V. E. Zarko

Chemical Analysis of Aluminum as a Propellant Ingredient and Determination of Aluminum and Aluminum Nitride in Condensed Combustion Products

A brief survey of typical problems in the analysis of aluminum powder in aluminized solid propellants and in analysis of condensed combustion products of these propellants was carried out. Recommendations for applying the versions developed by the authors of the known methods are given. The permanganatometric variant of the titrimetric method was found suitable for most tasks concerning the measuring of the metallic/unburned aluminum. The determination of aluminum nitride in combustion products using the combination of chemical and X-ray diffraction methods was described and illustrated by results obtained from condensed combustion products of propellant formulations containing highly active ultrafine aluminum powder. Even for this formulation the content of aluminum nitride in the final condensed combustion products was found to be negligibly small independently of the nature of the gas (argon or nitrogen) used for bomb pressurization.

Combustion of Nano Aluminum Particles (Review)

Nano aluminum particles have received considerable attention in the combustion community; their physicochemical properties are quite favorable as compared with those of their micron-sized counterparts. The present work provides a comprehensive review of recent advances in the field of combustion of nano aluminum particles. The effect of the Knudsen number on heat and mass transfer properties of particles is first examined. Deficiencies of the currently available continuum models for combustion of nano aluminum particles are highlighted. Key physicochemical processes of particle combustion are identified and their respective time scales are compared to determine the combustion mechanisms for different particle sizes and pressures. Experimental data from several sources are gathered to elucidate the effect of the particle size on the flame temperature of aluminum particles. The flame structure and the combustion modes of aluminum particles are examined for wide ranges of pressures, particle sizes, and oxidizers. Key mechanisms that dictate the combustion behaviors are discussed. Measured burning times of nano aluminum particles are surveyed. The effects of the pressure, temperature, particle size, and type and concentration of the oxidizer on the burning time are discussed. A new correlation for the burning time of nano aluminum particles is established. Major outstanding issues to be addressed in the future work are identified.

Nanoparticles of energetic materials: synthesis and properties (review)

The replacement of micrometer-sized metal fuel powders in gas-generating solid propellants with nanosized metal powders has become a common trend in the design of new types of propellants in recent decades. This trend has been motivated by the unique properties of propellants containing nanocomponents. The emergence of nanostructured gas-generating propellants suggests new directions for the development of highly concentrated and efficient energy sources. Technologies for large-scale production of nanometal powders and other nanostructured materials with tailored characteristics have also experienced an impetuous development in recent years. This paper presents a classification, description, and competitive analysis of the main methods of producing nanoscale and nanostructured materials used to produce gas-generating propellants. The main advantages and difficulties concomitant with the use of nanomaterials in propellant formulations are discussed. Specific issues related to the high reactivity and pyrophoricity of nanomaterials and related risks are analyzed. Methods for the preservation and passivation of the surface of nanomaterials are classified and discussed. The focus is on those methods that are most widely used, and those that are considered promising today.

Ignition and extinction of homogeneous energetic materials by a light pulse

Numerical calculations using a model of unsteady combustion of melting energetic materials were performed to simulate the results of qualitative experiments on the ignition and quenching of energetic materials by a light pulse. The parameters of the model composition were chosen to correspond to combustion with the burning-rate control reaction in the gas phase to ensure the stability of self-sustained combustion after the cessation of irradiation. Regions of stable ignition in the coordinates “radiant flux amplitude-irradiation time” were obtained for compositions with different transparency for igniting pulses of three shapes: rectangular, linearly decreasing to zero, and exponentially decreasing. Extinction conditions of the steadily burning composition by a rectangular light pulse were calculated.

Mechanism and kinetics of the thermal decomposition of cyclic nitramines

At present, considerable progress toward an understanding of the thermal decomposition and combustion of nitramines has been achieved. However, because of the lack of thorough experimental and theoretical data on the chemical structure of a combustion wave, the kinetics of the process in the narrow zone adjacent to the burning surface has not been adequately studied. The review systematizes literature data on the thermal decomposition of nitramines that are of interest in studies of chemical processes in a combustion wave.

Nonstationary combustion of condensed substances subjected to radiation

Results of an experimental and theoretical investigation of the nonstationary combustion of condensed substances are represented, where the double-based propellants H, H + 1% C, H + 1% PbO and miscible compositions on an ammonium perchlorate base were the substances. Attention was paid to the specifics of physical and mathematical modeling of the processes under irradiation and interrelation of the responses of the burning system to pressure and radiation flux perturbations, and the possibilities of quantitative predictions of the combustion rate under irradiation were analyzed. A xenon lamp, a carbon dioxide laser, and a neodymium laser were used as the radiation sources.

Charges and Fractal Properties of Nanoparticles — Combustion Products of Aluminum Agglomerates

The disperse, structural, and electrophysical characteristics of fine alumina produced by combustion of metal droplet agglomerates were studied experimentally. Data were obtained by transmission electron microscopy and video recording of aerosol particles moving in a homogeneous electric field. The aerosol particles are aggregates with sizes ranging from a fraction of a micrometer to a few micrometers and a fractal dimension of 1.60± 0.04 which consist of primary particles with sizes of a few to hundred nanometers. Most of the aggregates have electric charges, both positive and negative. The characteristic charge of the aggregates is equal to a few units of elementary charge. Some large aggregates rotate when the electric field polarity changes, i.e., they are dipoles.

Investigation of the Properties of a Kinetic Mechanism Describing the Chemical Structure of RDX Flames. I. Role of Individual Reactions and Species

For description of the chemical structure of RDX flames, key reactions and species are selected by numerical solution of the system of equations describing one–dimensional flows of a viscous, heat–conducting, reacting gas at pressures of 0.5—90 atm. The kinetic mechanism consists of 263 elementary steps and 43 species. Literature data on rate constants of elementary steps are considered. Flame structure is calculated for RDX combustion under irradiation. Various reaction paths in the RDX vapor decompositon zone are considered. The effects of the mass flow rate and two–dimensional nature of the gas flow on the flame structure are discussed. Calculation results are compared to experimental data. The structure of various flame zones and the role of individual steps and species in the chemical process are investigated.

MODELING OF CYCLIC-NITRAMINE COMBUSTION

The theoretical and experimental data on the combustion of cyclic nitramines published in the past 30 years are systematized and critically reviewed. Results of studies of combustion-wave parameters and flame chemical structure are presented. Simplified and detailed models of nitramine combustion are examined. Reduction of the chemical mechanism in a flame and general problems of the adequate description of nitramine-combustion waves are discussed. The review materials are also of interest in analysis of the combustion processes of composite propellants based on nitramines.

Investigation of the Properties of a Kinetic Mechanism Describing the Chemical Structure of RDX Flames. II. Construction of a Reduced Kinetic Scheme

A reduced kinetic mechanism is constructed taking into account various boundary conditions and the considerable spread of data on rate constant of elementary steps. Kinetic schemes describing the chemical structure of flame with various degrees of accuracy are considered. The “shortest” mechanism consists of 83 steps and 29 species. The heat fluxes, temperature profiles, and concentration profiles of the main (by mass) species calculated from the complete and reduced mechanisms are in good agreement.