Electrodeposition of Cu-Ni Incorporated with Layered Silicates for Microbial Corrosion Protection

Electrodeposition of different metals and alloys has become popular for corrosion resistance and hardness in the oil and gas industry because of the major problems that persist with corrosion.  The off-shore oil rigs in the ocean are exposed to highly corrosive spray zones and low flow submerged components.  The cost of corrosion weighs a heavy burden of about $1.372 billion dollars on the oil and gas industries in the United States [1].  Breaking down the total amount, this accounts for $589 million in surface pipeline and facility costs, $463 million in down hole tubing expenses and $320 million in capital expenditures related to corrosion [1].

Electrodeposition has become a popular technique to produce new materials for science and engineering applications.  The technique has become favorable in synthesizing coatings because of low cost, convenience, and the ability to work at low temperatures.  When determining the structure, morphology, and composition of the film; the pH, current, and applied potential play an important role [2]. 

For use in marine environments, copper alloys are used to defend against biofouling of materials by inhibiting microbial induced corrosion (MIC). Copper ions are able to eliminate bacteria, viruses, fungi, algae and other microbes.  Copper alloys have been examined due to their increased feasibility, material strength, and cost as compared to pure copper coatings [3].  The two major copper alloys that are most commonly examined are Cu-Ni 90-10 and Cu-Ni 70-30.  90-10 Cu-Ni coatings show good protection in more stagnant conditions, where as the 70-30 Cu-Ni coatings are employed in higher flow conditions because of the increased hardness provided by the higher concentration of nickel.  Copper alloys are usually employed when long term durability is needed. 

Incorporation of ceramics into the metal coating improve the mechanical properties.  Layered silicates are the ceramic compounds being analyzed in this study, which hold many lucrative properties such as a high surface area, good chemical resistance, resistance to extreme temperatures, and resistance to pH.  Scientists have been able to prove that layered silicates improve the resistance to corrosion when it comes to conductive polymer composite coatings, scientists have proved that layered silicates increase the resistance to corrosion [4].  With the addition of montmorillonite (MMT) into the Cu-Ni matrix, an increase in strength, adhesion, wear and fracture toughness of the coating occurs, which provides for better corrosion resistance and hardness.

The Cu-Ni-MMT coatings were analyzed with many different instrumental and electrochemical techniques.  Scanning electron microscopy (SEM) was chosen to analyze the morphology of the electrodeposited films.  X-ray diffraction (XRD) was used to analyze the crystal structure of the films.  The copper to nickel metal ratio was determined using atomic absorption spectroscopy (AAS) and the presence of the clay in the film; silicon, alumina, magnesium and iron was confirmed with energy dispersion x-ray spectroscopy (EDX).  The corrosion resistance and hardness of the films were analyzed using Tafel polarization, immersion tests, impedance spectroscopy, and nanoindentation.  Also, solution studies were performed with zeta potential, particle size, and viscosity to determine the optimum amount of loading for MMT into the Cu-Ni films.

In conclusion, copper and copper alloys are commonly used in marine environments to resist biofouling of materials by inhibiting microbial growth.  Two major alloys of copper-nickel, 90-10 and 70-30, were electrodeposited with a layered silicate, montmorillonite, for microbial corrosion protection in marine environments on a stainless steel substrate.  The overall corrosion resistance and hardness was improved with the film in comparison to the bare stainless steel substrate, which proves to be advantageous for the off-shore drilling environment in the oil and gas industry.

References

[1] "Corrosion in the oil and gas industry," 2013. http://www.nace.org/Corrosion-Central/Industries/Oil---Gas-Production/

[2] H.A. Conrad, J.R. Corbett and T.D. Golden. Journal of the Electrochemical Society, 159, 1, C29-C32, 2012.

[3] W. Schleich, R. Feser, G. Schmitt, S. Haarmann, K. Schnier. Eurocorr, CDA Publication, 1-14, 2007.

[4] D. Zaarei, A.A. Sarabi, F. Sharif and S.M. Kassiriha. Journal of Coating Technology Research, 5, 241-249, 2008.