Artificial neural network (ANN) potential, which is an interatomic potential constructed by machine-leaning, attracts attention as a promising method to achieve extra-large-scale molecular dynamics (MD) simulation with first-principles accuracy. Application of this ANN-MD to far-from-equilibrium phenomena is very important in not only materials science but also high-pressure research field. In this article, a research example of ANN-MD simulation for elastic- and plastic-shock compression behavior in crystalline silica was described.
In this article we first review the roles of hypervelocity impacts in volatile partitioning on planetary surfaces and thermodynamics of shock vaporization/devolatilization of geologic materials. Impact experiment in an open system is essential to accurately estimate the shock pressure required for incipient vaporization/devolatilization, and we introduce a newly-developed open system experimental technique applied to two-stage light gas guns. This experimental apparatus allows us to measure impact-generated gases with a mass spectrometer at the same geometry of natural impacts with a limited risk of chemical contamination from the gun operation. The threshold pressures of vaporization/devolatilization for halite and gypsum were measured to be 18-31 GPa and <11 GPa, respectively. The new open system method is expected to serve as a powerful tool to explore the nature of shock vaporization/devolatilization of geologic materials.
Shock-recovery experiment can be elucidated shock-induced changes in a material at the micro level, although transient behavior of a material under dynamic compression is not studied in a direct way and pressure in the material studied is completely released. The shock-recovery experiments have been applied to a way of a material processing including structural transitions, introducing strain and defects, promoting chemical reactions, and densification. Structural transition of a material is one of an important subject for the material processing because physical properties of the material are strongly affected by its crystalline structure. Here, some examples of the shock-recovery experiments to evaluated are presented; (1) silicon and (2) gallium oxide.
Some meteorites have experienced heavy impacts on their parent bodies. High-pressure minerals are found in such heavily shocked meteorites. FIB-assisted TEM observations have contributed to disclose efficiently the occurrences and formation mechanisms of high-pressure minerals. In this article, the recent advances of research about high-pressure minerals in shocked meteorites are summarized. In the latter chapter, the implications of high-pressure minerals found in shocked meteorites into collision phenomena are also mentioned.
Shock-compressed high-pressure states of planetary materials have been analyzed using high-power lasers and ultrafast diagnosctic schemes in combination. Here we review our recent results. Uranus and Neptune in the outer solar system are made of planetary ice materials made of hydrogen, oxygen, carbon and nitrogen. At high pressure and temperature conditions relevant to the interiors of these planets, the planetary ices were proved to become a good electronic conductor, which is the best-possible rationale of strong magnetic fields originating from insides of these planets. On the other hand, microscopic structure evolution of planetary minerals, as represented by α-Mg2SiO4, are being analyzed as a function of time during their shock compression. For this purpose, X-ray free electron laser has been successfully combined with a high-power laser to enable ultrafast diffraction analysis of relevant crystal structures.