SPINEL INVERSION AND LATTICE PARAMETERS IN CHROMIUM-FREE SPINEL SOLID SOLUTIONS

The objective of this work was to investigate the amount of inversion in complex spinel solid solutions in order to understand the synthesis and sintering of magnesia-rich chromium-free complex spinels and their solid solutions. It has been observed that chromium-free spinels can be sintered at much lower temperatures (1350-1550 degrees C) than the Cr3+ bearing versions, which require firing at 1720-1800 degrees C, in order to achieve equivalent properties. The low temperature synthesis is due to the low temperature defect structure, leading to activated synthesis and sintering of the complex spinels. The inversion of the spinel was calculated using theoretical considerations and correlated to the observed inversion for experimental samples fired at various temperatures. The inversion in the complex spinel phase versus firing temperatures and composition were correlated to the densification of the ceramic specimens fired in air at temperatures ranging from 1350 degrees C to 1550 degrees C for 3 hours, in order to understand the effect of crystallographic changes in terms of the values of the lattice parameters of the complex spinel phase and their effects on the bulk density, open porosity and compressive strength of this new type of chromium-free basic refractory ceramics.