The Effects of Citric Acid on the Mechanical and Corrosion Resistant Properties of Ni-Y2O3 Coatings for Enhanced Corrosion Protection

Abstract

The need to reduce the corrosion rate of metal structures in the oil and gas industry leads to increasing cost. Among different methods of protecting metals in corrosive environments; addition of coatings as a protective layer on the surface of metal components has been a useful technique in minimizing the impact of corrosion. Nanocomposite materials are composite materials that are made of two or more materials in which at least one dimension is in the nanometer scale. By decreasing the size of a particle embedded in a matrix, it helps to enhance the interactions between the metal matrix and reinforcements at phase interfaces. Therefore, incorporating nanoparticles into a metal or alloy matrix has shown an improvement to the mechanical and physical properties of the resulting coating. Yttrium oxide (Y2O3) is included in the rare earth (RE) sesquioxides group, it has a number of interesting properties such as high mechanical strength, high thermal conductivity, high melting point (2410 oC), wide bandgap (Eg is approximately 5.5 eV), and photoluminescence. It is also known to improve corrosion protection in corrosive environments when incorporate into metal and alloy coatings such as nickel, titanium, zinc, and Fe-Cr alloys. However, yttrium oxide was found to have high potential of absorbing hydrogen ions in aqueous solution to become a hydroxide, which leads to agglomeration of the nanoparticles in the electrolyte solution, making it difficult to form the coating when increasing the concentration of added Y2O3 nanoparticles. This agglomeration makes it difficult to insert high enough concentrations of nanoparticles to affect the corrosion resistance properties. A nickel-yttrium(III) oxide nanocomposite has been electrodeposited onto metal substrates using varying concentrations of yttrium(III) oxide nanoparticles in the nickel plating bath. In this environment, nickel and hydrogen ions tends to naturally absorb onto the surface of the yttrium(III) oxide nanoparticles during the electrodeposition process of Ni-Y2O3 coatings, thus, making the formation of Ni-Y2O3 coatings more challenging . Therefore, citric acid has been added to the electrolytic bath, not only as a buffer to aid in controlling the pH of the system, but also as a stabilizing agent for the nanoparticles prior to deposition. The effect of citric acid on the formation, morphology, and composition of the nickel-yttrium(III) oxide coatings was investigated by solution studies, powder x-ray diffraction, scanning electron microscopy, and microhardness measurement. The corrosion resistant properties of the coatings were investigated by exposure to chloride solutions, potentiodynamic polarization, and electrochemical impedance spectroscopy. The addition of Y2O3 nanoparticles was found to enhance the mechanical properties of the coatings which leads to an inherent improvement in their corrosion resistance. Figure 1