Silicon carbide (SiC) ceramics have good high temperature stability, corrosion resistance, high temperature oxidation resistance, high strength, hardness, and low thermal expansion coefficient. They are not only widely used in traditional industrial fields, but also in advanced energy and space technology. Applications in the field are also expanding. Traditional SiC ceramics are prepared by mixing SiC powder and sintering aids by ball milling and then forming and sintering. The sintering methods include atmospheric sintering, hot pressing sintering, reaction sintering, hot isostatic pressing sintering, spark plasma sintering, recrystallization sintering, etc. . The precursor conversion ceramics (PDCs) method is to form the target product by crosslinking and curing precursors such as polycarbosilane (PCS) and high-temperature ceramization. It has the advantages of strong molecular design, low synthesis temperature, and easy molding of complex ceramic structures. Considered to be one of the transformative technologies in the ceramics field.
Solid PCS materials have become one of the most commonly used precursors of advanced ceramic matrix composites due to their easy melting and dissolution, adjustable silicon-to-carbon stoichiometric ratio, and rich element composition. However, there are also many challenges. On the one hand, when PCS is cross-linked by air infusibility, more oxygen needs to be introduced, which affects the temperature resistance of the final SiC ceramic; on the other hand, the lower ceramic yield of PCS (usually around 60%) will result in low composite material bulk density , The cracking process produces a lot of micro-cracks, long immersion cycle and other problems. Researchers from the Advanced Energy Materials Engineering Laboratory of Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences explored a catalytic system to react acrylonitrile (AN), which is usually not easy to hydrosilation, with PCS, and synthesized a new precursor containing cyano-containing polycarbonate Silane (PCSCN). The experimental results show that PCSCN maintains the characteristics of being easily soluble and meltable, the molecular weight and chemical composition can be customized, and the ceramic yield is greatly increased to more than 80%. In addition, PCSCN containing cyano groups inherits the excellent spinnability of PCS (as shown in the figure) and can be used as an alternative material for continuous SiC fibers. Related results were published in the high-level journal J. Eur. Ceram. Soc. (2020, 40, 5226-5237) in the ceramics field, and applied for a Chinese patent (CN201811355027.7, CN201811354984.8).
Solid polyaluminumcarbosilane (PACS) has become one of the most important precursors of silicon carbide fiber synthesis due to its excellent rheological properties at high temperatures. However, conventional high-temperature and normal-pressure synthesis of PACS will be accompanied by more cyclic and branched structures, which will reduce the content of precursor linear molecules, thereby affecting the spinning of the precursor and the performance of the final product. Researchers in the Advanced Energy Materials Engineering Laboratory of Ningbo Institute of Materials have developed a method to synthesize PACS using liquid polysilicon carbosilane (PSCS) and aluminum-containing compounds at high temperature and high pressure, which effectively reduces the synthesis temperature. The research results show that, under similar conditions, the PACS developed by the high-temperature and high-pressure method has lower branching degree, higher Si-H content and higher ceramic yield than the PACS prepared by the high-temperature and atmospheric pressure method, which significantly improves PACS spinning capability. Related research results were published in the international professional journals Appl. Organometal. Chem. (2019, 33, e4720) and Ceram. Int. (2019, 45, 16380-16386), and applied for a Chinese patent (CN201910160345.6, CN2019110438617). With the support of the President’s Fund of the Chinese Academy of Sciences, the laboratory researchers independently designed the precursor synthesis engineering equipment based on the small-scale high temperature and high pressure synthesis PACS process, and initially realized the high temperature and high pressure engineering preparation of the solid precursor.