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

Abstract

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 10000C. 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 10000C to avoid aluminum diboride formation. Keywords: thermodynamic analysis, Gibbs's energy, equilibriums constant, enthalpy, entropy, aluminum dodecaboride, aluminum, boron nitride, boron carbide, aluminum diboride.