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Studies conducted in NaF-containing hydrothermal fluids have shown that the oxide compounds Sb5+ are unstable at 800 °C, Рtotal = 200 MPa and fO2 (fH2) specified by Co–CoO and Ni–NiO buffers interact with the Pt material of the ampoule, forming antimony intermetallics with platinum on the inner surface of the ampoule. The formation of the following intermetallics was established through the analysis of data obtained from studies conducted on an electronic microscope: Pt90.3±0.8Sb9.7 (~ Pt10Sb), Pt82.8±1.3Sb17.2 (~ Pt5Sb) and Pt69.2±4.4Sb30.8. Pt10Sb compound which was obtained on the inner surface of the Pt ampoule is the limiting solid solution of antimony in platinum at 800 °C. It exhibits a cubic crystal system with a lattice constant of a = 3.943(3) Å and forms an underdeveloped surface < 111>. Pt5Sb compound, presumably hexagonal P6/mmm crystal system with unit cell parameters a = b = 4.56(4), c = 4.229(2) Å, α = β = 90°, γ = 120°, forms a thin film (≤ 10 μm) on the Pt surface and appears to be a metastable phase. The intermetallic compound of Pt69Sb31 is a rapidly cooled melt of appropriate composition. A mechanism for deep penetration of Sb into the walls of the Pt ampoule is proposed. [ABSTRACT FROM AUTHOR]

The Tianshanbeilu cemetery is the largest Bronze Age cemetery in eastern Xinjiang, China, and plays important roles in connecting the Eurasian interior to the Hexi Corridor, and further to the Central Plains region. Utilizing micro-XRF and Raman spectroscopy techniques, we identified a fluorite bead at this cemetery. This barrel bead is the earliest record of such a fluorite bead in China, dating back to approximately 1385–1256 BCE. Comparing the unearthed records of fluorite beads in eastern China spanning from the Neolithic Age to the Western Zhou dynasty, we notice that in the early Western Zhou period, fluorite beads found in élite burials are only in barrel or biconical shapes, both of which first appeared in the eastern region of Xinjiang, such as the Tianshanbeilu cemetery in Hami and the Yanghai cemetery in the Turpan Basin. We proposed that the barrel fluorite bead drilled by metal tubular drill first appearing in the Tianshanbeilu cemetery might have spread eastward to the Central Plains region and finally constituted a component of the ritual revolutions during the Western Zhou dynasty. [ABSTRACT FROM AUTHOR]

The maximum values of the mobility and concentration of charge carriers in fluoride superionic conductors of the fluorite (CaF2, SrF2, BaF2, and PbF2) and tysonite (LaF3) structural types have been calculated within the crystallophysical model. It is shown that the upper limits of the ionic conductivity and carrier mobility and concentration in the crystalline state of fluoride superionics are, respectively, 4 ± 1 S/cm, (5 ± 1) × 10−3 cm2/(V s), and (5 ± 2) × 1021 cm−3 (10 ± 4% of the total amount of fluorine ions). [ABSTRACT FROM AUTHOR]

This article considers the features and fundamental difficulties of studying low-temperature phase equilibria associated with an exponential increase in the required duration of syntheses with a decrease in temperature. Methods for accelerating the achievement of equilibrium, including the use of salt solvents, are also considered. The results of phase equilibria studies in the SrF2–LaF3 system using sodium nitrate and in the ZrO2–Sc2O3 system using sodium sulfate as fluxes are presented. The methods of extrapolation of phase diagrams to absolute zero temperature in accordance with the third law of thermodynamics are considered. Phase diagrams of the Au–Cu, Cu–Pd, Ni–Pt, and ZrO2–Y2O3 systems are presented. Phase equilibria with plagioclase ordering are considered separately, and the phase diagram of the albite–anorthite (NaAlSi3O8–CaAl2Si2O8) system is presented. As the temperature approaches absolute zero, the homogeneity region of labradorite shrinks to the compound NaCaAl3Si5O16. [ABSTRACT FROM AUTHOR]

The ionic mobility and conductivity of composites and compounds of the eutectic and close composition obtained by different methods in the PbF2–SnF2 system are studied based on the 19F NMR and impedance data. The stages of transformation of the 19F NMR spectra of these samples, their connection with the types of ionic movements, and the possible factors determining their ionic conductivity are considered. It is shown that the composition of the majority of composites includes the fluorite phase characterized by the high values of ionic mobility and conductivity. In the region close to the eutectic, a single-phase sample with the fluorite structure is obtained for the first time. The conductivity of this phase (5 × 10–3 S/cm at 390 K) makes it possible to consider it as the basis for synthesizing functional materials. [ABSTRACT FROM AUTHOR]

Flotation separation of calcite from fluorite is a challenge on low-grade fluorite flotation that limits the recovery and purity of fluorite concentrate. A new acid leaching–flotation process for fluorite is proposed in this work. This innovative process raised the fluorite's grade to 97.26wt% while producing nanoscale calcium carbonate from its leachate, which contained plenty of calcium ions. On the production of nanoscale calcium carbonate, the impacts of concentration, temperature, and titration rate were examined. By modifying the process conditions and utilizing crystal conditioning agents, calcite-type and amorphous calcium carbonates with corresponding particle sizes of 1.823 and 1.511 µm were produced. The influence of the impurity ions Mn2+, Mg2+, and Fe3+ was demonstrated to reduce the particle size of nanoscale calcium carbonate and make crystal shape easier to manage in the fluorite leach solution system compared with the calcium chloride solution. The combination of the acid leaching–flotation process and the nanoscale calcium carbonate preparation method improved the grade of fluorite while recovering calcite resources, thus presenting a novel idea for the effective and clean usage of low-quality fluorite resources with embedded microfine particles. [ABSTRACT FROM AUTHOR]

Optically transparent single-crystal blocks are prepared by the fusion of a barium fluoride charge with yttrium and erbium fluorides using sodium fluoride as a flux. The crystal structures were solved and composition of the following phases were determined: Na0.75Ba1.26Er1.99F9.24 (cubic crystal system, space group, a = 11.4192(4) Å), Na0.25BaY2.75F10.5 (cubic crystal system, space group, a = 11.4350(19) Å), Na0.05Ba0.9Y1.05F5 (orthorhombic crystal system, Cmmm space group, a = 5.7205(5) Å, b = 17.2348(11) Å, c = 5.7648 (4) Å). [ABSTRACT FROM AUTHOR]

The congruent melting compositions in the MF2–M'F2–RF3 systems (M ≠ M' = Ca, Sr, Cd, Ba, Pb; R are rare-earth elements (REEs)) have been determined based on thermodynamic topological analysis. Crystals of fluorite solid solution in the PbF2–CdF2–RF3 (R = Tb, Ho, Er, Tm, Yb, Lu) systems were grown by the vertical directional crystallization technique. Their phase composition and distribution of components over the crystalline boule length were investigated. Crystals of congruently melting solid solutions (Pb0.67Cd0.33) RxF (R = Tb, Ho, Er, Tm, Yb, Lu) were grown for the first time. Traces of low-temperature transformation—a phase isostructural to the Pb2YF7 compound (sp. gr. I4/m), in which Y sites are occupied by the corresponding R cations and Pb sites can be partially occupied by Cd cations—were found in the crystals with R = Ho, Er, Tm, and Yb. The crystals with R = Tb and Lu have a high degree of homogeneity and are suitable for optical studies. [ABSTRACT FROM AUTHOR]

New data on roméite (CaNa)Sb2O6F solubility in the NaF–H2O system of P–Q type have been obtained within a wide range of sodium fluoride concentrations (from 0 to 25 wt % NaF). The concentration of antimony, in equilibrium with roméite and fluorite, in the range of NaF concentrations from 1 to 8 mol kg–1 H2O (25 wt % NaF), is in the range of 0.02–0.2 mol kg–1 H2O. According to the data, the concentration of antimony in phases L1 and L2 in the region of fluid immiscibility of the NaF–H2O system at 800°C, 200 MPa and fO2 = 50 Pa, specified by the Cu2O–CuO buffer, is 0.4 and 2.1 wt % Sb, respectively. Our experiments were the first ever to produce skeletal fluorite crystals and the intermetallic compound Pt5Sb, which belongs the hexagonal crystal system and has the following lattice parameters (LP): a = b = 4.56(4) Å, c = 4.229(2) Å, and α = β = 90°, γ = 120°. Pentaplatinum antimonide was formed on the inner surface of the Pt capsules at 800°C, Р = 200 MPa, and fO2 ≤ 10–3.47 Pa (Cu–Cu2O buffer) in experiments on the incongruent dissolution of roméite, which causes a sharp decrease (more than 1000 times) in antimony concentration in the solution. [ABSTRACT FROM AUTHOR]

Late Devonian felsic volcanic rocks of the Grand Beach complex (GBC) of Avalonia from the Burin Peninsula, southeastern Newfoundland (northwestern Appalachians) are part of an overstep sequence overlying the Neoproterozoic basement. The volcanic complex is composed of volcanic and volcaniclastic rocks deposited in a post-tectonic extensional setting proximal to the St. Lawrence granite (SLG), a Devonian pluton associated with a prominent vein-type fluorite mineralization. The volcanic rocks are alkali rhyolites, which are weakly peraluminous and exhibit geochemical characteristics of A-type felsic magmas, such as low FeOt, MgO, CaO, and TiO2 but high contents of alkalis, Nb, Y, and Zr and high Ga/Al and FeOt/MgO ratios. They have positive ɛNd(t) values (~ + 2.5) and their Nd-depleted mantle model ages (~ 0.9 Ga) are consistent with derivation of the parental magma from metasomatized dry Avalonian lower crustal basement via partial melting followed by fractional crystallization. The U–Pb zircon age for the volcanic complex (375.6 ± 1.1 Ma) is closely comparable to the age of the SLG, suggesting that they were emplaced during the same magmatic episode. They also have similar chemical and isotopic compositions, suggesting that the GBC represents a volcanic equivalent of the SLG. The compositional differences between the volcanic rocks and the main phase of the granite pluton, including higher oxidation state of the GBC, reflect the interaction of the parental magma with crustal material and fluids. The close proximity of SLG and GBC suggests that the volcanic complex could host fluorite mineralization. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This document is a correction notice for an article titled "Evaluation of the antibacterial activity of Enamelast® and Fluor defender® fluoride varnishes against Streptococcus mutans biofilm: an in vitro study in primary teeth" published in the European Archives of Paediatric Dentistry. The correction states that certain figures of Scanning Electron Microscopy in the original version of the article have been replaced. The corrected version of the article is now available. The publisher, Springer Nature, remains neutral in terms of jurisdictional claims and institutional affiliations. The authors of the article are M. A. Matar, S. S. Darwish, R. S. Salma, and W. A. Lotfy. [Extracted from the article]

Analyses of fluorine concentrations in the waters of the Dead Sea and Lake Urmia yielded the values of 5.3 ± 0.1 and 10.5 ± 0.1 mg/L, which in terms of the mass of the salt residue gives 15.9 and 26.0 mg F per 1 kg of anhydrous salts. Fluorine concentration in the salt residue of water in the examined hypersaline water bodies is far less than that for the normal seawater (37.1 mg F/kg). Experimental data show that the waters of the Dead Sea and Lake Urmia are strongly undersaturated in CaF2, because of which spontaneous chemogenic precipitation of fluorite in them is impossible. [ABSTRACT FROM AUTHOR]

The possibilities of the mechanochemical synthesis of new fluorine-conducting solid electrolytes based on tysonite and fluorite structures were considered. For the first time, solid solutions in the CeF3–SnF2 system with SnF2 content of 5–30 mol % were synthesized. The possibility of stabilizing the structure of fluorite in solid solutions based on lead(II) fluorine under the conditions of mechanochemical synthesis has been demonstrated. [ABSTRACT FROM AUTHOR]

At present, the separation technology of fluorite and calcite is still immature, and the research in this paper can promote the improvement of the separation technology of fluorite and calcite. The selective inhibition mechanism of tannin and humate sodium on calcite was studied by means of actual ore flotation test, single mineral flotation test, Zeta potential measurement and FT-IR spectroscopy. The results show that the mixture of tannin and sodium humate inhibitor has a good inhibitory effect on carbonate under weak alkaline condition. The reaction products of sodium humate, tannin and calcium ions in solution interact with organic compounds adsorbed on the surface of calcite, forming multilayer adsorption on the surface of calcite, making calcite more hydrophilic. Based on density functional theory, Materials Studio (MS) was used to calculate the relevant adsorption energy, and the result was as follows: (a) compared with fluorite, tannin and humate sodium molecules are more easily adsorbed on the surface of calcite. (b) Compared with calcite alone adsorption of tannin molecules or sodium humate molecules, the adsorption state will be more stable, and the effect of tannin and sodium humate synergistic inhibition of calcite is better than the effect of inhibition alone. Therefore, using tannin and sodium humate as a combination inhibitor can effectively separate fluorite and calcite, which will promote the development and utilization of fluorite ore in industry. [ABSTRACT FROM AUTHOR]

CeO2 and Y:ZrO2 (YSZ) fluorite films were deposited on NdGaO3 (NGO) tilted-axes substrates by pulsed laser deposition technique after oxygen or vacuum annealing, the orientation features of the resulting films were studied. The fluorite films on oxygen-annealed substrates showed good agreement with the graphoepitaxial growth mechanism. An excessive tilt over the calculated values is observed for substrate tilt angles of 10°–15°, presumably as a result of generation of regular dislocations. On vacuum-annealed substrates the YSZ films showed no additional tilt, instead a re-orientation towards (012) and (013) crystallographic planes of the film is observed for tilt angles 13°–15° and 18°–20°, respectively. Similar effects are observed for CeO2 films after relaxation at critical thickness. The CeO2 films on vacuum annealed substrates are seeded with alignment of (111) plane with the (110) plane of the substrate instead of standard (001) CeO2 plane. Some part of the CeO2 grains is oriented with the (111) plane along the substrate surface. The angular vicinity of a small-index crystallographic plane to the graphoepitaxial tilt value may result in an "accidental" epitaxial alignment. [ABSTRACT FROM AUTHOR]

The technological process of steel smelting at "ArcelorMittal Temirtau" JSC includes three stages: converter smelting of semi-finished products, ladle treatment, and continuous casting of slabs. According to the current technology, a desired flowability of the refining slag is created in the ladle-furnace unit by thinner additives, such as fluorspar. When using fluorspar, toxic fluorine emissions aggravate the environmental situation at the worksite. In addition, the presence of fluoride compounds in the slag adversely affects the durability of the ladle lining. Without modifying the technological process and the consumption of slag-forming agents (lime), solid slag mixtures, based on aluminum oxide, can be used in the ladle-furnace unit to eliminate fluorine emissions into the workshop atmosphere, neutralize the negative effect on the resistance of the ladle lining slag belt, as well as reduce the cost of steel due to the refusal of fluorspar and reduced consumption of aluminum for slag deoxidization. [ABSTRACT FROM AUTHOR]

We present the status of research and development of a new highly efficient liquid scintillator based on linear alkylbenzene and organosilicon scintillation fluor, so called NOL (Nanostructured Organosilicon Luminophore). The measurements of the emission kinetics under irradiation by gamma-quanta and alpha-particles were performed. The results of long term stability measurements are decribed. [ABSTRACT FROM AUTHOR]

Purpose: The aim of the current work was to compare the antibacterial activity of Enamelast® and Fluor defender® fluoride varnish on biofilm generation by Streptococcus mutans on extracted primary teeth. Methods: Thirty-six primary molars were collected and sliced into seventy-two test model disks. All specimens were examined, and the cracked or broken ones were discarded. A total number of specimens (n = 54) were divided into two experimental analyses viz; biofilm formation (n = 27) and microscopic examination (n = 27). Specimens of each analysis were tested under different experimental conditions: a negative control group (n = 9), Fluor defender group (n = 9), and Enamelast group (n = 9). Following treatment, biofilms were generated by adherent Streptococcus mutans on the test model disks on three time intervals: 24 h (n = 3), 48 h (n = 3), and 72 h (n = 3) for each analysis. Then, for biofilm formation analysis, the biofilm was detected spectrophotometrically at 620 nm after being stained by crystal violet. For microscopical analysis, the surfaces of the test model disks were visualized by scanning electron microscopy (SEM), and each image was processed and analyzed using ImageJ software. Results: At 48 and 72 h, Enamelast® and Fluor defender®-treated group showed significantly (p < 0.001) slight adhered bacterial cells when compared with the negative control group as revealed by the absorbance and SEM. Compared with the Fluor defender®-treated group, the absorbance of the Enamelast®-treated group showed a significant (p < 0.001) increase by approximately 7- and 16.5-fold at 48 and 72 h, respectively. Similarly, SEM showed that the number of bacterial cells adhered to enamel surfaces in the Fluor defender®-treated group was significantly (p < 0.001) fewer than the Enamelast®-treated group by approximately 36.55% and 20.62% at 48 and 72 h after exposure, respectively. Conclusion: We conclude that the anti-biofilm activity of Fluor defender® against Streptococcus mutans was significantly (p < 0.001) greater than Enamelast® fluoride varnish. The use of Fluor defender® is encouraged as a preventive measure in children with the high risk of developing dental caries. [ABSTRACT FROM AUTHOR]

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The available data on the fluorite potential of the Khabarovsk krai, the Jewish Autonomous Region and Amur oblast have been synthesized. Fluorite deposits and occurrences were ascribed to the rare-earth–fluorite, beryllium–fluorite, fluorite–tin-ore, base-metal–fluorite, and fluorite mineralization types. Fluorite also occurs in the ore and phosphorite deposits of the fluorite-bearing mineralization type. The features of their localization in different tectono-stratigraphic areas of the region are shown. Fluorite-bearing districts were identified and their economic potential was assessed. Most promising fluorite occurrences are located along the periphery of the Siberian platform and in the southern part of the Bureya massif. Inferred fluorite resources were calculated and the prospects for their industrial development were estimated. [ABSTRACT FROM AUTHOR]

The scale-free ferroelectric polarization of fluorite MO2 (M = Hf, Zr) due to flat polar phonon bands are promising for nonvolatile memories. Defects are also widely introduced to improve the emergent ferroelectricity. However, their roles are still not fully understood at the atomic-level. Here, we report a significant effect of point-defect-driven flattening of polar phonon bands with more polar modes and polarization contribution in doped MO2. The polar phonon bands in La-doped MO2 (M = Hf, Zr) can be significantly flattened, compared with pure ones. However, the lower energy barrier with larger polarization of VO-only doped MO2 compared with La-doped cases suggest that VO and local lattice distortion should be balanced for high-performance fluorite ferroelectricity. The work is believed to bridge the relation between point defects and the generally enhanced induced ferroelectricity in fluorite ferroelectrics at the atomic-level and inspire their further property optimization via defect-engineering. [ABSTRACT FROM AUTHOR]

The long-known presence of a sharp OH absorption band in the tetragonal fluoride mineral sellaite, MgF2, inspired us to conduct a detailed study of the OH incorporation modes into this IR-transparent (where IR stands for Infrared) material as well as to search for hydrogen traces in two other IR-translucent halides—villiaumite (NaF) and fluorite (CaF2). Among these three phases, sellaite is the only one to incorporate 'intrinsic' OH groups, most commonly as O–H∙∙∙F defects oriented nearly perpendicular to the c-axis along the shortest edge of the constituent MgF6 polyhedra, in analogy with the isostructural mineral rutile, TiO2. Another defect type, seen only scarcely in untreated natural material, develops when subjecting sellaite to temperatures above 900 °C. It involves an O–H∙∙∙O cluster along the 2.802 Å edge of the original MgF6 dipyramid, as fluorine atoms are progressively expelled from the structure, being replaced by O2- anions. This is corroborated by the appearance of spectral absorption features typical for brucite (Mg(OH)2) and ultimately periclase (MgO), the presence of which could be proven via powder diffraction of the heat-treated material. Except for a 'dubious' peak most probably caused by included phases, neither villiaumite (NaF) nor fluorite (CaF2) showed any presence of 'intrinsic' OH defects. They do however decompose along a similar route into the respective oxide and hydroxide phases at high temperature. This thermal decomposition of the studied halide phases is accompanied by the emission of gaseous (HF)n species at temperatures well below their established melting point - a subject which seems to be quite overlooked. [ABSTRACT FROM AUTHOR]

Recently, rapidly increased demands of integration and miniaturization continuously challenge energy densities of dielectric capacitors. New materials with high recoverable energy storage densities become highly desirable. Here, by structure evolution between fluorite HfO2 and perovskite hafnate, we create an amorphous hafnium-based oxide that exhibits the energy density of ~155 J/cm3 with an efficiency of 87%, which is state-of-the-art in emergingly capacitive energy-storage materials. The amorphous structure is owing to oxygen instability in between the two energetically-favorable crystalline forms, in which not only the long-range periodicities of fluorite and perovskite are collapsed but also more than one symmetry, i.e., the monoclinic and orthorhombic, coexist in short range, giving rise to a strong structure disordering. As a result, the carrier avalanche is impeded and an ultrahigh breakdown strength up to 12 MV/cm is achieved, which, accompanying with a large permittivity, remarkably enhances the energy storage density. Our study provides a new and widely applicable platform for designing high-performance dielectric energy storage with the strategy exploring the boundary among different categories of materials. Here, the authors propose a strategy to create amorphous oxides by bridging fluorite HfO2 and perovskite hafnate, which exhibit ultrahigh breakdown strength of 12 MV/cm and energy density of 155 J/cm3. [ABSTRACT FROM AUTHOR]

Objectives: Exposure to ionizing radiation may increase the risk of circulatory diseases, including heart disease. A limited number of cohort studies of underground miners have investigated these associations. We previously reported a positive but non-statistically significant association between radon progeny and heart disease in a cohort of Newfoundland fluorspar miners. In this study, we report updated findings that incorporate 15 additional years of follow-up. Methods: The cohort included 2050 miners who worked in the fluorspar mines from 1933 to 1978. Statistics Canada linked the personal identifying data of the miners to Canadian mortality data to identify deaths from 1950 to 2016. We used previously derived individual-level estimates of annual radon progeny exposure in working-level months. Cumulative exposure was categorized into quantiles. We estimated relative risks and their 95% confidence intervals using Poisson regression for deaths from circulatory, ischemic heart disease and acute myocardial infarction. Relative risks were adjusted for attained age, calendar year, and the average number of cigarettes smoked daily. Results: Relative to the Newfoundland male population, the standardized mortality ratio for circulatory disease in this cohort was 0.82 (95% CI 0.74–0.91). Those in the highest quantile of cumulative radon progeny exposure had a relative risk of circulatory disease mortality of 1.03 (95% CI 0.76–1.40) compared to those in the lowest quantile. The corresponding estimates for ischemic disease and acute myocardial infarction were 0.99 (95% CI 0.66–1.48), and 1.39 (95% CI 0.84–2.30), respectively. Conclusions: Our findings do not support the hypothesis that occupational exposure to radon progeny increases the risk of circulatory disease. [ABSTRACT FROM AUTHOR]

Barium lanthanum fluoride powders have been prepared by reacting barium nitrate and lanthanum nitrate in molten sodium nitrate at 350 and 450°C, using a sodium fluoride as a fluorinating agent. A fivefold excess of sodium fluoride has been shown to prevent pyrohydrolysis. We have identified a phase of variable composition with the fluorite structure, Ba1–xLaxF2+x (0.3 < x < 0.5), which has high ionic conductivity (2.3 × 10–4 S/cm at 500 K) and an activation enthalpy for ionic transport of 0.50 ± 0.01 eV. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using the hard-sphere model with the existing tabulated values of ionic radii to calculate the lattice parameters of minerals does not always match experimental data. An adaptation of this crystallographic model is proposed by considering the cations and anions as hard and soft close-packed spheres, respectively. We demonstrate the relevance of this "hybrid model" by combining Pauling's first rule with experimental unit-cell parameters of fluorite and antifluorite-structured systems to revise the ionic radii of their constitutive species. [ABSTRACT FROM AUTHOR]

Alkaline intrusions of the Sakju Complex distributed in the western area, DPR Korea were formed in mid-Proterozoic era. The REE and fluorite mineralization occurs in Ryongpho alkaline intrusion of the Sakju Complex. In general, the most important REE resources are associated with alkaline igneous rocks and carbonatites, although REE deposits are also known from a range of other geological settings. REE deposits associated with alkaline igneous rocks are typically lower grade but with larger tonnage and a higher content of the most critical HREE. The Sakju Complex mostly consists of alkaline pyroxenite, alkaline gabbro, alkaline amphibole syenite and alkaline feldspar syenite which reflect well the magmatic differentiation, and their metasomatic rocks. The contents of REEs in intrusions of the Sakju Complex are much higher than the average contents of the earth's crust and those in alkaline rocks. The study of the REE and fluorite mineralization characteristic of Ryongpho alkaline intrusion indicates that the contents of REEs and fluorite gradually decrease in the order from alkaline pyroxenite, alkaline gabbro, alkaline amphibole syenite to alkaline feldspar syenite. The constituent rocks have the similar chondrite-normalized REE distribution patterns, i.e., rich in LREE and deficient in HREE, and no or weak negative anomaly of Eu. The REE distribution curves are rightward inclined, indicating LREE > HREE as a whole. REEs are concentrated in the fluorite zone experienced Ca-F metasomatism in alkaline pyroxenite and alkaline gabbro to form a medium-high grade REE ore body. Fluid inclusion data of fluorites in the constituent rocks indicates that the metasomatic temperature is 250–450°C. Also, the total of rare earth element contents in the fluorites range from 1807 to 5201 ppm. The Tb/Ca and Tb/La ratios of fluorites in the constituent rocks varies respectively between 5.68 × 10–6 and 0.277 × 10–6, and between 0.0491 and 0.0074, and these ratios indicate a formation from a hydrothermal and less pegmatite stage. Also, the results suggest that the darker the fluorite color becomes, the stronger the intensity of REE mineralization and fluorite mineralization, and the higher the total REE contents in the rocks become. [ABSTRACT FROM AUTHOR]

This paper describes the stratiform fluorite and fluorite–base-metal mineralization within the Baikal area, Aldan Shield, Sette-Daban Ridge, and Omulyovka uplift in the Kolyma region. It is assumed to have developed in the Bureya, Khanka, and East Chukchi massifs. Fluorite was concentrated in terrigenous–carbonate rocks of the predominant dolomite range, in the shallow shelf zones separated from the open sea by coral reefs. The fluorite accumulation within layers and horizons at the diagenesis stage was followed by its redistribution with the formation of commercial ore bodies at the catagenesis stage. The Baikal stratiform fluorite mineralization is typical for stratiform deposits of fluorite–base-metal ores. The Aldan type occurs as deposits of high-quality fluorite ores in the carbonate cover of the Siberian Platform. The examples of typical deposits are considered and the forecast fluorite resources are estimated. [ABSTRACT FROM AUTHOR]

Rare earth element (REE) fluorcarbonates are found for the first time in the ore-hosting sequence of the Saf’yanovka Cu–Zn massive sulfide deposit, Middle Urals: bastnäsite, synchysite-(Ce), and synchysite-(Y) in an assemblage with fluorite, calcite, barite, pyrite, and sphalerite. Samples with fluorcarbonates were found at a depth of 262 m in quartz veinlets of an altered zone of pyrite–carbonate–kaolinite–sericite–quartz rocks at the contact with massive pyrite–chalcopyrite and pyrite–sphalerite ores. It is suggested that the REE fluorcarbonates formed from a hydrothermal fluid synchronously with fluorite and calcite. This event can be related to hydrothermal activity at the postcollision stage of the evolution of the Urals fold system. [ABSTRACT FROM AUTHOR]

The solubility of pyrochlore (NaCa)Nb2O6F was studied experimentally in the NaF–H2O system covering both the homogeneous region of hydrothermal solutions and the region of fluid immiscibility in the NaF concentration range from 0.1 to 16 mol kg–1 H2O at 800°С and a pressure of 170–230 MPa. It was shown that the content of Nb in solutions saturated with pyrochlore and fluorite is in the range from 10–5 to 10–3 mol kg–1 H2O. A decrease in mNb is detected with an increasing NaF concentration in the region of fluid immiscibility. It is shown that the most likely forms of niobium in the studied fluoride solutions may be species of HNbO and NbO2F0. A comparative analysis of the experimental data indicates that the concentration of Nb in equilibrium with pyrochlore and fluorite in 10–2–10 m NaF solutions is 10–50 times higher than the concentration of Ta in equilibrium with microlite and fluorite. [ABSTRACT FROM AUTHOR]

We present the results of our ultrasonic studies in a fluorite (CaF2) single crystal with isovalent substitution of Ca2+ ions by copper ions performed at frequencies 23–163 MHz in the temperature range 4–240 K. Anomalies typical for the relaxational contributions of systems of Jahn–Teller complexes have been found in the temperature dependences of the attenuation and velocity of the longitudinal and transverse normal modes associated with the elastic moduli cL = c44 + (c11 + c12)/2 and cE = (c11 – c12)/2 at temperatures below 80 K. The Cu2+ ions in a cubic environment in the ground state possess threefold orbital degeneracy, are described by the T (e + t2) Jahn–Teller effect problem, and have an adiabatic potential energy surface specified in the five-dimensional space of trigonal and tetragonal symmetrized coordinates. An analysis of the experimental data has allowed us to determine the symmetry properties of the extrema (global minima and saddle points) of the lowest adiabatic potential energy sheet and to find the linear (tetragonal and trigonal) and quadratic vibronic coupling constants of the Jahn–Teller Cu2+ complexes in the CaF2 matrix appearing in the vibronic Hamiltonian, the Jahn–Teller stabilization energies, and the coordinates of these extrema in the five-dimensional space of normal coordinates. [ABSTRACT FROM AUTHOR]

Bubble evolution behaviors have been thoroughly documented from the solidified slags detached from EH36 shipbuilding steel weld metals processed by CaO–Al2O3–SiO2–CaF2 fluxes. As the CaF2 content decreases, bubble retention tendency attenuates, which is largely rendered by the disappearance of fluorite and cuspidine and the formation capacity of amorphous phases. Thermodynamic calculations show that bubbles are mostly induced by the synergistic effect of decreased amount of CaF2(g) and increased amount of SiO(g). [ABSTRACT FROM AUTHOR]

High quality steels have a low sulfur content. Steel is purified from sulfur by treating it with highly basic slags. Scarce fluorspar is used to provide slags with the required fluidity, which decomposes during smelting with the liberation of toxic fluorine into a workshop atmosphere. Alumina is also a thinner for highly basic slags, which is present in sufficient concentrations in aluminothermic production slags that are sent to landfill and create pressure on the environment. Slag dumps are "technogenic deposits" that can be a raw material base. In particular, industrial ferroalloy slags with a high alumina content may be used to prepare a thinning slag-forming mixture that can be used in steelmaking instead of scarce fluorspar. Preparation of a slag-forming mixture from waste slag will reduce the environmental pressure on slag dumps and their use as a slag thinner during steel refining in the working area of a steelmaking workshop by eliminating toxic fluorine emissions released during fluorspar decomposition. Replacement of scarce fluorspar with a slag-forming mixture in steelmaking will reduce steel cost by lowering aluminum consumption for slag deoxidation. [ABSTRACT FROM AUTHOR]

It has been established that the reactions of sulfur dioxide oxidation and carbon dioxide conversion take place in aqueous suspensions of calcium fluoride at room temperature and atmospheric pressure. The optimal flow rates of gases and concentration of calcium fluoride suspension for their maximum absorption were determined. It has been shown that the suspension of CaF2 can be repeatedly used after its regeneration with atmospheric oxygen. [ABSTRACT FROM AUTHOR]

An inexpensive and controllable CeMnOx composite oxides catalyst for the liquid-phase catalytic oxidation of toluene was conveniently prepared by ultrasound-assisted co-precipitation method. The physical–chemical properties of CeMnOx composite oxides catalyst have been systematically characterized. MnOx as catalytic active species was highly dispersed in the cubic fluorite structure CeO2. The cooperation of CeO2 and MnOx evidently improved the catalytic performance. CeMnOx composite oxides with a Ce/Mn molar ratio of 2:1 was showed the good catalytic performance. 7.0% of toluene conversion and 95.6% of overall selectivity to benzylalcohol, benzaldehyde and benzoic acid was acquired under optimal reaction conditions. The present catalyst has the advantages of low cost, good catalytic performance and stability. This work provides a simple, benign and controllable approach for the selective oxidation of toluene to valuable oxidation products. [ABSTRACT FROM AUTHOR]

The Baoshan Cu–Pb–Zn deposit, located in the central part of the Qin–Hang belt in South China, is closely related to the granodiorite-porphyry. However, the characteristics and the source of the ore-forming fluid are still ubiquitous. According to the crosscutting relationships between veinlets and their mineral assemblages, three stages of hydrothermal mineralization in this deposit were previously distinguished. In this contribution, two different colored fluorites from the major sulfide mineralization stage are recognized: (1) green fluorites coexisting with Pb–Zn ores; and (2) violet fluorites coexisting with pyrite ores. Y/Ho ratios verify the green fluorites and violet fluorites were co-genetic. The fluorites display elevated (La/Yb)N ratios, which decrease from 1201 to 5710 for green fluorites to 689–1568 for violet fluorites, indicating that they precipitated at the early hydrothermal sulfide stage, and Pb–Zn ores crystallized earlier than pyrite ores. The similar Tb/La ratios of the fluorites also indicate that they precipitated at an early stage within a short time. From the green fluorites to violet fluorites, the total rare earth element (ΣREE) concentrations decrease from 1052–1680 ppm to 148–350 ppm, indicating that the green fluorites precipitated from a more acidic fluid. The Eu/Eu* ratios increase from 0.17 to 0.30 for green fluorites to 0.29–0.48 for violet fluorites, and the Ce/Ce* ratios decrease from 1.08–1.13 to 0.93–1.11, suggesting a gradual increase in oxygen fugacity (fO2) and pH value of the mineralization fluid. Though the fluorites display similar REE patterns to the granodiorite-porphyry and limestone, the ΣREE concentrations of the fluorites are significantly higher than those of limestone and the granodiorite-porphyry, suggesting that an important undetected non-magmatic source is involved to provide sufficient REE for fluorites. The most plausible mechanism is fluid mixing between magma fluid and an undetected non-magmatic fluid. [ABSTRACT FROM AUTHOR]

A series of MnOx–ZrO2 catalysts is prepared by coprecipitation with variation of the calcinationtemperature from 400 °C to 800 °C. It is shown that the catalyst calcined at 650-700 °C exhibits the highest activity in the propane oxidation reaction. The MnOx–ZrO2 catalyst is studied by operando X-ray diffraction under conditions of the propane oxidation reaction. The structural features of the catalyst are examined upon heating in propane or oxygen media or at the propane:oxygen ratio of 1:6. It is found that in pure propane, there is the dehydrogenation reaction on the catalyst with the formation of propylene and hydrogen and is accompanied by a change in the catalyst structure. The initial catalyst consists of a (Mn, Zr)O2 solid solution and Mn2O3 oxide. During the reaction, Mn cations are reduced in both (Mn, Zr)O2 solid solution bulk and compositions of crystalline oxides: Mn2O3 → Mn3O4 → MnO. Under the catalytic conditions of the propane oxidation reaction and in pure oxygen, the catalyst structure remains unchanged. [ABSTRACT FROM AUTHOR]

The Illinois-Kentucky ore district hosts the largest deposits of fluorite in the USA. A long-standing hypothesis for the formation of the Illinois-Kentucky deposits is that the ore fluid was a sedimentary brine infused with F-rich fluids exsolved from Permian ultramafic magmas. This ore fluid may have had a F concentration between 680 and 4,300 ppm, three orders of magnitude greater than typical F concentrations in sedimentary brines, and a highly acidic pH between 0 and 1.4. The ore fluid likely ascended faults that intersected permeable limestone formations where neutralization of the ore fluid by reaction with limestone likely drove fluorite precipitation. The present study was undertaken to test the implications of such an acidic F-rich fluid for fluorite ore formation using reactive transport modeling. The models show that an acidic F-rich fluid could have ascended a silicified fault transecting 100s of meters of limestone without becoming neutralized. Upon exiting the fault into a limestone aquifer, the F-rich fluid would have reacted with the limestone and become neutralized within a few meters, producing intense localized limestone dissolution. The models indicate that the neutralization of acidic F-rich fluid is an efficient fluorite precipitation mechanism that can quickly produce a large fluorite-dominant mineral deposit and abundant host rock dissolution consistent with field observations. Conversely, an ore fluid that has a low F concentration and a higher pH more typical of sedimentary brines cannot produce a fluorite-dominant deposit as large as those observed in the field within a geologically reasonable amount of time. [ABSTRACT FROM AUTHOR]

Phase formation in the barium fluoride–lanthanum fluoride (BaF2–LaF3) system at 350–450°С was studied using fluxed melt syntheses. The precursors used were barium nitrate and lanthanum nitrate, the fluorinating agent used was sodium fluoride, and the solvent used was sodium nitrate. The characterization methods used were X-ray powder diffraction and scanning electron microscopy (SEM). Ba1 –xLaxF2 +x fluorite solid solution (ss), where х = 0.3–0.5 (30–50 mol % LaF3), was found to be formed. The ss particles had submicron sizes and a cubic morphology as probed by SEM. Lanthanum fluoride-base ss was not formed under the synthesis conditions used; the LaF3 product was thin hexagonal platelets. [ABSTRACT FROM AUTHOR]

And, Similarly, the constitutive species' ionic radii of the italic and bold fluorite compounds in Table 1 were re-evaluated (Table 3 in supplementary materials). now reads: Similarly, the constitutive species' ionic radii of the bold fluorite compounds in Table 1 were re-evaluated (Table 3 in supplementary materials). Also, In the peculiar case of the fluorites highlighted in italic and bold in Table 1, the r SB cation sb /r SB anion sb ratio is smaller than the lower stability limit, so cations and anions are not in contact in this configuration. now reads: In the peculiar case of the fluorites highlighted in bold in Table 1, the r SB cation sb /r SB anion sb ratio is smaller than the lower stability limit, so cations and anions are not in contact in this configuration. [Extracted from the article]

The Ouenza region represents the most important zone for Fe-Pb–Zn (Ba, F, Cu) mineralization in Algeria. The hematitezed iron (siderite) mineralization is mostly controlled by diapiric structures hosted in carbonate sedimentary rocks of the Lower Cretaceous. Polymetallic mineralization (Pb–Zn-Ba, F, Cu) is mainly in epigenetic vein fillings and fractures. Most of the ore bodies are structurally controlled by NE-SW-trending faults. The study of fluid inclusions using Raman and cryo-Raman data in the fluorite and quartz associated with the mineralization confirms the existence of CO2 in the inclusions. The presence of CO2 associated with CH4 and graphite trapped in the fluid inclusions of the fluorite deposited suggest an epigenetic origin for these mineral deposits and allows to characterize the fluid responsible for the fluorite and other associated mineralization deposits. The methods used in this study, including micrometry, Raman, cryo-Raman, and crush leaching, and stable isotopes of sulfur, carbon, and oxygen, suggest an epigenetic origin for these mineral deposits allow the characterization of the fluid responsible for the fluorite deposits and other associated mineralization. The presence of graphite entrapped in the fluid inclusions of the fluorite deposits results from diapiric upward from the basement. Two stages of fluids were examined: (1) an SiO2-rich fluid deposited black quartz crystals with solid inclusions of calcite (H2O-NaCl-CaCl2 system) and CO2 in the vapor phase and (2) a second fluid flowed to depth, recharged with fluorite, sulfide, and sulfate deposited quartz, fluorite, barite, and galena. The crush leaching study in the barite, fluorite, and siderite samples shows lower values of Cl/Br. These results suggest that halite dissolution compared to the Cl/Br ratio varies between 1330 and 9641. The stable isotope results of calcite associated with fluorite and galena mineralization are between 2.6 and − 1.0‰ for δ13CPDB and between 17.0 and 25.5‰ for δ18OSMOW. The values obtained for δ34SCDT in barite range from + 20.8 to + 23.2‰. The combined results suggest that fluids responsible for mineralization are related to basin fluids (formation water) similar to those usually reported for Mississippi Valley (MVT) deposits. [ABSTRACT FROM AUTHOR]

The fluorite trigadolinium ruthenium heptaoxide, Gd3RuO7(s), an interesting ternary oxide containing two magnetic cations and known to show complex magnetic behavior was synthesized by the solid-state reaction route. A solid-state galvanic cell was set up to determine the standard molar Gibbs energy of formation of Gd3RuO7(s) from elements in their standard state, employing oxide ion–conducting electrolyte. A differential scanning calorimeter was employed to determine the isobaric standard molar heat capacity of this ternary oxide. Low-temperature standard molar heat capacity measurements were measured in the temperature range from 126 to 299 K while the high-temperature range was from 307 to 846 K and revealed a first-order phase transition, the smoothed values could be fitted to a mathematical expression: C°p,m (Gd3RuO7,s,T)(J⋅K−1⋅mol−1) = 252.05 + 3.72 ∙10−2 T(K)—31.49 ∙105/T2(K). The isobaric standard molar heat capacity of the titled oxide, C°p,m, at 298.15 K is 227.7 J⋅K−1⋅mol−1. The calorimetric values along with the Gibbs energy determined were used to determine all other thermodynamic functions for Gd3RuO7. Combined isobaric standard molar heat capacity of Gd3RuO7(s) in the entire temperature range from 126 K to 846 K [ABSTRACT FROM AUTHOR]

In the search for novel ceramics for use within nuclear fuel–related applications and nuclear waste-form matrices, a major focus has been on the development of radiation-tolerant materials. Of particular interest in this field have been numerous compounds with either pyrochlore or the related fluorite-type structures. In this study, we look to expand the family of compounds with defect fluorite–type structure. We have fabricated three new compounds; Yb2Sn1.125O5.25, Yb2Sn1.25O5.5, and Yb2Sn1.375O5.75. The compound Yb2Sn1.125O5.25 was determined, via x-ray diffraction, to have the long-range defect fluorite structure, Fm-3 m symmetry, with cell parameter a = 5.17233(1). Further to this, Sm2ZrO5 and Yb2TiO5 compounds were also fabricated and crystal structures characterised. The use of transmission electron microscopy has revealed a much more complex crystal structure than that of the relatively high symmetry fluorite, with the presence of structural modulations being detected. The ion-irradiation response of these compounds was tested via bulk specimen irradiation using 15-MeV gold ions with grazing incidence x-ray diffraction characterisation. The results show that both Sm2ZrO5 and Yb2Sn1.25O5.5 are highly tolerant to ion-irradiation exposure whilst Yb2TiO5 is susceptible to amorphisation. [ABSTRACT FROM AUTHOR]

Fluorine rubber (FKM) is often used in bearing seals, bearing seal will be affected by high temperature in the process of use and performance decline. Therefore, in this paper, the effect of CeO2 on the high temperature composite properties of FKM was studied by filling CeO2 nanoparticles into FKM. 5% CeO2/FKM composites were prepared by mechanical blending and hot-pressing process after nano CeO2 was treated with silane coupling agent KH-570. After mechanical and high temperature friction tests of CeO2/FKM composites, the morphology of CeO2/FKM composites was characterized by three-dimensional topography instrument and scanning electron microscope. The mechanical strengthening mechanism and anti-wear and anti-friction mechanism of CeO2 on FKM were expounded. The results showed that the microstructure of Fluor elastomer with CeO2 particles was reinforced, and the defects of fluorine rubber itself were filled. Specifically, compared with the original FKM, the strength of CeO2/FKM composite was improved, in which the tensile strength reached 20.75 MPa, increased by 18.5%, and the tear strength reached 43.44 N/mm, increased by 3.5%. CeO2/FKM composites show outstanding anti-wear and low friction coefficient properties at high temperature (200 °C). The main mechanism is that nano-CeO2 keeps high hardness of FKM, and CeO2/FKM composites have high crosslinking density. [ABSTRACT FROM AUTHOR]

Sb-doped Y2O3, a compound with excellent optical properties, is used in laser applications. Recently, it has been found that it coexists in two distinct polymorphs upon doping with various levels of Sb. Therefore, the electronic structure and optical properties of Sb-doped Y2O3 corresponding to two distinct phases, i.e., bixbyite and fluorite, are explored in this paper using the CASTEP density functional theory (DFT) code. Sb is substituted at Y sites in pure Y2O3 in both phases, and the corresponding band structure, density of states, and various optical properties, namely the dielectric function, refractive index, reflectivity, and optical loss functions, are investigated. The results reveal that Sb-doped Y2O3 in fluorite phase is conductive for 12.5% doping but shows a small gap of 0.45 eV in the case of 25% Sb doping. Moreover, the fluorite phase of Sb-doped Y2O3 has defect states in the bandgap above the Fermi level, while the bixbyite phase exhibits insulating behavior. Moreover, the bandgap of the bixbyite phase steadily decreases with increasing Sb doping concentration. The results for the optical properties reveal that new kinds of excitation and plasmonic states emerge in Sb-doped bixbyite Y2O3 whereas no such transitions appear upon doping of the fluorite structure. [ABSTRACT FROM AUTHOR]

Crystals of fluorite solid solution Sr1 −xTbxF2 +x have been grown by the Bridgman technique from melts with the initial compositions x0 = 0.05, 0.12, and 0.15. The distribution x(L) of components along the crystal length is studied using densitometry and X-ray diffraction analysis. The effective impurity-distribution coefficients keff in these crystals are calculated within the Pfann model for the case of convective mass-transfer mechanism in melt. The position of the composition of temperature maximum in the melting curves of the Sr1 −xTbxF2 +x solid solution is refined. The applicability of the developed technique for nondestructive control of the composition of solid solution crystals with incongruent melting character is demonstarated. [ABSTRACT FROM AUTHOR]