Spark plasma sintering (SPS), also known as field assisted sintering technique (FAST) or pulsed electric current sintering (PECS), or plasma pressure compaction (P2C) is a

sintering Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...

technique. The main characteristic of SPS is that the pulsed or unpulsed DC or AC current directly passes through the

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...

die, as well as the powder compact, in case of

conductive In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gener ...

samples.

Joule heating Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor (material), conductor produces heat. Joule's first law (also just Joule's law), also known in c ...

has been found to play a dominant role in the densification of powder compacts, which results in achieving near theoretical density at lower sintering temperature compared to conventional sintering techniques. The heat generation is internal, in contrast to the conventional

hot pressing Hot pressing is a high-pressure, low-strain-rate powder metallurgy process for forming of a powder or powder compact at a temperature high enough to induce sintering and creep processes. This is achieved by the simultaneous application of heat a ...

, where the heat is provided by external

heating element A heating element converts electrical energy into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independe ...

s. This facilitates a very high heating or cooling rate (up to 1000 K/min), hence the sintering process generally is very fast (within a few minutes). The general speed of the process ensures it has the potential of densifying powders with nanosize or nanostructure while avoiding coarsening which accompanies standard densification routes. This has made SPS a good method for preparation of a range of materials with enhanced

magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...

magnetoelectric In its most general form, the magnetoelectric effect (ME) denotes any coupling between the magnetic and the electric properties of a material. The first example of such an effect was described by Wilhelm Röntgen in 1888, who found that a dielectric ...

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied Stress (mechanics), mechanical s ...

thermoelectric The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa via a thermocouple. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when ...

, optical or biomedical properties. SPS is also used for sintering of

carbon nanotubes A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon nan ...

for development of

field electron emission Field electron emission, also known as field emission (FE) and electron field emission, is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into a vacuum. However, field emissio ...

electrodes. Functioning of SPS systems is schematically explained in a video link. While the term "spark plasma sintering" is commonly used, the term is misleading since neither a spark nor a plasma is present in the process. It has been experimentally verified that densification is facilitated by the use of a current. SPS can be used as a tool for the creation of functionally graded soft-magnetic materials and it is useful in accelerating the development of magnetic materials. It has been found that this process improves the oxidation resistance and wear resistance of sintered tungsten carbide composites compared to conventional consolidation methods. Spark Plasma Sintering

Hybrid heating

By means of a combination of the FAST/SPS method with one or several additional heating systems acting from the outside of the pressing tool systems it's possible to minimize the thermal gradients thus allowing the enhancement of the heating rates at simultaneously optimized homogeneity. In 2012 the world's largest hybrid SPS-hot press sintering system was set up in Spain and the fabrication of fully dense large ceramic blanks of up to 400mm with this system is in progress within the frame of th
FP7 European Project HYMACER - Hybrid sintering and advanced machining of technical ceramics
Spark plasma sintering, also known as plasma pressure compaction (P2C) sintering, equipment are commercially available now and are no longer limited to laboratory research work. Products like body armor, rocket nozzles, carbon fiber composites and several other hybrid materials can be produced in commercial scale using these equipment.plasma pressure compaction
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References

{{Authority control Industrial processes Metalworking

Hybrid heating

See also

References