In recent years, high-energy density materials (HEDMs) have become a significant class of materials within the energetic materials and chemical science communities. Current challenges within this field surround the design and synthesis of materials which possess the highest possible density and chemical stability. A team of Researchers from China have synthesized a highly energetic compound, named ICM-101, which exhibits a high density and a good environmental stability.
The discovery and development of high-energy density materials (HEDMs) has gathered a lot of interest within the last decade, with continuous calls to make said materials possess greater densities and stabilities.
As the name suggests, the core principal and most important factor of these materials is their ability to possess a high density. Within these materials, which are also referred to as energetic materials, the density has a big impact on the materials detonation velocity, where the detonation pressure increases with the square of the density.
Whilst it is desirable to produce materials with an ultra-high density (up to 2.0 gcm-3), the synthesis of highly-energetic organic molecules using carbon, hydrogen, nitrogen and oxygen atoms (CHNO materials) presents a density limit, hence, it has traditionally been difficult to achieve such densities.
It has been made further challenging as such materials are also required to possess a low water solubility, a good thermal stability (greater than 200 °C), be of low cost, be sensitive towards accidental stimuli, provide a simple synthetic setup and have a detonation velocity comparable to that produced by 2,4,6,8,10,12-(hexanitrohexaaza)cyclododecane (CL-20)- A highly powerful explosive (2.035 gcm-3), but one which is hindered for commercial munitions use due to its unstable and sensitive nature to mechanical stimuli.
The team of Researchers from China have now synthesized [2,2′-bi(1,3,4-oxadiazole)]- 5,5′-dinitramide (ICM-101), as a new type of energetic material. The synthesis followed a simple two-step reaction using wet chemical techniques and commercially available reagents, prompting a simple synthetic approach.
The first-step involved the formation of a [2,2′-bi(1,3,4-oxadiazole)]-5,5′-diamine intermediate complex through reacting oxalyl dihydrazide and cyanogens bromide. The second-step treated the intermediate species with nitric acid for 24 hours, using a fuming process, before being poured into iced water. The ICM-101 product was formed as a white solid precipitate with an intermediate yield of 90.5% and a final product yield of 66.8%.
To characterize the HEDM, the Researchers used a combination of X-ray diffraction (XRD, Bruker D8 Advance), infrared (IR) spectroscopy (PerkinElmer Spectrum Two IR Spectrometer), multinuclear nuclear magnetic resonance (NMR) spectroscopy (Bruker AVANCE 600), field emission scanning electron microscopy (FE-SEM, Ultra-55, Carl Zeiss), elemental analysis (Vario Micro cube elemental analyser), differential scanning calorimetry (DSC, Mettler Toledo), bomb calorimetry (IKA C5000), liquid chromatography mass spectrometry with ion-trap time-of-flight technology (LCMS-IT-TOF, Shimadzu) and impact and friction sensitivity measurements (BAM friction tester). Quantum chemical calculations were also utilized to deduce the energetic properties of ICM-101 (Gaussian 09 and Explo5).
ICM-101 was found to possess a very high density, of 1.99 gcm-3 at room temperature, as well being insoluble in water, organic solvents, possessing a good thermal stability of 210.4 °C, a positive heat of formation and excellent detonation properties. It was also found possible to increase the density up to 2.037 gcm-3 when subjected to cold temperatures of 170 K (-103.15 °C). Alongside the density, the low water solubility is a highly beneficial property as it allows the material to be compatible with practical formulation applications for insensitive munitions.
The energetic and sensitivity properties were also found to be comparable with CL-20.
The complex was found to adopt a planar structure, with a high packing coefficient, a high amount of hydrogen bonding interactions/large hydrogen bonded network and interlayer π–π stacking interactions, all of which contributed to the high density observed by the material.
The material was also found to be oxygen and nitrogen rich, which contributed to the high detonation performance; where a detonation velocity of 9481 ms-1 and a detonation pressure of 41.9 GP was showcased.
The combination of high stability and detonation properties lead ICM-101 to be a promising material for HEDM applications. The successful synthesis of the material has given a fresh example of a CHNO-based HEDM, and given its easy synthetic route, could be easily scaled up for commercial applications, such as in the insensitive munitions industry.
“A promising high-energy-density material”- Zhang W., et al, Nature Communications, 2017, DOI: 10.1038/s41467-017-00286-0