Influences of powder morphology on the densification and microstructure of a ZrO2-based nanocrystalline glass–ceramic
Morphology is an important characteristic of raw powder utilized for ceramic sintering but the role of powder morphology is mostly overlooked. In this study, two types of ZrO2–SiO2 powder with different morphologies (fiber and particle) were synthesized by blow spinning and sol–gel method, respectively, followed by direct current electric field-assisted hot pressing (FAHP) to obtain nanocrystalline glass–ceramics (NCGCs). Results showed that the two as-synthesized powders had different pyrolysis behaviors. The two types of as-synthesized powders were amorphous and tetragonal-ZrO2 nanocrystallites first formed after calcination at 800°C. During FAHP, the particle powder can be densified at a lower temperature than that of the fiber powder, due to the facts that the particle powder showed higher specific surface area and higher densification driving force. The fiber powder was predominately densified by fiber fusion and plastic deformation, whereas the particle powder was densified via particle fusion. Both the two types of powder can be fully densified to obtain ZrO2–SiO2 NCGCs at 1230°C for 4 min. Tetragonal-ZrO2 nanocrystallites in the NCGCs with particles as raw powder showed higher stability than those in the NCGCs with fibers as raw powder.
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