Sintering of a Powder Compact
The processes governing powder metallurgy and one type of ceramic material processing are greatly dependent on diffusional processes that combine distinct powdered grains into one cohesive material. This process, also known as sintering, is the "welding" together of separate powder particles into a single solid material, which takes place below the melting point of the material, but at a temperature sufficiently high to allow an acceptable rate of diffusion to occur, usually at greater than one-half of the melting point on the Kelvin scale. The powder particles, whether for powder metallurgy or ceramic firing, are pressed together, forming a compacted mass of powder particles that resembles a close packed crystal structure, with the powder particles being analogous to the atoms of the crystal (use your imagination on this one and click here to see a schematic representation).
The powder compact is then heated to allow diffusion to occur, and the initially separated powder particles become fused together thanks to the diffusion mechanism (see figure above). The final product consists of grains of the material that were initially powder particles, but diffusion has allowed atoms of one particle to intermix with atoms of another, forming one particle out of an initial two. Click here to see a photomicrograph of an aluminum oxide powder compact that has been sintered.
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