28-October-2024
Recrystallized silicon carbide (R-SiC) is a high-performance ceramic material produced at high temperatures (2100-2300°C) through the evaporation-condensation mechanism, which facilitates the transport and migration of atoms to achieve the sintering of the green body. This process involves the evaporation of small-sized SiC particles and their preferential deposition on the neck regions of larger particles, leading to the growth of the necks of the larger particles while consuming the smaller ones, ultimately resulting in the direct bonding of SiC grains and enhancing the material's strength.
In the preparation process, recrystallized silicon carbide uses two different particle size distributions of high-purity silicon carbide as raw materials, with the addition of an appropriate amount of temporary binder but no sintering aids. The forming methods can include slip casting or gel casting, followed by sintering under high temperature and protective atmosphere. Due to the absence of volume change during the sintering process, complex shapes with high precision can be produced.
The characteristics of recrystallized silicon carbide include:
1. No volume change during the sintering process, allowing for the fabrication of complex shapes with high precision.
2. The density remains almost unchanged after sintering.
3. It contains no glass phase or impurities, resulting in very clear and clean grain boundaries, as any oxides or metallic impurities have evaporated at high temperatures.
4. It has a high porosity after firing, containing 10%-20% residual pore rate, which provides excellent high-temperature performance and thermal shock resistance.
5. The fracture strength of recrystallized silicon carbide at high temperatures is higher than at room temperature, attributed to the formation of a dense oxide film from silicon carbide oxidation, which passivates micro-cracks in the samples, thereby enhancing the material's fracture strength.
In terms of applications, recrystallized silicon carbide is widely used in high-temperature environments, particularly in high-temperature kiln furniture and diesel vehicle exhaust purification systems, due to its high-temperature strength, excellent thermal stability, and thermal shock resistance in the temperature range of 1350-1600°C. It can also serve as a heat exchange material and electrical heating element, used in solar energy collectors for solar power towers and high-temperature igniters.
