Effect of TiO 2 doping on rapid densification of alumina by plasma activated sintering
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Effect of TiO2 doping on rapid densification of alumina by plasma activated sintering R. S. Mishra and A. K. Mukherjee Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616
K. Yamazaki Department of Mechanical and Aeronautical Engineering, University of California, Davis, California 95616
K. Shoda Sodick Co. Ltd., Yokohama, Japan (Received 10 July 1995; accepted 22 January 1996)
The effects of plasma cycle and TiO2 doping on sintering kinetics during plasma activated sintering (PAS) of g –Al2 O3 have been studied in the temperature range of 1473–1823 K. Multiple plasma cycle leads to higher densification. Also, TiO2 doping enhances the sintering kinetics during PAS. In TiO2 doped specimens, near full density was obtained at 1673 K in less than 6 min using multiple plasma cycle. It is suggested that the dielectric properties of a material are critical for the success of the PAS process.
There is considerable interest in rapid sintering processes, which provide opportunities for producing consolidated specimens of nanocrystalline ceramics. There are a number of synthesis techniques for the production of nanocrystalline oxide ceramics. Gas condensation is a well-established technique. The advantages of gas condensation synthesized g –Al2 O3 are fine particle size (,15 nm) and spherical shape.1 However, the microwave sintering2 and plasma activated sintering1,3 of gas condensation synthesized g –Al2 O3 did not succeed in producing high density nanocrystalline alumina. The results of Mishra et al.1,3 indicate that plasma activated sintering is a better consolidation technique as compared to microwave sintering2 for the consolidation of g –Al2 O3 . Plasma activated sintering has also proved to be a versatile technique for a number of materials including metallic alloys, ceramics, and superconducting materials.1,3–9 The purpose of the present study was to address the problem of retaining fine grain size in high density alumina. TiO2 was selected as a dopant because it has been shown to enhance densification of g –Al2 O3 and it is also effective in the inhibition of grain growth.10 In addition, the role of single and multiple pulsing cycle on sintering has been evaluated.
(up to 66 MPa) and resistance heating. The pulse cycle current was 750 A, pulse duration 60 ms, and pulse cycle 60 s. Single pulse cycle was applied at 293 K, whereas multiple pulse cycles were applied at 293 K, 473 K, 773 K, and 1273 K. The applied pressure was 66 MPa for all specimens. The gas condensation synthesized g –Al2 O3 and TiO2 were obtained from Nanophase Technologies Corporation (Darien, IL 60651). The average particle size of g –Al2 O3 was ,15 nm and that for anatase TiO2 was ,30 nm. The microstructure was examined by Scherrer x-ray line broadening (XRLB), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The XRLB grain sizes are not reported because a large discrepancy was observed in grain size value obtaine
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