Surface modification method of superfine diamond micropowder

Abstract

The invention discloses a surface modification method of superfine diamond micro-powder, which comprises the following steps: S1, putting the superfine diamond micro-powder into deionized water for ultrasonic dispersion, filtering and then drying to obtain pretreated diamond micro-powder; s2, a silane coupling agent KH550 is added into absolute ethyl alcohol to be stirred, and modified liquid with the concentration being 1%-5% is obtained; s3, adding the pretreated diamond micro-powder obtained in the step S1 into the modified liquid obtained in the step S2, and stirring and reacting for 1-3 hours at the temperature of 30-60 DEG C; s4, filtering the mixture obtained after the reaction in the step S3, cleaning the mixture with absolute ethyl alcohol for 2-3 times, and drying the mixture to obtain the superfine diamond micro-powder after surface modification; the silane coupling agent KH550 is adopted to perform surface modification on the diamond micro-powder, so that the dispersity of the diamond micro-powder and the compatibility of the diamond micro-powder with other materials can be remarkably improved. Compared with the prior art, the method is simple in process, convenient to operate, low in cost and stable in modification effect.

Description

Technical Field

[0001] The present invention relates to a surface treatment technology for superhard materials, in particular to a surface modification method for ultrafine diamond powder. Background Art

[0002] Ultrafine diamond powder, an important superhard material, is widely used in precision machining, electronic device manufacturing, and other fields. However, its high surface energy, prone to agglomeration, and poor compatibility with other materials limit its performance. While existing surface modification methods can improve the surface properties of diamond powder to a certain extent, they suffer from unstable modification effects, complex processes, and high costs. Summary of the Invention

[0003] The present invention overcomes the deficiencies of the prior art and provides a surface modification method for ultrafine diamond powder.

[0004] To achieve the above object, the present invention adopts the following technical solution: a surface modification method of ultrafine diamond powder, comprising the following steps:

[0005] S1, ultrasonically dispersing ultrafine diamond powder in deionized water, filtering and drying to obtain pretreated diamond powder;

[0006] S2. Add silane coupling agent KH550 to anhydrous ethanol and stir to obtain a modified solution with a concentration of 1% to 5%;

[0007] S3, adding the pretreated diamond powder obtained in step S1 to the modified solution obtained in step S2, and stirring the mixture at 30-60° C. for 1-3 hours;

[0008] S4. Filter the mixture after the reaction in step S3, wash it with anhydrous ethanol 2 to 3 times, and dry it to obtain surface-modified ultrafine diamond powder.

[0009] In a preferred embodiment of the present invention, in step S1, the ultrasonic dispersion time is 10 to 30 minutes.

[0010] In a preferred embodiment of the present invention, in step S1, the drying temperature is 50-80°C, and the drying time is 2-4 hours.

[0011] In a preferred embodiment of the present invention, in step S3, the stirring speed is 200-400 rpm.

[0012] In a preferred embodiment of the present invention, in step S4, the drying temperature is 50-80° C., and the drying time is 2-4 hours.

[0013] In a preferred embodiment of the present invention, the concentration of the silane coupling agent KH550 in the modifying liquid is 2% to 4%.

[0014] In a preferred embodiment of the present invention, in step S3, the reaction temperature is 40-50° C., and the reaction time is 1.5-2.5 hours.

[0015] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0016] (1) The present invention uses the silane coupling agent KH550 to modify the surface of diamond micropowder, significantly improving its dispersibility and compatibility with other materials. Compared with the prior art, the present invention has a simple process, convenient operation, low cost, stable modification effect, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0018] Figure 1 It is a flow chart of the modification process of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0021] like Figure 1 As shown, a surface modification method of ultrafine diamond powder comprises the following steps:

[0022] S1. Ultrafine diamond powder is ultrasonically dispersed in deionized water, filtered, and dried to obtain pretreated diamond powder. In step S1, the ultrasonic dispersion time is 10 to 30 minutes. In step S1, the drying temperature is 50 to 80° C., and the drying time is 2 to 4 hours.

[0023] In a preferred embodiment, the raw powder is first placed in a 3-5wt% HNO3 solution and refluxed at 60-80°C for 1-2 hours to remove surface metallic impurities and amorphous carbon. After filtration, the powder is washed with deionized water until neutral, then ultrasonically treated in a 2-4wt% NaOH solution for 15-30 minutes to etch the weakly crystalline layer on the surface, exposing more C-OH active groups. The principle: Acid-base etching removes surface contaminants while simultaneously introducing hydroxylation active sites on the diamond surface, providing anchor points for subsequent coupling agent grafting.

[0024] S2. Add silane coupling agent KH550 to anhydrous ethanol and stir to obtain a modified solution with a concentration of 1% to 5%; the concentration of silane coupling agent KH550 in the modified solution is 2% to 4%.

[0025] In a preferred embodiment, a modified solution is prepared by mixing anhydrous ethanol and deionized water in a 3:1 volume ratio using a ternary compound system consisting of 0.5-2 wt% silane coupling agent KH550, 0.3-1.5 wt% titanate coupling agent NDZ-101, and 0.1-0.5 wt% Span-80 surfactant. The silane coupling agent binds to the hydroxyl groups on the diamond surface via Si-OC bonds, the titanate coupling agent enhances interfacial polarity matching through chelation, and the Span-80 reduces surface tension and promotes dispersion, creating a synergistic modification effect.

[0026] S3. Add the pretreated diamond powder obtained in step S1 to the modified solution obtained in step S2, and stir the mixture at 30-60°C for 1-3 hours. In step S3, the stirring speed is 200-400 rpm. In step S3, the reaction temperature is 40-50°C, and the reaction time is 1.5-2.5 hours.

[0027] In a preferred embodiment, a constant magnetic field of 0.1-0.3T is applied to the periphery of the reactor, while ultrasonic vibration at 20-40kHz is activated. The reaction temperature is controlled at 40-50°C, the stirring speed is 300-500 rpm, and the reaction time is 1.5-2.5 hours. The ultrasonic cavitation effect breaks up nanoaggregates and enhances mass transfer, while the magnetic field aligns the coupling agent molecules in an orderly and directional manner, improving grafting efficiency and film uniformity.

[0028] S4. Filter the mixture after the reaction in step S3, wash it with anhydrous ethanol 2-3 times, and dry it to obtain surface-modified ultrafine diamond powder. In step S4, the drying temperature is 50-80° C. and the drying time is 2-4 hours.

[0029] In a preferred embodiment, after modification and cleaning, the powder is added to an ethanol-water solution containing 0.5-1 wt% TEOS, the pH is adjusted to 8-9, and a hydrolysis reaction is carried out at 50-60°C for 30-60 minutes to form a 5-10 nm thick SiO2 transition layer. Finally, the powder is calcined in an inert atmosphere at 500-600°C for one hour. This nano-SiO2 layer forms a chemical bond bridge between diamond-CO-Si-O-Si, further enhancing the interfacial bonding strength with different substrates such as resins and metals.

[0030] Example 1

[0031] 10 g of ultrafine diamond powder was put into 100 ml of deionized water, ultrasonically dispersed for 10 minutes, then filtered and dried at 50° C. for 2 hours to obtain pretreated diamond powder.

[0032] Add 1g of silane coupling agent KH550 to 100ml of anhydrous ethanol and stir evenly to obtain a modified solution with a concentration of 1%.

[0033] The pretreated diamond powder was added to the modified solution and stirred at 30° C. and 200 rpm for 1 hour.

[0034] After the reaction was completed, the mixture was filtered, washed twice with anhydrous ethanol, and dried at 50° C. for 2 hours to obtain surface-modified ultrafine diamond powder.

[0035] Example 2

[0036] 10 g of ultrafine diamond powder was put into 100 ml of deionized water, ultrasonically dispersed for 20 minutes, then filtered and dried at 60° C. for 3 hours to obtain pretreated diamond powder.

[0037] Add 3g of silane coupling agent KH550 to 100ml of anhydrous ethanol and stir evenly to obtain a modified solution with a concentration of 3%.

[0038] The pretreated diamond powder was added to the modified solution and stirred at 45° C. at a speed of 300 rpm for 2 hours.

[0039] After the reaction was completed, the mixture was filtered, washed with anhydrous ethanol three times, and dried at 60° C. for 3 hours to obtain surface-modified ultrafine diamond powder.

[0040] Example 3

[0041] 10 g of ultrafine diamond powder was put into 100 ml of deionized water, ultrasonically dispersed for 30 minutes, then filtered and dried at 80° C. for 4 hours to obtain pretreated diamond powder.

[0042] Add 5g of silane coupling agent KH550 to 100ml of anhydrous ethanol and stir evenly to obtain a modified solution with a concentration of 5%.

[0043] The pretreated diamond powder was added to the modified solution and stirred at 60° C. and 400 rpm for 3 hours.

[0044] After the reaction was completed, the mixture was filtered, washed with anhydrous ethanol three times, and dried at 80° C. for 4 hours to obtain surface-modified ultrafine diamond powder.

[0045] The performance of the surface-modified ultrafine diamond powder obtained in Examples 1 to 3 was tested, specifically:

[0046] (1) Dispersion stability test;

[0047] Using the deionized water test method, weigh 0.5g of modified micropowder and add it to a 50mL stoppered measuring cylinder. Add 40mL of deionized water and ultrasonically disperse for 10 minutes. After standing for 24 hours and 72 hours, observe the volume of the sediment at the bottom and calculate the sedimentation rate: The evaluation index is: the lower the sedimentation rate, the better the dispersibility.

[0048] (2) Surface contact angle test;

[0049] Using a DSA25 contact angle meter, the modified micropowder was pressed into a smooth sheet. 2 μL of deionized water was added to the sheet at room temperature and the contact angle was measured five times, taking the average value. The evaluation metric is: the smaller the contact angle, the more hydrophilic the surface, meaning the better the coupling agent grafting effect.

[0050] (3) Infrared spectroscopy analysis

[0051] The powder was mixed with KBr in a ratio of 1:100 and ground into a pellet using a Nicolet iS5 Fourier transform infrared spectrometer. The scanning range was 4000–400 cm -1 , with a resolution of 4cm -1 , scanned 32 times. Characteristic peak verification: detect whether there are Si-OC bond and C-Si bond absorption peaks of silane coupling agent.

[0052] (4) Interface bonding strength test;

[0053] The modified micropowder was mixed with epoxy resin and triethylenetetramine as a curing agent in a mass ratio of 10:1 to prepare a composite slurry containing 5 wt% micropowder; the slurry was poured into a mold for curing. The curing conditions included two stages: 60 ° C, 2 h; 80 ° C, 2 h, and processed into 10mm×20mm cylindrical specimen. Use Instron 5967 universal materials testing machine, set the axial shear rate to 1mm / min, record the maximum shear force at failure, and calculate the shear strength: .

[0054] The performance test results are shown in Table 1:

[0055] Table 1

[0056] Test items Unmodified sample Example 1 Example 2 Example 3 Dispersion stability (sedimentation rate) 24-hour sedimentation rate: 65±2%; 72-hour sedimentation rate: 82±3%; 24-hour sedimentation rate: 35±1.5%; 72-hour sedimentation rate: 55±2.0% 24-hour sedimentation rate: 22±1.2%; 72-hour sedimentation rate: 30±1.5% 24-hour sedimentation rate: 28±1.8%; 72-hour sedimentation rate: 45±2.5% Surface contact angle 85±2° 68±1.5° 55±1.0° 62±1.2° FT-IR characteristic peaks No Si-O bond <![CDATA[1050cm -1 (√)]]> <![CDATA[1055cm -1 (√)]]> <![CDATA[1060cm -1 (√)]]> Interface shear strength 8.5±0.5MPa 12.2±0.8MPa 15.5±1.0MPa 13.8±0.9MPa

[0057] Result analysis: The sedimentation rate of the modified sample within 72 hours was significantly lower than that of the unmodified sample, among which the 30% dispersion effect of Example 2 was the best, proving that the synergistic effect of ultrasonic time, modification liquid concentration and reaction time improved the dispersibility.

[0058] The contact angle decreased from 85° to 55°-8°, indicating that the silane coupling agent was successfully grafted onto the diamond surface, and the introduction of polar groups, such as -OH and -NH2, improved the compatibility with polar media.

[0059] The characteristic peak of Si-OC bond was detected in all modified samples, confirming that the coupling agent was fixed on the diamond surface through chemical bonding, while the unmodified samples did not have this peak.

[0060] The shear strength is increased by 43%-82% compared with the unmodified sample, with 15.5 MPa in Example 2 reaching the highest value, indicating that the moderate concentration of the modifying liquid and the appropriate reaction conditions optimize the interfacial chemical bonding density.

[0061] Example 4

[0062] Add 20 g of micropowder to 200 ml of 4 wt% HNO3 solution, reflux at 70 °C for 1.5 hours, filter and wash, then transfer to 150 ml of 3 wt% NaOH solution, ultrasonically treat for 20 minutes, filter and dry at 60 °C for 3 hours.

[0063] 1.2 g KH550, 0.8 g NDZ-101, and 0.3 g Span-80 were dissolved in a mixed solvent of 150 ml anhydrous ethanol and 50 ml deionized water, and magnetically stirred for 30 minutes until completely dissolved.

[0064] The pretreated micropowder was added to the modified solution, and 25 kHz ultrasound was turned on with a power of 200 W. A 0.2 T magnetic field was applied at the same time, and the mixture was reacted at 45° C. and 400 rpm for 2 hours.

[0065] After the reaction, the product was filtered and washed, and an ethanol aqueous solution containing 0.8 wt% TEOS was added, with a pH of 8.5, and hydrolyzed at 55°C for 45 minutes. After filtering, the product was calcined at 550°C in an Ar atmosphere for 1 hour.

[0066] The modified micropowder obtained in Example 4 was subjected to a performance test, and the test process included:

[0067] (1) Dispersion stability test: Same as in Examples 1 to 3, except that the medium is deionized water, the sedimentation rates are calculated after 24 h and 72 h.

[0068] (2) Surface contact angle test: Same as above, with the addition of verification of the hydrophilicity of the silica transition layer.

[0069] (3) Infrared spectroscopy analysis: New detection of Si-O-Si bonds and Si-OH bonds to verify the existence of the SiO2 layer.

[0070] (4) Interface bonding strength test: Same as before, test the shear strength with epoxy resin.

[0071] (5) Thermogravimetric analysis: A TA Q500 thermogravimetric analyzer was used with the following settings: nitrogen atmosphere, heating rate 10°C / min, range 30-800°C, to detect the high temperature resistance of the modified layer. The weight loss rate reflects the stability of the modified layer.

[0072] The results are shown in Table 2:

[0073] Table 2

[0074] Test items Example 4 Dispersion stability (sedimentation rate) 24-hour sedimentation rate: 15±1.0%; 72-hour sedimentation rate: 20±1.2%; Surface contact angle 48±0.8° FT-IR characteristic peaks <![CDATA[1055cm -1 (Si-OC);1090cm -1 (Si-O-Si);3420cm -1 (Si-OH);]]> Interface shear strength 22.3±1.2MPa Thermogravimetric analysis 500℃ weight loss rate: 8%

[0075] Result analysis: As shown in Tables 1 and 2, the 72-hour sedimentation rate of Example 4 was 20%, which was 33% lower than that of Example 2, which was 30%. This was due to the triple effects of acid-base pretreatment to remove surface impurities, ultrasonic-magnetic field synergistically breaking up agglomerates, and Span-80 surfactant to reduce surface tension. The dispersion was improved to the long-term stability of the water-based system.

[0076] The contact angle dropped to 48°, which was 13% lower than 55° in Example 2, indicating that the composite coupling agent and the silica transition layer introduced a large number of polar groups, significantly improving the compatibility with polar media such as water-based and resin-based media.

[0077] FT-IR revealed the addition of Si-O-Si and Si-OH bonds, proving that the nano-SiO2 layer generated by TEOS hydrolysis was successfully grafted to form a gradient interface layer of diamond-CO-Si-O-Si-. Compared with the modification of single silane, it has an additional layer of chemical anchoring, which improves the bonding strength.

[0078] The shear strength reaches 22.3 MPa, which is 44% higher than the 15.5 MPa of Example 2. The reason for this breakthrough is that the titanate coupling agent NDZ-101 enhances the interface matching between non-polar diamond and polar resin through chelation. The magnetic field causes the coupling agent molecules to align in a directional manner, forming a denser graft layer. The SiO2 transition layer acts as a molecular bridge to form hydrogen bonds and chemical bonds with the epoxy groups in the epoxy resin.

[0079] The weight loss rate at 500°C is only 8%, indicating that the inorganic protective layer formed after the calcination of silica effectively inhibits the high-temperature desorption of the modified layer, solving the problem of traditional silane modification failing above 200°C.

[0080] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A surface modification method for ultrafine diamond powder, characterized in that: The following steps are involved: S1, ultrasonically dispersing ultrafine diamond powder in deionized water, filtering and drying to obtain pretreated diamond powder; S2. Add silane coupling agent KH550 to anhydrous ethanol and stir to obtain a modified solution with a concentration of 1% to 5%; S3, adding the pretreated diamond powder obtained in step S1 to the modified solution obtained in step S2, and stirring the mixture at 30-60° C. for 1-3 hours; S4. Filter the mixture after the reaction in step S3, wash it with anhydrous ethanol 2 to 3 times, and dry it to obtain surface-modified ultrafine diamond powder.

2. The surface modification method of ultrafine diamond powder according to claim 1, characterized in that: In step S1, the ultrasonic dispersion time is 10 to 30 minutes.

3. The surface modification method of ultrafine diamond powder according to claim 1, characterized in that: In step S1, the drying temperature is 50-80° C., and the drying time is 2-4 hours.

4. The surface modification method of ultrafine diamond powder according to claim 1, characterized in that: In step S3, the stirring speed is 200-400 rpm.

5. The surface modification method of ultrafine diamond powder according to claim 1, characterized in that: In step S4, the drying temperature is 50-80° C., and the drying time is 2-4 hours.

6. The surface modification method of ultrafine diamond powder according to claim 1, characterized in that: The concentration of the silane coupling agent KH550 in the modified solution is 2% to 4%.

7. The surface modification method of ultrafine diamond powder according to claim 1, characterized in that: In step S3, the reaction temperature is 40-50° C., and the reaction time is 1.5-2.5 hours.

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