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.     

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.     

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.     

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.     

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).     

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.     

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.     

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.     

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.     

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.     

Cobalt‐catalyzed amination of 1,3‐cyclohexanediol and 2,4‐pentanediol in supercritical ammonia

The onestep procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixedbed reactor. Application of supercritical NH₃ as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8–10%). The main reason for the low diamine selectivity of 1,3dihydroxy compounds is water elimination leading to undesired monofunctional products via ,unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3propanediol.     

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.     

Lean NOx catalysis over alumina‐supported catalysts

aluminasupported catalysts show promise as lean NO_x catalysts. The role of alumina in influencing the structural and chemical properties of the active phase supported on it is discussed using some effective aluminabased lean NO_x catalysts. These include Ag/Al₂O₃, CoO_x/Al₂O₃ and SnO₂/Al₂O₃. Alumina plays an important role in stabilizing Ag in the oxidic phase and cobalt in the 2+ oxidation state. For SnO₂/Al₂O₃, alumina increases the SnO₂ surface area. On both Ag/Al₂O₃ and SnO₂/Al₂O₃, alumina also participates actively in the NO_x reduction reaction. An active organic intermediate is formed on Ag or Sn oxide which reacts with NO_x subsequently on alumina to form N₂.     

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.     

Combustion of a Mixture of Aluminum and a Titanium‐Containing Raw Material in the Presence of Additives

A model of the gasphase component of combustion of an aluminum mixture with metal oxides is described. By the example of titanium reduction from its oxide, it is shown that atomic oxygen formed thereby facilitates gasphase oxidation of aluminum and decreases metal yield. The effect of graphite, activated carbon, and diesel fuel on combustionwave velocity and temperature is considered. Two waves (cold and hot ones) are observed in the system titanium oxide–ferric oxide–aluminum–carboncontaining additives. Hydrocarbon additives inhibit the aluminumoxidation reaction by oxygen contained in air in the first wave, and graphite and activated carbon play the same role in the second wave in the titaniumreduction reaction. Experimental confirmation is found for the fact that the action of additives increases the amount of aluminum consumed directly for titanium reduction in the second wave, which enhances exothermality of the process.     

Analysis of the Thermal Explosion in Systems Porous Reagent–Active Gas–Solid Product

The specific features of dynamics of the thermal explosion in systems porous reagent–active gas–solid product under conditions where the heattransfer and masstransfer regions are separated from the ambient medium are considered. In addition to the competition of heat release and heat removal, the process of initiation of exothermal chemical interaction in these systems under normal pressures depends significantly on conditions of filtration transport of the gaseous reagent. The induction and postinduction periods of the thermal explosion are studied. The theoretical analysis of thermalexplosion issues is supplemented by an experimental study of the process for the porous titanium–nitrogen–titanium nitride system.     

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.     

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.     

Gas‐Dynamic Method of Determining Combustion Efficiency in a Model with Combustion

A method of determining combustion efficiency and testgas parameters along the combustion chamber with a supersonic velocity of air at the entrance is considered. The composition and properties of the test gas are determined by a thermodynamic calculation with allowance for dissociation and temperature dependence of the energy of internal degrees of freedom. The sources of errors and the influence of accuracy of initial data definition in a zerodimensional approach to determining the combustion curve and flow parameters are studied.     

Fuel Combustion in Combustion Chambers of a Gas–Turbine Engine with a Rotating Injector

Specific features of combustion in combustion chambers of a gasturbine engine with a rotating injector are considered. The region of the combustion site and the temperature field are found. A method for threedimensional simulation of heat and mass transfer is described. The calculation results are compared with the temperature fields of real engines.