Method for preparing yellow artificial diamond by taking hair as carbon source and nitrogen source

Abstract

The invention discloses a method for preparing a yellow artificial diamond by taking hair as a carbon source and a nitrogen source, and relates to the technical field of artificial diamond preparation. The method comprises the following steps that 1, hair is placed in a closed pyrolyzing furnace and pyrolyzed in the oxygen atmosphere at the temperature of 1250-1300 DEG C, the ratio of the hair to oxygen is 1 g: (1.2-1.5) L, and pyrolyzed gas is obtained; 2) sequentially removing sulfur oxide gas and water vapor in the pyrolysis gas; 3, the seed crystal is placed in an MPCVD cavity for diamond workblank growth, nitrogen and carbon elements in the hair are converted into gaseous products which can be directly used for preparing the yellow artificial diamond through the MPCVD method by controlling the hair pyrolysis condition, and the nitrogen element can be effectively doped into crystal lattices in combination with the specific diamond workblank growth technology.

Description

Technical Field

[0001] The present invention relates to the technical field of synthetic diamond preparation, and particularly relates to a method for preparing yellow synthetic diamonds by using hair as a carbon source and a nitrogen source through microwave plasma chemical vapor deposition (MPCVD). Background Art

[0002] The synthetic technologies of synthetic diamonds mainly include the high-pressure high-temperature method (HPHT) and the chemical vapor deposition method (CVD). The high-pressure high-temperature method (HPHT) simulates the high-temperature environment of 1300 - 1600 °C and high-pressure environment of 5 - 6 GPa for natural diamond formation, and uses metal catalysts (such as iron, nickel, cobalt, etc.) to convert graphite into diamonds. The chemical vapor deposition method (CVD) is a technology for depositing diamond thin films on the surface of a substrate through gas-phase chemical reactions. In a high-temperature and low-pressure environment, carbon-containing gases (such as methane) and hydrogen are decomposed to generate carbon atoms and hydrogen atoms. The carbon atoms are deposited on the surface of the substrate to form a diamond structure, and the hydrogen atoms help to remove non-diamond carbon. The chemical vapor deposition method (CVD) and the high-pressure high-temperature method (HPHT) have obvious advantages in terms of purity, controllability, applicability, energy consumption, and environmental protection, and are particularly suitable for the production of high-purity and high-quality diamonds. Their broad application prospects and low production costs make them important diamond synthesis technologies.

[0003] As a biomass material rich in carbon, hair can be pyrolyzed into raw materials for synthetic diamonds. Making diamonds from hair for jewelry has commemorative significance and economic value. Some related technologies have also been disclosed in the prior art. For example, CN115198359A discloses a method for cultivating hair carbon source into diamonds using an MPCVD device. The hair bundle is etched by plasma, and the carbon source gas generated by the etching of the hair bundle helps the growth of single-crystal diamond. CN201711250553.2 - A method for growing single-crystal diamond using human hair as a carbon source with a dual-substrate stage MPCVD reaction device also discloses a method for growing single-crystal diamond by etching the hair bundle with plasma and using the generated carbon source gas. CN116949432A discloses a method for cultivating hair carbon source into diamonds using an MPCVD device. After crushing the hair sample into smaller particle hair sample particles and placing them in a sample container, the container is then placed in a preheating furnace or a high-temperature furnace for decomposition treatment, and an inert atmosphere is used to control the reaction environment. Then, the hair sample particles decompose under the action of high temperature and inert gas to generate reaction gas, and the reaction gas is introduced into the MPCVD reaction chamber to cultivate into diamonds.

[0004] The above technology directly decomposes hair into carbon source gas for cultivating diamonds. However, hair contains various elements such as carbon, hydrogen, oxygen, nitrogen, and sulfur. The carbon source gas obtained from the direct decomposition of hair contains impurity gases, and the presence of impurity gases will reduce the growth quality and purity of diamond, making it difficult to ensure the quality of diamond.

[0005] Furthermore, CN201711353968.2 discloses a method for growing single crystal diamond by using MPCVD method with hair as a carbon source. The hair is vaporized by plasma to form a gas mixture, and the gas mixture is purified by a gas purification device. The purified gas and hydrogen are mixed and used as gas raw materials, and then single crystal diamond is deposited on a natural single crystal diamond sample by microwave plasma chemical vapor deposition method. This technology removes the impurities contained in the hair, making the mass ratio of carbon atoms, hydrogen atoms, and oxygen atoms in the purified gas exceed 99.99% of the gas mass, ensuring the quality of diamond. However, this method can only utilize the carbon in the hair, and other elements are excluded as impurities.

[0006] In the process of synthesizing diamonds, nitrogen can be effectively incorporated into the lattice. Usually, when synthesizing diamonds by CVD method, nitrogen gas or ammonia gas can be introduced as a dopant to obtain yellow diamonds. For example, CN116856054A discloses a production process of yellow diamonds. Using a diamond seed as the mother stone, with high-purity methane, assisted by gases such as hydrogen and nitrogen, in the cultivation chamber, methane and carbon molecules similar to diamonds are continuously accumulated on the diamond rough stone. Through layer-by-layer growth, nitrogen elements can be fully and evenly distributed inside the diamond, making the diamond show yellow under natural light.

[0007] Hair also contains nitrogen elements, but to convert it into common nitrogen gas or nitrogen gas as a dopant gas for the preparation of yellow artificial diamonds, the conversion process is slow and costly, and the practicability is not strong. Moreover, there is currently no technical solution for directly using hair as a carbon source and nitrogen source to prepare yellow artificial diamonds. The present invention aims to solve the above problems and provides a method for preparing yellow artificial diamonds with low cost and environmental protection. Summary of the Invention

[0008] Hair is mainly composed of keratin, and its chemical composition includes carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S). The pyrolysis gas components produced under different pyrolysis conditions are different. Under the condition of sufficient oxygen supply and complete combustion, about 2.5 grams of oxygen (about 1.75 liters under standard conditions) is required for 1 gram of hair to completely burn, and the combustion products are carbon dioxide , water , sulfur dioxide , nitrogen , in an incomplete combustion and high-temperature (above 1200 °C) environment, carbon and nitrogen elements may be converted into pyrolysis gases containing , CO, , and other more complex components.

[0009] The object of the present invention is to use hair as a carbon source and a nitrogen source, explore the pyrolysis conditions of hair, and ensure that nitrogen and carbon elements in hair are converted into gaseous products that can be used for the preparation of yellow artificial diamonds required by the MPCVD method; secondly, explore the nitrogen element gas obtained from hair pyrolysis as a nitrogen dopant to optimize the existing MPCVD process, so that during the synthesis of diamonds from the obtained gaseous products, nitrogen can be effectively incorporated into the lattice and has a relatively fast growth rate; furthermore, explore the influence of other elements and impurities in hair on the quality of yellow artificial diamonds.

[0010] The ultimate object of the present invention is to prepare yellow artificial diamonds with a color grade reaching from Fancy Yellow to Fancy Vivid Yellow, a clarity reaching from VS2 (Very Slightly Included 2) to VVS1 (Very Very Slightly Included 1), and a rough diamond weight of 4 - 10 ct.

[0011] Basic exploration experiments The collected hair is chopped and mixed and then divided into 10 portions, which are pyrolyzed into pyrolysis gases respectively according to the following schemes of Experiment 1 - Experiment 10: Experiment 1: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1000 °C. The ratio of hair to oxygen is 1 g: 1.0 L to obtain the pyrolysis gas of Experiment 1; Experiment 2: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1000 °C. The ratio of hair to oxygen is 1 g: 1.2 L to obtain the pyrolysis gas of Experiment 1; Experiment 3: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1000 °C. The ratio of hair to oxygen is 1 g: 1.5 L to obtain the pyrolysis gas of Experiment 1; Experiment 4: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1000 °C. The ratio of hair to oxygen is 1 g: 1.8 L to obtain the pyrolysis gas of Experiment 1; Experiment 5: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1000 °C. The ratio of hair to oxygen is 1 g: 2.0 L to obtain the pyrolysis gas of Experiment 1; Experiment 6: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen is 1 g: 1.0 L to obtain the pyrolysis gas of Experiment 2; Experiment 7: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen is 1 g: 1.2 L to obtain the pyrolysis gas of Experiment 3. Experiment 8: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen is 1 g: 1.5 L to obtain the pyrolysis gas of Experiment 2. Experiment 9: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen is 1 g: 1.8 L to obtain the pyrolysis gas of Experiment 3. Experiment 10: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen is 1 g: 2.0 L to obtain the pyrolysis gas of Experiment 2.

[0012] After the high-temperature pyrolysis gases of the above Experiments 1 - 10 are respectively desulfurized by calcium carbonate suspension and the water vapor is removed by a condenser, the mixed gases of Experiments 1 - 10 are obtained respectively.

[0013] The mixed gases obtained from Experiments 1 - 10 are respectively used for the preparation of synthetic diamond blanks by the MPCVD method in the following processes: Process 1: The carrier gas is H 2 , with a flow rate range of 1000 ml / min; the mixed gas is a carbon source and a nitrogen source, and the flow rate is 5% of H 2 ; the growth pressure is 110 Torr; the growth power is 8 kW; the growth temperature is 1100 °C; the growth rate is 15 μm / h; the growth time is 400 h; Process 2: The carrier gas is H 2 , with a flow rate range of 500 ml / min; the mixed gas is a carbon source and a nitrogen source, and the flow rate is 5% of H 2 ; the growth pressure is 110 Torr; the growth power is 5 kW; the growth temperature is 1100 °C; the growth rate is 15 μm / h; the growth time is 400 h.

[0014] Inspect the clarity of the synthetic diamond blanks of Experiments 1 - 10. Those without defects or with a small amount of visible inclusions (such as small crystals, feather cracks, clouds, pinpoint, surface shallow lines, surface local defects, etc.) are qualified, and those with obvious internal cracks or bubbles, large crystal inclusions, etc. are unqualified. The test results are shown in Table 1 below: Table 1

[0015] The synthetic diamond blank prepared from the mixed gas of Experiment 2 by Process 1 is as shown in Figure 1 a; the synthetic diamond blank prepared from the mixed gas of Experiment 5 by Process 1 is as shown in Figure 1 b; the synthetic diamond blank prepared from the mixed gas of Experiment 6 by Process 1 is as shown inFigure 1 as shown in c; the synthetic diamond blanks prepared from the mixed gas of Test 7 by Process 1 are as Figure 2 shown in a (local surface defects); the synthetic diamond blanks prepared from the mixed gas of Test 8 by Process 1 are as Figure 2 shown in b (local surface defects); the synthetic diamond blanks prepared from the mixed gas of Test 9 by Process 1 are as Figure 2 shown in c; the synthetic diamond blanks prepared from the mixed gas of Test 5 by Process 2 are as Figure 3 shown in a; the synthetic diamond blanks prepared from the mixed gas of Test 7 by Process 2 are as Figure 3 shown in b; the synthetic diamond blanks prepared from the mixed gas of Test 8 by Process 2 are as Figure 3 shown in c.

[0016] The above experimental results show that the pyrolysis gas obtained from hair under pyrolysis conditions of high temperature and lack of oxygen is more suitable for the preparation of yellow synthetic diamonds by the MPCVD method. The possible reason is that in an oxygen-rich and low-temperature environment, carbon in hair is converted into carbon dioxide and nitrogen is converted into nitrogen gas, and the carbon source and nitrogen source of this component are not applicable to the above Process 1 or Process 2. Moreover, excessive oxygen generates too much O· in the MPCVD cavity and combines with H· decomposed from the carrier gas H 2 to form OH·, which further affects the deposition of carbon and nitrogen, resulting in internal defects in the synthetic diamond blanks.

[0017] Based on the above research tests and further exploration, the present invention provides a method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source, comprising the following steps: 1) Pyrolysis: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250 - 1300 °C, with the ratio of hair to oxygen being 1 g : (1.2 - 1.5) L, to obtain pyrolysis gas; 2) By-product removal: Remove sulfur oxide gas and water vapor in the pyrolysis gas in sequence to obtain a mixed gas containing carbon and nitrogen elements; 3) Place the seed crystal in the MPCVD cavity for the growth of diamond blanks; the growth conditions are as follows: the carrier gas is H 2 , with a flow rate range of 1000 - 1200 ml / min; the mixed gas is used as the carbon source and nitrogen source, with a flow rate of 1 - 5% of H 2 ; the growth pressure is 100 - 120 Torr; the growth power is 8 - 10 kW; the growth temperature is 1100 - 1200 °C; the growth rate is 10 - 15 μm / h.

[0018] Preferably, in the step 2), sulfur oxide gas in the high-temperature pyrolysis gas is removed by desulfurization with a calcium carbonate suspension, and then water vapor in the pyrolysis gas is removed by a condenser. More preferably, the high-temperature pyrolysis gas is desulfurized by spraying with a calcium carbonate suspension.

[0019] Preferably, in step 3), MPCVD uses a microwave frequency of 2.4 - 2.5 GHz; the side length of the seed crystal is 7 - 50 mm, and the directions of the four sides are parallel to the <100> crystal phase; the growth time is 200 - 400 hours.

[0020] Preferably, in step 1), the pyrolysis time is not less than 1 hour, preferably 2 - 4 hours.

[0021] Furthermore, before the hair is placed in the closed pyrolysis furnace, the hair is also washed and dried.

[0022] Preferably, the hair is human hair.

[0023] In some specific embodiments, the method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source according to the present invention includes the following steps: 1) After washing and drying the hair, it is placed in a closed pyrolysis furnace, and the ratio of hair to oxygen is 1 g: 1.4 L; it is pyrolyzed in an oxygen atmosphere at 1250 °C for 2 hours to obtain pyrolysis gas; 2) The high-temperature pyrolysis gas in the pyrolysis furnace is led out, first absorbed by a calcium carbonate suspension to remove sulfur oxide gases, and then the water vapor in the pyrolysis gas is removed by a condenser to obtain a mixed gas containing carbon and nitrogen elements; 3) The seed crystal is placed in the MPCVD cavity, and diamond blank growth is carried out using a microwave frequency of 2.45 GHz; the growth conditions are as follows: the carrier gas is H 2 , with a flow rate of 1100 ml / min; the mixed gas is used as a carbon source and a nitrogen source, with a flow rate of 2% of H 2 ; the growth pressure is 110 Torr; the growth power is 9.5 kW; the growth temperature is 1150 °C; the growth rate is 15 μm / h.

[0024] The method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source according to the present invention controls the pyrolysis conditions of the hair to convert the nitrogen and carbon elements in the hair into gaseous products that can be directly used for preparing yellow synthetic diamonds by the MPCVD method. Combining with the specific diamond blank growth process of the present invention, the nitrogen element in the hair can be effectively incorporated into the lattice without the need to additionally provide a nitrogen source or remove the nitrogen in the hair pyrolysis products, and has a relatively fast growth rate. Finally, yellow synthetic diamonds with a blank weight of 4 - 10 ct, a color grade from Fancy Yellow to Fancy Vivid Yellow, and a clarity of VS2 to VVS1 are prepared.

[0025] Further, the components and contents of the gaseous products directly used in the present invention for preparing yellow artificial diamonds by the MPCVD method can be detected, and a mixed gas can be formulated according to the components and contents as the carbon source and nitrogen source mixed gas for preparing yellow artificial diamonds by the MPCVD method. The structure of the existing MPCVD device can be improved, and the gas supply pipeline of the MPCVD device can be reduced. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other similar drawings can also be obtained based on these drawings.

[0027] Figure 1 Synthetic diamond blanks prepared from the mixed gases of Test 2, Test 5, and Test 6 using Process 1; Figure 2 Synthetic diamond blanks prepared from the mixed gases of Test 7, Test 8, and Test 9 using Process 1; Figure 3 Synthetic diamond blanks prepared from the mixed gases of Test 5, Test 7, and Test 8 using Process 2; Figure 4 Measurement results of the sizes of the yellow synthetic diamond blanks in Example 1; Figure 5 Rough stones after cutting the yellow synthetic diamond blanks in Example 1; Figure 6 Finished products after cutting and polishing the rough stones in Example 1; Figure 7 Yellow synthetic diamond blanks, rough stones, and finished products in Example 2; Figure 8 Yellow synthetic diamond blanks, rough stones, and finished products in Example 3; Figure 9 Synthetic diamond blanks prepared in Comparative Example 1; Figure 10 Synthetic diamond blanks prepared in Comparative Example 2; Figure 11 Synthetic diamond blanks prepared in Comparative Example 13. Detailed Embodiments

[0028] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0029] It should be understood that when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0030] Example 1 A method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source, comprising the following steps: 1) Wash, dry and chop the hair, place it in a closed pyrolysis furnace, and the ratio of hair to oxygen is 1 g: 1.4 L; pyrolyze in an oxygen atmosphere at 1250 °C for 2 hours to obtain pyrolysis gas; 2) Export the high-temperature pyrolysis gas in the pyrolysis furnace, first spray and absorb sulfur oxide gas with a suspension of calcium carbonate, and then remove the water vapor in the pyrolysis gas through a condenser to obtain a mixed gas containing carbon and nitrogen elements; 3) Place the seed crystal in the MPCVD cavity. The side length of the seed crystal is 10 mm * 12 mm, and the directions of the four sides are parallel to the <100> crystal phase. Use a microwave frequency of 2.45 GHz to grow diamond blanks; the growth conditions are: the carrier gas is H 2 , with a flow rate of 1100 ml / min; the mixed gas is used as a carbon source and a nitrogen source, and the flow rate is 2% of H 2 ; the growth pressure is 110 Torr; the growth power is 9.5 kW; the growth temperature is 1150 °C; the growth rate is 15 μm / h; the growth time is 400 h.

[0031] The measurement results of the size of the yellow synthetic diamond blanks prepared in this example are as Figure 4 shown. As Figure 4 can be seen, the size of the yellow synthetic diamond blank is 13.44 * 15.39 * 8.75, and there are only local defects on the surface; the rough stone after cutting is as Figure 5 shown; the finished product after cutting and polishing the rough stone is as Figure 6 shown, with a color grade of Fancy Vivid Yellow, a clarity reaching VVS1, and a weight of 4.26 ct.

[0032] Example 2 A method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source, comprising the following steps: 1) Wash, dry and chop the hair, place it in a closed pyrolysis furnace, and the ratio of hair to oxygen is 1 g: 1.2 L; pyrolyze in an oxygen atmosphere at 1300 °C for 1 hour to obtain pyrolysis gas; 2) Export the high-temperature pyrolysis gas in the pyrolysis furnace, first spray and absorb sulfur oxide gas with a suspension of calcium carbonate, and then remove the water vapor in the pyrolysis gas through a condenser to obtain a mixed gas containing carbon and nitrogen elements; 3) Place the seed crystal in the MPCVD cavity. The side length of the seed crystal is 14 mm * 16 mm, and the directions of the four sides are parallel to the <100> crystal phase. Use a microwave frequency of 2.45 GHz to grow diamond blanks; the growth conditions are as follows: the carrier gas is H 2 , with a flow rate of 1000 ml / min; the mixed gas is a carbon source and a nitrogen source, and the flow rate is 1% of H 2 ; the growth pressure is 100 Torr; the growth power is 10 kW; the growth temperature is 1200 °C; the growth rate is 15 μm / h; the growth time is 400 h.

[0033] The yellow synthetic diamond blank prepared in this example is as shown in Figure 7 a in Figure 7 . As can be seen from a in Figure 7 , only local surface defects exist in this yellow synthetic diamond blank; the rough stone after cutting is as shown in Figure 7 b in

[0034] Example 3 A method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source, comprising the following steps: 1) Wash, dry and chop the hair, and place it in a closed pyrolysis furnace. The ratio of hair to oxygen is 1 g: 1.5 L; pyrolyze in an oxygen atmosphere at 1280 °C for 2.5 hours to obtain pyrolysis gas; 2) Export the high-temperature pyrolysis gas in the pyrolysis furnace. First, spray and absorb sulfur oxide gases with a suspension of calcium carbonate, and then remove the water vapor in the pyrolysis gas through a condenser to obtain a mixed gas containing carbon and nitrogen elements; 3) Place the seed crystal in the MPCVD cavity. The side length of the seed crystal is 10 mm * 10 mm, and the directions of the four sides are parallel to the <100> crystal phase. Use a microwave frequency of 2.45 GHz to grow diamond blanks; the growth conditions are as follows: the carrier gas is H 2 , with a flow rate of 1200 ml / min; the mixed gas is a carbon source and a nitrogen source, and the flow rate is 5% of H 2 ; the growth pressure is 120 Torr; the growth power is 8 kW; the growth temperature is 1150 °C; the growth rate is 10 μm / h; the growth time is 300 h.

[0035] The yellow synthetic diamond blank prepared in this example is as shown in Figure 8 a in Figure 8 . As can be seen from a in Figure 8 , only local surface defects exist in this yellow synthetic diamond blank; the rough stone after cutting is as shown in Figure 8As shown in c, the color grade is Fancy Yellow and the clarity reaches VS2.

[0036] Based on Example 1, for the preparation method of the present invention, the following comparative examples were also explored.

[0037] Comparative Example 1 The difference from Example 1 is that in step 2), the treatment of removing water vapor is not carried out.

[0038] Comparative Example 2 The difference from Example 1 is that in step 2), the treatment of absorbing sulfur oxide gas is not carried out.

[0039] Comparative Example 3 The difference from Example 1 is that in step 3), the flow rate range of the carrier gas H 2 is 1500 ml / min.

[0040] Comparative Example 4 The difference from Example 1 is that in step 3), the flow rate range of the carrier gas H 2 is 800 ml / min.

[0041] Comparative Example 5 The difference from Example 1 is that in step 3), the flow rate of the mixed gas is 0.5% of H 2 .

[0042] Comparative Example 6 The difference from Example 1 is that in step 3), the flow rate of the mixed gas is 8% of H 2 .

[0043] Comparative Example 7 The difference from Example 1 is that in step 3), the growth pressure is 90 Torr.

[0044] Comparative Example 8 The difference from Example 1 is that in step 3), the growth pressure is 120 Torr.

[0045] Comparative Example 9 The difference from Example 1 is that in step 3), the growth power is 7 kW.

[0046] Comparative Example 10 The difference from Example 1 is that in step 3), the growth power is 11 kW.

[0047] Comparative Example 11 The difference from Example 1 is that in step 3), the growth temperature is 1000 °C.

[0048] Comparative Example 12 The difference from Example 1 is that the growth temperature in step 3) is 1300 °C.

[0049] Comparative Example 13 The difference from Example 1 is that the growth rate in step 3) is 22 μm / h.

[0050] The clarity of the synthetic diamond blanks obtained in Comparative Examples 1-13 was detected. Those without defects or with a small amount of visible inclusions (such as small crystals, feather cracks, clouds, pinpoint defects, surface shallow lines, local surface defects, etc.) were qualified, and those with obvious internal cracks or bubbles, large crystal inclusions, etc. were unqualified. The test results are shown in Table 2 below; Table 2

[0051] The synthetic diamond blank prepared in Comparative Example 1 is as Figure 9 shown; the synthetic diamond blank prepared in Comparative Example 2 is as Figure 10 shown; the synthetic diamond blank prepared in Comparative Example 13 is as Figure 11 shown.

[0052] The above test results show that Examples 1-3 adopt the hair pyrolysis process of the present invention, combined with the specific diamond blank growth process of the present invention, which can convert nitrogen and carbon elements in hair into gaseous products directly used for preparing yellow synthetic diamonds by the MPCVD method, enabling the nitrogen element in hair to be effectively incorporated into the lattice, and having a relatively fast growth rate, preparing yellow synthetic diamonds with a blank weight of more than 4 ct, a color grade from Fancy Yellow to Fancy Vivid Yellow, and a clarity from VS2 to VVS1. The test results of Comparative Examples 3-13 show that the gaseous products obtained by the hair pyrolysis process of the present invention are closely related to the carrier gas flow rate, mixed gas flow rate, growth pressure, growth power, growth temperature, and growth rate of the diamond blank growth process for preparing the required yellow synthetic diamonds.

[0053] The detection results of Comparative Examples 1 and 2 show that water vapor and sulfur elements in the hair pyrolysis products have an obvious negative impact on the growth of diamond blanks.

[0054] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing yellow artificial diamonds using hair as a carbon source and a nitrogen source, characterized in that: The following steps are involved: 1) Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250-1300°C, with the ratio of hair to oxygen being 1g:(1.2-1.5)L, to obtain pyrolysis gas; 2) Sequentially remove sulfur oxide gas and water vapor from the pyrolysis gas to obtain a mixed gas containing carbon and nitrogen elements; 3) Placing the seed crystal in the MPCVD chamber to grow diamond blank; the growth conditions are: the carrier gas is H2, the flow range is 1000-1200ml / min; the mixed gas is a carbon source and a nitrogen source, the flow rate is 1-5% of H2; the growth pressure is 100-120Torr; the growth power is 8-10kW; the growth temperature is 1100-1200℃; the growth rate is 10-15um / h.

2. The method for preparing yellow artificial diamonds using hair as carbon source and nitrogen source according to claim 1, characterized in that: In the step 2), calcium carbonate suspension is used for desulfurization to remove sulfur oxide gas in the high-temperature pyrolysis gas.

3. The method for preparing yellow artificial diamond using hair as carbon source and nitrogen source according to claim 1, characterized in that: In the step 2), water vapor in the pyrolysis gas is removed by a condenser.

4. The method for preparing yellow artificial diamond using hair as carbon source and nitrogen source according to claim 1, characterized in that: In the step 3), MPCVD uses a microwave frequency of 2.4-2.5 GHz.

5. The method for preparing yellow artificial diamond using hair as carbon source and nitrogen source according to claim 1, characterized in that: In the step 3), the seed crystal has a side length of 7-50 mm, and the directions of the four sides are <100> The crystal phases are parallel.

6. The method for preparing yellow artificial diamond using hair as carbon source and nitrogen source according to claim 1, characterized in that: In the step 3), the growth time of the diamond blank is 200-400 hours.

7. The method for preparing yellow artificial diamond using hair as carbon source and nitrogen source according to claim 1, characterized in that: In the step 1), the pyrolysis time is not less than 1 hour.

8. The method for preparing yellow artificial diamond using hair as carbon source and nitrogen source according to claim 1, characterized in that: In the step 1), the hair is placed in front of a closed pyrolysis furnace, and the hair is also cleaned and dried.

9. The method for preparing yellow artificial diamond using hair as carbon source and nitrogen source according to claim 1, characterized in that: The hair is head hair.

10. The method for preparing yellow artificial diamond using hair as carbon source and nitrogen source according to claim 1, characterized in that: The following steps are involved: 1) Wash and dry the hair and place it in a closed pyrolysis furnace with a hair to oxygen ratio of 1g:1.4L; pyrolyze it in an oxygen atmosphere at 1250℃ for 2 hours to obtain pyrolysis gas; 2) The high-temperature pyrolysis gas in the pyrolysis furnace is discharged, firstly the sulfur oxide gas is absorbed by the calcium carbonate suspension, and then the water vapor in the pyrolysis gas is removed by the condenser to obtain a mixed gas containing carbon and nitrogen elements; 3) The seed crystal is placed in the MPCVD chamber and a microwave frequency of 2.45 GHz is used to grow diamond blanks; the growth conditions are: the carrier gas is H2, the flow rate is 1100 ml / min; the mixed gas is a carbon source and a nitrogen source, the flow rate is 2% of H2; the growth pressure is 110 Torr; the growth power is 9.5 kW; the growth temperature is 1150 ° C; the growth rate is 15 um / h.

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