Experimental study on the heating of silicate aggregates and the formation of chondrules by nebula shock

我们研制了一种在气体中产生大马赫数强激波的新仪器。该仪器由一个二级轻气炮和一个安装在真空抽空样品室中的小型高压容器组成。利用该装置模拟了产生激波时星云气体之间的碰撞和尘埃与气体的相互作用。一枚1.6毫米大小的尼龙弹被发射到充满1bar空气的高压容器中，该弹丸侵彻空气后产生强烈冲击波。我们用高速摄影观测到了弹丸周围马赫数大于9的弓形激波，但没有观察到激波压缩气体的发射和气阻加热弹丸表面。观察到弹丸在侵彻气体后完好无损，没有任何破裂和熔化。我们还研究了高速气流对水滴的破坏实验。这项研究模拟了由星云激波引起的完全熔融的硅酸盐液滴，这些液滴被气体拖曳压缩或剪切。根据球粒陨石的粒度分布和形状特征等证据，硅酸盐熔体的破碎可能与球粒陨石的成因有关。在马赫数为1.01-1.12的条件下，用空气中的激波管对直径为0.3~5 mm的水滴进行了实验。用高速数字摄像机观察了破碎过程，分析了破碎液滴的尺寸分布。我们的结果表明，破碎液滴的累积质量分布具有指数关系，并且这种指数关系的斜率取决于韦伯数(4-400)。

We have developed a new instrument to generate a strong shock wave with a large Mach number in gas. This instrument was consisted of a two-stage light gas gun and a small high-pressure vessel set in a sample chamber evacuated in a vacuum. Collisions among nebula gas and the dust-gas interaction in a generated shock wave were simulated with this instrument. A nylon projectile with the size of 1.6mm was launched into the high-pressure vessel filled with 1 bar air and this projectile generates a strong shock wave after it penetrates into the air. We have observed a bow shock with the Mach number larger than 9 around the projectile by using a high-speed photography, but we didn't observe any emission from the shock compressed gas and the surface of the projectile heated by gas drag. The projectile was observed to be intact without any disruption and melting after the penetration into the gas.We have also studied a disruption experiment of a water droplet by high velocity gas flow. This study simulates a completely molten silicate droplets caused by nebula shock, which are compressed or sheared by gas drag. The disrupted silicate melts could be related to the origin of chondrules based on the evidence such as the size distribution and the characteristics of the shape. We have conducted this experiment with a water droplet whose size is 0.3 to 5mm at the condition with the Mach number from 1.01-1.12 by using a shock tube in air. The disruption was observed by a high-speed digital video and the size distribution of the disrupted droplets was analyzed. Our result shows that the disrupted droplets have an exponential relationship for the cumulative mass distribution and the slope of this exponential relation is found to depend on a Weber number (4-400)