l198 L Zhang et al. Joumal of the European Ceramic Society 30(2010)1195-1202 lated texture index of thi e Is 3.2. Horizontal downward deposition from a fowing suspension the bottom and suspension flowing through. The platelets in the deposit however were not well aligned as shown in the eBsd of the perper (Fig. 6(b)). As shown in Fig. 6(e), the peaks are relatively weak and are not homogenously distributed implying that the pris matic planes are not well aligned. The corresponding X-ray pole 如Em figure confirms a very weak texturing after grain growth with a limited texture index of 1.60 (b) 3.3. Deposition from a stagnant suspension The abov nat the cell ical factor for platelet alignment during EPD. The electric field Eg force, gravity and hydrodynamic force applied on the platelets are believed to be the main factors influencing platelet alignment The influence of these forces is studied using 3 additional con- figurations as summarised in Table 1. in order to investigate the electric field force effect, an upward deposition was performed the horizontal cell without suspension flowing through(con- figuration 3). In order to investigate the gravity effect, EPD was performed from a stagnant suspension in the horizontal cell(con- figuration 4). In order to study the impact of the hydrodynamic force, the suspension is stirred comparing with stagnant suspen sion(configuration 5)or pumped through the cell as described in Sections 3.1 and 3.2 Fig. 5. Textured alumina deposited in a horizontal cell, cross-sectioned (a) Table 1 summarises the Lotgering factor and texture index parallel and (b) perpendicular to the deposition electrode. measured on the parallel cross-sectioned sintered deposits obtained under different EPd cell configurations, as well as the porosity,the residual porosity also results from platelet particle green and sintered density. The green relative density of all the constrained sintering, as discussed in literature. 6, 7 Since th deposits was in the 58.9-62.7% range, which is quite compara template platelets are essential for texture development, all fur. ble. After sintering, quite dense ceramics with some remaining ther investigated grades were prepared from platelet containing porosity due to constrained sintering were obtained. The den- sification of the powder matrix is significantly retarded by the suspensions. presence of large inclusions, i.e., platelets, resulting in a lower EBSD of perpendicularly cross-sectioned grades was investi- densification as reported in literature. 16. I The sintered density gated to characterize the texture. The EBSD pattern and inverse pole figure(IPF) of the above material grade are presented is proportional to the green density of the samples, as shown in ig. 6(a)and (d). The platelets are well aligned parallel to th Table 1. EPD from a stirred suspension in a vertical cell(con- deposition electrode surface, positioned at the bottom of the figuration 1)results in the highest Lotgering factor and texture picture in Fig. 6(a), revealing that the c-axis has been well- index, which indicates that the best texture was formed. The extent of texturisation is quite different for the five investigated aligned perpendicular to the surface of the deposition electrode, configurations. The mechanism of texture formation is discussed in Fig. 6(d)is large and the peak is homogeneously distributed at the edge of the IPF, proving that the prismatic planes are well ori- ented in the normal direction. The a-and b-axes are not aligned. 4. Discussion i.e., the material has no preferred in-plane orientation(a-axis or 4.1. Influence of the electric field force b-axis orientation)as indicated by the fact that the peak intensity is homogeneously distributed at the edge of the IPF. The electric field force is the driving force for powder con- In order to investigate the global sample area, X-ray pole solidation during EPD. In order to investigate the impact of the figures were used to characterize the macro-texture. The calcu- electric field force on platelet alignment, EPD from a stagnant1198 L. Zhang et al. / Journal of the European Ceramic Society 30 (2010) 1195–1202 Fig. 5. Textured alumina deposited in a horizontal cell, cross-sectioned (a) parallel and (b) perpendicular to the deposition electrode. porosity, the residual porosity also results from platelet particle constrained sintering, as discussed in literature.16,17 Since the template platelets are essential for texture development, all fur￾ther investigated grades were prepared from platelet containing suspensions. EBSD of perpendicularly cross-sectioned grades was investi￾gated to characterize the texture. The EBSD pattern and inverse pole figure (IPF) of the above material grade are presented in Fig. 6(a) and (d). The platelets are well aligned parallel to the deposition electrode surface, positioned at the bottom of the picture in Fig. 6(a), revealing that the c-axis has been well￾aligned perpendicular to the surface of the deposition electrode, as shown in Fig. 6(a). The peak intensity of the [0 0 1] IPF shown in Fig. 6(d) is large and the peak is homogeneously distributed at the edge of the IPF, proving that the prismatic planes are well ori￾ented in the normal direction. The a- and b-axes are not aligned, i.e., the material has no preferred in-plane orientation (a-axis or b-axis orientation) as indicated by the fact that the peak intensity is homogeneously distributed at the edge of the IPF. In order to investigate the global sample area, X-ray pole figures were used to characterize the macro-texture. The calcu￾lated texture index of this sample is 18.32, which implies a sharp texture formation. 3.2. Horizontal downward deposition from a flowing suspension The same suspension composition was used for EPD in the horizontal cell, shown in Fig. 2, with the deposition electrode at the bottom and suspension flowing through. The platelets in the deposit however were not well aligned as shown in the EBSD pattern of the perpendicular cross-section of the sintered ceramic (Fig. 6(b)). As shown in Fig. 6(e), the peaks are relatively weak and are not homogenously distributed implying that the pris￾matic planes are not well aligned. The corresponding X-ray pole figure confirms a very weak texturing after grain growth with a limited texture index of 1.60. 3.3. Deposition from a stagnant suspension The above results clearly show that the cell geometry is a crit￾ical factor for platelet alignment during EPD. The electric field force, gravity and hydrodynamic force applied on the platelets are believed to be the main factors influencing platelet alignment. The influence of these forces is studied using 3 additional con- figurations as summarised in Table 1. In order to investigate the electric field force effect, an upward deposition was performed in the horizontal cell without suspension flowing through (con- figuration 3). In order to investigate the gravity effect, EPD was performed from a stagnant suspension in the horizontal cell (con- figuration 4). In order to study the impact of the hydrodynamic force, the suspension is stirred comparing with stagnant suspen￾sion (configuration 5) or pumped through the cell as described in Sections 3.1 and 3.2. Table 1 summarises the Lotgering factor and texture index measured on the parallel cross-sectioned sintered deposits obtained under different EPD cell configurations, as well as the green and sintered density. The green relative density of all the deposits was in the 58.9–62.7% range, which is quite compara￾ble. After sintering, quite dense ceramics with some remaining porosity due to constrained sintering were obtained. The den￾sification of the powder matrix is significantly retarded by the presence of large inclusions, i.e., platelets, resulting in a lower densification as reported in literature.16,17 The sintered density is proportional to the green density of the samples, as shown in Table 1. EPD from a stirred suspension in a vertical cell (con- figuration 1) results in the highest Lotgering factor and texture index, which indicates that the best texture was formed. The extent of texturisation is quite different for the five investigated configurations. The mechanism of texture formation is discussed below, based on these experimental findings. 4. Discussion 4.1. Influence of the electric field force The electric field force is the driving force for powder con￾solidation during EPD. In order to investigate the impact of the electric field force on platelet alignment, EPD from a stagnant