Effects of K<Subscript>4</Subscript>Fe(CN)<Subscript>6</Subscript> on electroless copper plating using hypophosphite as reducing agent

K₄Fe(CN)₆ was used to improve the microstructure and properties of copper deposits obtained from hypophosphite baths. In electroless copper plating solutions using hypophosphite as the reducing agent, nickel ions (0.0038 M with Ni²⁺/Cu²⁺ mole ratio 0.12) was used to catalyze hypophosphite oxidation. However, the color of the copper deposits was dark or brown and its resistivity was much higher than that obtained in formaldehyde baths. The effects of K₄Fe(CN)₆ on the deposit composition, resistivity, structure, morphology and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The deposition rate and the resistivity of the copper deposits decreased significantly with the addition of K₄Fe(CN)₆ to the plating solution and the color of the deposits changed from dark-brown to copper-bright with improved uniformity. The nickel and phosphorus content in the deposits also decreased slightly with the use of K₄Fe(CN)₆. Smaller crystallite size and higher (111) plane orientation were obtained by addition of K₄Fe(CN)₆. The electrochemical current–voltage results show that K₄Fe(CN)₆ inhibited the catalytic oxidation of hypophosphite at active nickel sites and reduced the reduction reaction of cupric ions on the deposit surface by adsorption on the electrode. This results in lower deposition rate and a decrease in the mole ratio of NaH₂PO₂/CuSO₄ consumed during plating.     

Verification de la linearite et de la stationnarite des systemes electrochimiques lors de la mesure de leur impedance par une methode de bruit

A transfer-function analysis employing white-noise excitation is used to measure the impedance of some electrochemical systems (platinium disc electrode in a K₃Fe(CN)₆/K₄Fe(CN)₆ solution, Leclanché cell). The coherence function is calculated to determine the validity of transfer-function measurement and its is shown that this method provides an internal check on the validity of the measurements.     

Fire suppression by aerosols of aqueous solutions of salts

Results of laboratory experiments were verified by full-scale tests in which two types of model fire sources were extinguished by salt-solution aerosols. The tests showed that short-term action of an aerosol cloud of an aqueous solution of potassium ferricyanide K₃[Fe(CN)₆] on the flame front of a surface forest fire led to suppression of the gas-phase combustion, and in the case of a model fire source of class A (burning wood) to its complete extinction. The minimum extinguishing mass concentration of K₃[Fe(CN)₆] in these experiments — 4.5 g/m³ — is close to that measured earlier in laboratory experiments. It was found that, in fire suppression by an aerosol of the aqueous solution of K₃[Fe(CN)₆], the volumetric flow rate of this fire suppressant was 30 times lower than the standard flow rate of pure water from a fire hose.     

Electron transfer across anodic films formed on tin in carbonate-bicarbonate buffer solution

Impedance and steady-state data were recorded in order to study the kinetics of electron transfer between passive tin electrodes and an electrolytic solution containing the K₃Fe(CN)₆-K₄Fe(CN)₆ redox couple. Film thickness plays a key role in determining the type of electronic conduction of these oxide covered electrodes. Electron exchange with the oxide takes place with participation of the conduction band in the semiconducting film. A mechanism involving direct electron tunneling through the space charge barrier is the most suitable to interpret the experimental evidence.     

Electrochemical behavior of K<Subscript>4</Subscript>Fe(CN)<Subscript>6</Subscript> in [bmim]PF<Subscript>6</Subscript>/TX-100/H<Subscript>2</Subscript>O based microemulsions

The electrochemical behavior of potassium ferrocyanide [K₄Fe(CN)₆] at Pt/ionic liquid (IL) microemulsion interfaces was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). H₂O/TX-100/bmimPF₆ was used to prepare three IL microemulsions: water in 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆) (W/IL), bicontinuous (WIL) and bmimPF₆ in water (IL/W). The results show that the IL microemulsion systems have relatively narrower potential windows compared with the pure IL system. The redox potential gap is about 100 mV in the pure water and the three IL microemulsions. The redox potentials of K₄Fe(CN)₆/K₃Fe(CN)₆ and the redox peak currents decrease in the order pure water, IL/W, WIL, W/IL. Furthermore, the peak currents increase linearly with the square root of the scan rate, while the diffusion coefficient increased in the order W/IL, WIL, IL/W. The Nyquist plots obtained in the WIL and IL/W systems show capacitive resistance arcs at high frequencies and 45° straight lines at low frequencies, implying that the electrochemical reactions are controlled by charge transfer and diffusion steps. For the W/IL system there is only a 45° straight line in the Nyquist plot, indicating that diffusion is the controlling step at all frequencies.     

Characteristics of photoelectrochemical cells with iron oxide/n-Si heterojunction photoanodes

The iron oxide/n-Si heterojunction electrode was studied as a photoanode for a regenerative photoelectrochemical (PEC) cell. The influence of modifying the top layer of the electrode with Pd or RuO₂ was investigated. The photocurrent at the heterojunction electrode was produced by the holes which were photo-excited in both iron oxide andn-Si. The addition of Pd or RuO₂ on the heterojunction electrode surface enhanced the optical-to-electrical conversion efficiency. The efficiencies for a stable working PEC cell were found to be 1.34% and 1.60% for a Pd-and a RuO₂-modified electrode, respectively. This was measured in a 0.2 M KOH solution containing 0.2 M K₄[Fe(CN)₆] and 0.01 M K₃[Fe(CN)₆ at a xenon lamp intensity of 55 mW cm⁻². The use of iron oxide made the photoanode highly stable, as compared to an electrode such as RuO₂/n-Si. From a constant open-circuit voltage independent of the redox potential in 0.2 M KOH, it was concluded that Fermi level pinning occurs at the interface.     

An experimental study of mass transfer to ring — disc jet electrode

Mass transfer when a jet of solution impinges at 90° to a stationary ring disc electrode has been investigated using an electrochemical method. The influence of various parameters such as the fluid velocity, the distance between the nozzle and the electrode surface as well as the concentration of the reacting species on the disc and the ring current was examined experimentally using the cathodic reduction of CuCl₂ and of K₃Fe(CN)₆ in KCl. It has been found that the stationary ring can be used for detection of intermediate species formed at the disc. An application of this system for the study of the anodic dissolution of a metal is given.     

Limiting current on porous graphite electrodes under flow conditions

The flow electrolysis of a solution of 2.0×10^–3 M K₃Fe(CN)₆ in 2 M KCl in water on porous graphite electrodes is described. The electrodes have been composed of crushed graphite of three grain size ranges: 0.7÷1.0, 0.4÷0.7, and 0.25÷0.4 mm. Electrodes of three different heights have been investigated, and the solution flow rate ranged between 0.009 and 0.25 ml s^–1. The dependence of the logarithm of the limiting current and of the limiting degree of conversion on the logarithm of the flow rates is shown for the electrodes. The obtained experimental results are interpreted by means of the described earlier semiempirical model of the limiting current on flow-through porous electrodes.     

Corrosion and passivation of iron and its nitrided layer in borate buffer

The aim of this work was to gain better understanding of the reasons of enhanced resistance to pitting corrosion of nitrogen-containing iron. Gas nitrided (570 °C, 4 h) and untreated Armco iron were examined in a borate solution of pH 8.4 without and with chlorides or ammonia. Enhanced pitting resistance and enhanced anodic currents were exhibited by nitrided Fe and also by untreated Fe in the solution with added ammonia. XPS showed that anodic films on nitrided Fe contained much larger amounts of iron oxides, in particular of magnetite, than those on untreated Fe. It is suggested that the anodic behaviour of nitrided Fe is determined mainly by the effect of evolving ammonia on corrosion products. Increased anodic dissolution can be explained by the formation of soluble complexes with ammonia, whereas increased amounts of magnetite can be due to the ammonia-promoted conversion of FeOOH + Fe(II) to Fe₃O₄. It is proposed that the enhanced pitting resistance of nitrided Fe results mainly from the formation of large amounts of iron oxides and from binding of chloride anions into a Fe-NH₃-Cl complex.     

Nickel-iron catalysts prepared by homogeneous deposition-precipitation of cyanide complexes on a titania support

Nickel-iron catalysts have been prepared by homogeneous deposition-precipitation of complex nickel-iron cyanides on a titania support. The nickel-iron alloys obtained after calcination and reduction of the cyanide precursors were characterized by Mössbauer spectroscopy, high-temperature X-ray diffraction, and magnetic measurements. Fischer-Tropsch experiments show remarkable results. Catalysts prepared from K₃Fe(CN)₆ and Na₂Fe(CN)₅NO cyanide precursors exhibit a high activity and selectivity, whereas catalysts prepared from K₄Fe(CN)₆ do not show any activity. This lack of activity is caused by the presence of potassium in catalysts prepared from K₄Fe(CN)₆. Potassium or iron titanate inhibits the adsorption of CO on the nickel-iron surface. Deactivation of active nickel-iron catalysts was caused by the deposition of inactive carbon during Fischer-Tropsch synthesis.     

Influence of surface inhomogeneities of boron doped CVD-diamond electrodes on reversible charge transfer reactions

The electrochemical behaviour of reversible charge transfer reactions on boron doped diamond (BDD) was studied by cyclic voltammetry and electrochemical impedance spectroscopy using rotating disc electrodes under defined convection. Diamond films of 5 m thickness with doping levels of 200, 3000 and 6000 ppm were prepared by hot filament chemical vapour deposition on niobium substrate. The electrochemical measurements were carried out on BDD electrodes in deaerated 0.5 M Na₂SO₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆] solution at rotation frequencies 0 < f _rot < 4000 rpm. Comparative measurements were carried out on an active Pt electrode. The BDD electrodes exhibit distinct irreversibilities indicated by a larger peak potential difference in the cyclic voltammograms, lower diffusion limiting current densities and an additional impedance element at high frequencies. Mechanical polishing with carbon fleece and SiC paper strongly affects the irreversible behaviour of the BDD electrodes. The experimental results are explained by a partial blocking of the diamond surface with reversible charge transfer at active sites. The impedance spectra are analysed quantitatively using a transport impedance model for reversible reactions on partially blocked electrode surfaces.     

Flow-through electrodes composed of parallel screens

The electrolysis of 2.0 × 10^?3 M K₃Fe(CN)₆ in 1 M KCl in water at room temperature (22°C) has been investigated on flow-through porous electrodes composed of parallel platinum screens. The effect of changing the number of screens on the limiting current and the limiting degree of conversion of substrate has been studied. The results obtained confirm the previously derived model of limiting current on porous electrodes under conditions of solution flow. The experimental results have also been presented in form of mass transfer correlations for Sherwood number and j_D-factor. The potential drop in the electrode composed of six screens has been measured and compared with a theoretical equation. The effect of error in the determination of flow rate on the accuracy of presentation of experimental data is discussed.     

Faradaic impedance titration and control of electron transfer of 1-(12-mercaptododecyl)imidazole monolayer on a gold electrode

In this work, we studied interfacial proton transfer of the self-assembled monolayer (SAM) of 1-(12-mercaptododecyl)imidazole on a gold electrode by faradaic impedance titration method with Fe(CN)₆³⁻ as an anionic redox probe molecule. The surface pK_1/2 was found to be 7.3, which was nearly the same as that of 1-alkylimidazole in solution. We also investigated the electrochemical properties of the SAM-modified electrode by cyclic voltammetry. Cyclic voltammetry was performed (1) in the solution containing Fe(CN)₆³⁻ with repeated alternation of pH values to investigate the electrostatic interaction of the protonated or deprotonated imidazole with Fe(CN)₆³⁻ and (2) in the acidic or basic electrolyte containing Ru(NH₃)₆³⁺ as a cationic redox probe to verify the effect of the polarity of a redox probe. We observed the reversible adsorption/desorption of Fe(CN)₆³⁻ and concluded that the adsorbed Fe(CN)₆³⁻ catalyzed the electron transfer of both Fe(CN)₆³⁻ itself and cationic Ru(NH₃)₆³⁺.     

Separation of Oxygen and Nitrogen by Porous Cyanometallates

The adsorption-based separation in porous solids takes place through steric, kinetic, or equilibrium effect selectivity. In this contribution the oxygen-nitrogen separation by four porous frameworks representative of cyanometallates was studied by inverse gas chromatography. The following materials were considered: Cd₃[Co(CN)₆]₂ (cubic), Zn₃[Co(CN)₆]₂ (rhombohedral), Zn₃K₂[Fe(CN)₆]₂ (rhombohedral) and Co[Fe(CN)₅NO] (cubic). Chromatographic separation profiles from gases mixtures using columns of these materials were recorded. For columns prepared from rhombohedral zinc hexacyanocolbaltate(III) excellent separation of O₂ and N₂ was observed. Such behavior was attributed to a kinetic-based selectivity related to the size and shape for the pore windows of this material. The porous framework of this zinc phase is formed by ellipsoidal cavities (12.5 × 9 × 8 Å) communicated by elliptical windows of ～ 5 Å. For Cd₃[Co(CN)₆]₂ and Co[Fe(CN)₅NO] also kinetic-based selectivity was observed while for Zn₃K₂[Fe(CN)₆]₂ the K⁺ ion located close to the cavity windows hinders the porous windows accessibility for nitrogen and oxygen molecules. All the samples to be studied were characterized from X-ray diffraction, infrared spectroscopy, termogravimetric and adsorption data.     

A Comparison of the Effect of Lead (Pb) on the Slow Vacuolar (SV) and Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

Little is known about the effect of lead on the activity of the vacuolar K⁺ channels. Here, the patch-clamp technique was used to compare the impact of lead (PbCl₂) on the slow-activating (SV) and fast-activating (FV) vacuolar channels. It was revealed that, under symmetrical 100-mM K⁺, the macroscopic currents of the SV channels exhibited a typical slow activation and a strong outward rectification of the steady-state currents, while the macroscopic currents of the FV channels displayed instantaneous currents, which, at the positive potentials, were about three-fold greater compared to the one at the negative potentials. When PbCl₂ was added to the bath solution at a final concentration of 100 µM, it decreased the macroscopic outward currents of both channels but did not change the inward currents. The single-channel recordings demonstrated that cytosolic lead causes this macroscopic effect by a decrease of the single-channel conductance and decreases the channel open probability. We propose that cytosolic lead reduces the current flowing through the SV and FV channels, which causes a decrease of the K⁺ fluxes from the cytosol to the vacuole. This finding may, at least in part, explain the mechanism by which cytosolic Pb²⁺ reduces the growth of plant cells.     

Liquid phase deposition of mesoporous TiO2/DNA hybrid film: Characterization and photoelectrochemical investigation

A photoelectroactive TiO₂/DNA hybrid film was synthesized via the liquid phase deposition (LPD) process. Scanning electron microscopic (SEM) characterization showed that the compact TiO₂ film was changed to a mesoporous structure when DNA was present in the deposition solution, which might be the result of TiO₂ particles growing along the backbones of the double-helical structure of DNA molecules. Although UV absorption spectra and cyclic voltammograms indicated that the deposited TiO₂ on the substrate surface was decreased in the presence of DNA, an enhanced photocurrent response was observed. The electrochemical impedance and cyclic voltammetric measurements using K₃[Fe(CN)₆] as a redox probe suggested that the mesoporous film provided a relatively more efficient electron transfer interface, which could improve the photoelectron transfer rate from the semiconducting film to the electrode and reduce the recombination of photoelectrons and holes. This results in an enhanced photocurrent. Even after long-term and continuous UV irradiation, the mesoporous film exhibited a promoted photoelectrochemical response. The promoted photoelectrocatalytic degradation of methylene blue was obtained on the TiO₂/DNA composite film, which is consistent with the enhanced photocurrent, and this demonstrates that DNA behaved as a useful biomaterial for the synthesis of a photoelectroactive hybrid film with improved performance.     

Characterization of boron-doped diamond electrodes by electrochemical impedance spectroscopy

Charge transfer on boron doped diamond (BDD) electrodes was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The diamond films of 5 μm thickness and boron content between 200 ppm and 3000 ppm were prepared by the hot filament CVD technique on niobium substrate and mounted in a Teflon holder as rotating disk electrodes. The electrochemical measurements were carried out in aqueous electrolyte solutions of 0.5 M Na₂ SO ₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆]. Significant deviation in the redox behaviour of BDD and active Pt electrodes was indicated by a shift of the peak potentials in the cyclic voltammograms with increasing sweep rate and lower limiting diffusion current densities under rotating disk conditions. In the impedance spectra an additional capacitive element appeared at high frequencies. The potential and rotation dependence of the impedance spectra can be described quantitatively in terms of a model based on diffusion controlled charge transfer on partially blocked electrode surfaces. Direct evidence for the non-homogeneous current distribution on the diamond surface was obtained by SECM measurements.     

Enhancement of the Rates of Liquid-Solid Heat and Mass Transfer in Annular Ducts by Using Circular Fins

Rates of solid-liquid mass and heat transfer (by analogy) were measured at the outer surface of the inner tube of an annular duct under developing flow conditions using the electrochemical method that elaborates the measurement of the limiting current of the reduction of K₃Fe(CN)₆ at the tested model surface. Variables examined were physical features of the solution (density ρ, viscosity μ, and diffusivity D), solution superficial velocity, tube active length, and tube diameter. The experimental results were correlated by a dimensionless equation involving all affecting parameters. Due to the presence of the circular fins at the tube surface, the degree of mass transfer was enhanced by a factor ranging from two to six subject to the operative settings. Applications of the current findings in the design of catalytic reactors, membrane dialyzers, and double-pipe heat exchangers were discussed.     

Mass transfer characteristics of electrochemical reactors employing gas evolving mesh electrodes

Mass transfer rates were measured at a single screen and a fixed bed of closely packed screens for the simultaneous cathodic reduction of K₃Fe(CN)₆ and anodic oxidation of K₄Fe(CN)₆ in alkaline solution with H₂ and O₂ evolution, respectively. Variables studied were gas discharge rate, number of screens per bed and position of the electrode (vertical and horizontal). For single screen electrodes, the mass transfer coefficient was related to the gas discharge rate by the equations: $$\begin{gathered} K = aV^{0.190} , for H_2 evolving electrodes, \hfill \\ K = aV^{0.469} , for O_2 evolving electrodes \hfill \\ \end{gathered} $$ . Electrode position was found to have no effect on the rate of mass transfer for single and multiscreen electrodes in the case of H₂ and O₂ evolution. Mass transfer coefficients were found to increase with an increasing number of screens per bed in the case of H₂ evolution, while in the case of O₂ evolution the mass transfer coefficient decreased with an increasing number of screens per bed. A mathematical model was formulated to account for the behaviour of the H₂ evolving electrode which, unlike the O₂ evolving electrode, did not obey the penetration model. Power consumption calculations have shown that the beneficial effect of mass transfer enhancement is outweighed by the increase in the voltage drop due to gas evolution in the bed electrode.     

Influence of ionic speciation on electrocatalytic performance of polyaniline coated platinum electrode: Fe(III)/Fe(II) redox reaction

Porous-polyaniline coated Pt electrode (PANI/Pt) was electro-synthesized potentiodynamically in 0.1 M aniline + 0.5 M H₂SO₄ and morphologically characterized by scanning electron microscopy (SEM). Nature of predominant Fe-species in HCl and H₂SO₄ was checked by UV-vis spectrophotometry. Electrocatalysis of Fe(III)/Fe(II) reaction was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for three different solution compositions viz. (i) FeCl₃/FeCl₂ in 1 M HCl, (ii) FeCl₃/FeCl₂ in 0.5 M H₂SO₄ and (iii) Fe₂(SO₄)₃/FeSO₄ in 0.5 M H₂SO₄. For different thicknesses of PANI, the peak current increased irrespective of the nature of the Fe-species, but the polarity of the charge on the Fe-species showed great influence on reversibility of electrocatalysis by PANI/Pt. The Donnan interaction of the polyaniline modified electrode for the three compositions was investigated with respect to [Fe(CN)₆]³⁻/H₂[Fe(CN)₆]²⁻ which are believed to be the predominant species present in K₃[Fe(CN)₆]/K₄[Fe(CN)₆] solution in 0.5 M H₂SO₄. The electrocatalytic performance of PANI/Pt for Fe(III)/Fe(II) redox reaction was found superior in HCl compared to that in H₂SO₄.