Green body fabrication

A ceramic suspension consists of ceramic powder, a solvent, often a dispersant to stabilize the ceramic powder ag2iinst a omeration, a polymeric binder to provide green strength after the green body has been dried, and often a plasticizer to lower the glass transition of the polymeric binder. All these additives must be compatible so the ceramic suspension has the desirable properties needed for green body fabrication. Many of these formulations used in industry are very secretive. 

This section discusses the flow of paste through an extruder, through a die, and in a mold in various detail allowing the reader to comprehend the basics of these green body fabrication methods. 

To remove the solvent used to suspend the ceramic powder for green body fabrication, the green body is heated or placed in an atmosphere... 

Because of their strong chemical bonds, bulk ceramics are most efficiently fabricated by means of densification of powders. The fabrication process involves two main stages (1) consolidation of the powder to form a porous, shaped article (the green body), also referred to as forming, and (2) heating of the shaped powder form to produce a dense article, referred to as firing or sintering. The final product commonly consists of a relatively dense polycrystal with some residual porosity (Fig. 1). The microstructure, which... 

A ceramic support is formed by shaping a powder and then consolidation of the green body by sintering. The fabrication process consists of four main stages the choice of inorganic material, paste preparation, shaping, and firing (Fig. 5.2). 

Ceramic processing typically consists of three main steps (i) synthesis or preparation of precursor powders, (ii) consolidation or packing of the powders into green bodies, and (iii) sintering [44]. Every step has a significant effect on the microstructure and optical performance of the final transparent ceramics. There are a number of parameters relevant to the quality of the powders, facility, and way of consolidation and techniques of sintering, which can be used to optimize the fabrication process as a whole. 

Surface area of a powder increases geometrically with decreasing particle size, so that the volume fraction of the outermost layer of ions on the surface increase significantly, which has a significant effect on properties of the powder. With the development of nanotechnology, it is readily to synthesize powders with nanosized particles (1-100 nm). Therefore, characterization of surface properties becomes more and more important. Specifically for ceramics or transparent ceramics, the consolidation of fine ceramic powders with liquid suspensions to produce more uniform green bodies has been shown to play an important role in the fabrication ceramics, especially when special or complex structures are required. Because the quality of microstructure of the consolidated body is determined by the dispersion behavior of the powder and the interaction between the particles in the suspension, which is closely related to the surface properties of the particles, controlling the physical and chemical properties of particles is a critical to ceramics fabrication. 

Figure 4.38c shows fracture morphology of the green body, which had a very dense microstracture. No gap was observed across the fracture surface, implying the close compaction of the slices. Fracture morphology of pohshed surface of the YAG ceramics is shown in Fig. 4.38d. The sintered ceramics were nearly fully dense, without the presence of cracks on the surface, i.e., no delamination occurred during the binder removal and the sintering process. The average grain size of the YAG ceramics sintered at 1750 °C for 10 h was about 15 pm, while the in-line transmittance of the sample is 81.5 % at 1064 nm. Therefore, this is a flexible and feasible method to fabricate transparent ceramics with composite structures [163].

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