High-temperature, high-pressure and high-heat-conductivity diamond synthesis block and diamond preparation method

Abstract

The invention provides a high-temperature, high-pressure and high-thermal-conductivity diamond synthesis block and a diamond preparation method, the diamond synthesis block structurally adopts a multi-layer structure formed by stacking a graphite core column, a catalyst metal sheet and diamond seed crystals with 111 crystal faces upwards from top to bottom, and impurity discharge holes are formed in the bottom of a crystal bed. A specific stepped temperature curve is adopted in the diamond synthesis process and comprises the stages of preheating and impurity removal, constant-temperature growth and stepped cooling. Through the synergistic effect of the structural process, impurities and defects in diamond crystals are effectively reduced, high-thermal-conductivity diamond with the thermal conductivity ranging from 1200 W / (m.K) to 2000 W / (m.K) can be stably synthesized, the problems that a product obtained through a traditional method is low in thermal conductivity and unstable are solved, and the method is suitable for the industrial field with the high requirement for heat dissipation performance.

Description

Technical Field

[0001] This invention belongs to the field of superhard material synthesis technology, specifically relating to high-temperature, high-pressure, high-thermal-conductivity diamond synthesis blocks, and also to a method for preparing high-temperature, high-pressure, high-thermal-conductivity diamond. Background Technology

[0002] High temperature and high pressure method is currently the main method for synthesizing large-particle diamond single crystals. However, diamond synthesized by traditional process contains a lot of metal catalyst inclusions, impurity atoms (such as nitrogen) and lattice defects, which cause severe scattering of phonon transmission, resulting in generally low thermal conductivity (usually below 1000W / (mK)). This makes it difficult to meet the growing demand for heat dissipation materials in high-end heat dissipation fields (such as high-power LEDs, laser diodes, integrated circuits, etc.).

[0003] While using high-purity raw materials and optimizing processes can improve thermal conductivity to some extent, problems such as high cost, low yield, or unstable performance often exist. In particular, for (111) crystal plane growth, although the diamond grown has high purity, the growth rate is slow, it is prone to internal stress cracks, and the process window is narrow, making it difficult to stably prepare products with thermal conductivity above 1200 W / (mK). Therefore, developing a temperature-synthesizing method and process for diamond ingot structures with thermal conductivity in the range of 1200-2000 W / (mK) has significant industrial application value. Summary of the Invention

[0004] The purpose of this invention is to provide a high-temperature, high-pressure, and high-thermal-conductivity diamond synthetic block, which solves the problem of low and unstable thermal conductivity of diamond synthesized from existing diamond synthetic blocks.

[0005] The present invention also aims to provide a method for preparing high-temperature, high-pressure, and high-thermal-conductivity diamond.

[0006] The first technical solution adopted in this invention is: a high-temperature, high-pressure, high-thermal-conductivity diamond synthetic block, the structure of which includes, from the inside out, a pyrophyllite shell, a pressure-transmitting medium, and a crystal bed; the reaction chamber is located inside the crystal bed, and the upper part of the inner side of the crystal bed is arranged from top to bottom as follows: Graphite core: as a carbon source; Catalyst metal sheet: located below the graphite core column; Seed crystal: Located at the bottom, with its (111) crystal face facing upwards, placed on a catalyst metal sheet; The graphite core, catalyst metal sheet, and seed crystal are stacked closely to form a multi-layer growth structure; The bottom of the crystal bed is provided with at least one impurity removal hole for removing impurities and excess catalyst during the synthesis process.

[0007] The invention is further characterized in that, Preferably, the seed crystal is a high-quality type Ib or type IIa diamond single crystal that has been precision polished, and the surface roughness Ra of its (111) facet is less than 10 nm.

[0008] Preferably, the catalyst / solvent metal is an FeNi alloy, an FeCo alloy, or FeNiCo, with a purity of not less than 99.9%.

[0009] Preferably, the diameter of the impurity discharge holes is 0.3-1.5 mm, and the number is 2-4.

[0010] The second technical solution adopted in this invention is: a method for preparing a high-temperature, high-pressure, high-thermal-conductivity diamond synthetic block, the specific operation steps of which are as follows: Step 1: Assembly: Following the above multi-layer structure sequence, place the processed (111) facet seed crystal, catalyst metal sheet, and graphite core into the crystal bed in sequence, and encapsulate the crystal bed in the pressure transmission medium and pyrophyllite cube.

[0011] Step 2: Loading and pressurizing: Place the synthetic block into the six-sided top press and first apply pressure to the target synthesis pressure of 5.5-6.0 GPa.

[0012] Step 3: Heating and Growth: Heating is performed according to the preset process curve; Step 4: Cooling and depressurization: After growth is complete, cool down according to the process curve; Step 5: Post-processing: Remove the synthetic block and use chemical treatment methods to remove the metal catalyst and graphite adhering to the diamond surface to obtain a high thermal conductivity diamond product.

[0013] The invention is further characterized by: Step 3 is as follows: Step 3.1: Raise the temperature to the first temperature plateau T1 (about 30-80℃ lower than the melting point of the catalyst metal sheet) at the first heating rate (60-120 ℃ / min) and hold at t1 (3-10 minutes) to ensure uniform heating of the system and initial removal of low melting point impurities.

[0014] Step 3.2: Then, the temperature is raised to the final synthesis temperature T2 (1320-1400℃) at the second heating rate (20-40 ℃ / min), and the synthesis pressure is 5.7±0.1GPa to start the growth of the (111) facet of diamond; Preferably, the synthesis temperature T2 is 1350±20℃, and the isothermal growth time is 20h-30h; Step 3.3: Maintain a constant temperature of t2 (15-40 hours) under the synthesis pressure and temperature T2 to complete the epitaxial growth of diamond crystals; Step 4 is as follows: Step 4.1: First, lower the temperature to T1 at the first cooling rate (10-15℃ / min) and hold it at that temperature briefly (3-8 minutes) to relax the crystal stress and promote the removal of residual impurities; Step 4.2: Then, slowly cool down to below 800°C at a second cooling rate (5-8°C / min), then stop heating and allow it to cool naturally to room temperature, while simultaneously depressurizing slowly.

[0015] The beneficial effects of this invention are: (1) Structural innovation: The vertical multi-layer structure of “graphite core column-catalyst-(111) face seed” is adopted, and the impurity and excess catalyst are provided with an escape channel through the impurity removal hole design at the bottom of the crystal bed, which effectively reduces the content of inclusions in the crystal and lays the foundation for improving thermal conductivity.

[0016] (2) Crystal plane selection: The (111) plane is used as the growth plane. Taking advantage of its relatively slow growth rate but high crystal quality, it is beneficial to grow diamond with fewer impurities and defects and better crystal integrity, which is the key to obtaining high thermal conductivity.

[0017] (3) Process optimization: A stepped process curve was designed, including the steps of "preheating and impurity removal - heating and growth - cooling and stress relaxation". The heating rate and the heat preservation platform were precisely controlled, which effectively matched the characteristics of (111) plane growth, thus ensuring a reasonable growth rate and minimizing the generation of thermal stress and lattice defects.

[0018] (4) Stable performance: Through the combination of the above structure and process, the present invention can stably and repeatedly synthesize high thermal conductivity diamond in the range of 1200-2000W / (mK), with good product performance consistency, high yield, and suitable for industrial production. Attached Figure Description

[0019] Figure 1 This is a cross-sectional schematic diagram of the synthetic block structure of the present invention.

[0020] Figure 2 This is a bottom view of the bottom of the crystal bed of the present invention.

[0021] Figure 3 This is a schematic diagram of the temperature-time process curve used in this invention.

[0022] In the figure, 1-pyrophyllite cube; 2-pressure transmission medium; 3-crystal bed; 4-graphite core column; 5-catalyst metal sheet; 6-seed crystal ((111) face up); 7-extraction pore. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, so that the advantages and features of the present invention can be more readily understood by those skilled in the art.

[0024] Example 1 This invention relates to a high-temperature, high-pressure, high-thermal-conductivity diamond composite block, such as... Figure 1-2 As shown, it includes a pyrophyllite shell 1, a pressure transmission medium 2, and a crystal bed 3. The upper inner side of the crystal bed 3 is provided with a graphite core column 4, a catalyst metal sheet 5, and a diamond seed crystal 6 with the 111 crystal face facing upwards, arranged sequentially from top to bottom. The three are in close contact to form a multi-layer growth structure. The bottom of the crystal bed 3 is provided with at least one impurity removal hole 7 for removing impurities.

[0025] The diameter of the impurity discharge hole 7 is 0.3-1.5mm, and the number is 2-4.

[0026] The seed crystal is a precision-polished type Ib or type IIa diamond single crystal with a surface roughness Ra of less than 10 nm on its 111 facet.

[0027] The catalyst metal sheet 5 is made of FeNi alloy, FeCo alloy or FeNiCo, and its purity is not less than 99.9%.

[0028] Example 2 The method for preparing high-temperature, high-pressure, and high-thermal-conductivity diamond according to the present invention comprises the following specific steps: S1. A type Ib diamond seed crystal 6 with a diameter of 0.6 mm was selected, and its (111) face was polished to Ra < 5 nm and placed at the bottom of a magnesium oxide crystal bed 3. A FeNiCo alloy sheet with a thickness of 0.05 mm (purity 99.95%) was placed on it as a catalyst. A graphite core pillar 4 with a diameter of 60 mm was then inserted. Three impurity removal holes 7 with a diameter of 1 mm were prefabricated at the bottom of the crystal bed. The whole thing was encapsulated in a pyrophyllite block 1.

[0029] S2. Assembly: Place the assembly block into a six-sided press.

[0030] a. Increase the pressure to 5.7 GPa.

[0031] b. Heating: Increase the temperature to 1200℃ at 100℃ / min (T1 alloy, FeNiCo alloy melting point is about 1300℃), hold for 5 minutes, and then increase the temperature to 1350℃ at 30℃ / min (T2).

[0032] c. Growth: The cells were grown at a constant temperature of 5.7 GPa and 1350 °C for 25 hours (e.g., ...). Figure 3 (As shown).

[0033] d. Cooling: Reduce the temperature to 1200℃ at a rate of 12℃ / min and hold for 5 minutes. Then slowly cool the temperature to room temperature at a rate of 6℃ / min while releasing the pressure.

[0034] S3. Post-treatment: After acid washing, a light yellow diamond single crystal is obtained.

[0035] S4. Test: The thermal conductivity of this diamond is 1650 W / (mK).

[0036] Example 3 The method for preparing high-temperature, high-pressure, and high-thermal-conductivity diamond according to the present invention comprises the following specific steps: Step 1: Place the diamond seed crystal with the 111 crystal face facing up, the FeCo alloy sheet, and the graphite core into the crystal bed in order from bottom to top, and encapsulate the crystal bed in the pressure transmission medium and the pyrophyllite shell to form a composite block; Step 2: Place the synthesis block into the six-sided press and first apply pressure to the target synthesis pressure of 5.5 GPa; Step 3: Heating and growth are carried out according to the preset process curve; details are as follows: Step 3.1: Raise the temperature to the first temperature plateau T1 at a first heating rate of 60℃ / min, where T1 is 50℃ lower than the melting point of the FeCo alloy sheet, and hold at this temperature for 4 minutes to ensure uniform heating of the system and to initially remove low-melting-point impurities; Step 3.2: The temperature is then increased to the final synthesis temperature T2 at a second heating rate of 20 / min, where T2 is 1340℃ and the synthesis pressure is 5.7 GPa, to initiate the 111-facet growth of diamond; Step 3.3: Maintain a constant temperature of T2 and synthesis pressure for 20 hours to complete the epitaxial growth of diamond crystals.

[0037] Step 4: After growth is complete, cool down according to the process curve; details are as follows: Step 4.1: First, lower the temperature to T1 at a first cooling rate of 10℃ / min and hold for 4min4 to relax the crystal stress and promote the removal of residual impurities; Step 4.2: Then, slowly cool down to below 800°C at a second cooling rate of 5°C / min, then stop heating and allow it to cool naturally to room temperature, while simultaneously depressurizing slowly.

[0038] Step 5: Remove the synthetic block and use chemical treatment to remove the metal catalyst and graphite adhering to the diamond surface to obtain a high thermal conductivity diamond product.

[0039] Example 4 The method for preparing high-temperature, high-pressure, and high-thermal-conductivity diamond according to the present invention comprises the following specific steps: Step 1: Place the diamond seed crystal with the 111 crystal face up, the FeNiCo metal sheet, and the graphite core into the crystal bed in order from bottom to top, and encapsulate the crystal bed in the pressure transmission medium and the pyrophyllite shell to form a composite block; Step 2: Place the synthesis block into the six-sided press and first apply pressure to the target synthesis pressure of 5.6 GPa; Step 3: Heating and growth are carried out according to the preset process curve; details are as follows: Step 3.1: Raise the temperature to the first temperature plateau T1 at a first heating rate of 100℃ / min, where T1 is 70℃ lower than the melting point of the FeNiCo metal sheet, and hold at this temperature for 8 minutes to ensure uniform heating of the system and to initially remove low-melting-point impurities; Step 3.2: Then, the temperature is raised to the final synthesis temperature T2 at a second heating rate of 40 / min, where T2 is 1380℃ and the synthesis pressure is 5.8GPa, to start the 111-facet growth of diamond; Step 3.3: Maintain a constant temperature of T2 and synthesis pressure for 30 hours to complete the epitaxial growth of diamond crystals.

[0040] Step 4: After growth is complete, cool down according to the process curve; details are as follows: Step 4.1: First, lower the temperature to T1 at a first cooling rate of 12℃ / min and hold for 6 minutes to relax the crystal stress and promote the removal of residual impurities; Step 4.2: Then, slowly cool down to below 800°C at a second cooling rate of 5°C / min, then stop heating and allow it to cool naturally to room temperature, while simultaneously depressurizing slowly.

[0041] Step 5: Remove the synthetic block and use chemical treatment to remove the metal catalyst and graphite adhering to the diamond surface to obtain a high thermal conductivity diamond product.

[0042] Example 5 The method for preparing high-temperature, high-pressure, and high-thermal-conductivity diamond according to the present invention comprises the following specific steps: Step 1: Place the diamond seed crystal with the 111 crystal face facing up, the FeNi alloy sheet, and the graphite core into the crystal bed in order from bottom to top, and encapsulate the crystal bed in the pressure transmission medium and the pyrophyllite shell to form a composite block; Step 2: Place the synthesis block into the six-sided press and first apply pressure to the target synthesis pressure of 5.7 GPa; Step 3: Heating and growth are carried out according to the preset process curve; details are as follows: Step 3.1: Raise the temperature to the first temperature plateau T1 at a first heating rate of 110℃ / min, where T1 is 40℃ lower than the melting point of the FeNi alloy sheet, and hold at this temperature for 7 minutes to ensure uniform heating of the system and to initially remove low-melting-point impurities; Step 3.2: Then, the temperature is raised to the final synthesis temperature T2 at a second heating rate of 25 / min, where T2 is 1350℃ and the synthesis pressure is 5.6GPa, to initiate the 111-facet growth of diamond; Step 3.3: Maintain a constant temperature of T2 and synthesis pressure for 25 hours to complete the epitaxial growth of diamond crystals.

[0043] Step 4: After growth is complete, cool down according to the process curve; details are as follows: Step 4.1: First, lower the temperature to T1 at a first cooling rate of 12℃ / min and hold for 5 minutes to relax the crystal stress and promote the removal of residual impurities; Step 4.2: Then, slowly cool down to below 800°C at a second cooling rate of 6°C / min, then stop heating and allow it to cool naturally to room temperature, while simultaneously depressurizing slowly.

[0044] Step 5: Remove the synthetic block and use chemical treatment to remove the metal catalyst and graphite adhering to the diamond surface to obtain a high thermal conductivity diamond product.

[0045] Example 6 The method for preparing high-temperature, high-pressure, high-thermal-conductivity diamond according to the present invention includes the following specific steps: Step 1: Place the diamond seed crystal with the 111 crystal face facing up, the FeCo alloy sheet, and the graphite core into the crystal bed in order from bottom to top, and encapsulate the crystal bed in the pressure transmission medium and the pyrophyllite shell to form a composite block; Step 2: Place the synthesis block into the six-sided press and first apply pressure to the target synthesis pressure of 5.5 GPa; Step 3: Heating and growth are carried out according to the preset process curve; details are as follows: Step 3.1: Raise the temperature to the first temperature plateau T1 at a first heating rate of 70℃ / min, where T1 is 60℃ lower than the melting point of the FeCo alloy sheet, and hold at this temperature for 7 minutes to ensure uniform heating of the system and to initially remove low-melting-point impurities; Step 3.2: The temperature is then increased to the final synthesis temperature T2 at a second heating rate of 35 / min, where T2 is 1380℃ and the synthesis pressure is 5.7 GPa, to initiate the 111-facet growth of diamond. Step 3.3: Maintain a constant temperature of T2 and synthesis pressure for 25 hours to complete the epitaxial growth of diamond crystals.

[0046] Step 4: After growth is complete, cool down according to the process curve; Specifically as follows: Step 4.1: First, lower the temperature to T1 at a first cooling rate of 12℃ / min and hold for 6 minutes to relax the crystal stress and promote the removal of residual impurities; Step 4.2: Then, slowly cool down to below 800°C at a second cooling rate of 6°C / min, then stop heating and allow it to cool naturally to room temperature, while simultaneously depressurizing slowly.

[0047] Step 5: Remove the synthetic block and use chemical treatment to remove the metal catalyst and graphite adhering to the diamond surface to obtain a high thermal conductivity diamond product.

Claims

1. A high-temperature, high-pressure, high-thermal-conductivity diamond composite block, characterized in that, The crystal bed (3) includes a pyrophyllite shell (1), a pressure transmission medium (2), and a crystal bed (3). The upper inner side of the crystal bed (3) is provided with a graphite core column (4), a catalyst metal sheet (5), and a diamond seed crystal (6) with the 111 crystal face facing upwards. The three are in close contact to form a multi-layer growth structure. The bottom of the crystal bed (3) is provided with at least one impurity removal hole (7) for removing impurities.

2. The high-temperature, high-pressure, high-thermal-conductivity diamond composite block according to claim 1, characterized in that, The diameter of the discharge holes (7) is 0.3-1.5 mm, and the number is 2-4.

3. The high-temperature, high-pressure, high-thermal-conductivity diamond composite block according to claim 1, characterized in that, The seed crystal is a precision-polished type Ib or type IIa diamond single crystal with a surface roughness Ra of (111) facet less than 10 nm.

4. The high-temperature, high-pressure, high-thermal-conductivity diamond composite block according to claim 1, characterized in that, The catalyst metal sheet (5) is an FeNi alloy, FeCo alloy or FeNiCo, and its purity is not less than 99.9%.

5. A method for preparing high-temperature, high-pressure, high-thermal-conductivity diamond, characterized in that, The specific steps are as follows: Step 1: Place the diamond seed crystal (6) with the 111 crystal face facing up, the catalyst metal sheet (5), and the graphite core column (4) into the crystal bed (3) in order from bottom to top, and encapsulate the crystal bed (3) in the pressure transmission medium (2) and the pyrophyllite shell (1) to form a composite block; Step 2: Place the synthetic block into the six-sided press and first apply pressure to the target synthesis pressure of 5.5-6.0 GPa; Step 3: Heating and growing according to the preset process curve; Step 4: After growth is complete, cool down according to the process curve; Step 5: Remove the synthetic block and use chemical treatment to remove the metal catalyst and graphite adhering to the diamond surface to obtain a high thermal conductivity diamond product.

6. The method for preparing high-temperature, high-pressure, high-thermal-conductivity diamond according to claim 2, characterized in that, Step 3 is as follows: Step 3.1: Raise the temperature to the first temperature plateau T1 at a first heating rate of 60-120℃ / min, where T1 is 30℃-80℃ lower than the melting point of the catalyst metal sheet (5), and hold the temperature for 3-10 minutes to ensure uniform heating of the system and initial removal of low-melting-point impurities; Step 3.2: Then, the temperature is raised to the final synthesis temperature T2 at a second heating rate of 20 / min - 40 / min, where T2 is 1320℃-1400℃, to start the growth of the (111) facet of diamond; Step 3.3: Maintain a constant temperature of T2 and synthesis pressure for 15-40 hours to complete the epitaxial growth of diamond crystals.

7. The method for preparing high-temperature, high-pressure, high-thermal-conductivity diamond according to claim 5, characterized in that, Step 4 is as follows: Step 4.1: First, lower the temperature to T1 at a first cooling rate of 10℃ / min - 15℃ / min, and hold for 3min - 8min to relax crystal stress and promote the removal of residual impurities; Step 4.2: Then, slowly cool down to below 800°C at a second cooling rate of 5°C / min - 8°C / min, then stop heating and allow it to cool naturally to room temperature, while simultaneously depressurizing slowly.

8. The method for preparing high-temperature, high-pressure, high-thermal-conductivity diamond according to claim 6, characterized in that, In step 3, the synthesis pressure is 5.7±0.1GPa, the synthesis temperature T2 is 1350±20℃, and the isothermal growth time is 20h-30h.

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