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The purpose of this paper is to propose an efficient and low cost defluoridation process based on electrocoagulation with aluminium bipolar electrodes. The performance of a pilot scale electrochemical reactor equipped with aluminium bipolar electrodes with an anode active area surface of about 1.6 m2 was studied. The pilot study yielded promising results, suggesting that further in-depth development studies are justified.

A technique for activation of granular activated carbon (GAC) is presented based on the electrochemical method. In this study, we investigate the effectiveness of the electroactivated GAC in removing phenol from water and determine the optimum conditions for activation. Electro-activation of the GAC appears to be an interesting technique; it requires a short electro-activation time Ta = 30 min and an optimum potential ranging from +200 mV/SCE to 400 mV/SCE. Phenol adsorption isotherms gave a limiting adsorption capacity Qm dependent on the applied potential, which at potential E=+300 mV/SCE was improved by about 55%, giving Qm = 75 mgphenol g−1 GAC.

The purpose of this paper was to determine the effect of the static deployed metal sheet on the performance in the ultrafiltration process. The sheet was first utilized to provoke turbulence near the membrane, and at the same time as an anode to create a pulsed electric field. The electro-ultrafiltration module reduced the global membrane resistance by combining three factors: turbulence created by the static metal deployed sheet, the turbulence induced by the formation of oxygen bubbles just near the membrane skin and the electrophoresis of the protein by the pulsed electric field. The application of pulsed electric field of about E = 700 V/m allowed an increase of the permeate flux by about 300%. The addition to the feed solution of activated alumina (AA) as a dynamic turbulence promoter shows that the presence of the AA considerably reduced the effect of the turbulence induced by the formation of oxygen bubbles and the electrophoresis of the protein. Nevertheless, the utilization of an electric field (E = 700 V/m) made an increase of the permeate flux of about 10% possible.

A process was developed for producing high quality activated carbon from Algerian mill waste. The solid olive mill residue was carbonized at 800 °C and physically activated with CO2, air or steam. An optimum activation temperature of about 850 °C was determined for all the activation agents used. Steam appeared to be the most efficient activator as compared with air and CO2. An optimal activation time of about 2 h was then determined with steam as the optimum activation agent. The porous structure of the activated carbon was characterized by nitrogen adsorption at −196 °C, and in all cases the surface areas, calculated by DR and BET methods, confirmed the production of a material with good microstructural characteristics and specific surfaces exceeding 1500 m2 g−1 for the carbon prepared by steam activation. Phenol adsorption isotherms gave the adsorption properties and the adsorption capacity of about 11.24 mg of phenol per gram of the activated carbon produced. The kinetics of the phenol adsorption onto the porous material was evaluated by means of two models: the external resistance model and the linear model. The second model appeared to constitute a more appropriate fit for the experimental data. © 2000 Society of Chemical Industry

The purpose of this work was to determine the effect of the static metal deployed sheet on the performance of the ultrafiltration process. The sheet was first utilised to provoke turbulence near the membrane, and at the same time as an anode to create an electric field. It was shown that the electro-ultrafiltration module was more efficient for both low crossflow velocity and BSA initial concentration. The global hydraulic membrane resistance may be reduced by half in all cases. The polarisation layer and fouling membrane appeared reversible phenomena, which may be controlled by appropriate electric field strength.

Because of its good radiopacity, superelasticity, and shape memory properties, nickel-titanium (NiTi) is a potential material for fabrication of stents because these properties can facilitate their implantation and precise positioning. However, in vitro studies of NiTi alloys report the dependence of alloy biocompatibility and corrosion behavior on surface conditions. Surface oxidation seems to be very promising for improving the corrosion resistance and biocompatibility of NiTi. In this work, we studied the effect on corrosion resistance and surface characteristics of electropolishing, heat treatment, and nitric acid passivation of NiTi stents. Characterization techniques such as potentiodynamic polarization tests, scanning electron microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy were used to relate corrosion behavior to surface characteristics and surface treatments. Results show that all of these surface treatments improve the corrosion resistance of the alloy. This improvement is attributed to the plastically deformed native oxide layer removal and replacement by a newly grown, more uniform one. The uniformity of the oxide layer, rather than its thickness and composition, seems to be the predominant factor to explain the corrosion resistance improvement.

The mechanism of tin cementation by zinc powders in alkaline solution (300 g/l NaOH + 74.7 g/l ZnO + 0.113 g/l SnO) was investigated and the reaction kinetics were characterized under different experimental conditions. Diffusion coefficients of tin in the solution were determined from 35 to 80°C using a rotating disk electrode. Assessment of the experimental results and activation energy of the cementation reaction indicates that the process is controlled by diffusion of tin cations.

Cathodic potential oscillations were previously reported for the electrodeposition of metals. Similar oscillations are reported here for the first time using a redox couple. The previously identified rules governing the appearance of these oscillations (applied current density larger than the limiting one, hydrogen overpotential larger than a minimum value) were either confirmed or demonstrated and expanded. Surface films, which may be linked to the reaction product solubility, are formed that limit oscillation duration. The added criteria allows a more focused search for other redox couples that may lead to unlimited oscillation durations.

NiTi Shape Memory Alloys (SMA) are potential biomaterial candidates. However, due to its possible corrosion in physiological solution, dissolution of toxic Ni might be happening, rendering this material nonbiocompatible. We have used excimer laser surface treatment to improve corrosion resistance of NiTi SMA plates. Potentiodynamic tests in physiological Hank's solution show that the laser treatment performed in air improved all corrosion parameters. The surface is homogenized and a Scanning Electron Microscopy (SEM) observation indicates a decrease of corrosion pit size and numbers. Laser treatment improvement resistance is explained by a combination of the homogenization of the surface by melting, the hardening due to N incorporation and the thickening of the oxide layer.

Electroflotation studies on sphalerite fine particles, conducted under careful pH control using buffer electrolytes, reveal that for either H2 or 02 electrolytic gases there exists an optimum pH range at which electroflotation is most effective. This can be explained by the observed dependence of electrolytic gas bubble size on the pH of the electrolyte.

The electrochemical active surface area at oxide electrodes of Pt and electrodeposited Ni, Co and Ni20Co80 alloys was evaluated in 5m KOH solutions based on the charge for electrochemical desorption of a monolayer of overpotential deposited oxygen (OPD O) species. Thein situ technique empllyed for the charge measurement involves galvanostatic charging (OPD O) adsorption), followed by simple discharging (OPD O desorption) experiments. It is observed that surface area estimated by this new technique for the oxidized surfaces of the metals studied here are consistent with those from a.c. impedance spectroscopy. The activity of the metal towards the oxygen evolution reaction (OER) is also discussed in terms of their active surface area estimated in this study.

The dissolution rate of pure ZnO in NaOH solution occurs under mixed control by the surface reaction and diffusion. The contribution of diffusion control to the leaching rate was calculated using a...

An in situ method has been developed for the determination of real active surface area of electrodes through the charge required for monolayer coverage of the electrode surface by overpotential deposited hydrogen (OPD H), i.e., Q OPD,H , by means of simple discharging (OPD H desorption) following galvanostatic charging (OPD H adsorption), experiments. The procedure requires simple equipment and easy subsequent data treatment. Surface area measurements on platinum and stainless steel 304 electrodes in 5M KOH aqueous solutions obtained by this method are consistent with those from ac impedance spectroscopy

Computer-generated simulation, previously described by the authors, was used to explain the effects of temperature and powder morphologies on the cementation rate of copper in alkaline zinc solution (300 g/liter NaOH, 60 g/liter Zn, and 0.2 g/liter Cu). It reveals good reliability on predictin the cementation behavior. Results of laboratory-scale experiments fit the computer simulation for a temperature range of 35 to 15 o C. A rise in temperature increases the cementation rate, and the activation energy was equal to 5.5 kcal/mol as predicted by computer. Zinc powders were obtained by alkaline electrolysis at various current densities (from 1000 to 9000 A/m 2 ) and their reactivity were compared to the industrial atomized powder

Electrodeposited nickel-molybdenum, nickel-tungsten, cobalt-molybdenum, and cobalt-tungsten were characterized for the hydrogen evolution reaction (HER) in the electrolysis of 30 w/o KOH alkaline water at 25 C. The rate-determining step (rds) of the HER was suggested based on the Tafel slope of polarization and the capacitance of electrode-solution interface determined by ac impedance measurement. The HER on the nickel- and cobalt-based codeposits was enhanced significantly compared with that o the electrolytic nickel and cobalt with comparable deposit loadings. The decrease in the HER overpotential was more pronounced on the molybdenum-containing codeposits, particularly on cobalt-molybdenum which also showed a high stability. The enhancement of the HER was attributed to both the synergetic composition and the increased active surface of the codeposits. The real electrocatalytic activity of te electrodes and the effect of their and the increased active surface of the codeposits. The real electrocatalytic activity of the electrodes and the effect of their surface increase were distinguished quantitatively. The linear relations between HER overpotential and surface roughness factor of the electrodes on a Y-log(X) plot were obtained experimentally and interpreted based on the Tafel law.

Cobalt-molybdenum and nickel-molybdenum gas diffusion electrodes with different compositions were prepared by sintering the metallic powders with filler material at different temperatures, and characterized for hydrogen oxidation in a 30wt% KOH solution at 25°C. Hydrogen oxidation was apparently enhanced on the cobalt-molybdenum as compared with the nickel-molybdenum and the electrodes composed of only cobalt, nickel or molybdenum. The reaction speed of hydrogen oxidation was significantly influenced by electrode composition and sintering temperature, which were optimized for the reaction.

The cementation of copper in alkaline zinc solution (300 g/liter NaOH, 60 g/liter Zn, and 0.2 g/liter Cu) was studied and a method based on mathematical simulation was used to identify the mechanisms governing the process. Results suggest that activation was the initial mechanism, since copper ions do not deposit easily on zinc. However, the mechanism changed to diffusion after a few minutes of cementation, when copper ion deposition was facilitated by the presence of metallic copper partly covering the zinc surface. The mathematical procedure as well as the results of simulation are presented. Experimental cementations were performed and the data coincided with the predictions obtained by simulation, The present simulation method can be applied also to cementation in acid media

Electrolytic cobalt deposits, as electrocatalytic materials, were prepared from baths containing chloride, sulphate or acetate. Electrodeposition was conducted at 200 A m−2 with or without oxygen bubbling at the cathode. The hydrogen evolution reaction (h.e.r.) on the cobalt electrodes was performed in 30 wt % KOH at 25, 40, 50, 60 and 70 °C. Without oxygen bubbling during deposition, the cobalt electrodes prepared from the acetate bath gave superior performance for h.e.r. than electrodes deposited from the other baths. With oxygen bubbling, however, the lowest h.e.r. over-potential was obtained on the cobalt prepared from the chloride bath.

Nickel electrodes were prepared by electrodeposition in electrolytes of various anionic compositions. The deposition conditions and bath types were evaluated with special emphasis on the electrocatalytic properties for the oxygen evolution reaction (OER). Electrochemical characterizations in a 5 mol/L KOH solution at 25°C showed that the electrode deposited from the chloride bath, having a low Tafel slope of 50 mV/dec and an overpotential of 396 mV at 100 mA/cm2, is the most catalytically active among electrodes prepared in electrolytes of various anionic compositions. The electrode activity for the OER is related to the real surface areas, which depend on the anion compositions in the deposition bath and the deposition conditions. Des electrodes de nickel ont ete preparers par electrodeposition dans des solutions de differentes composition anionique. Les conditions de deposition ainsi que les types de bains ont ete evalus a ľaide de leurs caracteristiques electrocatalytiques pour la reaction de degagement ďoxygene. II a ete montre lors des caracterisations electrochimiques effectuees dans une solution 5 mol/L KOH a 25°C, que ľelectrode deposee en utilisant un bain chlorure et ayant une pente de Tafel de 50 mV/decade ainsi q'une surtension de 396 mV a 100 mA/cm2, presente la meilleure activite catalytique. Ľactivite catalytique des electrodes de Ni pour le degagement ďoxygene depend de la presence de fissures a la surface de celles-ci et dont la quantite varie en fonction des conditions de deposition et du bain utilise.

Nickel-cobalt and nickel-iron electrodeposits were characterized as hydrogen electrodes in alkaline water electrolysis (6 mol/L KOH, 25°C). The nickel-based codeposits were fabricated with different bath compositions and at different current densities. The hydrogen evolution in water electrolysis on the nickel-based codeposits was apparently enhanced as compared with that on nickel. The improvement of the electrocatalytic behaviour of the hydrogen electrodes is attributed to their composition and an increase of their active surface, which are dependent on the electrodeposition conditions. Les depǒts electrolytiques de nickel-cobalt et nickel-fer ont ete caracterises comme electrodes ďhydrogene pour ľelectrolyse de ľeau alcaline (6 mol/L KOH, 25°C). Ces depǒts a base de nickel ont ete fabriques avec compositions de bains et densites de courant differentes. Le degagement ďhydrogene durant ľelectrolyse de ľeau sur les depǒts a base de nickel a ete significativement ameliore par rapport a celui des depǒts de nickel pur. Cette amelioration du comportement electrocatalytique des depǒts est reliee a leur composition et a une augmentation de leur surface active. qui dependent des conditions ďelectrodeposition.

The hydrogen evolution reaction (HER) on cobalt electrodes has been investigated in both alkaline (30 wt% KOH) and acid (1m H2SO4) media at 25°C. The electrocatalytic cobalt materials were produced under different electrodeposition conditions, namely deposition in the absence or presence of bubbling oxygen or nitrogen gas with two gas flow rates (80 and 230 ml min−1) and at different current densities (50–800 A m−2) and deposition in a cobalt powder-containing bath. It has been shown that the electrocatalytic behaviour of the cobalt deposits can be significantly affected by deposition current density via a change of surface area of the cobalt deposits. A considerable HER overpotential decrease (up to 150mV) has been achieved on the highly porous and active cobalt electrodes deposited in the presence of bubbling oxygen and chloride ions in deposition solution. However, the HER overpotential was increased on the cobalt electrodes deposited with bubbling nitrogen in the bath.

Sherwood numbers were determined for mass transfer of zinc in alkaline solutions with coevolution of hydrogen (0.15-0.9 mmol/cm 3 ZnO+8.4 mmol/cm 3 KOH, 300 K). The separation between the zinc and the hydrogen current was performed using polarization curves. The separation between Sherwood numbers due to natural and bubble convection was obtained by an additive law since hydrogen evolution took place only at current densities higher than the zinc limiting current density

Concentration profiles near a copper cathode immersed in a 0.3 mol/L CuSO4 aqueous solution were determined by theoretical computation and by measurement with a Jamin optical interferometer. The semi-infinite diffusion and convective diffusion equations corrected by an experimental factor corresponded well with the experimental results. Les profils de concentration pres d'une cathode de cuivre immergee dans une solution 0.3 mol/L CuSO4 ont ete determines par calcul et experimentalement avec un interferometre de Jamin. L'utilisation d'un facteur experimental de correction a permis d'obtenir, avec les equations de diffusion lineaire semi-infinie et de diffusion convective, une bonne prediction des profils obtenus experimentalement.

Applying a new theory developed in a previous paper, linear sweep voltammetry was used to determine the reaction order and the transfer coefficient for the oxidation reaction of to , using platinum and lead oxide as substrates. Solutions containing up to 50 weight percent were studied. Results show that the oxidation reaction is of the second order when lead oxide is used and of the first order with the platinum substrate. These observations will be used in a subsequent paper to determine the mechanism involved at the lead oxide substrate. The results were verified by measuring hydrogen cathodically evolved and comparing it with the values calculated in this study. Thus, the present work shows the applicability of the new generalized theory of linear sweep voltammetry for irreversible electrode processes.

The oxygen evolution reaction (OER) is the anodic reaction in several industrial electrolytic processes. The objective of this work was to develop a new electrocatalytic material for long-lasting and economical high performance electrodes. New electrodes were prepared by electrodeposition of nickel, nickel-ruthenium and nickel-iridium alloys. They were then activated by anodic polarization at 100 mA cm−2 to form an oxide layer. The electrocatalytic activity was characterized for the OER in 5M KOH solution. The results show that nickel-iridium alloys provide greater electrocatalytic activity for the OER and better corrosion resistance than nickel-ruthenium in alkaline solution. The effects of transition elements on improving the performance of the nickel electrode are then discussed.

A detailed investigation of the mechanism of cathodic potential oscillations of zinc in alkaline solutions is described and analyzed here. The oscillation period is divided into three successive times, each corresponding to a particular phenomenon, which are defined as: the depletion, supersaturation, and recovery time. They are studied experimentally using chronopotentiometric recordings over a large range of conditions (−0.0055 to −0.17 A/cm2 and 0.15–0.9 mmol/cm3 in 8.4 mmol/cm3 aqueous at room temperature) and the results are analyzed theoretically. The nature and relative importance of the different overpotentials are determined and discussed during each one of the three times occurring in each period. The controlling mechanism for both the zinc reaction and zinc complex ion transport is thus deduced and discussed.

Laboratory‐scale experiments of zinc electrowinning under periodical reverse current (PRC) were carried out in acidic sulfate solutions. To study the effects of lead impurities on the zinc cathode, 0.3–15 mg/l of lead were added to the electrolyte. A square wave of current was used to produce the PRC. Current densities of 500 and 1500 A/m2 were investigated under both direct current and PRC. In the case of PRC, the direct and reverse pulses had respective durations of 100s and 0.1–1.0s. The current density of the reverse pulse was set at half the value of the direct pulse. Comparisons were made with conventional dc electrolysis. The presence of 5 mg/l of lead lowered the current efficiency in dc from 94.1 to 93.2%, while in PRC it raised it from 93.2 to 97.6%, using a reverse pulse duration of 0.1s. Correlation between the current efficiencies and the presence of the crystallographic plane (101) was also observed. It suggests that lead in the zinc deposit and the use of PRC influence the crystallographic growth of the zinc deposit. The presence of plane (101) increases the oyerpotential of hydrogen evolution on zinc, and this results in a higher current efficiency. A way of obtaining the beneficial plane is to use PRC and lead in the electrolyte together.

The effects of nickel impurities were investigated during the electrowinning of zinc in acidic media using periodical reverse current (PRC) along with anodic potential current response and cathodic current efficiency. The chemical and structural characteristics of the cathode deposit were also determined using nickel concentrations of 3, 5 and 10 mg l−1 in sulphuric acid (200 gl−1 H2SO4) containing 60 gl−1 of zinc. The cathodic current efficiency drop caused by nickel was less detrimental in PRC than DC. It was found that the morphology of the deposit plays an important role in the redissolution process caused by impurities. The levelling effect caused by PRC decreases the rate of zinc redissolution, which results in an increase of current efficiency. However for concentrations equal to or greater than 10 mgl−1, the levelling effect caused by PRC is no longer dominant. On the anode nickel did not affect the overpotential of the lead-silver electrode in PRC or DC modes.

The purpose of this work is to evaluate the possibility of utilising an ultrafiltration process for the treatment of water from the dam in the Kabylia region of Algeria and, in particular, for the provision of drinking water to people living in dispersed small villages. The water quality was determined by measuring turbidity, and natural organic matter concentration. The results obtained with an ultrafiltration process indicate that this technique can considerably reduce suspended and organic matter. It also improves the bacteriological quality of the treated water. An economic evaluation for ultrafiltration of surface water is presented. The economic study was performed for a drinking water unit of 20 m3/h . It was found that the cost per m3 of treated water ($ 0.235/m3) obtained would not be excessively high for the states of the North African region. WaterSA Vol.27(2) 2001: 199-204

Factorial experiments provide a comprehensive understanding of the impact of operational variables on process performance. Utilisation of the Hadamard matrix taking into account all interaction effects, appeared to be efficient for giving a mathematical model that conformed to criteria validity. The predictions given by the factorial experiments model were confirmed by the experiments. Phenol oxidative degradation kinetics were not significantly influenced by pH or hardness of the solution to be treated, as is predicted by factorial experiments. On the other hand, initial H2O2 concentration, initial phenol concentration and temperature significantly influenced the efficiency of the process. Optimal values were determined: a temperature of about 20°C and a C H2O2 /C phenol ratio of 120 (mg/mg). WaterSA Vol.27(4) 2001: 551-558

Nickel-titanium (NiTi) offers many advantages for the fabrication of coronary stents: shape memory, superelasticity, and radiopacity. However, many authors highlighted the selective dissolution of Ni from the alloy during the corrosion process that could lead to potential toxicity. The improvement of the NiTi stent's corrosion resistance by different surface treatments (electropolishing, heat treatment, and nitric acid passivation) was reported in a previous article. In the present study a comparative biocompatibility evaluation of such stents was performed through in vitro and in vivo assays. A cell proliferation test was completed to evaluate the cytotoxicity of surface treated NiTi using human fibroblasts. Then a stent implantation was performed in rabbit paramuscular muscle to study the inflammatory response generated by the same implants. Cell proliferation tests generally indicated an in vitro biocompatibility of our samples similar to the control group. An in vivo implantation study demonstrated the gradual overall reduction with time of the fibrocellular capsule thickness surrounding the implants. After a 12-week implantation period, the fibrous capsules surrounding the different implants tended toward the same value of 0.07 mm, which suggested that all surface treatments produced a similar biological response. This low value of the fibrocellular capsule indicated that our NiTi surface treated implants were relatively inert.

The growing cost of industrial production and international competition give an increased importance to research in alternative zinc extraction technologies. Among the possibilities, electrowinning in alkaline solutions was presented previously as the most promising. Experiments have been done at high current densities to obtain cell voltage and current efficiency data necessary for specific energy computations

Because of its good radiopacity, superelasticity, and shape memory properties, nickel-titanium (NiTi) is a potential material for fabrication of stents because these properties can facilitate their implantation and precise positioning. However, in vitro studies of NiTi alloys report the dependence of alloy biocompatibility and corrosion behavior on surface conditions. Surface oxidation seems to be very promising for improving the corrosion resistance and biocompatibility of NiTi. In this work, we studied the effect on corrosion resistance and surface characteristics of electropolishing, heat treatment, and nitric acid passivation of NiTi stents. Characterization techniques such as potentiodynamic polarization tests, scanning electron microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy were used to relate corrosion behavior to surface characteristics and surface treatments. Results show that all of these surface treatments improve the corrosion resistance of the alloy. This improvement is attributed to the plastically deformed native oxide layer removal and replacement by a newly grown, more uniform one. The uniformity of the oxide layer, rather than its thickness and composition, seems to be the predominant factor to explain the corrosion resistance improvement.

NiTi shape Memory Alloys (SMA) are potential biomaterial candidates for medical devices such as osteosynthesis staples. However, Ni dissolution induced by uniform or localized corrosion could lead to toxicity. In this work, plasma polymerized tetrafluoroethylene (PPFTE) coating is used to improve the corrosion resistance of NiTi plates and corresponding NiTi stables. The scratch test indicates a good surface adhesion of the film but that it lacks cohesiveness. Potentiodynamic tests in physiological Hank's solution show that PPTFE coating improved the pitting corrosion resistance. The passivation range is increased from 35% to 96% compared to the untreated sample and the pit diameter is decreased from 100 microns to 10 microns. The uniformity of the deposited film is a very important parameter. When the film is damaged, the corrosion seems to increase in comparison to the untreated samples. Otherwise, if the staple is carefully manipulated, the coating follows the large deformations induced by the memory effect of the alloy without cracking, and then, protects efficiently the staple from pitting.

NiTi shape memory alloy presents interesting mechanical properties as surgical implants. However, due to its high amount of Ni which may dissolve and release toxic ions in human fluids, the medical use of this material is a great concern. We have developed a laser treatment which modifies the oxide layer and enhances uniform and localised corrosion resistance of NiTi alloy.In this paper we further analysed the effect of this treatment with potentiostatic and AC impedance measurements in physiological Hank's solution. We conclude that the laser treatment creates a stable passive film which results in improved corrosion resistance of this alloy.

Because of its optimal radiopacity, superelasticity and shape memory properties Nickel-Titanium (NiTi) is an ideal material for the fabrication of stents. Indeed, these properties can facilitate the implantation and precise positioning of those devices. However, in vitro studies on NiTi report the dependency of the alloy biocompatibility and corrosion behavior to surface treatments. Oxidation of the surface seems to be very promising to improve both the corrosion resistance and the biocompatibility of NiTi. The present study investigate the effect of electropolishing, heat treatment (in air and in a salt bath) and nitric acid passivation to modify the oxide layer on NiTi stents. Techniques such as potentiodynamic polarization tests, Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) have been used to develop relationships between corrosion behavior, surface characteristics and surface treatment. Results show that all surface treatments improve the corrosion behavior of the alloy. SEM results indicate that treated stents which exhibit a smooth and uniform surface show a higher corrosion resistance than non treated stents which possess a very porous oxide layer. AES results, indicate that the best corrosion behavior was observed for the stents which exhibit the thinnest oxide layer (electropolished and passivated samples).

Periodical reversed curve experiments were conducted in H2SO4 (200g l−1) and Zn2+ (60 gl−1) solutions at 40°C. The direct current densities were between 300 and 2000 A m−2, and the inverse current densities were half of these values. The cycle durations were 10,30 and 100s, while the inversion times were 2.00, 0.10, 0.30, 0.01 and 0.03sFor the lowest cycle frequency and inversion ratios (f = 0.60 cycle min−1 and τ = 0.1%), we obtained an increase in current efficiency and also in productivity. Power consumption was greatly reduced. The quality of the deposits was equal or better than those obtained by direct current. The effect of the inversion was more apparent at current densities greater than 500 A m−2. Resume Des essais d'application de courants periodiques inverses ont ete effectues a 40°C en solution aqueuse d'H2SO4 (200g l−1) et de Zn2+ (60gl−1). Les densites de courant direct de 300 a 2000 Am−2 ont ete utilisees, alors que les densites de courant inverses etaient la moitie de ces valeurs....

Electrode kinetic studies of molten lead in fused chloride have shown anodic and cathodic passibation. This process can be predicted from phase diagrams, and results from solid precipitates on the metal. For small polarization, the process is diffusion-controlled, and permits chronoamperometric determination of the diffusion coefficient. Resume La cinetique de la reduction et de l'oxydation d'une electrode en plomb liquide dans des melanges de chlorures fondus est etudiee. Des passivations anodiques et cathodiques ont pu etre mis en evidence lors de polarisations potentiostatiques. Ce phenomene est predictable a partir de diagrammes de phase et resulte de precipitations solides sur le metal. Pour de faibles polarisations, le procede d'electrode est controle par diffusion, et le coefficient de diffusion a pu etre determine par chronoamperometrie.

Zinc electrowinning tests from acidic chloride solutions showed that metallic impurities can be classified in the following order of detrimental effect on current efficiency: Sb>Co, Ni>Cu. This effect increased with higher HCl concentrations. Analysis of the impurity content of the zinc deposits showed the regular codeposition of Cu and the anomalous codeposition of Ni and Co.

The development of new cheaper technological alternatives to water electrolysis for the production of hydrogen creates the need for a better understanding of irreversible electrode reactions with a reaction order higher than 1. This communication presents in the first part the mathematical derivation of a generalized theory of linear sweep voltammetry for irreversible electrode processes. It makes it possible to study the mechanisms and electrochemical reactions and to determine reaction orders of 1 and higher. Previously, electrode kinetics investigations were limited in this case to the study of processes characterized by a reaction order of 1. In the second part, an experimental investigation of the anodic oxidation of will show reaction orders of 1 and 2, depending on the nature of the substrate.

Essais de laboratoire en milieu sulfate acide, sous des densites de courant entre 500 et 1500 A/m 2 , avec une impulsion directe d'une duree de 100 s, et une impulsion inverse de 0,1 a 1,0 s. Comparaison avec l'electrolyse habituelle en courant continu. Proposition d'un mecanisme confirmant l'effet benefique de ce procede sur la consommation specifique d'energie

Cathodic galvanostatic polarization studies of niobium in aqueous acid solutions at 25 C show a Tafel slope of 138 mV/decade and a reactional order of unity with respect to the concentration of hydrogen ions. This observation coupled with published thermodynamic and kinetic data indicates that the mechanism of Heyrovsky is valid for the hydrogen evolution reaction on niobium. Studies on the anodic behavior of the metal based on potentiostatic anodic polarization followed by chronoamperometry, and scanning electron microscopy confirm the formation of stable films during the polarization process.

The corrosion behavior of a series of Nb-Ni alloys containing 10 to 98% Ni was investigated in a 25% KOH solution at 25 C. It was found that the alloys containing 10 and 31% Ni, which are composed of δ and γ phases, essentially disintegrate during corrosion in this environment. Disintegration is caused not by dissolution, but by selective hydride formation in the δ phase between the grains of the γ phase. Alloys containing more than 47% Ni have very high corrosion resistance to the solution and do not exhibit rapid disintegration.