Method for manufacturing a synthetic column for polycrystalline diamond synthesis

Abstract

The application discloses a preparation method of a synthesis column for polycrystalline diamond synthesis, which adopts a wet mixing method of a composite mixing medium to improve mixing efficiency and mixing uniformity, reduces mixing time from 15 hours to 4 hours or below, and saves time cost; meanwhile, the supercritical CO2 extraction drying and atmosphere furnace reduction technology are adopted for the first time, the water removal rate is increased by 5-8% compared with a conventional drying method, the oxygen between the gaps of the particles is further replaced, the oxidation layer of the catalyst surface layer is further treated, the influence of the oxidation layer of the catalyst surface on the nucleation and growth of the diamond is reduced, and the yield of the polycrystalline diamond is further increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of synthetic diamond synthesis, in particular to a preparation method of a synthesis column for polycrystalline diamond synthesis. BACKGROUND

[0002] In the synthesis of polycrystalline diamond by HTHP method, graphite is usually purified and mixed with catalyst, and then pressed into a synthesis column. Under the conditions of 5-6 GPa and 1200-1500℃, the graphite is converted into diamond by high-temperature and high-pressure synthesis with the catalytic action of metal catalyst.

[0003] The uniformity of the mixture of metal catalyst and graphite powder system is the key to the synthesis of polycrystalline diamond by powder catalyst, and is directly related to the uniformity of nucleation of polycrystalline diamond and determines the later growth of diamond.

[0004] Since the specific gravity of metal is about 8 and the specific gravity of graphite is about 2.3, the difference in specific gravity is very large. Even if the mixture is uniform, the phenomenon of separation of metal particles and graphite in different degrees will occur under the action of gravity after a long period of storage.

[0005] When the mixture is not uniform, there is too much metal and the diamond is concentrated, which may cause continuous crystal; there is too little metal and the diamond growth is limited due to insufficient catalysis.

[0006] The industry usually uses a step-by-step mixing method to mix the powder, which is then pressed into a shape, broken, sieved, mixed again, and so on until the required standard is reached. The process is complex and costly.

[0007] In addition, using the step-by-step mixing method, the amount of graphite and powder catalyst used on the same day needs to be calculated in advance, and the blocks need to be prepared in advance. Once a sudden situation occurs, the entire batch of synthesis blocks will be discarded and reprocessed. Mixing takes a very long time.

[0008] For example, the Chinese patent with application number CN201711444179.X discloses a wet mixing method using ethylene glycol or alcohol as a single solvent. The wet mixing is performed after the catalyst is formed into a ball, and vacuum drying is performed after the synthesis column is pressed. It is difficult to fully remove the oxidized substances and moisture from the core position of the synthesis column, which has a certain impact on the synthesis degree of the final diamond. SUMMARY

[0009] The technical problem to be solved by the present application is to overcome the existing defects and provide a preparation method of a synthesis column for polycrystalline diamond synthesis, which effectively improves the uniformity and efficiency of the mixture of graphite and powder catalyst, inhibits the re-separation phenomenon of powder catalyst and graphite after a long period of storage, and further purifies the oxidation layer on the surface of graphite and catalyst, which is beneficial to the nucleation and growth of polycrystalline diamond, improves the production efficiency, saves the production cost, and effectively solves the problems in the background art.

[0010] To achieve the above object, the present application provides the following technical scheme: a preparation method of a synthesis column for polycrystalline diamond synthesis, comprising the following steps:

[0011] (1) mixing graphite, catalyst and mixing medium; the mixing ratio is 14:12:7-14:12:2; the mixing is carried out by adding a planetary ball mill, and the mixing time is 1-4h;

[0012] The mixing medium comprises ethanol and acetone, and the mixing ratio is 0.5:1-1:1;

[0013] (2) supercritical CO2 extraction; after the mixed raw materials are initially screened, they are placed in an extraction container, CO2 is used to replace the air in the container, CO2 is filled, the temperature is raised to 35-45℃, the pressure is 5-10MPa, drying is carried out for 10-45min, CO2 is slowly released to normal pressure, CO2 is filled again, drying is carried out for 15min, CO2 is released, and the step is recycled until complete drying;

[0014] (3) granulation; the dried raw materials are granulated by using a pair roller extruder, and the particle size is 1-2mm;

[0015] (4) atmosphere furnace reduction; the particles are placed in an atmosphere furnace, inert gas is filled, impurities are removed by purification at 800-900℃ for 15h, and natural cooling is carried out to room temperature;

[0016] (5) pre-pressing forming; the purified particles are pre-pressed by using an automatic four-column press to obtain a synthesis rod, and the density of the synthesis rod reaches 2.1-2.5g / cm 3 .

[0017] As a preferred technical scheme of the present application, the rotor diameter of the pair roller extruder in step 3 is 500-700mm, the pair roller gap is 0.5-1mm, the rotor rotating speed during the granulation process is 1000-1500r / min, and particle size screening is carried out after granulation.

[0018] As a preferred technical scheme of the present application, the unused synthesis rod is placed in a supercritical CO2 extraction container, CO2 is filled, the temperature is raised to 80℃, the pressure is 5-10MPa, and storage is carried out.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] 1、 the preparation method of the synthesis column for polycrystalline diamond synthesis uses a wet mixing method, improves the mixing efficiency and mixing uniformity, reduces the mixing time from the original 15h to within 4h, and saves time cost;

[0021] 2. After the mixture is homogeneous, the particle size distribution of polycrystalline diamond increases from the original 65% to about 81.5%, and the single yield increases from 120 carats to 180 carats.

[0022] 3. For the first time, a compound solvent is used as the mixing medium. The influence of the material, viscosity and amount of the mixing medium on the mixing is considered. The material is selected as a solvent with low boiling point, easy volatility and low cost.

[0023] 4. This is the first time that supercritical CO2 extraction drying technology has been used, which improves the water removal rate by 5-8% compared with conventional drying methods;

[0024] 5. For the first time, atmosphere furnace reduction and supercritical CO2 extraction drying technology are combined to remove oxygen between particles to the maximum extent. CO2 gas is used to fill the gaps between particles to prevent graphite and catalyst from being oxidized again; this is beneficial to the synthesis of polycrystalline diamond. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the present invention;

[0026] Figure 2 The graph shows the effect of different mixing media on the mixing efficiency of graphite-catalyst.

[0027] Figure 3 The figure shows the effect of the viscosity coefficient of different mixing media on the mixing efficiency of graphite-catalyst. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1:

[0030] (1) Weigh 140g of graphite, 120g of iron powder and nickel powder, 25g of ethanol and 25g of acetone, add them to a planetary ball mill for mixing, and mix for 2 hours.

[0031] (2) After filtering the mixture, put it into a supercritical CO2 extraction container, replace the air in the container with CO2, fill it with CO2, raise the temperature to 35-45℃, the pressure to 5-10MPa, dry for 15min, slowly release CO2 to atmospheric pressure, fill it with CO2 again, dry for 15min, release CO2, repeat this step until it is completely dry.

[0032] (3) After drying, the mixture is granulated by a pair of roller extruders, the rotor diameter of the pair of roller extruders is 500 mm, the gap between the rollers is 0.8 mm, the rotor rotating speed is 1250 r / min during the granulation process, the particle size is 1.5 mm, and the screening particle size is 1.5 mm;

[0033] (4) The granules are put into an atmosphere furnace, purified and impurity-removed at 800-900℃ for 15 h under nitrogen protection, and naturally cooled to room temperature;

[0034] (5) The purified granules are pre-pressed into synthetic rods by an automatic four-column press, and the density of the synthetic rods reaches 2.5 g / cm 3 ;

[0035] (6) The synthetic rods are put into a supercritical CO2 extraction container, filled with CO2, heated to 80℃, and pressurized to 5-10 MPa, to obtain synthetic polycrystalline diamond;

[0036] (7) The synthetic rods are synthesized by a cylinder 700 press and an existing process, and after purification treatment, the single yield is increased from 120-130 carats to 180 carats, and the proportion of peak particle size 80 / 120 is increased from 60-65% to 81.5%.

[0037] Example Two:

[0038] Different from Example One, the mixing medium is 50 g of ethanol.

[0039] Example Three:

[0040] Different from Example One and Example Two, the mixing medium is 50 g of acetone.

[0041] Example Four:

[0042] Different from Comparative Example One, the supercritical CO2 extraction and atmosphere furnace reduction of Step 2 and Step 4 are cancelled.

[0043] After synthesized by a cylinder 700 press and an existing process, and after purification treatment, the single yield is 135 carats, and the proportion of peak particle size 80 / 120 is 67.3%.

[0044] Referring to Figure 2 After mixing for the same length of time 2 h, in the experimental group in which 1:1 ethanol and acetone mixing medium is added, the mixing efficiency of graphite-catalyst is 96.2%; the mixing efficiency is 98.1% when the same weight of ethanol is added; and the mixing efficiency is 98.4% when the same mass of acetone is added.

[0045] Referring to Figure 3 When the viscosity coefficient is close to 0.5η(10 -3 Pa·s), the graphite-catalyst mixture has good uniformity, and the relative density difference at each place is the smallest;

[0046] The viscosity coefficients of different kinds or proportions of mixing media are as follows:

[0047]

[0048] The preparation method of the synthesis column for polycrystalline diamond synthesis adopts a wet mixing method, greatly improves the mixing efficiency, and the mixing is more uniform; compared with the traditional step-by-step dry mixing which needs 15 hours, the wet mixing only needs 4 hours or less to mix uniformly;

[0049] Ethanol and acetone are used as mixing media to inhibit the phenomenon that the uniformity of mixing decreases with the increase of mixing time during dry mixing, and the influence of mixing time is reduced; the viscosity and amount of the mixing medium are related to the uniformity of mixing, the larger the viscosity and the less the amount, the more difficult the powder aggregation is to break up; the lower the viscosity and the more the amount, the more difficult the powder is to stick together; by adjusting the viscosity of the mixing medium, the problem of separation of metal particles and graphite during storage after mixing can be effectively improved, and the storage time of the mixed material can be effectively prolonged;

[0050] At the same time, the use of composite mixing medium can further control the viscosity of the mixing medium, thereby further improving the uniformity of mixing;

[0051] At the same time, supercritical CO2 extraction drying is used, which uses CO2 gas with strong permeability as the flow medium, penetrates between the particles, and the interfacial bonding force between CO2 and ethanol, acetone is greater than that between ethanol and graphite, catalyst, so as to maximize the removal of medium molecules between particles, thereby achieving the purpose of drying the mixed material. Compared with the conventional drying method, the water removal rate is increased by 5-8%; at the same time, CO2 gas is used to fill the gaps between particles to prevent air oxidation; the water content between particles is reduced to avoid the influence of oxygen generated during synthesis on the nucleation and growth of polycrystalline diamond;

[0052] Granulation and particle size screening, the more concentrated particles, the more conducive to the particle size concentration of polycrystalline diamond and the improvement of single yield;

[0053] The particles are reduced in an atmosphere furnace, and nitrogen is used as the filling gas to reduce and remove oxygen from the particles; oxygen affects the nucleation and growth of diamond during polycrystalline diamond synthesis; especially on the surface of the catalyst, if an oxide layer is formed, it is difficult for the carbon source to penetrate the metal film layer at high temperature and high pressure, and to infiltrate into the catalyst, resulting in the catalyst being unable to catalyze, and finally the single yield of polycrystalline diamond is low;

[0054] In the pre-press forming, the greater the density of the synthetic rod, the more beneficial to the pressure transmission and the improvement of the quality of the polycrystalline diamond; the density of the synthetic rod is improved, and the pressure of the press is improved; but the pressing of the synthetic rod is the mutual extrusion between the particles, and no physical phase change is produced, and the essence is the plastic deformation of the powder particles and the compression of the gap between the particles; with the increase of the pressure, the plastic deformation limit of the synthetic rod is reached, the density of the synthetic rod is stable, and at the same time, the bearing capacity of the mold under high pressure is also considered, so the density of the synthetic rod reaches 2.1-2.5 g / cm 3 when the best state can be reached.

[0055] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a synthetic column for polycrystalline diamond synthesis, comprising the following steps: (1) mixing graphite, catalyst and mixing medium; the mass ratio of the mixing is 14:12:7-14:12:2; the mixing is performed in a planetary ball mill for 1-4 hours; the mixing medium comprises ethanol and acetone, and the mass ratio of the mixing is 0.5:1-1:1; (2) supercritical CO2 extraction; after the mixed raw material is initially sieved, it is placed in an extraction container, CO2 is used to replace the air in the container, CO2 is filled in, the temperature is raised to 35-45℃, the pressure is 5-10 MPa, and the drying is performed for 10-45 minutes, the CO2 is slowly released to normal pressure, CO2 is filled in again, the drying is performed for 15 minutes, the CO2 is released, and the step is recycled until complete drying; (3) granulation; the dried raw material is granulated by a pair-roller extruder, and the particle size is 1-2 mm; (4) atmosphere furnace reduction; the granules are placed in an atmosphere furnace, inert gas is filled in, impurities are removed by purification at 800-900℃ for 15 hours, and natural cooling is performed to room temperature; (5) Pre-pressing forming; the purified particles are pre-pressed by an automatic four-column press to obtain a synthetic rod, and the density of the synthetic rod reaches 2.1-2.5 g / cm 3 .

2. The method of producing a synthetic column for polycrystalline diamond synthesis according to claim 1, characterized in that: in step 3, the rotor diameter of the pair-roller extruder is 500-700 mm, the pair-roller gap is 0.5-1 mm, the rotor speed during the granulation is 1000-1500 r / min, and the particle size is sieved after the granulation.

3. The method of producing a synthetic column for polycrystalline diamond synthesis according to claim 1, characterized in that: unused synthetic rods are placed in a supercritical CO2 extraction container, CO2 is filled in, the temperature is raised to 80℃, the pressure is 5-10 MPa, and the storage is performed.

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