Sintering of silicon nitride with Mg-exchange zeolite additive

The possibility of using Mg-exchanged zeolite as additive for densification of Si3N4 ceramic was studied. The zeolitic precursor was previously heated at 800 degrees C to obtain an amorphous powder with a composition corresponding to MgO center dot Al2O3-nSiO(2). The powder was mixed with Si3N4 and the sintering additive was homogenized by attrition milling in the presence of isopropanol and finally compacted by cold isostatic pressure. Pushrod dilatometry was used to measure the shrinkage behaviour of green bodies under a nitrogen atmosphere from room temperature to 1500 degrees C. The chemical reactions and phase evolution during pressureless sintering were also followed by means of X-ray and dilatometric analysis. Results show that the first liquid forms as low as 1070 degrees C, sharing in a significant reduction of sintering temperature. The final phase composition obtained at 1500 degrees C consist of crystalline alpha-Si3N4 phase which is emended in oxynitride glassy phase The results show that the Mg-exchanged zeolite is a very effective low-temperature sintering additive for silicon nitride.5th International Conference on New Research Trends in Materials Science, Sep, 2007, Sibiu, Romani