Scientific interests

My research is in the general area of Applied Superconductivity, and more specifically Conductor Optimisation. At present, I work exclusively on low-temperature niobium-based superconductors. My work may be separated into two distinct projects.

1. Characterisation and optimisation of conductors by in-situ resistometry

The first of these exploits the dependence of the electrical resistivity of a composite on the proportions, properties and distribution of its components. Superconducting wires containing a brittle A15 phase, for example Nb₃Sn, must first be processed as a composite of more ductile components, the A15 phase being subsequently formed during heat treatment once the conductor is of its final dimensions. The heat treatment conditions and the detailed design of the wire cross-section strongly influence the resulting superconducting properties, but discovering the optimum wire design and heat treatment schedule for a given application is difficult and time-consuming. The electrical resistivity may, however, be measured in situ during heat treatment, and its variation is indicative of the changing dimensions and properties of the wire components. Separating the influences of these components so that the thicknesses of the A15 intermetallic layers and their grain sizes can be obtained is the aim of this research, as this will permit a system to be developed that will allow these parameters to be optimised. To achieve this aim, models and calculations are being constructed to express the resistivity of the composite in terms of the dimensions, compositions and properties of its components. Diffusion models for the specific case of Vacuumschmelze Nb-Sn bronze process wires are also in development to predict the evolution of component dimensions as a function of time and temperature. This computational work is supported by experimental resistance measurements, many of which are performed by Kai Sin Tan, of superconducting wires during heat treatment and their components. I am grateful to European Advanced Superconductors (formerly Vacuumschmelze) for the provision of wire samples used in this work.

2. Fabrication of niobium-based materials by the Direct Electrochemical Reduction of Oxides for superconducting applications

The other project, in collaboration with Antony Cox of the Materials Chemistry Group in my department, applies the process for the Direct Electrochemical Reduction of Oxides (DERO) developed and patented by Fray, Farthing and Chen (FFC) to niobium and its intermetallic compounds. Many oxides, when made the cathode of an electrochemical cell containing calcium chloride, can be reduced to their metals. For elements like titanium and niobium, this eliminates the complex and costly sequence of processes applied in the current industrial route. More importantly in this context, by using a suitable mixture of oxides alloys and intermetallic compounds may be directly produced. I am working to optimise the production of superconducting intermetallic compounds by this route, which could permit the development of novel low cost, high critical current superconducting wires.