Ceramic suspensions slip casting

Slip casting of metal powders closely follows ceramic slip casting techniques (see Ceramics). SHp, which is a viscous Hquid containing finely divided metal particles in a stable suspension, is poured into a plaster-of-Paris mold of the shape desired. As the Hquid is absorbed by the mold, the metal particles are carried to the wall and deposited there. This occurs equally in all directions and equally for metal particles of all sizes which gives a uniformly thick layer of powder deposited at the mold wall. 

A common method to slip-cast ceramic membranes is to start with a colloidal suspension or polymeric solution as described in the previous section. This is called a slip . The porous support system is dipped in the slip and the dispersion medium (in most cases water or alcohol-water mixtures) is forced into the pores of the support by a pressure drop (APJ created by capillary action of the microporous support. At the interface the solid particles are retained and concentrated at the entrance of pores to form a gel layer as in the case of sol-gel processes. It is important that formation of the gel layer starts... 

Controlling the stability of suspended particles, and the filtration characteristics of cast suspensions, are very important in the ceramics industry. Here the casting suspensions may comprise clays, silica, oxides, carbides or nitrides [357,793], In slip casting, a suspension is pored into a porous mould and allowed to stand. Water dif-... 

In the slip-casting process the ceramic powder is suspended in a fluid vehicle, usually water. The suspension, or slip , has a high solids content, typically 50vol.%, and the individual particles are fine, usually less than 10 /mi. Deflocculants, which modify the electrical environment of each particle so that they repel one another, are added to the slip. The fineness of the powder and consequent high surface area ensure that electrostatic forces dominate gravity forces so that settling does not occur. When exceptionally heavy powder particles... 

In the ceramic industry the rheology of clay suspensions plays a major role. Their colloidal properties are of especial significance in the process of slip-casting, in which a clay slurry is put in contact with a porous plaster mould, which sucks up the water to leave a solid form ready for firing, Here the suction provided by the porous mould in relation to the rate of flow of water through the clay matrix is important. The structure of the clay slurry, as determined by its degree of dispersion, has also to be controlled by suitable additives. 

Zhang L, Vleugels J, Van der Biest O (2010) Slip casting of alumina suspensions in a strong magnetic field. J Am Ceram Soc 93 3148-3152... 

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