Bubble-free electrophoretic deposition of aqueous zirconia suspensions with hydroquinone

Electrophoretic deposition (EPD) is a colloidal processing technique for ceramics in which charged particles move toward, and are deposited upon an electrode with the opposite charge [1–3]. The EPD technique has many advantages, such as the fast, easy, and uniform formation of complex shapes, good control of deposition thickness, high green density. This method has been used to fabricate thin films, multilayered composites, functional materials, etc. Non-aqueous suspensions are usually preferred for the EPD process to prevent electrolysis of the solvent and to obtain bubble-free deposition. On the other hand, an aqueous shaping system is advantageous from the viewpoints of ecology, safety, and cost. Water is decomposed into hydrogen and oxygen when a DC current is passed through an aqueous medium. There have been some reports of the fabrication of a bubble-free deposit from aqueous suspension [4, 5]. Recently, Uchikoshi et al., investigated the EPD characteristics of positively charged particles onto various cathodic substrates using aqueous alumina suspensions [5]. They found that no macro pores were formed in the EPD deposit on a palladium cathode, and that the green density and sintered properties of the deposits were the same as those produced by the slip casting process. It is well known that hydroquinone (HQ) is readily oxidized to quinone (Q) at high pH in alkaline solution [6]: