Showing papers on "Hydrofluoric acid published in 2011"

Fluoride-containing bioactive glasses: Fluoride loss during melting and ion release in tris buffer solution

Abstract: Melt-derived bioactive glasses (SiO2–P2O5–CaO–Na2O–CaF2; CaF2 0 to 17.76 mol%) lost fluoride during melting, but nominal and analysed CaF2 contents in the glass correlated linearly. Analysed CaO contents were increased, showing that fluoride was lost as hydrofluoric acid after reaction with atmospheric water during melting. Weight loss on ignition reduced linearly with increasing CaF2, suggesting that CaF2 impedes absorption of atmospheric water. pH changes in tris buffer solution showed that pH is controlled by the silicate matrix (via ion exchange processes), and fluoride release contributes less to the overall pH. Glasses formed apatite in tris buffer; phosphate concentration of the glass was the limiting factor, resulting in fluorite formation for increasing fluoride content in the glass and calcite formation for the fluoride-free composition. These results allow for tailoring of novel fluoride-containing bioactive glasses to address specific needs, particularly in dentistry and for remineralising toothpastes.

Liquid structures of water, methanol, and hydrogen fluoride at ambient conditions from first principles molecular dynamics simulations with a dispersion corrected density functional

Abstract: Using first principles molecular dynamics simulations in the isobaric–isothermal ensemble (T = 300 K, p = 1 atm) with the Becke–Lee–Yang–Parr exchange/correlation functional and a dispersion correction due to Grimme, the hydrogen bonding networks of pure liquid water, methanol, and hydrogen fluoride are probed. Although an accurate density is found for water with this level of electronic structure theory, the average liquid densities for both hydrogen fluoride and methanol are overpredicted by 50 and 25%, respectively. The radial distribution functions indicate somewhat overstructured liquid phases for all three compounds. The number of hydrogen bonds per molecule in water is about twice as high as for methanol and hydrogen fluoride, though the ratio of cohesive energy over number of hydrogen bonds is lower for water. An analysis of the hydrogen-bonded aggregates revealed the presence of mostly linear chains in both hydrogen fluoride and methanol, with a few stable rings and chains spanning the simulation box in the case of hydrogen fluoride. Only an extremely small fraction of smaller clusters was found for water, indicating that its hydrogen bond network is significantly more extensive. A special form of water with on average about two hydrogen bonds per molecule yields a hydrogen-bonding environment significantly different from the other two compounds.

Extremely High Surface Area Metallurgical-Grade Porous Silicon Powder Prepared by Metal-Assisted Etching

Abstract: Nanostructured mesoporous silicon powders are being developed for a diverse range of applications including drug delivery, therapeutics, biosensors, and explosives. Such powders are easily produced through mechanical milling of membranes taken from electrochemically anodized silicon wafers. Where applications require highvolume, low-cost production, however, wafer feedstock is not viable and alternative feedstocks such as metallurgical-grade silicon powders become more attractive. Porosification of powders can be achieved using electro-less processing such as stain etching. Although much of the stain-etch literature has been developed around silicon wafers, the process, involving immersion of the silicon in an aqueous solution of hydrofluoric and nitric acids, has been readily transferred to powders. 1,2 Scalable synthesis methodologies have been reported for powders, 3 albeit with limitations on achievable surface area (143 m 2 /g), pore volume (0.3 ml/g), and yield (5%). Encouraging results have been reported 4 on the use of alternative oxidants, containing transition metals, for porosification of wafers, thus avoiding issues such as quiescence periods, inhomogeneity and irreproducibility usually associated with hydrofluoric-nitric acid processing. Metal-assisted chemical etching of silicon wafers has been the subject of two reviews. 5,6 For the first time, to our knowledge, we have applied metal-assisted etching using the hydrofluoric acid (HF)-ferric chloride (FeCl3) process, 7,8 in modified form, to metallurgical-grade silicon powders. The metal-assisted etch reaction can be described as

The Composition of Fly Ash Glass Phase and Its Dissolution Properties Applying to Geopolymeric Materials

Abstract: Using X-ray diffraction combined with Rietveld method and chemical analysis with hydrofluoric acid (HF) solution, the content and composition of glass phase of a class F fly ash are quantified, and the initial Si/Al ratio of glass phase is calculated as well. The dissolution of Si4+ and Al3+ in different chemical solution (HF, NaOH, and NaF) in various concentrations and with different reaction time of NaOH solution was studied. The dissolved Si/Al ratio was compared with the initial value, and following conclusions are drawn: (1) only a very small part of Si and Al dissolved in NaOH solution, knowing as available Si and Al; (2) the dissolution is influenced by alkali concentration. When the concentration of NaOH was 10M, the dissolved Si/Al ratio at 5, 15, and 30 min was lower than initial value, but increased greatly at 240 min, which means Al is more prone to dissolve than Si, due to the weaker Al–O bonds than Si–O bonds. However, when the alkali concentration was 15M, the dissolved Si/Al ratio increased, and the dissolution of Si and Al both get accelerated.

Synthesis of a new nanocrystalline titanium aluminum fluoride phase by reaction of Ti2AlC with hydrofluoric acid

Abstract: A new nanocrystalline phase of titanium aluminum fluoride, with a stoichiometry of Ti(2)AlF(9)-exact stoichiometry measured herein is Ti(2.1)Al(0.9)F(9),-was synthesized by the fluorination of Ti(2 ...

Sodium Fluoride-Assisted Modulation of Anodized TiO2 Nanotube for Dye-Sensitized Solar Cells Application

Abstract: This work reports the use of sodium fluoride (in ethylene glycol electrolyte) as the replacement of hydrofluoric acid and ammonium fluoride to fabricate long and perpendicularly well-aligned TiO2 nanotube (TNT) (up to 21 μm) using anodization. Anodizing duration, applied voltage and electrolyte composition influenced the geometry and surface morphologies of TNT. The growth mechanism of TNT is interpreted by analyzing the current transient profile and the total charge density generated during anodization. The system with low water content (2 wt %) yielded a membrane-like mesoporous TiO2 film, whereas high anodizing voltage (70 V) resulted in the unstable film of TNT arrays. An optimized condition using 5 wt % water content and 60 V of anodizing voltage gave a stable array of nanotube with controllable length and pore diameter. Upon photoexcitation, TNTs synthesized under this condition exhibited a slower charge recombination rate as nanotube length increased. When made into cis-diisothiocyanato-bis(2,2-bi...

Method for preparing silicon nanowire array with smooth surface

Abstract: The invention relates to a method for preparing a length-controlled silicon nanowire array with a smooth surface, and belongs to the technology of the preparation of nanometer materials. The method comprises the following steps of: firstly, performing wet chemical cleaning on a silicon wafer; secondly, depositing a silver nanometer granular layer on the surface of the silicon wafer in mixed solution containing hydrofluoric acid and silver nitrate by an electroless chemical deposition method; thirdly, performing chemical etching by mixed solution containing the hydrofluoric acid and hydrogen peroxide; and finally, removing silver nanometer granules by using nitric acid to obtain the silicon nanowire array. In the method, length-controlled silicon nanowires with the smooth surfaces are prepared by regulating the concentration and etching time of the hydrogen peroxide serving as an oxidant simply in a chemical etch system, so the technical problem of preparing the silicon nanowires with fewer surface defects in metal-assisted chemical etching is solved.

Rare earth fluoride nanoparticles obtained using charge transfer complexes: a versatile and efficient route toward colloidal suspensions and monolithic transparent xerogels.

Abstract: Crystalline rare earth fluoride nanoparticles were synthesized by reacting rare earth ions with charge-transfer complexes, in solution, under mild conditions. An infrared study showed that these intermediate complexes are made up of solvent molecules (amide: N,N-dimethylformamide, 1-methyl-2-pyrrolidinone, etc.) and fluoride ions coming from hydrofluoric acid. The size and shape of the particles can be controlled through the process parameters. The complete study of the particles obtained through this process is carried out in this document, especially for the YbF3 system. However, the process can easily be extended to the whole series of rare earth elements. We also show the ability of these objects to be transferred from an aqueous medium to an organic phase thanks to their surface modification. Finally, transparent monolithic xerogels of rare earth fluoride have been developed starting from the prepared colloidal solutions.

Interaction of water with the fluorine-covered anatase TiO2(001) surface

Abstract: The interaction of water with the fluorine-covered (001) surface of anatase titanium dioxide (TiO2) has been studied within the framework of density functional theory (DFT). Our results show that water dissociation is unfavorable due to repulsive interactions between surface fluorine and oxygen. We also found that the reaction of hydrofluoric acid with a surface hydroxyl group to form a surface Ti–F bond is exothermic, while the removal of fluorine from the surface needs additional energy of about half an eV. Therefore, water molecules are predicted to remain intact at the interface with the F-terminated anatase (001).

Detection of hydrofluoric acid by a SiO2 sol-gel coating fiber-optic probe based on reflection-based localized surface plasmon resonance.

Abstract: A novel fiber-optic probe based on reflection-based localized surface plasmon resonance (LSPR) was developed to quantify the concentration of hydrofluoric acid (HF) in aqueous solutions. The LSPR sensor was constructed with a gold nanoparticle-modified PMMA fiber, integrated with a SiO2 sol-gel coating. This fiber-sensor was utilized to assess the relationship between HF concentration and SiO2 sol-gel layer etching reduction. The results demonstrated the LSPR sensor was capable of detecting HF-related erosion of hydrofluoric acid solutions of concentrations ranging from 1% to 5% using Relative RI Change Rates. The development of the LSPR sensor constitutes the basis of a detector with significant sensitivity for practical use in monitoring HF solution concentrations.

New Hybrid Zirconium Aminophosphonates Containing Piperidine and Bipiperidine Groups

Abstract: The reaction of N-(phosphonomethyl)piperidine and N,N′-bis(phosphonomethyl)bipiperidine with zirconium(IV) in hydrofluoric acid media led to the preparation of two new zirconium fluoride phosphonat...

Interaction of water with the fluorine-covered anatase TiO2(001) surface

Abstract: The interaction of water with the fluorine-covered (001) surface of anatase titanium dioxide (TiO2) has been studied within the framework of density functional theory (DFT). Our results show that water dissociation is unfavorable due to repulsive interactions between surface fluorine and oxygen. We also found that the reaction of hydrofluoric acid with a surface hydroxyl group to form a surface Ti–F bond is exothermic, while the removal of fluorine from the surface needs additional energy of about half an eV. Therefore, water molecules are predicted to remain intact at the interface with the F-terminated anatase (001).

Novel texturing method for sputtered zinc oxide films prepared at high deposition rate from ceramic tube targets

Abstract: Sputtered and wet-chemically texture etched zinc oxide (ZnO) films on glass substrates are regularly applied as transparent front contact in silicon based thin film solar cells. In this study, chemical wet etching in diluted hydrofluoric acid (HF) and subsequently in diluted hydrochloric acid (HCl) on aluminum doped zinc oxide (ZnO:Al) films deposited by magnetron sputtering from ceramic tube targets at high discharge power (~10 kW/m target length) is investigated. Films with thickness of around 800 nm were etched in diluted HCl acid and HF acid to achieve rough surface textures. It is found that the etching of the films in both etchants leads to different surface textures. A two steps etching process, which is especially favorable for films prepared at high deposition rate, was systematically studied. By etching first in diluted hydrofluoric acid (HF) and subsequently in diluted hydrochloric acid (HCl) these films are furnished with a surface texture which is characterized by craters with typical diameter of around 500 − 1000 nm. The resulting surface structure is comparable to etched films sputtered at low deposition rate, which had been demonstrated to be able to achieve high efficiencies in silicon thin film solar cells.

Solvothermal aluminophosphate zeotype synthesis with ionic liquid precursors

Abstract: We have carried out a study of aluminophosphate framework synthesis using several amine based ionic liquids and their parent amines as solvent and template. The results suggest that in the presence of fluoride ions from hydrofluoric acid the ionic liquids and their parent amines produce the same frameworks, while in synthesis without fluoride ions the products are not related. The results include the synthesis and crystal structure of a novel extra-large pore material using 1-methylpyrrolidine as solvent and template. The relationship between this and sodalite, which can be synthesised in cobalt aluminophosphate form using an ionic liquid prepared from 1-methylpyrrolidine is described. The crystal structures of two other new layered materials are also presented.

ACO-zeotype iron aluminum phosphates with variable Al/Fe ratios controlled by F⁻ ions.

Abstract: Three new iron aluminum phosphates |(C2H10N2)4|[Fe8 − xAlxFx(H2O)2 − x(PO4)8]·2H2O (χ = 1.64, 1.33, 0.80) with ACO-zeotype structures denoted as FeAPO-CJ66(a), FeAPO-CJ66(b), and FeAPO-CJ66(c), respectively, have been synthesized in the fluoride ion system. Their framework structures are made of double 4-ring (D4R) building units formed by the alternating connection of Fe(Al)O4F(O) trigonal bipyramids and PO4 tetrahedra, which possess 3D intersecting 8-ring channels running along the [001], [010], and [100] directions. Fluoride ions or water molecules reside in the center of D4Rs, and diprotonated ethylenediamine cations and water molecules are occluded in the free space of channels to stabilize the whole structure. Notably, the Al/Fe ratios in the frameworks can be effectively controlled from 1/3.9 to 1/5.0 to 1/9.0 by adjusting the amounts of phosphoric acid and hydrofluoric acid added to the initial reaction mixture. Mossbauer and magnetic measurements show that the Fe ions in the compounds are bivalen...

Method for measuring contents of silicon-calcium elements in silicon-calcium alloy

Abstract: The invention relates to a method for measuring the contents of silicon-calcium elements in a silicon-calcium alloy. After a sample is grinded and passes through an analysis sieve with 180-200 meshes, the method provided by the invention is characterized in that the sample is fused at high temperature by adopting an alkali fusion method; the fusion course comprises the steps of: weighing and adding the sample and sodium hydroxide solid to a nickel crucible; after adding the mixture to a high temperature furnace to be heated, taking out and cooling; washing the fused analysis sample to an evaporation dish by utilizing deionized water and hydrochloric acid; drying and adding the hydrochloric acid to be acidized; adding warm water to be stirred until soluble salts are completely dissolved; instantly filtering by utilizing quantitative filter paper; enabling the filtrate to be constant volume in a volumetric flask to prepare a sample analysis solution; and maintaining the precipitations to be analysis components. The method for respectively measuring the contents of silicon and calcium provided by the invention comprises the following steps: measuring the content of the silicon with precipitation and filter paper by utilizing a weight analysis method after ashing, firing, cooling and weighing; and measuring the content of the calcium with the sample analysis solution by utilizing a volumetric method. The method provided by the invention has the advantages of once sample weighing, multi-element continuous measurement, time and labor saving, energy conservation, consumption reduction and the like and can reduce the damage of hydrofluoric acid to human bodies and environments.

Texturing method for polycrystalline silicon solar cells

Abstract: The embodiment of the invention discloses a texturing method for polycrystalline silicon solar cells, which comprises the following steps of: texturing the polycrystalline silicon solar cells by using mixed solution of nitric acid and hydrofluoric acid for the first time; and texturing the polycrystalline silicon solar cells by using mixed solution of nitric acid and hydrofluoric acid for the second time, wherein a mass concentration ratio of the nitric acid to the hydrofluoric acid during the second-time texturing of the polycrystalline silicon solar cell is less than that of the nitric acidto the hydrofluoric acid during the first-time texturing of the polycrystalline silicon solar cells. By the method provided by the invention, a uniform textured structure can be formed on the surfaceof the polycrystalline silicon solar cells so as to improve the photoelectric conversion efficiency of the polycrystalline silicon solar cells.

Analysis of gaseous reaction products of wet chemical silicon etching by conventional direct current glow discharge optical emission spectrometry (DC-GD-OES)

Abstract: Major parts of the mechanism of the wet chemical etching of Si using mixtures of nitric and hydrofluoric acid are still in question. One of them is the issue about the formation of H and its relevance in the oxidation of Si. In the present work H evolution during acid etching of Si was estimated as a function of the HF/HNO3 mixing ratio and the temperature. A commercial GD-OES instrument with an unchanged Grimm type glow discharge chamber was used to determine the amount of formed H. A small fraction of the reaction gases, originated by etching of Si in a PTFE apparatus under Ar atmosphere, was fed by a constant Ar flow via a drying column into the discharge chamber. The gases were excited by the plasma of a continuously DC sputtered Fe sample. Numerous elements like Si, N, O, H, and even B from the B-doped Si were detected. However, only the H emissions at 121.5 nm and 656.3 nm were used for the estimation of the released H. The obtained results show that H is preferentially generated in HNO3-poor etch solutions (HNO3 < 40% (v/v)). In the range from −10 to 35 °C the temperature of the etch solution shows a negligible influence on the H generation, but affects the amount of nitrous gases. This indicates that particularly in HNO3-poor etch solutions the oxidation of Si proceeds to a considerable extent via the formation of H parallel to the already known pathway via the reduction of HNO3.

Study of the processes of carbonization and oxidation of porous silicon by Raman and IR spectroscopy

Abstract: Porous silicon layers were produced by electrochemical etching of single-crystal silicon wafers with the resistivity 10 Ω cm in the aqueous-alcohol solution of hydrofluoric acid. Raman spectroscopy and infrared absorption spectroscopy are used to study the processes of interaction of porous silicon with undiluted acetylene at low temperatures and the processes of oxidation of carbonized porous silicon by water vapors. It is established that, even at the temperature 550°C, the silicon-carbon bonds are formed at the pore surface and the graphite-like carbon condensate emerges. It is shown that the carbon condensate inhibits oxidation of porous silicon by water vapors and contributes to quenching of white photoluminescence in the oxidized carbonized porous silicon nanocomposite layer.

Effect of etchant variability on shear bond strength of all ceramic restorations - an in vitro study

Abstract: The present study was carried out to evaluate the effect of pre-luting surface treatments by 3 different etchant used at 3 different etching periods and their effect on shear bond strength of IPS Empress 2 luted to tooth by dual cure resin cement. Fifty samples of ceramic were divided into four groups as group I control group: No surface treatment, group II: Etched with Hydrofluoric (HF) acid (4.9%), group III: Etched with Ammonium bifluoride acid (9.4%) and group IV: Etched with Phosphoric acid (37%). Group II, III and IV were further divided into 3 Subgroups; namely A, B and C according to the etching periods (20, 60 and 120 s) respectively. The shear bond strength was determined by using a Universal testing Machine. The morphological changes of the surface treated ceramic samples prior to luting to tooth and mode of the fracture failure after shear bond test were observed by using a Scanning Electron Microscope. The mean shear bond strength was highest when IPS Empress 2 ceramic samples were surface treated using 4.9% Hydrofluoric acid gel and 9.4% Ammonium bifluoride acid for 120 s. The least mean shear bond strength was noticed in case of control group, where no surface treatment was done and samples treated by 37% Phosphoric acid. Thus it could be concluded, that Ammonium bifluoride could be an appropriate alternative to be used instead of HF acid. 120 s etching showed highest bond strength values for HF acid (4.9%) and Ammonium bifluoride (9.4%).

Method for preparing sequentially arranged bent silicon nano-wire array

Abstract: The invention discloses a method for preparing a sequentially arranged bent silicon nano-wire array. The method comprises the following steps of: 1) placing etching solution in a hydrofluoric acid corrosion resistant vessel, cleaning a crystal orientation mono-crystalline silicon wafer (111), immersing in the etching solution, and sealing the vessel, wherein the etching solution consists of silver nitrate, hydrofluoric acid and deionized water, the concentration of silver ions in the etching solution is between 0.01 and 0.04mol/L, and the concentration of the hydrofluoric acid is between 1 and 5mol/L; and 2) placing the vessel in a constant-temperature water bath to ensure the silicon wafer reacts with the etching solution, and taking the silicon wafer out after the reaction is completed to obtain the sequentially arranged bent silicon nano-wire array on the surface of the silicon wafer. In the method, the metal ion assisted solution etching technology and selective effect of different crystal orientations of the silicon wafer are organically combined so as to prepare the sequentially arranged bent silicon nano-wire array on the surface of the silicon wafer. The method is simple and convenient and has mild reaction conditions, and by the method, the sequentially arranged bent silicon nano-wire array material can be prepared in one step at room temperature.

Sulfuric acid–methanol electrolytes as an alternative to sulfuric–hydrofluoric acid mixtures for electropolishing of niobium

Abstract: Attainment of the greatest possible interior surface smoothness is critical to meeting the performance demands placed upon niobium superconducting radiofrequency (SRF) accelerator cavities by next generation projects. Electropolishing with HF–H2SO4 electrolytes yields cavities that meet SRF performance goals, but a less-hazardous, more environmentally-friendly process is desirable. Reported studies of EP on chemically-similar tantalum describe the use of sulfuric acid–methanol electrolytes as an HF-free alternative. Reported here are the results of experiments on niobium samples with this electrolyte. Voltammetry experiments indicate a current plateau whose voltage range expands with increasing acid concentration and decreasing temperature. Impedance spectroscopy indicates that a compact salt film is responsible for the current plateau. Equivalent findings in electropolishing chemically-similar tantalum with this electrolyte were interpreted due to as mass transfer limitation by diffusion of Ta ions away from the anode surface. We infer that a similar mechanism is at work here. Conditions were found that yield leveling and brightening comparable to that obtained with HF–H2SO4 mixtures.

Metallurgy purification method for polysilicon

Abstract: The invention discloses a method for metallurgical purification of a polysilicon, which particularly to a purification technology being capable of decreasing the contents of boron and phosphor which influence the battery efficiency. The method comprises the following steps: sodium oxide, lime and fluorite are added during the slagging and oxidation process, boron and phosphor are made into oxide by a displacement reaction, the oxide is dissolved in slag, the melting temperature is reduced by adding with the fluorite, the fluxing medium dissolves in the leaching process of the dilute acid, theoxidizing acid oxidizes and dissolves boride and metallic compounds at the transition zone, and then the complexant for hydrofluoric acid and boron corrodes the surface of silicon, and the boron impurity is extracted from the surface of silicon particles to a solvent under the effect of complexant. The method has low energy consumption and no pollution, and can improve the purity of polysilicon.

Analytical methods for SiO2 and other inorganic oxides in titanium dioxide or certain silicates for food additive specifications

Abstract: An analytical method has been developed for the detection of SiO(2) and other oxides in titanium dioxide and certain silicates used in food additives using inductively coupled plasma (ICP) atomic emission spectrometry without hydrofluoric acid. SiO(2) and other oxides in titanium dioxide or certain silicates were resolved by alkali fusion with KOH and boric acid and then dissolved in dilute hydrochloric acid as a test solution for ICP. The recovery of SiO(2) and Al(2)O(3) added at 0.1 and 1.0%, respectively, in TiO(2) was 88-104%; coefficient of variation was <4%. The limit of determination of SiO(2) and Al(2)O(3) was about 0.08%, and the accuracy of the ICP method was better than that of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) test method. The recovery of SiO(2) and other oxides in silicates was 95-107% with a coefficient of variation of <4%. Using energy dispersive X-ray fluorescence spectrometry (EDX) with fundamental parameter determination, the content of SiO(2) and other oxide in titanium dioxide and silicate showed good agreement with the ICP results. ICP with alkali fusion proved suitable as a test method for SiO(2), Al(2)O(3) and other oxides in titanium dioxide and certain silicates, and EDX proves useful for screening such impurities in titanium dioxide and componential analysis of certain silicates.