Abstract
Intergranular glassy phase of sintered Si3N4 was quantitatively evaluated by three methods. Four specimens with 6 to 15wt% additives were sintered for evaluation. The amounts of glassy phase in these specimens were evaluated by the three methods and compared with the mechanical properties. The following results were obtained.
(1) The XRD analysis was thought to be most reliable for the quantification of glassy phase in sintered Si3N4, considering the objectivity of the method. Highly pure and homogeneous β-Si3N4 was required as the standard material for increasing the accuracy.
(2) The results of image analysis agreed with those of XRD analysis in this study. However, the results were remarkably influenced by the definition of threshold intensity of back-scattered electron image. This method was found to have experimental difficulties to apply for fine-grained Si3N4 ceramics.
(3) The calculation method was found to overestimate the glassy phase content when a large amount of additives was contained. The reason was thought to be caused by the inadequete estimation of glass composition.
(4) The differences between the glassy phase contents evaluated by experimental methods and the amounts of additives were 1 to 3.6wt%. It was considered that the differences depended on the impurity oxygen in the Si3N4 powder.
(5) The high temperature strength of sintered Si3N4 decreased dependng on the glassy phase content.
