February 2006 AlPO, Coating on Alumina Mullite Fibers Q 5 um (c) (um) (c)element P, ( d)element Al Fig. 11. Cross section and energy dispersive spectroscopy(EDS) examination of the aluminium orthophosphate- coated fibers(embedded in epoxy) Scanning electron microscopy images(a, b); EDS line scanning for element P(c) and Al(d phous stoichiometric AlPO4 precipitates. The latter has a nar- tic phase Al2O3 /mullite fiber bundles, pre-treated with cationic row particle size distribution of mean size 30-100 nm when polyelectrolyte to induce a positive surface charge have been [AP]=0.05-01M. The IEP of this material is pH <4.7. dipped in the AlPOA sol at pH 7.5(negative particle surface morphous AlPO4 crystallizes to"tridymitic"and"cristobal- charge), and a uniform and continuous coating formed by tic" phases at 1100C, gradually changing to a 100% cristobal- lectrostatic attraction. AlPOa-coated, fiber-reinforced AL,O3 Fig 12. Fracture surface of AlPOa coated fiber/Al2O3 composite, hot-pressed at 1250C for I h.phous stoichiometric AlPO4 precipitates. The latter has a nar￾row particle size distribution of mean size 30–100 nm when [Al31] 5 0.05–0.1M. The IEP of this material is pH B4.7. Amorphous AlPO4 crystallizes to ‘‘tridymitic’’ and ‘‘cristobali￾tic’’ phases at 11001C, gradually changing to a 100% cristobali￾tic phase. Al2O3/mullite fiber bundles, pre-treated with cationic polyelectrolyte to induce a positive surface charge, have been dipped in the AlPO4 sol at pH B7.5 (negative particle surface charge), and a uniform and continuous coating formed by electrostatic attraction. AlPO4-coated, fiber-reinforced Al2O3 Fig. 11. Cross section and energy dispersive spectroscopy (EDS) examination of the aluminium orthophosphate-coated fibers (embedded in epoxy). Scanning electron microscopy images (a, b); EDS line scanning for element P (c) and Al (d). Fig. 12. Fracture surface of AlPO4 coated fiber/Al2O3 composite, hot-pressed at 12501C for 1 h. February 2006 AlPO4 Coating on Alumina/Mullite Fibers 469