A. P. Il'in

Reactivity of Aluminum Powders

The reactivity of aluminum powders is determined using the following parameters: the temperature of the onset of oxidation, maximum oxidation rate, degree of conversion (degree of oxidation) of aluminum, reduced (conditional) ratio of the thermal effect to the weight increment. These parameters for estimating the activity of aluminum powders were chosen from the results of nonisothermal oxidation of powders of various particle sizes under conditions of programmed heating (oxidizer–air). In accordance with the testing method proposed, the most reactive powder studied was STPA‐4 ultrafine aluminum powder produced by electrical explosion of conductors.

Combustion of Agglomerated Ultrafine Aluminum Powders in Air

It is shown experimentally that agglomeration of ultrafine aluminum powders decreases their reactivity during nonisothermal oxidation in air. Under normal and low pressures, the concentration of bound nitrogen in combustion products is lower for agglomerated powders than for unagglomerated powders, and under high pressures (>120 kPa), it is higher for agglomerated powders. Key words: ultrafine powder, aluminum, agglomeration, combustion, reactivity, aluminum nitride.

Combustion of Ultrafine Aluminum in Air

The paper reports results of studying the combustion of ultrafine aluminum (surface average diameter of particles is ≈ 0.1 μm) in a sealed bomb at an initial air pressure of 1 atm. The combustion proceeds in two stages, similarly to combustion in air. It is shown that during the two‐stage combustion of ultrafine aluminum powder in the bomb, the mass concentration of chemically bound nitrogen in the final products increases by ≈ 20% in terms of aluminum nitride. An increase in nitrogen content in confined combustion validates the previously proposed mechanism of binding air nitrogen with participation of the gas phase during aluminum combustion.

Combustion of Mixtures of Ultrafine Powders of Aluminum and Boron in Air

Results of investigation of the combustion of mixtures of ultrafine aluminum and boron powders (the oxidizer is air) are presented. It is shown that the combustion proceeds in two steps, which differ in temperature. The addition of boron influences the concentrations of AlN, residual Al, and α-Al2O3 in the end products of combustion of mixtures of ultrafine powders of Al and B in air. For a fixed sample weight of 4 g, the maximum AlN content is observed in the combustion of an Al+20% B mixture of ultrafine powders, and the combustion temperature is also maximum in this case. When the sample weight is smaller than a certain critical value, the combustion proceeds in one step. Increasing the sample weight of the starting mixture of ultrafine powders of Al and B leads to an increase in the AlN content in the combustion products with simultaneous rise in the combustion temperature. A considerable part of the combustion products stabilizes as acicular polycrystals of micron and submicron sizes formed with participation of a gas phase during combustion.

Combustion of Mixtures of Commercial Aluminum Powders and Ultrafine Aluminum Powders and Aluminum Oxide in Air

The paper studies the combustion of mixtures of commercial aluminum powders (ASD-1 and ASD-4) and ultrafine powders of Al and γ-Al2O3 in air. It is shown that the combustion of coarsely dispersed commercial powders is accompanied by binding of air nitrogen with formation of AlN and AlON. The combustion of mixtures proceeds in two stages with the possible formation of intermediate gaseous and liquid products. The processes of sintering and incomplete combustion play an important role in the combustion of mixtures of commercial powders and ultrafine powders of aluminum.

Products of Combustion of Aluminum Hydride in Air

The paper reports results of studying the process and products of combustion of aluminum hydride in air. It is shown that the final combustion products of aluminum hydride contain ≈50% aluminum nitride (by weight) for large sample weights of 1000 g. The formation mechanism of the final combustion products of aluminum hydride is similar to that of ultradisperse aluminum powder.

Influence of additives on combustion of ultradisperse aluminum powder and chemical binding of air nitrogen

Experimental results are presented on combustion in air of ultradisperse aluminum powder with additives of ultradisperse powders of copper, nickel, iron, tin, silicon, graphite, boron, tungsten, and molybdenum.X-Ray diffraction and chemical analyses were used to study the composition of the end products. A tin additive has an inhibiting action on the chemical combining of air nitrogen as aluminum nitride and oxynitride, whereas iron, tungsten, and molybdenum additives favor an increase in nitrogen content. As is established, the influence of additives on the processes determining the duration of two combustion stages is greater than on the content of bound nitrogen in the products.

Properties of Ultrafine Aluminum Powder Stabilized by Aluminum Diboride

The paper studies properties of an ultrafine aluminum powder produced by electric explosions of conductors, whose particles are stabilized by coating with aluminum diboride immediately during the synthesis of the powder. The ultrafine aluminum powder stabilized in such a manner has special properties: narrow particle size distribution, increased dispersity, and higher resistance to oxidation upon heating.