Showing papers on "Hydrofluoric acid published in 2017"

Effect of Hydrofluoric Acid Concentration and Etching Time on Bond Strength to Lithium Disilicate Glass Ceramic.

Abstract: Clinical Relevance The minimum HF concentration and time for proper bonding to lithium disilicate ceramics is 5% and 20 seconds.

Investigation of Enhanced Leaching of Lithium from α-Spodumene Using Hydrofluoric and Sulfuric Acid

Abstract: An effective method using hydrofluoric and sulfuric acid was proposed to enhance the leaching of lithium from α-spodumene, without calcination that is subjected to 1000 °C for phase transformation. The thermodynamic feasibility of the reactions was firstly verified. Dissolution conditions were tested to maximize the leaching efficiency of lithium and with efficient utilization of hydrofluoric acid (HF) served as evaluation criteria. The results showed that 96% of lithium could be transferred into lixivium with an ore/HF/H2SO4 ratio of 1:3:2 (g/mL/mL), at 100 °C for 3 h. Due to the fact that HF molecules were the main reaction form, the dissolution behaviors were theoretically represented and investigated by dissolution in HF/H2SO4. When combined with chemical elements analyses and characterizations, the results of the dissolution behaviors revealed that α-spodumene and albite were preferentially dissolved over quartz. Insoluble fluoroaluminates, such as AlF3, cryolite (Na3AlF6) and cryolithionite (Na3Li3Al2F12), were generated and might be further partially dissolved by H2SO4. Fluorosilicates, such as K2SiF6, Na2SiF6, or KNaSiF6, were also generated as a part of the insoluble residues. This work provides fundamental insight into the role of HF/H2SO4 played in the dissolution of α-spodumene, and sheds light on a novel and promising process to efficiently extract lithium.

Hydrometallurgical Processing Technology of Titanomagnetite Ores

Abstract: In this paper, we study the possibility of obtaining iron and titanium-vanadium concentrates with highest contents of iron and titanium, respectively, through hydrometallurgical processing of the titanomagnetite ores of the Chineisk deposit. We varied two key parameters to determine the efficiency of the process: (a) concentration of leaching solution (ammonium fluoride); and (b) acidity of solution. Ammonium fluoride concentration was varied from 0.08 mol/L to 4.2 mol/L with the other fixed parameters. It was shown that optimum ammonium fluoride concentration for leaching the ore is 0.42 mol/L; at these concentrations iron and titanium contents are about 62.8 wt % and 3.5 wt % in solid phase, respectively. The acidity of solution was changed by adding of hydrofluoric acid with varied concentration (from 0.86 mol/L to 4.07 mol/L) to ammonium fluoride solution with fixed concentration of 0.42 mol/L. The best results (degree of titanium extraction = 63.7%) were obtained when using a solution of hydrofluoric acid with concentration 4.07 mol/L. In this case, the addition of acid makes it possible to increase the Fe/Ti ratio by 3.4 times in comparison with the original ore. Thus, we conclude that acidity and the concentration of ammonium fluoride solution significantly influences the selectivity of the hydrometallurgical process.

Hydrometallurgical Purification of Metallurgical Grade Silicon with Hydrogen Peroxide in Hydrofluoric Acid

Abstract: The effect of adding hydrogen peroxide (H2O2) as an oxidizing agent on purifying metallurgical grade silicon (MG-Si) by leaching with hydrofluoric acid (HF) was studied as a function of leaching temperature, particle size, leaching duration, and concentration of leaching agents. It was found that the extraction capacity for metallic impurities could be significantly enhanced with introduction of H2O2 into HF lixiviant with little dependence on HF concentration. Upon leaching with 1 mol·L–1 HF and 2 mol·L–1 H2O2 for only 0.25 h at 55 °C, the MG-Si purity could be upgraded from 99.74% to 99.96%, to 99.99% with further prolonging of leaching duration. The sensitivity sequences of precipitates to each etchant were obtained through revealing the microstructural evolution of MG-Si before and after etching. With the help of Raman spectrometry and transmission electron microscopy, the chemical etching mechanism is discussed.

Zn-Assisted TiO2–x Photocatalyst with Efficient Charge Separation for Enhanced Photocatalytic Activities

Abstract: A new Zn-assisted method has been employed to synthesize reduced TiO2(TiO2–x) photocatalyst via a one-step hydrothermal process. In order to prevent the oxidation of TiO2–x in air, hydrofluoric acid is introduced in the preparative process for the stabilization of the Ti3+ and oxygen vacancies, as confirmed by low-temperature electron paramagnetic resonance. The obtained reduced TiO2 presents a wide-spectrum solar light absorption, including the near-infrared region. In addition, {110}–{111} and {101}–(001) dual-facet exposures are generated by Cl- and F-based surface-terminated reagents, respectively. The generated {001} and {101} facets on reduced TiO2 samples act as hole and electron collectors, respectively, which contributes to the charge separation of the catalyst. Finally, the synergistic effect between Ti3+ doping and dual-facet exposure results in the high photocatalytic performance for degradation of Rhodamine B and formic acid.

Does acid etching morphologically and chemically affect lithium disilicate glass ceramic surfaces

Abstract: BackgroundThis study evaluated the surface morphology, chemical composition and adhesiveness of lithium disilicate glass ceramic after acid etching with hydrofluoric acid or phosphoric acid.Methods...

Anodic processes in the chemical and electrochemical etching of Si crystals in acid-fluoride solutions: Pore formation mechanism

Abstract: The interaction of heavily doped p- and n-type Si crystals with hydrofluoric acid in the dark with and without contact with metals having greatly differing work functions (Ag and Pd) is studied. The dependences of the dissolution rates of Si crystals in HF solutions that contain oxidizing agents with different redox potentials (FeCl3, V2O5 and CrO3) on the type and level of silicon doping are determined. Analysis of the experimental data suggests that valence-band holes in silicon are not directly involved in the anodic reactions of silicon oxidation and dissolution and their generation in crystals does not limit the rate of these processes. It is also shown that the character and rate of the chemical process leading to silicon dissolution in HF-containing electrolytes are determined by the interfacial potential attained at the semiconductor–electrolyte interface. The mechanism of electrochemical pore formation in silicon crystals is discussed in terms of selfconsistent cooperative reactions of nucleophilic substitution between chemisorbed fluorine anions and coordination- saturated silicon atoms in the crystal subsurface layer. A specific feature of these reactions for silicon crystals is that vacant nonbonding d 2 sp 3 orbitals of Si atoms, associated with sixfold degenerate states corresponding to the Δ valley of the conduction band, are involved in the formation of intermediate complexes. According to the suggested model, the pore-formation process spontaneously develops in local regions of the interface under the action of the interfacial potential in the adsorption layer and occurs as a result of the detachment of (SiF2) n polymer chains from the crystal. Just this process leads to the preferential propagation of pores along the crystallographic directions. The thermodynamic aspects of pore nucleation and the effect of the potential drop across the interface, conduction type, and free-carrier concentration in the crystal on the pore size and structure are discussed. The concepts developed in the study can consistently account for experimental facts characterizing the etching of silicon crystals with various electrical parameters under various conditions providing the anodic polarization of crystals in HF-containing solutions.

Fluoride etching of mordenite and its influence on catalytic activity

Abstract: Due to its structure and high Si/Al ratio, zeolite mordenite has high thermal and acidic stability. Mordenite-type of zeolites have been used as catalysts in many industrially important reactions such as hydrocracking, hydroisomerization, alkylation, acid-catalyzed isomerization of alkanes and aromatics, reforming. In order to overcome the problem of the limited access to the active sites, OSDA-free synthesized mordenite undergoes fluoride etching as a post-synthetic treatment. The post-synthetic treatment is performed with hydrofluoric acid in combination with ammonium fluoride. Thus, the porosity is enhanced additionally without changing considerably the Si/Al ratio of the zeolite framework. All samples have been characterized by X-ray diffraction analysis, nitrogen adsorption, scanning electron microscopy, high-resolution transmission electron microscopy and solid-state nuclear magnetic resonance spectroscopy. The catalytic activity of the samples obtained has been investigated in the reaction of m-xylene transformation. All mordenite samples having undergone post-synthetic treatment exhibit catalytic activity higher than that of the parent sample.

Hydrofluoric Acid-Free Electroless Deposition of Metals on Silicon in Ionic Liquids and Its Enhanced Performance in Lithium Storage

Abstract: Metal nanoparticles such as Au, Ag, Pt, and so forth have been deposited on silicon by electroless deposition in the presence of hydrofluoric acid (HF) for applications such as oxygen reduction reaction, surface-enhanced Raman spectroscopy, as well as for lithium ion batteries. Here, we show an HF-free process wherein metals such as Sb and Ag could be deposited onto electrodeposited silicon in ionic liquids. We further show that, compared to electrodeposited silicon, Sb-modified Si demonstrates a better performance for lithium storage. The present study opens a new paradigm for the electroless deposition technique in ionic liquids for developing and modifying functional materials.

Treatment method for solar cell silicon chip

Abstract: The invention relates to a treatment method for a solar cell silicon chip. The method includes: using an alkali solution to perform chemical corrosion treatment on a silicon chip surface at 40-90DEG C to remove a damaged layer from the silicon chip surface; immersing the treated silicon chip into a first treatment solution for hole digging treatment at 5-40DEG C, then conducting immersion into a second treatment solution at 10-40DEG C for washing off precious metals, wherein the first treatment solution comprises hydrofluoric acid, hydrogen peroxide, precious metal ions and water, and the second treatment solution includes ammonia water and water; immersing the treated silicon chip into a third treatment solution at 20-40DEG C for pore-enlarging treatment, wherein the third treatment solution comprises hydrofluoric acid, nitric acid and water; immersing the treated silicon chip into a fourth treatment solution for modification treatment, wherein the fourth treatment solution includes alkali and water; and immersing the treated silicon chip into an aqueous solution of hydrochloric acid and hydrogen peroxide 40-90DEG C so as to remove residual metal ions, then conducting immersion in an aqueous solution of hydrofluoric acid at 20-40DEG C to remove an oxide layer, and then carrying out washing and drying.

Ultraviolet–visible/fluorescence behaviors of a spiropyran/polydimethylsiloxane composite film under acid vapors

Abstract: A spiropyran (SP)/polydimethylsiloxane (PDMS) composite film was prepared in this study, and its ultraviolet–visible/fluorescence behaviors under acid vapors were investigated. With UV irradiation, the ring-closed SP in the PDMS matrix transformed to a ring-opened merocyanine, which contained phenolate oxygen and could be further protonated by the hydrogen offered by the acid vapor. Such a protonation process endowed the composite film with not only an obvious color change from purple to yellow but also a strong fluorescent emission. As a result, some common volatile acids, hydrochloric acid, hydrofluoric acid, nitric acid, trifluoroacetic acid, formic acid, acetic acid, and propionic acid, could be distinguished with this method either via color or fluorescent emission. Meanwhile, the film showed good recyclability during the processes of irradiation and protonation. The method, therefore, displayed good processing in real time and was fast and recyclable; this makes it suitable as an alternative for applications related to environmental and safety monitoring of acid vapors. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45199.

Electrochemical impedance spectroscopic studies on niobium anodic dissolution in HF

Abstract: The dissolution of niobium electrode in anodic regime in hydrofluoric acid was studied using electrochemical techniques In the active region, complex plane plots of the impedance spectra exhibited mainly two capacitive loops In the passive region, the spectra exhibited a mid-frequency pseudo-inductive loop and a low-frequency negative resistance X-ray photoelectron spectroscopic analysis showed that the surface contains Nb2+ and Nb5+ The impedance data were analysed using equivalent circuit with Maxwell elements as well as mechanistic modelling A four-step mechanism with a chemical and electrochemical dissolution step is proposed to explain the results The results show that Nb with an oxidation state of 2 is likely to be an intermediates species The simulations predict that at low over potentials, the surface is covered mainly with bare metal, whereas at high over potentials, the surface is entirely covered by passivating Nb5+ film

Environmental friendly electroless copper metallization on FDM build ABS parts

Abstract: In this paper, environment-friendly electroless metallization of copper (Cu) on acrylonitrile–butadiene–styrene (ABS) parts fabricated through fused deposition modelling route of rapid prototyping process has been proposed The metallization process eliminates etching as well as the use of high cost palladium (Pd) for activation For surface preparation, aluminium (Al)-enamel paste has been used Five different acidic baths are used for electroless Cu deposition Each bath contains 15 wt% copper sulfate (CuSO4) solution and 5 wt% of any one solution among hydrofluoric acid (HF), sulfuric acid (H2SO4), phosphoric acid (H3PO4), nitric acid (HNO3) and acetic acid (CH3COOH) Metallization of Cu on ABS part has been made at different deposition time (2, 24, 48 and 72 h) in ambient condition After successful deposition of Cu, the surfaces are characterized by scanning electron microscopy and energy dispersive X-ray spectrometry Adhesion assessment of samples in different baths has been made It is observed that all baths are capable of formation of Cu crystals on ABS surface However, superior deposition on surface in terms of electrical conductivity and uniformity in deposition surface is obtained in HF, H2SO4 and H3PO4 baths

Understanding of a new approach for silicon nitride spacer etching using gaseous hydrofluoric acid after hydrogen ion implantation

Abstract: Silicon nitride spacer etching is one of the most critical step for the fabrication of CMOS transistors in microelectronics. It is usually done by plasma etching using a fluorocarbon based chemistry. However, from the 14 nm technology node and beyond, this etching process no longer allows the etch specifications to be reached (nonformation of a foot, poor critical dimension control below 1 nm). To overcome this issue, a new process was developed. It consists of two steps: in a first step, the silicon nitride film is modified by light ion implantation (hydrogen), and then followed by a removal step of this modified film by hydrofluoric acid (HF). In this paper, the authors propose to remove the implanted/modified silicon nitride using gaseous HF and understand the associated etching mechanisms using infrared spectroscopy and x-ray photoelectron spectroscopy at different stages of the process sequence (after implantation/modification, gaseous HF process, and post-treatment).

Method for preparing Mn(IV)-activated fluoride red fluorescent powder

Abstract: The invention discloses a method for preparing Mn(IV)-activated fluoride red fluorescent powder The fluorescent powder is composed of a material represented by a general formula of Aa-xBxMX6:Mn4+y, wherein A and B independently represent Na, K, Cs, Rb, Mg, Ba or Zn; M represents Si, Ge, Ti, Sn or Zr; X represents halogen; y is 003-016, a=1 or 2, and x is 0-2 The Mn(IV)-activated fluoride red fluorescent powder is prepared by using K2MnF6, Aa-xMX6 and BxMX6 as raw materials, and adding hydrofluoric acid and an adjuvant in the raw materials for reaction at 20-200 DEG C under a sealed condition The method is easy to operate, short in reaction period and environmentally friendly; the reaction requires only an extremely small amount of hydrofluoric acid, the ratio of an activation agent in the obtained fluorescent powder can be controlled, fluorescent brightness is high, the particle size of the powder can be controlled, the luminescent property is good, moreover, the wavelength of emitted light of the powder is not changed, and the Mn(IV)-activated fluoride red fluorescent powder is suitable for a field in which white light LED lighting devices and backlight sources have high requirements for luminescent materials

Texturing method of diamond wire slice polycrystalline black silicon

Abstract: The invention discloses a texturing method of diamond wire slice polycrystalline black silicon. The texturing method comprises the following steps in turn: a silicon chip is arranged in a solution containing nitric acid and hydrofluoric acid to be preprocessed; the preprocessed silicon chip is arranged in a solution containing metal salt to perform pre-deposition of oxidized metal nanoparticles; the silicon chip after pre-deposition is arranged in a solution containing hydrofluoric acid and an oxidizing agent to perform deposition of the oxidized metal nanoparticles; the silicon chip after deposition is arranged in a solution containing hydrofluoric acid, the oxidizing agent and metal salt ions to perform longitudinal and transverse broaching corrosion; the silicon chip after broaching is arranged in an acid solution to remove the metal ions; and the silicon chip of which the metal ions are removed is arranged in an alkaline solution containing a texturing additive to perform modification of the nanostructure so as to form the final textured surface. The non-uniformity and the chromatic aberration of the appearance after texturing can be effectively avoided.

Effect of acetic acid on the leaching behavior of impurities in metallurgical grade silicon

Abstract: To explore the potential of acid leaching in purification metallurgical grade silicon (MG-Si) for solar cells, the effect of acetic acid on the leaching behavior was investigated in the present work by focusing on the behavior of impurities affected by the addition of acetic acid to a conventional acid mixture composed of hydrochloric acid and hydrofluoric acid. The etching results reveal that the HCl–HF–CH3COOH mixture is a better lixiviant for dissolving impurity inclusions in MG-Si. The extraction yield of impurities in HCl–HF–CH3COOH leaching was found to increase by 7% compared to conventional HCl–HF leaching.

Kinetics of anodic dissolution of Zr in acidic fluoride media

Abstract: The kinetics of anodic dissolution of Zr in hydrofluoric acid (HF) was investigated using potentiodynamic polarization experiments. At lower potentials, an active region with a rapid increase in current with the potential was observed and at higher potentials, a large passivation current plateau was observed. The current decreased only slightly with potential in the passive region. Scanning electron micrographs confirmed that the passivation is incomplete in the region where current exhibits a plateau and x-ray photoelectron spectroscopic analysis showed that oxides and oxyfluorides are present on the surface. A four-step mechanism with two adsorbed intermediate species was evaluated and the model captures the essential characteristics of the polarization plots. The results suggest that \( {HF}_2^{-} \) species participates in the chemical dissolution step and actual HF participates in the electrochemical dissolution step.

Hydrogen Reduction in MEP Niobium Studied by Secondary Ion Mass Spectrometry (SIMS)

Abstract: Niobium, as pure metal and alloying element, is used in a variety of applications, among them in nuclear industries. Niobium is incorporated into nuclear fission reactors due to its enormous strength and low density. Surface finishing of niobium is often performed in electrochemical polishing processes in view of improving its smoothness, corrosion resistance and its surface cleanability. However, the presently used electropolishing process (EP) is intrinsically linked to the subsurface hydrogenation of niobium, which measurably degrades its properties. This is why the annealing operation is used to remove hydrogen from electropolished niobium that is a costly and time-consuming process. The traditional electrolyte consisting of a mixture of 96% H2SO4/49% HF acids by volume in a 9:1 ratio has been substituted for the new one, being a mixture of 70% methanesulfonic acid with 49% hydrofluoric acid by volume in a 3:1 ratio. Moreover, the additional imposition of a magnetic field during the electropolishing process (MEP) further increases hydrogen removal, when compared to the hydrogen content achieved by the electropolishing process alone. The aim of the study is to reveal a methodic approach and showing decreasing hydrogenation of niobium samples after consecutive steps of electrochemical polishing. Secondary ion mass spectrometry (SIMS) was used to measure the hydrogen content in the surface layer of as-received AR niobium and in the samples after EP and MEP processes.

Low-temperature phase formation in CaF 2 –HoF 3 system

Abstract: Phase formation in CaF2–HoF3 system has been studied by coprecipitation followed by X-ray powder diffraction Aqueous nitrate solutions have been used as initial substances, while hydrofluoric acid has been employed as fluorinating agent Formation of hydrated nanophases: solid solution Ca1–x Ho x F2 + x (х ≤ 01) and HoF3 has been revealed Dehydration proceeds on heating to 600°C

Preparation method of GO@PDA@MIL-101 nano composite material

Abstract: The invention provides a preparation method of a GO@PDA@MIL-101 nano composite material. The method includes the steps of: 1. preparing GO@PDA; 2. taking para toluic acid, A GOPDAMIL 101 nano composite material preparation method comprises the following steps: 1, preparation of GOPDA, 2, take on the quality of benzoic acid, chromium nitrate nonahydrate and GO@PDA in a mass ratio of 41:100:10, and taking deionized water and 40% hydrofluoric acid in a mass ratio of 96:1 for standby use; 3. firstly dissolving para toluic acid and chromium nitrate nonahydrate in a reaction kettle holding deionized water, then dissolving the GO@PDA prepared in step 1 in the mixed solution, conducting ultrasonic treatment for 15min, and performing magnetic stirring for 20min; 4. adding hydrofluoric acid into the mixed solution, and carrying out reaction under 493k for 8h; and 5. cooling the reaction product to room temperature, then conducting washing with N, N-dimethylformamide, ethanol and distilled water in order, and then performing drying, thus obtaining the GO@PDA@MIL-101 nano composite material. The method provided by the invention has the advantages of simple operation and low cost, the prepared GO@PDA@MIL-101 nano composite material has a nano-scale particle size, uniform particles, good dispersion, and strong adsorption capacity. The preparation process does not cause environmental pollution and is harmless to the health of operators.

Polyimide and titanium dioxide nano-sheet composite film and making method thereof

Abstract: The invention discloses a polyimide and titanium dioxide nano-sheet composite film and a making method thereof The method comprises the following steps: 1, fully mixing tetrabutyl titanate with hydrofluoric acid, and heating and reacting tetrabutyl titanate and hydrofluoric acid to obtain nano-sheet titanium dioxide powder; and 2, adding an organic solvent to the nano-sheet titanium dioxide powder obtained in step 1, uniformly distributing the nano-particles in the organic solvent, adding diamine and dianhydride, carrying out a polymerization reaction to obtain a precursor polyamide acid/titanium dioxide slurry, making a film with a certain thickness by using the slurry, heating the film to carry out thermal imidization on polyamide acid, and carrying out an imidization reaction to produce the polyimide and titanium dioxide nano-sheet composite film The method effectively increases the dielectric constant of the composite film, and substantially prolongs the corona ageing-resistant life of the film