Silicon nitride ceramic precursor and method for preparing the same

Abstract

The application relates to the field of high polymer materials, and particularly provides a silicon nitride ceramic precursor and a preparation method thereof. The preparation method comprises the following steps: S100, carrying out an ammonolysis reaction on trimethylsilyl-substituted amine halosilane, adding an acid-binding agent, and obtaining an oligomeric silazane; and S200, carrying out a heating treatment on the oligomeric silazane under an inert atmosphere, and obtaining the silicon nitride ceramic precursor. The trimethylsilyl-substituted amine halosilane is introduced into a liquid ammonia system, and the ammonolysis is carried out in cooperation with the acid-binding agent, the standing and separation and the cross-linking and solidification, so that the treatment process of by-products such as ammonium halide can be obviously simplified, and the chemical purity and the ceramic yield of the silicon nitride ceramic precursor and pyrolysis products can be improved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, it provides a silicon nitride ceramic precursor and its preparation method. Background Technology

[0002] Silicon nitride is an important structural ceramic material with outstanding properties such as high thermal shock resistance, high temperature stability, high hardness and high wear resistance. Silicon nitride materials have been widely used in the automotive, metal processing and microelectronics fields.

[0003] Precursor conversion refers to the process of obtaining a polymer through chemical synthesis, followed by processing, molding, and heat treatment to obtain ceramic materials. Precursor conversion can achieve a uniform atomic distribution at the molecular level. By designing and optimizing the precursor composition through molecular structure design, effective control over the microstructure and purity of the material can be achieved, thus enabling controllable structure and properties of the ceramic material. The most commonly used precursor for preparing silicon nitride ceramics using precursor conversion is the perhydropolysilazane developed by Japanese scientists. This involves the ammonolysis reaction of a dichlorosilane-pyridine complex with ammonia to obtain an oligomeric silazane composed of linearly linked rings. Because the Si / N ratio in the perhydropolysilazane structure is approximately 1, the resulting silicon nitride ceramic is a silicon-rich product. It requires pyrolysis in an ammonia or hydrazine atmosphere to nitride excess silicon, yielding high-purity Si3N4 ceramics. Summary of the Invention

[0004] This invention provides a silicon nitride ceramic precursor and its preparation method. By introducing trimethylsilyl-substituted amine halosilane into a liquid ammonia system and combining it with an acid-binding agent for ammonolysis, static separation, and cross-linking curing, the processing flow of by-products such as ammonium halides can be significantly simplified, and the chemical purity and ceramic yield of the silicon nitride ceramic precursor and pyrolysis products can be improved.

[0005] This invention provides a method for preparing a silicon nitride ceramic precursor, the method comprising the following steps: S100, subjecting a trimethylsilyl-substituted amine halosilane to an ammonolysis reaction, adding an acid-binding agent to obtain an oligomeric silazane; S200, subjecting the oligomeric silazane to a heat treatment under an inert atmosphere to obtain the silicon nitride ceramic precursor.

[0006] In any of the above technical solutions, step S100 specifically includes: S110, reacting trimethylsilyl-substituted amine halosilane with ammonia to undergo ammonolysis reaction to obtain a suspension; S120, adding an acid-binding agent to the suspension to obtain a polymerization product; S130, after the polymerization product reaction is completed, allowing it to stand and separate to obtain an oligomeric silazane.

[0007] In any of the above technical solutions, ammonia exists in liquid phase in step S110.

[0008] In any of the above technical solutions, in step S100, the preparation method is carried out at a temperature of -40~25℃ for 0.5~24h.

[0009] In any of the above technical solutions, in step S100, the acid-binding agent includes at least one of triethylamine, diisopropylethylamine, N,N-dimethylcyclohexylamine, N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, pyridine, N,N,N',N'-tetramethylethylenediamine, triethylenediamine, 4-dimethylaminopyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and pentamethyldiethylenetriamine.

[0010] In any of the above technical solutions, in step S100, the molar ratio of the acid-binding agent to the trimethylsilyl-substituted amine halosilane is 1:(1~100).

[0011] In any of the above technical solutions, in step S200, the heating temperature is 25~300℃ and the time is 1~10h.

[0012] In any of the above technical solutions, in step S200, the inert atmosphere includes at least one of nitrogen and argon.

[0013] The present invention also provides a silicon nitride ceramic precursor, which is prepared using any of the preparation processes described in the above-described technical solutions. Therefore, it includes the beneficial effects of any of the above-described technical solutions, which will not be elaborated further here.

[0014] The technical effects that can be achieved by adopting the technical solution of the present invention are as follows: 1. This invention uses trimethylsilyl-substituted amine halosilanes as reactants to prepare precursors, which can ensure the chemical stability of the precursors, reduce the probability of precursor oxidation and hydrolysis, and significantly reduce the oxygen content of silicon nitride products. At the same time, it is easy to detach during pyrolysis, which can reduce the silicon content and carbon content of silicon nitride products, making the product a high-purity silicon nitride ceramic with near stoichiometry. 2. This invention uses liquid ammonia as both reactant and solvent, optimizes the molecular structure of the precursor and the preparation reaction process, and improves the ceramic yield of silicon nitride ceramic precursors; 3. This invention allows for control over the polymerization degree of silicon nitride ceramic precursors, enabling the preparation of liquid and solid precursors as needed, thus expanding the application range of the product and demonstrating high application value. Detailed Implementation

[0015] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0016] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0017] To make the above-mentioned objectives, features and advantages of this aspect more apparent and understandable, specific embodiments of this aspect are described in detail below.

[0018] Silicon nitride is an important structural ceramic material with outstanding properties such as high thermal shock resistance, high temperature stability, high hardness, and high wear resistance. Silicon nitride materials have been widely used in the automotive, metal processing, and microelectronics industries. The precursor conversion method is a route that uses chemical synthesis to obtain processable polymer precursors, which are then shaped and heat-treated to obtain ceramic materials. This method can achieve uniform atomic distribution at the molecular level, and optimize the material composition and microstructure through precursor molecular design, thereby enabling control over the ceramic's properties and purity.

[0019] In existing technologies, common routes for preparing silicon nitride precursors include ammonolysis of halosilanes with ammonia and polymerization of amino-substituted silanes in organic solvents or inert atmospheres to prepare polysilazane precursors. For example, ammonolysis of dichlorosilane-pyridine complexes with ammonia can yield cyclic or chain-like oligosilazanes linked by linear segments. However, since the Si / N ratio of commonly used all-hydrogen polysilazanes is approximately 1, the pyrolysis products tend to be silicon-rich, requiring further nitridation of excess silicon in an ammonia or hydrazine atmosphere to obtain high-purity Si3N4. Furthermore, traditional processes still have shortcomings in terms of precursor chemical stability, impurity control, separation process complexity, and controllability of the degree of polymerization, affecting the purity and performance of the final ceramic.

[0020] Therefore, there is an urgent need to develop a preparation method that can improve the chemical stability of the precursor and reduce the impurity content, while simplifying the separation process and increasing the ceramic yield and final ceramic purity. This embodiment introduces trimethylsilyl-substituted amine halosilanes into a liquid ammonia system and, in conjunction with an acid-binding agent, performs ammonolysis, static separation, and cross-linking curing. This significantly simplifies the processing of byproducts such as ammonium halides and improves the chemical purity and ceramic yield of the silicon nitride ceramic precursor and pyrolysis products.

[0021] Specifically, the preparation method of the silicon nitride ceramic precursor in this embodiment includes the following steps: S100. Trimethylsilyl-substituted amine halosilanes are subjected to ammonolysis, and an acid-binding agent is added to obtain oligomeric silazanes. S200. Under an inert atmosphere, oligomeric silazane is heated to obtain a silicon nitride ceramic precursor.

[0022] Preferably, in step S100, trimethylsilyl-substituted amine halosilanes undergo ammonolysis, and an acid-binding agent is added to obtain oligomeric silazanes. Ammonia molecules undergo nucleophilic substitution of the silicon center of the halosilane, with Si-X being replaced by -NH- or -NH2 fragments to form Si-N building blocks, while simultaneously releasing HX. The added acid-binding agent rapidly reacts with HX to generate an organic ammonium salt, driving the substitution reaction and controlling the condensation rate by altering the acid-base / ionic environment. Finally, linear / cyclic / short-chain polysilazane oligomers are obtained through condensation, dehydrogenation coupling, and other reactions. Constructing Si-N bond-containing oligomeric silazane precursors at the molecular level yields precursor molecules with controllable chemical composition and low impurity content, significantly reducing oxygen and carbon residues in the ceramic after pyrolysis, and improving the chemical purity and yield of the ceramic. This step can directly generate processable liquid or solid precursors, facilitating subsequent molding; by controlling the acid-binding agent and process parameters, it can also reduce processing steps and solvent recovery costs, improving process economy and scale-up feasibility.

[0023] Furthermore, when the molar ratio of the acid-binding agent to the trimethylsilyl-substituted amine halosilane is 1:(1~100), and the reaction is carried out at -40~25℃ for 0.5~24h, a higher amount of acid-binding agent can rapidly neutralize the generated HX, forming more organic ammonium salts, increasing ionic strength and changing the polarity of the medium, promoting more complete halogen substitution, inhibiting acid-catalyzed side reactions, and simultaneously slowing down disordered crosslinking through ion pairing and solvation effects, which is beneficial for obtaining oligomers with more controllable molecular weight and narrower distribution. Conversely, a lower amount results in a slower reaction, which is beneficial for local crosslinking or the formation of products with a higher degree of polymerization. The temperature range of -40~25℃ can be used to precisely control the reaction rate and selectivity: lower temperatures slow down condensation and side reactions, which is beneficial for the formation and stability of liquid precursors, while higher temperatures promote condensation and shorten the reaction time; the reaction time is used to complete ammonolysis and reach the desired degree of polymerization.

[0024] Preferably, in step S200, heating in an inert atmosphere causes the terminal reactive groups of the oligomeric silazane to crosslink through dehydrogenation coupling, condensation, or rearrangement, forming a three-dimensional inorganic / organic hybrid network. Simultaneously, the thermally unstable organic substituents break down at a lower temperature and escape as volatile products, reducing residual carbon and creating favorable conditions for subsequent inorganic phase transitions. Transforming the oligomer into an insoluble and infusible crosslinked network precursor ensures shape stability and minimal volatilization loss during subsequent high-temperature pyrolysis, thereby improving pyrolysis yield and facilitating the acquisition of dense, uniform Si3N4 ceramics. The crosslinked and cured precursor is easy to store and transport for long periods, reducing the risk of deformation before processing or heat treatment. The degree of crosslinking is adjustable, thereby optimizing the porosity, grain growth, and mechanical properties of the final ceramic, adapting to the performance requirements of different application scenarios.

[0025] Furthermore, by heating at 25–300 °C for 1–10 h in an inert atmosphere, the oligomeric silazane undergoes thermally induced condensation and devolatification processes. The terminal reactive groups undergo dehydrogenation coupling or condensation crosslinking, forming an insoluble and infusible three-dimensional network. This ensures shape retention and provides a stable precursor for subsequent high-temperature ceramization. Simultaneously, easily pyrolyzed or volatile organic substituents partially pyrolyze and escape during this stage, reducing residual carbon content and improving the purity of the ceramic after pyrolysis. At the lower temperature limit, mild curing and structural rearrangement are achieved, which helps maintain a certain level of processability. Temperatures closer to the upper limit promote deeper crosslinking and removal of volatile components, which is beneficial for improving pyrolysis yield, but must be controlled to avoid premature densification or crack formation. Choosing an inert atmosphere prevents high-temperature oxidation and introduces fewer oxygen impurities.

[0026] For example, step S100 specifically includes: S110. Trimethylsilyl-substituted amine halosilane is reacted with ammonia to undergo ammonolysis to obtain a suspension; S120. Add an acid-binding agent to the suspension to obtain the polymerization product; S130. After the polymerization product reaction is complete, allow it to stand and separate into liquids to obtain oligomeric silazane.

[0027] Preferably, in step S110, ammonia, as a strong nucleophile, replaces Si-X in the liquid phase. The resulting Si-NH or Si-N-Si fragments, along with unreacted substances and the generated salts, form a dispersed phase or suspended particles due to the difference in polarity of the medium. Solvent / phase behavior, particle size, and interfacial tension determine that the system is in suspension, thus creating favorable conditions for subsequent acid-binding agent regulation and phase separation. High-efficiency halogen replacement is achieved under mild conditions in a high-concentration ammonia environment, with the product in a suspended / two-phase state, which facilitates subsequent phase separation and purification, and yields intermediates with a narrower molecular weight distribution and better uniformity. The suspension system enhances mass transfer, increases the reaction rate, and reduces local over-polymerization or side reactions, facilitating continuous or batch industrial production. The two-phase / suspension state provides a physical basis for simple static stratification, reducing subsequent processing costs and equipment requirements.

[0028] Preferably, in step S120, the acid-binding agent undergoes acid-base neutralization with the generated HX to form an organic ammonium salt, thereby reducing the free H. + The concentration of acid-binding agents alters the protonation state of active centers in the reaction, thereby controlling the condensation equilibrium and active center density between Si and NH4+. Acid-binding agents can also influence ionic strength and interfacial behavior through solvation / coordination, fundamentally regulating the polymerization pathway. By rapidly neutralizing generated hydrogen halides and altering local acid-base conditions, acid-binding agents promote controlled polymerization, resulting in polymers with target molecular weights and degrees of polymerization, avoiding disordered crosslinking or excessive aggregation. Polymerization kinetics can be adjusted by selecting the type, molar ratio, and timing of addition of the acid-binding agent, enabling on-demand preparation of liquid / solid precursors. Acid-binding agents cause byproducts to exist as organic ammonium salts, facilitating recovery and treatment, and reducing environmental and safety risks.

[0029] Furthermore, the acid-binding agent includes at least one of triethylamine, diisopropylethylamine, N,N-dimethylcyclohexylamine, N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, pyridine, N,N,N',N'-tetramethylethylenediamine, triethylenediamine, 4-dimethylaminopyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and pentamethyldiethylenetriamine. Acid-binding agents can rapidly neutralize hydrogen halides generated during ammonolysis, producing organic ammonium salts, thereby driving the Si-X to Si-N substitution reaction and inhibiting acid-catalyzed side reactions. Furthermore, acid-binding agents can regulate condensation / polymerization kinetics by altering the local acid-base environment, ionic strength, and solvent polarity, thus controlling the degree of polymerization and molecular weight distribution, and preventing disordered crosslinking or excessive aggregation. Additionally, acid-binding agents affect phase behavior and solubility; the resulting organic ammonium salts are typically soluble in polar or ammoniatic phases, while hydrophobic oligomers tend to migrate to the organic phase, which facilitates phase separation and purification.

[0030] Preferably, in step S130, since the organic oligomeric silazane exhibits a relatively hydrophobic / organic phase tendency, and the generated organic ammonium or inorganic salt is more soluble in the polar ammonia phase or forms solid particles, the two phases naturally separate due to differences in density and miscibility. After standing, separation is achieved based on density difference, phase tension, and solubility difference. Mechanical separation can enrich the target product and remove salt byproducts. Utilizing the phase selectivity of the system achieves efficient separation of ammonium halide and other ionic byproducts from the organic oligomeric phase, obtaining oligomeric silazane with high purity, controllable molecular weight, and high recovery rate, significantly simplifying the purification process. Standing separation replaces complex extraction / reduced pressure distillation steps, reducing energy consumption and equipment investment; the obtained organic phase can be directly subjected to cross-linking and solidification, while the salt-containing phase and organic ammonium salt can be recovered or further processed, facilitating industrial scale-up.

[0031] Furthermore, when ammonia exists in liquid phase, it can simultaneously serve as a high-concentration nucleophile and reaction solvent, providing a uniform and highly active reaction environment for the ammonolysis of halosilanes under relatively mild temperature / pressure conditions. This significantly improves the displacement rate and suppresses side reactions such as hydrolysis / oxidation. Liquid-phase ammonia can also effectively dissolve or disperse the generated ammonium halide byproducts, making it easy for the products and salts to separate due to differences in polarity / hydrophobicity. This simplifies the separation process and improves the purity and recovery rate of the target oligomeric silazane. Liquid-phase ammonia provides a large number of NH3 molecules to nucleophilically attack Si-X sites, generating Si-NH or Si-N-Si fragments. Simultaneously, the generated HX is captured by acid-binding agents as organic ammonium salts or dissolved in the ammonia phase. Changes in ionic strength and phase behavior regulate condensation / polymerization kinetics, making the degree of polymerization controllable and the molecular weight distribution narrower, ultimately facilitating the acquisition of high-purity, easily crosslinked precursors.

[0032] In summary, this embodiment...

[0033] Example 1 This embodiment provides a silicon nitride ceramic precursor and its preparation method, including the following steps: S110. Trimethylsilyl-substituted amine halosilane is reacted with liquid ammonia to undergo ammonolysis to obtain a suspension; S120. Triethylamine is added to the suspension to obtain the polymerization product; S130. After the polymerization product reaction is complete, allow it to stand and separate into liquids to obtain oligomeric silazane; S200. Under a nitrogen atmosphere, the oligomeric silazane was heated at 150°C for 5 hours to obtain a silicon nitride ceramic precursor. In steps S110-130, the preparation method is carried out at a temperature of -20℃ for 12 hours, and the molar ratio of triethylamine to trimethylsilyl-substituted amine halosilane is 1:50.

[0034] Example 2 This embodiment provides a silicon nitride ceramic precursor and its preparation method, including the following steps: S110. Trimethylsilyl-substituted amine halosilane is reacted with liquid ammonia to undergo ammonolysis to obtain a suspension; S120. Add diisopropylethylamine to the suspension to obtain the polymerization product; S130. After the polymerization product reaction is complete, allow it to stand and separate into liquids to obtain oligomeric silazane; S200. Under a nitrogen atmosphere, the oligomeric silazane was heated at 300°C for 1 hour to obtain a silicon nitride ceramic precursor. In steps S110-130, the preparation method is carried out at a temperature of -40℃ for 24 hours, and the molar ratio of triethylamine to trimethylsilyl-substituted amine halosilane is 1:100.

[0035] Example 3 This embodiment provides a silicon nitride ceramic precursor and its preparation method, including the following steps: S110. Trimethylsilyl-substituted amine halosilane is reacted with liquid ammonia to undergo ammonolysis to obtain a suspension; S120. N,N-dimethylcyclohexylamine was added to the suspension to obtain the polymerization product; S130. After the polymerization product reaction is complete, allow it to stand and separate into liquids to obtain oligomeric silazane; S200. Under a nitrogen atmosphere, the oligomeric silazane was heated at 25°C for 10 hours to obtain a silicon nitride ceramic precursor. In steps S110-130, the preparation method is carried out at a temperature of 25°C for 0.5 hours, and the molar ratio of triethylamine to trimethylsilyl-substituted amine halosilane is 1:1.

[0036] Example 4 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1, except that in step S120, the acid-binding agent is N,N-dimethylaniline.

[0037] Example 5 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1, except that in step S120, the acid-binding agent is N,N-diethylaniline.

[0038] Example 6 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1, except that in step S120, the acid-binding agent is N,N-dimethyl-p-toluidine.

[0039] Example 7 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1, except that in step S120, the acid binding agent is pyridine.

[0040] Example 8 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1, except that in step S120, the acid-binding agent is N,N,N',N'-tetramethylethylenediamine.

[0041] Example 9 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1, except that in step S120, the acid binding agent is triethylenediamine.

[0042] Example 10 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1, except that in step S120, the acid binding agent is 4-dimethylaminopyridine.

[0043] Example 11 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1. The difference is that in step S120, the acid binding agent is 1,8-diazabicyclo[5.4.0]undec-7-ene.

[0044] Example 12 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1. The difference is that in step S120, the acid binding agent is 1,5-diazabicyclo[4.3.0]non-5-ene.

[0045] Example 13 This embodiment provides a silicon nitride ceramic precursor and its preparation method. The specific steps are as shown in Example 1, except that in step S120, the acid-binding agent is pentamethyldiethylenetriamine.

[0046] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0047] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a silicon nitride ceramic precursor, characterized in that, The preparation method includes the following steps: S100. Trimethylsilyl-substituted amine halosilanes are subjected to ammonolysis, and an acid-binding agent is added to obtain oligomeric silazanes. S200. The oligomeric silazane is heated under an inert atmosphere to obtain a silicon nitride ceramic precursor.

2. The preparation method according to claim 1, characterized in that, Step S100 specifically includes: S110. The trimethylsilyl-substituted amine halosilane is contacted with ammonia to carry out the ammonolysis reaction, and a suspension is obtained; S120. Add an acid-binding agent to the suspension to obtain the polymerization product; S130. After the polymerization product reaction is completed, the mixture is allowed to stand and separate to obtain oligomeric silazane.

3. The preparation method according to claim 2, characterized in that, In step S110, the ammonia exists in liquid phase.

4. The preparation method according to claim 1, characterized in that, In step S100, the preparation method is carried out at a temperature of -40 to 25°C for 0.5 to 24 hours.

5. The preparation method according to claim 1, characterized in that, In step S100, the acid-binding agent includes at least one of triethylamine, diisopropylethylamine, N,N-dimethylcyclohexylamine, N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, pyridine, N,N,N',N'-tetramethylethylenediamine, triethylenediamine, 4-dimethylaminopyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and pentamethyldiethylenetriamine.

6. The preparation method according to claim 1, characterized in that, In step S100, the molar ratio of the acid-binding agent to the trimethylsilyl-substituted amine halosilane is 1:(1~100).

7. The preparation method according to claim 1, characterized in that, In step S200, the temperature of the heat treatment is 25~300℃ and the time is 1~10h.

8. The preparation method according to claim 1, characterized in that, In step S200, the inert atmosphere includes at least one of nitrogen and argon.

9. A silicon nitride ceramic precursor, characterized in that, The silicon nitride ceramic precursor is prepared by the preparation method according to any one of claims 1 to 8.