Effect of Milling on Size Reduction and Microstructural Changes to Gamma-Alumina

This thesis sets out to evaluate the effects of milling on the microstructural changes to gamma-Alumina, a well-used catalyst support. It reviews the literature as it relates to the characterisation that has been done so far on this material, different milling methods and effects of milling.
The review section considers the strengths and weaknesses of previous work in the areas of structural characterisation of gamma-Alumina as well as reports on the effects of milling of the material with particular interest in size reduction and phase transformation.
Working from the base of current knowledge, experiments that can fill in the gap identified from the review are designed. The material under investigation is characterised as received for particle size and morphology and this gives a base for further experimental investigations.
Various experiments are designed centred around exposure of gamma-Alumina to different milling conditions. These include the use of different mills, variation of milling conditions and isolation of stress modes. Furthermore, results from Discrete Element Method simulations of one selected mill, provided by Professor Junya Kano of Tohoku University in Japan are analysed for energy quantification. Data processing of the results of the operation of a second mill, simulated by Discrete Element Method at the University of Leeds by Dr Colin Hare and Dr Ali Hassanpour is also used to quantify energies associated with the milling process.
It is concluded that microstructural changes to gamma-Alumina are very much energy driven processes. The jet mill has proven a worthy candidate for size reduction in small scale processes. The size reduction analysis shows that gamma-Alumina requires the presence of a dispersive agent such as water or compressed air for efficient size reduction. The characterisation work combined with the simulation results show that the amount of energy dissipated into the microstructure of gamma-Alumina during a collision governs the extent of microstructural effects.
Results also show that with the supply of different energies to milling processes, mechanical energy can achieve a phase transformation from gamma-Alumina to alpha-Alumina similar to that achieved by calcination where delta-alumna and theta-Alumina are observed as intermediate phases. Simulation also provides a tool for prediction and selection of milling processes appropriate for the required end product.