Application of the electrochemical quartz crystal microbalance technique to copper sonoelectrochemistry: Part 1. Sulfate-based electrolytes

The applicability of the electrochemical quartz crystal microbalance technique in an ultrasonic field created by an ultrasound probe is demonstrated for the electrodeposition of copper. Cyclic voltammetry and potentiostatic depositions in acidic sulfate-based copper electrolytes were performed at different ultrasonic intensities. The electrochemical quartz crystal microbalance was operated in ultrasonic fields with intensities up to 30 W cm⁻². For cyclic voltammetry, potential resolved and averaged (apparent) current efficiencies were calculated from mass and charge data in function of the amplitude of the ultrasonic horn. Ultrasound slightly affected the current efficiencies during copper deposition in cyclic voltammetry, but did not change the efficiencies during dissolution. During potentiostatic depositions the current efficiency increased from 84% to almost 100% upon application of ultrasound. Morphology of deposits prepared by potentiostatic depositions was analyzed by scanning electron microscopy, and found to be different at high ultrasonic intensities.     

Non-isothermal ionic mass transfer at vertical parallel plate electrodes under natural convection.: Comparison and validity range of dimensionless correlations

For non-isothermal ionic mass transport-controlled electrochemical reactions on vertical parallel plate electrodes under steady state natural convection, the dimensionless correlation Sh=0.9 (ScGr*)^1/4, Sh, Sc and Gr* being Sherwood, Schmidt and Grashof number, respectively, earlier proposed (Electrochim. Acta 13 (1968) 1657; 14 (1969) 741), was extended covering almost two decades of (ScGr*)^1/4. Data from different test reactions in the range −10≤ΔT′≤15 °C, utilising cells of similar geometry and cathode height in the range 0.025≤X≤1 cm were considered. Using the above correlation as reference, other dimensionless correlations later derived, considering data from the same test reactions and using electrochemical cells of approximately the same design, were critically reviewed. The validity range of these correlations covered a smaller range of (ScGr*)^1/4 than the reference correlation, and their differences were explained in terms of cell designs and operating conditions.     

Electroless versus electrodriven deposition of silver crystals in polyaniline: Role of silver anion complexes

Electrocrystallization of silver is studied at polyaniline-coated electrodes using silver cations and two silver anion complexes (silver thiosulfate and silver-EDTA) as reducing species. Use of the silver thiosulfate complex results in a significant shift of the silver deposition potential window in the negative direction and highly impeded metal crystallization. The silver cation and silver-EDTA plating solutions allow to perform both electrodriven and electroless metal deposition. Number and size of silver crystals obtained by the two deposition methods in the different plating solutions are compared. Electroless precipitation in the silver-EDTA solution results in the highest number (∼10⁸ cm⁻²) of small-sized crystals. This result is discussed in terms of the special role of the EDTA anions for the redox state of the polyaniline layers. It is demonstrated that factors such as polyaniline redox charge, concentration of reducing ions and dipping time allow effective control over the amount of electroless deposited metal.     

Polyaniline fibres as electrodes.: Electrochemical characterisation in acid solutions

Polyaniline fibre microelectrodes prepared from a doped solution of polyaniline protonated with 2-acrylamido-2-methyl-1-propanesulphonic acid in dichloracetic acid were characterized electrochemically for the first time. Low scan rate cyclic voltammetry was used for characterisation in different acid electrolyte solutions, hydrochloric, nitric, perchloric, sulphuric and phosphoric, at low pH values with varying positive potential limits. Electrochemical impedance spectroscopy was also utilised. The electrochemical behaviour of polyaniline (PANI) fibres was found to be similar to that of PANI films obtained by electropolymerisation on metallic electrode substrates. The conduction potential window was found to be from +0.20 to +0.60 V versus SCE, with small variations in the different acid solutions as well as with pH. The standard electrochemical redox couple hexacyanoferrate(III), was found to behave quasi-reversibly in the conduction potential region and rate constants were evaluated.     

Zn electrodeposition in the presence of surfactants: Part I. Voltammetric and structural studies

The zinc electrodeposition onto steel substrates in the presence of surfactants with different charged head groups, namely anionic sodium dodecylsulphate (SDS), cationic dodecyltrimethylammonium bromide (CTAB), and non-ionic octylphenolpoly(ethyleneglycolether)_n, n = 10 (Triton X-100) was studied by cyclic voltammetry. The effect of the switching potential and scanning rate on the deposition process was investigated. The structural characterisation and the chemical composition of the samples prepared potentiostaticaly, in the potential range where the voltammetric cathodic peaks appear, was performed by X-ray powder diffraction (XRD) and by energy-dispersive X-ray analysis (EDS), respectively. The experimental results show that the voltammetric behaviour, namely the deposition potential depends on the presence, nature and concentration of the tested surfactants. Zn deposition occurs at potential values more positive than the estimated equilibrium potential, peak C1, simultaneously with hydrogen formation. This fact is confirmed by XRD measurements. Zn bulk deposits prepared in the absence of surfactants and in the presence of SDS are more crystalline and with a higher grain size than the ones obtained in the presence of CTAB and Triton X-100. These facts may be justified by an increase on the overpotential deposition as the electrochemical study confirms.     

Electrochemical chlorination of azulene derivatives: Insight into the mechanism of anodic oxidative chlorination

The cyclic voltammetry behavior of a series of five 1-substituted azulenes has been investigated as well as the electrochemical chlorination of these compounds. In the case of azulene compounds containing electron withdrawing groups which have higher oxidation potentials than that of the chloride ion, the electrochemical chlorination led usually to 3-chloro derivatives. The electrochemical chlorination fails for azulenes with lower oxidation potentials. Additionally some polyhalogenated compounds were obtained by controlled potential electrolyses. The paper also discusses the reaction mechanism of the electrochemical halogenation of 1-substituted azulenes.     

Experimental study of cement grout: Rheological behavior and sedimentation

Three basic elements (cement, water and admixture) usually make up injectable cement grouts used for prestressed cable coating, repair and consolidation of masonry, soil grouting, etc. The present study was divided into two parts. First, in order to characterize rheologically fresh cement paste with water/cement ratios (W/C) varying between 0.35 and 1, an experimental study was carried out and has revealed that the cement past behaves like a shear-thinning material, whatever is the W/C ratio. Second, to study the time evolution of their density, a γ-densitometer bench was used. Relying on the water content and the density measured, we demonstrate that the computation of the degree of hydration of cement is possible.The cement/geotechnics interdisciplinary approach proposed here has made it possible to obtain a large range of original results useful to improve our understanding of the sedimentation processes for cement pastes with different W/C ratios.     

Influence of anode material on the electrochemical oxidation of 2-naphthol: Part 1. Cyclic voltammetry and potential step experiments

The anodic oxidation of 2-naphthol has been studied by cyclic voltammetry and chronoamperometry, using a range of electrode materials such as Ti-Ru-Sn ternary oxide, lead dioxide and boron-doped diamond (BDD) anodes. The results show that polymeric films, which cause electrode fouling, are formed during oxidation in the potential region of supporting electrolyte stability. IR spectroscopy verified the formation of this organic film. While the Ti-Ru-Sn ternary oxide surface cannot be reactivated, PbO₂ and BDD can be restored to their initial activity by simple anodic treatment in the potential region of electrolyte decomposition. In fact, during the polarization in this region, complex oxidation reactions leading to the complete incineration of polymeric materials can take place on these electrodes due to electrogenerated hydroxyl radicals. Moreover, it was found that BDD deactivation was less pronounced and its reactivation was faster than that of the other electrodes.     

ZnFe anomalous electrodeposition:: stationaries and local pH measurements

The kinetics of ZnFe codeposition was investigated in acid solutions. The effects of solution composition and pH were analyzed. Inhibition of H⁺ reduction and Fe deposition occurs with increasing Zn⁺⁺ concentration in sulfate solution. An activation of Zn deposition is also observed. Increasing pH causes Zn deposition activation during ZnFe codeposition. The anomalous codeposition is also favored in chloride medium. When alloy deposition becomes the main process, the interfacial pH is governed by the individual metal deposition that controls the kinetic behavior. The interfacial pH increases during separate Fe deposition, meaning that it occurs with simultaneous consumption of H⁺. Individual Zn deposition brings about an H⁺ inhibition. A correlation between the codeposition behavior of ZnFe and ZnNi in sulfate and chloride solutions suggests that the prevailing cathodic reaction governs the interfacial pH. Anomalous codeposition process does not seem to be associated with a saturation of any thermodynamic species at the electrode surface. It can only be described by kinetic arguments.     

Electrochemistry of fluoren-9-one based conjugated copolymers: Analysis of voltammograms and correlation with spectroscopic data

Voltammetric and spectroscopic data for novel copolymers of fluoren-9-one with benzene, thiophene, and furan have been used to explore the relationship between the formal potentials and optical band gaps of conjugated polymers. It is shown that the optical band gap measured from the onset of absorption corresponds to the difference in the formal potentials for n- and p-doping. Voltammograms have been analyzed to establish how formal potentials should be defined for these and other conjugated polymers.     

Pyrrole nanoscaled electropolymerization: Effect of the proton

Polypyrrole (Ppy) nanowires are electrochemically synthesized using the nanochannels of a proton-modified natural zeolite clinoptilolite (HNZ). The synthetic inorganic structures Y zeolite and clay montmorillonite (M) in acid form (HY and HM) are also employed for pyrrole polymerization. The generation of Ppy with electrochemical activity is favored in a strongly acidic nanoscaled environment, in comparison with the polymer synthesized in the hosts without previous proton modification. It is proposed that the reduction/oxidation responses are a consequence of the polymer protonation/deprotonation where the H⁺ ions possibly act as charge transfer promoters. The well defined redox signals of Ppy included in HNZ, compared to the HY and HM, suggest that the polymeric units are held more tightly to the channels walls due to its complex framework. The TEM image of HNZ-Ppy reveals the presence of the polymer nanowires inside the natural zeolite framework. It is also found that the one electron oxidation process do not depend on first order monomer concentration but lower (0.38) for Ppy growth in HNZ, which is related to the spatial restriction of the host.     

Catalytic filamentous carbon: Structural and textural properties

Catalytic filamentous carbon (CFC) synthesized by the decomposition of methane over iron subgroup metal catalysts (Ni, Co, Fe or their alloys) is a new family of mesoporous carbon materials possessing the unique structural and textural properties. Microstructural properties of CFC (arrangement of the graphite planes in filaments) are shown to depend on the nature of catalyst for methane decomposition. These properties widely vary for different catalysts: the angle between graphite planes and the filament axis can be 0° (Fe-Co-Al₂O₃), 15° (Co-Al₂O₃), 45° (Ni-Al₂O₃), 90° (Ni-Cu-Al₂O₃). The textural properties of CFC depend both on the catalyst nature and the conditions of methane decomposition (T, °C). The micropore volume in CFC is very low, 0.001-0.022 cm³ g⁻¹ at the total pore volume of 0.26-0.59 cm³ g⁻¹. Nevertheless, the BET surface area may reach 318 m² g⁻¹. Results of the TEM (HRTEM), XRD, Raman spectroscopic, SEM and adsorption studies of the structural and textural properties of CFC are discussed.     

Redox-active silica nanoparticles : Part 2. Photochemical hydrosilylation on a hydride modified silica particle surface for the covalent immobilization of ferrocene

The surface of spherical nonporous monodisperse silica particles (diameter: 200 nm) is covalently modified with hydride by means of hydrosilanization. A direct silicon-carbon link between the hydride modified silica surface and 10-undecylenic acid is obtained by photochemical radical initiated hydrosilylation. A ferrocene unit is attached through an amide link to the carboxylic acid modified surface. Solid-state NMR and DRIFT spectroscopy indicate success of the reactions. The electrochemical oxidation and reduction of the ferrocene modified silica particles are observed after their adsorption on a platinum electrode. The cyclic voltammograms indicate, in addition to the charge transfer between ferrocene units on the particle surface, an interparticle charge transfer.     

Characterization of the ASR rim: Application to the Potsdam sandstone

Chemical properties of the reaction rim associated with alkali-silica reaction (ASR) were investigated using microprobe and scanning electron microscope (SEM). The studied aggregate is the Potsdam sandstone, a Cambrian siliceous sandstone well known for its reactivity. This particular rock is composed of well-crystallized quartz grains surrounded by a poorly crystallized siliceous cement that is considered to be the reactive constituent. Research was conducted on laboratory concrete specimens having reached various expansion levels and on some samples taken from an ASR-affected dam. Results indicate that the dark rim surrounding reactive particles is mainly composed of silica. This suggests that the reaction rim is formed by the precipitation of dissolved silica. Some alkalis and calcium were detected inside the thin intergranular joints in concentration ranging from 1% to 10%. These ions come from the cement paste and play a major role in dissolving original reactive silica.     

Technology update: Vacuum infusion

Vacuum, or resin, infusion techniques are becoming increasingly popular, especially in the marine industry where they can produce high quality boat hulls quickly and cleanly (see Reinforced Plastics' Marine Supplement, October 2003).     

Initial oxidation of silver electrode in weakly acidic sodium fluoride solutions: Potential shifts induced by laser heating

The behavior of a silver electrode in weakly acidified NaF solutions is studied by the methods of potential shifts induced by laser heating, impedance spectroscopy, and cyclic voltammetry. These methods make it possible to observe the time effects that reflect the electrochemical adsorption of oxygen on the Ag electrode/solution interface in the potential range from −0.7 to 0.2 V (SCE). The analysis of experimental data allows one to assess the effects of the potential and time of the electrode exposure (after its cathodic reduction or mechanical renewal) in the electrolyte on the amount of chemisorbed oxygen and also the effect of the latter on the electric double layer structure.     

Electrochemistry in confined microsystems: Part 1. CV-SECM of reversible system at a confined disk ultramicroelectrode

This work is the first part of a series of papers concerning the study of electrochemical method in case of ultramicroelectrode (UME) confinement in integrated chemical microsystems. This paper is devoted to the discussion of numerical simulation obtained in the case of a transient electrochemical method - i.e. cyclic voltammetry (CV) - applied to a finite disk ultramicroelectrode confined in front of an insulating surface. This configuration corresponds to scanning electrochemical microscopy (SECM) in negative feedback configuration. We describe a new electrochemical method, with acronym CV-SECM, based on the coupling of cyclic voltammetry with scanning electrochemical microscopy. The main advantage of this method is the obtention of a time resolved measurement simultaneously with a high local resolution. The results of the simulation show that adjusting the scan speed of the potential sweep allows the exploration of a controlled range of distance between the UME and the insulating surface. The reverse peak current obtained in cyclic voltammetry exhibits unexpected variations with the approach distance of the UME: (i) a regime of depletion of the electroactive reactant during the forward scan at short distance, associated to a decrease of the peak current and (ii) a regime of accumulation of the electroactive product at larger distance, associated to an increase of the reverse peak current identified in comparison with the free diffusion regime.     

Interphex 2004: Conference programme

Interphex 2004 is split into four concurrent events offering pharmaceutical technology solutions, under the banner of the exhibition, and educational opportunities, under the banner of the conference. The four segments, which will run alongside each other, are: Pharma Manufacturing; Pharma Discovery; Pharma IT; and Pharma Sourcing & Services. A separate conference programme has been organised for each strand providing industry professionals with the chance to learn about the latest trends or to advance their career with accredited short courses. Education providers include the International Society of Pharmaceutical Engineers (IPSE) and the Institute for International Research (IIR), amongst others.Below we highlight some of the more relevant presentations for professionals involved in the field of filtration and separation. For more detailed information and a full conference program please visit the Interphex 2004 website (www.interphex.com)