What is SiC Ceramic?

SiC ceramic is a ceramic material produced by the reaction of silicon (Si) and carbon (C) elements, featuring extremely high hardness, heat resistance and chemical stability. It not only has extensive applications in industry, but also holds an important position in the high-tech field.

The properties and characteristics of SiC ceramics

1. High hardness

The hardness of SiC ceramics is extremely high, second only to that of diamond. Its Mohs hardness reaches 9, making it capable of easily wearing and cutting other softer materials. For this reason, SiC ceramics are often used to manufacture cutting tools, wear-resistant components, and other applications that require wear resistance.

2. High heat resistance

Silicon carbide has excellent high-temperature stability and can maintain the stability of its physical and chemical properties in high-temperature environments above 1600℃. This makes SiC ceramics have irreplaceable advantages in applications at high temperatures, such as engine components and boiler materials.

3. Excellent chemical stability

SiC ceramics have strong resistance to most acidic and alkaline solutions and corrosive gases. This has enabled it to be widely applied in highly corrosive environments in industries such as chemical engineering and metallurgy.

4. Low density

Although SiC ceramics have high hardness and strong heat resistance, their density is relatively low, and they have good lightweight characteristics. This is particularly important for the aerospace and automotive industries that require lightweight materials.

The sintering process of SiC  ceramics is of great importance. Through extensive research and exploration by numerous researchers, various sintering techniques have been successively developed, including pressureless sintering, hot pressing sintering, reaction sintering, hot isostatic pressing sintering, and more.

Pressureless Sintering

Pressureless sintering is regarded as the most promising sintering method for SiC. According to different sintering mechanisms, pressureless sintering can be divided into solid-phase sintering and liquid-phase sintering. By simultaneously adding an appropriate amount of B and C(with an oxygen content of less than 2%) to the ultrafine β-SiC powder, the SiC sintered body with a density higher than 98% will be sintered at 2020℃.

Hot Pressed Sintering

Pure SiC can only be densely sintered at very high temperatures without any sintering additives. Therefore, many people implement hot-pressing sintering processes for SiC. Aluminum and iron are the most effective additives for promoting the hot-pressing sintering of SiC. Additionally, the hot-pressing sintering process can only produce SiC parts with simple shapes, and the quantity of products produced by the one-time hot-pressing sintering process is very small, which is not conducive to industrial production.

Reactive Sintering

Reaction-sintered silicon carbide, also known as self-bonded silicon carbide, refers to the process in which porous steel billets react with gas or liquid phases to improve the quality of the billets, reduce porosity, and sinter the finished products with certain strength and dimensional accuracy. The α-SiC powder is mixed with graphite in a certain proportion and heated to about 1650℃ to form a billet. Meanwhile, it penetrates through the gas-phase Si or penetrates into the billet, reacts with graphite to form β-SiC, and combines with the existing α-SiC particles. When Si is fully infiltrated, a reactive sintered body with complete density and no dimensional shrinkage can be obtained. Compared with other sintering processes, the dimensional change of reaction sintering during the densification process is relatively small, and products with precise dimensions can be produced. However, the presence of a large amount of SiC in the sintered body deteriorates the high-temperature performance of reaction-sintered SiC ceramics.

Isostatic Pressing Sintering

In order to overcome the shortcomings of the traditional sintering process, the hot isostatic pressing sintering technology is adopted. Under the condition of 1900℃, fine crystalline phase ceramics with a density greater than 98 were obtained, and the bending strength at room temperature could reach 600mpa. Although hot isostatic pressing sintering can produce complex-shaped and dense phase products with good mechanical properties, hip sintering must seal the blank, making it difficult to achieve industrial production.