Simulation of Agglomerate Dispersion in Combustion of Aluminized Solid Propellants

The paper deals with mathematical simulation of dispersion of agglomerates formed in combustion of aluminized solid propellants. A substantial effect of the separation conditions of agglomerating metal particles from the surface of the burning propellant on the size of agglomerates is demonstrated. A mathematical model of agglomerate formation is constructed for propellants whose typical feature is active burning of the metallic fuel in the surface layer. Satisfactory quality of simulation is validated by the agreement of experimental and numerical data.     

Model of Air Gasification of a Solid Fuel in a Filtration Regime

A twotemperature mathematical model of steady filtration combustion is proposed. The model takes into account the finite length of the reactor and the dependence of heat capacities of the phases on temperature and composition. The model describes the process of gasification of a solid fuel in a filtration regime. Calculation results for the gasification reaction of a carbon–nert component mixture are presented. The range of fractions of the fuel component is determined in which neither a purely normal nor a purely inverse wave is formed (an approach of a transitional wave is proposed for this interval). It is shown that the combustion temperature is finite within the entire interval of fractions of the fuel component.     

Aluminum Combustion in Nitrogen

The process of nitration of aluminum and aluminumcontaining mixtures in the regime of selfpropagating hightemperature synthesis with a high pressure (up to 300 MPa) of the reacting gas (nitrogen) is considered. The dependences of ignition temperatures and also burning temperatures and burning rates of these initial mixtures on test conditions (nitrogen pressure and composition of the initial mixture) are studied. The dependence of the burning rate of initial mixtures on factors affecting spreading of the liquid component (melt containing aluminum and nitrogen) over the surface of the second component (aluminum nitride or titanium diboride), such as the equilibrium wetting angle, interaction at the interface, and melting of the second component, is studied. The microstructure and some properties of materials obtained are examined. Based on these studies, the combustion mechanism is determined, a mechanism of phase formation in combustion of these mixtures is suggested, and the structure of the combustion wave is determined.     

Ammonia synthesis over multi‐promoted iron catalysts obtained by high‐energy ball‐milling

The feasibility of producing ammonia synthesis catalysts from highenergy ballmilling of a simple mixture of the constituent oxides has been investigated. The effect of ballmilling the fused oxidic precursor of the industrial KM1 ammonia synthesis catalyst has also been studied. The results show that highenergy ballmilling offers some interesting possibilities for preparing novel catalytic materials. It is observed that ballmilling of the powder oxides mixture leads to formation of solid solutions and the catalytic activity is significantly higher than that of the starting material. Furthermore, ballmilling of fused oxidic KM1 precursor is seen to give rise to more homogeneous promoter distribution and slightly higher activity. The quite small activity increase observed in this case probably reflects the fact that the fusion process has already resulted in a close to optimal promoter distribution. The choice of atmosphere during ballmilling is also seen to offer possibilities for regulating the phase composition.     

Localization of Deformation in Copper Single Crystals During Explosive Collapse

It is established that highrate axisymmetric loading of single crystals by the method of explosive collapse of a hollow thickwalled cylinder causes deformation that involves all active closepacked slip systems. The spatial distribution of macroscopic sites of strain localization is determined by the crystallography of the active systems in singlecrystalline samples. The established correlation between the observed shear bands in the microstructure of copper single crystals and {111} active slip <110> systems of facecentered cubic (FCC) crystals and their symmetric arrangement show that deformation at a rate of 5 · 10⁴ sec^-1 occurs according to the crystalline structure of the materials.     

Side-product inhibition of the catalyst in electrophilic aromatic substitutions and Friedel-Crafts reactions

Electrophilic substitutions on aromatics such as C₆H₅X often lead to mixtures of the ortho- and para-disubstituted products C₆H₄XY. The former can chelate a metallic center and hence be a potential catalyst inactivator, whenever the (X, Y) substituents have atoms with lone pairs. This general principle operates in the Friedel-Crafts acylation of anisole, a reaction of industrial importance.     

CO oxidation catalyzed by Cu‐exchanged zeolites: a density functional theory study

The catalytic oxidation of CO by Cuexchanged highsilica zeolites (e.g., ZSM5) has been investigated theoretically using density functional theory. Calculations reveal two distinct, parallel pathways for oxidation of CO: (i) adsorption of O₂= on a reduced Cu site followed by O atom abstraction by CO, and (ii) adsorption of CO followed by its reaction with O₂= to form a cyclic compound which decomposes to form CO₂=. The reduced site is regenerated via two different pathways, both of which involve oxidation of one or more CO molecules: (i) abstraction of atomic oxygen by CO from the oxidized active site, and (ii) formation of a carbonate species followed by its reaction with a molecule of CO. The relevance of these reactions to the reduction of NO is discussed.     

Experimental Study of Ignition of a Gasoline–Air Mixture in a Constant‐Volume Combustion Chamber

The characteristics of flamekernel development in a premixed gasoline–air mixture in a cylindrical constantvolume combustion chamber are measured. The experiments are performed with an initial temperature of 393 K, pressure of 6 bar, and equivalence ratio = 0.8 with the use of various ignition systems and spark plugs. The schlieren pictures of the process are presented, and the measured results for flame velocity, heatrelease rate, and mass fraction of the burnt fuel are analyzed.     

Mathematical Simulation of Lifting and Ignition of Particles in Coal Deposits

The problem of coalparticle lifting and ignition in a flow field formed by a shock wave passing along a dusty surface is considered. The particle dynamics is described on the basis of the previously developed and verified mathematical model, which takes into account the action of the Saffman forces and aerodynamic interference. Simulation of the coalparticle reaction is based on the concepts of the surrounding film theory. Calculations that reveal qualitative and quantitative features of coalparticle dynamics and ignition are performed. The combined mathematical model is verified by experimental data on trajectories and the dependence of the coalparticle ignition delay on gas temperature behind the front of the transient shock wave.     

Deformation Dynamics of a Reactive Medium During Gasless Combustion

Deformation during gasless combustion of 5Ti + 3Si and Ti + C samples was studied experimentally. The dynamics of motion of the material in a gasless combustion wave was studied using highspeed video recording (500 frames/sec) with a spatial resolution of the order of 10 m. It was shown that behind the combustion front, the medium was first expanded and then compressed. The dimensions of the expansion and compression zones were determined.     

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.     

Layers Produced by Entrapment of a Shaped‐Charge Jet in a Titanium Target

An xray diffraction study was performed of layers produced on titanium targets by a shapedcharge explosion. Mixtures of fine powders of graphite and ammonium nitrate in different proportions were used as liners. The phase compositions of the central and peripheral zones of the target were shown to be different. The unitcell parameters of the detected crystalline phases and sample microhardness were measured.     

Effect of Some Catalysts on Combustion of Double‐Base Propellants

The effect of PbO₂, SnO₂, TiO₂, and Bi on the combustion of propellants of various compositions is investigated. It is established that SnO₂, TiO₂, and Bi have a significant effect on the burning rate of propellants without carbon black and additional plastifiers. A marked catalytic effect of PbO₂ is manifested only when its content is higher than 5%. It is shown that the addition of SnO₂ and PbO₂ to propellants leads to formation of a carbon black matrix on the burning surface, on which catalyst particles build up. With the addition of carbon black to propellants, the catalytic action of TiO₂ and Bi is enhanced only slightly, and the effect of SnO₂ at moderate pressures is markedly reduced due to a considerable increase in the degree of reduction of the active form of (SnO₂) catalyst up to its inactive forms (SnO and Sn).     

Phase Compositions of Coatings Applied to Titanium Targets by Means of Shaped‐Charge Jets

Coatings containing titanium carbides of the cubic and hexagonal modifications were applied to titanium targets by a shapedcharge explosion. In the experiments, a conical liner with a cone angle of 30° made from a mixture of fine powders of boron and ammonium nitrate were used. A quantitative Xray phase analysis of various segments of the coating was performed. The values of the unit cell parameters indicate the formation of complex phases. In some regions of the target, the microhardness reaches 3800 kg/mm².     

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.     

Mechanism of Upper Temperature Limits in a Wave of Filtration Combustion of Gases

A physical mechanism is established, responsible for the experimentally observed strong deceleration of the growth rate of the maximum skeleton temperature in a wave of filtration combustion of gases with increasing flow rate. The maximum temperatures of the gas and skeleton become commensurable, and the length of the thermalrelaxation zone becomes much shorter. A classification of regimes based on the temperatureheterogeneity criterion ₁ is proposed. Explicit analytical solutions are obtained for the wave for ₁1 and ₁1. A correction to reverse reactions in combustion products is considered. The effect of composition on wave behavior is studied by means of numerical calculations with a detailed kinetic scheme. The activation energy for ultrarich and ultralean methane–air mixtures is evaluated. It is concluded that the limiting efficiency of the heatrecuperation cycle in the wave is reached as ₁1; methods for maximizing the efficiency are suggested.     

Heat Conduction of Copper–Molybdenum Explosive Compacts

The thermal conductivity of explosive compacts produced from a copper–molybdenum powder mixture was determined experimentally for the first time. Thermal conductivity was measured by a KT6 comparator designed at the Siberian State Institute of Metrology. It is shown that the thermal conductivity of explosive compacts depends on the composition of the starting powder mixture and increases significantly after three hours in a vacuum furnace at a temperature of 900°C. An explosive compaction method was developed to produce cylindrical samples of 30 mm diameter with homogeneous properties without singularities at the center.     

Radiographic Study of the Evolution Material of the Density Profile behind the Front of a Divergent Shock Wave in an Explosive

The evolution of the material density profile behind the front of a divergent initiating shock wave in HMX and RDX based explosives in the transitional regime of explosive transformation was studied using flash radiography. The explosives were loaded by a divergent shock wave through a Plexiglas layer of varied thickness. Distinctive features were found in the evolution of the density profile behind the front of a divergent initiating shock wave that did not become a detonation wave and behind the front of an initiating shock wave that became a detonation wave.     

Surface of a Titanium Target After Interaction with Shaped‐Charge Jet Particles

Coatings containing WC_1-x and W₂C_1-x tungsten carbides were produced on titanium targets by a shapedcharge explosion. The experiment used conical liners with a cone angle of 30° manufactured from a mixture of fine powders of tungsten, graphite, and ammonium nitrate. A comparative quantitative xray analysis of the top and bottom layers of the coating was performed. For the phase WC_1-x in the bottom layer, the value of the cubic unit cell parameter falls outside the range known in the literature. Microhardness in different segments of the target was studied.     

Interaction of a High‐Velocity Steel Projectile with a High‐Porous Copper–Duralumin Two‐Layer Bumper

The impact of a steel sphere 2 mm in diameter flying with a velocity of 2–7.3 km/sec on a twolayer bumper is considered. The first layer of the bumper is made of finely disperse copper powder with a density of 2.8 g/cm³, and the second layer is made of Duralumin. For identical impact velocities of 3–5 km/sec and identical thicknesses and areal densities of the bumpers, the twolayer bumper leads to better failure of the steel projectile than the Duralumin bumper. In the case of the twolayer bumper used, the maximum penetration depth of fragments into the witness plate and the number of the largest craters are smaller. The order of the bumper layers does not exert any noticeable effect on projectile failure. With the impact velocity increased to 7 km/sec, the difference in shielding properties of the bumpers almost vanishes.