Electrophoretic deposition of bi-layered nano-sized silicon carbide/mullite coating from stabilized suspensions

Abstract

Nano-sized silicon carbide/mullite bi-layered film was applied onto the surface of graphite using electrophoretic deposition (EPD) method from stabilized suspensions. The suspensions were prepared adding 5 g L−1 SiC and 10 g L−1 mullite in ethanol. The effects of adding various amounts of polyethylene imine (PEI) on the stability of suspensions were investigated by visual inspection (sedimentation height), measuring the zeta potential, and particle size distribution. As a result, the addition of 6.0 dwb% and 1.5 dwb% PEI to SiC and mullite suspensions were found to be an effective way in dispersing of nanoparticles. The zeta potential values of well-stabilized suspensions were determined 37.6 mV and 42.4 mV for SiC and mullite suspensions, respectively. Therefore, the coating processes were conducted with the optimal amounts of PEI. In the deposition process, the optimal distance between electrodes was determined 10 mm. In order to investigate the coating process parameters, the optical microscopy (OM) was used for single-layer coatings. The results reveal that applied voltages of 40 V and 10 V with deposition periods of 50 s and 60 s bring about uniform coatings. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were carried out to evaluate the microstructure. The thicknesses of green coatings were measured about 24.15 μm for SiC layer and 7.23 μm for the mullite layer.