亚微米Al2O3对重结晶碳化硅的作用机制

使用不同粒径的SiC和亚微米Al₂O₃添加剂制备重结晶烧结碳化硅并表征其物相组成、微观形貌、孔径分布和耐压性能，研究了亚微米Al₂O₃对重结晶碳化硅的作用机制。结果表明，在亚微米Al₂O₃作用下，重结晶碳化硅的烧结过程可分为液相烧结和重结晶烧结两个阶段。在液相烧结过程中高活性的亚微米Al₂O₃促进了液相的形成，使SiC的传质方式由扩散传质演变为粘性流动传质。在重结晶烧结温度SiC的传质以蒸发-凝聚为主，形成含铝气相并与SiC固溶促进了6H-SiC向4H-SiC晶型的转变。引入亚微米Al₂O₃后，重结晶碳化硅材料的孔径分布由单峰分布转变为多峰分布，其中孔径较小的特征峰对应重结晶烧结形成，而较大孔径的特征峰则来源于液相烧结的形成；同时，随着保温时间的延长SiC晶粒生长发育更为完全，由不规则颗粒状转变为较规则六方结构。但是，体积密度的下降、SiC晶粒尺寸不均一以及材料孔径的多...

Effect of Submicron Al2O3 Addition on Sintering Process of Recrystallized Silicon Carbide

The recrystallized SiC was prepared via argon atmosphere sintering with SiC of different particle sizes as raw material and submicron Al₂O₃ as additives, and its phase composition, microstructure, pore size distribution and compression resistance were characterized by means of universal testing machine, X-ray diffractometer, plasma spectrometer, scanning electron microscope and mercury porosimeter. The results show that due to the presence of submicron Al₂O₃, the sintering process of the recrystallized SiC can be differentiated into two stages: liquid phase sintering and recrystallization sintering. The highly active sub-micron Al₂O₃ promotes the formation of liquid phase during liquid phase sintering stage, therewith, the mass transfer mode of SiC changed from diffusion to viscous flow. During recrystallization sintering stage, the mass transfer of SiC at high temperature is dominated by evaporation and condensation, forming Al-containing gas phase and solid solution with SiC, which promotes the crystallographic transformation of the recrystallized SiC, i.e., from 6H-SiC to 4H-SiC. After introducing submicron Al₂O₃, the pore size distribution of recrystallized SiC material changes from unimodal to multimodal, of which, the characteristic peak of small size pores correspond to the course of recrystallization and sintering, whereas, the characteristic peak of large pore size presents the course of liquid phase sintering. At the same time, the SiC grains grow and develop much perfectly with the prolonging of holding time, correspondingly, the SiC grains change from irregular granular to more regular hexagonal structure. However, the decrease of bulk density, the inhomogeneity of SiC grain size and the multi-peak distribution of pore size, so that decrease the compressive strength of the SiC product.