TABLE OF CONTENTS The spinels are a class of double oxide of general formula AB 2O 4: industrially important members of this class include aluminates (e.g. MgAl 2O 4), ferrites (e.g. MgFe 2O 4) and chromites (e.g. MgCr 2O 4).
Magnesium aluminate spinel (MgAl 2O 4) is an important constituent of magnesia-based refractory materials. The melting point of MgAl 2O 4 is 2135 C. There are no natural deposits of MgAl 2O 4, which is therefore normally obtained by reaction of mixtures of magnesium and aluminium oxides. The theoretical stoichiometric composition of magnesium aluminate spinel is 71.68% Al 2O 3 and 28.32% MgO by weight, but compositions can vary because of a limited range of solid solution. Its density is 3.579 Mg m ?3, approximately the same as MgO (3.583 Mg m ?3).
Commercial sintered magnesia-spinel refractory materials are divided into three categories: magnesia rich, stoichiometric, and alumina rich. [1] Typical properties of magnesia rich spinel bricks are given in Table 14.1 [2]
| Properties | Magnesia-spinel | Magnesia-spine |
|---|---|---|
| MgO (%) | 96 86 | 90 80 |
| Al 2O 3 (%) | 3 8 | 9 18 |
