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Common Sintering Methods for Advanced Ceramics and Composite

Common Sintering Methods for Advanced Ceramics and Composites

The sintering methods of special ceramic materials include conventional sintering, reactive sintering, gas pressure sintering, hot pressing sintering, isostatic pressing sintering, microwave sintering, spark plasma sintering and high temperature self-propagating sintering.

1Conventional sintering

Conventional sintering is usually carried out by resistance heating in traditional electric furnace, which is the most commonly used sintering method in the production of ceramic materials and composite materials.

 

2Reactive sintering

Reactive sintering is limited to a few systems: silicon nitride, silicon oxynitride, silicon carbide, etc.

The advantages of reactive sintering are: no additional additives are needed; the shape and size of the product are basically unchanged, and the product with complex shape and precise size can be produced; the process is simple, economical and suitable for mass production.

The disadvantage is that the density of sintered billet is low and the mechanical properties of materials are not high.

3Gas pressure sintering

Pressure sintering is a special atmosphere pressure sintering furnace, which exerts a certain pressure atmosphere during the set period of high temperature sintering process to meet the sintering requirements of some special ceramic materials. Si3N4 has excellent comprehensive properties, but it has been sublimated and decomposed before sintering at high temperature without effective protective measures. The most commonly used method is to increase the pressure of nitrogen atmosphere, such as pressure sintering of silicon nitride.

Pressure sintering is mainly used in the sintering of some special ceramic materials, such as anti-decomposition. At the same time, at the later stage of thermal insulation, a uniform pressure process similar to the cold isostatic pressing process is produced under certain pressure atmosphere, which is conducive to the further improvement of the properties of sintered materials. At present, most silicon nitride products in China are sintered under atmospheric pressure.

In addition, oxygen partial pressure in atmosphere is very important when sintering some oxide products, especially some semiconductor ceramics.

4Hot pressing sintering

Hot pressing sintering is accomplished by using a special hot press under single-phase or dual-phase pressure at high temperature. The interaction between temperature and pressure strengthens the viscous and plastic flow of particles, facilitates the densification of billets, and produces products with almost no porosity. Therefore, hot pressing sintering is also called "full densification process".

The advantages of hot pressing sintering are: high density, short sintering time, low temperature, inhibited grain growth and improved product performance.

The disadvantage is that the application range is limited, and the products with simple shape can only be manufactured. At the same time, the microstructure after Hot-pressing Sintering is anisotropic, which leads to the anisotropy of service performance and limits its application range. In addition, due to the high hardness, the subsequent processing of hot-pressed products is particularly difficult.

 

5Isostatic pressing sintering

Cold isostatic pressing sintering is accomplished by using a special cold isostatic press and uniform pressure in all directions at high temperature. Cold isostatic pressure sintering is a common sintering method for high performance ceramics.

The advantages of cold isostatic pressing sintering are: uniform product density, excellent mechanical properties and isotropy, especially suitable for complex shape parts, large single furnace processing capacity and low average cost.

The disadvantage is that cold isostatic pressing sintering equipment is expensive and one-time investment is large.

6Microwave sintering

Microwave sintering is a process of sintering and densification of ceramics by using dielectric loss of ceramics in microwave electromagnetic field to bring materials to sintering temperature. According to the utilization of microwave energy, microwave sintering can be divided into microwave heating sintering, microwave plasma sintering, microwave-plasma distribution sintering and so on.

7High temperature self-propagating sintering

High temperature self-propagating sintering (SHS) is based on the principle of exothermic chemical reaction, using external energy to induce local chemical reaction and form chemical reaction frontier (combustion wave). Thereafter, the chemical reaction proceeds with the support of its own heat release. With the advance of combustion wave, combustion spreads to the whole system and synthesizes the required materials. 。

At present, the self-propagating sintering technology has been developed rapidly and successfully applied to industrial production. Combining with many other technologies, a series of related technologies have been formed, such as SHS powder synthesis technology, SHS sintering technology, SHS densification technology, SHS metallurgical technology and so on.

The advantages of high temperature self-propagating sintering are simple equipment and process, rapid reaction, high purity of products and low energy consumption. It is suitable for synthesizing non-stoichiometric compounds, intermediate products and metastable equivalents.

8Spark plasma sintering

Spark plasma sintering (SPS) is a fast sintering technology based on the spark discharge phenomenon (instantaneous formation of high temperature plasma) produced by powder in the initial stage of pulse discharge, which uses instantaneous high temperature field to achieve densification. At present, there is no unified understanding of its sintering mechanism. However, it is generally believed that the SPS process not only has the Joule heat of hot pressing sintering and the plastic deformation caused by compression to promote sintering, but also generates DC pulse voltage between the powder particles. Only by using the spontaneous heating effect of the discharge between the powder particles, can some special phenomena of the SPS process be produced.

The advantage of spark plasma sintering technology is that it has the advantages of fast heating rate, short heating time and low sintering temperature, and can form ultrafine grains or even nano-grains without obvious anisotropy.

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