Spark Plasma Sintering

Spark plasma sintering (SPS ) is comparable with hot-pressing sintering process. It is also among the synonyms of "Field Activated Sintering " (FAST ) and DC -Current Sintering known. The spark plasma sintering term is controversial, since no evidence was provided that Sparks ( " Sparks ") or a plasma during the sintering process can occur. Sintering method used for the compaction of powdered materials.

Sintering procedure

The powder is filled in a graphite crucible which has the shape of a hollow cylinder. About two graphite temples, are fitted into the hollow cylinder, the powder is first pre-compacted manually. Then the crucible is fitted with the punches in the SPS machine. There, under protective gas or vacuum can be the actual sintering process. A hydraulic press, a defined pressure on the material is first applied, typically in the range of a few megapascals. This pressure is maintained throughout the sintering process. The sintering is carried mainly by electricity. For this purpose, a direct current is used with currents in the range of a few kilo Ampere and voltages of a few volts. The characteristic feature of this method is that the direct current is passed directly through the powder. This is ensured by an electrically insulating film between powder and graphite crucible. By the ohmic resistance of the powder, the electric power of the current is converted into heat power, whereby the powder is heated. Viscous flow, or by ( partially ) melted at a high pressure, and then cooling the particles to occur, and thus the fusion of the powder. Thus, the sintering is heated from the inside out and not as hot pressing from the outside. The advantage of this method is that the potential heating and cooling ramp is extremely steep (up to 1000 K / min), also < (90 % of theoretical density ) are short process times (range, 30 min) at high compaction > possible. The method also allows for compaction of materials well below the actual melting point of a solid body of the same material.

Use

In addition, the classic uses of the spark plasma sintering sintering techniques comes more recently in the field of nanotechnology for use. It is used to bring nanoscale powder in macroscopic forms without losing the nanostructures. This is made possible by the high heating and cooling rates and short processing times. The spark plasma sintering allows it, to materials to transmit unique properties of the nano-world at the macroscopic scale and thus material or to open up new opportunities in energy technology.

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