ELECTROPHORETIC DEPOSITION: FUNDAMENTALS AND APPLICATIONS NIVERSITAT Lahrturl fu 40 mm Figure 4 Silica tubes(green state) shaped by EPD from an aqueous suspension of nanosized fumed silica(OX50)and silica glass tube after sintering complex components can be shaped fast and with out- particles occurs during shaping because this can result standing quality in inhomogeneous sintering behaviour and distortion of the component. Therefore, EPD seems to be a pror ing shaping technique for such powder mixtures, be- 3.1. Near shape manufacturing cause deposition rate is independent from particle size of complex-shaped glasses and (cp Fig. 2). The process was successfully used for shap. ceramics by EPD of powder mixtures ing of silica glass components[27] and within the scope Due to the high surface area of nano-particles the solids of this work adapted to ceramic materials. As shown in content of suspensions is limited(about 60 wt% in case Fig. 2 nanosized zirconia can be deposited very fast by of OX50) and so is the green density (up to 50%TD) EPD. But again only low green densities(<35%TD) [25]. The low green density results in a high shrink- can be reached due to the high surface area of the nano- age during drying and sintering of about 15 to 30% particles. This low green density results in a very high (OX50). Thus sophisticated process control is neces- shrinkage during sintering(M30%)and leads to the fo sary for larger and more complex-shaped components. mation of micro cracks. Thus the maximum densit This makes near-shape manufacturing very compli- reached is app. 96%TD at 1400oC [23]. By combin- cated. One possible solution is to increase green density ing nanosized powders with micrometer powders green significantly. This can be achieved by combining pow- density could be increased significantly and shrinkage ders with distinctly different particle size distribution, could be minimized(<12%). No particle separation like mixtures of nanosized and microsized particles. It is due to the different sizes was observed within the de most important that no size dependent separation of the posit. Fig. 5 shows a porous polymer mould that was mm 2 40 mm Figure 5 Porous polymer mould and sintered zirconia component shaped by EPD(membrane method) from an aqueous suspension ofELECTROPHORETIC DEPOSITION: FUNDAMENTALS AND APPLICATIONS Figure 4 Silica tubes (green state) shaped by EPD from an aqueous suspension of nanosized fumed silica (OX50) and silica glass tube after sintering (1320◦C). complex components can be shaped fast and with out￾standing quality. 3.1. Near shape manufacturing of complex-shaped glasses and ceramics by EPD of powder mixtures Due to the high surface area of nano-particles the solids content of suspensions is limited (about 60 wt% in case of OX50) and so is the green density (up to 50%TD) [25]. The low green density results in a high shrink￾age during drying and sintering of about 15 to 30% (OX50). Thus sophisticated process control is neces￾sary for larger and more complex-shaped components. This makes near-shape manufacturing very compli￾cated. One possible solution is to increase green density significantly. This can be achieved by combining pow￾ders with distinctly different particle size distribution, like mixtures of nanosized and microsized particles. It is most important that no size dependent separation of the Figure 5 Porous polymer mould and sintered zirconia component shaped by EPD (membrane method) from an aqueous suspension of nano- and microsized zirconia. particles occurs during shaping because this can result in inhomogeneous sintering behaviour and distortion of the component. Therefore, EPD seems to be a promis￾ing shaping technique for such powder mixtures, be￾cause deposition rate is independent from particle size (cp. Fig. 2). The process was successfully used for shap￾ing of silica glass components [27] and within the scope of this work adapted to ceramic materials. As shown in Fig. 2 nanosized zirconia can be deposited very fast by EPD. But again only low green densities (<35%TD) can be reached due to the high surface area of the nano￾particles. This low green density results in a very high shrinkage during sintering (≈30%) and leads to the for￾mation of micro cracks. Thus the maximum density reached is app. 96%TD at 1400◦C [23]. By combin￾ing nanosized powders with micrometer powders green density could be increased significantly and shrinkage could be minimized (<12%). No particle separation due to the different sizes was observed within the de￾posit. Fig. 5 shows a porous polymer mould that was 807