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Evaporation Experiments on Planetary Materials.

行星材料的蒸发实验。

基本信息

批准号：
05833009
负责人：
TSUCHIYAMA Akira
金额：
$ 1.34万
依托单位：
Osaka University
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 rates and their evaporation coefficients of important minerals forming terrestrial planets (forsterite, metallic iron, and troilite) were determined by evaporation experiments. Forsterite evaporates congruently, and the evaporation obeys a linear rate law. Its evaporation coefficient showed that the evaporation of forsterite under a H_2-rich atmosphere occurs by mechanism similar to that of free evaporation. From the results, evaporation rates of forsterite in a primordial solar nebula can be estimated. Evaporation of metallic iron also obeys a linear rate law, and its evaporation coefficient is close to unity. Incongruent evaporation of troilite with metallic iron residue obeys a linear rate law due to reaction at the troilite-metallic iron interface as a rate-determining process. From the experimental results together with previous data, evaporation rates of important minerals forming terrestrial planets were complied. Elemental fractionation (Mg/Si and Fe/S) due to evaporation of mineral dust in the primordial solar nebula was discussed based on the complied data. It was suggested that incongruent evaporation of enstatite did not occur but apparent congruent evaporation of enstatite occurred, and thus no Mg/Si fractionation is expected. However, Mg/Si fractionation is possible as long as the dust was amorphous Mg-silicate. Fe/S fractionation was expected due to incongruent evaporation of troilite. A model for isotopic mass fractionation due to evaporation of solids was also constructed based on the evaporation rates of the minerals. The fractionation depends on the evaporation rate, diffusion coefficient in the solid, the size of the solid, and isotopic fractionation factor which is determined from the mass of evaporated molecules. Based on the model, conditions for isotopic mass fractionation found in meteorites were estimated successfully.

通过蒸发实验测定了类地行星形成的重要矿物（镁橄榄石、金属铁和陨硫铁）的蒸发速率和蒸发系数。镁橄榄石的蒸发是一致的，蒸发速率服从线性规律。其蒸发系数表明镁橄榄石在富氢气氛下的蒸发机理与自由蒸发相似。根据这些结果，可以估算出原始太阳星云中镁橄榄石的蒸发速率。金属铁的蒸发也服从线性速率定律，蒸发系数接近于1。由于硫铁矿-金属铁界面的反应是一个速率控制过程，硫铁矿与金属铁残渣的不一致蒸发服从线性速率定律。根据实验结果并结合以前的数据，得出了形成类地行星的重要矿物的蒸发速率。根据整理的资料，讨论了原始太阳星云中矿物尘埃蒸发引起的元素分馏（Mg/Si和Fe/S）。结果表明，顽火辉石的不一致蒸发没有发生，但明显的顽火辉石的一致蒸发发生，因此没有Mg/Si分馏预期。然而，Mg/Si分馏是可能的，只要粉尘是无定形硅酸镁。铁硫分异是由于陨硫铁的不一致蒸发造成的。基于矿物的蒸发速率，建立了固体蒸发引起的同位素质量分馏模型。分馏取决于蒸发速率、固体中的扩散系数、固体的尺寸和同位素分馏因子，同位素分馏因子由蒸发分子的质量确定。在此基础上，成功地估算了陨石中同位素质量分馏的条件。