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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.

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