Theses

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A long essay or dissertation or thesis involving personal research, written by postgraduates of University of Ghana for a university degree.

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    Ensemble learning prediction of transmittance at different wavenumbers in natural hydroxyapatite
    (Scientific African, 2020) Okafor, E.; Dodoo-Arhin, D.; Obada, D.O.
    Material engineering-based research has often relied so much on tedious human exper iments for generating specific engineering properties with a major draw-back of high time demand that can span between an hour and days. Hence to deviate from the usual paradigm, we provide an alternative approach which employs artificial intelligence (AI) based ensemble learning methods for predicting the degree of transmittance for a range of wavenumbers of infrared radiation through hydroxyapatite (HAp) samples. The effective samples (transmittance and wavenumber) were passed as input to the predictive systems. For this, we trained two ensemble learning methods: Extreme Gradient Boosting (XGBoost) and Random Forest on variants of HAp (density and time variations), while considering a fixed amount of 10,000 base estimators. The results show that Random Forest marginally outperforms the XGBoost in the testing phase but requires a much longer computing time. However, XGBoost is much faster than the Random Forest. Furthermore, the examined en semble learning models yielded a coefficient of determination (R2 > 0.997): which are in close agreement with experimental data, depicting an excellent generalization capacity. Additionally, the examined ensemble learning models showed a significant ≥ 99.83% de crease in computational complexity relative to the time spent when generating the exper imental data. Overall, the use of ensemble learning models is very important for validating material engineering properties
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    Prediction of the reflection intensity of natural hydroxyapatite using generalized linear model and ensemble learning methods
    (Engineering Reports, 2020) Okafor, E.; Dodoo-Arhin, D.; Obada, D.O.; Ibrahim, Y.
    Laboratory data acquisition and analysis of X-ray diffraction (XRD) data involves a lot of tedious human engineering and is time-consuming. To put it in context, a summation of the material synthesis procedure leading to the analysis of the structure of the material can span several days. To curb this challenge and to enhance innovations in engineering pedagogy, this article investigates an alternative method that uses supervised learning algorithms based on ensemble techniques and a generalized linear model (GLM) for predicting reflection intensity (XRD patterns) of raw and natural hydroxyapatite under varying sinter ing temperature conditions given Bragg angles as input to the machine learning algorithms. For the experiment, we trained GLM and ensemble learning models (CatBoost, LightGBM, and two variants of XGBoost based on manual and genetic algorithms for tuning the hyperparameters). The results show that most instances of the XGBoost yielded a robust performance that surpasses all other approaches when predicting X-ray reflection intensities ascribed to the biomaterials subjected to varying sintering temperature conditions. In addition, the results show that all the ensemble techniques significantly outperform the GLM indicates that the former exhibits better generalization capacity. The ensemble learning techniques and the GLM present a reduced computational complexity.
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    Effect of mechanical activation on mullite formation in an alumina-silica ceramics system at lower temperature
    (World Journal of Engineering, 2016) Obada, D.O.; Dodoo-Arhin, D.; Dauda, M.; et al.
    Purpose – This work aims to analyze the effect of mechanical activation on structural disordering (amorphization) in an alumina-silica ceramics system and the formation of mullite most notably at a lower temperature using X-ray diffraction (XRD). Also, an objective of this work is to focus on a low-temperature fabrication route for the production of mullite powders. Design/methodology/approach – A batch composition of kaolin, alumina, and silica was manually pre-milled and then mechanically activated in a ball mill for 30 and 60 min. The activated samples were sintered at 1,150°C for a soaking period of 2 h. Mullite formation was characterized by XRD and scanning electron microscopy (SEM). Findings – It was determined that the mechanical activation increased the quantity of the mullite phase. SEM results revealed that short-milling times only helped in mixing the precursor powders and caused partial agglomeration, while longer milling times, however, resulted in greater agglomeration. Originality/value – It is noted that a manual pre-milling of approximately 20 min and a ball milling approach of 60 min milling time can be suggested as the optimum milling time for the temperature decrease succeeded in the production of mullite from the specific stoichiometric batch formed.
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    Mechanical measurements of pure and kaolin reinforced hydroxyapatite-derived scaffolds: A comparative study
    (Materials Today: Proceedings, 2020) Obada, D.O.; Dodoo-Arhin, D.; Dauda, E.T.; et al.
    This study describes the mechanical properties of pure hydroxyapatite (HAp) and kaolin-reinforced hydroxyapatite (K-HAp) is produced from non-separated animal bones using compression pressure under different sintering regimes. The HAp microparticles were synthesized separately using a facile heat treatment method and reinforced with 15 wt% of beneficiated kaolin (HAp/15 wt% BK) using the sol-gel method. The HAp and K-HAp-derived scaffolds were fabricated by cold pressing with a compaction pressure of 500 Pa. Next, the scaffolds were sintered at 900 C, 1000 C, and 1100 C with a 2 h dwell time in the air atmosphere. Subsequently, the mechanical properties of the scaffolds were examined. The effect of sintering temperature and compaction pressure on the hardness and the compressive strength of the pure and reinforced HAp showed that at all points of measurement (with and without compaction pressure), the mechanical properties increased with an increase in sintering temperature, and the most significant mechanical properties were obtained at 1100 C. The values of hardness at the maximum sintering temperature (1100 C) are 0.93 and 1.09 GPa with and without the application of compaction pressure, respectively, for pure HAp-derived scaffolds and 0.74 and 0.78 GPa with and without the application of compaction pressure, for K-HAp-derived scaffolds. The compressive strength for K HAp had the value of 7.84 MPa as compared with 0.69 MPa for the non-reinforced HAp matrix with the application of compaction pressure (500 Pa). The findings show that the mechanical properties of the synthesized kaolin-reinforced HAp about the scaffolds produced with the low compaction pressure of 500 Pa are suitable for human trabecular bone. 2020 The Authors. Published by Elsevier Ltd. This is an open-access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by nc-and/4.0) Selection and Review under the responsibility of the scientific committee of the International. Conference & Exposition on Mechanical, Material, and Manufacturing Technology.
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    Potentials of fabricating porous ceramic bodies from kaolin for catalytic substrate applications
    (Applied Clay Science, 2016) Obada, D.O.; Dodoo-Arhin, D.; Dauda, M.; et al.
    In this work, the suitability of using kaolin–styrofoam, sawdust, and high-density polyethylene to produce porous ceramic bodies was experimentally investigated. The kaolin samples (raw and beneficiated) were characterized by the XRD, SEM, TGA/DSC, and FTIR methods. Batch formulations of the samples including the kaolin and pore formers were formed into green bodies and fired to 1150 °C. The porosities of sintered bodies were calculated and given the following: apparent porosity: 28.63%–67.13% for all the samples investigated. Samples with high-density polyethylene (HDPE) pore formers showed minor surface cracks after firing but exhibited the highest porosity levels while samples with styrofoam and saw dust exhibited uniform surface characteristics with pores, thermal stability, and no visible surface cracks. It can be concluded that formulations containing 80% kaolin can be used for the production of ceramics with porosities as high as 67% if the right pore formers are used.
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    Physical and Mechanical Properties of Porous Kaolin Based Ceramics at Different Sintering Temperatures
    (The West Indian Journal of Engineering, 2016) Obada, D.O.; Dodoo-Arhin, D.; Dauda, M.; et al.
    In this work, kaolin-based ceramics using styrofoam, sawdust, and powdery high-density polyethylene as pore formers were experimentally investigated. Before batch formulations, the kaolinite used was wet-beneficiated. This was followed by mixing starting materials with pore formers, producing green bodies which were then uni-axially compacted into standard sample dimensions and fired at various sintering temperatures of 850°C, 1000°C, and 1150°C for 2 hours in a furnace. The physical and mechanical properties of the sintered samples were investigated and the generated data was analyzed. It was observed that the apparent porosity and water absorption of the samples decreased with increased sintering temperature, while the bulk density, apparent density, and cold crushing strength of the samples increased with increased sintering temperature. It was concluded that the samples that were sintered at 850°C with 5% wt pore former of powdery high-density polyethylene gave the optimum properties in terms of the porosity and mechanical strength of the samples.
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    Characterization of zeolites as environmental washcoat materials on cordierite ceramics
    (Conference Paper, 2016) Obada, D.O.; Dodoo-Arhin, D.; Dauda, M.; et al.
    Small engines, such as conventional two-stroke engines used in marine outboards and personal watercraft (PWC), are high polluters relative to their engine size and usage. Porous structures based on zeolites show promising characteristics as wash coat materials on cordierite ceramics for tailpipe exhaust emission control. This study reports the characterization of commercial grades of zeolites (Ammonium form of ZSM-5, Zeolite Y, and Mordenite) and several transition phases of these zeolites aiming at their use as environmental washcoat materials. Thermogravimetry, X-ray diffraction, specific surface area, and electron microscopy were used to characterize the zeolites. ZSM-5 shows high thermal and structural stability compared to the other zeolites investigated. As porogenic and increased active site agents, the transition phases showed a large quantity of meso-macro pores and a variation in the specific surface areas of the zeolites still large enough, which highlights their potential to be used in environmental catalysis.
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    Flame Temperature Characteristics and Flue Gas Analysis of an Improvised Biogas Burner
    (The West Indian Journal of Engineering, 2016) Obada, D.O.; Dodoo-Arhin, D.; Dauda, M.
    This study presents the results of an experimental investigation of an initial burner prototype and an improved prototype to report on the quality of biogas, which was produced from a mixture of cattle dung and poultry droppings, operated as feedstock in the ratio of 1 part of dung and droppings to 2 parts of water at a retention time of 30 days. A liquefied natural gas burner was also used for a comparative analysis. The flame temperature testing was carried out with the aid of a Kane–May (KM340) thermocouple. The ambient temperature of the flame produced was taken at three positions—the cone flame, the burning flame, and the flue gas. The results showed that the improved burner had the lowest temperature at the three positions of measurement and needs improvement for household use. Also, a flue gas analysis was carried out to establish the emissions of the stove. The combustion efficiency of the improved stove recorded by the flue gas analyzer was 86.9%.