Water Based Colloidal Processing of Ceramic Laminates

Abstract

Multilayered materials and coating are complex structures proposed among others to face the structural requirements of ceramics. The development of reinforcement mechanism by laminated structures can be due to deflection criteria or to the presence of residual stresses and requires of tailored laminates. These designs are characterized by the phases, thickness and distribution of the layers as well as the joining strength between them. In this sense water based colloidal processing techniques are used to fabricate layered structures by consolidating the layers from fluid dispersions of the powders in water. In these processing methods the phases presented in the final laminate are mainly given by the composition of the starting slurries while the changes in thickness and sharpness of the layers are controlled by acting on the processing parameters. The achievement of stable slurries is a shared step for all the colloidal processing techniques. In the water based slurries the stability will be dominated by the polar media, the surface behavior of the particles and the presence of dispersant additives to increase the repulsion between particles. The stable slurry ensures an effective milling and dispersion of the phases as well as high solid loadings, if required. Further processes associated to shaping and consolidation of the layers requires the incorporation of additives and-or water removal. The shaping methods based on aqueous slurries can be classified taking into account the process of solid-water separation. For each of those shaping methods, the nature and amount of the additives is different in order to get the optimum rheological behavior and green strength after drying. Depending on the thickness of layers and coatings as well as the shape and dimensions of the samples, the shaping method can be selected alone and combined with others.