Fluoride Melts Research Articles

Calculation of oxygen distribution coefficients of RF3 (R = La, Gd) fluorides with the tysonite structure during their crystallization from a melt

Using the method of modified cryoscopy, the thermodynamic distribution coefficients of oxygen k0 in LaF3 and α-GdF3 with a tysonite structure (sp. gr. )were calculated from the fusibility diagrams of condensed systems RF3–R2O3 (R = La, Gd). The calculated coefficients k0 are 1.02 and 1.12 for lanthanum and gadolinium trifluorides, respectively. The values of the coefficients k0 satisfy the condition k0 1, which confirms the formation of maxima in the fusibility curves of tysonite solid solutions tys- RF3–2xOx. For LaF3, the proximity of the distribution coefficient to k0 = 1 corresponds to an almost uniform distribution of oxygen in the volume of the crystallized fluoride melt. Knowledge of oxygen distribution coefficients during crystallization from a melt is important for choosing a strategy for crystallophysical purification of trifluorides RF3 from oxygen impurities and obtaining oxofluorides tys-RF3–2xOx with a given impurity distribution.

Investigation of the Relationship between Molten Fluoride Salt Structure and Fluoroacidity Using Chromium As a Probe Redox Ion

Molten fluoride salts have been studied for decades due to their applications in the production of aluminum as well as in the operation of advanced nuclear reactors. Advanced fission and fusion nuclear reactor designs may include molten fluoride salts as coolants, fuel carriers (fission), or fuel breeding blankets (fusion). Relevant to their nuclear applications are the thermophysical and thermochemical properties of the salt. These include viscosity and thermal conductivity, as well as density, vapor pressure, and heat capacity. Underlying these properties are the interactions of the ions constituting the liquid, characterized by their coordination number, correlation times, and the possible formation of polymeric networks in the melt. The composition and structure of a melt, that is, what ions are present and how they interact, dictates the macroscopic properties relevant to reactor operation. Fluoroacidity, or the activity of dissociated fluoride anions, is one metric that may be used to describe the relationship between salt chemistry and structure. Overall, understanding the relationship between molten fluoride salt chemistry and structure enables deeper understanding and, thus, prediction of property changes that may take place throughout a reactor’s lifetime.In this poster, we present cyclic and square wave voltammetry studies of chromium speciation and diffusivity in various molten fluoride salts, connecting results with current understanding of the structure of the melts. Chromium is a thermodynamically favored corrosion product in molten salt systems, and in this study, it serves as a probe ion in different fluoride melts. Chromium trifluoride is added to various fluoride solvents and the diffusion coefficients of its various oxidation states are calculated and interpreted in light of salt structure. Experimental apparatus design and know-how for high-temperature molten salt electrochemistry are also highlighted.

The giant Baerzhe rare-earth-element–Nb–Zr–Be deposit, Inner Mongolia, China, an Early Cretaceous analogue of the Strange Lake rare-metal deposit, Quebec

The Baerzhe deposit represents world-class mineralization of rare metals, in particular rare earth elements (REEs) and Nb, and shares mineralogical and geochemical similarities with the Strange Lake deposit in Canada. However, the mechanisms responsible for the rare-metal enrichment at Baerzhe are still under debate. Mineralization at Baerzhe is characterized by multiple stages of dissolution, re-precipitation and enrichment of rare-metal elements, as with the Strange Lake deposit. Zirconium was concentrated during magmatic fractionation of elpidite in a transsolvus agpaitic granite (Stage I), and was redistributed into zircon–quartz pseudomorphs during Na-metasomatism (Stage II). Rare earth elements, Nb and Be occur as a variety of mineral assemblages, mainly as pseudomorphs after complete replacement of unknown precursor minerals that are disseminated through the hematized transsolvus granites and were precipitated in three sequential stages (Stages III–V): Stage III is characterized by the mineralization of hingganite, aeschynite-(Y), columbite-(Fe) and euxenite-group minerals, accompanied by hematite alteration; the following Stage IV is defined mainly by monazite-(Ce) crystallization, and Stage V by the preceding REE minerals being replaced by light REE minerals (i.e. bastnäsite-(Ce) and fluocerite-(Ce)). The formation of various pseudomorphs as replacement for precursor minerals is also a common feature documented at Strange Lake. Our results call for a re-evaluation of the timing and role of meteoric waters at Baerzhe, which were suggested by previous researchers to have entered the ore-forming system prior to the mineralization of zircon. New in situ O isotopic analyses on pseudomorph-hosted mineral pairs and investigation of silicate melt–fluoride melt immiscibility through observations and analyses of melt inclusions could provide further insights into the nature of the Baerzhe system.

The basic intermediate-range order structures in the FLiNaK–LaF3–Li2O melt: identification and characterisation

ABSTRACT In this paper, we investigate the structure of FLiNaK–LaF3 melt with small addition of Li2O through the theoretical approach combining ab initio molecular dynamics and simulation of the isolated structural units. The structure of the melt was studied in detail by calculation of radial distribution functions along with coordination numbers and radii. We found that oxyfluoride intermediate-range structure is formed in the melt. Our observations support the suggestions of other authors on formation of intermediate-range structures in fluoride melts containing metal oxides. Given structure shows long lifetime, the consideration of the isolated specie is valuable. We performed a simulation of ‘gas-phase’ [O2La4Fn] structure in order to calculate its Raman spectrum. It was found that the spectrum of the isolated structure agree in semi-quantitative manner with the vibrational density of states of the oxygen ions in the melt.

Mechanism of interaction between zirconium dioxide and fluoride melts

In this work, the mechanism of interaction between zirconium dioxide and fluoride melts was studied. Dissolution rates and maximum permissible oxide contents in the KF-AlF3 and NaF-AlF3 melts were determined under natural convection conditions at a temperature of 750 °C. The results of solubility measurement show that the limiting content of ZrO2 in the KF-AlF3 melt ([KF]/[AlF3] = 1.3) is 0.69 ± 0.10 mol. %, and in the NaF-AlF3 melt ([NaF]/[AlF3] = 1.3) at 800 °C it is 0.54 ± 0.04 mol. %. The calculated dissolution rate of zirconium oxide under these conditions in melts based on potassium fluoride and sodium fluoride is 0.022 mol/min and 0.017 mol/min, respectively. The influence of the cationic composition of the medium and the concentrations of additives on the liquidus temperatures of the melts was studied. It has been established that the increase in liquidus and solidus temperatures is facilitated by the addition of zirconium and aluminium oxides, as well as by the replacement of potassium fluoride with sodium fluoride while maintaining the molar ratio of the replaced cations. Analysis of thermal effects by differential scanning calorimetry (DSC) shows that, regardless of the molar ratio of the components, the onset of the thermal effect in melts based on potassium fluoride occurs at a temperature of 542 °C and in the systems with sodium fluoride additives at a temperature of 597 °C. Presumably, this dependence is associated with the melting of the KAlF4 and K2NaAl3F12 phases formed in the melts based on KF-AlF3 and KF-NaF-AlF3, respectively. It has been established that the melting of the KF-AlF3 mixture is accompanied with a mass loss of up to 1.3 wt. %, which is associated with partial evaporation of KAlF4.

The lithium oxide solubility in molten fluoride system CeF3 - FLiNaK

Molten systems based on alkali metal halides with lithium oxide additives are promising as a working medium on pyrochemical reprocessing of nuclear waste. A mixture of alkali metal fluorides of eutectic composition (FLiNaK) is a suggesting solvent due to the high solubility of actinide oxides, low viscosity, high boiling points, low vapor pressure, and resistance to radiation damage. Thermal analysis, XRD, Raman spectroscopy and thermodynamic simulations were used to obtain evidences on the phase equilibria and liquidus points of the system (0.85 FLiNaK - 0.15 CeF3) - Li2O, containing up to 8.8 mol % lithium oxide. The solubility of lithium oxide in the fluoride melt FLiNaK - CeF3 and the thermodynamic parameters of dissolution were obtained. The eutectic point (the Li2O content is 3.1 mol %, Tm = 489??) and two peritectic points (lithium oxide content are 3.2 and 4.2 mol %, and liquidus points are 497 and 549??, respectively) were found. Thermodynamic simulation results show an exothermic effect due to interaction between lithium oxide and fluoride melt. The interaction product oxyfluoride CeOF was detected by XRD analysis and Raman spectroscopy.

High Temperature Corrosion of Inconel 625 and Pure Nickel in Contact with Fluoride Melts

Considering the fact that fossil fuels are not inexhaustible, and they pollute the environment, the automotive industry is transitioning from internal combustion to electric engines. As a result, batteries are becoming a strategic component of cars and thus battery ingredients are considered as important raw materials. Therefore, these batteries need to be recycled as well, since the natural resources for producing them are limited and some of the elements like nickel which are used in these batteries can be hazardous if left in the environment. In order to recycle electric batteries, furnaces with high temperature corrosion resistance are necessary. Maintaining these furnaces for longer periods is of great interest and necessitates it for the challenges to be dealt with, especially in case of high temperature corrosion.In the present study, high temperature corrosion behavior of Inconel 625 is compared with pure nickel. Both metals have been exposed to fluoride melts (to mimic the recycling process) for different durations of time. The performances of these two bulk metals are investigated mainly through scanning electron microscope and X-ray diffraction. Element leaching, oxidation, depth of internal attack and depletion profile are among the main parameters studied here. Experiments are carried out both in dry and humid condition to see how humidity changes the reactions. Since there are different alloying elements in Inconel 625, and humidity is involved, pure nickel is used as the baseline to see the effect of different parameters involved. Filtered air is used as the main environment in this study and lithium fluoride is used as the main salt.

Coordination Structure of Si(II) Ions in Binary Melts (LiF-KF, LiF-NaF, and NaF-KF) and Ternary Melt (LiF-NaF-KF).

The formation of Si(II) by the comproportionation reaction between electrodeposited silicon and Si(IV) ions [Si(IV) + Si0 ⇄ 2Si(II)] in fluoride melts has been discussed in many previous reports on the electrochemical processing of silicon. In this study, the coordination structure of Si(II) ions in LiF-KF, LiF-NaF, NaF-KF, and LiF-NaF-KF melts was investigated by high-temperature Raman spectroscopy and quantum chemical calculation based on density functional theory. The formation of Si(II) ions was induced by mixing metallic silicon powder as the source of Si0, with the melts containing hexafluoro silicate or silicon dioxide as the source of Si(IV) ions. The simulated vibrational modes of the Si(II) species and the experimental Raman bands showed good agreement. It was found that both Si(II) and Si(IV) species were detected in either fluoride melt, demonstrating that the proposed comproportionation reaction between Si0 and Si(IV) occurred. In addition, the interaction between Si(II) and F-, O2-, Li+, Na+, and K+ ions significantly changed depending on the composition of fluoride melts. The coordination structure of the Si(II) ions reported in this study will provide clues for controlling the electrodeposition process of silicon in fluoride melts.

PROTECTIVE METAL COATINGS MADE OF MOLYBDENUM ON STEEL 12Cr18Ni10Ti FOR FLUORIDE MELTS. OBTAINING, CERTIFICATION, EFFICIENCY

The successful use of molten alkali metal fluorides as an electrolyte for high-temperature devices requires the development of such reactor materials that have high corrosion resistance in melts with compositions characteristic of liquid-salt mixing reactors. This is one of the most important unresolved problems. One of the effective ways to reduce corrosion losses is to create a layer on the surface of the material that protects the metal from the corrosive effects of the environment. In this paper, molybdenum insulating coatings on steel 12Kh18Ni10Ti obtained in molten salts of various compositions and by various methods are considered as protective layers. Experiments were carried out on the electrodeposition of molybdenum coatings on structural materials based on iron (steel 12Cr18Ni10Ti). The coatings obtained by the electrochemical method are inhomogeneous and easily exfoliating. The thickness of molybdenum coatings obtained from molten salts is 8.15 and 20.34 μm on steel in FLiNaK and LiCl–KCl melt, respectively. Corrosion tests have shown the inefficiency of the molybdenum coating obtained from both chloride and fluoride melts. The corrosion rate of 12Cr18Ni10Ti steel in FLiNaK/FLiNaK + 5% CeF3 melts at 650°C and a holding time of 100 hours decreases in the following row: 12Cr18Ni10Ti + Mo (0.75/0.77 mm/year) 12Cr18Ni10Ti (0.45/0.50 mm/year).

Electrochemical and Spectroscopic Study on Electrochemical Processing of Silicon in Fluoride Melt

For sustainable space utilization on the Moon and the Mars, it is essential to establish in-situ resources and energy utilization systems in space. Because of the large amount of silica in the regolith which composed of metallic oxides on the Moon and the Mars, the technology development for the covering the silica to silicon and oxygen is indispensable. The silicon can be used as a key material for silicon photovoltaics. Against this background, the authors have studied the electrochemical reduction of silica to silicon in fluoride melt. We propose a one-step process to obtain a silicon film on the cathode by electrolysis using molten salts containing silica. To determine the feasibility of the proposed process, it is necessary to understand the effects of the physicochemical properties such as the coordination structure of Si ions in the fluoride melt since the difference in the melt structure affects the nucleation and growth mechanisms of the silicon electrodeposition. However, there are few reports on the dissolved state of silicon ions in fluoride melt. The author thus clarified the relationship of the electrochemical behavior of coordination structure of Si ions in fluoride melts composed of LiF, KF, and NaF.The coordination structure of Si ions in the fluoride melt was investigated by high-temperature Raman spectroscopy and quantum chemical calculations based on the density functional theory (DFT). The vibrational modes of the Si ions were detected through high-temperature Raman spectroscopy and the Raman bands were simulated by DFT calculations. We clarified the interaction between Si ions and cation and anion species such as Li+, Na+, K+, O2−, and F−. In addition, the electrochemical behavior of Si ions was investigated by electrochemical measurements. The effect of O2− ions on the dissolution of SiO2 and the electrodeposition process of Si in fluoride molten salts revealed a significant increase in the reduction current of Si ions as well as in the film thickness and current efficiency of deposited Si. The molten fluoride system, which can fabricate Si films from SiO2 at low temperatures, has the potential to develop environmentally friendly and sustainable electrolytic systems.

Modification of SnF2 cathode material of a fluoride-ion electrochemical cell with carbon additives

This article presents studies of carbon additives (graphite, thermally expended graphite (TEG), expandable graphite (EG), graphene, single-walled carbon nanotubes (SWCNT), nanocomposite SnF2@SWCNT) in the cathode material (SnF2) of solid-state fluoride-ion galvanic cells. The cells are made in the form of multilayer pellets: metallic cerium anode, tysonite solid solution of barium fluoride in the lanthanium fluoride La1−xBaxF3−x (x ≈ 0.05) electrolyte, SnF2 cathode with carbon additive. The pellets are investigated by scanning electron microscopy, cyclic voltammetry, impedance spectroscopy. Carbon additives are characterized by Raman spectroscopy. The original galvanic cell with SnF2 cathode without additives has open-circuit voltage (OCV) 1.69 V (at room temperature) and ∼1.46 V (at 180 °C). The galvanic cell with EG additive (mechanical mixture) has OCV 2.45 V at room temperature. The introduction of a carbon additive into the tin fluoride melt, followed by mechanical grinding to create a cathode material, reduces the current density. The use of SnF2@SWCNT nanocomposite increases the current density (1.295 A/m2) by more than 2.5 times compared to pure nanotubes. The current density of FIB with SnF2@SWCNT exceeds the values obtained with other carbon additives in the cathode material.

Charge Transfer Kinetics of the Ti(IV)/Ti(III) Redox Couple in the Cesium Chloride-Cesium Fluoride Melt with Addition of Alkaline Earth Metal Cations

The electrochemical behavior of the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt%)-K2TiF6 melt was studied by cyclic voltammetry. The diffusion coefficients of the Ti(IV) complexes were calculated using the Randles-Sevcik equation. The standard rate constants of charge transfer for the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt%)-K2TiF6 melt without and with additions of alkaline Earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) were determined. It was found that the rate constants of charge transfer increase with increasing ionic potential of the addition, reaching a maximum value for complexes with outer-sphere cations of magnesium, and this dependence is rectilinear. The activation energies of the charge transfer process in melts with additions of alkaline Earth metal cations were calculated and these values are significantly lower than the activation energy of the initial system CsCl-CsF(10 wt%)-K2TiF6. The kinetic parameters of the Ti(IV)/Ti(III) redox couple in chloride-fluoride melts with different second coordination sphere composition of the complexes were compared.

Determination of the Oxygen Content in the LiF-NaF-KF Melt.

The present paper is dedicated to the quantitative determination of oxygen-containing impurities in the LiF-NaF-KF eutectic using electrochemical (cyclic and square-wave voltammetry) and reduction melting methods. The LiF-NaF-KF melt was analyzed before and after purifying electrolysis. The amount of oxygen-containing impurities removed from the salt during purification was determined. It was found that after electrolysis, the concentration of oxygen-containing impurities decreased by 7 times. The results obtained via electrochemical techniques and reduction melting were well-correlated, which made it possible to evaluate the quality of the LiF-NaF-KF F melt. To verify the analysis conditions, mechanical mixtures of LiF-NaF-KF containing Li2O were analyzed using the reduction melting method. The oxygen concentration in the mixtures varied from 0.672 to 2.554 wt. %. Based on the analysis results, the dependence approximated by the straight line was obtained. These data may be used to draw calibration curves and to further develop the procedure of oxygen analysis of fluoride melts.

Origin of Amphibole-Biotite-Fluorite-Rich Enclaves from Gabal El-Ineigi Fluorite-Bearing Granite, Central Eastern Desert of Egypt: Insights into Fluoride–Calcium and Silicate Liquid Immiscibility

Gabal El-Ineigi fluorite-bearing rare-metal granite with A-type affinity, located in the Central Eastern Desert of Egypt, is distinguished by its abundance of large fluorite-quartz veins and mafic enclaves. Plagioclase (labradorite to oligoclase), Mg-rich biotite, and Mg-rich hornblende are the main components of mafic enclaves, with significant amounts of fluorite as essential phases, and titanite and Fe-Ti oxides (Nb-free rutile and ilmenite-rutile solid solution) as the main accessories. These enclaves are monzodioritic in composition, Si-poor, and highly enriched in Ca, Fe, Mg, and F compared to the host alkali feldspar F-poor Si-rich granites. Given the conflicting evidence for a restitic, xenolithic, magma mixing/mingling, cumulate, or bimodal origin for these enclaves, we propose that the mafic enclaves and felsic host granites are two conjugate liquids, with contrasting compositions, of a single parental melt. This is inferred by the normalized REE patterns that are similar. As a result, liquid immiscibility is proposed as a probable explanation for this mafic–felsic rock association. These enclaves can be interpreted as transient melt phases between pure silicate and calcium-fluoride melts that are preserved from the early stages of separation before evolving into a pure fluoride (Ca-F) melt during magma evolution. Due to element partitioning related to melt unmixing, the enclaves are preferentially enriched in Ca, F, Li, Y, and REE and depleted in HFSE (such as Zr, U, Th, Ta, Nb, Hf, and Ga) in comparison to the host granites. Furthermore, mafic enclaves exhibit W-type tetrad effects, while host granites exhibit M-type tetrad effects, implying that the REE partitioning, caused by liquid immiscibility, is complementary.

Molecular Dynamics Simulation of Thin Silicon Carbide Films Formation by the Electrolytic Method.

Silicon carbide is successfully implemented in semiconductor technology; it is also used in systems operating under aggressive environmental conditions, including high temperatures and radiation exposure. In the present work, molecular dynamics modeling of the electrolytic deposition of silicon carbide films on copper, nickel, and graphite substrates in a fluoride melt is carried out. Various mechanisms of SiC film growth on graphite and metal substrates were observed. Two types of potentials (Tersoff and Morse) are used to describe the interaction between the film and the graphite substrate. In the case of the Morse potential, a 1.5 times higher adhesion energy of the SiC film to graphite and a higher crystallinity of the film was observed than is the case of the Tersoff potential. The growth rate of clusters on metal substrates has been determined. The detailed structure of the films was studied by the method of statistical geometry based on the construction of Voronoi polyhedra. The film growth based on the use of the Morse potential is compared with a heteroepitaxial electrodeposition model. The results of this work are important for the development of a technology for obtaining thin films of silicon carbide with stable chemical properties, high thermal conductivity, low thermal expansion coefficient, and good wear resistance.

Mechanism and Kinetics of Interaction of FLiNaK–CeF3 Melt with Water Vapors and Oxygen in the Air Atmosphere

The mechanism and kinetic parameters of the interaction of the FLiNaK–CeF3 melt with water vapors and oxygen in the air atmosphere were determined using Raman and IR spectroscopy, XRD analysis, and thermodynamic modeling of processes. The presence of the 4CeF3(solution) + 6H2O (gas) + O2(gas) = 4CeO2(solid) + 12HF(gas) reaction, which disturbs the fluoride melt homogeneity, was verified in situ by Raman spectroscopy adopted for high-temperature, chemically aggressive fluoride systems. Based on the obtained spectral data, the type of the kinetic equation, order, and rate constant of the chemical reaction were determined. The concentration of cerium dioxide was found to increase linearly in time and a zero reaction order with respect to CeO2 was detected. The change in the concentration of CeO2 over time at T = 510 °C is described by the equation C = 0.085t; the reaction rate constant is 0.085 mol. %∙min−1. The obtained kinetic parameters may be used to model emergencies related with the depressurization of the coolant circuit or the working area of the molten salt reactor.

Chemical Interactions between Thorium(IV) and O2- in the FLiBe and FLiNaK Molten Salt Systems

The chemical interactions between thorium(IV) and O2- in the LiF-BeF2 (2 : 1 mol%) (FLiBe) and LiF-NaF-KF (46.5 : 11.5 : 42 mol%) (FLiNaK) molten salt systems were studied at 873 K. The precipitation-dissolution behavior of Th(IV) oxide/oxyfluoride species, as well as the speciation law of these species and their relationship with oxide concentration in fluoride melts, were clarified. The results showed that the interactions between Th(IV) and O2- in the FLiBe melt would only produce ThO2. The saturated solubility of ThO2 in the FLiBe melt was 0.057 mol/kg, and its corresponding apparent solubility product ( K s p ′ ) was 8.8 ± 0.1 × 10 − 4 mol3/kg3 and 8.6 ± 0.7 × 10 − 4 mol3/kg3 by dissolution and oxide titration methods, respectively. However, in the FLiNaK melt, the interactions between Th(IV) and O2- were more complex than that in FLiBe, and Th(IV) oxyfluoride species (i.e., Th2OF104- and ThOF2) were produced. Th2OF104- was initially formed with the ratio of r ≤ 0.5 ( r = O 2 − added / Th IV initial ), and the Th2OF104- was converted to ThOF2 precipitate when r > 0.5 . Therefore, the soluble Th2OF104- is the important intermediate between Th(IV), O2-, and ThOF2 precipitation. The difference in results of the FLiBe and FLiNaK melts was attributed to the difference of free F- content in the two systems. The present work provided important reference and fundamental data for understanding the nature of thorium fuel precipitation and how to control it in the molten fluoride media, which is of significant importance for the safe operation of molten salt reactor (MSR).

HIGH-TEMPERATURE PASSIVATION OF THE SURFACE OF CANDIDATE MATERIALS FOR LSR BY ADDING O<sup>2–</sup> TO THE SALT PHASE OF THE HALIDE MELT

Experiments were carried out to determine the corrosion rate of stainless steel AISI 316 in a fluoride melt with different concentrations of O2– (by adding lithium oxide to the melt in the concentration range from 0 to 5 wt %). The corrosion rate decreases by an order of magnitude at an oxygen anion concentration in the melt from 0.2 to 0.4 wt %, which may indicate the detection of the phenomenon of high-temperature passivation of the material due to the modification of the composition of the fluoride melt and a decrease in its corrosion activity. In addition, the type of intergranular and pitting corrosion typical of stainless steels in fluoride melts, which is the most dangerous from the point of view of the structural reactor material, changes to continuous when lithium oxide is added due to the “healing” of individual corrosion centers with excess oxygen-containing compounds. The formation of a protective layer of the spinel type with a thickness of 1 μm was established.

Development of ultralight, tough and hydrophobic polymethylmethacrylate/polyvinylidene fluoride shape memory foams for heat insulation applications

Thermal insulation is vital for achieving efficient thermal management, energy conservation, and emission reduction. However, the existing polymer foams still have some performance limitations and cannot meet the application demands in a wider range of situations. Accordingly, herein, an innovative strategy based on polyvinylidene fluoride (PVDF) melt blending and CO2 microcellular foaming was proposed for the fabrication of lightweight high-performance polymethylmethacrylate (PMMA) foams for heat insulation, and ultralight, tough, and hydrophobic foams with outstanding heat insulation and shape memory performances were successfully prepared. Because of the plasticization of PVDF and nucleation of PVDF microcrystals, the foaming temperature window of PMMA substantially descended, and the cellular structure of PMMA became refined. Blend foams with expansion ratios of 36.2, cell sizes of 15.8 μm, and foam densities of 0.0357 g∙cm−3 were obtained at 130 °C. Due to higher porosity and strong infrared absorption ability of PMMA, the resulting foams exhibited thermal conductivities of less than 32 mW∙m−1∙K−1. Owing to the hydrophobicity and incombustibility of PVDF and its microcrystals, the blend foams demonstrated better hydrophobicities, shape memory properties, and flame retardancies. This study provides an effective way for the green and mass production of high-performance polymer foams with appropriate thermal insulation performances.

Coordination Structure of Titanium Ions in Molten LiF-KF Mixture with the Addition of TiO2 and Bulk Titanium

The difference between Ti(III) and Ti(IV) significantly influences the electrodeposition process of Ti in fluoride melt. In this study, we investigated the melt structure of LiF-KF with the addition of TiO2 for Ti(IV) and with the addition of both TiO2 and bulk titanium (Ti0) for Ti(III) by combining high-temperature Raman spectroscopic technique and density functional theory calculations. The Raman spectra were characterized by three kinds of coordination structures: polyatomic ion-like structures such as TiO2F2 2−, polyatomic cation-coordinated ion-like structures such as [TiF6−K]−, and molecule-like structures such as TiOF3−K. The results showed that the K+ ions are more likely to form structures with the titanium oxyfluorides. We also found that the melt with and without Ti0 showed almost completely different Raman bands. The information gained in this study for the coordination structure around titanium ions in the fluoride melts is significant towards the electrodeposition process of titanium-based materials in fluoride melt and marks an important step towards further understanding of the dissolution process of titanium oxyhalide structure in the melt.