Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Chemistry

Supervisor

Noël, James J.

Abstract

The deposition of copper oxide films on copper substrates was investigated by the electrochemical, thermal, and hydrothermal oxidation of copper. The formed oxides were characterized using various surface analytical techniques to determine the film’s morphology, composition, and thickness. The results show that by growing oxides electrochemically, a duplex layer composing of CuO and Cu2O film was formed on the copper surface, having characteristics of being porous and possessing needle-like structures. An oxide film composed of CuO and Cu2O, which shows minimal porosity and possess mixtures of crystalline and non-crystalline structures, is formed on the copper surface by the thermal oxidation of copper. A compact film having thickness in the micrometer range with only Cu2O crystal deposits was achieved by the hydrothermal oxidation of copper. The ultimate goal of this work is to determine how the presence of different types of oxide film will influence the corrosion of copper-coated containers for the safe isolation of used nuclear fuel.

Summary for Lay Audience

Fifteen percent of Canada’s electricity comes from nuclear power, and currently there are 19 nuclear reactors being used for this clean energy source. The high-level radioactive waste material produced by these reactors will eventually be disposed indefinitely in a multi-barrier system within a deep geological repository (DGR). One of the key barriers protecting the environment from release of radioactive materials is the carbon steel container, which is coated with a 3-mm outer layer of Cu for corrosion protection. The Cu will exhibit many corrosion behaviours during its lifetime in the DGR as repository conditions change over time. Therefore, further studies are needed to assess the longevity and durability of the Cu.

Upon emplacement, the container will be exposed to an environment that is initially warm and oxidizing, due to the decay of radionuclides from the fuel and the oxygen entrapped during repository excavation. This environment will evolve over time to conditions that are cool and oxygen-free as oxidants are consumed and radioisotopes decay. When the Cu coating is exposed to the O2 that will be unavoidably trapped in the DGR upon closure, some of this O2 will be consumed to oxidize the Cu, resulting in formation of an oxide film on the surface of the container. During the cool and anoxic phase, other oxidants such as SH- are anticipated to be present. SH- can oxidize the Cu surface even further, but it may first convert the copper oxide present on the container surface to cuprous sulfides chemically. This process, if it occurred, would delay and diminish the amount of sulfide-driven corrosion of the copper, as it would consume some of the incoming SH- ions, preventing them from reacting with metallic copper in the container coating..

The purpose of this research is to grow and characterize oxide films on Cu by a variety of methods, for later investigations of their interactions with SH- ions, a corrosion scenario that is expected during the emplacement of Cu-coated steel containers in the DGR. One method is to grow an oxide film on a Cu coupon by electrochemical oxidation which simulates a corrosion process occurring in aqueous environment. Another method is hydrothermal oxidation, a corrosion process occurring at elevated temperature and pressure. Lastly, thermal oxidation method was also investigated for growing oxides, which is a corrosion scenario involving the reaction between the metal and its environment at elevated temperatures. By growing oxides under different conditions, a reproducible and optimal procedure for growing oxide films with specific characteristics on Cu can be developed.

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