Immersion In HF Solution Research Articles

Chemical control of the surface of WS2 nanoparticles

Tungsten disulfide is an inorganic compound with layer structure. Nanoparticles of WS2 were found to be excellent candidates for reinforcing various polymer materials. However, long storage times in ambient conditions lead to sorption of water molecules and slow oxidation of defect sites. In the present study, the influence of various treatments on the surface composition and reactivity of several kinds of WS2 nanoparticles, were investigated. This study reveals some complex interplay between water and organic moieties desorption and the subsequent oxidation of “nascant” surfaces. Remarkably, simple immersion in HF solution seems to produce the ultimately cleanest surface of these particles.

Relationship between microstructure and formation-biodegradation mechanism of fluoride conversion coatings synthesised on the AZ31 magnesium alloy

The aim of the present work was to evaluate the influence of the microstructure on the formation-biodegradation mechanism of conversion coatings synthesised on the AZ31 magnesium alloy by immersion in HF solutions under different concentrations and treatment times. The experimental results revealed the formation of a magnesium hydroxyfluoride layer, which enhanced the corrosion resistance of the AZ31 alloy in Hanks' solution. Furthermore, the presence of intermetallic particles within the α-Mg matrix favoured the formation of defects that promoted the growth of corrosion products causing the detachment of the fluoride coating, all before it may start to be noticeably biodegraded.

Dealloying Behaviours of an Equiatomic TiCu Alloy

The crystalline Ti50Cu50 ribbon was prepared by annealing its amorphous counterpart at 773K, 84K higher than its crystallization temperature. An equiatomic TiCu intermetallic phase dominated in the matrix coexisting with trace Ti2Cu phase segregated on the grain boundary. A bi-continuous nanoporous copper from tenths of nanometers to hundredths of nanometers was obtained after dealloying the crystalline Ti50Cu50 ribbons in 0.03 and 0.13kmol/m 3 HF solutions. The TiCu phase stayed inert at the initial immersion and the Ti2Cu zone preferentially dissolved to form trenches. After a prolonged immersion in HF solutions, both TiCu and Ti2Cu phases were fully dealloyed. Final nanoporous Cu had a multiple-channel characteristic in different regions where various intermetallic phases distributed. Finer nanoporous Cu formed in the regions where the TiCu phase with a higher electrochemical stability dominated. [doi:10.2320/matertrans.M2013033]

Evidence for H 2 at high pressure in the silicon nanocavities after dipping in HF solution

The immersion in HF solutions of silicon containing nanocavities (produced by the annealing at high temperature, 950 °C, of silicon implanted with helium at high fluence, 2 × 10 16 cm −2) results in the injection of hydrogen in an infrared-mute state (most likely H 2) into the nanocavities. The pressure achieved in the cavities is sufficiently high to stabilize the hydrogen coverage of the inner surfaces at temperatures exceeding by 200 °C the one of complete desorption from the outer surface.

Impact of H2O2 Inclusion in HF Solution on Bulk and Silicon-on-Insulator Wafer Surfaces

This paper describes the influence of in HF solution on the surface roughness of bulk and silicon-on-insulator (SOI) wafers. Experiments are carried out for 0-, 2-, and 5°-tilted bulk wafers with (100) surface orientation and various (100) SOI wafers. Atomic force microscopy images show that surface roughness is decreased by immersing the samples in an HF solution that includes . It has been found that the significant improvement of surface roughness is observed in separation by implanted oxygen (SIMOX) SOI substrates in comparison to bulk silicon wafers. From X-ray photoelectron spectroscopy analyses, in the case of bulk Si wafers, it has been shown that much oxygen adsorption and suboxides cover over the surfaces of Si wafers immersed in the HF solution with . The coverage rate of suboxides on bulk silicon wafers is related to the roughness of postcleaned surfaces. The suboxide on the postcleaned surface suppresses the degradation of surface roughness in the case of bulk wafers. In the case of SIMOX SOI wafers, surface suboxides are not left behind after immersion in HF solution with ; a clean Si surface with a step and terrace structure is observed after immersion in the HF solution with .

Nitric oxide reduction catalyzed by amorphous copper–zirconium and copper–titanium alloys

Amorphous alloys have been regarded as interesting from the catalytic point of view because they lack of long range ordering. Moreover, the surface of amorphous alloys is rich in low-coordination sites and defects which play an important role in catalysis. Amorphous Cu–Zr and Cu–Ti ribbons were produced by melt spinning methods. The surface of amorphous materials was prepared, before catalytic tests, by immersion in HF solutions or by H 2 flow reduction. A selective dissolution of first transition metals was exhibited by HF surface pre-treatment. A porous and Cu-rich surface was obtained. In the reduction of NO x with propylene in presence of O 2, amorphous ribbons exhibited an initial high activity that decreased until the steady-state was reached. This behaviour can be explained with the oxidation of copper active sites by the oxygen contained in the reaction stream. Cu–Zr alloys showed higher catalytic activity than Cu–Ti alloys. Moreover, the HF treatment increased the activity of the materials, and the HF treated alloys were more active than the H 2 treated alloys.

Electrochemical behaviour of Cu–Zr and Cu–Ti glassy alloys

Hydrogen evolution is a fundamental reaction for better understanding of electrochemical activity of electrode materials. Amorphous Cu–Zr and Cu–Ti ribbons were produced by melt spinning methods and were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The electrocatalytic efficiency was evaluated on the basis of electrochemical data obtained from cathodic polarization curves carried out in both acid and basic medium at 25°C. The surfaces of amorphous materials were prepared, before electrochemical measurements, by immersion in HF solutions. The results were compared to those obtained on polycrystalline copper and on untreated ribbons. The HF treatment yielded a porous copper structure with a higher roughness factor which had improved electrocatalytic activity compared with that of polycrystalline copper electrode.

Effect of cathodic reduction on catalytic activity of amorphous alloy electrodes for electrooxidation of sulfite

Active electrode materials for a new zinc electrowinning process, in which the thermodynamic cell voltage is about half that of the conventional process by replacing oxygen evolution by anodic oxidation of SO2 produced in the zinc smelting process have been studied. Immersion in HF solution and subsequent cyclic voltammetry (CV) in sulfuric acid are known to be effective surface activation treatments of the amorphous alloy electrodes. The galvanostatic cathodic reduction (CR) treatment was applied to obtain further activation for sulfite oxidation for HF- and CV-treated electrodes prepared from amorphous nickel-valve metal-platinum group metal alloys. This treatment has been found to be effective in enhancing the activity. Among the amorphous Ni-40Nb alloys containing platinum group elements, the platinum-containing electrode showed the highest catalytic activity, which was higher than that of platinized platinum. Furthermore, the electrocatalytic activities of CR-treated electrodes prepared from amorphous alloys containing platinum and rhodium, and platinum and ruthenium were higher than that of the electrode containing only platinum. According to XPS analysis of the amorphous Ni-40Nb-1Pt-1Ru alloy specimen the enrichment of platinum and ruthenium occurred by CV treatment, and a small amount of oxidized platinum and ruthenium species remained on the electrode surfaces, but most of them were cathodically reduced to the metallic state by CR treatment. High catalytic activities for sulfite oxidation can be attributed to the metallic state of platinum and ruthenium contained in the alloy electrodes, even though the activity of these electrocatalysts is higher than that of pure Pt or Ru.

Fluorine Adsorption and Etching on Si(111):SiH Surface during Immersion in HF Solution

We examined the infrared spectrum of Si(111) after terminating its surface with silicon monohydride and immersing it in various concentrations of HF solution to induce fluorine adsorption. After immersion in HF solution, a part of the silicon monohydride surface was etched and (100), (010) and (001) steps composed of strained dihydrides appeared. The silicon-hydrogen stretching frequency for the monohydride was shifted by the fluorine adsorption. Angle-resolved X-ray photoelectron spectroscopy revealed that fluorine penetrates the silicon lattice as well as exists close to the surface. We conclude that fluorine does not terminate the surface silicon dangling bond but inhabits interstitial sites just below the silicon surface.

Laser and electron beam processing of electrodes consisting of amorphous nickel-valve metal-platinum-group metal surface alloys on valve metals

When melt-spun amorphous nickel-valve metal alloys containing small amounts of platinum-group metals are activated by immersion in HF solutions they exhibit unusually high activities for chlorine evolution in electrolysis of NaCl solutions. In order to eliminate a high electrical resistance resulting from the thickness limitation of melt-spun amorphous alloys, laser and electron beam processing was successfully used to prepare amorphous NiNbplatinum-group surface alloys having superior electrocatalytic activity on niobium by using specimens composed of a niobium substrate on which nickel and platinum-group metals were electro-deposited. The composition range vitrifiable over a wide area is significantly narrower than that vitrifiable by conventional methods for the preparation of amorphous alloys because overlapped traverses by the beams for vitrification of a wide area often result in crystallization in the heat-affected zone in the previously vitrified phase. The electron beam, which exhibits almost no reflection by metals, is more convenient and effective for processing than the laser beam, which has a high reflectance by metals.

Amorphous alloy catalysts for electro-oxidation of methanol and its derivatives in a sulphuric acid solution

Surface activation treatment by immersion in HF solution was applied to amorphous NiTi, NiZr, NiNb and NiTa alloys containing a few atomic per cent of platinum group metals and a few other metals. These activated amorphous alloys containing platinum possess high electrocatalytic activities for oxidation of methanol, formaldehyde and formic acid as well as a high corrosion resistance in sulphuric acid. Some of them exhibited far higher activities than platinized platinum. Substitution of a portion of the platinum by ruthenium, silicon, germanium, tin or lead further enhanced the catalytic activity. The surface activation is attributed to enrichments of platinum, ruthenium and/or tin in the surface layer in addition to surface roughening due to preferential dissolution of nickel and valve metals.