Date of Graduation

Spring 2018

Document Type

Honors Research Project

Degree Name

Bachelor of Science

Major

Corrosion Engineering

Research Sponsor

Dr. Hongbo Cong

First Reader

Dr. Robert Lillard

Second Reader

Dr. Rajeev Gupta

Abstract

Electrical circuitry is an industry, among many others, heavily using the element of copper. Ensuring the mechanical integrity of Cu is crucial, especially in salt environments, for the multifaceted composition of circuits. 4N NaCl solution (equilibrium concentration in ~84% RH) simulated this three-phase system. Rectangular Cu samples were partially immersed in both ambient and continuous lab air sparging atmospheres to understand waterline corrosion of the metal. Open circuit potentials (OCP) were continuously taken during the immersion testing for a maximum of 5 days. A scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS), Raman spectroscopy, and 3-D microscopy afforded a closer look at the morphology and compositions of the degradation. One conclusion was chloride-containing corrosion product formed on the metal surface. This copper hydroxychloride corrosion product was more concentrated on immersed Cu directly in the waterline zone. Copper oxides (CuO and Cu2O) formed in the spreading zone above the waterline, where cathodic reactions are thought to take place because of a higher pH. The copper oxides are thought to be pH dependent as they correspond location with pH. Three-day immersion experiments of pure Cu in ambient NaOH solutions with different pH values were further conducted to verify that the formation of copper oxides is pH dependent. The results presented CuO formed in pH less than 12 while Cu2O formed in pH more than 12. The continuous sparging of the headspace with lab air significantly altered the corrosion morphology and corrosion production formation, both in the waterline and secondary spreading zones. Cyclic potentiodynamic polarization (CPP) experiments of Cu in NaOH solutions with different pH values were conducted to further elucidate the corrosion behavior of Cu in different pH environments. Finally, the Cu/NaCl/Air three-phase corrosion phenomenon is tentatively explained by pH and potential variation based on thermodynamic and kinetic considerations.

Comments

This project report could not have been completed with Dr. Cong and Dr. Li. They were wonderful mentors and supporters of this research and me as a student.

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