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412 results on '"Tohji, K."'

51. Production of monodispersed particles by using effective size selection

Author

Perales-Perez, O., Sasaki, H., Kasuya, A., Jeyadevan, B., Tohji, K., Sumiyama, K., and Hihara, T.

Subjects
Solvents -- Magnetic properties, Surface active agents -- Magnetic properties, Physics
Abstract

The results of two size selection methods that are based on the control of interfacial interaction between nanosize particles, using either suitable ionic surfactants or nonpolar solvents, are reported. Using these methods, stable suspensions of monodispersed magnetic nanoparticles (standard deviation, sigma, below 0.2) having various diameters, were obtained.

Published
2002

53. Method for the synthesis of CrO[sub 2] at ambient pressure and temperature.

Author

Ye, H., Zhang, Q., Saito, F., Jeyadevan, B., Tohji, K., and Tsunoda, M.

Subjects
CHROMIUM compounds, ATMOSPHERIC temperature, ATMOSPHERIC pressure, THERMOMAGNETISM
Abstract

In this article, we report the synthesis of metastable chromium dioxide at ambient temperature and pressure. The formulation of this method is based on the fact that the CrO[SUB2] particles used in magnetic recording tapes are chemically unstable and react with the organic binder, leading to a disproportionate reaction that produces nonmagnetic Cr(III)OOH and H[SUB2] Cr(VI)O[SUB4] compounds. This suggests that it is also possible to synthesize CrO[SUB2] by reacting Cr(III) with Cr(VI) under appropriate conditions. Thus, metastable chromium dioxide (CrO[SUB2]) powder was synthesized by mechanically grinding a mixture of CrO[SUB3] and Cr(OH)[SUB3] to induce a solid-solid reaction at atmospheric temperature and pressure. The characteristics of the product obtained after mechanical grinding of the above mixture depended on parameters such as the preparation conditions for the starting material Cr(OH)[SUB3], the grinding time, the rotational speed of the mill and the mole ratio of CrO[SUB3] and Cr(OH)[SUB3]. An x-ray diffraction pattern of the product obtained under optimum conditions was in excellent agreement with the profile of CrO[SUB2] Furthermore, the powder was strongly ferromagnetic, with saturation magnetization of 63 emu/g in an applied field of 1 T. [ABSTRACT FROM AUTHOR]

Published
2003
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54. Ferrimagnetic ordering in nanostructured CdFe[sub 2]O[sub 4] spinel.

Author

Chinnasamy, C. N., Narayanasamy, A., Ponpandian, N., Joseyphus, R. Justin, Chattopadhyay, K., Shinoda, K., Jeyadevan, B., Tohji, K., Nakatsuka, K., and Greneche, J.-M.

Subjects
SPINEL, METAL powders, FERRIMAGNETISM
Abstract

Nanostructured CdFe[sub 2]O[sub 4] spinel powders with various grain sizes ranging from 60 to 4 nm were synthesized by ball milling the bulk material. The magnetization measurements at 1 and 9 T reveal a spin-glass-like surface structure and the material is found to have a large anisotropy. Mo¨ssbauer studies at 10 K in external magnetic fields of 6 and 8.5 T applied parallel to the direction of gamma rays could clearly show that CdFe[sub 2]O[sub 4] behaves like a mixed spinel on reducing the grain size to nanometer level and exhibits ferrimagnetic ordering. Fe[sup 3+] spins at both A and B sites exhibit spin canting. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001
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55. Neel temperature enhancement in nanostructured nickel zinc ferrite

Author

Ponpandian, N, Narayanasamy, A, Chinnasamy, CN, Sivakumar, N, Greneche, JM, Chattopadhyay, K, Shinoda, K, Jeyadevan, B, and Tohji, K

Subjects
Materials Engineering (formerly Metallurgy)
Abstract

The Neel temperature of Ni0.5Zn0.5Fe2O4 spinel ferrite increases significantly from 538 K in the bulk state to 592 K when the grain size is reduced to 16 nm by milling in a high-energy ball mill. This has been attributed to an increase in the AB superexchange interaction strength due to a possible enhancement in the magnetic ion concentration in the A-site on milling, as is evident from extended x-ray absorption fine structure and in-field Mossbauer measurements. (c) 2005 American Institute of Physics.

Published
2005

56. Mechanical pretreatment of lead-based alloy anodes for zinc electrowinning.

Author

Aichi T., T.T. Chen honorary symposium on hydrometallurgy, electrometallurgy and materials characterisation Orlando, Florida 11-Mar-1215-Mar-12, Muramatsu M., Sato R., Takahashi H., Tohji K., Aichi T., T.T. Chen honorary symposium on hydrometallurgy, electrometallurgy and materials characterisation Orlando, Florida 11-Mar-1215-Mar-12, Muramatsu M., Sato R., Takahashi H., and Tohji K.

Abstract

Experiments were carried out using an Al plate cathode and a Pb-0.7 wt% Ag anode to investigate the effect of physical treatment methods on the Pb content of electrolytic Zn. The original blank anodes were subjected to 10 types of treatment including milling 90 micrometres from both sides, sanding the surface with 40-grit waterproof sandpaper to remove the oxide film and blast treatment using SiO2 at an air pressure of 0.4 MPa, Al2O3 at air pressures of 0.4, 0.6 and 0.9 MPa, steel grit at 0.9 MPa and Zn cut wire at 0.9 MPa. The results showed that the improvement in Zn grade was greater using surface roughening treatments than removal of the oxide layer. The arithmetic mean surface roughness, Ra, of the anodes varied with the surface treatment employed and it is important to achieve the optimum Ra by controlling the blasting media and air pressure. Increasing the surface roughness resulted in the formation of dense Mn oxide scales on the anode so that release of Pb into the electrolyte was suppressed., Experiments were carried out using an Al plate cathode and a Pb-0.7 wt% Ag anode to investigate the effect of physical treatment methods on the Pb content of electrolytic Zn. The original blank anodes were subjected to 10 types of treatment including milling 90 micrometres from both sides, sanding the surface with 40-grit waterproof sandpaper to remove the oxide film and blast treatment using SiO2 at an air pressure of 0.4 MPa, Al2O3 at air pressures of 0.4, 0.6 and 0.9 MPa, steel grit at 0.9 MPa and Zn cut wire at 0.9 MPa. The results showed that the improvement in Zn grade was greater using surface roughening treatments than removal of the oxide layer. The arithmetic mean surface roughness, Ra, of the anodes varied with the surface treatment employed and it is important to achieve the optimum Ra by controlling the blasting media and air pressure. Increasing the surface roughness resulted in the formation of dense Mn oxide scales on the anode so that release of Pb into the electrolyte was suppressed.

Published
2012

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