Electrophoretic Coatings

Abstract

Conventional coating techniques used in the sol-gel field like dip-coating and spin-coating are excellent methods for the fabrication of uniform thin films on various kinds of substrates [1,2]. It is also known that it is difficult to get films with thickness larger than about one micrometer because of cracking [3,4]. Electrophoretic deposition is a useful procedure for the preparation of thick films [5]. In this process, charged particles are deposited on an electrode by applying a DC voltage. This process has been widely applied to various fields such as preparation of phosphors for displays, solid electrolytes for electrochromic displays, cathodes for lithium secondary batteries, superconductors, ferroelectric materials and biomaterials [6--11]. The main advantage of the electrophoretic deposition is that thick films can be prepared on various substrates with a complicated shape in a much shorter time compared to the other coating techniques. The film thickness can be controlled by varying the preparation conditions such as applied voltage, deposition time and concentration of the suspensions. In practice, however, the preparation of stable suspensions with fine and uniform particles, which is essential to obtain high quality thick films, is not easy. For example, when raw materials are ground using a conventional ball mill, the shape of the particles is not uniform and the size distribution is broad. The sol-gel method permits the preparation of uniform, spherical and fine particles.