Combustion Catalyst: Nano‐Fe2O3 and Nano‐Thermite Al/ Fe2O3 with Different Shapes

In order to enable the energetic materials to possess a more powerful performance, adding combustion catalysts is a quite effective method. Granular, oval, and polyhedral Fe2O3 particles have been prepared by the hydrothermal method and used to fabricate Al/Fe2O3 thermites. All the Fe2O3 and Al/Fe2O3 thermite samples were characterized using a combination of experimental techniques including scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and high‐resolution TEM (HRTEM). The non‐isothermal decomposition kinetics of the composites and nitrocellulose (NC) can be modeled by the Avrami‐Erofeev equation f(α)=3(1–α)[–ln(1–α)]1/3/2 in differential form. Through the thermogravimetric analysis infrared (TG‐IR) analysis of decomposition processes and products, it is speculated that Fe2O3 and Al/Fe2O3 can effectively accelerate the thermal decomposition reaction rate of NC by promoting the O‐NO2 bond cleavage. Adding oxides or thermites can distinctly increase the burning rate, decrease the burning rate pressure exponent, increase the flame temperature, and improve the combustion wave structures of the ammonium perchlorate/hydroxyl‐terminated polybutadiene (AP/HTPB) propellants. Among the three studied, different shapes of Fe2O3, the granular Fe2O3, and its corresponding thermites (Al/Fe2O3(H)) exhibit the highest burning rate due to larger surface area associated with smaller particle size. Moreover, Al/Fe2O3(H) thermites have more effective combustion‐supporting ability for AP/HTPB propellants than Fe2O3 structures and the other two as‐prepared Al/Fe2O3 thermites

Automatic 2.5D cartoon modelling

Non-photorealistic arts have been an invaluable form of media for over tens of thousands of years, and are widely used in animation and games today, motivating research into this field. Recently, the novel 2.5D Model has emerged, targetting the limitations of both 2D and 3D forms of cartoons. The most recent development is the 2.5D Cartoon Model. The manual building process of such models is labour intensive, and no automatic building method for 2.5D models exists currently. This dissertation proposes a novel approach to the problem of automatic creation of 2.5D Cartoon Models, termed Auto-2CM in this thesis, which is the first attempt of a solution to the problem. The proposed approach aims to build 2.5D models from real world objects. Auto-2CM collects 3D information on the candidate object using 3D reconstruction methods from Computer Vision, then partitions it into meaningful parts using segmentation methods from Computer Graphics. A novel 3D-2.5D conversion method is introduced to create the final 2.5D model, which is the first method for 3D-2.5D conversion. The Auto-2CM framework does not mandate specific algorithms of reconstruction or segmentation, therefore different algorithms may be used for different kinds of objects. The effect of different algorithms on the final 2.5D model is currently unknown. A perceptual evaluation of Auto-2CM is performed, which shows that by using different combinations of algorithms within Auto-2CM for specific kinds of objects, the performance of the system maybe increased significantly. The approach can produce acceptable models for both manual sketches and direct use. It is also the first experimental study of the problem

Reactive Molecular Dynamic Simulation of Thermal Decomposition for Nano-Aluminized Explosives

Aluminized explosives have important applications in civil construction and military armaments, but their thermal decomposition mechanisms are not well characterized. Here, the thermal decomposition of TNT, RDX, HMX and CL-20 on Al nanoparticles is examined by reactive dynamics simulations using a newly parameterized reactive force field with low gradient correction (ReaxFF-lg). Partially passivated Al nanoparticles were constructed and mixed with TNT, RDX, HMX and CL-20 crystals and then the mixed systems are heated to a high temperature in which the explosives are fully decomposed. The simulation results show that the aluminized explosives undergo three main steps of thermal decomposition, which were denoted "adsorption period" (0-20 ps), "diffusion period" (20-80 ps) and "formation period" (80-210 ps). These stages in sequence are the chemical adsorption between Al and surrounding explosive molecules (R-NO2-Al bonding), the decomposition of the explosives and the diffusion of O atoms into the Al nanoparticles, and the formation of final products. In the first stage, the Al nanoparticles decrease the decomposition reaction barriers of RDX (1.90 kJ g-1), HMX (1.95 kJ g-1) and CL-20 (1.18 kJ g-1), respectively, and decrease the decomposition reaction barrier of TNT from 2.99 to 0.29 kJ g-1. Comparing with the crystalline RDX, HMX and CL-20, the energy releases are increased by 4.73-4.96 kJ g-1 in the second stage. The number of produced H2O molecules increased by 25.27-27.81% and the number of CO2 molecules decreased by 47.73-68.01% in the third stage. These three stages are further confirmed by the evolutive diagram of the structure and temperature distribution for the CL-20/Al system. The onset temperatures (To) of generating H2O for all the aluminized explosives decrease, while those of generating CO2 for aluminized HMX and CL-20 increase, which are in accord with the experiment of aluminized RDX

Microflower-like Fe-Co-MOF with enhanced catalytic performance for decomposition of ammonium perchlorate and combustion of ammonium perchlorate-based composite propellants

Ammonium perchlorate (AP) serves as a crucial component in solid propellants. Enhancing its thermal decomposition with catalysts improves the combustion performance of solid propellants significantly. To enhance the catalytic performance of metal-organic frameworks (MOFs) on AP, this study controlled the morphology of MOFs by adding metal atoms, resulting in a Fe-Co-MOF catalyst with higher specific surface area and dual-metal synergistic effect. The catalytic effect of the catalyst on AP was investigated using DSC and TG-IR, followed by studying its influence on the combustion performance of AP-based composite propellants. The results show that the introduction of 5% Fe-Co-MOF reduced the decomposition temperature of AP to 298.6 °C, decreased the activation energy to 151.6 kJ mol-1, and increased the heat release by 110.6%. Additionally, the ignition delay of the propellant decreased by 71 ms, and the combustion rate increased by 43.8%. Mechanistic studies demonstrate that the abundant catalytic sites and oxygen vacancies of Fe-Co-MOF facilitate the charge transfer rate during the AP thermal decomposition process and promote the increase in AP heat release by suppressing the high-temperature conversion of N2O. This research paves the way for enhancing the application of MOF materials in AP-based solid propellants

Morphology-dependent catalytic activity of Fe2O3 and its graphene-based nanocomposites on the thermal decomposition of AP

The spherical, hollow and tubular Fe2O3 (s, h and t) and their graphene-based nanocomposites rGO-Fe2O3 (s, h and t) were fabricated using the facile solvothermal methods. The morphologies and compositions of the as-synthesized Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites were systematically characterized by SEM, TEM, XRD, FTIR and XPS methods. Then, the effect of the catalytic performance of Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites on the thermal decomposition of ammonium perchlorate (AP) were studied by DSC method. The DSC results showed that all of the Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites can effectively promote the thermal decomposition of AP. Besides, rGO-Fe2O3(s) nanocomposite has the best catalytic performance, and the high-temperature decomposition exothermic peak of AP was significantly reduced after its mixing with rGO-Fe2O3 (s) nanocomposite. It can be seen that the effects of Fe2O3 on AP decomposition is mainly reflected in the high temperature process, while the effects of rGO-Fe2O3 (s) on AP decomposition is reflected in both high and low temperature stages, and the effect on the high temperature stage is more significant. The excellent catalytic performance of rGO-Fe2O3 (s) nanocomposite can be attributed to the in-situ growth of Fe2O3 on the surface of rGO, which contributes to the low temperature decomposition process of AP

Thermolysis, specific heat capacity and adiabatic time-to-explosion of 2,3-dihydro-4-nitro-3-(dinitromethylene)-1H-pyrazol-5-amine potassium salt

2,3-Dihydro-4-nitro-3-(dinitromethylene)-1H-pyrazol-5-amine potassium salt [K(NNMPA)] was first synthesized through an unexpected reaction. Thermal decomposition of K(NNMPA) was studied with TG-FTIR-MS method. The gas products were analyzed. The specific heat capacity of K(NNMPA) was determined with a micro-DSC method and molar heat capacity is 298.9 J mol(-1) K-1 at 298.15 K. Adiabatic time-to-explosion of K(NNMPA) was calculated to be about 40s. K(NNMPA) exhibits lower thermal stability than K(AHDNE), but is relatively less sensitive. (C) 2013 Elsevier B.V. All rights reserved

Thermal Decomposition Behavior and Thermal Safety of Nitrocellulose with Different Shape CuO and Al/CuO Nanothermites

Bamboo leaf-like CuO(b) and flaky-shaped CuO(f) were prepared by the hydrothermal method, and then combined with Al nanoparticles to form Al/CuO(b) and Al/CuO(f) by the ultrasonic dispersion method. The phase, composition, morphology, and structure of the composites were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy scattering spectrometer (EDS). The compatibility of CuO, Al/CuO and nitrocellulose (NC) was evaluated by differential scanning calorimetry (DSC). The effects of CuO and Al/CuO on the thermal decomposition of NC were also studied. The results show that the thermal decomposition reactions of CuO-NC composite, Al/CuO-NC composite, and NC follow the same kinetic mechanism of Avrami-Erofeev equation. In the cases of CuO and Al/CuO, they could promote the O-NO2 bond cleavage and secondary autocatalytic reaction in condensed phase. The effects of these catalysts have some difference in modifying the thermolysis process of NC due to the microstructures of CuO and the addition of Al nanopowders. Furthermore, the presence of Al/CuO(f) can make the Al/CuO(f)-NC composite easier to ignite, whereas the composites have strong resistance to high temperature. Compatibility and thermal safety analysis showed that the Al/CuO had good compatibility with NC and it could be used safely. This contribution suggests that CuO and Al/CuO played key roles in accelerating the thermal decomposition of NC

Experimental Insight into the Catalytic Mechanism of MFe2O4 (M = Ni, Zn and Co) on the Thermal Decomposition of TKX-50

Synthesized dihydroxylammonium 5,5’-bistetrazole-1,1’-diolate (TKX-50) owes its outstanding application prospects in the field of insensitive solid propellants not only to its high energetic performance but also to its low mechanical sensitivity. Based on the excellent catalytic activity of bimetallic iron oxides for the thermal decomposition of TKX-50, the catalytic mechanism of bimetallic iron oxides (NiFe2O4, ZnFe2O4 and CoFe2O4) for TKX-50 pyrolysis has been explored. For this study, the decomposition process of TKX-50, before and after mixing with the bimetallic iron oxides NiFe2O4, ZnFe2O4 and CoFe2O4 was monitored by in-situ FTIR and gas-phase MS-FTIR instruments. Of the different catalysts, ZnFe2O4 gave the best result for reducing the initial decomposition temperature of TKX-50. Additionally, the activation energy of functional group cleavage of TKX-50, before and after mixing with ZnFe2O4, was also calculated for mechanism analysis from the results of the in-situ FTIR measurements. The results showed that the condensate and the gas-phase decomposition products of TKX-50 remained unchanged after mixing with different catalysts, while the activation energy of tetrazole ring cleavage was significantly reduced. The results of this study will be helpful for the rational design of insensitive solid propellant formulations containing TKX-50, and for understanding the pyrolysis mechanisms of TKX-50 before and after mixing with the efficient catalyst ZnFe2O4

Study on Thermodynamics and Kinetics for the Reaction of Magnesium Diboride and Water by Microcalorimetry

An exothermic reaction between MgB2 and water was observed in our laboratory at high temperature, although no obvious reaction occurred at room temperature. The reaction process of MgB2 and water was therefore studied by using microcalorimetry. The results showed that the reaction enthalpies of MgB2 with water and the formation enthalpies of MgB2 at T = (323.15, 328.15, 333.15 and 338.15) K are (–313.15, –317.85, –322.09, –329.27) kJ�mol –1, and (–238.96, –237.73, –236.50, –234.30) kJ�mol –1, respectively. The standard enthalpy of formation and standard molar heat capacity of MgB2 obtained by extrapolation method are –245.11 kJ�mol –1 and 246 J mol –1 �K –1, respectively. The values of activation energy E, pre-exponential factor A and the reaction order for the reaction of MgB2 and water over the temperature range from 323.15 K to 338.15 K are 50.80 kJ�mol –1, 10 4.78 s –1 and about 1.346, respectively. The positive values of G � � and H and negative value of indicate that the reaction can take place easily above 314.45 K