The stoichiometry of β"-alumina: Phase diagram studies in the system Na2O−MgO−Li2O−Al2O3
1988; Elsevier BV; Volume: 28-30; Linguagem: Inglês
10.1016/s0167-2738(88)80060-2
ISSN1872-7689
Autores Tópico(s)Nuclear materials and radiation effects
Resumoβ"-alumina has, ideally, a spinel-like stoichiometry with an overall cation: anion ratio of 3:4. This has been shown by phase diagram studies of the system Na2O−Li2O−MgO−Al2O3, which determined the range of β"-alumina compositions in lithia-stabilised, magnesia-stabilised and lithia/magnisia-stabilised systems at 1500°C. In lithia-stabilised material, β"-alumina exists with compositions given by the formula Na1−xLixAl5O8, 0.18<x<0.28, which lie on the "spinel join", LiAl5O8−"NaAl5O8" and also with a limited range of compositions containing up to a few percent excess alumina compared with the above formula. In magnesia-stabilised material, it exists on the "spinel join", MgAl2O4−"NaAl5O8", with a formula Na1−xMg2xAl5−xO8, x=0.175. Literature data at 1600–1650°C indicate that it forms a limited range of solid solutions based on the above formula but containing excess alumina. In material containing both Li and Mg, a range of β" compositions with spinel-like stoichiometry forms at 1500°C. These lie on the pseudoternary section "NaAl5O8"−LiAl5O8−MgAl2O4. The significance of these results for crystallographic studies on the β"-aluminas is discussed.
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