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Highlights • Additions of TMOs can accelerate 5AT pyrolysis and combustion processes. • Catalytic effects of TMOs on 5AT perform on polyaddition and ring-opening reaction. • Thermal pyrolysis mechanisms of 5AT without and with TMOs are proposed. • Reaction kinetic models for 5AT are investigated by model-fitting method. • Logarithm of pre-exponential factor shows good linearity with activation energy. Abstract The employment of TMOs as catalyst has been widely popularized in thermal decomposition and combustion process, especially in propellants and explosives application areas. The focus of this study is on investigating catalytic effects of Fe 2 O 3 , CuO, and NiO nanoparticles on thermal decomposition mechanism and kinetics behavior of 5-Amino-1 H -Tetrazole (5AT), one typical energetic material. Experimental result reveals that thermal decomposition process of 5AT can be simplified from three steps to two steps with the additions of above TMOs. Thermal decomposition mechanisms of 5AT with and without TMOs are deduced by TG-FTIR-MS analysis. Results indicate that the interaction between TMOs and dissociation products shows the catalytic effect together with the variation of production phase. Both model-free and model-fitting methods are employed to evaluate thermal kinetics of catalyzed 5AT. During low temperature reaction range (below 300 °C), no obvious change is observed in activation energies or mastering reaction models (F 3 model). Conversely, catalytic effect of TMO is discovered mainly during high temperature range (above 300 °C), particularly during the polyaddition reaction of N-containing heterocycle and the ring-opening reaction of melem. The results of this study suggests that introducing TMOs nanostructure as catalysts into 5AT is a promising way to accelerate its combustion process in gas generation and propellant areas. [ABSTRACT FROM AUTHOR]

In firefighting area, the novel CH 3 N 5 -Sr(NO 3 ) 2 is of growing interest as solid propellant gas generating agent. However, undesirable reaction temperature and burning rate of CH 3 N 5 -Sr(NO 3 ) 2 limit their applications to fire-fighting systems, which forces fire researchers to find more fitting ingredient proportions or burning rate catalysts. This paper presents a detailed experimental study adding nanosized metal oxides (Fe 2 O 3 , CuO, and NiO) effects on CH 3 N 5 -Sr(NO 3 ) 2 burning behaviors, including thermal analysis, scanning electron microscopy, specific surface area measurement, and thermal conductivity test. Results show, the additions of transition metal oxides (TMOs) increase the burning rate of the CH 3 N 5 -Sr(NO 3 ) 2 -based propellants and decrease reaction temperature. The modifying effects of TMOs on combustion behavior alter both the condensed phase and gas phase reactions in a synergistic manner. The novel propellant formulation has shown a superior property to promote CH 3 N 5 -Sr(NO 3 ) 2 -based propellants’ application into fire-fighting area. [ABSTRACT FROM AUTHOR]

[Display omitted] • Catalytic effect of boron powder mainly exerts on latter stages for 5AT pyrolysis. • Solution recrystallization method has better modification effect for 5AT pyrolysis. • Copper powder can optimize the pyrolysis behaviors for 5AT pyrolysis. • Kinetic models for 5AT in each stage have been deduced by model-fitting method. As a novel rich nitrogen content material, 5-Amino-1 H -Tetrazole (5AT) has been considerably popularized in the propellants area recently. The pyrolysis is deemed as the prelude of combustion for solid phase 5AT, which plays a crucial role in combustion process and grasping the pyrolysis characteristics will be more beneficial to further explore the combustion properties of 5AT-based propellant. In this paper, several efforts have been made to enhance the pyrolysis behaviors of 5AT, including employing metal particles as catalysts, and modifying the surface treatment method. Due to the calorific value, the boron and copper powder are selected as the potential catalysts. The solvent/non-solvent (S/NS) and solution recrystallization method are compared to explore the impact of these two modification methods. TG-FTIR technique is applied to capture evolved signals of organic compounds to further deduce the most probable decomposition pathway. Moreover, model-free and model-fitting methods are both employed to calculate the kinetic parameters. The results reveal that, for the modified 5AT samples with the same boron powder catalyst, the activation energies and reaction model (all governed by F4) in the initial stage (100–330 °C) are not significantly impacted by these two modification methods. However, during the latter stages (400–750 °C), the catalytic actions of boron powder appear to be more active, and solution recrystallization method exerts better modification effect, the activation energies was reduced 18.3 kJ/mol and 10.9 kJ/mol respectively for the latter stages compared to S/SN method. Also, the reaction model is transformed from n th -dimensional model (D3) to n th -order model (F1) in the third stage. Particularly, the catalytic actions of copper powder results in the simplification of decomposition steps for 5AT, the activation energies was 138.8 kJ/mol and the catalytic effect of which was improved about 25% compared to the catalytic effect of boron powder in the first stage and its reaction model is also found to be changed into F3. It illustrates that copper powder could embody a better catalytic effect than boron powder under the same modification method. The conclusions of this study could provide a worthwhile guidance for the understanding, designs and applications of the 5AT-based propellants. [ABSTRACT FROM AUTHOR]

Thermal stability, kinetics, and dynamics data of the novel energetic material 5-amino-1h-tetrazole (5AT) are of the essence to obtain safety information for safety storage, handling, and even demilitarization. This study will seek to find particle size effects on thermal kinetics and pyrolysis mechanisms of 5AT with the employments of model-free and model-fitting methods. Results showed that a significant variation existed in thermal hazards of 5AT for different particle sizes. As the particle diameter increased from 70.9 to 236.5 μm, a monotonous increase in activation energy occurred from 276.4 to 313.2 kJ mol −1 . Particularly, the smallest average particle size 70.9 μm was the most sensitive with self-accelerating temperature 200.6 °C, critical ignition temperature 201.8 °C, and thermal explosion temperature 203.1 °C. When 5AT particle diameter reduced, there was a distinct decrease on enthalpy of activation by 36.7 kJ mol −1 , and entropy of activation by 75.5 J mol −1 . Decomposition mechanisms of four 5AT samples were all found to be mastered by third-order (F3) model. Results of this study have implications concerning designs for 5AT storage and transportation, which can help to get better understandings of particle size effects on 5AT pyrolysis kinetics and mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalytic effect of PbO is better than SiO 2 and MnO 2. • The bond breakage processes in 5AT molecular structures are promoted by catalysts. • Catalysts mainly affect the escape of (NH 2) 2 CN but little effect on NH 2 CN and NH 3. • Pyrolysis models are converted into F 3/2 due to catalysts with conversion over 0.5. 5-Amino-1 H -Tetrazole (5AT), as a novel energetic material, has been widely applied in propellant, airbags, and fire extinguisher areas due to its excellent combustion properties. However, suboptimal combustion performance limits its extensive application. Thermal behaviors investigation could provide guidance on the control of combustion performance, which can be effectively optimized by adding catalysts. Therefore, exploring the thermal decomposition behaviors of 5AT is more beneficial to its combustion performance optimization, management and applications. Traditional catalysts for 5AT, such as coolants (CaCO 3), hydrohalide salts (HCl), and guanidine (CH 4 N 4 O 2) are easy to release harmful gas to destroy the environment when they catalyze the pyrolysis and combustion process. Moreover, different catalysts can play various catalytic mechanism. Therefore, a highly effective catalysts that are not easy to be occurred for pyrolysis on their own are required. In this study, three kinds of catalysts (acid oxide (SiO 2), alkaline oxide (PbO), amphoteric oxide (MnO 2)) are mixed with 5AT by means of ball milling, which is for the purpose of investigating the effect of multi-type oxides on the catalytic pyrolysis behaviors about 5AT. The TG test is conducted to analyze the thermal behaviors and the isoconversion method (Advanced Vyazovkin) is applied to evaluate the thermal activation energy ranging from 100 ∼ 300 ℃. The results reveal that the catalyst PbO embodies the best catalytic effect. The Criado method is employed to determine the pyrolysis model. The results indicates that the pyrolysis model is not governed by a specific model but all followed by F n model when the conversion is below 0.5 while the model is mainly charged by F 3/2 model when the conversion is over 0.5 with the addition of catalysts. Moreover, the TG-FTIR technology is also employed to capture the evolved gas products and further to infer the most likely pyrolysis route of 5AT. The conclusions in this study will provide a theoretical support for the storage, transportation, application, management, combustion investigation and the computer simulation of 5AT-based solid propellant. [ABSTRACT FROM AUTHOR]

• The detonation behaviors in annular tubes with circular obstacles was investigated experimentally. • Smoked foil technique was adopted to record the cellular pattern evolution. • The diffraction-retonation of detonation wave was analyzed in detail. • Special vertical bands was observed, and the formation mechanism of which was analyzed. Experiments were performed to investigate the detonation behaviors of stoichiometric hydrogen-oxygen mixtures (at sub-atmospherical pressures) in annular tubes with circular obstacles. The annular tube was 1000 mm long and 48 mm in diameter (D). The circular obstacles were with the diameters of 37.20 mm and 30.36 mm, corresponding to the BR = 0.57, 0.36 (BR : blockage ratio), respectively. Two types of obstacle spacing S was set in the test, which are S = D and S = 2 D. The detonation velocities were obtained based on the time of arrival of the wave front monitored by pressure transducers. Smoked foils were used to register the detonation cellular evolution though the test section. The results showed that the propagation limit in this test was 2 ω / λ ≈ 1 (ω indicates the channel width, λ represents the cell width), which was consistent with the previous results in round tubes with orifice plates. The obstacle spacing presented no noticeable effect on detonation propagation limit. However, it played a significant role on detonation velocity. What is more, larger flow blockage for BR = 0.57 caused the more violent velocity fluctuation and higher propagation limit than in smaller blocking ratio. The process of diffraction-retonation for interaction between wave front and obstacle was analyzed in detail. In further, special vertical bands with periodic variation characteristic were observed between two adjacent obstacles. The vertical bands were spaced as same as the obstacle spacing and attached very fine cells which were caused by the head-on collision of the detonation wave propagating in the compressed region with high temperature and pressure. [ABSTRACT FROM AUTHOR]