Theses and Dissertations

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Theses and Dissertations ( Metallurgy and Materials Enginering)

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    Austempering of Spheroidal Cast Iron.
    (Obafemi Awolowo University, 1986) Onuoha, Enyinnaya Martin; Afonja, Adeniyi. A.
    The effect of austempering on the hardness, ultimate tensile strength and per cent elongation of twenty pre-annealed unalloyed spheriodal cast iron specimens have been investigated and evaluated. The specimens were solution treated at 800°C and 900°C, each for 10 and 90 minutes, and isothermally transformed at 300°C and 400°C for 3 hours. The test results indicated hardness and ultimate tensile strength improvements through variations in the three factors. Solution treatment at 900°C for 56.35 minutes followed by isothermal transformation at 352°C for 3 hours yielded a Brinell Hardness Number (BHN) of 315, which was much higher than an average Brinell Hardness Number of 157 obtained in the untreated specimens. Solution treatment temperature appeared to be the most potent of the three factors considered for hardness and strength improvements in the unalloyed spheriodal cast iron. Isothermal transformation temperature exhibited the least positive effect on the mechanical properties tested within the range of temperatures investigated. The per cent elongations obtained at the improved strengths of the unalloyed spheroidal cast iron specimens are indicative of the overall effects of austempering on the mechanical properties.
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    Open Access
    Effect of Composition on the Dielectric Properties of Electrical Porcelain.
    (Obafemi Awolowo University, 1987) Akinbami, John-Fekix Kayode; Adewoye, O. O.
    The effect of compositional change on the dielectric properties (i.e. dielectric constant, dielectric resistance, dissipation factor, loss factor) of Electrical Porcelain has been investigated. The evaluation was carried out using six different compositions. The capacitance and resistance of the samples of the six different compositions over a frequency range of 10 to 105 Hertz were measured. From these experimentally obtained values of resistance and capacitance, the values of the dielectric properties mentioned above were calculated. The samples of the six different compositions were compacted under four different compaction pressures: 2.2 x 108 N/m2, 3.0 x 108 N/m2, 3.2 x 108 N/m2 and 3.5 x 108 N/m2, and fired at four different temperatures: 1250°C, 1300°C, 1350°C and 14000C, and the samples were of varying thicknesses ranging from 2.5mm to 8mm. Available information from the present work suggest that sample “C” with composition, Kaolin, 39.25%; Feldspar, 24.50%; and Quartz, 36.25% gives the best dielectric properties of all the six different compositions. The most probable firing temperature, so as to avoid over firing as well as allow for dense formation to give good dielectric properties of the wares produced, is 1350°C.
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    Effects of Microstructures on the Thermal Properties of Refractory Materials.
    (Obafemi Awolowo University, 1986) Adeoye, Mosobalaje Oyebamiji; Adewoye, O. O.
    The factors controlling the thermal properties of refractory clays obtained from Omi-Adio were investigated. Methods of controlling these factors in refractory bricks were also looked into. A complete feasible step in making of typical refractory bricks out of these clays was suggested, taking note of critical parameters like water content, particle size, compaction pressure and firing temperatures involved. It was found that porosity and pore size played major roles in controlling the thermal properties of the refractories obtained from the clays. Strengths after firing at various temperatures were noted too, including source and mode of failure. The suitability of the bricks as structural materials in terms of strength, and as decorating materials in terms of colour, was found to be good.