Ti-suboxides (TiO2-x) have been widely studied and tested for many potential applications, mostly for their tuneable electrical conductivity and chemical resistance. When the material has a low x (0 <x< 0.10), the dominant point defects in the structure consist of Ti3+ and Ti4+ interstitials and oxygen vacancies. However, for x=0.10-0.34 (Magnéli phases) the lattice is characterised by extended planar defects and crystallographic shear planes that offer metallic conductivity (104 S/m). Depending on the extent of the reduction their properties can be tuned to match the requirements of various applications such as cathodic protection, batteries, catalyst support for fuel cells and optical memory devices. This research has focused on the manufacture and characterisation of Magnéli phases fine scale fibres, with the aim to use them in a wear sensor and as electrodes in redox flow batteries. The manufacturing process was optimised to tune the properties and achieve reproducibility. A main part of the work was studying the electrical properties using Impedance Spectroscopy to analyse the electrical response of the samples across a wide range of frequencies. Additionally, the structure, density/porosity, hardness, wear rate, thermal expansion coefficient and the thermal stability were investigated to match the requirements of the applications. Thermal stability is the main disadvantage of Ti-suboxides, since a high temperature and oxygen rich environment can cause re-oxidation. Thermo-gravimetric analysis was used to determine the re-oxidation temperature and the kinetic mechanism. The Magnéli phases fibres were successfully used as the sensing element in a wear sensor that was based on resistivity measurements. They also gave very promising results when tested as electrodes for redox flow batteries.
|Date of Award||17 Mar 2015|
|Supervisor||Chris Bowen (Supervisor) & John Taylor (Supervisor)|