Ignition and combustion of high-energy materials containing aluminum, boron and aluminum diboride

Boron and its compounds are among the most promising metal fuel components to be used in solid propellants for solid fuel rocket engine and ramjet engine. Papers studying boron oxidation mostly focus on two areas: oxidation of single particles and powders of boron, as well as boron-containing composite solid propellants. This paper presents the results of an experimental study of the ignition and combustion of the high-energy material samples based on ammonium perchlorate, ammonium nitrate, and an energetic combustible binder. Powders of aluminum, amorphous boron and aluminum diboride, obtained by the SHS method, were used as the metallic fuels. It was found that the use of aluminum diboride in the solid propellant composition makes it possible to reduce the ignition delay time by 1.7–2.2 times and significantly increase the burning rate of the sample (by 4.8 times) as compared to the solid propellant containing aluminum powder. The use of amorphous boron in the solid propellant composition leads to a decrease in the ignition delay time of the sample by a factor of 2.2–2.8 due to high chemical activity and a difference in the oxidation mechanism of boron particles. The burning rate of this sample does not increase significantly.

Thermodynamic Analysis of Perspective AlB12 Synthesis Reactions from Industrially Accessible Oxygen-Free Compounds

Reactions of aluminum dodecaboride synthesis from oxygen free industrially available boron compounds by interaction of condensed and gaseous aluminum with boron nitride and carbide were the subject of thermodynamic analysis in this work. It was shown, that both reactions are thermodynamically advantageous at low temperatures rather than at high and the probability of their occurrence rises significantly for gaseous aluminum in comparison with condensed aluminum. Calculated values of Gibbs’ free energy and equilibrium constants and the analysis of contributions into them clearly demonstrate the advantages of reaction with boron nitride. The probability of polyphase product composition imposes minimum temperature restrictions on the synthesis; it should be carried out at temperatures above 1000 ℃. Hypothetical mechanisms of reactions between aluminum and boron containing compounds differ by the place of interaction — any place on the surface of each layer of BN and only open surface of B4C — and by the transport of reaction participants in the reaction zone. From the results of analysis, we suggest indicative synthesis conditions: vacuum thermal synthesis to provide oxygen free environment and temperature above 1000 ℃ to avoid aluminum diboride formation.