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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

Specific permeability

Specific permeability KK(m²) s / m² S Figure 4.37 Permeability of the preforms parallel (KSP) and perpendicular (KSI) to the pressing direction of the initial green part, respectively. The following permeability measurements were performed using a water pressure of 0.1 MPa, as this was a compromise between keeping preform integrity and a high volume flow, enabling short measuring times. The specific permeability of the preforms was measured perpendicular (KSI) and parallel (KSP) to the green part pressing direction. Ratio Ratio K / K () SI SI / K SP SP 1x10 -12 1x10 -13 1x10 -14 5 4 3 2 1 0 parallel perpendicular AOPC20 AOPF20 AGPC15 TOPC10 TOPC20 MOPC20 AODY30 FATO K SP K SP K SI AOPC20 AOPF20 AGPC15 TOPC10 TOPC20 MOPC20 AODY30 FATO Figure 4.38 Ratio of specific permeabilities in the preforms. K SI 131

Figure 4.37 shows that the TOPC20 preform showed the highest permeability (6.4x10 -13 m²) which was in the perpendicular direction, and the MOPC20 preform the lowest (1.6x10 -14 m²), which was in the parallel direction. Apart from the procured preforms AODY30 and FATO, all the preforms tested were made using pore forming additives (PFA) and all had a higher permeability in the perpendicular direction than in the parallel direction. The anisotropy in permeability was calculated as the ratio KSI to KSP and values are shown in Figure 4.38. The ratios for the preforms fabricated with PFA lay between 1.5 for AOPC20 (low anisotropy) and 4 for TOPC20 (high anisotropy). The permeability of AODY30 and FATO lay between 2.0·10 -13 m² and 4.2·10 -13 m² which was similar to the values reported for AOPC20 and TOPC20. In contrast to the preforms formed with PFA, there was no significant anisotropy, as indicated by ratio values close to unity in Figure 4.38. Table 4.4 gives an overview of the specific permeability of the preforms in the different directions and the ratio between them. Table 4.4 Evaluated preform permeability parameters KSI and Ksp and their ratios. Permeability 132 Ratio KSI KSP KSI/KSP 10 -14 m² 10 -14 m² AOPC20 23.7 15.9 1.5 AOPF20 19.0 7.4 2.6 AGPC15 19.3 6.7 2.9 TOPC10 13.1 7.0 1.9 TOPC20 64.2 16.4 3.9 MOPC20 4.8 1.6 3.0 AODY30 19.7 23.4 0.8 FATO 41.9 37.3 1.1

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