No abstract

No abstract

No abstract

No abstract

Abstract. The measurements of the Hugoniot and sound velocity pressure dependence in β-Si 3 N 4 porous samples under shock loading up to 55 GPa are presented. The Hugoniot and experimental particle velocity profiles demonstrate no peculiarities arising from the phase transition into high density c-Si 3 N 4 . Nevertheless, it follows from the comparison of measured Hugoniot with the Hugoniot for monolithic samples that phase transition does take place, starting at a much lower pressure of approximately 25 GPa, where the two Hugoniots intersect. The analysis of the positional relationship of the Hugoniots for monolithic and porous samples allowed us to confirm that the transformation pressure threshold decreases with the temperature increase due to a greater heating of porous material under loading. Measurements of sound velocity in shocked samples showed that sound velocity pressure dependence has a kink near 23 GPa, which is very close to the presumable pressure of the transition to c-Si 3 N 4 in porous samples.

No abstract

The influence of shock-wave pressure treatment up to 65 GPa on the crystal structure and the superconducting transition temperature of a polycrystalline MgB 2 sample has been investigated. X-ray diffraction measurements have revealed that the shock-wave pressure does not result in any irreversible structural phase transitions in the MgB 2 , except for microdistortions formed in the crystal structure of the shockwave pressure-treated MgB 2 sample. This conclusion is in agreement with the results of superconducting transition temperature measurements of a MgB 2 sample performed before and after its shock-wave pressure treatment.

No abstract