ELECTROPHORETIC DEPOSITION: FUNDAMENTALS AND APPLICATIONS 100 after sintering (1525oC) 1 cm 合E=1.5Vcm 一E=3.0Vcr 10 0 300 600900120015001800 distance from impregnation surface(um) Figure 9 Densification of silica green bodies as function of distance from impregnation surface for different electric field strength during EPI and silica glass samples with graded density after sintering(vacuum, 1525.C) 0,18 0,15 ≥0,12 0,09 silica glass P5 0,03 wave number(cm) 10 Silica glass/cristobalite composite with gradual decrease of cristobalite content from surface to bulk: Position sensitive characterization of 3 mm from the surface(P5) only the silica glass and subsequently sintered to fully dense and transparent spectrum was found At points P2 to P4 a superposi- silica glass tubes tion of both spectra was found with decreasing inten- Using three-dimensional shaped porous polymer sity of the cristobalite peaks with increasing distance moulds as ion-permeable deposition surface complex from surface. This shows that a graded impregnation ceramic and glass components can be produced. But was achieved, although this measurement was only a due to the high specific surface area the density of green semI-quantitative one bodies shaped of nano-particles is comparably low and high shrinkage(up to 30%)occurs during drying and sintering. To enable near-shape manufacturing shrink 4. Conclusions age had to be reduced. This was achieved by EPD of Electrophoretic deposition from aqueous suspensions mixtures of nanosized and microsized particles by the membrane method is a fast, low-cost and flexible Furthermore, Sic was electrophoretically co- shaping technique for glasses and ceramics. High depo- deposited with B4C and carbon black, as sintering ad- sition rates are reached that allow shaping of large com- ditives. Co-deposition was successfully carried out at ponents with thick walls within several seconds to min- pHIl, where all particles have a s-potential of the same utes even for nano-particles. Thus a silica green body sign, and at a pH of 7, where the carbides show a nega- with a thickness of 12 mm was deposited within 3 min tive surface charge whereas the carbon black particles (E=10 V/cm). Silica tubes of different diameter and have a positive s-potential. In both cases solid state sin- wall thickness were shaped of nanosized fumed silica tering was observed, with a better sintering behaviour 810ELECTROPHORETIC DEPOSITION: FUNDAMENTALS AND APPLICATIONS Figure 9 Densification of silica green bodies as function of distance from impregnation surface for different electric field strength during EPI and silica glass samples with graded density after sintering (vacuum, 1525◦C). Figure 10 Silica glass/cristobalite composite with gradual decrease of cristobalite content from surface to bulk: Position sensitive characterization by Raman microscopy. of 3 mm from the surface (P5) only the silica glass spectrum was found. At points P2 to P4 a superposi￾tion of both spectra was found with decreasing inten￾sity of the cristobalite peaks with increasing distance from surface. This shows that a graded impregnation was achieved, although this measurement was only a semi-quantitative one. 4. Conclusions Electrophoretic deposition from aqueous suspensions by the membrane method is a fast, low-cost and flexible shaping technique for glasses and ceramics. High depo￾sition rates are reached that allow shaping of large com￾ponents with thick walls within several seconds to min￾utes even for nano-particles. Thus a silica green body with a thickness of 12 mm was deposited within 3 min (E = 10 V/cm). Silica tubes of different diameter and wall thickness were shaped of nanosized fumed silica and subsequently sintered to fully dense and transparent silica glass tubes. Using three-dimensional shaped porous polymer moulds as ion-permeable deposition surface complex ceramic and glass components can be produced. But due to the high specific surface area the density of green bodies shaped of nano-particles is comparably low and high shrinkage (up to 30%) occurs during drying and sintering. To enable near-shape manufacturing shrink￾age had to be reduced. This was achieved by EPD of mixtures of nanosized and microsized particles. Furthermore, SiC was electrophoretically co￾deposited with B4C and carbon black, as sintering ad￾ditives. Co-deposition was successfully carried out at pH 11, where all particles have a ζ -potential of the same sign, and at a pH of 7, where the carbides show a nega￾tive surface charge whereas the carbon black particles have a positive ζ -potential. In both cases solid state sin￾tering was observed, with a better sintering behaviour 810