Zone-specific temperature distribution, densification trajectory and grain-growth kinetics of microwave-hybrid-sintered and conventionally sintered Al₂O₃ slip casts

Figures & data

Figure 1. Schematic of temperature measurement for an Al₂O₃ uniaxially pressed sample, using PTCR in a (a) conventional furnace and (b) microwave furnace.

Table 1. Temperature measurement results

Ring Type	Temperature Range (°C)	Set Temperature (°C)	Measured Temperature (°C) CS s	Measured Temperature (°C) CS c	Measured Temperature (°C) MS s	Measured Temperature (°C) MS c
ETH	850–1100	950	950	850	930	945
STH	1130–1400	1250	1250	1217	1232	1248
HTH	1450–1750	1550	1550	1489	1525	1540

Figure 2. Schematic of an Al₂O₃ slip cast sample and the points of interest (s: surface; c: center).

Figure 3. (a) FE–SEM microstructure, and (b) particle-size analysis of Al₂O₃ AKP–50 powder.

Figure 4. Rheology of Al₂O₃ slurry prepared for slip casting.

Figure 5. Measured temperature versus set temperature of the (a) conventionally sintered samples and (b) microwave-hybrid-sintered samples.

Figure 6. X-ray diffraction patterns of sintered Al₂O₃ (s: surface; c: center).

Figure 7. FE–SEM microstructures of conventionally sintered samples (s: surface; c: center).

Figure 8. FE–SEM microstructures of microwave-hybrid-sintered samples (s: surface; c: center).

Figure 9. Relative density of sintered samples (f: full compact; s: surface; c: center).

Figure 10. Grain-size distributions of (a) conventionally sintered samples and (b) microwave-hybrid-sintered samples, (c) average grain sizes at the surface and center points after different holding times, and (d) schematic showing the directions of the temperature gradient and grain growth during conventional and microwave sintering.

Table 2. Estimated temperatures from the measured temperatures using PTCRs

Set Temperature (°C)	Estimated Temperature (°C) CS s	Estimated Temperature (°C) CS c	Estimated Temperature (°C) MS s	Estimated Temperature (°C) MS c
1400	1400	1345	1378	1393
1450	1450	1398	1427	1442
1500	1500	1451	1477	1492

Figure 11. Estimated temperatures obtained from the linear-intercepts of the measured temperatures.

Figure 12. FE–SEM images showing the microstructures of the conventionally sintered samples at different set temperatures with no holding time (s: surface; c: center).

Figure 13. FE–SEM images showing the microstructures of microwave-hybrid-sintered samples at different set temperatures with no holding time (s: surface; c: center).

Figure 14. Average grain sizes at the surface and center points after sintering at different estimated temperatures.

Figure 15. Estimated activation energy for grain-growth at the (a) surface and (b) center of the conventionally sintered samples, and that at the (c) surface and (d) center of the microwave-hybrid-sintered samples.

Figure 16. Grain-growth mechanism estimation with grain-growth constants n of (a) 2 and (b) 3, and (c) grain-growth rate (K) for conventionally sintered and microwave-hybrid-sintered Al₂O_3.