Concentrated suspensions casting

To remedy the disadvantages of traditional shaping techniqnes of complex pieces such as slip casting or injection molding, the consolidation of concentrated suspensions, by destabilization or gelation in a non-porons mold, provides an innovating alternative to mannfactnre at a low cost in a reliable and reproducible way, near net shape pieces of complex geometry with final shapes and dimensions. 

In low viscosity fluids, considerable effort has been devoted to the dispersion of concentrated suspensions for slip casting or tape casting. In aqueous media it is the electrical behaviour of the solid-liquid interface which is used to preserve dispersion In non-aqueous media dispersion and deflocculation have been achieved by employing strongly polar solvents or by adding surfactants. ... 

Suspending enzyme in polymer solution instead of in pure organic solvent not only simplifies preparation of the casting solution, the enzyme suspensions became more uniform and stable. It was also found that at certain concentrations (enzyme, polyelectrolyte, and water) the resulting membranes exhibited extremes in both stability and... 

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... 

This is suitable for the formulations in which the percentage of solid ingredients, suspended in liquid is to be increased. The advantage of density difference between the molten medium and suspended particles is used in this process. The concentration of heavier particles is increased in the lower part of the casing either by natural sedimentation or by forced sedimentation caused by vibrating the whole casting assembly. The sedimentation process is controlled by a number of parameters such as particle size of solid suspension, temperature of melt, period of sedimentation, viscosity of melt, concentration of solid ingredients and column of melt etc. 

Esters of methacrylic acid are obtained directly from acetone cyanohydrin by reaction of the latter with concentrated sulfuric acid to give methacrylamide sulfate, followed by reaction with an alcohol. The process is continuous and the methacrylamide sulfate is not isolated. Acetone cyanohydrin is derived from acetone and hydrogen cyanide (Pig. 15-39), Polymerization Procedures. Of particular importmice to the acrylics is the cast or bulk method of polymerization. This method is employed to produce cast polymethyl methacrylate sheets which are widely used in industrial applications. Careful control of polymerization is required to obtain a bubble-free product with good optical clarity. A typical flow sheet for the production of cast eet is shown in fig. lfi-40. Solution, suspension, and particularly emulsion polymerizations are also, widely used with the acrylics. Such polymerization reactions involve relatively conventional batch-type processes. i... 

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