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In this study, we developed a novel method for synthesising Al2OC-AlNss using a solid nitrogen source: a Si3N4 mesophase. The two-step sintered Al–Al2O3 and Si3N4–Al–Al2O3 samples were prepared under an atmosphere of nitrogen to investigate the effect of Si3N4 on the formation of Al2OC-AlNss in resin-bonded Al–Al2O3 composites. The samples were investigated via XRD and SEM. The results indicated that the synthesis of Al2OC-AlNss with different morphologies was achieved via the Si3N4 mesophase, and its morphology was influenced by the source of AlN. Both Al2OC-AlNss and Al4O4C were formed in the two-step sintered Al–Al2O3 sample, whereas only Al2OC-AlNss was formed in the two-step sintered Si3N4–Al–Al2O3 sample. Induced by the AlN formed by the nitridation of Al, needle-like Al2OC-AlNss was generated. Compared to that formed by the nitridation of Al, more AlN nuclei were provided by the reaction between Si3N4 and Al. Subsequently, columnar and granular Al2OC-AlNss were formed. Furthermore, fibre-like Al2OC-AlNss was also generated via the VS and VLS mechanism. The reaction model was established in this study.

Graphene bubbles (GBs) are of significant interest owing to their distinguished electrical, optical, and magnetic properties. GBs can also serve as high-pressure reaction vessels to numerous chemical reactions. However, previous strategies to produce GBs are relatively elaborate and random. Therefore, their potential applications are severely restricted. Here, a facile and effective protocol is proposed to construct position-controllable GBs in liquid nitrogen (LN) with the assistance of laser and graphene wrinkles. Specifically, a film of graphene mounted on a SiO2 substrate (G@SiO2) is subjected to irradiation by a low-power laser in LN and then many GBs emerge from the surface of G@SiO2. Most impressively, the domain where GBs arise is the position of the laser beam spot. Hence, we demonstrated that the high collimation of laser facilitates the position definition of GBs. The microscopic results indicate that some GBs split into three parts when they were subjected to irradiation by an electron. Meanwhile, some GBs degenerate into pores with a diameter of 500 nm when they are exposed to air. To grasp the properties of GBs in depth, the molecular dynamics (MD) simulations are performed, and the corresponding results indicate that temperature has very little impact on the GBs' shape. A phase transition process of the substance inside GBs is also revealed. Moreover, a two-dimensional (2D) solid nitrogen is discovered by MD simulations. The simplicity of our protocol paves the way to engineer high-pressure microreaction vessels and fabricate porous graphene membranes.

Features of the high-resolution IR spectra of the SiН4 molecule in low-temperature matrices of N2 and Ar at 6.6–20 K, depending on the experimental conditions, are analyzed. It was found that, in the nitrogen matrix, in the stretching region of 28SiH4, three narrow bands are observed and, in the region of bending vibration (ν4), there are two monomer bands instead of one, which is explained by the change in the symmetry of the molecule from Td in gas to $${{C}_{{3v}}}$$ in solid nitrogen. The spectra in the argon matrix change even more, where, in addition to narrow bands, rather wide components are also detected. The spectrum of SiН4 in an Ar matrix was calculated based on the QM/MM approach, which confirms the reality of the change in the symmetry of the molecule as a result of its interaction with the matrix environment.

International audience; We report in this contribution the first photochemical study of benzene trapped in solid nitrogen at low temperature (16 K) and irradiated with a mercury lamp (λ > 230 nm). We identify three benzene isomers (fulvene, Dewar benzene and benzvalene) and two radicals (phenyl and benzyne) as photo-dissociation products, along with acetylene derivatives and substituted benzene. We present for the first time the infrared spectrum of fulvene trapped in benzene ice, which is obtained after nitrogen sublimation. This solid-state characterization could be particularly useful for a better understanding of the photochemical fate of benzene ices recently detected in Titan's atmosphere.

Due to the diversity of solid nitrogen structure, its phase transition has been a hot topic for many scientists. Herein, we first studied the structural softening of rhombohedral solid nitrogen under pressure using first-principles calculations. Then, a new criterion, Egret criterion, was proposed to predicting the whole process from beginning to end of structural phase transition of solid nitrogen. Based on the discussion of acoustic phonons, we concluded that the phase transition of rhombohedral solid nitrogen starts from k-point F along the [-1, -1, 0] direction in a-axis, and the structural phase transition velocity is slow. Also, we use the Egret criterion proposed by us to predict the emergence of ξ-N2 and the stability of ξ-N2 at 17 GPa and 22 GPa, respectively, and this result is in good agreement with the phase diagram of nitrogen.

In this article, we present a miniature solid nitrogen cooling system designed for high-transition temperature (high- ${T_\mathrm{C}}$ ) superconductor Josephson devices operating in the temperature range of 40–55 K. The system utilizes a small fiberglass Dewar and an external pump to solidify nitrogen in thermal contact with a circuit board insert. Our cooling tests of two different Dewars with 100 mL and 200 mL capacity reveal that the systems can hold at their lowest base temperature of 42 K for 1.2 hours and 45 K for 4.7 hours for the 100 mL and 200 mL Dewars, respectively. This can provide a low power, low weight cooling solution for ultra-portable superconductive electronics and other cryogenic sensors.

A combined FTIR matrix isolation and theoretical B3LYP/6-311++G(2d,2p) study of 2-(tetrazol-5-yl)benzoic acid isolated in solid nitrogen was performed. Out of fifteen stable isomers of this molecule located on the singlet potential energy surface the most stable one, comprising the intramolecular N H⋯O hydrogen bond, was detected experimentally in nitrogen matrices after deposition. Upon irradiation with λ = 305 nm a new conformer of the precursor was generated and upon λ = 280 nm radiation a reverse photorotamerization reaction was induced. Simultaneously with the photoisomerizations, a cleavage of the tetrazole ring with dinitrogen elimination was observed proceeding with a very small rate and leading to formation of a carbodiimide derivative.

The amorphous structures of poly-CO, P-N and N-CO extended solids at high pressures were predicted using density functional theory (DFT) and evolutionary algorithms employing variable and fixed concentrations of components methods. Compression of random network of poly-CO up to 45 GPa results in elimination of small rings of the amorphous network. The amorphous structure with stoichiometry N9P was found to be dynamically stable (no imaginary frequencies in phonon-dispersion curve), stable relative transformation to solid nitrogen and phosphorus, but metastable according to convex hull calculations. The amorphous structure of the N-CO extended solid was obtained with various concentrations of N atoms under isotropic compression up to 50 GPa and release of pressure down to 5 GPa calculated using DFT. The higher concentration of CO is found to be favourable for stabilization of an amorphous covalent N-C-O network consisting of chains and a cage of the network. Upon lowering the pressure and decomposition of the compressed extended solid, atoms are disconnected first from the ends of polymeric chains, while rings of random network are sustained almost intact. Results of a calculated Raman spectra are compared with available experimental results.

The quench properties for REBCO conductor in SN2 and conduction cooled system are studied. The normal zone propagation velocity determined by voltage, temperature, and strain methods is compared to demonstrate the feasibility of strain method to detect the quench of the REBCO conductor.

Supplementary Materials: The following are available:Figure S1: The optimized structures of the HCHO-NH2OH complexes, Figure S2: The optimized structures of the CHOCHO-NH2OH complexes, Figure S3: The spectra of the CHOCHO/Ar (a), ND2OD/Ar (b) and CHOCHO/ND2OD/Ar (c) matrices recorded after matrix deposition at 11 K, Figure S4: The spectra of the CHOCHO/N2 (a), ND2OD/N2 (b) and CHOCHO/ND2OD/N2 (c) matrices recorded after matrix deposition at 11 K, Figure S5: The optimized structures of the CH3COCHO-NH2OH complexes, Figure S6: The spectra of the CH3COCHO/Ar (a), ND2OD/Ar (b) and CH3COCHO/ND2OD/Ar (c) matrices recorded after matrix deposition at 11 K, Figure S7: The MP2 optimized structures of the formaldehyde, glyoxal and methylglyoxal complexes with hydroxylamine assigned to the structures isolated in argon matrix, Figure S8: The MP2 optimized structures of the formaldehyde, glyoxal and methylglyoxal complexes with hydroxylamine assigned to the structures isolated in nitrogen matrix, Table S1: Selected geometrical parameters of the hydroxylamine and formaldehyde subunits in their binary complexes, Table S2. Selected geometrical parameters of the hydroxylamine and glyoxal subunits in their binary complexes, Table S3: The comparison of the observed wavenumbers (cm-1) and wavenumber shifts (Δν = νGH – νM) for the CHOCHO-NH2OH (GH) complexes present in the Ar and N2 matrices with the corresponding calculated values for the complexes IGH - IVGH, Table S4: The comparison of the observed wavenumbers (cm-1) and wavenumber shifts (Δν = νGH – νM) for the CHOCHO-ND2OD (GH) complexes present in the Ar and N2 matrices with the corresponding calculated values for the complexes IGH - IVGH, Table S5: Selected geometrical parameters of the hydroxylamine and methylglyoxal subunits in their binary complexes, Table S6: The comparison of the observed wavenumbers (cm-1) and wavenumber shifts (Δν = νMH – νM) for the CH3COCHO-NH2OH (MH) complexes present in the Ar and N2 matrices with the corresponding calculated values for the complexes IMHk – IVMHk and IMHa – IVMHa, Table S7: The comparison of the observed wavenumbers (cm-1) and wavenumber shifts (Δν = νMH – νM) for the CH3COCHO-ND2OD (MH) complexes present in the Ar and N2 matrices with the corresponding calculated values for the complexes IMHk – IVMHk and IMHa – IVMHa.

The low heat capacity of helium gas limits overall cooling capacity of helium gas cooled high temperature superconducting power cable and makes them susceptible to large temperature rises during unexpected events such as electrical faults or cryogenic system failures. Solid nitrogen has been explored as an additional cooling agent in the HTS cable termination. Additional cryogenic thermal storage in the form of solid nitrogen in the superconducting cable terminations can mitigate the risk by keeping the system in superconducting state until the appropriate contingency is activated. An external tank filled with activated carbon is used as an adsorption buffer tank for gaseous nitrogen to minimize the operational pressure. The use of activated carbon minimizes the volume of the buffer tank and prevents pressure rise due to the phase change from solid to gas. In addition, when the HTS cable system is back to normal operational condition, the activated carbon can provide the system back with the required nitrogen to establish cryogenic thermal storage in the form of solid nitrogen as a reversible and self-contained system. Comprehensive experiments were performed to explore the feasibility of using the activated carbon and its performance. It was found that the proposed system performs as a cryogenic thermal buffer to enable the superconducting cable system to tolerate unexpected heat surge and recover in an autonomous fashion while keeping the pressure below the desired value. In addition to integrate the concept into real applications, the mass of solid nitrogen has been quantified based on the required protection time and possible emergency heat load.

The search for the stable polymeric forms of solid nitrogen is of great importance in view of its potential application as a high-energy-density material. Using first-principles calculations combined with an effective crystal structure search method, we demonstrate that nitrogen can react with methane under relatively moderate pressures. The structures and the stability strongly depend on the composition. ${\mathrm{CN}}_{2}{\mathrm{H}}_{4}$ and ${\mathrm{CN}}_{4}{\mathrm{H}}_{4}$ compounds become stable in $Pca{2}_{1}$ and $I\text{\ensuremath{-}}42d$ phases under pressures of 11 and 41 GPa, respectively. Especially, ${\mathrm{CN}}_{4}{\mathrm{H}}_{4}$ is recoverable as a metastable high energy material at ambient condition, and can release enormous amount of energy ($6.43\phantom{\rule{0.28em}{0ex}}\mathrm{kJ}\phantom{\rule{0.28em}{0ex}}{\mathrm{g}}^{\ensuremath{-}1}$) while decomposing to molecular nitrogen and methane.

In immersion cooling superconducting equipment, the refrigerant plays the double role of cooling and electrical insulation, but electric field concentration on the refrigerant causes partial discharge (PD), which can be a weak point in electrical insulation. Although slush nitrogen, which is a mixed refrigerant of liquid nitrogen and solid nitrogen particles, has high cooling performance; however, the effects of the introduction of solid nitrogen particles on the insulation performance has not been clarified. From the analysis of PD waveform characteristics, it was shown that the solid nitrogen particles have a certain barrier effect against discharge, but basically act as a weak point in electrical insulation. On the other hand, the breakdown voltage of slush nitrogen with high solid phase ratio is about 80% of that of liquid nitrogen. It was suggesting that the high cooling performance and sufficient insulation performance may be compatible depending on the insulation design.

In support of NASA’s Triton Hopper project, mechanical response data for solid nitrogen are needed for concept validation and development. Available mechanical properties data is sparse with only three known indentation measurements existing between 30 and 40 K. To generate more data, a custom instrumented hardness tester was developed to interface with a cryostat. The system was used to conduct cylindrical punch indentation testing at Triton-relevant thermodynamic conditions. Pressure versus displacement curves and hardness values were obtained. In the experiments the hardness ranged between about 2 kg/mm(2) and 0.5 kg/mm(2) in the aforementioned temperature range. A suspected brittle fracture is observed at lower temperatures in the range.

Accurate calculation of electric field gradients (EFGs) in molecular crystals, despite big advances in ab initio techniques, is still a challenge. Here, we present a new approach to calculate the EFGs in molecular crystals by employing the many-body expansion (MBE) technique with electrostatic embedding. This allows for (i) a reduction in the computational cost or an alternative increase in the level of theory (we use the MP2/6-311++G) and (ii) the ability to monitor EFG convergence by progressively adding more surrounding molecules and/or adding higher many-body interactions. We focus on the 14N EFG and study four (model) compounds in more detail: solid nitrogen, ethylamine, methylamine, and ammonia. Solid nitrogen is rather insensitive to neighbors; for ethylamine and methylamine, the 3-body interactions are found sufficient for a converged EFG, whereas for ammonia, even the inclusion of 5-body interactions is insufficient although convergence is anticipated. We then validate our technique by comparing the experimental and ab initio14N EFGs for 116 organic compounds utilizing their known crystal structures and published EFG. Overall, we find a very good agreement, with a small EFG rms error, which is probably due to other sources, rather than the MBE approximation.

A new extended solid nitrogen, referred to post-layered-polymeric nitrogen (PLP-N), was observed by further heating the layered-polymeric nitrogen (LP-N) to above 2300 K at 161 GPa. The new phase is found to be very transparent and exhibits ultra-large d-spacings ranging from 2.8 to 4.9 {\AA} at 172 GPa, suggesting a possible large-unit-cell 2D chain-like or 0D cluster-type structure with wide bandgap. However, the observed X-ray diffraction pattern and Raman scattering data cannot match any predicted structures in the published literature. This finding further complicates the phase diagram of nitrogen and also highlights the path dependence of the high-pressure dissociative transition in nitrogen. In addition, the forming boundary between cg-N and LP-N has been determined., Comment: 13 pages, 4 figures, 1 table

With no moving parts at the cold end, pulse tube cryocooler has the advantages of high reliability and long lifetime, which makes it widely used in infrared detection. The contamination of working medium is one of the typical failure mechanisms of pulse tube cryocoolers. With the development of pulse tube cryocooler from the temperature of liquid nitrogen to lower temperatures, nitrogen has become a main kind of impurity gas that deteriorates the performance of pulse tube cryocooler. It is of great significance to study the influence mechanism of nitrogen contamination for improving the service life of pulse tube cryocooler at temperatures lower than liquid nitrogen. A real-time gas adding device has been developed to add nitrogen to the pulse tube cryocooler to obtain the critical values and the principles of gas impurity affecting pulse tube cryocoolers. By comparing the experimental and numerical simulation data, we know that the main reason for the performance deterioration is the adhesion of solid nitrogen in a tiny part of the regenerator, and the temperature fluctuation is caused by the repeated phase transition of nitrogen. Based on this, the method of standing after shutdown and then restarting can be used to avoid the temperature fluctuation.

ZrN and AlN nitride ceramic powders have been synthesized by combustion synthesis using Si 3 N 4 and BN as solid nitrogen sources. The experimental results show that the metallic particles of Zr and Al are fully nitridized by the solid nitrogen sources and are converted into ZrN and AlN. Zr reacts with both Si 3 N 4 and BN in a self-sustained way, while Al reacts only with Si 3 N 4 and does not react with BN. By using Si 3 N 4 and BN as solid nitridizing agents, this work provides an alternative way to synthesize the nitrides of ZrN and AlN, which differs from the conventional nitridation method using N 2 gas as a nitridizing agent.

High-performance high-temperature superconductor superconducting magnetic energy storage (HTS-SMES) is a promising technology to play an important role in stabilizing the future power system. However, due to the high prices of HTS materials, a hybrid energy storage system consisting of micro HTS-SMES and Li-ion battery is proposed as a transitional solution. In this paper, a 30-K/4-kJ HTS-SMES magnet is designed and manufactured. The solenoidal magnet spends 500-m 4.55-mm-wide rare-earth-barium-copper-oxide (REBCO) tape and its geometry is optimized to achieve a balance between energy capacity and charging/discharging rate. A flexible and extensible cryogenic system with dual Gifford-McMahon (G-M) cryocoolers is designed for maintaining the operating temperature of the magnet. Solid nitrogen is utilized to enhance the thermal stability during dynamic operation. According to our design, the magnet can deliver/absorb an instant high power with a minimum risk of thermal runaway. A preliminary test of the cryogenic system successfully demonstrated the capability of nitrogen solidification.

In power system application of high temperature superconducting (HTS) equipment, large amount of heat caused by thermal disturbance or over current during sudden electric interruptions will endanger the thermal stability of HTS devices. However, solid nitrogen (SN2) with large heat capacity can enhance the thermal stability of HTS magnets. In this paper, the quench characteristics of SN2 and conduction cooled REBCO coil under thermal disturbance and over current pulse has been investigated at 60 K. For the thermal disturbance experiment, the minimum quench energy, longitudinal and transverse normal zone propagation velocities in SN2, and conduction cooled system are compared and discussed. The strain response property of the coil from quench to complete cooled down after power off during the quench process has also been preliminarily discussed. What is more, the accumulated peak voltage and strain of the coil during the over current pulse test has been studied. These results show that SN2 can help to enhance the thermal stability of REBCO coil under thermal disturbance and over current pulse.

Slush nitrogen is the low-temperature two-phase fluid with solid nitrogen particle suspended in the liquid nitrogen. The flow characteristics of slush nitrogen in a horizontal pipe with the diameter of 16 mm have been experimentally and numerically investigated, under the operating conditions with the inlet flow velocity of 0–4 m/s and the solid volume fraction of 0–23%. The numerical results for pressure drop agree well with those of the experiments, with the relative errors of ±5%. The experimental and numerical results both show that the pressure drop of slush nitrogen is greater than that of subcooled liquid nitrogen and rises with the increasing particle concentration, under the working conditions in present work. Based on the simulation result, the flow pattern evolution of slush nitrogen with the increasing slush Reynolds number has been discussed, which can be classified into homogenous flow, heterogeneous flow and moving bed. The slush effective viscosity and the slush Reynolds number are calculated with Cheng & Law formula, which includes the effects of particle shape, size and type and has a high accuracy for high concentration slurries. Based on the slush Reynolds number, an experimental empirical correlation considering particle conditions for the friction factor of slush nitrogen flow is obtained.

Iron nitrides composed of abundant and inexpensive Fe and N compounds such as α′′-Fe16N2 and γ’-Fe4N are in the spotlight as potential magnetic materials for the next generation of electric vehicles. Extensive applications of iron nitrides, however, have not been reported since their mass production is yet to be established. Due to the low solubility of nitrogen in liquid iron, the production of iron nitrides through conventional steelmaking processes is difficult. Moreover, α′′-Fe16N2 with a high saturation magnetization is known to be metastable and can form below 200 °C where diffusional phase transformations are slow. In this study, we propose a nonequilibrium process that can enhance the kinetics for iron nitride formation at low temperatures. Thermodynamically metastable Fe-based glassy alloy with a relatively open atomic packing structure was used as the starting material. Synthesis of iron nitrides during the mechanical alloying of Fe-based amorphous powders and solid nitrogen compounds was systematically studied to understand the mechanism of solid state nitriding reactions. In addition, thermal and magnetic properties were studied to provide a basis for practical applications of iron nitrides as rare-earth free magnetic materials.

The recent successful characterization of black phosphorus alike N8 compound at 140 GPa has spurred interest in solid nitrogen and its potential industrial applications. In this work, the previously unexplored mechanical and optical properties of nitrogen at 140 GPa has been systematically studied using first-principles calculations and various physically motivated empirical approaches. Experimentally proven orthorhombic-N8 structure was correctly reproduced. Body-centered cubic-N4 phase of much lower formation enthalpy was also uncovered under similar pressure. Both the superdense, wide bandgap compounds have sufficient mechanical and dynamical stabilities. While their Vickers hardness of 40.29 and 39.45 GPa indicates a softer degree than diamond under similar pressure, analyses of their elastic parameters and linear optical dielectric function reveal strong covalent bonding, anomalously high elastic moduli, fracture toughness (5.86 and 6.26 MPa m1/2) that bear close comparison with those of diamond, large refractive index (> 2.2) over broad energy spectrum and high absorption coefficient (104-105 cm−1) in ultraviolet range. Moreover, cubic-N4 with a charge energy density of 79.93 J cm−3 could be potential material for energy storage devices.