[en] Full text: Glassy carbon (GC) is a predominately sp² bonded disordered carbon material which is temperature resistant up to ~3000°C making it a non-graphitizing carbon and is superelastic meaning that it retains its original structure following compression. The pressure limits for these properties are not known. In this study, the structural changes in GC after compression in a diamond anvil cell at room temperature are investigated. Figure 1(a) shows a transmission electron microscopy (TEM) image of uncompressed GC showing its tangled graphitic microstructure (red circle). Also shown is a selected area diffraction pattern (SADP) (inset) which can be indexed to graphite. Figure 1(b) shows an image of a GC sample recovered after compression to 45 GPa. The tangled graphitic microstructure of GC has clearly changed with the SADP (inset) showing strong permanent orientation of graphitic layers as indicated by the strong {002} arcs oriented parallel to the high stress direction. These TEM results along with measurements obtained from Raman spectroscopy reveal that the threshold for permanent structural change in GC occurs at ~40 GPa. We propose that this pressure also represents the limit to the non-graphitizing and superelastic properties of GC. (author)