W Li, Z.H. Chen /Ceramics International 35(2009)747-753 COpm 03 sum I5pm Bundle 0.5pm Bundle #:, 5从m Fig. 8. Longitudinal cross-section of 3D-CdSiC at the initial fabrication by 6. PSD curves of the partially densified (after only 3 PIP recycles, 3 PIP) SEM Symbol A represents the pore chamber at the surface, B is the inside one nished 3D-C/SiC by MIP. C and D are both channels between bundles and d leads to the outside of sample directly the first, which is opposite to the finished one. The critical sizes of the second peak are 40 um and 5 um, and the top point specimens are, the weaker this form becomes. At 14th PIP, it locates at 9 m, which are all higher than those of the finished has become too faint to distinguish. One speculation about this (20 um, 0.1 um and 1.5 um). Apparently, at the beginning of splitting is that 4-5 um is the dividing line of the channels size fabrication, the densification of 3D-C / Sic has not been very and the chamber's, i.e., the intrusion volume among 20-4 um high yet, and the inside pores(chambers, channels) are still belongs to channels, while the one among 40.1 um belongs rge, due to the low percentage of the matrix filling. For the chambers being shielded, actually. According to this nstance,in Fig. 8, channel C links the exposed and inside assumption, in Table 1, the pores above 0. 1 um are separated hambers, whose smallest size reaches as high as 50 p into three categories, and their contents' evolution is presented Reasonably, the predominant content of 2nd peak can be also. It is clear that the channels'volumes are lower than those attributed to the summed volumes of the channels and they of the shielded chambers and only amount to approximately shielded chambers, which even exceeds the volumes of the one third of the latters. Both volumes of the channels(20- exposed chambers. With the fabrication continues, each kind of 4 um) and the shielded chambers (4-0. 1 um) decrease with pores reduces in both sizes and contents(Fig. 7), and the fabrication proceeding, but their volume ratio is maintained. aforementioned two peaks' heights and areas decrease However, the volume variations of the uncovered large simultaneously, the critical peaks sizes move towards the chambers(>20 um) are not so regular, which is attributed low level and have become stable since now. Moreover, at about to the heterogeneity of the specimens'surfaces derived from the 4-5 um, the PSD curves of specimens after 7-10 PIP cycles random slicing of the samples. The 3D-C /SiC after 14 PIP (7-10 PIP specimens)all present a weak fluctuation, splitting cycles were characterized twice, the second measureme the peak among 20-0. 1 um into two. And the denser the includes the additional re-injection and re-extrusion of Hg These characterizations have good reproducibility among 20- 0 I um, which indicates the reliability and precision of MIP Table 1 Contents of pores with different sizes from mercury intrusion data of 3D-CfSiC at different fabrication stages E0.08 Pore volumes(ml/g) >20pm 204um 0.0186 0.04 8 PIP 00118 10 PIP 12 000 14 PIP-2-2nd 0.0594 0.00464 Diameter(A) the no. 1 MIP measurement Fig. 7. Evolution of PSD of partially densified 3D-C/SiC with the fabrication primary intrusion of the no. 2 measurement. continuing(from 7 to 14 PIP cycles). injection of the no. 2 measurementhe first, which is opposite to the finished one. The critical sizes of the second peak are 40 mm and 5 mm, and the top point locates at 9 mm, which are all higher than those of the finished (20 mm, 0.1 mm and 1.5 mm). Apparently, at the beginning of fabrication, the densification of 3D-Cf/SiC has not been very high yet, and the inside pores (chambers, channels) are still large, due to the low percentage of the matrix filling. For instance, in Fig. 8, channel C links the exposed and inside chambers, whose smallest size reaches as high as 50 mm. Reasonably, the predominant content of 2nd peak can be attributed to the summed volumes of the channels and they shielded chambers, which even exceeds the volumes of the exposed chambers. With the fabrication continues, each kind of pores reduces in both sizes and contents (Fig. 7), and the aforementioned two peaks’ heights and areas decrease simultaneously, the critical peaks’ sizes move towards the low level and have become stable since now. Moreover, at about 4–5 mm, the PSD curves of specimens after 7–10 PIP cycles (7–10 PIP specimens) all present a weak fluctuation, splitting the peak among 20–0.1 mm into two. And the denser the specimens are, the weaker this form becomes. At 14th PIP, it has become too faint to distinguish. One speculation about this splitting is that 4–5 mm is the dividing line of the channel’s size and the chamber’s, i.e., the intrusion volume among 20–4 mm belongs to channels, while the one among 4–0.1 mm belongs to the chambers being shielded, actually. According to this assumption, in Table 1, the pores above 0.1 mm are separated into three categories, and their contents’ evolution is presented also. It is clear that the channels’ volumes are lower than those of the shielded chambers and only amount to approximately one third of the latter’s. Both volumes of the channels (20– 4 mm) and the shielded chambers (4–0.1 mm) decrease with fabrication proceeding, but their volume ratio is maintained. However, the volume variations of the uncovered large chambers (>20 mm) are not so regular, which is attributed to the heterogeneity of the specimens’ surfaces derived from the random slicing of the samples. The 3D-Cf/SiC after 14 PIP cycles were characterized twice, the second measurement includes the additional re-injection and re-extrusion of Hg. These characterizations have good reproducibility among 20– 0.1 mm, which indicates the reliability and precision of MIP results. Fig. 6. PSD curves of the partially densified (after only 3 PIP recycles, 3 PIP) and finished 3D-Cf/SiC by MIP. Fig. 7. Evolution of PSD of partially densified 3D-Cf/SiC with the fabrication continuing (from 7 to 14 PIP cycles). Fig. 8. Longitudinal cross-section of 3D-Cf/SiC at the initial fabrication by SEM. Symbol A represents the pore chamber at the surface, B is the inside one, C and D are both channels between bundles, and D leads to the outside of sample directly. Table 1 Contents of pores with different sizes from mercury intrusion data of 3D-Cf/SiC at different fabrication stages Stage Pore volumes (ml/g) >20 mm 20–4 mm 4–0.1 mm 7 PIP 0.0445 0.0186 0.0299 8 PIP 0.0613 0.0118 0.0314 10 PIP 0.0293 0.0124 0.0318 12 PIP 0.0261 0.00760 0.0234 14 PIP-1a 0.0217 0.00610 0.0220 14 PIP-2-1stb 0.0597 0.00610 0.0213 14 PIP-2-2ndc 0.0594 0.00464 0.00683 a the no. 1 MIP measurement. b primary intrusion of the no. 2 measurement. c re-injection of the no. 2 measurement. W. Li, Z.H. Chen / Ceramics International 35 (2009) 747–753 751