Publication Date

12-2012

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

Supervisory Committee Chair

Darryl P. Butt

Abstract

The kinetics and mechanisms of oxidation of titanium wire were assessed using a large test matrix in Ar-20% O2 at 800 to 1200°C, and N2-20% O2 at 1000°C, for 0.5 to 24 hours. The effects of geometry on oxidation were evaluated by investigating the behavior of six high purity Ti wires with diameters varying from 50 to 2000 μm, with an objective of producing hollow TiO2 tubes.

Oxidation behavior was characterized by measuring oxide thicknesses and morphology by optical microscopy, and the phases were characterized using a combination of SEM and TEM. The kinetics was evaluated using a shrinking core model derived for cylindrical geometry. Activation energies for oxidation were obtained from fits of experimental data to the model and calculated values generally agreed well with values reported in the literature for bulk Ti.

It is suggested that oxygen dissolution in the residual Ti is the overall rate limiting mechanism between 800-1200°C at shorter oxidation durations. At longer durations, the oxide is multi-layered, susceptible to spallation, and consequently the mechanism is complex. It is demonstrated that due to the fast outward diffusion of Ti, the oxide grows outward, resulting in the separation of the oxide from the oxygen-saturated metal core, in some cases leading to the formation of hollow TiO2 tubes.

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