Nitrogen is the main component of the Earth’s atmosphere, accounting for about 78% by volume. At room temperature and pressure, nitrogen is combined into stable diatomic molecules in the form of triple bonds (N≡N). Under the action of extreme high pressure, nitrogen can dissociate into a solid polynitrogen structure containing double bonds (N＝N) or even single bonds (N—N). Due to the huge energy difference between N≡N and N＝N or N—N, the transformation process is accompanied by huge energy release, so polynitrogen is a high energy density substance that attracts much attention. However, elemental polymerized nitrogen must be prepared in an environment above millions of atmospheric pressure (100 GPa) which is too harsh, greatly limiting the development and application of such materials. Interestingly, the introduction of metal elements can reduce the reaction barrier and provide chemical pressure, which can effectively reduce the synthetic pressure of polynitrogen and form a rich variety of polynitrogen configurations. This paper focuses on the research progress of main group metal nitriding compounds under high pressure, the physical mechanism of stabilities for metal nitrogen-rich compounds under high pressure, and puts forward the prospect of future design and preparation of new nitrogen-rich compounds.

Nitrogen is a highly stable element that exists in the form of nitrogen molecules under ambient pressure. Researchers have found that nitrogen can form polymeric structures under high temperature and pressure, which have extremely high energy density and decompose into pollution-free nitrogen. From the perspective of application, it can be used as a new type of environmentally friendly high-energy-density material. Subsequently, a large number of studies have been conducted on nitrogen, resulting in phase diagrams of nitrogen under high-pressure conditions and the synthesis of structures such as cubic gauche nitrogen and layered polymeric nitrogen. However, the synthesis conditions for pure nitrogen polymeric structures are relatively harsh, and it is also difficult to preserve them under ambient pressure. People have turned to methods such as molecular nitrogen and inert gas nitrides in the hope of obtaining stable high-energy-density nitrogen structures under normal pressure. This article briefly introduces the current theoretical and experimental progress of high-energy-density nitrogen and discusses the future development direction of high-energy-density nitrogen.

The high-pressure structure and physical properties of RbNO₃ at zero temperature was systematically explored using first-principles calculations based on density generalized theory combined with CALYPSO crystal structure predictions. The accuracy of four different functionals was compared based on experimental data of the RbNO₃-Ⅳ phase, and the revised PBE for solids (PBEsol) functional was found to be the most reliable. The zero-temperature phase transition sequence of RbNO₃ predicted is R3m→Pnma→Pmmn (experimental phaseⅤ) based on the PBEsol functional, and the two phase transition pressures are 1.7 and 8.2 GPa. The two phase transitions are first-order phase transitions, and the volume collapse rates reach 3.73% and 2.54%, respectively. This suggests that RbNO₃ at low pressure may have new low-temperature phases those are different from P3₁ structure given by experiment in the room temperature and ambient pressure. In the energy-stabilized pressure interval, all three phases satisfy the “Born-Huangkun” elastic stability criteria, and there is no phonon virtual frequency phenomenon in the whole Brillouin zone, which indicates that they are dynamically stable structures. The electronic property analysis showed that the three phases are semiconductors, and the band gap changes caused by the phase transition are generally small, but the pressure generally inhibits the charge transfer from alkali metal ions to nitrate ions. The high-pressure phase transition sequence predicted in this paper and the elasticity, lattice dynamics, and electronic structure properties of the individual phases can provide a reference for subsequent experimental and theoretical studies.

The crystal structure prediction of K₂N₂ in the pressure range of 0–150 GPa using an advanced particle swarm crystal structure search method was conducted. The results show that the stable ground state phase of K₂N₂ is a monoclinicC2/mstructure, and three high-pressure structures including Na₂N₂-type,Cmmm, andC2/care identified at pressures of 1.7, 3.6, 122 GPa, respectively. The volume dependence on pressure shows that the three phase transitions, i. e.,C2/m→Na₂N₂-type, Na₂N₂-type→Cmmm, andCmmm→C2/c, are all first order phase transitions, corresponding to volume collapses of 14.4%, 22.5%, and 4.0%, respectively. During the high pressure phase transitions of K₂N₂, the coordination number of K atom increases from 5 to 10, and a change in the nature of the N-N bonding from N＝N dimmer in the ground state ofC2/mstructure to N―N single bond chain in the high-pressureC2/cphase is accompanied. The high-pressureC2/cphase exhibits semiconducting properties with a band gap of 2.0 eV, whileC2/m, Na₂N₂-type, andCmmmphases have metallic behaviors. Electronic structure calculation and electron-localized function analysis indicate that the high-pressure structural phase transition of K₂N₂ is due to the K-plone-pair electrons activation and their participation in bonding with N atoms under high pressure.

Under the extreme conditions of high temperature and high pressure, molecular crystal nitrogen breaks the traditional three-bond mechanism and transforms into a single-bond polymerization state. The unique dissociation mechanism of nitrogen under high pressure makes the research significance of polymeric nitrogen beyond the scope of energetic materials, and also has profound scientific significance in the field of fundamental physics. Following the cubic gauche polymeric nitrogen cg-N (space group I2₁3), the second experimentally discovered layered structure polymeric nitrogen LP-N (space group Pba2) has been controversial. The main problem is that, in addition to not being verified by other high-pressure X-ray diffraction experiments, LP-N structure has the similar synthesis temperature and pressure conditions and synthesis pathways, as well as almost the same Raman spectral characteristics as the subsequently discovered black phosphorus structure polymeric nitrogen BP-N (space group Cmca). The high-temperature and high-pressure synthesis of LP-N is likely to have a unique phase transition kinetic barrier. In this work, we started from the low-temperature solid-state molecular nitrogen λ-N₂, used double-sided laser-heated diamond anvil cell (LHDAC) technology, combined with high-pressure X-ray diffraction based on the synchrotron radiation and high-pressure Raman scattering spectroscopy, supplemented by first-principles calculations, and observed the Pba2 structure of polymeric nitrogen LP-N at the conditions of about 141 GPa and about 2600 K. Combined with first-principles calculations, we compared and analyzed its pressure-dependent evolution of the volume per atom (p-V curve) and discussed the kinetic factors of LP-N synthesis at high temperature and high pressure. In addition to a more comprehensive understanding of LP-N, this paper further reveals the high-pressure path-dependent characteristics of polymeric nitrogen.

The graphitization process of nano-crystalline diamond (NCD) under high pressure significantly influences the performance of sintered polycrystalline diamond bulks. Here, we investigated the graphitization temperature of both pure nano-diamond, with an average grain size of 50 nm, and a mixture of NaCl and nano-diamond powder in a pressure and temperature range of 5−9 GPa and 600−1500 ℃, respectively. With a quantitative analysis method employing powder X-ray diffraction, we analyzed the graphitization degree of NCD under different pressures and temperatures, examining both non-hydrostatic pressure conditions (pure NCD powder) and quasi-hydrostatic pressure conditions (NaCl-NCD mixed powder). Our findings indicate that the initial graphitization temperature of pure NCD powder exceeds 800 ℃ at 5 GPa, and ranges between 1000 and 1300 ℃ at 9 GPa. Notably, under quasi-hydrostatic pressure conditions at about 7 GPa, the graphitization temperature of NCD increases from 1000 ℃ in non-hydrostatic pressure conditions to 1500 ℃ or higher within a short holding time.

In this work, the B-C-N-Ti quaternary superhard composite was prepared by high pressure and high temperature sintering with diamond, cubic boron nitride (cBN) and titanium (Ti) as starting materials. The characterization results show that Ti reacts with diamond and cBN to form TiC_0.7N_0.3 and TiB₂ under high pressure and high temperature, which acts as the binding additives for diamond and cBN grains. The addition of appropriate amount of Ti can effectively improve the toughness of the sintered composite specimen. The formation of TiC_0.7N_0.3 and TiB₂ ceramics and cBN coated the diamond grains and greatly enhanced the oxidation ability. When the molar ratio of diamond, cBN and Ti is 2∶1∶0.10 and sintered at 12 GPa and 2000 ℃ for 5 min, the specimen exhibits the best performance with Vickers hardness of (49.0±1.2) GPa, fracture toughness of (14.2±0.6) MPa·m^1/2 and oxidation temperature of 921 ℃ under air condition.

In order to study the adiabatic shear failure behavior and evolution characteristics of 30CrMnMo steel under pulse stress impact, a split Hopkinson pressure bar was used to conduct an axisymmetric cap shaped specimen for impact shear experiments. The shear failure evolution and temperature distribution in the shear zone under different incident pulse stress loads were numerically simulated using LS-DYNA dynamic finite element software. The results indicate that the adiabatic shear failure of the cap shaped specimen is related to the specific impulse of the pulse stress. For cap shaped specimen of 30CrMnMo steel, the specific impulse of pulse stress corresponding to the adiabatic shear failure is approximately constant. In numerical simulation, when the grid size is smaller than the width of the shear band, the local temperature rise of hot spot within the shear band can be effectively simulated. The evolution of adiabatic shear instability is characterized by simultaneous propagation from the corner of the shear zone to the center, and the materials inside and outside the shear zone mainly undergo two stages: uniform shear deformation and rapid expansion of instability.

In some engineering applications and accidents, the detonation performance of explosives may change if subjected to multiple shocks and releases. Therefore, an experimental loading device with multiple shocks and releases is needed in order to study the detonation response of explosives under complex loads. In this paper, an experimental detonation loading device that can achieve complete release of shock-release-reshock is proposed and designed. The device is optimized through numerical simulations, and the accuracy of the numerical simulation is validated by the corresponding experiments. The results indicate that the designed detonation loading device can achieve complete release of shock-release-reshock loading procesure of TATB-based insensitive explosives, where the detonation loading device drives tungsten magnesium double-layer flyers. The design provides a new experimental technique for further study on the detonation response of explosives under complex loads and multiple shocks.

In order to explore the anti-penetration property of carbon fiber composite materials, a series of experiments need to be carried out. In experiments, 8 g cubic steel fragments penetrated carbon fiber reinforced plastics whose thickness are 5, 10 and 15 mm respectively. The velocity of fragments was obtained, the situation of target was observed, fragments and carbon fiber were recovered. The numerical simulations were carried out according to the situation of experiments. The process of fragments penetrating carbon fiber composite target was explored, and the failure mechanism of carbon fiber composite target was also explored. The relationship between the failure mode and velocity of fragments could be described as follows: when the fragment velocity exceeds the ballistic limit, the main form of target damage is fiber shear failure; when the fragment velocity is lower than the ballistic limit, the damage forms of the target include fiber shear failure, fiber tensile failure, matrix cracking and fiber layer delamination, and their proportions change with the fragment velocity.

Combining the laser interferometry system, using the newly developed experimental device at medium strain rates to conduct the dynamic loading experiment of paper honeycomb structure. The purpose is to study the mechanical properties of paper honeycomb structure at medium strain rates. The deformation process and dynamic failure mechanism of paper honeycomb structure were obtained by high-speed photography and digital image correlation method. Numerical methods were used to further explore the dynamic failure mechanism. The results show that the paper honeycomb structure exhibits obvious strain rate effect. The yield strength of 2.10 mm thick paper honeycomb is obviously lower than the other three sizes, showing abnormal size effect. The descending section of stress-strain curve of 2.10 mm thick paper honeycomb is also different. The main reason for it is that the failure mode of paper honeycomb structure changes with the increase of sample size. The failure mechanism of paper honeycomb structure during the loading process at medium strain rates is the change of two failure modes, namely from out-of-plane buckling to in-plane shear. The effect of cell width on mechanical properties of the structure was analyzed by numerical model. This study is a good reference significance for the optimal design of thin-walled structures.

Bulletproof glass exhibits excellent impact resistance and protective capabilities against bullets, explosive fragments, high-speed projectiles, and various other aggressive threats, making it extensively utilized in the field of safety and security. To investigate the dynamic mechanical properties and constitutive relation of the inorganic glass layers in bulletproof glass under impact loading, we firstly employed an electronic universal testing machine and a split Hopkinson pressure bar (SHPB) test setup to obtain the tensile and compressive mechanical properties of the material at different strain rates. Results reveal a noticeable strain rate effect that the material’s strength increases with the strain rate. Secondly, drawing on the experience of geotechnical triaxial compression tests, we designed a high-strength confinement sleeve suitable for assessing the mechanical properties of glass particles under conditions of complete damage. Results show a significantly lower strength compared to that of the intact state of inorganic glass. Finally, by integrating test data, an JH2 constitutive model for inorganic glass with damage was established. By using the non-linear finite element software LS-DYNA, the SHPB test process was simulated. The effectiveness of the constitutive model was verified by comparing test and simulated results.

In order to investigate the influence of projectile structure design on the detonation reliability, a low-cost and portable static test device for fuze-warhead coordination is designed in this paper to carry out the tests of detonation transfer margin under different conditions. Based on the moving least square method, the multivariable response function is constructed to evaluate the detonation reliability and quantitatively analyze influence of the sensitive factors and coupled effects. The results indicate that the gap distance and the thickness of inert buffer layer have more significant impact on the detonation of the warhead charge while the influence of the interlayer thickness is relatively small within the preset range of 3–5 mm. To ensure the reliability of kinetic energy penetrators under ambient temperature, the relative position of fuze, the interlayer thickness, the gap distance and the thickness of inert buffer layer should not exceed 25, 3.5, 25, and 22 mm, respectively. The test device, analysis method and research results will provide a good reference and guideline for structural design and reliability verification of kinetic energy penetrators.

The decline of explosive properties of emulsion explosives will seriously affect the blasting effect in the environment of low temperature. The study on the evolution law of explosive properties of the emulsion explosives in coordination with the temperature variation of the emulsion explosives presents a certain engineering application value. A series of precise temperature control devices for emulsion explosives were designed, and then the detonation velocity, the brisance, the working capacity and the overpressure of air shock wave were measured with various temperature of 25, 0, −5, −10 and −15 ℃. Meanwhile, the microstructure of the emulsion explosives was characterized. The experimental results showed that when the temperature of the emulsion explosives was reduced from 25 ℃ to −15 ℃, the detonation velocity of the explosive was reduced from 4227 m/s to 3291 m/s, the brisance of the explosive was reduced from 13.0 mm to 5.2 mm, the working capacity of the explosives was reduced from 323 mL to 208 mL, and the overpressure of air shock wave was reduced from 284.9 kPa to 115.8 kPa. With the decrease of the temperature of the emulsion explosives, the precipitation of ammonium nitrate crystal increased along with the partial structure failure of the emulsion particles, resulting in changes in the microstructure and declines in the explosive properties of the emulsion explosives. Low-temperature environment mostly affected the brisance of emulsion explosives, but slightly affected the detonation velocity. With the decrease of temperature, the decline amplitude of explosive properties would be accelerated. It is suggested that the design of blasting properties should be adjusted according to the decline amplitude of explosive properties.

In order to study the influence of plateau environment on emulsion explosive sensitized by different methods, three typical sensitization materials were selected to prepare emulsion explosive samples. The changes in microstructure and detonation performance of samples stored in simulated plateau environment (−20 ℃, about 0.05 MPa) were analyzed. The results showed that the low temperature and low pressure of plateau environment mainly affects the performance of explosives from the aspects of aggravating the stability of emulsion system and the distribution of hot spots. In the plateau environment, the crystallization degree of chemically sensitized explosives is lower than that of physically sensitized explosives but the hot spots change greatly, leading to a decrease in detonation performance. In the physical sensitization, the growth mode of expanded perlite explosive crystal is more complex, so it is easier to demulsify and crystallize, and the storage stability and detonation performance are significantly reduced. The degree of crystallization and detonation performance of resin microsphere explosive are relatively stable under low temperature and low pressure. In general, resin microspheres emulsion explosive has better adaptability to plateau.

Lithium-ion batteries (LIBs) will cause internal short-circuits and even induce thermal runaway when they are subjected to compression and impact loadings. It is of great significance to explore the influencing factors of battery failure under different mechanical abuses for the crashworthiness design of the cells. In this paper, taking cylindrical LIBs as the research object, the force-electrical-thermal responses of the cells under different compression/impact conditions were studied by using a self-made plane compression and local indentation experimental system. The experimental results were compared with the corresponding finite element (FE) ones, and there was in good agreement with each other. Based on the explicit nonlinear FE method, the effects of loading velocity, indenter shape, and indenter diameter on the failure behaviors and mechanical responses of LIBs were also discussed. It is shown that localized indentation is more likely to induce the failure of the cells compared with plane compression. The peak force significantly decreases with the decrease of the indenter diameter, and the failure displacement also decreases correspondingly. It is noted that the failure displacement increases with the increase of the impact velocity, however, the failure displacement will decrease gradually when the impact velocity is more than 15 m/s. These results will provide some guidance for the multi-objective optimal design and safety assessment of LIBs.

Aiming at the current groove blasting problems of additional damage, the feasibility of double base propellant for groove blasting was explored. Based on the propellant gas release behavior, the pressure change of the double base propellant in the closed hole was calculated. Combined with high-speed photography and digital image correlation (DIC) method, two groups of experiments were carried out with propellant loading density of 0.84 and 0.96 g/cm³ to investigate the dynmic destruction process of granite slabs under the action of propellant. The results show that the granite slabs in the two groups of experiments were cracked along the groove direction at 100 μs after ignition, and the cracks penetrated through the slabs at 200 μs; the specimen with a charge density of 0.96 g/cm³ had a larger separation speed between the upper and lower slabs after fracture, and the upper and lower slabs were cracked by the friction of the blocking rubber and the inertia of the specimen, and the cracks were in the vertical direction at 2 500 μs. The grooves around the blast hole provide space for the effect of the propellant gas, and the grooves can effectively guide the direction of crack propagation, no crushing zone formed around the hole wall. The quasi-static pressure generated by the combustion of double-base propellant is the main driving force for crack initiation and propagation. The experimental results have some implications for the use of double base propellant in controlled rock blasting projects.

Ultra high static pressure processing technology holds promise for food sterilization, improving food quality, and extracting active ingredients. Traditional research typically assesses the analysis of the structure and function of organic matter under high static pressure after pressure release, capturing only irreversible changes occurring during compression. In-situ monitoring under pressure is rarely conducted. In-situ technology provides dynamic insights into sample behavior, offering a deeper understanding of its transformation process. Consequently, recent years have witnessed a surge in-situ studies performed under high pressure. This article reviews the advancement of high-pressure in-situ analysis technology and its application in high static pressure food processing. Key areas covered, include structural changes and phase transition intervals of protein folding and denaturation under high pressure, in-situ investigations into the mechanism of starch gelatinization, microbial in-situ monitoring and the challenges of in-situ technology in food processing.