Magnesium and Silicon are the most abundant rock forming elements in the terrestrial planets, and Mg/Si fractionation among planets and meteorites is believed to have occurred in the early solar nebula. In order to evaluate Mg/Si fractionation in the solar nebula, evaporation and condensation of magnesium silicates moving vertically in the protoplanetary disk are simulated based on experimental kinetics and an astrophysical model. Evaporation of forsterite dust particles is shown to be a rapid process and be regarded as an equilibrium reaction during the vertical drift. Evaporation of enstatite is controlled by diffusion through the forsterite layer that is formed as an evaporation residue. Since the diffusion distance under kinetic conditions during the vertical drift is about 1μm, evaporation of enstatite grains would be nearly equilibrium for grains of 1μm and non-equilibrium for grains of 10μm. Condensation of forsterite is simulated as grain growth after heterogeneous nucleation on pre-existed refractory grains. It is found that condensation of forsterite proceeds with keeping equilibrium. Enstatite is formed in the nebula via a reaction between forsterite and gas, and the formation reaction is controlled by diffusion through the enstatite layer. Formation of enstatite would be kinetically inhibited due to its slow diffusion kinetics. The present result implies that the temperature range, in which forsterite is a dominant solid component, would be widened to lower temperature than at equilibrium, and Mg/Si fractionation, which has been explained by extraction of materials with a high Mg/Si ratio such as forsterite from the system, would occur more easily than that in the equilibrium model.
Using ultrasonic cavitation, it was found that atoms of all supplied gases inside sono vessel can be easily implanted into various metals placed in H2O, D2O and mixed water. Gases used were inert gases (3He, 4He, Ne and Ar) and other ones (N2, air, H2 and D2), and all of them were strongly implanted into such metals as Ti, Pd, Ag, Ta, Pt and Au. During implantation, these metals were broken up to very fine metal powders, and a large amounts of implanted gases released from these powders by heating were measured by mass spectroscopic analyses.
Dispersions of ionic polymer latex (diameter=600nm) consisted of 10 to 1000 particles were confined in spherical voids having diameters of several tens pm formed in a hydrogel (agarose) matrix. The system was constructed first by confining the latex dispersions in giant liposomes, immobilizing the liposomes by using the hydrogel matrix, and then removing the liposome membranes from the matrix. The latex particles inside the voids showed an extensive Brownian motion. This system, as a whole, could be regarded as a model system of one superfine particle. The solid-liquid phase transition was examined both for bulk and the confined colloids, by applying confocal laser scanning microscopy and phase contrast microscopy. The salt concentration was 2μM. In bulk, the solid-liquid phase boundary laid at particle concentration, Cp=1.0-1.5vol%. On the other hand, the confined dispersion took a liquid state even at Cp=2.5vol%. The present observation might correspond to a size effect for the melting point of a superfine particle system.