L Besra, M. Liu/Progress in Materials Science 52(2007)1-61 2000 4000 6000 Time(sec) Fig 9. Schematic of EPD kinetics [47] deposition, surface area of deposit, and the electric field. EPD can be conducted under constant current or constant voltage mode with either constant or changing concentration ( decreasing concentration of suspension) with deposition time. Sarkar et al. [47] demon strated the kinetic aspects of EPD through schematic plots(Fig. 9) of deposit weight against time of deposition for four possible deposition conditions: curve A(constant-cur- rent and constant-suspension concentration), curve B(constant-current but decreasing suspension concentration ), curve C(constant-voltage and constant-suspension concentra tion)and curve D(constant-voltage but decreasing suspension concentration). Except curve a where the rate of deposition is constant with time, the rate of deposition decreases asymptotically with deposition time in either curve B, C, or D. After allowing for sufficient deposition time, the final yield and rate of deposition are highest in curve A, followed by curve B, C, and D, respectively. The effect of decreasing suspension concentration on the reduction of the final yield and rate of deposition is obvious during either constant-current (curves A and B)or constant-voltage curve C and D) EPD. Comparison of curve A(con stant-current)and curve C(constant-voltage) clearly reveals that even if the suspension concentration is kept constant during deposition in both of them, (a) the rate of deposition was constant in curve a while it decreased asymptotically with time in curve C and(b) final yield was considerably higher in curve A than that in curve C. Thus the deviation of curve A from curve C is not due to decreasing suspension concentration but is due to a decrease of particle velocity as a function of deposition time. Such decrease in particle velocity during constant-voltage EPD is due to the fact that deposited mass acts as shielding effect and has higher electrical resistance than the suspension from which depo- electrical driving force or voltage per unit length of suspension decreases with ti able sition takes place. Consequently, as the deposit grows with deposition time, the avail 5. Role of polymer binders in EPD Polymer binders are common additives in ceramic processing. The EPD processing employs binder only seldom or minimal. The role of binders in EPD processing isdeposition, surface area of deposit, and the electric field. EPD can be conducted under constant current or constant voltage mode with either constant or changing concentration (decreasing concentration of suspension) with deposition time. Sarkar et al. [47] demon￾strated the kinetic aspects of EPD through schematic plots (Fig. 9) of deposit weight against time of deposition for four possible deposition conditions: curve A (constant-cur￾rent and constant-suspension concentration), curve B (constant-current but decreasing suspension concentration), curve C (constant-voltage and constant-suspension concentra￾tion) and curve D (constant-voltage but decreasing suspension concentration). Except in curve A where the rate of deposition is constant with time, the rate of deposition decreases asymptotically with deposition time in either curve B, C, or D. After allowing for sufficient deposition time, the final yield and rate of deposition are highest in curve A, followed by curve B, C, and D, respectively. The effect of decreasing suspension concentration on the reduction of the final yield and rate of deposition is obvious during either constant-current (curves A and B) or constant-voltage curve C and D) EPD. Comparison of curve A (con￾stant-current) and curve C (constant-voltage) clearly reveals that even if the suspension concentration is kept constant during deposition in both of them, (a) the rate of deposition was constant in curve A while it decreased asymptotically with time in curve C and (b) final yield was considerably higher in curve A than that in curve C. Thus the deviation of curve A from curve C is not due to decreasing suspension concentration but is due to a decrease of particle velocity as a function of deposition time. Such decrease in particle velocity during constant-voltage EPD is due to the fact that deposited mass acts as a shielding effect and has higher electrical resistance than the suspension from which depo￾sition takes place. Consequently, as the deposit grows with deposition time, the available electrical driving force or voltage per unit length of suspension decreases with time. 5. Role of polymer binders in EPD Polymer binders are common additives in ceramic processing. The EPD processing employs binder only seldom or minimal. The role of binders in EPD processing is Fig. 9. Schematic of EPD kinetics [47]. L. Besra, M. Liu / Progress in Materials Science 52 (2007) 1–61 15