Method for preparing CVD blue gradient diamond based on lead electron irradiation carrier

Abstract

The invention relates to a method for preparing a CVD (Chemical Vapor Deposition) blue gradient diamond based on a lead electron irradiation carrier, and aims to solve the problem that the existing color diamond cracks in the subsequent processing of the diamond by controlling the doping concentration of impurity gas in the growth process of the diamond and regulating and controlling the color. The preparation method comprises the following steps: S1, pretreating a diamond seed wafer; s2, performing plasma etching on the seed crystal; s3, methane and hydrogen are introduced into the vacuum cavity, and microwave plasma chemical vapor deposition growth is carried out; s4, obtaining a diamond blank; s5, polycrystals on the surface of the diamond blank are cut off; s6, the cut blank is subjected to HPHT treatment; and S7, the diamond blank is placed on the bottom plate of the irradiation carrier, and the shielding cavity and the diamond blank are irradiated through high-energy electron beams. According to the method, the diamond blank is placed in the specially-made irradiation carrier, partial area irradiation of the diamond blank is achieved, the blue diamond with the gradually-changed color is prepared, and the purity degree of the diamond is improved.

Description

Technical Field

[0001] The invention belongs to the field of diamond color modification, and particularly relates to a method for preparing CVD blue gradient diamond based on a lead electron irradiation carrier. Background Art

[0002] The name of the diamond mineral is diamond. It is a single crystal mineral produced in a high temperature and high pressure environment deep in the earth. Carbon is its main component. Pure diamond is colorless and transparent. When some defects or element doping occur during the growth of diamond due to environmental changes, it often presents a variety of colors, such as red, green, pink, blue, yellow, etc. Diamond has a high dispersion, so the cut diamond shows a colorful fire under the light. With the improvement of people's living standards, not only the demand for white diamonds has increased, but also the demand for high-quality colored diamonds has greatly increased. However, the more harsh growth environment and extremely low production have made the price of colored diamonds very expensive.

[0003] At present, the main methods for synthesizing diamonds are HPHT (High Pressure High Temperature) and CVD (Chemical Vapor Deposition). The CVD method has the advantages of simple growth equipment, fast growth rate, and high crystal growth, and is widely used in industrial diamond production. With the increasing demand for diamonds and the continuous development of synthetic diamond technology, synthetic diamonds have entered the jewelry market with their advantages such as beauty that is not inferior to natural diamonds, low cost, high yield, low carbon and environmental protection, and are sought after by the public.

[0004] At present, the preparation of colored diamonds is mainly pure color, and the color is relatively single. In order to improve the ornamental value of colored diamonds, some researchers have carried out the synthesis of multi-color diamonds. For diamonds grown by the MPCVD method, whether it is gradient pink diamonds or gradient blue diamonds, the color is regulated by controlling the concentration of impurity gas doping during the growth of diamonds. This method has high requirements for the airtightness of the equipment and can easily lead to obvious stratification of diamonds, cracking in the subsequent processing of diamonds, reducing the yield of diamonds and affecting their prices. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the existing colored diamonds are easily stratified by controlling the doping concentration of impurity gases during the growth of diamonds to adjust the color, and cracking occurs during the subsequent processing of diamonds, and to provide a method for preparing CVD blue gradient diamonds based on a lead electron irradiation carrier.

[0006] The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier of the present invention is implemented by the following steps:

[0007] Step S1, placing a HPHT (high-temperature and high-pressure method) diamond seed crystal in a mixed acid for pretreatment, and washing to obtain a pretreated seed crystal;

[0008] Step S2, placing the pretreated seed crystal into a vacuum chamber of the MPCVD device, introducing hydrogen or oxygen after evacuation, and using hydrogen or oxygen to excite plasma to perform plasma etching on the pretreated seed crystal to obtain an etched seed crystal;

[0009] Step S3, introducing methane and hydrogen into the vacuum chamber, controlling the volume concentration of methane to be 2% to 10%, the volume concentration of hydrogen to be 90% to 98%, controlling the growth temperature to be 700 to 1000° C., and the pressure to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth;

[0010] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank;

[0011] Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a cut blank;

[0012] Step S6, performing HPHT treatment on the cut blank at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain a diamond blank;

[0013] Step S7, placing a diamond blank on the bottom plate of an irradiation carrier, with a portion of the diamond blank located in the shielding cavity and another portion of the diamond blank exposed outside the shielding cavity, irradiating the shielding cavity and the diamond blank with a high-energy electron beam, controlling the electron energy of the high-energy electron beam irradiation to be 3-6 MeV, and the irradiation power to be 5-25 kW, to obtain a CVD blue gradient diamond;

[0014] The irradiation carrier is made of metal lead and comprises a bottom plate and a shielding cavity. The shielding cavity is arranged on the upper surface of the bottom plate, and the side of the shielding cavity is open.

[0015] Compared with the prior art, the method for preparing CVD blue gradient diamond based on lead electron irradiation carrier of the present invention has the following beneficial effects:

[0016] The present invention places a diamond blank in a special irradiation carrier to irradiate a part of the diamond blank, control the distribution of GR1 color centers, and prepare a blue diamond with a color gradient. The method is simple to operate, does not require the gas components to be regulated during the diamond growth process, can effectively reduce impurities and defects introduced into the diamond due to changes in the growth environment, improve the purity of the diamond, and avoid diamond growth stratification leading to diamond breakage due to uneven stress during processing, which affects the yield. Compared with colored diamonds with a single color, the color layers of the gradient blue diamond are rich and beautiful, and are more suitable for the inlay of high-end luxury jewelry or artistic jewelry. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a blue gradient diamond processing flow chart;

[0018] Figure 2 This is a schematic diagram of the irradiation and processing of the diamond blank prepared by the present invention;

[0019] Figure 3 Schematic diagram of the structure of the irradiation vehicle. DETAILED DESCRIPTION

[0020] Specific implementation method 1: The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier in this implementation method is implemented according to the following steps:

[0021] Step S1, placing a HPHT (high-temperature and high-pressure method) diamond seed crystal in a mixed acid for pretreatment, and washing to obtain a pretreated seed crystal;

[0022] Step S2, placing the pretreated seed crystal into a vacuum chamber of the MPCVD device, introducing hydrogen or oxygen after evacuation, and using hydrogen or oxygen to excite plasma to perform plasma etching on the pretreated seed crystal to obtain an etched seed crystal;

[0023] Step S3, introducing methane and hydrogen into the vacuum chamber, controlling the volume concentration of methane to be 2% to 10%, the volume concentration of hydrogen to be 90% to 98%, controlling the growth temperature to be 700 to 1000° C., and the pressure to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth;

[0024] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank;

[0025] Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a cut blank;

[0026] Step S6, performing HPHT treatment on the cut blank at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain a diamond blank;

[0027] Step S7, placing a diamond blank on the bottom plate of an irradiation carrier, with a portion of the diamond blank located in the shielding cavity and another portion of the diamond blank exposed outside the shielding cavity, irradiating the shielding cavity and the diamond blank with a high-energy electron beam, controlling the electron energy of the high-energy electron beam irradiation to be 3-6 MeV, and the irradiation power to be 5-25 kW, to obtain a CVD blue gradient diamond;

[0028] The irradiation carrier is made of metal lead and comprises a bottom plate and a shielding cavity. The shielding cavity is arranged on the upper surface of the bottom plate, and the side of the shielding cavity is open.

[0029] This embodiment uses the MPCVD method to prepare diamond blanks. During the growth of the blanks, the temperature, microwave energy and pressure are normally controlled. The crystal growth gas only needs to be introduced into hydrogen and methane (oxygen can be selected according to special etching needs), and no other impurity gases need to be introduced. After the crystal is grown, all polycrystalline needs to be removed, and blanks with no internal stratification and basically no impurities are selected for HPHT treatment to remove brown. The processed blank is placed in a lead irradiation carrier, and the carrier is placed on an electron irradiation platform for electron irradiation. After the irradiation is completed, the blank is processed into a finished diamond with a blue gradient according to demand. This method uses lead to block a part of the electron beam from irradiating the diamond blank, thereby achieving coarse control of the distribution position of the GR1 color center to form a diamond with a color gradient. This method solves the obvious color stratification of the gradient blue diamond grown by controlling the growth gas, reduces production costs, improves the yield rate, enriches the beauty of the diamond, and has good repeatability and stability.

[0030] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the mixed acid described in step S1 is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. The HPHT diamond seed wafer is placed in the mixed acid, heated to 250-300°C and soaked for 2-3 hours, and then ultrasonically cleaned using anhydrous ethanol and pure water in turn.

[0031] Specific implementation method three: The difference between this implementation method and specific implementation method one or two is that in step S2, the plasma etching time is controlled to be 30 to 60 minutes.

[0032] Specific implementation method 4: This implementation method is different from any one of specific implementation methods 1 to 3 in that the microwave power is controlled in the range of 3 to 6 kW in step S3.

[0033] Specific embodiment five: The difference between this embodiment and any one of specific embodiments one to four is that in step S3, the volume concentration of methane is controlled to be 4% to 6%, the volume concentration of hydrogen is controlled to be 94% to 96%, the growth temperature is controlled to be 750 to 900°C, and the pressure is controlled to be 11 to 13 kPa for microwave plasma chemical vapor deposition growth.

[0034] Specific implementation method 6: The difference between this implementation method and any one of specific implementation methods 1 to 5 is that the growth thickness of the diamond blank in step S4 is 5 to 7 mm.

[0035] Specific embodiment 7: This embodiment is different from any one of specific embodiments 1 to 6 in that the HPHT treatment time in step S6 is 2 to 3 hours.

[0036] Specific implementation example eight: This implementation example is different from any one of specific implementation examples one to seven in that in step S7, the electron energy of the high energy electron beam irradiation is controlled to be 4 to 5 MeV, and the irradiation power is controlled to be 12 to 15 kW.

[0037] Specific embodiment 9: This embodiment is different from specific embodiment 8 in that the time for irradiating the diamond blank with a high-energy electron beam is 3 to 5 hours.

[0038] Specific implementation example ten: This implementation example is different from any one of specific implementation examples one to nine in that in step S7, the CVD blue gradient diamond is cut and ground.

[0039] In this embodiment, the diamond is cut in a radiant, emerald or princess cut to make the color of the diamond more obvious.

[0040] Embodiment 1: The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier in this embodiment is implemented according to the following steps:

[0041] Step S1, selecting a HPHT diamond seed crystal with a flat surface, no obvious impurities under a 20x microscope, and a crystal face of (100), heating the HPHT diamond seed crystal to 280° C. and soaking it for 2 hours in an acid solution, wherein the acid solution is a mixture of 98% sulfuric acid and 67% nitric acid in a volume ratio of 3:1, and then ultrasonically cleaning it with alcohol and pure water for 30 minutes in sequence to obtain a pretreated seed crystal;

[0042] Step S2, placing the pretreated seed crystal into the vacuum chamber of the MPCVD device, introducing hydrogen after evacuation, and when the temperature reaches 750° C., the microwave energy is 3 kW, and the pressure is 10 kPa, the hydrogen excites plasma to perform plasma etching on the pretreated seed crystal for 30 minutes to obtain an etched seed crystal;

[0043] Step S3, introducing methane and hydrogen into the vacuum chamber, controlling the volume concentration of methane to 5% and the volume concentration of hydrogen to 95%, without doping with other gases, controlling the growth temperature to 800°C, the microwave energy to 5kW, and the pressure to 12kPa for microwave plasma chemical vapor deposition growth, and growing a 7×7mm diamond blank for 300h;

[0044] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced, the microwave source and the vacuum pump are turned off, air is filled into the chamber to make the pressure in the chamber close to the atmospheric pressure, and the diamond blank is taken out;

[0045] Step S5, using a laser cutting machine to cut off the black polycrystalline on the surface of the diamond blank, and cutting into blocks to obtain the cut blank;

[0046] Step S6, selecting a nearly pure blank with no color stratification on the side and internal impurities that cannot be observed under a 20x microscope from the cut blanks, placing the blanks in a six-sided top press, and subjecting the cut blanks to HPHT treatment for 2.5 hours at a temperature of 900° C. and a pressure of 1000 Pa to obtain a diamond blank without brown tones;

[0047] Step S7, placing the diamond blank on the bottom plate of the irradiation carrier and at the side opening, so that a part of the diamond blank is located in the shielding cavity and the other part of the diamond blank is exposed outside the shielding cavity, using a high-energy electron beam to vertically irradiate the shielding cavity and the diamond blank downward, controlling the electron energy of the high-energy electron beam to be 4.5 MeV, the irradiation power to be 15 kW, and the irradiation time to be 4 hours, using a laser to cut out the rough outline of the diamond, and then manually cutting and polishing the other small faces to obtain a CVD blue gradient diamond;

[0048] The material of the irradiation carrier is metal lead. The irradiation carrier includes a bottom plate 1 and a shielding cavity 2. The shielding cavity 2 is arranged on the upper surface of the bottom plate 1. The shielding cavity 2 is composed of three side wall plates 2-1 and a top plate 2-2. The three side wall plates 2-1 are vertically arranged on the bottom plate 1, and the top plate 2-2 is covered on the top (top edge) of the three side wall plates 2-1 to enclose the shielding cavity 2. One side of the shielding cavity 2 is open.

[0049] This embodiment designs a carrier for diamond irradiation. Through the lead carrier, the position of the hole formed by the electron irradiation inside the diamond is effectively controlled. Since the electron does not move in a straight line after entering the interior of the diamond blank, a gradient effect can be formed at the shielding boundary of the carrier, and the color is not completely layered. The method for preparing CVD blue gradient diamond is simple to operate. In addition to hydrogen and methane (oxygen can be added during the etching process if necessary), there is no need to add other gases containing elements such as nitrogen or boron, which reduces the preparation cost of the gradient blue diamond, and also avoids the situation that the diamond is layered due to the change of gas components during the diamond growth process, the internal stress of the diamond increases, and the risk of diamond breakage increases during the processing. Therefore, the gradient blue diamond prepared by this method has good repeatability and stability, small differences within and between batches, simple process flow, high repetition rate, good stability, low cost, and has high market application value.

[0050] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing CVD blue gradient diamond based on a lead electron irradiated carrier, characterized in that The method for preparing CVD blue gradient diamond is achieved by the following steps: Step S1, placing the HPHT diamond seed crystal in mixed acid for pretreatment, and washing to obtain a pretreated seed crystal; Step S2, placing the pretreated seed crystal into a vacuum chamber of the MPCVD device, introducing hydrogen or oxygen after evacuation, and using hydrogen or oxygen to excite plasma to perform plasma etching on the pretreated seed crystal to obtain an etched seed crystal; Step S3, introducing methane and hydrogen into the vacuum chamber, controlling the volume concentration of methane to be 2% to 10%, the volume concentration of hydrogen to be 90% to 98%, controlling the growth temperature to be 700 to 1000° C., and the pressure to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth; Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank; Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a cut blank; Step S6, performing HPHT treatment on the cut blank at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain a diamond blank; Step S7, placing a diamond blank on the bottom plate of an irradiation carrier, with a portion of the diamond blank located in the shielding cavity and another portion of the diamond blank exposed outside the shielding cavity, irradiating the shielding cavity and the diamond blank with a high-energy electron beam, controlling the electron energy of the high-energy electron beam irradiation to be 3-6 MeV, and the irradiation power to be 5-25 kW, to obtain a CVD blue gradient diamond; The irradiation carrier is made of metal lead and comprises a bottom plate and a shielding cavity. The shielding cavity is arranged on the upper surface of the bottom plate, and the side of the shielding cavity is open.

2. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 1, characterized in that The mixed acid described in step S1 is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:

1. The HPHT diamond seed wafer is placed in the mixed acid, heated to 250-300° C. and soaked for 2-3 hours, and then ultrasonically cleaned with anhydrous ethanol and pure water in turn.

3. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 1, characterized in that In step S2, the plasma etching time is controlled to be 30 to 60 minutes.

4. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 1, characterized in that In step S3, the microwave power is controlled in the range of 3-6 kW.

5. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 1, characterized in that In step S3, the volume concentration of methane is controlled to be 4% to 6%, the volume concentration of hydrogen is controlled to be 94% to 96%, the growth temperature is controlled to be 750 to 900° C., and the pressure is controlled to be 11 to 13 kPa for microwave plasma chemical vapor deposition growth.

6. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 1, characterized in that The growth thickness of the diamond blank in step S4 is 5 to 7 mm.

7. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 1, characterized in that The HPHT treatment time in step S6 is 2 to 3 hours.

8. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 1, characterized in that In step S7, the electron energy of the high energy electron beam irradiation is controlled to be 4-5 MeV, and the irradiation power is controlled to be 12-15 kW.

9. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 8, characterized in that The time for irradiating the diamond blank with a high-energy electron beam is 3 to 5 hours.

10. The method for preparing CVD blue gradient diamond based on lead electron irradiation carrier according to claim 1, characterized in that In step S7, the CVD blue gradient diamond is cut and ground.

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