3044 Y Bao, PS. Nicholson /Journal of the European Ceramic Sociery 28(2008)3041-3048 E 的04 0.2 si Mullite Seeds PEI concentration (wt%) Fig. 6. Effect of PEl on mobility dering them the same sign. Fig. 6 illustrates the influence of PEI on the RBM-precursor-particle-mobility in ethanol. When [PEI]>0.15 wt%, all particles are positively charged. No change of particle mobility is observed for [PEI] >0.4 wt%. Fig. 7 shows the electrokinetic sonic amplitude(ESA)values for a 2.5 vol% mixed suspension of alumina, Si, MREO and mullite seeds(3Al2O3-2Si +5 wt% mullite seeds +7.5 wt %o MREO)ver us PEI concentration. The eSa value increases with Pel and plateaus at 0.3 wt%o Thus 0.5 wt% Pei was used toensure well-dispersed suspensions for the EPID process. As PEI also absorbs on the AlPO4-coated fiber surface, it renders the fibers repulsive to the particles. The fiber adsorption of PEl causes particles passing through them to be repelled as they pass, i. e, particles are"streamed Fig 8 shows the morphology of an AlPO4-coated Nextel 720 fiber-reinforced composite prepared by EPID(current density 0.07 mA/cm") pressurelessly sintered at 1300C for 2h. Sin- Fig 8. Morphology of fiber/RBM composite prepared by EPID tered fiber-reinforced composites have -25% open porosity and 25 vol% fiber Macro cracks do not occur and particles are well for 2h. It is a mixture of alumina, cristobalite and mullite, sug infiltrated into the fiber preform. After polishing, the weakly- gesting non-uniform distribution of the mREo in the matrix. bonded AlPO4 coating polished away and grooves appeared MREO promotes matrix mullite formation via low temperature around the fibers. An uncoated Nextel 720/RBM composite eutectics formed with alumina and silica. As the MREO pow was employed for matrix phase analysis due to the very similar der has high density, it also may sediment during fiber preform XRD patterns for AlPO4 and Sio2 Fig 9 is an XRD pattern for uncoated Nextel 720 Fiber/RBM composite sintered at 1300oC Mullite D SiO2 05 Fig 9. X-ray diffraction pattern of fiber/RBM composite prepared by EPID and Fig. 7. Effect of PEl on ESA of 2.5 vol% suspension sintered at1300°C3044 Y. Bao, P.S. Nicholson / Journal of the European Ceramic Society 28 (2008) 3041–3048 Fig. 6. Effect of PEI on mobility. dering them the same sign. Fig. 6 illustrates the influence of PEI on the RBM-precursor-particle-mobility in ethanol. When [PEI] >0.15 wt%, all particles are positively charged. No change of particle mobility is observed for [PEI] >0.4 wt%. Fig. 7 shows the electrokinetic sonic amplitude (ESA) values for a 2.5 vol% mixed suspension of alumina, Si, MREO and mullite seeds (3Al2O3–2Si +5 wt% mullite seeds +7.5 wt% MREO) ver￾sus PEI concentration. The ESA value increases with PEI and plateaus at [PEI] >0.3 wt%. Thus 0.5 wt% PEI was used to ensure well-dispersed suspensions for the EPID process. As PEI also absorbs on the AlPO4-coated fiber surface, it renders the fibers repulsive to the particles. The fiber adsorption of PEI causes particles passing through them to be repelled as they pass, i.e., particles are “streamed”. Fig. 8 shows the morphology of an AlPO4-coated Nextel 720 fiber-reinforced composite prepared by EPID (current density 0.07 mA/cm2) pressurelessly sintered at 1300 ◦C for 2 h. Sin￾tered fiber-reinforced composites have ∼25% open porosity and ∼25 vol% fiber. Macro cracks do not occur and particles are well infiltrated into the fiber preform. After polishing, the weakly￾bonded AlPO4 coating polished away and grooves appeared around the fibers. An uncoated Nextel 720/RBM composite was employed for matrix phase analysis due to the very similar XRD patterns for AlPO4 and SiO2. Fig. 9 is an XRD pattern for uncoated Nextel 720 Fiber/RBM composite sintered at 1300 ◦C Fig. 7. Effect of PEI on ESA of 2.5 vol% suspension. Fig. 8. Morphology of fiber/RBM composite prepared by EPID. for 2 h. It is a mixture of alumina, cristobalite and mullite, sug￾gesting non-uniform distribution of the MREO in the matrix. MREO promotes matrix mullite formation via low temperature eutectics formed with alumina and silica.11 As the MREO pow￾der has high density, it also may sediment during fiber preform Fig. 9. X-ray diffraction pattern of fiber/RBM composite prepared by EPID and sintered at 1300 ◦C