Electrophoretic deposition of nano-ceramics for the photo-generated cathodic corrosion protection of steel substrates

Electrophoretic deposition (EPD) was employed to deposit crystalline TiO2/WO3 nanoparticles onto stainless steel to fabricate a photo-generated cathodic protection layer. The electrophoretic mobility of the colloidal particles was determined by measuring the zeta-potential of the particles in the suspension. The surface morphology of the EPD layers was observed using scanning electron microscopy (SEM), and the composition of the EPD layer was determined from the peak intensity using an X-ray diffractometer (XRD). Furthermore, the open circuit potential (OCP) of the TiO2-WO3-deposited sample was measured under UV irradiation to evaluate the photo-generated cathodic protection ability of the EPD layers on stainless steel. Through the zeta-potential measurement, it was verified that the TiO2 particle was effectively charged by phosphoric acid di-butyl ester in iso-propanol, but the WO3 particle was slightly negatively charged because of the different zero point of charge. However, TiO2 and WO3 particles were deposited simultaneously via an EPD process at the same rate despite their different electrophoretic mobilities in the suspension. The TiO2-WO3 co-deposited layer was uniformly deposited, and no noticeable homo-aggregation of the same type of particle was observed. Using the OCP measurement, it was also found that stainless steel was cathodically protected from corrosion by UV light irradiation because the potential of the photo-stimulated EPD layers was more negative than the corrosion potential of stainless steel. Because the WO3 contents in the EPD layer were increased, the time of potential recovery was gradually delayed. Moreover, the addition of binders enhanced the adhesion strength between the metal and the layer that hindered the delamination and improved the cathodic protection performance. The potential recovery time of the EPD sample containing 40% TiO2-60% WO3 was approximately 6 h after 3 h of light irradiation, which implied that the steel was cathodically protected for 6 h in dark conditions.