阅读说明：本技术 一种金刚石合成坯料及采用该坯料合成金刚石的方法 (Diamond synthesis blank and method for synthesizing diamond by using same ) 是由 张相法 王永凯 于 2021-01-15 设计创作，主要内容包括：本发明属于金刚石合成技术领域,具体涉及一种金刚石合成坯料及采用该坯料合成金刚石的方法。所述金刚石合成坯料,包括带有包覆层的镀覆金刚石、触媒和石墨Ⅰ,所述带有包覆层的镀覆金刚石、触媒和石墨Ⅰ的质量比为1:(30～59):(40～69)；所述触媒包括以下重量百分比的原料：Ni 40.98～42.58%、Al 0.10～1.00%、Pt 0.05～0.50%、Ti 0.01～0.50%、Co 0.01～0.50%、Mn 0.01～0.50%,余量为Fe。本发明合成的金刚石晶粒尺寸分散均匀、晶型一致,品质高。(The invention belongs to the technical field of diamond synthesis, and particularly relates to a diamond synthesis blank and a method for synthesizing diamond by using the same. The diamond synthesis blank comprises a plated diamond with a coating layer, a catalyst and graphite I, wherein the mass ratio of the plated diamond with the coating layer to the catalyst to the graphite I is 1 (30-59) to (40-69); the catalyst comprises the following raw materials in percentage by weight: ni 40.98-42.58%, Al 0.10-1.00%, Pt 0.05-0.50%, Ti 0.01-0.50%, Co 0.01-0.50%, Mn 0.01-0.50%, and the balance of Fe. The diamond grains synthesized by the invention have the advantages of uniform size dispersion, consistent crystal form and high quality.)

1. A diamond synthesis blank is characterized by comprising a coated diamond with a coating layer, a catalyst and graphite I, wherein the mass ratio of the coated diamond with the coating layer to the catalyst to the graphite I is 1 (30-59) to (40-69);

the catalyst comprises the following raw materials in percentage by weight: ni 40.98-42.58%, Al 0.10-1.00%, Pt 0.05-0.50%, Ti 0.01-0.50%, Co 0.01-0.50%, Mn 0.01-0.50%, and the balance of Fe.

2. The diamond composite blank according to claim 1, wherein the coated diamond is formed by coating a Ni or Ni-Fe alloy layer on the surface of diamond particles to form a coated diamond, and coating graphite ii on the surface of the coated diamond.

3. The diamond composite blank according to claim 2, wherein the diamond particles have a particle size of 30 to 50 μm.

4. A method of making a diamond compact as claimed in any one of claims 1 to 3, comprising the steps of:

(1) cleaning the diamond particles by using acid liquor and alkali liquor to remove impurities and adsorbates on the surfaces of the diamond particles, and then washing by using water;

(2) plating the surfaces of the diamond particles obtained in the step (1) by adopting a magnetron sputtering method, and plating a Ni or Ni-Fe alloy metal catalyst layer on the surfaces of the diamond particles to form plated diamonds;

(3) uniformly mixing the plated diamond in the step (2) with graphite II, polyvinyl alcohol, deionized water and ethanol, and then dehydrating and drying to obtain a mixed material of the plated diamond with the graphite coated on the surface and the graphite II;

(4) sieving the mixture obtained in the step (3) to obtain the coated diamond with a coating layer, and then weighing the catalyst,

And uniformly mixing the graphite I and the coated diamond with the coating layer to obtain the diamond synthetic blank.

5. A method of synthesising diamond using a diamond synthesis blank according to any one of claims 1 to 3 comprising the steps of:

(1) pressing and forming the diamond synthetic blank, and assembling to obtain a synthetic block; then carrying out reduction sintering treatment on the synthesized block;

(2) and synthesizing the synthetic block subjected to the reduction sintering treatment into diamond under the conditions of high temperature and high pressure, wherein the synthesis pressure is 5.0-6.0 GPa, and the synthesis temperature is 1200-1400 ℃.

6. The method for preparing a diamond compact according to claim 4, wherein the magnetron sputtering method in the step (2) comprises the following specific steps: when Ni plating is carried out, a Ni plate is selected to act as a target material; when Ni-Fe alloy plating is carried out, a Ni-Fe alloy plate with the Ni content of 41.98wt% is selected as a target material.

7. The method for synthesizing diamond according to claim 5, wherein in the step (2), the synthesizing pressure and the synthesizing temperature are respectively performed by using a control pressure curve and a control power curve, and the control pressure curve is: increasing the pressure to 60-65 MPa within 35-50 s, then starting heating, maintaining the pressure for 200-300 s, increasing the pressure to 75-81 MPa for 10-20 s, then increasing the pressure to 85-98 MPa for 20-30 s, maintaining the pressure for 2000-2500 s, then stopping heating, and releasing the pressure after stopping heating;

the control power curve is: the initial power is 3000W, the heating is gradually increased to 4500-5000W within 30-50 s, the power is kept for 150-200 s, then the heating is increased to 5000-6000W at a constant speed within 250-600 s, and the heating is stopped after the power is kept for 1800-2000 s.

Technical Field

The invention belongs to the technical field of diamond synthesis, and particularly relates to a diamond synthesis blank and a method for synthesizing diamond by using the same.

Background

Diamond has extremely excellent physical and chemical properties. The main method for synthesizing diamond single crystal at present stage is to use cubic press, under the condition of high-temp. and high-pressure synthesis, utilize the catalytic action of metal catalyst and make the graphite finally be converted into diamond by means of specific synthesis method.

In the process of synthesizing diamond, the physical properties of the synthesized diamond, such as grain size, crystal form, impact strength and the like, can be influenced by factors such as synthesis temperature, synthesis pressure, synthesis time and the like, and in addition, the manufacturing method and the quality of the diamond synthetic column are also important factors influencing the synthesis quality of the diamond.

For the synthetic column of diamond, it is now common to carry out press forming after graphite material and catalyst are directly mixed, but because the proportion difference between graphite powder and catalyst powder is big, the reunion phenomenon of different proportion materials is very easily appeared in the mixing process, in the actual production process, usually mix graphite powder, metal catalyst powder and the bonding agent of certain granularity and weight ratio in three-dimensional blendor at room temperature and stir more than 8h, through the extension of compounding time in order to increase the homogeneity of compounding, but still can have the material segregation phenomenon to a certain extent for diamond synthetic quality and output have great fluctuation, finally lead to synthetic diamond grain size dispersion, the grain shape is very non-uniform, the quality discreteness is big.

The method can synthesize high-grade diamonds with uniform particle size dispersion, small crystal form difference and low impurity content in large batch, and is always a difficult problem to be solved urgently in the superhard material industry.

Disclosure of Invention

To overcome the problems of the prior art, the present invention provides a diamond composite blank. The diamond composite blank adopts the plated diamond with the coating layer, so that the quality of the synthesized diamond is greatly improved.

The invention also provides a preparation method of the diamond synthesis blank.

The invention also provides a method for synthesizing diamond by adopting the diamond blank, and the synthesized diamond has the advantages of uniform grain size dispersion, consistent crystal form and high quality.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a diamond blank comprises a coated diamond with a coating layer, a catalyst and graphite I, wherein the mass ratio of the coated diamond with the coating layer to the catalyst to the graphite I is 1 (30-59) to (40-69);

the catalyst comprises the following raw materials in percentage by weight: ni 40.98-42.58%, Al 0.10-1.00%, Pt 0.05-0.50%, Ti 0.01-0.50%, Co 0.01-0.50%, Mn 0.01-0.50%, and the balance of Fe.

Preferably, the content of Fe is 54.02-58.84 wt%.

Preferably, the plated diamond with the coating layer is formed by plating a Ni or Ni-Fe alloy layer on the surface of diamond particles to form the plated diamond and then coating graphite II on the surface of the plated diamond; the metal catalyst layer plated in advance is beneficial to the peripheral film forming of the preset diamond crystal nucleus, the film forming quality is improved, and the smooth conversion of the graphite phase to the diamond phase is ensured.

More preferably, the diamond particles have a particle size of 30 to 50 μm.

The preparation method of the diamond synthesis blank comprises the following steps:

(1) cleaning the diamond particles by using acid liquor and alkali liquor to remove impurities and adsorbates on the surfaces of the diamond particles, and then washing by using water;

(2) plating the surfaces of the diamond particles obtained in the step (1) by adopting a magnetron sputtering method, and plating a Ni or Ni-Fe alloy metal catalyst layer on the surfaces of the diamond particles to form plated diamonds;

(3) uniformly mixing the plated diamond in the step (2) with graphite II, polyvinyl alcohol, deionized water and ethanol, and then dehydrating and drying to obtain a mixture of the plated diamond with the graphite coated on the surface and the graphite II;

(4) sieving the mixture obtained in the step (3) to obtain the coated diamond with a coating layer, and then weighing the catalyst,

And uniformly mixing the graphite I and the coated diamond with the coating layer to obtain the diamond synthetic blank.

Further preferably, the magnetron sputtering method in the step (2) comprises the following specific processes: when Ni plating is carried out, a Ni plate is selected to act as a target material; when Ni-Fe alloy plating is carried out, a Ni-Fe alloy plate with the Ni content of 41.98wt% is selected as a target material.

Further preferably, the thickness of the Ni or Ni-Fe plated layer in step (2) is 15 to 20 μm.

Further preferably, when mixing is performed in the step (3), the graphite II, the polyvinyl alcohol, the deionized water and the ethanol can be premixed, and then the plated diamond is added and mixed uniformly; or all of them can be added together and mixed.

The method for synthesizing the diamond by adopting the diamond synthesis blank is characterized by comprising the following steps:

(1) pressing and forming the diamond synthetic blank, and assembling to obtain a synthetic block; then carrying out reduction sintering treatment on the synthesized block;

(2) and synthesizing the synthetic block subjected to the reduction sintering treatment into diamond under the conditions of high temperature and high pressure, wherein the synthesis pressure is 5.0-6.0 GPa, and the synthesis temperature is 1200-1400 ℃.

Further preferably, in the step (2), the synthesizing pressure and the synthesizing temperature are respectively completed by adopting a control pressure curve and a control power curve, wherein the control pressure curve is as follows: increasing the pressure to 60-65 MPa within 35-50 s, then starting heating, maintaining the pressure for 200-300 s, increasing the pressure to 75-81 MPa for 10-20 s, then increasing the pressure to 85-98 MPa for 20-30 s, maintaining the pressure for 2000-2500 s, then stopping heating, and releasing the pressure after stopping heating;

the control power curve is: the initial power is 3000W, the heating is gradually increased to 4500-5000W within 30-50 s, the power is kept for 150-200 s, then the heating is increased to 5000-6000W at a constant speed within 250-600 s, and the heating is stopped after the power is kept for 1800-2000 s.

The invention overcomes the problems that the metal catalyst powder and graphite powder needed by diamond in the prior art are easy to be mixed unevenly due to large specific gravity difference, and the molten catalyst in the synthesis process slowly moves downwards, so that the synthetic block catalyst and graphite powder are dispersed unevenly, and the growth rate, the crystal form, the grain size and the finished product quality of the diamond are influenced. Based on the method, the Ni or Ni-Fe alloy metal catalyst layer is plated on the surface of the diamond, so that the sufficient and uniform dispersion of the catalyst at the periphery of the crystal grains in the synthetic process is guaranteed, the growth efficiency of the diamond is effectively improved, then the diamond particles plated with the Ni or Ni-Fe alloy metal catalyst layer are coated with graphite powder, the sufficient and uniform dispersion of a carbon source in the growth process of the diamond crystal grains is guaranteed, the activity of the graphite powder and the catalyst is improved through reduction sintering treatment, and the diamond with uniform granularity dispersion, small crystal form difference and good quality consistency is finally synthesized.

Compared with the prior art, the invention has the beneficial effects that:

1. according to the invention, the diamond particle surface is pretreated and placed in the synthesis block, so that the synthesized diamond crystal can grow on the basis of the preset crystal nucleus in the synthesis process, and the growth rate of each crystal nucleus can be basically kept consistent;

2. according to the invention, the surface of the diamond particles is plated with the Ni or Ni-Fe alloy metal catalyst layer by pretreating the diamond particles, so that the catalyst sufficiency of diamond in the synthesis process is ensured, the growth efficiency is improved, the metal catalyst layer plated in advance is beneficial to the peripheral film formation of the preset diamond crystal nucleus, the film formation quality is improved, and the smooth conversion of the graphite phase to the diamond phase is ensured; in addition, the method can ensure the dispersion uniformity of the catalyst around the crystal grains, can also effectively reduce the problem of different concentrations of the catalyst around the crystal grains caused by uneven stirring of different diamond particles, can effectively reduce the influence of the concentration change of the catalyst around the crystal grains in the growth process, can ensure that the crystal forms of the synthesized diamond are more consistent, and effectively improves the yield of high-grade diamond;

3. according to the invention, the surfaces of the diamond particles plated with the Ni or Ni-Fe alloy metal catalyst layer are coated with graphite II, so that the sufficiency and uniformity of a carbon source around the diamond particles can be effectively ensured at the initial stage of growth of the diamond particles, and the size dispersion uniformity and the crystal form uniformity of the synthesized diamond particles are further ensured;

4. the proportion of the high-grade diamond synthesized by the method is obviously higher than that of the high-grade diamond synthesized by a common method through the processes of type selection, microscopic examination detection and the like, and the proportion of the I-type material (namely, the low-quality diamond, which is a conventional term in the field) can be greatly reduced, so that considerable economic benefit can be brought.

Drawings

FIG. 1 is a schematic representation of the formation of a coated diamond with a coating layer according to the present invention;

fig. 2 is a power curve and a pressure curve of the synthetic diamond of example 1, in which: (1) power curve, (2) pressure curve;

fig. 3 pictures of synthetic diamonds of comparative example 1 and example 2, wherein: (1) comparative example 1 and example 2 were prepared.

Detailed Description

The invention is further illustrated, but not limited, by the following examples and the accompanying drawings. The diamond particles used in the following examples were purchased from diamond superhard materials, Inc. of south China. The coated diamond with a coating layer according to the present invention is schematically formed as shown in fig. 1, 1 is a diamond particle, 2 is a coated diamond, and 3 is a coated diamond with a coating layer.

The graphite I and the graphite II mentioned in the invention are the same common commercially available graphite powder, and the purity is 99.9%; the definitions I and II are provided to distinguish graphite in the diamond composite blank from graphite coated with a diamond coating layer.

Example 1

The diamond synthesis blank of the embodiment: the catalyst comprises a coated diamond with a coating layer (also called a diamond coated with a Ni metal catalyst layer coated with graphite powder), a catalyst and graphite I, wherein the mass ratio of the coated diamond with the coating layer to the catalyst to the graphite I is 1:49: 50;

the catalyst comprises the following raw materials in percentage by weight: ni 41.98%, Fe56.52%, Al 0.85%, Pt 0.05%, Ti 0.20%, Co 0.10%, Mn 0.30%.

The coated diamond with the coating layer is formed by coating Ni layers on the surfaces of diamond particles to form the coated diamond and then coating graphite II on the surfaces of the coated diamond.

The method for synthesizing the diamond by adopting the diamond synthesis blank comprises the following steps:

(1) selecting diamond particles with the particle size range of 30-50 mu m and the D50 of 35 mu m, treating the diamond particles by using a sulfuric acid solution (1 mol/L) and a sodium hydroxide solution (1 mol/L), removing impurities and adsorbates on the surface of the diamond, and washing the diamond particles for 3 times by using deionized water;

(2) placing the diamond particles in the step (1) in a magnetron sputtering furnace, selecting high-purity Ni metal as a target material, and plating a high-purity Ni layer on the surfaces of the diamond particles to obtain the diamond with the Ni metal catalyst layer plated on the surfaces, wherein: the thickness of the plating layer is 10 mu m, and the purity of the high-purity Ni is more than 99.9 percent;

(3) mixing 100g of graphite II, 9g of polyvinyl alcohol, 500ml of deionized water and 500ml of ethanol, fully stirring, then carrying out ultrasonic treatment by using an ultrasonic instrument to ensure that the polyvinyl alcohol can be fully mixed with the graphite II, then weighing 10g of diamond with the surface plated with the Ni metal catalyst layer in the step (2), putting the diamond into the diamond, and mixing to obtain a mixture;

(4) dehydrating, drying and granulating the mixture obtained in the step (3) by using a freeze dryer to obtain a mixture of diamond coated with a Ni metal catalyst layer coated with graphite powder on the surface and graphite II;

(5) screening the mixture obtained in the step (4) by selecting a 200-mesh screen and a 270-mesh screen, and taking 270-mesh screen material to obtain the diamond coated with the Ni metal catalyst layer with the graphite powder coated on the surface; then weighing the diamond coated with the Ni metal catalyst layer with graphite powder on the surface, the catalyst and the graphite I according to the mass ratio of 1:49:50, and uniformly mixing to obtain a diamond synthetic blank;

(6) pressing and forming the diamond synthetic blank, assembling to obtain a synthetic block, and performing reduction sintering treatment on the synthetic block, wherein the adopted reduction gas is hydrogen;

(7) synthesizing the synthetic block subjected to reduction sintering treatment into high-grade diamond under the conditions of high temperature and high pressure, wherein the specific process comprises the following steps: the control pressure curve is: increasing the pressure to 63MPa within 50s, then starting heating, maintaining the pressure for 250s, increasing the pressure to 80MPa, increasing the pressure for 15s, then increasing the pressure to 90MPa, increasing the pressure for 25s, maintaining the pressure for 2000s, then stopping heating, and then releasing the pressure after stopping heating (the pressure curve is shown in (2) in figure 2);

the control power curve is: the initial power is 3000W, the heating gradually increases the power to 4750W within 45s, then maintains 175s, then increases to 5500W at a constant speed for 480s, and stops heating after maintaining 1800s (the power curve is shown in (1) in FIG. 2).

In the diamond synthesized by the embodiment, the percentage of diamond with 40/50 and 50/60 particle sizes is 53wt% and 32wt%, respectively, and the high quality content in the synthesized diamond is screened to be more than or equal to 60wt% by testing the diamond such as type selection, microscopic examination, impact strength and the like (which is a conventional technology in the field and is not described herein again).

Example 2

The diamond synthesis blank of the embodiment: the catalyst comprises a coated diamond with a coating layer (also called a diamond coated with a Ni-Fe alloy metal catalyst layer coated with graphite powder), a catalyst and graphite I, wherein the mass ratio of the coated diamond with the coating layer to the catalyst to the graphite I is 1:59: 40;

the catalyst comprises the following raw materials in percentage by weight: 42.00 percent of Ni, 57.47 percent of Fe, 0.20 percent of Al, 0.05 percent of Pt, 0.01 percent of Ti, 0.25 percent of Co and 0.02 percent of Mn.

The plating diamond with the coating layer is formed by plating a Ni-Fe alloy layer on the surface of diamond particles to form the plating diamond and then coating graphite II on the surface of the plating diamond.

The method for synthesizing the diamond by adopting the diamond synthesis blank comprises the following steps:

(1) selecting diamond particles with the particle size of 30-50 microns and the particle size of 39 microns D50, treating the diamond particles by using a nitric acid solution and a sodium hydroxide solution (the concentrations are both 0.5 mol/L), removing impurities and adsorbates on the surface of the diamond, and washing the diamond particles for 2 times by using deionized water;

(2) placing the diamond particles obtained in the step (1) in a magnetron sputtering furnace, selecting Ni-Fe alloy with the Ni content of 41.98wt% as a target material, and plating a high-purity Ni-Fe alloy metal catalyst layer on the surfaces of the diamond particles to obtain the diamond with the Ni-Fe alloy metal catalyst layer plated on the surfaces, wherein: the thickness of the plating layer is 15 mu m, and the purity of the Ni-Fe alloy is more than 99.9 percent;

(3) weighing 10g of the diamond coated with the Ni-Fe alloy metal catalyst layer on the surface in the step (2), mixing the diamond with 80g of graphite II, 9g of polyvinyl alcohol, 500ml of deionized water and 500ml of ethanol, and fully stirring to uniformly mix the diamond with the polyvinyl alcohol, so as to obtain a mixture, wherein the surface of the diamond is ensured to be coated with a uniform graphite powder layer;

(4) dehydrating and drying the mixture obtained in the step (3) to prepare a sample, wherein the dehydration mode is drying under the nitrogen protection condition to obtain a mixture of diamond coated with a Ni-Fe alloy metal catalyst layer of which the surface is coated with graphite powder and graphite II;

(5) screening the mixture obtained in the step (4) by selecting a 200-mesh screen and a 270-mesh screen, and taking 270-mesh screen material to obtain the diamond coated with the Ni-Fe alloy metal catalyst layer and graphite powder on the surface; then weighing the diamond coated with the Ni-Fe alloy metal catalyst layer with the graphite powder on the surface, the catalyst and the graphite I according to the mass ratio of 1:59:40, and uniformly mixing to obtain a diamond synthesis blank;

(6) pressing and forming the diamond synthetic blank, assembling to obtain a synthetic block, and performing reduction sintering treatment on the synthetic block, wherein the adopted reduction gas is hydrogen;

(7) synthesizing the synthetic block subjected to reduction sintering treatment into high-grade diamond under the conditions of high temperature and high pressure, wherein the specific process comprises the following steps: the control pressure curve is: increasing the pressure to 63MPa within 45s, then starting heating, maintaining the pressure for 200s, increasing the pressure to 80MPa, increasing the pressure for 15s, then increasing the pressure to 93MPa, increasing the pressure for 25s, maintaining the pressure for 2450s, then stopping heating, and relieving the pressure after stopping heating;

the control power curve is: the initial power is 3000W, the heating gradually increases the power to 4800W within 35s, then the power is maintained for 180s, then the heating is uniformly increased to 5500W within 475s, and the heating is stopped after the power is maintained for 2000 s.

In the diamond synthesized by the embodiment, the proportions of 30/40 and 40/50 diamond particles are 48wt% and 33wt%, respectively, and the high-quality content in the synthesized diamond is more than or equal to 60wt% by testing the diamond through type selection, microscopic examination, impact strength and the like. The picture of the diamond synthesized in the embodiment is shown in (2) in fig. 3, and it can be seen from the picture that the diamond single crystal prepared in the embodiment has complete crystal grains, consistent crystal form and quite regular shape.

Example 3

The diamond synthesis blank of the embodiment: the catalyst comprises a coated diamond with a coating layer (also called a diamond coated with a Ni-Fe alloy metal catalyst layer coated with graphite powder), a catalyst and graphite I, wherein the mass ratio of the coated diamond with the coating layer to the catalyst to the graphite I is 1:59: 40;

the catalyst comprises the following raw materials in percentage by weight: 41.09% of Ni, 58.38% of Fe, 0.18% of Al, 0.05% of Pt, 0.03% of Ti, 0.25% of Co and 0.02% of Mn.

The plating diamond with the coating layer is formed by plating a Ni-Fe alloy layer on the surface of diamond particles to form the plating diamond and then coating graphite II on the surface of the plating diamond.

The method for synthesizing the diamond by adopting the diamond synthesis blank comprises the following steps:

(1) selecting diamond particles with the particle size of 30-50 microns and the D50 particle size of 42 microns, treating the diamond particles by using a sulfuric acid solution and a sodium hydroxide solution (the concentration of the sulfuric acid solution and the sodium hydroxide solution is 1.5 mol/L), removing impurities and adsorbates on the surface of the diamond, and washing the diamond particles for 3 times by using deionized water;

(2) placing the diamond particles obtained in the step (1) in a magnetron sputtering furnace, selecting Ni-Fe alloy with the Ni content of 41.98wt% as a target material, and plating a high-purity Ni-Fe alloy metal catalyst layer on the surfaces of the diamond particles to obtain the diamond with the Ni-Fe alloy metal catalyst layer plated on the surfaces, wherein: the thickness of the plating layer is 15 μm, and the purity of the plating layer is more than 99.9%;

(3) mixing 120g of graphite II, 9g of polyvinyl alcohol, 500ml of deionized water and 500ml of ethanol, performing ultrasonic treatment for 30min by using an ultrasonic instrument, then fully stirring to uniformly mix the graphite II, 9g of polyvinyl alcohol, 500ml of deionized water and 500ml of ethanol, then weighing 10g of the diamond plated with the Ni-Fe alloy metal catalyst layer in the step (2), uniformly stirring the diamond and the diamond to obtain a mixture, and ensuring that the surface of the diamond can be coated with a uniform graphite powder layer;

(4) dehydrating and drying the mixture obtained in the step (3) to prepare a sample, wherein the dehydration mode is drying under the nitrogen protection condition to obtain a mixture of diamond coated with a Ni-Fe alloy metal catalyst layer of which the surface is coated with graphite powder and graphite II;

(5) screening the mixture obtained in the step (4) by using a 200-mesh screen and a 270-mesh screen, taking 270-mesh screen material, weighing diamond, catalyst and graphite I with the surface coated with a Ni-Fe alloy metal catalyst layer plated with graphite powder according to the mass ratio of 1:59:40, and uniformly mixing to obtain a diamond synthesis blank;

(6) pressing and forming the diamond synthetic blank, assembling to obtain a synthetic block, and performing reduction sintering treatment on the synthetic block, wherein the adopted reduction gas is hydrogen;

(7) synthesizing the synthetic block subjected to reduction sintering treatment into high-grade diamond under the conditions of high temperature and high pressure, wherein the specific process comprises the following steps: the control pressure curve is: increasing the pressure to 63MPa within 45s, then starting heating, maintaining the pressure for 200s, increasing the pressure to 80MPa, increasing the pressure for 15s, then increasing the pressure to 93MPa, increasing the pressure for 25s, maintaining the pressure for 2200s, then stopping heating, and then releasing the pressure;

the control power curve is: the initial power is 3000W, the heating gradually increases the power to 4800W within 35s, then the power is maintained for 180s, then the heating is uniformly increased to 5500W within 475s, and the heating is stopped after the power is maintained for 1800 s.

In the diamond synthesized by the embodiment, the proportion of diamond with 40/50 and 50/60 particle sizes is 58wt% and 25wt%, respectively, and the high-quality content in the synthesized diamond is more than or equal to 60wt% through detection of type selection, microscopic examination, impact strength and the like of the diamond.

Comparative example 1

This comparative example differs from example 2 in that: the common diamond particles are used in the formula, namely the common diamond particles are directly bought for use; that is, the diamond particles have no coating layer and no metal catalyst is plated on the surface of the diamond.

In the diamond synthesized by the comparative example, the proportion of diamond with 30/40 and 40/50 particle sizes is 41wt% and 27wt%, respectively, and the high-quality content in the synthesized diamond is not less than 48wt% by detecting the type selection, microscopic examination, impact strength and the like of the diamond.

The diamond picture synthesized by the comparative example is shown in (1) in fig. 3, and as can be seen by comparing with (2) in fig. 3 of example 2, the surface of the diamond single crystal grain of (1) in fig. 3 is uneven, the shape of the grain is irregular, the diamond single crystal grain of (2) in fig. 3 is complete, the crystal form is consistent, and the shape is quite regular; the diamond prepared by the method has better quality.