**1. Introduction**

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24 Sintering Techniques of Materials

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Spark plasma sintering (SPS), also known as field assisted sintering technique (FAST), belongs to a class of sintering techniques in which densification is enhanced by the simultaneous application of axial pressure and elevated temperature generated by a high current flow [1, 2]. SPS has been successfully used in the preparation of functionally graded materials [3], ceramics [4-6], magnetic materials [7, 8], alloy [9], etc. It is believed that the SPS has a significant advantages in decreasing the sintering temperature and sintering periods, and also preparing high density ceramics [10]. Although SPS has been widely used to prepare dense transparent and structural ceramics, little reports focus on the application of this technique to prepare dense ceramics for negative temperature coefficient (NTC) thermistor applications [11,12]. So this chapter first provides a summary of fundamental theoretical aspects of spark plasma sintering, and then the application of spark plasma sintering in NTC thermistor ceramics are introduced emphatically. At the end, the future research and application of spark plasma sintering in the NTC thermistor ceramics are forecasted.
