Prepassive Film Research Articles

Improvement of the erosion-corrosion resistance of magnesium by electroless Ni-P/Ni(OH)2-ceramic nanoparticle composite coatings

Abstract In this study, Ni-P/Ni(OH) 2 -ceramic nanoparticle composite coatings were directly deposited onto commercially pure magnesium in order to improve its resistance to erosion-corrosion damage. The effect of three incorporated ceramic nanoparticles (TiO 2 , SiC and diamond) on the erosion-corrosion resistance of the composite coatings was also investigated. The composite coatings were obtained by an electroless process and were characterized using scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The erosion-corrosion behavior of fabricated composite coatings was elucidated using in situ techniques of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). It was found that the simultaneous formation of Ni-P and β-Ni(OH) 2 phases in the coating and the improvement in the micro hardness of the coating were due to the incorporation of nanoparticles. According to the polarization curves and EIS spectra, the β-Ni(OH) 2 compound behaves like a pre-passive film which is responsible for substantial improvement in the anticorrosion properties of the coating. Better erosion-corrosion resistance was obtained for the composite coatings than the neat Ni-P coating. This was a consequence of the β-Ni(OH) 2 co-deposition. The formation of the β-Ni(OH) 2 compound in the coating does not depend on the nature and concentration of the nanoparticles.

Influence of Pb ++ ions on the dissolution and passivation of nickel and Ni–21Cr in acidic solutions

The deleterious effect of dissolved Pb ++ on passivity of Ni and Ni–21Cr has been explored at 90 °C using two solutions: 0.1 M perchloric acid, and a pH 3.5 acetic acid/sodium acetate buffer. Pb ++ strongly inhibits true (low-potential) active dissolution of pure Ni; this is consistent with underpotential deposition (UPD) of elemental Pb, apparently a new observation. The range of potentials where this occurs is greater for the more acidic solution. By inoculating Pb ++ at different potentials, the maximum underpotential can be shown to be at least 300 mV. In the less-aggressive acetic acid environment, a ‘pre-passive’ state of Ni is more noticeable than in the perchloric acid, and in contrast to the true active region, this region is subject to a strong activating effect of Pb. Dissolution of Ni proceeds rapidly on a surface that is trying to form its pre-passive film but is partly covered by Pb. The time-dependence of the passive current in the acetic solution is altered subtly by incorporation of Pb into the metal-film interface, such that the normal decay with time is truncated, leading to a higher long-term dissolution or film thickening rate. The presence of 21% Cr suppresses active dissolution, greatly ennobles the open-circuit potential, and eliminates (for these particular conditions) both the inhibiting and the activating effects of Pb. The relevance of these results to corrosion and SCC caused by lead in nuclear power systems is briefly discussed.

A study on transition of iron from active into passive state

An investigation was carried out on the transition of an iron electrode from active to passive state in a sulphuric acid solution. It was found that the active–passive transition was an auto-catalytic process in which a pre-passive film grew on the electrode surface. The growing pre-passive film had a fractal edge whose dimension was affected by the applied passivating potential and the presence of chlorides in the solution. Applying a more positive passivating potential led to a faster active–passive transition and resulted in a more irregular pre-passive film. If chlorides were introduced into the sulphuric acid solution, the active–passive transition became more rapid and the pre-passive film more irregular. Apart from the influence on the growth of the pre-passive film, the presence of chlorides in the passivating solution was found to deteriorate the stability of the final passive film. All these phenomena can be understood if the passivating iron electrode is regarded as a dissipative system. To explain these results, a fractal pre-film model is proposed in this paper.

Effect of the Scan Rate on the Kinetic Parameters of Active Dissolution and Passivation of Iron in a Neutral Solution

The effect of the potential scan rate (V = 0.2–100 mV/s) of a rotating disk electrode (rotational speed ν = 6000 rpm) on the kinetics of active anodic dissolution and active-passive transition of Armco iron in a deaerated borate buffer (pH 7.40) was studied by cyclic voltammetry. The rates of active dissolution and the formation of a prepassive film were found to be determined, under free-diffusion conditions, by slow electrochemical steps of electron transfer throughout the V range studied; the cyclic voltammogram is a transient, thermodynamically nonequilibrium curve. The anodic current peak linearly grows and its potential is shifted in the positive direction with an increase in logV. The apparent coefficients of electron transfer for active anodic dissolution depend on V in the whole range studied. This can provide explanation to a large scatter of literature data on the active anodic dissolution and active-passive transition of iron in neutral media.

Passivity and pitting of carbon steel in chromate solutions

The passivity and pitting behavior of A516-70 carbon steel in chromate solutions were studied using electrochemical measurements. The anodic Tafel slopes in the active region show that carbon steel dissolution involves two mechanisms in this range: formation and further oxidation of a pre-passive film of Fe(OH) 2. The first current peak at −0.228 V (Ag | AgCl) in cyclic voltammograms is caused by the oxidation of the pre-passive film and the formation of a stable passive film of Cr 3++Fe 3+. The second peak at 0.612 V is ascribed to the oxidation of Cr 3+ in passive film to Cr 6+. The charge-transfer step at the electrode/solution interface controls the film formation and dissolution; the role of diffusion is negligible. Chromate ions play a prominent role in the formation of passive film, but hardly affect the stability of the passive state. More chromate ions in solution enhance the dissolution of Cr 3+ at the second peak potential. Upon addition of chloride ions metastable pits are initiated, as indicated by a typical current transient: a quick current rise followed by a slow recovery. A maximum exists in the potential dependence of the pit initiation rate. Metastable pit growth is controlled by the ohmic potential drop mainly across the cover over the pits. Increasing potential is beneficial to the repassivation of metastable pits, as indicated by the decreasing average repassivation time. A pit stabilization criterion, the ratio of peak pit current to pit radius, must exceed 6×10 −2 A cm −1 during pit growth to avoid repassivation in the present system.

The passivation of nickel in 0.5m sulphuric acid

The aim of the work presented here is to investigate the formation of the prepassive film on nickel at the corrosion potential in order to obtain more knowledge about the influence of the formation of such a film on the voltammograms from which conclusions are often drawn with respect to the mechanism of the initiation of film formation and of the growth mechanism of the passive film

On the corrosion characteristics of some commercial magnetic metallic glasses in NaCl solution

The corrosion characteristics of six commercial magnetic metallic glasses, namely Fe78B13Si9 (Metglas 2605-S-2), Fe67Co18B14Si (Metglas 2605 Co), Fe40Ni40B20 (Vitrovac 0040), Fe39Ni39Mo2(SiB)20 (Vitrovac 4040), Fe40Ni38Mo4B18 (Metglas 2826 MB) and Fe40Ni40P14B6 (Metglas 2826) in which iron and boron are common base elements have been studied by immersion tests and potentiostatic techniques in various concentrations of NaCl solutions at room temperature. In exposure for up to six days, weight loss observations indicated that the corrosion rates in 3.5% NaCl were in the following increasing order: 2826 < 4040 < 0040 < 2826 MB < 2605 Co < 2605-S-2. During exposure for up to four hours under open-circuit conditions, 2826 alloy showed the noblest behaviour while 2605-S-2 was the least noble. All the alloys, except 2826, showed rapid dissolution without any passivation during anodic polarization. Phosphorus addition to Fe-Ni-B glass enhanced the active dissolution and resulted in the formation of a black prepassive film in the active region (0.2V) which becomes protective in the passive region (0.3 to 1.25V). The values ofIcrit. andIpass. (the critical and passive current densities) decreased with a decrease of concentration from 3.5 to 0.01% NaCl, while in 0.001% NaClIpass. slightly increased and the passivation potential range decreased. The corrosion resistance of Fe-B metallic glasses increased with metal addition in the order Co < Mo < Ni and with metalloid addition in the order Si < P.

Passivation of zinc in concentrated alkaline solution—II. Role of various experimental factors and the distinction between the solid-state and dissolution—precipitation mechanisms

Pseudo steady-state current—potential measurements have been made during the dissolution and passivation of zinc electrodes in 6.8 mol dm−3 (30% w/w) KOH solutions over a wide potential range. Thepre-passive characteristics are very sensitive to impurities,viz. iron. Similarly,ir drop has an appreciable effect in this region necessitating full correction if measured potentials are to have any quantitative significance. Amalgamation exerts a considerable influence but only in the pre-passive region where the pre-passive film is considerably more inhibiting than that formed on unamalgamated zinc. It is suggested that this film could be derived from intermediates of the form Zn (OH)−2 when the potential reaches a critical value. A high degree of reproducibility observed in thetransition region upon sweep reversal indicates that the potential is also the important parameter controlling the initiation of thepassive Zno/Zn (OH)2 film and not supersaturation/solubility effects. Active—passive characteristics are identical on single crystal and polycrystalline electrodes except in the transition region, where cosiderably less stability exists in the case of the polycrystal. This is interpreted in terms of an electrochemical spectrum for passive film formation/removal on different crystal planes. Polarization data from rotating disc experiments have been analysed in respect of the formation of both thepre-passive andpassive films. Evidence has been sought which would support a solid-state mechanism (constant potential of passivation under conditions where the supersaturationdecreases with increase in electrode rotation speed) or a dissolution—precipitation mechanism (constant supersaturation at the point of passivation under conditions where the passivation potentialincreases with increase in electrode rotation speed). Only evidence in favour of the former mechanism has been obtained for both film types.

The electrochemical behaviour of iron in stagnant and stirred potassium carbonate-bicarbonate solutions in the 0–75°C temperature range

The corrosion and passivation of polycrystalline iron electrodes in carbonate-bicarbonate solutions are studied in the 0–75°C temperature range. The influence of the solution ionic strength, stirring velocity, and potential scan rate on the electrodissolution of the base metal and the formation of both the prepassivating and the passivity surface layers are considered. The chemical dissolution of the prepassive film and the electroformation of the different surface compounds are discussed in terms of a complex reaction pathway involving both simultaneous and consecutive stages including the corresponding ionic equilibria.

Anodic Corrosion Rate Measurements in LiCl ‐ KCl Eutectic: II . Results on Nickel, Molybdenum, and Stainless Steel

The anodic dissolution characteristics of nickel, molybdenum, and 304 stainless steel have been examined in pure and eutectic melt. Molybdenum and nickel show Tafel‐type dissolution kinetics in pure eutectic which permit estimates of long‐term corrosion rates as a function of voltage. Nickel exhibits a sharp threshold potential for dissolution in melt, forming a nonpassivating layer. Comparative voltammetry and open‐circuit potential measurements with iron in this melt suggest that care may be required in using nickel as an iron sulfide current collector. The anodic dissolution of 304 stainless steel in melt appears to be rate limited by diffusion through a reaction layer, showing a dependence that may be applicable to long‐term corrosion predictions. Dissolution is strongly inhibited by dissolved , apparently by formation of a protective anodic oxide layer. Molybdenum appears to owe its excellent anodic corrosion resistance in melt both to a chemically formed prepassive film and to a well‐defined anodic passivation process. However, repetitive cycling to voltages cathodic of 1.5V vs. the lithium electrode may be deleterious. Anodic corrosion of metals should, in general, occur more readily in the melt than in pure for straight‐forward thermodynamic reasons.

Kinetics and mechanism of the nickel electrode—II. Acid solutions containing a high concentration of sulphate and nickel ions

The kinetics of the Ni electrode in acid solutions with a high sulphate and nickel ion concentration has been investigated in the range of 25–75°C. The active dissolution and the passive regions and the active-passive transition phenomena have been studied employing different potential perturbation techniques using both still and stirred solutions. Two electrochemical processes are competing within the prepassive film potential region, namely, the active Ni dissolution to Ni(II) ions and the Ni(OH) 2 film formation. Nickel passivation is explained by reaction pathways involving successive electrochemical and chemical steps implying the occurrence of hydroxo- and oxo-species as reactions intermediates. The advanced mechanism is based upon a positively charged Ni surface structure and attributes the onset of the complete passivity to a particular surface oxide species.

ChemInform Abstract: THE ANODIC DISSOLUTION OF NICKEL. II. BROMIDE AND IODIDE ELECTROLYTES

AbstractDie Kinetik der anodischen Ni‐Auflösung in sauren Bromid‐ und Jodidlösungen wird mit Hilfe einer potentiostatischen "sweep"‐Methode untersucht.

The anodic dissolution of nickel—II. Bromide and iodide electrolytes

The kinetics of the anodic dissolution of nickel were studied in acidic bromide and iodide solutions using a potentiostatic sweep technique. The rate of dissolution is almost unaffected by the halide at low concentrations due to the presence of a prepassive film. At higher halide concentrations the prepassive film is removed and active dissolution occurs. The reaction is first order in Br −, zero order in I − and independent of pH for pH < 2. The Tafel slope is 82 mV, in accord with earlier work in chloride solutions.

ChemInform Abstract: CYCLIC VOLTAMMETRIC STUDIES OF ELECTROLESS COBALT IN NAOH

Abstract The electrochemical behaviour of electroless cobalt in 1N NaOH was studied at 35, 60 and 85°C by cyclic voltammetry. Three anodic peaks corresponding to the formation of Co(OH) 2 /CoO, Co 3 O 4 , Co OOH were observed. The observed cathodic peaks were due to the reduction of the higher cobalt oxides to Co(OH) 2 and also due to the reduction of Co(OH) 2 to cobalt. The variation of peak potential with sweep rate was found to be appreciable only in the case of anodic peak (I). The total charge Q T , for the passivation to occur was obtained by estimating the area under the first anodic peak at each sweep rate. It was found that the Q T value decreases with increase of sweep rate. The increase of peak current with increase of sweep rate has been explained as due to the insufficient time available for the film growth at the reversible potential, and that the dissolution of the metal continues until a potential at which the rate of film growth exceeds that of active dissolution is reached. It has been suggested that the passivating film is CoO while the prepassive film is Co(OH) 2 . The shift of the anodic peak (I) potentials to more anodic values compared to that for pure cobalt is probably due to the presence of phosphorus in the cobalt deposit.

Cyclic voltammetric studies of electroless cobalt in NaOH

The electrochemical behaviour of electroless cobalt in 1N NaOH was studied at 35, 60 and 85°C by cyclic voltammetry. Three anodic peaks corresponding to the formation of Co(OH) 2/CoO, Co 3O 4, Co OOH were observed. The observed cathodic peaks were due to the reduction of the higher cobalt oxides to Co(OH) 2 and also due to the reduction of Co(OH) 2 to cobalt. The variation of peak potential with sweep rate was found to be appreciable only in the case of anodic peak (I). The total charge Q T , for the passivation to occur was obtained by estimating the area under the first anodic peak at each sweep rate. It was found that the Q T value decreases with increase of sweep rate. The increase of peak current with increase of sweep rate has been explained as due to the insufficient time available for the film growth at the reversible potential, and that the dissolution of the metal continues until a potential at which the rate of film growth exceeds that of active dissolution is reached. It has been suggested that the passivating film is CoO while the prepassive film is Co(OH) 2. The shift of the anodic peak (I) potentials to more anodic values compared to that for pure cobalt is probably due to the presence of phosphorus in the cobalt deposit.

The anodic dissolution of nickel—1: Perchlorate and fluoride electrolytes

A potentiostatic sweep technique has been used to study the anodic dissolution of nickel in acidic perchlorate, acetate and fluoride solutions. At slow potential sweep rates a prepassive film exists throughout the anodic region in perchlorate and acetate electrolytes. By the use of fast sweeps, or by the addition of F −, film formation and growth is sufficiently reduced to reveal a linear anodic. Tafel region. The rate of active dissolution, which is independent of [H +] and [F −], obeys the following rate law; i = 2 Fka w exp [β FE/RT], with β = 0·53. The following mechanism is proposed for active dissolution, with the first step rate-determining: (1) Ni + H 2O → NiOH ads + H + + e −, (2) NiOH ads → NiOH + + e −, (3) NiOH + + H + ⇌ Ni 2+ + H 2O. Prepassivation is thought to occur from the intermediate NiOH ads through a solid state mechanism.

Electrodissolution Kinetics of Iron in Chloride Solutions: IV . Alkaline Solutions Containing Benzotriazole

The anodic dissolution of iron in alkaline chloride solutions in the presence and absence of benzotriazole has been investigated by potentiostatic, galvano‐static, and potential sweep polarization. The steady‐state and transient polarization experiments indicate that iron dissolution occurs in the absence (active region) and presence (prepassive region) of a porous prepassive surface film. Anodic Tafel slopes of 60 mV/decade were obtained below (active region) and above (prepassive region) the formation potential of the prepassive film on both uninhibited and inhibited iron indicating the same mechanism of iron dissolution. The results suggest that the prepassive film merely decreases the effective surface area for iron dissolution. The effect of benzotriazole is to decrease further the effective surface area.

Ellipsometric investigations of anodic film growth on iron in neutral solution. Prepassive film

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEllipsometric investigations of anodic film growth on iron in neutral solution. Prepassive filmJ. O'M. Bockris, H. Wroblowa, and V. BrusicCite this: J. Phys. Chem. 1971, 75, 18, 2823–2829Publication Date (Print):September 1, 1971Publication History Published online1 May 2002Published inissue 1 September 1971https://doi.org/10.1021/j100687a019RIGHTS & PERMISSIONSArticle Views62Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (702 KB) Get e-Alerts

The mechanism of formation of pre-passive films on nickel: a chronoellipsometric study

The authors have previously shown that the anodic passivation of nickel in acid solutions is a two-stage process; the first stage of which involves the formation of a pre-passive film. In this study, the mechanism of formation of the precursor film on nickel in a 0.5 M K2SO4 (pH = 3.1) solution has been investigated by means of the technique of chronoellipsometry which consists of the ellipsometric in situ monitoring of the anode surface during a galvanostatic experiment. The main finding is that, before the pre-passive film forms, there must elapse an induction time which is affected by the current density and mass-transport factors. The nature of the dependence of the induction time upon current density indicates that the pre-passive film is formed by a dissolution–precipitation mechanism. It is proposed that the pre-passive film consists of precipitated Ni(OH)2.

The mechanism of passivation of nickel as determined by an automatic recording ellipsometer

The process of anodic passivation of nickel in acid solutions has been investigated by means of an automatic recording ellipsometer in which the light emerging from a rotating analyzer has been electronically processed to yield a continuous read-out of the changes of polarization state of light reflected from a nickel anode during a galvanostatic transient. Digital computer analysis of the ellipsometric data has revealed: (a) the existence of an induction time for film formation; (b) a linear growth law for the film during a time interval commencing with the induction time and ending before the passivation time; (c) the occurrence of passivation when the absorption coefficient of the film jumps from a near-zero value to a fractional value; and (d) continuous changes of the refractive index of the film during the period of film growth. These phenomena are consistent with a model in which (a) a pre-passive film forms and thickens by a dissolution–precipitation mechanism, (b) the growth of the film is accompanied by its electrochemical oxidation, (c) the film growth–oxidation process continues until the pre-passive film is transformed into an electronically-conducting material, and (d) the conversion of the pre-passive film into an electronic conductor constitutes the essence of the so-called active–passive transition.