Composition of the corrosion products of galvanic alloys Zn–Co and their influence on the protective ability

Boshkov, N.; Petrov, Κ.; Vitková, S.; Nemska, S.; Raichevsky, G.

doi:10.1016/s0257-8972(02)00161-5

Cited by 69 publications

(64 citation statements)

References 7 publications

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“…For the chromated coatings (Fig.3c), the 2h time interval depicts highest corrosion resistance for the ZnP0.1GP coating (current drop around +125mV), which is consistent with the derived highest Rp value from EIS measurements for this coating in the group of Table 1). Further, within longer treatment the chromated composite coatings ZnP0.1GP and ZnP0.3GP (Fig.3d) present higher resistance with external polarization (current drop around 0V), which is again in line with the EIS response, where similarly higher (360 and 340 Ohm.cm 2 ) Rp values were recorded for the chromated composite coatings, compared to chromated pure Zn (for ZnGP 180 Ohm.cm 2 was recorded). The best corrosion resistance after 120h, however, is recorded for the non-chromated composite coating ZnP0.3 (Fig.3b), exhibiting significantly lower anodic current in the region after corrosion potential (similarly, the highest Rp values were recorded for this coating via EIS i.e.…”

Section: Potentio-dynamic Polarizationsupporting

confidence: 74%

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Corrosion Performance of Composite Galvanic Coatings with Variable Concentration of Polymeric Nanoaggregates and/or Cr(III) Conversion Layers

Koleva¹,

Taheri²,

Tsvetkova³

et al. 2011

ECS Trans.

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This paper reports on the corrosion performance of composite zinc layers (~ 8µm) on a steel substrate, considering the influence of nano-aggregates and Cr(III) conversion layers, compared to control (only Zn layers) conditions. The main factors, influencing the corrosion performance of Zn in this study are: a) the effect of two concentrations of polymeric nano-aggregates (0.1g/l and 0.3g/l PEO 113 -b-PS 218 core-shell micelles in the starting electrolyte); b) the effect of Cr(III) conversion layers on both pure Zn and composite Zn layers. For most of the hereby investigated time intervals i.e. treatment in aerated 5% NaCl from 2h until 120h, the composite coatings present higher corrosion resistance, especially within longer treatment. Corrosion current densities are similar to Zn, however, anodic currents are significantly lower. After treatment in NaCl, the composite Zn coatings present a more homogenous product layer, formed as a result of the presence of the nano-aggregates. The additional Cr(III) treatment does not significantly improve the corrosion resistance of the composite coatings for the hereby investigated time intervals.

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Section: Potentio-dynamic Polarizationsupporting

confidence: 74%

“…Various methods and techniques are reported with this respect [1][2][3][4][5][6][7][8][9][10]; including the utilization of environmentally friendly compounds [11][12][13]. Composite coatings incorporating micro-or nano-sized aggregates are a more recent approach [14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Corrosion Performance of Composite Galvanic Coatings with Variable Concentration of Polymeric Nanoaggregates and/or Cr(III) Conversion Layers

Koleva¹,

Taheri²,

Tsvetkova³

et al. 2011

ECS Trans.

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“…These results show that the corrosion performance of these electrodeposits is superior to that of plain Zn coatings. [1][2][3][4][5][6][7][8][9][10][11][12] An important aspect, from a practical and technological standpoint, is that these coatings must still have a high Zn content to maintain the cathodic protection of the steel substrate while still remaining less active than just Zn coatings. Additionally, due to environmental and health considerations, these zinc alloy coatings have been proposed as potential candidates to replace highly carcinogenic Cd coatings in anticorrosive applications.…”

Section: Introductionmentioning

confidence: 99%

Corrosion study of electrodeposited Zn and Zn-Co coatings in chloride medium

Lima‐Neto¹,

Correia²,

Colares³

et al. 2007

J. Braz. Chem. Soc.

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A corrosão de eletrodepósitos de Zn e Zn-Co em solução aquosa de NaCl 0.1 mol dm -3 foi investigada usando as técnicas de microscopia eletrônica de varredura (SEM), energia dispersiva de raios-X (EDX), dissolução anódica sob controle galvanostático (GES), impedância eletroquímica (EIS) e medidas de potencial de circuito aberto (E oc ). Todos os eletrodepósitos foram feitos sobre aço carbono. Fases intermetálicas foram identificadas nas camadas de ZnCo com teor de Co superior a 1 at.%. Os resultados de GES, SEM e EDX mostraram que o mecanismo de corrosão das camadas de Zn-Co com mais alto teor de Co está relacionado ao surgimento de trincas devido à dissolução de fases intermetálicas ricas em Zn, enquanto que a corrosão das camadas de Zn e Zn-1Co foi caracterizada pela dissolução destas. Os produtos de corrosão identificados foram os mesmos em todas as camadas testadas, os quais atuaram como barreira, mas não foram capazes de prevenir o processo corrosivo. A melhor resistência à corrosão das camadas de Zn-Co obtidas a partir do banho não aditivado, em comparação à camada de Zn-1Co obtida do banho aditivado, é devido ao elevado teor de Co que promove um enobrecimento da camada. Todas as camadas de Zn-Co apresentaram resistência à corrosão superior às camadas de Zn. A camada Zn-18Co apresentou o melhor desempenho anticorrosivo com uma durabilidade 3 vezes superior a camada de Zn.The corrosion behavior of electrodeposited Zn and Zn-Co coatings in 0.1 mol dm -3 NaCl aqueous solutions was investigated using scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), galvanostatic electrochemical stripping (GES), electrochemical impedance spectroscopy (EIS) techniques and open circuit measurements (E oc ). All coatings were electrodeposited on mild steel. Using GES it was possible to identify Zn-Co intermetallic phases in the coatings with Co content higher than 1 at.%. The GES, SEM and EDX results revealed that the corrosion mechanism of the Zn-Co layers with high Co content is related to the appearance of cracks due to the dissolution of the γ Zn-rich phases, while the corrosion of the Zn and Zn1Co layers was characterized by dissolution of the coatings. The Zn and Zn-Co coatings were found to contain the same insoluble corrosion products, which act as a corrosion barrier that delays but does not prevent corrosion. The better corrosion resistance of the Zn-Co coatings obtained in the bath without additive, in comparison with Zn-1Co obtained in the bath containing additive is due to the high Co content which leads to an ennoblement of the coating. All Zn-Co electrodeposits showed greater corrosion resistance than the Zn electrodeposits. The Zn-18Co layer showed the best corrosion resistance, with a lifetime about three times longer than that of the Zn layer.

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“…Zinc hydroxy chloride has a very low solubility, and ensures higher protective ability for Zn-Co alloy coatings [7,10]. We can easily conclude that the film obtained from bath containing 20 g l −1 of borax has the highest corrosion resistance among studied films.…”

Section: Resultsmentioning

confidence: 74%

“…Therefore, the cobalt content in the Zn-Co alloys, produced from aqueous coating baths, is still at low rates. In spite of the fact that there are numerous publications regarding Zn-Co alloy with low Co content [6][7][8][9][10][11], there has not been much work reported on Zn-Co alloys consisting of considerably higher Co contents. Most results reported on the electrodeposition of Zn-Co alloy coatings showed that the maximum amount of cobalt * e-mail: ikarahan@mku.edu.tr in their deposits was about 6-7 wt.% [12,13].…”

Section: Introductionmentioning

confidence: 99%

Effect of Borax Pentahydrate Addition to Acid Bath on the Microstructure and Corrosion Resistance of Zn-Co Coating

Karahan

2015

Acta Phys. Pol. A

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In this work, the Zn-Co coatings were synthesized on AISI 4140 steel and aluminum plates by using potentiostatic electrodeposition technique in sulphate-based acidic baths with 0, 20, 40 and 60 g l −1 of borax pentahydrate, as additive. The effect of borax pentahydrate on the microstructure of the samples was observed using scanning electron microscopy and X-ray diffractometer. The deposition process was investigated by cyclic voltammetry. The effect of borax pentahydrate on the corrosion resistance of the samples was studied by potentiodynamic polarization technique. The results have demonstrated, that the addition of borax pentahydrate was in favor of the growth of grains. The morphology of pyramidal islands on the surface was changed to a more flat structure. The results have also demonstrated that the effect of borax pentahydrate was not monotonous. With increasing concentration, the corrosion potential was at minimum and the charge transfer resistance Rt was at maximum for the sample obtained from the bath with 60 g l −1 of borax pentahydate, indicating that this sample showed the best corrosion resistance. It was found that current density first decreased and than increased, due to adsorption of a complex of borax pentahydrate and/or changes in the morphology, however, the initial deposition potential was not affected. The addition of borax pentahydrate to the bath led to formation of the best Zn-Co deposits, composed of coalesced globular fine grains, smaller than ≈2 µm in diameter. In addition, all of the studied Zn-Co deposits consisted of η phases. It is suggested that Zn-Co deposits produced in the bath containing 60 g l −1 of borax pentahydrate probably offer sacrificial protection to the steel substrate.

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Composition of the corrosion products of galvanic alloys Zn–Co and their influence on the protective ability

Cited by 69 publications

References 7 publications

Corrosion Performance of Composite Galvanic Coatings with Variable Concentration of Polymeric Nanoaggregates and/or Cr(III) Conversion Layers

Corrosion Performance of Composite Galvanic Coatings with Variable Concentration of Polymeric Nanoaggregates and/or Cr(III) Conversion Layers

Corrosion study of electrodeposited Zn and Zn-Co coatings in chloride medium

Effect of Borax Pentahydrate Addition to Acid Bath on the Microstructure and Corrosion Resistance of Zn-Co Coating

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