Experimental Investigations on Aggregate-Aggregate Collisions in the Early Solar Nebula
Experimental Investigations on Aggregate-Aggregate Collisions in the Early Solar Nebula
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早期太阳星云中聚合体-聚合体碰撞的实验研究
DOI：
10.1006/icar.1993.1163
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发表时间：
1993
期刊：
影响因子：
3.2
通讯作者：
M. Münch
中科院分区：
文献类型：
--
作者：
J. Blum;M. Münch
摘要 在前行星状星云中固体积累的第一阶段，低速聚集体-聚集体碰撞对于聚集体尺寸的发展起着重要作用。为了研究此类碰撞，开发了一种实验装置，其中两个毫米大小的灰尘聚集体在真空中以~0.15和~4 m sec -1 之间的相对速度碰撞。碰撞的冲击参数是任意的，因此可以研究中心碰撞和掠过碰撞。使用两种类型的骨料，(1) ZrSiO 4 ，其成分粒径≤1μm，孔隙率74%；(2) Aerosil 200 (SiO 2 )，其成分粒径~12 nm，孔隙率97%。对于相同尺寸的骨料（ZrSiO 4 (I)、Aerosil 200）以及平均质量比为~66的骨料（ZrSiO 4 (II)），碰撞实验在上述速度范围内的五个窄速度窗口中进行。没有观察到聚集体的凝结（即粘附）。低速碰撞导致恢复（即弹跳），而在较高速度下，ZrSiO 4 (I) 在 ν ∼ 1 m sec -1 处观察到从恢复到碎裂的转变，对于 Aerosil 200 在 ν ∼ 4 m sec -1 处观察到了从恢复到碎裂的转变。对于 ZrSiO 4 (II)，仅在两种情况下发现了 ν ∼ 4 m sec -1 处的碎裂。由于转变速度较低，对 ZrSiO 4 (I) 的碎裂进行了更详细的研究。较小碎片的丰度随着速度的增加和冲击参数的减小而增加。在 ν ∼ 4 m sec -1 处，碎片数量遵循幂律质量分布 v ( m ) dm ∼ m -9/8 dm 。使用基于以下假设的简单破碎模型，对相同尺寸聚集体之间灾难性碰撞的碎片质量分布进行了外推：（1）组成颗粒质量和聚集体质量之间的幂律质量分布，（2）碎片每单位表面积具有恒定的自由表面能，以及（3）动碰撞能转换为碎片自由表面能的与冲击参数相关的效率。该模型预测，当碰撞速度≥50 m sec -1 时，ZrSiO 4 (I) 聚集体会完全分解成其构件。对于由半径为 0.1 μm 的范德华键合颗粒组成的聚集体，这些灾难性的碰撞速度要小得多，预计为 ∼3 m sec -1 。这些是前行星状星云的典型速度，因此如果太阳星云中由于表面力较弱而形成聚集体，灾难性的碎片可能会频繁发生。
Abstract Low-velocity aggregate-aggregate collisions play an important role for the developement of aggregate sizes during the first stages of accumulation of solid bodies in the preplanetary nebula. To study such collisions, an experimental setup was developed where two millimeter-sized dust aggregates collide in vacuum with relative velocities between ∼0.15 and ∼4 m sec -1 . The impact parameters of the collisions are arbitrary so that central collisions as well as grazing collisions can be investigated. Two types of aggregates were used, (1) ZrSiO 4 with constituent particle sizes ≤1 μm and 74% porosity and (2) Aerosil 200 (SiO 2 ) with constituent particle sizes ∼12 nm and 97% porosity. The collision experiments were carried out in five narrow velocity windows in the above velocity regime for equal-sized aggregates (ZrSiO 4 (I), Aerosil 200) as well as for aggregates with a mean mass ratio of ∼66 (ZrSiO 4 (II)). Coagulation (i.e., sticking) of the aggregates was not observed. Low-velocity collisions resulted in restitution (i.e., bouncing), and at higher velocities, a transition from restitution to fragmentation was observed at ν ∼ 1 m sec -1 for ZrSiO 4 (I), as well as at ν ∼ 4 m sec -1 for Aerosil 200. For ZrSiO 4 (II), fragmentation at ν ∼ 4 m sec -1 was found in two cases only. Due to the lower transition velocity, the fragmentation of ZrSiO 4 (I) was investigated in more detail. The abundance of smaller fragments increases with increasing velocity and with decreasing impact parameter. At ν ∼ 4 m sec -1 , the fragment numbers follow a power law mass distribution v ( m ) dm ∼ m -9/8 dm . Extrapolation of the fragment mass distribution for catastrophic collisions between equal-sized aggregates were performed using a simple fragmentation model based on the following assumptions: (1) power law mass distribution between the constituent particle mass and the aggregate mass, (2) fragments have constant free surface energies per unit surface area, and (3) impact parameter-dependent efficiency for the transition of kinetic collision energy into free surface energy of the fragments. This model predicts a complete disintegration of the ZrSiO 4 (I) aggregates into their building blocks for collision velocities of ≥50 m sec -1 . For aggregates consisting of van der Waals-bonded constituent particles of 0.1 μm radii, these catastrophic collision velocities are much smaller and are predicted to be ∼3 m sec -1 . These are typical velocities for the preplanetary nebula, so catastrophic fragmentations could be frequent events if aggregates in the solar nebula formed due to weak surface forces.