Yoshiaki Kashiwaya

Reduction of haematite to magnetite induced by hydrogen ion implantation

Microstructural changes induced by hydrogen ion implantation in haematite () have been investigated by transmission electron microscopy. It has been found that the hydrogen ion implantation causes the haematite magnetite () reduction at room temperature. From electron diffraction patterns after the hydrogen implantation, the following orientation relationship was found to exist between haematite and magnetite: . Since these results agree with those in previous studies, microstructural changes during the reduction were obtained by using the implantation technique. The reduction mechanism of magnetite from haematite is discussed in terms of the experimental results on crystallographic relationships.

Factors on the Measurement of Effective Thermal Diffusivity of Molten Slag Using Double Hot Thermocouple Technique

The molten slags that are used not only in the continuous caster but also in every metal industry play an important role and affect the quality of products. The authors initially developed the double hot thermocouple technique (DHTT) for in situ observation of mold slag crystallization. In this study, the DHTT was further developed to allow the measurement of the overall thermal diffusivity of molten slag applying the principle of the laser flash method. The affecting factors (finite pulse time, shape of pulse and heat loss from sample surface) on the measurement of thermal diffusivity using the DHTT were discussed theoretically using both the analytical and the numerical methods. New relationship between the thermal diffusivity a and the time at half-maximum temperature to 5 was obtained as follows: α(×10 4 m 2 /s) = 0.000707(t 0.5 /t p ) -1.8946 The thermal diffusivity obtained from the experimental half-maximum time t 0.5 /t p (t p is the time of peak on the heat pulse) was in good agreement with the one from literature.

Nanocrack formation in hematite through the dehydration of goethite and the carbon infiltration from Biotar

The cracks in nano-order are generated and propagated when the combined water is released during the dehydration. If the nanopore can be utilized for a reaction site, the overall reaction can be extremely accelerated. On the other hand, it is well known that woody biomass is an attractive alternative fuel for the reduction of CO2 emission. However, the process of biomass pyrolysis is disturbed by the tar which causes a clogging in gas tubing system. Hata et al. found that the tar was consumed almost 100% in the iron ore layer having nanocrack or nanopore. The nanocracks formed in hematite crystals after dehydration of goethite were about 4 nm in width, which is in excellent agreement with the result of BET measurement. When the carbon deposited from tar into the nanocracks, reduction reactions were occurred simultaneously. The deposited carbons completely infilled into the nanocracks and the void in the sample.

Phosphorous Partition in Dephosphorization Slag Occurring with Crystallization at Initial Stage of Solidification

Basicity and the amount of FetO were investigated for their effects on the crystallization behavior of the simulated dephosphorizing slags. Twelve kinds of slags were prepared (C/S=1.0–2.5, FetO=10–20%, P2O5=5%). In the present experiment, the Hot Thermocouple Technique was used to melt and quench the samples. After quenching, the microstructure of the slag and the distributions of elements were examined by SEM and EDS analysis.The diameter of the crystal which precipitated in the sample increased with increasing basicity (C/S) and decreasing FetO content. In addition, glassy regions were observed in the two samples whose FetO content was 20% and whose basicity was 1.0 or 1.5. The samples (10% FetO, 5% P2O5), whose basicity was 1.0 (sample-1) precipitated as a monocalcium silicate (CaO·SiO2); the sample (10% FetO, 5% P2O5) whose basicity was 1.5 (sample-4) precipitated as a dicalcium silicate (2CaO·SiO2). In higher FetO (15–20%) slags, the crystals of the solid solution between 3CaO·P2O5 and 2CaO·SiO2 ((C3P–C2S)ss) were observed. When the amount of CaO increased from C/S=1.5 to C/S=2.5, 2CaO·SiO2 appeared with phosphorous content, but phosphorous was not found in CaO·SiO2.

Thermodynamic Properties of Solid Solutions between Di-calcium Silicate and Tri-calcium Phosphate

Abstract For a better understanding of phosphorus removal from hot metal, the Gibbs free energies of solid solutions between di-calcium silicate and tri-calcium phosphate were derived through applications of solutions models. The regular solution model with the parameters determined in this study gave the activities of the components thermodynamically consistent with the literature data and the phase diagrams.

Effect of B2O3 on Crystallization Behavior, Structure, and Heat Transfer of CaO-SiO2-B2O3-Na2O-TiO2-Al2O3-MgO-Li2O Mold Fluxes

The effect of B2O3 on crystallization behavior, structure, and heat transfer of CaO-SiO2-Na2O-B2O3-TiO2-Al2O3-MgO-Li2O fluorine-free mold fluxes was investigated using hot thermocouple technique (HTT), Raman spectroscopy, and infrared emitter technique (IET), respectively. The critical cooling rate in continuous cooling experiments decreased and the incubation time determined in isothermal experiments increased with increasing B2O3 content, both implying a decreasing crystallization tendency. The major phases of mold fluxes determined using X-ray diffraction changed from Ca2MgSi2O7 and Ca11Si4B2O22 to CaSiO3 with the increasing amount of B2O3. B2O3 increased the degree of polymerization in silicate network, forming 3D borate structures. Addition of B2O3 decreased the flux melting temperature which has a significant impeding effect on the crystal nucleation and growth. The heat flux of mold fluxes measured using IET showed that the increase of B2O3 from 4.7 to 6.8 mass pct impeded the heat flux; while a further increase of B2O3 from 6.8 to 10.4 mass pct promoted the heat transfer. This phenomenon was attributed to the variation of crystallization behavior and crystal morphology with different B2O3 content in the mold fluxes.

Recovery of Zinc from Used Alkali-Manganese Dry Cells

AbstractA new method that does not require pre-processing or the use of auxiliary materials has been investigated to recover zinc, manganese, and copper from mercury-free used alkaline-manganese dry cells. The anode product, zinc oxide, was reduced by carbon which is added to the positive reactants to improve electrical conductivity, and is also generated through thermal decomposition of separators and resin gaskets. Subsequently, metallic zinc was recovered by vaporization. With respect to the residues, copper could be separated quite easily from the steel container. With the proposed method, after the removal of zinc and copper, there is the possibility for promoting utilization of the remainder of the used dry cells as steel scrap.

Formation of Nano-porous Structure in a Cathode at the Interface between Pt Electrode and YSZ during CO2 Electrolysis at 1,000 °C

Abstract The electrolysis of CO2 was investigated using a simple Pt/YSZ/Pt cell (yttria-stabilized zirconia (YSZ)). The cell performance increased drastically after applying the overvoltage of 4.0 V for ~5 min. The current density increased 30 times at 1.4 V and 11 times at 2.0 V. Using a laser microscope and field emission scanning electron microscopy (FE-SEM), the structural changes of the surface of the Pt electrode and the interface between the YSZ and Pt electrode were investigated to understand the reaction mechanism at the cathode for increasing the cell performance. The results showed that the Pt electrode surface became smooth after the experiment. Moreover, the interface between YSZ and the Pt cathode greatly changed after the electrolysis experiment, while that of the anode showed only a minor change. The structure of the cathode interface consisted of a 1-μm-thick nano-porous Pt layer and a micro-porous structure comprising YSZ and Pt. These structures are involved in CO2 electrolysis. Possible elementary reactions are also presented in this paper.

Effect of Na 2 O on Crystallisation Behaviour and Heat Transfer of Fluorine-Free Mould Fluxes

Most of the commercial mould fluxes contain fluorides which bring about serious environmental problems. The major challenge in the application of fluorine-free mould fluxes is to control the heat transfer from the strand to copper mould which is closely related to crystallisation behaviour. In this study, the effects of Na2O on the crystallisation behaviour and heat transfer of CaO-SiO2-Na2O-B2O3-TiO2-Al2O3-MgO-Li2O mould fluxes were investigated using single /double hot thermocouple technique (SHTT/DHTT) and infrared emitter technique (IET), respectively. Continuous cooling transformation (CCT) and time-temperature transformation (TTT) diagrams constructed using SHTT showed that the increase of Na2O concentration led to higher critical cooling rate and shorter incubation time. The crystallisation behaviour in a thermal gradient was examined using DHTT. The heat flux measured by IET showed that the increase of Na2O concentration decreased the heat flux when Na2O was lower than 9 mass% but the further increase of Na2O raised the heat flux. The relationship between flux crystallisation and heat transfer was also discussed.

Thermodynamics of Impurities in Pure Iron Obtained by Hydrogen Reduction

水素は一次エネルギーでは無く,その製造にコストとエ ネルギーを要し,多かれ少なかれ製造プロセスの過程で CO2が排出される。しかしながら,エネルギー供給に関係 する社会的状況は変化しており,化石燃料は永遠に存在す るものでは無く,その使用に限りがある。さらに,大きな人 口を抱えている国々が,経済的に上昇しており自身の国を 開発するためのエネルギーを必要としている。また,大気 中のCO2含有量は増加し続けており,地球環境は急速に変 化している。我々は,遅かれ早かれ化石燃料の使用を止め なければならない。しかしながら,止める時期は,明確では なく経済的な状況にも大きく影響されるものと思われる。 現在,日本では福島原発の事故の影響が大きく,またヨー ロッパでは財政危機が進行している,そのためCO2排出削 減はトーンダウンしたように見える。CO2排出削減に関す る現在の背景は研究の状況にも影響を与えるが,我々は予 め最善の方法によって準備をしておかなければならない。 一方,酸化鉄または鉄鉱石の水素還元は約90年前から広 く研究され始めた。Kamuraは,鉄鉱石の水素還元の先駆者 の一人である 。熱力学的研究,平衡状態図に関する研究 は20世紀初頭に行われ,系統的にデータが蓄積されてき た 。多くの還元挙動は詳細に解析され,未反応核モデル のような数学モデル が開発され,実験や実プロセスに 応用されている。これらのような基礎的な研究を基に,鉄 鉱石還元反応の理解は顕著に進展してきた。 水素還元は,CO還元に比較して速い速度を持っている が,水素それ自身の製造にはコストとエネルギーが必要で ある。したがって水素還元の実際のプロセスは存在せず, ただ天然ガス(主にCH4)を利用した直接還元プロセスが 存在するのみである。しかしながら,近年,CO2削減問題 が重要な問題となってきている。 CO2排出を伴わないグリーン水素が製造されたとき,水 素還元プロセスは,現在の鉄鋼プロセスの代替プロセスと なり得るものである。加えて,化石燃料が枯渇し,化石燃 料ベースのエネルギーコストが急激に上昇した場合,水素 還元プロセスは,現在のプロセスと競争できるものとなる。 さらに,水素還元によって得られた金属鉄は炭素の無 い純鉄に近い。加えて,水素雰囲気下では不純物元素(Si, MnおよびP)が熱力学的に還元されない(式(1),(2)およ 水素還元によって得られた純鉄中の不純物の熱力学