Showing papers on "Hydrofluoric acid published in 2019"

A hydrofluoric acid-free method to dissolve and quantify silica nanoparticles in aqueous and solid matrices.

Abstract: As the commercial use of synthetic amorphous silica nanomaterials (SiO2-NPs) increases, their effects on the environment and human health have still not been explored in detail. An often-insurmountable obstacle for SiO2-NP fate and hazard research is the challenging analytics of solid particulate silica species, which involves toxic and corrosive hydrofluoric acid (HF). We therefore developed and validated a set of simple hydrofluoric acid-free sample preparation methods for the quantification of amorphous SiO2 micro- and nanoparticles. To circumvent HF, we dissolved the SiO2-NPs by base-catalyzed hydrolysis at room temperature or under microwave irradiation using potassium hydroxide, replacing the stabilizing fluoride ions with OH-, and exploiting the stability of the orthosilicic acid monomer under a strongly basic pH. Inductively coupled plasma - optical emission spectroscopy (ICP-OES) or a colorimetric assay served to quantify silicon. The lowest KOH: SiO2 molar ratio to effectively dissolve and quantify SiO2-NPs was 1.2 for colloidal Stober SiO2-NPs at a pH >12. Fumed SiO2-NPs (Aerosil®) or food grade SiO2 (E551) containing SiO2-NPs were degradable at higher KOH: SiO2 ratios >8000. Thus, hydrofluoric acid-free SiO2-NP digestion protocols based on KOH present an effective (recoveries of >84%), less hazardous, and easy to implement alternative to current methods.

Purification of Metallurgical-Grade Silicon by Acid Leaching

Abstract: Purification of metallurgical-grade silicon (MG-Si), used in many applications such as the medical industry, polymer industry and the solar cells manufacturing. Removal of impurities from MG-Si is critical in these applications. The MG-Si studied in the present research contained various iron, calcium, and aluminum impurities. The hydrometallurgical purification method with different types of acids as solvents was chosen to refine MG-Si. Effects of hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid in combination with each other as a solvent for purification of MG-Si were investigated. Additionally, the effects of temperature and particle size of MG-Si were evaluated. In this study, in comparison with previous studies, samples with a larger particle size (in the range of 53 to 300 microns), less refining time (1 to 6 h) and relatively higher temperatures (30 to 70 ∘C) were studied. The results indicated that the highest purity of MG-Si was achieved by HCl (25%) + HF (5%) and followed by HCl (25%) + H2SO4 (30%), HNO3 (25%) + HCl (25%), HNO3 (5%) and H2SO4 (25%), respectively. It was also found that with particle size 53μm, applying a temperature of 50 ∘C for 6 h resulted in high efficiency and purity (99.96%) of MG-Si.

Straightforward and Relatively Safe Process for the Fluoride Exchange of Trivalent and Tetravalent Group 13 and 14 Phthalocyanines

Abstract: To avoid the use of hydrofluoric acid, a series of fluorinated trivalent and tetravalent metal-containing phthalocyanines (MPcs) were synthesized using a straightforward one-step halide substitution process using cesium fluoride (CsF) as the fluoride source and by reflux in N,N-dimethylformamide for less than an hour. The resulting fluoro MPcs were characterized and compared to the parent chloro MPcs. In some cases, very little change in properties was observed between the fluoro MPcs and the chloro MPcs. In other cases, such as fluoro aluminum phthalocyanine, a blue shift in the absorbance characteristics and an increase in oxidation and reduction potential of as much as 0.22 V was observed compared to the chloro derivative. Thermo gravimetric analysis was performed on all halo-MPcs, indicating that the choice of halo substitution on the axial position can have an effect on the decomposition or sublimation temperature of the final compound. After initial establishment and characterization of the fluoro MPcs, the halide substitution reaction of difluoro silicon phthalocyanine (F2-SiPc) was further explored by scaling the reaction up to a gram scale as well as considering tetrabutylammonium fluoride (TBAF) as an additional safe fluoride source. The scaled-up reactions producing F2-SiPc using CsF and TBAF as fluoride exchange sources were successfully reproducible, resulting in reaction yields of 100 and 73%, respectively. Both processes led to pure final products but results indicate that CsF, as the fluoride exchange reagent, appears to be the superior reaction process as it has a much higher yield.

Structural and Optical Properties of Silicon Nanowire Arrays Fabricated by Metal Assisted Chemical Etching With Ammonium Fluoride.

Abstract: Here we report on the metal assisted chemical etching method of silicon nanowires (SiNWs) manufacturing, where the commonly used hydrofluoric acid (HF) has been successfully replaced with ammonium fluoride (NH4F). The mechanism of the etching process and the effect of the pH values of H2O2: NH4F solutions on the structural and optical properties of nanowires were studied in detail. By an impedance and Mott-Schottky measurements it was shown that silver-assisted chemical etching of silicon can be attributed to a facilitated charge carriers transport through Si/SiOx/Ag interface. It was shown that the shape of nanowires changes from pyramidal to vertical with pH decreasing. Also it was established that the length of SiNW arrays nonlinearly depends on the pH for the etching time of 10 minutes. A strong decrease of the tоtаl reflectance to 5-10 % was shown for all the studied samples at the wavelength less than 800 nm, in comparison with crystalline silicon substrate (с-Si). At the same time, the intensities of the interband photoluminescence and the Raman scattering of SiNWs are increased strongly in compare to c-Si value, and also they were depended on both the length and the shape of SiNW: the biggest values were for the long pyramidal nanowires. That can be explained by a strong light scattering and partial light localization in SiNWs. Hereby, arrays of SiNWs, obtained by using weakly toxic ammonium fluoride, have great potential for usage in photovoltaics, photonics, and sensorics.

Kinetics of Hydrogen Storage on Catalytically-Modified Porous Silicon

Abstract: Porous silicon has been demonstrated as a hydrogen storage media with surface-bound hydrogen content as high as 6.6% by weight. Hydrogenated porous silicon is readily synthesized by electrochemical etching in a solution of hydrofluoric acid . Hydrogen gas can be released thermally at temperatures starting at 280 °C. It has been proposed that a suitable catalyst at the pore mouth can both reduce the desorption temperature and facilitate gaseous recharge of the silicon matrix. This work presents a detailed kinetic study using density functional theory (DFT) of a reversible hydrogen storage system based on porous silicon via the mechanisms of dissociation, spillover, and bond-hopping of hydrogen atoms. For each of these steps, activation energy values and vibrational frequency has been determined. Using these activation energies along with vibrational frequency values evaluated from the micro level DFT study, the kinetic performance of catalytically-modified porous silicon as a potential hydrogen storage material has been completed for the first time. The energy difference between full and empty charge is computed at the atomic scale and compared to macroscopic calculations, showing close agreement. These results show the potential for rapid recharge at 8 bar at temperatures commensurate with waste heat from a proton-exchange membrane fuel cell.

Direct Determination of Lead in Sea Water by High-Resolution Atomic Absorption Spectroscopy Using a Mixed Modifier Barium Nitrate–Hydrofluoric Acid

Abstract: A procedure is proposed for the direct determination of lead in sea water by electrothermal atomization high-resolution atomic absorption spectrometry. The effect of background interferences due to sea water matrix is eliminated using a mixed modifier barium nitrate–hydrofluoric acid. The optimum amount of the modifier matrix is 60 µg Ba (NO3)2 + 1.52 µg HF. The conditions of analysis are as follows: pyrolysis temperature 600°C, atomization temperature 1200°C. The limit of detection for the developed procedure is 0.0003 mg/L.

System and process for fluorine-circulation magnesium removal of sulfate solution

Abstract: The invention discloses a system and process for fluorine-circulation magnesium removal of sulfate solution. The process includes: step one, magnesium removal, to be more specific, adding a fluoride serving as a magnesium removal agent into magnesium-containing sulfate solution, filtering a reaction product, and performing liquid-solid separation, wherein filter residue is magnesium fluoride; steptwo, defluorination, to be more specific, adding a calcium-containing fluorine removal agent into zinc sulfate solution subjected to magnesium removal, filtering a reaction product, and performing liquid-solid separation, wherein filter residue is calcium fluoride; step three, magnesium fluoride conversion, to be more specific, subjecting sulfuric acid and magnesium fluoride generated in the stepone to co-heating reaction in a reaction tank, absorbing hydrogen fluoride by water to obtain hydrofluoric acid, cooling the solution to crystallize, separating out magnesium sulfate crystal, neutralizing obtained hydrofluoric acid by a metal oxide to obtain fluoride solution, and returning the fluoride solution obtained in reaction to the step one to serve as the magnesium removal agent. Therefore, the process realizes fluorine recycling, so that treatment cost is sharply reduced.

Recycling method for waste cathode carbon blocks of electrolytic aluminum electrolysis cell

Abstract: The invention discloses a recycling method of waste cathode carbon blocks of an aluminum electrolysis cell. The method comprises the following steps: breaking, crushing and ball milling the waste cathode carbon block raw material of the aluminum electrolysis cell to form powder, and then adding hydrogen peroxide to remove cyanide; adding concentrated sulfuric acid to react to generate hydrogen fluoride gas, introducing the hydrogen fluoride gas into a condensation absorption tower, and circularly absorbing the hydrogen fluoride gas with deionized water or a low-concentration hydrofluoric acidsolution to obtain a 25-40% hydrofluoric acid product; neutralizing carbon powder by adding NaOH, filtering and drying the carbon powder to use as a raw material for processing a new cathode for recycling; finally, concentrating a large amount of sodium sulfate contained in filtrate to obtain sodium sulfate crystals. The recycling method has the advantages of advanced technology and obvious advantages, and realizes zero emission of environmental pollutants in the recycling process. The treated waste cathode carbon blocks can be reused to process new cathode carbon blocks, and the main harmfulcomponent fluorine in the original waste cathode carbon blocks is converted into high side addition hydrogen fluoride to realize the recycling of fluorine.

Improved Oxygen Reduction Activity of Transition Metal-Chelating Ordered Mesoporous Carbon Fuel Cell Catalysts by Milder Template Removal

Abstract: In the synthesis of iron-chelating ordered mesoporous nitrogen-functionalized carbon (Fe–OMC) catalysts, the removal of the silica template is a crucial and critical step. The silica removal method used today for the Fe–OMCs is based on the very toxic hydrofluoric acid (HF), which usage should be limited where possible. Therefore, the aim of this study is to establish a mild (user-friendly), yet efficient, etch method based on dilute sodium hydroxide (NaOH), which does not impair the catalytic performance of the catalyst, to replace the currently used HF method. A comparison between catalysts etched with HF versus NaOH was performed in order to gain understanding how the two etch methods influence the final catalysts in terms of electrochemical, structural and catalytic properties. The NaOH etch was found to successfully remove the silica template, and interestingly, also improve the catalytic performance. The improved activity is explained by a carbon activation process occurring in the catalyst treated with the NaOH etch. With these findings, we show that it is possible to remove the silica in a more user-friendly way and simultaneously increase the catalysts’ performance by activation of the carbon.

Nitrogen-terminated silicon nanoparticles obtained via chemical etching and passivation are specific fluorescent probes for creatinine

Abstract: A method is described here to prepare water-dispersible nitrogen-functionalized silicon nanoparticles (N-SiNPs). It consists of two steps, viz. etching of the oxidized shell of SiNPs and nitrogen-passivation of the exposed silicon. The resulting N-SiNPs have an average diameter of 2.6±0.7 nm and show blue fluorescence (with excitation/emission peaks at 340/420 nm). The fluorescence quantum yield is 23% and the decay time is in the nanosecond regime. Compared to etching methods using a plasma or hydrofluoric acid, the process described here (etching and passivation) is mild, continuous, fast, and air-compatible. The N-SiNPs modified with chlorotetracycline are shown to be a viable fluorescent probe for creatinine. Fluorescence drops in the 0 to 20 μM creatinine concentration range, and the limit of detection is 0.14 μM.

Preparation method of lithium difluorobisoxalate phosphate solution

Abstract: The invention provides a preparation method of a lithium difluorobisoxalate phosphate solution. The preparation method of the lithium difluorobisoxalate phosphate solution comprises the following steps that (1) dichlorodimethylsilane and oxalic acid are reacted in the presence of a non-aqueous solvent to generate dimethyl silicon-based oxalate; and (2) lithium hexafluorophosphate is added into thereaction solution in the step (1), and reacting is carried out to obtain the lithium difluorobisoxalate phosphate solution. The preparation method is simple and practical, and industrial production can be achieved; the prepared lithium difluorobisoxalate phosphate solution can be directly used as an additive of a non-aqueous electrolyte battery; and the prepared lithium difluorobisoxalate phosphate solution has few chlorine compounds and free acids, wherein the chlorine compounds in terms of chlorine concentration are less than 5 mass ppm, and the free acids in terms of acid concentration converted from hydrofluoric acid are less than 200 mass ppm.

Method of determining content of rare earth elements in solid sample by microwave digestion-inductively coupled plasma mass spectrometry

Abstract: The invention discloses a method of determining the content of rare earth elements in a solid sample by microwave digestion-inductively coupled plasma mass spectrometry The method comprises the following steps of: dissolving a test sample to be tested in a mixed acid of concentrated nitric acid and concentrated hydrofluoric acid, sealing, carrying out microwave digestion, then removing acid by heating, adding a few drops of concentrated sulfuric acid at the beginning of heating, evaporating a sample digestion solution till the test sample is soybean-sized, adding the concentrated nitric acid,and continuously heating till the test sample is completely dissolved; after cooling, determining the volume of testing liquid by using ultrapure water; and preparing a standard working solution, drawing a standard curve, fitting a linear equation, and testing the testing liquid by using an inductively coupled plasma mass spectrometer (ICP-MS) to determine the content of the rare earth elementsThe concentrated sulfuric acid is added at the initial stage of removing the acid by heating, thereby greatly promoting the decomposition of rare earth fluoride, improving the testing precision and optimizing the working condition of the instrument; and the detection limit of the method is in the range of 00001 ppb to 0005 ppb; the recovery rate is in the range of 8471% to 11174% The method has the advantages of low detection limit, fastness, accuracy and the like, and can simultaneously determine 15 kinds of rare earth elements

Direct Synthesis of Ti-Containing CFI-Type Extra-Large-Pore Zeolites in the Presence of Fluorides

Abstract: Ti-containing zeolites showed extremely high activity and selectivity in numerous friendly environmental oxidation reactions with hydrogen peroxide as a green oxidant. It will be in high demand to synthesize Ti-containing crystalline extra-large-pore zeolites due to the severe restrictions of medium-pore and/or large-pore zeolites for bulky reactant oxidations. However, the direct synthesis of extra-large-pore Ti-zeolites was still challengeable. Here, we firstly report a strategy to directly synthesize high-performance Ti-containing CFI-type extra-large-pore (Ti-CFI) zeolites assisted with fluorides. The well-crystallized Ti-CFI zeolites with framework titanium species could be synthesized in the hydrofluoric acid system with seed or in the ammonium fluoride system without seed, which showed higher catalytic activity for cyclohexene oxidation than that synthesized from the traditional LiOH system.

Etching solution for silicon wafer

Abstract: The invention discloses an etching solution for a silicon wafer. The etching solution is mainly prepared from electronic-grade nitric acid, electronic-grade hydrofluoric acid, electronic-grade sulfuric acid, electronic-grade phosphoric acid, electronic-grade acetic acid, a surfactant and ultrapure water, wherein the nitric acid serves as an oxidizing agent and can oxidize silicon into silicon oxide, the hydrofluoric acid serves as a dissolving agent and can dissolve and remove the silicon oxide so as to realize etching of the silicon wafer, the sulfuric acid can improve the viscosity of the solution, stabilize the reaction rate, not change the etching morphology and improve the etching uniformity, the phosphoric acid can also improve the viscosity of the solution, improve the mass transferresistance, decrease the etching rate and not change the etching morphology, the acetic acid serves as a diluent and can reduce the ionization degree of the nitric acid, inhibit the oxidation capacity of the nitric acid, decrease the reaction rate and influence the surface morphology after etching, and the surfactant can reduce the surface tension of the solution and improve the surface morphology of the etched silicon wafer. The etching solution has the advantages of being stable and controllable in etching rate and uniform and flat in etching surface.

Preparation method of ultrapure anthracite

Abstract: The invention discloses a preparation method of ultrapure anthracite. The preparation method comprises the following steps that step one, anthracite blocks are broken and mixed with hydrofluoric acid, a reaction is conducted at 150-250 DEG C and 0.4-1.0 MPa, and through filtration, washing and drying, coal leached by the hydrofluoric acid is obtained; step two, the coal leached by the hydrofluoric acid is mixed with acid liquid, and through heating leaching, filtration, washing and drying, the ultrapure anthracite is obtained. According to the preparation method, by simply pre-breaking the anthracite blocks, under the high temperature and high pressure conditions, the hydrofluoric acid has a higher infiltration capacity and can react with impurities in large particle-size coal, under the high pressure condition, the hydrofluoric acid solution more easily flows into pores of the anthracite blocks to react with the impurities and highly adapts to the coal particle size, and the purity of the obtained ultrapure anthracite duff is greater than or equal to 99.90%.