The steel industry relies heavily on the direct reduction of iron ore pellets, which is a more environmentally friendly alternative to traditional blast furnaces, by reducing CO2 emissions. This study investigated the effects of different TiO2 contents on the reducibility of high-grade iron ore pellets using hydrogen (H2). The research employed HSC chemistry, COMSOL Multiphysics, and X-ray tomography to analyse the thermodynamics and kinetics of hematite reduction. The results indicate that TiO2 significantly affects reducibility; pellets with less than 0.5% TiO2 show improved reducibility due to favorable microstructural changes, while higher TiO2 content reduces porosity and slows down reduction rates. However, increasing the H2 pressure to 8 bar mitigated the detrimental effects of the high TiO2 content and improved the porosity and reduction kinetics. These results support the theoretical predictions, provide guidelines for optimizing pellet formulations, and emphasize the importance of controlling the TiO2 content and operating conditions for efficient reduction processes.

Research on the high-temperature oxidation of metals and alloys is experimentally challenging due to the requirement for long-term corrosion exposure, and in the case of porous alloys, due to their complex internal microstructure. In this study, a corrosion model based on the morphological operations of dilation and erosion has been developed. This approach allows for a utilization of various raster representations of the microstructure as input to investigate the microstructure evolution of porous alloys during the corrosion process. Herein, porous microstructures of the porous Fe-Cr steels obtained from SEM imaging, X-ray tomography, and artificial 3D models generated with the use of Generative Adversarial Networks were used as test cases. The obtained results demonstrated high compliance with the experimental evaluation of porosity evolution and chromium content decrease during oxidation at 700 degrees C for 3000 h. Additionally, new material microstructures were studied and the influence of initial porosity on the chromium content depletion and alloy lifetime during long-term oxidation was revealed.

Pre-oxidation of porous ferritic Fe22Cr alloys was extensively studied in this paper. Weight gain measurements and SEM analysis revealed that pre-oxidation performed at 900°C for 40 min increased the lifespan of the alloy. A Cr evaporation study did not disclose any significant influence of the pre-oxidation process on the Cr content in the alloy. For a more detailed assessment, TEM imaging and X-ray tomography measurements of pre-oxidized samples were performed. These analyses showed that alteration in the grain and grain boundary diffusion fluxes might be the key for explaining the corrosion prevention role of pre-oxidation.

This paper presents a comprehensive study on the production and reduction of high-quality iron ore pellets characterized by a basicity index nearing 0.5 and diameters ranging from 1 to 2 cm. The reduction process was carried out in a hydrogen atmosphere at temperatures spanning 800-1000 degrees C and a pressure of 8 bar. Initial findings revealed substantial variations in pellet density and compressive strength, attributed to their mean dimensions. To delve into the microstructural transformations occurring during reduction, meticulous microtomographic analyses were conducted on each pellet before and after the reduction process. The research assessed reducibility factors such as porosity, pore size, and tortuosity adjustments across diverse reduction conditions. The study highlights the intimate connection between the reduction process rate, processing parameters, and pellet microstructure. Furthermore, the metallization tendencies were explored through extensive reduction experiments involving multiple pellets. These findings offer crucial insights into optimizing iron ore pellet performance during production and reduction processes, contributing to advancements in industrial applications.

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Carburization is a critical aspect in the iron and steel industry as it significantly affects the mechanical and chemical properties of the final product. This study provides a comprehensive analysis of the carburization potential of high-grade quality iron ore pellets after direct reduction in pure hydrogen. The results show that the porosity of the pellets has a significant impact on the efficiency and success of the direct reduction process with hydrogen. The reduction process can be completed at a lower temperature in pure hydrogen compared to carbon monoxide, with the iron carbide concentration peaking at temperatures up to 500 °C before decreasing with further temperature increases. The uniform distribution of SiO2, Al2O3, and CaO is critical to the carburizing process and affects the final properties of the steel. An increased degree of metallization and porosity are associated with an improved carburizing tendency. This study highlights the intricate interplay between temperature, carbon sources, and the resulting equilibrium concentration of iron carbides and provides insights into the complex dynamics of this phenomenon.

High grade pellets with basicity index close to 0.5 were directly reduced in pure hydrogen atmosphere. The reduction experiments were performed in the temperature range 800 -1000 degrees C at the pressure of 8 bar. The pellets internal structure was analysed through micro tomography observations in the unreduced and reduced conditions. After reduction, the pellets showed a variation of porosity up to more than 15% with a remarkable change in the pore dimensions and aspect. Given the pores aspect variations, tortuosity strongly varied. This is believed to have large influence on the pellets reduction kinetics depending on the reduction conditions. After reduction, the pellets were re-oxidized in the temperature range 200-700 degrees C for different times. Up to 500 degrees C the weight increase due to oxidation resulted very slow, for higher temperatures the re-oxidation behaviour showed a very remarkable acceleration. (c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

The transition to more environmentally friendly steel production methods has intensified research into hydrogenbased direct reduction (HyDR) of iron oxide pellets. The aim of this study is to systematically investigate the kinetics of the reduction process, the evolution of porosity and the resulting microstructural changes on the reduction behavior of high-quality pellets during HyDR of iron ore at different temperatures. A modified mathematical model is developed based on the shrinkage kernel model, taking into account both mass and heat transport in a hydrogen atmosphere. The effects of temperature, particle size and time on the reduction behavior of the pellets are investigated. The simulated results are validated and discussed by the results of a batch of iron oxide pellets consisting of ten almost spherical pellets subjected to the direct reduction process with pure hydrogen. The results show that the total energy input to the HyDR process is a complex balance of factors, including chemical reaction rates, diffusion dynamics and entropy generation. The increase in free volume and simultaneous decrease in pore diameter reflect the dynamic nature of the microstructure, which includes additional free volume and defects due to the volume discrepancies and associated stresses between the reactant and product phases. Furthermore, the data show that higher temperatures accelerate the reduction reactions, especially the transformation of wustite into metallic iron. This phase transition is characterized by a significant volume change that cannot be accommodated by elastic deformation alone, leading to the development of lattice defects such as cracks, creep pores and dislocations that serve as stress relief mechanisms. The trends for porosity change at 950 degrees C and 1000 degrees C observed in the experimental results are correct and in good agreement with the numerical and simulated results.

This paper presents the hydrogen reduction behaviour of industrial pellets designed for the efficient hydrogen based direct reduction. The pellets were provided with very low non ferrous oxides percentage (0.52 of basicity index) and with the absence on TiO2 oxides. The pellets measured diameters in the range 1.14-1.72 cm and were characterized in terms of porosity, pores size, tortuosity and compression strength. The pellets were reduced in hydrogen atmosphere in a laboratory shaft furnace in the temperature ranges of 600-1200 degrees C at the pressures of 1 and 5 bar. The pellets' reduction behaviour was analysed in terms of time to reduction, rate of reduction and kinetics constant. All the obtained results were analysed through the employment of a commercial multiobjective optimization tool (modeFrontier) in order to precisely define the effect of each single parameter on the pellets' reduction. It was also defined the effect of the ongoing reduction rate of the final metallization of the starting iron oxides.

In this work, the oxidation properties of austenitic 316L stainless steel powder and sintered porous support were investigated at the temperature range of similar to 600-750 degrees C for 100 hours in ambient air. Oxidation kinetics was determined by continuous thermogravimetry and analyzed employing parabolic rate law. It was observed that oxidation leads to the formation of an oxide scale, with substantial oxidation occurring at >= 650 degrees C in the powder. The porous steel support was fabricated using the tape casting method with two distinct pore former concentrations. The micro-structural features of both the powder and support were investigated by X-ray diffractometry and scanning electron microscopy coupled with energy-dispersive X-ray analysis. The mechanical properties of the metal support were examined before and after oxidation via a microhardness test. The effect of porosity on the resulting properties of the metal support was also highlighted. In summary, 316L stainless steel support suits SOCs applications below 600 degrees C.

In response to the imperative for sustainable iron production with reduced CO2 emissions, this study delves into the intricate role of TiO2 in the direct reduction of iron oxide pellets. The TiO2-dependent reducibility of iron oxide pellets utilizing H2 and CO gas across varied temperatures and gas compositions is thoroughly investigated. Our findings unveil the nuanced nature of the TiO2 effect, underscored by its concentration-dependent behavior, revealing an optimal range between 1 and 1.5 pct TiO2, where a neutral or positive impact on reduction kinetics and diffusion coefficient is observed. Notably, the synergistic interplay of CO and H2 at 1000 °C emerges as particularly efficacious, suggesting complementary effects on the reduction process. The introduction of H2 into the reducing atmosphere regulated by CO not only extends the transition range but also markedly expedites the rate of reduction. Furthermore, our study highlights the temperature sensitivity of the TiO2 effect, with higher TiO2 content correlating with prolonged reduction time in a 100 pct H2 atmosphere at 900 °C. In a 100 pct H2 atmosphere, the non-contributory role of TiO2 stems from the water-gas shift reaction. Conversely, introducing H2 into a CO-controlled reducing atmosphere with TiO2 enhances the transition range and expedites the reduction rate. Additionally, our findings underscore the role of total iron content, revealing a direct correlation with the reduction process.

In this work, a long-term (up to 6000 hours) corrosion evaluation of three porous ( 30 pct of initial porosity) ferritic iron-chromium alloys with different Cr contents (20, 22, and 27 wt pct of Cr) was carried out at 600 °C, 700 °C, 800 °C, and 900 °C in air. Mass gain measurements and SEM analyses revealed that at temperatures above 600 °C, all alloys exhibit breakaway corrosion, whereas at 600 °C, none of the alloys were heavily oxidized even after 6000 hours. Based on the results, the diffusion character of the corrosion of porous chromia-forming alloys was identified. The microstructure changes at high temperatures in porous alloys containing 22 wt pct of Cr were determined in detail by transmission electron microscopy. The proposed prediction model indicated that the lifetimes of the Fe20Cr and Fe22Cr alloys were determined as 1250 hours (± 535 hours) and 1460 hours (± 640 hours), respectively. It is in agreement with the long-term oxidation experiment. For the Fe27Cr alloy, the deviation between predicted and observed lifetimes occurs. The proposed model allows for qualitative estimation of the porous alloys’ lifetime with experimentally validated accuracy.

The influence of the method applied to synthesize Cu-Mn-O spinel was evaluated. The methods selected for the investigation were EDTA gel processes and solid-state reaction synthesis. From the obtained powders, sinters were prepared and assessed in terms of their properties as potential coating materials. Additionally, the influence of Ni and Fe dopants was evaluated. The results show that the EDTA gel processes method seems to be more suitable for spinel synthesis. This method yields spinels that exhibit electrical conductivity above the required threshold (>50 S/cm) over a temperature range of 400-850 ?, and it also ensures continuous spinel matrices and high spinel content. Spinels obtained via solid-state reactions exhibit inferior properties. A higher concen-tration of Ni allows electrical conductivity to be improved further, while the opposite tendency is observed for Fe. Finally, it was shown that spinels obtained via EDTA gel processes are promising protective-conducting coating materials for SOEC/SOFCs steel interconnects.

The effect of high-temperature oxidation at 850 °C (10 h, 30 h, 100 h) and 900 °C (10 h) on porous (∼30 % porosity) ferritic stainless steel (Fe22Cr) has been investigated using synchrotron tomographic microscopy, which allowed for visualisation, separation and quantitative analysis of the metallic core, closed pores, open pores and oxide scale phase. The same regions within the samples were investigated before and after oxidation performed at different conditions. Quantitative analysis of the tomographic data provided information on changes upon oxidation of the relative volume of the different phases, the specific surface area (SSA) of the metallic core, the thickness of the oxide scale and pore size distribution. The results were discussed in the context of thermogravimetric analysis of the samples and supported by SEM imaging. It was observed that oxidation leads to an increase of the SSA of steel and the largest increase (∼50 %) was obtained for the sample processed for 100 h at 850 °C. It is demonstrated the open porosity forms a network of connected channels within the sample and it dominates in the volume. In addition, the 3D imaging revealed breakaway oxidation areas for samples, for which this phenomenon remained undetected using 2D SEM analysis.

This work deals with the joining of porous Fe22Cr ferritic stainless steel to a dense Crofer22APU plate by using a silica-based, Ba-containing glass-ceramic. The chemical and interfacial stability and the mechanical properties of the joints were evaluated before and after thermal ageing at 700 degrees C for 500hrs. The sintering behaviour of the glass was assessed by using heating stage microscopy (HSM) to study the influence of a porous metal substrate on the shrinkage of the joining material. Scanning electron microscopy revealed that there were no defects or cracks at the porous alloy/glass-ceramic interface for both the as-joined samples and the samples after thermal ageing at 700 degrees C for 500 h. However, at this exposure temperature, the porous alloy started to form an oxide scale at the interface with the glass-ceramic and the internal surface of the porous alloy. Finally, the evaluation of the mechanical properties by tensile testing showed that the properties were not affected by thermal ageing at 700 degrees C.

The friction stir welding method is increasingly attracting interest in the railway sector due to its environmental friendliness, low cost, and ease of producing high-quality joints. Using aluminum alloys reduces the weight of structures, increasing their payload and reducing fuel consumption and running costs. The following paper presents studies on the microstructure, strength, and corrosion resistance of AA6082 aluminum alloy sheets joined via friction stir welding. The sheets were joined by employing two different traverse speeds (200 and 250 mm/min), two different rotational speeds (1000 and 1250 rpm), and two different tool tilt angles (0° and 2°). It was observed that the use of the inclined tool provides finer microstructure in the nugget zone, higher value of microhardness, and better corrosion resistance, compared to the tilt angle equal to 0°. By increasing the value of revolutionary pitch, finer grains are observed in the nugget zone and the measured hardness is higher. It was also observed that the change in process parameters strongly influences the radius of the nugget zone and the potentiodynamic properties of the friction stir-welded material. The joints produced with the tool tilt angle equal to 2°, the tool traverse speed of 200 mm/min, and its rotational speed of 1250 rpm revealed the highest hardness in the nugget zone (about 92% of the base material). Moreover, the finest grain size in the nugget with the average value of 9.8 ± 1.5 µm was found. The lowest corrosion current density equal to 16.029 µA cm−2 was noted for the sample with the highest strength, which also provides its good corrosion resistance.

This work describes a high temperature corrosion kinetics study of -30 % porous Fe22Cr alloys. The surface area of the alloy (-0.02 m2 g-1) has been determined by tomographic microscopy. The weight gain of the alloys was studied by isothermal thermogravimetry in the air for 100 h at 700-900 degrees C. Breakaway oxidation was observed after oxidation at 850 degrees C (-100 h) and 900 degrees C (-30 h). The lifetime prediction shows the investigated porous alloy can be used for 700 degrees C. At temperatures 700 degrees C, the lifetime of the porous alloy is limited by the available chromium reservoir.

High-temperature reactions between glass–ceramic sealants and Fe-Cr alloy interconnects may lead to the formation of undesirable phases, and consequently degradation of solid oxide fuel/electrolyser devices. In this work, three different glass–ceramic sealants (Na-containing, Ba-containing, Sr-containing compositions) and Fe22Cr stainless steel powders (raw and pre-oxidised) are considered in order to test their chemical reactivity at 750 °C and 850 °C for 500 h in static air. The novelty of this approach is related to the use of powder mixtures instead of studying the reactivity on planar interfaces, which allows a better evaluation the materials’ reactivity. Oxidation tests indicate that the Sr-containing glass–ceramic/steel couple is the least reactive among the aged samples. For the Ba-containing samples, the formation of an undesirable phase of BaCrO4 is observed by diffractometry and photoelectron spectroscopy analyses. The present research explores, for the first time, the effects of exposing the high surface area of the alloy powder and glass–ceramic sealant interface, assessed by oxidation testing and microstructural analysis. The results show that by using mixed powders with large interface surface areas, degradation of the materials can be observed after relatively short times, allowing accelerated screening of the reactivity of materials, and thus their further development.