A new sintering aid for magnesium aluminate spinel

A dense MgAl2O4 sintered spinel has been prepared following a conventional double stage firing process. A new type of sintering aid, AlCl3, can improve the bulk density, apparent porosity and water absorption of MgAl2O4 spinel sintered at 1550°C devoid of any contamination. In order to see the effect of AlCl3 on densification and formation of a MgAl2O4 spinel, 0.01–0.03 mol% AlCl3 was added separately prior to calcination, subsequent to calcination as well as simultaneously at both stages. AlCl3 is found to be equally effective in enhancing spinel formation during calcination as well as in increasing sintered density. The efficacy of AlCl3 as a “spinelizer” or as a sintering aid is also compared with the conventional mineralizer, AlF3, which is generally added only prior to calcination to enhance the spinel formation. AlCl3 is found to be active as a sintering aid provided the powder contains some free Al2O3 and MgO and probably the hygroscopic nature of AlCl3 is responsible for its effectiveness as a sintering aid.