CN112064120B

CN112064120B - Seed crystal for large-size cultivation of diamond and preparation method thereof

Info

Publication number: CN112064120B
Application number: CN202010810387.2A
Authority: CN
Inventors: 刘乾坤; 易良成; 赵鹏; 申幸卫; 卢洋; 胡来运; 昝亚男
Original assignee: Zhongnan Diamond Co Ltd
Current assignee: Zhongnan Diamond Co Ltd
Priority date: 2020-08-13
Filing date: 2020-08-13
Publication date: 2021-09-03
Anticipated expiration: 2040-08-13
Also published as: CN112064120A

Abstract

The invention discloses a seed crystal for cultivating diamond in large size and a preparation method thereof, wherein the preparation method comprises the following steps: the catalyst is synthesized by high temperature and high pressure with high purity graphite according to the mass ratio of (60-70) to (30-40), the catalyst is composed of Fe powder, Ni powder, Cu powder, Co powder, Ce powder and diamond powder, and the synthetic core column is prepared by adopting a general process. When the high-temperature high-pressure synthesis is carried out, the synthesis time is 40-50 hours, and large-size typical (100) surface seed crystals with the size of 3-5 mm are obtained. The seed crystal synthesized by the method is precisely polished on the (100) surface of the seed crystal on a high-precision polishing machine, so that the surface smoothness of the crystal surface of the seed crystal (100) is improved, the defects of the crystal surface are reduced, and meanwhile, the deviation angle of the crystal surface of the (100) is ensured to be less than 5 degrees and is used as a preset seed crystal for synthesizing and cultivating diamond.

Description

Seed crystal for large-size cultivation of diamond and preparation method thereof

Technical Field

The invention belongs to the technical field of synthetic production of artificial cultivated diamonds, and relates to a seed crystal for large-size cultivated diamonds and a preparation method thereof.

Background

The cultivated diamond is obtained by an artificial method, and can be made into the cultivated diamond through specific cutting and grinding after the weight, the cleanliness and the chromaticity all reach the requirement of gem grade. Scientific development shows that the cultured diamond has huge application potential in the fields of optics, semiconductors, machinery and quantum science, the progress of the existing production technology and the development of the society promote the cultured diamond to have very high heat in the jewelry industry, and the key reason is that the largest raw material producing country of the cultured diamond is in China. China, as the biggest world producing country for cultivating diamond blanks, is equal to having resources which are dozens of times larger than the total reserve of all natural diamond ores around the world, so that the high monopoly of foreign institutions at the source of the natural diamond industry chain is broken at one stroke in the category, and the market for cultivating diamonds is gradually mature. Therefore, the application and development of the cultured diamonds are accelerated, the rare opportunity is created for culturing the diamonds, manufacturers are stimulated to expand production, scientific research investment is increased, and the product quality is further improved.

The artificial cultivation of large-size diamonds has very strict technical requirements, wherein the preparation of the preset seed crystals is a key technology for the production of the large-size cultivation diamonds. The invention aims to synthesize high-quality large-size cultivated diamond, and ensures that the diamond seed crystal with a high-quality (100) crystal face is synthesized through researching a catalyst formula and a matching process in the high-temperature high-pressure synthesis process of the seed crystal, and then the synthesized seed crystal is selected and polished and precisely processed according to the technical requirements, so that the seed crystal for the large-size cultivated diamond is obtained.

Disclosure of Invention

The invention provides a seed crystal for culturing diamond in large size and a preparation method thereof, the seed crystal prepared by the method provided by the invention has a (100) crystal face which is complete and free of defects, and the size of the seed crystal can reach more than 3 mm. The single diamond grain cultivated by the seed crystal can reach more than 20ct, and the single crystal has good quality such as crystal form, internal purity and the like, stable synthesis process and high success rate.

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

the preparation method of seed crystal for cultivating diamond in large size includes the following steps:

the mass ratio of the catalyst to the high-purity graphite is (60-70) (30-40), the catalyst consists of Fe powder, Ni powder, Cu powder, Co powder, Ce powder and diamond powder, wherein Fe 65-70%, Ni 25-30%, 0.1< Cu < 1%, 1< Co < 3%, the sum of the four raw materials is 100%, 0.1-0.5% of rare earth element Ce and 100/200-granularity diamond micro powder with the mass fraction of 0.01-0.015% are added in the total weight of the four raw materials, the elements are added in the form of nano-elementary powder, and the granularity of the Fe powder, the Ni powder, the Cu powder, the Co powder and the Ce powder is 300 meshes and is fine.

The core column preparation process adopts the currently general production processes of high-speed mixing, granulation, compression molding, vacuum reduction treatment and the like. Since they are not innovative herein, they will not be described in detail. The purpose of adding the Cu element is to: the diamond synthesized by the conventional catalyst has a large amount of continuous crystals grown by spontaneous nucleation, the overall quality of the diamond is seriously influenced, and after Cu is added, the spontaneous nucleation of the diamond can be effectively reduced, and the quality of the synthesized diamond is improved. Co element is added into the FeNi-based catalyst, so that the carbon atom diffusion activation energy in the synthesis process is effectively reduced, the carbon activity is further improved, and the growth speed of the crystal is accelerated. Meanwhile, a certain mass fraction of Ce element is added to achieve the purposes of purifying the catalyst and improving the catalytic activity.

The graphite core column is put into a synthesis cavity of the synthesis block, the pressure in the synthesis cavity is 6.0-6.1GP, the synthesis temperature is 1200-1250 ℃, and the synthesis time is 40-50 hours. When the seed crystal is prepared at static ultrahigh pressure and high temperature, a special heating and pressurizing process is adopted, and the method specifically comprises the following steps: the design of the core column formula effectively reduces the pressure and temperature required by synthesis, the pressure in a synthesis cavity only needs to be about 6.0-6.1GP, which is obviously lower than the traditional 6.5GP requirement, and the synthesis temperature is 1200-1250 ℃ and is also lower than the traditional 1300-1400 ℃. In order to ensure that the synthesized diamond seed crystal reaches more than 3mm, the synthesis time needs 40-50 hours.

The diamond seed crystal synthesized by the method has a typical (100) crystal face, the size of the crystal face can reach more than 3mm, but the (100) crystal face needs to be precisely polished, the polishing treatment aims to improve the surface smoothness of the (100) crystal face, reduce crystal face defects, and simultaneously ensure that the deviation angle of the (100) crystal face is less than 5 degrees, so that the production quality of large-size diamond cultivation can be ensured. Preferably, during polishing, the synthesized seed crystal is precisely polished on a high-precision polishing machine to ensure that the surface smoothness of the crystal face of the seed crystal (100) is more than delta 10 and the deviation angle of the crystal face of the seed crystal (100) is less than 5 degrees.

The invention has the beneficial effects that:

1. by designing the core column catalyst formula, Cu, Co and Ce with certain mass fractions are added into the iron-nickel based catalyst, so that the growth speed is effectively improved and the time required for normally synthesizing the seed crystals is shortened on the basis of fully ensuring the crystal quality in the seed crystal growth process.

2. The design of the core column catalyst formula effectively reduces the pressure and power required during synthesis in the process of synthesizing the seed crystal at high temperature and high pressure, has high equipment stability, and simultaneously reduces energy consumption and production cost.

3. The surface of the seed crystal (100) is precisely polished and further optimized, so that the surface finish of the surface of the seed crystal (100) is improved, and meanwhile, the stability of the synthetic process of the cultivated diamond is further ensured by the technical scheme of the off-angle of the crystal surface (100).

The invention has the advantages of clear process route, simple, convenient and stable synthesis method, strong repeatability, capability of obtaining the large-size seed crystal with high-quality (100) surface and wide popularization and application value.

Drawings

FIG. 1 is a schematic diagram of a structure of a synthesis block;

FIG. 2 is a diagram of the seed crystals synthesized in example 1;

FIG. 3 is a graph showing the results of measuring the off-angle of the seed crystal after polishing in example 1;

FIG. 4 is a schematic view of an assembled structure of cultured diamonds;

FIG. 5 is a diagram of the diamond grown in example 1;

FIG. 6 is a graph of the grown diamond of example 2;

in the

drawings

1 and 4, 1 is a pyrophyllite synthetic block, 2 is a conductive steel ring, 3 is a pyrophyllite ring, 4 is a dolomite outer lining, 5 is a carbon paper tube, 6 is a carbon paper sheet, 7 is a magnesium oxide cup, 8 is a carbon source, 9 is a FeNi catalyst, 10 is a crystal bed, 11 is a seed crystal.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the following specific examples, but the scope of the present invention is not limited thereto.

The purity of the high-purity graphite is more than or equal to 99.9999 percent.

Example 1

A preparation method of seed crystals for large-size cultivation of diamonds comprises the following steps:

(1) firstly, a synthetic block is prefabricated, and the synthetic block of the diamond is synthesized by adopting a static high-temperature high-pressure method (the specific structure is shown in patents 2016208984018 and 2016106838825 in detail), and as shown in figure 1, the synthetic block comprises a pyrophyllite synthetic block 1, a conductive plug 2, a pyrophyllite ring 3, a dolomite outer lining 4, a carbon paper tube 5, a carbon paper sheet 6, a dolomite ring 7 and a graphite core column 8.

The mass ratio of the catalyst to the high-purity graphite is 65:35, and the powdery catalyst comprises the following components in percentage by mass: fe 68%, Ni 30%, Cu 0.5%, Co 1.5%, adding rare earth element Ce 0.3% and 100/200-size diamond micropowder 0.015% by mass. The graphite core column is prepared by adopting the currently general production processes of high-speed mixing, granulation, compression molding, vacuum reduction treatment and the like. Specifically, the method comprises the following steps: the catalyst and the high-purity graphite are uniformly mixed by using a three-dimensional mixer according to the proportion, the mixing time is 6 hours, the mixed material is added to a double-roller extrusion granulator with the diameter of 4mm for granulation, a four-column hydraulic machine is used for compression molding after the granulation is finished, and the specification of a grinding tool in the four-column hydraulic machine is as follows: selecting a vacuum heating furnace, placing the raw material core column into the vacuum heating furnace after being coiled, carrying out vacuum reduction and purification, keeping the temperature at 850 ℃, keeping the temperature for 3 hours, then introducing hydrogen for reduction, closing a vacuumizing system before introducing the hydrogen, introducing the hydrogen until the pressure in the furnace reaches 0.02MPa, keeping the temperature for 15 minutes, then starting the vacuumizing system and vacuumizing for 15 minutes, repeating the cycle for 5 times, keeping the temperature for 2 hours, then finishing the process, introducing argon into the furnace after finishing the heat preservation until the pressure reaches 0.12MPa, starting a cooling fan until the temperature in the furnace is lower than 60 ℃, and then discharging the core column to obtain the raw material core column for synthesis.

(2) High-pressure high-temperature synthesis, namely assembling the prepared synthetic core column into an assembly block for high-temperature high-pressure synthesis according to the attached drawing 1, putting the assembly block into a domestic cubic press for high-temperature high-pressure synthesis, wherein the synthesis pressure is 6.1GP, the synthesis temperature is 1230 +/-5 ℃, the synthesis time is 48 hours, taking out the synthetic block after the synthesis is finished, and purifying by acid treatment to obtain the large-size typical (100) surface seed crystal with the size of 3.74mm as shown in the attached drawing 2.

(3) Performing precise polishing processing on a high-precision polishing machine (ATM-ZD-250) according to the technical requirements, so that the surface smoothness of the surface of the seed crystal (100) is more than delta 10, and the deviation angle of the crystal face of the seed crystal (100) is less than 5 degrees, and the seed crystal is used as a preset seed crystal for synthesizing and cultivating diamond, as shown in figure 2.

Wherein, the deviation angle is measured by adopting a JF-7 type high-power automatic peak searching crystal orientation instrument, the standard is 59 degrees, 45 minutes and 25 seconds, the absolute value of the difference value is the deviation value, and the average angle of the crystal plane of the seed crystal (100) prepared in the embodiment is 59 degrees, 06 minutes and 03 seconds, as shown in figure 3, therefore, the deviation angle of the crystal plane of the seed crystal (100) prepared in the embodiment 1 is less than 1 degree.

(4) Synthesizing cultured diamonds at high temperature and high pressure by adopting a temperature gradient method, assembling the assembled blocks for synthesizing the cultured diamonds according to a drawing 4, and synthesizing the diamond in a domestic cubic press, wherein the preset mode of seed crystals 11 on a crystal bed 10 adopts the upward distribution of the seed crystals (100) to fully ensure the preferential growth of the cultured diamonds, the synthesis process adopts the currently general production process (specifically, refer to the methods in patents ZL201610683882.5 and ZL 201620898401.8), the detailed description is omitted, the synthesis time is 200 hours, the synthesized blocks are taken out after the synthesis is finished, and the synthesized blocks are purified by acid treatment to obtain the cultured diamond single crystals with the purity of more than 20ct (specifically, 21.85 ct), the single crystal chromaticity reaches D level and the purity VVS level, as shown in a drawing 5.

Example 2

A method of growing diamond using the seed crystal prepared in example 1,

synthesizing cultured diamonds at high temperature and high pressure by adopting a temperature gradient method, assembling the assembled blocks for synthesizing the cultured diamonds according to a diagram 4, and synthesizing the diamond in a domestic cubic press, wherein the preset mode of seed crystals 11 on a crystal bed 10 adopts the upward distribution of the seed crystals (100) to fully ensure the preferential growth of the cultured diamonds, the synthesis process adopts the currently general production process (specifically, the method in a patent ZL201610683882.5 can be referred to), the detailed description is omitted, the synthesis time is 240 hours, the synthesized blocks are taken out after the synthesis is finished, and the synthesized blocks are purified by acid treatment to obtain the cultured diamond single crystals with the purity of more than 20ct (specifically, 30.10 ct), the chromaticity of the single crystals reaches D level and the purity VVS level, as shown in a diagram 6.

The above embodiments are only for illustrating the preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention within the knowledge of those skilled in the art should be considered as the protection scope of the present application.

Claims

1. A preparation method of seed crystals for large-size cultivation of diamonds is characterized by comprising the following steps: the catalyst consists of Fe powder, Ni powder, Cu powder, Co powder, Ce powder and diamond powder according to a mass ratio of (60-70) - (30-40), wherein Fe 65-70%, Ni 25-30%, 0.1< Cu < 1%, 1< Co < 3%, the sum of the four raw materials is 100%, and 0.1-0.5% of rare earth element Ce and 0.01-0.015% of 100/200-granularity diamond micro powder are added according to the total weight of the four raw materials; the particle sizes of the Fe powder, the Ni powder, the Cu powder, the Co powder and the Ce powder are all 300 meshes;

the preparation process comprises the following steps:

(1) taking raw materials of the catalyst and high-purity graphite according to a proportion, mixing the raw materials of the catalyst and the high-purity graphite, granulating, pressing and molding, and carrying out vacuum reduction treatment to prepare a graphite core column;

(2) the graphite core column is arranged in a synthesis cavity of the synthesis block, the pressure in the synthesis cavity is 6.0-6.1GP, the synthesis temperature is 1200-1250 ℃, and the synthesis time is 40-50 hours;

(3) after the synthesis is finished, polishing and grinding the synthesized product to obtain the product; during polishing, the synthesized seed crystal is precisely polished on the (100) surface of the seed crystal on a high-precision polishing machine, so that the surface smoothness of the crystal surface of the seed crystal (100) is more than delta 10, and the deviation angle of the crystal surface of the seed crystal (100) is less than 5 degrees.