Development and Principle of Plasma Sintering Furnace

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SPS is the abbreviation of Spark Plasma Sintering, spark plasma sintering. Spark plasma sintering furnace(SPS-Series) is a fast, low-temperature, energy-saving and environmentally friendly material preparation technology.

With the development of high-tech industries, the types and demands of new materials, especially new functional materials, continue to increase, and the new functions of materials call for new preparation technologies. Spark Plasma Sintering (SPS) Spark Plasma Sintering (SPS) is a new type of rapid sintering technology developed in recent years. Because plasma activation sintering technology integrates plasma activation, hot pressing, and resistance heating, it has Fast heating speed, short sintering time, uniform crystal grains, it is beneficial to control the fine structure of the sintered body, the obtained material is dense, and the performance is good. This technology uses pulse energy, discharge pulse pressure and instantaneous high temperature field generated by Joule heat To achieve the sintering process, it is of great significance for the realization of high-efficiency, low-cost and low-cost material preparation. It has shown great advantages in the preparation of nanomaterials, composite materials, etc., and has been applied to metals, ceramics, composite materials and nanomaterials. Preparation of bulk materials, amorphous bulk materials, gradient materials and other functional materials. At present, many universities and scientific research institutions at home and abroad use SPS for research and development of new materials, and conduct in-depth research and exploration of its sintering mechanism and characteristics, especially Because of its rapid heating characteristics, it can be used as an effective means to prepare nano-bulk materials, which has attracted special attention from the material science community. However, there are still controversies about the sintering mechanism of SPS, especially the intermediate process of sintering still needs in-depth study.

Spark plasma sintering can produce many effects that are beneficial to rapid sintering because of the strong pulse current applied between the powder particles. Compared with conventional sintering technology, it has the following advantages: improved ceramic microstructure and improved material performance. Spark plasma sintering integrates plasma activation, hot pressing and resistance heating, fast heating speed, short sintering time, low sintering temperature and uniform grain . It is beneficial to control the fine structure of the sintered body, obtain high density of the material, and has the advantages of simple operation, high reproducibility, safety and reliability, space saving, energy saving and low cost.

SPS sintering mechanism has not yet reached a more unified understanding, and the intermediate process of sintering needs to be further studied. At present, it is generally believed that in addition to the Joule heat of hot press sintering and plastic deformation caused by pressure to promote the sintering process, the SPS process also generates a DC pulse voltage between the powder particles, and effectively utilizes the self-heating effect generated by the discharge between the powder particles. Resulting in some unique phenomena of the SPS process. The effect of applying DC switching pulse current in SPS:

1.  Due to the discharge shock wave generated by pulse discharge and the high-speed flow of electrons and ions in the opposite direction in the electric field, the gas adsorbed by the powder can be dissipated, and the initial oxide film on the surface of the powder is to a certain extent the upper part is broken down , so that the powder can be purified and activated;

2. Because the pulse is instantaneous, intermittent, and high-frequency. The discharge heat generated in the non-contact part of the powder particle and the Joule heat generated in the contact part of the powder particle are greatly affected. It promotes the diffusion of powder particles, and its diffusion coefficient is much larger than that under normal hot pressing conditions, so as to achieve rapid powder sintering;

3. The addition of ON-OFF rapid pulses makes the discharge parts and Joule heating components in the powder move quickly, so that the powder sintering can be uniform. Focusing the pulse at the junction of the grains is a characteristic of the SPS process.

During the SPS process, when the particles are discharged, local high temperatures of up to several thousand degrees to 10,000 degrees will be generated instantaneously, causing evaporation and melting on the surface of the particles, forming a neck at the point of contact of the particles, as the heat is immediately transferred from the heating center to the particles The surface and spread to the surroundings, the neck quickly cools down and the vapor pressure is lower than other parts. The vapor phase material condenses on the neck to form a higher evaporation-solidification transfer than the ordinary sintering method is another important feature of the SPS process. The crystal grains are heated by the pulse current and the vertical unidirectional pressure, and the bulk diffusion and the grain boundary diffusion are strengthened, and the sintering densification process is accelerated. Therefore, a high-quality sintered body can be obtained with a lower temperature and a relatively short time. The SPS process can be regarded as the result of the combined effects of particle discharge, conductive heating and pressure. SW Wang and LDChen et al. conducted SPS sintering studies on conductive Cu powder and non-conductive Al2O3 powder respectively. They believed that conductive materials and non-conductive materials have different sintering mechanisms. There are Joule heating effects and pulse discharge effects in conductive powders, but not conductive. The sintering of the powder is mainly due to the heat conduction of the mold. The intermediate processes and phenomena of spark plasma sintering are very complicated, and many scientists have established models for the sintering process of SPS. U. Anselmi-Tamburini et al. simulated the distribution of current and temperature in the SPS process, and believed that the distribution of temperature and current are closely related.

SPS equipment provides the possibility for the manufacture of very special new materials, such as, Nanomaterials can be sintered without significant growth of crystal grains;Composite materials;Tungsten carbide or other hard materials ;Structure Ceramics and functional ceramics.