Origin of the strength change of silicon nitride ceramics with the alteration of spray drying conditions

The effect of changing the spray drying conditions on the microstructure of green bodies and on the strength variation of sintered bodies was examined for silicon nitride ceramics. Novel characterization techniques were applied to observe the internal structure of granules, green bodies and the resultant ceramics. As a result, the difference of the fracture strength of sintered bodies made from the granular compaction route could be explained quantitatively by the difference of the pore size distribution in the sintered bodies. Those potential flaws were introduced by the incomplete collapse of dimples in granules and of interstices between granules. Different characteristics of granules exerted a serious influence on the size and concentration of potential flaws in green compacts and on the resultant mechanical strength of sintered bodies after densification.