http://197.159.135.214/jspui/handle/123456789/754 Thu, 23 Apr 2026 15:06:17 GMT 2026-04-23T15:06:17Z http://197.159.135.214/jspui/handle/123456789/817 Investigation for the Response of High Strength Steel 42CrMo4 to in-situ Hydrogen Loading through Tensile Testing Omar, Marena Hydrogen embrittlement remains a significant challenge in industries requiring high-strength materials operating in hydrogen-rich environments. This study examined the Investigation for the Response of High Strength Steel 42CrMo4 to in-situ hydrogen loading through tensile testing, aiming to unravel the intricate relationship between electrochemical conditions, hydrogen exposure, and the mechanical properties of the alloy steel. Slow strain rate tests were employed to comprehensively explore the material's response under varying conditions. The uncharged specimen in test-1 exhibited remarkable mechanical properties, including high tensile strength, appreciable hardness, and substantial elongation. The microstructural analysis confirmed the presence of a martensitic structure, reflecting inherent strength. However, as the current density increased in tests-2 and 3, hydrogen-induced embrittlement manifested. These tests revealed diminished mechanical integrity, evidenced by decreased ultimate tensile strength, reduced hardness, and limited elongation. The fracture modes observed, characterized by brittle fractures and distinctive fracture surfaces, underscored the susceptibility of 42CrMo4 to hydrogen embrittlement. In conclusion, this research advances the understanding of how current density interacts with hydrogen loading, influencing the mechanical properties of 42CrMo4 alloy steel. The findings contribute to theoretical knowledge, practical applications, and the pursuit of materials that thrive in demanding hydrogen-rich environments. As industries seek to fortify their materials against evolving challenges, the insights from this study provide a solid foundation for the development of hydrogen-resistant components, ensuring safer and more reliable structures in the face of adverse conditions. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use, the Université Felix Houphouët-Boigny, Cote d’Ivoire, and the Jülich Forschungszentrum in partial fulfillment of the requirements for the International Master Program in Renewable Energy and Green Hydrogen (Green Hydrogen Production and Technology) Fri, 01 Sep 2023 00:00:00 GMT http://197.159.135.214/jspui/handle/123456789/817 2023-09-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/816 Synthesis of Co-Fe powder using Ultrasonic Spray Pyrolysis and Hydrogen reduction Keita, Saliha The automotive industry is transitioning from traditional fossil fuel-powered vehicles to electric ones. This change aligns with the growing energy transition and may raise demand for vital metals like nickel and cobalt, essential for battery production. Due to problems with cobalt production from primary sources, switching to secondary sources was the obvious choice. Recycling is seen as an alternative supply option by extracting cobalt from secondary resources. In this study the synthetizes of cobalt powder from the industrial waste solution derived from leaching of industrial polycrystalline diamond blank at temperature range 600-950 C was performed using ultrasonic spray pyrolysis and hydrogen reduction method to recover cobalt. The investigation involved 21 experimental runs using two distinct reactors with varying residence times (7.19 sec and 23 sec) and different precursors solution A (1.12g/l Co, 0.002g/l Fe), solution B (1.87g/l Co, 0.03g/l Fe), solution C (2.81g/l Co, 0.05g/l). The aerosol droplets underwent hydrogen reduction within the temperature range of 600 to 950°C, yielding cobalt powder. The volumetric flow rate of 3 l/min (1 l/min Ar, 2 l/min H2) and a 2-hour reaction time were employed. The effect of the reaction temperature, the concentration of cobalt in the precursor, the residence time, and the on the morphology, composition, specific surface area, and crystal structure of the synthesized iron-cobalt particles was investigated also the collection of particle using magnet. Results indicated that higher temperatures resulted in increased cobalt production. Furthermore, altering the cobalt concentration in the solution influenced particle size, showing that higher concentration led to larger particles. A short residence time (7.9 seconds) at 900°C was found to be more suitable for cobalt nanoparticle synthesis, with spherical particles ranging from 191.1nm to 1222nm. While the potential for powder collection using a magnet was evident, the limited cobalt powder recovery could be attributed to precursor concentration or magnetic strength insufficiency. Despite successful powder capture, addressing the challenge of powder recovery from the tube is crucial. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use, the Université Felix Houphouët-Boigny, Cote d’Ivoire, and the Jülich Forschungszentrum in partial fulfillment of the requirements for the International Master Program in Renewable Energy and Green Hydrogen (Green Hydrogen Production and Technology) Fri, 29 Sep 2023 00:00:00 GMT http://197.159.135.214/jspui/handle/123456789/816 2023-09-29T00:00:00Z http://197.159.135.214/jspui/handle/123456789/815 Model-based Comparative Assessment of Frequency Response Diagnostic Methods for Electrochemical Energy Devices Kebe, Mamadou Moustapha Electrochemical energy devices, including electrolyzers, batteries, and fuel cells, hold significant promise as sustainable solutions for energy storage and conversion. Among fuel cells, polymer electrolyte fuel cells are currently the most widely studied technology and the most promising candidate for sustainable power generation in a wide range of applications. To ensure their reliable operation and optimal performance, accurate diagnostic methods are essential. Frequency response analysis has proven to be a valuable tool for evaluating the dynamic behavior and internal characteristics of electrochemical energy devices. The thesis starts with a comprehensive literature review that focuses on diagnostic methods for frequency response analysis in electrochemical energy devices, especially in polymer electrolyte fuel cells. Various approaches, including electrochemical impedance spectroscopy, electrochemical pressure impedance spectroscopy, concentration-alternating frequency response analysis, and concentration admittance spectroscopy, are explored. The aim of this master thesis is to develop and test a method to characterize and quantitatively compare different frequency response diagnostic methods for polymer electrolyte fuel cells. In order to find the best frequency response analysis method or combination of methods, a framework based on linear system theory is used to evaluate the strength or weakness of a given method. An existing analytical solution of a simple electrochemical impedance spectroscopy model of the cathode catalyst layer of a polymer electrolyte fuel cell is utilized to characterize observability, controllability, and parameter sensitivity. A transmission line model of the cathode catalyst layer is used as well to calculate the impedance response and compared with this analytical solution. Next, a transmission line model that takes into account oxygen transport in the cathode catalyst layer is constructed to calculate the impedance response and compared it with an existing analytical result. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use, the Université Felix Houphouët-Boigny, Cote d’Ivoire, and the Jülich Forschungszentrum in partial fulfillment of the requirements for the International Master Program in Renewable Energy and Green Hydrogen (Green Hydrogen Production and Technology) Fri, 01 Sep 2023 00:00:00 GMT http://197.159.135.214/jspui/handle/123456789/815 2023-09-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/814 The Recovery of Rare Earth Metals from Bauxite Residues Kamara, Mary Dora With the rising use of contemporary, environmentally friendly technology, there is an increase in the demand for crucial commodities like scandium and rare earth elements (REEs) and other valuable metals, which necessitates the use of innovative resources to secure supply. This thesis includes both pyrometallurgical and hydrometallurgical methods aiming decarbonizattion process for recovering valuable metals from bauxite residues, with the hydrogen plasma reduction and direct acid leaching serving as the primary approaches. The objectives of adopting these procedures are to provide alternative and/or creative techniques for the recovery of REEs and other valuable metals from materials like bauxite residue, which cannot be disposed of in an ecologically responsible manner following the Bayer chemical process, which extracts aluminum. As carbon smelting, which was previously used to recover REEs from BR, was inefficient due to using carbon as a reagent, hydrogen is now being investigated as a replacement. Hydrogen plasma reduction recovers about 99,9% of iron as crude metallic iron, which can be separated from slag that contains aluminum and silicon. In order to recover valuable metals like scandium and aluminum, the slag is treated or leached by acids. Bauxite residue is also subjected to direct acid leaching (hydrometallurgy) in order to extract rare earth elements such as yttrium, scandium. To obtain more effective and optimum outcomes, the pyrometallurgy and hydrometallurgy combination of the two techniques was also investigated. Effective characterisation techniques for examining the results of hydrogen plasma reduction and direct acid leaching studies for their mineralogical, chemical (macro component), and micro impurity investigations were described. The goal of extracting Fe, Al, Ti, and Si was accomplished since the data clearly indicate their presence and provide proof that they are vital for a sustainable future and all facets of human existence. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use, the Université Felix Houphouët-Boigny, Cote d’Ivoire, and the Jülich Forschungszentrum in partial fulfillment of the requirements for the International Master Program in Renewable Energy and Green Hydrogen (Green Hydrogen Production and Technology) Fri, 01 Sep 2023 00:00:00 GMT http://197.159.135.214/jspui/handle/123456789/814 2023-09-01T00:00:00Z