Search

ZrO2-5CrMnMo composite samples were prepared by hot press sintering. When NiCoCrAlY powders were used as the bonding layer and the different mixtures of NiCoCrAlY alloy and 3YSZ (3mol% yttria stabilized zirconia) ceramic powders were used as the transition layers, the connection between zirconia ceramic and 5CrMnMo steel were strengthened. Three composite samples with different structures were fabricated by heat spraying and hot press sintering. Shear and thermal shock cycle tests were conducted to characterize connection strength and thermal shock resistance of these samples. The shear strength reached 95.69 MPa, and the heating shock cycles achieved to the maximum value of 27.7 times. Microstructures and connection interfaces were analyzed by scanning electron microscopy. The hardness and wearing resistance of 3YSZ coat and 5CrMnMo substrate were compared, and the heat insulation property of composite samples were also discussed. It is shown that these composite materials fabricated in this research are benefited to be used as squeeze casting dies.

Herein, warm drawing technology assisted by an electric current heating system is proposed to minimize the formation of wrinkles and cracks on the surface of Q390A high-strength steel V-shaped stiffeners during cold forming. V-shaped stiffeners with excellent properties were obtained by elevating the forming temperature and improving the material plasticity. The influence of temperature and tensile rate on the mechanical properties of the Q390A high-strength steel at 400-800°C was investigated. The effects of blankholder force and friction coefficient on the formed parts were simulated and analyzed by the finite element simulation software DYNAFORM. The law of heating and cooling for the formed parts during the forming process was studied through the electric current heating experiments. The forming temperature was controlled from 530 to 720 °C as the current density was maintained in the range from 7.3 to 8.5 A/mm2. Surface oxidation, cracks, sheet warping degree, sectional thickness distribution, mechanical properties, and microstructure of the V-shaped stiffeners formed at 400 to 700 °C were analyzed. The results show that the V-shaped stiffeners formed at 600 °C possess excellent overall properties.

In order to significantly enhance the performance of graphene in metal matrix composites, in situ SiC nanorods were successfully fabricated to enhance graphene nanoplatelets (GNPs)-reinforced Al2024 composite, which was prepared by powder semi-solid processing and friction stir processing. The SiC–GNPs dispersed in the Al matrix uniformly, SiC nanorods were randomly grown on GNPs sheets in any direction, bridging GNPs as well as GNPs and the Al matrix. Meanwhile, the interfacial bonding was effective. The hybrid reinforcement of SiC and GNPs endowed composites with superior mechanical properties and thermal conductivity. The in situ SiC nanorods transfer phonons and reduce phonon scattering effect in the through-plane direction of GNPs, which conducive to heat transmission. The composite exhibits improved mechanical properties, maximum tensile strength and hardness of 589 MPa and 193 HV are obtained, with 1.0 wt% GNPs addition, respectively. The thermal conductivity of composite increases with the content of SiC–GNPs. When the content of SiC–GNPs reaches 1.5 wt%, the composite has significantly enhanced thermal conductivity (224 W m−1 K−1), which is 115% times higher than that of Al2024. Moreover, the effects of SiC–GNPs on the properties were discussed.

When lithium-ion batteries (LIBs) are located at high altitude and low pressure,the characteristics of thermal runaway (TR) and its propagation are different,such as time to TR, the toxicity of TR gases, TR propagation time, mass loss rate, etc. In this article, the author summarized a series of relevant literatures and proposed an instrument that can be used to analyse the TR behavior at different pressure. It is found that: with the decrease of ambient pressure, the TR trigger time becomes longer and the maximum surface temperature decrease. Moreover, the gas released by TR becomes more toxic as the environmental pressure decreases. Beside, the average propagation time between adjacent LIBs is not much difference when the environmental pressure decreases, and when the 18,650 battery module is distributed in a cylindrical shape, the thermal runaway propagation path is basically unchanged as the environmental pressure decreases. This work details TR and its propagation feature under different pressure, and can provide the guidelines for the Air transportation of LIBs.

During the process of liquid forging, a host of hot cracking defects were found in the Al-Cu-Mg-Zn aluminum alloy. Therefore, mechanical tests and analyses by optical microscope, scanning electron microscope, and X-ray diffraction were performed to research the influences of zinc, magnesium, and copper (three main alloying elements) on hot cracking tendency and mechanical properties. It was concluded that all the three alloying elements exerted different effects on the performances of newly designed alloys. And the impact of microstructures on properties of alloys was stronger than that of solution strengthening. Among new alloys, Al-5Cu-4.5Mg-2.5Zn alloy shows better properties as follows: σb=327 MPa, δ=2.7%, HB=107 N/mm2, and HCS=40.

In this study, catalyst formation [Pb(H2O)6][ATZ]·H2O (ATZ = azo tetrazolium anion) was successfully synthesized originally; meanwhile, the single-crystal structure of the compound was cultivated and analyzed by diffraction single-crystal method. The influence of the compound in which [Pb(H2O)6][ATZ]·H2O was used as combustion catalyst on the decomposition temperature of potassium nitrate was studied by TG–DSC. The result proved that [Pb(H2O)6][ATZ]·H2O can effectively reduce the decomposition temperature. In other words, [Pb(H2O)6][ATZ]·H2O can reduce the decomposition temperature of potassium nitrate, so the addition of [Pb(H2O)6][ATZ]·H2O can make potassium nitrate better to be used in the fields of initiating explosive device and fire engineering.

2-Methyl-4,5-dicyano-2H-1,2,3-triazole was synthesized with 4,5-dicyano-2H-1,2,3-triazole as the raw material for the first time. Its structure was characterized by elemental analysis, infrared spectrum, and nuclear magnetic resonance spectrum. The thermal stability of 2-methyl-4,5-dicyano-2H-1,2,3-triazole was investigated by TG–DSC technique. Its kinetic parameters including activation energy and pre-exponential factor were calculated by Kissinger equation. The combustion heat, heat of formation, impact and friction sensitivity of 2-methyl-4,5-dicyano-2H-1,2,3-triazole were measured. Also, 2-methyl-4-acylamino-5-cyano-2H-1, 2,3-triazole was formed by the hydrolysis of one of the cyano groups of the 2-methyl-4,5-dicyano-2H-1,2,3-triazole, and its single crystal was cultivated. The molecular structure of 2-methyl-4-acylamino-5-cyano-2H-1,2,3-triazole was determined using X-ray diffraction [triclinic P-1, a = 4.956(2) A, b = 10.058(5) A, c = 14.142(7) A, β = 91.169(4)°, V = 658.7(6) A3, Z = 4]. It exhibited potential application prospect in gas generant, explosive, and solid propellant field.

Al-Zn-Mg-Cu alloys are the strongest aluminum alloys which have been widely used for aerospace applications. They are usually machined from the wrought state usually with a high waste percentage. To reduce waste, it is important to thixoform these alloys in near net shape. In this work, the thixoformability of a commercial high performance Al-Zn-Mg-Cu alloy 7075 was studied. A novel multistep reheating regime was developed in recrystallization and partial melting (RAP) route to obtain spheroidal semi-solid microstructures. The as-extruded 7075 alloy was fully recrystallized for a short holding time using the multistep reheating regime. Semi-solid microstructures with fine and spherical solid grains with a grain size of 40-50 μm embedded in liquid matrix were obtained. The advantage of the multistep reheating regimes over those conventional routes was also discussed. Some wheel-shaped components were thixoformed from the as-received 7075 alloy. The ultimate tensile strength, yield strength and elongation to fracture of the thixoformed component based on multistep reheating regime, are 510 MPa, 446 MPa and 17.5% respectively. These values are superior to those of the products manufactured with the conventional RAP route. As the results indicated, thixoforming could be conducted based on commercial extruded Al-Zn-Mg-Cu alloys, which has important practical significance.

1,1′-Diamino-5,5′-azotetrazole (DAZT) has been synthesized using acetic acid (HAc) and 1,1′-diisopropylideneamino-5,5′-azotetrozole (DPrZT) as the raw material. Three of the most important factors which affect the yield of DAZT are the reaction temperature, the reaction time, and n(DPrZT):n(HAc). Based on single-factor experiments, orthogonal experiments were carried out. The most optimal experimental conditions were determined to be: a reaction temperature of 70 °C, a reaction time of 20 min, and a reactant ratio n(DPrZT)–n(HAc) of 1:48. The maximum yield was 97.6 % under optimum reaction conditions. Elemental analysis, IR, and NMR confirmed the structure of DAZT. The morphology was analyzed by SEM. The thermal decomposition behavior of DAZT was investigated by TG-DSC and DTA techniques. The mode of thermal decomposition was analyzed. The kinetic parameters including activation energy and pre-exponential factor were calculated from the Kissinger equation. The mechanical sensitivity on this compound was evaluated. Results suggest that it might be useful as an energetic material.

In order to study the thermal safety of cylindrical battery and solve the three-dimensional cylindrical battery thermal explosion problem, a common thermal explosion physical model of cylindrical battery and three-dimensional thermal explosion mathematical model of cylindrical fireworks with non-uniform heat dissipation of the lateral surface were established for the first time. By applying the theory of heat transfer, the boundary conditions of cylindrical battery were simplified reasonably. The seven-point difference method was introduced to disperse the model. The three-dimensional numerical program was written by homotopy continuation method and Newton iteration method based on Matlab. Comparison of two-dimensional numerical solutions obtained by taking ϕ = 0 and classical solutions proved the accuracy of model. A common kind of fireworks was calculated in this paper. When this single cylinder firework stored individually, the criterion of thermal explosion is 1.796, and critical ambient temperature is 450.484 K. When stored in combination form (that is battery), the criterion of thermal explosion is 1.363 and critical ambient temperature is 447.964 K. The results show that the cylindrical fireworks stored in combination form is more dangerous than this single cylinder firework stored individually, so the cylindrical battery is the focus of safety prevention of fireworks.

In view of the complexity of the storage environment in the process of storage and transportation, typical storage environment of cylindrical battery was analyzed in this paper. The corresponding three-dimensional thermal explosion models were established which considering non-uniform heat dissipation of the lateral surface and different heat dissipation of top and bottom surfaces. Based on the seven-point difference method and Newton–homotopy method, calculation algorithm and program of partial differential equation group have been established and verified. The influence of H and Biot on the criticality of system was analyzed. The results of a kind of cylindrical battery which stored in two typical environments (shelf and ground) were obtained by the calculation program. The critical thermal explosion ambient temperature of cylindrical battery is, respectively, 568.0 and 566.6 K. When the ambient temperature is 575 K, the thermal explosion time to ignition is, respectively, 1.504 (5194.7 s) and 1.596 (5512.1 s).

1,1′-diisopropylideneamino-5,5′-azotetrozole (DPrZT) was synthesized with 1-isopropylideneamino-5-aminotetrozole as the raw material and sodium urate isocyanide dichloride as oxidant. Three of the most important factors which affect the yield of DPrZT were gained from the single factor experiments. Based on the single factor experiments, the orthogonal experiments were carried out. The most optimal experimental condition was gained as follows: In the first stage, the reaction temperature was 30 °C, the reaction time was 20 min, and the dropping temperature was 30 °C; In the second stage, the reaction temperature was 30 °C, the reaction time was 20 min, and n(HAc):n(SDCI) was 0.5. The maximum yield was 89.6 % under the optimum reaction condition. The structure and performance of DPrZT were studied in detail in this paper. It showed good thermal stability and explosive performance. It exhibited prospective application in explosion field.

1,5-Diaminotetrazolium nitrate (HDATN) was synthesized with 1,5-diaminotetrazole (DAT) as the raw material. The maximum yield of HDATN was 95.3 %. The structure was characterized by elemental analysis, infrared spectrum, nuclear magnetic resonance spectrum and mass spectrum, and the possible fragmentation mechanism was discussed. The morphology was analyzed by SEM. The thermal stability of HDATN was investigated by TG-DSC and DTA techniques. The kinetic parameters including activation energy and pro-exponential factor were calculated by Kissinger equation. The performance of combustion, combustion heat, and formation enthalpy of HDATN were measured. The detonation products of HDATN were most nitrogen, which were analyzed by gas chromatograph and smoke analyzer. The density, formation heat, detonation pressure, and detonation velocity of HDATN were calculated. It exhibited prospective application in environmentally friendly gas generant and explosion field.

To study the influence of temperature on cylindrical fireworks and crackers in production and storage, this article establishes a physical and mathematical model of thermal explosion critical ambient temperature of finite cylindrical fireworks with shell based on two-dimensional steady state thermal explosion theory. The numerical program is written by difference method and Newton-homotopy method. The partial differential equations of thermal explosion model are calculated in Matlab. Comparison of numerical solutions and classical solutions proves the accuracy of model. The influence of Biot number of each surface and length diameter ratio on critical ambient temperature is analyzed. It is founded that the scope of length diameter ratio is \( 0.08 < H < 4.3 \) when Biot number tends to infinite. The thermal safety temperature of the fireworks without inner barrel when it is stored individually is obtained. This provides theoretical support for the safety of fireworks and crackers in production, storage transportation, and setting off process.

A pyrotechnical battery is successfully prepared, including an anode and cathode having pyrotechnic charges with Zr, CuO and asbestos. The anode and cathode are separated by a separator formed from LiF, ZrO2, and a fibrous sponge. A digital phosphor oscilloscope (DPO) is used to analyze discharge characterization of the pyrotechnical battery. Then the properties of the electrode materials are characterized by EDS, SEM and a temperature recorder, respectively. The discharge mechanism and safety characteristic are also discussed. The results indicate that the combustion temperature of electrode materials is determined as 1 500.6 °C according to thermometry analysis (the case temperature of the battery is lower). The combustion product is identified as ZrO2, Cu2O and Cu by X-ray diffraction (XRD). When the diaphragm is completely melted, Li+ migration and an embedded-based conductive process are formed. Then an electromotive force will immediately reach to the maximum. The discharge performance of the pyrotechnical battery then takes on stability. The electromotive force is up to 2.29 V, and that discharge time continues for more than 18 s. The current density in the small area (less than 2.88 Acm−2) is most effective. The conversion efficiency of electric energy is 96%. The pyrotechnical battery is very safe for the production and use processes.

In order to analyze thermal safety of fireworks and crackers, thermal explosion models of three kinds of sphere fireworks and crackers with different structures are achieved on the basis of thermal explosion theory, and thermal resistance of shell and effective Biot number are deduced as for boundary conditions. Two models are calculated with target-shooting method in Matlab program, and the rationality is proved through comparison of numerical solution and classical solution. Meanwhile, calculation steps are shown about a type of firework. The study has a great significance to thermal safety analysis of fireworks and crackers.