O. G. Glotov

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.

Condensed combustion products of aluminized propellants. II. evolution of particles with distance from the burning surface

Condensed combustion products of a model propellant on the basis of ammonium perchlorate and aluminum were studied using the sampling technique. The granulometric composition of combustion products and the content of metal aluminum in particles of size from 1.2 µm to maximum were determined within the pressure range of 0.6–7.5 MPa at a distance from the burning surface up to 190 mm. A multimode structure of mass distributions of oxide particles within the size range of 1.2–40 µm was found. An empirical dependence of burnout of metal aluminum from agglomerates on the residence time of particles in the plume of combustion products of the propellant sample was obtained.

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.

Macrokinetics of Combustion of Monodisperse Agglomerates in the Flame of a Model Solid Propellant

The paper describes a procedure for studying the macrokinetics of combustion of agglomerates in a solid propellant flame using special samples of a model propellant generating monodisperse agglomerates. Empirical dependences of the incompleteness of aluminum combustion in the combustion products of a propellant based on ammonium perchlorate and HMX on time and pressure were established. The mass fraction of oxide accumulated on a burning agglomerate versus the degree of aluminum conversion was determined. For fine agglomerates (310–350 μm), this fraction decreases with increase in the degree of conversion. For large agglomerates (400–540 μmum), it increases, and, hence, the mass of large agglomerates increases as aluminum burns out. Because of accumulation of oxide, the agglomerate size does not change markedly in the examined range of parameters.

Problems and prospects of investigating the formation and evolution of agglomerates by the sampling method

Problems related to the interpretation of information obtained from an analysis of collected particles of condensed combustion products of aluminized propellants are considered. It is shown that the difficulties that arise are due to three main factors: the complex statistical character of the combustion of heterogeneous propellants, which results in formation of agglomerates with a substantially polydisperse distribution in size and different (even for identical size) structure, the features of burnout of the agglomerates related to the accumulation of oxide on the burning particle, and the specific character of the motion of burning agglomerates in the gas flow. An experimental approach is proposed that makes it possible to eliminate the polydispersity of the agglomerates and uncertainty in the parameters of the gaseous products flowing away from the burning surface.

Condensed Combustion Products of Aluminized Propellants. III. Effect of an Inert Gaseous Combustion Environment

The effect of gaseous combustion environment on particle size distribution and chemical compositions of condensed combustion products of a model propellant containing ammonium perchlorate, binder, and 23.4% aluminum was studied. Experiments were conducted at pressures of 0.6, 4.0, and 7.5MPa. Oxide particles with sizes of 1.2–60 μm and agglomerates with sizes from 60 μm to maximum were investigated. In experiments with nitrogen and helium, the difference in the mean sizes of the sampled agglomerates does not exceed the experimental error. The difference in the amount of unreacted (metallic) aluminum in the agglomerates sampled in nitrogen and helium is also negligible. Replacement of nitrogen by helium affects the size distribution of the oxide particles by increasing the mass fraction of particles with sizes of 1.2–10 μm, and this effect is enhanced with pressure.

Combustion of spherical agglomerates of titanium in air. I. Experimental approach

This paper describes a method for studying the combustion of titanium particles with a diameter of 300–500 µm obtained by agglomeration of many small particles. Burning monodisperse particles of titanium were produced by ignition of miniature pieces of a pyrotechnic composition containing 69% titanium powder placed in the burning sample. The resultant agglomerated particles burned in free fall in air. Their motion and evolution, including fragmentation, were video-recorded. Condensed combustion products were quenched, sampled, and studied.

Combustion of spherical agglomerates of titanium in air. II. Results of experiments

Combustion of titanium particles in free fall in air were investigated. Burning monodisperse particles with a diameter of 300, 390, and 480 µm were obtained by merging of many small particles during ignition of miniature pieces of a pyrotechnic composition comprising 69% powdered titanium. Motion parameters and the drag of the burning particles were determined. The fragmentation phenomenon (the onset time and duration of the phenomenon, dispersion dynamics of fragments, fragment size distribution functions) were described qualitatively. For the investigated particles, the dispersion of fragments has the form of a spruce branch: the mother particle is retained and ejects small fragments. The distance and velocity of a particle at the moment of fragmentation and at the end of combustion were determined. Data are given on the structure and morphology of the combustion product particles represented by the reside of the mother particle and the set of small fragmented particles and data on changes in the size and glow intensity of the burning particle. At the end of combustion, the mother particle is transformed to a sphere consisting of a mixture of oxides of the averaged composition TiO2.76.

Size and morphology of the nanooxide aerosol generated by combustion of an aluminum droplet

The increasing recent interest in characteristics ofsubmicron oxide smoke generated by combustion ofaluminum droplets stems from environmental problemsassociated with application and utilization of alumi-nized propellant rocket motors and from the develop-ment of technologies of production of metal nanoox-ides in aerodisperse flames [1, 2]. Oxide particles rang-ing from nanometer to submicrometer size form andgrow in the flame zone surrounding a burning particle,this process being the starting point for their furtherevolution. Rational design of particle combustion pro-cesses in technical devices is based on an understand-ing of physicochemical processes that occur duringcombustion of a particle and on knowledge of how theircharacteristics depend on combustion conditions. Oneof the challenges in studying the aluminum particlecombustion mechanism is to study the formation andproperties of oxide nanoparticles. In this work, we stud-ied how the size distribution and morphology of theoxide aerosol formed by combustion of aluminum par-ticles in atmospheric air depends on the size of a burn-ing droplet. We intend to extend the pressure range inthe future.Burning droplets were produced by combustion of asmall sample (from 2 × 2 × 20 to 2 × 4 × 40 mm in size)of aluminized solid propellant, which was burnt in a20-L container in air filtered from aerosols. Duringcombustion, the sample expelled burning aluminumdroplets (agglomerates), which fell freely under grav-ity. The combustion lasted a few seconds. During thistime, the container was filled with “oxide smoke,” a fineaerosol. After completion of combustion, aerosol parti-cles coagulated, sedimented, and were partially depos-ited on the walls of the container. To study the evolutionof particles after burning, the resulting aerosol wasperiodically sampled. The aerosol sample was fedeither into a thermophoretic precipitator, to collect par-ticles for subsequent dispersion and morphologicalanalysis based on their electron microscopic images, orinto a Millikan cell, to observe aerosol particles andrecord their motion by a video camera with a micro-scope lens and a laser illuminator. The cell constructionimplies that a homogeneous electric field can beapplied. This, in combination with video recording ofparticle motion, makes it possible to determine the elec-tric charge of the particles. The sampling, video record-ing, and image processing techniques were describedelsewhere [1, 3].We carried out four series of experiments with pro-pellants differing in the size of generated burning drop-lets.In series 1, a model solid propellant containing25 wt % ammonium perchlorate (AP), 35 wt %cyclotetramethylenetetranitramine (HMX), 20 wt %binder, and 20 wt % aluminum was used. Inasmuch asaluminum droplets are agglomerated as the propellantburns, the distribution function of burning droplets gen-erated by the propellant was estimated in the followingmanner. The size distribution of agglomerates, as wellas the fraction of the metal involved in agglomeration(≈0.6), was determined using the technique in [4]. If weassume that the metal not involved in agglomerationpasses into the gas phase in the same form as it has inthe propellant, the set of particles generated by combus-tion consists of agglomerates and particles of initialaluminum. The distribution function of initial alumi-num was preliminarily determined on a Malvern 3600Eparticle size analyzer. Table 1 summarizes the charac-teristics of the set of polydisperse particles calculatedtaking into account the weight fractions. Hereinafter,D

Formation of Nanosized Products in Combustion of Metal Particles

Abstract The necessity and practical importance of studying the characteristics of oxide nanoparticles formed in combustion of aluminum (Al) and titanium (Ti) microparticles are substantiated. Experimental techniques and results are reviewed. Priority is given to the methods developed at the Institute of Сhemical Kinetics and Combustion and to the original results obtained by these methods. It is shown that despite distilnctions in the mechanisms of aluminum and titanium combustion, the oxide nanoparticles, Al2O3 and TiO2, are of almost the same dimensions and display similar morphological and charge properties. Future investigations should be concerned with a mutual influence of the macrokinetics of the consumption of active particle metal on the formation of disperse oxide. The problems of high priority are formulated.