Reduction of New Zealand Titanomagnetite Ironsand by Hydrogen Gas in a Fluidised Bed System

<p>Titanomagnetite (TTM) ironsand has been used to produce steel in New Zealand (NZ) for about 40 years. However, the current steelmaking process in NZ produces high emissions of CO2 because it uses coal as a primary reducing agent. The fluidised bed (FB) process allows the use of pure hydrogen gas to reduce ironsand, and as a result, does not produce CO2 gas. However, for conventional hematite ores, reduction in a FB system is usually limited by the onset of particle sticking at temperatures ≳ 800°C. This thesis investigates the reduction of NZ TTM ironsand by hydrogen gas in the FB system with a key focus on ore sticking behaviour. Initially, this thesis reports preliminary fluidisation tests by nitrogen and helium gases at room temperature, carried out to determine key fluidisation parameters for ironsand powder. From these results, a laboratory-scale experimental FB reactor has been designed and built for the hydrogen reduction study at high temperatures. A key feature of the reactor is a novel in-situ sampling system, which enables extraction of multiple samples during a single experimental run without interrupting operation of the FB. Quantitative X-ray diffraction (q-XRD) has been used to determine the metallisation degree of partially reduced samples. Phase evolution during the reaction has also been analysed using q-XRD alongside scanning electron microscopy/energy dispersed spectroscopy (SEM/EDS). Additionally, the water vapour compositions in the exhaust gas were calculated from the q-XRD data and also measured in real-time using a high-temperature humidity sensor. The effect of various parameters has been investigated within the FB reduction experiments: hydrogen gas concentrations, hydrogen gas flow rate, bed mass, particle size, and temperature. The results indicate that across the entire range of controlled studied, the FB reduction rate of TTM ironsand is simply controlled by the rate of hydrogen gas supply. Interestingly, there were no occurrences of the sticking phenomenon at any point during the reduction by hydrogen gas at high temperatures of up to 1000°C. Sticking appears to be prevented by the formation of a protective titanium-rich oxide shell around each particle during the initial reduction stage. Importantly, this shell remains present throughout the reduction process, and as a result, the reduction reaction proceeds rapidly to completion with a metallisation degree of ~93%. The influence of temperature on the reaction progress has also been investigated. The reduction pathway appears to vary within different temperature regimes. At low temperatures (750°C-800°C), TTM is directly reduced to metallic iron and ilmenite without any evidence of wüstite phase. At ‘intermediate temperatures’ (850°C-900°C) small amount of short-lived wüstite is observed. Some of the amount of TTM appears to be reduced to wüstite, and some is directly reduced to metallic iron. At high temperatures (≥ 950°C), approximately half of the initial TTM phase is quickly reduced to wüstite. After that point, wüstite is then reduced to metallic iron whilst the reduction of TTM stops. This is due to the enrichment of Ti species in TTM phase, which stabilises TTM crystal. Once wüstite has been fully reduced, the reduction of TTM then resumes. Throughout the entire experimental program for this thesis, particle sticking was observed to occur only under two specific sets of experimental conditions. These were: reduction by 100% H2 gas at 1050°C (case A) and reduction by 7.5 mol.% H2O – 92.5 mol.% H2 at 950°C (case B). In both cases, sticking occurred as a sinter which nucleated at the reactor wall surface, while most particles remained fluidised as loose powder. The mechanism of these sticking cases has been analysed by XRD and SEM. The results suggest that silica from the quartz reactor wall reacted and bonded with Fe from particles to nucleate the initial sinter. In summary, the findings in this thesis show that the hydrogen-FB process is highly effective in reducing NZ ironsand to a direct reduced iron (DRI) product. These findings open up the possibility of developing a new industrial FB technology for the direct reduction of NZ TTM ironsand, with extremely low CO2 emissions.</p>

Reduction of New Zealand Titanomagnetite Ironsand by Hydrogen Gas in a Fluidised Bed System

<p>Titanomagnetite (TTM) ironsand has been used to produce steel in New Zealand (NZ) for about 40 years. However, the current steelmaking process in NZ produces high emissions of CO2 because it uses coal as a primary reducing agent. The fluidised bed (FB) process allows the use of pure hydrogen gas to reduce ironsand, and as a result, does not produce CO2 gas. However, for conventional hematite ores, reduction in a FB system is usually limited by the onset of particle sticking at temperatures ≳ 800°C. This thesis investigates the reduction of NZ TTM ironsand by hydrogen gas in the FB system with a key focus on ore sticking behaviour. Initially, this thesis reports preliminary fluidisation tests by nitrogen and helium gases at room temperature, carried out to determine key fluidisation parameters for ironsand powder. From these results, a laboratory-scale experimental FB reactor has been designed and built for the hydrogen reduction study at high temperatures. A key feature of the reactor is a novel in-situ sampling system, which enables extraction of multiple samples during a single experimental run without interrupting operation of the FB. Quantitative X-ray diffraction (q-XRD) has been used to determine the metallisation degree of partially reduced samples. Phase evolution during the reaction has also been analysed using q-XRD alongside scanning electron microscopy/energy dispersed spectroscopy (SEM/EDS). Additionally, the water vapour compositions in the exhaust gas were calculated from the q-XRD data and also measured in real-time using a high-temperature humidity sensor. The effect of various parameters has been investigated within the FB reduction experiments: hydrogen gas concentrations, hydrogen gas flow rate, bed mass, particle size, and temperature. The results indicate that across the entire range of controlled studied, the FB reduction rate of TTM ironsand is simply controlled by the rate of hydrogen gas supply. Interestingly, there were no occurrences of the sticking phenomenon at any point during the reduction by hydrogen gas at high temperatures of up to 1000°C. Sticking appears to be prevented by the formation of a protective titanium-rich oxide shell around each particle during the initial reduction stage. Importantly, this shell remains present throughout the reduction process, and as a result, the reduction reaction proceeds rapidly to completion with a metallisation degree of ~93%. The influence of temperature on the reaction progress has also been investigated. The reduction pathway appears to vary within different temperature regimes. At low temperatures (750°C-800°C), TTM is directly reduced to metallic iron and ilmenite without any evidence of wüstite phase. At ‘intermediate temperatures’ (850°C-900°C) small amount of short-lived wüstite is observed. Some of the amount of TTM appears to be reduced to wüstite, and some is directly reduced to metallic iron. At high temperatures (≥ 950°C), approximately half of the initial TTM phase is quickly reduced to wüstite. After that point, wüstite is then reduced to metallic iron whilst the reduction of TTM stops. This is due to the enrichment of Ti species in TTM phase, which stabilises TTM crystal. Once wüstite has been fully reduced, the reduction of TTM then resumes. Throughout the entire experimental program for this thesis, particle sticking was observed to occur only under two specific sets of experimental conditions. These were: reduction by 100% H2 gas at 1050°C (case A) and reduction by 7.5 mol.% H2O – 92.5 mol.% H2 at 950°C (case B). In both cases, sticking occurred as a sinter which nucleated at the reactor wall surface, while most particles remained fluidised as loose powder. The mechanism of these sticking cases has been analysed by XRD and SEM. The results suggest that silica from the quartz reactor wall reacted and bonded with Fe from particles to nucleate the initial sinter. In summary, the findings in this thesis show that the hydrogen-FB process is highly effective in reducing NZ ironsand to a direct reduced iron (DRI) product. These findings open up the possibility of developing a new industrial FB technology for the direct reduction of NZ TTM ironsand, with extremely low CO2 emissions.</p>

Characterization of iron-doped crystalline silicon nanoparticles and their modification with citrate anions for in vivo applications

Objectives. This paper presents data on the development and study of the structural properties of iron-doped crystalline silicon (nc-Si/SiOx/Fe) nanoparticles obtained using the plasma-chemical method for application in magnetic resonance imaging diagnostics and treatment of oncological diseases. This work aimed to use a variety of analytical methods to study the structural properties of nc-Si/SiOx/Fe and their colloidal stabilization with citrate anions for in vivo applications.Methods. Silicon nanoparticles obtained via the plasma-chemical synthesis method were characterized by laser spark emission spectroscopy, atomic emission spectroscopy, Fouriertransform infrared spectroscopy, and X-ray photoelectron spectroscopy. The hydrodynamic diameter of the nanoparticles was estimated using dynamic light scattering. The toxicity of the nanoparticles was investigated using a colorimetric MTT test for the cell metabolic activity. Elemental iron with different Fe/Si atomic ratios was added to the feedstock during loading.Results. The particles were shown to have a large silicon core covered by a relatively thin layer of intermediate oxides (interface) and an amorphous oxide shell, which is silicon oxide with different oxidation states SiOx (0 ≤ x ≤ 2). The samples had an iron content of 0.8–1.8 at %. Colloidal solutions of the nanoparticles stabilized by citrate anions were obtained and characterized. According to the analysis of the cytotoxicity of the modified nanosilicon particles using monoclonal K562 human erythroleukemia cells, no toxicity was found for cells in culture at particle concentrations of up to 5 µg/mL.Conclusions. Since the obtained modified particles are nontoxic, they can be used in in vivo theranostic applications.

Near-infrared-active upconverting niobium-doped black titanium dioxide photocatalysts

Black titanium dioxide is a broadband-absorbing photocatalyst characterized by integration of atomic hydrogen within the outer layers of anatase nanomaterials. In addition to is broad absorbance of visible to near-infrared light, the material has some intrinsic upconversion ability, which is greatly enhanced by the addition of a niobium oxide shell. This yields a highly active photocatalyst as demonstrated in photodegradation experiments.

The Architectonics Features of Heterostructures for IR Range Detectors Based on Polycrystalline Layers of Lead Chalcogenides

A model is developed for the formation of porous intragranular architectonics of nanostructured polycrystalline layers of lead chalcogenides for photodetectors and IR emitters. The layers are obtained under the conditions of thermal evaporation in a quasi-closed volume by the “hot wall” method followed by sensitizing heat treatment in an iodine-containing atmosphere. Model concepts are developed considering the experimental results of studying the intragranular structure of lead chalcogenides through original combined AFM methods over the cross-section of porous grains (cores) encapsulated by an oxide shell (lateral force microscopy and local tunneling I–V spectroscopy).

Evolution of Structural and Magnetic Properties of Fe-Co Wire-like Nanochains Caused by Annealing Atmosphere

Thermal treatment is a post-synthesis treatment that aims to improve the crystallinity and interrelated physical properties of as-prepared materials. This process may also cause some unwanted changes in materials like their oxidation or contamination. In this work, we present the post-synthesis annealing treatments of the amorphous Fe1−xCox (x = 0.25; 0.50; 0.75) Wire-like nanochains performed at 400 °C in two different atmospheres, i.e., a mixture of 80% nitrogen and 20% hydrogen and argon. These processes caused significantly different changes of structural and magnetic properties of the initially-formed Fe-Co nanostructures. All of them crystallized and their cores were composed of body-centered cubic Fe-Co phase, whereas their oxide shells comprised of a mixture of CoFe2O4 and Fe3O4 phases. However, the annealing carried out in hydrogen-containing atmosphere caused a decomposition of the initial oxide shell layer, whereas a similar process in argon led to its slight thickening. Moreover, it was found that the cores of thermally-treated Fe0.25Co0.75 nanochains contained the hexagonal closest packed (hcp) Co phase and were covered by the nanosheet-like shell layer in the case of annealing performed in argon. Considering the evolution of magnetic properties induced by structural changes, it was observed that the coercivities of annealed Fe-Co nanochains increased in comparison with their non-annealed counterparts. The saturation magnetization (MS) of the Fe0.25Co0.75 nanomaterial annealed in both atmospheres was higher than that for the non-annealed sample. In turn, the MS of the Fe0.75Co0.25 and Fe0.50Co0.50 nanochains annealed in argon were lower than those recorded for non-annealed samples due to their partial oxidation during thermal processing.

TiO2 (Core)/Crumpled Graphene Oxide (Shell) Nanocomposites Show Enhanced Photodegradation of Carbamazepine

The presence of pharmaceuticals and personal care products (PPCPs) in aquatic systems is a serious threat to human and ecological health. The photocatalytic degradation of PPCPs via titanium oxide (TiO2) is a well-researched potential solution, but its efficacy is limited by a variety of environmental conditions, such as the presence of natural organic macromolecules (NOM). In this study, we investigate the synthesis and performance of a novel photoreactive composite: a three-dimensional (3D) core (TiO2)-shell (crumpled graphene oxide) composite (TiGC) used as a powerful tool for PPCP removal and degradation in complex aqueous environments. TiGC exhibited a high adsorption capacity (maximum capacity 11.2 mg/g, 100 times larger than bare TiO2) and a 30% enhancement of photodegradation (compared to bare TiO2) in experiments with a persistent PPCP model, carbamazepine (CBZ). Furthermore, the TiGC performance was tested under various conditions of NOM concentration, light intensity, CBZ initial concentration, and multiple cycles of CBZ addition, in order to illustrate that TiGC performance is stable over a range of field conditions (including NOM). The enhanced and stable performance of TiCG to adsorb and degrade CBZ in water extends from its core-shell composite nanostructure: the crumpled graphene oxide shell provides an adsorptive surface that favors CBZ sorption over NOM, and optical and electronic interactions between TiO2 and graphene oxide result in higher hydroxyl radical (•OH) yields than bare TiO2.

Atomic-Scale Layer-by-Layer Deposition of FeSiAl@ZnO@Al2O3 Hybrid with Threshold Anti-Corrosion and Ultra-High Microwave Absorption Properties in Low-Frequency Bands

Developing highly efficient magnetic microwave absorbers (MAs) is crucial, and yet challenging for anti-corrosion properties in extremely humid and salt-induced foggy environments. Herein, a dual-oxide shell of ZnO/Al2O3 as a robust barrier to FeSiAl core is introduced to mitigate corrosion resistance. The FeSiAl@ZnO@Al2O3 layer by layer hybrid structure is realized with atomic-scale precision through the atomic layer deposition technique. Owing to the unique hybrid structure, the FeSiAl@ZnO@Al2O3 exhibits record-high microwave absorbing performance in low-frequency bands covering L and S bands with a minimum reflection loss (RLmin) of -50.6 dB at 3.4 GHz. Compared with pure FeSiAl (RLmin of -13.5 dB, a bandwidth of 0.5 GHz), the RLmin value and effective bandwidth of this designed novel absorber increased up to ~ 3.7 and ~ 3 times, respectively. Furthermore, the inert ceramic dual-shells have improved 9.0 times the anti-corrosion property of FeSiAl core by multistage barriers towards corrosive medium and obstruction of the electric circuit. This is attributed to the large charge transfer resistance, increased impedance modulus |Z|0.01 Hz, and frequency time constant of FeSiAl@ZnO@Al2O3. The research demonstrates a promising platform toward the design of next-generation MAs with improved anti-corrosion properties.

Effect of Oxide Shell on Aluminium Nanoparticle Oxidation Using Molecular Dynamics Simulation

Molecular dynamics simulation using reactive force field (ReaxFF)potential was implemented to study the oxidation mechanism in aluminium particles with two different alumina shells. That is, without an oxide shell and with a 1 nm oxide shell. In particular, this research investigated the atomic diffusivity of the system on the oxide shell effect. The results showed that in the heating process, oxygen molecules were adsorbed on the surface of the shell and then diffused to the particle core as the heating temperature increased. The diffusivity of oxygen molecules in the aluminium core which causes the oxidation process to occur, shows that the particles without the oxide shell are faster than the particles with the oxide shell. Although after relaxation, there are similarities in having an oxide shell. However, the thickness is different. This shows that the coating on Al particles can inhibit the rate of oxidation. The thickness of the oxide shell also affects the rate of oxidation.