Abstract
The main objective of this dissertation is to study the extrusion and surface modification process of porous ceramics. The relationship among processing microstructure and properties will be investigated. The results drawn from the present work are shown as the following.一、 The rheological behavior of alumina and kaolin slurriesThe slurries consist of dispersed alumina and kaolin particles in deionized water with additives such as sodium salt of polyacrylic acid（PAA-Na）, carboxymethyl cellulose（CMC）, hydroxypropyl methylcellulose（HPMC）, glycerol and stearic acid sodium salt. The viscosity data from Brookfield rheometer were satisfactorily fitted with an empirical equation modified from Brodnyan equation. The cpvc was then calculated from the best-fit k value as 1/k=cpvc. These cpvc values were then compared with the compositions which provide successful extrusion process. Our experimental results showed that all tested samples exhibit the pseudoplastic behavior. The additions of PAA-Na, glycerol, and stearic acid sodium salt reduce the viscosities of the slurries. On the other hand, the addition of binder, CMC or HPMC, significantly increase the viscosities of slurries.二、 Extrusion process for making porous ceramic substrateExtrusion was performed using a horizontal single screw extruder. The influence of the amount of binder and volumetric ratio of alumina to kaolin, as well as sintering conditions on the microstructure and properties of the porous discs were investigated. In general, when the volume ratio of alumina to kaolin or binder quantity increases, both porosity and mean pore size increases as well. However, when the sintering temperature and time are increased, the porosity decreases while mean pore diameter increases. Empirical equations were also estabilished to relate porosity and mean pore diameter to the processing variables.三、 Surface modification of porous ceramic substratesThe objective of this part of work is to reduce the surface pore size of the support. TiO2 particles of 0.5mm are first dispersed in water with PVA and then coated onto the support using cross flow filtration. When the content of the slurry is 0.72wt.%PVA + 9wt.% TiO2 + 90.28wt.%D.I.water, particles can be well dispersed and then the coating process will be in a good condition. Surface roughness can be greatly reduced via this coating procedure, and then the overall permeability will decrease markedly. During coating process, the thickness of the membrane will increase with increasing TMP, and then, the permeance will decrease. We also used uniform polystyrene particles to characterize the pore size of products.