A. A. El-Geassy

The present review handles the main characteristics of iron oxide reduction and its industrial applications. The reduction of iron oxide is the basis of all ironmaking processes, whether in a blast furnace or by direct reduction and/or direct smelting processes. The reduction characteristics of iron ores control the efficiency of any ironmaking process and the quality of the produced iron as well. Many controlling parameters should be considered when discussing the reducibility of iron ores such as equilibrium phase diagrams, reduction temperature, pressure, gas composition, and the nature of both iron ores and reducing agent. The different factors affecting the main routes of ironmaking will be highlighted in the present review to give a clear picture for each technology. Moreover, further innovations regarding the reduction of iron oxides such as reduction by green hydrogen will be discussed.

The present review handles the main characteristics of iron oxide reduction and its industrial applications. The reduction of iron oxide is the basis of all ironmaking processes, whether in a blast furnace or by direct reduction and/or direct smelting processes. The reduction characteristics of iron ores control the efficiency of any ironmaking process and the quality of the produced iron as well. Many controlling parameters should be considered when discussing the reducibility of iron ores such as equilibrium phase diagrams, reduction temperature, pressure, gas composition, and the nature of both iron ores and reducing agent. The different factors affecting the main routes of ironmaking will be highlighted in the present review to give a clear picture of each technology. Moreover, further innovations regarding the reduction of iron oxides such as the reduction by green hydrogen will be discussed.

Nano-structured Mo/Fe intermetallics were synthesized from precursors that contained 72/28% and 30/70% molar ratios of Mo/Fe, which were given as precursors A and B, respectively. These precursors were prepared from the co-precipitation of aqueous hot solutions of ammonium heptamolybdate tetrahydrate (AHM) and ferrous oxalate. The dry precipitates were thermally treated using TG-DSC to follow up their behavior during roasting, in an Ar atmosphere of up to 700 °C (10° K/min). The TG profile showed that 32.5% and 55.5% weight losses were measured from the thermal treatment of precursors A and B, respectively. The DSC heat flow profile showed the presence of endothermic peaks at 196.9 and 392.5–400 °C during the thermal decomposition of the AHM and ferrous oxalate, respectively. The exothermic peak that was detected at 427.5 °C was due to the production of nano-sized iron molybdate [Fe₂(MoO₄)₃]. An XRD phase analysis indicated that iron molybdate was the only phase that was identified in precursor A, while iron molybdate and Fe₂O₃ were produced in precursor B. Compacts were made from the pressing of the nano-sized precursors, which were roasted at 500 °C for 3 h. The roasted compacts were isothermally reduced in H₂ at 600–850 °C using microbalance, and the O₂ weight loss that resulted from the reduction reactions was continuously recorded as a function of time. The influence of the reduction temperature and precursor composition on the reduction behavior of the precursors was studied and discussed. The partially and completely reduced compacts were examined with X-ray powder diffraction (XRD), a reflected light microscope (RLM), and a scanning electron microscope (SEM-EDS). Depending on the precursor composition, the reduction reactions of the [Fe₂(MoO₄)₃] and Fe₂O₃ proceeded through the formation of intermediate lower oxides, prior to the production of the MO/Fe intermetallic alloys. Based on the intermediate phases that were identified and characterized at the early, intermediate, and final reduction degrees, chemical reaction equations were given to follow up the formation of the MoFe and MoFe₃ intermetallic alloys. The mechanism of the reduction reactions was predicted from the apparent activation energy values (Ea) that were computed at the different reduction degrees. Moreover, mathematical formulations that were derived from the gas–solid reaction model were applied to confirm the reduction mechanisms, which were greatly dependent on the precursor composition and reduction temperature. However, it can be reported that nano-structured MoFe and MoFe₃ intermetallic alloys can be successfully fabricated via a gas–solid reaction technique at lower temperatures.

The development of nanomaterials and nanotechnology enables the production of nanosized metallic alloys with advanced characteristics from their oxides via a thermal reduction technique. The aim of the present work was to produce metallic iron, nickel, and tungsten through the gaseous reduction of nanosized metal oxide powders as a preliminary step towards the fabrication of nanosized heavy tungsten alloys with unique properties. Nanosized NiO, Fe₂O₃, and WO₃ were isothermally and non-isothermally reduced with H₂, and the oxygen weight loss was continuously recorded as a function of time. The Thermogravimetric TG-DTA technique was applied in the non-isothermal reduction up to 1000 °C. The reduction extents were calculated from the TG curve, whereas the accompanying heat of the reaction was measured from the DTA curve. The results revealed that NiO was reduced at 2O₃ was reduced at 950 °C. In the isothermal process, metal oxides were reduced with H₂ at 700–1000 °C; a micro-force balance was used and the O₂ weight loss was continuously recorded. At a given temperature, the rate of reduction increased in the order NiO > Fe₂O₃ > WO₃. The nano-oxide powders and the reduced products were physically and chemically characterized. The activation energy (Ea) values were computed from the isothermal reduction in the initial and later stages to elucidate the corresponding reduction mechanism. The Ea values indicated that the reduction of metal oxides was controlled by the gas diffusion mechanism at both the initial and later stages of reduction. The results of the present study determined the optimal operation parameters at which the thermal gaseous reduction technique could be applied for preparing metallic alloys from nanosized metal oxides.

Iron ore fines was isothermally and non-isothermally reduced with CO and the total mass loss was continuously recorded. The different phases developed during the reduction process were identified by X-ray diffraction analysis. The structural changes accompanying the reduction reactions were microscopically examined. During the isothermal reduction tests, temperature has a significant effect on the reduction reaction. At a given temperature, the highest rate was obtained at initial stages whereas the minimum rate was observed at the later stages due to the formation of dense iron layer. The activation energy values (Ea) at the early stages was 39.23kJ mol^-1 revealed that the reduction is most likely controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanism. At later stages, the Ea values were 54.19 kJ mol-1 indicated that the interfacial chemical reaction is the rate controlling mechanism. Testing of the mathematical formulations derived from the gas-solid reaction model confirmed these controlling mechanisms. The non-isothermal reduction experiments were carried out using different heating rates which showed a considerable effect on the degree of reduction. The reduction conversion continuously increased with rise in temperature. The reduction mechanism was predicted from model free and model fitting. The activation energy values were ranging from 135-40 kJ.mol-1 indicating that gas diffusion is the rate controlling step.

The quality of product pellets is a result of the physico‐chemical phenomena involved in the induration process. Sintering is the primary phenomenon, and its degree or extent contributes substantially to the evolution of the metallurgical and mechanical properties of a pellet. During the induration of magnetite pellets, sintering proceeds through the oxidized and non‐oxidized magnetite phases. Sintering of these phases has been previously studied on a single pellet at the macroscopic scale using an optical dilatometer. A deeper understanding requires corroboration of these studies through characterization at the microscopic scale. In the present work, the observations recorded at the microscopic scale are quantified using image processing techniques to correlate them to the macroscopic measurements. Distance transformation, which is an image processing principle, is adapted in a novel way to digitize the microstructures and to determine the degree of sintering in a pellet quantitatively. This methodology has potential applications as a generic tool to follow the sintering phenomenon and process kinetics at any stage during induration.

Valence instability of iron oxide ultrafine particles on ferroelectrics studied by Mössbauer spectroscopy Jun Kano, Takumi Okamoto, Shin Nakamura et al.-Influence of reactive oxygen species during deposition of iron oxide films by high power impulse magnetron sputtering V Stranak, Z Hubicka, M Cada et al.

Ammonium molybdate and ferrous oxalate were used for the synthesis of nano-structured Mo-Fe intermetallics. Co-precipitation technique was applied to produce Mo/Fe precursors containing 58/42, 72/28 and 30/70 mass% respectively. The different phases formed were identified by XRD. The macro- and microstructures were microscopically examined by Reflected Light Microscope (RLM) and Scanning Electron Microscope (SEM) coupled with Electron Dispersion Spectroscopy (EDS). TG-DTA-DSC technique was applied to follow up the behavior of precursors up to 900^oC (10K/min.). Endothermic peaks were detected at 97.8, 196.9 and 392.7^oC due to the decomposition reactions to produce MoO₃ and Fe₂O₃. The exothermic peak resulted at 427.8^oC is due to the solid state reaction between these oxides to form Fe₂(MoO₄)₃. Precursors were isothermally reduced at 600-850^oC in a flow of purified H₂ and the O₂-weight loss from the reduction reactions was continuously recorded as a function of time. The isothermal reduction behavior of precursors was investigated. The structures of reduced products and the different phases formed were investigated and correlated with the reduction conditions. At >60% reduction extents, Fe₂(MoO₄)₃] phase was first reduced to Fe₂MoO₃O₈ before the formation of FeMo, while FeMoO₄ and MoO₂ were reduced to FeMo and Mo. In precursors containing higher content of Fe₂O₃, FeMo, Fe₃Mo and Fe phases were produced. The visual observation of reduced samples showed that the volume was gradually shrinking with rise in temperature up to 800^oC and beyond which a measurable swelling was observed reaching about 170% at 900^oC.