L Besra, M. Liu Progress in Materials Science 52(2007)1-61 -Zeta Potential114 Qg Fig. 8. Zeta potential and conductivity of the PZT suspension at varying pH in aqueous media [4 hence, give rise to poorer deposition results. At the alkaline range, similar phenomenon is observed but with the adsorption of oH ions in the suspension. It is, however, noted that at the alkaline range, the zeta potential measured appeared to be much lower in absolute magnitude compared to that at the acidic range. The ionic concentration not only affects the zeta potential, but is also closely related to the suspension electrical conductivity. This can be seen from Fig. 8 which shows that the electrical conductivity is low when the ionic concentration in the suspension is low. However, as the ionic concentration in the suspen sion increases, the conductivity of the suspension increases rapidly. It is found that at high ionic concentration, not only the rate of agglomeration will increase and form larger agglomerates that have lower mobility, but also the large amount of free ions in the suspen- sion may become the main current carrier and, hence, reduce the electrophoretic mobility of the particles. The conductivity of suspension is also directly related to dielectric constant of the suspending medium and it increases with increase in dielectric constant [32]. Hence the choice of the suspension parameters needs to be made judiciously for preparation of a suit- able EPD suspension. Once the parameters related to the suspension are fixed, the process parameters can be altered conveniently for attaining desired deposition. Obviously, the most dominant parameters influencing the electrophoretic deposition are the process parameters such as applied voltage, deposition time and particle concentration in the sus- pension. Invariably, high applied potential leads to higher deposition rate but care has to be taken to ensure stable current density to obtain uniform deposit. Similarly, higher deposi- tion rate is expected with increasing particle concentration and deposition time [44] 4. Kinetics of electrophoretic deposition To make EPD process commercially more viable, a knowledge of the kinetics of EPD process is necessary in order to(a)control and manipulate deposition rate, and(b) achieve flexibility in microstructural manipulation. Hamaker [1]observed a linear dependence of the deposited weight or yield of the EPD with the amount of charge passed, and proposed that the amount deposited is proportional to the concentration of the suspension, time ofhence, give rise to poorer deposition results. At the alkaline range, similar phenomenon is observed but with the adsorption of OH ions in the suspension. It is, however, noted that at the alkaline range, the zeta potential measured appeared to be much lower in absolute magnitude compared to that at the acidic range. The ionic concentration not only affects the zeta potential, but is also closely related to the suspension electrical conductivity. This can be seen from Fig. 8 which shows that the electrical conductivity is low when the ionic concentration in the suspension is low. However, as the ionic concentration in the suspen￾sion increases, the conductivity of the suspension increases rapidly. It is found that at high ionic concentration, not only the rate of agglomeration will increase and form larger agglomerates that have lower mobility, but also the large amount of free ions in the suspen￾sion may become the main current carrier and, hence, reduce the electrophoretic mobility of the particles. The conductivity of suspension is also directly related to dielectric constant of the suspending medium and it increases with increase in dielectric constant [32]. Hence the choice of the suspension parameters needs to be made judiciously for preparation of a suit￾able EPD suspension. Once the parameters related to the suspension are fixed, the process parameters can be altered conveniently for attaining desired deposition. Obviously, the most dominant parameters influencing the electrophoretic deposition are the process parameters such as applied voltage, deposition time and particle concentration in the sus￾pension. Invariably, high applied potential leads to higher deposition rate but care has to be taken to ensure stable current density to obtain uniform deposit. Similarly, higher deposi￾tion rate is expected with increasing particle concentration and deposition time [44]. 4. Kinetics of electrophoretic deposition To make EPD process commercially more viable, a knowledge of the kinetics of EPD process is necessary in order to (a) control and manipulate deposition rate, and (b) achieve flexibility in microstructural manipulation. Hamaker [1] observed a linear dependence of the deposited weight or yield of the EPD with the amount of charge passed, and proposed that the amount deposited is proportional to the concentration of the suspension, time of Fig. 8. Zeta potential and conductivity of the PZT suspension at varying pH in aqueous media [46]. 14 L. Besra, M. Liu / Progress in Materials Science 52 (2007) 1–61