Influence Of Fluoride Ions Research Articles

The Influence of Fluoride Ions on the Forms of Lanthanide Migration in Natural and Polluted Waters of the Lovozero Massif (The Kola Peninsula)

A comprehensive study (monitoring, thermodynamic modeling) of natural and anthropogenically polluted waters of the Lovozero Massif has been carried out. A thermodynamic study of the weathering of the Lovozero Massif within the “water-rock-atmosphere” system at a temperature of 5 °C showed that the elements contained in the rocks of the studied massif influence the formation of the chemical composition of natural waters. It has been established that an increase in the degree of “water-rock” interaction leads to an increase in the concentrations of F−, Cl−, SO42−, and HCO3− in the solution. This affects the mobility of lanthanum, cerium, and other elements due to the formation of complex compounds with them. The relatively high content of fluorine, phosphorus, and HCO3− (weak and medium acids) in the solution promotes the dissolution of silicates while Si, Al, and P are released into the solution. Monitoring of water from a flooded mine in which there is an increase in the degree of interaction of water with rock showed higher pH values for the concentrations of Na, HCO3−, F−, P, Al, Si, V, U, La, and Ce. The conclusions are relevant in the context of the use of groundwater for drinking water supply purposes. The obtained information is useful to evaluate the health of the population of the region under study.

Influence of Fluoride Ions on Electrochemical Behavior of Lanthanum and Neodymium Ions in Molten LiCl

Influence of Fluoride Ions on Electrochemical Behavior of Lanthanum and Neodymium Ions in Molten LiCl

Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts

The electrochemical behavior of ytterbium in NaCl-KCl, KCl and CsCl melts was studied in the temperature range 973-1173 K by different electrochemical methods. The diffusion coefficients (D) of Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The formal redox potentials E* Yb(III)/Yb(II) were obtained in alkali chlorides melts from the cyclic voltammetry data. The influence of fluoride ions on the standard rate constants in the NaCl-KCl melt was investigated.

Dissolution of tungsten carbide and valence analysis of tungsten ions in chloride–fluoride molten salts

The main obstacles to the production of metals such as tungsten are the multi-step reaction processes and disproportionation reactions. Tungsten has more metastable valence states in molten salt and is more likely to undergo side reactions. To implement the low-valence reduction of tungsten, the composition of the molten salt system was changed. The influence of fluoride ions on the valence states of tungsten ions was determined by experiments and simulation analysis. The preliminary results suggested that a one-step direct reduction to metallic tungsten could be achieved by selecting a proper [Cl−]/[F−] ratio. This change of the valence state, which is the primary issue for tungsten reduction, was overcome by understanding the interactions between the ions and the coordination form. More specific details related to the variation of the reaction process and coordination form were provided by simulations. The simulation results showed that low-valence tungsten ions were dissolved from tungsten carbide at appropriate [Cl−]/[F−] ratios, and the change of the coordination form of the tungsten ions affected the reduction process of these ions with various valence states.

Synthesis and structures of fluoride-bridged dysprosium clusters: influence of fluoride ions on magnetic relaxation behaviors

The synthesis of fluoride-bridged 1Dy, 2Dy and hepta-nuclear 3Dy dysprosium complexes is reported here and a hydroxy-bridged dinuclear dysprosium complex 4Dy is synthesized for comparison.

Influence of Fluoride Ions on the Speciation and Electrochemical Behavior of Th(IV) in Molten LiCl-KCl with a Copper Electrode

The speciation and electrochemical behavior of thorium (IV) fluoride in molten LiCl-KCl with a copper working electrode was investigated. In addition to the reduction of Th(IV) [ThCl6 2− and ThCl7 3−] to metallic thorium, there is a minor peak in the cyclic and square wave voltammagrams that results from the reduction of Th(IV) [ThCl6−xFx 2− and ThCl7−xFx 3−] to metallic thorium on the basis of the square wave voltammetry and X-ray diffraction results. This is also supported by the formation of metallic thorium deposits upon potentiostatic electrolysis. In addition, the diffusion coefficient and diffusion activation energy of Th(IV) with a copper electrode was determined, which show similarity in comparison to those obtained using inert working electrodes.

INTENSITY OF NITRIC OXIDE SYNTHESIS IN THE BLOOD OF RATS UNDER THE INFLUENCE OF SODIUM FLUORIDE

The influence of fluoride ion as a chemical agent affects the metabolism, the change of which is manifested in functional and structural changes. The final stable metabolites of NO include nitrite and nitrate anions (NO2, NO3), the concentration of which serves as an indirect method for estimating the intensity of NO synthesis. The concentration of NO is a major factor in its numerical biological effects (regulatory, protective). At low NO concentrations, direct effects aimed at maintaining homeostasis, such as the vascular, respiratory, and nervous systems, predominate; at high concentrations of NO, indirect effects prevail, due primarily to the formation of peroxynitrite. It is known that when the rate of free radical reactions in the body increases, NO can react with a superoxide anion radical to form peroxynitrite, a highly reactive compound with destructive properties against proteins and lipids. Oral administration of FN to rats in doses of 1/10 and 1/100 DL50 leads to an increase in the content of nitrite and nitrate anions in the blood plasma during the first 30 days, which indirectly indicates excess production of nitric oxide, which in the initial stages of intoxication may play a compensatory role, but subsequently cause pathological reactions associated with the activation of oxidative stress. The decrease in nitrite and nitrate anions at the end of long-term action of FN indirectly indicates a decrease in nitric oxide generation, which may be associated, in particular, with an increase in peroxynitrite concentration due to the use of nitric oxide in reaction with superoxide anion radical and antioxidant deficiency.

Effect of fluoride on corrosion behavior of UNS N08904 stainless steel in polluted phosphoric acid

The influence of fluoride ions on the corrosion behavior of UNS N08904 stainless steel in polluted phosphoric acid solution was investigated using electrochemical measurements and UV–Vis-NIR spectroscopy. The potentiodynamic polarization curves showed that fluoride accelerates the anodic process by increasing the critical and passive current densities, while the transpassive potential modified towards more active values. The EIS exhibited that the interface solution/metal has a passive film character influenced by the fluoride ions addition. In addition, the UV–Vis-NIR spectroscopy of the surface showed that the fluoride ion increases the iron (III) phosphate dissolution, and the metal oxides into the solution. In contrast, the apparitions of large peaks of the maghemite were a proof that the fluoride ion favors the iron oxidation to Fe3+. It is noted also that the fluoride peaks were identified at 2530 nm, 2556 nm, 2613 nm, which can be interpreted as adsorbed fluoride or a metal-F complex formation. On the other hand, the UV–Vis-NIR spectroscopy of the test solutions showed that the nickel was affected but less than iron and chromium. Those results explain the drastic increase of the local corrosion as shown by Scanning Electron Microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).

Influence of Fluoride Ions in Artificial Saliva Solution to Corrosion Behavior of Ti-6Al-4V and Ti-10Mo-4Zr Titanium Alloys

Titanium alloys used in medical applications (especially dentistry) are exposed to the actions of various compounds that appear periodically in the mouth. Fluorine compounds are dangerous for the surface of titanium alloys, because they generate a dissolution of the passive layer. In this way, they destroy the surface of dental implants and cause the absorption of metal ions into the human body. The presented work was aimed to describe the effect of fluoride ions on the corrosive behavior of the commercial Ti-6Al-4V and new Ti-10Mo-4Zr alloys that can be used in stomatology. Electrochemical measurements such as open circuit potential (OCP), linear sweet voltamperometry (LSV) and impedance spectroscopy (EIS) were performed to get information on the corrosive behavior of titanium in artificial saliva solutions (MAS) with different concentrations of NaF. It has been revealed that a high concentration of fluoride ions enhance the current density in the anodic domain, especially for the Ti-10Mo-4Zr alloy. EIS measurements performed at a potential of 0.5 V vs. AgCl (3 M KCl) show that the Ti-10Mo-4Zr alloy has a typical two-layer structure of its passive film. This passive film consists of the outer and inner layers, respectively. The resistance of the outer layer is significantly lower than the resistance of the inner layer.

Influence of fluoride ions on the structure-directing effect of organic amine in the synthesis of aluminophosphate open-frameworks

The crystallization behavior of the initial mixture with the composition of Al2O3:4.0P2O5:3.0 diethylene-triamine(DETA):xHF:153H2O was investigated at 180 °C, where 0⩽x⩽3. If x⩽1.8, three-dimensional open-framework aluminophosphate AlPO-CJ31 was obtained. If 2⩽x⩽3, a chain-like aluminophosphate(1) was obtained. The crystallization process of both compounds was investigated by means of powder X-ray diffraction(XRD) and the concentrations of Al and P in the liquid product during the crystallization process were analysed by means of inductively coupled plasma atomic emission spectroscopy(ICP-AES). The evolution of the coordination state of Al, P and F during the crystallization was monitored with 27Al, 31P and 19F MAS NMR technique. The influence of the fluoride ions and the source of fluoride ions on the structure-directing effect of DETA was discussed. It was found that the fluoride ions changed the crystallization direction of the initial mixture, i.e., the structure-directing effect of DETA, via altering the distribution or micro-structure of the inorganic fragments.

Investigation of Fluoride Tolerance in<i> Acidithiobacillus ferrooxidans</i>

Anionic ion species occur in gangue minerals and impact the bioleaching efficiency even at low concentrations. Recently, the detrimental influence of fluoride ions on bioleaching microorganisms has caused great attention in research. However, the tolerance mechanisms of bioleaching microorganisms for fluoride are still unclear. In order to reveal fluoride tolerance, culture experiments with different concentrations of fluoride and ferrous iron-grown Acidithiobacillus ferrooxidans were carried out. The results showed that oxidation-reduction potential, oxidation capacity of iron and cell density were all negatively correlated to the fluoride concentration. The growth of A. ferrooxidans showed a longer delayed time and a slower growth rate when fluoride concentration increased. The fluoride tolerance for A. ferrooxidans could be attributed to the generated ferric ions from ferrous oxidation. Ferric ions reacted with HF to decrease the concentration of F- and finally reduced the toxicity of fluoride on A. ferrooxidans.

Activation energy determination and kinetic modeling of thorium oxide dissolution in nitric acid/ hydrofluoric acid system: Influence of fluoride ion on ThO2 dissolution

The dissolution of thorium oxide (ThO2) is investigated in nitric acid/hydrofluoric acid (HNO3/HF) system as a function of several parameters such as reaction fluoride ion content, HNO3 concentration and reaction temperature using an experimental reactor. Based on results, the dissolution of ThO2 increased with increasing of HNO3 concentration and temperature. The normalized weight losses (NL) and normalized dissolution rate (RL) of ThO2 were evaluated to determine the partial order related to the proton concentration (n) and apparent activation energy (EApp). The value of EApp was found to be 21.4 (kJ/mol) for pure HNO3 system and 6.9 (kJ/mol) for HNO3/HF system over the reaction temperature range of 25 °C–85 °C. The applicability of eleven different kinetic models was studied to describe ThO2 dissolution. The kinetic data was best fitted by Kabai equation and kinetic results indicated that the dissolution process is controlled by the surface chemical reaction at the liquid-solid interface.

The influence of fluoride ions on the equilibrium between titanium ions and titanium metal in fused alkali chloride melts.

KF is employed as a source of fluoride ions added to the melt to disclose the influence of fluoride on the disproportionation reactions of titanium ions, 3Ti(2+) = 2Ti(3+) + Ti, and 4Ti(3+) = 3Ti(4+) + Ti. The results reveal that the equilibrium transferred to the right direction for the first reaction and the apparent equilibrium constant increased sharply, mainly because of the formation of coordination compounds: TiFi(3-i). The accurate values of the equilibrium constants referring to the formation reactions of Ti(3+) + iF(-) = TiFi(3-i) (i = 1-6) in NaCl-KCl melt at 1023 K were evaluated with a best fit least squares method. It is also revealed that the stable states of the coordination compounds are TiF(2+), TiF2(+), TiF4(-) and TiF6(3-). Moreover, the Gibbs free energies for complex formation were estimated. Ti(2+) was undetectable when the concentration of fluoride ion was high enough. The equilibrium constant for the formation reaction, Ti(4-) + 6F(-) = TiF6(2-), was evaluated. The equilibrium constant, Kc2, for the disproportionation reaction 4Ti(3+) = 3Ti(4+) + Ti, in chloride melt was determined as 0.015.

Influence of Fluoride Ion on the Performance of Pb-Ag Anode During Long-Term Galvanostatic Electrolysis

Anodic potential, morphology and phase composition of the anodic layer, corrosion morphology of the metallic substrate, and oxygen evolution behavior of Pb-Ag anode in H2SO4 solution without/with fluoride ion were investigated and compared. The results showed that the presence of fluoride ions contributed to a smoother anodic layer with lower PbO2 concentration, which resulted in lower double layer capacity and higher charge transfer resistance for the oxygen evolution reaction. Consequently, the Pb-Ag anode showed a higher anodic potential (about 35 mV) in the fluoride-containing electrolyte. In addition, the fluoride ions accelerated the detachment of loose flakes on the anodic layer. It was demonstrated that the anodic layer formed in the fluoride-containing H2SO4 solution was thinner. Furthermore, fluoride ions aggravated the corrosion of the metallic substrate at interdendritic boundary regions. Hence, the presence of fluoride ions is detrimental to oxygen evolution reactivity and increases the corrosion of the Pb-Ag anode, which may further increase the energy consumption and capital cost of zinc plants.

Surface fluorination on TiO2 catalyst induced by photodegradation of perfluorooctanoic acid

The photoabatement of perfluorooctanoic acid in aqueous solution has been performed with a commercial nano-sized TiO2-based photocatalyst content of 0.66g/L under an UV irradiation of 95W/m2. PFOA degradation intermediates were investigated by HPLC–MS and 19F-NMR analysis. Evidences of a degradation mechanism based on two competitive pathways are discussed: photo-redox and β-scission pathways. Shorter perfluorinated carboxylic acids, CnF2n+1COOH (n=1–6), as expected degradation intermediates, were identified and their concentration trends over time were determined. The apparent pseudo-first order kinetic constant expressed as rate of PFOA disappearance was also measured: kapp 0.1296h−1. The influence of fluoride ions on TiO2 surface was analyzed by XPS technique, revealing a surface modification that affects the performances of the catalyst.

The interaction of plasma proteins with nano-size fluoride-substituted apatite powders

Phase pure (HAp) and fluoride-substituted apatite (FHAp) powders were synthesized by the hydrothermal method and their specific surface area was determined by atomic force microscopy (AFM). Human osteoblast cells were used to evaluate the bioactivity of the samples. The influence of fluoride ions on the alteration of cell medium components was analyzed using UV–visible spectroscopy in different exposure times. The protein interaction behavior with the pure and substituted powders was assessed by the Bradford method and SDS-PAGE analysis. The mRNA expression level was detected by real time PCR and it was observed that the presence of an optimal level of fluoride ions in the apatite structure has an inductive effect on collagen I and alkaline phosphatase (ALP) expression levels. A similar trend was also observed in the protein adsorption profile indicating that the fluoride content in the apatite lattice has a significant impact on controlling its biological performance. The maximum protein adsorption was observed on the sample with the chemical composition of Ca 10 (PO4) 6 (OH) 1.33 F 0.67 .

Influence of fluoride ions on corrosion performance of 316L stainless steel as bipolar plate material in simulated PEMFC anode environments

Corrosion performance of 316L stainless steel as a bipolar plate material in proton exchange membrane fuel cell (PEMFC) is studied under different simulated PEMFC anode conditions. Solutions of 1 × 10−5 M H2SO4 with a wide range of different F− concentrations at 70 °C bubbled with hydrogen gas are used to simulate the PEMFC anode environments. Electrochemical methods, both potentiodynamic and potentiostatic, are employed to study the corrosion behavior. Scanning electron microscope (SEM) and atomic force microscope (AFM) are used to examine the surface morphology of the specimen after it is potentiostatic polarized in simulated PEMFC anode environments. X-ray photoelectron spectroscopy (XPS) analysis is used to identify the compositions and the depth profile of the passive film formed on the 316L stainless steel surface after it is polarized in simulated PEMFC anode environments. Mott–Schottky measurements are used to characterize the semiconductor passive films. The results of potentiostatic analyses show that corrosion currents increase with F− concentrations. SEM examinations show that no localized corrosion occurs on the surface of 316L stainless steel and AFM measurement results indicate that the surface topography of 316L stainless steel becomes slightly rougher after polarized in solutions with higher concentration of F−. From the results of XPS analysis and Mott–Schottky measurements, it is determined that the passive film formed on 316L stainless steel is a single layer n-type semiconductor.

The Influence of Aggressive Environment with a High Content of Fluoride Ions on the Alloy TiAl6V4 with a Protective Ti-Al-Si Layer

This work presents results on the influence of fluoride ions on the behavior of layers whose main component is the phase TiAl0.3Si1.7 (called t2 phase), formed on TiAl6V4 substrate. Layers were prepared in AlSi20 melt at 650 ° C for 60 min. Potentiodynamic curves were measured in a chloride solution with 0 and 5000 ppm fluoride. Layer were shifted corrosion potential to more negative values and at the some time reduce the corrosion current density (Im). Values of Im are in the potential range of 300 – 1500 mV (SCE) for TiAl6V4 with Ti-Al-Si layers significantly lower in comparison with Im values found for TiAl6V4 in chloride solution containing 5000 F-. The electrochemical tests showed that Ti-Al-Si layer had marked positive effect on corrosion resistance of TiAl6V4 alloys in aggressive environment with high content of F-.

Influence of fluoride ion on the electrochemical behaviour of β-Ti alloy for dental implant application

The corrosion behaviour of Ti–15Mo alloy in 0.15 M NaCl containing 0.01, 0.03, 0.06 and 0.5 M NaF is evaluated and its protective ability is compared with that of CP-Ti and Ti–6Al–4V alloy, to ascertain their suitability for dental implant application. The steady state current density of CP-Ti and, Ti–15Mo and Ti–6Al–4V alloys in 0.15 M NaCl containing 0.03 M NaF at 200 mV vs. SCE is found to be 1, 2 and 6 μA/cm 2, respectively, which indicate that all of them could offer a better corrosion resistance in the potential range that could exists in the oral environment.

On the reactions of trifluorovinylsilanes with aromatic ketones – Expected and some unexpected results

The reactions of aromatic ketones with trialkyl(trifluorovinyl)silanes in the presence of fluoride ions were studied. The conditions for the selective addition of trialkyl(trifluorovinyl)silanes to the carbonyl function of aromatic ketones in the presence of cesium fluoride and absence of any solvents to form the trifluorovinyl containing “silylated” alcohols have been worked out. The analogous reactions in common organic solvents are not terminated on the stage of “silylated” alcohols formation; consecutive reactions lead to fluorinated olefins and acids under the influence of fluoride ions.