Spark plasma sintering

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Spark Plasma Sintering (SPS) is a sintering process comparable to hot pressing . It is also known by the synonyms "Field Activated Sintering" (FAST) and DC-Current Sintering. The name Spark Plasma-Sintering is controversial because experimental investigations have shown neither sparks nor a plasma during the sintering process. Sintering processes are used to compact powdery materials into technical ceramics .

Sintering procedure

The powder is filled into a graphite crucible that has the shape of a hollow cylinder. The powder is first manually pre-compressed using two graphite punches that are fitted into the hollow cylinder. The crucible with the stamps is then installed in the PLC machine. The actual sintering process can take place there under protective gas or vacuum. A hydraulic press is used to exert a defined pressure on the material, usually in the range of a few megapascals. This pressure is maintained throughout the sintering process. Sintering is essentially done by electricity . A direct current is used for this purpose, with currents in the range of a few kiloamps and voltages of a few volts. The characteristic of this process is that the direct current is passed directly through the powder. This is ensured by an electrically insulating film between the powder and the graphite crucible, if this does not already have a significantly higher resistance than the powder compact. Due to the ohmic resistance of the powder, the electrical power of the current is converted into thermal power, whereby the powder is heated. Through viscous flow or through (partial) melting under high pressure and subsequent cooling of the particles, these and thus the powder melt. The sintered body is thus heated from the inside and not from the outside as in hot pressing. The advantage of this process is that the possible heating or cooling ramp is extremely steep (up to 1000 K / min), and short process times (range <30 min) with high compaction (> 90% theoretical density) are possible. The process also enables materials to be compacted far below the actual melting point of a solid made of the same material.

commitment

In addition to the classic areas of application of sintering techniques, spark plasma sintering has recently also been used in the field of nanotechnology. It is used to bring nanoscale powder into macroscopic forms without losing the nanostructures. This is made possible by the high heating and cooling rates and short process times. Spark plasma sintering makes it possible to transfer unique properties of the nano world to materials on a macroscopic scale, thus opening up new possibilities in material or energy technology.

Individual evidence

  1. ^ O. Guillon et al .: Field-Assisted Sintering Technology / Spark Plasma Sintering: Mechanisms, Materials, and Technology Developments. In: ADVANCED ENGINEERING MATERIALS 2014, doi : 10.1002 / adem.201300409 .
  2. ↑ Dustin M. Hulbert, André Anders, Dina V. Dudina, Joakim Andersson, Dongtao Jiang, Cosan Unuvar, Umberto Anselmi-Tamburini, Enrique J. Lavernia, Amiya K. Mukherjee: The absence of plasma in “spark plasma sintering”. In: Journal of Applied Physics. 104, 2008, p. 033305, doi : 10.1063 / 1.2963701 .