Ion exchange resins have been used for retrieving radiocaesium from aqueous waste streams since the earliest days of the nuclear power industry. The physical and chemical properties of Lewatit DN ion exchange resins encapsulated in silica fume (SF)-blended cement were investigated with the aim of producing a stable solid wasteform for possible future disposal in an underground repository. Expansive reactions involving resin swelling in the high pH pore fluid and Ca(OH)2 formation around the resin particles can be suppressed by the addition of 50-75% SF at w/c ratios of 1.400-1.71. The basis of this suppression is the pozzolanic reaction between Ca(OH)2 and SF which consumes Ca(OH)2 and lowers the pH of the pore fluid to less than 10. The total heat evolution of blended cements is similar to that of a neat Portland cement, demonstrating the exothermic nature of the pozzolanic reaction. The use of high w/c ratios in cements containing 50% SF increases the permeability of the matrix. Porosity measurements indicate that this is due to the high free water content of the paste and the relatively high porosity of SF agglomerates. Elevated curing temperatures (up to 85oC) also increase the permeability as a result of coarsening of the microstructure. Despite the inferior physical immobilisation of caesium in high SF-content cements, leach tests, sorption measurements and pore fluid analysis show that chemical retention of caesium is enhanced by blending, more so in blends containing a permanent excess of SF, due to the formation of highly sorptive silica gel and low ratio C-S-H (Ca/Si as low as 0.80). On the other hand, SF-blended cements are more susceptible to physiochemical degradation in simulated groundwater's containing MgSO4. Chemical attack by MgSO4 converts C-S-H gel and silica gel to a non-cementitious magnesium silicate hydrate (identified as sepiolite) in 50-75% SF pastes, resulting in extensive deterioration of the attacked zone.

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Thesis (M.Phil)--University of Hong Kong, 1994. / Includes bibliographical references. Also available in print.

Color is a visual characteristic which imparts the ability to categorize different objects. When light strikes an object, there are three possibilities as to what can happen. The light may be reflected, refracted or scattered. Human perception of color is due to a combination of these. Plastics are polymeric materials. Polymers are generally colorless and need colorants in order to have some color. One or more pigments in certain ratios can be used to give a specific color to plastics. Slight variations in the proportions of either of the used pigments, or their dispersion, may result in a color that is different from the desired one. There can also be many other reasons for color mismatch such as processing or degradation effects. This study utilized the historical data records of SABIC IP to look at effects of changing Grade on color (i.e. when the same color is produced from resin blends which may have different amounts of resins, pigments or additives). These records were also used to study effects of change in screw diameter and configuration on color (i.e. when the same grade of a color is produced on two different production lines, different screw diameters and configurations). The effects of the processing parameters on the colors were also investigated by carrying out experiments using a twin screw extruder at SABIC IP’s plant in Cobourg. Resins, pigments and additives were dry blended and extruded while being subjected to different processing conditions. Three processing parameters, namely temperature, rpm and feed-rate, were chosen for the study. A three level factorial design of experiments was used. An analysis of variance (ANOVA) has been utilized to find the effects of individual parameters on color and the interaction between two parameters and their cumulative effect on color. / UOIT

Inaug.-Diss.--Bern.

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