Research On Phase Transformation From G-C₃N₄ To β-C₃N₄ Under Strong Shock Compression

The superhard carbon nitride materials predicted by theory may have wide application prospects with the excellent properties in mechanics, photology, electricity, thermology. Synthesis and properties of the carbon nitride materials attracted the interests of scholars from many countries. Many achievements have been obtained. However, the synthesis of the pureβ-C3N4 need further research by now. High temperature and high pressure synthesis technology is an effective way to synthesize superhard materials. Specifically, the high temperature and high pressure provided by shock compression can make instantaneous changes in material structures and properties. This thesis discussed the research of the pioneers for C3N4 compendious and searched the synthetic conditions ofβ-C3N4 under strong shock compression.A nitrogen-rich precursor of g-C3N4 is the thermal decomposition product of melamine. Using a two-stage light gas gun and shock recovery technology, a series of experiments up to 40-65GPa were carried out on the precursor g-C3N4. The purification products were tested and analyzed by XRD, TEM, SAED and XPS. The results showed that the precursor g-C3N4 was stable under 51 GPa pressure, while only a new crystalline phaseβ-C3N4 was obtained during 51～65GPa pressure and some polycrystalline P-C3N4 particles with size of 200nm～500nm were observed. Comparing the results of XPS for the part of no phase change g-C3N4, the chemical bond states were basically identical before and after shock compression. The duration of the second shock process was found to have an obvious effect on the phase transformation from g-C3N4 toβ-C3N4 by comparing the different experiments. Duration of the time is important for synthesizingβ-C3N4.