April 2007 Constant Current EPID of Fiber-Reinforced Ceramic Composites 1065 SoY Fig 4. Cross section of a fiber/alumina green composite fabricated by electrophoretic infiltration deposition through the inter-fiber voids to form a well-infiltrated board thickness. For current > 2.0 mA, the porous board with few macro-pores r uniform, fiber/alumina covered with deposit in 60 min composites were produc a I vol% alumina susp Figure 9 tracks the voltage change during epld. at 0.3 mA at pH 4. For a large uced using a >0.3 he voltage change is almost linear with time. When the curren deposits in the preform >0.6 mA, the voltage increases to a maximum(1000 V). Figure 10 shows the deposited alumina volume over the total pore vol- ume of the porous board. The maximum deposition occurs at a (4) EPID of Al,O3 into a Model Porous Media(PE)Under urrent of 0.3 mA. After EPID for 7h, alumina powder occupies Constant Current condition 53%of the PE-board pore volume, i.e., the infiltrated alumina Figure 5 shows a pe board, infiltrated with alumina for 3 h u in the pe board pores has 53% green density, the density of ing 0.3 mA current. The interface of the board /deposited alu- a monolithic alumina green body produced by EPD mina is clear(the right side of the pe board is attached to the The deposited alumina volume percentage decreases with cathode). Alumina particles first infiltrate the inter-connected creasing current. When the current >0.6 mA, the deposited pores to deposit on the front of the cathode. They then build alumina only occupies 45% of the pore volume. Too low a cur- backwards through the pores toward the board/ suspension in- rent(0. 1 mA)requires more than 40 h to infiltrate fully. This terface, i.e, the front pores do not clog as per conductive fibers. decreases the deposit density as concurrent sedimentation occurs Figure 6 shows an alumina deposit in a 10-um pore. It is well in the porous board. filtrated with alumina Figure 7 shows a plot of deposited alumina versus depo time t(current 0.3 mA). For t<270 min, the weight gain is linear I. Discussion with time, i.e., 10 mg/min. When 1>270 min, the outer surface is (1) Analysis of the electric Field Inside a Conductive Fiber overed with deposit until fully covered Bundle Figure 8 shows the effect of current value on the pyrrole-coated eight after 60 min. The deposited-alumina weight the fiber bundle is less than one tow fiber arly below 2.0 mA if the deposit thickness is less eight tows is used. central voids are left Suspension/PE Interface board interface Electrode Position (b) Fig. 5. Porous polyethylene(PE) board infiltrated with alumina particles.through the inter-fiber voids to form a well-infiltrated matrix with few macro-pores. Similar uniform, fiber/alumina green composites were produced using a 1 vol% alumina suspension at pH 4. For a large current ( 0.3 mA/cm2 ), less alumina deposits in the preform. (4) EPID of Al2O3 into a Model Porous Media (PE) Under Constant Current Conditions Figure 5 shows a PE board, infiltrated with alumina for 3 h us￾ing 0.3 mA current. The interface of the board/deposited alu￾mina is clear (the right side of the PE board is attached to the cathode). Alumina particles first infiltrate the inter-connected pores to deposit on the front of the cathode. They then build backwards through the pores toward the board/suspension in￾terface, i.e., the front pores do not clog as per conductive fibers. Figure 6 shows an alumina deposit in a 10-mm pore. It is well infiltrated with alumina. Figure 7 shows a plot of deposited alumina versus deposition time t (current 0.3 mA). For to270 min, the weight gain is linear with time, i.e.,10 mg/min. When t4270 min, the outer surface is covered with deposit until fully covered. Figure 8 shows the effect of current value on the deposit weight after 60 min. The deposited-alumina weight increases linearly below 2.0 mA if the deposit thickness is less than the board thickness. For current 2.0 mA, the porous board is covered with deposit in 60 min. Figure 9 tracks the voltage change during EPID. At 0.3 mA, the voltage change is almost linear with time. When the current 0.6 mA, the voltage increases to a maximum (1000 V). Figure 10 shows the deposited alumina volume over the total pore vol￾ume of the porous board. The maximum deposition occurs at a current of 0.3 mA. After EPID for 7 h, alumina powder occupies 53% of the PE-board pore volume, i.e., the infiltrated alumina in the PE board pores has 53% green density, the density of a monolithic alumina green body produced by EPD. The deposited alumina volume percentage decreases with in￾creasing current. When the current 0.6 mA, the deposited alumina only occupies 45% of the pore volume. Too low a cur￾rent (0.1 mA) requires more than 40 h to infiltrate fully. This decreases the deposit density as concurrent sedimentation occurs in the porous board. IV. Discussion (1) Analysis of the Electric Field Inside a Conductive Fiber Bundle Al2O3 particles deposit well on conductive, polypyrrole-coated Nextel 720 fibers when the fiber bundle is less than one tow fiber. When a fiber bundle of eight tows is used, central voids are left Fig. 4. Cross section of a fiber/alumina green composite fabricated by electrophoretic infiltration deposition. Electrode Position Suspension/PE board interface (a) (b) Interface 2mm 200µm Fig. 5. Porous polyethylene (PE) board infiltrated with alumina particles. April 2007 Constant Current EPID of Fiber-Reinforced Ceramic Composites 1065