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。该仪器由两级轻气枪和置于真空样品室中的小型高压容器组成。利用该仪器模拟了星云气体间的碰撞和激波中的尘埃-气体相互作用。将1.6mm的尼龙弹丸发射到充有1bar空气的高压容器中，弹丸进入空气后产生强烈的冲击波。我们用高速摄影的方法观察到了弹丸周围的马赫数大于9的弓形激波，但没有观察到激波压缩气体和弹丸表面被气体阻力加热的辐射。弹丸在侵彻气体后没有发生破碎和熔化现象，并进行了水滴在高速气流中破碎的实验研究。这项研究模拟了由星云冲击引起的完全熔融的硅酸盐液滴，这些液滴被气体阻力压缩或剪切。硅酸盐熔体的破碎可能与球粒的形成有关。我们在马赫数为1.01-1.12的条件下，用激波管在空气中对0.3 - 5 mm的水滴进行了实验。通过高速数字视频观察了破碎过程，并分析了破碎液滴的尺寸分布。结果表明，破碎液滴的累积质量分布呈指数关系，其斜率与韦伯数（4-400）有关

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)