Influence of the structure of MgO· n Al 2 O 3 spinel lattices on transparent ceramics processing and properties

It is demonstrated that a complete elimination of pores on sintering is governed not only by the size of the ceramic powder particles and by the homogeneity of their mutual coordination but similarly strongly by the state of the crystal lattice: with different cation disorder at fixed stoichiometry (n=1) the sintering temperatures may differ by as much as 200°C at constant powder particle size and equal homogeneity of the green bodies. Additionally, the impact of stoichiometry was investigated over the range between n=1 and n=3 with retarded reactive sintering at moderately increased Al2O3 concentrations but promoted densification of alumina-rich compositions. Taking advantage of the observed effects, sintered spinel ceramics were derived by reactive sintering of undoped MgO/Al2O3 mixtures resulting in an in-line transmittance which equals spinel single crystals of similar composition from 200nm wave length up to the IR range.