PhD Theses & Dissertations

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    Effects of microstructure on mechanical strength of selected clays from Uganda
    (Makerere University (unpublished work), 2004-04) Obwoya, Kinyera Sam
    This thesis presents results of a study of the dependence of modulus of rupture (MOR), Young's modulus, {.E), and flexural rigidity,{ DJ, of sintered clay specimens on microstructure, average particle size and production variables. The production variables considered were sintering time, sintering temperature, and compaction pressure. The study shows that the MOR, Young's modulus and flexural rigidity of the clay product increase as compaction pressure, sintering temperature and sintering time are increased, but decrease as the particle size increases for all the processing conditions. The microstructure of clay specimens of higher strength are such that, the pores are well rounded and fewer in number. The grain boundaries are also thin and well defined with glassy phase being dominant as compared to liquid and pore phases. Higher strength of the clay specimens is also associated with formation of mullite which forms needle-shaped crystals with an interlocking network that gives high stability at elevated temperatures. The variation between MOR and sintering time, t, can be described by a relation of the form MOR = ot2 + /3t + 9 where a, /3 and 9 are constants with some of their mean values for samples compacted at 49.584MPa and sintered at 12oooc are: a = -0 .37±0.16MPas2, /3 =4.93x0.87MPas·1 and 9 = 21.05±7.26MPa
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    Optical activity and faraday effect in some mineral and vegetable oils.
    (Makerere University (unpublished work), 2000-03) Mucunguzi-Rugwebe.R.E.R
    This Thesis presents results of a study of Optical Activity and Faraday Effect (OAFE) in some mineral and vegetable oils in the temperature range of 6°C to 45°C and magnetic field up to 140mT. Intrinsic birefringences responsible for Optical Activity were found in vegetable oils with impurities and all mineral oils. The results of Optical Activity in both types of oils obeyed the equation (0. 1) where Qw .,, is the angle at which minimum irradiance I min occurs in water and other substances which are optically inactive, is the rotation angle in the medium and A is a rotation due to impurity concentration. The results show that, the more the impurity concentration is in the vegetable oil, the greater the rotation angle. The rotation angle is almost directly proportional to impurity concentration. When static magnetic field was applied to mineral oils and vegetable oil with impurities, the rotation angle obeyed the equation = Ml