SPS spark plasma sintering technology introduction

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To extend pressure beyond 500 MPa, various modifications can be made. Researchers have been working on enhancing this range by altering the reaction chamber and hydraulic pressure device. These components are essential to the SPS system, which utilizes a DC generator connected to steel rams and graphite punches. The direct current is regulated by pulses, enabling rapid heating rates up to 1000 °C/min.

The basic SPS system incorporates a hydraulic pressure device (typically 250 kN) with a vertical pressurization axis. Pressure is transferred to a reaction chamber, typically placed in a vacuum or protected atmosphere. The system uses water-cooled steel cylinders, graphite spacers, and cylindrical dies.

Detailed descriptions of SPS technology are widely available, focusing on the dual application of pulsed high DC current and uniaxial pressure to densify powders or synthesize new compounds. Despite its efficiency, thermocouples used in SPS devices often break, so gradual electric power increases are preferred over direct temperature measurements. Typical heating rates are 100 °C/min, with temperature limits up to 900 °C for high-pressure modules.

Using a very high-pressure module, researchers have attained pressures of up to 2 GPa with pre-compacted samples in graphite tubes, supported by tungsten carbide anvils. Enhanced pressurization mechanisms, such as HP-SPS hybrid tools and SiC punches with inner and outer graphite dies, enable pressures up to 1 GPa, with heating rates of 12.5-50 °C/min.

Modification of the Reaction Chamber and the Hydraulic Pressure Device

Commercial SPS models usually have limited press capacity (50-250 kN). For higher pressures, modifications in the reaction chamber and hydraulic pressure devices are necessary. New HP-SPS systems have been developed, such as a cubic press technology achieving hydrostatic compression through six tungsten carbide anvils. This system can generate pressures of 5-7 GPa and temperatures up to 2000 °C.

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Later developments include a Bridgman-type toroidal large-volume apparatus achieving pressures up to 8 GPa and sintering temperatures ranging from 20-2400 °C. Calibration of the HP-SPS device is essential to obtain accurate pressure and temperature measurements. The Krakow HP-SPS device, for instance, enables targeted densification of composites like ZrC-Mo and ZrC-TiC, yielding improved mechanical properties. Comparative studies have shown the advantages of HP-SPS over conventional high-pressure high-temperature systems for diamond composite sintering.

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The introduction of belt-type HP-SPS systems, using devices like the one developed at ICMCB laboratory, are also noteworthy. These systems allow pressures up to 6 GPa and temperatures up to 1800 °C. Applications include the densification of high-pressure phases such as diamond, and the assembly of tools for industrial drilling purposes.

Overall, HP-SPS technology continues to push the boundaries in material science, offering promising solutions for the synthesis and densification of various advanced materials.