloy ЕP975–CaF2 system with high physical mechanical and tribotechnical properties performing well in more severe conditions than the already known sintered alloy. The new materials have an advantageous level of tribotechnical characteristics due to the tribofilms formed on the contact surfaces by dragging of calcium fluoride to cover the entire friction area.The full-scale industrial tests of ЕP975–CaF2 bearings showed increase in wear resistance by a factor up to 10 compared with the already known bearings in high speed printing machines’ friction units (in particular, Heidelberg Speedmaster SM-102-FPL and KBA Rapida-105) at a load up to 5 MPa and a rotation speed up to 6000 rpm.

Phase diagram of the NaF–CaF2 system and the electrical conductivity of a CaF2-based solid solution

The phase diagram of the NaF–CaF2 system was studied by thermal analysis and X-ray powder diffraction analysis with the determination of the chemical composition. The system was found to be of the eutectic type. A narrow range of the existence of solid solution Ca1–xNaxF2–x was established. The NaF solubility reaches a maximal value of x = 0.035 at 1200 ± 50°C (the temperature at which there is a diffuse phase transition in fluorite). At 920 ± 25°C, the NaF solubility reaches a minimum (<0.4 mol %) and increases again to 2.2 ± 0.2 mol % at a eutectic temperature (818°C). The ionic conductivity increases by three orders of magnitude after adding NaF to CaF2.

Ionic mobility and conductivity in PbSnF4 doped with CaF2 from the NMR and impedance spectroscopy data

The ionic mobility and conductivity in the crystalline phases of PbSnF4–x CaF2 systems (x = 2.5 mol.%, 5 mol.%, 7.5 mol.%, and 10 mol.%) in the temperature range of 150-500 K are studied by NMR and impedance spectroscopy. The parameters of 19F NMR spectra, types of ion motions, and ionic conductivity in the PbSnF4 compound doped with calcium fluoride are found to be determined by the temperature and concentration of calcium fluoride. The specific conductivity of the crystalline phases in the PbSnF4–CaF2 systems is rather high at room temperature, and hence, one cannot exclude the possibility to use them for the creation of functional materials with a high ionic (superionic) conductivity.

Influence of ZrO2 oxide on the properties and crystallization of calcium fluoro-alumino-silicate glasses

The impact of ZrO2 content of the glass on the formation, properties and crystallization of glass ionomer cements (GICs) was investigated. Glass series based on SiO2–Al2O3–ZrO2–P2O5–CaO–CaF2 system was synthesized and studied. The cements were characterized using a setting time, flexural strength, fracture toughness and in vitro biocompatibility test. The setting time of the ionomer cement increased with increasing the ZrO2 content of the glass. The cements showed a slight decrease of cell biocompatibility with increase the ZrO2 oxide content in the glasses. The results also showed that the flexural strength and the fracture toughness of the cements increased with immersion time and ZrO2 oxide content. The crystallization characteristics of the glasses were investigated by differential scanning calorimeter (DSC) and X-ray diffraction analysis (XRD). The addition of ZrO2 oxide in the glasses led to increase both the glass transition and crystallization temperatures. Fluorapatite [Ca5(PO4)3F], mullite [Al6Si2O13], cristobalite [SiO2] and zircon [ZrSiO4] phases were crystallized from the investigated glasses. The role played by the glass oxide constituents in determining the setting time, mechanical properties and crystallization characteristics of the prepared glass ionomer was discussed.

Apatite formation of bioactive glasses is enhanced by low additions of fluoride but delayed in the presence of serum proteins

Five bioactive glass compositions in the SiO2–P2O5–CaO–Na2O–CaF2 system (0–32mol% CaF2) and Bioglass® 45S5 were evaluated for their apatite forming ability in serum-free and serum-containing cell culture media for up to seven days. While F− ions in low concentrations were found to enhance apatite formation, higher fluoride content caused formation of fluorite and calcite. The presence of serum proteins delayed apatite precipitation for all compositions, while Bioglass® 45S5, despite considerably higher phosphate content (2.6 vs. ≤1.1mol% P2O5) and high concentrations of Ca2+ and PO43− in solution, formed only amorphous calcium phosphate.