Diamond / silicon carbide double-phase homogeneous suspension slurry and preparation method thereof

Abstract

The invention relates to the technical field of ceramic composite material preparation, in particular to diamond / silicon carbide double-phase homogeneous suspension slurry and a preparation method thereof. Comprising the following steps: setting the total integral number of diamond and silicon carbide in slurry as well as the volume ratio of diamond to silicon carbide according to requirements; preparing a water-based suspension according to a set total integral number and volume ratio; measuring Zeta potentials of the suspension under different pH values, and recording the pH value corresponding to the maximum absolute value of the Zeta potential as an optimal pH value A; selecting a dispersing agent according to the optimal pH value A; adding a dispersing agent into the suspension, and determining the optimal addition amount of the dispersing agent by taking approaching the optimal pH value A as a standard; diamond particles, silicon carbide particles, deionized water and a dispersing agent are mixed in proportion, and diamond / silicon carbide double-phase homogeneous suspension slurry is obtained through dispersing treatment. The preparation method has the advantages that the double-phase proportion and distribution can be accurately regulated and controlled, and the slurry is low in viscosity, good in stability and suitable for various forming processes.

Description

Technical Field

[0001] This invention relates to the field of ceramic composite material preparation technology, and in particular to a diamond / silicon carbide biphase homogeneous suspension slurry and its preparation method. Background Technology

[0002] Diamond / silicon carbide composites possess both high specific stiffness and excellent thermal stability, making them ideal materials for precision instruments, optical components, and semiconductor equipment. The mainstream manufacturing process is a two-step method of "preform forming + silicon infiltration densification." Wet forming (such as slip casting and tape casting) is suitable for preparing complex shapes and highly uniform preforms, but the key lies in obtaining a ceramic suspension with high solid content, low viscosity, and good stability.

[0003] Existing technologies mostly focus on the preparation of single-phase silicon carbide or diamond suspensions. For example, CN105645968A, published on June 8, 2016, entitled "A Method for Preparing High-Performance Slurry of Ultrafine Silicon Carbide Powder," discloses a method for preparing ultrafine silicon carbide slurry with a solid content of 51-55% and a viscosity of 0.01-0.5 Pa·s. CN111484330A, published on August 4, 2020, entitled "Diamond-Reinforced Silicon Carbide Substrate and Its Preparation Method and Electronic Products," discloses a method for preparing diamond casting slurry with a viscosity of approximately 8000 mPa·s, and obtains a diamond-reinforced silicon carbide substrate through silicon reaction infiltration. When preparing diamond / silicon carbide biphase composite materials, a common process route is: first, prepare a diamond preform (containing other carbon sources), then densify it through silicon infiltration. During the infiltration process, silicon reacts with diamond and other carbon sources to generate a silicon carbide phase, thereby obtaining the diamond / silicon carbide composite material. While this method is widely used, the specific structure and content of the silicon carbide phase within the composite material are mainly determined by the silicon-carbon reaction during the infiltration process. It is difficult to precisely control the ratio of the two phases at the slurry stage, and true "uniform two-phase composite" cannot be achieved. Due to the significant differences in surface properties between diamond and silicon carbide particles, selective agglomeration or phase separation easily occurs in water-based media, resulting in poor slurry uniformity, high viscosity, and insufficient stability. Simply superimposing the dispersion scheme of two single-phase slurries cannot achieve synergistic stability of the two-phase particles, making it difficult to simultaneously meet the process requirements of high solids content and low viscosity. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a diamond / silicon carbide two-phase homogeneous suspension slurry and its preparation method.

[0005] The primary objective of this invention is to provide a method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry, specifically comprising the following steps: S1. Set the total volume fraction of diamond and silicon carbide in the slurry, as well as the volume ratio of diamond to silicon carbide, according to requirements; S2. Prepare a water-based suspension according to the set total volume fraction and volume ratio; measure the Zeta potential of the water-based suspension at different pH values, and record the pH value corresponding to the maximum absolute value of the Zeta potential as the optimal pH value A. S3. Select a dispersant based on the optimal pH value A; add a dispersant to the suspension, and determine the optimal amount of dispersant to add based on the system pH value approaching the optimal pH value A. S4. Diamond particles, silicon carbide particles, deionized water and the dispersant determined in step S3 are mixed in proportion and dispersed to obtain a diamond / silicon carbide two-phase homogeneous suspension slurry.

[0006] Preferably, in step S1, the total volume fraction of diamond and silicon carbide is 20-70%, and the volume ratio of diamond to silicon carbide is 0.1-10.

[0007] Preferably, the particle size of the diamond and the silicon carbide is 0.5~100μm.

[0008] Preferably, in step S1, the diamond and silicon carbide are hydroxylated using a silane coupling agent.

[0009] Preferably, in step S3, the dispersant is classified into acidic dispersant and alkaline dispersant according to the acidity or alkalinity of the optimal pH value A; When the optimal pH value A < 7, the acidic dispersant is selected from at least one of polyacrylic acid, citric acid, tartaric acid, polymethacrylic acid, and polyacrylic acid-maleic anhydride copolymer; When the optimal pH value A > 7, the alkaline dispersant is selected from at least one of tetramethylammonium hydroxide, polyethyleneimine, ammonium polyacrylate, polyethylene glycol, polyvinylpyrrolidone, sodium hydroxide, potassium hydroxide, and ammonia water.

[0010] Preferably, in step S4, the dispersion treatment includes pre-stirring and ball milling dispersion; The pre-stirring speed is 300~500 r / min, and the time is 0.1~0.5 h; The ball milling dispersion time is 3~12h.

[0011] Preferably, in step S4, molding aids are added during mixing according to molding requirements, and the molding aids include at least one of binders, plasticizers, and defoamers.

[0012] The second objective of this invention is to provide a diamond / silicon carbide two-phase homogeneous suspension slurry, which is prepared using the aforementioned method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry.

[0013] The third objective of this invention is to provide the application of diamond / silicon carbide biphase homogeneous suspension slurry in the preparation of ceramic composite preforms, wherein the slurry is prepared into a green body using processes such as slurry casting, tape casting, pressure filtration, 3D printing, or surface coating.

[0014] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) By identifying the global optimal electrostatic stability point (point A) of the two-phase system and accurately matching the dispersant accordingly, an electrostatic-steric synergistic stabilization mechanism was established, which effectively solved the technical problem of difficult synergistic dispersion of diamond and silicon carbide due to differences in surface properties, and realized long-term uniform dispersion of two-phase particles.

[0015] (2) A viscosity of only 0.3~0.7 Pa·s (shear rate 100 s) can be obtained at a solid content of up to 55~65 vol%. -1 It is a highly stable slurry that combines high solids content with good rheological properties.

[0016] (3) The slurry composition (total volume fraction V of diamond and silicon carbide and volume ratio R) is flexible and adjustable, with strong process adaptability. It is suitable for various wet molding processes such as slurry molding, pressure filtration molding, tape casting, 3D printing, and surface coating, and can also be used for spray granulation.

[0017] (4) This method is based on a water-based system, which is environmentally friendly, low-cost, has a clear process flow, and is easy to scale up.

[0018] In summary, the slurry preparation method provided by this invention overcomes the bottleneck of traditional high-performance diamond / silicon carbide composite materials, which can only generate the silicon carbide phase through "post-reaction" and where the uniformity of the two phases is difficult to control. It achieves precise control and direct molding of the two-phase ratio and particle distribution uniformity during the slurry preparation stage, providing an innovative front-end material preparation solution for the fabrication of high-performance ceramic components with complex structures, gradient compositions, or customized functions (such as optical mirror blanks, semiconductor thermal management substrates, and wear-resistant components for extreme environments). Furthermore, this invention employs a fully water-based system, aligning with the development trend of green manufacturing and possessing significant cost advantages and industrialization potential in large-scale production applications. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry according to an embodiment of the present invention.

[0020] Figure 2The figure shows the Zeta potential (DSZ) curves of diamond / silicon carbide suspensions with pH changes at different diamond to silicon carbide volume ratios (R) according to embodiments of the present invention; DSZ-0, DSZ-0.5, DSZ-1, DSZ-1.5, and DSZ-2 correspond to sample systems with diamond to silicon carbide volume ratios of 0, 0.5, 1, 1.5, and 2, respectively.

[0021] Figure 3 The figures show the relationship between the pH value and Zeta potential of the slurry and the amount of dispersant D under different diamond to silicon carbide volume ratios according to embodiments of the present invention. In the figures, DSZ-0, DSZ-0.5, DSZ-1, DSZ-1.5, and DSZ-2 correspond to sample systems with diamond to silicon carbide volume ratios of 0, 0.5, 1, 1.5, and 2, respectively.

[0022] Figure 4 This is a viscosity data graph of diamond / silicon carbide two-phase suspension slurry under different combinations of total solid phase integral V and diamond to silicon carbide volume ratios according to embodiments of the present invention.

[0023] Figure 5 The image shows a SEM image of the microstructure of a diamond / silicon carbide composite material according to an embodiment of the present invention; wherein the black area represents the diamond phase and the gray area represents the silicon carbide phase. The image shows that the diamond and silicon carbide particles are uniformly distributed without obvious agglomeration or segregation. Detailed Implementation

[0024] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0026] This invention provides a method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry. The core technology principle is the precise matching of acid-base dispersants guided by optimal electrostatic potential. This principle overturns the traditional dispersion approach of treating the two types of particles separately and then simply mixing them, treating the two-phase particles as a synergistically dispersed overall system. By identifying the globally optimal electrostatic stability point (point A) of this system and selecting a dispersant that can drive the system to reach and reside at this point, a strong and synergistic electrostatic-steric hindrance dual stabilization mechanism is established between the particles. This not only solves the dispersion problem but also enables predictable and controllable design of slurry properties (such as viscosity and stability). Specifically, the method includes the following steps: S1. Composition Design: Set the total volume fraction V (percentage of slurry volume) of diamond and silicon carbide in the slurry, as well as the volume ratio R of diamond to silicon carbide, according to requirements; Specifically, the total integral V is 20-70 vol%, and the volume ratio R is 0.1-10; The particle size of diamond and silicon carbide is 0.5~100μm; the gradation design can be carried out as needed. For particles with inert surfaces or larger particle sizes, hydroxylation pretreatment with silane coupling agent is used to enhance their surface activity and dispersion stability; the preferred silane coupling agent is KH-550 silane coupling agent.

[0027] S2. Determine the optimal pH value A of the system: Prepare a water-based suspension according to the set total volume fraction V and volume ratio R, measure the Zeta potential of the water-based suspension at different pH values, and record the pH value corresponding to the largest absolute value of the Zeta potential as the optimal pH value A.

[0028] S3. Selection and Dosage Determination of Dispersant: Select the corresponding type of dispersant based on the optimal pH value A; add the dispersant to the water-based suspension, and determine the optimal dosage D of the dispersant by using the system pH value as close as possible to the optimal pH value A; Specifically, when the optimal pH value A < 7, an acidic dispersant is selected, preferably at least one of polyacrylic acid (PAA), citric acid, tartaric acid, polymethacrylic acid, and polyacrylic acid-maleic anhydride copolymer. When the optimal pH value A > 7, an alkaline dispersant is selected, preferably at least one of tetramethylammonium hydroxide (TMAH), polyethyleneimine (PEI), ammonium polyacrylate (PAA-NH4), polyethylene glycol, polyvinylpyrrolidone, sodium hydroxide, potassium hydroxide, and ammonia.

[0029] S4. Slurry preparation: Diamond particles, silicon carbide particles, deionized water and the dispersant determined in step S3 are mixed in proportion and dispersed to obtain a diamond / silicon carbide two-phase homogeneous suspension slurry. Specifically, the dispersion treatment includes pre-stirring and ball milling dispersion; the pre-stirring speed is 300~500 r / min and the time is 0.1~0.5 h; the ball milling dispersion time is 3~12 h. In this step, molding aids may also be added according to specific needs. Molding aids include at least one of binders, plasticizers, and defoamers. The binder is selected from at least one of polyvinyl alcohol (PVA), hydroxypropyl methylcellulose (HPMC), carboxymethyl cellulose (CMC), acrylamide, starch, and waterborne polyurethane. The plasticizer is selected from at least one of glycerol, ethylene glycol, polyethylene glycol (PEG), and butanediol. The defoamer is selected from at least one of silicone defoamers, polyether defoamers, and higher alcohol defoamers.

[0030] Example 1 This embodiment provides a method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry, which specifically includes the following steps: S1. Composition Design: The total integral number of diamond / silicon carbide dual-phase particles in the slurry is set to V=20vol%, and the volume ratios R of diamond to silicon carbide are 0, 0.5, 1, 1.5, and 2, respectively; diamond particles with a median particle size of 3.3μm and silicon carbide particles with a median particle size of 4.8μm are selected.

[0031] S2. Determining the optimal pH value A: The diamond particles, silicon carbide particles, and deionized water were mixed to obtain an initial aqueous suspension; under stirring at 300 r / min, the pH value of the suspension was adjusted using 1 mol / L hydrochloric acid solution and 1 mol / L sodium hydroxide solution, respectively, and the Zeta potential of the suspension at different pH values ​​was measured. Results ( Figure 2 The results show that under different volume ratios R, the absolute value of the zeta potential of the suspension reaches its maximum at pH=11, thus determining the optimal pH value of the system as A=11.

[0032] S3. Selection and Dosage Determination of Dispersant: Based on the optimal pH value A=11 (alkaline range), tetramethylammonium hydroxide (TMAH) was selected as the dispersant. Using the total mass of the powder as a baseline, dispersant concentrations of 0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1% were added respectively. The pH value and Zeta potential of the suspension were measured, and the results are shown in [Figure number missing]. Figure 3 Using the system pH value approaching the optimal pH value A as the criterion, determine the optimal amount of dispersant D corresponding to each volume ratio R; When R is 0, 0.5, 1, 1.5, and 2, the optimal addition amount D is 1%, 0.8%, 0.6%, 0.6%, and 0.4%, respectively.

[0033] S4. Slurry preparation: According to the above optimal parameters, diamond particles, silicon carbide particles, deionized water and the optimal amount of dispersant are mixed, pre-stirred and dispersed (400 r / min, 0.5 h), and then ball-milled and dispersed for 5 h to obtain a homogeneous and stable diamond / silicon carbide biphase homogeneous suspension slurry.

[0034] Example 2 This embodiment provides a method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry, which specifically includes the following steps: S1. Composition Design: The total integral number V of diamond / silicon carbide dual-phase particles was set to 55 vol%, 60 vol%, and 65 vol%, respectively, and the volume ratio R of diamond to silicon carbide was 0, 0.5, 1, 1.5, and 2, respectively; diamond particles with a median particle size of 39.5 μm and silicon carbide particles with a median particle size of 53.4 μm were selected.

[0035] S2. Determine the optimal pH value A of the system: Mix the diamond particles, silicon carbide particles and deionized water to obtain an initial water-based suspension; adjust the pH value of the suspension and measure the Zeta potential to determine that the optimal pH value A of the coarse particle system in this embodiment is in the range of 10~11.

[0036] S3. Selection and Dosage of Dispersant: Tetramethylammonium hydroxide (TMAH) was selected as the dispersant based on the optimal pH value A. The amount of dispersant added was adjusted to bring the pH value of the system closer to the optimal pH value A, and the optimal amount of dispersant D for each ratio condition was determined.

[0037] S4. Slurry preparation: Taking a system with a total integral number V=60vol% and a volume ratio R=1 as an example, diamond particles, silicon carbide particles, deionized water and dispersant are mixed, pre-stirred at 300~500r / min for 0.1~0.5h, and then ball-milled and dispersed for 3~12h to obtain a homogeneous and stable suspension slurry.

[0038] Acrylamide monomer and methylenebisacrylamide crosslinking agent were added to the slurry, stirred evenly, and then poured into a plaster mold for casting. Testing showed that the slurry in this embodiment achieved a shear rate of 100 s⁻¹. -1 The viscosity of the slurry is 0.3~0.7 Pa·s, exhibiting good flowability and formability. The molded green body after slurry injection has uniform density, and after drying, it shows no cracking or delamination, meeting the requirements for subsequent degreasing and penetration treatment. The slurry viscosity is as follows: Figure 3 As shown.

[0039] The results of this embodiment show that, for large-sized particles and high-solids-content systems, the method of the present invention can still effectively prepare slurries with low viscosity and good stability, and has been successfully applied to grouting molding to obtain high-performance composite material preforms.

[0040] Example 3 This embodiment provides a method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry, which specifically includes the following steps: S1. Composition design and particle pretreatment: The total integral number of diamond / silicon carbide dual-phase particles was set to V=60vol%, and the volume ratio of diamond to silicon carbide was R=1; diamond particles with a median particle size of 15μm and silicon carbide particles with a median particle size of 10μm were selected. Diamond particles and silicon carbide particles were pretreated with KH-550 silane coupling agent by hydroxylation (as the experimental group), while untreated diamond particles and silicon carbide particles served as the control group; the particle size and ratio of the two groups were consistent.

[0041] S2. Determine the optimal pH value A of the system: Prepare initial water-based suspensions for the control group and the experimental group respectively, adjust the pH value and measure the Zeta potential to determine the optimal pH value A for each; among them, the optimal pH value A of the pretreated system (experimental group) is 10.8, and the absolute value of the Zeta potential is higher at the optimal pH, and the dispersion stability is stronger; the optimal pH value A of the untreated system (control group) is 9.5.

[0042] S3. Selection and determination of dispersant dosage: Tetramethylammonium hydroxide (TMAH) was selected as the dispersant. The dosage was adjusted to make the pH value of the system approach the optimal pH value A. The optimal dosage D was determined: the optimal dosage D for the pretreated system was 0.4 wt%, and the optimal dosage D for the untreated system was 0.6 wt%.

[0043] S4. Slurry preparation: The two groups of particles are mixed with deionized water and the corresponding optimal amount of dispersant, respectively, and then pre-stirred and dispersed by ball milling to obtain two groups of suspension slurries.

[0044] At a shear rate of 100s -1 The viscosity of both slurries was approximately 0.5 Pa·s; the pretreated slurry exhibited more significant shear thinning characteristics and was more suitable for molding complex structures. After casting and drying, the slurry yielded a blank with no macroscopic phase separation on its surface; a dense diamond / silicon carbide composite material was obtained through reaction sintering.

[0045] like Figure 4 SEM characterization showed that the diamond / silicon carbide composite material made from the treated slurry had uniform distribution of diamond and silicon carbide particles, with no obvious agglomeration or segregation, and good two-phase dispersion.

[0046] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0047] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry, characterized in that: Specifically, the steps include the following: S1. Set the total volume fraction of diamond and silicon carbide in the slurry, as well as the volume ratio of diamond to silicon carbide, according to requirements; S2. Prepare a water-based suspension according to the set total volume fraction and volume ratio; measure the Zeta potential of the water-based suspension at different pH values, and record the pH value corresponding to the maximum absolute value of the Zeta potential as the optimal pH value A. S3. Select a dispersant based on the optimal pH value A; add a dispersant to the suspension, and determine the optimal amount of dispersant to add based on the system pH value approaching the optimal pH value A. S4. Diamond particles, silicon carbide particles, deionized water and the dispersant determined in step S3 are mixed in proportion and dispersed to obtain a diamond / silicon carbide two-phase homogeneous suspension slurry.

2. The method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry according to claim 1, characterized in that: In step S1, the total volume fraction of diamond and silicon carbide is 20-70%, and the volume ratio of diamond to silicon carbide is 0.1-10.

3. The method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry according to claim 1, characterized in that: The diamond and silicon carbide have a particle size of 0.5~100μm.

4. The method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry according to claim 3, characterized in that: In step S1, the diamond and silicon carbide are hydroxylated using a silane coupling agent.

5. The method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry according to claim 1, characterized in that: In step S3, the dispersant is classified into acidic dispersant and alkaline dispersant according to the acidity or alkalinity of the optimal pH value A. When the optimal pH value A < 7, the acidic dispersant is selected from at least one of polyacrylic acid, citric acid, tartaric acid, polymethacrylic acid, and polyacrylic acid-maleic anhydride copolymer; When the optimal pH value A > 7, the alkaline dispersant is selected from at least one of tetramethylammonium hydroxide, polyethyleneimine, ammonium polyacrylate, polyethylene glycol, polyvinylpyrrolidone, sodium hydroxide, potassium hydroxide, and ammonia water.

6. The method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry according to claim 1, characterized in that: In step S4, the dispersion treatment includes pre-stirring and ball milling dispersion; The pre-stirring speed is 300~500 r / min, and the time is 0.1~0.5 h; The ball milling dispersion time is 3~12h.

7. The method for preparing a diamond / silicon carbide two-phase homogeneous suspension slurry according to claim 1, characterized in that: In step S4, molding aids are added during mixing according to molding requirements. The molding aids include at least one of binders, plasticizers, and defoamers.

8. A diamond / silicon carbide two-phase homogeneous suspension slurry, characterized in that: The diamond / silicon carbide biphase homogeneous suspension slurry was prepared using the method described in claim 1.

9. The application of the diamond / silicon carbide biphase homogeneous suspension slurry according to claim 9 in the preparation of ceramic composite preforms, characterized in that: The slurry is prepared into a blank using processes such as slurry casting, casting, pressure filtration, 3D printing, or surface coating.

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