Coal gasification poses many problems to the materials engineer due to the high temperatures and corrosive gases involved in the process. The main aim of this research is to investigate the influence of a simulated coal gasification environment on the mechanical properties and surface chemistry of a clay bonded SiC filter. This type of material is presently used to filter combustion gases and it is proposed that it may be used in gasification systems between the gasifier and gas turbine to filter particulates that would damage the turbine blades and lining. Three separate gases are used to investigate the corrosive effects of low pO<SUB>2</SUB>/high pS<SUB>2</SUB>, high pHC1 and increases in water vapour. Corrosion tests are performed at 1273K/1073K/873K at exposure times of 50, 100 and 200 hours. All physical and chemical observations are supported by theoretical modelling. The filter material is first characterised and found to be composed of SiC particles held together in an aluminosilicate clay binder. The only crystalline material identified in the clay is mullite. The 3-point fracture strength of the filter decreases substantially with increases in exposure time and temperature. It is concluded that the fluxing effects of the sodium present in the clay substantially lower its softening temperature. As a consequence, at temperatures of 1073K and above the filter is above its working temperature. Massive reductions in fracture strength of up to 40% seem to reflect this. The cause of the strength loss is believed to be due to both micro-cracking in the clay bond associated with the differential cooling rates of the clay and SiC, and mass loss from the clay bond due to volatile gas formation. The composition of the gas is found to significantly effect the chemistry of the surface reactions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:597354 |
| Date | January 1998 |
| Creators | Cash, M. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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