J Mater sci(2006041:8093-8100 8095 Fig 2(a)-SEM micrograph of um-SiC, (b)-TEM powder, (c),(d)-HRTEM particle in um-SiC and nano- SiC powders;(e),(f-EDX and bulk particle in um-SiC 650 nm 2n In order to better understand the process, suspen- deposit (i.e, before drying) was found to contain only sions of um-SiC powder were deposited without any 59.1 wt %(26.8 vol %)solids( Fig 3a). Due to the low sintering additive on steel electrodes. The pH values solids content, such a visco-elastic deposit is not able to were selected in accordance with the characteristic resist its own weight: when the force of gravity points in the ZP VS pH graph in Fig. 1: the natural pH overcomes the weak interparticle forces, the viscous of the suspension (pH 5.0)and the pH values where flow behaviour predominates over the elastic beha the ZP appears highly positive or negative(pH 2.8 and iour and the deposit returns to the state of a viscous 11, respectively). The solids content in the starting liquid. uspension was 50 wt. and the density was 1.26 g/ As expected, at pH values close to the Pzc no cm. In another set of experiments, the solids content deposit was formed. At pH ll the deposit formed in the suspensions was varied from 30 to 70 wt %, the anode in accordance with the ZP vS. pH keeping the pH value constant. The solids content in relationship presented in Fig. 1. It containe the as-formed(wet)deposits, the deposition rate and 67.8 wt %(34.9 vol %) of solids(Fig 3a), which is the current change during the depositions are pre- higher than that obtained from the suspension sented in Figs. 3a-f natural pH. The rate of deposition was also higher The EPD of the suspension with the natural pH (i.e, than at pH 2.8 and pH 5(Fig 3c): this could be pH 5.0) resulted in a very loose deposit being formed related to the larger amount of electrolyte needed for at the cathode. After approximately 10 min, when its the pH adjustment, which is also reflected in the weight exceeded approximately 10 g, it slipped from higher initial current(Fig. 3e). Resulting lower solids the electrode. Obviously, under the given conditions, content and a lower density of the deposit formed the initially low-viscosity suspension flocculated at the pH ll can be explained by the lower ZP than at electrode and hence its viscosity increased. The fresh pH 2.8In order to better understand the process, suspen￾sions of lm-SiC powder were deposited without any sintering additive on steel electrodes. The pH values were selected in accordance with the characteristic points in the ZP vs. pH graph in Fig. 1: the natural pH of the suspension (pH 5.0) and the pH values where the ZP appears highly positive or negative (pH 2.8 and 11, respectively). The solids content in the starting suspension was 50 wt.% and the density was 1.26 g/ cm3 . In another set of experiments, the solids content in the suspensions was varied from 30 to 70 wt.%, keeping the pH value constant. The solids content in the as-formed (wet) deposits, the deposition rate and the current change during the depositions are pre￾sented in Figs. 3a–f. The EPD of the suspension with the natural pH (i.e., pH 5.0) resulted in a very loose deposit being formed at the cathode. After approximately 10 min, when its weight exceeded approximately 10 g, it slipped from the electrode. Obviously, under the given conditions, the initially low-viscosity suspension flocculated at the electrode and hence its viscosity increased. The fresh deposit (i.e., before drying) was found to contain only 59.1 wt.% (26.8 vol.%) solids (Fig. 3a). Due to the low solids content, such a visco-elastic deposit is not able to resist its own weight: when the force of gravity overcomes the weak interparticle forces, the viscous- flow behaviour predominates over the elastic behav￾iour and the deposit returns to the state of a viscous liquid. As expected, at pH values close to the PZC no deposit was formed. At pH 11 the deposit formed at the anode in accordance with the ZP vs. pH relationship presented in Fig. 1. It contained 67.8 wt.% (34.9 vol.%) of solids (Fig. 3a), which is higher than that obtained from the suspension at natural pH. The rate of deposition was also higher than at pH 2.8 and pH 5 (Fig. 3c); this could be related to the larger amount of electrolyte needed for the pH adjustment, which is also reflected in the higher initial current (Fig. 3e). Resulting lower solids content and a lower density of the deposit formed at pH 11 can be explained by the lower ZP than at pH 2.8. Fig. 2 (a) - SEM micrograph of lm-SiC, (b) - TEM micrograph of nano-SiC powder, (c), (d) - HRTEM micrographs of the amorphous layer on SiC particle in lm-SiC and nano￾SiC powders; (e), (f) - EDX spectra of the surface layer and bulk particle in lm -SiC sample J Mater Sci (2006) 41:8093–8100 8095 123