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Gelcasting
Gel casting is a direct foaming technique used to produce ceramic and polymeric scaffolds. History Gel casting was developed in Canada in the 1960s and ever since it became an interesting manufacturing forming process for near-net-shape, very large, high-quality, complex ceramic parts with specified threshold strength. Process In this technique, the precursor materials typically consist of a monomer, cross linker, free radical initiator or catalysts are placed into an aqueous suspension. Such precursor conforms to a slurry that is then foamed before it undergoes a direct consolidation step. In this step, the binder becomes polymerized to consolidate the particle structure within the precursor slurry. The process then forms a gel type of mixture, which is then cast into a proper mould. The next step, after the gel solidification, it is removed from the mould in a controlled manner and then being dried to form a green body. The outcome here has interesting mechanical properties and is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Freeze Gelation
Freeze-gelation, is a form of sol-gel processing of ceramics that enables a ceramic object to be fabricated in complex shapes, without the need for high-temperature sintering. The process is similar to freeze-casting. The process is simple, but the science is, as of 2005, not well understood. The most common process involves the mixing of a silica solution with a filler powder. For example, if we were making a component out of alumina, aluminium oxide, then we would still use a silica sol, but alumina filler powder. The relative amounts used differ, normally between 3 and 4 times more filler than sol is added by weight. A wetting agent is added, such that the filler powder disperses properly in the sol, which is mostly water. This makes the mixture doughy and stiff. The mixture is, however, highly thixotropic, so that when vibrated it turns liquid. The stiff dough is placed in a mold and the mold vibrated to liquefy the mixture, filling the mold and releasing any trapped air. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Colloidal Crystal
A colloidal crystal is an Order (crystal lattice), ordered array of colloid particles and fine grained materials analogous to a standard crystal whose repeating subunits are atoms or molecules. A natural example of this phenomenon can be found in the gem opal, where spheres of silica assume a Close-packing of spheres, close-packed locally periodic structure under moderate compression (physical), compression. Bulk properties of a colloidal crystal depend on composition, particle size, packing arrangement, and degree of regularity. Applications include photonics, materials processing, and the study of self-assembly and phase transitions. Introduction A colloidal crystal is a highly ordered array of particles which can be formed over a long range (to about a centimeter). Arrays such as this appear to be analogous to their atomic or molecular counterparts with proper scaling considerations. A good natural example of this phenomenon can be found in precious opal, where brilliant re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Casting (manufacturing)
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various ''time setting'' materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. Heavy equipment like machine tool beds, ships' propellers, etc. can be cast easily in the required size, rather than fabricating by joining several small pieces. Casting is a 7,000-year-old process. The oldest surviving casting is a copper frog from 3200 BC. History Throughout history, metal casting has been used to make tools, weapons, and religious objects. Metal casting history and de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
