Silicon carbide (SiC) ceramics have excellent comprehensive properties such as high temperature resistance, wear resistance, corrosion resistance, radiation resistance, oxidation resistance, low thermal expansion and high thermal conductivity. They are key in aerospace, nuclear power, high-speed locomotives, weapons and equipment. The field has important application value. However, SiC ceramics are also difficult to form due to their extremely high thermal stability and strength.
At present, the preparation of ceramic materials in the world mainly adopts traditional powder molding methods, including fine powder preparation, molding (including calendering, extrusion, dry pressing, isostatic pressing, pouring, injection, etc.), sintering (including hot pressing sintering, reaction sintering). , Atmospheric pressure sintering, atmospheric pressure sintering, hot isostatic sintering, discharge plasma sintering, etc.) to processing. In the past 30 years, new types of ceramic material manufacturing processes have emerged endlessly and have made breakthroughs in all aspects, but there are still limitations. Including high preparation temperature (although the addition of sintering aid can reduce the sintering temperature, but the sintering aid will affect the performance of ceramics), it is not easy to obtain uniform chemical composition and microstructure, it is difficult to finish the processing, and the high brittleness of ceramic materials is difficult to solve. .
Advanced ceramic preparation technology must make breakthroughs in raw material preparation, molding, and sintering. Since Yajima and others successfully prepared SiC ceramic fibers with polycarbosilane in 1975, the precursor conversion ceramic technology has begun to enter people's field of vision. According to a BCC Research survey report, the global ceramic precursor market was US $ 437.6 million in 2017 (of which, SiC ceramic precursors accounted for 40.4% of the market share), and it is expected to reach US $ 712.4 million by 2022, with an average annual growth of 10.2%. The so-called precursor conversion ceramic is a polymer that can be converted into a ceramic material through high-temperature pyrolysis first through a chemical synthesis method. After molding, the ceramic material is obtained through high-temperature conversion. It has many advantages, including: (1) molecular designability: the molecular composition and structure of the precursor can be designed and optimized through molecular design, and then the ceramic composition, structure, and performance can be adjusted; (2) good technology Properties: The ceramic precursor is an organic polymer, inheriting the advantages of good polymer processability, such as: soluble impregnation, spinnable, moldable, foamable, 3D printing, etc., so it can be used to prepare traditional Low-dimensional materials and complex configurations that are difficult to obtain in powder sintering processes, such as ceramic fibers, ceramic films, complex three-dimensional components, etc .; (3) can be ceramicized at low temperatures without the need to introduce sintering aids; (4) ternary and multivariate copolymers can be prepared Valence compound ceramics; (5) Fiber-toughened ceramic materials can be obtained, thereby solving the problem of high brittleness of ceramic materials.
In summary, the precursor-transformation ceramic technology can flexibly control and improve the chemical structure, phase composition, atomic distribution, and microstructure of ceramic materials, etc., which has advantages unmatched by traditional ceramic preparation technology. The key to the preparation of ceramic materials by the precursor conversion method is whether a suitable precursor can be prepared, which directly determines whether a ceramic material with excellent properties can be successfully prepared. At present, the SiC ceramic precursors successfully developed and applied are mainly solid polycarbosilane (PCS). However, PCS as a precursor of SiC ceramics still has shortcomings, such as: C / Si in PCS is 2, and its pyrolysis product is rich in carbon, which ultimately affects the performance of SiC ceramics; PCS ceramics have low yields; they are solid at room temperature. When forming a ceramic matrix in a composite material, solvents such as xylene and tetrahydrofuran are required during the impregnation process, and these solvents need to be evaporated before cracking, resulting in long preparation cycles and complicated processes.
After a long period of research, the Nuclear Energy Materials Engineering Laboratory of the Ningbo Institute of Materials Technology and Engineering, the Chinese Academy of Sciences has prepared a fluidity (plural viscosity 0.01 ～ 0.2Pa · S), long storage time (> 6 months), and oxygen content. Low (~ 0.1 wt%), high ceramic yield (1600oC ceramic yield ~ 79wt%), C / Si in the ceramic product is ~ 1.1 and the mass change after static oxidation at 1500oC is less than 3% of liquid hyperbranched polycarbosilane ( LHBPCS). The sample quality has also been confirmed by multiple application units. In addition, the Nuclear Energy Materials Engineering Laboratory has also conducted in-depth research on the mechanism of LHBPCS curing and cross-linking, which can achieve its light curing molding and low temperature thermal curing molding, gelation time is only a few minutes, and the structure is dense without cells.