Grain boundary glassy phase and abnormal grain growth of silicon nitride ceramics

The microstructure of pressureless sintered Si3N4 With MgO-CeO2 additives h as been studied by TEM. The grain boundary glassy phase is observed and con firmed directly by microdiffraction. EDAX analysis suggests that the main f unction of CeO2 lies in the formation of a glassy phase, which contains har dly any MgO. This cerium silicate glassy phase is good to wet Si3N4. MgOCeO 2 is an excellent sintering aid for Si3N4. Abnormal grain growth of Si3N4 o ccurred at a sintering temperature of above 1850 degreesC, which leads to m icrocracks and dislocations and is harmful to mechanical properties. (C) 20 01 Elsevier Science Ltd and Techna S.r.l. All rights reserved.