Showing papers on "Hydrofluoric acid published in 2012"

Creation of superhydrophobic stainless steel surfaces by acid treatments and hydrophobic film deposition.

Abstract: In this work, we present a method to render stainless steel surfaces superhydrophobic while maintaining their corrosion resistance. Creation of surface roughness on 304 and 316 grade stainless steels was performed using a hydrofluoric acid bath. New insight into the etch process is developed through a detailed analysis of the chemical and physical changes that occur on the stainless steel surfaces. As a result of intergranular corrosion, along with metallic oxide and fluoride redeposition, surface roughness was generated on the nano- and microscales. Differences in alloy composition between 304 and 316 grades of stainless steel led to variations in etch rate and different levels of surface roughness for similar etch times. After fluorocarbon film deposition to lower the surface energy, etched samples of 304 and 316 stainless steel displayed maximum static water contact angles of 159.9 and 146.6°, respectively. However, etching in HF also caused both grades of stainless steel to be susceptible to corrosion. By passivating the HF-etched samples in a nitric acid bath, the corrosion resistant properties of stainless steels were recovered. When a three step process was used, consisting of etching, passivation and fluorocarbon deposition, 304 and 316 stainless steel samples exhibited maximum contact angles of 157.3 and 134.9°, respectively, while maintaining corrosion resistance.

Nanopores in GaN by electrochemical anodization in hydrofluoric acid: Formation and mechanism

Abstract: We report the use of hydrofluoric acid (HF) as an electrolyte in etching and porosifying GaN. HF is found to be effective in rendering a wide range of nanoporous morphology, from curved branches to highly parallel straight pores. Under suitable conditions, the porosification proceeds at a rate greater than 100 μm/min. To elucidate the etching mechanism, cyclic voltammetry is performed, together with a parametric mapping of electrolysis variables such as the doping of GaN, the concentration of HF electrolyte, and the anodization voltage. We demonstrate that the formation of nanoporous structures is largely due to the local breakdown of the reverse-biased semiconductor junction. A quantitative agreement between the estimated width of space-charge region and the observed variation in morphology lends support to a depletion layer model developed previously in the etching of porous-Si.

Effect of hydrofluoric acid concentration on the evolution of photoluminescence characteristics in porous silicon nanowires prepared by Ag-assisted electroless etching method

Abstract: We report on the structural and optical properties of porous silicon nanowires (PSiNWs) fabricated using silver (Ag) ions assisted electroless etching method. Silicon nanocrystallites with sizes <5 nm embedded in amorphous silica have been observed from PSiNW samples etched using the optimum hydrofluoric acid (HF) concentration. The strongest photoluminescence (PL) signal has been measured from samples etched with 4.8 M of HF, beyond which a significant decreasing in PL emission intensity has been observed. A qualitative model is proposed for the formation of PSiNWs in the presence of Ag catalyst. This model affirms our observations in PL enhancement for samples etched using HF < 4.8 M and the eventual PL reduction for samples etched beyond 4.8 M of HF concentration. The enhancement in PL signals has been associated to the formation of PSiNWs and the quantum confinement effect in the Si nanocrystallites. Compared to PSiNWs without Si-Ox, the HF treated samples exhibited significant blue PL peak shift of 1...

Wavelength-Controlled Etching of Silicon Nanocrystals

Abstract: A detailed investigation of the photochemical etching of silicon nanocrystals (Si-NCs) in aqueous hydrofluoric acid (HF) mixtures is described. By increasing the HF concentration and lowering the pH upon addition of hydrochloric acid (HCl), oxide-embedded Si-NCs were rapidly etched, and photoluminescence (PL) from the resulting hydride-terminated Si-NCs tailored from the near-IR to the yellow/green spectral region by irradiating the reaction mixture at the desired PL wavelength. These results are consistent with a hole-driven etching pathway rather than the chemically induced oxidation/etch pathway commonly exploited for Si nanostructures. The relationship among NC size, polydispersity, and PL was investigated using small-angle X-ray scattering. We suggest the defect density of Si-NCs is a crucial parameter for effective size control via photochemical exciton-mediated HF etching. Improved HF etching methods are expected to enable Si-NC applications through the realization of narrow polydispersity and PL b...

Effect of Acid Pickling Pretreatment on the Properties of Cerium Conversion Coating on AZ31 Magnesium Alloy

Abstract: The rare earth metal conversion coating process is recognized for its simple electrolyte composition, which is generally considered to be environmentally friendly. In this study, cerium conversion coatings were made in a cerium nitrate/hydrogen peroxide solution on AZ31 magnesium alloys after 20 s of pickling in hydrochloric acid (HCl) or hydrofluoric acid (HF) solutions. Results show that acid pickling in HF or HCl enhanced the adhesion and corrosion resistance of the cerium conversion coating. This enhancement is due to the inhibition of the blister formation, which presumably results from the rupture of the cerium oxide layer by hydrogen bubbles. Finally, the mechanism of HF and HCl acid pickling effect on the reaction rate and defect of the cerium conversion coating was discussed in detail.

Surface Characterization of Titanium Implants Treated in Hydrofluoric Acid

Abstract: The results of XPS measurements of commercially pure titanium cp-Ti) before and after chemical treatment are presented. We have measured XPS spectra of core levels (Ti 2p, O 1s, C 1s, F 1s) and valence bands of coarse-grained cp-Ti before and after standard acid treatment accepted in dentistry (in 1% HF and 40% HF for 1 min). It is found, that acid treatment of cp-Ti reduces the content of hydrocarbons increasing the surface energy and bio-compatibility of Ti-implants. On the other hand, it is fixed that oxygen concentration on the surface of the acid treated cp-Ti is much higher than for the untreated sample, because the acid treatment removes the contaminated surface layers, increases their reactivity, provides a better passivation and formation of thick protecting TiO2 layer.

Effect of lithium boron oxide glass coating on the electrochemical performance of LiNi1/3Co1/3Mn1/3O2

Abstract: The effect of the lithium boron oxide glass coating on the electrochemical performance of LiNi1/3Co1/3Mn1/3O2 has been investigated via solution method. The morphology, structure, and electrochemical properties of the bare and coated LiNi1/3Co 1/3Mn1/3O2 are characterized by scanning electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, and charge-discharge tests. The results showed that the lattice structure of LiNi1/3Co1/3Mn1/3O2 is not changed after coating. The coating sample shows good high-rate discharge performance (148 mAh g-1 at 5.0 C rate) and cycling stability even at high temperature (with the capacities retention about 99% and 87% at room and elevated temperature after 50 cycles). The Li+ diffusion coefficient is also largely improved, while the charge transfer resistance, side reactions within cell, and the erosion of Hydrofluoric Acid all reduced. Consequently, the good electrochemical performances are obtained.

Treatment fluids containing a boron trifluoride complex and methods for use thereof

Abstract: Treatment fluids for use in subterranean formations, particularly sandstone and other siliceous formations, may contain a source of fluoride ions to aid in mineral dissolution. In some cases, it may be desirable to generate the fluoride ions from a fluoride ion precursor, particularly a hydrofluoric acid precursor, such as a boron trifluoride complex. Methods for treating a subterranean formation can comprise providing a treatment fluid that comprises an aqueous base fluid, a boron trifluoride complex, and a chelating agent composition, and introducing the treatment fluid into a subterranean formation.

Etchant composition and etching method

Abstract: This invention is concerning an etchant composition used to etch a silicon-containing film formed on a target substrate. The etchant composition includes at least one selected from the group consisting of an organic compound containing a hydroxyl group, an organic compound containing a carbonyl group, an inorganic acid and inorganic salt, hydrofluoric acid, ammonium fluoride and an organic acid.

Method for cleaning silicon substrate, and method for producing solar cell

Abstract: Provided is a method for cleaning a silicon substrate involving: a first step for forming a porous layer on the surface of a silicon substrate by etching the surface of the silicon substrate by using a mixed aqueous solution of an oxidant and hydrofluoric acid, said mixed aqueous solution containing metal ions; a second step for texturizing the surface of the silicon substrate by etching the holes on the porous layer with a mixed acid of mainly hydrofluoric acid and nitric acid; a third step for etching the texturized surface of the silicon substrate by using an alkaline chemical liquid; and a fourth step for removing metal and organic impurities in the holes by generating air bubbles within the holes formed on the silicon substrate as a consequence of processing the silicon substrate etched by means of the alkaline chemical liquid with water containing ozone.

Method for observing metallographic structure of niobium-titanium alloy

Abstract: The invention relates to a method for observing the metallographic structure of niobium-titanium alloy, which is characterized by comprising the following steps of: firstly, grinding a sample on a grinding machine, polishing the sample on a polishing machine, and chemically polishing the sample in a mixed solution of sulfuric acid + nitric acid + hydrofluoric acid; then, selecting a reagent of sulfuric acid + nitric acid + hydrochloric acid + hydrofluoric acid to erode the sample, and observing the metallographic structure By using the method, the metallographic structure of niobium-titanium alloy can be observed clearly The method provided by the invention is easy to operate without any special equipment, and good effect is achieved in the preparation of a metallographic sample of niobium-titanium alloy

Lithium Extraction Mechanism from α-Spodumene by Fluorine Chemical Method

Abstract: In order to decrease lithium extraction cost, pollution and energy. A new and efficient technology was particularly discussed in this paper, the fluorine chemical method to extract lithium from spodumene. The reaction mechanism had also been analysed by studying the crystal structure variation and reaction products. The results show that hydrofluoric acid corroded α-spodumene in low temperature, damaged the compact chemical bonds: Li-O, Al-O, Si-O, and Al-O-Si, and generated Li3AlF6 and AlF3, which can be dissolved in sulfuric acid. Our research provides theoretical guidance for the lithium extraction process from α-spodumene.

Chemical leaching of an Indian bituminous coal and characterization of the products by vibrational spectroscopic techniques

Abstract: High volatile bituminous coal was demineralized by a chemical method. The vibrations of the “aromatics” structure of graphite, crystalline or non-crystalline, were observed in the spectra at the 1600 cm−1 region. The band at 1477 cm−1 is assigned as VR band, the band at 1392 cm−1 as VL band and the band at 1540 cm−1 as GR band. Graphite structure remains after chemical leaching liberates oxygenated functional groups and mineral groups. The silicate bands between 1010 and 1100 cm−1 are active in the infrared (IR) spectrum but inactive in the Raman spectrum. Absorption arising from C-H stretching in alkenes occurs in the region of 3000 to 2840 cm−1. Raman bands because of symmetric stretch of water molecules were also observed in the spectrum at 3250 cm−1 and 3450 cm−1. Scanning electron microscopy analysis revealed the presence of a graphite layer on the surface. Leaching of the sample with hydrofluoric acid decreases the mineral phase and increases the carbon content. The ash content is reduced by 84.5wt% with leaching from its initial value by mainly removing aluminum and silicate containing minerals.

Characteristics of SnO 2 :F Thin Films Deposited by Ultrasonic Spray Pyrolysis: Effect of Water Content in Solution and Substrate Temperature

Abstract: Fluorine doped tin oxide, SnO2:F, thin films were deposited by ultrasonic chemical spray starting from tin chloride and hydrofluoric acid. The physical characteristics of the films as a function of both water content in the starting solution and substrate temperature were studied. The film structure was polycrystalline in all cases, showing that the intensity of (200) peak increased with the water content in the starting solution. The electrical resistivity decreased with the water content, reaching a minimum value, in the order of 8 × 10-4 Ωcm, for films deposited at 450℃ from a starting solution with a water content of 10 ml per 100 ml of solution; further increase in water content increased the corresponding resistivity. Optical transmittances of SnO2:F films were high, in the order of 75%, and the band gap values oscillated around 3.9 eV. SEM analysis showed uniform surface morphologies with different geometries depending on the deposition conditions. Composition analysis showed a stoichiometric compound with a [Sn/O] ratio around 1:2 in all samples. The presence of F into the SnO2 lattice was detected, within 2 at % respect to Sn.

Method for comprehensively recovering tungsten and fluorine from minerals

Abstract: The invention provides a method for comprehensively recovering tungsten and fluorine from minerals, namely a mixed acid of phosphoric acid and sulfuric acid is adopted for decomposing complex calcium-containing minerals containing fluorite, scheelite, apatite, and calcite, wherein the fluorite is decomposed to fluorine hydride or silicon tetrafluoride to escape, and absorption treatment is performed for preparing hydrofluoric acid or a fluoride salt; and the scheelite is transformed to phosphotungstic acid to enter into a solution, and filtrate after filtration is supplemented into the consumed sulfuric acid and the phosphoric acid after extraction of the tungsten and returned to the new-round mineral leaching The method disclosed by the invention has the advantages of comprehensively recovering the fluorine and the tungsten from the minerals, reducing the requirements on the fluorite or the tungsten ore raw material, reducing the pressure on a mineral dressing link, improving the comprehensive recovery rate and simultaneously ensuring the decomposition rate of the fluorite and the scheelite, wherein the decomposition rate of the fluorite is above 98%, and WO3 contained in decomposition slag is reduced to below 05%; furthermore, a leaching agent can be recycled, so that leaching cost and wastewater emission are greatly reduced; and the method also has the advantages of simple leaching equipment, convenience in operation and easiness in realization of industrialization

Manganese dioxide modified silicon nanowires and their excellent catalysis in the decomposition of methylene blue

Abstract: A redox between hydrofluoric acid and ammonium fluoride-treated silicon nanowires and potassium permanganate solution was investigated. The results showed that MnO2 nanoparticles might grow on the surface of silicon nanowires, which was confirmed with the transmission electron microscope. These MnO2 modified silicon nanowires were employed as catalysts in the decomposition of methylene blue using sodium borohydride as the reducing agent, which exhibited excellent catalysis with its reaction rate 6 times larger than the unsupported MnO2.

Film treating agent for treatment before electro-coating of die-cast aluminum alloy workpiece and preparation method thereof

Abstract: The invention relates to a film treating agent for treatment before electro-coating of die-cast aluminum alloy workpiece, containing the following raw materials in percentage by mass: 2-10% of fluorozirconate, 1-13% of nitric acid, 1-5% of citric acid, 1-8% of phytic acid, 0.5-3% of hydrofluoric acid, 0.3-1.2% of ammonium bromate, 3-8% of ammonium bicarbonate, and the balance of tap water. The preparation method comprises the steps as follows: adding metered tap water in a reaction kettle; turning on a stirrer at normal temperature and normal pressure with rotational speed 450-550 revolutions/min; and, adding ammonium bicarbonate, ammonium bromate, fluorozirconate, nitric acid, citric acid, phytic acid and hydrofluoric acid in sequence, completely dissolving and packing. The film treating agent for treatment before electro-coating of die-cast aluminum alloy workpiece produces no toxic or harmful substance during the treating process and has no influence on the operator and the environment; besides, the treatment can be carried out at normal temperature without heating, so that the device is simplified and the energy is saved.