Effect of synthesis atmosphere, wetting, and compaction on the purity of AlB₂
- University of Utah, 122 S. Central Campus Drive, Salt Lake City, UT 84112 (United States)
AlB₂ is attractive as an energetic fuel because of its large heat of combustion on a volumetric basis. The formation of AlB₂ from its elements is thermodynamically limited by decomposition into liquid aluminum and α-AlB₁₂ at temperatures approaching 950 °C, and kinetically limited in the reverse reaction, making synthesis of high-purity powders difficult. Minimizing unreacted Al and B makes AlB₂ more resistant to moisture degradation. AlB₂ yield for similarly prepared samples was observed to be significantly higher in He–6% H₂ or vacuum compared to a high-purity Ar atmosphere. Lower AlB₂ yield was generally associated with higher Al₂O₃ content in the reaction products, suggesting that poor Al wetting on oxide surfaces generated by the reaction of Al with B₂O₃ and other sources of oxygen prevented complete reaction. Compaction decreased the amount of oxygen available to the interior of the pellet, and the vacuum and He–6% H₂ environments reduced the amount of oxide impurities in the system, possibly by reducing or subliming them. By optimization of synthesis parameters the purity of AlB₂ was measured as 93 wt%, which was better than the previously reported bulk syntheses. Accounting for unreacted boron is important when using XRD to assess purity since the quantification of secondary phases, such as Al, Al₂O₃, and Al₃BC, allow the amount of boron, which is not easily detected in the scan, to be calculated. - Graphical abstract: Atmosphere and compaction pressure affect AlB₂ purity. Highlights: • Vacuum or He–6% H₂ yielded higher AlB₂ than Ar due to reduced Al₂O₃. • Compaction at 25 MPa prior to heating improved the AlB₂ yield. • XRD can be used to quantify AlB₂ if Al is used to assess the free B content. • Elimination of oxide impurities is the key to making higher purity AlB₂.
- OSTI ID:
- 22306272
- Journal Information:
- Journal of Solid State Chemistry, Vol. 201; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
Similar Records
Synthesis and crystal structures of the new metal-rich ternary borides Ni{sub 12}AlB{sub 8}, Ni{sub 12}GaB{sub 8} and Ni{sub 10.6}Ga{sub 0.4}B{sub 6}-examples for the first B{sub 5} zig-zag chain fragment
Oxidation kinetics of aluminum diboride