Electrochemical study of the activating solution for electroless plating of polymers

This paper presents an electrochemical study about the activating solutions of the electroless plating of polymers, containing Pd(II), Sn(II) and Sn(IV) mixtures in HCl as main components. The objective of the study is the voltammetric characterization of these solutions by cyclic and linear voltammetry in order to study the recovery of tin and palladium from these solutions. The effect of concentration and rotation rate on the current−potential curves was studied using the RDE technique. The electrochemical behaviour of solutions prepared in the laboratory was performed as a prior step to the further study of real activating rinsing solutions. The electrochemical reduction of Pd(II) takes place in two one-electron transfer steps which are mass transport controlled. The electrochemical reduction of Sn(II) and Sn(IV) is also mass transport controlled and takes place with direct formation of metallic tin, although the electrochemical reduction of Sn(IV) only takes place in solutions with HCl concentrations higher than 1 M. The presence of additives in the real solutions prevent the chemical reduction of Pd(II) and the formation of Sn(IV) hydroxylated complexes. This causes the appearance of well defined diffusion waves attributable to the electrochemical reduction of Pd(II) and Sn(IV). Hence, the recovery of both species simultaneously as well as separately could be carried out, if appropriate conditions are selected.     

The effect of pH on oxygen and hydrogen peroxide reduction on polycrystalline Pt electrode

Oxygen reduction (ORR) and hydrogen peroxide reduction (HPRR) reactions were studied on polycrystalline Pt by the rotating disc electrode technique in sulphate solutions over the entire pH range. Initial potentials for both ORR and HPRR coincide with the potential region of PtOH formation and shift negatively with the increase of the pH of the solution. For pHs lower than 3.0 and higher than 10.0, the ORR takes place through 4e-series pathways from acid and alkaline solutions, respectively. For 3.0 < pH < 6.0, the overall number of electrons exchanged depends on the potential and falls below 4 for ORR and below two for HPRR. This indicates that both reactions occur in a limited extent due to the changes of the local pH in the course of these reactions which gives rise to the double wave in the polarization curves (as observed for ORR for pH 3.5 and pH 4.0 and for HPRR for pH 4.0). The change of the Tafel slopes with potential indicate the change in reaction pathway from one that takes place in acid – to one that takes place in alkaline solution.     

Electrochemical Catalytic Reduction of Oxygen by a Self-Doped Polyaniline–Co-Porphyrin Complex-Modified Glassy Carbon Electrode

The four-electron reduction of oxygen to water takes place on a glassy carbon electrode by electrocatalysis using the Co-porphyrin–polyaniline complex. The four-electron transfer processes were confirmed by electrochemical measurements such as cyclic voltammetry, rotating disk voltammetry (RDV), and rotating ring-disk voltammetry (RRDV). The number of electrons transferred was determined on the basis of the Koutecky–Levich plot in RDV. Large amounts of H₂O₂ formation were not detected by RRDV. RRDV revealed that the direct four-electron reduction of oxygen proceeded without the formation of H₂O₂. The process obeys a mechanism in which the four-electron reduction takes place through a multiple electron injection from the polyaniline to the cobalt complex after electron transfer from Co to oxygen. The four-electron reduction of oxygen also proceeds in a pseudo-neutral medium (pH 6.2). Poly(2,3-dicarboxyaniline) acts as an excellent electron mediator from the electrode to the Co-porphyrin matrix and shows stable redox activity over a wide pH range due to the self-dopable carboxy substituents in the polymer chain.     

Some observations on the electrochemical reduction of pyridazin-3-ones

Controlled potential electroreduction of three pyridazin-3-ones has been investigated in protic medium. Whatever the acidity, the first reduction always takes place at the 4,5-double bond. In an ammoniacal buffer, further reduction leads to the tetrahydro derivative. In acidic medium, reduction of N-2 unsubstituted 4,5-dihydropyridazine-3-ones gives N-amonipyrrolidin-2-ones, whereas 2-methyl 4,5-dihydropyridazin-3-one leads to a pyrrolin-2-one.     

Chlorate formation and reduction in undivided hypochlorite cells

The accumulation of chlorate in a recirculating undivided brine electrolysis cell is followed. A variety of cathode materials were used and it is apparent that cathodic reduction of the ClO₃ ion takes place. This reaction appears to be activation-controlled.     

The behaviour of high polar organic solvents at platinum electrode — II. Adsorption and electrode reactions of acetonitrile

The adsorption of acetonitrile and reduction of adsorbed molecules at platinized platinum electrode were studied by potentiodynamic and radiometric techniques. During acetonitrile adsorption the reversibly and irreversibly adsorbed species are formed. One electron reduction process occurs in the potential range 0.45-0.15 V. Below 0.15 V the deeper reduction of adsorbed acetonitrile takes place — the final products are ammonia and ethane. The differences of smooth and platinized platinum electrodes properties are briefly discussed.     

Macrokinetics and mathematical modelling of quinone reduction by cyanobacteria

The kinetics of the reduction of externally added 2-hydroxy-1,4-naphthoquinone by blue-green algae of the strains Anabaena PCC 7120 and Anacystis nidulans PCC 6301 were studied in aqueous cell suspensions by electrochemical monitoring of the concentration of the formed hydroquinone. This reaction is of potential interest for bioelectrochemical fuel cells. The experimental curves obtained could be interpreted by a model that takes into account that both substrate and product have to be transported through the microbial cell walls and that the conversion reaction takes place with firstorder kinetics within the microbial cells. No clear evidence was found for the involvement of photosynthesis. It is suggested that the reduction of the quinone probably occurs via the enzyme-catalyzed oxidation of endogenous storage product(s), presumably glycogen.     

A study of the structure of an Aln-based ceramic obtained from ultrafine powders

Conclusions The specimens obtained by hot pressing plasma-chemical AlN powder contain a mixture of AlN of the hexagonal modification and AlON of the cubic modification.Lattice deformation of the hexagonal phase of AlN takes place during the hot pressing process of the AlN specimens. This is accompanied by a reduction of the lattice parameters in the direction of thea and c axes.The lattice parameters of the hexagonal phase of AlN increase after vacuum-annealing in the 1200–1600°C range.A decrease in the content of AlON and its lattice parameter takes place in the temperature range 1300–1600°C. This is related to the change in the chemical composition of the oxynitride phase.Translated from Ogneupory, No. 4, pp. 24–26, April, 1986.     

Reactivity of some acetylenic derivatives in electroinitiated polymerization

Summary The charge distribution in phenylacetylene, methyl propiolate, diphenyldiacetylene as well as in their anion-radieals was calculated by GNDO/2 and EHT methods. According to the obtained results, the electroinitiated polymerization of these monomers takes place by their direct reduction. A good agreement between theoretical and electroanalytical data was observed.     

Spectroelectrochemical study of trichloroacetic acid reduction at copper electrodes in an aqueous sodium sulfate medium

The electrochemical reduction of trichloroacetic acid (TCAA) in water has been analyzed through voltammetric studies with a copper rotating disc electrode supported by controlled-potential bulk electrolysis and electrochemical surface-enhanced Raman spectroscopy (SERS) experiments. The influences of the mass-transport conditions and concentration were studied. It has been pointed out that the electrochemical reduction of trichloroacetic acid takes place prior to the massive hydrogen evolution. Strong adsorption was observed on the electrode surface, and dichloroacetic acid (DCAA), monochloroacetic acid (MCAA), and chloride anions were detected as reduction products. The SERS experiments point to a secondary mechanism in which dissociative adsorption of the trichloroacetic acid gives rise to the adsorption of CO, and therefore, to the production of 1C molecules as by-products of the electrochemical reduction.     

Mechanism of dialuric acid oxidation on a mercury electrode

A study was carried out on the oxidation mechanism over dme of dialuric acid in the pH range 1–12. Voltagrams of dialuric acid show the existence of one oxidation wave but no reduction wave. The two-electron transfer takes place through a post-kinetic mechanism. A scheme is proposed for the overall reaction together with several reaction mechanisms at potentials corresponding to the foot of the wave.     

Nitric oxide reduction and carbon monoxide oxidation over carbon-supported copper-chromium catalysts

Carbon supported copper-chromium catalysts are shown to be very active for both the reduction of nitric oxide with carbon monoxide and the oxidation of carbon monoxide with oxygen. Mixed copper-chromium oxide active phases have good activity in the simultaneous removal of nitric oxide and carbon monoxide from exhaust gases. The influence of several catalyst variables has been investigated. The activity per volume of catalyst increases with increasing loading, while the intrinsic activity shows a maximum around C/M=100−50. An optimum catalyst for nitric oxide reduction and carbon monoxide oxidation has a copper/chromium ratio of 2/1. The apparent activation energy for the carbon monoxide oxidation over carbon supported copper-chromium catalysts is 77 kJ/mol, suggesting that the Cu---O bond rupture is the rate-limiting process. The reduction of nitric oxide takes place at higher temperatures. Since all catalysts have a low selectivity for molecular nitrogen formation at lower temperatures, the dissociation of nitric oxide is probably rate determining, resulting in a slightly reduced catalyst system. In an excess of carbon monoxide the reaction is first-order in nitric oxide and zero-order in carbon monoxide. Moisture inhibits the reaction by reversible competitive adsorption, whereas carbon dioxide does not. Oxygen completely inhibits the reduction of nitric oxide due to the more rapid reoxidation of the catalytic sites compared to nitric oxide. Therefore, the reduction of nitric oxide takes place only when all oxygen has been converted and, hence, is shifted to higher temperatures. As a possible consequence, the production of nitrous oxide is reduced. Nitric oxide and molecular oxygen react preferentially with carbon monoxide, so, in an excess of oxidizing component, gasification of the carbon support occurs at higher temperatures after carbon monoxide has been completely consumed.     

Electrocatalysis of the Reduction of Dioxygen by π-Conjugated Polymer Complexes with Dinuclear Cobalt Porphyrin

Catalysis of polymer complexes using polyanilines and dinuclear cobalt porphyrin (Co₂P) was investigated by electrochemical measurement. Poly(2,3-dicarboxyaniline) with CoTPPS–CoTMPyP acts as an excellent catalyst for a four-electron reduction of oxygen even under pseudo-neutral conditions. Various polymer complexes were made using synthesized electroresponsive polymers. The selectivity of the four-electron reduction dramatically decreases with an increase in the potential gap between the polymer and the porphyrin. This result indicates that a sequential electron transfer takes place from the polymer to the porphyrin with a potential similar to that of the cobalt porphyrin.     

Polarographic behaviour of some potential antidiabetic benzylsulphonylarylazopyrazoles

The reduction of N′-benzylsulphonyl-3-methyl/phenyl-5-methyl/phenyl-4-arylazopyrazoles takes place in a single 2 e transfer, giving a diffusion controlled irreversible wave in B.R. buffer at dme corresponding to the reduction of azo group. A plausible mechanism has also been suggested on the basis of number of protons involved in the rate determining step and number of electrons involved in the reduction. Effect of various cations, anions and solvent percentage on the reduction have been discussed. The effect of substituents and ranges of potentials have been determined quantitatively by the application of Hammett equation in all the three series of compounds.     

Thermal properties of sulfo-containing cation exchangers based on copolymers of vinylidene fluoride

It was found that when sulfo-containing cation exchangers based on PVDF and its copolymers are heated in air, the reaction of dehydrofluorination of the sulfonated unit in VDF takes place in the 50–100°C temperature region and the reaction of formation of sulfones with the participation of sulfo groups and macromolecules of the polymer takes place in the 220–250°C region. Treating sulfo-containing PVDF cation exchangers with an excess of ammonia with subsequent heat treatment at 110°C and reduction with hydrochloric acid increases the thermal stability of the sulfo-containing cation exchangers, and the temperature of initial weight loss is 200°C. The apparent activation energies of dehydrofluorination, formation of sulfones, and degradation of the macromolecular chain were determined and were in satisfactory agreement with the published data.Translated from Khimicheskie Volokna, No. 6, pp. 43–47, November–December, 1994.     

Preparation of metal powders of groups VI and VIII (Fe,Co, Ni) by the vapor phase reduction of their chlorides pure or in binary mixtures

The reduction of some metallic chlorides in the vapor phase, particularly chromium, is difficult and takes place selectivity in contact with a wall. The influence of several parameters has been investigated in order to minimize this effect.On the other hand, the chlorides of Mo, W, Co or Ni are reduced homogeneously in the gas phase with relative ease. This fact led us to determine the extent to which they would be likely to initiate chromium nucleation during the reduction of a mixture of two chlorides, CrCl₂ and one of the above chlorides.An examination of the metal powders obtained show that this is actually the case. In comparison with pure CrCl₂, deposits on the walls decline considerably and the reduction yield reaches 90%.     

On the nature of the adsorbed species and mechanism of adsorption of In(III) from iodide solutions at the dme

The reduction of In(III) in solutions containing 0.05, 0.1 and 0.25 M of NaI and with an ionic strength of 1.00 maintained with sodium perchlorate, has been studied by means of interfacial admittance measurements at different frequencies and dc potentials of the dropping mercury electrode.

Our results demonstrate that the process takes place with specific adsorption of electroactive species. The adsorption parameters and their dependence with potential have been determined. From the analysis of our results, together with those obtained in a previous study at higher concentrations of I⁻, it can be deduced than InI⁺₂ is the species preferentially adsorbed, this adsorption taking place via a bridge-like mechanism, through I⁻ ions previously adsorbed.     

Mixed Crystals as Host-Guest Systems for Probing Molecular Interactions

A method is described for probing interactions between molecules at the surfaces of growing crystals. For this purpose, mixed crystals have been treated as unique host-guest systems where the guest molecules are occluded into the host crystal through stereospecific interactions occurring at the different growing surfaces of the host. Owing to the process of molecular recognition at such surfaces, the adsorption and occlusion of the guest molecules takes place at specific sites, resulting in a reduction in symmetry of the mixed crystal compared to the pure host. The concept of reduction in symmetry is general, and has been instrumental for probing subtle molecular interactions at the surfaces of growing crystals, for the transformation of centrosymmetric single crystals into crystals with polar arrangement, and for “absolute” asymmetric synthesis inside centrosymmetric crystals.     

Hydrolysis of aluminium alkoxides and bayerite conversion

A study of hydrolysis of aluminium alkoxides as a function of water temperature, and structural transformation of the resultant hydroxides was conducted. Hot water hydrolysis of aluminium alkoxides produces boehmite, whereas cold water hydrolysis results in formation of amorphous monohydroxide. This amorphous phase contains OR groups whose removal by water during aging causes the material to convert to bayerite or boehmite. Bayerite conversion takes place below 80 °C by a dissolution-recrystallisation process in which the gradual liberation of OR groups by water appears to play an important role. Boehmite conversion takes place above 80 °C where vigorous liberation of OR groups occurs and the slow stoichiometric bayerite conversion diminishes. Neither conversion takes place in pure alcohol.     

On the use of the imperfect tracer pulse method for determination of hold-up and axial mixing

The imperfect pulse method is a powerful technique for experimental analysis of chemical engineering flow systems. The authors have employed this method in studies of holdup and mixing in gas-liquid fluidized beds. In the present paper are discussed two problems connected with reduction of the experimental data obtained in such studies. Tailing is a phenomenon that may seriously affect the accuracy of mixing coefficients determined by the imperfect pulse method. Accurate methods of data reduction, based upon analysis of moments, have been developed, and their applicability is demonstrated by analysis of experimental data. Interphase transfer of tracer material is of particular importance in investigations of gas phase mixing in a gas-liquid system where absorption of tracer gas into the liquid phase normally takes place. A semiempirical method is described for correction of the experimental data in such cases.