Diamond microspheres and methods for making the same
By controlling the preparation parameters of diamond microspheres using microwave plasma CVD technology, the problems of uncontrollable particle size and irregular shape in existing technologies have been solved, and diamond microspheres with uniform particle size and regular shape have been prepared, thus improving their application performance.
Patent Information
- Application Number
- CN202311562205.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-22
- Publication Date
- 2026-03-03
- Estimated Expiration
- 2043-11-22
AI Technical Summary
Existing technologies make it difficult to prepare diamond powders or particles with regular shapes and controllable particle sizes, resulting in unstable performance in practical applications.
Polycrystalline diamond microspheres were prepared by using microwave plasma CVD technology, by controlling carbon ion concentration, deposition gas pressure, temperature and time. The particle size was controllable from 1 to 100 μm, and the microspheres had regular shapes and high sphericity.
This technology significantly improves the uniformity of diamond microsphere size and shape, resulting in more stable application performance. It is suitable for high thermal conductivity filler materials, polymer coatings, and biomedical fields.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of micro-nano powder material synthesis technology, and specifically relates to a diamond microsphere and its preparation method. Background Technology
[0002] Carbon exists in various forms, from nanoscale to bulk materials, with known structures including graphite, graphene, carbon nanotubes, fullerenes, and diamond. Chemical vapor deposition (CVD) can synthesize various carbon material variants, such as diamond, graphene, and carbon nanotubes, under extremely low pressure and temperature conditions in an environment containing atomic hydrogen and carbon-containing groups. Diamond is a material with excellent mechanical, thermal, optical, and electrical properties, and is widely used in fields such as machine tools, coatings, electronics, and optics.
[0003] Since the development of CVD diamond synthesis technology, bulk or thin-film diamonds have been successfully prepared by CVD. However, existing powder or granular diamonds can only be obtained by high temperature and high pressure or explosion methods. The diamonds obtained by these methods are mostly irregular in shape, and the particle size of the powder or granules is poorly controllable and the particle size distribution is not concentrated, which has caused great trouble for the practical use of diamonds.
[0004] This invention reveals that decreasing parameters such as plasma energy density, atomic hydrogen concentration, diamond surface temperature, and gas pressure during CVD synthesis of diamond, or increasing carbon ion supersaturation, will cause the diamond to gradually transform from a well-crystallized coarse-grained structure to a nanocrystalline spherical structure. This transformation occurs as a gradual transition from the diamond growth region to the graphite growth region. Under conditions of low atomic hydrogen density, surface temperature, and deposition gas pressure, or high carbon ion supersaturation, numerous twins and stacking fault crystal defects, as well as secondary nucleation phenomena, will occur during CVD diamond deposition, ultimately affecting the diamond's growth morphology.
[0005] To overcome the problems existing in existing technologies, this invention provides a method for preparing diamond microspheres using CVD technology, based on the aforementioned technical principles. The diamond microspheres prepared by this method have a regular and approximately spherical shape, controllable and uniform particle size. Compared to diamond powders or particles obtained by existing methods, the shape consistency of diamond microspheres is significantly improved, and their application performance is more stable. They have broad application prospects in high thermal conductivity filling materials, polymer coatings, and diagnostic, imaging, and therapeutic carriers in biomedicine. Summary of the Invention
[0006] The purpose of this invention is to provide a diamond microsphere and its preparation method. The diamond microsphere prepared by this method has controllable particle size, high sphericity and uniform particle size.
[0007] To achieve the above objectives, the method for preparing diamond microspheres according to the present invention includes the following steps:
[0008] A method for preparing diamond microspheres, comprising the following steps:
[0009] 1) Substrate surface treatment: Using single-crystal silicon as the substrate, chemical etching is performed on the substrate surface to remove the mechanical damage layer and obtain a surface structure that is conducive to uniform diamond nucleation; preferably, the next step is performed after cleaning.
[0010] 2) Deposition of diamond microspheres on substrate surface: Then, using CVD technology, diamond microspheres are deposited on a single-crystal silicon substrate under supersaturated carbon ion concentration conditions by controlling the deposition pressure, temperature and time.
[0011] Specifically, the monocrystalline silicon is preferably polished (100)-faceted monocrystalline silicon to obtain a relatively flat surface. Commercially available polished monocrystalline silicon products can be purchased directly, or polishing can be performed using conventional techniques in the field. Since this is not the innovation of this invention, it will not be elaborated further.
[0012] Furthermore, the chemical etching can be performed by etching single-crystal silicon at a constant temperature of 80-90°C for 8-20 minutes; the etching solution is composed of 1-5g sodium hydroxide, 80-110ml water and 8-20ml ethanol.
[0013] Specifically, the surface structure is a 1-50 μm single-crystal silicon (111) faceted pyramid.
[0014] Furthermore, the CVD technology is hot-wire CVD or microwave plasma CVD, that is, hot-wire CVD or microwave plasma CVD is used to deposit diamond microspheres; the present invention preferably uses microwave plasma CVD, using H2 as the carrier gas and CH4 as the carbon source.
[0015] Specifically, the supersaturated carbon ion concentration condition refers to a volume ratio of CH4 to H2 of 4-10%.
[0016] Furthermore, the deposition process parameters (including deposition pressure, temperature, time, etc.) are as follows: CH4 / H2 mixed gas pressure 10-14 kPa, single crystal silicon surface temperature 840-920℃, and deposition time 4-12 h.
[0017] This invention provides diamond microspheres prepared using the above-described method. These diamond microspheres are polycrystalline diamond, composed of numerous twin stacking fault defects or secondary nucleation crystals; the microspheres are composed of a relatively pure diamond phase and may contain a small amount of graphite or sp. 2 Bonded carbon; and the microspheres have a controllable particle size of 1-100μm, regular shape and near-spherical shape, high sphericity and uniform particle size.
[0018] This invention also provides applications of the aforementioned diamond microspheres in the fields of high thermal conductivity filling materials, polymer coatings, polymer coatings, and diagnostic, imaging, and therapeutic carriers in biomedicine.
[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0020] This invention overcomes the shortcomings of existing high-temperature, high-pressure, or explosive methods for synthesizing powdered or granular diamond, such as irregular shape, poor particle size controllability, and non-concentrated particle size distribution. It employs microwave plasma CVD technology, controlling carbon ion concentration, deposition gas pressure, temperature, and time parameters to achieve the preparation of diamond microspheres with controllable particle size, high sphericity, and uniform particle size. Compared to existing technologies, the diamond microspheres of this invention exhibit significantly improved shape consistency and more stable application performance. This method is simple, highly reproducible, and conducive to industrial production, showing broad application prospects in high thermal conductivity filling materials, polymer coatings, and diagnostic, imaging, and therapeutic carriers in biomedicine.
[0021] This invention tests the prepared diamond microspheres. The morphology of the diamond microspheres is observed using scanning electron microscopy (SEM), and the particle size of the diamond microspheres is statistically analyzed. The composition of the diamond microspheres is analyzed using Raman spectroscopy. The diamond microspheres are polycrystalline diamond, composed of numerous twin stacking fault defects or secondary nucleation crystals; the microspheres are composed of a relatively pure diamond phase and may contain small amounts of graphite or sp. 2 Bonded carbon; and the microsphere size is controllable from 1 to 100 μm, with high sphericity and uniform particle size. Attached Figure Description
[0022] Figure 1 The surface structure of the single-crystal silicon (111) faceted pyramid prepared in Example 1;
[0023] Figure 2 For diamond microspheres prepared in Example 1, (a) SEM image of the microspheres, with the inset being a magnified local image; (b) Statistical results of the particle size of the microspheres; (c) Raman spectrum of the microspheres;
[0024] Figure 3 For diamond microspheres prepared in Example 2, (a) SEM image of the microspheres, with the inset being a magnified local image; (b) Statistical results of the particle size of the microspheres; (c) Raman spectrum of the microspheres;
[0025] Figure 4 For the diamond microspheres prepared in Example 3, (a) SEM image of the microspheres, with the inset being a magnified local image; (b) Statistical results of the particle size of the microspheres; (c) Raman spectrum of the microspheres;
[0026] Figure 5For diamond microspheres prepared in Example 4, (a) SEM image of the microspheres, with the inset being a magnified local image; (b) Statistical results of the particle size of the microspheres; (c) Raman spectrum of the microspheres. Detailed Implementation
[0027] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.
[0028] Example 1
[0029] A method for preparing diamond microspheres, the specific process of which is as follows in this embodiment:
[0030] 1) Select polished (100) facet monocrystalline silicon as the substrate, and etch the monocrystalline silicon substrate at 85℃ in an etching solution (the etching solution is composed of 1g sodium hydroxide, 90ml water and 10ml ethanol) for 10 minutes to obtain a 1-5μm monocrystalline silicon (111) facet tetrahedral pyramidal surface structure, such as Figure 1 As shown. After rinsing with deionized water, it was ultrasonically cleaned in anhydrous ethanol for 10 min.
[0031] 2) Diamond microspheres were deposited on the surface of the above-treated single-crystal silicon substrate using microwave plasma CVD. The volume ratio of CH4 to H2 was controlled to be 10%, the pressure of the CH4 / H2 mixed gas was 10 kPa, the surface temperature of the single-crystal silicon was 840℃, and diamond microspheres were obtained after 4 hours of deposition.
[0032] Figure 2 The diamond microspheres prepared in this embodiment are shown in the following: (a) SEM image of the microspheres, with the inset being a magnified view of a portion; (b) statistical results of the particle size of the microspheres; and (c) Raman spectrum of the microspheres.
[0033] SEM observation of the diamond microspheres prepared by the above method, such as Figure 2 As shown in Figure a, the microspheres are uniformly distributed on the substrate, with relatively smooth surfaces and good sphericity. The microspheres are composed of a large number of secondary nucleated crystals. Statistical analysis of the particle size of 360 microspheres yielded an average particle size of 3.5 μm and a standard deviation of 0.9 μm (see Figure a). Figure 2 (b) The Raman spectra of the microspheres show (see...) Figure 2 (middle c): 1333cm -1 The presence of a severely broadened first-order Raman peak in the diamond microspheres at 1580 cm⁻¹ indicates that the diamond microspheres are composed of nanostructured diamond crystals. -1 The presence of a significantly broadened graphite G peak indicates the presence of microcrystalline graphite within the microspheres.
[0034] Example 2
[0035] A method for preparing diamond microspheres, the specific process of which is as follows in this embodiment:
[0036] 1) Using polished (100) facet monocrystalline silicon as a substrate, the monocrystalline silicon substrate was etched at 85°C in an etching solution (composed of 1.5g sodium hydroxide, 90ml water, and 10ml ethanol) for 10 minutes to obtain a 5-20μm monocrystalline silicon (111) facet tetrahedral pyramidal surface structure. After rinsing with deionized water, it was ultrasonically cleaned in anhydrous ethanol for 10 minutes.
[0037] 2) Diamond microspheres were deposited on the surface of the above-treated single-crystal silicon substrate using microwave plasma CVD. The volume ratio of CH4 to H2 was controlled at 8%, the pressure of the CH4 / H2 mixed gas was 12 kPa, the surface temperature of the single-crystal silicon was 860℃, and diamond microspheres were obtained after 8 hours of deposition.
[0038] Figure 3 The diamond microspheres prepared in this embodiment are shown in the following: (a) SEM image of the microspheres, with the inset being a magnified view of a portion; (b) statistical results of the particle size of the microspheres; and (c) Raman spectrum of the microspheres.
[0039] SEM observation of the diamond microspheres prepared by the above method, such as Figure 3 As shown in Figure a, the microspheres are uniformly distributed on the substrate, with relatively smooth surfaces and good sphericity. The microspheres are composed of a large number of secondary nucleated crystals. Statistical analysis of the particle size of 303 microspheres yielded an average particle size of 10.5 μm and a standard deviation of 0.8 μm (see Figure a). Figure 3 (b) The Raman spectra of the microspheres show (see...) Figure 3 (middle c): 1333cm -1 A first-order Raman peak containing relatively sharp diamonds is present, with a half-height width of 26 cm. -1 This indicates that the diamond microspheres are composed of diamond crystals with submicron or nanostructures, 1580 cm⁻¹ -1 The graphite G peak disappears at 1500-1600 cm. -1 A broadband peak exists at this location, therefore there is no graphite phase inside the microspheres, but there is sp corresponding to the broadband peak. 2 Bonded carbon.
[0040] Example 3
[0041] A method for preparing diamond microspheres, the specific process of which is as follows in this embodiment:
[0042] 1) Using polished (100) facet monocrystalline silicon as a substrate, the monocrystalline silicon substrate was etched at 85°C in an etching solution (composed of 1.5g sodium hydroxide, 90ml water, and 10ml ethanol) for 10 minutes to obtain a 5-20μm monocrystalline silicon (111) facet tetrahedral pyramidal surface structure. After rinsing with deionized water, it was ultrasonically cleaned in anhydrous ethanol for 10 minutes.
[0043] 2) Diamond microspheres were deposited on the surface of the above-treated single-crystal silicon substrate using microwave plasma CVD. The volume ratio of CH4 to H2 was controlled at 4%, the CH4 / H2 mixed gas pressure was 14 kPa, the single-crystal silicon surface temperature was 860℃, and diamond microspheres were obtained after 12 h of deposition.
[0044] Figure 4 The diamond microspheres prepared in this embodiment are shown in the following: (a) SEM image of the microspheres, with the inset being a magnified view of a portion; (b) statistical results of the particle size of the microspheres; and (c) Raman spectrum of the microspheres.
[0045] SEM observation of the diamond microspheres prepared by the above method, such as Figure 4 As shown in Figure a, the microspheres are uniformly distributed on the substrate, with relatively smooth surfaces and good sphericity. Numerous structural features caused by crystal defects such as twins and stacking faults appear on the surface. Statistical analysis of the particle size of 191 microspheres yielded an average particle size of 17.4 μm and a standard deviation of 3.6 μm (see Figure a). Figure 4 (b) The Raman spectra of the microspheres show (see...) Figure 4 (middle c): 1333cm -1 A first-order Raman peak containing sharp diamonds, with a half-height width of 13cm. -1 This indicates that the diamond microspheres are composed of diamond crystals with a micron or submicron structure, and do not contain 1580 cm⁻¹. -1 The graphite G peak at 1500-1600 cm⁻¹ -1 The broadband peak at this location indicates that there is no graphite phase and no obvious sp24-particle density within the microspheres. 2 The bonded carbon microspheres are composed of a relatively pure diamond phase.
[0046] Example 4
[0047] A method for preparing diamond microspheres, the specific process of which is as follows in this embodiment:
[0048] 1) Select polished (100) facet monocrystalline silicon as the substrate. Etch the monocrystalline silicon substrate at 85°C in an etching solution (the etching solution is composed of 5g sodium hydroxide, 90ml water and 10ml ethanol) for 10 minutes to obtain a 30-50μm monocrystalline silicon (111) facet tetrahedral pyramidal surface structure. Rinse with deionized water and then ultrasonically clean in anhydrous ethanol for 10 minutes.
[0049] 2) Diamond microspheres were deposited on the surface of the above-treated single-crystal silicon substrate using microwave plasma CVD. The volume ratio of CH4 to H2 was controlled at 4%, the CH4 / H2 mixed gas pressure was 14 kPa, the single-crystal silicon surface temperature was 920℃, and diamond microspheres were obtained after 12 h of deposition.
[0050] Figure 5 The diamond microspheres prepared in this embodiment are shown in the following: (a) SEM image of the microspheres, with the inset being a magnified view of a portion; (b) statistical results of the particle size of the microspheres; and (c) Raman spectrum of the microspheres.
[0051] SEM observation of the diamond microspheres prepared by the above method, such as Figure 5 As shown in Figure a, the microspheres are uniformly distributed on the substrate, with relatively smooth surfaces and good sphericity. Numerous structural features caused by crystal defects such as twins and stacking faults appear on the surface. Statistical analysis of the particle size of 178 microspheres yielded an average particle size of 74.8 μm and a standard deviation of 15.6 μm (see Figure a). Figure 5 (b). The Raman spectra of the microspheres are shown (see...) Figure 5 c): shows 1333cm -1 A first-order Raman peak containing sharp diamonds, with a half-height width of 7 cm. -1 This characteristic indicates that the diamond microspheres are composed of diamond crystals with a micron-sized structure, and do not contain 1580 cm⁻¹ diamond. -1 The graphite G peak at 1500-1600 cm⁻¹ -1 The broadband peak at this location indicates that there is no graphite phase and no obvious sp24-particle density within the microspheres. 2 The bonded carbon microspheres are composed of a relatively pure diamond phase.
[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing diamond microspheres, characterized in that, Includes the following steps: A surface structure conducive to uniform diamond nucleation was obtained by chemical etching using single-crystal silicon as a substrate. Then, diamond microspheres were deposited on the single-crystal silicon substrate using CVD technology under supersaturated carbon ion concentration conditions. The chemical etching involves etching single-crystal silicon at a constant temperature of 80-90°C in an etching solution for 8-20 minutes; the etching solution is composed of 1-5g sodium hydroxide, 80-110ml water, and 8-20ml ethanol. The surface structure is a 1-50 μm monocrystalline silicon (111) faceted tetrahedron; The supersaturated carbon ion concentration condition refers to a volume ratio of CH4 to H2 of 4-10%. The deposition process parameters are: CH4 / H2 mixed gas pressure 10-14 kPa, single crystal silicon surface temperature 840-920℃, and deposition time 4-12 h.
2. The method for preparing diamond microspheres according to claim 1, characterized in that, The monocrystalline silicon is polished (100)-face monocrystalline silicon.
3. The method for preparing diamond microspheres according to claim 1, characterized in that, The CVD technology is either hot-wire CVD or microwave plasma CVD.
4. Diamond microspheres prepared by any one of the preparation methods described in claims 1 to 3.
5. The diamond microspheres as described in claim 4, characterized in that, The diamond microspheres are regular in shape and approximately spherical, with a controllable and uniform particle size in the range of 1-100 μm.
6. The application of the diamond microspheres according to claim 5 in high thermal conductivity filler materials and polymer coatings.