Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Chemistry

Supervisor

Yang Song

Abstract

Nitrogen-rich materials have been considered as the most promising replacement of traditional energetic materials due to the large energy gap between the different nitrogen allotropes as well as the generation of environmental friendly nitrogen gas as the end-product. As a result, methods of synthesizing the nitrogen-rich materials have received increasing attention. Apart from the traditional chemical synthesis, high-pressure technique had been proved an effective tool to create such kinds of materials. However, several issues still existed concerning the high-pressure synthesis of energetic materials. Therefore, searching for precursors is of great interest. Here we report studies of four promising precursors, 5-aminotetrazole, 5-methyltetrazole, 5, 5´-bis(2-methyltetrazolyl)amine monohydrate and cyanuric triazide, under high pressure by Raman and IR spectroscopy, among which 5, 5´-bis(2-methyltetrazolyl)amine monohydrate and cyanuric triazide were also studied using X-ray diffraction. Besides, the high-pressure behavior of s-triazine was also investigated to have an in-depth understanding of the properties of cyanuric triazide.

In chapter 2, 5-aminotetrazole and 5-methyltetrazole were investigated and compared to examine the pressure effects on the ring structures and the high-pressure behaviors. No phase transitions for 5-aminotetrazole were found in the whole pressure range. However, four phase transitions were observed for 5-methyltetrazole, evidenced by the by the appearance of new lattice modes, the changes in peak profile as well as the pressure dependence of Raman lattice modes over different pressure ranges. Upon decompression, the tetrazole ring vibration modes in both compounds were fully recovered, suggesting the high stability of the tetrazole ring. The Raman and IR spectroscopic data together allowed for the analysis of the possible reasons of the stability of the tetrazole ring.

In chapter 3, another tetrazole derivative, 5, 5´-bis(2-methyltetrazolyl)amine monohydrate, was investigated by vibrational spectroscopy and X-ray diffraction. The Raman and IR spectroscopic data together with the XRD patterns collectively suggested there were no phase transitions in the entire investigated pressure range. Several changes were observed during compression and possible mechanisms were proposed. Upon decompression, all the Raman and IR modes were completely recovered, indicating the reversibility and good stability of this material.

Chapter 4 focuses on the high-pressure studies of two six-member aromatic rings, s-triazine and cyanuric triazide. A total of four phase transitions for s-triazine were observed, evidenced by changes in peak profile, the number of vibrational modes, as well as the pressure dependence of Raman lattice modes over different pressure ranges. The transition was identified irreversible for the lattice modes were not recovered upon decompression. In addition, a ring-opening reaction took place, suggested by the recovered Raman and IR internal modes. For cyanuric triazide, no phase transitions were observed in the pressure range of 0-26 GPa and one chemical reaction above 26 GPa. In addition, the transition was partially irreversible evidenced by the different Raman profiles in different parts of the sample. Possible reaction mechanisms were proposed accordingly.


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