Abstract
It has already been clarified in the authors' previous study on Si3N4-10 mol%MgO-5.5 mol%Al2O3 ceramics that the annealing at about 1370 K caused a sharp decrease in the strength of ceramics with the formation of MgSiO3. In this study, the effects of contents of MgO (7-20 mol%) and Al2O3 (3.5-9.5 mol%) and additional amount of SiO2 (1-3 moloo) on the formation of MgSiO3 and the change in the strength due to the annealing were investigated.
It was found that the increasing of MgO content and decreasings of Al2O3 and SiO2 contents depressed the formation of MgSiO3. In particular, the increasing of MgO content was most effective and the formation of MgSiO3 was completely inhibited at about 20 mol%MgO. In accordance with this, the strength of ceramics with 20 mol%MgO was hardly varied by the annealing. Some discussions were made on these results, using MgO-Al2O3-SiO2 psuedo-ternary phase diagram.
