Effect of the Structural State of Graphitic Materials on Their Phase Transformations under Shock Compression.

The effect of structural disordering of graphitic materials on their phase transformations into dense modifications of carbon under shock compression conditions ( P = 30 GPa, T = 3000 K) is studied. It is shown that a lower degree of three-dimensional ordering of initial structure (P) first decreases and then increases the overall yield of dense phases, reaching the maximum at P = 0. The content of lonsdaleite simultaneously decreases and that of the dense amorphous phase ( C) increases. The results obtained are attributed to gradual change of the predominant martensite transformation mechanism to predominant diffusion-controlled mechanism, and also to the fact that the metastable phases (lonsdaleite and C) that form at the initial transformation stage partly transform into a stable diamond phase. [ABSTRACT FROM AUTHOR]