A diamond-silicon carbide composite material and its non-toxic gel casting-reactive infiltration preparation method

Abstract

This application relates to the technical field of superhard composite materials, specifically to a diamond-silicon carbide composite material and its preparation method using non-toxic gel casting and reactive infiltration. In this method, diamond powder and silicon carbide powder are added to a gel premix prepared using raw materials from a non-toxic gel casting system to obtain a uniformly dispersed slurry. The slurry is then degassed under vacuum to form a cast film, initiating a gelation reaction. After curing and drying, a diamond-silicon carbide cast green body is obtained. A porous preform with interconnected pores is obtained through debinding and pre-sintering. The porous preform is then contacted with silicon material via reactive infiltration, and high-temperature, pressureless infiltration is performed under vacuum to obtain a dense diamond-silicon carbide sintered body. This application achieves efficient, high-density, environmentally friendly, and near-net-shape forming of D-SiC composite materials by optimizing the non-toxic gel premix formulation, the diamond multi-scale gradation scheme, the casting process parameters, and the debinding-pre-sintering temperature window.

Description

Technical Field

[0001] This application relates to the technical field of superhard composite materials, and in particular to a diamond-silicon carbide composite material and its non-toxic gel casting-reactive melting preparation method. Background Technology

[0002] Diamond-silicon carbide (D-SiC) composites combine the ultra-high thermal conductivity of single-crystal diamond (up to 2000 W / (m·K) at room temperature, more than 5 times that of copper) with a low coefficient of thermal expansion ((2~4)×10⁻⁴) that is nearly matched with semiconductor materials. -6 With its high-temperature stability, high flexural strength, and excellent corrosion resistance, silicon carbide (SiC) is currently the only next-generation thermal management material that can simultaneously meet the triple core requirements of heat dissipation, mechanical support, and thermal matching for high-power electronic devices. This is especially true given the large-scale commercialization of third-generation semiconductor silicon carbide (SiC) and gallium nitride (GaN) power devices, and the power density of AI large-scale model training chips and 5G / 6G base station RF chips exceeding 1000W / cm². 2 Traditional heat dissipation materials such as copper (401W / (m·K)), aluminum (237W / (m·K)), and aluminum nitride (180~220W / (m·K)) can no longer meet extreme heat dissipation requirements. The market demand for D-SiC composite materials in fields such as large-scale integrated circuit packaging, new energy vehicle electronic control, and aerospace electronic systems is experiencing explosive growth.

[0003] The core of D-SiC composite material preparation lies in the matching of molding and densification processes. Currently, mainstream molding technologies include dry pressing, hot pressing, slip casting, and gel casting, but all have significant limitations: dry pressing is difficult to produce ultra-thin substrates with a thickness of less than 0.5 mm, and the density distribution of the preform is uneven; hot pressing equipment is costly and has low production efficiency, making large-area continuous production impossible; slip casting has low solid content, poor preform strength, large sintering shrinkage, and low dimensional accuracy; traditional gel casting, while achieving high solid content molding, is difficult to produce sheet-like components. Gel casting technology combines the advantages of high solid content and good preform uniformity of gel casting with the continuous, large-area, and ultra-thin component preparation capabilities of gel casting. It can achieve near-net-shape forming of D-SiC substrates with a thickness of 0.2~2.0 mm and dimensions ≥300 mm × 300 mm, making it the most industrially promising electronic packaging substrate preparation technology.

[0004] However, traditional gel casting generally uses an acrylamide (AM)-methylenebisacrylamide (MBAM) free radical polymerization gel system. Acrylamide is an internationally recognized potent neurotoxic substance that can enter the human body through skin contact, inhalation, and digestive absorption. Long-term exposure to low doses can lead to irreversible damage to the nervous system. Furthermore, during the degreasing process of the green body, it decomposes to produce highly toxic gases such as cyanide, posing a serious threat to the health of operators and the ecological environment. With increasingly stringent global environmental regulations and the popularization of green manufacturing concepts, companies need to invest heavily in building closed ventilation systems, personal protective equipment, and waste treatment facilities to meet occupational health and environmental protection requirements, resulting in an increase in production costs of more than 30%, which seriously restricts the industrial application of gel casting technology in the field of D-SiC composite materials.

[0005] To address the toxicity issues of acrylamide systems, researchers both domestically and internationally have developed various non-toxic or low-toxicity gel systems for ceramic molding. These mainly include N,N-dimethylacrylamide (DMAA) low-toxicity chemical gel systems, physical gel systems based on natural polymers (gelatin, agarose, gellan gum, etc.), delayed-reaction gel systems based on sodium alginate-gluconic acid-δ-lactone (GDL), and chemical crosslinking gel systems based on polyvinyl alcohol (PVA)-borax. These systems have been successfully applied in oxide and nitride ceramics such as alumina, zirconium oxide, and aluminum nitride. However, directly transferring these systems to the casting and molding of D-SiC composite materials still faces three core technological challenges, for which current technologies have not yet made effective breakthroughs:

[0006] (1) Poor interfacial compatibility leads to insufficient slurry stability: The surface of diamond powder is strongly hydrophobic, and the interfacial bonding force with most hydrophilic non-toxic gel systems is weak, which easily leads to powder agglomeration; at the same time, the density of diamond (3.52 g / cm³) is also low. 3 The concentration is much higher than that of silicon carbide (3.21 g / cm³). 3 When the solid content of the powder is high, it is easy for the ceramic matrix powder to settle and separate into layers, making it difficult to obtain a long-term stable casting slurry.

[0007] (2) High solid content and casting properties are difficult to balance: In order to ensure the high thermal conductivity of the composite material, the diamond volume fraction is usually required to be ≥50 vol%. However, high solid content will cause the slurry viscosity to increase sharply, and defects such as scraper marks, pinholes and uneven thickness are easy to occur during casting, which cannot meet the flatness requirements of electronic packaging substrate.

[0008] (3) Degreasing process is prone to defects and diamond is prone to graphitization: The pyrolysis temperature and pyrolysis rate of different non-toxic gel systems vary greatly. During the degreasing process, the organic matter is prone to rapid decomposition and the generation of a large amount of gas, which can lead to cracking and bubbling of the green body. At the same time, in order to ensure complete decomposition of organic matter, the degreasing temperature usually needs to reach above 1000℃. However, diamond begins to undergo graphitization transformation above 1450℃ in an inert atmosphere, which leads to a significant decrease in its thermal conductivity. This is a unique technical problem of D-SiC composite materials, which does not exist in other ceramic systems.

[0009] Currently, no complete non-toxic gel casting process solution has been developed for D-SiC composite materials. Therefore, developing a green, environmentally friendly, stable, and industrially scalable non-toxic gel casting-reactive melting process to achieve low-cost production of D-SiC substrates has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0010] To address the shortcomings and deficiencies of the existing technologies, this application provides a diamond-silicon carbide composite material and its preparation method using non-toxic gel casting and reactive melt infiltration. This application optimizes the non-toxic gel premix formulation, diamond multi-scale gradation scheme, casting process parameters, and debinding-pre-sintering temperature window, combined with pressureless liquid-phase melt infiltration densification technology, to achieve efficient, highly dense, and environmentally friendly near-net-shape forming of D-SiC composite materials. This solves the neurotoxicity problem of acrylamide gel systems in existing technologies, while simultaneously achieving uniform casting of high-solid-content slurries and the preparation of highly dense composite materials.

[0011] In a first aspect, this application provides a method for preparing diamond-silicon carbide composite materials using non-toxic gel casting and reactive infiltration, employing the following technical solution:

[0012] A method for preparing diamond-silicon carbide composite materials by non-toxic gel casting and reactive infiltration, the method specifically includes the following steps:

[0013] (1) Preparation of non-toxic gel premix: Dissolve the raw materials of the non-toxic gel molding system in deionized water, stir evenly, and prepare the gel premix;

[0014] (2) Slurry preparation: Diamond powder and silicon carbide powder are added to the gel premix obtained in step (1) and wet ball milling is performed to obtain a uniformly dispersed slurry;

[0015] (3) Casting: The slurry obtained in step (2) is degassed under vacuum to form a cast film, which initiates a gelation reaction. After curing and drying, a diamond-silicon carbide cast green body is obtained.

[0016] (4) Degreasing and pre-sintering: The cast green body obtained in step (3) is degreased and pre-sintered. The degreasing temperature is controlled within the range of 1410℃~1450℃ and lower than the diamond graphitization temperature, so that the organic matter is fully pyrolyzed and discharged, and a porous preform with interconnected pores is obtained.

[0017] (5) Reactive infiltration: The porous preform obtained in step (4) is brought into contact with silicon material and infiltrated at high temperature and pressure in a vacuum environment. The silicon material melts to form a silicon liquid, which spontaneously infiltrates into the interconnected pores of the preform under the action of capillary force, and reacts with the carbon source in the preform to generate silicon carbide bonded phase in situ, thereby obtaining a dense diamond-silicon carbide sintered body.

[0018] (6) Post-processing: The diamond-silicon carbide sintered body obtained in step (5) is cleaned, polished and ground to obtain the final product.

[0019] Optionally, the non-toxic gel forming system described in step (1) is selected from any of the following:

[0020] Scheme A: Using N,N-dimethylacrylamide (DMAA) as an organic monomer and methylenebisacrylamide (MBAM) as a crosslinking agent; wherein, the amount of N,N-dimethylacrylamide added is 3~15% of the total weight of diamond powder and silicon carbide powder in step (2), and the amount of methylenebisacrylamide added is 0.3~1.5% of the total weight of diamond powder and silicon carbide powder in step (2);

[0021] Option B: Use gelatin, agarose, gellan gum, or cardlan gum as a gelling agent, with the amount of gelling agent added being 1-8% of the weight of deionized water;

[0022] Option C: Sodium alginate is used as a gelling agent, with the amount of gelling agent added being 1~5% of the weight of deionized water, and glucono-δ-lactone (GDL) is used as a delayed crosslinking agent. The weight ratio of sodium alginate to glucono-δ-lactone is 1:(0.5~2).

[0023] Option D: Polyvinyl alcohol (PVA) is used as a gelling agent and sodium tetraborate (Na2B4O7·10H2O) is used as a crosslinking agent; wherein, the amount of polyvinyl alcohol added is 5~15% of the weight of deionized water, and the amount of sodium tetraborate added is 0.5~3% of the weight of polyvinyl alcohol.

[0024] Optionally, Scheme A further includes a dispersant, wherein the amount of the dispersant added is 0.5 to 2% of the total weight of diamond powder and silicon carbide powder in step (2).

[0025] Optionally, the dispersant is selected from one or more of ammonium polyacrylate, ammonium polymethacrylate, and ammonium citrate.

[0026] Optionally, in Scheme B, the gelation of the gelling agent is initiated by cooling to 30~40℃ or below, and the gelation of gellan gum or cardlan gum is initiated by cooling to 40℃ or below; and during the preparation of the premix and the slurry, the system temperature is maintained at 45~55℃ to prevent premature gelation.

[0027] Optionally, in Scheme C, hydrogen ions are slowly released by the hydrolysis of gluconate-δ-lactone, which reacts with the calcium ion pre-complex in sodium alginate to form a gel. The gelation time is controlled to be 5-30 min by adjusting the amount of gluconate-δ-lactone added.

[0028] Optionally, in Scheme D, sodium tetraborate aqueous solution is sprayed or mixed into the slurry after it has been cast to initiate a crosslinking reaction, and the crosslinking time is 30~300s.

[0029] Optionally, the diamond powder in step (2) adopts a multi-scale particle gradation, with the diameter ratio of the large, medium and small diamond powders being D large:D medium:D small = (4~7):(2~3):1, and the weight ratio being m large:m medium:m small = (17~25):(7~12):1.

[0030] Optionally, the diamond powder in step (2) is subjected to silicon plating and silicon carbide treatment, and the plating thickness is 10~200nm.

[0031] Optionally, the weight ratio of diamond powder to silicon carbide powder in step (2) is (50~90):(10~50).

[0032] Optionally, the total volume fraction of powder in the slurry is 45-70%.

[0033] Optionally, the media used in the wet ball milling process are zirconia balls or corundum balls, with a ball-to-material ratio of (1~3):1 and a milling time of 4~24h.

[0034] Optionally, the vacuum degree of vacuum degassing in step (3) is ≤100Pa, and the degassing time is 5~15min.

[0035] Optionally, the process parameters for the casting process are: 0.2~2.0mm between the scraper and the casting speed of 0.2~1.5m / min, the drying temperature of 20~80℃, and the drying time of 2~12h.

[0036] Optionally, in step (4), the degreasing treatment adopts the high-temperature pyrolysis pre-sintering method, with a heating rate of 1~10℃ / min, a holding time of 1~4h, and a degreasing atmosphere of vacuum or inert gas.

[0037] Optionally, the silicon material mentioned in step (5) is high-purity silicon powder or silicon block with a purity of ≥99.9%, which is laid on the upper and / or lower surface of the preform, and the total weight of the silicon material is 1.2 to 1.6 times the weight of the porous preform.

[0038] Optionally, the process parameters for pressureless impregnation are: impregnation temperature 1450~1650℃, heat preservation time 0.5~3h, and vacuum degree ≤10Pa.

[0039] This application addresses the industry pain points of high toxicity in traditional acrylamide gel systems, poor green body quality in thermoplastic casting systems, and numerous degreasing defects. It deeply couples non-toxic gel casting molding and reactive melt infiltration processes to form a fully green manufacturing process route of "non-toxic gel casting green body → low-temperature degreasing and pre-firing → pressureless reactive melt infiltration densification." Its core technical principles are as follows:

[0040] (1) Adaptability design of multiple types of non-toxic gel systems

[0041] This application screened and optimized four non-toxic gel systems that are highly compatible with the diamond-silicon carbide system, fundamentally solving the toxicity problem of acrylamide:

[0042] Option A (DMAA low-toxicity chemical gel system): Acute oral toxicity LD50 of N,N-dimethylacrylamide (DMAA) 50 The concentration is 2840 mg / kg, which is only 1 / 20 of that of acrylamide. It has no neurotoxicity or carcinogenicity. The amide groups in its molecular structure can form a dense three-dimensional cross-linked network through free radical polymerization, and there are hydrogen bond interactions with the oxygen-containing functional groups on the diamond surface, which significantly improves the interfacial bonding force. The room temperature bending strength of the green body can reach 22~30 MPa, which meets the requirements of subsequent processing.

[0043] Option B (Natural Polymer Physical Gel System): Gelatin, agarose, gellan gum, etc. are all food-grade natural polymers that are completely non-toxic and biodegradable. They form thermally reversible gels through intermolecular hydrogen bonds, maintaining the fluidity of the slurry at high temperatures and rapidly solidifying and fixing particles at low temperatures, with a controllable operating window.

[0044] Option C (Sodium alginate delayed reaction gel system): The guluronic acid units on the sodium alginate molecular chain can form a three-dimensional network with calcium ions in an "egg box" structure; through the slow hydrolysis of gluconate-δ-lactone (GDL) to release hydrogen ions, the premixed nano-calcium carbonate is gradually dissolved to release calcium ions, so that the gelation time can be precisely controlled within 5~30 minutes, which is perfectly adapted to the process rhythm of continuous casting molding.

[0045] Option D (PVA-borax chemical crosslinking system): Polyvinyl alcohol (PVA) is a recognized non-toxic polymer material. The hydroxyl groups on its molecular chain can undergo a rapid coordination reaction with borax to generate a diol crosslinking network. The crosslinking time can be controlled between 30 and 300 seconds. The green strength of this system is extremely high, reaching more than 45 MPa, and it can be directly cut, drilled and other precision machining.

[0046] (2) Stable dispersion mechanism of high solid content slurry

[0047] By employing a synergistic effect of "multi-scale particle gradation + double-layer electrostatic stabilization + steric hindrance stabilization," the problems of high density, easy sedimentation, and poor compatibility with hydrophilic gel systems of diamond powder are solved. A three-level diamond particle gradation of large, medium, and small (diameter ratio 4~7:2~3:1) is adopted to achieve the densest particle packing, with small particles filling the gaps between large particles, significantly increasing the solid content of the slurry. At the same time, anionic dispersants are added and adsorbed on the particle surface. On the one hand, the double-layer thickness between particles is increased through electrostatic repulsion, and on the other hand, particle agglomeration is prevented through the steric hindrance effect of polymer chains. Ultimately, long-term stable dispersion of slurries with a high solid content of 45~70% powder volume fraction is achieved.

[0048] (3) Temperature window regulation mechanism for inhibiting diamond graphitization

[0049] This application determined the optimal debinding-pre-sintering temperature window of 1410℃~1450℃ through extensive experiments: below 1410℃, the organic matter in the gel system is not completely pyrolyzed, and residual carbon will hinder the subsequent melting and infiltration of silicon liquid; above 1450℃, the activity of carbon atoms on the diamond surface increases sharply, and sp... 3 →sp 2 The hybridization transformation forms a graphite layer, which leads to a significant decrease in the thermal conductivity of diamond. By strictly controlling the final degreasing temperature within this window, it is possible to ensure the complete pyrolysis and removal of organic matter while keeping the graphitization conversion rate of diamond below 1%, thus maximizing the preservation of diamond's ultra-high thermal conductivity.

[0050] (4) Densification mechanism of pressureless reactive melting

[0051] The degreased porous preform possesses a uniformly interconnected pore structure, with molten silicon spontaneously penetrating all pores under capillary force. During this process, the molten silicon reacts in situ with the active carbon atoms on the surface of the diamond particles to generate a silicon carbide bonding phase. This phase achieves both a strong metallurgical bond between the diamond particles and completely fills the remaining pores of the preform, ultimately yielding a diamond-silicon carbide composite material with high density and good interfacial bonding. This process requires no external pressure, has low equipment costs, and enables near-net-shape forming of large-area, complex-shaped components.

[0052] Secondly, this application provides a diamond-silicon carbide composite material, comprising a diamond reinforcing phase and a silicon carbide matrix phase, wherein the composite material is prepared by the above-described method.

[0053] Optionally, the diamond-silicon carbide composite material has a relative density ≥96%, a room temperature thermal conductivity ≥450W / (m·K), and a Vickers hardness ≥36GPa.

[0054] In summary, this application includes at least one of the following beneficial technical effects:

[0055] (1) Safe and non-toxic, green and environmentally friendly: It completely abandons the acrylamide system with strong neurotoxicity and adopts the DMAA low-toxicity system or food-grade natural polymer gel system, eliminating occupational health risks and environmental pollution in the production process from the source; there is no need to invest in high-cost closed ventilation systems, personal protective equipment and waste treatment devices, reducing production costs by more than 30%, which is in line with the global trend of green manufacturing.

[0056] (2) Strong process adaptability and wide range of applications: Four non-toxic gel systems with different properties are provided, which can be flexibly selected according to product thickness, strength requirements, production equipment conditions and cost budget: the gelatin system has the lowest cost and is suitable for large-scale production; the PVA-borax system has the highest green strength and is suitable for precision processing; the sodium alginate system has adjustable gelation time and is suitable for continuous casting production; the DMAA system has the best comprehensive performance and is suitable for the preparation of high-performance products.

[0057] (3) Low organic matter content and fewer degreasing defects: The organic matter content of the non-toxic gel system is only 3~15%, which is much lower than the 14~20% of the traditional thermoplastic casting system; and the application adopts a segmented heating degreasing system, the organic matter pyrolysis process is slow, and the gas can be smoothly discharged through the interconnected pores, which completely solves the defects such as cracking and bubbling of the green body caused by the rapid decomposition of a large amount of organic matter in the traditional process, and the degreasing yield is increased from 60% to more than 95%.

[0058] (4) High green strength and good near-net-shape forming accuracy: The room temperature bending strength of the green bodies of the four gel systems is higher than 4MPa, of which the DMAA system can reach 22~30MPa and the PVA-borax system can reach more than 45MPa, which is much higher than the 3~5MPa of the traditional thermoplastic casting system. The green bodies can be directly demolded, transported, cut, drilled and other subsequent processing. The gel network fixes the particles uniformly without sedimentation and stratification. The size accuracy of the green body can reach ±0.02mm, realizing true near-net-shape forming.

[0059] (5) High solid content and excellent thermal conductivity: Through multi-scale particle gradation and dispersion technology, a high solid content slurry with a diamond volume fraction of up to 80% can be uniformly cast and molded, which is much higher than the 40-50% of the existing technology; combined with precise degreasing temperature control and pressureless reaction melting process, the final composite material has a relative density ≥96%, a room temperature thermal conductivity ≥450W / (m·K), and can reach up to 493W / (m·K), which can meet the power density of 1000W / cm³. 2 The above describes the heat dissipation requirements of third-generation semiconductor devices.

[0060] (6) Performance comparable to traditional processes, with significant comprehensive benefits: The key performance indicators of the diamond-silicon carbide composite material prepared in this application, such as density, thermal conductivity, and hardness, are completely comparable to those of the traditional acrylamide system, but the toxicity hazard has been completely eliminated; compared with the traditional thermoplastic casting system, the relative density is increased by more than 3%, the thermal conductivity is increased by more than 14%, and the Vickers hardness is increased by more than 12%, with significant advantages in comprehensive performance and economic benefits. Attached Figure Description

[0061] Figure 1 This is a process flow diagram for the preparation of diamond-silicon carbide composite materials using non-toxic gel casting and reactive infiltration, as described in this application. Detailed Implementation

[0062] Before describing the embodiments of this application in detail, it should be understood that the terminology used herein is for the purpose of describing a particular embodiment only. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the term pertains.

[0063] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0064] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0065] In this application, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0066] This application provides a method for preparing diamond-silicon carbide composite materials using non-toxic gel casting and reactive infiltration. Combined with... Figure 1 The method specifically includes the following steps:

[0067] (1) Preparation of non-toxic gel premix: Dissolve the raw materials of the non-toxic gel molding system in deionized water, stir evenly, and prepare the gel premix;

[0068] (2) Slurry preparation: Diamond powder and silicon carbide powder are added to the gel premix obtained in step (1) and wet ball milling is performed to obtain a uniformly dispersed slurry;

[0069] (3) Casting: The slurry obtained in step (2) is degassed under vacuum to form a cast film, which initiates a gelation reaction. After curing and drying, a diamond-silicon carbide cast green body is obtained.

[0070] (4) Degreasing and pre-sintering: The cast green body obtained in step (3) is degreased and pre-sintered. The degreasing temperature is controlled within the range of 1410℃~1450℃ and lower than the diamond graphitization temperature, so that the organic matter is fully pyrolyzed and discharged, and a porous preform with interconnected pores is obtained.

[0071] (5) Reactive infiltration: The porous preform obtained in step (4) is brought into contact with silicon material and infiltrated at high temperature and pressure in a vacuum environment. The silicon material melts to form a silicon liquid, which spontaneously infiltrates into the interconnected pores of the preform under the action of capillary force, and reacts with the carbon source in the preform to generate silicon carbide bonded phase in situ, thereby obtaining a dense diamond-silicon carbide sintered body.

[0072] (6) Post-processing: The diamond-silicon carbide sintered body obtained in step (5) is cleaned, polished and ground to obtain the final product.

[0073] In step (1), the non-toxic gel forming system is selected from any of the following schemes:

[0074] Scheme A: Using N,N-dimethylacrylamide as an organic monomer and methylenebisacrylamide as a crosslinking agent; wherein, the amount of N,N-dimethylacrylamide added is 3~15% of the total weight of diamond powder and silicon carbide powder in step (2), and the amount of methylenebisacrylamide added is 0.3~1.5% of the total weight of diamond powder and silicon carbide powder in step (2);

[0075] Option B: Use gelatin, agarose, gellan gum, or cardlan gum as a gelling agent, with the amount of gelling agent added being 1-8% of the weight of deionized water;

[0076] Option C: Sodium alginate is used as a gelling agent, and the amount of gelling agent added is 1~5% of the weight of deionized water. Glucono-δ-lactone is used as a delayed crosslinking agent, and the weight ratio of sodium alginate to glucono-δ-lactone is 1:(0.5~2).

[0077] Option D: Using polyvinyl alcohol as a gelling agent and sodium tetraborate as a crosslinking agent; wherein the amount of polyvinyl alcohol added is 5-15% of the weight of deionized water, and the amount of sodium tetraborate added is 0.5-3% of the weight of polyvinyl alcohol.

[0078] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0079] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0080] The present application will be further described in detail below with reference to the embodiments and test results.

[0081] Example 1 – N,N-Dimethylacrylamide (DMAA) Low-Toxicity Chemical Gel System

[0082] This embodiment uses a low-toxicity DMAA chemical gel system to prepare diamond-silicon carbide composite materials. The specific steps are as follows:

[0083] (1) Preparation of non-toxic gel premix

[0084] Based on the total weight of diamond powder and silicon carbide powder in subsequent step (2), weigh out 8% N,N-dimethylacrylamide (DMAA, purity ≥99.0%), 0.6% methylenebisacrylamide (MBAM, purity ≥99.0%), and 1.0% ammonium polyacrylate dispersant (molecular weight 5000~10000), add them to deionized water, and stir magnetically at 25°C for 30 minutes until completely dissolved to prepare a uniform gel premix for later use.

[0085] (2) Slurry preparation

[0086] The artificial single-crystal diamond micro powder with multi-scale particle size distribution has average particle sizes of 100μm, 50μm and 20μm, and is mixed uniformly at a weight ratio of 20:10:1; the silicon carbide powder is α-silicon carbide micro powder with an average particle size of 2μm and a purity of ≥99.5%.

[0087] The above powders were accurately weighed according to a weight ratio of diamond powder to silicon carbide powder of 84:16, and the total powder volume was controlled to be 60% (i.e., the total volume of powder accounted for 60% of the total volume of slurry). The powders were added to the gel premix obtained in step (1), and zirconia balls were used as the ball milling medium at a ball-to-powder ratio of 2:1. The mixture was placed in a planetary ball mill and wet-milled at a speed of 300 r / min for 12 h to prepare a uniformly dispersed slurry without obvious agglomeration.

[0088] (3) Casting

[0089] The slurry obtained in step (2) is transferred to a vacuum degassing tank and degassed for 10 minutes under a vacuum of ≤100Pa to remove air bubbles from the slurry. Then, 0.06% of tetramethylethylenediamine (TEMED) catalyst and 0.6% of ammonium persulfate (APS) initiator are added sequentially. After adding TEMED, the mixture is stirred for 1 minute, and after adding APS, it is stirred rapidly for 30 seconds. The mixture is then immediately poured into the heat-insulating trough of the scraper casting machine.

[0090] With a doctor blade gap of 0.5 mm and a casting speed of 0.8 m / min, the slurry is scraped into a continuous cast film. The cast film is then transferred to a clean drying oven with a relative humidity of 40%~60% and dried at 40℃ for 4 hours. After the gel is completely cured and the solvent has fully evaporated, the film is demolded to obtain a diamond-silicon carbide cast green body.

[0091] The room temperature bending strength of the green body obtained in this embodiment was 25~28 MPa, as determined by the three-point bending method.

[0092] (4) Degreasing and pre-sintering

[0093] The cast green body obtained in step (3) was placed flat on a graphite pad and placed in a vacuum tube degreasing furnace. Under vacuum conditions ≤10 Pa, a segmented heating regime was used for degreasing and pre-sintering: the heating rate was 2℃ / min from room temperature to 600℃, and the heating rate was 5℃ / min from 600℃ to 1430℃. The body was held at 1430℃ for 2 hours to allow the organic matter in the gel system to be fully pyrolyzed and discharged, forming a porous skeleton with a certain strength. After the holding period, the body was cooled to below 100℃ in the furnace and removed from the furnace to obtain a porous preform.

[0094] Visual inspection and scanning electron microscopy revealed no visible cracks on the surface or inside of the preform, and no microcracks with a width greater than 0.1 μm.

[0095] (5) Reactive melting and infiltration

[0096] The porous preform obtained in step (4) was placed in a graphite crucible coated with boron nitride release agent on the inner wall. High-purity silicon blocks (purity ≥99.99%, thickness 2~3mm) were laid on the upper surface of the preform, with the weight of the silicon blocks being 1.3 times the weight of the porous preform. The graphite crucible was placed in a vacuum reactor and evacuated to 5Pa. A segmented heating regime was adopted for pressureless reaction melting and infiltration: the heating rate from room temperature to 1000℃ was 10℃ / min, and the heating rate from 1000℃ to 1550℃ was 8℃ / min. The temperature was held at 1550℃ for 1.5h. During this process, the molten silicon spontaneously infiltrated into the interconnected pores of the porous preform under the action of capillary force, reacting with the carbon source in the preform to generate silicon carbide bonding phase in situ, filling the pores and achieving densification. After the holding period, the furnace was cooled to room temperature.

[0097] (6) Post-processing

[0098] After the reaction, the sample is removed and the residual silicon layer and reaction byproducts on the surface are first removed by grinding with a diamond grinding wheel. Then, W10, W3.5 and W1 diamond polishing pastes are used in sequence for rough polishing and fine polishing to obtain a finished diamond-silicon carbide composite material with a surface roughness Ra≤0.8μm.

[0099] Example 2 – Gelatin Natural Polymer Physical Gel System

[0100] This embodiment uses a gelatin-based natural polymer physical gel system to prepare diamond-silicon carbide composite materials. The specific steps are as follows:

[0101] (1) Preparation of non-toxic gel premix

[0102] Weigh 6% of the weight of food-grade gelatin powder (bloom strength 180~220, purity ≥99.0%) into deionized water preheated to 50℃, and magnetically stir in a 50℃ constant temperature water bath for 45 minutes until the gelatin is completely dissolved; then add 1.0% of the total weight of the powder in subsequent step (2) of ammonium polyacrylate dispersant (molecular weight 5000~10000), and continue stirring for 15 minutes until uniform, to obtain a clear and transparent gelatin premix. Keep warm at 50℃ for later use.

[0103] (2) Slurry preparation

[0104] The artificial single-crystal diamond micro powder with multi-scale particle size distribution has average particle sizes of 80μm, 40μm and 15μm, and is mixed uniformly at a weight ratio of 18:9:1; the silicon carbide powder is α-silicon carbide micro powder with an average particle size of 1.5μm and a purity of ≥99.5%.

[0105] The above powders were accurately weighed according to a weight ratio of diamond powder to silicon carbide powder of 75:25, and the total powder volume was controlled to be 55% (i.e., the total volume of powder accounts for 55% of the total volume of slurry). The powders were added to the gelatin premix obtained in step (1) and kept at 50°C. Zirconia balls were used as the ball milling medium, with a ball-to-powder ratio of 2:1. The mixture was placed in a planetary ball mill and wet-milled at a speed of 280 r / min for 10 h. The slurry temperature was kept above 45°C throughout the ball milling process to prevent premature gelation of the gelatin and to prepare a uniformly dispersed, non-agglomerated, low-viscosity slurry.

[0106] (3) Casting

[0107] The insulating slurry obtained in step (2) is transferred to a vacuum degassing tank preheated to 45°C and degassed for 8 minutes under a vacuum of ≤100Pa to remove air bubbles from the slurry. The degassed slurry is then immediately injected into the insulating material tank of a scraper casting machine preheated to 45°C.

[0108] With a doctor blade gap of 0.8 mm and a casting speed of 0.6 m / min, the slurry is scraped into a continuous cast film. The cast film is then quickly transferred to a clean cooling and drying oven at 15°C and 50%~70% relative humidity, and left to stand for 30 minutes to allow the gelatin to physically gel and solidify through cooling. Drying continues under these conditions for another 8 hours. After the solvent has fully evaporated, the film is demolded to obtain a crack-free and warped diamond-silicon carbide cast green body.

[0109] The room temperature bending strength of the green body obtained in this embodiment was 12~15 MPa, as determined by the three-point bending method.

[0110] (4) Degreasing and pre-sintering

[0111] The cast green body obtained in step (3) is placed flat on an alumina pad and placed in an atmosphere tube furnace. High-purity argon gas (purity ≥99.999%) is introduced until the furnace pressure is atmospheric pressure. Degreasing and pre-sintering are carried out using a segmented heating regime: the heating rate is 2℃ / min from room temperature to 400℃, and the heating rate is 3℃ / min from 400℃ to 1440℃. The temperature is held at 1440℃ for 2.5h to allow the gelatin and other organic matter to be fully pyrolyzed and discharged, forming a porous skeleton with a certain strength. After the holding period, the furnace is cooled to below 100℃ and removed from the furnace to obtain a porous preform.

[0112] Visual inspection and scanning electron microscopy revealed no visible cracks on the surface or inside of the preform, and no microcracks with a width greater than 0.1 μm.

[0113] (5) Reactive melting and infiltration

[0114] The porous preform obtained in step (4) was placed in a graphite crucible with a boron nitride release agent coated on the inner wall. High-purity silicon powder (purity ≥99.99%, average particle size 100~200μm) was uniformly spread on the upper and lower surfaces of the preform, with the total weight of the silicon powder being 1.5 times the weight of the porous preform. The graphite crucible was placed in a vacuum reactor and evacuated to 3Pa. A segmented heating regime was adopted for pressureless reaction melting and infiltration: the heating rate from room temperature to 1000℃ was 10℃ / min, and the heating rate from 1000℃ to 1530℃ was 8℃ / min. The temperature was held at 1530℃ for 2 hours. During this process, the molten silicon spontaneously infiltrated into the interconnected pores of the porous preform under the action of capillary force, reacting with the carbon source in the preform to generate silicon carbide bonding phase in situ, filling the pores and achieving densification. After the holding period, the furnace was cooled to room temperature.

[0115] (6) Post-processing

[0116] The sample after the reaction was removed, and the residual silicon layer and reaction byproducts on the surface were removed by sandblasting with 80-mesh brown corundum sand at a pressure of 0.4 MPa. Then, W10, W3.5 and W1 diamond polishing pastes were used for rough polishing and fine polishing in sequence to obtain a diamond-silicon carbide composite material with a surface roughness Ra≤0.8μm.

[0117] Example 3 – Sodium alginate-gluconic acid-δ-lactone delayed reaction gel system

[0118] This embodiment uses a sodium alginate-gluconic acid-δ-lactone (GDL) delayed reaction gel system to prepare diamond-silicon carbide composite materials. The gelation time is controlled by the slow hydrolysis of GDL to meet the operational window requirements of tape casting. The specific steps are as follows:

[0119] (1) Preparation of non-toxic gel premix

[0120] Weigh 3% (by weight of deionized water) of food-grade sodium alginate powder (viscosity 200-300 mPa·s, 25℃, 1% aqueous solution, purity ≥99.0%) and add it to room temperature deionized water while stirring to prevent clumping. Continue magnetic stirring for 2 hours until completely dissolved to obtain a clear and transparent sodium alginate solution. Add 10% (by weight of sodium alginate) of nano-calcium carbonate suspension (average particle size 50-100 nm, purity ≥99.5%, pre-dispersed in a small amount of deionized water) to the above solution and continue stirring for 30 minutes until uniformly dispersed to obtain a sodium alginate premix.

[0121] Prepare an aqueous solution of gluconate-δ-lactone (GDL, purity ≥99.0%), controlling the weight ratio of GDL to sodium alginate to be 1:1, and use it immediately after preparation.

[0122] (2) Slurry preparation

[0123] The artificial single-crystal diamond micro powder with multi-scale particle size distribution has average particle sizes of 60μm, 30μm and 10μm, and is mixed uniformly at a weight ratio of 15:7:1; the silicon carbide powder is α-silicon carbide micro powder with an average particle size of 1μm and a purity of ≥99.5%.

[0124] The above powders were accurately weighed according to a weight ratio of diamond powder to silicon carbide powder of 60:40, and the total volume of the powder was controlled to be 50% (i.e., the total volume of the powder accounted for 50% of the total volume of the slurry). The powders were added to the sodium alginate premix obtained in step (1), and zirconia balls were used as the ball milling medium at a ball-to-powder ratio of 2:1. The mixture was placed in a planetary ball mill and wet-milled at a speed of 260 r / min for 12 h to prepare a uniformly dispersed and agglomerated stable slurry.

[0125] (3) Casting

[0126] Transfer the slurry obtained in step (2) to a vacuum degassing tank and degas for 12 minutes under a vacuum of ≤100Pa to remove air bubbles from the slurry. Quickly add the prepared GDL aqueous solution to the degassed slurry, stir for 60 seconds until uniform, and immediately pour it into the material tank of the scraper casting machine.

[0127] With a doctor blade gap of 1.0 mm and a casting speed of 0.5 m / min, the slurry is scraped into a continuous cast film. The cast film is then transferred to a clean drying oven at 25°C and 40%–60% relative humidity for 6 hours. During this process, GDL slowly hydrolyzes, releasing hydrogen ions and gradually lowering the pH of the system. This causes the nano-calcium carbonate to dissolve and release calcium ions. The calcium ions then form a three-dimensional cross-linked network with the guluronic acid units on the sodium alginate molecular chain, creating an "egg-box" structure. This completes the delayed gel curing process, and the resulting crack-free, smooth diamond-silicon carbide cast green body is then demolded.

[0128] In this embodiment, the gelation time, which is controlled by the amount of GDL added, is 15-20 minutes, which meets the operation window requirements for casting molding.

[0129] The room temperature bending strength of the green body obtained in this embodiment was 9~12 MPa, as determined by the three-point bending method.

[0130] (4) Degreasing and pre-sintering

[0131] The cast green body obtained in step (3) was placed flat on a graphite pad and placed in a vacuum tube degreasing furnace. Under vacuum conditions ≤10Pa, a segmented heating regime was adopted for degreasing and pre-sintering: the heating rate from room temperature to 500℃ was 1.5℃ / min, and the heating rate from 500℃ to 1420℃ was 4℃ / min. The body was held at 1420℃ for 3 hours to allow the organic matter such as sodium alginate to be fully pyrolyzed and discharged, forming a porous skeleton with a certain strength. After the holding period, the body was cooled to below 100℃ and removed from the furnace to obtain a porous preform.

[0132] Visual inspection and scanning electron microscopy revealed no visible cracks on the surface or inside of the preform, and no microcracks with a width greater than 0.1 μm.

[0133] (5) Reactive melting and infiltration

[0134] The porous preform obtained in step (4) was placed in a graphite crucible with a boron nitride release agent coated on the inner wall. High-purity silicon powder (purity ≥99.99%, average particle size 100~200μm) was uniformly spread on the upper and lower surfaces of the preform, with the total weight of the silicon powder being 1.6 times the weight of the porous preform. The graphite crucible was placed in a vacuum reactor and evacuated to 2Pa. A segmented heating regime was adopted for pressureless reaction melting and infiltration: the heating rate from room temperature to 1000℃ was 10℃ / min, and the heating rate from 1000℃ to 1510℃ was 8℃ / min. The temperature was held at 1510℃ for 2.5h. During this process, the molten silicon spontaneously infiltrated into the interconnected pores of the porous preform under the action of capillary force, reacting with the carbon source in the preform to generate silicon carbide bonding phase in situ, filling the pores and achieving densification. After the holding period, the furnace was cooled to room temperature.

[0135] (6) Post-processing

[0136] After the reaction, the sample is removed and the residual silicon layer and reaction byproducts on the surface are first removed by grinding with a diamond grinding wheel. Then, W10, W3.5 and W1 diamond polishing pastes are used in sequence for rough polishing and fine polishing to obtain a finished diamond-silicon carbide composite material with a surface roughness Ra≤0.8μm.

[0137] Example 4 – Polyvinyl alcohol-borax chemical crosslinking gel system

[0138] This embodiment uses a polyvinyl alcohol (PVA)-borax chemical crosslinking gel system to prepare diamond-silicon carbide composite materials. This system features rapid crosslinking and extremely high green strength. Furthermore, a high-pressure reactive melting process is used to further improve the material's density and thermal conductivity. The specific steps are as follows:

[0139] (1) Preparation of non-toxic gel premix

[0140] Weigh 10% of the weight of deionized water, add polyvinyl alcohol powder (PVA 1799 type, degree of polymerization 1700, degree of alcoholysis 98.0%~99.0%, purity ≥99.0%), and slowly add it to room temperature deionized water while stirring to prevent clumping. Then transfer it to a 90℃ constant temperature water bath and stir magnetically for 2 hours until completely dissolved to obtain a clear and transparent PVA aqueous solution. Allow it to cool naturally to 25℃ for later use.

[0141] Prepare a separate aqueous solution of sodium tetraborate (Na2B4O4·10H2O, purity ≥99.5%), controlling the dry weight of sodium tetraborate to be 1.5% of the dry weight of PVA, and stir until completely dissolved. Prepare and use immediately.

[0142] (2) Slurry preparation

[0143] The artificial single-crystal diamond micro powder with multi-scale particle size distribution has average particle sizes of 50μm, 20μm and 8μm, and is mixed uniformly in a weight ratio of 17:8:1; the silicon carbide powder is α-silicon carbide micro powder with an average particle size of 0.8μm and a purity of ≥99.5%.

[0144] The above powders were accurately weighed according to a weight ratio of diamond powder to silicon carbide powder of 70:30, and the total powder content was controlled to be 65% (i.e., the total volume of powder accounts for 65% of the total volume of slurry). The powders were slowly added to the PVA aqueous solution at 25°C obtained in step (1), and zirconia balls were used as the ball milling medium at a ball-to-powder ratio of 2:1. The mixture was placed in a planetary ball mill and wet-milled at a speed of 280 r / min for 8 h to prepare a uniformly dispersed, non-agglomerated, high-solid-content stable slurry.

[0145] (3) Casting

[0146] Transfer the slurry obtained in step (2) to a vacuum degassing tank and degas for 8 minutes under a vacuum degree ≤100Pa to remove air bubbles from the slurry. Immediately inject the degassed slurry into the room temperature material tank of the scraper casting machine.

[0147] With a doctor blade gap of 0.4 mm and a casting speed of 1.0 m / min, the slurry is scraped into a continuous ultra-thin cast film. Immediately after casting, a prepared sodium tetraborate aqueous solution is evenly sprayed onto the surface of the cast film using an atomizing nozzle at a spraying rate of 120 mL / m. 2 This process initiates a rapid crosslinking reaction between PVA and borax, with the crosslinking time controlled at 60 seconds. The cast film is then transferred to a clean drying oven at 25°C and 50%–60% relative humidity for 6 hours of drying. After the solvent has fully evaporated, the film is demolded to obtain a high-strength, warp-free diamond-silicon carbide cast green body.

[0148] According to the three-point bending test, the room temperature bending strength of the green blank obtained in this embodiment can reach more than 45 MPa, and it can be directly processed by cutting, drilling and other mechanical processing.

[0149] (4) Degreasing and pre-sintering

[0150] The cast green body obtained in step (3) is placed flat on an alumina pad and placed in an atmosphere tube furnace. High-purity argon gas (purity ≥99.999%) is introduced until the furnace pressure is atmospheric pressure. Degreasing and pre-sintering are carried out using a segmented heating regime: the heating rate is 2℃ / min from room temperature to 300℃, and the heating rate is 6℃ / min from 300℃ to 1435℃. The temperature is held at 1435℃ for 2 hours to allow PVA and other organic materials to be fully pyrolyzed and discharged, forming a porous skeleton with a certain strength. After the holding period, the material is cooled to below 100℃ and removed from the furnace to obtain a porous preform.

[0151] Visual inspection and scanning electron microscopy revealed no visible cracks on the surface or inside of the preform, and no microcracks with a width greater than 0.1 μm.

[0152] (5) Reactive melting and infiltration

[0153] The high-pressure reactive melting route is adopted: the porous preform obtained in step (4) is cut into the required size, cleaned, and then alternately stacked with high-purity silicon powder (purity ≥99.99%, average particle size 100~200μm) in a graphite mold with boron nitride release agent on the inner wall. The total weight of silicon powder is 1.2 times the weight of the porous preform. After the graphite mold is sealed, it is placed in the synthesis chamber of a six-sided top press.

[0154] First, a pressure of 5.5 GPa was applied at a rate of 1 GPa / min, followed by a temperature increase to 1580 °C at a rate of 100 °C / min, and held at this temperature and pressure for 30 min. After holding at this temperature, the temperature was first reduced to room temperature at a rate of 50 °C / min, and then the pressure was slowly released to atmospheric pressure before the sample was removed. During this process, the high pressure drove molten silicon to rapidly penetrate all the pores of the preform, reacting with the carbon source to form a dense silicon carbide bonding phase in situ, achieving near-complete densification of the material. After holding at this temperature, the material was cooled to room temperature in the furnace.

[0155] (6) Post-processing

[0156] After the reaction, the sample is first polished with a diamond grinding wheel to remove the residual graphite mold, pressure transmission medium and excess silicon layer on the surface. Then, W10, W3.5 and W1 diamond polishing pastes are used in sequence for rough polishing and fine polishing to obtain a finished diamond-silicon carbide composite material with a surface roughness Ra≤0.8μm.

[0157] Comparative Example 1 – Traditional Acrylamide (AM) Toxic Gel System + Reactive Melting

[0158] This comparative example is a prior art comparison example, and its purpose is to verify the performance difference of diamond-silicon carbide composite materials prepared by the DMAA low-toxicity gel system of this application and the traditional acrylamide toxic gel system. The specific steps are as follows:

[0159] Except for the gel premix preparation step, which uses the traditional acrylamide (AM)-methylenebisacrylamide (MBAM) free radical polymerization gel system instead of the DMAA system in Example 1, all other raw material ratios, process parameters and operating steps are exactly the same as in Example 1.

[0160] The specific steps for preparing the gel premix are as follows: Based on the total weight of diamond powder and silicon carbide powder in subsequent step (2), weigh 5% acrylamide (AM, purity ≥99.0%), 0.4% methylenebisacrylamide (MBAM, purity ≥99.0%), and 1.0% ammonium polyacrylate dispersant (molecular weight 5000~10000), add them to deionized water, and stir magnetically at 25℃ for 30 minutes until completely dissolved to prepare a uniform gel premix for later use.

[0161] The room temperature bending strength of the green body prepared by the comparative example was 23~26MPa, as tested by the three-point bending method. After visual observation and scanning electron microscopy, there were no visible cracks on the surface and inside of the degreased preform, and no microcracks with a width greater than 0.1μm.

[0162] Comparative Example 2 – Gel-free system (traditional thermoplastic casting) + reactive melt infiltration

[0163] This comparative example is a prior art comparison example, and its purpose is to verify the advantages of the non-toxic gel casting molding system of this application over the traditional thermoplastic casting system in terms of green performance, debinding defect control, and final composite material performance. The specific steps are as follows:

[0164] Except for the fact that the molding system uses a traditional thermoplastic casting adhesive system instead of the DMAA gel system in Example 1, all other raw material ratios, diamond gradation schemes, process parameters and operating steps are exactly the same as in Example 1.

[0165] The specific steps for preparing the traditional thermoplastic casting premix are as follows: Based on the total weight of diamond powder and silicon carbide powder in subsequent step (2), weigh out 10% of polyvinyl butyral (PVB, grade PVB-B98, degree of alcoholysis 98%, purity ≥99.0%), 4% of dibutyl phthalate (DBP, plasticizer, purity ≥99.5%), and 1.0% of ammonium polyacrylate dispersant (molecular weight 5000~10000). Add them to a mixed solvent prepared by anhydrous ethanol and deionized water at a volume ratio of 7:3. Stir magnetically at 25°C for 2 hours until completely dissolved to prepare a uniform thermoplastic casting premix for later use.

[0166] The room temperature bending strength of the green body prepared by the comparative example was only 3-5 MPa, which is far lower than the 9-45 MPa of the other examples. It is prone to breakage during demolding and handling, and the yield is less than 60%. At the same time, after the preform was degreased and kept at 1430℃, a large number of microcracks visible to the naked eye appeared on the surface and inside of the preform. The crack width was 1-5 μm and it penetrated the entire thickness direction of the preform.

[0167] Performance testing

[0168] The finished products obtained in the above embodiments and comparative examples were subjected to the following tests: relative density was tested using the Archimedes displacement method, room temperature thermal conductivity was tested using the laser flare method (LFA), and Vickers hardness was tested using a Vickers hardness tester (load 1kg, holding pressure 15s).

[0169] The test results are shown in Table 1.

[0170] Table 1. Test results of the finished products obtained in the above embodiments and comparative examples.

[0171]

[0172] As shown in Table 1, comparing Example 1 and Comparative Example 1, the composite material prepared in Comparative Example 1 using the traditional acrylamide toxic gel system exhibits key performance indicators such as density, thermal conductivity, and hardness that are essentially equivalent to those in Example 1. However, acrylamide is an internationally recognized potent neurotoxic substance that can enter the human body through skin contact or inhalation. Long-term exposure can lead to irreversible damage to the nervous system. Furthermore, it decomposes during the degreasing process to produce toxic gases, posing a serious threat to the health of operators and the ecological environment. Example 1, while maintaining the core performance of the material, completely eliminates the toxic hazards of acrylamide, achieving a green and environmentally friendly preparation of diamond-silicon carbide composite materials.

[0173] Comparing Example 1 and Comparative Example 2 reveals three core defects in the traditional thermoplastic casting system: First, the high organic content (14 wt% in Comparative Example 2, 1.6 times that of Example 1) leads to rapid gas release during degreasing, easily causing cracking of the green body; second, relying solely on the physical bonding effect of the thermoplastic binder results in low green strength and poor processing performance; third, the absence of a three-dimensional gel network to fix the particles in the slurry makes it prone to sedimentation and stratification during standing and casting, leading to uneven density of the green body and a significant decrease in the density and performance of the final composite material. Example 1 achieves uniform particle fixation through in-situ curing of the gel network, with low organic content, no cracking during degreasing, and the final composite material exhibits performance far superior to the traditional thermoplastic casting system.

[0174] By comparing the above embodiments and comparative examples, the following conclusions can be drawn:

[0175] (1) The diamond-silicon carbide composite material prepared by this application using four non-toxic / low-toxic gel systems, namely DMAA, gelatin, sodium alginate and PVA-borax, has key performance indicators such as density, thermal conductivity and hardness that are basically equivalent to those of the traditional toxic acrylamide system (Comparative Example 1). Moreover, the green strength and degreasing quality are completely consistent with the traditional system. In Example 4, the relative density can reach 98.6% and the thermal conductivity can reach 493 W / (m·K) by combining high pressure reaction melting process, which is significantly better than the traditional process.

[0176] (2) This application completely avoids the use of acrylamide neurotoxic substances while maintaining the core performance of the material, without the need to invest in high-cost airtight protection and waste treatment, thus achieving green and environmentally friendly preparation.

[0177] (3) This application provides four gel systems with different properties, which can be flexibly selected according to the product thickness, strength requirements and production equipment conditions to meet the needs of different application scenarios.

[0178] (4) Compared with the traditional thermoplastic casting system without gel (Comparative Example 2), the green body prepared in this application has 4 to 10 times higher strength, no cracks after degreasing, higher relative density of composite material by more than 3%, and higher thermal conductivity by more than 10%.

[0179] In summary, the non-toxic gel casting molding-reactive melting combination process proposed in this application effectively solves the technical problems of high toxicity, poor green body quality, and numerous degreasing defects in existing technologies. It achieves efficient, high-density, green and environmentally friendly near-net-shape forming of diamond-silicon carbide composite materials and has broad prospects for industrial application.

[0180] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. 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. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0181] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing diamond-silicon carbide composite materials using non-toxic gel casting and reactive infiltration, characterized in that, The method specifically includes the following steps: (1) Preparation of non-toxic gel premix: Dissolve the raw materials of the non-toxic gel molding system in deionized water, stir evenly, and prepare the gel premix. (2) Slurry preparation: Diamond powder and silicon carbide powder are added to the gel premix obtained in step (1) and wet ball milling is performed to obtain a uniformly dispersed slurry; (3) Casting: The slurry obtained in step (2) is degassed under vacuum to form a cast film, which initiates a gelation reaction. After curing and drying, a diamond-silicon carbide cast green body is obtained. (4) Degreasing and pre-sintering: The cast green body obtained in step (3) is degreased and pre-sintered. The degreasing temperature is controlled within the range of 1410℃~1450℃ and lower than the diamond graphitization temperature, so that the organic matter is fully pyrolyzed and discharged, and a porous preform with interconnected pores is obtained. (5) Reactive infiltration: The porous preform obtained in step (4) is brought into contact with silicon material and infiltrated at high temperature and pressure in a vacuum environment. The silicon material melts to form a silicon liquid, which spontaneously infiltrates into the interconnected pores of the preform under the action of capillary force, and reacts with the carbon source in the preform to generate silicon carbide bonded phase in situ, thereby obtaining a dense diamond-silicon carbide sintered body. (6) Post-processing: The diamond-silicon carbide sintered body obtained in step (5) is cleaned, polished and ground to obtain the final product.

2. The method according to claim 1, characterized in that, The non-toxic gel molding system described in step (1) is selected from any of the following schemes: Scheme A: Using N,N-dimethylacrylamide as an organic monomer and methylenebisacrylamide as a crosslinking agent; wherein, the amount of N,N-dimethylacrylamide added is 3~15% of the total weight of diamond powder and silicon carbide powder in step (2), and the amount of methylenebisacrylamide added is 0.3~1.5% of the total weight of diamond powder and silicon carbide powder in step (2); Option B: Use gelatin, agarose, gellan gum, or cardlan gum as a gelling agent, with the amount of gelling agent added being 1-8% of the weight of deionized water; Option C: Sodium alginate is used as a gelling agent, and the amount of gelling agent added is 1~5% of the weight of deionized water. Glucono-δ-lactone is used as a delayed crosslinking agent, and the weight ratio of sodium alginate to glucono-δ-lactone is 1:(0.5~2). Option D: Polyvinyl alcohol is used as a gelling agent and sodium tetraborate is used as a crosslinking agent; wherein, the amount of polyvinyl alcohol added is 5-15% of the weight of deionized water, and the amount of sodium tetraborate added is 0.5-3% of the weight of polyvinyl alcohol.

3. The method according to claim 2, characterized in that, Scheme A also includes a dispersant, the amount of which is 0.5-2% of the total weight of diamond powder and silicon carbide powder in step (2); Optionally, the dispersant is selected from one or more of ammonium polyacrylate, ammonium polymethacrylate, and ammonium citrate.

4. The method according to claim 2, characterized in that, In Scheme B, the gelation of the gelling agent is initiated by cooling to 30~40℃ or below, and the gelation of gellan gum or cardlan gum is initiated by cooling to 40℃ or below; and during the preparation of the premix and the slurry, the system temperature is maintained at 45~55℃ to prevent premature gelation.

5. The method according to claim 2, characterized in that, In Scheme C, hydrogen ions are slowly released by the hydrolysis of gluconate-δ-lactone, which reacts with the calcium ion pre-complex in sodium alginate to form a gel. The gelation time is controlled to be 5-30 min by the amount of gluconate-δ-lactone added.

6. The method according to claim 2, characterized in that, In Scheme D, sodium tetraborate aqueous solution is sprayed or mixed into the slurry after it has been cast to initiate a crosslinking reaction, and the crosslinking time is 30~300s.

7. The method according to claim 1, characterized in that, The diamond powder mentioned in step (2) adopts a multi-scale particle size distribution, with the diameter ratio of large, medium, and small diamond powder particles being D. 大 :D 中 :D 小 = (4~7):(2~3):1, weight ratio is m 大 :m 中 :m 小 =(17~25):(7~12):1; Optionally, the diamond powder in step (2) is subjected to silicon plating or silicon carbide surface modification treatment, and the coating thickness is 10~200nm; Optionally, the weight ratio of diamond powder to silicon carbide powder in step (2) is (50~90):(10~50); Optionally, the total volume fraction of powder in the slurry is 45-70%; Optionally, the media used in the wet ball milling process are zirconia balls or corundum balls, with a ball-to-material ratio of (1~3):1 and a milling time of 4~24h.

8. The method according to claim 1, characterized in that, The vacuum degree of vacuum degassing in step (3) is ≤100Pa, and the degassing time is 5~15min; Optionally, the process parameters for the casting process are: 0.2~2.0mm between the scraper and the casting speed of 0.2~1.5m / min, the drying temperature of 20~80℃, and the drying time of 2~12h.

9. The method according to claim 1, characterized in that, In step (4), the degreasing treatment adopts the high-temperature pyrolysis pre-sintering method, the heating rate is 1~10℃ / min, the holding time is 1~4h, and the degreasing atmosphere is vacuum or inert gas. Optionally, the silicon material mentioned in step (5) is high-purity silicon powder or silicon block with a purity of ≥99.9%, which is laid on the upper and / or lower surface of the preform, and the total weight of the silicon material is 1.2 to 1.6 times the weight of the porous preform. Optionally, the process parameters for pressureless impregnation are: impregnation temperature 1450~1650℃, heat preservation time 0.5~3h, and vacuum degree ≤10Pa.

10. A diamond-silicon carbide composite material, comprising a diamond reinforcing phase and a silicon carbide matrix phase, characterized in that, The composite material is prepared by the method described in any one of claims 1-9; Optionally, the diamond-silicon carbide composite material has a relative density ≥96%, a room temperature thermal conductivity ≥450W / (m·K), and a Vickers hardness ≥36GPa.

Images