Slip casting compositions

A recent review of slip casting is given by Fries and Rand (35) and much practical details of the process can be found in a set of earlier articles (36). In the process, a slurry is poured into a microporous plasto- of Paris mold. The porous nature of the mold provides a capillary suction pressure, estimated to be of the ordo- of —0.1-0.2 MPa, which draws the liquid from the slurry into the mold. A consolidated layer of solids, referred to as a cast (or cake), forms on the walls of the mold (Fig. 6.33). After a sufficient thickness of the cast is formed, the surplus slip is poured out and the mold and cast are allowed to dry. Normally, the cast shrinks away from the mold during drying and can be easily removed. Once fully dried, the cast is heated to burn out the binder and sintered to produce the final article. Examples of slip casting compositions are given in Table 6.9. 

Table 7.8 Composition of Some Common Slip Casting Slurries...

A widely used technique for ceramic/ceramic gradient materials is sequential slip casting where slips of different compositions are cast one after and over another (Requenna et al., 1993). By using a premixing system, the casting composition can be tailored continuously (Chu et al., 1993). 

Ceramic Ablators, Several types of subliming or melting ceramic ablators have been used or considered tor use in dielectric applications particulady with quartz or boron nitride [10043-11-5] fiber reinforcements to form a nonconductive char. Fused silica is available in both nonporous (optically transparent) and porous (slip cast) forms. Ford Aerospace manufactures a 3D silica- fiber-reinfo reed composite densified with colloidal silica (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see Composite materials, ceramic matrix). 

Sommer F, Kern F, El-Maghraby HF, Abou El-Ezz M, Awaad M, Gadow R et al (2012) Effect of preparation route on the properties of slip-casted AI2O3/YAG composites. Ceram... 

J. S. Lyons and T. L. Starr, Strength and Toughness of Slip-Cast Fused-Silica Composites, 7. Am. Ceram. Soc. 77, 1673-1675 (1994). 

There are several factors in slip casting method. The porosity of the plaster mould is controlled by water content. The particle size of the powder should be relatively coarse to permit high level of vehicle permeability through the cast wall. Slip casting is widely used commercially because it enables the casting of complex shapes from an almost unlimited variety of ceramic composition, at a low cost. The most disadvantage of this process are low production rates and relatively short life of mould. 

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