Since CO₂ is inevitably generated in the iron-making process, steel industries have made many efforts to reduce CO₂ emissions for decades. On the other hand, demanded steel production has increased in developing countries. In contrast, a considerable amount of steel products are accumulated in the society, and the amount of steel scrap has been increasing in the developed countries. In addition, the grade of iron ore is becoming worse every year due to the increasing demand for steel. To achieve carbon neutrality, innovative technologies need to be developed considering the future market trends for steels and the supply of iron resources, including iron ores and steel scraps. In this paper, recent studies on iron ores and steel scraps and efforts to reduce CO₂ emission were reviewed, and issues to achieve carbon neutrality in the future were discussed.

Since the 1960s, extensive studies have been made on rare earth (RE) - transition metal (TM) alloys due to their excellent functional properties. Most of functional properties of these alloys including magnetic properties are closely related to the 4f electrons of RE elements. The use of RE-TM alloys has increased significantly in a number of industrial fields over the past few decades. In particular, the demand for Dy-added Nd-Fe-B magnets is rapidly increasing because these magnets are indispensable for high-performance motors in electric vehicles and hybrid electric vehicles. These magnets need to possess sufficient thermal stability for use in such motors in high-temperature environments. The addition of Dy is necessary to improve the thermal stability of Nd-Fe-B magnets. However, Dy resources are scarce and unevenly located in the earth crust. Thus, it is necessary to develop an inexpensive and effective recovery/separation process of Dy from scraps of the Dy-added Nd-Fe-B magnet. In this review paper, one of the practical refining process, molten salt electrolysis, of rare earth elements such as Dy and Nd is described. Moreover, new recovery/separation process of Dy and Nd from Nd magnet scraps proposed by our group is introduced.

The development of innovative storage batteries for carbon neutrality is an urgent issue. In particular, magnesium has huge potentialities as an anode material from its theoretical volumetric capacity superior to that of lithium. Secondly, magnesium has been one of the most abundant elements in the Earth’s crust. In general, magnesium-based materials as an anode has been manufactured by cold rolling which requires multistage process including heat treatment. We have studied rapid solidification process to develop low-cost mass production technology. In this study, we have focused on Mg-3mass%Al-1mass%Zn alloy (AZ31), which is the most commonly rolled magnesium alloy, and prepared it by rapid solidification to evaluate its electrochemical activity with the rolled material. The AZ31 ribbons that exhibited superior electrochemical activity had a random orientation and fine microstructure. These experimental results suggest that the presence of electrochemically inactive crystal planes as well as an increase in the grain boundary area is important.

To realize the removal of Sn from iron scraps by a solidification segregation, we demonstrated the Sn segregation in liquid Fe–C–Sn alloy by unidirectional solidification of utilizing a temperature gradient. The effect of cooling rate on the segregation behavior of Sn is investigated in the present work. The segregation ratio of Sn between solid and liquid is determined based on the experimental data. We found out that the unidirectional solidification of liquid Fe–4.2mass%C–2.0mass%Sn alloy results in the Sn segregation in liquid alloy. The segregation coefficient of Sn is 0.84 for the unidirectional solidification of liquid Fe–4.2mass%C–2.0mass%Sn alloy.

The electrochemical formation of Ce-Ni alloys was investigated in a molten LiCl-KCl-CeCl₃ at 723 K under an Ar gas atmosphere. Open-circuit potentiometry was performed with a Ni electrode after electrodepositing Ce metal at 0.40 V (vs. Li⁺/Li) for 20 s. Four potential plateaus were observed at 0.54 V, 0.72 V, 1.19 V and 1.64 V, which were considered to correspond to the potentials of two-phase coexisting states of different Ce–Ni alloys. Potentiostatic electrolysis was conducted at 0.50 V for 1 h using Ni plate electrodes, and XRD analysis indicated the formation of CeNi₂. After the formation of CeNi₂ on the Ni plate electrodes, potentiostatic electrolysis was also conducted at 0.65 V, 0.80 V, 1.40 V and 2.00 V for 1 h. The formed CeNi₂ was transformed to CeNi₃ at 0.65 V, Ce₂Ni₇ at 0.80 V, CeNi₅ at 1.40 V and Ni at 2.00 V. On the other hand, an alloy sample was prepared at 0.50-0.60 V for 1 h using a Ni electrode in molten LiCl-KCl-CeCl₃(0.50 mol%)-LaCl₃(0.50 mol%). The highest mass ratio of Ce/La in the alloy samples was 84 at 0.51-0.53 V.

Aiming to further improve decarbulization of molten iron with oxygen jet in BOF, a course of study on cavity formation with water model was carried out using CO₂ gas as dissolving gas. Ar gas, CO₂ gas, or a mixture of them was blown from the lance onto aqueous bath of various composition. The cavity formed under CO₂ blowing was larger compared to that under Ar blowing of the same flow rate, beyond the difference of gas density. Such behaviour would reflect that dissolving reaction proceeds the cavity formation. The cavity depth formed under Ar and CO₂ blowing onto aqueous surfactant solution was slightly larger compared to those on ion-exchanged water, and what on aqueous surfactant+NaOH solution was much deeper. Those results suggest that decrease in surface tension would help cavity formation, and dissolving reaction of gas would exceedingly promote the cavity formation. Those consideration corresponds to the classical findings such as the increase in interfacial area between molten slag and metal droplet during desulfurization reaction.

It is essential to reduce the oxygen potential in steel to lower the sulfur content. The addition of calcium is considered the most effective. Therefore, many researchers have investigated the deoxidation and desulfurization equilibria of liquid iron by calcium; there is a scatter among previous studies because of the difficulties of the experiments due to the high vapor pressure and the limited solubility of calcium in the molten iron. This work reveals that the activity of calcium in molten iron can be controlled by equilibrating with Ca-Pb alloy, and the deoxidation and desulfurization equilibria of liquid iron by calcium are re-investigated. The following thermodynamic values have been derived from the experimental results in the present and previous studies.

　　　　　　　　CaS(s) = Ca_{(mass% in Fe)} + S_{(mass% in Fe)}

　　　　　　　　e_S^Ca= −23.7

　　　　　　　　e^S_Ca= −29.6

　　　　　　　　logK_CaS= −6.11 (1873 K)

Using the derived thermodynamic data, deoxidation and desulfurization equilibria of liquid iron by calcium are proposed. Deoxidation and desulfurization limits of liquid iron by calcium are calculated to be 2 mass ppm O at 20 mass ppm Ca and 4 mass ppm S at 40 mass ppm Ca under the condition of a_CaO = a_CaS = 1 at 1873 K.

In order to achieve carbon neutrality, CO₂ emission from ironmaking processes must be decreased. Blast furnace operation with an injection of hydrogen gas and capturing CO₂ from the exhaust gas is one of the promising technologies to reduce CO₂ emission from the ironmaking process. When hydrogen gas is enriched in a blast furnace, reduction of iron oxide with both H₂ and CO gas occur. Because reduction of iron oxide with H2 is endothermic, the gaseous reduction rate of solid iron oxide must be improved. Therefore, it is necessary to understand the reduction rate of iron oxide with an H₂-CO gas mixture in a wide H₂/CO ratio range. In this work, simulated iron oxide pellet was reduced with H₂-CO gas mixture at 1093 and 1273 K, and the kinetic analysis was performed using an unreacted core shrinking model assuming H₂-CO gas mixture as a single component of the reducing agent. The obtained apparent rate constants were linearly increased with the hydrogen content of reducing gas. Furthermore, the apparent rate constants were increased with hydrogen content at 1273 K much more than at 1093 K, which would be caused by the increasing driving force of hydrogen reduction at a higher temperature.

This paper concerns the λ-type enforcement braking device (EBD), which aims the traffic accident prevention. The device is supposed to be installed in a road construction region, according to the actual traffic-lane regulations. We contend, the forced halting of an automobile by means of EBD, would result in the significant increase of drivers’, pedestrians’ as well as road construction workers’ safety. The ongoing improvement of EBD mechanisms concerns their performance, structural optimization as well as continuing efforts to reduce the braking distance. In a consequence, our previous report tackled the influence of the arm-shape and arm-length on braking characteristics, while the present one discusses the role of the connecting height of the arm to the mast on the EBD’s operation. Simple model collision tests and theoretical calculations based on the principle of energy conservation were utilized in our study, which in turn, made us to conclude that the breaking distance remains unaffected by the arm shape. We found, however, the reduction of breaking distance markedly dependent on the length of the arm, which extends and completes our previous article. The collision tests concerned three selected velocities of a vehicle and a simple model of EBD with long-arm. We demonstrate that changes in the connecting height of the arm in the λ-type EBD, substantially affect the braking characteristics.

A biaxial fatigue test rig using four large hydraulic actuators was equipped with a superimposed wave generation function in order to conduct fatigue tests simulating complex loading from multiple directions on the hull structure. As a result of the operation confirmation of this system using the cruciform specimen, it was confirmed that the center point of the specimen was retained, and that the in-plane bending did not occur in the specimen, and that only the load in the axial direction was accurately loaded. The application of this system to the fatigue crack propagation test was verified, and it was possible to control with a constant error rate even if the rigidity changed by the crack growth, and good test results were obtained.

A Pulsating Heat Pipe (PHP) is getting attention as one of the efficient heat transfer devices. However, a thermal fluid property inside PHP is so complicated and still unclear. In this study, temperature distribution and flow inside the PHP were visualized simultaneously by using Temperature-sensitive Paint (TSP) and dissolved fluorescence dye, respectively. The TSP was painted on a glass plate in stripe shape to cover a half of a channel. The TSP was excited by UV LED light and the intensity of luminescence was captured by high-speed camera in insulated area of the PHP. The intensity of luminescence was converted into temperature by means of getting a calibration function. The temperature of inner wall of the PHP changed corresponding to passages of liquid phase and vapor phase. The temperature decreased when liquid phase passed through and increased when vapor phase passed through. Moreover, the temperature changed when a liquid droplet or a vapor bubble passed through. It is suggested that these temperature changes were caused by both a difference of heat transfer coefficient between liquid phase and vapor phase and a phase change. These experimental results have possibility that determine boundary temperature corresponding to flow condition.