Corrosion and impressed current cathodic protection of copper-based materials using a bimetallic rotating cylinder electrode (BRCE)

A bimetallic rotating cylinder electrode (having individual electrode areas of 10 cm² and rotating at 200-1400 rpm) has been used to examine the corrosion and protection characteristics of copper/nickel aluminium bronze and 90-10 copper-nickel/nickel aluminium bronze galvanic couples in filtered seawater at 25 °C. The flow-influenced electrochemistry of the systems was determined using zero resistance ammetry, corrosion potential measurements and a potential step current transient technique. In each case, the galvanic corrosion potential and corrosion rate displayed a Reynolds number dependency where mass transport control of the anodic dissolution reaction partially controlled the reaction rate. Bimetallic impressed current cathodic protection (ICCP) has also been demonstrated for a range of applied protection potentials and Reynolds numbers. A comparison has been made between the directly measured bimetallic ICCP current demand and that determined from independent, single-metal rotating cylinder electrode measurements. In this case, the mixed charge and mass transport controlled rate of oxygen reduction was examined.     

A Flow Line for Laser Diagnostics of Corrosion Damage

A method of laser ellipsometric diagnostics of corrosion layers on a great number of samples in laboratory and field conditions is presented. A procedure of laser monitoring is proposed and verified; it allows to remotely control the corrosion layer thickness. A highly sensitive return-path double-reflection optical-electrochemical cell is developed. Basic methodological aspects of using a remote-control laser-ellipsometric probe in a flow line for the laser corrosion monitoring in corrosion tests are illustrated by the example of continuous corrosion monitoring of copper–nickel alloy in saline water.     

Electrochemical oxidation of binary copper-nickel alloys in cryolite melts

Anodic oxidation of copper, nickel and two copper-nickel alloys was studied in cryolite melts at 1000 °C. In an oxide-free melt, anodic dissolution of each material was observed, and the dissolution potential increases with the content of copper. SEM characterization of a Cu55-Ni45 alloy showed that nickel is selectively dissolved according to a de-alloying process. In an alumina-containing melt, a partial passivation occurs at the copper-containing electrodes, at potentials below the oxygen evolution potential. A passive film forms on the copper electrode, while on the nickel electrode no dense oxide layer develops. Copper-nickel alloys were found to form a mixed oxide layer. At higher potentials, the formation of oxygen bubbles on the electrodes results in a degradation of the passive films and a strong corrosion.     

The electropolymerization of pyrrole at a CuNi electrode: corrosion protection properties

Pyrrole was successfully electropolymerized at a copper–nickel electrode in a near-neutral sodium oxalate solution containing Cu²⁺ cations to generate a homogenous and adherent polypyrrole film. The presence of the Cu²⁺ ions increased both the rate of the electropolymerization reaction and the adherence of the polymer at the CuNi interface. In the absence of these cations, oxidation of the electrode occurred generating a nickel-rich layer that was not sufficiently conducting, under the electropolymerization conditions employed, to facilitate the electron-transfer reaction and the electropolymerization of pyrrole.These films remained stable and exhibited significant corrosion protection properties in acidified and neutral 0.1 mol dm⁻³ NaCl solutions even on polarization of the electrodes to high anodic potentials.     

Electrodeposition of tin, copper and tin-copper alloys from a methanesulfonic acid electrolyte containing a perfluorinated cationic surfactant

Tin, copper and tin-copper alloys were electrodeposited from a methanesulfonic acid electrolyte containing a perfluorinated cationic surfactant at 296 K. The electrolyte composition was 0.02 to 0.05 mol dm^− 3 SnSO₄, 0.02 to 0.2 mol dm^− 3 CuSO₄, 12.5 to 15% vol MSA (1.9 to 2.3 mol dm^− 3 CH₃SO₃H, pH < 1), 0.01 mol dm^− 3 hydroquinone and 0.008 to 0.012% vol perfluorinated cationic surfactant. Electrodeposition was studied at a rotating disc electrode (RDE), a rotating cylinder electrode (RCE) and a rotating cylinder Hull (RCH) cell. Cyclic voltammetry and linear sweep voltammetry were used to investigate the current-potential relationships at static and rotating disc electrodes. Tin-copper alloys were deposited over a wide range of operating conditions to produce surface finishes from dark-grey (3 to 9 wt.% Cu), light-brown (50 to 60 wt.% Cu) and golden-yellow (70 to 80 wt.% Cu). The influences of copper(II) and surfactant concentration, applied current and surfactant adsorption were investigated; while the surface microstructure and composition of the deposits were studied.     

Untersuchungen zur Korrosion und zum Korrosionsschutz von meerwassergekühlten Rohrkondensatoren aus Kupferbasislegierungen-Versuche mit rotierenden Proben

Investigations on the corrosion and corrosion protection of seawater cooled condensor tubes of copper-base alloys - Experiments with rotating samples Experiments have been done on rotating disc and cylinder electrodes of CuZn20Al2, CuNi10Fe and CuNi30Fe in 3 w/o sodium chloride solution and in artificial sea water at 25 and 40 ° C. Erosion corrosion of sea water cooled tube condensors should be simulated and studied. The corrosion mechanism of copper base alloys in clean and polluted sea water was intensely studied with particular consideration to the influence of ammonia, sulfides and chlorine. The effectiveness of iron sulfate dosing was tested. With the rotating samples under test no erosion corrosion could be detected on free corroding specimens.     

EDM performance of Cr/Cu-based composite electrodes

Electrode materials for electrical discharge machining (EDM) are usually graphite, copper and copper alloys because these materials have high melting temperature, and excellent electrical and thermal conductivity. The electrodes made by using powder metallurgy technology from special powders have been used to modify EDM surfaces in recent years, to improve wear and corrosion resistance. However, electrodes are normally fabricated at high temperatures and pressures, such that fabrication is expensive. This paper proposes a new method of blending the copper powders contained resin with chromium powders to form tool electrodes. Such electrodes are made at low pressure (20 MPa) and temperature (200 °C) in a hot mounting machine. The results showed that using such electrodes facilitated the formation of a modified surface layer on the work piece after EDM, with remarkable corrosion resistant properties. The optimal mixing ratio, appropriate pressure, and proper machining parameters (such as polarity, peak current, and pulse duration) were used to investigate the effect of the material removal rate (MRR), electrode wear rate (EWR), surface roughness, and thickness of the recast layer on the usability of these electrodes. According to the experimental results, a mixing ratio of Cu–0wt%Cr and a sinter pressure of 20 MPa obtained an excellent MRR. Moreover, this work also reveals that the composite electrodes obtained a higher MRR than Cu metal electrodes; the recast layer was thinner and fewer cracks were present on the machined surface. Furthermore, the Cr elements in the composite electrode migrated to the work piece, resulting in good corrosion resistance of the machined surface after EDM.     

Influence of copper on amorphous nickel based brazing alloy

Abstract

Brazing of stainless steel using nickel based alloys has sometimes been avoided, in spite of its various advantages, because it is a somewhat unreliable process in terms of the mechanical characteristics and corrosion resistance of the brazed joints. Addition of copper to amorphous Ni–Cr–B–Si brazing alloys has been shown to be a promising method of improving the performance of joints. Because copper can form a solid solution with nickel at any concentration, addition of copper has a great effect on the microstructures of the nickel based filler metal and braze seam, by improving the volume ratio of nickel based solid solution to the embrittled intermetallic compounds. As a result, a significant increase in the critical brazing clearance (CBC) was obtained in the present work. Furthermore, copper might increase the electrode potential of nickel based solid solution, so that addition of copper could improve the corrosion resistance of the brazed joints. The results show that an appropriate copper addition to the present Ni–Cr–B–Si group amorphous brazing foil provides an effective method of overcoming the weaknesses of joints brazed using conventional nickel based filler metals, such as low value of CBC and low corrosion resistance.     

Corrosion–electrochemical Behavior of Al–Zn–rem Alloys in the Presence of Polyvanadate-ions

The corrosion behavior of Al–Zn–REM alloys in vadanate solutions is studied by voltammetry and X-ray photoelectron spectroscopy. Zinc is found to selectively dissolve from the alloys in solutions with a low content of hydroxide-ions. Diffusivities in an Al–Zn–Sc alloy are determined depending on the potential. The corrosion resistance of Al–Zn (45 at. %) alloy can be substantially enhanced by microalloying with REM (0.1 at. % of Sc, Pr, Nd, Ce, or Y).     

Peculiarities of the Anodic Dissolution of a Powder NiSi Electrode

The dissolution of solid and powder NiSi electrodes in a 0.5 M H₂SO₄containing 0–50 mM sodium fluoride is studied by methods of quasi-steady-state and cyclic voltammetry. The powder electrodes are inferior to solid ones in corrosion resistance and are less readily passivated compared to smooth NiSi and even Ni electrodes. The anodic dissolution rate of NiSi considerably increases in the presence of fluoride; the effect being more pronounced in the case of smooth electrode.     

Oxidation of Two Ternary Cu–Ni–20 wt.% Cr Alloys at 700–800°C in 1 atm O2

Two ternary Cu–Ni–Cr alloys containing approximately 20 wt.% chromium, but with a different Cu and Ni content, have been oxidized in 1 atm of pure oxygen at 700–800°C. The alloy containing about 60 wt.% nickel (Cu–60Ni–20Cr) was composed of a single solid-solution phase and formed external scales of chromium ocide with an outermost layer containing a mixture of copper and nickel oxides. The alloy comprised of about 40 wt.% nickel (Cu–40Ni–20Cr) contained a mixture of two metal phases and formed complex external scales, containing copper oxide and a nickel–chromium spinel plus a region where islands of the metallic phase richer in chromium surrounded by a thin chromia layer were mixed with oxidized islands rich in copper and nickel, producing a situation out of equilibrium. With time, a very irregular and thin but essentially continuous layer of chromia formed at the base of the mixed internal region for this alloy, producing a gradual decrease of the corrosion rate down to very low values. The oxidation behavior of the two alloys is interpreted in terms of their different microstructure. In particular, the fast initial oxidation of Cu–40Ni–20Cr, associated with the formation of large amounts of copper oxides, is attributed to restrictions in chromium diffusion in the alloy due to the simultaneous presence of two metal phases.     

Morphology and Corrosion Properties of Electroplated Ni–Cr Alloy Coatings in Salt Solutions

The relationship between the morphologic and corrosion properties of electroplated binary Ni–Cr alloys is examined. Codeposition of chromium with nickel changes the morphology of the coating, through the microcracks of which the corrosion of copper starts and accelerates by forming corrosion cells (between the substrate and coating) in an acidic 5% NaCl solution (pH 3.1). In neutral media, the substrate is protected from corrosion not only by the passive Ni–Cr coating, but also by insoluble copper compounds that block the coating microcracks, which manifests itself in inhibiting the corrosion. Upon a long exposure to acidic NaCl solutions, uniform corrosion of the Ni coating gives way to pitting corrosion.     

Corrosion and corrosion testing of magnesium alloys

The corrosion behaviour of magnesium alloys is not substantially comparable to other metals, such as iron, nickel and copper. It is always accompanied by hydrogen evolution. More hydrogen is evolved at a more positive potential or a higher anodic current density. The ‘strange’ hydrogen evolution behaviour is a common phenomenon for magnesium alloys and it is called negative difference effect (NDE). The NDE continues to receive considerable discussion. Furthermore, the corrosion behaviour of magnesium alloys depends mainly on the pH value of the surrounding electrolyte. Voluminous reaction products, formed in neutral electrolytes, lead to a diffusion‐controlled dissolution on the surface of the underlying magnesium alloy. Therefore, influences from structure and alloying are suppressed very strongly. In alkaline environments, passivation occurs as a result of the formation of a hydroxide layer on the magnesium surface. Therefore, differences in the corrosion behaviour between the alloys are hardly detectable. Measurable effects can only be detected using very ‘aggressive’ corrosion conditions. Present methods do not adequately take into account the specific character of the corrosion of magnesium alloys. It can be better characterized using a rotating disc electrode for electrochemical measurements, which enables model defined flow conditions on the surface. Furthermore, the application of electrochemical noise offers the possibility of a simple and sensitive assessment of the corrosion susceptibility of magnesium alloys. Due to the high sensitivity of this measurement procedure, it is also possible to carry out examinations under more practical conditions.     

Effect of boron and hafnium on the corrosion resistance of high-temperature nickel alloys

Conclusion Introduction of 0.1% B and 1% Hf into low-carbon corrosion-resistant nickel alloys makes it possible to increase their resistance to high-temperature salt corrosion. In this case, it becomes possible to increase the heat resistance of the alloys while maintaining the high corrosion resistance as a result of the increase in the titanium and aluminum content.Central Scientific-Research Institute of Corrosion of Metals "Prometei" St. Petersburg. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 17–20, April, 1992.     

Corrosion of metals and alloys in molten glasses. Part 2: nickel and cobalt high chromium superalloys behaviour and protection

Electrochemical methods have been used for the characterisation of high chromium alloys corrosion in molten glasses (cobalt and nickel base alloys in a borosilicate glass at 1050 °C, with rotating working electrodes). All the tested alloys are active but passivable materials. The active state is characterised by a rapid dissolution of the constitutive elements of the alloy in the glass melt. The passive state can be obtained by an air oxidation of the alloys (called preoxidation) or with a temporary anodic polarisation of the alloy. The obtained passive state is due to the presence of a thin protective chromia scale.     

Comparing the anodic reactions of Ni and Ni–P amorphous alloy in alkaline solution

The anodic reactions of amorphous Ni–P alloys prepared by electroless plating were compared with pure Ni in 6 M KOH. The structure and surface components of Ni–P alloys before and after cyclic voltammetry (CV) scan were verified by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The CVs of Ni and Ni–P show many differences. Their CV properties are compared in different potential regions. The variation of the total anodic charge density suggests that the corrosion resistance of Ni is superior to that of amorphous Ni–P alloy in 6 M KOH under potential polarization.     

Electrochemical studies of propargyl alcohol as corrosion inhibitor for nickel, copper, and copper/nickel (55/45) alloy

The electrochemical behaviour of copper, nickel and copper/nickel (Cu55/Ni45) alloy in 0.50 M H₂SO₄ in the absence and presence of propargyl alcohol has been studied. The results indicate that the electrochemical behaviour of the copper/nickel alloy is similar to that of nickel. The interaction between the electrode surface and the organic compound is a relatively fast process and depends on the adsorption potential and alcohol concentration. Anodic currents associated with the electrooxidation of the metals decrease in the presence of propargyl alcohol. Differences in inhibition experience by the three electrodes are discussed in terms of cyclic voltammetry, potentiometry and impedance measurements.     

Effect of Mg Additions and Thermal Treatment on Corrosion Properties of Al–Li–Cu-Base Alloys

An investigation on the corrosion and electrochemical behavior of experimental and industrial semifinished items of Al–Li–Cu–base alloys offers possibilities of increasing the corrosion resistance of aluminum–lithium alloys by alloying and an nontraditional thermal treatment. Magnesium added in a concentration of no more than 0.4% leads to a improvement of the corrosion and mechanical characteristics of the alloy, whereas increasing its concentration up to 1.0% deteriorates all the corrosion characteristics. An investigation of the effect of the cathodic additions of Zr, Mn, and Mn + Cr shows that the corrosion properties are nonchanged by substitution of Mn or Mn + Cr for Zr. The resistance to general corrosion, exfoliation corrosion, and corrosion cracking is enhanced by a nontraditional artificial aging.     

Mechanism of Stress Corrosion Cracking of Al–Li Alloys

G.V. Akimov's concepts of the corrosion–electrochemical properties of aluminum alloys containing lithium are developed. It is found that binary Al–Li alloys are insusceptible to stress corrosion cracking, even though their dissolution rate under normal conditions can increase by up to 30 times because of the selective dissolution of lithium. The interaction of dislocations with phases formed upon heat treatments is demonstrated to play a determining role in the stress corrosion cracking of all the basic aluminum–lithium alloys, namely Al–Li, Al–Li–Cu, Al–Li–Cu–Mg, and Al–Li–Mg alloys. The stress corrosion cracking of both binary aluminum–lithium alloys and alloys which are in addition alloyed with copper and magnesium has mainly a dislocation–electrochemical mechanism. The effect of electrochemical factors is well represented by the difference in the magnitude between the pitting initiation potential and the repassivation potential.     

Untersuchung der Korrosionsschutzwirkung von Wärmeträgern Teil 2: Chemische Korrosionsuntersuchungen mit dem Rotations-Zylinder und zum Schutz gegen Spaltkorrosion

Testing the corrosion protection of heat-transfer fluids Part 2: Chemical corrosion tests using the rotating cylinder and for the protection against crevice corrosion The second part of the report refers to chemical corrosion tests of the protective effect of inhibited heat-transfer fluids provided with anti-freeze mixtures of water and glycol on metals by means of the rotary cylinder testing method. The metals to be tested were plain steel, cast iron, wrought and cast aluminium alloys, copper materials as well as a solder alloy. Moreover the influence of time, dilution ratio and flow on the corrosion protection of some metals was investigated. Based on the test results of part one and two, standard testing methods and limiting maximum values were defined for the evaluation of the protective effects proved by these testing methods. Finally investigations for the protection against crevice corrosion are described. This publication will end with a third part reporting on electrochemical investigations according to the RZ-testing method.