Model Detonation of Solid Explosives by the Homogeneous Mechanism

A twophase detonation model of solid porous explosives, which takes into account the compression of solidstate particles and the presence of a solid component in detonation products, is developed. The homogeneous detonation mechanism based on the Arrheniustype reaction is studied. Detonation is initiated by the region of highpressure and hightemperature gases modeling the detonator explosion. A numerical experiment confirms that there exists an initiationpressure limit below which no homogeneous mechanism of detonation is active. The detonation wave has the leading front in which the explosive is precompacted and the gas in the porous volume is compressed up to a pressure of 100 GPa without any significant change in particle density. Then the gas compresses the particles themselves up to the pressure and temperature of the thermal explosion. As a result, the leading front is followed (after a certain delay) by a narrow reaction zone where detonation products are formed with a further increase in pressure.     

Triggering of Detonation upon Flame Interaction with an Expansion Wave

The transition of a deflagration wave into an abruptly expanding part of a plane channel, where a quasisteady supersonic underexpanded jet of an unburned gas is formed, is studied for a propane–oxygen mixture using schlieren pictures. Two explosioninitiation modes (weak and strong) are registered. In the first case, almost instantaneous onset of the detonation wave occurs when the flame front enters the expanding section; the initial velocity of this wave is approximately 1.5 times the Chapman–Jouguet detonation velocity (D_CJ) and then decreases to a value corresponding to selfsustaining detonation. In the second case, the front velocity gradually increases from 0.4D _CJ to 1.0D _CJ. It is established that the starting pulse triggering the transformation of turbulent combustion to explosion and detonation regimes is generated by interaction of the flame front with expansion waves, which are elements of the structure of the initial section of the jet.     

Effect of framework aluminum in proton‐ or copper‐exchanged MFI ferrialuminosilicates on their activity for the reduction of nitric oxide with ammonia

Reduction of NO with ammonia in excess oxygen has been carried out on protonform and Cu²⁺exchanged MFI ferrialuminosilicate. Though HZSM5 showed very low activity, the framework Al in Hferrialuminosilicate greatly enhanced the activity. The framework Al in Cu²⁺exchanged ferrialuminosilicate also enhanced the activity to some extent.     

Structure of the Reaction Zone of a Steady Detonation Wave in Dinitrodiazapentane

The massvelocity profiles in 2,4dinitro2,4diazapentane samples of different densities were registered by a laser interferometer and the electromagnetic technique. The reaction time was shown to reach 300 nsec and weakly depend on density, while the pressure in the chemical spike can be twice as high as that at the Chapman–Jouguet point. No special features due to diamond formation were observed in the massvelocity profiles registered in the chemical reaction zone.     

Convective Regime of Filtration Combustion of Energetic Materials in a Cocurrent Flow of Their Combustion Products

The convective regime of filtration combustion of energetic materials in a cocurrent flow of their combustion products is studied using a model with extremely simplified kinetics and heat transfer, which shows instability of the process. It is shown that the more accurate twotemperature model describes a steadystate regime. In this regime, the gas temperature on the hot boundary of the heating zone is well below the combustion temperature, and the solidphase temperature is well below the temperature proposed in recent studies on this topic. It is pointed out that the twotemperature approach is unjustified and intragranular nonisothermicity must be taken into account for convective regimes. It is shown that the threetemperature model, which takes into account this effect, does not give a stable steadystate solution.     

Experimental Investigation and Numerical Simulation of an Expanding Multifront Detonation Wave

Results of experimental investigations of an expanding multifront detonation wave are presented. Two stages of spontaneous formation of new disturbances and transverse waves on the expanding detonationwave front are observed. The main mechanisms of reinitiation of detonation waves are discussed. Twodimensional numerical simulation of the dynamics of a multifront detonation wave in a linearly expanding channel is performed. The effect of spontaneous formation of new disturbances and new transverse waves is confirmed by computations, and the main mechanism of multiplication of transverse waves is the instability of detonationwavefront elements at the stage they cease to be in the overdriven state and are attenuated during expansion.     

Passage of a Bubble‐Detonation Wave into a Chemically Inactive Bubble Medium

Passage of detonation waves from a chemically active bubble medium into a chemically inactive bubble medium is studied experimentally. The structure of incident (detonation) and transmitted (postdetonation) waves is investigated, and the pressures of these waves for different parameters of bubble media are measured. The evolution of postdetonation waves is traced. Decay constants of postdetonation waves are determined. The speeds of propagation of detonation and postdetonation waves are measured. The energydissipation mechanisms for detonation and postdetonation waves in bubble media are analyzed qualitatively.     

Effect of Channel Geometry and Mixture Temperature on Detonation‐to‐Deflagration Transition in Gases

Results from theoretical and experimental studies of deflagrationtodetonation transition in hydrocarbon–air mixtures are reported. The effects of internal geometry, turbulence transition of the flow, and the temperature and fuel concentration in the unburned mixture on detonation initiation are considered.     

Chemistry of Combustion Waves in Substances with a Complicated Structure of Reagent Molecules. 1. Structure of the Front of Rich Isopentane Flame

Results on the structure of the lowtemperature relaxation zone of the front of a laminar Bunsen flame of isoC₅H₁₂ (2methylbutane) under atmospheric pressure are presented. The flame of a premixed mixture isoC₅H₁₂ + O₂ + Ar with a fueltoair equivalence ratio of 1.7 is examined. The mass fluxes, total rates of reactions of matter consumption and expenditure, balance of substances, and profiles of bulk heatrelease rates are calculated on the basis of the experimental concentration and temperature profiles. The results obtained indicate that there is a vast region of lowtemperature conversion of isopentane in the flame front. It is found that only part of the products sampled by the microprobe from different points of the flame front results from transformations in the lowtemperature region, namely, oxygen, isopentane, water, carbon monoxide, propane, methane, and methanol. Ethylene, propylene, hydrogen dioxide, and formaldehyde are present in the lowtemperature zone in insignificant amounts; they are secondary products of conversion of methyl and propyl radicals. It is assumed that the observed feature is a result of the competing interaction of two mechanisms of fuelmixture conversion: selfcatalysis and thermal selfacceleration. Based on the previously suggested mechanism of oxidation pyrolysis by the scheme of intramolecular quadratic destruction, experimentally observed fragmentation of the isopentane molecule is demonstrated. In contrast to npentane, formation of methyl alcohol has been found in isopentane convection products.     

Synthesis of nanosized platinum cluster in cubic mesoporous material via a direct introduction method

Platinumclustercontaining cubic mesoporous material (PtMCM48) has been synthesized by direct introduction of chloroplatinic acid during the synthesis of MCM48. In addition, we have also studied the incipient wetness impregnation and ionexchange method to obtain the platinumcontaining cubic mesoporous material. The nature of the platinumMCM48 catalyst has been characterized by different techniques such as XRD, N₂ adsorption, TEM, XPS, and NMR. The catalyst obtained by direct introduction of platinum in the synthesis gel shows higher activity in the hydrogenation of benzene and toluene.     

Quasi‐Homogeneous and Pseudospin Modes of Zirconium‐Wire Combustion in Air

A novel experimental technique is proposed for examining the transition mechanism from quasihomogeneous to heterogeneous combustion — burning of a variablepitch spring. Depending on the pitch of aircombustible zirconium springs, two combustion modes are possible. Quasihomogeneous (layerbylayer) combustion is observed in the case of smallpitch springs; as the spring pitch increases, quasihomogeneous combustion transforms into heterogeneous (pseudospin) combustion. Conditions for the occurrence of various combustion modes, depending on the spring diameter and pitch, are studied.     

Postinduction Processes During Thermal Explosion in the Systems “Porous Material–Reactive Gas–Solid Product”

A complete solution of the unsteadystate filtration problem of thermal explosion incorporating the postinduction period is given for the first time. The paper describes a study of the temperaturefield dynamics, poregas pressure, and the degree of condensedphase conversion versus the reactivegas deficiency in a reactive porous material. Focus is on the formation and propagation of frontal regimes of exothermic chemical reactions (their number, direction, and velocity of propagation, degree of condensedphase conversion at the front). The study revealed double selfignition phenomena and combustionwave propagation regimes with incomplete conversion at the front. A surface regime of thermal explosion limited by gas filtration from the outside was considered. The regularities in the dynamics of the exothermic chemical reaction found in the present study allow one to qualitatively control hightemperature synthesis under thermal explosion conditions.     

Variable‐temperature IR spectroscopic studies of CO adsorbed on Na‐ZSM‐5 and Na‐Y zeolites

CO interacts with extraframework alkali metal cations (M⁺=) of zeolites to form both M⁺CO and M⁺OC species. By using variabletemperature FTIR spectroscopy, these Cbonded and Obonded species were found to be in a temperaturedependent equilibrium. For the same cation, the difference in interaction energy depends upon the zeolite framework. Thus, for the equilibrium process ZNa⁺=CO ZNa⁺OC, where Z represents the zeolite framework, H ⁰ was found to take the values 3.8 and 2.4 kJ mol^– for CO/NaZSM5 and CO/NaY, respectively. The Cbonded species show always the highest cation–CO interaction energy.     

Location of Mn in MnAPO‐11: influence of synthesis from aqueous and non‐aqueous media

MnAPO11 samples were synthesized from aqueous (MnAPO11(A)) and ethylene glycol (MnAPO11(NA)) media. The crystallinity of the samples was more when the synthesis was carried out in ethylene glycol. Chemical and thermogravimetric analyses reveal greater incorporation of Mn in the framework of MnAPO11(NA) than in MnAPO11(A). At least five different types of Mn(II) species are detected in the samples by ESR. The studies suggest that Mn is more homogeneously distributed in MnAPO11(NA) than in MnAPO11(A).     

Fabrication and characterization of the Ag‐based high‐technology model nanocluster catalyst for ethylene epoxidation manufactured by electron beam lithography

Nanocluster catalysis is an area where greater fundamental knowledge is needed to understand the behavior of aggregates of metal atoms in determining product selectivity of chemical reactions. While catalysis is practiced industrially with economic success there is still a great need to eliminate wasteful sidereactions which hurt overall yields. Here we report on fabrication of a Agbased hightechnology model nanocluster catalyst by using electron beam lithography (EBL) designed for systematic studies of the ethylene epoxidation reaction. The catalyst is made of a square array of cylindershaped Ag nanoclusters that are 200 Å in diameter, deposited on a four inch silicon wafer, precovered with a 100 Å thick film of alumina. The height of the particles and interparticle distance can vary, and were chosen to be 150–300 and 1000 Å, respectively. The high technology catalyst was characterized by Xray photoelectron spectroscopy (XPS), highresolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The thermal stability of Ag nanoclusters in vacuo was investigated.     

Mechanical Sensitivity and Detonation Parameters of Aluminized Explosives

Experiments were performed to study the effect of the species particle size and structure of aluminized mixture samples on the sensitivity and detonation parameters of HMX, nitroguanidine, bis(2,2,2trinitroethyl)nitramine, and their mixtures with an Al powder with a mean particle size of 0.1 – 150 m. The addition of ultrafine Al to HMX and bis (2,2,2trinitroethyl)nitramine substantially increases the sensitivity to mechanical effects and decreases the detonation velocity. In compositions with nitroguanidine, the detonation velocity practically does not vary. For nitroguanidine, the width of the chemicalreaction zone and Chapman–Jouguet parameters were determined by recording the detonationpressure profiles. The pressure profiles for bis(2,2,2trinitroethyl)nitramine show that detonation decomposition can occur in two stages. A twopeak detonationwave structure was detected for mixtures of HMX with Al. Temperature measurements indicate that Al interacts with detonation products in the immediate proximity to the front. The highest temperature was recorded for compositions containing ultrafine aluminum and an aluminum dust.     

Modeling and Large Eddy Simulation of Deflagration Dynamics in a Closed Vessel

The paper describes a large eddy simulation model of gaseous deflagration in a closed vessel and simulation results for stoichiometric hydrogen–air premixed combustion initiated at the center of a closed 6.37m³ spherical vessel. The model is based on the large eddy simulation approach to turbulence modeling and the gradient method to model the mass burning rate in premixed combustion. The method for simulated flamefront thickness reduction is suggested, and its performance is investigated. The solutionadaptive mesh refinement is used to decrease the CPU time required for simulation. The simulated deflagrationpressure dynamics is in agreement with published experimental data, and the flamefront velocity is in agreement with simulation results obtained according to the lumped parameter model for the same experiment.     

Vapor‐phase synthesis of acetophenone in benzene acylation over CeHZSM‐5(30) zeolite

The benzene acylation was carried out with acetic anhydride as an acylating agent in vapor phase over HZSM5, Si/Al =30 and 280, HY and Ce, Vmodified HZSM5(30) zeolite catalysts at atmospheric pressure. The yield of acylated product acetophenone was found to be 82.1 wt% with 95.0% selectivity at 86.4 wt% conversion of acetic anhydride over Cemodified HZSM5(30) where Brønsted acidic sites are active for this reaction.     

Shock‐Induced Polarization of Materials

A new computational method of calculating signals of shockinduced electric polarization of materials is proposed and used to analyze previous experimental results on the shockinduced electric polarization of Plexiglas. Experimental results on the shockinduced electric polarization of granite are presented.     

Impact of Structural Factors on Unsteady Combustion Modes of Gasless Systems

Based on the twotemperature, twovelocity timedependent model of gasless combustion, taking into account structural transformations related to the force action of the gas filtering in the pores and vitrification and volume variation of the condensed phase during the chemical transformation, selfoscillatory combustion modes are studied. Structural transformations are shown to have a pronounced effect on the propagation pattern of combustion waves and can either stabilize or destabilize combustion. The major structural parameters appreciably affecting combustionwave stability are the initial porosity, particle size, and pressure.