Ceramic Shapes

Most ceramic shapes do not consist of one single crystal, but are composed of numerous crystals joined together to form polycrystalline structures. The characteristics of the grain boundaries between crystals can influence the strength, chemical stability, and electrical properties as much us do the crystalline structures within Ihe individual grains. 

Sofie, S., Dogan, F. Ceramic shape forming by freeze-drying of aqueous and non-aqueous slurries. Ceram.Trans. 108, Innovative Processing/Synthesis of Ceramics, Glasses and Composites III, 235-243, 2000... 

To make membranes or typically membrane supports possessing relatively large pores (i.e., diameters larger than 1 pm), traditional polymer or ceramic shape forming... 

Statham, M., Hammett, E., Harris, B. et al.. Net-shape manufacture of low-cost ceramic shapes by freeze-gelation, J. Sol-Gel Sci. TechnoL, 13, 171, 1998. 

Fig. 3 Classification of powder-based forming methods used to make ceramic shapes.

Fig. 4 Schematic of the slip casting process for a ceramic shape. A slurry of ceramic particles and a carrier fluid is poured into a porous mold. The carrier fluid flows into the pores of the mold, and the ceramic particles remain behind and build up a solid cake in the mold. After the fluid has drained from the part, the cast shape can be removed from the mold.

Fig. 5 (A) Schematic of screw extrusion of a ceramic shape. The ceramic feed material dispersed in a binder flows from the hopper into the barrel where the rotating screw transports the material through the die opening. (B) Schematic of injection molding of a ceramic shape. The ceramic feed material dispersed in a binder flows from the hopper into the barrel where the rotating screw transports the material through the sprue into a closed mold. After the mold is opened, the part is ejected.

Fig. 7 Schematic of dry pressing of a ceramic shape. The ceramic particle feed flows into the die cavity. Force is applied to one or both punches and the powder is pressed into shape. The part is then ejected from the die cavity.

Such powders have been used in a variety of fabrication techniques to prepare technically interesting ceramic shapes such as wires and thin sheets. We confirm the tendency of the precursor powders to form the BaCO -CuO eutectic leading to a phase separation that degrades the desired properties, and the tendency of the 1-2-3 compound to degrade under contact with moisture and CC. ... 

Silbond . [Akzo] Silicates intermediate for binders for inoiganic zinc coatings, investment casting molds, cores, ceramic shapes, coatings. 

The plastic forming of ceramic shapes is based on the application of external forces to a mixture of ceramic powder and binder. The plastic mixture deforms and flows under applied stresses. The external forces cause the plastic mix to be adjusted to any die or mold, which dictates the eventual shape. Therefore, the flow behavior of such mixes during plastic forming has a major effect on the quality of the ceramic parts. Again, the flow stability of the mix during forming depends on the homogeneity of the ceramic powder and binder mixture. 

Ceramic shapes made in this way have excellent insulating characteristics and relatively low weight when compared to firebrick types of insulation. Fiber bonded refractories also have very good thermal shock characteristics. 

In his contribution entitled Shaping in ceramic technology - an overview , Andrea Bresciani, who is with the world s largest ceramic plant equipment contractor SACMI, describes and compares the three most important ceramic shaping methods. 

Finally, to illustrate the characteristics of the various ceramic shaping methods more clearly, comparative tables have been added to briefly explain the pros and cons of the various forming systems, as well as their main applications. 

Ceramic shaping is an inexhaustible subject, with a basically constant framework, but it is very complex and heterogeneous due to the plethoric parameters one encounters between the raw material and the finished product. The above article roughly describes the state of the art in terms of extrusion tools, pressure heads and dies. 

Handle F (1975) Perspectives in the Ceramic Shaping Technology. J Inter-ceram vol 24 No 4 pp 262-265... 

The electromechanical devices that convert electric energy into mechanical energy are generally made from ferroelectric ceramics, shape memory alloys, and EAPs, typically... 

Sodium sulfate, which possesses good electrolytic properties and a good chemical stability towards gases, appeared a good choice for such an application. Unfortunately, this material cannot be used under a ceramic shape because it does not withstand the temperature variations. Indeed, at about 300°C, there is an allotropic change, that is, in the useful field of the sensor the mechanical tensions this transformation implies favoring the crackling of the sintered material. 

Fig. 4.26 XRD patterns of top slices of alumina ceramics shaped at magnetic fields of 0, 4, 6, 8, and 12 T. Reproduced with permission from [141]. Copyright 2012, Elsevier...

As mentioned in Chapter 8, some vegetable oil-based polymers exhibit shape memory properties. The discovery of smart materials is one of the revolutionary steps in the held of active materials research. Among different types of smart materials (metals, alloys and ceramics), shape memory polymers (SMPs) have attracted considerable research interest in last few years because of their advantages over other categories of materials, as discussed in Chapter 1. Shape memory polymers which are deformed and... 

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