Abstract:
To study the effect of microwave sintering comparing with conventional sintering and the effect of zirconia addition on microstructure and optical transmittance of transparent alumina ceramic. The experiment was concentrated on increasing the transmittance of alumina ceramic by reducing grain size of alumina to submicron level. Alumina powder was used as raw material. Green samples were prepared by biaxial hydraulic pressing with 20 MPa and followed by cold isostatic press (CIP) of 200 MPa. Sintering was performed at temperatures ranging from 1300 to 1500 ํC for 2 hr followed by hot isostatic press (HIP) at temperatures ranging from 1250 to 1300 ํC for 0.5, 1 and 2 hr with pressure of 150 MPa under Ar atmosphere. Microwave sintering resulted in the fast processing time and accelerated densification to sinter alumina ceramic, but did not show the higher density than that of conventional sintering. The transmittance of microwave sintered specimens was lower than that of conventional one because of the larger grain size distribution. The optimum HIP condition selected from the results was 1300 ํC for 0.5 hr with a heating rate of 10 ํC/min. Zero, 0.2, and 0.4 wt% of zirconia were added to alumina powder together with 0.03 wt% of MgO. Zirconia addition inhibited grain growth of alumina grain. However, it also disturbed densification. The sintering temperature of alumina with zirconia to attain the same high density shifted to higher temperature than alumina with zirconia composition. Then the grain size of the full density specimen with zerconium was a little larger than that without zirconia. As a result, better optical transmittance was not attained from the composition with zirconia.
