Influence of ethanol on the electrocodeposition of Ni/Al2O3 nanocomposite films

The effect of ethanol on the electrocodeposition of nickel alumina nanocomposites was investigated using an acidic nickel sulfamate electrolyte. The surface charge and sedimentation behaviour of the 13 nm alumina particles in the nickel plating bath were characterized as a function of the ethanol concentration and the pH of the electrolyte. High ethanol contents cause a decrease in the surface charge and dispersion stability of the alumina particles in the plating electrolyte. The effects of the deposition conditions, i.e. ethanol content, current density, and particle content of the electrolyte on the codeposition of nickel alumina composites were investigated systematically. Low values of current density and high amounts of ethanol in the plating bath were found to be beneficial for the particle entrapment. The structure as well as the microhardness of the nickel films were investigated as a function of the electrolyte composition and the particle incorporation. A textural modification combined with a distinct grain refinement was found with increasing ethanol content of the electrolyte and due to the alumina incorporation. The microhardness of the layers increased with decreasing ethanol content of the electrolyte and increasing nanoparticle incorporation.     

Sonocrystallization: effect on lactose recovery and crystal habit

Sonocrystallization is the use of power ultrasound to control the crystallization process, commonly used during the nucleation phase of crystallization. However, in the present study a different approach has been tried, in which the whole process of lactose crystallization from model reconstituted lactose solutions was completed rapidly with the aid of ultrasound, in the presence of 'ethanol' as an anti-solvent, at temperature of 30+/-2 degrees C (ambient temperature). The lactose recovery and crystal properties from sonicated samples were compared with non-sonicated samples. For optimization of sonocrystallization process for rapid lactose recovery, variations in the time of sonication, lactose concentration, protein concentration and pH were tried. A lactose recovery of 91.48% was obtained in 5 min of sonication time, from a reconstituted lactose solution (17.5% w/v, pH 4.2) as against 14.63% under only stirring. Lactose recovery decreased with lowering of pH from 4.2 to 2.8. The protein showed maximum influence on lactose recovery even at concentration of 0.2% w/v. A rapid process of crystallization gave a better uniformity in crystal size distribution of lactose samples.     

Electrodeposition of Al in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquids: in situ STM and EQCM studies

In the present paper, the electrodeposition of Al on flame-annealed Au(111) and polycrystalline Au substrates in two air- and water-stable ionic liquids namely, 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]Tf(2)N, and 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide, [EMIm]Tf(2)N, has been investigated by in situ scanning tunneling microscopy (STM), electrochemical quartz crystal microbalance (EQCM), and cyclic voltammetry. The cyclic voltammogram of aluminum deposition and stripping on Au(111) in the upper phase of the biphasic mixture of AlCl(3)/[EMIm]Tf(2)N at room temperature (25 degrees C) shows that the electrodeposition process is completely reversible as also evidenced by in situ STM and EQCM studies. Additionally, a cathodic peak at an electrode potential of about 0.55 V vs Al/Al(III) is correlated to the aluminum UPD process that was evidenced by in situ STM. A surface alloying of Al with Au at the early stage of deposition occurs. It has been found that the Au(111) surface is subject to a restructuring/reconstruction in the upper phase of the biphasic mixture of AlCl(3)/[Py(1,4)]Tf(2)N at room temperature (25 degrees C) and that the deposition is not fully reversible. Furthermore, the underpotential deposition of Al in [Py(1,4)]Tf(2)N is not as clear as in [EMIm]Tf(2)N. The frequency shift in the EQCM experiments in [Py(1,4)]Tf(2)N shows a surprising result as an increase in frequency and a decrease in damping with bulk aluminum deposition at potentials more negative than -1.8 V was observed at room temperature. However, at 100 degrees C there is a frequency decrease with ongoing Al deposition. At -2.0 V vs Al/Al(III), a bulk aluminum deposition sets in.     

Novel amperometric sensors for nitrite detection using electrodes modified with PEDOT prepared in ionic liquids

Journal of Solid State Electrochemistry - Novel amperometric sensors based on poly-3,4-ethylenedioxythiophene (PEDOT) were prepared and characterized for nitrite detection. An experimental matrix...     

Stripping to analog resonances

Stripping to analog resonances is studied by expressing the DWBA cross section in terms of the resolvent operator appropriate to the system composed of the proton and the target. The resolvent operator is decomposed, by means of the Feshbach projection operator technique, into parts corresponding to the entrance channel, the analog state and the compound states. The approximation scheme is similar to that used in our previous treatment of proton scattering at an analog resonance. The complex proton form factor depends on the Green function satisfying the inhomogeneous Schrödinger equation corresponding to elastic scattering and on the Coulomb potential generated by the target. The method is applied to (³He, d) stripping to analogs in ^{93, 95, 97}Tc.     

Stereochemical consequences of oxygen atom transfer and electron transfer in imido/oxido molybdenum(IV, V, VI) complexes with two unsymmetric bidentate ligands

Two equivalents of the unsymmetrical Schiff base ligand (L(tBu))(-) (4-tert-butyl phenyl(pyrrolato-2-ylmethylene)amine) and MoCl(2)(NtBu)O(dme) (dme = 1,2-dimethoxyethane) gave a single stereoisomer of a mixed imido/oxido Mo(VI) complex 2(tBu). The stereochemistry of 2(tBu) was elucidated using X-ray diffraction, NMR spectroscopy, and DFT calculations. The complex is active in an oxygen atom transfer (OAT) reaction to trimethyl phosphane. The putative intermediate five-coordinate Mo(IV) imido complex coordinates a PMe(3) ligand, giving the six-coordinate imido phosphane Mo(IV) complex 5(tBu). The stereochemistry of 5(tBu) is different from that of 2(tBu) as shown by NMR spectroscopy, DFT calculations, and X-ray diffraction. Single-electron oxidation of 5(tBu) with ferrocenium hexafluorophosphate gave the stable cationic imido phosphane Mo(V) complex [5(tBu)](+) as the PF(6)(-) salt. EPR spectra of [5(tBu)](PF(6)) confirmed the presence of PMe(3) in the coordination sphere. Single-crystal X-ray diffraction analysis of [5(tBu)](PF(6)) revealed that electron transfer occurred under retention of the stereochemical configuration. The rate of OAT, the outcome of the electron transfer reaction, and the stabilities of the imido complexes presented here differ dramatically from those of analogous oxido complexes.     

Roughness-induced acoustic second-harmonic generation during electrochemical metal deposition on the quartz-crystal microbalance

This paper reports on the relation between the surface roughness and emission of compressional waves from the surface of an electrochemical quartz-crystal microbalance. The detection of the compressional waves took place with an ultrasonic microphone and the quartz crystal itself. As a model process, the electrochemical deposition of copper from an acidic copper sulfate solution has been chosen. For this system, the roughness of the layer can be tuned via the current density. Roughness may be a source of the longitudinal waves at twice the frequency of the exciting shear wave (acoustic second-harmonic generation, ASHG) if the flow profile above the quartz-crystal surface is not entirely laminar. Slight deviations from the laminar flow can be reached at high amplitudes of oscillation. Comparing the ASHG efficiency of a rough and smooth surface, we find that the rough surface is more efficient in generating second-harmonic waves. This suggests that ASHG can be used to obtain a roughness parameter independent from the resonance frequency or bandwidth (damping) of a quartz-crystal resonator. Such an independent determination of roughness should be very interesting in practical applications.     

An EQCM study of the electropolymerization of benzene in an ionic liquid and ion exchange characteristics of the resulting polymer film

The direct electropolymerization of benzene dissolved in the ionic liquid 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate was studied at room temperature applying the electrochemical quartz-crystal microbalance technique. Analysis of the damping changes showed that the Sauerbrey equation could be applied for data evaluation. In the polymer, every third to fourth benzene ring carried a positive charge in the oxidized state. During electropolymerization, some ionic liquid was absorbed in the growing polymer. The redox behavior was characterized by wide peaks typical for conducting polymers. Charge neutrality of the polymer during redox cycling was maintained by anion and cation exchange with the ionic liquid. With increasing scan rate, cation exchange became more and more important.     

Effect of continuous magnetic field on the growth mechanism of nanoporous anodic alumina films on different substrates

The effects induced by an external homogeneous magnetic field on the oxide film growth on aluminum in aqueous solutions of oxalic and sulfuric acid and on surface morphology of the alumina films were studied. Aluminum films of 100 nm thickness were prepared by thermal evaporation on SiO₂/Si and glass-ceramic substrates. The pore diameter for oxalic acid alumina films on the SiO₂/Si substrate decreased by 0.8 nm, the interpore distance by 5.9 nm, and cell diameter by 6.9 nm if a magnetic field of 0.5 T was applied. When aluminum was anodized in sulfuric acid on the same substrate, the significant changes in parameters of porous structure of alumina, which were similar to the ones in oxalic acid, are firstly observed in stronger magnetic fields (of 0.7 T). On the basis of data obtained in this study and of previous investigation on the negative space charge and thermally activated defects in anodic alumina, we concluded that the intensity of the magnetic field is associated with energy of electron traps and that the changes of cell diameter characterize the trap concentration. The energy of electron traps in oxalic acid alumina films was proved to be smaller than the one in films formed in sulfuric acid, but the concentration of traps was of the same order of magnitude. When the substrate was replaced with the glass-ceramic one, the pore diameter in oxalic acid alumina films increased to ca. 17.6 nm.     

On the electrodeposition of titanium in ionic liquids

The ability to electrodeposit titanium at low temperatures would be an important breakthrough for making corrosion resistant layers on a variety of technically important materials. Ionic liquids have often been considered as suitable solvents for the electrodeposition of titanium. In the present paper we have extensively investigated whether titanium can be electrodeposited from its halides (TiCl(4), TiF(4), TiI(4)) in different ionic liquids, namely1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIm]Tf(2)N), 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)amide ([BMP]Tf(2)N), and trihexyltetradecyl-phosphonium bis(trifluoromethylsulfonyl)amide ([P(14,6,6,6)]Tf(2)N). Cyclic voltammetry and EQCM measurements show that, instead of elemental Ti, only non-stoichiometric halides are formed, for example with average stoichiometries of TiCl(0.2), TiCl(0.5) and TiCl(1.1). In situ STM measurements show that-in the best case-an ultrathin layer of Ti or TiCl(x) with thickness below 1 nm can be obtained. In addition, results from both electrochemical and chemical reduction experiments of TiCl(4) in a number of these ionic liquids support the formation of insoluble titanium cation-chloride complex species often involving the solvent. Solubility studies suggest that TiCl(3) and, particularly, TiCl(2) have very limited solubility in these Tf(2)N based ionic liquids. Therefore it does not appear possible to reduce Ti(4+) completely to the metal in the presence of chloride. Successful deposition processing for titanium in ionic liquids will require different maybe tailor-made titanium precursors that avoid these problems.