In-situ synchrotron x-ray study of phase transitions in melamine under high pressures and high temperatures

摘要

We report a synchrotron energy-dispersive x-ray diffraction study of melamine at high pressure and high temperature. Pressure was generated using a Paris-Edinburgh cell to employ larger sample volumes for weakly scattering organic samples. High temperatures were created using a resistive/graphitic cup surrounding the sample. The PT phase diagram was explored by first pressurizing the sample to 3.5 GPa at room temperature and then heating it up to 1197 K with a concomitant pressure increase to just above 5 GPa. Above 4.85 GPa and 967 K, an irreversible phase transition was observed. Upon cooling the sample, another phase transition was observed which is likely associated with polymerization observed in earlier ex-situ HPHT experiments.