Kazuto Tokumitsu

Reduction of metal oxides by mechanical alloying method

Abstract The reduction of metal oxides is usually carried out at high temperature in appropriate conditions with respect to equilibrium thermodynamics. However using the high activity of fresh surfaces enables mechanically activated reduction. After ball-milling of silver oxide, Ag2O, copper oxide, CuO, and hematite, Fe2O3, respectively, with carbon powder, metallic silver and copper could be obtained at room temperature and hematite was reduced to magnetite. The reduction processes were investigated by X-ray diffraction and 57Fe Mossbauer spectroscopy.

Appearance of ferromagnetism in f.c.c. solid solutions of binary and ternary Fe–Cu-based systems prepared by mechanical alloying technique

Abstract The ferromagnetic f.c.c. solid solutions are formed by mechanical alloying in the Fe–Cu binary systems containing less than 60% of iron. The Curie temperature of the alloy decreases with decreasing iron concentration. The expansion of average atomic volume of the alloys is about 1.6% of pure copper and 5.3% of f.c.c. γ-iron regardless of copper content except for dilute iron alloys. It is suggested from the present work that the ferromagnetism in the Fe–Cu alloys originates when the atomic volume is expanded by a certain value (5.3% of γ-iron is enough), and when a certain number of neighboring iron atoms exist to percolate the ferromagnetic interaction and possibly to generate the magnetic moment of iron. In the studies of ternary systems silver atoms hardly dissolved in Fe–Cu solution, whereas gold atoms formed solid solution.

Thermal Conductivity of the Molten CaO-SiO 2 -FeO x System

Thermal conductivity measurements were carried out on synthetic steelmaking slag using the hot-wire method. Furthermore, local structure analysis in the melts was carried out in order to investigate the relationship with the composition dependence. The thermal conductivity of the CaO-SiO2-FeOx melts significantly decreased as the content of FeOx increases, particularly at lower basicity. Both chemical analysis and the observation show that the amount of Fe2+ increases when CaO/SiO2 is smaller, implying more basic behavior of FeO than FeO1.5. According to further analyses by Mössbauer spectroscopy, the degree of basicity of FeO1.5 remains virtually unchanged in the composition range of interest. From the experimental results, it could be concluded that the thermal conductivity of the silicate melt containing iron oxide is highly dependent on the valence of the Fe ion and comparatively independent of the amphoteric behavior of FeO1.5.

Crystallization Behavior and Curie Temperature for Melt-Spun Amorphous Fe100-XGdX(18?X?70) Alloys

The crystallization behavior and Curie temperature, Tc, for the amorphous Fe100-XGdX alloys prepared with a melt quenching method with wide range concentration (18≤X≤70) were studied by means of a thermomagnetization measurement. Final stable phases were determined from the measurement in the cooling process from 800°C. They are (i) α-Fe, Fe23Gd6 and Fe2Gd for X=22, (ii) α-Fe, Fe2Gd and α-Gd for 33.3≤X≤58, and (iii) Fe2Gd and α-Gd for X=70. The concentration dependence of Tc has a maximum value of 320°C around X=40. Tc in the present melt-spun ribbons is higher than that of thin films by about 100 degrees.

Ferrimagnetic ordering in melt-spun Fe100−xGdx (18≤x≤70) alloys

Abstract The magnetic properties for the melt-spun amorphous Fe 100− x Gd x (18≤ x ≤70) alloys were investigated. Saturation magnetization at low temperature was explained by a simple ferrimagnetic structure assuming the magnetic moment of 2μ B for Fe and 7μ B for Gd. The temperature dependence of the magnetization was analyzed in terms of molecular field theory. Three exchange constants ( J Gd-Gd , J Gd-Fe and J Fe-Fe ) were estimated for the alloys with the concentration of 18≤ x ≤60.

Magnetic Properties of Nano-Particulate Cu-Co Alloy on the Route of Bulk Mechanical Alloying

Bulk mechanical alloying was used to fabricate the supersaturated solid solution of Cu 80 Co 20 . The nano-Co particulates Cu-matrix alloy was made by low-temperature annealing. Both the annealing temperature and time were parametrically varied to describe the relationship between process condition and magnetic properties. The maximum magnetoresistance ratio under 1.0 MA/m at room temperature of 4.9 % was measured for this nano-particulate material with the mean Co-particulate size of 6 nm. From the measured magnetic properties, the effect of particulate size of Co in Cu-matrix on the magnetic properties was discussed.

Phase Stabilities and Magnetic Properties of Fe-Cu Solid Solution Prepared by Mechanical Alloying

Fe 100-X Cu X solid solutions with X = 5, 10, 15, 20 have been obtained by mechanical alloying of elemental Fe and Cu powders. The structure and the atomic configuration of these solutions have been studied by X-ray diffraction and 57 Fe Mossbauer spectroscopy. X-ray diffractions showed that bcc Fe(Cu) solutions were formed after 15, 20 and 30 hours milling respectively. Mossbauer spectra were composed of 3 or 4 magnetically splitted sextets. Each hyperfine fields were (A) 327-329 kG, (B) 316-318 kG, (C) 302-304 kG, (D) 284 kG. These components correspond to (A) Fe atoms surrounded with 8 Fe, (B) Fe with 1 Cu + 7 Fe, (C) Fe with 2 Cu + 6 Fe, (D) Fe with 3 Cu + 5 Fe in bcc lattice. Mossbauer spectra for Fe-Cu solutions could be considers by the distribution change of these components with Cu concentrations.

Formation of metal hydride powders and metal-hydrogen amorphous powders by mechanochemical reaction

Abstract The formation of metal hydride powders was examined where pure metals powders were milled with liquid hydrocarbons, the source of hydrogen atoms. Niobium and tantalum were transformed to their crystalline hydrides when being milled with n -heptane (C 7 H 16 ) or cyclohexane (C 6 H 12 ). Chromium was transformed to an amorphous hydride. These transformations from metal to metal hydride are suggested as being caused by the absorption of hydrogen atoms which originated from the dehydrogenation of hydrocarbons.

Crystallization process and Mössbauer study of the melt-quenched amorphous FeGd alloys

Abstract Amorphous FeGd alloys, from 16 to 70 at.% Gd, were prepared with a melt-quenching method in a vacuum. An X-ray diffraction study on the crystallization process showed that these amorphous alloys crystallized into two phases, that is the h.c.p. Gd phase and the Laves phase (F 2 Gd). Mossbauer measurements of the amorphous phases showed that the internal hyperfine field was at its maximum of 276 kOe in the neighborhood of 42 at.% Gd. The isomer shifts were about + 0.1 mm s −1 .

Stability of ferromagnetism in FCC Fe–Cu–Au alloys prepared by mechanical alloying

Abstract We have studied the relation between the stability of ferromagnetism and the atomic volume of FCC Fe–Cu–Au alloys prepared by mechanical alloying by means of X-ray diffraction, magnetization measurement and Mossbauer effect. The atomic volume of the FCC Fe 0.5 Cu 0.5 alloy increased almost linearly with the substitution of Au atoms for Cu from original 12.09×10 −3 to 13.31×10 −3 nm 3 for 40% replacement. The Curie temperature of the alloy also increased in the same manner from 489 to 582 K. It is found that the increase in atomic volume stabilizes the ferromagnetic state of the FCC alloys. The values of magnetic moment of iron in Fe 0.5 Cu 0.4 Au 0.1 and Fe 0.5 Cu 0.3 Au 0.2 were estimated to be 2.34 and 2.44 μB, respectively, which are larger than that of α-iron (2.22 μB). The magnetic hyperfine field of iron in Fe 0.5 Cu 0.4 Au 0.1 showed wide distribution from 22 to 38 T at 82 K, which is probably caused by the variation of species of surrounding atoms of iron.