High-boron content silicon-boron-carbon-nitrogen precursor and preparation method thereof

Abstract

The invention relates to a high-boron content silicon-boron-carbon-nitrogen precursor and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing functional, bifunctional and trifunctional chlorosilane containing unsaturated groups and hexamethyl-disilazane at a low temperature according to a certain ratio, raising the temperature and completely reacting, dropping 1,3-diethyl cycloborazane under low temperature conditions according to a certain ratio, fully reacting the reactants, and finally performing reduced pressure distillation to obtain the solvent and by-products produced by the reaction, thereby obtaining faint yellow viscous liquid or a solid product, namely the SiBCN ceramic precursor. According to the synthetic method disclosed by theinvention, a novel Polyborosilicate resin is prepared by adopting a 'double boron source', the boron content of the prepared SiBCN ceramic can reach 20%, and the problems that the boron content is low and improvement of high temperature resistance and oxidation resistance of the ceramic is not obvious can be solved. The elementary composition regulation range of the precursor disclosed by the invention is wide, and resins which are suitable to serve as a high-temperature-resistant coating, a fiber reinforcement or a ceramic-based composite material matrix and have different elementary compositions can be prepared.

Description

technical field [0001] The invention relates to a silicon-boron-carbon-nitrogen precursor with high boron content and a preparation method thereof, in particular to a method for preparing a silicon-boron-carbon-nitrogen precursor with high boron content by introducing a double boron source, which belongs to the technical field of new resin materials , Background technique [0002] With the continuous development of the advanced ceramics industry, especially the surge in demand for high-performance ceramic fibers and ceramic matrix composites in the fields of aviation, aerospace, and military industry, the technology of preparing multi-component ceramics by precursor conversion method has received more and more research at home and abroad. attention. Compared with the binary system of SiC, S 3 N 4 Ceramics and SiCN ceramics of the ternary system, SiBCN ceramics of the quaternary system prepared by the precursor conversion method have greatly improved the high temperature r...

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Problems solved by technology

According to the different mechanism of the introduction of B element, the precursor synthesis method can be divided into three types. The first method is firstly proposed by Riedel to introduce boron element into chlorosilane through the boron hydrogen addition reaction of borane and double bond, and then through The SiBCN precursor prepared by further aminolysis reaction, because borane is a trifunctional compound, the product obtained by the reaction has a high degree of crosslinking, is solid at room temperature, and has poor processability, and the prepared ceramics have low B element content and are not More than 6wt%; the second is to use the dehydrogenation coupling reaction of B-H bond and N-H bond to introduce B element into the system to synthesize the SiBCN precursor, because the borazine used contains more B-H bonds and N-H bonds, so in addition to In addition to the reaction of polysilazane, borazine will also undergo cross-linking reaction itself, resulting in excessive cross-linking of the system and poor processability. Sneddon et al. used a boracyclic ring containing only one B-H bond to react with polysilazane , the rheological properties of the prepared sample are good, but due to the low content of B elements in the synthesized sample, it fails to improve the high temperature stability and oxidation resistance of the system; the third is to use chlorosilane, boron trichloride and hexa Methyldisilazane reaction, and then through aminolysis to obtain SiBCN precursor. Since boron trichloride is a trifunctional compound, the viscosity of the precursor will be too high if the feeding ratio is too high. Otherwise, the content of B element will be low.

Moreover, the above several synthesis methods all have problems such as complex synthesis steps, high cost, and difficult removal of by-products. The prepared SiBCN ceramics have low B element content, which is not enough to improve the high-temperature stability and oxidation resistance of ceramics.

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