In the 21st century, with advancements in science and technology, the development of modern productivity has concentrated on areas like information technology, energy, materials, and bioengineering. Silicon carbide (SiC) materials, owing to their stable chemical properties, high thermal conductivity, low thermal expansion coefficient, low density, excellent wear resistance, high hardness, mechanical strength, and resistance to chemical corrosion, have rapidly emerged in the field of materials.

SiC ceramics originated in the 1960s. Before that, SiC was primarily used as an abrasive and refractory material. However, with the advent of advanced ceramics, traditional SiC ceramics were no longer satisfactory. In recent years, composite ceramics based on SiC have been developed, improving the performance of single-phase materials. SiC ceramics are now widely applied in ceramic ball bearings, valves, semiconductor materials, measuring instruments, and the aerospace industry.

The chemical stability of SiC is closely related to its oxidation properties. While SiC is prone to oxidation, it forms a thin silica (SiO₂) film upon oxidation, which gradually hinders further oxidation.

• Oxidation Behavior: In air, SiC starts oxidizing at 800°C, albeit slowly. As the temperature rises, the oxidation rate accelerates rapidly. In oxygen, the oxidation rate is 1.6 times faster than in air, though it decreases over time.

• Physical Appearance: Pure SiC is a colorless, transparent crystal. Industrial SiC exhibits various colors, including colorless, light yellow, light green, deep green, light blue, deep blue, and black, with transparency decreasing as the color darkens. SiC is classified into green SiC (colorless to deep green) and black SiC (light blue to black).

• Green SiC is more brittle and ideal for making self-sharpening abrasives.

• Black SiC is tougher and used differently than green SiC.

The preparation of ultrafine SiC powders, vital in high-tech applications, falls into three main categories:

• Solid-phase methods:

a. Carbothermal reduction method.

b. Direct Si-C reaction method, including high-temperature self-propagating synthesis and mechanical alloying.

• Liquid-phase methods:

a. Sol-gel method.

b. Polymer pyrolysis method.

c. Solvothermal method.

• Gas-phase methods:

a. Chemical vapor deposition (CVD).

b. Plasma-assisted method.

c. Laser-induced vapor deposition.

Due to the strong covalent bonds and low diffusion coefficient of SiC, densification cannot be achieved using conventional sintering methods. Sintering aids or external pressure must be employed to lower surface energy or enhance densification.

• Reaction-Bonded SiC Ceramics:

α-SiC and carbon are molded with a binder and dried. The preform is placed in Si-containing materials, heated above 1400°C, allowing molten or vaporized Si to infiltrate the pores and react with carbon to form SiC, ultimately densifying the material.

• Hot-Pressed SiC Ceramics:

Applying pressure during sintering accelerates atomic diffusion and increases sintering efficiency. However, this can lead to grain growth perpendicular to the pressure direction. Hot isostatic pressing (HIP) can mitigate this issue.

• Pressureless Sintered SiC Ceramics:

This method is promising for producing complex-shaped, large-sized SiC components. It includes solid-phase and liquid-phase sintering, depending on the sintering mechanism.

Precision balls are crucial in roundness measurement instruments, gyroscopes, bearings, and precise measurement devices. Conventional metal balls are prone to wear and deformation due to temperature. SiC ceramic balls, with their lightweight, high hardness, wear resistance, high-temperature resistance, and low thermal expansion, have been widely adopted in precision bearings and components.

SiC’s high hardness (Mohs scale: 9.2–9.6) makes it suitable for abrasives like grinding wheels, sandpaper, and polishing compounds, primarily used in mechanical processing industries. SiC ranks just below diamond and boron carbide as a commonly used abrasive.

The inherent brittleness of ceramics limits their application in aerospace and other high-tech fields. Toughening SiC with fiber reinforcements improves strength and modulus. SiC-based composites, with their high toughness, strength, and excellent oxidation resistance, are extensively used in high-temperature structural applications in the aerospace industry.