Powerful oxidizer N₂O was incorporated into an organic lattice cavity through aeration crystallization, and smart host–guest energetic materials with highly-energetic and low-sensitivity performance were obtained.

The crystal structure transformation and step-by-step thermal decomposition behavior of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) under thermal stimulation were studied and the whole process included thermal expansion, primary decomposition and secondary decomposition. The thermal expansion and primary decomposition of TKX-50 were studied using in situ powder X-ray diffraction (in situ XRD) together with Rietveld refinement, by which the crystal structure transformation process can be accurately traced. The results showed that the thermal expansion of TKX-50 was anisotropic. In particular, the a-axis exhibited a negative thermal expansion (NTE) that may be attributed to the distortion of the six-membered ring, which results in H-transfer between the cation and dianion. The crystal structure of the intermediate product after primary decomposition was also obtained. The secondary decomposition process was analysed using thermogravimetric-differential scanning calorimetry (TG-DSC) due to the safety risk of TKX-50 analyzed by in situ XRD. The crystal structure transformation process from TKX-50 to the intermediate product under heat stimulation was deduced. Meanwhile, the morphological change of the whole process was obtained using hot stage microscopy (HSM). Combined with TG-FTIR technology, the gaseous decomposition products at each step were analysed and the thermal decomposition mechanism of TKX-50 was proposed. This study further reveals the thermal decomposition behavior of TKX-50 and is helpful for better understanding the thermal decomposition mechanism.

Small-angle X-ray scattering (SAXS) is an effective method to obtain microstructural information of materials. However, due to the influence of crystal surface effects, SAXS has a deviation in the characterization of the crystal microstructure. In order to solve the influence of crystal surface effect on the internal defect signal, the microstructure of Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal was characterized by soaking the sample in the matching solution. We found that the absolute scattering intensity, specific surface and volume fraction of the sample in the matching solution are significantly lower than the initial sample, which solves the influence of the crystal surface effect on the test results. Comparing the scattering results of the samples in different electron density matching solutions, it was found that the best result was obtained when using GPL-107 perfluoropolyether (PFPE) matching solution and the same law was obtained by controlling the experiment with 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) crystal. The fitting density was calculated according to the theoretical density and void volume fraction of the sample, and the calculated results are close to the test results of Particle Density Distribution Analyzer (PDDA). Based on this paper, we provide a method to obtain the correct information of crystal microstructure.

Low sensitivity octahydro-1,3,4,7-tetranitro-1,3,5,7-tetrazocine (HMX) has garnered significant attention from researchers due to its reduced shock sensitivity. However, the crystallization process poses challenges due to the high solidity and viscosity of the metastable α phase. Despite efforts to address this with additional energy sources like ultrasonic irradiation, prolonged exposure duration often results in small particle sizes, hindering the production of HMX with a consistent particle size distribution, thus limiting its applicability. To overcome these challenges, a method combining ultrasonic irradiation and trace H⁺ additive was proposed and investigated for their impact on the polymorphic transformation of HMX. The H⁺ additive was found to modify barriers, thus there was a lack of competitive driving force for the nucleation or growth of the metastable α form, thereby shortening the transformation pathway and duration. Moreover, the H⁺ additive significantly accelerated the nucleation rate of the β form (67.7 orders of magnitude faster with 0.10 wt ‰ H⁺) and the growth rate of β form HMX (5.8 orders of magnitude faster with 0.10 wt ‰ H⁺). While H⁺ additive alone was insufficient to induce spontaneous nucleation of the β form, combining it with short-duration ultrasonic irradiation further promoted β nucleation and shortened the polymorphic transformation duration (almost 20 orders of magnitude shorter). This rational approach led to effective control of the transformation process. The resulting low sensitivity HMX crystals exhibited varying mean sizes ranging from 20 to 340 μm, with purity exceeding 99.6 %, an apparent density greater than 1.8994 g/cm³, and few internal defects, fully meeting the requirements of low-sensitivity HMX, thus significantly expanding its potential applications. Our study sheds light on the mechanisms governing HMX polymorphic transformation in the presence of additives and ultrasonic irradiation, offering guidance for the rational control of this complex transformation.

Crystal density is one of the crucial properties that should be pursued in developing novel high energy density materials (HEDMs) since it can obviously affect the detonation performance of energetic materials. However, the dense packing of sensitive HEDM molecules can seriously increase the unpleasant mechanical sensitivity. Here, the host–guest intermolecular explosives showed a promising potential to resolve this inherent contradiction of famous high explosive 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) by self-assembly with insensitive methanoic acid (MA) under environmental conditions. Based on the perfect space matching between MA and lattice cavities of HNIW, the crystallographic density of HNIW-MA has exceeded the gold standard regarding the density of HEDMs and was determined to be 2.003 g cm⁻³ at 296 K. More importantly, the safety performance of HNIW-MA was improved while maintaining high crystal density due to the regulation by a small amount of insensitive guest molecules. Experimental results have shown the H₅₀ of HNIW-MA was 20.8 cm, which is significantly higher than that of α-HNIW of 14.8 cm and ε-HNIW of <14.1 cm.

Plate-like β-HMX crystals are grown in the hydroxylated interlayer space. Experimental and theoretical results indicate that they have the most morphologically important (011) face adopting a layer-by-layer growth mode.