Showing papers on "Hydrofluoric acid published in 2008"

Pure Silica Zeolite-type Frameworks: A Structural Analysis

Abstract: Since the last major study of silicate crystal structures, many new pure silica zeolite-type frameworks have been discovered. These materials have many interesting properties that are dependent on their structure. We have brought together and analyzed the structures in 35 well-defined frameworks to see how they differ from one another depending on the synthetic route, template, calcination, and composition, and how they differ from the dense silicate phases previously examined. The grand mean values of the Si−O bond distance and the O−Si−O angle are found to be 1.594 A and 109.5°, respectively. The variation and flexibility of the Si−O−Si bond from 133.6 to 180° is discussed, as is the role of fluoride in influencing the O−Si−O bond angles in phases prepared using hydrofluoric acid and ammonium fluoride as mineralizers.

Calcium-Assisted Glass-to-Glass Bonding for Fabrication of Glass Microfluidic Devices

Abstract: Glass is a desired material for many microfluidics applications. It is chemically resistant and has desirable characteristics for capillary electrophoresis. The process to make a glass chip, however, is lengthy and inconvenient, with the most difficult step often being the bonding of two planar glass substrates. Here we describe a new glass bonding technique, which requires only washing of the glass surfaces with a calcium solution and 1−2 h of bonding at 115 °C. We found calcium uniquely allows for this simple and efficient low-temperature bonding to occur, and none of the other cations we tried (e.g., Na+, Mg2+, Mn3+) resulted in satisfactory bonding. We determined this bond is able to withstand high applied field strengths of at least up to 4 kV·cm−1. When intense pressure was applied to a fluid inlet, a circular portion of the coverslip beneath the well exploded outward but very little of the glass−glass interface debonded. In combination with the directed hydrofluoric acid etching of a glass substrat...

Method of recycling useful metal

Abstract: A method of recycling useful metals is provided. The method enables useful metals including indium, zinc, yttrium, europium, lanthanum, terbium, gadolinium, antimony, lead, copper, tin, and silver to be recovered from wastes, such as wasted flat panel displays, and recycled economically with small energy consumption. The method of recycling useful metals includes: a step in which wastes comprising various flat panel displays, e.g., liquid-crystal display panels, are crushed/powdered; a step in which the resultant particles are dissolved in an aqueous hydrofluoric acid solution; and a step in which various metal oxides and various metal fluorides which remain undissolved are filtered off and the aqueous hydrofluoric acid solution containing various metal ions is electrolyzed to deposit and recover metals for transparent-electrode oxides, such as indium and zinc, and other useful metals.

Photo-catalysis using titanium dioxide nanotube layers

Abstract: Photo-degradation of acid orange 7 in aqueous solution was used as a probe to assess the photo-catalytic activity of titanium dioxide nanotube layers under UV irradiation. The nanotube layers were prepared by anodization of Ti foil in 0.4 wt% hydrofluoric acid solution and then annealed at different temperatures between 300 °C and 600 °C for 1 h. The nanotube layers were characterized using X-ray diffraction and scanning electron microscopy. After the 500 °C anneal, the anatase and rutile mass fractions were measured to be about 55% and 45%, respectively. After annealing at 500 °C, the anatase crystallite size was maximum while the size and shape of the nanotubes remain unaffected. Such TiO 2 nanotube layers showed strong photo-catalytic activity. During UV irradiation, we measured the total disappearance of the organic carbon and the formation of anion species to confirm the total mineralization of the acid orange 7.

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

Abstract: Porous silicon (PS) samples were obtained by anodization etching process of n-type silicon wafer phosphorus-doped. Electrochemical oxidation of PS was investigated in aqueous hydrofluoric acid (HF) containing additive such as ethanol or acetonitrile. Pore formation was studied with the variation of type and resistivity of the silicon wafer, taking into account the most important anodization process parameters such as: acid concentration, current density and anodization time. Scanning Electron Microscopy (SEM) and Raman Scattering Spectroscopy measurements were used to characterize the macropore morphology changes and sample photoluminescense responses, respectively. PS layer formed in HF-acetonitrile solution showed more uniform and homogeneous macropore distributions with different shapes and sizes. Behavior may be explained because acetonitrile surface tension is greater than that of ethanol. Therefore, acetonitrile molecules might passivate the silicon surface dissolved during the anodization process.

Novel Synthesis and Thermal Behavior of Aluminum Hydroxy Fluorides AlFx(OH)3−x

Abstract: A new synthesis route to nonhydrated, X-ray amorphous aluminum hydroxy fluorides was explored by sol−gel synthesis with aqueous hydrofluoric acid Followed by XRD, MAS NMR, and DTA-TG, it can be shown that the product composition after thermal annealing critically depends on the gaseous atmosphere Dependent on the fluorine content, corundum formation can occur at temperatures as low as 900 °C Additional mechanical activation of the starting material enhances effects of pyrohydrolysis on thermal annealing and consequently favors early corundum formation in addition

Metal propionate synthesis of epitaxial YBa 2 Cu 3 O 7-x films

Abstract: A modified TFA-MOD method, using only barium trifluoroacetate, is presented. The yttrium and copper triflouroacetates were replaced by the alcoholic solutions of Cu and Y acetates dispersed in propionic acid. Fourier transformed infrared spectroscopy (FT-IR), thermal analyses (DTA/TG) coupled with mass spectrometry (MS) and X-ray diffraction analyses were used to study the decomposition of the precursor. The method permits the shortening of the pyrolysis time by a factor 4, with respect to conventional TFA-MOD method, due to the smaller amount of evolved hydrofluoric acid. Using this method 600 nm thick YBCO films were grown both on (100)SrTiO3 and on CeO2/YSZ/CeO2/Pd buffered Ni-5at.%W substrates. The as obtained films exhibit good morphological, structural and superconducting properties with Tc (R=0) greater than 91K and with an out-of-plain texture of 0.240 and 1.90, respectively.

Determination of fluoride in human whole blood and urine by gas chromatography-mass spectrometry

Abstract: We developed a simple and sensitive method for determination of fluoride in human whole blood and urine using gas chromatography-mass spectrometry (GC-MS). Fluoride was alkylated with pentafluorobenzyl bromide in a mixture of acetone and phosphate buffer (pH 6.8). The derivative obtained was analyzed by GC-MS in the positive-ion electron-impact mode. The lower limit of detection for the compound was 0.5 mg/l for both matrices. The calibration curve for fluoride was linear over the concentration range of 1–100 mg/l. The precision and accuracy of the method were evaluated, and relative standard deviation was within 10%. Using this method, levels of fluoride in whole blood and urine were determined in a case of poisoning caused by hydrofluoric acid exposure.

The electronic structure of the C2H4O...2HF tri-molecular heterocyclic hydrogen-bonded complex: a theoretical study.

Abstract: The geometries of three isomers of the C2H4O···2HF tri-molecular heterocyclic hydrogen-bonded complex were examined through B3LYP/aug-cc-pVDZ calculations. Analysis of structural parameters, determination of CHELPG (charge electrostatic potential grid) intermolecular charge transfer, interpretation of infrared stretching modes, and Bader’s atoms in molecules (AIM) theory calculations was carried out in order to characterize the hydrogen bonds in each isomer of the C2H4O···2HF complex. The most stable structure was determined through the identification of hydrogen bonds between C2H4O and HF, (O···H), as well as in the hydrofluoric acid dimer, (HFD–R···HFD). However, the existence of a tertiary interaction (Fλ···Hα) between the fluoride of the second hydrofluoric acid and the axial hydrogen atoms of C2H4O was decisive in the identification of the preferred configuration of the C2H4O···2HF system.

The surface state of Si (100) and (111) wafers after treatment with hydrofluoric acid

Abstract: Si wafers (CZ, boron doped, 3–20 Ohm cm) with (100) or (111) oriented surfaces were treated in aqueous HF (0.2%, 1%, 5%, 40%) and measured with X‐Ray Photoelectron Spectroscopy (XPS) and High Resolution Electron Energy Loss Spectroscopy (HREELS). The HREELS spectra exhibit vibrational excitations characteristic of a predominant coverage with Si‐dihydride on Si (100) and with Si‐monohydride on Si (111). After treatment in diluted HF additional OH groups could be observed. The coverage with fluorine is shown to be dependent on the HF concentration and amounts to roughly 1–1.5⋅1014 F/cm2 or 10% of a monolayer after a 40% HF dip. Some hydrocarbon and spurious oxygen contamination could be observed, too.Water rinsing after the HF dip lowered the fluorine coverage via a substitution reaction Si‐F+H2O→Si‐OH+HF, as OH groups were detected afterwards. Prolonged water exposure led to the development of a hydrous oxide on part of the surface. A mechanism for the preferential attachment of H to the Si surface is disc...

Process for treating metal surfaces

Abstract: The corrosion resistance of a metal substrate surface treated with an acidic aqueous composition to form a conversion coating is improved by first contacting the surface with an oxidizing acidic pre-rinse, such as an aqueous solution of nitric acid and hydrogen peroxide, or nitric acid and hydrofluoric acid, or Fe+3 cations and hydrofluoric acid.

Nanoparticle-based etching of silicon surfaces

Abstract: A method ( 300 ) of texturing silicon surfaces ( 116 ) such to reduce reflectivity of a silicon wafer ( 110 ) for use in solar cells. The method ( 300 ) includes filling ( 330, 340 ) a vessel ( 122 ) with a volume of an etching solution ( 124 ) so as to cover the silicon surface 116 ) of a wafer or substrate ( 112 ). The etching solution ( 124 ) is made up of a catalytic nanomaterial ( 140 ) and an oxidant-etchant solution ( 146 ). The catalytic nanomaterial ( 140 ) may include gold or silver nanoparticles or noble metal nanoparticles, each of which may be a colloidal solution. The oxidant-etchant solution ( 146 ) includes an etching agent ( 142 ), such as hydrofluoric acid, and an oxidizing agent ( 144 ), such as hydrogen peroxide. Etching ( 350 ) is performed for a period of time including agitating or stirring the etching solution ( 124 ). The etch time may be selected such that the etched silicon surface ( 116 ) has a reflectivity of less than about 15 percent such as 1 to 10 percent in a 350 to 1000 nanometer wavelength range.

Method for producing fluorine series compounds and white carbon black

Abstract: The invention relates to a method utilizing waste gas containing fluoride in fertilizer production or fluorine-containing gas or sodium fluorosilicate in fluorine chemical production as raw materials to product series compounds of fluorine and white carbon black The ammonium fluoride and/or ammonia are/is introduced into an absorption system to get a (NH4) 2SiF6 solution with the absorbing solution concentration of 25 to 37 percent or the ammonium fluoride and the sodium fluorosilicate react to get a reaction product of sodium fluoride crystallization, fluosilicic acid solution and septenary-fluorine compound NH4F(NH4)2SiF6 crystallization The absorption liquid or the reaction product is aminated to get precipitated silica (white carbon black) with the specific surface of 100-180m /g, and the latter can get a sodium fluoride product and an NH4F solution with the concentration of 30 to 45 percent The solution used as a starting point can nearly prepare all inorganic fluoride chemical products, and ammonium fluoride, sodium fluoride, potassium fluoride, ammonium bifluoride, cryolite, aluminum fluoride, sodium hydrogen diffluoride and hydrofluoric acid production, etc are main The method has simplicity, effectiveness and higher economic benefit, and simultaneously, fluorine and silicon in the waste gas containing fluoride of phosphate fertilizer for the pollution of environment can be basically eliminated, and basically no waste water, waste gas and waste residue are discharged

Trapping proton transfer intermediates in the disordered hydrogen-bonded network of cryogenic hydrofluoric acid solutions.

Abstract: A molecular-level description of the structural and dynamical aspects that are responsible for the weak acid behaviour of dilute hydrofluoric acid solutions and their unusual increased acidity at near equimolar concentrations continues to elude us. We address this problem by reporting reflection–absorption infrared spectra (RAIRS) of cryogenic HF–H2O binary mixtures at various compositions prepared as nanoscopic films using molecular beam techniques. Optical constants for these cryogenic solutions [n(ω) and k(ω)] are obtained by iteratively solving Fresnel equations for stratified media. Modeling of the experimental RAIRS spectra allow for a quantitative interpretation of the complex interplay between multiple reflections, optical interference and absorption effects. The evolution of the strong absorption features in the intermediate 1000–3000 cm−1 range with increasing HF concentration reveals the presence of various ionic dissociation intermediates that are trapped in the disordered H-bonded network of cryogenic hydrofluoric acid solutions. Our findings are discussed in light of the conventional interpretation of why hydrofluoric acid is a weak acid revealing molecular-level details of the mechanism for HF ionization that may be relevant to analogous elementary processes involved in the ionization of weak acids in aqueous solutions.

Laser processing of sapphire by strongly focused femtosecond pulses

Abstract: The high-temperature annealing (1500°C for 15 min) of the shock-amorphized and compressed sapphire around the voids rendered the amorphous sapphire insoluble in aqueous solution of hydrofluoric acid. There were no observable back relaxation and reflow of the compressed amorphous phase. The overlapping of femtosecond pulses by >70% of the focal diameter also made the photomodified regions insoluble in aqueous solution of hydrofluoric acid. Femtosecond laser cutting of hard dielectric materials is discussed.

Preparation of silicon nanowire array

Abstract: The invention relates to a method for preparing silicon nanowires, belonging to the nanophase material preparation technical field The method comprises the following steps that: a silicon chip is washed and shaken by acetone and alcohol and is processed by an acid cleaning liquid and a No1 standard cleaning solution; a silicon dioxide spheres solution with a weight percentage density between 002 and 20 percent is added on the silicon chip surface which is washed off in the step one drop by drop by a micro pipette, the processed silicon chip is placed in air to air naturally; the silicon chip with silicon dioxide sphere arrays is annealed for one to three hours at a temperature of between 900 and 1000 DEG C; afterwards, the silicon chip is put into a diluent hydrofluoric acid solution to be eroded for 2 to 20 minutes so that the diameters of the spheres become small; an Ag film with a thickness between 20 and 80nm is deposited on the silicon chip surface by the plating technique or the vacuum evaporating technique; and a sample deposited with the Ag film is dipped into the hydrofluoric acid and hydrogen peroxide etching solution (or ferric nitrate) to be eroded for 4 to 100 minutes The preparation method can rapidly prepare a large area of silicon nanowire arrays, thereby being suitable for the large-scale industrial production

Semiconductor wafer cleaning with dilute acids

Abstract: In a method for cleaning wafers using ultra-dilute acids, the wafers are placed into a rotor in a process chamber. As the rotor spins, the wafers are with de-ionized water and ultra-dilute hydrofluoric acid. Ozone gas is introduced into the process chamber. The wafers are then sprayed with an ultra-dilute solution of hydrochloric acid. Ozone gas is purged from the chamber. The wafers are then rinsed and dried. The ultra-dilute acids may be used in water to acid concentrations on the order of about 1000-2400:1.

Surface treatment solution for the fine surface processing of a glass substrate containing multiple ingredients

Abstract: A surface treatment solution for finely processing a glass substrate containing multiple ingredients is used for the construction of liquid crystal-based or organic electroluminescence-based flat panel display devices without invoking crystal precipitation and/or increasing surface roughness. An etching solution of the invention contains, in addition to hydrofluoric acid (HF) and ammonium fluoride (NH4F), at least one acid whose dissociation constant is larger than that of HF. The concentration of the acid in the solution can advantageously be adjusted to maximize the etching rate.

Substrate processing apparatus and substrate processing method for performing etching process with phosphoric acid solution

Abstract: An additive containing a hexafluorosilicic acid solution (H 2 SiF 6 +H 2 O) is sequentially inputted into a phosphoric acid solution pooled in an immersion bath from an additive input mechanism. Further, a trap agent containing a fluoroboric acid solution (HBF 4 +H 2 O) is inputted into the phosphoric acid solution from a trap agent input mechanism. F − which accelerates etching of a silicon nitride film is added as appropriate by sequentially inputting the additive and siloxane which increases by the sequential input is etched with hydrofluoric acid generated by decomposition of the fluoroboric acid, to thereby suppress a significant increase in the concentration of siloxane. This makes it possible to maintain respective initial etching rates of the silicon nitride film and a silicon oxide film.

Representation of Excess Properties and Liquid Composition of Aqueous Solutions of the HF+Water System

Abstract: The electrolyte-NRTL model was used to describe the thermodynamic excess properties and the liquid composition of aqueous hydrofluoric acid solutions for overall HF concentrations ranging from dilute to a molality of 20 mol⋅kg−1. Within the framework of this model, three different mechanisms were tested. The first one considers only the dissociation of HF into H+ and F−. The second mechanism takes into account the dissociation of HF and the chemical reaction for formation of HF 2 − . The third mechanism considers, in addition to these two chemical reactions, the reaction that leads to formation of the dimer H2F 3 − . The experimental osmotic coefficients of the HF + H2O system were used to estimate the interaction parameters of this model. The resulting parameters yield an accurate description of the Gibbs-Duhem relation for the three mechanisms. The estimated liquid phase speciation for fluoride in the HF+H2O system is comparable to the experimental values of Braddy et al.

Influence of Doping Density on the Current−Voltage Characteristics of p-Type Silicon in Dilute Hydrofluoric Acid

Abstract: The mechanism of p-type porous silicon formation in dilute hydrofluoric acid has been examined over a wide range of resistivities. The current−voltage curves show a negative potential shift as the resistivity of the silicon is reduced, a phenomenon that is explained in terms of a corresponding shift in the flat-band potential. Furthermore it is found that for all resistivities the flat-band potential is negative of the so called “Jps peak”, and an argument is presented that shows that this observation effectively disproves previous literature that has postulated that the “Jps peak” marks the transition between porous silicon formation and electropolishing. An observed decrease in the magnitude of the Jps peak for the two most heavily doped samples can be accounted for if the rate-determining step in PSi formation becomes the breaking of the Si−Si back-bonds, a process that should be potential dependent.

Silicon surface preparation

Abstract: Methods are provided for producing a pristine hydrogen-terminated silicon wafer surface with high stability against oxidation. The silicon wafer is treated with high purity, heated dilute hydrofluoric acid with anionic surfactant, rinsed in-situ with ultrapure water at room temperature, and dried. Alternatively, the silicon wafer is treated with dilute hydrofluoric acid, rinsed with hydrogen gasified water, and dried. The silicon wafer produced by the method is stable in a normal clean room environment for greater than 3 days and has been demonstrated to last without significant oxide regrowth for greater than 8 days.

Method for purifying ultra-pure hydrofluoric acid

Abstract: The invention relates to a purifying method of ultrahigh pure hydrofluoric acid, comprising the technological steps as follows: filling industrial anhydrous hydrogen fluoride liquid into a rectifying still, and adding potassium permanganate with 0.16 to 1 percent weight, stirring, then stopping; after that, adding hydrogen peroxide with 0.16 to 1 percent weight, stirring, then stopping; heating up to 60 to 80 DEG C, the hydrogen fluoride liquid is gasified and generated into purified hydrogen fluoride gas; subsequently, filling the purified hydrogen fluoride gas which goes out of the rectifying still into a cooler for cooling and filtering; injecting deionized water into an absorption tower whose bottom is provided with a gas distribution plate tube, after that, filling the hydrogen fluoride gas which goes out of the cooler into the gas distribution plate tube at the bottom of the tower; after sprayed out of the gas distribution holes on the tube wall of the gas distribution plate tube, the hydrogen fluoride gas is absorbed by the deionized water and produced into semi finished product of hydrofluoric acid; finally, filling the semi finished product of hydrofluoric acid which goes out of the absorption tower into a filter in 0.05Mum, after that, obtaining the finished product of ultrahigh pure hydrofluoric acid. The product prepared by the method of the invention has high fineness and output, according to the requirements of the environmental protection.

Method of acid fracturing a sandstone formation

Abstract: Methods and compositions useful in acidizing a subterranean formation with an oil-in-water emulsion that includes a sulfonate ester, a fluoride salt, a proppant, and water. The reaction of the ester and fluoride salt is delayed so that hydrofluoric acid is produced in-situ.

Transition State for the Gas-Phase Reaction of Uranium Hexafluoride with Water

Abstract: Density Functional Theory and small-core, relativistic pseudopotentials were used to look for symmetric and asymmetric transitions states of the gas-phase hydrolysis reaction of uranium hexafluoride, UF{sub 6}, with water. At the B3LYP/6-31G(d,p)/SDD level, an asymmetric transition state leading to the formation of a uranium hydroxyl fluoride, U(OH)F{sub 5}, and hydrogen fluoride was found with an energy barrier of +77.3 kJ/mol and an enthalpy of reaction of +63.0 kJ/mol (both including zero-point energy corrections). Addition of diffuse functions to all atoms except uranium led to only minor changes in the structure and relative energies of the reacting complex and transition state. However, a significant change in the product complex structure was found, significantly reducing the enthalpy of reaction to +31.9 kJ/mol. Similar structures and values were found for PBE0 and MP2 calculations with this larger basis set, supporting the B3LYP results. No symmetric transition state leading to the direct formation of uranium oxide tetrafluoride, UOF{sub 4}, was found, indicating that the reaction under ambient conditions likely includes several more steps than the mechanisms commonly mentioned. The transition state presented here appears to be the first published transition state for the important gas-phase reaction of UF{sub 6} with water.

Methods of underground formation consolidation

Abstract: Unconsolidated formation sand in the near wellbore region may be uniformly consolidated using a system including a sodium silicate solution and a hardener, such as at least one dialkyl ester of a dicarboxylic acid. Subsequently, a low concentration acid, such as hydrofluoric (HF) acid, is pumped through and into the consolidated sand to create channels or passageways to connect the formation hydrocarbons with the wellbore for production of the hydrocarbons through the wellbore. Hydrofluoric acid may be generated in situ by hydrolyzing a substance to hydrofluoric acid where the substance may include ammonium bifluoride, ammonium fluoride, alkali metal fluorides, alkali metal bifluorides, transition metal fluorides, and the like, and mixtures thereof. The acid may instead or additionally include organic acids and other mineral acids.

Palladium Enhanced Etching of n-type Silicon in Hydrofluoric Acid Solution

Abstract: Pd-particle-modified n-Si can be etched at a high rate in a hydrofluoric acid solution without a particular oxidizing agent under dissolved oxygen free and dark conditions. In this study, Pd thin film patterned n-Si is used. The etching is localized at the boundary between the 29-nm-thick-Pd film and the non-Pd-deposited area of the n-Si surface at the initial stage. Then Pd particles form on the non-Pd-deposited area toward which the etched area extends. Thin (4.3 nm) Pd films localize the etching under the films.