Dense aluminum borate (Al18B4O33) ceramics by direct sintering of milled powders

DR. GUSTAVO SUAREZ; ESTEBAN AGLIETTI; FLORENCIA HERNANDEZ; PILAR PENA; CARMEN BAUDIN; N.M. RENDTORFF

Foz de Iguazu

Congreso; ICC7. 7th International Congress on Ceramics; 2018

The formation of boron-aluminates (BA: Al18B4O33 and Al4B2O9) from alumina and boron oxide occurs at intermediate temperatures (around 600-800 °C) and present a typical whisker or needle morphology. In comparison with other alumina binary systems, these materials present a high refractoriness, accompanied by chemical inertness in some environments [1].The utilization of aluminum borates needles or whiskers for aluminum and aluminum based alloys reinforcement are the principal application of these phases [2]. Furthermore, dense aluminum borate (Al18B4O33) materials are difficult to obtain. In this work, BA materials were processed by a simple milling-sintering route of aluminum borate powders obtained by thermal reaction of calcined alumina and fine boric acid.The milling effect was established. The sintering characteristics were determined. This starts around 1000°C and is limited by the thermal decomposition (T> 1300 °C) of the borate to alumina and boron oxide, which at this temperature volatilize. Sub angular and medium spherical sintered grain microstructure was developed.The achieved results encourages the structural application of the borate materials, the results also bring important information of the thermal behavior of the Al2O3-B2O3 system that is being proposed as setting (bonding) phase at intermediate temperatures (700-1200 °C) of high alumina and/or spinel refractory castables.1. A. R. Studart, et al., Processing routes to macroporous ceramics: a review. J. Am. Ceram. Soc. 89 (6) (2006) 1771-1789.2. K.P. Peil, L.G. Galya, G. Marcelin, Acid and catalytic properties of nonstoichiometric aluminum borates, J. Catal. 115 (1989) 441-451.