A method for preparing yellow artificial diamonds using hair as a carbon source and a nitrogen source

Abstract

The present invention discloses a method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source, which relates to the technical field of synthetic diamond preparation. The method comprises the following steps: 1) placing the hair in a closed pyrolysis furnace, pyrolyzing 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) sequentially removing sulfur oxide gas and water vapor from the pyrolysis gas; 3) placing the seed crystal in an MPCVD cavity for the growth of diamond blanks. By controlling the pyrolysis conditions of the hair, the present invention converts 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, nitrogen elements can be effectively incorporated into the crystal lattice.

Description

Technical Field

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

[0002] The synthetic techniques of artificial diamonds mainly include the high-pressure high-temperature method (HPHT) and the chemical vapor deposition method (CVD). The high-pressure high-temperature method (HPHT) is to convert graphite into diamonds by using metal catalysts (such as iron, nickel, cobalt, etc.) under the high-temperature environment of 1300 - 1600 °C and high-pressure environment of 5 - 6 GPa that simulate the formation of natural diamonds. The chemical vapor deposition method (CVD) is a technique for depositing diamond films on the surface of a substrate through gas-phase chemical reactions. Under 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 and 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 techniques.

[0003] As a biomass material rich in carbon, hair can be pyrolyzed into raw materials for synthesizing 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 a double-substrate stage MPCVD reaction device with human hair as a carbon source 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 putting them into a sample container, the container is then put into 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 to generate reaction gases under the action of high temperature and inert gas, and the reaction gases are 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 diamonds, making it difficult to ensure the quality of diamonds.

[0005] Furthermore, CN201711353968.2 discloses a method for growing single crystal diamonds 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 is mixed with hydrogen and used as a gas raw material, and then single crystal diamonds are 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 ratio of the mass of carbon atoms, hydrogen atoms, and oxygen atoms in the purified gas exceed 99.99% of the gas mass, ensuring the quality of diamonds. However, this method can only utilize the carbon in the hair, and other elements are excluded as impurities.

[0006] During the synthesis of 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 like diamonds are continuously accumulated on the diamond rough stone. Through layer-by-layer growth, nitrogen elements can be fully and evenly distributed inside the diamonds, making the diamonds 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 practicality is not strong. Moreover, there is currently no technical solution for directly using hair as a carbon source and a 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 with more complex components containing , CO, , and other 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 diamond rough weight of 4 - 10 ct.

[0011] Basic exploration experiments

[0012] 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:

[0013] 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;

[0014] 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;

[0015] 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;

[0016] 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;

[0017] 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;

[0018] Experiment 6: The hair was placed in a closed pyrolysis furnace and pyrolyzed in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen was 1 g: 1.0 L, and the pyrolysis gas of Experiment 2 was obtained.

[0019] Experiment 7: The hair was placed in a closed pyrolysis furnace and pyrolyzed in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen was 1 g: 1.2 L, and the pyrolysis gas of Experiment 3 was obtained.

[0020] Experiment 8: The hair was placed in a closed pyrolysis furnace and pyrolyzed in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen was 1 g: 1.5 L, and the pyrolysis gas of Experiment 2 was obtained.

[0021] Experiment 9: The hair was placed in a closed pyrolysis furnace and pyrolyzed in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen was 1 g: 1.8 L, and the pyrolysis gas of Experiment 3 was obtained.

[0022] Experiment 10: The hair was placed in a closed pyrolysis furnace and pyrolyzed in an oxygen atmosphere at 1250 °C. The ratio of hair to oxygen was 1 g: 2.0 L, and the pyrolysis gas of Experiment 2 was obtained.

[0023] After the high-temperature pyrolysis gases of the above Experiments 1-10 were desulfurized by calcium carbonate suspension and the water vapor was removed by a condenser, the mixed gases of Experiments 1-10 were obtained respectively.

[0024] The mixed gases obtained from Experiments 1-10 were respectively used in the MPCVD method for preparing synthetic diamond blanks in the following processes:

[0025] Process 1: The carrier gas was H2, and the flow rate range was 1000 ml / min; the mixed gas was a carbon source and a nitrogen source, and the flow rate was 5% of H2; the growth pressure was 110 Torr; the growth power was 8 kW; the growth temperature was 1100 °C; the growth rate was 15 μm / h; the growth time was 400 h;

[0026] Process 2: The carrier gas was H2, and the flow rate range was 500 ml / min; the mixed gas was a carbon source and a nitrogen source, and the flow rate was 5% of H2; the growth pressure was 110 Torr; the growth power was 5 kW; the growth temperature was 1100 °C; the growth rate was 15 μm / h; the growth time was 400 h.

[0027] The clarity of the synthetic diamond blanks of Experiments 1-10 was detected. 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.) were qualified, and those with obvious internal cracks or bubbles, large crystal inclusions, etc. were unqualified. The detection results are shown in Table 1 below:

[0028] Table 1

[0029]

[0030] The synthetic diamond blanks prepared from the mixed gas of Experiment 2 by Process 1 are as shown in a of Figure 1 ; the synthetic diamond blanks prepared from the mixed gas of Experiment 5 by Process 1 are as shown in b of Figure 1 ; the synthetic diamond blanks prepared from the mixed gas of Experiment 6 by Process 1 are as shown in c of Figure 1 ; the synthetic diamond blanks prepared from the mixed gas of Experiment 7 by Process 1 are as shown in a of Figure 2 (local surface defects); the synthetic diamond blanks prepared from the mixed gas of Experiment 8 by Process 1 are as shown in b of Figure 2 (local surface defects); the synthetic diamond blanks prepared from the mixed gas of Experiment 9 by Process 1 are as shown in c of Figure 2 ; the synthetic diamond blanks prepared from the mixed gas of Experiment 5 by Process 2 are as shown in a of Figure 3 ; the synthetic diamond blanks prepared from the mixed gas of Experiment 7 by Process 2 are as shown in b of Figure 3 ; the synthetic diamond blanks prepared from the mixed gas of Experiment 8 by Process 2 are as shown in c of Figure 3 .

[0031] The above experimental results show that the pyrolysis gas obtained from hair under pyrolysis conditions of high temperature and oxygen deficiency 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. The carbon source and nitrogen source of this component are not applicable to the above Process 1 or Process 2, and excessive oxygen generates too much O· in the MPCVD cavity and combines with H· decomposed from the carrier gas H2 to form OH·, which further affects the deposition of carbon and nitrogen, resulting in internal defects in the synthetic diamond blanks.

[0032] Based on the above research experiments 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:

[0033] 1) Pyrolysis: Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250 - 1300 °C. The ratio of hair to oxygen is 1 g : (1.2 - 1.5) L to obtain pyrolysis gas;

[0034] 2) Removal of by-products: Sequentially remove sulfur oxide gas and water vapor from the pyrolysis gas to obtain a mixed gas containing carbon and nitrogen elements;

[0035] 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 H2, and the flow rate ranges from 1000 to 1200 ml / min; the mixed gas is a carbon source and a nitrogen source, and the flow rate is 1-5% of that of H2; 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 um / h.

[0036] Preferably, in step 2), first remove the sulfur oxide gas in the high-temperature pyrolysis gas by desulfurization with a calcium carbonate suspension, and then remove the water vapor in the pyrolysis gas through a condenser. More preferably, spray the high-temperature pyrolysis gas with a calcium carbonate suspension for desulfurization.

[0037] Preferably, in step 3), the 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.

[0038] Preferably, in step 1), the pyrolysis time is not less than 1 hour, preferably 2-4 hours.

[0039] Furthermore, before placing the hair in the closed pyrolysis furnace, the hair is also washed and dried.

[0040] Preferably, the hair is human hair.

[0041] 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:

[0042] 1) Wash and dry the hair and then place it in a closed pyrolysis furnace. 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.

[0043] 2) Export the high-temperature pyrolysis gas from the pyrolysis furnace. First, absorb the sulfur oxide gas with a calcium carbonate suspension, and then remove the water vapor in the pyrolysis gas through a condenser to obtain a mixed gas containing carbon and nitrogen elements.

[0044] 3) Place the seed crystal in the MPCVD cavity and grow diamond blanks using a microwave frequency of 2.45 GHz. The growth conditions are as follows: the carrier gas is H2, and the flow rate is 1100 ml / min; the mixed gas is a carbon source and a nitrogen source, and the flow rate is 2% of that 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.

[0045] The method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source converts nitrogen and carbon elements in hair into gaseous products that can be directly used in the MPCVD method for preparing yellow synthetic diamonds by controlling the pyrolysis conditions of hair. Combining with the specific diamond blank growth process of the present invention, the nitrogen element in hair can be effectively incorporated into the lattice without the need to additionally provide a nitrogen source or remove nitrogen from the pyrolysis products of hair, and it 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.

[0046] Furthermore, the components and contents of the gaseous products directly used in the MPCVD method for preparing yellow synthetic diamonds of the present invention can be detected, and a mixed gas can be prepared according to these components and contents as the carbon source and nitrogen source mixed gas for the MPCVD method for preparing yellow synthetic diamonds. The structure of the existing MPCVD device is improved to reduce the gas supply gas path of the MPCVD device. Description of the Drawings

[0047] 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.

[0048] Figure 1 Synthetic diamond blanks prepared from the mixed gas of Test 2, Test 5, and Test 6 using Process 1;

[0049] Figure 2 Synthetic diamond blanks prepared from the mixed gas of Test 7, Test 8, and Test 9 using Process 1;

[0050] Figure 3 Synthetic diamond blanks prepared from the mixed gas of Test 5, Test 7, and Test 8 using Process 2;

[0051] Figure 4 Measurement results of the size of the yellow synthetic diamond blank in Example 1;

[0052] Figure 5 The rough stone after cutting the yellow synthetic diamond blank in Example 1;

[0053] Figure 6 The finished product after cutting and polishing the rough stone in Example 1;

[0054] Figure 7 The yellow synthetic diamond blanks, rough stones, and finished products in Example 2;

[0055] Figure 8Yellow synthetic diamond blanks, rough stones and finished products of Example 3;

[0056] Figure 9 Synthetic diamond blank prepared in Comparative Example 1;

[0057] Figure 10 Synthetic diamond blank prepared in Comparative Example 2;

[0058] Figure 11 Synthetic diamond blank prepared in Comparative Example 13. Detailed implementation manners

[0059] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0060] 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 exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0061] Example 1

[0062] A method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source, comprising the following steps:

[0063] 1) Wash, dry and chop the hair, and place it in a closed pyrolysis furnace. The ratio of hair to oxygen is 1 g: 1.4 L; pyrolyze in an oxygen atmosphere at 1250 °C for 2 hours to obtain pyrolysis gas;

[0064] 2) Export the high-temperature pyrolysis gas in the pyrolysis furnace. First, spray and absorb sulfur oxide gas with a calcium carbonate suspension, and then remove the water vapor in the pyrolysis gas through a condenser to obtain a mixed gas containing carbon and nitrogen elements;

[0065] 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 H2, and the flow rate is 1100 ml / min; the mixed gas is a carbon source and a nitrogen source, and 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; the growth time is 400 h.

[0066] The measurement results of the size of the yellow synthetic diamond blanks prepared in this example are asFigure 4 As shown, from Figure 4 It can be seen that the size of this rough yellow synthetic diamond is 13.44 * 15.39 * 8.75, and there are only local defects on the surface; the original stone after cutting is as Figure 5 shown; the finished product after cutting and polishing the original 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.

[0067] Example 2

[0068] A method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source, comprising the following steps:

[0069] 1) Wash, dry and chop the hair, place it in a closed pyrolysis furnace, with the ratio of hair to oxygen being 1 g: 1.2 L; pyrolyze in an oxygen atmosphere at 1300 °C for 1 hour to obtain pyrolysis gas;

[0070] 2) Export the high-temperature pyrolysis gas in the pyrolysis furnace, first spray and absorb sulfur oxide gas with a calcium carbonate suspension, and then remove the water vapor in the pyrolysis gas through a condenser to obtain a mixed gas containing carbon and nitrogen elements;

[0071] 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: the carrier gas is H2, with a flow rate of 1000 ml / min; the mixed gas is used as the carbon source and nitrogen source, with a flow rate of 1% of H2; 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.

[0072] The rough yellow synthetic diamond prepared in this example is as Figure 7 shown in a of Figure 7 As can be seen from a of Figure 7 shown, there are only local defects on the surface of this rough yellow synthetic diamond; the original stone after cutting is as Figure 7 shown in b of

[0073] Example 3

[0074] A method for preparing yellow synthetic diamonds using hair as a carbon source and a nitrogen source, comprising the following steps:

[0075] 1) Wash, dry and chop the hair, place it in a closed pyrolysis furnace, with the ratio of hair to oxygen being 1 g: 1.5 L; pyrolyze in an oxygen atmosphere at 1280 °C for 2.5 hours to obtain pyrolysis gas;

[0076] 2) Export the high-temperature pyrolysis gas in the pyrolysis furnace. First, spray and absorb the sulfur oxide gas with a calcium carbonate suspension, and then remove the water vapor in the pyrolysis gas through a condenser to obtain a mixed gas containing carbon and nitrogen elements.

[0077] 3) Place the seed crystal in the MPCVD cavity. The side length of the seed crystal is 10mm * 10mm, 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 H2, with a flow rate of 1200 ml / min; the mixed gas is a carbon source and a nitrogen source, with a flow rate of 5% of H2; the growth pressure is 120 Torr; the growth power is 8 kW; the growth temperature is 1150 °C; the growth rate is 10 um / h; the growth time is 300 h.

[0078] The yellow artificial 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 this yellow artificial diamond blank only has local surface defects; the rough stone after cutting is as shown in Figure 8 b in

[0079] Based on Example 1, the following comparative examples were explored for the preparation method of the present invention.

[0080] Comparative Example 1

[0081] The difference from Example 1 is that in step 2), the water vapor removal treatment is not carried out.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that in step 2), the sulfur oxide gas absorption treatment is not carried out.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that in step 3), the flow rate range of the carrier gas H2 is 1500 ml / min.

[0086] Comparative Example 4

[0087] The difference from Example 1 is that in step 3), the flow rate range of the carrier gas H2 is 800 ml / min.

[0088] Comparative Example 5

[0089] The difference from Example 1 is that in step 3), the flow rate of the mixed gas is 0.5% of H2.

[0090] Comparative Example 6

[0091] The difference from Example 1 is that in step 3), the flow rate of the mixed gas is 8% of H2.

[0092] Comparative Example 7

[0093] The difference from Example 1 is that in step 3), the growth pressure is 90 Torr.

[0094] Comparative Example 8

[0095] The difference from Example 1 is that in step 3), the growth pressure is 120 Torr.

[0096] Comparative Example 9

[0097] The difference from Example 1 is that in step 3), the growth power is 7 kW.

[0098] Comparative Example 10

[0099] The difference from Example 1 is that in step 3), the growth power is 11 kW.

[0100] Comparative Example 11

[0101] The difference from Example 1 is that in step 3), the growth temperature is 1000 °C.

[0102] Comparative Example 12

[0103] The difference from Example 1 is that in step 3), the growth temperature is 1300 °C.

[0104] Comparative Example 13

[0105] The difference from Example 1 is that in step 3), the growth rate is 22 μm / h.

[0106] The clarity of the synthetic diamond blanks obtained in Comparative Examples 1 - 13 was inspected. Those without defects or with only a small amount of visible inclusions (such as small crystals, feather cracks, clouds, pinpoint, surface shallow lines, surface local flaws, etc.) were considered qualified, while those with obvious internal cracks or bubbles, large crystal inclusions, etc. were considered unqualified. The test results are shown in Table 2 below;

[0107] Table 2

[0108]

[0109] 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.

[0110] The above detection results show that in Examples 1 - 3, by adopting the hair pyrolysis process of the present invention and combining with the specific diamond blank growth process of the present invention, nitrogen and carbon elements in the hair can be converted into gaseous products directly used for preparing yellow artificial diamonds by the MPCVD method, enabling the nitrogen element in the hair to be effectively incorporated into the lattice, and having a relatively fast growth rate, preparing yellow artificial diamonds with a blank weight of more than 4 ct, color grades from Fancy Yellow to Fancy Vivid Yellow, and clarity 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 when used to prepare the required yellow artificial diamonds.

[0111] The detection results from Comparative Examples 1 and 2 show that in the hair pyrolysis products, water vapor and sulfur elements have obvious negative impacts on the growth of diamond blanks.

[0112] As described above, the above are only specific embodiments 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 shall 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, It includes the following steps: 1) Place the hair in a closed pyrolysis furnace and pyrolyze it in an oxygen atmosphere at 1250 - 1300 °C. The ratio of hair to oxygen is 1 g : (1.2 - 1.5) L to obtain pyrolysis gas; 2) 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 diamond blank growth. The growth conditions are as follows: the carrier gas is H2, and the flow rate range is 1000 - 1200 mL / min; the mixed gas is a carbon source and a nitrogen source, and the flow rate is 1 - 5% of that of H2; 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.

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

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

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

5. The method for preparing yellow artificial diamonds using hair as a carbon source and a nitrogen source according to claim 1, characterized in that, In step 3), 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.

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

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

8. The method for preparing yellow artificial diamonds using hair as a carbon source and a nitrogen source according to claim 1, wherein, Before placing the hair in the closed pyrolysis furnace in step 1), the hair is also washed and dried.

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

10. The method for preparing yellow artificial diamonds using hair as a carbon source and a nitrogen source according to claim 1, characterized in that, It includes the following steps: 1) Wash and dry the hair and then place it in a closed pyrolysis furnace. The ratio of hair to oxygen is 1 g : 1.4 L; pyrolyze it 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, absorb the sulfur oxide gas with a calcium carbonate suspension, 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 and use a microwave frequency of 2.45 GHz for diamond blank growth. The growth conditions are as follows: the carrier gas is H2, and the flow rate is 1100 mL / min; the mixed gas is a carbon source and a nitrogen source, and the flow rate is 2% of that 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 μm / h.

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