J Mater Sci(2006)41:7425-7436 7429 The linear shrinkage ratios(the ratio of the sintering Ka) shrinkage of the compact perpendicular and parallel to the original seed platelets) were also measured, as shown in Fig. 2. Increasing the initial platelet content leads to increased constraint in the plane of the platelets, so that more densification occurs normal to the platelets. Thus, platelet alignment is accompanied by anisotropic densification, as has been reported fo an alumina-platelet-reinforced Ce-ZrO2/Al2O3 com- The volume of dramatically during sintering through growth of the aligned seed platelets at the expense of the surround um ing, randomly oriented, fine Al2O, particles [2]. The microstructure of a cross-section of a sintered alumina compact with 4.8 vol% initial seed platelet content is (b) shown in Fig. 3 and the microstructural anisotropy of the monolithic ta is evident in both the micrograph in Fig 3a and the SEM image in The seed platelets have acted as templates for both sintered grain morphology and crystalline texture development, so that the strong 0001 texture(c-axis perpendicular to the sample surface and normal to the tape-casting direction) is accompanied by morpholog ical anisotropy(flattened grains parallel to the surface) Figure 3c shows a bright-field TEM image taken from a cross-section of TA layer, in which a grain boundary between two Ta grains is accurately parallel to both basal planes(see inserted SAD pattern) with no sign of 10 Hm any glassy phase or second-phase precipitation X-ray diffraction patterns from a green body and c sintered (1550C, 2 h) samples with different initial latelet contents are shown in Fig 4. The 00.6 and 00. 12 peaks for the sintered, platelet-containing zA.[210 sintered textured alumina (TA)with 4.8 vol% initia (b) SEM micrograph of the cross-section of fully sir with 4.8 vol% initial platelets:(c) bright-field TEM basal grain boundary between two Ta grains Platelet Content(vol%) les are much more prominent than those from either Fig 2 Linear shrinkage ratios for the textured alumina(TA) the green body or a sintered, platelet-free sample samples with different initial seed platelet contents Similarly, the near-basal-plane peaks, such as 10.10 andThe linear shrinkage ratios (the ratio of the sintering shrinkage of the compact perpendicular and parallel to the original seed platelets) were also measured, as shown in Fig. 2. Increasing the initial platelet content leads to increased constraint in the plane of the platelets, so that more densification occurs normal to the platelets. Thus, platelet alignment is accompanied by anisotropic densification, as has been reported for an alumina-platelet-reinforced Ce–ZrO2/Al2O3 com￾posite [30]. The volume of textured (aligned) crystals increased dramatically during sintering through growth of the aligned seed platelets at the expense of the surround￾ing, randomly oriented, fine Al2O3 particles [2]. The microstructure of a cross-section of a sintered alumina compact with 4.8 vol% initial seed platelet content is shown in Fig. 3 and the microstructural anisotropy of the monolithic TA is evident in both the optical micrograph in Fig. 3a and the SEM image in Fig. 3b. The seed platelets have acted as templates for both sintered grain morphology and crystalline texture development, so that the strong 0001 texture (c-axis perpendicular to the sample surface and normal to the tape-casting direction) is accompanied by morpholog￾ical anisotropy (flattened grains parallel to the surface). Figure 3c shows a bright-field TEM image taken from a cross-section of TA layer, in which a grain boundary between two TA grains is accurately parallel to both basal planes (see inserted SAD pattern) with no sign of any glassy phase or second-phase precipitation. X-ray diffraction patterns from a green body and sintered (1550 C, 2 h) samples with different initial platelet contents are shown in Fig. 4. The 00.6 and 00.12 peaks for the sintered, platelet-containing sam￾ples are much more prominent than those from either the green body or a sintered, platelet-free sample. Similarly, the near-basal-plane peaks, such as 10.10 and 1.0 1.5 2.0 2.5 3.0 0 5 10 15 20 Linear Shrinkage Ratio (Y/X Shrinkage Ratio) Platelet Content (vol%) X X Y Fig. 2 Linear shrinkage ratios for the textured alumina (TA) samples with different initial seed platelet contents Fig. 3 (a) Optical micrograph of the cross-section of fully sintered textured alumina (TA) with 4.8 vol% initial platelets; (b) SEM micrograph of the cross-section of fully sintered TA with 4.8 vol% initial platelets; (c) bright-field TEM image of a basal grain boundary between two TA grains J Mater Sci (2006) 41:7425–7436 7429 123