L Besra, M. Liu/ Progress in Materials Science 52(2007)1-61 3. Factors influencing EPD The mechanism of EPD involve charged particles in a suspension being deposited onto n electrode under the influence of an applied electric field. Two groups of parameters determine the characteristics of this process; (i)those related to the suspension, and (ii) those related to the process including the physical parameters such as the electrical nature of the electrodes, the electrical conditions( voltage/intensity relationship, deposition time etc. ) For the EPd of particles, part of the current should be carried not only by the particles but by free ions co-existing in the suspension. Therefore the amount of deposited particle is not simply related to the current. However, the current carried by the free ions could be ignored when the amount of free ions is negligible. Indeed the amount of free ions is generally small in organic suspensions such as ketones. On the other hand, it is believed that the accumulation of anionic and cationic charge at the electrodes during electropho resis suppresses the subsequent deposition rate. However the effect of accumulated ions are negligible in the initial period The first attempt to correlate the amount of particles deposited during EPD with differ nt influencing parameters was described by Hamaker [l] and Avgustnik et al. [28] Hamakers law relates the deposit yield (w)to the electric field strength(E), the electropho retic m y (u), the surface area of the electrode(A), and the particle mass concentration in the sion(C) through the following equation w=/μ·E·A·C.dr Avgustinik's law is based upon cylindrical, coaxial, electrodes and the electrophoretic mobility has been expanded and is represented in terms of permittivity (a), the zeta poten tial ($), and the viscosity of the suspension(n) l·E·E·5 where /and a are the length and radius of the deposition electrode, respectively, b is the radius of the coaxial counter electrode(b>a) e Biesheuval and Verweij [29] improved upon these classical equations and developed ore complex model of the deposition process by considering the presence of three distinct phases namely (i) a solid phase(the deposit), (ii)a suspension phase, and (iii)a phase con- taining little or no solid particles. The deposit phase and the particle-free liquid phase both grow at the expense of the suspension phase. By considering the movement of the bound ary between the deposit and the suspension phase with time along with the continuity equation and expression for velocity of particles in the suspension, Biesheuval and Verweij [29]derived the following equation based on that of Avgustinik et al. [28]: 2·兀·H·l·E·Cdφ where s and d are the volumetric concentration of particles in suspension and deposit respectively, Cd is the mass concentration of particles in the deposit, u is the electropho- retic mobility (=sc/6n)3. Factors influencing EPD The mechanism of EPD involve charged particles in a suspension being deposited onto an electrode under the influence of an applied electric field. Two groups of parameters determine the characteristics of this process; (i) those related to the suspension, and (ii) those related to the process including the physical parameters such as the electrical nature of the electrodes, the electrical conditions (voltage/intensity relationship, deposition time, etc.). For the EPD of particles, part of the current should be carried not only by the charged particles but by free ions co-existing in the suspension. Therefore the amount of deposited particle is not simply related to the current. However, the current carried by the free ions could be ignored when the amount of free ions is negligible. Indeed the amount of free ions is generally small in organic suspensions such as ketones. On the other hand, it is believed that the accumulation of anionic and cationic charge at the electrodes during electropho￾resis suppresses the subsequent deposition rate. However the effect of accumulated ions are negligible in the initial period. The first attempt to correlate the amount of particles deposited during EPD with differ￾ent influencing parameters was described by Hamaker [1] and Avgustnik et al. [28] Hamakers law relates the deposit yield (w) to the electric field strength (E), the electropho￾retic mobility (l), the surface area of the electrode (A), and the particle mass concentration in the suspension (C) through the following equation: w ¼ Z t2 t1 l E A C dt ð1Þ Avgustinik’s law is based upon cylindrical, coaxial, electrodes and the electrophoretic mobility has been expanded and is represented in terms of permittivity (e), the zeta poten￾tial (n), and the viscosity of the suspension (g) w ¼ l E e n C t 3 lnða=bÞ g ð2Þ where l and a are the length and radius of the deposition electrode, respectively, b is the radius of the coaxial counter electrode (b > a). Biesheuval and Verweij [29] improved upon these classical equations and developed more complex model of the deposition process by considering the presence of three distinct phases namely (i) a solid phase (the deposit), (ii) a suspension phase, and (iii) a phase con￾taining little or no solid particles. The deposit phase and the particle-free liquid phase both grow at the expense of the suspension phase. By considering the movement of the bound￾ary between the deposit and the suspension phase with time along with the continuity equation and expression for velocity of particles in the suspension, Biesheuval and Verweij [29] derived the following equation based on that of Avgustinik et al. [28]: w ¼ 2 p l l E Cd lnða=bÞ /s /d /s t ð3Þ where /s and /d are the volumetric concentration of particles in suspension and deposit, respectively, Cd is the mass concentration of particles in the deposit, l is the electropho￾retic mobility (=en/6pg). L. Besra, M. Liu / Progress in Materials Science 52 (2007) 1–61 5