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Prof C M F Rae

Handling and processing of powders is central to many areas of science and technology. Most ceramic materials can only be formed via powder processing, but powder metallurgy is also an important branch of materials science and polymers are frequently handled as (coarse) particles. Powder processing is also pivotal in many other industrial sectors, such as food, pharmaceuticals, agriculture, mining etc. Moreover, an understanding of the behaviour of assemblies of solid particles in fluids is essential in areas as diverse as filtration of Diesel exhaust and avoiding explosions in flour mills. Particle sizes of interest vary from a few nm to several mm (although most technological activity is focussed on the range from 100 nm to 100 microns).

The first part of the course covers methods of powder production, techniques for their characterisation and approaches to handling and controlling of particle assemblies. The second part describes the methods used for consolidation of powders, including the forming of powder blends into "green" compacts, sintering of such compacts and spraying of powders to produce coatings or monolithic materials. Some relevant scientific background is also incorporated, including that governing particles in fluid streams and the flow of fluids through permeable media.

This lecture course will cover:

  • Production of Powders. Definition of powder. Overview of production routes. Mechanical comminution. Melt atomisation. Reactive processing. Spray drying.
  • Particles in Fluids and Powder Characterisation. Powder particles in a fluid stream. Reynolds number and laminar flow. Drag forces, Stokes law and terminal velocities. Characterisation of particle size and shape. Microscopy. Sieving. Sedimentation. Light scattering. X-ray diffraction peak broadening. Surface area measurement. X-ray tomography.
  • Classification and Handling of Powders. Sieving. Air classification (elutriation). Cyclone separation. Hazards of powder handling. Inhalation of particulate and the Stokes number. Explosion risks.
  • Removal of Particulate from Fluids (Filtration). Filtration size ranges. Permeabilities, pressure gradients and flow rates. An example of filtration technology - Diesel particulate filters. Requirements and DPF design. Microstructure of DPFs. Performance of DPFs. Choice of material for DPFs.
  • Powder Consolidation: Moulding and Sintering. Powder moulding. Diffusion during sintering. Liquid phase sintering and cermets. Reactive consolidation of powders. Hot isostatic pressing (HIP).
  • Powder Consolidation: Thermal Spraying. Fluid dynamics and heat transfer during thermal spraying. Particle velocities and impact on the substrate. Particle thermal histories. Thermal spray techniques. Microstructure of thermal spray coatings. Combustion spraying. Plasma spraying.