Vaporization of sodium from a partially molten chondritic material

In order to examine vaporization behavior of sodium for partially molten chondritic materials, heating experiments were carried out using two starting materials prepared from the Etter (L5) chondrite (grain-sizes : sample A, φ torr, and heating duration up to 160min. Chemical analyses and petrographical examinations were carried out for starting materials and run products. The rates of vaporizations for sodium were estimated for partial melts (degree of melting=11-34%) at 1200-1400℃. Differences in the vaporization rates for the partially molten charges obtained from different starting materials were not detected clearly at the same temperatures. Systematically different trends of sodium vaporization rate are found between those obtained in this work and those previously reported for total melts (at 1450-1600℃) from similar starting materials (TSUCHIYAMA et al., 1981). It appears that the vaporization mechanism of Na is basically the same in the temperature range from 1200 to 1600℃ for partially to completely molten charges

Volatilization of alkali metals from the heated Murchison (CM2) meteorite

In order to examine volatilization processes of alkali metals at high temperature, heating experiments were carried out using a starting material prepared from Murchison (CM2) (grain-size : ∿10μm) at temperatures of 1200-1400℃ under a constant pressure of 8×10^ Torr, and heating duration up to 80min. Analyses of alkalis (Na, K, Rb), major and minor elements and petrographic examinations were performed for run products. Results show that fractional volatilization of alkali metals occurred during heating. It is suggested that the volatilization rates of alkali metals are influenced by the chemical composition of partial melt

Very Low Nucleation Rates of Glucose Isomerase Crystals under Microgravity in the International Space Station

In situ observation of the nucleation and growth of glucose isomerase (GI) crystals under microgravity was conducted using an optical microscope during the first flight of the Advanced Nano Step project undertaken in the International Space Station (ISS). Very low apparent nucleation rates (J’) of GI crystals in the solution and on the substrate of the growth container were confirmed compared with those on the ground. In particular, J’ of GI crystals in the solution were a few times lower than that on the substrate. The growth rates (R) of the {101} faces of GI crystals on the substrate and the apparent growth rates (R’) in the solution were measured. The very low nucleation rates allowed us to successfully measure R at a very high supersaturation region (up to ln(C/Ce) = 6), at which R cannot be measured on the ground

Oscillations and accelerations of ice crystal growth rates in microgravity in presence of antifreeze glycoprotein impurity in supercooled water

The free growth of ice crystals in supercooled bulk water containing an impurity of glycoprotein, a bio-macromolecule that functions as 'antifreeze' in living organisms in a subzero environment, was observed under microgravity conditions on the International Space Station. We observed the acceleration and oscillation of the normal growth rates as a result of the interfacial adsorption of these protein molecules, which is a newly discovered impurity effect for crystal growth. As the convection caused by gravity may mitigate or modify this effect, secure observations of this effect were first made possible by continuous measurements of normal growth rates under long-term microgravity condition realized only in the spacecraft. Our findings will lead to a better understanding of a novel kinetic process for growth oscillation in relation to growth promotion due to the adsorption of protein molecules and will shed light on the role that crystal growth kinetics has in the onset of the mysterious antifreeze effect in living organisms, namely, how this protein may prevent fish freezing

Highly Purified Glucose Isomerase Crystals Under Microgravity Conditions Grow as Fast as Those on the Ground Do

Suppression of convection flows (solute transportation) and of impurity incorporation into crystals seem to be the main reasons why the quality of protein crystals improves under microgravity, although their precise mechanisms have not been completely discovered yet. We tried to clarify effects of suppression of convection flows on crystallization processes by in-situ observation of straight steps on parallelogram-shaped spiral growth hillocks on the {110} faces of highly purified glucose isomerase (GI) crystals under microgravity conditions and on the ground. Lateral growth rates Vlateral of a spiral hillock on the {110} face of a glucose isomerase crystal in situ under microgravity and step velocities Vstep of the same configuration on the ground had similar maximum values. This similarity indicates the convection flow has a small, if any, influence on the growth rates of protein crystals, contrary to conventional expectations. From Vstep of the straight step in a particular direction, we calculated the vibrational frequency of a GI tetramer at a kink site of a step as (1182±3) s^(-1) with the assumption of zero activation energy of kink incorporation processes

Very Low Nucleation Rates of Glucose Isomerase Crystals under Microgravity in the International Space Station

In situ observation of the nucleation and growth of glucose isomerase (GI) crystals under microgravity was conducted using an optical microscope during the first flight of the Advanced Nano Step project undertaken in the International Space Station (ISS). Very low apparent nucleation rates (J’) of GI crystals in the solution and on the substrate of the growth container were confirmed compared with those on the ground. In particular, J’ of GI crystals in the solution were a few times lower than that on the substrate. The growth rates (R) of the {101} faces of GI crystals on the substrate and the apparent growth rates (R’) in the solution were measured. The very low nucleation rates allowed us to successfully measure R at a very high supersaturation region (up to ln(C/Ce) = 6), at which R cannot be measured on the ground