Applications slip casting

Slip Casting. Slip casting of metal powders into useful articles is an interesting process but has only limited industrial application (30,31). It is sometimes used to produce large, very complicated parts from refractory metals (see Refractories). 

The synthesis of 5 lan thick Ti02 Si02 layers on a porous support can be performed using the procedure given below. First a mixed Ti[(OMe)3]4 alkoxide is synthesized by reacting partially hydrolyzed Si(OMe)4 with Ti-isopropoxide. This inorganic polymer is hydrolyzed at pH 11.0 and treated with 2-methyl-2-4-pentanediol and a binder. This solution is then slip-cast onto a porous support, dried and calcined at 700°C. The membrane can be useful in reverse osmosis applications. 

Common consolidation methods include variations on pressing powders, plastic forming, slip casting and tape casting. The choice of which method to use for a given application is very dependent upon the shape, size and required dimensional tolerances of the final product, available capital outlay and desired productivity. Each of these methods is examined in turn below, followed by sintering, which turns the consolidated powders into a monolithic body with mechanical integrity. 

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). 

Plaster of Paris is employed extensively for the making of moulds for slip-casting in this application, the porosity of the set product is important, since water is removed locally from the casting-slip by the capillary action of the pores. Gypsum products however have many other uses, notably in the cement and building industries, and in dentistry and surgery. 

However, the application of much higher pressure (<40 bar or 4.0 MPa) makes casting cycles much faster than in slip casting processes where the capillary forces correspond to a pressure of just 1-2 bar (0.1-0.2 MPa). 

By this method, the grain size, particle shape, agglomerate size, and specific surface area can be modified within a certain degree by controlling the precipitation and calcination conditions. Furthermore, its purity is also more easily controlled. For the applications of zirconiain the slip casting, tape casting, mold injection, particle size, specific surface, etc. are important characteristics. Well-controlled precipitated zirconia powder can be fairly uniform and fine. 

The colloidal techniques described in Chapter 4 provide considerable benefits for the control of the packing uniformity of the green body. The production of green bodies with uniform microstructure from a fully stabilized colloidal suspension of spherical, fine, monodisperse particles has not been incorporated into industrial applications where mass production is desired and fabrication cost is a serious consideration. Colloidal techniques, however, play an important role in the low-cost forming methods of slip casting and tape casting, as well as in the less commonly used methods of eletrophoretic deposition and gel casting. 

Slip casting of ceramics Is a technique that has long been used for the manufacture of traditional ceramics. The technique, sometimes referred to as colloidal filtration. Is also applied to forming some ceramic bodies used by the electronics Industry. One of the most well known applications Is In the manufacture of aluminium oxide radomes. The requirements of a stable slip for casting have been covered earlier under tape casting. 

It Is difficult to forecast a realistic timescale for the commercial development of microwave assisted processing techniques. Some, such as drying, are already In operation In a number of countries, whilst other processes, such as slip casting, are expected to have been commercialised to a greater or lesser extent by the early 1990 s. For the Other applications, considerably more research and development is still required however, given the interest currently being shown, progress Is expected to be rapid. 

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