Solid Fluoride Research Articles

Evaluate the Limits of F Covalent Bonding with Transition Metals at High Valent States in Li2MO2f ( M = Mn, Co, Ni ) Oxyfluoride

The capacity of transition metal oxides as Li-ion battery cathodes are limited by instabilities that arise when high states of charge are achieved1. Oxyfluorides with a disordered rock-salt structure have emerged as attractive alternatives2, but the role of F in their electrochemical function, particularly when metals reach high formal oxidation states, remains to be ascertained so far. In our recent study3, using X-ray Absorption Spectroscopy (XAS) measurements of Mn, O and F, we revealed the existence of Mn-F covalent interactions in Li2MnO2F. The results challenged the assumption of F as largely a spectator ion, providing instead a nuanced picture of redox compensation in oxyfluorides. They suggested the existence of unique knobs of design of battery cathodes in these chemical spaces, by manipulating the covalent interactions between transition metals and two different anions. To further expand the understanding of F participation in the covalent bonding and its electrochemical effect on oxyfluoride materials, we synthesized Li2CoO2F and Li2NiO2F4. Solid fluorides of ions like Co(IV) and Ni(IV) are known to be aggressive oxidizers5. Analysis of the transition metal fluoride literature reveals that oxidation states of IV and higher could lead to unstable phases for late transition metals, particularly Co or Ni5. Unlike oxides, rather than reductively releasing F2, they have a strong propensity to act as highly oxidizing F- donors6,7, being able to oxidize even other halogen cations to their VII state. Yet the oxidation of Ni(II) features prominently in oxyfluoride cathodes that were recently discovered. This puzzle and the exact role of F in modulating the formal redox chemistry of a late metal like Ni and Co in the presence of O remains to be elucidated. To address this question and determine a periodic trend on the role of a mixture of anions in improving the energy density in such cathode materials, we conducted a deep dive into Li2CoO2F and Li2NiO2F. We interrogated the covalent interaction between the oxygen 2p states, fluorine 2p states, and the transition metal 3d orbitals, and their respective contribution to the charge compensation mechanism using XAS. These two oxyfluorides data were compared with the previous Li2MnO2F data to understand the effect of varying the transition metal and how that affects the overall electrochemistry of these materials. We also have estimated the M-O and M-F hybridization and provided a periodic trend. This study allowed us to define a rule to manipulate each element in a oxyfluoride that determines the electrochemical properties of these cathode materials.

CONDUCTIVITY OF SOLID FLUORIDE-CONDUC­TING PHASES BaxPb0.86-xSn1.14F4

This work presents the results of research of complex solid fluoride ion conducting phases based on lead and tin fluorides. Structure and conductive properties of solid solutions based on PbSnF4 were investigated. Series of samples were synthesized with replacement of lead cations with barium cations in structure of Pb0.86Sn1.14F4 in the concentration range of 0 ≤x ≤0.86. The barium cation has a larger radius and does not have a stereoactive lone pair of electrons, which can have a significant contribution to the conductivity of the synthesized phases and the characteristics of fluoride ion transportation in them.
 It was established that with partial or complete replacement of lead cations with barium cations in the fluoride ion conducting phases in Pb0.86Sn1.14F4 solid solutions of BaxPb0.86‑xSn1.14F4 , where x takes the values 0 ≤x ≤0.86 are formed. The symmetry of the crystal lattice of the synthesized phases in the concentration range of 0 ≤x ≤0.43 corresponds to the structural type of β-PbSnF4 (space group P4/ nmm). Farther increase in the content of barium fluoride cause their crystal lattice to rearrange and approach the structural type of BaSnF4 with preservation of the space group symmetry. The conductive properties of the synthesized phases were investigated.
 We register increase in conductivity of samples bound to increase of barium cation content in the range of 0 ≤x ≤0.43. After reaching peak in conductivity of samples it gradually lowers with increase of barium cation content in the range of 0.43 ≤x ≤0.86.
 The fluoride ion conducting phase Pb0.43Ba0.43Sn1.14F4, isostructural to β-PbSnF4, in comparison with the currently known fluoride-conducting phases has have the highest electrical conductivity in a wide temperature range. Its conductivity is almost two orders of magnitude higher than that of β-PbSnF4 and is 0.12 S/cm at 373 K. With 19FNMR method, it was determined that electrical conductivity is mainly provided by internodal fluorine anions, which are localized between layers of barium and stanium cations. The transfer numbers for fluorine anions in the synthesized phases correspond to the theoretical ones.

CALPHAD modeling of uranium nitride (UN) fabrication routes enabled by first-principles calculations

The thermochemical details of fabricating uranium nitride (UN) by ammonolysis of uranium tetraflouride (UF4) were determined using density functional theory (DFT) and CALculation of PHAse Diagrams (CALPHAD) computational methods. The thermochemical data of all binary, ternary, and quaternary U–H–N–F phases were computed using DFT, and the data for the phases that have not been measured experimentally, including UN2 and NH4F(g), were combined with existing experimentally-determined data for CALPHAD modeling. The DFT data were benchmarked using experimental Gibbs energy of reaction and experimental thermochemical data for individual species. Phase diagrams relevant to the ammonolysis reaction are depicted, showing regions of stability for solid U–N, U–F and U–N–F phases. An unidentified phase produced in a previous experiment was identified as UN0.95F1.2 (UNF) by comparing its X-ray diffraction spectrum to the experimental spectrum, and its formation during the fabrication of UN from UF4 is supported by the simulated phase diagram. It is calculated that UN2 can be produced by the ammonolysis of UF4, but requires elevated temperatures, high NH3(g) partial pressure, and large amounts of flowing NH3(g) to avoid solid fluoride impurities in the uranium nitride. Likewise, U2N3 can be produced instead at temperatures greater than 980 K. The use of silane (SiH4) gas was investigated as a potential additive in the ammonolysis fabrication route to speed removal of fluorine. The addition of SiH4(g) offers little advantage to the removal of fluorine, and adds the complication of Si3N4 formation. The use of DFT to fill in missing data to perform CALPHAD calculations demonstrated here allows for the determination of more comprehensive and trustworthy phase diagrams than the use of existing experimental data alone.

Technical Note: Corrosion Behavior of 316 Stainless Steel With and Without an Ni Coating in Solid-State Fluoride Salt

With the rapid development of molten salt reactors, the problem of post-treatment of spent fuel salt discharged from the core becomes increasingly prominent. Like molten fluoride salts, solid fluoride salts are also highly corrosive, which poses a serious challenge to container materials. This paper describes the corrosion behavior of 316 stainless steel (316 SS) with and without Ni coating in low-temperature solid fluoride salt. Results show that 316 SS without Ni coating experiences pitting corrosion with the prolongation of corrosion time. 316 SS with Ni coating experiences intergranular corrosion. In addition, a loose hollow interlayer is formed between Ni coating and matrix. Corrosion of both samples increases with the extension of exposure time with solid fluoride salts.

Determination of Sr to Ca ratio in solid carbonate, fluoride, and nitrate samples using the fundamental parameters of EDXRF: experimental and empirical evaluation of non-destructive assays in light matrices

Various aspects of the intensity ratio method of EDXRF, as applied to binary carbonate mixtures of Sr and Ca, are illustrated.

MAMMALS IN THE CONDITIONS OF ANTHROPOGENIC IMPACT ON THE HABITAT

Mammals are distributed everywhere on the territory of the Pavlodar region (North-East of Kazakhstan). The narrow-crusted vole and steppe mouse species dominate in the anthropogenic habitats. Small mammals live in the conditions of emission of large enterprises of heavy industry. There are oxides of sulfur (IV) and nitrogen (IV), carbon monoxide (II), solid fluorides, hydrogen fluoride, benz(a)pyrene; V, Cr, Mn, Fe, Ni, Cu, Zn, Pb near large factories and highways. Animals receive toxic substances from food through trophic levels and through respiration. Insectivorous mammals suffer from pollution more than rodents. Fluoride accumulates in the bone tissue. Heavy metals are present in the coat, liver, kidneys, lungs, genitals and musculoskeletal system of mammals. The most dangerous for animal health is benz (a) pyrene, which is a mutagen in small quantities. The degree of influence of toxic substances decreases with the remoteness of the habitat from the sources of pollution.

Study of the content of fluorides in atmospheric air in Bokhtar region and Tursunzade city of Tajikistan

Background: The emission and presence of air pollutants such as fluorides has over burdenized the public healthcare issues. The current study aimed to determine the content of fluorides in atmospheric air in Bokhtar region and Tursunzade city of Tajikistan. Methods: Based on the direction of wind, two zones were selected in the current study: experimental and control. In the first (experimental) zone, those areas were selected where the western, northern and northeastern directions of wind was significant. Dzhura Rakhmonov was assigned to the control zone with the shortest time for the eastward winds. In general, 72 samples of atmospheric air were taken in 12 settlements of the city of Tursunzade and 90 samples of atmospheric air in the Bokhtar region of the Khatlon province. To determine fluorine in air, a potentiometric method with an ion-selective electrode was used, which makes it possible to measure the potential concentrations of fluorides in atmospheric air. Results: Compounds of gaseous (hydrogen fluoride) and solid fluorine (salts of hydrofluoric acid), which are the main emission from various sources, were found in the atmospheric air of the populated areas of the city of Tursunzade, where the aluminum plant industry is located. The maximum amount of hydrogen fluoride in the experimental zone (Jamoat and Navobod) with a western wind direction was found in the autumn, which exceeded the MPC. However, the amount of solid fluorides in the western direction of the wind ranged from 0.01 to 1.0 mg / m3, which did not exceed the MPC value and was not significant. In control zone (Dzhura Rakhmonov) the said pollutants hydrogen fluoride and solid fluorine were not significant in autumn within accordance to MPC limit. The results of the study of atmospheric air in 15 administrative cities and districts of the Bokhtar region showed a complete absence of solid fluorides in all samples of atmospheric air. Conclusion: Compounds of gaseous fluorine and salts of hydrofluoric acid were found in the atmospheric air of populated areas of the city of Tursunzade, and no significant amounts in the Bokhtar region according to MPC and control. The maximum amount of fluorine compounds was found in the experimental zone (Jamoat Navobod) of the city of Tursunzade.

Initiating a Room‐Temperature Rechargeable Aqueous Fluoride‐Ion Battery with Long Lifespan through a Rational Buffering Phase Design

AbstractPreviously reported fluoride‐ion batteries (FIBs) can only work at high temperatures (>150 °C) with solid electrolytes or organic electrolytes. Aqueous FIB has barely been reported due to the unstable F– electrochemistry in aqueous electrolytes. In addition, the electrode materials commonly suffer from serious and adverse volume expansion during the conversion reaction. Herein, a stable aqueous F– electrochemistry is realized by a rational buffering phase design in which stagger distribution of BiF3 and Bi7F11O5 phases is achieved. The enhanced F– electrochemistry is systematically studied and suggests that the Bi7F11O5 phase plays a vital role in the stability and reversibility of the electrode due to its lower volume change and higher electronic conductivity. Pulverization and dissolution of active species issues are also suppressed. As a result, the assembled battery delivers excellent cycling stability, high reversibility, and superior rate capability, which is far better than conventional solid fluoride shuttle batteries. Mechanism studies demonstrate that the capacity comes from reversible conversion between Bi3+ and Bi0 with an intermediate phase of Bi7F11O5. This work initiates room‐temperature FIBs with aqueous electrolytes and provides a good cycling lifespan, which pave the way to a more practical fluoride ion storage system.

Reprocessing of fluorination ash surrogate in the CARBOFLUOREX process

Abstract This work presents the results of laboratory scale tests of the CARBOFLUOREX (CARBOnate FLUORide EXtraction) process – a novel technology for the recovery of U and Pu from the solid fluorides residue (fluorination ash) of Fluoride Volatility Method (FVM) reprocessing of spent nuclear fuel (SNF). To study the oxidative leaching of U from the fluorination ash (FA) by Na2CO3 or Na2CO3–H2O2 solutions followed by solvent extraction by methyltrioctylammonium carbonate in toluene and purification of U from the fission products (FPs) impurities we used a surrogate of FA consisting of UF4 or UO2F2, and FPs fluorides with stable isotopes of Ce, Zr, Sr, Ba, Cs, Fe, Cr, Ni, La, Nd, Pr, Sm. Purification factors of U from impurities at the solvent extraction refining stage reached the values of 104–105, and up to 106 upon the completion of the processing cycle. Obtained results showed a high efficiency of the CARBOFLUOREX process for recovery and separating of U from FPs contained in FA, which allows completing of the FVM cycle with recovery of U and Pu from hardly processed FA.

High surface area chromium(III) fluoride – Preparation and some properties

Reaction of hydrated hydrazinium fluorochromate(III), [N2H6][CrF5]·H2O, with fluorine (F2) in anhydrous hydrogen fluoride (aHF) medium at room temperature yields completely amorphous CrF3-based materials with exceptionally high specific surface areas of 180–420 m2 g−1 (HS-CrF3). The stepwise reaction starts with the oxidative decomposition of the cationic part of the precursor with F2 that gives a CrF3 intermediate with low surface area. In the following step, part of Cr3+ is oxidized to Cr>3+, and in the presence of residual H2O/[H3O]+ species Cr>3+ fluoride oxides are formed. Formation of volatile chromium compounds, mainly CrO2F2, is apparently the key step in HS-CrF3 formation. Removal of these components from the final product reduces the oxygen content, and generates microporosity. The HS-CrF3 materials are completely amorphous with a bulk composition that is close to stoichiometric CrF3. Small amounts of Cr>3+ and oxygen in the final product very likely originate from the retained non-volatile CrOF3. The HS-CrF3 materials are Lewis acids and exhibit a high reactivity towards chlorofluorocarbons (CFCs) evidenced by substantial F/Cl exchange between CFCs and the solid fluoride. High reactivity of these new materials can be ascribed to their nanoscopic nature, exceptionally high surface area, and low levels of impurities. As such, they represent an interesting new class of benchmark fluoride materials applicable in fluorocarbon chemistry.

Crystal phase and surface defect driven synthesis of Pb1−xSnxF2 solid solution electrolyte for fluoride ion batteries

Pb1−xSnxF2 layered fluoride super-ionic conductors have become of increased interest for its potential use for all-solid-state secondary fluoride-ion based batteries. By planetary high-energy ball-milling, we have prepared solid-solutions for different stoichiometries: x=0.4–0.6. These materials were investigated by X-ray Diffraction (XRD), Electrochemical Impedance Spectroscopy (EIS), Field Emission Scanning Electron Microscope (FESEM), High-Resolution Transmission Electron Microscope (HRTEM) and Nuclear Magnetic Resonance (NMR) from which a dominant γ-phase (β-PbF2 form) cubic structure with crystal and surface defects have been revealed. Crystallite sizes of around 17nm were achieved. The ionic conductivity of the materials provided a maximum for x=0.45 reaching a value of 2.5·10−3S·cm−1 at room temperature, with an activation energy of 0.30eV. This solid-state fluorite type electrolyte was applied for testing a solid fluoride ion battery assembly consisting of Bi-cathode and CeF3-anode.

Собственная фтор-ионная проводимость кристаллических матриц фторидных супериоников: BaF-=SUB=-2-=/SUB=- (тип флюорита) и LaF-=SUB=-3-=/SUB=- (тип тисонита)

AbstractThe intrinsic fluorine-ion conductivity σ_lat of BaF_2 (CaF_2 fluorite type) and LaF_3 (tysonite type) crystals is studied by the impedance spectroscopy method. These compounds represent two major structural types taken as the basis to form the best nonstoichiometric fluorine-conducting solid electrolytes. The conductivity σ_lat caused by thermally activated defects is manifested in the field of high temperatures, where conductometric measurements are complicated by pyrohydrolysis. The experiments carried out in inert atmosphere with application of the impedance method have for the first time produced the reliable values of σ_lat of fluoride crystals in conditions of suppression of pyrohydrolysis (BaF_2) or partial pyrohydrolysis (LaF_3). Values of the σ_lat at 773 K for BaF_2 and LaF_3 crystals grown from melt by the Bridgman method using the vacuum technology are 2.2 × 10^–5 and 8.5 × 10^–3 S/cm differing by a factor of ~400. The tysonite structural type has been proved feasible for making high-conductivity solid fluoride electrolytes based on the analysis of energy characteristics of formation and migration of anionic defects.

The Intrinsic Fluorine-Ion Conductivity of Crystalline Matrices of Fluoride Superionics: BaF2 (Fluorite Type) and LaF3 (Tysonite Type)

The intrinsic fluorine-ion conductivity σlat of BaF2 (CaF2 fluorite type) and LaF3 (tysonite type) crystals is studied by the impedance spectroscopy method. These compounds represent two major structural types taken as the basis to form the best nonstoichiometric fluorine-conducting solid electrolytes. The conductivity σlat caused by thermally activated defects is manifested in the field of high temperatures, where conductometric measurements are complicated by pyrohydrolysis. The experiments carried out in inert atmosphere with application of the impedance method have for the first time produced the reliable values of σlat of fluoride crystals in conditions of suppression of pyrohydrolysis (BaF2) or partial pyrohydrolysis (LaF3). Values of the σlat at 773 K for BaF2 and LaF3 crystals grown from melt by the Bridgman method using the vacuum technology are 2.2 × 10–5 and 8.5 × 10–3 S/cm differing by a factor of ~400. The tysonite structural type has been proved feasible for making high-conductivity solid fluoride electrolytes based on the analysis of energy characteristics of formation and migration of anionic defects.

Enhancing predicted fluoride varnish efficacy and post-treatment compliance by means of calcium-containing gummy bears

ObjectivesThis study determined whether consumption of calcium-containing gummies prior to fluoride varnish application enhances plaque fluoride retention and compliance with post-varnish application instructions. MethodsThe present study followed a multi-center, parallel, randomized, and laboratory analyst-blind design. Following IRB approval, parent consent and child assent, 44 subjects (7–12 years), were randomized to either gummy or no-gummy study groups. A baseline plaque sample was obtained after a wash-out period. Fluoride varnish (5% NaF) was applied; subjects in the gummy group received two calcium-containing gummies prior to varnish application. Subjects were given two questionnaires to complete (subject and parent) to investigate adherence to post-treatment instructions. Three days later, a second plaque sample was obtained. Plaque was analyzed for plaque fluid and solid fluoride concentrations. Fluoride data were analyzed using Wilcoxon Rank Sum tests, questionnaire data using Pearson chi-square tests. ResultsPlaque fluid fluoride did not change pre- to post-treatment in the gummy group (mean ± sd: 8.8 ± 5.7 μmol/l vs. 10.0 ± 6.3 μmol/l; p = 0.265) or in the no-gummy group (8.1 ± 4.4 μmol/l vs. 16.1 ± 20.0 μmol/l; p = 0.058). Groups were not different for plaque fluid fluoride pre-treatment (p = 1.000), post-treatment (p = 0.904), or change (p = 0.904). Plaque solid fluoride did not change pre- to post-treatment in the gummy group (0.89 ± 1.10 μmol/g vs. 1.37 ± 1.77 μmol/g; p = 0.073) or in the no-gummy group (0.68 ± 0.77 μmol/g vs. 2.01 ± 5.00 μmol/g; p = 0.190). Groups were not different for plaque solid fluoride pre-treatment (p = 1.000), post-treatment (p = 0.466), or change (p = 0.874). No significant differences were found between groups for questionnaire responses. ConclusionThis study failed to demonstrate an effect of calcium-containing gummies in enhancing plaque fluoride retention. Clinical significanceThe consumption of calcium-containing gummies prior to fluoride varnish application does not promote greater intra-oral fluoride retention or better adherence to post-treatment instructions.

Solid Fluoride Electrolytes and Their Composite with Carbon: Issues and Challenges for Rechargeable Solid State Fluoride-Ion Batteries

Solid-state batteries relying on fluoride-ion shuttle are still at their early stage of development. Assessing the fluoride solid electrolyte’s electrochemical stability and its conduction properties in a mixture with carbon, as well as the possible interaction of fluoride-ion with carbon both during the electrode preparation and upon electrochemical reactions, are mandatory to enable future practical applications. Here, we discuss these points using LaF3 doped with BaF2 (La0.95Ba0.05F2.95, LBF) as a benchmark solid fluoride electrolyte. We establish that lithium may be used as a pseudoreference electrode to assess the electrochemical stability window of LBF and support the experiment with thermodynamic calculations. We demonstrate the chemical compatibility of LBF with carbon upon ball-milling and investigate the electrical conductivity of the formed LBF-C composite. We use a LBF|LBF-C|LBF cell (in this configuration, LBF serves as electronically blocking electrode) to assess the ionic conductivity of th...

Experimental study on elemental behaviors in fluorination of nuclear spent fuel with flame reactor

Our proposed spent nuclear fuel reprocessing technology named FLUOREX is a hybrid system based on reprocessing technologies of fluorination and solvent extraction for light water reactor fuel. In the current research, we experimentally clarified solid–gas transfer behaviours of the fluorides in the FLUOREX process and identified the volatile and non-volatile compounds in the fluorination. We carried out a fluorination experiment for simulated spent nuclear fuel and solid separation from the UF6 gas stream. The distribution ratios of fission product elements in the experimental apparatus were evaluated. Molybdenum, Te, Nb, and Ru were volatilized by fluorination and they accompanied the UF6 gas. However, 22.9% of the Ru and 3.4% of the Nb were retained as solids in the experimental apparatus, contrary to the fact that their partial pressures in the experiment were lower than their vapor pressures. Rubidium, Sr, Zr, Ce, and Nd were completely recovered as solid fluorides, and these results agreed with the prediction based on boiling points of their fluorides. Antimony was completely recovered as a solid; nevertheless, the boiling point of antimony pentafluoride was lower than the process temperature, and that was attributed to the formation of a non-volatile antimony oxyfluoride.

Comparative studies of casein phosphopeptide-amorphous calcium phosphate and fluoride products in inhibiting enamel demineralization

To evaluate casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and several fluoride products in inhibiting enamel demineralization. Seventy healthy premolars extracted before orthodontic treatment were divided into seven groups (A: CPP-ACP; B: CPP-ACP + fluoride mouth rinses; C: fluoride mouth rinses; D: fluoride glass ionomer protection; E: fluoride resin binder; F: fluoride varnish; G: control group). There were ten samples in each group. The teeth were dipped into an artificial caries solution ten minutes at a time, then applied separately with CPP-ACP, CPP-ACP + fluoride mouth rinses, fluoride mouth rinses, fluoride glass ionomer protection, fluoride resin binder and fluoride varnish on labial enamel. The samples were dipped into an artificial saliva solution (37°C). Then all samples were examined with atomic force microscope (AFM) at the end of first, second and third monthes. At the end of the first month, surface roughness in group D [(114 ± 1) nm] was significantly lower than that in group G[(172 ± 9) nm]. At the end of the second month and the third month, significant difference was found in surface roughness between group G and the rest of groups (P < 0.05); between group B and the rest of groups; and between group C and groups (D, E and F). CPP-ACP and fluoride could both inhibit enamel demineralization in vitro. Solid fluoride (groups D, E and F) had better results than liquid fluoride (group C).

Preparation and Use of Polystyryl‐DABCOF2: An Efficient Recoverable and Reusable Catalyst for β‐Azidation of α,β‐Unsaturated Ketones in Water

AbstractNovel solid fluorides were prepared to optimize the β‐azidation of α,β‐unsaturated ketones. The higher loading of these catalysts compared to that of commercially available fluorides has allowed the use of a smaller mass of catalyst helping the mixing of the reaction mixture. Porous polymeric supports have proved to be more efficient in the presence of water as reaction medium. Water has played a crucial role showing a beneficial effect on the reactivity by improving dispersion of the reaction mixture and also by avoiding organic fouling caused by the retention of the reaction mixture within the polymeric matrix. This has facilitated the recovery of the products from the catalyst. The protocol reported has allowed a significant reduction in the organic solvent required for the complete recovery of the pure product whilst leaving the catalyst clean and reusable. E‐factors are in the range of 5.9–10.5 and therefore ca. 3 times smaller than previous procedures operating under solvent‐free conditions. To further improve the efficiency of our approach we have developed a protocol operating in a continuous‐flow manner that has allowed us to achieve an E‐factor of 1.7–1.9, with a reduction of ca. 80% of the corresponding batch conditions. The continuous‐flow protocol has allowed us to minimize the use of trimethylsilyl azide making the recovery and reuse of water and catalyst 5f very efficient and simple. Finally, a novel reduction system using palladium on alumina (5 mol%) and equimolar amount of formic acid has been used in the presence of 1 equivalent of di‐tert‐butyl pyrocarbonate to set a multistep protocol operating in continuous‐flow conditions for the preparation of two representative N‐Boc‐β‐amino ketones starting from the corresponding enones with E‐factors of 3.2 and 2.7, respectively.

The Preparation Method of Solid Electrolyte Lanthanum Fluoride Powder

LaF3 powder is prepared by means of three methods . The traditional precipitation of LaC13 with HF action, sol-gel of La (CH3COO) 3 with NH4F action then gel is handled by infrared furnace and microwave method of La (CO3)3 as La source with NH4F action to become LaF3 Ultra-fine powder under the action of microwave. Through the SEM photographs, it can be revealed that the powder particles are different. Precipitation particles diameter is 10 μm; sol-gel method of particle is 1 um and there are a lot of needle-like particles; microwave particles is 100nm.

Behavior of secondary alumina during heating

The losses of weight and F-containing compounds by secondary alumina at various temperatures which can be reached in a bunker of automated feeding by alumina (AFA)—i.e., to 80, 100, 200, 300, and 400°C-are evaluated. The fluorine content in alumina after being held at a specified temperature was determined by the photocolorimetric method. Upon the heating of secondary alumina, noticeable losses of weight and fluorine were observed in it starting from t > 80°C, which is associated with the removal of the latter with physically adsorbed moisture. However, the larger part of fluorine remains in secondary alumina even at t = 400°C, because it consists of solid fluorides and chemisorbed particles. The desorption of fluorine from alumina even at relatively low temperatures (starting from 80°C) means that constructive and technological measures are necessary to decrease them in AFA bunkers.