The interfacial impedance between FeO-CaO-SiO2 slags and solid iron in the anodic reaction were measured by using AC impedance method, and factors on kinetics of the electrode reaction, such as Warburg parameter and charge transfer resistance were determined in order to reveal the kinetic behavior of this system. The supplied DC potential of a working electrode against a counter electrode of iron crucible was set in the range from 20 to 100 mV. The measurements were made in the frequency range from 0.01 Hz to 20 kHz at 1573, 1623 and 1673 K under an argon atmosphere. The Warburg parameter decreased from 4.0×10−7 Ωm2 s−1⁄2 to 2.3×10−7 Ωm2 s−1⁄2 with the increase of the supplied DC potential. The charge transfer resistance was 1×10−7 Ωm2 at 1623 K and it decreased with the increase of temperature. These results show that the charge transfer resistance is rather small and that the mass transfer behaves as a rate-control step in the dissolution reaction of iron into FeO-CaO-SiO2 slag.
Effects of Be, Cu and Ag as microalloying elements on age hardening and two-step aging behavior of an Al-1.3 mass%Mg2Si alloy have been investigated by hardness measurement, electrical resistivity measurement, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). These microalloying elements markedly increase both the hardening rate and peak hardness in artificial aging at 453 K. Their effects on two-step aging, however, much differ from each other. Negative and positive effects of two-step aging are reduced by Cu addition. On the contrary, negative effect is increased and positive effect turns into negative by Ag addition. The complex cluster formation model was proposed to explain the effects of microalloying elements.
The influence of cooling rate on phase constitution and tensile properties of Ti-2.9Fe-4.9Cr and Ti-4.2Fe-6.9Cr alloys was investigated by electrical resistivity and Vickers hardness measurements, X-ray diffraction, optical microstructure observation and tensile testing. In only Ti-2.9Fe-4.9Cr alloy quenched at an average cooling rate of 25 Ks−1, reflections from isothermal omega phase were identified, whereas only reflections from beta phase were identified by XRD with no reflections of isothermal omega phase present in Ti-2.9Fe-4.9Cr alloy cooled at other cooling rates and Ti-4.2Fe-6.9Cr alloy quenched at all cooling conditions. HV for Ti-2.9Fe-4.9Cr alloy cooled at 25 Ks−1, was about 400 and HV of Ti-4.2Fe-6.9Cr alloy cooled at all cooling conditions, even 25 Ks−1, was around 320. Therefore, quench sensitivity of Ti-4.2Fe-6.9Cr alloy is lower than that of Ti-2.9Fe-4.9Cr alloy. Tensile strength and reduction in area of Ti-2.9Fe-4.9Cr alloy cooled at three different cooling rates except for 25 Ks−1 showed about 1200 MPa and 45%, respectively. About 1050 MPa in σB and 60% in φ were obtained in all quenched Ti-4.2Fe-6.9Cr alloys, respectively. The strength/ductility balances of Ti-4.2Fe-6.9Cr alloy quenched at four different cooling rates are comparable with those of developed beta titanium alloys in solution treated and quenched state.
Nano-sized processing is reported to realize distinctive features in physical properties. We found a remarkable microwave absorption property caused by the increase of permeability and permittivity when nanocomposing ferromagnetic metals (Fe) and high electrical resistance ceramics (SiO2). The microwave absorption property was identified by comparing polymer composites containing Fe-SiO2 nanocomposite powder prepared by mechanical alloying and simple mixing of Fe-SiO2 powder in the frequency range of 0.1-18 GHz. We attributed these to the decrease in electrical conductivity and magnetostriction of Fe and improvement in the magnetic coupling between Fe grains.
It had been experimentally found that the rate constant (K) of the coarsening cubic-law for Y2BaCuO5 (Y211) particles in Ba-Cu-O melts has been classified into two groups for the volume fraction (Vf), under 15% and over 20%, of Y211 particles, in which the drastic reduction of K existed from the low Vf to the high Vf groups. In the present study, coarsening kinetics for the Y211 particles was simulated using a two dimensional phase field model (PFM) that was proposed for the interface movement of Y211 particles to be tracked. The coarsening simulation of Y211 particles as a stoichiometric compound was performed by solving the diffusion equation, in which the deviation of the solute concentration in the solid phase was restricted to be a negligibly small value. The present PFM calculation indicated that this significant reduction of K appeared between 15% and 20% of the area fraction (Af) of Y211. It was implied that the rate constant reduction was caused by the transition of the coarsening mechanism from the mean field model to the communicating neighbor one, which was quantitatively confirmed by the observation of the different shapes of solute concentration contour lines around disappearing particles and the radical shape transformation of the particles size distribution from Af15% to Af20%.
Orientation relationship formations at early stage of the solidification and rod-lamella transition for uni-directionally solidified Al2O3/LnAlO3 eutectic system were examined. Al2O3 was the first phase to nucleate in the Al2O3/LnAlO3 eutectic microstructure. In the case of Al2O3 phase nucleated as the primary phase, firstly some specific orientation to the solidification direction for Al2O3 phase were constructed and then the orientation to the solidification direction for LnAlO3 phase were gradually fix to some specific directions. The microstructures for Ln=Sm and Nd showed irregularity lamella and rod type, respectively.
We have developed new ferromagnetic shape memory alloys, Co2Ni2−xGax(x=1, 1.12, 1.15, 1.17), which have large strain caused by the magnetic-field-derived re-arrangement of martensite twin. The ribbon samples formed by rapidly solidified, melt-spinning methods showed strong anisotropy and large magnetostriction, ε∼180×10−6 at applied magnetic field, 0.8 T in low temperature. In contrast to poor ductility of the well-known ferromagnetic shape memory alloy Ni2MnGa, some of the ribbons have good ductility and are not broken even after bending to an angle of 180°.
In order to clarify the growth mechanism of Y123 film in the MOD process using TFA, TEM observation of the quenched samples during the growth, and measurement of the growth rate under several different conditions were carried out. TEM observation showed that the Y2Cu2O5, BaF2 and CuO are converted into Y123 by release of HF due to supplying H2O at the reaction interface. The MOD-TFA process using the multi-coating method was applied to form thicker Y123 films on LaAlO3 substrates, and the growth mechanism for the Y123 crystallization was investigated. In order to evaluate the growth rate, the electrical resistance of the precursor films during the crystallization was measured by the DC 4-probe method. It was observed that the growth thickness of the Y123 linearly increases with increasing annealing time. This result suggests that the growth rate is not limited by the HF diffusion in the precursor film. According to the gas flow rate dependence of the growth rate, it was suggested that the growth of Y123 films in this process might be limited by both the HF diffusion in the boundary layer and the interface kinetics. Then, the growth model, which includes the two limiting systems, was proposed. This model reveals a basic idea of the mechanism to determine the steady state growth rate.
Ti-2 at%Fe-10 at%Si, Ti-4 at%Fe-10 at%Si and Ti-6 at%Fe-10 at%Si powders were synthesized by mechanical alloying (MA) of pure Ti, Fe and Si powders using a planetary ball milling for 720 ks. After milling for 720 ks, the amount of collectable powder decreased with increasing Fe content in the MA powder. The formation of an amorphous phase was observed at all compositions in this study after 720 ks milling. The crystallization temperature of Ti-2 at%Fe-10 at%Si powder synthesized by MA for 720 ks was higher than that of other MA powders. Ti-2 at%Fe-10 at%Si powder prepared by milling for 720 ks, which contained amorphous phase, was consolidated using a pulsed current sintering (PCS) apparatus under a high pressure. The compact consolidated at 673 K under a pressure of 1500 MPa was almost densified with the retention of amorphous phase. The pulsed current sintering under a high pressure is a powerful technique to consolidate amorphous powder into a bulk material.
Magnetic properties and structures of TiN-, TiCN- and TiC-coated silicon steel sheets were investigated. The tensile stress in these ceramic coated silicon steel sheets and adhesion were also determined by measuring the angle curvature after coating one side with ceramic and by observation after 180° bend-forming, respectively. Both magnetic flux density B8(T) and iron loss W17⁄50(W/kg) improved in the order of TiN-, TiCN-, and TiC-coated silicon steel sheets. The X-ray diffraction pattern for the TiN film showed a strong (111) peak of TiN, while those for TiCN and TiC showed a comparatively strong (111) peak and weak (200) and (220) peaks. Moreover, tensile stress due to coating one side with ceramic and adhesion became strong in the order of TiN, TiCN, and TiC. It is considered that the ultra low iron loss of TiN-coated silicon steel sheets was achieved, leading to strong tensile stress, good adhesion and a sharp (111)TiN peak.
Nano-scale structures of rusts formed on weathering steel surfaces were investigated. It has been shown that the key structure is Fe(O, OH)6 network, which is different from crystalline FeOOH. Atomic structures were analyzed quantitatively by combination of different methods sensitive to middle range order (MRO): x-ray absorption fine structures (XAFS), anomalous x-ray scattering with reverse Monte-Calro simulation, and electron microscopy. It has been shown that Fe(O, OH)6 network structure evolves during the process of corrosion, and a small amount of additional elements change its development and the final morphology of rusts.
We have investigated the initial oxidation process of Cu(001) surface and the role of translational energy of incident O2 on the initial oxidation using supersonic molecular beam techniques. In the initial oxidation, the Cu(001) surface is oxidized in a layer-by-layer manner up to one monolayer, followed by forming the Cu2O epitaxial islands on the layer. At the initial stage of the layer-by-layer oxidation, a direct activated dissociation of O2 is a dominant process and the process is promoted by the increasing translational energy of incident O2. At the stage of the subsequent oxidation in which the Cu2O islands are formed on the oxide layer, dissociative adsorption of O2 proceeds by thermal activation via a trapping precursor and the process is promoted by the decreasing translational energy of the incident O2 and/or by increasing surface temperature. Our results demonstrate that the initial oxidation can be controlled by the adjustment of the translational energy of incident O2.
The mechanical properties of Nbss/Nb5Si3in-situ composites alloyed with Mo and W have been studied in relation to the microstructure. The samples were prepared by arc-melting, or floating zone melting method to produce a directional structure. Microstructures were characterized by XRD, EPMA and BEI. Room temperature fracture toughness and high temperature strength were examined by three point bending test and compression test, respectively. In Nb-5Mo-xW-16Si and Nb-5Mo-xW-20Si(x=0∼15 mol%) alloy series, the strength increased and fracture toughness decreased monotonously with increasing content of W. Furthermore, the strength of Nb-15Mo-18Si produced by directional solidification was slightly higher than arc-melted samples, but the fracture toughness was extremely low. It is suggested that intrinsic toughness of Nbss and thickness of Nbss phase in the microstructures are very important to room temperature fracture toughness.
Solid-solution lead chalcogenide semiconductors are expected to be applied as tunable laser diodes that can operate in the mid-infrared wavelength region between 3 and 4×10−6 m. In the present study, we investigated the growth of high-quality PbS single crystals, paying particular attention to obtaining a crystal with a large, flat facet and a well-controlled composition close to the stoichiometric composition. Such a crystal would be useful as a substrate for laser diodes. We employed a two-step process. In the first step, PbS was vapor transported under the partial pressure of S, which was regulated by using an S reservoir. In the second step, we removed the reservoir from the ampoule and then performed crystal growth under nearly thermal equilibrium condition. The maximum size of the facets obtained was about 5×10−5 m2. Crystals obtained at S reservoir temperatures below 530 K had n-type conductivity, while those obtained at higher temperatures had p-type conductivity. This demonstrates that the deviation from stoichiometry of the PbS single crystal can be controlled well by the S reservoir temperature. The electrical properties of the present as-grown crystals are favorable for substrate materials used to fabricate laser diodes. It has generally been reported in the literatures that some heat treatment is always needed to obtain reasonable properties for laser diode substrates. Therefore, the present method for PbS crystal growth is much more advanced than the previous ones, since the as-grown (100) facet can be used for a substrate without any heat-treatment. In addition, the mechanical polishing and chemical etching processes can be eliminated.
Preparation and thermoelectric properties of n-type SiC were studied. Nitrogen doping was performed by mixing 3-10 mass%Si3N4. The pellets were prepared by spark plasma sintering (SPS) at 2000°C. The crystal structure of every sintered material is cubic β-type and relative density was higher than 80%. All sintered materials showed n-type conduction and the carrier concentration increased with increasing Si3N4 concentration. Seebeck coefficient decreased and electrical conductivity increased with increasing Si3N4 concentration. Power factor was improved by the Si3N4 doping and the maximum power factor of 1.5×10−4 W/mK2 was obtained for SiC-7 mass%Si3N4 at 700°C.