Thermogelation of Composite Films Produced by Electrophoretic Codeposition

There is a growing interest to develop reliable, economic and environmentally-friendly methods for manufacturing thick coatings and layered systems. For thick films, the adhesion to the substrate and the shape retention become important problems that lead to low density, cracking, and heterogeneous surfaces. To overcome these problems, a processing route is proposed consisting in the formation of a thick deposit by EPD in water and its immediate consolidation by thermogelation of polysaccharides. The process is based on the use of aqueous suspensions containing low concentration of biopolymers (i.e. carrageenan) and the formation of the film by dipping and/or EPD on suspensions heated at 60ºC. On withdrawal at constant rate a film is obtained after cooling at room conditions. Maintaining the stability of the hot suspensions and during gelation is a key parameter to produce controlled deposits with good adhesion to the substrate and uniform microstructure. In this work, ceramic suspensions or Ni-containing suspensions have been stabilized with acrylic-based polyelectrolytes at controlled pH. Self-supported films of Al2O3/Y-TZP have been produced by dipping and EPD on graphite substrates that are burnt out on heating. On the other hand, Ni/YSZ composites have been deposited on graphite to produce either monolithic or laminated films. The optimization of the rheological behaviour of the suspensions and the EPD kinetics allows manufacturing a variety of complex structures with layers having controlled thickness ranging from 10 to 200 6m.