This study investigates the physicochemical and volume properties of neodymium-containing cryolite-based melts and the NaF + NdF3 system. Densities were measured using the Archimedean method, showing a linear decrease with increasing temperature and an increase with the NdF3 or Nd2O3 content. Calculated molar and partial molar volumes indicate local expansion upon addition of neodymium compounds. However, the partial molar volumes of NdF3 at infinite dilution are lower than those of Nd2O3, due to stronger Nd3 +-F- interactions and more compact local structures in fluoride melts. In cryolite-based melts, the [AlF6]3- network enhances packing, resulting in higher partial molar volumes for Nd2O3. Direct calculations are in good agreement with predictive procedures (1A and 1B), validating the data set. These results provide a detailed thermophysical description of Nd-containing melts, offering a valuable basis for modeling and optimizing industrial processes for neodymium separation and refining.

In molten salt reactors, oxygen impurities accelerate structural material corrosion. Moreover, the ingress of oxide species may promote the formation of insoluble actinide oxychlorides or oxides, potentially raising safety concerns. To limit the undesired precipitation of such phases, MgCl2 has been proposed as a complementary fuel component to sequester oxygen by enhancing the solubility of actinide oxide species. In this study, we provide direct, molecular-level evidence of an MgCl2-mediated oxygen solubility mechanism. This was achieved through high-temperature 17O nuclear magnetic resonance spectroscopy on NaCl-MgCl2-LaCl3 melts with various amounts of dissolved 17O-enriched LaOCl, corroborated by classical molecular dynamics with the polarizable ion model and first-principles NMR calculations. Experiment and simulation both show that adding MgCl2 promotes the sharing of O2- coordination between Mg2+ and La3+ ions, disrupting La-O clustering that facilitates oxide precipitation. Altogether, these results establish a mechanistic framework for tuning oxygen speciation and solubility through compositional design in high-temperature molten salt systems.

Bi-doped (0.25, 0.50, and 1.50 mol.% of Bi2O3) 2CaO-Al2O3-SiO2 glasses were prepared in two different ways (flame synthesis with a combination of solid-state reaction and conventional melting) to compare the influence of the preparation method on their thermal, optical, magnetic, and structural properties. All prepared samples were X-ray amorphous. Differential thermal analysis revealed significant differences in thermal properties of the prepared glasses depending on the preparation method. In the case of glasses prepared by flame synthesis, the glass crystallizes in one or two-steps, depending on the Bi content. Glasses prepared by the conventional melting method crystallize in a single step, independent of the bismuth content. A higher tendency toward crystallization with increasing Bi3+ addition was observed for both types of glasses, indicating the role of Bi as a nucleating agent. The photoluminescence properties of the prepared systems were studied in the visible spectral range. All prepared systems exhibited broad emissions in the spectral range from 350 to 750 nm, centered at similar to 485 nm and similar to 425 nm for glasses prepared by conventional melting and flame synthesis, respectively. Glasses prepared by conventional melting exhibit less complex magnetic properties than those prepared by flame synthesis. In glasses prepared by melting, the diamagnetic (at 300 K) and the paramagnetic (at 2 K) component of magnetization prevails, even at low magnetic fields. The glass microspheres prepared by flame synthesis were diamagnetic or weakly ferromagnetic at 300 K and paramagnetic or weakly ferromagnetic/antiferromagnetic at 2 K. These findings indicate that Bi-doped calcium-aluminosilicate glasses offer promising applications not only in optical but also, e.g., in magneto-optical devices.

Three polymorphs were found to exist for Cs3ScF6 in the room temperature range of up to 280 degrees C. Two phase transitions were identified by differential scanning calorimetry (DSC) analyses at 92 and 196 degrees C upon heating. In situ high-temperature solid-state NMR, synchrotron and laboratory X-ray diffraction, and neutron powder diffraction were used for structural characterization. The crystal structure of the high-temperature (gamma) phase adopts the cubic Fm3m (Z = 4) space group with a = 9.6048(7) & Aring; at 250 degrees C. The other two polymorphs, alpha and beta, have tetragonal symmetry with space groups I41/a (Z= 80) and I4/m (Z= 10), and lattice parameters are a = 21.15222(6) & Aring;, c = 38.21648(8) & Aring; and a = 15.0401(2) & Aring;, c = 9.6341(2) & Aring; at RT and 150 degrees C, respectively.

The new mineral vegrandisite (BaCl2) was discovered at the porphyry gold deposit Biely Vrch, 3.5 km southeast of the town Detva, in the Central Slovak Volcanic Field. It occurs as a minor phase in salt melt inclusions hosted by vein quartz, where it forms small anhedral and transparent crystals up to 4 mu m long, accompanied by halite and several other daughter minerals, mainly javorieite, rinneite, chlorocalcite and hibbingite. Vegrandisite was identified by techniques embedded in transmission electron microscopy but many mineral properties, including optical and structural ones, are known from the synthetic BaCl2 analogue. Strongest bands in the Raman spectra include 114, 125, 187 cm(-1) and in the IR spectra in the region between 2852 and 2944 cm(-1). Vegrandisite in inclusions approaches the composition of BaCl2, but Sr (up to similar to 4.5 wt. %) and Br (up to similar to 2.1 wt. %) are also incorporated. It is orthorhombic, belongs to the space group Pnma. Obtained unit-cell parameters a = 7.80(3) angstrom; b = 4.71(2) angstrom; c = 9.60(9) angstrom, V = 352.68 (54) angstrom 3 are consistent with the published parameters of alpha-BaCl2 that exhibits a PbCl2-type (cotunnite) structure. Solid phases in salt melt inclusions, including vegrandisite, have crystallized from the salt melt on cooling of the inclusions. Late crystallization of BaCl2 is related to accumulation of the incompatible element barium in the residual salt melt. Parental salt melt evolved from a hypersaline liquid, accompanied by a magmatic vapor, that were exsolved from a shallow dioritic magma.

The structures and phase transitions of cryolite-related rubidium and cesium aluminum fluoride phases are investigated and related to the dynamic motions of AlF6 octahedra. Low-temperature synchrotron powder diffraction data were collected on Rb3AlF6 and Cs3AlF6 to search for new polymorphs, and MAS NMR was used to study changes in dynamic motion occurring across the phase transitions. Rb3AlF6 is found to undergo a subtle phase transition around 270 K and then a second, more substantial phase transition around 250 K. The low temperature polymorphs maintain essentially the same framework as the room temperature Fddd structure, but are more complex due to an ordered freezing of dynamic rotations of AlF6 octahedra. Freezing of octahedral rotations is observed in Cs3AlF6 around room temperature, but the same C2/m structure is maintained down to 80 K without any phase transitions. The dynamic motions and local structure in the high-temperature cubic polymorph of Cs3AlF6 are also examined jointly by MAS NMR and reverse Monte Carlo modeling of X-ray pair distribution function data.

For the first time, the mechanism of metal aluminum dissolution in NaF-ScF3 eutectic melts and the chemical interaction between the constituents of this mixture have been thoroughly studied by a combination of differential thermal analysis (DTA), high temperature and solid-state nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) coupled with the molecular dynamic simulations. The formation of an insoluble Al3Sc alloy in molten (NaF-ScF3)(eut) system was proven, and the chemical mechanism of this aluminothermic Al3Sc alloy production was elucidated. Corresponding ex situ examinations bring to light the formation of NaScF4 and solid solution of Na-3(Al,Sc)F-6 in cooled bath. The molecular dynamics calculations of the bath allow us to construct the structural model and to predict viscosity, density and electrical conductivity of the reagent melt to help to optimize the conditions of the alloy synthesis.

A new way of preparing YAG, Y3Al5O12, materials at low temperatures has been discovered using a molten Na3AlF6-Y2O3 reaction mixture. For the successful synthesis of YAG, a precise examination of the cryolite part of the phase diagram of the Na3AlF6-Y2O3 system was carried out up to 45 mol % of Y2O3 using thermal analysis with a larger amount of sample (12 g). The phase diagram of the Na3AlF6-Y2O3 system was discovered to be likely a simple eutectic system with one inflection point on the liquidus curve (coordinates: 22.0 mol % Y2O3, 920 degrees C) and one eutectic point (coordinates: 43.0 mol % Y2O3, 620 degrees C). The spontaneously solidified samples of Na3AlF6-Y2O3 after thermal analysis have been investigated using solid-state NMR (F-19, Na-23, and Al-27) spectroscopy and X-ray powder diffraction over a broad range of compositions. The minimal synthesis temperature used in this work for the preparation of YAG was 630 degrees C, and the Y2O3 concentration was 43 mol %. Besides the synthesis of YAG, the molten Na3AlF6-Y2O3 system with the addition of Nd2O3 has been successfully used also for the preparation of the neodymium-doped YAG powders (Nd:YAG). Rietveld refinement has been used to quantitatively assess the incorporation of neodymium into YAG and beta-Na(Y1.5Na0.5)F-6 materials.

Phase diagrams of the systems Na 3 AlF 6 -NdF 3 and (Na 3 AlF 6 -NdF 3 ) eut -Nd 2 O 3 were experimentally determined by thermal analysis up to 60 mol.% NdF 3 and 45 mol.% Nd 2 O 3 , respectively. The Na 3 AlF 6 -NdF 3 system was found to be a simple eutectic system with the eutectic point with the following approximate coordinates: 49 mol.% NdF 3 and 905°C. This eutectic composition was then used for the thermal analysis of the (Na 3 AlF 6 -NdF 3 ) eut -Nd 2 O 3 system. The coordinates of the eutectic point of the (Na 3 AlF 6 -NdF 3 ) eut -Nd 2 O 3 system were found to be approximately 46 mol.% Nd 2 O 3 and 733°C. After the thermal analysis, the x-ray diffraction analysis of the solidified samples of both systems was performed. The XRD analysis of the Na 3 AlF 6 -NdF 3 system has shown the formation of two new compounds; NaNdF 4 and NdOF. The formation of NdOF is probably the product of the high-temperature hydrolysis between the moisture in the atmosphere and NdF 3 . The XRD analysis of the solidified samples of the (Na 3 AlF 6 -NdF 3 ) eut -Nd 2 O 3 system has shown the formation of the following new compounds: NaNdF 4 , NdOF, NdAlO 3, and NaF.

Five compositions in the system Al2O3-Y2O3 with high level of homogeneity were prepared in the form of glass microspheres by flame synthesis. The amorphous nature of prepared glasses with highly disordered structure was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. In the NMR spectra, typical signals with chemical shifts of 75, 42 and 12 ppm were observed, which were attributed to the presence of AlO4, AlO5 and AlO6 motifs in the glass structure. The ratio of individual motifs in glass samples did not change significantly with the composition. The crystallization of yttrium-aluminium garnet (YAG) phase was observed as a major process in the glasses thermally treated up to 1450 degrees C, with slow crystallization of 0- and a-Al2O3 phases detected in the temperature interval 980-1450 degrees C. IR and Raman spectra of the microspheres crystallized at 998, 1300 and 1500 degrees C for 4 h contained typical bands, that were assigned to the vibrations of AlO4 and AlO6 groups in YAG and Al2O3 structures. The comparison of 27Al and 89Y magic angle spinning (MAS) NMR spectra showed the presence of only YAG and a-Al2O3 phase in the samples crystallized at 1500 degrees C and the presence of a trace amount of 0-Al2O3 in the sample crystallized at 998 and 1300 degrees C. The yttrium aluminium perovskite (YAP) and yttrium aluminium monoclinic (YAM) phases, expected in this system, were no detected. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC

In an experiment combining various approaches, a precise examination of a portion of the phase diagram of a CsF-Al2O3 system was carried out up to 40 mol% Al2O3. CsF-Al2O3 solidified mixtures have been investigated using high-field solid-state NMR (133Cs, 27Al, and 19F) spectroscopy and X-ray powder diffraction over a broad range of compositions with synchrotron powder diffraction and Rietveld analysis. A new cesium oxo-fluoro-aluminate, Cs2Al2O3F2, was discovered, prepared, and structurally analyzed by synchrotron diffraction analysis. In addition to Cs2Al2O3F2, we have synthesized the following pure compounds in order to aid in the interpretation of NMR spectra of the solidified samples: CsAlF4, Cs3AlF6, and CsAlO2.

Electrically conductive nitrogen-doped SiC ceramics were exposed to molten FLiNaK at 700 degrees C for 100, 200, and 500 h, and at 1000 degrees C for 100 h in Ar atmosphere. The SEM-EDX investigations of corroded samples showed that the main corrosion attack proceeds through the intergranular phase, where the fluoride melt interacts with the oxide phases and partly dissolves also the SiC grains. It was proved that N-doped SiC has good corrosion resistance against molten FLiNaK. After corrosion at 700 degrees C for 100, 200, and 500 h the corroded layer thick-nesses were 85, 90, and 120 & mu;m, respectively.

The rate of alumina dissolutionAlumina dissolution in cryolitic meltsMelt is critical for the management of aluminiumAluminium production pots. The kinetics of the dissolutionDissolution reaction depends on the combined effects of physical and chemical characteristics of aluminaAlumina. The literature mentions several methods to follow the rate of dissolutionDissolution, with variable degrees of complexity and success. We report a combination of analytical tools to evaluate the dissolutionDissolution rates of various industrial aluminasAlumina in an industrial cryoliteCryolite bath collected shortly before the anodeAnode effect. Batches of powders were sequentially added to an electrochemical cell specifically designed for this test. The dissolutionDissolution rate was measured electrochemically, and an automatic script was developed to measure the flotation time of the alumina raftsAlumina rafts from digital recordings. We correlate the alumina dissolutionAlumina dissolution rate and flotation times, with the initial characteristics of the aluminaAlumina powder.

Experimental measurements were made to assess the electrical conductivity as a function of temperature and NdF 3 concentration (0–20 mol %) of molten systems of (LiF–CaF 2 ) eut –NdF 3 , (LiF–NaF) eut –NdF 3 , (NaF–CaF 2 ) eut –NdF 3 and (LiF–MgF 2 ) eut –NdF 3 . The experiment used an altering current impedance spectroscopy technique with a platinum–rhodium electrode positioned in a pyrolytic BN tube and graphite a crucible/counter electrode. The conductivity of all systems under study increased with rising temperatures and decreasing NdF 3 concentrations. The Arrhenius equation and linear regression have both been used to describe the experimental data. The results of the ionic conductivity for the temperature 850 °C and NdF 3 concentrations 0, 10 and 15 mol %, respectively, can be compared as follows: the conductivity of the molten system of (LiF–CaF 2 ) eut –NdF 3 was determined to be 6.10, 5.95 and 5.10 S.cm −1 , the results for the system (LiF–NaF) eut –NdF 3 were 6.16, 5.56 and 4.13 S.cm −1 , the results for the system (NaF–CaF 2 ) eut –NdF 3 were 3.78, 3.56 and 2.32 S.cm −1 , and finally, the results for the system (LiF–MgF 2 ) eut –NdF 3 were determined to be for the same temperature as 5.35, 4.79 and 4.14 S.cm −1 , respectively.

The electrical conductivity of molten systems of (LiF - CaF2)(eut) - NdF3 and (LiF - NaF)(eut) - NdF3 was experimentally determined as a function of temperature and concentration of NdF3 (0 - 20 mol %). A platinum-rhodium electrode positioning in pyrolytic BN tube, graphite crucible, and altering current impedance spectroscopy were used for the study. The conductivity of both measured systems increases with the temperature and decreases with the increasing content of NdF3. The experimental data have been described by the linear regression and by the Arrhenius equation. The electrical conductivity of the molten system of (LiF - CaF2)(eut) - 5 mol % NdF3 has been identified to be 5.56 S.cm(-1) compares to the electrical conductivity of the molten system of (LiF - NaF)(eut) - 5 mol % NdF3, 5.52 S.cm(-1) (800 degrees C). The electrical conductivity of (LiF - CaF2)(eut )- 20 mol % NdF3 at the temperature of 800 degrees C is 4.02 S.cm(-1), and the electrical conductivity of (LiF - NaF)(eut) - 20 mol % NdF3 is at the same temperature 3.46 S. cm(-1). The XRD patterns of the solidified samples of the investigated systems (LiF - CaF2)(eut) - NdF(3 )and (LiF - NaF)(eut )- NdF3 were after the conductivity measurements also determined. (C) 2022 Elsevier B.V. All rights reserved.

Abstract Ferrous hydroxychlorides are geochemically important but less recognized mineral species due to their extreme sensitivity to oxidation and hydration in contact with air {typically they convert to akaganéite [Fe3+(O,OH,Cl)]}. Only the γ-form was previously known as the orthorhombic mineral hibbingite, associated with altered mafic intrusive rocks. In this study, we describe the β-polymorph of Fe2(OH)3Cl as a new mineral parahibbingite that was found in pyroxenite from the Karee platinum mine in the Bushveld Complex, South Africa. The two minerals were distinguished by a combination of Raman spectroscopy and FIB-SEM-TEM analytical techniques (TEM-EDX and TEM-SAED). They can be easily recognized by their distinct Raman spectra. Parahibbingite has two very strong vibration bands at ~3550 and 3560 cm–1, accompanied by much weaker bands at ~124 and 160 cm−1, while the Raman spectrum of hibbingite has a sharp, strong band at 3450 cm−1 and two moderate bands at 199 and 385 cm−1. Parahibbingite was found as fine-grained reaction rims at the contact of orthopyroxene phenocrysts and talc inside a drill core. It has a trigonal space group [R3m, a = 6.94(5) Å; c = 14.5(2) Å], with an empirical formula (Fe21.98+ Mn20.01+ Ca0.01)(OH)3.08Cl0.92. The origin of this mineral in the Bushveld Complex is most likely related to a late hydrothermal alteration of pyroxenite. Hibbingite forms as an abundant daughter mineral hosted by fluid inclusions and salt melt inclusions in hydrothermal quartz associated with granitic systems during cooling under reducing conditions. Such inclusions are common in Au-porphyry mineralization worldwide, such as the Biely Vrch (Slovakia) deposit studied in detail in this work. The lattice parameters obtained by TEM-SAED are a = 6.30 Å, b = 7.12 Å, and c = 9.89 Å. Hibbingite was recognized as the only phase that carries “water” (as a hydroxyl group) in otherwise water-free, salt melt inclusions. Furthermore, both hibbingite and parahibbingite should be considered as reservoirs for Cl and H2O in large volumes of altered basic and ultrabasic rocks. They can transport volatiles to shallow levels of subduction zones. Alternatively, their dissolution can fuel remobilization, transport, and deposition of sulfidic ores in saline fluids. Their detection, however, is difficult because of their sensitivity to oxidizing atmospheres. For example, in natural outcrops exposed to air, they may vanish, thus distorting estimates of their abundance and role in many processes that involve mineral-derived volatiles.

The crystal structures of three polymorphs of Rb3ScF6 have been determined through a combination of synchrotron, laboratory X-ray, and neutron powder diffraction, electron diffraction, and multinuclear high-field solid-state NMR studies. The room temperature (RT; α) and medium-temperature (β) structures are tetragonal, with space groups I41/a (Z = 80) and I4/m (Z = 10) and lattice parameters a = 20.2561(4) Å, c = 36.5160(0) Å and a = 14.4093(2) Å, c = 9.2015(1) Å at RT and 187 °C, respectively. The high-temperature (γ) structure is cubic space group Fm3̅m (Z = 4) with a = 9.1944(1) Å at 250 °C. The temperatures of the phase transitions were measured at 141 and 201 °C. The three α, β, and γ Rb3ScF6 phases are isostructural with the α, β, and δ forms of the potassium cryolite. Detailed structural characterizations were performed by density functional theory as well as NMR. In the case of the β polymorph, the dynamic rotations of the ScF6 octahedra of both Sc crystallographic sites have been detailed.

Molten system Na3AlF6 - SiO2 was examined by high temperature NMR. Further characterizations of the samples prepared by Rapid Solidification Processing (RSP) technique and by spontaneous solidification were performed by X-ray diffraction and solid state NMR. The high solubility of SiO2 in molten cryolite and the immiscibility phenomenon were observed. Using thermogravimetric analysis, weight losses were detected, which could be attributed to the formation of the volatile products. The results of the present study are the evidence that SiO2 reacts with molten Na3AlF6 under the formation of the volatile SiF4, non - volatile NaF, and alumino-silicate AlSi3O8- species. NMR spectroscopy coupled with diffraction-based methods was proved as a promising approach to obtain information about the structure and chemistry of this rather complex system. (C) 2021 Published by Elsevier B.V.

The electrical conductivity of molten K(3)AIF(6), Rb(3)AIF(6), Cs(3)AIF(6), and CsF was measured at various temperatures using a pyrolytic boron nitride tube, platinum-rhodium alloy electrode, and alternating current impedance method. The electrical conductivity of molten K(3)AIF(6) was found to be 2.64 S.cm(-1) at 1273 K The electrical conductivity of molten Rb(3)AIF(6) was found to be 2.06 S.cm(-1) at 1273 K. The conductivity of molten Cs(3)AIF(6) at the same temperature is 1.36 S-cm(-1) because the conductivity of CsF at 1273 K was found to be 2.57 S.cm(-1). The electrical conductivity values steadily drop from lithium fluoride/fluoroaluminate through sodium and potassium to cesium fluoride/fluoroaluminate. This fall in conductivity is probably because of the increase in the size and mass of the cations (activation energy increases with decreasing conductivity).

Solid daughter phases in fluid and salt melt inclusions in minerals provide important clues to characterization of mineral-forming processes. The analysis of the fluid inclusions often requires the exposure of the daughter minerals. Rinneite (K3NaFeCl6), which is a hygroscopic mineral, decomposes in air and cannot thus be identified by conventional methods. A combined approach has been applied for investigation of synthetic and natural rinneite to acquire its diagnostic Raman spectrum for a nondestructive identification. We used natural rinneite inclusions in halite, suitable for applying a complex of methods, to clear up the reference spectrum. Improved high-resolution X-ray diffraction (XRD) data obtained from natural rinneite inclusion are comparable with that of previously published, with similar unit cell dimensions. Polarized Raman spectra of natural inclusions were obtained using different geometries and polarization of the incident and scattered light. Interpretation of experimental Raman spectra was performed within the framework of lattice dynamics simulations and group analysis. Individual spectral bands are interpreted in terms of Raman-active vibrational modes of K(3)NaFeCl(6)structural units. Raman spectrum of synthetic rinneite with main peaks at 75, 91, 103, 143, 167, 171, 187, and 239 cm(-1)agrees well with the spectra of rinneite inclusions in halite from the Nepa potash deposit and rinneite daughter minerals in salt melt inclusions hosted by quartz veinlets from the porphyry gold systems in the Central Slovakia Volcanic Field. This provides a firm basis for any future identification of this mineral worldwide, using nondestructive Raman spectroscopy.