Showing papers on "Hydrofluoric acid published in 1990"

Suppression of boron volatilization from a hydrofluoric acid solution using a boron-mannitol complex

Abstract: Volatilization and mass fractionation of boron during evaporation of the hydrofluoric and hydrochloric acid solutions were investigated with varying mannitol/boron ratios. The formation of this complex in the acid solutions allows the use of hydrofluoric and hydrochloric acids for the dissolution of silicate rock samples and for the subsequent chemical separation of boron from the samples adopting anion-exchange chromatography in F − form

Method of making silicon quantum wires

Abstract: A method of making semiconductor quantum wires employs a semiconductor wafer (14) as starting material. The wafer (14) is weakly doped p type with a shallow heavily doped p layer therein for current flow uniformity purposes. The wafer (14) is anodised in 20 % aqueous hydrofluoric acid to produce a layer (5) microns thick with 70 % porosity and good crystallinity. The layer is subsequently etched in concentrated hydrofluoric acid, which provides a slow etch rate. The etch increases porosity to a level in the region of 80 % or above. At such a level, pores overlap and isolated quantum wires are expected to form with diameters less than or equal to 3 nm. The etched layer exhibits photoluminescence emission at photon energies well above the silicon bandgap (1.1 eV) and extending into the red region (1.6 - 2.0 eV) of the visible spectrum.

The synthesis of SAPO-34 and CoSAPO-34 from a triethylamine–hydrofluoric acid–water system

Abstract: The synthesis of the highly selective methanol-to-olefin catalysts SAPO-34 and CoSAPO-34, using a unique combination of triethylamine templating agent and fluoride ion mineralizer, is reported. The control of both the Si/Al/P ratio and template content of the reaction gel mixture allows the formation of the other SAPO-based zeolitic systems. The fluoride ion mineralizer causes a reduction in nucleation time and an increase in crystallinity of SAPO-34. The structure-directing effects of the triethylamine template are discussed and shown to predominate through steric influences, rather than electronic effects. This was confirmed by quantitative thermogravimetric analysis and molecular-graphics techniques.

Wide-range tuning of the titanium dioxide flat-band potential by adsorption of fluoride and hydrofluoric acid

Abstract: The adsorption of fluoride, (HF){sub n}F{sup {minus}} ions, and hydrofluoric acid at the surface of n-type TiO{sub 2{minus}x}F{sub x} (x {approx} 0.001) electrodes was studied by electrochemical methods. Adsorption of F{sup {minus}} from acetontrile/tetraethylammonium fluoride (TEAF) solution follows a Langmuir isotherm above a fractional coverage of about 0.5, and the equilibrium constant for adsorption is 8,300 M{sup {minus}1}. Specific adsorption of fluoride ions, at millimolar concentration in acetonitrile, results in a large negative shift in the flat-band potential, as manifested by capacitance measurements and cyclic voltammetry of Ru(bpy){sub 3}{sup 2+}. Fluoride ions are strongly complexed by HF in acetonitrile to form (HF){sub n}F{sup {minus}} ions (n = 1,2), which are also specifically adsorbed at the TiO{sub 2{minus}x}F{sub x}(001) surface.

Process for the wet-chemical treatment of semiconductor surfaces

Abstract: In the treatment of semiconductor slices, in particular silicon slices, w aqueous solutions containing hydrofluoric acid, a contamination of the slice surface with particles which interfere with the subsequent processes has been observed. This increase in particles can be markedly decreased by additionally adding to the solutions, organic ring molecules capable of forming inclusion compounds, such as, for instance, cyclodextrins, and/or acids with pKa below 3.14 which are incapable of oxidizing the semiconductor material. The actual treatment can be carried out in the usual way, for example, in immersion baths.

Hydrogen peroxide solutions

Abstract: It would be desirable to replace nitric acid based solutions for surface treating steels and like materials with a sulphuric acid based solution containing hydrogen peroxide, but such replacement solutions lose hydrogen peroxide rapidly through mainly iron-induced decomposition. A surface treatment solution that is based on sulphuric acid and hydrogen peroxide, but has improved stability, contains an effective amount in combination of hydrofluoric acid, a hydroxybenzoic acid and an N-alkoxyphenyl-acetamide. Preferably, the hydroxybenzoic acid is para-hydroxybenzoic acid and the N-alkoxyphenyl-acetamide is N-(4-ethoxyphenyl)-acetamide. It is preferable to employ a saturated solution of each of the two latter components, and this can be achieved practically and simply by adding the solid components in the shape of a block or blocks which maintain the saturated solution over an extended period of time.

Matte finishes on optical fibers and other glass articles

Abstract: A mixture of buffered hydrofluoric acid (e.g., HF and NH₄F) and a treating agent (e.g., acetic acid, phosphoric acid, hydrochloric acid, sulfuric acid or formic acid) is used to produce a matte finish (24) on the pure silica cladding of an optical fiber (16), on a borosilicate glass tube and on a sodium lime glass plate. The matte finish may be used to increase the adhesion of other materials to the glass (e.g., of metal coatings (26) to silica fibers) or to reduce glare.

Reaction of hydrofluoric acid and water with the GaAs(100) surface

Abstract: The chemical surface state of polished GaAs (100) wafers after treatments in hydrofluoric acid and in water were investigated by means of x‐ray photoelectron spectroscopy (XPS) and high‐resolution electron energy‐loss spectroscopy (HREELS). After the HF treatment, the wafer surface is As rich and partially covered with fluorine. The fluorine is bonded to Ga atoms as can be deduced out of a chemically shifted component in the XPS spectra. We cannot detect hydride groups using vibrational spectroscopy (HREELS). Fluorine on top of the wafer surface can be removed by a short water rinse. Depending on the storage time of GaAs wafers in HF the As enrichment of the surface increases. We present a model for the surface state after the HF treatment with an As overlayer on top of bulk GaAs. Consistent with our angular dependent XPS measurements, we can give values for the thickness of the As overlayer. Conditions of illumination and concentration of HF influence the reaction rate of HF on the GaAs surface. The reac...

An S/XPS study of hydrogen terminated, ordered silicon (100) and (111) surfaces prepared by chemical etching

Abstract: There is considerable current interest in the passivation of single crystal silicon surfaces, particularly with reference to the fabrication of epitaxially grown solid state device structures. In this paper, we discuss ordered Si(100) and (111) surfaces prepared by chemical etching in solutions of hydrofluoric acid and studied by use of Soft XPS, XPS and LEED. Despite transfer through the atmosphere before being loaded into the UHV of our analysis instruments, the hydrogen terminated surfaces observed are shown to be among the most perfect yet produced by such chemical means. Under optimum conditions, the etch can yield levels of carbon and oxygen impurities of less than 2% of a monolayer and lead to surfaces where the Fermi level is not pinned. The etched surfaces are modified by the hydrogen termination such that they are electrically passivated and ordered into a (1 × 1) periodicity. Upon annealing at (520 ± 10)°C in UHV, the hydrogen is removed, the surface changes to a (2 × 1) reconstruction and also exhibits band bending due to Fermi level pinning by surface strates. The relationship between residual contamination and etching parameters such as time and etchant concentration has been examined, together with the stability of the passivated surface under exposure to wet and dry environments. This has shown that the surface condition is sensitive to etching procedure and that the optimum surface may be obtained by using a 5% non-aqueous solution, or by pre-cleaning a surface using a UV generated ozone exposure prior to an aqueous etch. It has also been shown that a controlled reoxidation of an etched surface using UV-ozone can produce a non-abrupt Si-SiO2 interface. This may form a useful part of a reduced temperature surface preparation, compatible with any subsequent epitaxial overlayer growth.

Solution chemistry of HNO 3 /HF pickle mixtures

Abstract: Fundamental aspects of nitric and hydrofluoric mixed-acid pickle solution chemistry are discussed. Results from a computer model designed to predict the behavior of the pickle acid mixture are compared with measured parameters. There is a continuous increase in the complexed fluoride-to-iron ratio as the solution HF/Fe ratio and the F (total)/Fe ratio increases. Dissolved chromium only marginally reduces the HF concentration. The complexation reactions result in the generation of nitric acid with the consumption of hydrofluoric acid, leading to higher than expected nitric acid concentration values. Although further refinements to the computer model are needed, the model gives new insight to the behavior of pickle solutions, such as the distribution of various fluoride species at different F/Fe ratios.

Method of testing characteristic of single-crystal silicon

Abstract: PURPOSE: To evaluate the dielectric strength of oxide film simply by slicing a single-crystal semiconductor silicon ingot into wafers, etching the wafers with a solution of hydrofluoric acid and nitric acid to remove distortion, and further etching them with an aqueous liquid of K 2 Cr 2 O 7 and hydrofluoric acid. CONSTITUTION: A single-crystal semiconductor ingot obtained from silicon melt by the Czockralski technique or float zone process is sliced into wafers of a predetermined thickness. The wafers are etched with a solution of hydrofluoric acid and nitric acid to remove distortion, and further etched with an aqueous liquid of K 2 Cr 2 O 7 and hydrofluoric acid for a predetermined time. As a result, the electric characteristic of silicon wafers, i.e., dielectric strength of oxide film, can be evaluated only by counting the number of waves in a pattern appearing on the etched surface. Therefore, it is possible to decrease the time required for polishing wafers and evaluation processes associated with wafer polishing. COPYRIGHT: (C)1992,JPO&Japio

Process for the production or recovery of acids from metalliferous solutions of such acids

Abstract: During the pickling, etching, chemical shaping etc. of steels, stainless steels, special alloys and special metals and the dissolution of those metals, metalliferous solutions of the acids employed arise in the course of such processes which must either be disposed of by neutralization or be used for the recovery of the acids and metals by expensive processes. According to the invention the production or recovery of nitric acid or a mixture of nitric acid and hydrofluoric acid takes place by spray-roasting the solutions at temperatures of 200° to 500° in a reactor (1) and subsequent absorptions or condensation of the gases generated in column means (7, 8) at temperatures of 0° to 70° C.

Biocompatible polymer material and a process for producing same

Abstract: A biocompatible material which is the product of graft-copolymerization of a water-soluble vinyl and/or an acrylate monomer with a sorption complex of polysilicic acid and collagen that has been rid of pigments, glycoproteins and proteoglycans, or a product obtained by virtue of chemical destruction, with the aid of hydrofluoric acid, of the afore-mentioned product of graft-copolymerization, containing up to 25 mass percent of polysilicic acid (in terms of SiO2), up to 12 mass percent of protein, and maximum 1 10-6 mole/g of an anion of hydrofluoric and hydrofluoric acids, methods of making the same and products produced thereby.

Comparative Behavior of Titanium and Zirconium in Hydrofluoric-Nitric Acid Pickling Solutions

Abstract: The different behavior of titanium and zirconium in HF-HNO3 pickling solutions has been studied using electrochemical methods and Raman spectrometry. In each case, the depleting of the solutions during a pickling experiment could be correlated with the consumption of HF to form metal oxo or oxofluoro complexes. However, the mechanism of metal dissolution is quite different for the two metals. The titanium dissolution process in such solutions can be interpreted using a passivation model in which dissolution and passivation are two competing reactions at the surface of the bare metal. On the other hand, zirconium dissolution occurs through formation of an oxide film with ionic diffusion through the film being a rate-determining step. The particular role of strong acid added to the HF solution for pickling of titanium and zirconium is also discussed.

Effect of acid pretreatment of the silica substrate on the stability of octadecyl modified reversed phases

Abstract: Two stationary phases, identically modified and derived from the same experimental Chromspher substrate, but one of which has been pretreated with a hydrofluoric acid solution, are compared after ageing with various eluents under simulated routine conditions. The hydrothermal hydrofluoric acid treatment of the silica substrate prior to modification with dimethyloctadecyl-silane improved both the surface coverage and the stability of the resulting stationary phase compared to those of the original substrate. The stability of the silica-to-silane bonding after modification was characterized by means of chromatographic techniques and elemental analysis. Changes in the rigidity of the substrate were studied by means of solid state29Si NMR. The effect of the hydrothermal acid treatment on relevant substrate parameters, including formation of crystalline regions at the surface, is also discussed.

Tin (ii) stabilizer for hydrogen peroxide

Abstract: A method for stabilizing hydrogen peroxide and the stabilized composition are claimed employing as a stabilizer a tin (II) salt of an acid selected from the group hydrofluoric acid, C6 to C17 saturated monocarboxylic acids and C2 to C6 saturated polycarboxylic acids, preferably oxalic acid. The tin content of hydrogen peroxide prepared from a tin (II) oxalate stock solution can be reduced by filtration to less than 1 mg/l if the tin oxalate stock solution has been properly aged.

Investigation of HF etched hydrogenated amorphous silicon surfaces by X-ray photoelectron spectroscopy

Abstract: Clean hydrogen-terminated amorphous silicon surfaces have been generated by etching in various solutions based on hydrofluoric acid. The cleaned surfaces were characterised by X-ray photoelectron spectroscopy which showed the residual carbon and oxygen contaminations to be extremely low. It was also observed that the use of ethanol-based solutions led to an improved surface. Finally, it is shown that the contamination levels depend critically on the purity of the starting chemicals.

Method for the production of derivatives of alpha-fluoroacrylic acid

Abstract: Derivatives of alpha -fluoroacrylic acid are prepared by reacting a dihalopropene with an anhydrous mixture of nitric acid and hydrofluoric acid to give a 1-nitro-2,2-fluorohalo-3-halopropane, converting this compound in the presence of a strong acid and a little water at increased temperature to give a 2,2-fluorohalo-3-halopropionic acid, converting this compound into an ester or an amide, and finally treating the product with a dehalogenating agent.

Purification of potassium tantalum fluoride

Abstract: PURPOSE: To obtain highly purified potassium tantalum fluoride containing a slight radioactive element or metal of high melting point by dissolving crude potassium tantalum fluoride in a hydrofluoric acid solution at a specific temperature range and cooling the solution to below normal temperature to recrystallize. CONSTITUTION: Crude potassium tantalum fluoride is poured into hydrofluoric acid or a mixed solution containing hydrofluoric acid and resultant solution is heated to 50-95°C, then cooled to below 20°C. Potassium tantalum fluoride crystal re-crystallized by cooling is filtrated and sufficiently washed to become pH5-6 preferably in an alkaline solution, e.g., a solution having ≥9 of pH, then the recrystallized crystal is dried at 140-300°C. COPYRIGHT: (C)1992,JPO&Japio

Kinetic-potentiometric determination of aluminium in acidic solution using a fluoride ion-selective electrode

Abstract: A kinetic-potentiometric method is described for the determination of aluminium(III) based on monitoring its reaction with hydrofluoric acid using a fluoride ion-selective electrode at pH 2. At that pH the reaction Al3++ HF AlF2++ H+ is the predominant path for the initial consumption of aluminium in a complex with fluoride. The initial rate of the complex formation reaction was used to construct calibration graphs. There is a linear relationship between the initial rate of reaction and the amount of aluminium added. The method is rapid and can be used for the determination of aluminium down to 0.5 µmol with satisfactory precision (relative standard deviation < 6%).

Process for the preparation of 1,1,1-chlorodifluoroethane

Abstract: The invention relates to continuous production of 1,1,1-chlorodifluoroethane from 1,1,1-trichloroethane and hydrofluoric acid by reaction in liquid phase in the presence of at least one fluorination catalyst According to the invention, the process is carried out under an absolute pressure of between 6 and 30 bars and at a temperature of between 50° and 120° C, the content of catalyst(s) in the reaction mixture, expressed as a percentage by weight of metal, being between 005 and 10% and the content of organohalogenated by-products not belonging to series 140 in the reaction mixture being controlled at a value below 40% by weight This process makes it possible, at the same time, to obtain a high degree of conversion of hydrofluoric acid, to minimize the coproduction of 1,1,1-trifluoroethane and organohalogenated by-products and to facilitate the recovery of the hydrochloric acid formed

Surface treatment of rare earth-fe-b magnet

Abstract: PURPOSE:To improve an anticorrosive effect by dipping a rare earth-Fe-B magnet obtained by sintering a pressed-powder substance of a rare earth-Fe-B alloy powder into an acid water solution followed by heat treatment. CONSTITUTION:A magnet obtained by sintering a pressed-powder substance of rare earth-Fe-B alloy powder having rare earth elements B and Fe including Y as necessary elements is dipped into an acid water solution followed by heat treatment. This acid water solution contains 1 to 20volume% of one kind or more of hydrochloric acid sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid and organic carboxylic acid while being dipped at a liquid temperature of 0 to 50 deg.C for 1 to 30min. Next, heat treatment is performed in a vacuum or an inactive gas atmosphere at 300 to 900 deg.C. Thereby, a passivating oxide film is formed on the magnet surface so that an anticorrosive effect is improved.

Preparation of stannous oxide

Abstract: PURPOSE: To improve the yield and purity of stannous oxide without requiring the adjustment of pH and the control of temperature during the reaction by mixing a stanneous salt acidic solution with an alkali hydroxide aqueous solution at a prescribed high pH and adding an alkali carbonate to the mixture in a prescribed ratio during the reaction. CONSTITUTION: A stannous salt acidic aqueous solution (e.g. hydrofluoric acid, hydrochloric acid, sulfuric acid or boric acid) and an alkali hydroxide are prepared. Both the aqueous solution are mixed and made to react with each other at a pH of 11-12.5. The reaction solution is mixed with 2-10% (based or the alkali hydroxide) of an alkali carbonate during the reaction to provide plate-like stannous oxide reading soluble in an acid. COPYRIGHT: (C)1991,JPO&Japio