جستجوی مقالات مرتبط با کلیدواژه « explosives » در نشریات گروه « مواد و متالورژی »

In this study, some granulated and pressable formulations based on coating of pentaerythritol tetranitrate (PETN) explosives with high impact polystyrene polymer (HIPS), Viton fluoroelestomer and paraffin wax were developed. Thereafter, mechanical strength of pressed formulations and transition temperature of binders were evaluated using uniaxial compressive strength test and differential scanning calorimetric (DSC) method, respectively. Also, the effect of PETN particle size distribution on compressibility, mechanical strength, density and particle size of pressed samples based on HIPS binder were statistically studied and optimized using mixture design of experiments by Minitab software. In the optimized experimental conditions, the compressive strength and elastic modulus for PETN/HIPS mixture at ambient temperature and at the concentration of 4.0 wt.% of the binder, were 15.0 and 91.1 MPa, which is better than formulations based on expensive Viton polymer and paraffine wax. By using HIPS binder, increasing the amount of PETN particle size <150 μm, mechanical strength of pressed samples decrease, and also particle size distribution in the range of 150-300 μm , leads to production of better formulations.

As energy weapon carriers, high energy materials are of particular importance. Increasing explosive performance along with increased immunity or reduced sensitivity are the main goals of the field of research on high energy materials, but the increase in performance is somewhat contradictory with decreasing the sensitivity which should be followed by a balance between them. In designing new high performance molecular structures and low sensitivity, it is necessary to identify the factors affecting on sensitivity and consider them in design. In this paper, the factors affecting on sensitivity have been investigated from three perspectives, molecular, physical and crystalline factors that affect sensitivity, as well as strategies that can help to reduction the sensitivity of explosives without significantly reducing of performance.

In addition to performance requirements, safety aspects for production, transportation and storage are very important for explosives because involuntary instantaneous explosion can causes irreparable financial losses and casualties. Ability of explosives for response to the stimuli such as impact, friction, shock wave, flame and heat is called sensitivity and is a key factor in determining the practical application of an explosive material. For decreasing of the sensitivity of explosives with maintained efficiency, it is necessary to use desensitizer. For this purpose, waxes, polymers, or a mixture of waxes and polymers can be used. In this research, industrial wax parameters in explosives such as melting point, congealing point, softening point, insoluble organic matterials, percentage of exudation, acidity, alkalinity, flash point,needle penetration, oil content and Differential Scanning Calorimetry (DSC) for three wax samples were determined by the credible standards. Finally, the results of parameters were analyzed.

Use of explosives, without desensitization could be lead to tragic explosions. Therefore a great interest to how decreasing of explosives sensitivities has been created. Because sensitivity decreasing to impact and friction can be cause to reduce dangers of their production, transmission and maintenance. Furthermore due to special applications, it tries to along with reduce sensitivities, special properties to explosives are added and their capabilities will increase. One way to reduce sensitivity and also adding special properties to explosives is coating. Depending on the coating method process, type of coated compound and also weight percent of coating agent to coated compound it is possible to create different properties for explosives. These properties are detectable by various tests. In this overview article, within introducing of different methods for coating nitramine explosives, morphological characteristics as well as their thermal behavior before and after coating are investigated.

This paper investigates the interaction of tetryl on the surface of pure C24, Si-doped C24 and Ge-doped C24 by density functional theory. For this purpose, the structures of tetryl, pure and doped fullerenes and their complexes were optimized geometrically. Then, IR and frontier molecular orbital calculations were implemented on them. The obtained adsorption energies, Gibbs free energy variations, enthalpy changes, and thermodynamic equilibrium constants showed that the interaction of tetryl with pure and doped fullerenes is exothermic, spontaneous, irreversible and experimentally possible. The calculated specific heat capacity values proved the heat sensitivity has declined significantly after adsorption of tetryl on the surface of nanostructure. The N-O and C-O bond lengths and density of tetryl complexes with C24 exhibited the detonation pressure, explosion velocity and energetic features of tetryl have enhanced considerably after its coating on the fullerene. Molecular orbital parameters such as band gap, chemical potential, electrophilicity, chemical hardness, and maximum transferred charge capacity have also been evaluated and the results indicated that the electric conductivity of C24 has decreased after absorbing of tetryl on the surface of nano-adsorbent. Therefore, fullerene can be used as an electroactive sensing material in the construction of novel electrochemical sensors for the detection of tetryl.

Identifying minor amounts of explosives with sensitivity, selectivity, accuracy and speed can be a great advantage for applications related to national security and environmental monitoring.Unfortunately, identification with high reliability of explosives is still a challenge and is largely unfulfilled. Today, fluorescence-based methods are widely used to detect explosives and products derived from their destruction in complex matrices. Due to the special electrical properties and fluorescence emission of Quantume dots due to the interaction with various compounds, including explosives, the use of this nanopaticle for the development of various sensors has become a key factor in recent years. Nitro-aromatic explosives caused various quantum dots to be quenched by different mechanisms.For this reason, detection and identification of these species is carried out. In this review, the application of quantum dots as sensors of nitroaromatic compounds and their mechanism is investigated.

Increasing the explosion power simultaneously reduction of explosive sensitivity caused to preparing new species of explosives. One of the considerable compounds in this field is dihydroxyl ammonium 5,5′ bistetrazole-1,1′-diolate (TKX- 50). Evaluation of explosion properties of this material shows that its explosion efficiency is equal with CL-20. TKX-50 is compatible with most of the materials which used in explosive’s formulations, as in few papers, even introduced as some nitramines alternative. Evaluation of sensitivity to unwanted stimuli shows that despite this compound has high energy content and density; it has low sensitivity to impact and friction. Moreover, its toxicity is lower than most of the common explosives. These properties could be a promise to production of more effective meantime safe explosive at soon.

Explosives include elements such as H, C, N and O with specific the amount and ratio. Nitrogen and oxygen are more abundant than others and the amount of nitrogen is an excellent characteristic to detect explosives. The Probability of existing explosives in an environment could be found out by acquiring the amount of nitrogen accumulated in the environment. In this paper, the prompt gamma neutron activation analysis (PGNAA) technique has been used in order to detection and identification of explosives. Using this method, one could detect suspicious packages and bags containing explosives and they are prevented to entry into government agencies, military facilities, airports, ports, embassies, banks, power plants, major organizations and sensitive companies. The nitrogen nucleus emits the thermal neutrons and gamma radiation spectrum 10.83 MeV almost at the same time as it absorbs them. In the designed system, the source and NaI detector has been used as neutron generator and emitted gamma receiver respectively. MCNPX2.6 code has been exploited to simulate neutron - photon transport In this system. To design this system, different thickness of paraffin and lead have been utilized to moderate neutrons and comply with shielding principles and health physics respectively. The designed system is capable of detecting NG explosive with a weight of 323 g and 1023 g for 10 minutes and one minute respectively.

In this article charging of explosives through casting has been investigated. Melt casting of TNT-based explosives is one of the most common techniques to economic and mass production of explosives. TNT is the only molten explosive at low temperature (80.4 C), so it is a convenient matrix for casting. Shrinkage of TNT in amount of 11-12% during solidification causes some problems in melt casting. In this article a description of different aspects of melt casting including material, common formulations, Meisner process, numerical simulation and comparison of advantages and disadvantages have been discussed. Studies show that the melt casting is a simple and feasible technique which can be safely used at industrial scale.

Detecting explosives is a challenging task because of a number of factors, such as the low vapor pressures of most explosives, frequent introduction of novel explosive compositions, concealment and weapon delivery schemes. Also, selective and sensitive detection of explosive has received considerable attention for environmental monitoring/ restoration and national security applications. Nano sensors with increased sensitivity and selectivity and the ability to operate in a multimodal platform offer a potential paradigm for deploying a large number of sensors for detection. This review is intended to highlight recent advances in vapor detection of explosives by enabled nanotechnology sensors.