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Evaporation kinetics of minerals and isotopic fractination ; application to the solar nebula

矿物蒸发动力学和同位素分馏；

基本信息

批准号：
05833004
负责人：
TAKAHASHI Hiroko
金额：
$ 1.47万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

Evaporation rate of olivine in vacuum and hydrogen gas flow of various pressures were experimentally investigated. The evaporation rate has large dependence on the hydrogen gas pressures. The evaporation rate is equal to that in vacuum at P_<H2> below 10^<-6> bar, is dependent on P_<H2> with power of unity at P_<H2> between 10^<-6> and 10^<-4> bar, and has small dependence on P_<H2> above 10^<-4> bar. The relationship between evaporation rate and hydrogen pressure at P_<H2> below 10^<-4> bar is shown by the equation j=0.33P_<H2>+8x10^<-7>, where j is the evaporation flux from a unit surface area in a unit time. The power of unity suggests that the elementary reaction is between one mole of forsterite at the surface and one mole of adsorbed hydrogen molecule.By using above results, the life-time of forsterite grains in the solar nebula was estimated. The grains are assumed to be spherical with a uniform size, the nebula is assumed to consist of H_2, O_2 and C,and the system was assumed … More to go up to a high temperature instantaneously and kept at that temperature for a long time. The evaporation rate from the grains are the same as that in vacuum at the beginning of heating and gets smaller with time due to increase of partial pressure of Mg-or Si-bearing gas species. The change of grain size and evaporation flux are obtained as a function of a dimensionless parameter eta. Ethe represents the degree of enrichment of dust against hydrogen gas normalized to the solar system elemental abundance. At etasmaller than 3, forsterite grains evaporate totally and the evaporation rate is equal to that in vacuum. On the contrary at eta larger than 3, the system gets equilibrium between solid and gas resulted in cease of evaporation. The time required for getting equilibrium becomes longer with decreasing eta. It requires infinite time at eta around 3. In the solar nebula, is estimated to be between 0.1 to 100, and therefore, interstellar dust could survive from nebular heating when the degree of enrichment was high, and that they totally evaporated when the degree was small which resulted in homogenization of the system. Less

实验研究了橄榄石在真空和不同压力氢气流中的蒸发速率。蒸发速率对氢气压力有很大的依赖性。在P_（10）巴以下，蒸发速率与真空中的蒸发速率相等;<H2><-6>在<H2>P_<H2>（10）巴<-6>至10巴<-4>之间，蒸发速率与P_<H2>（10）<-4>巴的单位幂有关;当压力低于10 × 10 ~（-1）巴时，蒸发速率与氢压的关系<H2><-4>式为：j=0.33P_<H2>+8 × 10 ~（-1）巴<-7>，其中j为单位时间内单位表面积的蒸发通量。根据单位幂的概念，提出了一摩尔镁橄榄石与一摩尔吸附氢分子之间的基元反应，并据此估算了太阳星云中镁橄榄石颗粒的寿命。我们假定粒子是均匀大小的球形粒子，星云由H_2，O_2和C组成，系统假设 ...更多信息瞬间达到高温，并在此温度下保持很长时间。在加热开始时，晶粒的蒸发速率与真空中的蒸发速率相同，但由于含Mg或Si气体分压的增加，蒸发速率随时间的延长而减小。晶粒尺寸和蒸发通量的变化作为一个无量纲参数η的函数。Ethe代表尘埃相对于氢气的富集程度，标准化为太阳系元素丰度。当η小于3时，镁橄榄石颗粒完全蒸发，蒸发速率与真空蒸发速率相当。当η大于3时，体系达到固气平衡，蒸发停止。达到平衡所需的时间随着η的减小而变长。它需要无限的时间在eta大约3。在太阳星云中，估计在0.1到100之间，因此，星际尘埃可以在浓缩程度高的时候从星云加热中存活下来，当浓缩程度小时，它们完全蒸发，导致系统的均匀化。少