SYNTHESIS AND MICROSTRUCTURAL EVOLUTION OF SiC/Si_3N_4/Si_2N_2O NITRIDE POROUS CERAMIC COMPOSITES PROCESSED VIA HYSYCVD

摘要

The effect of using successive stages of infiltration and different atmosphere types on the microstructural evolution and physical properties of SiC/Si_3N_4/Si_2N_2O nitride porous ceramic composites was investigated. Composites were processed via solid-gas phase reactions using the hybrid precursor system chemical vapor deposition (HYSYCVD) route. SiC_p porous preforms were infiltrated in subsequent stages (S1, S2) according to the following schedule: S1-1 and S1-2 at 1300°C for 70 min in high purity nitrogen (HPN); S2 at 1350°C for 120 min in ultra high purity nitrogen (UHPN). The composites were characterized by XRD, SEM and by means of He picnometry, volume-measurement approach and immersion in Hg using Archimedes's principle. Results show that atmosphere type and stage-processing approach affect the type, morphology and size of the nitrides formed. Stage-infiltration approach allows establishing conditions to control morphology, size (including nanometric size) and distribution of deposited phases, thus determining the properties of the composites.