Catalyst for synthesizing artificial diamond and preparation method thereof

Abstract

The present invention belongs to the technical field of catalysts for superhard material synthesis, specifically relating to a catalyst for synthesizing artificial diamond and a preparation method thereof. The catalyst comprises a high-entropy alloy powder coated with potassium sulfate; the mass ratio of potassium sulfate to high-entropy alloy powder is 1:(4-9); the high-entropy alloy powder is composed of the following components in atomic percentage: 25-35 at% Fe, 15-25 at% Co, 15-25 at% Ni, 15-20 at% Mn, and 10-15 at% Sc. The present invention coats the high-entropy alloy powder with a potassium sulfate coating as a catalyst. This catalyst can improve the effective conversion rate of graphite, reduce the introduction of impurities during diamond synthesis, prevent impurities from entering the diamond lattice, and thus reduce defects caused by unevenness.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts for synthesizing superhard materials, and in particular relates to a catalyst for synthesizing artificial diamond and a preparation method thereof. Background Art

[0002] Diamond crystals, due to their unique crystal structure, possess exceptional physical properties such as high hardness, high modulus, low thermal expansion coefficient, high thermal conductivity, optical properties, and high-pressure stability. These properties are widely used in industrial precision machining and are of great significance to academic research. However, natural diamond ore resources are extremely scarce, are used to make jewelry, and mining has a significant environmental impact. Therefore, the synthesis of artificial diamonds has long been a research hotspot.

[0003] The main methods for synthesizing diamond are high-pressure and low-pressure methods. The low-pressure method is primarily achieved through chemical vapor deposition (CVD). The high-pressure method uses graphite as the raw material and transforms it into a diamond structure under conditions of high temperature and pressure. However, this transformation process faces extremely high energy barriers and places very high demands on experimental conditions. The addition of catalysts can effectively reduce the synthesis conditions, so suitable catalysts are of great significance to the diamond synthesis industry. Catalysts are divided into two types: metal catalysts and non-metallic catalysts. Among them, alloy metal catalysts are abundant in variety, widely used, low in cost, and effective. They can produce diamond crystals of various crystal forms and are widely used in industrial diamond synthesis. However, they also have some shortcomings in actual industrial applications. For example, the addition of catalyst materials will inevitably lead to the formation of related inclusions or impurities within the diamond.

[0004] Therefore, there is an urgent need for catalyst materials with stable structure, high catalytic efficiency and the ability to reduce the introduction of impurities. Summary of the Invention

[0005] The first object of the present invention is to provide a catalyst for synthesizing artificial diamond, which has excellent oxygen affinity and stable chemical properties, can reduce the introduction of impurities during the synthesis process, and can inhibit the diffusion of metal elements during the diamond synthesis process.

[0006] The second object of the present invention is to provide a method for preparing a catalyst for synthesizing artificial diamond.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A catalyst for synthesizing artificial diamond, comprising a high-entropy alloy powder coated with potassium sulfate; the mass ratio of the potassium sulfate to the high-entropy alloy powder is 1:(4-9); and the high-entropy alloy powder is composed of the following components in atomic percentage: 25-35 at% Fe, 15-25 at% Co, 15-25 at% Ni, 15-20 at% Mn, and 10-15 at% Sc.

[0009] Furthermore, the high entropy alloy powder consists of the following components in atomic percentage: 30 at% Fe, 20 at% Co, 20 at% Ni, 20 at% Mn, and 10 at% Sc.

[0010] By adopting the above scheme, doping the rare earth element Sc, which has the smallest atomic size, into the FeCoNiMn alloy can enhance the oxygen affinity of the catalyst while maintaining a lattice constant close to that of diamond, thereby reducing the content of impurities such as oxygen and sulfur in diamond; in addition, the high mixing entropy can also inhibit element segregation at high temperatures, maintain the structural stability of the catalyst, and extend the service life of the catalyst.

[0011] The method for preparing the catalyst for synthesizing artificial diamond comprises the following steps:

[0012] (1) mixing the components of the high entropy alloy powder and smelting them 3-5 times under an inert gas atmosphere to obtain a high entropy alloy ingot;

[0013] (2) heating and melting the high entropy alloy ingot to obtain a high entropy alloy liquid; and centrifugally atomizing the high entropy alloy liquid in an inert gas environment to obtain a high entropy alloy powder;

[0014] (3) Dissolve potassium sulfate in an ethanol-water mixed solution, adjust the pH to 4-6, then add the high entropy alloy powder and mix evenly, then remove the solvent, calcinate, grind, and sieve to obtain a catalyst.

[0015] Furthermore, the specific process of centrifugal atomization of the high entropy alloy liquid in an inert gas environment in step (2) is: transferring the molten high entropy alloy liquid to the alloy powder rotary atomization equipment, and while spraying the high entropy alloy liquid onto the rotating disk for centrifugation, blowing inert gas into the atomization system in the opposite direction of centrifugation to collect the high entropy alloy powder.

[0016] Furthermore, the centrifugal rotation speed is 20000-40000 r / min.

[0017] Furthermore, when the inert gas is introduced into the centrifugal atomization system in a direction opposite to the centrifugal direction, the inert gas inlet temperature is 10-20° C., and the inert gas inlet pressure is 10-15 MPa.

[0018] Furthermore, in step (3), the volume ratio of ethanol to water in the ethanol-water mixed solution is 1:(2-2.5); and the temperature for removing the solvent is 60-80°C.

[0019] Furthermore, in step (3), the calcination temperature is 200-300 °C and the calcination time is 1-2 h.

[0020] Furthermore, in step (3), the particle size of the catalyst is 5-15 μm.

[0021] The beneficial technical effects of the present invention are:

[0022] 1. The catalyst for synthesizing artificial diamond of the present invention is prepared by coating the surface of high-entropy alloy powder with a potassium sulfate coating. During the process of synthesizing artificial diamond, the catalyst can significantly increase the graphite-to-diamond conversion rate, reduce the impurity content in the synthetic diamond, and improve the mechanical properties of the diamond.

[0023] 2. Compared with ordinary alloy catalysts, the high entropy alloy used in the present invention has a higher lattice matching degree with diamond and a smaller interface mismatch, which can effectively reduce the nucleation barrier and is conducive to the epitaxial growth of diamond; and the electronic coupling between the multi-atoms of the high entropy alloy can form more active sites, promote the rearrangement of carbon atoms, and accelerate sp 3 The formation of bonds significantly increases the graphite-diamond conversion rate; in addition, the rare earth element Sc added to the alloy is the rare earth element with the smallest atomic size, which enhances the oxygen affinity of the catalyst, thereby reducing the content of impurities such as oxygen and sulfur in diamond.

[0024] 3. The potassium sulfate coating applied to the surface of the high-entropy alloy powder of the present invention can inhibit the diffusion of metal elements during the synthesis process, reducing the metal content in the finished diamond product. In addition, potassium sulfate can also improve the effective conversion rate to graphite. Potassium sulfate is also stable at high temperatures and can maintain chemical stability at high temperatures, reducing the introduction of impurities during the synthesis process. It works synergistically with the high-entropy alloy powder to achieve efficient diamond synthesis while also reducing catalyst costs.

[0025] 4. This invention utilizes a combined centrifugal atomization and gas atomization method to prepare powder catalysts. Fine metal droplets ejected by centrifugation are simultaneously gas-atomized. This combines the advantages of centrifugal atomization (uniform particle size and high sphericity) with the fine particle size of gas atomization, while improving raw material utilization and compatibility. The result is a powder catalyst with uniform particle size, fine particle size, and excellent sphericity. When mixed with graphite, the fine spherical particles distribute more evenly and have better fluidity, effectively reducing defects caused by localized reaction imbalances. Furthermore, the spherical catalysts have a smooth surface and low oxygen content, which reduces interfacial stress concentration, prevents impurities from entering the diamond lattice, reduces inclusions and bubbles, and improves the mechanical properties and thermal shock resistance of the synthetic diamond. DETAILED DESCRIPTION

[0026] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it is not intended that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art of the present invention, without departing from the inventive concept, several simple deductions or replacements can also be made, all of which should be considered to belong to the scope of protection of the present invention. The specific conditions not indicated in the examples are carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, unless otherwise specified, are conventional products obtained through commercial channels.

[0027] (1) Implementation

[0028] Example 1

[0029] Example 1 provides a catalyst for synthesizing artificial diamond, which is a high-entropy alloy powder coated with potassium sulfate, wherein the mass ratio of potassium sulfate to high-entropy alloy powder is 1:7, and the high-entropy alloy powder is composed of the following components in atomic percentage: 30 at% Fe, 20 at% Co, 20 at% Ni, 20 at% Mn, and 10 at% Sc.

[0030] This embodiment also provides a method for preparing the above-mentioned catalyst for synthesizing artificial diamond, comprising the following steps:

[0031] (1) According to the ratio of the components in the above high entropy alloy powder, weigh the metal raw materials and mix them, and use a medium frequency melting furnace to melt them. During the melting process, argon gas is continuously filled into the furnace mouth. After melting to a molten state, it is cooled. This operation is repeated 4 times to obtain a high entropy alloy ingot with uniform composition;

[0032] (2) The high entropy alloy ingot is remelted to obtain a high entropy alloy liquid. The high entropy alloy liquid is transferred to the alloy powder rotary atomization equipment in a flowing state. The high entropy alloy liquid is sprayed onto the rotating disk and centrifuged at a speed of 30,000 r / min to break the high entropy alloy liquid into metal droplets. While the high entropy alloy liquid is sprayed onto the rotating disk and centrifuged, argon gas is blown into the centrifugal atomization system in the opposite direction to the centrifugal direction (the temperature of the argon gas at the gas inlet is 15 °C and the pressure is 12 MPa) to make the argon gas fully contact with the metal droplets, and the high entropy alloy powder is collected;

[0033] (3) Potassium sulfate was first dissolved in an ethanol-water mixed solution according to the ratio of potassium sulfate, high entropy alloy powder, ethanol, and water (1 g:7 g:5 mL:10 mL). Citric acid was then added to adjust the pH of the mixed solution to 5. High entropy alloy powder was then added and ultrasonically dispersed uniformly. The solvent was removed at 70 °C. Finally, the mixture was calcined at 240 °C for 2 h. After grinding and sieving, a catalyst with a particle size of 10 μm was obtained.

[0034] Example 2

[0035] Example 2 provides a catalyst for synthesizing artificial diamond, which is a high-entropy alloy powder coated with potassium sulfate on the surface, wherein the mass ratio of potassium sulfate to high-entropy alloy powder is 1:9, and the high-entropy alloy powder is composed of the following components in atomic percentage: 35 at% Fe, 15 at% Co, 25 at% Ni, 15 at% Mn, and 10 at% Sc.

[0036] This embodiment also provides a method for preparing a catalyst for synthesizing artificial diamond, comprising the following steps:

[0037] (1) Weighing and mixing the various metal raw materials according to the above-mentioned high entropy alloy powder component ratio, smelting in a medium frequency smelting furnace, continuously filling argon gas into the furnace mouth during the smelting process, smelting to a molten state and then cooling, repeating this operation 5 times to obtain a high entropy alloy ingot with uniform composition;

[0038] (2) The high entropy alloy ingot is remelted to obtain a high entropy alloy liquid. The high entropy alloy liquid is transferred to the alloy powder rotary atomization equipment in a flowing state. The high entropy alloy liquid is sprayed onto the rotating disk and centrifuged at a speed of 40,000 r / min to break the high entropy alloy liquid into metal droplets. While the high entropy alloy liquid is sprayed onto the rotating disk and centrifuged, argon gas is blown into the centrifugal atomization system in the opposite direction to the centrifugal direction (argon gas at 20 °C and 15 MPa at the gas inlet) to fully contact the argon gas with the metal droplets, and the high entropy alloy powder is collected;

[0039] (3) Potassium sulfate was first dissolved in an ethanol-water mixed solution according to the ratio of potassium sulfate, high entropy alloy powder, ethanol, and water (1 g:9 g:6 mL:15 mL). Citric acid was then added to adjust the pH of the mixed solution to 6. High entropy alloy powder was then added and ultrasonically dispersed uniformly. The solvent was removed at 80 °C. Finally, the mixture was calcined at 300 °C for 2 h. After grinding and sieving, a catalyst with a particle size of 5 μm was obtained.

[0040] Example 3

[0041] Example 3 provides a catalyst for synthesizing artificial diamond, which is a high-entropy alloy powder coated with potassium sulfate on the surface, wherein the mass ratio of potassium sulfate to high-entropy alloy powder is 1:4, and the high-entropy alloy powder is composed of the following components in atomic percentage: 25 at% Fe, 25 at% Co, 15 at% Ni, 20 at% Mn, and 15 at% Sc.

[0042] This embodiment also provides a method for preparing a catalyst for synthesizing artificial diamond, comprising the following steps:

[0043] (1) Weigh and mix the metal raw materials according to the above-mentioned high entropy alloy powder component ratio, and use a medium frequency melting furnace to melt them. During the melting process, the furnace mouth is continuously filled with argon atmosphere, and then the mixture is melted to a molten state and then cooled. This operation is repeated 3 times to obtain a high entropy alloy ingot with uniform composition;

[0044] (2) The high entropy alloy ingot is remelted to obtain a high entropy alloy liquid. The high entropy alloy liquid is transferred to the alloy powder rotary atomization equipment in a flowing state. The high entropy alloy liquid is sprayed onto the rotating disk and centrifuged at a speed of 20,000 r / min to break the high entropy alloy liquid into metal droplets. While the high entropy alloy liquid is sprayed onto the rotating disk and centrifuged, argon gas is blown into the centrifugal atomization system in the opposite direction to the centrifugal direction (argon gas is at 10 °C and pressure of 10 MPa at the gas inlet) to make the argon gas fully contact with the metal droplets, and the high entropy alloy powder is collected;

[0045] (3) Potassium sulfate was first dissolved in an ethanol-water mixed solution according to the ratio of potassium sulfate, high entropy alloy powder, ethanol, and water (1 g:4 g:3 mL:7 mL). Citric acid was then added to adjust the pH of the mixed solution to 4. High entropy alloy powder was then added and ultrasonically dispersed uniformly. The solvent was removed at 60 °C. Finally, the mixture was calcined at 200 °C for 1 h. After grinding and sieving, a catalyst with a particle size of 15 μm was obtained.

[0046] (2) Comparative Example

[0047] Comparative Example 1

[0048] Comparative Example 1 is basically the same as Example 1, except that when preparing the catalyst, the high entropy alloy powder in step (3) is replaced by Fe 60 Ni 40 alloy.

[0049] Comparative Example 2

[0050] Comparative Example 2 is substantially the same as Example 1, except that step (3) is omitted when preparing the catalyst.

[0051] Comparative Example 3

[0052] Comparative Example 3 is substantially the same as Example 1, except that, when preparing the catalyst, step (3) is replaced by mixing potassium sulfate and high entropy alloy powder, and the mass ratio remains the same as that in Example 1.

[0053] Comparative Example 4

[0054] Comparative Example 4 is substantially the same as Example 1, except that: Step (2) only uses gas atomization, and the specific steps are: remelting the high-entropy alloy ingot to obtain a high-entropy alloy liquid, transferring the high-entropy alloy liquid to a smelting container of an atomizing furnace in a flowing state, heating the atomizing furnace to maintain the high-entropy alloy liquid in a flowing state, and simultaneously filling the atomizing furnace with high-purity argon gas for about 10 minutes, and then using high-pressure nitrogen (10 MPa) to crush the high-entropy alloy liquid into atomized powder, and collecting the obtained high-entropy alloy powder.

[0055] (3) Test examples

[0056] Diamond synthesis: The catalysts of Examples 1-3 and Comparative Examples 1-4 were mixed with 99.99 wt.% pure graphite powder in a mass ratio of 0.4:1, and after uniform mixing, they were pressed into 50 mm synthesis columns, and then placed in a 120°C oven for 2 h to ensure the removal of moisture. The synthesis blocks were assembled and placed in the high-temperature and high-pressure chamber of a six-sided top press. The pressurization was increased to 5.5 GPa, and then an electric current was passed to raise the temperature to 1300°C. The heat and pressure were maintained for 20 min to obtain diamond.

[0057] The diamonds synthesized using the catalysts of Examples 1-3 and Comparative Examples 1-4 were subjected to the following tests: oxygen content was determined using an automatic oxygen and nitrogen analyzer; TI and TTI performance tests were performed in accordance with GB / T 33144-2016 "Test Method for Impact Toughness of Superhard Abrasives". The relevant results are shown in Table 1.

[0058] Table 1 Diamond performance test

[0059]

[0060] As can be seen from Table 1, when the catalysts prepared in Examples 1-3 of the present invention are used to synthesize artificial diamonds, the diamonds grow at a fast speed, have large particle sizes, low impurity content, and high purity.

[0061] Compared with Example 1, when preparing the catalyst in Comparative Example 1, the high entropy alloy powder in step (3) is replaced by Fe 60 Ni 40 The performance of the diamond obtained by alloy powder is significantly reduced. Analysis of the reasons shows that: the lattice matching degree between high entropy alloy and diamond is higher, the interface mismatch degree is smaller, which can effectively reduce the nucleation barrier and is conducive to the epitaxial growth of diamond; and the electronic coupling between the multi-atoms of high entropy alloy can form more active sites, promote the rearrangement of carbon atoms, and accelerate sp 3 The formation of bonds significantly increases the graphite-diamond conversion rate; in addition, the rare earth element Sc added to the alloy is the rare earth element with the smallest atomic size, which enhances the oxygen affinity of the catalyst, thereby reducing the content of impurities such as oxygen and sulfur in diamond and improving diamond performance.

[0062] Compared with Example 1, when preparing the catalyst in Comparative Example 2, step (3) is omitted; when preparing the catalyst in Comparative Example 3, step (3) is replaced by mixing potassium sulfate and high entropy alloy powder, and the mass ratio is consistent with that in Example 1. The performance of the obtained diamond is reduced. The specific analysis is as follows: the potassium sulfate coating on the surface of the high entropy alloy powder can inhibit the diffusion of metal elements during the synthesis process and reduce the metal content in the finished diamond product. In addition, potassium sulfate can also improve the effective conversion rate of graphite. Potassium sulfate is stable at high temperatures and can still maintain chemical stability at high temperatures, reducing the introduction of impurities during the synthesis process. It works synergistically with the high entropy alloy powder to achieve efficient diamond synthesis while reducing the catalyst cost.

[0063] Compared with Example 1, Comparative Example 4 only uses atomization in step (2), and the performance of the resulting diamond is reduced, which indicates that the preparation process of the catalyst has an impact on its performance. Specific analysis shows that the fine metal droplets thrown out by centrifugation are simultaneously atomized, combining the advantages of uniform particle size and high sphericity of centrifugal atomized powder and fine particle size of atomized powder, and improving the utilization rate of raw materials and the compatibility range of raw materials, thereby obtaining a powder catalyst with uniform particle size, fine particle size and good sphericity. Spherical particles with fine particle size are more evenly distributed and have better fluidity when mixed with graphite, which can effectively reduce defects caused by uneven local reactions; at the same time, the spherical catalyst has a smooth surface and low oxygen content, which can reduce interfacial stress concentration, prevent impurities from entering the diamond lattice, reduce inclusions and bubbles, and improve the mechanical properties and thermal shock stability of synthetic diamonds.

[0064] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the same. The basic principles and main features of the present invention have been described above using specific implementation schemes. Modifications or substitutions may be made based on the present invention, but such modifications or substitutions do not detract from the essence of the corresponding technical solutions from the scope of protection claimed by the present invention.

Claims

1. A catalyst for synthesizing artificial diamond, characterized in that: The catalyst is a high entropy alloy powder coated with potassium sulfate; the mass ratio of potassium sulfate to high entropy alloy powder is 1:(4-9); the high entropy alloy powder is composed of the following components in atomic percentage: 25-35 at% Fe, 15-25 at% Co, 15-25 at% Ni, 15-20 at% Mn, and 10-15 at% Sc; The method for preparing the catalyst for synthesizing artificial diamond comprises the following steps: (1) mixing the components of the high entropy alloy powder and smelting them 3-5 times under an inert gas atmosphere to obtain a high entropy alloy ingot; (2) heating and melting the high entropy alloy ingot to obtain a high entropy alloy liquid; and centrifugally atomizing the high entropy alloy liquid in an inert gas environment to obtain a high entropy alloy powder; (3) Dissolve potassium sulfate in an ethanol-water mixed solution, adjust the pH to 4-6, then add the high entropy alloy powder and mix evenly, then remove the solvent, calcinate, grind, and sieve to obtain a catalyst.

2. The catalyst for synthesizing artificial diamond according to claim 1, characterized in that The high entropy alloy powder consists of the following components in atomic percentage: 30 at% Fe, 20 at% Co, 20 at% Ni, 20 at% Mn, and 10 at% Sc.

3. The method for preparing a catalyst for synthesizing artificial diamond according to claim 1, characterized in that: The following steps are involved: (1) mixing the components of the high entropy alloy powder and smelting them 3-5 times under an inert gas atmosphere to obtain a high entropy alloy ingot; (2) heating and melting the high entropy alloy ingot to obtain a high entropy alloy liquid; and centrifugally atomizing the high entropy alloy liquid in an inert gas environment to obtain a high entropy alloy powder; (3) Dissolve potassium sulfate in an ethanol-water mixed solution, adjust the pH to 4-6, then add the high entropy alloy powder and mix evenly, then remove the solvent, calcinate, grind, and sieve to obtain a catalyst.

4. The method for preparing a catalyst for synthesizing artificial diamond according to claim 3, wherein: The specific process of centrifugal atomization of the high entropy alloy liquid in an inert gas environment described in step (2) is: transferring the molten high entropy alloy liquid to the alloy powder rotary atomization equipment, and while spraying the high entropy alloy liquid onto the rotating disk for centrifugation, blowing inert gas into the centrifugal atomization system in the direction opposite to the centrifugal direction to collect the high entropy alloy powder.

5. The method for preparing a catalyst for synthesizing artificial diamond according to claim 4, characterized in that: The centrifugal speed is 20000-40000 r / min.

6. The method for preparing a catalyst for synthesizing artificial diamond according to claim 4, characterized in that: When the inert gas is introduced into the centrifugal atomization system in a direction opposite to the centrifugal direction, the inlet temperature of the inert gas is 10-20°C and the inlet pressure of the inert gas is 10-15 MPa.

7. The method for preparing a catalyst for synthesizing artificial diamond according to claim 3, characterized in that: In step (3), the volume ratio of ethanol to water in the ethanol-water mixed solution is 1:(2-2.5); and the temperature for removing the solvent is 60-80°C.

8. The method for preparing a catalyst for synthesizing artificial diamond according to claim 3, characterized in that: In step (3), the calcination temperature is 200-300 °C and the time is 1-2 h.

9. The method for preparing a catalyst for synthesizing artificial diamond according to claim 3, characterized in that: In step (3), the particle size of the catalyst is 5-15 μm.

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