Dispersants slip casting

Slip casting is common in the ceramics industry. The material to be cast is milled to a mean particle size of a few microns. A slip is made by mixing the finely divided material with a liquid suspending medium. The slip is then poured into a suitable mold (e.g., of plaster of pans). The liquid in the slip is drawn into the mold by capillary forces and the solids are deposited in a coherent form. For TiBj, ZrBj and CrBj a suspending medium of 5-7 wt% cyclopentadiene in xylene is recommended. A 3 wt% aqueous solution of carboxymethylcellulose is the best dispersing medium... 

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... 

In ceramics, a variation of slip-casting in which a stabilized colloidal dispersion of particles is poured into a mold for sintering. 

Commercial ceramic membranes are made by the slip-casting process. This consists of two steps and begins with the preparation of a dispersion of fine particles (referred to as slip) followed by the deposition of the particles on a porous support. 

Slip-Casting In ceramics, the process in which a slurry of dispersed particles is poured into a mold, the liquid removed, and the particles sintered to form the final product. 

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. 

Ceramic particles in organic liquid media behave differently from those in aqueous media. Many known ceramic-processing techniques involve fine particles dispersed in nonaqueous media. Some of the better known examples are tape casting of barium titanate and aluminum nitride powders and tape or slip casting, extrusion, and injection molding of ceramic high Tc superconductor powders. 

In general the size of the pores depends, among other factors, on the particle size of the aggregate. Particle size is the most important parameter in the production of ceramic products it must be optimized to ensure that the desired mechanical and physical properties are achieved. The majority of ceramic products are manufactured by the process of slip casting in a mold. Maintenance of the desired PSD requires control of the dispersion stabUity of the ceramic shp. Like all ceramic materials and castables, in alumina refractories a proper PSD is of importance. 

Electronic amplitude measurements were performed to evaluate the surface chemistry of the coated powders. Low zeta potentials were observed when electrostatic charge was used to disperse the experimental powders. Stable dispersions were achieved by adding low levels of polyelectrolyte. The results suggested that the experimental powders can be processed using typical slip casting procedures. 

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