Aqueous Hydrofluoric Acid Solution Research Articles

SYNTHESIS AND STUDY OF OPTICAL, ELECTRICAL PROPERTIES OF TIN DIOXIDE NANOWIRES IN A SiO<sub>2</sub>/Si TRACK TEMPLATE

This work presents a study of the structural, optical and electrical characteristics of tin dioxide (SnO2) nanowires obtained by chemical deposition (CD) into a SiO2/Si track template (template synthesis). Latent tracks in the SiO2 layer were created by irradiation with swift heavy ions (SHI) of Xe at an energy of 200 MeV with a fluence of Ф = 108 cm−2 and subsequent etching in a 4% aqueous solution of hydrofluoric acid (HF). The chosen CD method is widely used for the deposition of semiconductor oxide nanowires in SiO2 nanopores. The CD method is cost-effective because it does not require special equipment for deposition of nanowires. To carry out deposition, a solution of a coordination compound of a metal and a reducing agent is used. To analyze the filling of pores after the CD process, the surface morphology of the samples was studied using a Zeiss Crossbeam 540 scanning microscope. The crystallographic structure of SnO2/SiO2/Si nanostructures with SnO2 nanopore filling was studied by X-ray diffraction. X-ray diffraction analysis (XRD) is carried out on a Rigaku SmartLab X-ray diffractometer. As a result, a SnO2-NW/SiO2/Si nanoheterostructure with an orthorhombic crystal structure of SnO2 nanowires was obtained. Photoluminescence (PL) spectra were measured upon excitation with light at a wavelength of 240 nm using a CM2203 spectrofluorimeter (Solar). Gaussian decomposition of the photoluminescence spectrum of SnO2-NW/SiO2/Si structures showed that they have low intensity, which is mainly due to the presence of defects such as oxygen vacancies, interstitial tin or tin with damaged bonds. Electrical characterization studies were performed using a VersaStat 3 potentiostat (Ametek). Measurement of the current-voltage characteristic showed that the resulting SnO2-NW/SiO2/Si nanoheterostructure contains arrays of p-n junctions.

SYNTHESIS OF ORTHORHOMBIC TIN DIOXIDE NANOWIRES IN TRACK TEMPLATES

In this work, the synthesis of orthorhombic SnO2 nanowires (NWs) was carried out by electrochemical deposition into prepared SiO2/Si-p ion-track template. Track formations in the SiO2/Si structure were created by irradiation on a DC-60 cyclotron with swift heavy Xe ions with an energy of 200 MeV (Ф = 108 cm−2). A 4% aqueous solution of hydrofluoric acid (HF) was used to form nanoporous templates. Electrochemical deposition (ECD) of SnO2 into the track template was carried out at room temperature, the voltage at the electrodes was 1.75 V. During the ECD process, an electrolyte with the following chemical composition was used: 6 g/l SnCl2 (Sigma-Aldrich) – 25 ml H2O – 2 ml HCl (“reagent grade”; 35%; ρ = 1.1740 g/cm3). The surface morphology of the samples, after the ECD process, was studied on a Zeiss Crossbeam 540 two-beam scanning microscope. The phase composition and crystallographic structure of nanoheterostructures (SnO2-NP/SiO2/Si) with nanopores filled with tin dioxide were studied using X-ray diffraction (XRD) on a multifunctional X-ray diffractometer Rigaku SmartLab. Photoluminescence was measured in the optical range of 320–600 nm using a CM2203 spectrofluorimeter (Solar). The electrical characteristics of the synthesized tin dioxide nanowires were studied using a VersaStat 3 potentiostat from Ametek.As a result, a SnO2-NWs/SiO2/Si nanoheterostructure with orthorhombic crystal structure of SnO2 nanowires was obtained. Photoluminescence excited by light with a wavelength of 240 nm has a low intensity, arising mainly due to defects such as oxygen vacancies and interstitial tin or tin with damaged bonds. Measurement of the current-voltage characteristic showed that the SnO2-NP/SiO2/Si nanoheterostructure obtained in this way contains arrays of p-n junctions.

Synthesis under Normal Conditions and Morphology and Composition of AlF3 Nanowires.

AlF3 has interesting electrophysical properties, due to which the material is promising for applications in supercapacitors, UV coatings with low refractive index, excimer laser mirrors, and photolithography. The formation of AlF3-based nano- and micro-wires can bring new functionalities to AlF3 material. AlF3 nanowires are used, for example, in functionally modified microprobes for a scanning probe microscope. In this work, we investigate the AlF3 samples obtained by the reaction of initial aluminum with an aqueous hydrofluoric acid solution of different concentrations. The peculiarity of our work is that the presented method for the synthesis of AlF3 and one-dimensional structures based on AlF3 is simple to perform and does not require any additional precursors or costs related to the additional source materials. All the samples were obtained under normal conditions. The morphology of the nanowire samples is studied using scanning electron microscopy. We performed an intermediate atomic force microscope analysis of dissolved Al samples to analyze the reactions occurring on the metal surface. The surface of the obtained samples was analyzed using a scanning electron microscope. During the analysis, it was found that under the given conditions, whiskers were synthesized. The scale of one-dimensional structures varies depending on the given parameters in the system. Quantitative energy-dispersive x-ray spectroscopy spectra are obtained and analyzed with respect to the feedstock and each other.

Impacts of Wafer Doping Type on Structural and Optical Properties of Black Silicon Fabricated by Metal-Assisted Chemical Etching

In this work, the impacts of wafer doping type on structural and optical properties of black silicon (b-Si) fabricated by metal-assisted chemical etching (MACE) process are investigated. P-type and n-type mono-crystalline silicon (mono c-Si) wafers are etched in an aqueous solution of hydrofluoric acid (HF), silver nitrate (AgNO3) and deionised water (DI H2O) at room temperature and various durations from 5-20 minutes. Surface morphological results demonstrate the formation of b-Si nanowires (NWs) with average lengths of 0.4-0.8 μm for p-type wafers and 0.8-3.0 μm for n-type wafers. The higher length of the NWs for the n-type wafers is due to the minority charge carriers, which lead to a higher etching rate during the MACE process. Within the 300-1100 nm wavelength region, weighted average reflection (WAR) for the p-type and n-type wafers decreases to 6.6% and 6.4%, respectively, after 20 minutes of etching. The corresponding improvement in broadband light absorption results in maximum potential short-circuit current density (Jsc (max)) of 38.2 and 38.8 mA/cm2 for the p-type and n-type b-Si, respectively, which is an of enhancement of 39.9% and 42.1% when compared to the Jsc (max) of planar c-Si reference.

Transpassive and abnormal dissolution of titanium electrodes in hydrofluoric acid aqueous solution

One of the urgent problems of electrochemistry is the reuse of production waste of a relatively expensive metal – titanium, which is in great demand in mechanical, aircraft engineering, medicine, and nanotechnology. The purpose of this work is to study the abnormal cathodic and transpassive anodic dissolution behavior of a titanium electrode in an aqueous hydrofluoric acid solution. Methodology. The anode and cathode spaces are separated by an anion exchange membrane. As a result of the electrochemical dissolution of titanium Ti4+ ions are formed in the anode space, and Ti3+ ions are formed in the cathode space due to the chemical dissolution of titanium. The influence of the main electrochemical parameters on the titanium dissolution process in the anode and cathode spaces has been studied. Results and discussions. The current efficiency of titanium anodic dissolution slowly increased with increasing current density, and its maximum value (82.5%) was observed at a current density of 800 A/m2. With an increase in the concentration of hydrogen fluoride, the current efficiency rapidly increased, and its maximum value at a current density of 200 A/m2 was determined at a concentration of 0.6 mol/l and was equal to 78.1%. Titanium dissolves forming Ti3+ ions along with Ti4+ ions in the anode space with an increase in the electrolyte temperature. The current efficiency of Ti4+ ions decreases while sharply increasing for Ti3+ ions. Conclusion. The optimal conditions for transpassive anodic and anomalous cathodic dissolution of a titanium electrode in an aqueous solution of hydrofluoric acid and the kinetic parameters of the electrode process are determined.

Investigation of the Angle of Sliding a Drop of Water from the Surface of the SI (111)

Silicon is the main raw material for micro- and nanoelectronics. Achievements in these areas are based to a sufficient extent on knowledge of the processes occurring on the surface. Therefore, the study of these processes on a silicon surface is topical today. In this work, the dependences of the angles of water runoff from the silicon surface on the modes of their preparation are experimentally studied. The objects of study were Si single-crystal silicon wafers with (111) surface orientation. An aqueous solution of hydrofluoric acid was used to clean the surface from contamination and natural oxide. To assess the efficiency of cleaning and the state of the studied solid surfaces, the dynamic wetting angle was measured. Distilled water was used as a wetting liquid. It has been found that plates for which ethanol is used in the preparation procedure are better wetted with water. The obtained experimental data are confirmed by the Auger analysis — the plates treated with ethanol contain a smaller amount of carbon-containing impurities. The obtained surface topograms also indicate the effect of surface chemical treatment on its roughness.

Intrinsic properties of multi-component glass surfaces exposed to aqueous hydrofluoric (HF) and/or hydrochloric (HCl) acid-based treatments

Acids have been used to treat glass surfaces to achieve functional advantage for years. Despite how common these types of treatments are, it is surprisingly rare to find detailed studies that examine the potentially subtle changes to glass surface properties arising from different types of chemical exposures immediately following treatment. Here, we report on the intrinsic surface properties of an alkaline-earth boroaluminosilicate glass immediately following exposure to either (1) aqueous solutions of hydrofluoric acid (HF) with varied concentrations, or (2) mixtures of HF with hydrochloric acid (HCl) in variable concentration/component ratio(s). Surface properties investigated include surface free energy, zeta potential, shallow surface composition profiles using time of flight – secondary ion mass spectroscopy and nanoscale topography via atomic force microscopy. Activation energy calculations were used to investigate the energetics of dissolution as functions of treatment chemistry, where values of approximately ∼25–35 kJ/mol were observed across most of the ranges studied. Results suggest that the properties at the topmost surface of the treated glasses are highly dependent on the type and strength of formulation used, even when the same amount of glass is dissolved. In some cases, observed trends in the data appear to be directly related to perceived shifts in the dominant reaction mechanisms between the etchant and glass that are dictated by treatment chemistry.

The Effect of Ultraviolet Treatment on TiO2 Nanotubes: A Study of Surface Characteristics, Bacterial Adhesion, and Gingival Fibroblast Response

Titanium dioxide (TiO2) nanotubes are emerging as a provocative target for oral implant research. The aim of this study was to evaluate the effect of UV on the wettability behavior, bacterial colonization, and fibroblast proliferation rate of TiO2 nanotube surfaces prepared using different anodization voltages and aimed for use as implant abutment materials. Four different experimental materials were prepared: (1) TiO2 nanotube 10 V; (2) TiO2 nanotube 15 V; (3) TiO2 nanotube 20 V; and (4) commercial pure titanium as a control group. TiO2 nanotube arrays were prepared in an aqueous electrolyte solution of hydrofluoric acid (HF, 0.5 vol.%). Different anodization voltages were used to modify the morphology of the TiO2 nanotubes. Equilibrium contact angles were measured using the sessile drop method with a contact angle meter. The investigated surfaces (n = 3) were incubated at 37 °C in a suspension of Streptococcus mutans (S. mutans) for 30 min for bacterial adhesion and 3 days for biofilm formation. Human gingival fibroblasts were plated and cultured on the experimental substrates for up to 7 days and the cell proliferation rate was assessed using the AlamarBlue assayTM (BioSource International, Camarillo, CA, USA). The data were analyzed using one-way ANOVA followed by Tukey’s post-hoc test. Water contact angle measurements on the TiO2 after UV treatment showed an overall hydrophilic behavior regardless of the anodization voltage. The ranking of the UV-treated surfaces of experimental groups from lowest to highest for bacterial adhesion was: TiO2 nanotube 20 V < Ti and TiO2 nanotube 15 V < TiO2 nanotube 10 V (p < 0.05), and for bacterial biofilm formation was: TiO2 nanotube 20 V-TiO2 nanotube 10 V < Ti-TiO2 nanotube 15 V (p < 0.05). Fibroblast cell proliferation was lower on TiO2 nanotube surfaces throughout the incubation period and UV light treatment showed no enhancement in cellular response. UV treatment enhances the wettability behavior of TiO2 nanotube surfaces and could result in lower bacterial adhesion and biofilm formation.

Morphological and Optical Properties of Silicon Nanostructure, Obtained by One Step Ag-assisted Chemical Etching

Silver-assisted one-step chemical etching (AACE) is a low-cost, straightforward method for producing silicon nanostructures to improve their light absorption; it includes the etching of the wafers in aqueous hydrofluoric acid (HF), silver nitrate (AgNO3) and nitric acid (HNO3) solution. Influence of various parameters, such as AgNO3 concentration (0.47, 0.58, and 1.17 mM), HF concentration (0.67, 0.9, and 1.129 M), HNO3 concentration (0.12, 0.24, and 0.37 M), etching temperature (40, 50, and 60oC), and etching time (4, 5, and 6 min), on the Morphological and optical properties of silicon wafers were investigated. The results show that these parameters have a main role in determining the nanostructure size. The reflection measurements show that the minimum reflectance with 11% achieved with 0.58 mM AgNO3, 1.129 M HF, and 0.12M HNO3 recipe. Field Emission Scanning Electron Microscopy (FESEM) appears that the morphology of the manufactured silicon is semi-spherical nanostructures with the formation of the porous surface on the surface of the wafers.

Chemical speciation, thermodynamic properties, and salt solubility in aqueous hydrogen fluoride at various temperatures part I: Liquid chemical composition and thermodynamics properties of the HF-H2O system

A thermodynamic model of the aqueous hydrofluoric acid solutions is parameterized and applied to represent the osmotic coefficient, ionic mean activity coefficient, pH, and liquid chemical speciation of system HF-H2O. The developed model is suitable for temperature varying from 273.15 K up to 473.15 K and concentrations from infinite dilution to 20 mol.kg−1. Many obvious computational errors and a critical analysis of the measurement data of the aqueous solutions of the HF-H2O system in the literature are recorded and discussed.

NIOBIUM’S BEHAVIOR IN AQUEOUS HYDRO­FLUORIC ACID SOLUTION

Thanks to the unique combination of physicochemical properties, niobium and its compounds are widely used in various fields of science and technology. The main areas of niobium’s applications are the production of superconductors, nuclear energy, chemical engineering, metallurgy, manufacture of optically active materials, thin-film lithium batte­ries, fuel cells. The aim of this work is to study the processes that take place on the niobium electrode in aqueous solutions of hydrofluoric acid, as well as to establish the composition of niobium compounds that are formed. The paper presents the results of studies the behavior of the niobium electrode in aqueous solutions 0.25 N. hydrofluoric acid. The kinetic para­meters of the processes occurring at the phase boundary are determined. It was found that the anodic polarization of the niobium electrode is accompanied by the formation of a passive layer, the destruction of which is facilitated by increasing the polarization potential and fluorine anions, in the presence of which complex fluoroiobate anions [NbF7]2- and [NbOF5]2-are formed. Cathodic polarization of niobium is accompanied by the formation of hydrides on its surface, which causes an increase in the overvoltage of hydrogen evolution. The anodic polarization of the niobium electrode in a solution of hydrofluoric acid causes the formation on its surface of a passive layer, which is destroyed with increasing potential. In the Nbo–NbO2–0.25 –0.25 n HF system, [NbF7]2-anions are formed, as evidenced by bands in the region of 500 nm on the electron absorption spectra. The rate constants of [NbF7]2- and [NbOF5]2- formation are estimated at 3.78 • 10-3 s-1 and 5.18 • 10-3 s-1, respectively. The reduction of hydrogen at the niobium cathode from a solution of hydrofluoric acid is accompanied by the formation of hydrides, which causes an increase in the overvoltage of hydrogen evolution and high values of the angular coefficients of the Tafel dependence.

Luminescent Porous Silicon Filled with Nanoscopic Magnetic Structures – Assessment of the Optical and Magnetic Properties

Luminescent porous silicon which is denoted as microporous silicon offers a structure size of a few nanometers. It is filled with magnetic metals resulting in a composite system with specific optical and magnetic properties. The morphology of microporous silicon offers a branched network of pores. The luminescence which is observed in the red-orange region due to the small structure size is influenced by the metal filling. The magnetic response of the samples is related to the interconnected pores and differs significantly to mesoporous silicon filled with magnetic nanostructures of similar size.The luminescent porous silicon is etched in aqueous hydrofluoric acid solution by applying a current density of 10 mA/cm2 for 20 min resulting in a porous layer of about 0.8 µm thickness. The metal filling of microporous silicon is a challenging procedure which is carried out under cathodic conditions by pulsed electrodeposition. As electrolytes adequate metal salt solutions are used. The deposited nanosized metal structures are of the same interconnected sponge-like morphology as the template material.Mesoporous silicon offers oriented pores whereas the diameter is in the range of 50 nm [1]. Also in this case the metal nanoparticles are electrodeposited within the matrix material.The magnetic properties of the different systems rely on the morphology of the template material and the size and geometry of the incorporated metal deposits.The magnetic response offers a significant difference between filled luminescent and mesoporous silicon samples. Luminescent metal filled samples show strong magnetic anisotropy between the magnetization parallel and perpendicular to the surface. For these specimens also significant differences of the anisotropy can be observed depending on the kind of deposited metal, e.g. Ni or Co. These differences are not so distinctive in the case of mesoporous metal filled silicon because of weak magnetic interactions between the metal nanoparticles.Due to the merged optical and magnetic properties in the case of microporous silicon the nanocomposite could be promising for integrated magneto-optic devices.[1] P. Granitzer, K. Rumpf, Semiconductor Science and Technology 31, 4004, 2016.

(Invited) Nanostructured Silicon with Incorporated Bi-Metallic Nanostructures

Silicon/bi-metal nanocomposites are fabricated in using porous silicon and silicon nanotubes as templates which are filled with magnetic bi-metal nanostructures (NiCo, FePt) and the magnetic response of the different systems is investigated. The morphology such as pore diameter and inner tube diameter of the two systems are comparable. The different metals (NiCo and FePt) offer drastic differences of the magnetic properties for both, porous silicon and silicon nanotubes.The porous silicon (PSi) is fabricated by anodizing a highly n-doped silicon wafer in aqueous hydrofluoric acid solution. By applying a current density of 90 mA/cm2 pore diameters of 60 nm in average are achieved.The silicon nanotube (SiNTs) formation is performed by silicon deposition on a ZO wire array and finally etching off the ZO [1]. The inner diameter and the wall thickness of the tubes are dependent on the chosen fabrication parameters. For comparison the inner diameters of the SiNTs are chosen comparable to the porous silicon structure. Co as well as FePt nanoparticles are chemically grown inside the pores and the tubes, respectively. In the case of FePt the molar ratio of Fe is varied (Pt:Fe 1:1, 1:3 and 1:6).The magnetic properties of the different composite systems are investigated. PSi and SiNTs with deposited NiCo, Co and FePt nanoparticles show significant differences whereat the FePt filled samples offer higher coercivities and higher remanence and thus a high resulting energy product. The variation of the molar ratio of the FePt deposits shows a small impact in the magnetic response for both template types. Furthermore the differences between the two template materials are figured out. Such systems consisting of hard magnetic materials within nanostructured silicon are promising for on-chip applications using three dimensional arrays of nanomagnets.[1] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Comm. 49, 5760 (2013).

Adhesion characteristics of solution treated environmental dust

Environmental dust is modified towards self-cleaning applications under the gravitational influence. Dust particles are collected in the local area of Dammam in Saudi Arabia and they are treated with a dilute hydrofluoric acid solution. The changes in chemical and adhesion characteristics of the dust particles prior and after the solution treatment are analyzed. Force of adhesion and work required to remove dust from hydrophobic and hydrophilic glass surfaces are assessed, separately, for solution treated and collected dust. We show that aqueous hydrofluoric acid solution treatment modifies some dust components while causing the formation of submicron cracks and nano/submicron porous/pillars like textures on the dust particles. The texture generated on dust surfaces after the solution treatment has a great influence on dust adhesion characteristics. Hence, the solution treated dust particles result in lower adhesion on hydrophobic and hydrophilic glass surfaces as compared to that of untreated dust. The gravitational force enables to remove solution treated dust from inclined glass surfaces, which becomes more apparent for hydrophobic surfaces.

Influence of Cu addition on corrosion behavior and tensile performance of Ni-30Co-16Cr-15Mo-6Fe alloy

Corrosion behavior in 5.2 M aqueous hydrofluoric acid solution and tensile properties of Ni-30Co-16Cr-15Mo-6Fe-xCu (x = 0, 0.5, 2, and 6) (mass%) alloys are investigated. The corrosion resistance of alloy can be significantly improved by the slight additions of Cu (e.g. 0–2 mass%) without altering either the microstructure or the tensile properties of alloy. On the contrary, alloy with higher addition of Cu, characterized by Cu-rich phases both at grain boundaries and inside the matrix, demonstrates lower corrosion resistance and lower tensile strength. Interestingly, corrosion resistance in grain boundary of alloy gradually increases with Cu content increasing irrespective of the appearance of Cu-rich phases.

Selective deposition of gold particles onto silicon at the nanoscale controlled by a femtosecond laser through galvanic displacement.

Control of the deposition location and morphology of metals on semiconductors is of considerable importance for the fabrication of metal–semiconductor hybrid structures. For this purpose, selective nanoscale deposition of gold on silicon was successfully achieved by a two-step method in this paper. The first preparation step comprises the fabrication of ripples with a femtosecond laser. The second preparation step is to immerse the samples in a mixed aqueous solution of hydrofluoric acid (HF) and chloroauric acid (HAuCl4). The periodically ablated ripple structures on silicon surfaces fabricated by the femtosecond laser changed the physical and chemical properties of silicon and then controlled the nucleation positions of gold nanoparticles. Gold particles tend to grow in raised positions of the ripples and no substantial growth was observed in the recesses of the ablated ripple structures. Similar phenomena were observed on the modified ripple structures; this led to the formation of periodically distributed gold sub-micron wires. Above all, this paper proposes a new mask-free method of selective metal electroless deposition that can be realized without complicated experimental equipment and tedious experimental operations.

Origin of Mosaic Structure Obtained During the Production of Porous Silicon with Electrochemical Etching

So far, while producing porous silicon (PSi) with anodic etching of silicon in an aqueous solution of hydrofluoric acid, many researchers (including us) have obtained the crack-into-pieces (or mosaic) structure. Most of the authors believed that the cause of this structure is the collapse and the cracking of the porous, especially highly porous, silicon layer which took place during the drying of PSi after fabrication. However, our study showed that the mosaic structure was formed right during the course of silicon anodization at high anodic current density. Furthermore, our study also showed that at high anodic current density the real silicon etching has been replaced by the growth of a silicon oxide layer. This is a layer of another substance that grows on silicon, so when the layer is too thick (which is obtained when the anodic current density is too high and/or the anodization time is too long) it will crack, creating mosaic pieces. When the silicon oxide layer is cracked, the locations around the cracks will be etched more violently than elsewhere, creating trenches. Thus, the mosaic structure with mosaic pieces emerged between the trenches has formed.

Thermodynamic equilibrium of solid – liquid and solutions of system [formula omitted] at various temperatures

The thermodynamic equilibrium of solid–liquid and solutions of the mixed system of sodium and hydrogen fluorides were investigated at various temperatures. The chemical speciation of the NaF-HF in aqueous solutions was described; which the considered equilibrium is dissociating into the species Na+(aq), H+(aq), HF(aq), F-(aq), HF2-(aq) and H2F3-(aq). The species molalities are strongly dependent on the concentration in the solution, therefore directly influence the thermodynamic properties. Neglecting this concentration dependence leads to erroneous osmotic coefficients for weak electrolyte solutions. Then, the water activity measurements of the mixed system yHF+1-yNaFaq were performed at various temperatures from 298.15 K to 353.15 K using the hygrometric method. These measurements were made as a function of total molality ranging from dilution to saturation for different ionic-strength fractions y with respect to the support solute HF with y = 0.20, 0.50, and 0.80. The mixed aqueous electrolytes were considered as a polyelectrolyte system [Na+-HF0-H+-F--HF2--H2F3--H2O]. Based on the ion interaction model, the thermodynamic model was developed to describe the behavior of sodium and hydrogen fluorides in aqueous solutions at different temperatures. The species molalities of the HF(aq), Na+(aq), H+(aq), F-(aq), HF2-(aq) and H2F3-(aq) of the system were evaluated. The new ion interaction parameters ΦH+, Na+ and ΨH+, Na+,F- were determined at various temperatures and used to calculate the species activity coefficients as a function of total molality for different ionic-strength fractions (y). The developed model exhibits a high consistency for the treatment of polyelectrolyte system. The results allow describing the behavior of the mixed NaF-HF in aqueous solutions. The solubility of the sodium fluoride in hydrofluoric acid aqueous solutions were also performed, and the formed solid phases were characterized by X-ray diffraction analysis. The obtained crystal forms were identified to NaF (s) and NaHF2(s) for y = 0.20 and y= (0.50 and 0.80) respectively.

C(NH2)3]2TaF7 and [C(NH2)3]3TaF8: Guanidinium fluoride-tantalates with isolated anionic polyhedra

Two guanidinium fluoride tantalates have been prepared by the reacting of guanidinium carbonate with TaF5 in aqueous HF solutions. The reaction with [C(NH2)3]2CO3:TaF5 2.5:1 M ratio in 33% hydrofluoric acid aqueous solution resulted in the formation of [C(NH2)3]2TaF7 compound. Similar procedure with 3:1 M ratio performed in 5% HF aqueous solution resulted in the formation of a [C(NH2)3]3TaF8 salt. The X-ray single crystal structures of the compounds were determined to contain discrete TaF72– and TaF83- anions of capped trigonal prismatic and square antiprismatic shapes, respectively. Both compounds were also characterized by Raman spectroscopy.

Chemical speciation of aqueous hydrogen fluoride at various temperatures from 298.15 K to 353.15 K

The chemical speciation of aqueous hydrofluoric acid solutions was investigated at various temperatures. The experimental results and calculations were carried out to study a qualitative and quantitative speciation of the system HF-H2O. Literature review of thermodynamic and speciation studies of aqueous hydrogen fluoride were reported and revealed some deficiencies at various temperatures. The dissociation of HF in the aqueous solution is not complete, which exhibits a concentration-dependent stoichiometric coefficient and directly influences the thermodynamic properties. Neglecting this concentration dependence leads to erroneous osmotic coefficients for solutions of weak electrolytes. The water activities of the HF-H2O system were measured within the molality range from 0.10 mol kg−1 to 6.00 mol kg−1 at different temperatures from 298.15 K to 353.15 K using the hygrometric method. From these measurements, on the basis of the fluorine 19F nuclear magnetic resonance and the chemical equilibriums, the qualitative and quantitative speciation aqueous hydrofluoric acid solutions were performed respectively. The deployed approach was developed based on ion interaction model to describe the behavior of HF aqueous solutions, considering a polyelectrolyte system HF−H−F−HF2−H2F3−H2O. The calculated species HF(aq), H+, F−, HF2− and H2F3−were determined at various temperatures. From the complementary techniques and the developed model, the results reflect the present species and allow describing the behavior of hydrofluoric acid aqueous solutions.