This investigation was carried out to assess the behaviours of Cold Briquetted Iron (CBI) when exposed to increasing temperature changes up to its complete melting. High-temperature behaviours and melting characteristics of CBI were studied. Ground as-received CBI briquette and those heated to temperatures ranging from 500°C to 1000°C were sieved to maximum of 30 microns diameter size and their room-temperature x-ray diffraction (XRD) measured. CBI was found to contain among others, α-iron, cementite and silica phases. Cementite was found to commence decomposition at 500°C - 600°C and completed by 700°C with conspicuous increase in the concentration of α-iron phase. Only α-iron and silica phases were sustained in CBI at temperatures above 700°C. In an inert atmosphere, it was discovered that CBI melted over a temperature range of 1527.3°C to 1536.96°C accompanied by an irrecoverable weight loss of 9.6 wt.% of the starting material. It was concluded that melting CBI would require charging along it appropriate fluxes to take care of the unreduced iron oxide and incorporation into facility for melting CBI an effective deslagging mechanism to remove unavoidable possible voluminous slag that would be formed.

The demands for increasing the efficiency and lowering the environmental effects in iron and steelmaking industries have given rise to interests in application of direct reduction (DR) processes for production of iron by different gases. These advancements require comprehensive models for better control of the process conditions and the product properties. In the present thesis fundamental aspects in reduction of iron oxide were investigated. The experimental studies on reduction of iron oxide pellets were performed under well-controlled conditions in a setup designed for thermogravimetric investigations. The results indicated that the reaction rates by the applied procedure are higher compared to the procedure similar to conventional thermogravimetric analysis (TGA). This difference was caused by the time required for replacing the inert gas by the reaction gases. Reduction by H2-CO mixtures was accompanied by deposition of carbon and formation of cementite. The variations of cementite contents in the industrial iron ore pellets reduced isothermally for different durations, showed that cementite formation starts from the initial stages of reduction. The experimental conditions such as reaction temperature, carbon activity in the reaction gas and reaction time have a large impact on carbide content of the reduced samples. The kinetics of reduction of iron ore powder by H2 and CO gas mixtures with different compositions were studied using a commercial TGA setup. The results showed that the apparent rates of reaction vary linearly with the H2 and CO contents of the gas. Larger amount of H2 resulted in higher reaction rates. The data were employed in the developed reduction model for pellets. The model was based on the mechanism observed in the commercial iron ore pellets reduced by pure hydrogen. The microstructure of reacted pellets showed that reduction of the examined industrial samples is controlled by both chemical reaction and gaseous diffusion. The reduction model was developed by combining computations for the flow and mass transfer in the gas phase, diffusion of gases in the solid phase and chemical reaction at the reaction sites. The modelling and experimental results were in reasonably good agreement. The present model provides a good foundation for a dynamic multi-particle process model. The results highlighted the importance of considering the reduction mechanisms in different types of pellets prior to modelling. Experiments were undertaken to investigate the selective reduction of iron oxide in zinc ferrite. It was observed that gaseous reduction by hydrogen at temperatures up to 873 K is a potential method for reduction of iron oxide to metallic iron, while the zinc oxide remains in the product and losses of metallic zinc are negligible. Using this primary step in the hydrometallurgical processing of EAFD can overcome the difficulties for leaching of zinc ferrite. / <p>QC 20160823</p>

Iron carbides are amongst the crystalline phases formed during Fischer-Tropsch synthesis to produce hydrocarbons (Dry, 1990, Niemantsverdriet et al., 1980), using iron catalysts. The small crystallite size of the iron carbides causes peak broadening in XRD and prevented complete structure determinations in the past (Hagg, 1931; Retief, 1999; Senateur et al., 1962). Fortunately new instrumentation and techniques, such as fast powder X-ray diffractometers and software for structure determination, are now available to study crystal structures. Five different iron carbide phases are known to form during Fischer-Tropsch synthesis i.e. Hägg carbide (χ-Fe5C2), pseudo-hexagonal iron carbide (έ- Fe2.2C), hexagonal iron carbide (ε-Fe3C), Eckström-Adcock iron carbide (Fe7C3) and cementite (θ-Fe3C). Since the structure of cementite θ-Fe3C is well-known (Westgren & Phragmen, 1922) this study focused on the remainder, i.e. the determination of the crystal structures of the first four iron carbides: Hägg carbide (χ-Fe5C2), pseudo-hexagonal iron carbide (έ -Fe2.2C), hexagonal iron carbide (ε-Fe3C) and Eckström-Adcock iron carbide (Fe7C3). This study consisted of the preparation of iron carbides, structure determinations of these iron carbides, determination of reactions of the iron carbides during Fischer-Tropsch synthesis (FTS) (in situ XRD) and the stability of Hägg carbide (χ-Fe5C2) during FTS under commercial fixed bed reactor conditions. Time-temperature-transformation graphs were determined for iron catalysts with and without potassium promoter. The first step in the structure determination process was the preparation of almost pure samples. Samples of Hagg carbide (:t-FesC2), pseudo-hexagonal 8 -Fe22C iron carbide and hexagonal 1::-Fe3C iron carbide were prepared as pure as possible using the Anton Paar XRK600 reaction chamber attached to an X'Pert Pro multi-purpose diffractometer (N!PD). Eckstrom-Adcock iron carbide (Fe7C3) was available in spent catalyst from a fluidized-bed hydrocarbon synthesis plant at SASOL. These samples were characterized using room temperature and low temperature (77 K) Moss bauer absorption spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM, Philips CM200). Thermo-gravimetric analysis and conductivity measurements were done to characterize the carbonaceous species in the samples. Molecular modelling calculations were done using CASTEP (N!ilman et al., 2000; Payne et al., 1992) to determine the total lattice energies of the iron carbide structures.... / Prof. G.J. Kruger Prof. J.P.R. de Villiers

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Thesis (Ph. D.)--University of New South Wales, 2005. / Also available online.

O objetivo do presente trabalho, consistiu na obtenção de ferro fundidos nodulares, a serem utilizados na fabricação de eixos, com as seguintes características mecânicas após os tratamentos térmicos adequados: limites de resistência à tração e escoamento mínimos de 700 N/mm2 e 450 N/mm2 respectivamente, alongamento mínimo de 5% e dureza entre 235 à 285 HB. A microestrutura mais adequada à obtenção das características mecânicas desejadas deveria consistir de cementita esferoidizada numa matriz ferrítica, a ser obtida com o tratamento de recozimento ou revenimento de microestruturas previamente perlíticas ou martensíticas, respectivamente. No caso do tratamento de recozimento, as estruturas iniciais consistiram de perlita grossa mais ferrita, presentes no material no estado bruto de fusão, ou, de perlita fina mais ferrita, do material normalizado. Todos os tratamentos térmicos utilizados, dependendo do tempo de tratamento, permitiram a obtenção de cementita esferoidizada. O material normalizado e recozido durante 2 horas a 700ºC, possibilitou a obtenção das propriedades mecânicas desejadas: limites de resistência à tração e de escoamento de 827 N/mm2 e 547 N/mm2 respectivamente, alongamento de 7% e dureza de 277 HB, valores estes, dentro dos limites desejados no presente trabalho. No caso do material temperado e revenido a 700ºC durante 0,5 hora, obteve-se limites de escoamento de 542 N/mm2, alongamento de 6% e dureza de 246 HB. O tratamento de recozimento realizado durante 48 horas, produziu microestrutura quase totalmente ferrítica, com pequenas áreas de agregados de carbonetos. O restante do carbono migrou para os nódulos de grafita secundária ao redor dos mesmos. / The purpose of the present work, consisted in obtaining ductile casting iron, that will be used in the shaft production, with de following mechanical properties after the appropriated heat treatments: ultimate tensile strength and yield strength values of 700 N/mm2 and 450 N/mm2 minimum respectively, elongation of 5% minimum and hardness value from 235 to 285 HB. The microstructure more adequated to obtaining the desired mechanical characteristics should consist of spheroidized cementite in a ferritic matrix, to be obtained with the annealing or tempering treatments of microstructures previously pearlitic or martensitic respectively. In the case of the annealing treatment, the initial structures consisted of thick pearlite plus ferrite, wich were in the material in the ascast state, or fine pearlite plus ferrite, of the normalized material. All the used heat treatment, depending on the time of treatment, allowed the obtainment of spheroidized cementite. The material normalized and annealed for 2 hours at 700°C made possible the obtaining of the desired mechanical properties: ultimate tensile strength and yield strength value of 827 N/mm2 and 547 N/mm2 respectively, elongation of 7% and hardness values of 277 HB, values these, in acordance with the aims initially proposed in the present work. In the case of the material quenched and tempered at 700°C for 0,5 hour, it was obtained yield strength values of 542 N/mm2, elongation of 6% and hardness value of 246 HB. The annealing treatment made during 48 hours, produced a microstructure almost totally ferritic, with small areas of aggregated carbides. The remaining of the carbon migrated to the graphite nodules producing secondary graphite around them.

Samples are from I-Shou university Department of Materials Science and Engineering, Dr. Huy-Zu Cheng¡¦s laboratory, First, using sol-gel method to produce silicon dioxide (SiO2) with iron catalysts, and with chemical vapor deposition (CVD) to produce carbon nanotubes. To operate these instruments, for example X-Ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to analyze. The research point is judging the crystallographic orientation relationships between carbon nanotube and catalysts. Using transmission electron microscopy (TEM) to do diffraction patterns with carbon nanotubes and catalysts. From diffraction patterns results, we can decide what catalysts is? And it¡¦s crystallographic relationship. After affirming from diffraction patterns, there are three chemical compositions in the carbon nanotubes, including Fe3C¡B

The phenomenon of hydrogen embrittlement in steel has been known for over 150 years. Hydrogen-resistant alloys have been developed to mitigate this effect and three types of alloys with optimised structures have been enhanced over the years: nickel alloys, stainless steels, and quenched and tempered martensitic low alloy steels. Nevertheless, those alloys are limited in terms of strength and ductility. The aim of the work presented in this thesis was to design bainitic alloys with hydrogen embrittlement resistance, and with a better combination of strength and ductility than conventional alloys. In the novel alloys, two microstructural features were produced to mitigate the damaging effects of hydrogen: 1. A percolating austenite structure, in which hydrogen diffusion is orders of magnitude lower than in bainitic ferrite. This feature was introduced to impede the ingress of hydrogen through the structure. 2. Iron carbide traps, which can form at the bainite transformation temperature. This feature was introduced to trap diffusible hydrogen and prevent it from causing damage. The alloys, designed with the aid of computer models and phase transformation theory, contained a volume fraction of retained austenite above its percolation threshold, theorised as 0.1, which was proven to form an effcient barrier to hydrogen ingress. The effective diffusivity of hydrogen, measured using an electrochemical permeation technique, was shown to decrease with increasing austenite fraction up to the percolation threshold. It was seen to plateau for austenite fractions comprised between 0.1 and 0.18, and to decrease further for fractions above 0.18. The compositions of the alloys were precisely selected to allow for iron carbides to precipitate during the bainitic transformation reaction. Until the present work, only alloy carbides V4C3, TiC and NbC had been reported to strongly trap hydrogen. The literature was very inconsistent regarding the trapping ability of cementite, with reported trap binding energies ranging from 11 to 66 kJ mol−1. The carbides produced in the alloys were identified as cementite. The cementite fraction was measured to be 0.001 ± 0.0001 for one of the designed alloys, which is the lowest ever reported carbide fraction in steel measured using a simple X-ray diffraction technique. Experimental thermal desorption spectroscopy data were used to determine the binding energy of hydrogen to cementite to be 37.5 kJ mol−1, suggesting that cementite is not a strong hydrogen trap. Further tests performed after room temperature hydrogen degassing displayed insignifcant amount of trapped hydrogen, thus confrming the reversible nature of cementite traps. The comparison of two successive transients using the electrochemical permeation technique confirmed that result. The influence of the heat treatments on the microstructures and on the mechanical properties of the designed alloys was extensively studied. The novel alloys met all the set requirements, and successfully outperformed conventional alloys in terms of strength and ductility. They did not meet the NACE TM0316-2016 standard requirement for operation in hydrogen-rich environments, likely owing to the inadequate trapping ability of cementite. Future work should focus on exploring the possible use of alternative carbides for hydrogen trapping in bainitic structures.

O objetivo do presente trabalho, consistiu na obtenção de ferro fundidos nodulares, a serem utilizados na fabricação de eixos, com as seguintes características mecânicas após os tratamentos térmicos adequados: limites de resistência à tração e escoamento mínimos de 700 N/mm2 e 450 N/mm2 respectivamente, alongamento mínimo de 5% e dureza entre 235 à 285 HB. A microestrutura mais adequada à obtenção das características mecânicas desejadas deveria consistir de cementita esferoidizada numa matriz ferrítica, a ser obtida com o tratamento de recozimento ou revenimento de microestruturas previamente perlíticas ou martensíticas, respectivamente. No caso do tratamento de recozimento, as estruturas iniciais consistiram de perlita grossa mais ferrita, presentes no material no estado bruto de fusão, ou, de perlita fina mais ferrita, do material normalizado. Todos os tratamentos térmicos utilizados, dependendo do tempo de tratamento, permitiram a obtenção de cementita esferoidizada. O material normalizado e recozido durante 2 horas a 700ºC, possibilitou a obtenção das propriedades mecânicas desejadas: limites de resistência à tração e de escoamento de 827 N/mm2 e 547 N/mm2 respectivamente, alongamento de 7% e dureza de 277 HB, valores estes, dentro dos limites desejados no presente trabalho. No caso do material temperado e revenido a 700ºC durante 0,5 hora, obteve-se limites de escoamento de 542 N/mm2, alongamento de 6% e dureza de 246 HB. O tratamento de recozimento realizado durante 48 horas, produziu microestrutura quase totalmente ferrítica, com pequenas áreas de agregados de carbonetos. O restante do carbono migrou para os nódulos de grafita secundária ao redor dos mesmos. / The purpose of the present work, consisted in obtaining ductile casting iron, that will be used in the shaft production, with de following mechanical properties after the appropriated heat treatments: ultimate tensile strength and yield strength values of 700 N/mm2 and 450 N/mm2 minimum respectively, elongation of 5% minimum and hardness value from 235 to 285 HB. The microstructure more adequated to obtaining the desired mechanical characteristics should consist of spheroidized cementite in a ferritic matrix, to be obtained with the annealing or tempering treatments of microstructures previously pearlitic or martensitic respectively. In the case of the annealing treatment, the initial structures consisted of thick pearlite plus ferrite, wich were in the material in the ascast state, or fine pearlite plus ferrite, of the normalized material. All the used heat treatment, depending on the time of treatment, allowed the obtainment of spheroidized cementite. The material normalized and annealed for 2 hours at 700°C made possible the obtaining of the desired mechanical properties: ultimate tensile strength and yield strength value of 827 N/mm2 and 547 N/mm2 respectively, elongation of 7% and hardness values of 277 HB, values these, in acordance with the aims initially proposed in the present work. In the case of the material quenched and tempered at 700°C for 0,5 hour, it was obtained yield strength values of 542 N/mm2, elongation of 6% and hardness value of 246 HB. The annealing treatment made during 48 hours, produced a microstructure almost totally ferritic, with small areas of aggregated carbides. The remaining of the carbon migrated to the graphite nodules producing secondary graphite around them.

No description available.