C. Kaya, E.G. Butler / Journal of the European Ceramic Sociery 29(2009)363-367 of 14.3 m-/g were used as the matrix materials. Alumina pow ders were first dispersed in distilled water with the additions of dispersant, liquid binder which is a water-based acrylic polymer uramax B1014 Chesham Chemicals Ltd. UK)and a mixture of boehmite(y-AlOOH) and colloidal Y,O3 as sintering aid with average particle sizes of 20 and 10 nm, respectively and magnetically stirred for 2 h followed by mechanical ball-milling Coated and with alumina balls for h and finally ultrasonication for 0.5 h. impregnated The amount of sintering aids was 2 wt %o of the total powder and Uni-directional the solid-loading of the final suspension was 85 wt %o and the oH was adjusted to be around 4(the weight ratio of boehmite to fiber bundle Y2O3 was 1: 1) Unidirectional fiber bundles extracted from eight-harness satin woven mullite fiber mats(Nextel M 720, 1500-denier yarn 3M, USA)were used as reinforcement materials. Each fiber bundle contains approximately 1500 filaments with an average diameter of 12 um. Before the extraction process, the woven fiber mats were pre-treated by desizing at 500C for I h to remove the organic protection layer from the fiber surface and then the bundles were extracted from the desized mats NdPO4 interface material was prepared by the neutral reaction of neodymium nitrate with ammonium di-hydrogen phosphate(ADPH) at room temperature. Equimolar amounts of Cylindirical Nd(NO3 )3 and AdPh were dissolved into water to make 0.25 M hollow plastic solutions. Mixing of the two solutions by vigorous stirring and tube heating was followed by filtration. The resultant gel filtrate was then dried and calcined at 1000C for 3 h to yield stoichiomet- ric NdPO4 monazite powder with an average particle size of 60nm. A 15-wt %o aqueous-based suspension was prepared by ball milling for 4 h with the pH value adjusted to be 3 2.2. Fiber coating he required number of bundles was extracted from the mat and then immersed in an ammonia-based solution consisting of an ammonium salt of polymethacrylic acid (Versical KA21, pH Allied colloids, UK)in orderto create a strong negative surface charge on the fiber surface. Surface-modified fiber bundle was Fig. 1. Schematic representation of the model mini-composites produced en dipped in NdPO4 suspension for 1 min to allow NdPO4 particles to fully cover the fibers. Coated fiber bundles were then with a diameter of 2 mm and 40 vol% fiber loading were then sintered at 600 C for O5 h to increase the adhesion between the cut for mechanical testing and microstructural observat fiber and the coating layer 2.4. Mechanical tests 2.3. Processing of mini-composite Tubular tensile and flexural test specimens with a length of Dip-coated fiber bundle is impregnated with nano-size alu- 10 cm were cut from the sintered composites. Tensile ends of mina ceramic particles by electrophoretic deposition(EPD) the specimen were fixed in tubular aluminium tabs using a poly Ising a deposition voltage of 10V for 3 min. The details of meric resin which was cured at 280C for I h in order to provide the tech nique can be found elsewhere. 7-19,23-27 Coated and a strong adhesion between the sample and aluminium tabs so electrophoretically deposited fiber bundles were then put in a that sliding of the sample from grips was prevented during ten- polymer-based tube with an inner diameter of 4 mm as shown in sile tests. Room and high temperature four-point bend tests were Fig. 1. Then a hot gun was used to heat the surface of the plastic performed on an Instron Testing machine fitted with a furnace tube up to 150C so that it shrinks and squeezes the bundles which has tungsten mesh elements enabling tests to be carried homogeneously. The specimens compacted within the plastic out at temperatures up to 1500C Specimens to be tested at tube were then removed by cutting the plastic tube and pressure- 1300C, were held at the test temperature for at least I h prior less sintered at 1200C for 2h. The sintered mini-composites the testing to allow the system to equilibrate and to ensure that364 C. Kaya, E.G. Butler / Journal of the European Ceramic Society 29 (2009) 363–367 of 14.3 m2/g were used as the matrix materials. Alumina pow￾ders were first dispersed in distilled water with the additions of dispersant, liquid binder which is a water-based acrylic polymer (Duramax B1014, Chesham Chemicals Ltd., UK) and a mixture of boehmite (-AlOOH) and colloidal Y2O3 as sintering aids with average particle sizes of 20 and 10 nm, respectively and magnetically stirred for 2 h followed by mechanical ball-milling with alumina balls for 8 h and finally ultrasonication for 0.5 h. The amount of sintering aids was 2 wt.% of the total powder and the solid-loading of the final suspension was 85 wt.% and the pH was adjusted to be around 4 (the weight ratio of boehmite to Y2O3 was 1:1). Unidirectional fiber bundles extracted from eight-harness satin woven mullite fiber mats (NextelTM 720, 1500-denier yarn, 3M, USA) were used as reinforcement materials. Each fiber bundle contains approximately 1500 filaments with an average diameter of 12m. Before the extraction process, the woven fiber mats were pre-treated by desizing at 500 ◦C for 1 h to remove the organic protection layer from the fiber surface and then the bundles were extracted from the desized mats. NdPO4 interface material was prepared by the neutral reaction of neodymium nitrate with ammonium di-hydrogen phosphate (ADPH) at room temperature. Equimolar amounts of Nd(NO3)3 and ADPH were dissolved into water to make 0.25 M solutions. Mixing of the two solutions by vigorous stirring and heating was followed by filtration. The resultant gel filtrate was then dried and calcined at 1000 ◦C for 3 h to yield stoichiomet￾ric NdPO4 monazite powder with an average particle size of 60 nm. A 15-wt.% aqueous-based suspension was prepared by ball milling for 4 h with the pH value adjusted to be 3. 2.2. Fiber coating The required number of bundles was extracted from the mat and then immersed in an ammonia-based solution, consisting of an ammonium salt of polymethacrylic acid (Versical KA21, pH: 9, Allied colloids, UK) in order to create a strong negative surface charge on the fiber surface. Surface-modified fiber bundle was then dipped in NdPO4 suspension for 1 min to allow NdPO4 particles to fully cover the fibers. Coated fiber bundles were then sintered at 600 ◦C for 0.5 h to increase the adhesion between the fiber and the coating layer. 2.3. Processing of mini-composites Dip-coated fiber bundle is impregnated with nano-size alu￾mina ceramic particles by electrophoretic deposition (EPD) using a deposition voltage of 10 V for 3 min. The details of the technique can be found elsewhere.17–19,23–27 Coated and electrophoretically deposited fiber bundles were then put in a polymer-based tube with an inner diameter of 4 mm as shown in Fig. 1. Then a hot gun was used to heat the surface of the plastic tube up to 150 ◦C so that it shrinks and squeezes the bundles homogeneously. The specimens compacted within the plastic tube were then removed by cutting the plastic tube and pressure￾less sintered at 1200 ◦C for 2 h. The sintered mini-composites Fig. 1. Schematic representation of the model mini-composites produced. with a diameter of 2 mm and 40 vol.% fiber loading were then cut for mechanical testing and microstructural observations. 2.4. Mechanical tests Tubular tensile and flexural test specimens with a length of 10 cm were cut from the sintered composites. Tensile ends of the specimen were fixed in tubular aluminium tabs using a poly￾meric resin which was cured at 280 ◦C for 1 h in order to provide a strong adhesion between the sample and aluminium tabs so that sliding of the sample from grips was prevented during ten￾sile tests. Room and high temperature four-point bend tests were performed on an Instron Testing machine fitted with a furnace which has tungsten mesh elements enabling tests to be carried out at temperatures up to 1500 ◦C. Specimens to be tested at 1300 ◦C, were held at the test temperature for at least 1 h prior the testing to allow the system to equilibrate and to ensure that