[Microwave sintering of nanometer powder of alumina and zirconia-based dental ceramics].
OBJECTIVE
The objective of the present study was to investigate the feasibility and reliability of sintering alumina and zirconia-based all-ceramic materials through a recently introduced microwave heating technique. The variation of crystal phases, the growth of grain sizes and microstructural features of these materials were evaluated after sintering.


METHODS
Four different groups of powder (l00%Al2O3, 60%Al2O3+40%ZrO2, 40% Al2O3+60%ZrO2, 100% ZrO2) were respectively press-compacted to fabricate green disk samples, 5 specimen of each group were prepared. All the samples were surrounded by refractory materials for heat containment and processed at 1 600 degrees C in a domestic microwave oven (850 W, 2 450 MHz), 1 600 degrees C/5 min for heating rate, 10 min for holding time. After sintering, the phase composition and average grain size of these ceramics were examined using X-ray diffraction (XRD). Their microstructure characteristics were studied by scanning electron microscopy (SEM).


RESULTS
All the specimens were successfully sintered with the application of microwave heating system in combination with a suitable thermal insulator. No phase change was found in alumina while monoclinic-zirconia was found to be transformed to tetragonal-zirconia. A little grain size growth of Al2O3 and ZrO2 has been observed with Al2O3 24.1 nm/before and 51.8 nm/after; ZrO2 25.3 nm/before and 29.7 nm/after. The SEM photos indicated that the microwave-sintered Al2O3-ZrO2 ceramics had a uniform crystal distribution and their crystal sizes could be maintained within the range of nanometers.


CONCLUSIONS
It is expected that in the near future microwave heating system could be a promising substitute for conventional processing methods due to its unparalled advantages, including more rapid heating rate, shortened sintering time, superfine grain size, improved microstructure and much less expensive equipment.
Chen
Yi-Fan
YF
Dept. of Prosthodontics, West China College of Stomatology, Sichuan University, Chengdu 610041, China.
Lu
Dong-Mei
DM
Wan
Qian-Bing
QB
Jin
Yong
Y
Zhu
Ju-Mu
JM
D000537:Aluminum Oxide; D002516:Ceramics; D006358:Hot Temperature; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008872:Microwaves; D015203:Reproducibility of Results; D013499:Surface Properties; D015040:Zirconium
D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide