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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

fraction

fraction of coarse pores. The alteration of the sintering temperature from 1100°C for TOPC20 to 1050°C for TOPC10 resulted in smaller intragranular pores in the latter. Relative Relative pore pore volume volume () 0.3 0.2 0.1 0.0 10 -1 10 0 Pore diameter (µm) /µm 121 TOPC20 TOPC10 Figure 4.28 Incremental pore size distribution of TOPC10 and TOPC20. The composition and geometry of the pore former influenced the pore size distribution. The carbon fibre pore formation in AOPF20 led to a distinct peak at a diameter of about 8 µm as shown in Figure 4.29 which represents exactly the carbon fibre diameter. Relative pore pore volume volume () 0.3 0.2 0.1 0.0 10 -1 10 0 AOPC20 AOPF20 Pore diameter (µm) /µm Figure 4.29 Incremental pore size distributions of AOPC20 and AOPF20. 10 1 10 1

As shown in Figure 4.27, the pore size distribution of the magnesia preform MOPC20 sintered at 1300°C was significantly different from that of the other ceramic preforms with the same PFA. In the metal infiltration experiments, an equal pore size distribution was targeted in order to minimize the effect of differing pore size distributions on the comparative study. In order to increase the fraction of finer pores in MOPC20, the sintering temperature was reduced to 800°C with a constant holding time of 2 h. As shown in Figure 4.30, the preform sintered at 800°C shifted the pores to finer sizes while maintaining the bimodal profile. The coarse peak reduced from around 8 µm to about 2 µm and the fine peak reduced from 1.5 to 0.2 µm. The target to reduce the small pore size and to leave the coarse pores as they were, could not be achieved as the coarse pores shifted to smaller sizes when the sintering temperature was reduced. Relative Relative pore pore volume volume () 0.3 0.2 0.1 0.0 10 -1 10 -1 1300°C 800°C 10 0 10 0 Pore diameter (µm) /µm Figure 4.30 Influence of sintering temperature on pore size distribution of MOPC20. The influence of the sintering temperature on the median pore diameter, dHg , and the specific surface area, SsHg , of the MOPC20 preforms is shown in Figure 4.31. As the sintering temperature was lowered from 1300°C to 1200°C, the median pore diameter reduced from 1.50 µm to 0.25 µm and the specific surface area increased from 0.70 m²/g to 3.78 m²/g. 122 10 1 10 1

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