1360 . Corni et al /Journal of the European Ceramic Society 28(2008)1353-136 10 ur b Fig. 7. SEM micrographs of a Nextel M 720 fibre mat infiltrated with alumina nano particles, (a)shows the complete and homogeneous infiltration of the NextelTM 720 fibre mat with alumina and(b)shows the high "green"density of the alumina matrix by Stoll et al. 169(Published with permission of Elsevier. presented a significant increase in hardness and wear resis- fibres employed can be both electrically conductive(e.g. Sic tance compared with pure nickel coatings or stainless steel. Nicalon, carbon)and non-conductive(e.g. alumina or mullite). Wang et al. 46 deposited Co-YSZ/HA nanocomposite coatings When the fibres are non-conductive, the fibre weave is placed on Ti substrate using the combination of electrocodeposition in front of the deposition electrode, the ceramic deposit devel and electrophoretic deposition. They demonstrated that the ops on the electrode and grows around and through the fibre Co-YSZ/HA composite coatings exhibited better mechanical mat.8, 168 Stoll et al. 69 fabricated alumina-alumina CMCs by properties than nano-HA single coatings. Moreover the Co-YSZ means of EPD from a suspension of Al2 O3 nanoparticles using interlayer reduced the mismatch of the thermal expansion coef- Nextel-type(alumina) fibres. The same composite(alumina ficients between HA and Ti and the adhesive strength of the particles and Nextel-type fibres)was investigated recently by composite coating and Ti substrate was higher than that of nano- Bao and Nicholson. In this particular system it was shown that HA single coatings on Ti substrate. Pang and Zhitomirsky in order to be able to infiltrate fibre mats by EPD it is fundam deposited by EPD composite hydroxyapatite-chitosan coatings tal that both the suspended particles and the fibres have the same on stainless steel substrates. They observed that the addition polarity. In these conditions, when the particles approach the of chitosan to the HA suspension promoted the deposition of fibre mat repulsion forces take place between them, the mag- HA. Moreover, from the analysis of the coatings it was demon- nitude of these forces depends on the relative distance between strated that changing the concentration of the two chemicals particles and fibres. Due to the applied external electrical field, in the suspension resulted in a variation in the coating com- each charged particle is attracted to the fibre mat, which is fixed position. These composite coatings were adherent and uniform to the electrode, but, at the same time, the particles are repelled with increased corrosion protection properties. Louh et al. 67 before they can reach the fibre surfaces(coagulation point)due deposited by EPD nanosized platinum/carbon nanocatalysts and to the charge on the fibres. It has been hypothesised that under Nafion solution on carbon-based substrates for applications in the effect of the repulsive forces due to the surrounding fibres, proton exchange membrane fuel cells(PEMFCs). They obtained the particles follow the path with the fewest possible obstacles a uniform distribution of catalyst and Nafionon the electrodes, until reaching the next interstice between adjacent fibres. There in fact the Pt/C nanopowders covered the whole carbon fibre fore, when the particles reach the electrode or the surface of surface and also infiltrated into the gaps and voids between previously deposited particles, they cannot move further and consequently the electrophoretic ceramic deposit grows with a EPD has been also employed for the production of fibre high particle packing density. Fig. 7(a)and(b) shows the unifor reinforced ceramic and glass matrix composites with a variety mity of the infiltration of alumina particles in the Nextel -type of ceramic matrices and fibres. 168 This method is particu-(alumina)fibre mat and the high level of packing achieved by the larly attractive for the production of CMCs with complex fibre electrophoretically deposited alumina particles. 69 Conversely, structures(e. g. 2D fibre fabrics)as reinforcement because it if the fibre and particles exhibit opposite surface charge, coa allows adequate infiltration of ceramic(nano) particles into the lation is expected on the first layer of fibres encountered by the inter-fibre spaces, which would be difficult to be achieved by travelling particles. In this case a deposit on the outer fibre layer other routes. 68 Additionally, it should be emphasised that the will block the movement of the particles towards the interior1360 I. Corni et al. / Journal of the European Ceramic Society 28 (2008) 1353–1367 Fig. 7. SEM micrographs of a NextelTM 720 fibre mat infiltrated with alumina nano particles, (a) shows the complete and homogeneous infiltration of the NextelTM 720 fibre mat with alumina and (b) shows the high “green” density of the alumina matrix by Stoll et al.169 (Published with permission of Elsevier.) presented a significant increase in hardness and wear resis￾tance compared with pure nickel coatings or stainless steel.165 Wang et al.146 deposited Co-YSZ/HA nanocomposite coatings on Ti substrate using the combination of electrocodeposition and electrophoretic deposition. They demonstrated that the Co-YSZ/HA composite coatings exhibited better mechanical properties than nano-HA single coatings. Moreover the Co-YSZ interlayer reduced the mismatch of the thermal expansion coef- ficients between HA and Ti and the adhesive strength of the composite coating and Ti substrate was higher than that of nano￾HA single coatings on Ti substrate. Pang and Zhitomirsky166 deposited by EPD composite hydroxyapatite-chitosan coatings on stainless steel substrates. They observed that the addition of chitosan to the HA suspension promoted the deposition of HA. Moreover, from the analysis of the coatings it was demon￾strated that changing the concentration of the two chemicals in the suspension resulted in a variation in the coating com￾position. These composite coatings were adherent and uniform with increased corrosion protection properties. Louh et al.167 deposited by EPD nanosized platinum/carbon nanocatalysts and Nafion® solution on carbon-based substrates for applications in proton exchange membrane fuel cells (PEMFCs). They obtained a uniform distribution of catalyst and Nafion® on the electrodes, in fact the Pt/C nanopowders covered the whole carbon fibre surface and also infiltrated into the gaps and voids between them. EPD has been also employed for the production of fibre reinforced ceramic and glass matrix composites with a variety of ceramic matrices and fibres.8,168 This method is particu￾larly attractive for the production of CMCs with complex fibre structures (e.g. 2D fibre fabrics) as reinforcement because it allows adequate infiltration of ceramic (nano) particles into the inter-fibre spaces, which would be difficult to be achieved by other routes.168 Additionally, it should be emphasised that the fibres employed can be both electrically conductive (e.g. SiC Nicalon®, carbon) and non-conductive (e.g. alumina or mullite). When the fibres are non-conductive, the fibre weave is placed in front of the deposition electrode, the ceramic deposit devel￾ops on the electrode and grows around and through the fibre mat.8,168 Stoll et al.169 fabricated alumina–alumina CMCs by means of EPD from a suspension of Al2O3 nanoparticles using Nextel®-type (alumina) fibres. The same composite (alumina particles and Nextel®-type fibres) was investigated recently by Bao and Nicholson.170 In this particular system it was shown that in order to be able to infiltrate fibre mats by EPD it is fundamen￾tal that both the suspended particles and the fibres have the same polarity.169 In these conditions, when the particles approach the fibre mat repulsion forces take place between them, the mag￾nitude of these forces depends on the relative distance between particles and fibres. Due to the applied external electrical field, each charged particle is attracted to the fibre mat, which is fixed to the electrode, but, at the same time, the particles are repelled before they can reach the fibre surfaces (coagulation point) due to the charge on the fibres. It has been hypothesised that under the effect of the repulsive forces due to the surrounding fibres, the particles follow the path with the fewest possible obstacles until reaching the next interstice between adjacent fibres. There￾fore, when the particles reach the electrode or the surface of previously deposited particles, they cannot move further and consequently the electrophoretic ceramic deposit grows with a high particle packing density. Fig. 7(a) and (b) shows the unifor￾mity of the infiltration of alumina particles in the Nextel®-type (alumina) fibre mat and the high level of packing achieved by the electrophoretically deposited alumina particles.169 Conversely, if the fibre and particles exhibit opposite surface charge, coagu￾lation is expected on the first layer of fibres encountered by the travelling particles. In this case a deposit on the outer fibre layer will block the movement of the particles towards the interior