再结晶碳化硅及其复合材料的研究进展与应用

Abstract

Recrystallized silicon carbide (RSiC), a high-purity material sintered by using evaporation-condensation without additives, is one of the most important materials in high-temperature structural applications. However, its low density and porous structure, caused by the sintering mechanism in the absence of shrinkage, restrict the engineering applications of RSiC. This paper reviews research and related technologies on the preparation of high-density RSiC, porous RSiC, and RSiC composites. The fluidity of SiC slurries can be improved by electrostatic stabilization or steric stabilization, which has been achieved by modifying the surfaces of fine SiC raw powders with grafted polymers based on silane coupling agents; the resultant slurry had high solid content, and when sintered produced RSiC with a relatively high density (2.75 g/cm3). Using the interconnected pores of RSiC as a modification path, its density has been further increased (2.99 g/cm3) by combining polymer impregnation-pyrolysis of polycarbosilane (PIP, 1400℃) and recrystallization (2400℃). SiC has excellent chemical stability, thermal stability, and mechanical properties, and its sintering mechanism does not produce shrinkage. Because of these advantages, various porous RSiC elements have been manufactured with relative ease. These elements can be gradually substituted for those made from conventional materials, such as Al2O3, cordierite, reaction-bonded SiC, and mullite, in ceramic membranes used for concentrating hot corrosive solutions, filtering diesel particulate, and filtering fine particles from hot gases, as well as in volumetric honeycombs used to collect and convert solar energy. Because SiC is compatible with many metallic elements, RSiC-(inter)metallic composites have been prepared by infiltrating molten liquid through the interconnected pore structure of RSiC. Dense RSiC-MoSi2 composites directly infiltrated at 2050~2100℃ with molten MoSi2 exhibited excellent oxidation resistance, relatively low resistivity (~10-1 W cm) and a ~40% improvement in flexural strength compared to RSiC. The interface between SiC and MoSi2 has been modified by PIP pre-treatment of polycarbosilanes (PCS) (or phenolic resin), which either directly forms a SiC layer (with PCS) or reacts with Si while infiltrating the MoSi2-Si-X (X=Ti, Cr, Al) alloy, further improving strength (171.4 MPa) while decreasing the resistivity (10-3 W cm) and infiltration temperature (1800℃ for MoSi2-Si-X). This modified material can be used as structural material and as a high-temperature electrothermal material, substituting for MoSi2. Using molten infiltration assisted by gas pressure, a RSiC-Al composite with very high thermal conductivity (250 W/(m K)) and low thermal expansion coefficient has also been fabricated, a material which could meet the requirements of electronic packaging materials for high-power electronic components.