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Strontium Dialuminate SrAl 4 O 7 : Synthesis and Stability
Author(s) -
Capron Mickaël,
Douy André
Publication year - 2002
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2002.tb00575.x
Subject(s) - strontium , metastability , amorphous solid , crystallization , annealing (glass) , materials science , melting point , kinetics , atmospheric temperature range , thermal stability , hexagonal crystal system , mineralogy , crystallography , chemical engineering , analytical chemistry (journal) , thermodynamics , chemistry , metallurgy , organic chemistry , composite material , physics , quantum mechanics , engineering
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.