New Method for Synthesizing High-Energy Cubic Deflection Polymeric Nitrogen under Normal Pressure
TapTechNews October 8th news, the research team led by Researcher Wang Xianlong from the Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, based on first-principles calculations as the theoretical basis, using potassium azide as the precursor and relying on the independently developed plasma-enhanced chemical vapor deposition device, successfully synthesized high energetic cubic deflection polymeric nitrogen with a diamond-like structure under normal pressure, providing a simple and efficient method for the macroscopic preparation of cubic polymeric nitrogen. The relevant results were published in Science Advances.
High energy density materials are a kind of substances that can generate extremely large amounts of energy in a short period of time, and are widely used in fields such as mining and construction. Due to the huge energy difference between the N-N single bond of nitrogen and the N≡N triple bond of nitrogen gas molecules, and the product after releasing energy is nitrogen, which has the characteristics of being green and environmentally friendly, so cubic deflection polymeric nitrogen (cubic gauchenitrogen, cg-N) is one of the typical representatives of new high energy density materials.
Since 2004, there have been many reports of synthesizing cg-N under high pressure, but failed to capture the high-pressure synthesized cg-N to normal pressure, and the decomposition mechanism during the pressure reduction process is not yet clear.
In 2017, it was reported that based on the plasma-enhanced chemical vapor deposition (Chemical Vapor Deposition, CVD) method, using the highly toxic and highly sensitive sodium azide as the precursor, a trace amount of cg-N was synthesized under normal pressure, but the conversion rate needs to be improved through the confinement effect of carbon nanotubes. However, reasons such as carbon nanotube encapsulation and less effective ingredients have affected the research on the thermal stability, thermal decomposition and detonation properties of cg-N. Therefore, clarifying the instability mechanism of cg-N during pressure reduction and developing a safer and more efficient synthesis method suitable for macroscopic preparation are the two key scientific issues currently faced.
Since 2020, the research team of the Institute of Solid State Physics has carried out research on the above two key scientific issues. Using the first-principles method, the team systematically simulated the stability of the cg-N surface under different saturation states and different pressures and temperatures, and found that the decomposition mechanism of cg-N when reducing pressure is surface instability, proposing a method of saturating surface dangling bonds and transferring charges can stabilize cg-N to 477°Fahrenheit (Chin. Phys. Lett. (Express Letter) 40, 086102 (2023)).
On this basis, based on the fact that the electronegativity of potassium is weaker than that of sodium, a method of using safer and cheaper potassium azide to replace sodium azide as the precursor to synthesize cg-N was proposed.
The first-principles calculation results show that potassium adsorption is much better than sodium adsorption in enhancing the surface stability of cg-N. Based on the independently developed plasma-enhanced CVD device, without the assistance of nano-confinement effect, successfully synthesized cg-N under normal pressure, and the sample can be preserved for more than 2 months.
Synchronous thermal analysis (TG-DSC) measurement results show that cg-N has a thermal decomposition temperature of 488°Fahrenheit, which is in line with the theoretically predicted decomposition temperature of 477°Fahrenheit. The sharp exothermic peak of decomposition indicates that it has the typical thermal decomposition behavior of high energy density materials; the laser plasma-driven micro-explosion method test shows that the detonation velocity of the sample has been significantly improved. Because it does not require high pressure or carbon nanotube confinement and the precursor is safer and cheaper, this synthesis method has the technical advantages of macroscopic preparation and engineering application.
Master student Xu Yuxuan from the Institute of Solid State Physics is the first author of this paper, doctoral student Chen Guo and master student Du Fei are co-first authors, and Researcher Wang Xianlong is the corresponding author. Academician Lin Haiqing from the School of Physics, Zhejiang University and Researcher Zeng Zhi from the Institute of Solid State Physics provided important guidance. Professor Liu Ruibin from the School of Physics, Beijing Institute of Technology conducted the laser plasma-driven micro-explosion method test. Other collaborators also include Associate Researcher Li Ming from the Institute of Solid State Physics, Postdoctoral Wu Liangfei and Researcher Ding Junfeng.
TapTechNews attaches the paper link as follows:
https://www.science.org/doi/10.1126/sciadv.adq5299