Portal de Periódicos da CAPES

Strontium Dialuminate SrAl 4 O 7 : Synthesis and Stability

2002; Wiley; Volume: 85; Issue: 12 Linguagem: Inglês

10.1111/j.1151-2916.2002.tb00575.x

1551-2916

Mickaël Capron, André Douy,

Advanced ceramic materials synthesis

Up to now, strontium dialuminate, SrAl 4 O 7 (SA 2 ), could be synthesized only by solidification from the high‐temperature liquid state. We describe its synthesis from a spray‐dried amorphous precursor, and specify its stability domains. Its kinetics of formation is very low. It can be crystallized in the 900–1000°C temperature range either directly with a low heating rate or via two metastable solid solutions—hexagonal strontium monoaluminate (SrAl 2 O 4 (SA)) and γ‐alumina—by annealing at 950–1000°C. As the temperature is raised beyond 1100°C, SA 2 becomes metastable, its formation is no longer possible, and the crystallization of Sr 4 Al 14 O 25 (S 4 A 7 ) is favored. The latter compound, whose composition is close to that of SA 2 , is stable up to 1500°C. At higher temperature it decomposes into SA and SA 2 , which in its turn decomposes into SA and SA 6 (SrAl 12 O 19 ). There is again another stability domain for SA 2 , restricted to a narrow temperature scale close to its melting point (∼1800°C). The behaviors at crystallization from amorphous precursors at low temperature and from liquid at very high temperature are symmetrical: low heating or cooling rates produce pure SA 2 while too rapid kinetics result in mixtures of phases.