Journal of Student Research 2014

Journal of Student Research

be due to the fact that the Al 2 O 3 particles are much coarser with a smaller surface-to-volume ratio and inhibit sintering kinetics. Coarse powders are known to sinter slower than fine powders. Sintering temperatures in excess of 1,300°C caused warping and cracking in the composite samples with the result that 1,300°C was the highest temperature used. The warping and cracking could have resulted from the difference in the coefficients of thermal expansion (CTE) between BaTiO 3 (CTE: 6×10 -6 K -1 ) and Al 2 O 3 (CTE: 8.1×10 -6 K -1 ). Sintering occurs by atomic diffusion, usually in the solid state, and the diffusion rate is enhanced at elevated temperatures facilitated by sintering aids (e.g., minute quantities of additives such as MgO). No sintering aids were used either in the BaTiO 3 or in the Al 2 O 3 powders used in the composites. The higher melting temperature of aluminum oxide (2,072°C) compared to barium titanate (1,625°C) could have led to incomplete densification of BaTiO 3 /Al 2 O 3 composites when sintered at a temperature of 1,300°C. This is because undoped BaTiO 3 attained 88% densification at 1,400°C and with the additions of higher melting alumina, a temperature of 1,300°C would not suffice. To achieve full densification, hot pressing and use of finer barium titanate and alumina powders may be recommended. Figures 2 through 4 show optical and scanning electron microscopy images of undoped and Al 2 O 3 -doped BaTiO 3 sintered under different conditions.

Undoped BaTiO 3 sintered at 1,300°C, 4h (Fig. 2a & b) shows partially sintered grains together with intergranular porosity dispersed throughout the sample cross-section. At a higher temperature (1,400°C, Fig. 2c), there appears to be more

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