A method for synthesizing diamond, and a preparation method of iron-nickel-based composite catalyst powder

Abstract

The present application belongs to the technical field of diamond synthesis and catalyst powder, and provides a diamond synthesis method, an iron-nickel-based composite catalyst powder and a preparation method thereof. The synthesis method comprises the following steps: loading a graphite carbon source and an iron-nickel-based composite catalyst powder into a high-temperature and high-pressure synthesis cavity, and synthesizing diamond through heat preservation; the iron-nickel-based composite catalyst powder comprises an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy particles attached to the surface of the catalyst powder core material, the nickel-coated silicon-calcium alloy particles comprise silicon-calcium alloy particles and a nickel layer coated on the outside of the silicon-calcium alloy particles; the preparation method comprises the following steps: preparing the iron-nickel-based catalyst powder core material, mechanically coating silicon-calcium alloy powder and carbonyl nickel powder, and heat treatment. When the composite catalyst powder is used for artificial diamond synthesis, the surface composition and interface state of the catalyst powder can be adjusted, the influence of impurities on crystal growth in the synthesis process is reduced, and the crystal integrity and hardness level of the obtained diamond are improved.

Description

Technical Field

[0001] This invention belongs to the field of diamond synthesis and catalyst powder technology, and relates to a method for synthesizing diamond, an iron-nickel based composite catalyst powder and its preparation method. Background Technology

[0002] Diamond is typically obtained by converting graphite carbon sources under high temperature and pressure. The composition, surface state, and contact state of the catalyst powder with the carbon source affect the quality of diamond crystal formation. Existing iron-nickel-based catalyst powders are usually produced through processes such as smelting, atomization, drying, and sieving. During preparation, storage, and use, oxides on the surface of metal raw materials, oxides on the surface of atomized powder, and fine free particles in the powder can easily enter the high-temperature and high-pressure synthesis system. This makes the melt interface state formed by the catalyst powder in the synthesis chamber uneven, affecting the dissolution and migration process of the graphite carbon source in the catalyst system, and increasing the probability of the formation of inclusions, graphite residues, or local defects inside the diamond crystal.

[0003] To improve the performance of catalyst powder, existing technologies typically optimize it by reducing the oxygen content, adjusting the iron-nickel ratio, controlling the particle size, or improving powder uniformity. However, these methods mainly focus on adjusting the overall composition of the catalyst powder or conventional powder parameters, neglecting the local control of the interface between the catalyst powder and the carbon source. When oxides, fine free particles, or active components are randomly distributed at the interface, differences in the local catalyst melt state and carbon transport process can easily occur, leading to decreased stability of the crystal growth interface. Therefore, the technical problem to be solved in this field is: how to construct a controllable composite structure on the surface of iron-nickel-based catalyst powder to maintain a relatively stable interface state during the high-temperature and high-pressure synthesis of diamond, thereby reducing the impact of impurity phases and local defects on diamond crystal growth. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for synthesizing diamond, an iron-nickel-based composite catalyst powder, and a method for preparing the same. By attaching nickel-coated silicon-calcium alloy microparticles to the surface of the iron-nickel-based catalyst powder core material, the catalyst powder forms a metallic catalyst system with a surface composite structure. When this composite catalyst powder is used in the synthesis of high-temperature, high-pressure diamond, it can improve the compositional state of the interface between the catalyst powder and the graphite carbon source, reduce the influence of impurity phases and local defects on the crystal growth process, thereby improving the stability of diamond crystal formation and meeting the needs of practical production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for synthesizing diamond, comprising the following steps:

[0007] The graphite carbon source and the iron-nickel-based composite catalyst powder are loaded into a high-temperature and high-pressure synthesis chamber;

[0008] The high-temperature and high-pressure synthesis chamber is placed in a high-temperature and high-pressure device for heat preservation and synthesis.

[0009] After the heat preservation is completed, the temperature is reduced and the pressure is released. The composite block is then removed, crushed, acid-washed, and sorted to obtain diamond.

[0010] The iron-nickel-based composite catalyst powder includes an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy microparticles attached to the surface of the iron-nickel-based catalyst powder core material.

[0011] The nickel-coated silicon-calcium alloy microparticles include silicon-calcium alloy microparticles and a nickel layer coating the outside of the silicon-calcium alloy microparticles.

[0012] Preferably, the high-temperature and high-pressure equipment is a six-sided top press, with a combined pressure of 4.8-5.8 GPa, a temperature of 1250-1450℃, and a holding time of 15-45 min.

[0013] Preferably, the mass ratio of the graphite carbon source to the iron-nickel-based composite catalyst powder is (50-60):(40-50).

[0014] In a second aspect, the present invention provides an iron-nickel-based composite catalyst powder for diamond synthesis, the iron-nickel-based composite catalyst powder comprising an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy microparticles attached to the surface of the iron-nickel-based catalyst powder core material.

[0015] The nickel-coated silicon-calcium alloy microparticles include silicon-calcium alloy microparticles and a nickel layer coating the outside of the silicon-calcium alloy microparticles.

[0016] Preferably, in the iron-nickel-based catalyst powder core material, by mass percentage, Ni is 30%-35%, C is no more than 0.05%, the balance is Fe and unavoidable impurities, and the O content is 50-180 μg / g.

[0017] Preferably, the D50 particle size of the iron-nickel based catalyst powder core material is 20-30 μm, and the D50 particle size of the nickel-coated silicon-calcium alloy microparticles is 2-12 μm.

[0018] Preferably, when the O content of the iron-nickel-based catalyst powder core material is 50-100 μg / g, the mass of Ca element in the nickel-coated silicon-calcium alloy microparticles is 0.04%-0.10% of the mass of the iron-nickel-based catalyst powder core material.

[0019] Preferably, when the O content of the iron-nickel-based catalyst powder core material is greater than 100 μg / g and not greater than 180 μg / g, the mass of Ca element in the nickel-coated silicon-calcium alloy microparticles is 0.08%-0.15% of the mass of the iron-nickel-based catalyst powder core material.

[0020] Preferably, the mass of the nickel-coated silicon-calcium alloy microparticles is 0.2%-0.6% of the mass of the iron-nickel-based catalyst core material.

[0021] Preferably, in the silicon-calcium alloy microparticles, Ca is 25%-45% and Si is 55%-75% by mass percentage.

[0022] Preferably, the nickel layer accounts for 15%-45% of the total mass of the nickel-coated silicon-calcium alloy particles.

[0023] Preferably, in the iron-nickel-based composite catalyst powder, the mass of free nickel-coated silicon-calcium alloy particles with a particle size of less than 20 μm accounts for no more than 0.5% of the total mass of the iron-nickel-based composite catalyst powder.

[0024] Thirdly, the present invention provides a method for preparing iron-nickel-based composite catalyst powder, comprising the following steps:

[0025] S1, after surface deoxidation treatment of iron and nickel raw materials, the materials are batched, and then subjected to medium frequency melting, nitrogen-protected water atomization, vacuum drying and sieving to obtain iron-nickel based catalyst powder core material;

[0026] S2, silicon-calcium alloy micro powder and carbonyl nickel powder are mechanically coated under an inert atmosphere and then heat-treated to obtain nickel-coated silicon-calcium alloy microparticles.

[0027] S3, the iron-nickel-based catalyst powder core material and the nickel-coated silicon-calcium alloy microparticles are mechanically fused together under an inert atmosphere;

[0028] S4. Vacuum drying and sieving of the mechanically fused powder yields iron-nickel-based composite catalyst powder.

[0029] Preferably, in S1, the surface deoxidation treatment is shot blasting, with each shot blasting session weighing no more than 100 kg and the shot blasting time being 20 min.

[0030] Preferably, the medium-frequency melting current is 380-400A, the medium-frequency voltage is 700-780V, and the melting time is 15-17min.

[0031] Preferably, in S2, the mass ratio of the silicon-calcium alloy micro powder to the carbonyl nickel powder is (55-85):(15-45), the mechanical coating rotation speed is 800-1800 r / min, and the time is 20-60 min.

[0032] Preferably, the heat treatment temperature is 300-450℃ and the time is 0.5-2h.

[0033] Preferably, in S3, the rotational speed of the mechanical fusion is 1000-2500 r / min, and the time is 15-45 min.

[0034] Preferably, in step S4, the temperature of the vacuum drying is 60-90℃, and the vacuum gauge pressure is ≤-0.08MPa.

[0035] Iron-nickel based catalyst powder is melted under high temperature and high pressure to form an iron-nickel based metal melt. After the graphite carbon source comes into contact with the metal melt, carbon atoms dissolve into the iron-nickel melt and diffuse and migrate under the action of the concentration gradient. When the local carbon concentration reaches the crystallization condition, the carbon atoms rearrange themselves at the diamond phase growth interface, using sp... 3 Hybrid bonding leads to the formation of diamond crystals. Nickel in the iron-nickel-based catalyst powder core material regulates the dissolution behavior of carbon in the iron-based melt and the interfacial wetting state, creating a metal-carbon interface between the graphite carbon source and the catalyst melt. If iron oxide, nickel oxide, or other oxygen-containing substances are present on the catalyst powder surface, these oxides will cover the metal particle surface, blocking direct contact between the metal melt and the graphite carbon source. During melting, these oxides can form oxygen-containing inclusions or oxygen-containing reaction products, altering the mass transfer pathway of carbon atoms into the catalyst melt and affecting the nucleation and growth process of diamond.

[0036] After nickel-coated silicon-calcium alloy microparticles adhere to the surface of the iron-nickel-based catalyst powder core material, a metal-metal interface is formed between the nickel layer and the iron-nickel-based core material. During mechanical coating and heat treatment, carbonyl nickel powder forms a nickel coating layer on the outside of the silicon-calcium alloy microparticles. This nickel layer isolates the silicon-calcium alloy microparticles from the external air and oxides on the powder surface, reducing the degree of premature oxidation or reaction of the silicon-calcium alloy microparticles during storage, transfer, and mixing. After mechanical fusion treatment, the nickel-coated silicon-calcium alloy microparticles adhere to the surface of the iron-nickel-based catalyst powder core material. The silicon-calcium alloy microparticles are no longer dispersed in the powder system as a large amount of free fine powder, but instead enter the contact area with the graphite carbon source along with the iron-nickel-based catalyst powder core material, so that the release position of the calcium-silicon component corresponds to the surface area of ​​the catalyst powder.

[0037] During the high-temperature, high-pressure synthesis process, the nickel cladding layer and the iron-nickel-based catalyst powder core material enter the molten metal together. After the nickel layer is incorporated into the iron-nickel-based metal phase, the calcium and silicon in the silicon-calcium alloy particles are exposed to the catalyst melt and its interface region. Calcium can react with residual oxides on the surface of the iron-nickel-based catalyst powder, dissolved oxygen in the melt, and oxygen-containing substances at the interface with the graphite carbon source to generate calcium oxides or calcium-containing composite oxide phases. Silicon can form a silicon-oxygen structure with oxygen and further form a calcium-silicon-oxygen composite phase with calcium oxides. The above reactions cause oxygen to transfer from the metal melt interface and the oxides on the particle surface into the calcium-silicon-oxygen composite phase, reducing the dispersion of oxygen-containing substances in the iron-nickel melt.

[0038] The nickel coating on the outer surface of the silicon-calcium alloy microparticles concentrates the release of calcium and silicon near the surface of the iron-nickel-based catalyst powder core material, rather than allowing them to react randomly within the powder system. The resulting calcium-silicon-oxygen composite phase differs from the diamond crystal structure, making it difficult to enter the diamond lattice and instead remaining more in the residual phase of the catalyst melt or the outer region of the crystal. Consequently, the interfacial oxides between the iron-nickel-based catalyst melt and the graphite carbon source are reduced, the degree to which the contact between the metal melt and the graphite carbon source is blocked by the oxide film is decreased, and the local differences in carbon atoms during dissolution, migration, and crystallization are reduced.

[0039] The mechanically fused adhesion structure also restricts the free distribution of nickel-coated silicon-calcium alloy particles. If the silicon-calcium alloy particles exist in the form of free fine powder, the fine powder is prone to local aggregation in the synthesis cavity, causing the calcium-silicon reaction products to accumulate in local areas and potentially forming new sources of inclusions. When the nickel-coated silicon-calcium alloy particles adhere to the surface of the iron-nickel-based catalyst powder core material, they enter the catalyst melt region along with the iron-nickel-based catalyst powder. The formation location of the calcium-silicon reaction products corresponds to the area where the oxygen-containing substances on the catalyst powder surface are located. This structure allows the oxygen-containing components at the interface to be converted into a calcium-silicon-oxygen composite phase nearby, reducing the random intervention of oxide residues, graphite residues, and metal inclusions at the diamond crystal growth interface, thereby reducing the probability of internal defects and inclusion formation in the diamond crystal.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention attaches nickel-coated silicon-calcium alloy microparticles to the surface of the iron-nickel-based catalyst powder core material, so that the silicon-calcium alloy microparticles are not randomly dispersed in the form of free fine powder, but enter the graphite carbon source contact area with the iron-nickel-based catalyst powder; the nickel layer plays an isolating role for the silicon-calcium alloy microparticles during storage, transfer and mixing, reducing their premature oxidation or premature reaction; during the high temperature and high pressure synthesis process, the nickel layer is incorporated into the iron-nickel-based metal melt, so that the silicon-calcium component participates in the transformation of oxygen-containing components near the surface of the catalyst powder; thereby reducing the influence of oxides and interfacial oxygen-containing substances on the surface of the catalyst powder on the metal-carbon contact interface, and reducing the interference of local impurity phases, graphite residues and metal inclusions on the diamond crystal growth process; at the same time, the attachment structure formed by mechanical fusion can limit the free aggregation of nickel-coated silicon-calcium alloy microparticles, so that the reaction product generation position corresponds to the area where the oxygen-containing substances on the surface of the catalyst powder are located, thereby improving the interface state of the catalyst melt and improving the continuity, crystal integrity and hardness level of diamond crystal growth. Attached Figure Description

[0041] Figure 1 The flowchart illustrates the preparation method of the iron-nickel-based composite catalyst powder provided by this invention. Detailed Implementation

[0042] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0043] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0044] Example 1

[0045] This embodiment provides a method for synthesizing diamond, an iron-nickel-based composite catalyst powder, and a method for preparing the same. The flowchart of the method for preparing the iron-nickel-based composite catalyst powder is shown below. Figure 1 As shown, the specific steps include the following:

[0046] S1. After surface deoxidation treatment of iron and nickel raw materials, the mixture is batched, and then subjected to medium-frequency melting, nitrogen-protected water atomization, vacuum drying, and sieving to obtain iron-nickel-based catalyst powder core material. The surface deoxidation treatment is shot blasting, with each shot blasting weight not exceeding 100 kg and a shot blasting time of 20 min. The medium-frequency melting current is 380 A, the medium-frequency voltage is 780 V, and the melting time is 15 min. The vacuum drying temperature is 90 °C, and the vacuum gauge pressure is ≤ -0.08 MPa. In the iron-nickel-based catalyst powder core material, by mass percentage, Ni is 30%, C is not greater than 0.05%, the balance is Fe and unavoidable impurities, and the O content is 80 μg / g. The D50 particle size of the iron-nickel-based catalyst powder core material is 20 μm.

[0047] S2, silicon-calcium alloy micro powder with a D50 particle size of 2 μm and carbonyl nickel powder with a D50 particle size of 5 μm are mechanically coated under an inert atmosphere, followed by heat treatment to obtain nickel-coated silicon-calcium alloy microparticles. The mechanical coating speed is 800 r / min and the time is 60 min. The heat treatment temperature is 300℃ and the time is 2 h. In the silicon-calcium alloy micro powder, Ca is 25% and Si is 75% by mass percentage. In the nickel-coated silicon-calcium alloy microparticles, the nickel layer accounts for 15% of the total mass of the nickel-coated silicon-calcium alloy microparticles. The D50 particle size of the nickel-coated silicon-calcium alloy microparticles is 2 μm.

[0048] S3, the iron-nickel-based catalyst powder core material and the nickel-coated silicon-calcium alloy microparticles are mechanically fused under an inert atmosphere. The mass of the nickel-coated silicon-calcium alloy microparticles is 0.2% of the mass of the iron-nickel-based catalyst powder core material, the O content of the iron-nickel-based catalyst powder core material is 80 μg / g, the mass of Ca element in the nickel-coated silicon-calcium alloy microparticles is 0.04% of the mass of the iron-nickel-based catalyst powder core material, the mechanical fusion speed is 2500 r / min, and the time is 15 min.

[0049] S4. The mechanically fused powder is vacuum dried and sieved to obtain iron-nickel-based composite catalyst powder. The vacuum drying temperature is 60℃ and the vacuum gauge pressure is ≤-0.08MPa. The iron-nickel-based composite catalyst powder includes an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy microparticles attached to the surface of the iron-nickel-based catalyst powder core material. The nickel-coated silicon-calcium alloy microparticles include silicon-calcium alloy microparticles and a nickel layer coating the outside of the silicon-calcium alloy microparticles. In the iron-nickel-based composite catalyst powder, the mass of free nickel-coated silicon-calcium alloy microparticles with a particle size of less than 20μm accounts for no more than 0.5% of the total mass of the iron-nickel-based composite catalyst powder.

[0050] The graphite carbon source and the iron-nickel-based composite catalyst powder were loaded into a high-temperature and high-pressure synthesis chamber at a mass ratio of 50:50. The high-temperature and high-pressure synthesis chamber was placed in a six-sided top press and kept at a pressure of 4.8 GPa and a temperature of 1450℃ for 15 minutes. After the heat preservation was completed, the temperature was reduced and the pressure was released. The synthesized block was taken out and then crushed, acid-washed and sorted to obtain diamond.

[0051] Example 2

[0052] This embodiment provides a method for synthesizing diamond, an iron-nickel-based composite catalyst powder, and a method for preparing the same, specifically including the following steps:

[0053] S1. After surface deoxidation treatment of iron and nickel raw materials, the mixture is batched, and then subjected to medium-frequency melting, nitrogen-protected water atomization, vacuum drying, and sieving to obtain iron-nickel-based catalyst powder core material. The surface deoxidation treatment is shot blasting, with each shot blasting weight not exceeding 100 kg and a shot blasting time of 20 min. The medium-frequency melting current is 400 A, the medium-frequency voltage is 700 V, and the melting time is 17 min. The vacuum drying temperature is 105 °C, and the vacuum gauge pressure is ≤ -0.08 MPa. In the iron-nickel-based catalyst powder core material, by mass percentage, Ni is 35%, C is not greater than 0.05%, the balance is Fe and unavoidable impurities, and the O content is 150 μg / g. The D50 particle size of the iron-nickel-based catalyst powder core material is 30 μm.

[0054] S2, silicon-calcium alloy micro powder with a D50 particle size of 12 μm and carbonyl nickel powder with a D50 particle size of 1 μm are mechanically coated under an inert atmosphere, followed by heat treatment to obtain nickel-coated silicon-calcium alloy microparticles. The mechanical coating rotation speed is 1800 r / min and the time is 20 min. The heat treatment temperature is 450℃ and the time is 0.5 h. In the silicon-calcium alloy micro powder, Ca is 45% and Si is 55% by mass percentage. In the nickel-coated silicon-calcium alloy microparticles, the nickel layer accounts for 45% of the total mass of the nickel-coated silicon-calcium alloy microparticles. The D50 particle size of the nickel-coated silicon-calcium alloy microparticles is 12 μm.

[0055] S3, the iron-nickel-based catalyst powder core material and the nickel-coated silicon-calcium alloy microparticles are mechanically fused under an inert atmosphere. The mass of the nickel-coated silicon-calcium alloy microparticles is 0.6% of the mass of the iron-nickel-based catalyst powder core material, the O content of the iron-nickel-based catalyst powder core material is 150 μg / g, the mass of Ca element in the nickel-coated silicon-calcium alloy microparticles is 0.15% of the mass of the iron-nickel-based catalyst powder core material, the mechanical fusion speed is 1000 r / min, and the time is 45 min.

[0056] S4. The mechanically fused powder is vacuum dried and sieved to obtain iron-nickel-based composite catalyst powder. The vacuum drying temperature is 90℃ and the vacuum gauge pressure is ≤-0.08MPa. The iron-nickel-based composite catalyst powder includes an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy microparticles attached to the surface of the iron-nickel-based catalyst powder core material. The nickel-coated silicon-calcium alloy microparticles include silicon-calcium alloy microparticles and a nickel layer coating the outside of the silicon-calcium alloy microparticles. In the iron-nickel-based composite catalyst powder, the mass of free nickel-coated silicon-calcium alloy microparticles with a particle size of less than 20μm accounts for no more than 0.5% of the total mass of the iron-nickel-based composite catalyst powder.

[0057] The graphite carbon source and the iron-nickel-based composite catalyst powder were loaded into a high-temperature and high-pressure synthesis chamber at a mass ratio of 60:40. The high-temperature and high-pressure synthesis chamber was placed in a six-sided top press and kept at a pressure of 5.8 GPa and a temperature of 1250℃ for 45 minutes. After the heat preservation was completed, the temperature was reduced and the pressure was released. The synthesized block was taken out and then crushed, acid-washed and sorted to obtain diamond.

[0058] Example 3

[0059] This embodiment provides a method for synthesizing diamond, an iron-nickel-based composite catalyst powder, and a method for preparing the same, specifically including the following steps:

[0060] S1. After surface deoxidation treatment of iron and nickel raw materials, the mixture is batched, and then subjected to medium-frequency melting, nitrogen-protected water atomization, vacuum drying, and sieving to obtain iron-nickel-based catalyst powder core material. The surface deoxidation treatment is shot blasting, with each shot blasting weight not exceeding 100 kg and a shot blasting time of 20 min. The medium-frequency melting current is 390 A, the medium-frequency voltage is 750 V, and the melting time is 16 min. The vacuum drying temperature is 100 °C, and the vacuum gauge pressure is ≤ -0.08 MPa. In the iron-nickel-based catalyst powder core material, by mass percentage, Ni is 32%, C is not greater than 0.05%, the balance is Fe and unavoidable impurities, and the O content is 95 μg / g. The D50 particle size of the iron-nickel-based catalyst powder core material is 24 μm.

[0061] S2, silicon-calcium alloy micro powder with a D50 particle size of 8 μm and carbonyl nickel powder with a D50 particle size of 3 μm are mechanically coated under an inert atmosphere, and then heat-treated to obtain nickel-coated silicon-calcium alloy microparticles. The mechanical coating speed is 1200 r / min and the time is 40 min. The heat treatment temperature is 380℃ and the time is 1 h. In the silicon-calcium alloy micro powder, Ca is 35% and Si is 65% by mass percentage. In the nickel-coated silicon-calcium alloy microparticles, the nickel layer accounts for 30% of the total mass of the nickel-coated silicon-calcium alloy microparticles. The D50 particle size of the nickel-coated silicon-calcium alloy microparticles is 8 μm.

[0062] S3, the iron-nickel-based catalyst powder core material and the nickel-coated silicon-calcium alloy microparticles are mechanically fused under an inert atmosphere. The mass of the nickel-coated silicon-calcium alloy microparticles is 0.32% of the mass of the iron-nickel-based catalyst powder core material, the O content of the iron-nickel-based catalyst powder core material is 95 μg / g, the mass of Ca element in the nickel-coated silicon-calcium alloy microparticles is 0.08% of the mass of the iron-nickel-based catalyst powder core material, the mechanical fusion speed is 1800 r / min, and the time is 30 min.

[0063] S4. The mechanically fused powder is vacuum dried and sieved to obtain iron-nickel-based composite catalyst powder. The vacuum drying temperature is 75℃, and the vacuum gauge pressure is ≤-0.08MPa. The iron-nickel-based composite catalyst powder includes an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy microparticles attached to the surface of the iron-nickel-based catalyst powder core material. The nickel-coated silicon-calcium alloy microparticles include silicon-calcium alloy microparticles and a nickel layer coating the outside of the silicon-calcium alloy microparticles. In the iron-nickel-based composite catalyst powder, the mass of free nickel-coated silicon-calcium alloy microparticles with a particle size of less than 20μm accounts for no more than 0.5% of the total mass of the iron-nickel-based composite catalyst powder.

[0064] The graphite carbon source and the iron-nickel-based composite catalyst powder were loaded into a high-temperature and high-pressure synthesis chamber at a mass ratio of 55:45. The high-temperature and high-pressure synthesis chamber was placed in a six-sided top press and kept at a pressure of 5.2 GPa and a temperature of 1350℃ for 30 minutes. After the heat preservation was completed, the temperature was reduced and the pressure was released. The synthesized block was taken out and then crushed, acid-washed and sorted to obtain diamond.

[0065] Example 4

[0066] This embodiment provides a method for synthesizing diamond, an iron-nickel-based composite catalyst powder, and a method for preparing the same, specifically including the following steps:

[0067] S1. After surface deoxidation treatment of iron and nickel raw materials, the mixture is batched, and then subjected to medium-frequency melting, nitrogen-protected water atomization, vacuum drying, and sieving to obtain iron-nickel-based catalyst powder core material. The surface deoxidation treatment is shot blasting, with each shot blasting weight not exceeding 100 kg and a shot blasting time of 20 min. The medium-frequency melting current is 395 A, the medium-frequency voltage is 720 V, and the melting time is 16.5 min. The vacuum drying temperature is 95 °C, and the vacuum gauge pressure is ≤ -0.08 MPa. In the iron-nickel-based catalyst powder core material, by mass percentage, Ni is 34%, C is not greater than 0.05%, the balance is Fe and unavoidable impurities, and the O content is 110 μg / g. The D50 particle size of the iron-nickel-based catalyst powder core material is 28 μm.

[0068] S2, silicon-calcium alloy micro powder with a D50 particle size of 10 μm and carbonyl nickel powder with a D50 particle size of 4 μm are mechanically coated under an inert atmosphere, followed by heat treatment to obtain nickel-coated silicon-calcium alloy microparticles. The mechanical coating rotation speed is 1500 r / min and the time is 30 min. The heat treatment temperature is 400℃ and the time is 1.5 h. In the silicon-calcium alloy micro powder, Ca is 40% and Si is 60% by mass percentage. In the nickel-coated silicon-calcium alloy microparticles, the nickel layer accounts for 35% of the total mass of the nickel-coated silicon-calcium alloy microparticles. The D50 particle size of the nickel-coated silicon-calcium alloy microparticles is 10 μm.

[0069] S3, the iron-nickel-based catalyst powder core material and the nickel-coated silicon-calcium alloy microparticles are mechanically fused under an inert atmosphere. The mass of the nickel-coated silicon-calcium alloy microparticles is 0.4% of the mass of the iron-nickel-based catalyst powder core material, the O content of the iron-nickel-based catalyst powder core material is 110 μg / g, the mass of Ca element in the nickel-coated silicon-calcium alloy microparticles is 0.10% of the mass of the iron-nickel-based catalyst powder core material, the mechanical fusion speed is 2000 r / min, and the time is 25 min.

[0070] S4. The mechanically fused powder is vacuum dried and sieved to obtain iron-nickel-based composite catalyst powder. The vacuum drying temperature is 80℃ and the vacuum gauge pressure is ≤-0.08MPa. The iron-nickel-based composite catalyst powder includes an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy microparticles attached to the surface of the iron-nickel-based catalyst powder core material. The nickel-coated silicon-calcium alloy microparticles include silicon-calcium alloy microparticles and a nickel layer coating the outside of the silicon-calcium alloy microparticles. In the iron-nickel-based composite catalyst powder, the mass of free nickel-coated silicon-calcium alloy microparticles with a particle size of less than 20μm accounts for no more than 0.5% of the total mass of the iron-nickel-based composite catalyst powder.

[0071] The graphite carbon source and the iron-nickel-based composite catalyst powder were loaded into a high-temperature and high-pressure synthesis chamber at a mass ratio of 52:48. The high-temperature and high-pressure synthesis chamber was placed in a six-sided top press and kept at a pressure of 5.5 GPa and a temperature of 1400℃ for 25 minutes. After the heat preservation was completed, the temperature was reduced and the pressure was released. The synthesized block was taken out, and after crushing, acid washing and sorting, diamond was obtained.

[0072] Comparative Example 1

[0073] This comparative example provides a method for synthesizing diamond, an iron-nickel-based composite catalyst powder and its preparation method. The difference between this example and Example 1 is that, when synthesizing diamond, nickel-coated silicon-calcium alloy particles are not added, and iron-nickel-based catalyst powder core material is directly used as the catalyst powder. Other process parameters and operating conditions are exactly the same as in Example 1.

[0074] Comparative Example 2

[0075] This comparative example provides a method for synthesizing diamond, an iron-nickel based composite catalyst powder and its preparation method. The difference between this method and Example 1 is that, in the synthesis of diamond, nickel-coated silicon-calcium alloy microparticles are replaced with uncoated silicon-calcium alloy microparticles. Uncoated silicon-calcium alloy microparticles of the same mass as those in Example 1 are directly used, and carbonyl nickel powder is used to make up the total mass to the same as that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0076] Comparative Example 3

[0077] This comparative example provides a method for synthesizing diamond, an iron-nickel-based composite catalyst powder and its preparation method. The difference between this example and Example 1 is that mechanical fusion is not performed in S3. Instead, iron-nickel-based catalyst powder core material of the same mass as in Example 1 and nickel-coated silicon-calcium alloy microparticles are directly mixed. Other process parameters and operating conditions are exactly the same as in Example 1.

[0078] Performance testing:

[0079] Vickers hardness testing method: Diamond particles of the same size range are sieved, ultrasonically cleaned with anhydrous ethanol for 10 minutes, and then dried. Twenty diamond particles are randomly selected from each group, fixed with epoxy resin, and polished step-by-step with diamond polishing paste until a testable surface is formed. A micro Vickers hardness tester is used, with a loading force of 1.961 N and a holding time of 15 seconds. One indentation is obtained for each diamond, resulting in 20 valid indentations per group. Results with clear indentation boundaries and identifiable diagonals are considered valid; results with chipped edges, through-cracks, or overlapping indentations are discarded. The instrument calculates the Vickers hardness based on the diagonal length of the indentation and converts it to GPa. The arithmetic mean of the valid test results for each group is taken as the Vickers hardness.

[0080] Test method for impact hardness Ti value: Diamond particles of size 35 / 40 obtained from each example and comparative example (i.e., particles passing through a 35-mesh sieve but remaining on a 40-mesh sieve) were ultrasonically cleaned with anhydrous ethanol for 10 min, dried at 105℃ for 1 h, and cooled to room temperature. 5.00 ct of diamond was weighed as the initial sample for each group, denoted as m0. The sample was placed in the impact chamber of a diamond impact hardness tester, and a matching hard steel ball was added. Impact treatment was performed at an impact frequency of 2400 times / min and an impact time of 10 min. After impact, the sample was removed, sieved through a 40-mesh sieve for 3 min, and the diamond particles remaining on the 40-mesh sieve were collected and weighed, denoted as m1. The impact hardness Ti value was calculated as Ti = m1 / m0 × 100%.

[0081] Test method for the proportion of intact crystals: Particles of the same size range from the diamond sieves obtained in each example and comparative example were ultrasonically cleaned with anhydrous ethanol for 10 minutes and then dried. At least 200 diamond particles were randomly sampled from each group and observed under a stereomicroscope at 50x magnification. Particles with continuous crystal boundaries, clear main crystal edges, and no obvious crystal linkages, cracks, broken edges, or abnormal growth were identified as intact crystals; particles with crystal linkages, missing corners, cracks, obvious deformities, or broken edges were identified as incomplete crystals. The proportion of intact crystals was calculated as the percentage of intact crystal particles out of the total number of observed particles. Each group was tested three times, and the average value was taken as the proportion of intact crystals.

[0082] Test method for inclusion / graphite residue ratio: Particles of the same size range from the diamonds obtained in each example and comparative example were sieved, acid-washed, washed with deionized water, and dried for observation. At least 200 diamond particles were randomly sampled from each group and observed using a stereomicroscope and a reflected light microscope (magnification 50x and 200x). Particles with visible black opaque residues, metallic inclusions, graphite-like residue areas, or dot-like inclusions inside or on the crystal surface were identified as inclusion / graphite residue particles. The inclusion / graphite residue ratio was calculated as the percentage of inclusion / graphite residue particles to the total number of observed particles. Each group was tested three times, and the average value was taken as the inclusion / graphite residue ratio.

[0083] The test results are shown in Table 1.

[0084] Table 1. Diamond test results of Examples 1-4 and Comparative Examples 1-3

[0085]

[0086] As shown in Table 1, compared with Example 1, Comparative Example 1 showed a decrease in Vickers hardness, a decrease in impact hardness Ti value, a decrease in the proportion of intact crystals, and an increase in the proportion of inclusions / graphite residue; Comparative Example 2 showed a decrease in Vickers hardness, a decrease in impact hardness Ti value, a decrease in the proportion of intact crystals, and an increase in the proportion of inclusions / graphite residue; Comparative Example 3 showed a decrease in Vickers hardness, a decrease in impact hardness Ti value, a decrease in the proportion of intact crystals, and an increase in the proportion of inclusions / graphite residue.

[0087] This is because, in Comparative Example 1, without the addition of nickel-coated silicon-calcium alloy microparticles, the residual oxides on the surface of the iron-nickel-based catalyst powder and the oxygen-containing components at the interface lack a nearby source of conversion. The degree of oxide obstruction at the metal-carbon interface increases, leading to greater fluctuations in the carbon dissolution and crystallization processes. Consequently, the diamond hardness, impact hardness (Ti) value, and proportion of intact crystals decrease, while the proportion of inclusions / graphite residues increases. In Comparative Example 2, using uncoated silicon-calcium alloy microparticles, the silicon-calcium components are more prone to premature oxidation or random reactions during storage, mixing, and the initial heating phase. This results in fewer calcium-silicon components available for conversion when entering the catalyst melt interface, and the reaction sites are not concentrated, weakening the interface purification effect. This leads to an increase in inclusions and graphite residues within the crystals. With increased inclusions and graphite residues, localized stress concentration is more likely to occur at defect locations when the crystals are under load. This reduces the resistance to crack propagation in the indentation zone and during impact fracture, thus lowering the Vickers hardness and impact hardness (Ti) value. Comparative Example 3 did not undergo mechanical fusion treatment. The nickel-coated silicon-calcium alloy microparticles and the iron-nickel-based catalyst powder core material were simply mixed directly. The distribution of fine particles in the powder system was unstable, and they were prone to local aggregation or misalignment with the oxygen-containing areas on the core material surface. This resulted in the formation of calcium-silicon reaction products in a non-concentrated manner, increased interfacial state fluctuations, a decrease in the proportion of intact crystals, and an increase in the proportion of inclusions / graphite residues. Due to the fluctuations in the interfacial state, the continuity of crystal growth decreased, and the proportion of missing corners, cracks, and local inclusions in the resulting diamond increased. The particles were more prone to fracture under microindentation and impact loads, thus reducing the Vickers hardness and impact hardness Ti values.

[0088] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for synthesizing diamond, characterized in that, Includes the following steps: The graphite carbon source and the iron-nickel-based composite catalyst powder are loaded into a high-temperature and high-pressure synthesis chamber; The high-temperature and high-pressure synthesis chamber is placed in a high-temperature and high-pressure device for heat preservation and synthesis. After the heat preservation is completed, the temperature is reduced and the pressure is released. The composite block is then removed, crushed, acid-washed, and sorted to obtain diamond. The iron-nickel-based composite catalyst powder includes an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy microparticles attached to the surface of the iron-nickel-based catalyst powder core material. The nickel-coated silicon-calcium alloy microparticles include silicon-calcium alloy microparticles and a nickel layer coating the outside of the silicon-calcium alloy microparticles.

2. The method for synthesizing diamond according to claim 1, characterized in that, The high-temperature and high-pressure equipment is a six-sided top press, with a combined pressure of 4.8-5.8 GPa, a temperature of 1250-1450℃, and a holding time of 15-45 min. The mass ratio of the graphite carbon source to the iron-nickel-based composite catalyst powder is (50-60):(40-50).

3. A nickel-iron based composite catalyst powder, characterized in that, The iron-nickel-based composite catalyst powder includes an iron-nickel-based catalyst powder core material and nickel-coated silicon-calcium alloy microparticles attached to the surface of the iron-nickel-based catalyst powder core material. The nickel-coated silicon-calcium alloy microparticles include silicon-calcium alloy microparticles and a nickel layer coating the outside of the silicon-calcium alloy microparticles.

4. The iron-nickel-based composite catalyst powder according to claim 3, characterized in that, In the iron-nickel-based catalyst powder core material, by mass percentage, Ni is 30%-35%, C is no more than 0.05%, the balance is Fe and unavoidable impurities, and the O content is 50-180 μg / g; The D50 particle size of the iron-nickel based catalyst powder core material is 20-30 μm, and the D50 particle size of the nickel-coated silicon-calcium alloy microparticles is 2-12 μm.

5. The iron-nickel-based composite catalyst powder according to claim 4, characterized in that, When the oxygen content of the iron-nickel-based catalyst powder core material is 50-100 μg / g, the mass of the calcium element in the nickel-coated silicon-calcium alloy microparticles is 0.04%-0.10% of the mass of the iron-nickel-based catalyst powder core material. When the O content of the iron-nickel-based catalyst powder core material is greater than 100 μg / g and not greater than 180 μg / g, the mass of Ca element in the nickel-coated silicon-calcium alloy microparticles is 0.08%-0.15% of the mass of the iron-nickel-based catalyst powder core material.

6. The iron-nickel-based composite catalyst powder according to claim 3, characterized in that, The mass of the nickel-coated silicon-calcium alloy microparticles is 0.2%-0.6% of the mass of the iron-nickel-based catalyst core material; In the silicon-calcium alloy microparticles, by mass percentage, Ca is 25%-45% and Si is 55%-75%; The nickel layer accounts for 15%-45% of the total mass of the nickel-coated silicon-calcium alloy particles.

7. The iron-nickel-based composite catalyst powder according to claim 3, characterized in that, In the iron-nickel-based composite catalyst powder, the mass of free nickel-coated silicon-calcium alloy particles with a particle size of less than 20 μm accounts for no more than 0.5% of the total mass of the iron-nickel-based composite catalyst powder.

8. A method for preparing an iron-nickel-based composite catalyst powder, characterized in that, Includes the following steps: S1, after surface deoxidation treatment of iron and nickel raw materials, the materials are batched, and then subjected to medium frequency melting, nitrogen-protected water atomization, vacuum drying and sieving to obtain iron-nickel based catalyst powder core material; S2, silicon-calcium alloy micro powder and carbonyl nickel powder are mechanically coated under an inert atmosphere and then heat-treated to obtain nickel-coated silicon-calcium alloy microparticles. S3, the iron-nickel-based catalyst powder core material and the nickel-coated silicon-calcium alloy microparticles are mechanically fused together under an inert atmosphere; S4. Vacuum drying and sieving of the mechanically fused powder yields iron-nickel-based composite catalyst powder.

9. The method for preparing iron-nickel-based composite catalyst powder according to claim 8, characterized in that, In S1, the surface deoxidation treatment is shot blasting, with each shot blasting session weighing no more than 100 kg and the shot blasting time being 20 min. The medium-frequency melting current is 380-400A, the medium-frequency voltage is 700-780V, and the melting time is 15-17min.

10. The method for preparing iron-nickel-based composite catalyst powder according to claim 8, characterized in that, In S2, the mass ratio of the silicon-calcium alloy micro powder to the carbonyl nickel powder is (55-85):(15-45), and the mechanical coating rotation speed is 800-1800 r / min, and the time is 20-60 min; The heat treatment is performed at a temperature of 300-450℃ for a time of 0.5-2 hours.

11. The method for preparing iron-nickel-based composite catalyst powder according to claim 8, characterized in that, In S3, the rotational speed of the mechanical fusion is 1000-2500 r / min, and the time is 15-45 min; In S4, the vacuum drying temperature is 60-90℃, and the vacuum gauge pressure is ≤-0.08MPa.

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