S Novak et al. /Journal of the European Ceramic Society 28(2008)2801-2807 (a) (b) Fig. 3. SEM micrographs of deposits formed from a CTAB-stabilised suspension on a steel electrode(a and b), macroscopic view of the deposit formed on the copper electrode(c and d). As expected, a firm deposit formed on the cathode from the Dolapix is well dissociated and helps to produce dense and firm uspension with the addition of 0.5 wt. CTAB, characterised deposits by a high ZP. As illustrated in Fig 3a, the deposit contained large The above results suggest that for electrophoretic deposition deposition electrode, which led to a firm and non-porous deposit the deposits e apix and. t sions for cathodic deposition were channel-like pores due to water electrolysis, while the particles the most appropriate susp in the bulk were densely and homogeneously packed(Fig. 3b). In those containing CTAB, while for deposition on an anode, the further EPD experiments the presence of bubbles in the deposits addition of Do an increase in the pH seem to give the was prevented by placing a porous membrane in front of the best results, since they lead to a high particle-packing density in (Fig. 3c and d). By measuring the weight change during the in the deposit made by EPD increased to 67 wt% comparing to 3.3. Infiltration of Sic-fibre woven fabric the initial 25% solids in the starting suspension In the next set of experiments we explored the electrophoretic The EPD experiments using suspensions with the addition infiltration of SiC-fibre woven fabrics by SiC particles Based of PEI were less successful; no deposit was retained on the on the above results we selected the two compositions with the electrode after its removal from the suspension. In spite of the highest ZP: the suspension of positively charged particles with ZP increase, the further addition of 2 wt% of citric acid did a 0.5% CTAB addition(48 mV)and the suspension with neg- not significantly improve the deposition: the deposit was loose atively charged particles and Dolapix addition(-49mV).For and weak and, accordingly, the weight change during drying better understanding of the infiltration, the ZP of the Sic fibre revealed low solids content in the fresh deposit (54 wt %).A was also analysed, as shown in Fig 4. The as-received fibres used firm and dense deposit(64 wt % )was obtained from the suspen sion containing the 0.8%o PEI and the pH adjusted to 8 by HCl No deposit was obtained from the suspension containing citric id, which contrasts with the successful deposition in ethanol revIous In further experiments the deposit was formed on the anode 2-20 using negatively charged powder suspensions. In this case the presence of bubbles was prevented by using a Cu electrode R which consumes the oxygen formed during the electrolysis The alkaline suspension with the addition of TMA resul in a firm and dense deposit, containing 67 wt %o solids. A sim- non treated SDoss treated ilar result was obtained if the ph was adjusted to 9 by adding NaOH. In contrast, no deposit was formed from the suspen- Fig 4. Zeta-potential of non-treated (a)and (b)SDosS-treated Sit sion with Dolapix until the pH was adjusted to 9, where the function of pH(the fibres were cut and crushed for the analysed Sic fibres as a2804 S. Novak et al. / Journal of the European Ceramic Society 28 (2008) 2801–2807 Fig. 3. SEM micrographs of deposits formed from a CTAB-stabilised suspension on a steel electrode (a and b), macroscopic view of the deposit formed on the copper electrode (c and d). As expected, a firm deposit formed on the cathode from the suspension with the addition of 0.5 wt.% CTAB, characterised by a high ZP. As illustrated in Fig. 3a, the deposit contained large channel-like pores due to water electrolysis, while the particles in the bulk were densely and homogeneously packed (Fig. 3b). In further EPD experiments the presence of bubbles in the deposits was prevented by placing a porous membrane in front of the deposition electrode, which led to a firm and non-porous deposit (Fig. 3c and d). By measuring the weight change during the drying of the deposit, it was determined that the solids content in the deposit made by EPD increased to 67 wt.% comparing to the initial 25% solids in the starting suspension. The EPD experiments using suspensions with the addition of PEI were less successful; no deposit was retained on the electrode after its removal from the suspension. In spite of the ZP increase, the further addition of 2 wt.% of citric acid did not significantly improve the deposition: the deposit was loose and weak and, accordingly, the weight change during drying revealed low solids content in the fresh deposit (54 wt.%). A firm and dense deposit (64 wt.%) was obtained from the suspen￾sion containing the 0.8% PEI and the pH adjusted to 8 by HCl. No deposit was obtained from the suspension containing citric acid, which contrasts with the successful deposition in ethanol reported previously.17,18 In further experiments the deposit was formed on the anode using negatively charged powder suspensions. In this case the presence of bubbles was prevented by using a Cu electrode, which consumes the oxygen formed during the electrolysis. The alkaline suspension with the addition of TMAH resulted in a firm and dense deposit, containing 67 wt.% solids. A sim￾ilar result was obtained if the pH was adjusted to 9 by adding NaOH. In contrast, no deposit was formed from the suspen￾sion with Dolapix until the pH was adjusted to 9, where the Dolapix is well dissociated and helps to produce dense and firm deposits. The above results suggest that for electrophoretic deposition the most appropriate suspensions for cathodic deposition were those containing CTAB, while for deposition on an anode, the addition of Dolapix and an increase in the pH seem to give the best results, since they lead to a high particle-packing density in the deposits. 3.3. Infiltration of SiC-fibre woven fabrics In the next set of experiments we explored the electrophoretic infiltration of SiC-fibre woven fabrics by SiC particles. Based on the above results we selected the two compositions with the highest ZP: the suspension of positively charged particles with a 0.5% CTAB addition (48 mV) and the suspension with neg￾atively charged particles and Dolapix addition (−49 mV). For better understanding of the infiltration, the ZP of the SiC fibres was also analysed, as shown in Fig. 4. The as-received fibres used Fig. 4. Zeta-potential of non-treated (a) and (b) SDOSS-treated SiC fibres as a function of pH (the fibres were cut and crushed for the analysis)