Wed, 06 Jun 2018 02:18:46 +0000
Working principle of discharge plasma sintering system
It is difficult to guarantee the nanometer size of grain and meet the requirement of complete compactness. SPS technology can significantly inhibit grain coarsening due to its rapid heating and short synthesis time. SPS technology can significantly inhibit grain coarsening due to its rapid heating and short synthesis time.
SPS can quickly cool this feature is used to control the reaction mechanism of sintering process, and avoid some unnecessary reaction, defects and the structure of the powder could be preserved in the block after sintering material, in a broader sense, it is advantageous to the synthesis of dielectric materials, especially for the preparation of nanometer materials.
2. Gradient functional materials
(FGM) is a kind of composite material composed of gradient distribution in a certain direction. The sintering temperature of each layer is different. Using CVD,PVD and other methods to prepare gradient materials, the cost is very high and it is difficult to realize industrial production. SPS technology can overcome this difficulty.
SPS can manufacture ceramic/metal, polymer/metal and other materials with thermal gradient, wear-resistant gradient, hardness gradient, conductive gradient and porosity gradient. The gradient layer can reach more than 10 layers to realize the gradient distribution of sintering temperature.
3. Electromagnetic materials
The SPS technology can also make SiGe, PbTe, BiTe, FeSi, CoSb3 thermoelectric conversion components, systems, and is widely used for various functions in the field of electronic materials, superconducting materials, magnetic materials, such as target material, dielectric materials, hydrogen storage materials, shape memory materials, solid battery materials, optical materials, etc.
4. Intermetallic compounds
Intermetallic compounds have brittleness at room temperature and high melting point, so it requires special process to prepare or produce them. Using the melting method (edm melting, melting resistance and induction melting, etc.) preparation of intermetallic compounds are often required to high-energy, vacuum system, and the need for processing (forging) for the second time. Using SPS technology to prepare intermetallic compounds, because the effective utilization of the spontaneous heat effect between the particles and the surface activation, which can realize low temperature and fast sintering, so the SPS technique for the preparation of intermetallic compound is an effective method. At present, the intermetallic compound system prepared by SPS technology includes: Ti-Al system, Mo-Si system, Ni-Al system, etc.
5. High density, fine grain ceramics and metal ceramics
In the SPS process, each of the powder particles in the sample and the interstitial space between them may itself be a source of heat. The necessary heat transfer process for sintering with normal method is negligible in SPS process. Therefore, the sintering time can be greatly shortened and the sintering temperature can also be significantly decreased. SPS is an advantageous sintering method for the preparation of high density and fine grain ceramics.
6. Other materials
In addition, SPS technology has been successfully applied in the metal matrix composites (MMC), amorphous alloy, biological materials, superconducting materials and the preparation of porous materials and other new materials, and have gained more excellent performance. At the same time, SPS in cemented carbide sintering, layers of metal powder synchronous connection (bonding), ceramic powder and metal powder and solid powder – solid connection have been widely used.
7, SPS system consists of a vertical unidirectional pressure device and pressure automatic display system and a computer automatic control system, a special electricity with water cooling device and a tributary of sintering pulse generator, a water-cooled vacuum chamber and vacuum/air/hydrogen/oxygen/argon atmosphere control system, all kinds of lock safety devices and all of these devices in the central control operation panel.
SPS USES the direct dc pulse current to direct the sintering pressure sintering method, by regulating the size of the pulse dc current control the heating rate and sintering temperature. The whole sintering process can be carried out in a vacuum environment or in a protective atmosphere. Sintering process, the pulse current directly through the head up and down and sintered powder or graphite mould, thus heating system heat capacity is small, fast heating and heat transfer, so that the rapid heating sintering is possible.
8. Sintering atmosphere
The sintering atmosphere has a great influence on sample sintering (except for vacuum sintering).
Under oxygen atmosphere, because oxygen by sinter surface adsorption or chemical reaction, make the crystal surface forming type cation vacancy of stoichiometric compounds, positive ion space increases, at the same time make may go into the lattice oxygen in closed porosity, and along the surface of the diffusion and oxygen ion vacancies, diffusion speed and sintering. When sintering is controlled by cation diffusion, the oxidation atmosphere or oxygen partial pressure is high, which is conducive to the formation of cation vacancy and promote sintering. Under the control of negative ion diffusion, reduction atmosphere or low oxygen partial pressure will lead to oxygen ion vacancy and promote sintering.
Samples sintered in hydrogen atmosphere, due to a hydrogen atom radius is small, easy to spread and conducive to the elimination of closed porosity, type of material such as alumina sintering in hydrogen atmosphere can get close to the theoretical density of sintered body samples.
9. Sintering temperature is one of the key parameters of plasma rapid sintering. The determination of sintering temperature should take into account the phase transformation of sintered samples at high temperature, the growth rate of grains, the quality requirements of samples and the density requirements of samples. In general, with the increase of sintering temperature, sample density as a whole is on the rise, this suggests that the sintering temperature has obvious influence on degree of sample density, the higher the sintering temperature, sintering material in the process of transmission speed faster, the easier it is compacted samples.