Publication Search Results

Now showing 1 - 6 of 6
  • (2019) Hossain, Rumana
    Although 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.

  • (2014) Park, Hyunsik
    In the present thesis, the effect of CaO-SiO2-Al2O3 oxide system on the reduction behaviour of carbon composite pellet was studied at iron-making temperatures between 1000oC and 1500oC. Compositional differences in the CaO-SiO2-Al2O3 ternary system were confirmed to influence the reactions occurring in composite pellets at high temperatures from 1350°C to 1500°C. Changes in physical appearance and off-gas composition during the in situ reaction experiments demonstrated a strong correlation between the oxide composition and internal reactions. Microscopic observation using light optical microscopy and scanning electron microscope confirmed the correlation between the morphological change of pellets and the compositional difference of oxide systems. Samples were also analysed by X-ray diffraction to investigate phase change during the reduction process. Impact of oxide chemistry was established as each pellet illustrated different state of iron oxide as a function of time. Physical property of pellet was confirmed to be largely influenced by its associated oxide binder systems selected for this study. The influence of compositional changes in the CaO - FeOt - (Al2O3) or (SiO2) ternary oxide system on the reaction kinetics of carbon composite pellet was investigated by using Thermo-Gravimetric Analyser (TGA) at temperatures from 1000oC to 1200°C. Measured CO and CO2 gas by infrared gas analyser and surface area change using BET analysis assisted with the reaction kinetics of carbon composite pellet at 1200oC. As a result, alumina increased the reduction rate of iron oxide by increasing surface area, while silica decreased reduction rate by reducing surface area of pellet samples. A modified reaction kinetic model taking into account both the Boudouard reaction and surface area variation was developed for a better understanding of reduction mechanisms occurring in carbon composite pellets. The effect of alumina and silica on the reaction behaviour of carbon composite pellet was investigated at 1000°C and 1100°C respectively. The overall reaction was divided into three stages according to phase transformation of iron oxide analysed by X-ray diffraction. The Boudouard reaction was largely influenced by alumina and silica that changed CO gas concentration resulting in different reduction behaviour of the pellets.

  • (2014) Ye, Zhuozhu
    Coke performance in an operating blast furnace is often empirically related to popular bench-scale tests, which are performed at relative much lower temperatures. Due to difficulties of sampling, there is a limited understanding of the tuyere-level coke characteristics. An experimental study was performed to characterise the coke properties at tuyere level of a blast furnace as a function of different levels of supplementary oil injection. Coke samples were obtained through tuyere drilling and analysed using a range of analytical tools including XRD, SEM and high temperature reactors with emphasis on mineralogy, carbon structure and reactivity. Carbon structure was found to be a suitable indicator to assess tuyere-level temperature. Quartz and mullite were found to be significantly reduced in tuyere-level cokes while SiC and ferrosilicon alloys were the most notable Si bearing minerals formed. Recirculating alkalis were found to have most significant impact on coke apparent reactivity. Graphitization was found to contribute in -0.45 mm coke fines generation. The injection rate was found to have most distinct effect on the coke samples from the bosh and raceway regions. High injection rate cokes were distinguished by a greater degree of graphitization, less amount of SiC and complete absence of mullite phase. Ferrosilicon phases were not influenced. The apparent reaction rates of high injection rate cokes was shown to be marginally lower, which is attributed to higher degree of graphitization and less amount of adsorbed potassium. The study suggested that the effect of injection rate on the modification of coke properties is mainly attributed to changes in temperature profile of tuyere-level regions. The ferrosilicon alloys were found to catalyse coke graphitization intensity. The hot metal was shown to have a stronger effect on the ferrosilicon formation compare to in situ formation. Quartz particle size does not seem to be a critical factor in SiC formation in tuyere-level cokes due to such long reaction time at high temperatures. Both SiC and ferrosilicon phases did not increase the coke reactivity. The study established that conventional means of coke testing may not have any significant bearing on the coke properties as it descends into tuyere-level regions.

  • (2015) Ko, Kwang-Hyun
    In this study, pyrolysis of two types of biomass (macadamia nut shell: MNS and coconut shell: CNS), a synthetic plastic (polyethylene terephthalate: PET) and blends of the biomass with PET were investigated. The thermal degradation kinetics and the carbon structure evolution of the char residues were monitored as a function of heating rates, blending ratios and temperatures. Effects of heating rate and blending ratio on the degradation kinetics were studied in a large-scale thermogravimetric analyzer (TGA) reactor. The char structure was characterized by a combination of solid state 13C nuclear magnetic resonance (NMR) spectroscopy, Raman spectroscopy and XRD. The formation and evolution of radical concentration in the char were investigated using solid state 1H nuclear magnetic resonance (NMR) spectroscopy. Effects of carbon structure and microtexture on reactivity of the char was investigated by CO2 reactivity.

  • (2012) Mohd Yunos, Nur Farhana Diyana Binti
    Iron and steel making is an energy intensive industrial sector using mainly coal as the heat source and reduction agent. The industry gives rise to about 10 % of the anthropogenic CO2 emissions in the world. Due to the challenge for CO2 mitigation, interest for agricultural waste (palm and coconut shells) use as a renewable energy and carbon source as heating agent and reducing agent contributes to energy conservation and emission reduction, and can partially replace coal and coke. In the present study, the conventional material investigated was metallurgical coke which was blended with different proportions of palm and coconut shells as well as agricultural waste chars in order to reduce the waste in the landfill. Metallurgical coke, palm shell/coke blends and coconut shell/coke blends were combusted in a drop tube furnace (DTF) at 1200 °C under 20% O2 and 80% N2 gas mixture while palm char was devolatilized at 450 °C under N2 atmosphere. Subsequently, the residual materials were put in contact with an EAF iron oxide rich slags and their interfacial reactions and phenomena have been studied at 1550 °C in a horizontal tube furnace under inert atmosphere (1 L/min Ar) with off gases measured using an IR analyser. The initial devolatilization and the subsequent step of combustion of these samples are conducted in a Drop Tube Furnace (DTF) and in a Thermogravimetric Analyser (TGA), respectively, while the sessile drop approach was used to investigate the interfacial reactions taking place in the slag/carbon region. A Thermogravimetric Analyser coupled with Mass Spectrometer (TGA-MS) was also used to study the behavior of coke and agricultural wastes at high temperatures in order to understand the thermal behavior and gas products that evolved at high temperatures. The weight loss profiles, gas formation and products distribution were significantly different between the coke and agricultural waste samples. It was found that more gases were released from agricultural waste than from coke that participated in the subsequent carbon/slag reactions. In the gas phase reaction studies, the blends containing agricultural waste materials indicated higher combustion efficiencies compared to coke alone with an improved surface area resulted from volatile matter removal. The role of chemical structure and properties, as well as inorganic matter in agricultural waste blends also influenced the combustion performance. The rate of devolatilization appears to improve the coke/palm shell blends burnout as well as its foaming behavior when put in contact with an iron oxide rich slag. For carbon/slag interactions, experiments were conducted using the sessile drop technique (1550 °C) with off gases (CO, CO2) measured using an IR analyzer; the wetting behaviour was determined from contact angle measurements and estimation of slag foam volumes were calculated using specialized software. Off gas analyses following the carbon/slag interfacial reactions have been measured for all the carbonaceous materials and significantly different gas concentrations have been observed. The rates of total gas generation (CO+CO2) from palm char was comparable to those seen in coke; however the gases released from palm chars were extent over a longer period of time and allowed their entrapment in the slag matrix, enhancing the volume of the slag. A slower rate of FeO reduction is seen when coke reacted with the Electric Arc Furnace (EAF) slag, while the palm shell blends showed a faster reduction. Independent of the carbon material used as a substrate, the final stage of reaction reveals comparable contact angles due to similar extents of reduction and Fe deposition at the interface. The steady gas generation seen in palm char compared to coke allows the formation of a highly porous particle, promoting gasification and allowing more gases to be trapped in the slag phase. These results indicate that partial replacement of coke with palm shells is not only viable, but efficient leading to improved/sustained interactions with EAF slag. Optimization between the two phenomena, reduction and foaming is required for improved EAF process performance.

  • (2019) Assefi, Mohammad
    With 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.