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EXPERIMENTAL STUDY ON MINERAL CONDENSATION FROM GAS

天然气矿物凝结实验研究

基本信息

批准号：
12440152
负责人：
HIROKO Nagahara
金额：
$ 10.37万
依托单位：
THE UNIVERSITY OF TOKYO
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

In order to explore the time scale and controlling factors of phases appear during condensation in various stellar environments, experimental approach to get dusts in laboratory was employed. Condensation includes two elementary processes, nucleation and crystal growth, in which condensation is hard to control on the Earth due to the gravitational force. The most abundant elements that form solid materials in the universe are Si, Mg and Fe. Calculation of chemical equilibrium and astrophysical observation around young and evolved stars and interstellar space reveal that forserite, enstatite and metallic iron are the dominant phases. Therefore, experiments of condensation of forsterite, ensatite, and metallic iron dust on substrates without nucleation are planned at low pressure conditions.At first, development of an experimental equipment was attempted, and an vacuum chamber made of stainless steel with tungsten mesh heated and W and Mo thermal shields were prepared to obtain large amount of hot gas at the condensation spot. The results, however, were found to be unsuitable for condensation of silicate dusts, because the tungsten prevents condensation of oxygen atoms or molecules into silicates. Then, condensation of metallic iron was intended by using iron oxide (Fe2O3) as an evaporation source, and metallic Mo and forsterite for substrates. The source was heated at 1350℃ for 1 to 120 hours, and the reside and condensates were observed with a scanning electron microscopy (SEM) and analyzed with electron back scattered diffraction (EBSD) technique. Condensates were observed on both Mo and forsterite, of which size and amount increase with time, and are determined to be metallic iron. They show cubic shape and the size is larger on forsterite than Mo. The results show that the temperature of substance at a radiation field from a star plays key role on dust growth due to difference in actual temperature.

为了探索不同恒星环境下凝聚过程中出现的相的时间尺度和控制因素，采用实验室获取尘埃的方法。凝结包括成核和晶体生长两个基本过程，其中由于地球引力的影响，凝结在地球上很难控制。宇宙中形成固体物质的最丰富的元素是Si、Mg和Fe。化学平衡计算和天体物理观测表明，在年轻恒星和演化恒星周围以及星际空间，镁橄榄石、顽火辉石和金属铁是主要的物相。因此，我们计划在低压条件下进行镁橄榄石、顽火辉石和金属铁粉尘在基体上的无形核凝结实验。首先，我们尝试开发实验设备，并准备了一个由不锈钢制成的真空室，配有加热的钨网和W和Mo热屏蔽，以在凝结点获得大量的热气体。然而，结果被发现不适合硅酸盐粉尘的冷凝，因为钨阻止氧原子或分子冷凝成硅酸盐。然后，通过使用氧化铁（Fe 2 O3）作为蒸发源，并使用金属Mo和镁橄榄石作为基底，来进行金属铁的缩合。在1350℃下加热1 ~ 120 h后，用扫描电镜（SEM）观察残余物和冷凝物的形貌，用电子背散射衍射（EBSD）技术对残余物和冷凝物进行分析。在钼和镁橄榄石上都观察到冷凝物，其尺寸和数量随时间增加，并被确定为金属铁。它们呈立方体形状，在镁橄榄石上的尺寸大于Mo。结果表明，由于实际温度的差异，星星辐射场中物质的温度对尘埃的生长起着关键作用。