ChemInform Abstract: Crystal-Chemistry of Mullite-Type Aluminoborates Al18B4O33 and Al5BO9: A Stoichiometry Puzzle.

✍ Scribed by Martin Fisch; Thomas Armbruster; Daniel Rentsch; Eugen Libowitzky; Thomas Pettke

• Publisher: John Wiley and Sons
• Year: 2011
• Weight: 24 KB
• Volume: 42
• Category: Article
• ISSN: 0931-7597
• DOI: 10.1002/chin.201118012

✦ Synopsis

Crystal-Chemistry of Mullite-Type Aluminoborates Al 18 B 4 O 33 and Al 5 BO 9 : A Stoichiometry Puzzle. -Orthorhombic Al2O3-rich aluminoborate samples are synthesized by solid state reactions between α-Al2O3 and B2O3 or H3BO3 (Pt crucible, 1100-1200 °C). Single crystals are prepared from a Al2O3/B2O3 (9:2) mixture in a K2CO3/MoO3 (1:3) flux by cooling the melt from 1100 to 600 °C and from Al 2 O 3 /H 3 BO 3 (1:3.3) in B 2 O 3 flux by slow cooling from 1550 to 1250 °C. The products are characterized by powder and single crystal XRD, 11 B and 27 Al solid state MAS NMR, Raman, and FTIR spectroscopy, and laser-ablation ICP-MS. The materials crystallize in the space group Cmc21 with Z = 4. The suggested Al18B4O33 stoichiometry is excluded for all synthesized samples. All evidences indicate that the title compound should be reported as Al 5-x B 1+x O 9 with x < 0.038 which is close to Al 5 BO 9 . -(FISCH*, M.;