L Besra, M. Liu Progress in Materials Science 52(2007)1-61 Table 2 Physical properties of solvents [33] Solvents Viscosity (cP)=10-'Nsm Relative dielectric constant 0.557 32.63 Ethanol 885 24.55 20.33 Ethylene glycol .265 0.3087 dielectric constant is generally the product of relative dielectric constant and dielectric con- stant in vacuum. Table 2 shows physical properties such as viscosity and relative dielectric constant of some solvents [33]. 3.1.3. Conductivity of suspension Ferrari and Moreno [34], after a careful study proposed that the conductivity of the sus- pension is a key factor and needs to be taken into account in EPD experiments. It has been pointed out that if the suspension is too conductive, particle motion is very low, and if the suspension is too resistive, the particles charge electronically and the stability is lost. They observed increase in conductivity of the suspension with both temperature and with poly electrolyte(dispersant)concentration; but not all conductivity values were found useful for electrophoretic deposition. They found the existence of a narrow band of conductivity range at varying dispersant dosage and temperature, in which the deposit is formed. Con ductivity out of this region are not suitable for EPD, limiting the forming possibilities This suitable region of conductivity is however expected to be different for different sys- tems. The margin of conductivity region suitable for EPD, however can be increased by the applied current assuring the success of the EPd process [35] 3. 1.4. Viscosity of suspension In casting processes, the main controlling parameter is the viscosity. Rheological mea surements on concentrated slips give us a good idea about the optimum dispersing state when adding dispersants. In EPD process, the solid loading is very low and the viscosity cannot be used to evaluate the dispersion state [34, 35]. But the desired properties in the suspension vehicle are low viscosity, high dielectric constant and low conductivity 3.1.5. Zeta potential Fe the zeta potential of particles is a key factor in the electrophoretic deposition process It is imperative to achieve a high and uniform surface charge of the suspended particles. It plays a role in: (i)stabilization of the suspension by determining the intensity of repulsive interaction between particles, (ii) determining the direction and migration velocity of particle during EPD, (ii) determining the green density of the deposit. The overall stability of a system depends on the interaction between individual particles in the suspension. Two mechanisms affect this interaction which are due to electrostatic and van der waals forces The probability of coagulation of a disperse system depends on the interaction energ resulting from this forces and will be dealt with in detail later. a high electrostatdielectric constant is generally the product of relative dielectric constant and dielectric con￾stant in vacuum. Table 2 shows physical properties such as viscosity and relative dielectric constant of some solvents [33]. 3.1.3. Conductivity of suspension Ferrari and Moreno [34], after a careful study proposed that the conductivity of the sus￾pension is a key factor and needs to be taken into account in EPD experiments. It has been pointed out that if the suspension is too conductive, particle motion is very low, and if the suspension is too resistive, the particles charge electronically and the stability is lost. They observed increase in conductivity of the suspension with both temperature and with poly￾electrolyte (dispersant) concentration; but not all conductivity values were found useful for electrophoretic deposition. They found the existence of a narrow band of conductivity range at varying dispersant dosage and temperature, in which the deposit is formed. Con￾ductivity out of this region are not suitable for EPD, limiting the forming possibilities. This suitable region of conductivity is however expected to be different for different sys￾tems. The margin of conductivity region suitable for EPD, however can be increased by the applied current assuring the success of the EPD process [35]. 3.1.4. Viscosity of suspension In casting processes, the main controlling parameter is the viscosity. Rheological mea￾surements on concentrated slips give us a good idea about the optimum dispersing state when adding dispersants. In EPD process, the solid loading is very low and the viscosity cannot be used to evaluate the dispersion state [34,35]. But the desired properties in the suspension vehicle are low viscosity, high dielectric constant and low conductivity. 3.1.5. Zeta potential The zeta potential of particles is a key factor in the electrophoretic deposition process. It is imperative to achieve a high and uniform surface charge of the suspended particles. It plays a role in: (i) stabilization of the suspension by determining the intensity of repulsive interaction between particles, (ii) determining the direction and migration velocity of particle during EPD, (iii) determining the green density of the deposit. The overall stability of a system depends on the interaction between individual particles in the suspension. Two mechanisms affect this interaction, which are due to electrostatic and van der Waals forces. The probability of coagulation of a disperse system depends on the interaction energy resulting from this forces, and will be dealt with in detail later. A high electrostatic Table 2 Physical properties of solvents [33] Solvents Viscosity (cP) = 103 Nsm2 Relative dielectric constant Methanol 0.557 32.63 Ethanol 1.0885 24.55 n-Propanol 1.9365 20.33 Iso-propanol 2.0439 19.92 n-Butanol 2.5875 17.51 Ethylene glycol 16.265 37.7 Acetone 0.3087 20.7 Acetylacetone 1.09 25.7 8 L. Besra, M. Liu / Progress in Materials Science 52 (2007) 1–61