HF Aq Research Articles

Facile synthesis of β-Li3VF6: A new electrochemically active lithium insertion material

The β-modification of Li3VF6 is easily prepared following a precipitation reaction at moderate temperature avoiding the high temperature route normally used for preparing related fluorides. Precipitation conditions for Li3VF6 have been optimized for two different alcohols to obtain better electrochemical performances. Temperature has been found to play an important role in the progress of precipitation reaction and in the phase purity of the resulting product. Best results were achieved for 2-propanol based solutions at 60°C and for ethanol based solutions at 45°C containing VCl3, HF(aq) and Li2CO3 as starting compounds. In both cases large agglomerates, though of different size and shape, are obtained. These are composed of smaller particles of 20–30nm. Electrochemical performances of as prepared Li3VF6 materials as electrode in lithium rechargeable batteries are modest with a maximum capacity of only 30mAhg−1. However, processing these materials by ball milling with carbon allows the capacity to increase to its theoretical value, 144mAhg−1, accordingly to the complete reduction of V3+ to V2+. The observed average reduction potential for V3+ to V2+, 2V, may be certainly higher than that found in oxides but not high enough to be considered for application as the positive electrode. However, Li3VF6 is then another example of the β-Li3MF6 type-structure hosting lithium through an electrochemical insertion reaction. On the other hand, reversible oxidation of V3+ through lithium de-insertion, which would lead to the formation of Li3−xVF6 phases has not been successful yet. Taking into account the redox intercalation chemistry of vanadium in oxides, the reversible reduction of V3+ to V2+ and the irreversible oxidation of V3+ to V4+ in the herein presented fluoride make a significant difference derived from the nature of the non metal X. Then, research of fluorides is a path to find new chemistries for lithium batteries.

Development of Niobium Oxide Coatings on Sand-Blasted Titanium Alloy Dental Implants

The purpose of this study was to use scanning electron microscopy (SEM) evaluation to determine the optimal anodizetion conditions needed to generate niobium oxide coatings on titanium alloy dental implant screws. Sand-blasted titanium alloy dental implants were anodized in dilute hydrofluoric acid (HF(aq)) solution using a Sorensen DLM 300-2 power supply. The HF concentration and anodization time were varied and the resulting implant surfaces were evaluated using a Jeol JSM-5310LV Scanning Electron Microscope to determine the ideal anodization conditions. While HF is necessary to facilitate oxide growth, increasing concentrations resulted in proportionate increases in coating delamination. In a similar manner, a minimum anodization time of 1 hour was necessary for oxide growth but longer times produced more delamination especially at higher HF(aq) concentrations. SEM imaging showed that implants anodized for 1 hour in a 0.1% HF(aq) aqueous solution had the best results. Anodization can be used to generate niobium oxide coatings on sand-blasted Ti alloy dental implants by balancing the competing factors of oxide growth and coating delamination. It is believed that these oxide coatings have the potential to improve osseointegration relative to untreated dental implants when evaluated in an in vivo study.

The uptake of halogen (HF, HCl, HBr and HI) and nitric (HNO3) acids into acidic sulphate particles in quiescent volcanic plumes

The uptake of halogen and nitric acids into acidic sulphate particles has important implications for volcano monitoring and the environmental geochemistry of volcanic emissions. Using the Extended Aerosol Inorganics Model (E-AIM) for HCl, HBr and HNO3, combined with a simple three-parameter model for HF and HI, we show that equilibrium partitioning of halogen and nitric acids into sulphate particles is maximised at high relative humidity (RH), low temperature, low plume dilution (i.e., near-source) and high SO42−/SO2. The addition of metal chlorides (i.e., NaCl) enhances acidic gas partitioning at high RH, but diminishes acidic gas partitioning at low RH due to a decrease in the water content of particles and the formation of Na sulphate salts. We predict that acidic gas partitioning is quantitatively significant (>1%) only in cool humid conditions (e.g., >80% RH at 298K), adding confidence to spectroscopic and/or electrochemical determinations of gas ratios (e.g., SO2/HCl, HCl/HF) for volcano monitoring. However, acidic gas partitioning remains environmentally important over a wide range of conditions because of the significant variability in the amounts of acidic gases in particle form (Cl−(aq), Br−(aq), I−(aq), NO3−(aq), HF(aq)). This may result in diurnal and seasonal changes in acidic gas deposition downwind of the volcano.

Fluoride geochemistry of thermal waters in Yellowstone National Park: I. Aqueous fluoride speciation

Thermal water samples from Yellowstone National Park (YNP) have a wide range of pH (1–10), temperature, and high concentrations of fluoride (up to 50 mg/l). High fluoride concentrations are found in waters with field pH higher than 6 (except those in Crater Hills) and temperatures higher than 50 °C based on data from more than 750 water samples covering most thermal areas in YNP from 1975 to 2008. In this study, more than 140 water samples from YNP collected in 2006–2009 were analyzed for free-fluoride activity by ion-selective electrode (ISE) method as an independent check on the reliability of fluoride speciation calculations. The free to total fluoride concentration ratio ranged from <1% at low pH values to >99% at high pH. The wide range in fluoride activity can be explained by strong complexing with H + and Al 3+ under acidic conditions and lack of complexing under basic conditions. Differences between the free-fluoride activities calculated with the WATEQ4F code and those measured by ISE were within 0.3–30% for more than 90% of samples at or above 10 −6 molar, providing corroboration for chemical speciation models for a wide range of pH and chemistry of YNP thermal waters. Calculated speciation results show that free fluoride, F −, and major complexes ( HF ( aq ) 0 , AlF 2+, AlF 2 + and AlF 3 0 ) account for more than 95% of total fluoride. Occasionally, some complex species like AlF 4 - , FeF 2+, FeF 2 + , MgF + and BF 2 ( OH ) 2 - may comprise 1–10% when the concentrations of the appropriate components are high. According to the simulation results by PHREEQC and calculated results, the ratio of main fluoride species to total fluoride varies as a function of pH and the concentrations and ratios of F and Al.

Constructing Metal-Based Structures on Nanopatterned Etched Silicon

Silicon surfaces with nanoscale etched patterns were obtained using polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer films as templates, followed by brief immersion in HF(aq). The resulting interfaces were comprised of pseudohexagonal arrays of pits on the silicon, whose shapes depended upon the chosen silicon orientation. The top unetched face of silicon remains capped by the native oxide, and the pit interiors are terminated by Si-H(x). Selective chemical functionalization via these two chemical handles was demonstrated to be a viable approach toward building nanostructured metal oxide and metal features within these silicon pits and on the top face. Using a series of interfacial chemical reactions, including oxidation (of Si-H(x)-terminated regions), hydrosilylation, and alkoxysilane-based chemistry on silicon oxide, the growth of metal-based structures can be spatially controlled. In the first approach, titania nanobowls were grown within the etch pits, and in the second, galvanic displacement was used to produce gold nanoparticles either within the etch pits, on the top silicon face, or both.

Internally Referenced Remote Sensors for HF and Cl2 Using Reactive Porous Silicon Photonic Crystals

AbstractRemote detection of reactive analytes using optical films constructed from electrochemically prepared porous Si‐based photonic crystals is demonstrated. Porous Si samples are prepared to contain either surface oxide or surface Si‐H species, and analyte detection is based on irreversible reactions with HF(aq) or Cl2(g) analytes, respectively. HF dissolves silicon oxide from the porous matrix, causing an irreversible blue‐shift in the resonance peak of the photonic crystal. Cl2 reacts with the native Si‐H species present on the surface of as‐etched porous Si to generate reactive silicon halides that evaporate from the surface and/or react with air to convert to silicon oxide. Either Cl2‐related process reduces the net refractive index of the material that is detected as a blue shift in the spectrum. With sufficient analyte concentrations or exposure times, the spectral blue shifts are visible to the unaided eye. A portion of the porous nanostructure is filled with inert polystyrene, which acts as an internal spectral reference. The polymer fiducial protects that portion of the sensor from attack by the corrosive analytes. Reflectance spectra from both the polymer‐filled and the unfilled, reactive porous layers are acquired simultaneously. The fiducial marker also allows elimination of artifacts associated with shifts of the resonance peak upon changing the angle of incidence of the optical probe. Theoretical angle‐resolved spectra (transfer matrix method) show a good match with the experimental data. High‐temperature air or room‐temperature ozone oxidation reactions are used to prepare the HF‐reactive surface, and it is found that the ozone oxidation reaction produces a greater sensitivity to HF (LLOD of 0.1% HF in water).

Stain etching of silicon with V2O5

AbstractFormation of porous silicon by etching of silicon with vanadium pentoxide dissolved in HF(aq) has been studied with infrared spectroscopy and electron microscopy. The rate of film growth depends strongly on the V2O5 concentration. Addition of ethanol greatly decreases the etch rate and changes the pore morphology from a mixture of {100} + {110} planes to predominantly {100} planes. A plot of thickness vs. etch time in aqueous solutions evolves from a quadratic to a linear dependence. A model is developed in which the surface area depends linearly on film thickness and the thickness exhibits the measured functional form with respect to time. In this model pores with a uniform diameter nucleate randomly, initially grow rapidly before slowing to grow at a constant rate. The pore density increases linearly with time then saturates causing the transition to the linear growth rate phase. This model simultaneously fits both the short time and long time behaviour of the thickness and surface area. Pore formation does not involve an oxide intermediate. Films emit brilliant visible photoluminescence, and are highly uniform both in structure and photoluminescence. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Epitaxial Growth of Nanostructured Gold Films on Germanium via Galvanic Displacement

This work focuses on the synthesis and characterization of gold films grown via galvanic displacement on Ge(111) substrates. The synthetic approach uses galvanic displacement, a type of electroless deposition that takes place in an efficient manner under aqueous, room temperature conditions. Investigations involving X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques were performed to study the crystallinity and orientation of the resulting gold-on-germanium films. A profound effect of HF(aq) concentration was noted, and although the SEM images did not show significant differences in the resulting gold films, a host of X-ray diffraction studies demonstrated that higher concentrations of HF(aq) led to epitaxial gold-on-germanium, whereas in the absence of HF(aq), lower degrees of order (fiber texture) resulted. Cross-sectional nanobeam diffraction analyses of the Au-Ge interface confirmed the epitaxial nature of the gold-on-germanium film. This epitaxial behavior can be attributed to the simultaneous etching of the germanium oxides, formed during the galvanic displacement process, in the presence of HF. High-resolution TEM analyses showed the coincident site lattice (CSL) interface of gold-on-germanium, which results in a small 3.8% lattice mismatch due to the coincidence of four gold lattices with three of germanium.

PEMANFAATAN ARANG BATOK KELAPA DAN TANAH HUMUS BATURRADEN UNTUK MENURUNKAN KADAR LOGAM KROM (Cr)

Waste containing hazardous and toxic chemical compounds into the environment leads to water pollution, soil and air. These chemical compounds will endanger human life and environment. One type of compound that may pollute the environment is chromium. The metal is commonly found in industrial waste such as from exhaust and industrial wastewater from etal plating company.The purpose of this research is to utilize coconut shell charcoal and soil humus as a low-cost and ready-made alternative material to reduce the concentration chromium (Cr) on wastewater. Humus was taken from Baturraden region and was isolated using NaOH extraction and was furthermore purified using mixtures of HF(aq): HCl(aq). Coconut shell charcoal was produced and was mixed with the humus. Adsorption process was carried out by batch method on variations of charcoal: humus composition, pH, and contact time. Humus soil was identified using infrared spectrophotometry (IR). Determination of chromium concentration was performed using atomic absorption spectroscopy (AAS).The purified humus yielded was 25.92% (w/w), with 34.18% moisture, and ash content of 18.09%. The results showed that the variation of composition ratio of 2:1 charcoal and humus produced the greatest percent reduction of 18.20%, and the optimum pH for the adsorption is 9. For the variation of contacts time, the optimum reaction time is at 180minutes with decreasing concentration of Pb up to 56.07%.

ChemInform Abstract: The Standard Molar Enthalpy of Formation of ThMo2O8

Abstract The molar enthalpies of solution of ThMo 2 O 8 , Mo, and ThF 4 in (10 mol dm −3 HF(aq) + 4.41 mol dm −3 H 2 O 2 (aq)) have been measured using an isoperibol calorimeter. From these results and other auxiliary data, the standard molar enthalpy of formation of ThMo 2 O 8 has been calculated to be Δ f H m 0 (298.15 K) = (−2742.2 ± 4.5) kJ mol −1 . This value of enthalpy of formation of ThMo 2 O 8 is consistent with the second law enthalpy of formation of ThMo 2 O 8 determined in this laboratory by transpiration technique.

Room-Temperature Synthesis Leading to Nanocrystalline Ag2V4O11

This work highlights a room-temperature composition study of the Ag(2)O/V(2)O(5)/HF((aq)) ternary system, leading to the precipitation of either various silver vanadates having Ag/V ratios from 1/2 to 3/1 or the new silver vanadium oxyfluoride compounds Ag(4)V(2)O(6)F(2) and Ag(3)VO(2)F(4), and a synthetic procedure that affords nanocrystalline Ag(2)V(4)O(11) (SVO) at room temperature. The as-precipitated SVO particles exhibit an acicular morphology, 10-15 x 50-200 nm in size, and present a peculiar reactivity vs lithium notably through a Ag(+)/Li(+) displacement reaction that progresses in a reversible fashion. This step forward thus enables the reversible and simultaneous combination of two active redox processes (silver and vanadium), providing a significant enhancement in the cathode gravimetric capacity of 320 mAh/g at C rate and more than 250 mAh/g at 5C.

Assigning chemical configurations to the XPS features observed at pristine (1 0 0) Si surface resulting after etching in HF aqueous solution

While the analysis of the spectra resulting from energy- or angle-resolved X-ray photoelectron spectroscopy allows the in-depth atomic composition in the probed region to be determined even for complex samples, the determination of the bonding configuration is less trivial. In this paper it is shown that a description of the chemical shift in terms of partial charge and Madelung potential (as results from local modelling of the atom) can provide information even in complicate situations, like that characterizing the hydrogen-terminated (1 0 0) Si prepared by HF aq etching of the native oxide.

Physicochemical and Electrochemical Properties of Etched GaP(111)A and GaP(111)B Surfaces

The observable chemical, electrochemical, and morphological features of GaP(111) surfaces after wet chemical etching have been assessed using X-ray photoelectron spectroscopy, atomic force microscopy, and electrochemical impedance spectroscopy. HF(aq), , , HCl(aq), , and dilute in (with and without a follow-up alkaline etch) are all potent etchants for GaP(111) but yield distinctly different GaP(111)A and GaP(111)B surface conditions. Freshly etched GaP(111)B interfaces show higher residual oxide coverages and are generally rougher than similarly treated GaP(111)A surfaces. Differential capacitance measurements of n-GaP(111)A and n-GaP(111)B electrodes show that various etchants result in a wide range of apparent values for the conduction bandedge potentials, spanning approximately 700 mV in acetonitrile. These data show that these etched surfaces are not equivalent and that the observable physicochemical and electrochemical properties of GaP(111) are strongly influenced by the choice of wet chemical etchant. Additionally, X-ray photoelectron spectra show that adsorption of (4-fluorophenyl)methanethiol onto GaP(111) is insensitive to surface orientation or etching method, indicating no dominant covalent interaction between organic thiols and GaP(111) interfaces.

The growth kinetics and in vitro biocompatibility of Nb&lt;SUB align=right&gt;2O&lt;SUB align=right&gt;5 microcones

Metal oxides have been explored as potential surgical implant coatings designed to incorporate the biocompatibility of the surface oxide with the durable mechanical properties of the underlying metal. A novel anodisation process has been designed which generates an oxide composed of crystalline Nb2O5 microcones interspersed in an amorphous interface oxide. Thin sheets of niobium metal were anodised in a HF(aq) electrolyte for 1, 2 and 4 hrs. Scanning electron microscopy (SEM) was used to analyse the oxide features for each anodisation time. Larger and fewer microcones resulted from increased anodisation time. Due to the requirement of surgical implants to be autoclaved before implantation, the microcone features were analysed using SEM before and after autoclaving. Statistical analysis showed that the microcone features changed very little after autoclaving. MC3T3-E1 pre-osteoblast cells cultured on the autoclaved discs indicated that the 1 h and 4 h groups support the highest amount of cell proliferation.

Structural and transport evolution in the Li xAg 2V 4O 11 system

We investigated the effect of inserting lithium into Ag 2V 4O 11 ( ɛ-SVO) on the structure, electronic properties and redox committed by combining in situ XRD measurements, ESR spectroscopy and 4 probes DC conductivity coupled with thermopower measurements. The electrochemical discharge occurs in three consecutive steps above 2 V (vs. Li +/Li). The first one, between 0 < x < ∼0.7 in Li x -SVO, has been ascribed to the V 5+ reduction through a solid solution mechanism. This reduction competes with a Li +/Ag + displacement reaction which leads to a structural collapse owing to the ionic radii mismatch between the withdrawn Ag + and the inserted Li +. The silver reduction progresses continuously with two different slopes along two composition–potential plateaus at 2.81 V and 2.55 V. Finally, the reduction continues until we obtain an amorphous structure with V 4+ and a ɛ of V 3+. Although, the silver re-enters the structure during the subsequent recharge, the original structure is not recovered. The reduction of silver forming silver metal nano-clusters acts to increase the electronic conductivity from 3.8 × 10 −5 S cm −1 to 1.4 × 10 −3 S cm −1. In complement to this study, we also report on a low temperature hydro-(solvo)-thermal approach using HF (aq) as a mineralizer, which enables the synthesis of nano-sized ɛ-SVO particles that exhibit superior electrochemical performances compared to conventional particles synthesized by solid-state reaction.

Stain Etching with Ferric Ion to Produce Thick Porous Silicon Films

Stain etching of silicon in aqueous solutions composed of FeCl3 + HF + concentrated (HCl, HClO4 or H2SO4) leads to brilliantly luminescent porous Si with a unique dual layer structure. The upper layer (~2 µm or more thick) exhibits bluer luminescence (peaked at 520-590 nm). The lower layer exhibits redder luminescence (peaked at 630-660 nm). The peak PL wavelength and the PL intensity both depend strongly on the excitation wavelength. Photoluminescence excitation (PLE) spectroscopy indicates that the upper and lower layers are distinct because the PLE spectra of the two layers are different. Additionally, we demonstrate that two completely new stain etchants can produce visibly luminescent microporous silicon: V2O5 dissolved in HF(aq) and CeF4 dissolved in H2SO4(aq). In all cases bubble formation is suppressed and layer homogeneity greatly exceeds that obtained with nitrate based stain etchants.

The Role of Band Bending in Affecting the Surface Recombination Velocities for Si(111) in Contact with Aqueous Acidic Electrolytes

The role of band bending in affecting surface recombination velocity measurements has been evaluated by combining barrier height data with charge-carrier lifetime measurements for Si(111) surfaces in contact with a variety of acidic aqueous electrolytes. Charge-carrier lifetimes and thus surface recombination velocities have been measured by contactless radio frequency photoconductivity decay techniques for long bulk lifetime n-Si(111) samples in contact with 11 M (40% by weight) NH4F(aq), buffered (pH = 5) HF(aq), 27 M (48% by weight) HF(aq), or concentrated 18 M H2SO4. Regardless of the sample history or surface condition, long charge-carrier lifetimes were observed for n-Si(111) surfaces in contact with 11 M NH4F(aq) or buffered HF(aq). On the basis of previous barrier height measurements, this behavior is consistent with the formation of an electrolyte-induced surface accumulation layer that reduces the rate of steady-state surface recombination even in the presence of a significant density of surface trap sites. A straightforward evaluation of the surface trap state density from the measured surface recombination velocities, S, is thus precluded for such Si/liquid contacts. In contrast, a wide range of S values, depending on the history of the sample and the state of the surface, were observed for n-Si(111) surfaces in contact with 27 M HF(aq). These results in conjunction with previously measured barrier height data indicate that the charge-carrier lifetimes measured for n-Si(111) in contact with 27 M HF(aq) can be directly correlated with the surface condition and the effective surface-state trap density. These conclusions were confirmed by measurements of the apparent S values of n-Si(111) surfaces in contact with various solutions in the presence of the known deep trap, Cu. For Si(111)/HF(aq) contacts, very high (≥920 ± 270 cm s-1) surface recombination velocities were observed when 0.16 mM (10 ppm) Cu2+ was in the solution and/or adsorbed onto the Si(111) surface as Cu0 deposits, whereas low (100 ± 75 or 225 ± 20 cm s-1) apparent surface recombination velocities were measured for Cu-contaminated Si(111) samples in contact with 0.16 mM (10 ppm) Cu2+-containing 11 M NH4F(aq) or BHF(aq) solutions, respectively.

Chemical, energetic, and geometric heterogeneity of device-quality (1 0 0) surfaces of single crystalline silicon after HF aq etching

An analysis, based on angle-resolved X-ray photoelectron spectroscopy, multiple-internal-reflection infrared spectroscopy, and atomic force microscopy, of device-quality (1 0 0)silicon surfaces after etching in dilute aqueous solution of HF is presented. The analysis shows that the surface is mainly formed by a heterogeneous distribution of SiH, SiH 2and SiH 3 terminations, but contains sub-stoichiometric oxidized silicon. The analysis shows moreover the existence of a form of reduced silicon, not consistent with the currently accepted picture of the native HF aq-etched surface.

Interfacial Energetics of Silicon in Contact with 11 M NH4F(aq), Buffered HF(aq), 27 M HF(aq), and 18 M H2SO4

Open-circuit impedance spectra, channel impedance spectroscopy on solution-gated field-effect devices, and differential capacitance vs potential (Mott−Schottky) measurements were used to determine the energetics of n-Si(111), n-Si(100), and p-Si(111) electrodes in contact with aqueous 11 M (40% by weight) NH4F, buffered HF (BHF), 27 M (48%) HF(aq), and concentrated (18 M) H2SO4. A Mott−Schottky analysis of As2Csc-2-vs-E (where As is the interfacial area, and Csc is the differential capacitance as a function of the electrode potential, E) data yielded reliable barrier heights for some silicon/liquid contacts in this work. Performing a Mott−Schottky analysis, however, requires measurement of the differential capacitance under reverse bias, where oxidation or etching can occur for n-Si and where electroplating of metal contaminants can occur for p-Si. Hence, open-circuit methods would offer desirable, complementary approaches to probing the energetics of such contacts. Accordingly, open-circuit, near-surface channel conductance measurements have been performed using solution-gated n+-p-Si(111)-n+ and p+-n-Si(100)-p+ devices. Additionally, open-circuit impedance spectra were obtained for silicon electrodes in contact with these solutions. The combination of the three techniques indicated that the surfaces of n-Si(111) and n-Si(100) were under accumulation when in contact with either 11 M NH4F(aq) or BHF(aq). The barrier heights for n-Si(111) and n-Si(100) in 11 M NH4F(aq) were −0.065 ± 0.084 V and −0.20 ± 0.21 V, respectively, and were −0.03 ± 0.19 V and −0.07 ± 0.24 V, respectively, for these surfaces in contact with buffered HF(aq). Consistently, p-Si(111) surfaces were determined to be in inversion in contact with these electrolytes, exhibiting barrier heights of 0.984 ± 0.078 V in contact with 11 M NH4F(aq) and 0.97 ± 0.22 V in contact with buffered HF(aq). In contact with 27 M HF(aq), n-Si(111) and n-Si(100) were in depletion, with barrier heights of 0.577 ± 0.038 V and 0.400 ± 0.057 V, respectively, and p-Si(111) was under inversion with a barrier height of 0.856 ± 0.076 V. Measurements performed in 18 M H2SO4 revealed barrier heights of 0.75 ± 0.11 V, 0.696 ± 0.043 V, and 0.889 ± 0.018 V for n-Si(111), n-Si(100), and p-Si(111), respectively, demonstrating that in 18 M H2SO4, the band edge positions of Si were different for different doping types. The barrier height data demonstrate that the observed low recombination rates of silicon in contact with 11 M NH4F, BHF, or 18 M H2SO4 cannot necessarily be attributed to a reduction in the number of surface trap states. In part, low surface recombination rates are expected for such systems because the very large or very small barrier height for silicon in contact with these liquids provides a potential barrier that prevents one type of photogenerated carrier (either electrons or holes) from reaching the surface, thereby producing a low steady-state surface recombination rate.

The Ag2O—V2O5—HF(aq) System and Crystal Structure of α‐Ag3VO4.

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