Multiphase Electrodispersion Precipitation of Zirconia Powders
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EXPERIMENTAL A schematic diagram of the continuous EDR process is shown in Figure 1. The major components consist of the aqueous feed container, the electric dispersion reactor with the associated electrical components, the organic feed recycle tank, and the product gravity settler. The aqueous and organic flow rates ranged from 0.1 to 2 mL/min and 50 to 200 mL/min, respectively. Optimization of the electrodispersion process occurred when the peak electric field strength was 25 kV/cm, the pulsing frequency was 5000 s- 1, and the ratio of the aqueous to organic flowrate was 4 pm), respectively. BET surface areas of 24.2 and 82.1 m2 /g, respectively, were also measured for these runs. For the most part, the particles ranged in size from -200 0 U -240
S-280
LOSS AWEIGHT
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0.1
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0.3 0.5 0.7 0.9 1.1 DEGREES C (THOUSANDS)
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Figure 6. DTA and TGA of zirconia powder after air drying (10 "C/min in air;
Initial sample weight = 326 mg) The ZrO 2 powders were sintered by infrared (IR) and microwave heating. The initial pellet was formed by pressing at 12000 psi, 2 g of the zirconia powder into a pellet measuring 1.27 cm (0.5 in.) in diameter x 0.54 cm (0.21 in.) high. The unsintered pellet volume was 0.68 cm . In the IR heating experiments, the oven was heated to the desired temperature (e.g., 1100 or 1350 "C). The sample was rapidly placed in the oven and was heated for 1 h. The microwave heating experiments entailed using 1.1 175
Downloaded from https://www.cambridge.org/core. Access paid by the UCSB Libraries, on 23 Jul 2018 at 19:42:38, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-346-171
kW of 2.45-GHz microwave radiation to heat the pellet to the desired temperature and immediately deceasing the power to 500 W for 1 min. The sintered pellets cracked when heated to 1350 'C by IR heating. Conversely, pellets heated to 1100 "C were not as prone to cracking. The volume of the pellet sintered at 1100 "C by IR and microwave heating was 0.53 cm3 and 0.42 cm3, respectively. Pellets sintered at 1350 "C by microwave heating were 0.42 cm3. The pellets sintered by IR heating at 1350 "C broke apart; thus, the volume of the sintered pellet was not determined. The density of the IR- and microwave-sintered pellets heated to 1100 "C was 3.77 g/cm3 and 4.76 g/cm3 , respectively. Although the particles were sintered by IR and microwave heating, the measure densities of the sintered pellets are substantially less than the theoretical density of 5.71 to 5.73 g/cm 3 for tetragonal zirconia. CONCLUSIONS
The EDR was operated in the continuous mode to produce 130 ± 2 g of ultrafine ZrO 2 powder from a concentrated zirconyl nitrate solution. It was shown that the bulk of the particles aggregated t
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