Sam Cowart

Date of Award

January 2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

First Advisor

Juergen Fischer

Abstract

Tantalum is a tough, ductile, refractory metal that is highly corrosion resistant. The corrosion resistance of tantalum is evident in diverse conditions, including high temperature and severe chemical environments. Application of a tantalum layer onto other metal substrates would be a beneficial corrosion-resistance technique. The method investigated for application of tantalum onto various metal substrates was via electrodeposition from ionic liquid electrolytes. The use of ionic liquids allows the electrodeposition process to be performed at lower temperatures (less than 200 degrees Celsius) than the mainstream process of deposition at higher temperatures (750-800 degrees Celsius) from molten salt electrolytes. The lower operating temperature ultimately protects the substrate from increased rates of corrosion as well as strength loss through annealing.

Recently published literature on the electrodeposition of tantalum onto other substrates formed the basis for this research. This investigation attempted to determine whether previous research could be expanded upon through the variation of type of ionic liquid, the addition of organic solvents or alkali metal salts, and destabilization of tantalum-halide clusters. An electrochemical cell was constructed that utilizes a tantalum foil anode and a steel or nickel cathode. The electrolyte contained tantalum salts dissolved in various ionic liquids, with or without various organic solvents. The cell was protected from water vapor and oxygen by being placed into a glove box containing an ultra-high purity nitrogen atmosphere. The actual plating process was conducted galvanostatically, and the applied current and electrolyte composition were varied to determine the effect on the deposition process. Electrodeposits formed during experimental trials were analyzed through the use of scanning electron microscopy (SEM) with energy-dispersive x-ray spectroscopy (EDS).

This study represents particular advancements in the body of knowledge on electrodeposition of tantalum from ionic liquids. Individual ionic liquids were evaluated that had not been previously investigated as refractory metal electrolytes. Additionally, the thickest known tantalum electrodeposits, and electrodeposits with the highest reported concentrations of tantalum were produced in this study.

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