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Journal Articles

Sedimentation of substitutional solute atoms in In-Pb system alloy under strong gravitational field; Experiments and simulations

Ono, Masao; Kinoshita, Takahiro*; Ueno, Hideto*; Huang, X.*; Osakabe, Toyotaka; Mashimo, Tsutomu

Materials Transactions, 46(2), p.219 - 224, 2005/02

 Times Cited Count:7 Percentile:53.8(Materials Science, Multidisciplinary)

Ultracentrifuge experiments were performed on the In-Pb system to study the sedimentation of atoms and phase equilibrium. After the experiments, the graded structures were obtained. Pb-rich phase (f.c.c) and In-rich phase (tetragonal) appeared at the strong- and weak-gravitational field sides of the sample, respectively, from starting state of $$alpha$$-phase. And, the continuous changes in lattice parameters were observed in each phase. These observation results showed that the graded structure was continuous in atomic scale, and was formed by the sedimentation of atoms. Composition profiles of the centrifuged samples for 31.3 h, 60 h and 150 h showed that the composition change reached the steady state within 60 hours. The diffusion coefficient for sedimentation was estimated to be about 8 times larger than that for usual diffusion by the simulation. The result indicated that the diffusion mechanism of the sedimentation was different from the conventional ones.

Journal Articles

Sedimentation of substitutional solute atoms in condensed matter; New type of diffusion

Mashimo, Tsutomu

Defect and Diffusion Forum, 237-240(1), p.30 - 37, 2005/00

Mega-gravity field realizes the sedimentation of even atoms, and is expected to create a nonequilibrium crystal-chemical state in condensed matter. We presented a self-consistent diffusion equation for sedimentation of atoms in condensed matter. Next, we developed an ultracentrifuge to generate strong acceleration field of over 1 million g, and, recently, succeeded in realization of the sedimentation of substitutional solute atoms in some alloys. The diffusion coefficients of sedimentation on Bi-Sb alloy were estimated to be much greater than those of conventional one. It is suggested that the sedimentation of substitutional atoms in solids or liquids can be included in a new type of diffusion, where the diffusion mechanism was yet unknown. In this article, the recent progress in the investigation of sedimentation of atoms under mega-gravity field is reviewed, and the diffusion mechanism is discussed. The application of the mega-gravity field is also discussed.

Journal Articles

Effects of ultrastrong gravitational field on the crystalline state of a Bi-Sb alloy

Huang, X.*; Mashimo, Tsutomu; Ono, Masao; Tomita, Takeshi; Sawai, Tomotsugu; Osakabe, Toyotaka; Mori, Nobuo*

Journal of Applied Physics, 96(3), p.1336 - 1340, 2004/08

 Times Cited Count:11 Percentile:44.13(Physics, Applied)

Mega-gravity field experiments were performed on the Bi$$_{70}$$Sb$$_{30}$$(atomic percent) alloy and pure Bi below their melting points, to investigate the change in crystalline state. For the alloy centrifuged at 191-205 $$^{circ}$$C, no change in composition was observed, and the grain sizes of the crystals decreased from several mm to tens of $$mu$$m, while no distinct change in grain size was observed for the centrifuged pure Bi. The alloy centrifuged at 220-240 $$^{circ}$$C consisted of two regions with different morphologies-fine-grained crystals with grain sizes around tens of $$mu$$m in the low gravity region, and large crystals with grain sizes several mm long and hundreds of $$mu$$m wide along the direction of gravity in the high gravity region, where sedimentation of atoms was confirmed. The large crystals with hexagonal structures were formed by preferential crystal growth roughly along the c axes, and a large strain that increased as the gravitational field increased existed inside these crystals. Formation of this anomalous crystal state might be correlated with the sedimentation of atoms.

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