CN110681315B - Method for synthesizing gem-grade colorless diamond by seed crystal method - Google Patents
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Abstract
The invention discloses a method for synthesizing gem-grade colorless diamond by a seed crystal method, which comprises the following steps: (1) the method comprises the following steps of (1) inlaying a seed crystal on a crystal bed, wherein FeMnCo is used as a catalyst sheet, graphite is used as a carbon source, a Cu foil is used as a nitrogen removal agent, the upper end face of the seed crystal is flush with the upper end face of the crystal bed, and a synthetic block is assembled; (2) then starting high-temperature high-pressure synthesis, uniformly increasing the pressure to 60-70 MPa within 0-200s, then keeping the pressure for 2000-3000 s, and uniformly increasing the pressure to 90-100 MPa within 80-120 s; heating power is increased to 2.5-3.5 KW at a constant speed for 0-400s, then the temperature is kept for 2000-3000 s, and then the heating power is increased to 5-6 KW at a constant speed for 500-800 seconds; and (4) preserving heat and pressure until the power and pressure of the 1 st ten thousand seconds are gradually reduced and then gradually increased to the maximum value, wherein the total synthesis time is 90-100 ten thousand seconds, and the gem-grade colorless diamond with the particle size of 3-5 mm is obtained.
Description
Technical Field
The invention belongs to the technical field of diamond synthesis production, and particularly relates to a method for synthesizing gem-grade colorless diamond by a seed crystal method.
Background
In recent years, the synthetic technology of gem-grade cultivated diamonds at home and abroad is rapidly developed, and the cultivated diamond ornaments are more and more accepted and favored by consumers; many enterprises in China have the technical strength of industrial production of colorless diamonds, and the colorless diamonds have larger and larger particle sizes and excellent color; the synthesis of gem-grade colorless diamond has strict technical condition requirements, and mainly relates to how to control the crystal form, the growth direction and the growth speed of the crystal, inhibit the generation of impurity inclusions and the like; the seed crystal is used as a key element for synthesizing the colorless diamond by a temperature gradient method, and the growth trend of the colorless diamond is directly influenced under certain conditions due to different crystal forms, sizes and distribution modes of the seed crystal.
According to the theory and production experience, in the process of synthesizing the gem-grade colorless diamond by the temperature gradient method, because the mutual dissolution and the co-permeation of the carbon source and the graphite in the early stage and the conversion of the graphite into the diamond require higher energy, the power setting in the early stage is often higher, and in the growth process of the colorless diamond, the carbon source in the early stage is more sufficient, the axial temperature gradient and the radial temperature gradient of the crystal are relatively larger, and the growth speed of the crystal is very high at the moment; however, as the crystal grows, the carbon source is gradually reduced, and the temperature gradient of the growth surface in the axial direction and the radial direction of the crystal is gradually reduced compared with the temperature gradient in the early stage, at which the growth rate begins to slow. The growth speed is closely related to the crystal synthesis process, and when the growth speed is too high, the crystal is easy to yellow, deficient and incomplete in nitrogen removal, and has more internal defects, impurities and inclusions; when the growth speed is too slow, the crystal granularity is fine, the synthesis process time is too long, and the production cost is high. In the prior art, when gem-grade colorless diamonds with the grain size of 3-5 mm are synthesized, the changes of power and pressure are shown in figure 3, the pressure is uniformly increased to 65MPa within 200s, then kept at 2500s, and then uniformly increased to 95MPa within 100 s; heating power is increased to 3.0KW at a constant speed within 400s, then is kept at 2500s, and is increased to 5.5KW at a constant speed within 700 s; after the power and the pressure are increased to the maximum value within 90 ten thousand seconds of synthesis time, the synthesis power is kept to be W =5.5KW, and the gauge pressure is kept to be P =95MPa, so that the chroma and the purity of the colorless diamond synthesized by the synthesis method are not ideal.
Disclosure of Invention
The invention aims to provide a method for synthesizing gem-grade colorless diamond by a seed crystal method.
Based on the purpose, the invention adopts the following technical scheme:
a method for synthesizing gem-grade colorless diamond by a seed crystal method, which comprises the following steps:
(1) the method comprises the following steps of (1) inlaying a seed crystal on a crystal bed, wherein FeMnCo is used as a catalyst sheet, graphite is used as a carbon source, a Cu foil is used as a nitrogen removal agent, the upper end face of the seed crystal is flush with the upper end face of the crystal bed, and a synthetic block is assembled;
(2) then starting high-temperature high-pressure synthesis, uniformly increasing the pressure to 60-70 MPa within 0-200s, then keeping the pressure for 2000-3000 s, and uniformly increasing the pressure to 90-100 MPa within 80-120 s; heating power is increased to 2.5-3.5 KW at a constant speed for 0-400s, then the temperature is kept for 2000-3000 s, and then the heating power is increased to 5-6 KW at a constant speed for 500-800 seconds; and after the heat preservation and pressure maintaining are carried out for 1 ten thousand seconds, gradually reducing the heating power and the pressure and then gradually increasing the heating power and the pressure until the heating power and the pressure are recovered to the maximum value, wherein the total synthesis time is 90 ten thousand seconds to 100 ten thousand seconds, and the gem-grade colorless diamond with the particle size of 3-5 mm is obtained.
Further, the specific process that the heating power and the pressure are gradually reduced and then gradually increased when the temperature and the pressure are kept and maintained to 1 ten thousand seconds is as follows: setting parameter time nodes on a computer from 1 ten thousand seconds as T1, T2, T3, T4, T5, T6, T7, T8, T9 and T10 respectively, wherein T1=1 ten thousand seconds, T2=10 ten thousand seconds, T3=20 ten thousand seconds, T4=30 ten thousand seconds, T5=40 ten thousand seconds, T6=50 ten thousand seconds, T7=60 ten thousand seconds, T8=70 ten thousand seconds, T9=80 ten thousand seconds, T10=90 ten thousand seconds, and an equal difference sequence Wn = W1+ n d, d =0.01, -0.02, -0.03, -0.04, -0.05 corresponding to five time nodes from T1 to T5; pn = P1+ n × d, d = -0.1, -0.2, -0.3, -0.4, -0.5; corresponding to five time nodes from T6 to T10, the power pressure amplitude of rise conforms to an arithmetic progression Wn = W1+ n × d, d =0.01, 0.02, 0.03, 0.04 and 0.05; pn = P1+ n d, d =0.1, 0.2, 0.3, 0.4, 0.5, W1=5~6KW, P1=90~100MPa, n =1, 2, 3, 4, 5.
Further, it is specifically one of the following: in particular to one of the following: (1) the seed crystal A and the seed crystal B are circumferentially and crossly arranged to form a circle or a regular polygon; (2) the seed crystals A are circumferentially arranged to form a circular or regular polygon, and the center of the shape enclosed by the seed crystals A is provided with the seed crystals C; (3) the seed crystal A and the seed crystal B are circumferentially and crossly arranged to form a circle or a regular polygon, the seed crystal C is arranged at the center of the shape enclosed by the seed crystal A and the seed crystal B, the seed crystal A and the seed crystal B are different in size or shape, and the seed crystal A, B, C is a circle or a regular polygon.
Furthermore, the thickness of the catalyst piece is 10-20mm, the thickness of the carbon source layer is 4-8mm, and the diameters of the catalyst piece and the carbon source layer are 30-40 mm.
Further, the seed crystal is cut into slices with the thickness not greater than 2mm by adopting diamond with the particle size of 2-10 mm. In the conventional seed crystal method for synthesizing gem grade diamond, high-quality industrial diamond is generally adopted, hexahedral and octahedral poly-shaped crystal forms are taken as main materials, the whole gem grade diamond is inlaid in a crystal bed according to a specific size, and simultaneously, seed crystals with a certain particle size are inlaid on the crystal bed according to different production requirements in a certain amount and distribution. And the (111) or (100) surface is upward as a growth surface for the epitaxial growth of the crystal; the particle size of the commonly used seed crystal is 10/12, 12/14, 14/16, 16/18, 18/20/, 20/25, 25/30, 30/35, 35/40 and 40/45.
Further, the arrangement mode of the seed crystal is specifically as follows: the method comprises the steps of inlaying a large circular seed crystal with the diameter of 2mm at the center of a crystal bed, evenly inlaying four small circular seed crystals with the diameter of 1mm on the crystal bed around the large circular seed crystal, and enabling the distance between the small circular seed crystal and the large circular seed crystal to be 5 mm.
The inner cavity of the synthetic diamond is generally a cylinder, the crystal bed for embedding the seed crystal is a round surface, the seed crystal can be arranged on the round surface in various different ways, the seed crystal can be arranged irregularly or randomly, but the synthetic effect is unstable, the yield is low, the growth process is not easy to control, and the benefit is very low. The seed crystal points are arranged in a geometrically symmetric cross-synergetic mode, the seed crystal points are firstly symmetrical in inner circles, are centrosymmetric and are point-to-point called as basic basis, and meanwhile, the production distribution phenomenon of crops and garden flowers is referred to, so that the synthetic cavity and raw materials can be fully utilized, the growth promotion and growth inhibition are coordinated and unified, the growth speed is convenient to control, and the corresponding growth rule is better met.
The gem-grade colorless diamond is synthesized into a special internal structure, the seed crystal only provides a growth surface for crystal epitaxial growth, and the whole grain seed crystal is arranged in the seed crystal, so that the waste is avoided; however, in the conventional synthesis method, the seed crystal has fine granularity, large processing difficulty and less waste, and the whole hexahedral and octahedral poly-shaped diamond is inlaid in the seed crystal. Thus, there is a problem that the thickness of the seed bed in the synthesized structure is generally fixed and has special requirements, and the maximum grain size of the seed crystal which can be inlaid is generally about 10/12 grain size, so that the research and production of the seed crystal with a larger growth surface in the production practice are limited to a certain extent. In order to meet the growth requirement, an epitaxial growth surface with a larger size (a larger crystal seed method) is used in the synthesis of colorless diamond, high-quality diamond with the grain size of 2-10mm is cut into slices with different thicknesses of 0-2mm layer by a laser cutting process, the thickness of the slice meets the requirement of crystal bed inlaying, and the slice can be secondarily processed into slices with different shapes according to the requirement.
The invention has the beneficial effects that: the gem-grade colorless diamond is synthesized according to the special seed crystal method, the space of a synthesis cavity and raw materials can be fully utilized, the growth promotion and the growth inhibition are coordinated and unified, the growth speed is convenient to control, the corresponding growth rule is better met, the limitation that the size of the seed crystal cannot be larger in the synthesis of the gem-grade colorless diamond is broken through the flake-shaped large seed crystal method creatively, the growth speed of the crystal can be further improved, the larger-granularity gem-grade colorless diamond can be synthesized in a shorter time, the waste of the seed crystal is reduced at the same time, and more possibilities are provided for scientific research experiments and production practice. Meanwhile, the core column with a multilayer penetrating structure is adopted, the smoothness of the synthetic block is effectively guaranteed, pressure transmission, sealing and heat preservation are carried out through the pyrophyllite hollow block and the pyrophyllite ring, the powder pressure carbon tube improves the current stability, the uniformity of a temperature field is guaranteed, the synthetic block is stable and reliable in structure, the heat preservation effect is good, and the synthetic process is guaranteed to be carried out smoothly. Meanwhile, the multi-layer permeation assembly mode is adopted, so that the nitrogen removal efficiency is effectively improved, and the purity of the product is higher. Preferably, the product quality and the nitrogen removal efficiency can be further effectively improved by adopting FeMnCo catalyst sheets, graphite with the purity of 99 percent as a carbon source and Cu foil with the thickness of 0.03mm as a nitrogen removal agent.
The gem-grade colorless diamond synthesized by the special seed crystal method is easy to produce, stable in structure, good in synthesis effect, high in yield and strong in practicability, and the product quality is guaranteed, so that the gem-grade colorless diamond is worthy of further research and application.
Drawings
FIG. 1 is a schematic diagram of the structure of a composite block of the present invention;
FIG. 2 shows an exemplary arrangement of 12 seed crystals according to the present invention;
FIG. 3 is a graph of power and pressure for a prior art synthetic gem grade colorless diamond;
FIG. 4 is a graph of power and pressure for a synthetic gem-grade colorless diamond according to the present invention; in the figure: 1. pyrophyllite block, 2, pyrophyllite ring, 3, crystal bed, 4, Cu foil, 5, carbon source, 6, dolomite sheet, 7, carbon paper, 8, conductive plug, 9, magnesia lining, 10, carbon tube, 11, dolomite outer lining, and 12, catalyst sheet.
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 specific structure of the synthetic block in the following examples is described in detail in patents CN205925638U and CN 106215808A.
Example 1
A method for synthesizing gem-grade colorless diamond by a seed crystal method, which comprises the following steps:
(1) FeMnCo is used as a catalyst sheet, graphite with the purity of 99% is used as a carbon source, a Cu foil is used as a nitrogen removal agent, the thickness of the Cu foil is 0.03mm, a seed crystal is inlaid on a crystal bed, the upper end face of the seed crystal is flush with the upper end face of the crystal bed, and a synthetic block is assembled according to the figure 1;
(2) then starting high-temperature high-pressure synthesis, uniformly increasing the pressure to 65MPa within 200s, then keeping the pressure at 2500s, and uniformly increasing the pressure to 95MPa within 100 s; heating power is increased to 3.0KW at a constant speed within 400s, then is kept at 2500s, and is increased to 5.5KW at a constant speed within 700 s; and (3) preserving heat and maintaining pressure under the pressure of 95MPa and the heating power of 5.5KW until the heating power and the pressure of 1 ten thousand seconds are gradually reduced and then gradually increased to 5.5KW and 95MPa, wherein the total synthesis time is 90 ten thousand seconds, and the gem-grade colorless diamond with the particle size of 3-5 mm is obtained.
Wherein, the specific process that the heating power and the pressure are gradually reduced and then gradually increased from the heat preservation and pressure maintaining to the 1 ten thousand seconds is as follows:
setting parameter time nodes on a computer from 1 ten thousand seconds as T1, T2, T3, T4, T5, T6, T7, T8, T9 and T10 respectively, wherein T1=1 ten thousand seconds, T2=10 ten thousand seconds, T3=20 ten thousand seconds, T4=30 ten thousand seconds, T5=40 ten thousand seconds, T6=50 ten thousand seconds, T7=60 ten thousand seconds, T8=70 ten thousand seconds, T9=80 ten thousand seconds, T10=90 ten thousand seconds, and an equal difference sequence Wn = W1+ n d, d =0.01, -0.02, -0.03, -0.04, -0.05 corresponding to five time nodes from T1 to T5; pn = P1+ n × d, d = -0.1, -0.2, -0.3, -0.4, -0.5; corresponding to five time nodes from T6 to T10, the power pressure amplitude of rise conforms to an arithmetic progression Wn = W1+ n × d, d =0.01, 0.02, 0.03, 0.04 and 0.05; pn = P1+ n × d, d =0.1, 0.2, 0.3, 0.4, 0.5, W1=5.5KW, P1=95MPa, n =1, 2, 3, 4, 5.
Further, the arrangement mode of the seed crystal is specifically one of the following: (1) the seed crystal A and the seed crystal B are circumferentially and crossly arranged to form a circle or a regular polygon; (2) the seed crystals A are circumferentially arranged to form a circular or regular polygon, and the center of the shape enclosed by the seed crystals A is provided with the seed crystals C; (3) the seed crystal A and the seed crystal B are circumferentially and crossly arranged to form a circle or a regular polygon, the seed crystal C is arranged at the center of the shape enclosed by the seed crystal A and the seed crystal B, wherein the size or the shape of the seed crystal A is different from that of the seed crystal B, the size or the shape of the seed crystal C is different from that of the other seed crystal or the two seed crystals, the size or the shape of the seed crystal C can be the same as that of the other seed crystal or the two seed crystals, and the seed crystals A, B, C are all circles or regular polygons. The arrangement of the seed crystals is preferably 12 arrangements in fig. 2. The method is characterized in that the crystal seed points are arranged in a geometrically symmetric cross synergistic manner, firstly, the inner circle lines are symmetric, the centers are symmetric, the point pairs are called as basic basis on the premise of meeting the size of a crystal bed, meanwhile, the production distribution phenomenon of crops and garden flowers is referred to, the polycrystalline seed arrangement is further optimized, meanwhile, the crystal seeds with different particle sizes are distributed on the same crystal bed in a cross synergistic manner, and the distribution mode schematic diagram is shown as 2 (the crystal bed is in a wafer shape, and the schematic diagram is a crystal bed top view).
Specifically, the arrangement of the 1 st seed crystal is as follows: the seed crystal A is arranged in a regular quadrangle, the grain diameters of the seed crystal A and the seed crystal C are both circles with the diameter of 1mm, and the distance between every two adjacent seed crystals is equal and is 3 mm.
The seed crystal arrangement mode of the 2 nd seed crystal is as follows: seed crystal A and seed crystal B circumference are alternately arranged for positive quadrangle, and positive quadrangle's center department is equipped with seed crystal C, and center seed crystal C is the circular of diameter 4mm, and seed crystal A is the circular of diameter 2mm, and seed crystal B is the circular of diameter 1mm, and seed crystal C and seed crystal B interval are 3mm, and seed crystal C and seed crystal A are 2 mm.
The 3 rd seed arrangement mode is as follows: the seed crystal A is arranged in a regular quadrangle, the seed crystal A is located at four vertexes of the regular quadrangle, the center of the regular quadrangle is provided with the seed crystal C, the seed crystal A is circular with the diameter of 1mm, the seed crystal C is circular with the diameter of 2mm, and the distance between the seed crystal C and the seed crystal A is 5 mm.
The 4 th seed crystal arrangement mode is as follows: seed crystal A is circular arranging, and circular center department is equipped with seed crystal C, and seed crystal A is diameter 2 mm's circular, and seed crystal C is the regular hexagon of particle diameter 3mm, the interval 3mm between seed crystal C and the seed crystal A.
The 5 th seed crystal is arranged in the following way: the seed crystal A is arranged in a regular triangle and is positioned at three vertex points of the triangle, the center of the triangle is provided with the seed crystal C, the seed crystal A is a regular hexagon with the particle size of 3mm, the seed crystal C is a circle with the diameter of 2mm, and the distance between the seed crystal C and the seed crystal A is 3 mm.
The 6 th seed crystal arrangement mode is as follows: the seed crystal A is arranged in a regular quadrangle, the seed crystal A is located at four vertexes of the regular quadrangle, the center of the quadrangle is provided with the seed crystal C, the seed crystal A is a regular hexagon with the grain diameter of 3mm, the seed crystal C is a circle with the diameter of 2mm, and the distance between the seed crystal C and the seed crystal A is 3 mm.
The 7 th seed crystal arrangement mode is as follows: seed crystal A is circular arranging, and circular center department is equipped with seed crystal C, and seed crystal A is diameter 2 mm's circular, and seed crystal C is the regular quadrangle of particle diameter 3mm, the interval 3mm between seed crystal C and the seed crystal A.
The 8 th seed crystal arrangement mode is as follows: the seed crystal A is arranged in a regular triangle and is positioned at three vertex points of the triangle, the center of the triangle is provided with the seed crystal C, the seed crystal A is a regular quadrangle with the grain diameter of 3mm, the seed crystal C is a circle with the diameter of 2mm, and the distance between the seed crystal C and the seed crystal A is 2.5 mm.
The 9 th seed crystal arrangement mode is as follows: the seed crystal A is arranged in a regular quadrangle, the seed crystal A is located at four vertexes of the regular quadrangle, the center of the quadrangle is provided with the seed crystal C, the seed crystal A is a regular quadrangle with the grain diameter of 3mm, the seed crystal C is a circle with the diameter of 2mm, and the distance between the seed crystal C and the seed crystal A is 2.5 mm.
The 10 th seed crystal arrangement mode is as follows: the seed crystal A and the seed crystal B are arranged in a circumferential cross mode to form a regular quadrangle, the seed crystal A and the seed crystal B are respectively located at four vertexes of the regular quadrangle, the seed crystal A is a regular quadrangle with the grain size of 3mm, the seed crystal B is a regular hexagon with the grain size of 3mm, and the distance between the seed crystal A and the seed crystal B is 4 mm.
The 11 th seed crystal arrangement mode is as follows: the seed crystal A and the seed crystal B are circumferentially and alternately arranged to form a regular triangle, the seed crystal A is positioned at three vertexes of the triangle, the seed crystal A is a regular hexagon with the particle size of 3mm, the seed crystal B is a circle with the diameter of 2mm, and the distance between the seed crystal A and the seed crystal B is 1.5 mm.
The 12 th seed crystal arrangement mode is as follows: the seed crystal A and the seed crystal B are circumferentially and alternately arranged to form a regular quadrangle, the seed crystal A is positioned at four vertexes of the quadrangle, the seed crystal A is a regular quadrangle with the grain diameter of 3mm, the seed crystal B is a circle with the diameter of 2mm, and the distance between the seed crystal A and the seed crystal B is 1.5 mm.
Wherein the thickness of the crystal seeds with the grain diameter less than or equal to 1mm is 0.5-1mm, the thickness of the crystal seeds with the grain diameter of 2-5mm is 1-2mm, and the thickness of the corresponding crystal seeds is equal to the embedding depth.
The gem-grade colorless diamond synthesis is carried out in a 3 rd seed arrangement mode, namely the seed arrangement mode specifically comprises the following steps: the method comprises the steps of inlaying a large circular seed crystal (seed crystal C) with the diameter of 2mm at the center of a crystal bed, evenly inlaying four small circular seed crystals (seed crystals A) with the diameter of 1mm on the crystal bed around the large circular seed crystal, and enabling the distance between the small circular seed crystals and the large circular seed crystals to be 5 mm.
Furthermore, the thickness of the catalyst piece is 10-20mm, the thickness of the carbon source layer is 4-8mm, and the diameters of the catalyst piece and the carbon source layer are 30-40 mm.
The invention firstly adopts a variable control method, controls power or pressure parameters to be consistent with the conventional process, independently changes a variable to confirm the influence of the variable under independent factors, and provides a basis for the next optimization test; note: in all the following experiments, the temperature-pressure synthesis process curve of the conventional gem-grade colorless diamond with the granularity of 3-5 mm and the temperature-pressure synthesis process curve of 90 ten thousand seconds are taken as an example, the synthesis power W =5.5KW and the gauge pressure P =95MPa are set. The design tests are shown in table 1 below.
TABLE 1 setting of pressure or Power Single factor variables
On the premise that other conditions (a cubic hydraulic press, an intelligent computer control system, a synthetic assembly structure, a block mounting environment and the like) are relatively stable and unchanged, each group of the A-K test groups respectively and stably synthesizes 10 blocks, the average value of 10 blocks in each group is taken, and the test phenomenon is shown in the following table 2.
TABLE 2 weight, chroma and clarity results for gem grade colorless diamonds under single factor variation of pressure or power
The group A test is a control group, and the combination of test phenomena can show that the group C and the group D obtain better test effects under the condition of simply changing the power trend, wherein the group D has the best effect; under the condition of simply changing the pressure trend, the J experiment group and the K experiment group obtain better experiment effects, wherein the K experiment group has the best effect. Although the weight of the crystals in the B-K experimental group is reduced to different degrees, the weight of the C, D, J, K experimental group is slightly reduced, the improvement of the chroma and the cleanliness is obvious, and the overall effect is good.
According to the preferable results, the invention performs a second round of cross test of combining double variables of power and pressure, the test is performed under the same conditions of the above test, 10 blocks are respectively synthesized in each group of 1-4 test groups, and the average value of 10 blocks in each group is taken, and the results are shown in the following table 3.
TABLE 3 weight, chroma and clarity results for gem grade colorless diamonds in a cross-over test combining power and pressure bivariates
As shown in Table 3, the test results are in accordance with the theory, and the second round of test groups 1 to 4 can obtain better expected effect, wherein the effect of test group No. 4 is the best, namely T1-T10, W is firstly decreased and then increased, the specific change condition of the heating power is 5.47 KW,5.44 KW,5.41 KW,5.38 KW,5.35 KW,5.38 KW,5.41 KW,5.44 KW,5.47 KW,5.5 KW, P is firstly decreased and then increased, and the specific change condition of the synthetic pressure is as follows: 94.5MPa,94.0MPa,93.5MPa,93.0MPa,92.5MPa, 93.0MPa, 93.5MPa,
94.0MPa, 94.5MPa and 95MPa, and in the longer synthesis time process, the power pressure is reduced and then increased, so that the electric energy is saved, the workload of the cubic press caused by overhigh pressure is reduced, the weight reduction range is small, the chromaticity and the cleanliness are obviously improved, and the economic benefit is high.
Claims (4)
1. A method for synthesizing gem-grade colorless diamond by a seed crystal method, which is characterized by comprising the following steps:
(1) the method comprises the following steps of (1) inlaying a seed crystal on a crystal bed, wherein the seed crystal is used as a catalyst sheet, graphite is used as a carbon source, a Cu foil is used as a nitrogen removal agent, the upper end face of the seed crystal is flush with the upper end face of the crystal bed, a synthetic block is assembled, and the seed crystal is cut into a sheet with the thickness not greater than 2mm by adopting diamond with the particle size of 2-10 mm;
(2) then starting high-temperature high-pressure synthesis, uniformly increasing the pressure to 60-70 MPa within 0-200s, then keeping the pressure for 2000-3000 s, and uniformly increasing the pressure to 90-100 MPa within 80-120 s; heating power is increased to 2.5-3.5 KW at a constant speed for 0-400s, then the temperature is kept for 2000-3000 s, and then the heating power is increased to 5-6 KW at a constant speed for 500-800 seconds; after the heat preservation and pressure maintaining are carried out for 1 ten thousand seconds, the heating power and the pressure are gradually reduced firstly and then gradually increased until the heating power and the pressure are recovered to the highest value, the total synthesis time is 90 ten thousand seconds to 100 ten thousand seconds, and the gem-grade colorless diamond with the grain diameter of 3-5 mm is obtained, and the specific process that the heating power and the pressure are gradually reduced firstly and then gradually increased when the heat preservation and pressure maintaining are carried out for 1 ten thousand seconds is as follows:
setting time nodes from 1 ten thousand seconds as T1, T2, T3, T4, T5, T6, T7, T8, T9 and T10 respectively, wherein T1=1 ten thousand seconds, T2=10 ten thousand seconds, T3=20 ten thousand seconds, T4=30 ten thousand seconds, T5=40 ten thousand seconds, T6=50 ten thousand seconds, T7=60 ten thousand seconds, T8=70 ten thousand seconds, T9=80 ten thousand seconds, T10=90 ten thousand seconds, and corresponding power and pressure reduction amplitude coincidence with five time nodes from T1 to T5 is equal difference decreasing series Wn = W1+ n + d, d = -0.02, -0.03; pn = P1+ n × d, d = -0.4, -0.5, W1=5.5KW, P1=95 MPa; corresponding to five time nodes from T6 to T10, the power pressure amplitude of rise conforms to an arithmetic difference increasing sequence Wn = W1+ n × d; d =0.02, W1=5.4 KW; d =0.03, W1=5.35 KW; pn = P1+ n × d; d =0.4, P1=93 MPa; d =0.5, P1=92.5 MPa; n =1, 2, 3, 4, 5.
2. The method for synthesizing gem grade colorless diamonds according to claim 1, characterized in that the gem grade colorless diamonds are one of the following: (1) the seed crystal A and the seed crystal B are circumferentially and crossly arranged to form a circle or a regular polygon; (2) the seed crystals A are circumferentially arranged to form a circular or regular polygon, and the center of the shape enclosed by the seed crystals A is provided with the seed crystals C; (3) the seed crystal A and the seed crystal B are circumferentially and crossly arranged to form a circle or a regular polygon, the seed crystal C is arranged at the center of the shape enclosed by the seed crystal A and the seed crystal B, the seed crystal A and the seed crystal B are different in size or shape, and the seed crystal A, B, C is a circle or a regular polygon.
3. The method for synthesizing gem-grade colorless diamond through the seed crystal method according to claim 1, wherein the thickness of the catalyst piece is 10-20mm, the thickness of the carbon source layer is 4-8mm, and the diameters of the catalyst piece and the carbon source layer are 30-40 mm.
4. A method of seeded synthesis of gemstone-grade colorless diamond according to claim 1 or 2, wherein the seeds are arranged in a manner which is in particular: the method comprises the steps of inlaying a large circular seed crystal with the diameter of 2mm at the center of a crystal bed, evenly inlaying four small circular seed crystals with the diameter of 1mm on the crystal bed around the large circular seed crystal, and enabling the distance between the small circular seed crystal and the large circular seed crystal to be 5 mm.
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| US20070036896A1 (en) * | 2005-08-09 | 2007-02-15 | Chien-Min Sung | Mosaic diamond substrates |
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| CN205925638U (en) * | 2016-08-18 | 2017-02-08 | 中南钻石有限公司 | Colourless diamond of synthetic IIa type of cubic apparatus is with synthetic block structure |
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