Homogeneous distribution and quantitative evaluation of sintering additives in spray-dried silicon nitride granules

Quantitative phase evaluation of sintering additives and their homogeneous distribution in ceramics are critical issues in ceramic processing. In the present work, we report the characteristics of silicon nitride granules containing sintering additives (Y2O3-Al2O3-Yb2O3) prepared by spray drying. For homogeneous mixing of sintering additives, using fine and similar particle sizes for all sintering additives is essential. In this study, the particle size was reduced by ball milling based on the particle size of the as-received sintering additive. Systematic studies using scanning electron microscopy and particle size analysis were conducted on starting materials and spray-dried granules. Highly stable aqueous slurries consisting of 25 vol.% of silicon nitride particles, 5 wt.% sintering additives, and 0.5 wt.% each of dispersant, binder, and plasticizer, were used in preparing the granules. Quantitative phase analysis and homogenous distribution of sintering additives in the granules were assessed by examining the mixing index values through Rietveld analysis of X-ray diffraction data and energy dispersive X-ray spectroscopy studies.