Spark plasma sintering (SPS) is a sintering technique in which materials are compacted and condensed into higher densities. Systems designed for spark plasma sintering use direct current (DC) pulses to create spark energy between the particles of the material. This technology achieves fast fusing between particles and, unlike other sintering processes that are solely involved in metalworking, spark plasma sintering can be applied to ceramics, composite materials, and nanostructures.
The process operates on the principle of electric spark discharge, in which a high energy pulsing current creates spark plasma in the spaces between particles in the material. This spark plasma exists at incredibly high temperatures of 10,000° C (18,032° F), causing potential oxidation or contaminants on the particle surfaces to vaporize. The surfaces of the particles are also heated, causing these areas to melt and fuse together into structures known as necks. Over time, the necks will develop into the spaces, increasing the total solid density of the material to above 99% in some cases.
Advantages of the spark plasma sintering process include short completion time, low operating costs, wide range of applications, and good structural and material results. Due to the nature of the process, spark plasma sintering generally takes less than 20 minutes to complete. Costs are also generally lower with this technology, as the pulsating current does not require a high voltage, and the process does not take a long time to complete. This short cycle time, coupled with the low cost, makes the process efficient for a wide range of uses.
Spark plasma sintering can yield much greater densities than many other sintering processes, making it ideal for materials where a high solid density is desired. This process can be used for insulators as well as conductors, opening up more possible materials to be sintered. The precision of the heating process also makes spark plasma sintering applicable to nanostructures, such as crystals, which can be sintered without losing their structural integrity.
The fact that the spark plasma is able to generate intense heat from within a material, rather than externally, yields several advantageous results. First of all, the risk of the interior of the particles heating is minimized, as only the surfaces of the particles are heated. Second, the nature of the heating means that the material will be heated uniformly all at once, increasing the structural integrity and evenness of density throughout. Third, the process allows for increased control of various conditions, including pressure, heat, and cooling, which ultimately leads to greater control of the material’s density.