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(2019)ThesisAlthough high carbon martensitic steels with dual phase, i.e. retained austenite and martensite, are well known for their industrial utility in high abrasion and extreme operating environments, due to their hardness and strength, the compressive stability of their retained austenite, phase transformation behaviour under different load and the implications for the steels’ performance and potential uses, is not well understood. These aspects need to be understood in depth for creating a set of information which can be used for designing new application for this steel or for improving the performance of the steel. The phase transformation mechanism was identified, from the macro to the nano level which shows that, at the early stage of plastic deformation ε-martensite formation dominates, while higher compression loads trigger α’-martensite formation. Different strain rates transform austenite into martensite at different volume, simultaneously activate multiple micromechanisms, i.e., dislocation defects, nanotwining, etc. that enhanced the phase stability and refined the microstructure which led to an increase in the hardness. Increasing Cr %, altered the morphology and stability of the phases and the overall structure. Also, post-tempering heat treatment facilitates redistribution of carbon, decreased the hardness of martensite and overall hardness but increased the stability of austenite significantly. This research also identifies the hybrid structure of the white layer in high carbon steel and demonstrates the combination of phase transformations, strain hardening, and grain refinement led to a hybrid microstructure. This comprehensive study could enable the understanding of the precise control of the microstructures of high carbon martensitic steels, and hence their properties. Microstructural engineering through a controlled high compact deformation has been used to produce nano-grain martensitic structure (~40nm) which has ceramic-like hardness with metal-like toughness. An innovative method of transforming steel surface into multi layered ceramic-diffusion-metal structure using the waste source. Through a controlled high-temperature reaction, the outer layer of a steel surface was produced as an ultra-hard ceramic surface and the inner layer is produced as a metal matrix enriched with carbides. The result reveals that by turning the normal metal surface into a complex ceramic-diffusion-metal structure, extremely high hardness can be achieved.
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(2019)ThesisWith technological advancement and increasingly short production cycles of electronic devices, LCD with flat screen TV has become a major component of e-waste destined for landfills. According to published data, more than 200 million of LCD-TV are produced annually. Such massive production of LCD requires a high consumption of indium (i. e., approximately 55% to 85% of global indium generation is used in the form of indium-tin-oxide ITO layer in LCDs). However, indium as a scattered and rare element in the Earth’s crust is challenging to be extracted and the scrap LCD screens are one of the most favorable alternative resources for indium demand. On the other hand, the majority of the weight of the LCD screen is made of glass with no available method for industrial recycling in the market. This thesis investigates different chemical and physical methods aiming to propose scalable procedures for recycling of the indium and glass contents of the waste LCD panels. The thesis first studies the extraction and concentration of the indium content using an acidic leaching and adsorption/desorption process as a hydrometallurgical method. For the extraction section, inorganic acids with the help of ultrasonic waves were used. To concentrate extracted indium, three macroporous polystyrene-divinylbenzene resins (Lewatit TP 208, Lewatit TP 260 and Amberlite IRA 743) were employed and effective parameters on the efficiency of the adsorption/desorption process was investigated. The data showed that Lewatit TP 208 with an iminodiacetic as a functional group on its surface had better efficiency when adsorption process was operated at optimized parameters (i.e., pH of 2, resin loading mass of 0.5 g resin, the temperature of 25oC, and reaction time of 30 min). Thermodynamic and kinetic studies were also investigated and it was found that adsorption of indium had an endothermic and spontaneous nature which was fitted to the pseudo-second-order model. A new approach for recovery of the e-waste and its embedded valuable metals can be a direct conversion of them into value-added products such as nanostructured or functional materials. In this thesis, using of waste LCD panel as a precursor for the preparation of nanostructure indium borate (InBO3) was achieved in a relatively easy manner by acid leaching and precipitation methods. The oxalic acid was used to leach the indium from a crushed LCD sample. Through the leaching process, boric acid was also extracted along with the In content. This novel recycling method was followed by drying and thermal processing of the extracted compounds which resulted in the synthesis of nanoparticles of InBO3 with an average particle size of 20 nm. A multi-mechanism was also proposed to explain the reaction of the synthesis and the mechanism was confirmed by thermodynamic data using HSC software. In order to propose a holistic methodology for recycling of the LCD panels, in addition to the concentration of the indium and synthesis of InBO3, the glass content of the LCD was also considered as a valuable raw material for the preparation of functional products. Waste glasses can be used as a raw material for the preparation of glass foams, as porous ceramics with low density, and high thermal stability. Glass foams have demanding application as insulation panels in building industries aiming to reduce the energy consumption. Therefore, this thesis details a comprehensive study on the recycling of the glass proportion of the waste LCD by preparation of a glass foam with highlighted mechanical properties. In this work, the glass powder obtained from a shredded LCD panel was mixed with some foaming agents and subjected to a heating process at 900oC with a controlled ramping temperature. To propose a procedure with more sustainability, the foaming agents were chosen mostly from waste resources. By optimizing the concentration of the foaming agents such as 25 wt.% of spent coffee as an organic C-based foaming agent with 1.25 wt.% of MnO2 and Na2CO3 at 900oC for 30 minutes, promising mechanical properties such as compressive strength of 18.7 MPa, the high flexural strength of 6 MPa, at the low density of 0.85 g/cm3 were achieved. The XRD result showed that through the foaming process a silica phase had been formed into the glass foam ceramic leading to the enhancement of the crystallinity and mechanical properties of the as-prepared foams. The formation of bubbles into the foam structure was observed by SEM images. Finally, to propose another route for the direct conversion of the LCD into functional materials, the possibility of using the glass compounds from the LCD in the synthesis of the nanocatalysts was investigated. In this method, instead of consuming raw materials such as silica and alumina as a substrate in the synthesis of the catalysts, recycled glass was replaced. The glass part of the waste LCD is effectively used for the synthesis of two types of core-shell nanocatalysts consisting of glass as the core substrate, and NiO and Co3O4 as the shells. In the catalyst manufacturing, the precursor materials for the synthesis is always supplied from raw chemicals. However, in this work, instead of using raw synthetic precursors for NiO and Co3O4 synthesis, the metallic resources were also supplied from waste batteries such as Ni-Cd and Li-ion batteries, respectively. The core-shell structure of the observed products was examined using energy-dispersive X-ray spectroscopy (EDS) maps coupled with TEM technique. The photocatalytic activity data of NiO@substrate and Co3O4@substrate shows that using a low power UV (9W) irradiation can degrade an organic dye presenting a common pollution structure in wastewater resources.