The difference between silicon carbide reaction sintering and pressureless sintering

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Silicon carbide ceramics, this kind of ceramic material has the best high temperature strength, and its oxidation resistance is also the best among all non-oxide ceramics, so it is widely used in various industrial fields.

Pressureless sintering

Pressureless sintering is considered the most promising SiC sintering method. According to different sintering mechanisms, pressureless sintering can be divided into solid phase sintering and liquid phase sintering. By adding appropriate amounts of B and C (oxygen content less than 2%) to the ultrafine β-SiC powder, S. Proehazka was sintered to a SiC sintered body with a density higher than 98% at 2020°C. A. Mulla et al. Using Al2O3 and Y2O3 as additives, 0.5μm β-SiC (with a small amount of SiO2 on the surface of the particles) was sintered at 1850 to 1950°C. The relative density of the obtained SiC ceramics is greater than 95% of the theoretical density, and the crystal grain size is small and the average size. It is 1.5 microns.

Reaction sintering

Reaction sintered silicon carbide, also known as self-bonding silicon carbide, refers to the process of porous steel billet reacting with gas or liquid phase to improve the quality of the billet, reduce pores, and sinter the finished product with a certain strength and dimensional accuracy. The α-SiC powder and graphite are mixed in a certain proportion and heated to about 1650°C to form a square billet. At the same time, it infiltrates or penetrates into the steel billet through vapor phase Si, reacts with graphite to generate β-SiC, and combines with existing α-SiC particles. When Si is completely infiltrated, a reaction sintered body with complete density and no shrinkage in size can be obtained. Compared with other sintering processes, the size change of reaction sintering during the densification process is small, and products with precise dimensions can be produced. However, the presence of a large amount of SiC in the sintered body makes the high temperature performance of reaction sintered SiC ceramics worse.

Pressureless sintered SiC ceramics, hot isostatic pressing sintered SiC ceramics and reaction sintered SiC ceramics have different properties. For example, in terms of sintering density and flexural strength, SiC ceramics have relatively more hot pressing sintering and hot isostatic pressing sintering, and reaction sintering SiC is relatively low. On the other hand, the mechanical properties of SiC ceramics change with the change of sintering aids. The pressureless sintering, hot pressing sintering and reaction sintering of SiC ceramics have good acid and alkali resistance, but the reaction sintered SiC ceramics have poor resistance to super acid corrosion such as HF. When the temperature is lower than 900℃, the flexural strength of almost all SiC ceramics is greatly improved than that of high-temperature sintered ceramics. The flexural strength of reaction sintered SiC ceramics drops sharply when it exceeds 1400℃. (This is due to a certain amount of free Si, which is caused by a sharp decrease in the bending strength above a certain temperature on the sintered body.) For pressureless sintered and hot isostatic pressing sintered SiC ceramics, the high temperature performance is mainly affected by the types of additives .

These two sintering methods of SiC ceramics have their own advantages. However, in today’s rapid development of science and technology, there is an urgent need to improve the performance of SiC ceramics, continuously improve the manufacturing process, reduce production costs, and achieve low-temperature sintering of SiC ceramics. In order to reduce energy consumption, reduce production costs, and promote the industrialization of SiC ceramic products. Shanghai Gehang Vacuum Technology Co., Ltd. has been committed to the research of sintering process of silicon carbide products. Can provide very stable, very high quality, very cheap vacuum sintering furnace.

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Tags: SIC reactive sintering technology, SIC sintering furnace. Silicon carbide ceramics