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Processing and characterisation of submicron/nanometre alumina ceramics and alumina matrix nanocomposite ceramics

The microstructure and properties of alumina and alumina-matrix nanocomposites are strongly affected by the raw powders and the processing route. The significant effect of hydrothermal synthesis condition on the morphology of boehmite particle was observed. UF-SiC has more controllable oxidation behaviour for the preparation of nanometer SiC/mullite/alumina composites than P-SiC. Due to the crystallization and agglomeration of SiC at high temperature, oxidation at low temperature is suggested. The properties of the compacts prepared by pressure filtration were closely related to the state of the starting slurry, the particle size and morphology and the applied pressure. A desired slurry can be obtained by the controlling of pH value, the ionic strength and the addition of suitable dispersant. Due to the non-uniform distribution of the liquid pressure and solid pressure across the compact during pressure filtration, the density of the compacts is not uniform as well. Gradually increasing the pressure to the desired level is suggested in order to obtain a more homogeneous compact density. Cracking upon unloading after pressure filtration and during drying became severe for mono and binary boehmite system due to the high stress caused by its very small particle size. Drying rate and stress, hence cracking can be somehow controlled by the drying condition. All the sintered materials from the pressure filtered compacts of submicron/nanometer alumina and alumina-matrix composite show very homogeneous microstructures with fine grain size, confirming that colloidal pressure filtration is a good way to produce advanced materials
Date January 2002
CreatorsHe, Jingyan
PublisherUniversity of Birmingham
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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