Pure, low-oxygen zirconium samples have been observed to nucleate a solid phase under conditions during which the sample was expected to remain liquid. This phenomenon was first seen during Spacelab Mission MSL-1R (materials science laboratory) experiments and has since also been observed in the International Space Station (ISS) electromagnetic levitation (EML) facility on a different sample. Current work has been able to replicate these anomalous solidification events under a range of conditions in the ISS MSL-EML facility. The solidification events are not well explained by classical homogeneous or heterogeneous nucleation. The current theory is that collapsing voids in the melt create a local region of high pressure that results in local material being deeply undercooled and a strong driving force for solidification.

中文翻译：

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锆中异常成核的确认

已观察到纯的低氧锆样品在预期样品保持液态的条件下使固相成核。这种现象在 Spacelab Mission MSL-1R（材料科学实验室）实验中首次出现，此后也在国际空间站 (ISS) 电磁悬浮 (EML) 设施的不同样本中观察到。目前的工作已经能够在国际空间站 MSL-EML 设施的一系列条件下复制这些异常凝固事件。经典的均质或异质成核不能很好地解释凝固事件。目前的理论是，熔体中的塌陷空隙会产生局部高压区域，导致局部材料深度过冷并产生强大的凝固驱动力。