Spark plasma sintering
The main characteristic of SPS is that the pulsed DC current directly passes through the graphite die, as well as the powder compact, in case of conductive samples. Joule heating 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, where the heat is provided by external heating elements. 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. 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 [Hulbert]. It has been experimentally verified that densification is facilitated by the use of a current.
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.
- K. Sairam, J.K. Sonber, T.S.R.Ch. Murthy, C. Subramanian, R.K. Fotedar, P. Nanekar, R.C. Hubli, Influence of spark plasma sintering parameters on densification and mechanical properties of boron carbide, International Journal of Refractory Metals and Hard Materials, Available online 13 September 2013, ISSN 0263-4368, http://www.sciencedirect.com/science/article/pii/S0263436813001935
- M. Suárez, A. Fernández, J.L. Menéndez, R. Torrecillas, H. U. Kessel, J. Hennicke, R. Kirchner and T. Kessel."Challenges and Opportunities for Spark Plasma Sintering: A Key Technology for a New Generation of Materials. Sintering Applications. 2013"
- Installation of the World’s Largest SPS-HP Hybrid Furnace Commences
[Hulbert] = D. M. Hulbert, A. Anders, D. V. Dudina, J. Andersson, D. Jiang, C. Unuvar, U. Anselmi-Tamburini, E. J. Lavernia, and A. K. Mukherjee, "The absence of plasma in ``spark plasma sintering," J. Appl. Phys., vol. 104, pp. 033305–7, 2008.