Evaluation of the effect of extrusion velocity and paste water content on the microstructural variability and green strength of extruded titanium dioxide
Creators: name: Al-Azzawi, Mustafa Kanaan
Publisher: name: No Publisher Supplied
Year: 2017

description: Extrusion processes are used to form porous materials such as a catalyst supports. They are important in purifying the harmful gas emissions. Titanium dioxide is widely used as an extruded support because of its favorable properties such as high catalytic activity, high thermal, and chemical stability. Catalyst supports are used wildly in industries relating to automobiles, petroleum refining, and energy production where a high catalytic performance is essential. The catalytic performance and species diffusivity are affected by the microstructural variability and pore interconnectivity. Extrusion processes pose problems in the spatial variation of porosity and green strength of extrudate. Typically, the size distribution of an extrudate is measured and quantified using either a helium or mercury porosimetry, but both fail to quantify the spatial variation of porosity. Measuring the handling strength of an extrudate fails to provide a high level of precision that can be obtained from measuring the green strength of extrudate. In this thesis, the water content   effect on the green strength and microstructure of extrudate was examined. A quantitative approach using 2-D visualization and segmentation was developed to quantify the spatial variation of porosity. The effect of extrusion velocity on the green strength and spatial variation of porosity of extrudate was also assessed.  A wide range of water content and varying binder content of paste were analyzed using torque and capillary rheometer to determine the effect of water content. The effect was evaluated using SEM and green strength measurements. A range of extrusion velocities (shear rates) were conducted on two different paste formulations. Their effect on the spatial variation of porosity in the sheared region (at the die wall) compared to the unsheared region of the extrudate was quantified using a 2-D visualization and segmentation approach. The green strength measurements were also conducted on extrudates to evaluate the effect of extrusion velocity on the green strength.    The green strength measurements revealed that there is a clear relationship between the water content of paste and green strength of extrudate, where a high water content results in a high green strength. A relationship between the green strength and extrusion velocity of the extrudate was observed where a high extrusion velocity, the green strength of extrudate decreases because of high shear and ineffective particle arrangement.   SEM images showed a reduction in agglomerate size and porosity as a result of high water content. Varying the extrusion velocity has a large effect on the spatial variation of porosity of extrudate. Image analysis showed a low porosity in the sheared region (at the die wall) compared to an unsheared region for samples that were extruded at a low velocity. Conversely, high porosity is observed in the sheared region (at the die wall) compared to an unsheared region for samples that were extruded at a high velocity