Blue silicon carbide gemstone and preparation method thereof

Abstract

The invention provides a blue silicon carbide gemstone and a preparation method thereof, and particularly relates to the field of crystal growth. The preparation method of the blue silicon carbide gemstone comprises the following steps that multiple groups of silicon carbide materials with different aluminum contents are synthesized, the silicon carbide materials are divided and screened to obtain multiple groups of silicon carbide materials with different aluminum contents and different sizes, and the aluminum contents of the silicon carbide materials are in positive correlation with the particle sizes of the silicon carbide materials; the silicon carbide materials are sequentially placed in a crucible according to the aluminum content from high to low, and a slow release layer is placed between every two adjacent layers of silicon carbide materials; and carrying out crystal growth by adopting a physical vapor transport method to obtain the blue silicon carbide gemstone. Silicon carbide materials with different aluminum contents and different sizes are synthesized firstly, then the gradient hierarchical structure is formed through layered arrangement, and then the slow release layer is supplemented, so that concentrated release of aluminum elements in the initial stage can be avoided, and the blue silicon carbide gemstone with uniform color is obtained.

Description

Technical Field

[0001] The present invention relates to the field of crystal growth, in particular to a blue silicon carbide gemstone and a preparation method thereof. Background Art

[0002] Silicon carbide, a highly promising gemstone material, offers the following advantages: a Mohs hardness of 9.25, second only to diamond and significantly higher than traditional corundum gemstones (such as sapphire and ruby), giving it exceptional scratch resistance; excellent wear resistance, making it less susceptible to wear during long-term wear or use, and maintaining its surface gloss and wear resistance; outstanding optical properties, with a high refractive index (2.65-2.69), giving the gemstone an intense luster and brightness, and a dispersion value approximately 2.4 times that of diamond, producing a remarkable, rainbow-like fire effect under illumination, resulting in an extremely gorgeous visual appearance; extremely high chemical stability and durability, including resistance to high temperatures and chemical corrosion, including strong resistance to common acids, alkalis, ultraviolet radiation, and everyday chemicals, ensuring the gemstone's stability and durability under long-term wear; and a high cost-effectiveness, with the cost of synthetic carbide gemstones being far lower than that of natural diamonds, while highly similar in appearance to diamonds, making them an attractive economical alternative. In addition, synthetic silicon carbide gemstones can achieve rich color changes (such as blue, yellow, green, etc.) by adding different elements (such as aluminum, nitrogen, boron, vanadium, etc.) during the growth process, meeting the market demand for personalized colors.

[0003] In gemstone valuation, color type, saturation (depth), and uniformity of color distribution are key evaluation indicators. Currently, the mainstream method for synthesizing silicon carbide gemstones is physical vapor transport (PVT). However, this method cannot control the release rate of dopants, resulting in poor color uniformity in the resulting colored silicon carbide gemstones. In the early stages of growth, more dopants are released, resulting in a darker color near the seed crystal. By the end of growth, when the dopants are almost completely released, the silicon carbide color becomes very light. This seriously affects the overall quality and value of the gemstone.

[0004] Therefore, how to effectively solve the problem of color unevenness in the process of growing silicon carbide gemstones using the PVT method is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The present invention provides a blue silicon carbide gemstone and a preparation method thereof, so as to solve the technical problem of uneven color of silicon carbide gemstones.

[0006] The present invention provides a method for preparing a blue silicon carbide gemstone, the preparation method comprising the following steps:

[0007] synthesizing multiple groups of silicon carbide materials with different aluminum contents, and dividing and screening the silicon carbide materials with different aluminum contents to obtain multiple groups of silicon carbide materials with different aluminum contents and different sizes, wherein the aluminum content of the silicon carbide material is positively correlated with the particle size of the silicon carbide material;

[0008] Placing the silicon carbide materials in a crucible in descending order of aluminum content, and placing a slow-release layer between two adjacent layers of the silicon carbide materials;

[0009] The physical vapor transport method was used for crystal growth to obtain blue silicon carbide gemstones.

[0010] In one embodiment of the present invention, the steps of synthesizing multiple groups of silicon carbide materials with different aluminum contents include:

[0011] The aluminum-containing substance is mixed with carbon powder and silicon powder in different proportions to prepare multiple groups of mixed materials;

[0012] Placing multiple groups of the mixed materials in graphite crucibles respectively, and placing multiple groups of graphite crucibles containing the mixed materials in a furnace respectively;

[0013] The temperature is raised to 2200-2350° C. in an argon atmosphere, and after constant temperature growth for 10-50 hours, the material is cooled to room temperature to obtain multiple groups of silicon carbide materials with different aluminum contents.

[0014] In one embodiment of the present invention, the molar ratio of the carbon powder to the silicon powder is 1:(1-1.2), and the aluminum-containing substance accounts for 0.01%-20% of the total weight of the silicon powder and the carbon powder.

[0015] In one embodiment of the present invention, the aluminum-containing material includes one or more of aluminum oxide, aluminum nitride, aluminum carbide, mullite, yttrium aluminum garnet, aluminum boride, and aluminum-based high-temperature alloy.

[0016] In one embodiment of the present invention, multiple groups of silicon carbide materials with different aluminum contents include a first silicon carbide material, a second silicon carbide material, and a third silicon carbide material. The aluminum content of the first silicon carbide material is greater than the aluminum content of the second silicon carbide material, the aluminum content of the second silicon carbide material is greater than the aluminum content of the third silicon carbide material, the particle size of the first silicon carbide material is greater than the particle size of the second silicon carbide material, and the particle size of the second silicon carbide material is greater than the particle size of the third silicon carbide material.

[0017] In one embodiment of the present invention, the particle volume of the first silicon carbide material is 500-1000 mm 3 The particle size of the second silicon carbide material is 100 to 500 mm 3 The particle volume of the third silicon carbide material is 0 to 100 mm 3 .

[0018] In one embodiment of the present invention, the step of placing the silicon carbide materials in a crucible in descending order of aluminum content and placing a slow-release layer between two adjacent layers of the silicon carbide materials includes:

[0019] placing the first silicon carbide material at the bottom of a crucible, and placing a first slow-release layer on the first silicon carbide material;

[0020] placing the second silicon carbide material on the first slow-release layer, and placing a second slow-release layer on the second silicon carbide material;

[0021] The third silicon carbide material is placed on the second slow-release layer, and a third slow-release layer and metal particles are placed on the third silicon carbide material.

[0022] In one embodiment of the present invention, the first slow-release layer includes a first activated carbon and a first graphite felt, the second slow-release layer includes a second activated carbon and a second graphite felt, the thickness of the first activated carbon is 10 to 20 mm, the thickness of the first graphite felt is 10 to 20 mm, the thickness of the second activated carbon is 5 to 15 mm, and the thickness of the second graphite felt is 5 to 15 mm; the third slow-release layer includes a porous graphite plate, the thickness of the porous graphite plate is 5 to 10 mm, and the pore size is 0.2 to 2 mm; the metal particles include one or more of tantalum, tungsten, molybdenum, niobium, zirconium, tantalum carbide, and tungsten carbide.

[0023] In one embodiment of the present invention, the weight ratio of the first silicon carbide material, the second silicon carbide material, and the third silicon carbide material is (1-2): (1.5-2.5): (2-3).

[0024] The present invention also provides a blue silicon carbide gemstone, which is prepared by any of the above preparation methods.

[0025] Beneficial effects of the present invention: The present invention provides a silicon carbide gemstone and a preparation method thereof, which first synthesizes multiple groups of silicon carbide materials with different aluminum contents and different sizes, and then arranges them in layers to form a hierarchical structure with a gradient arrangement of aluminum content and particle size, thereby achieving control over the release of aluminum elements in the raw materials, avoiding the initial concentrated release of aluminum elements, and obtaining a blue silicon carbide gemstone with uniform color. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are incorporated into and constitute a part of the specification, illustrate embodiments consistent with the present application, and together with the specification, are used to explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be derived from these drawings without inventive effort.

[0027] In the attached figure:

[0028] Figure 1 This is a flow chart of a method for preparing a blue silicon carbide gemstone provided in one embodiment of the present invention;

[0029] Figure 2 This is a flow chart for preparing silicon carbide materials with different aluminum contents provided in one embodiment of the present invention;

[0030] Figure 3 This is a schematic structural diagram of silicon carbide material charging provided in one embodiment of the present invention;

[0031] Figure 4 A schematic structural diagram of a seed crystal cover provided in one embodiment of the present invention;

[0032] Figure 5 This is a schematic structural diagram of a graphite ring provided in one embodiment of the present invention;

[0033] Figure 6 A schematic structural diagram of a crucible body provided in one embodiment of the present invention;

[0034] Figure 7 This is a schematic structural diagram of layered arrangement of silicon carbide materials with different aluminum contents provided in one embodiment of the present invention;

[0035] Figure 8 This is a physical photo of a blue silicon carbide gemstone provided in one embodiment of the present invention;

[0036] Figure 9 This is a slice photo of the blue silicon carbide gemstone prepared in Example 1 of the present invention;

[0037] Figure 10 This is a slice photo of the blue silicon carbide gemstone prepared in Example 2 of the present invention;

[0038] Figure 11 This is a slice photo of the blue silicon carbide gem prepared for comparison 1.

[0039] The reference numerals are as follows:

[0040] 100. Seed crystal cover; 101. Seed crystal cover thread; 102. Boss; 200. Graphite ring; 201. Upper step; 202. Lower step; 300. Crucible body; 301. Crucible thread; 302. Step; 400. Silicon carbide material; 410. First silicon carbide material; 420. First sustained-release layer; 421. First activated carbon; 422. First graphite felt; 430. Second silicon carbide material; 440. Second sustained-release layer; 441. Second activated carbon; 442. Second graphite felt; 450. Third silicon carbide material; 460. Third sustained-release layer; 470. Metal particles. DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments. The details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. The following embodiments and features therein may be combined with one another without conflict.

[0042] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. The drawings only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0043] In the following description, numerous details are discussed to provide a more thorough explanation of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the embodiments of the present invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring the embodiments of the present invention.

[0044] Silicon carbide's strong dispersion and high refractive index make it a gemstone with even greater brilliance, imparting a more intense color and visual appeal. Furthermore, through doping, the crystal structure can be precisely manipulated to produce a variety of colors, such as blue, green, and yellow, meeting personalized needs and expanding its market potential. However, existing processes for controlling crystal color are affected by raw material volatilization, often resulting in color stratification.

[0045] Based on this, the present invention provides a blue silicon carbide gemstone and its preparation method. By synthesizing silicon carbide raw materials with different aluminum contents and then arranging these raw materials in layers, the same or similar concentrations of aluminum-containing silicon carbide raw materials are released and crystallized at the seed crystal at each stage of crystal growth, thereby obtaining a silicon carbide gemstone with uniform color. This method is not only applicable to blue silicon carbide gemstones, but also to the preparation of silicon carbide gemstones of other colors, such as red and yellow, by simply adjusting the doping element.

[0046] See also Figure 1 The present invention provides a method for preparing blue silicon carbide gemstone, which comprises at least the following steps:

[0047] S1. Synthesizing multiple groups of silicon carbide materials with different aluminum contents, and dividing and screening the silicon carbide materials with different aluminum contents to obtain multiple groups of silicon carbide materials with different aluminum contents and different sizes, wherein the aluminum content of the silicon carbide material is positively correlated with the particle size of the silicon carbide material;

[0048] S2. Place silicon carbide materials in a crucible in descending order of aluminum content, and place a slow-release layer between two adjacent layers of silicon carbide materials;

[0049] S3. Use physical vapor transport method to grow crystals and obtain blue silicon carbide gemstones.

[0050] Specifically, step S1 adjusts the ratio of the aluminum-containing substance to the carbon powder and the silicon powder to adjust the aluminum content in the silicon carbide material, thereby achieving the preparation of multiple groups of silicon carbide materials with different aluminum contents. In one embodiment, the synthesis of multiple groups of silicon carbide materials with different aluminum contents includes steps S11-S13:

[0051] S11. Mixing the aluminum-containing substance with carbon powder and silicon powder in different proportions to prepare multiple groups of mixed materials.

[0052] In this step, carbon powder and silicon powder are raw materials for synthesizing silicon carbide materials, and the molar ratio of carbon powder to silicon powder is 1: (1 to 1.2), for example, it can be 1: 1, 1: 1.1 or 1: 1.2. The aluminum-containing substance is used to dope aluminum elements into the silicon carbide material to obtain blue silicon carbide gemstones. The amount of aluminum-containing substance added depends on the aluminum content in the prepared silicon carbide material. In one embodiment, the amount of aluminum-containing substance added accounts for 0.01% to 20% of the total weight of the carbon powder and silicon powder. Exemplarily, the amount of aluminum-containing substance added can be 0.01%, 5%, 10%, 15% or 20%, etc. The number of groups of the mixed material prepared in this step is at least two, for example, three, four or more groups, which is determined according to the number of groups of silicon carbide materials with different aluminum contents actually prepared. In one embodiment, three groups of mixed materials are prepared, and the amount of aluminum-containing substances added to the three mixed materials is 0.1%, 1%, 10%, or 5%, 10%, 15%, etc., respectively, based on the total weight of silicon powder and carbon powder.

[0053] In some embodiments, aluminum-containing materials include aluminum oxide (Al2O3), aluminum nitride (AlN), aluminum carbide (Al4C3), mullite (3Al2O3·2SiO2), yttrium aluminum garnet (Y3Al5O 12 The aluminum-containing material may be selected from one or more of the following: aluminum oxide, aluminum nitride, yttrium aluminum garnet, aluminum nitride (YAG), aluminum boride (such as AlB2), and aluminum-based high-temperature alloys. Specifically, the aluminum-containing material may be any of the materials listed above, such as aluminum oxide, aluminum nitride, or yttrium aluminum garnet. Alternatively, the aluminum-containing material may be a combination of two or more of the materials listed above in any proportion, such as a combination of aluminum oxide and aluminum nitride, or a combination of aluminum carbide, mullite, and yttrium aluminum garnet. In other embodiments, the aluminum-containing material may also be selected from materials not listed above that can provide aluminum doping elements to the silicon carbide material.

[0054] S12, placing multiple groups of mixed materials in graphite crucibles respectively, and placing multiple groups of graphite crucibles containing the mixed materials in a furnace respectively.

[0055] After mixing is complete, multiple groups of mixed materials are placed in separate graphite crucibles, and these graphite crucibles are then placed in a synthesis furnace to complete the furnace loading process. In this step, multiple graphite crucibles containing mixed materials can be placed in the same furnace or in separate synthesis furnaces, allowing for simultaneous or sequential growth. This is not a limitation.

[0056] S13. Raise the temperature to 2200-2350° C. in an argon atmosphere, grow at a constant temperature for 10-50 hours, and then cool to room temperature to obtain multiple groups of silicon carbide materials with different aluminum contents.

[0057] After the furnace is loaded, the temperature is raised to the growth temperature, such as 2200℃, 2250℃, 2300℃ or 2350℃, in an argon atmosphere, and maintained at this temperature for 10h, 30h or 50h to allow the raw materials to fully react to form aluminum-doped silicon carbide material. After the growth is completed, it is cooled to room temperature and taken out.

[0058] Please continue reading Figure 1 After the growth of multiple groups of silicon carbide materials with different aluminum contents is completed in step S1, the multiple groups of silicon carbide materials with different aluminum contents are divided and screened to obtain silicon carbide materials with different aluminum contents and different sizes. Partitioning refers to dividing large pieces of silicon carbide material into small pieces or small particles, and then screening out silicon carbide materials that meet the expected size. It should be noted that the aluminum content of the silicon carbide material is positively correlated with the particle size of the silicon carbide material, that is, silicon carbide material with a high aluminum content corresponds to a large particle size, and silicon carbide material with a low aluminum content corresponds to a small particle size.

[0059] In one embodiment, step S1 prepares three groups of silicon carbide materials with different aluminum contents, which are respectively recorded as the first silicon carbide material, the second silicon carbide material and the third silicon carbide material, wherein the aluminum content of the first silicon carbide material is greater than the aluminum content of the second silicon carbide material, and the aluminum content of the second silicon carbide material is greater than the aluminum content of the third silicon carbide material. The aluminum content in the three groups of silicon carbide materials is distributed in a gradient, and the gradient value can be 0.1% to 0.2%, such as 0.1%, 0.15% or 0.2%. There is no specific restriction on the aluminum content in each layer of silicon carbide material, and it can be adjusted according to the color depth of the gemstone. Accordingly, the particle size of the first silicon carbide material is greater than the particle size of the second silicon carbide material, and the particle size of the second silicon carbide material is greater than the particle size of the third silicon carbide material. For example, the particle volume of the first silicon carbide material is 500 to 1000 mm 3 , further, it can be 500mm 3 , 700mm 3 , 1000mm 3 etc.; the particle volume of the second silicon carbide material is 100~500mm 3 , further, 100mm 3, 300mm 3 or 500mm 3 etc.; the particle size of the third silicon carbide material is 0-100mm 3 , further, it can be 10mm 3 , 50mm 3 , 80mm 3 or 100mm 3 wait.

[0060] See Figure 1 、 Figures 3 to 6 , step S2 is to place multiple groups of silicon carbide materials in the crucible in order from high to low aluminum content. The crucible in this step is a graphite crucible structure commonly used in growing silicon carbide crystals by the PVT method. As an example, the crucible includes a crucible body 300, a graphite ring 200 and a seed crystal cover 100, wherein the crucible body 300, as the main body for holding silicon carbide materials, can be any three-dimensional structure with a cavity, such as a cylindrical structure. A crucible thread 301 is provided on the top of the cavity of the crucible body 300, and a seed crystal cover thread 101 that cooperates with the crucible thread 301 is provided on the outer wall of the seed crystal cover 100, and the seed crystal cover 100 is connected and fixed to the crucible body 300 through the seed crystal cover thread 101 and the crucible thread 301. A boss 102 for mounting a seed crystal is provided on the side of the seed crystal cover 100 facing the body 300. The graphite ring 200 is positioned between the seed crystal cover 100 and the crucible body 300. Therefore, a step 302 is provided on the inner wall of the crucible body 300 to support the graphite ring 200. The top of the graphite ring 200 is provided with an upper step 201, and the bottom of the graphite ring 200 is provided with a lower step 202. The upper step 201 mates with the boss 102 of the seed crystal cover 100, and the lower step 202 mates with the step 302 on the inner wall of the crucible body 300, thereby completing the assembly of the crucible. The cavity below the graphite ring 200 (step 302) in the crucible body 300 is used to accommodate the silicon carbide material 400. During the loading process in step S2, the silicon carbide material 400 is first placed in the crucible body 300 in descending order according to the aluminum content, and a slow-release layer is laid each time a layer of silicon carbide material 400 is placed. After all the silicon carbide material 400 is placed, the graphite ring 200 and the seed crystal cover 100 are installed on the crucible body 300, and the loading is completed.

[0061] See also Figure 7In one embodiment, a large-particle first silicon carbide material 410 is first placed at the bottom of the crucible body 300, and a first slow-release layer 420 is placed on the first silicon carbide material 410. A medium-particle second silicon carbide material 430 is then placed on the first slow-release layer 420, and a second slow-release layer 440 is placed on the second silicon carbide material 430. A small-particle third silicon carbide material 450 is then placed on the second slow-release layer 440, and a third slow-release layer 460 is placed on the third silicon carbide material 450. If there are more groups of silicon carbide materials with different aluminum contents, the same process is repeated. Finally, metal particles 470 are placed on the topmost slow-release layer. Large-particle silicon carbide materials release slowly and are resistant to high temperatures, providing material for crystal growth in the later stages of growth. Small-particle materials decompose quickly and provide material for crystal growth in the early stages of growth. The slow-release layer can mitigate the rapid release of aluminum from the raw materials, preventing concentrated release of aluminum from the raw materials during the initial growth phase.

[0062] The weight ratio of each layer of silicon carbide material is from bottom to top: (1-2): (1.5-2.5): (2-3): (2.5-3.5), and so on. For example, the weight ratio of the first silicon carbide material 410, the second silicon carbide material 430, and the third silicon carbide material 450 can be 1:1.5:2, or 1.5:2:2.5, or 2:2.5:3, and so on.

[0063] In one embodiment, the first slow-release layer 420 includes a first activated carbon 421 and a first graphite felt 422, wherein the thickness of the first activated carbon 421 is 10 to 20 mm, for example, 10 mm, 15 mm or 20 mm, and the thickness of the first graphite felt 422 is 10 to 20 mm, for example, 10 mm, 15 mm or 20 mm. Both activated carbon and graphite felt are carbon materials, and even if they are corroded by silicon during the crystal growth process, no other impurities will be introduced. In addition, since the first silicon carbide material 410 is heavily doped and the aluminum content in the raw material is high, the activated carbon and graphite felt used in the slow-release layer are relatively thick, which can better alleviate the release of aluminum.

[0064] The second slow-release layer 440 includes a second activated carbon 441 and a second graphite felt 442. The second activated carbon 441 has a thickness of 5 to 15 mm, for example, 5 mm, 10 mm, or 15 mm, and the second graphite felt 442 has a thickness of 5 to 15 mm, for example, 5 mm, 10 mm, or 15 mm. The second silicon carbide material 430 has a moderate content of doped aluminum. Therefore, the activated carbon and graphite felt in the second slow-release layer 440 are thinner than those in the first slow-release layer 440.

[0065] The third slow-release layer 460 comprises a porous graphite plate having a thickness of 5 to 10 mm, for example, 5 mm, 8 mm, or 10 mm, and a pore size of 0.2 to 2 mm, for example, 0.2 mm, 1 mm, 1.5 mm, or 2 mm. Since the third silicon carbide material 450 is the topmost raw material and has a relatively low temperature, using a porous graphite plate with larger pores as the slow-release layer can prevent premature crystallization of the gaseous raw material.

[0066] Metal particles are made of high-temperature resistant materials and laid on the top layer of the raw materials. They absorb excess carbon dust that evaporates at high temperatures through physical or chemical adsorption, preventing carbon from volatilizing to the seed crystals and forming defects such as micropipes. Metal particles include, but are not limited to, one or more of tantalum, tungsten, molybdenum, niobium, zirconium, tantalum carbide, and tungsten carbide. The metal particles can be a single type, such as tantalum, molybdenum, or niobium, or a combination of two or more types, such as a combination of tantalum and tantalum carbide, or a combination of tantalum, tungsten, and molybdenum.

[0067] After the discharge is completed, the graphite ring 200 and the seed crystal cover 100 are installed in the crucible body 300, and the loading is completed.

[0068] Please continue reading Figure 1 In step S3, the crucible after loading is placed in a crystal growth furnace, and silicon carbide crystals are grown using the PVT method according to conventional processes. After the growth is completed, a blue silicon carbide gemstone is obtained. For example, in an argon atmosphere, the temperature in the furnace is first raised to 2000°C at a heating rate of 10-50°C, for example, 30°C; then the temperature is slowly raised to 2200-2300°C, for example, 2250°C, at a heating rate of 1-10°C, for example, 5°C. During this process, the pressure is reduced from 300-500mbar, for example, 400mbar, to a growth pressure of 1-5mbar, for example, 3mbar. Then, the growth is carried out in a stable pressure section for 100-150h, for example, 130h.

[0069] See also Figure 8 Another aspect of the present invention provides a blue silicon carbide gemstone produced using the aforementioned preparation method. Because the aforementioned preparation method mitigates the release of aluminum, a doping element, from the synthesized blue silicon carbide gemstone, the resulting blue silicon carbide gemstone exhibits uniform color.

[0070] The technical scheme of the present invention is described in detail below through several specific examples and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following examples are all commercially available commodities, or can be prepared by conventional methods in the art, and the instruments used in the examples are all commercially available. The described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0071] Example 1

[0072] This embodiment provides a method for preparing a blue silicon carbide gemstone, comprising the following steps:

[0073] Step 1: synthesize silicon carbide with an aluminum content of 0.1%, silicon carbide with an aluminum content of 0.2%, and silicon carbide with an aluminum content of 0.4%, respectively, and then divide and sieve the silicon carbide with an aluminum content of 0.1% to obtain 50mm 3 Silicon carbide particles, the silicon carbide material with an aluminum content of 0.2% is divided and sieved to obtain 200mm 3 Silicon carbide particles, the aluminum content of 0.4% of the silicon carbide material is divided and sieved to obtain 500mm 3 of silicon carbide particles;

[0074] Step 2: Prepare the pellets with aluminum content of 0.4% and a volume of 500 mm 3 The silicon carbide material is placed at the bottom of the crucible, and a 10mm thick layer of activated carbon and a 10mm thick layer of graphite felt are placed on the silicon carbide material;

[0075] Step 3: Prepare the pellets with aluminum content of 0.2% and particle size of 200 mm 3 The silicon carbide material is placed in the middle, and a layer of activated carbon with a thickness of 5mm and a layer of graphite soft felt with a thickness of 5mm are placed on it;

[0076] Step 4: Prepare the pellets with an aluminum content of 0.1% and a volume of 50 mm 3 Place it on the upper part, and place a porous graphite plate with a pore size of 0.2mm and tungsten particles on the material; among them, the weight ratio of silicon carbide materials with aluminum contents of 0.4%, 0.2% and 0.1% is 1:1.5:2; then install the graphite ring 200 and the seed crystal cover 100 in the crucible body 300, and the loading is completed.

[0077] Step 5. Place the loaded crucible in a crystal furnace and use the physical vapor transport method to grow crystals: first, in an argon atmosphere, quickly raise the temperature in the furnace to 2000°C at a rate of 10°C, and then slowly raise the temperature to 2300°C at a rate of 5°C. During this process, the pressure drops from 300mbar to the growth pressure of 3mbar. Then, stably grow under this condition for 150 hours. After the crystal growth is completed, cool to room temperature to obtain a blue silicon carbide gemstone.

[0078] The method for synthesizing silicon carbide materials with different aluminum contents in step 1 comprises the following steps:

[0079] A. Mix alumina, carbon powder and silicon powder in a certain proportion;

[0080] B. Place the mixed material in a graphite crucible, and place the graphite crucible in a synthesis furnace;

[0081] C. Raise the temperature to 2200-2350°C in an argon atmosphere, keep constant temperature for 10-50 hours, and then cool to room temperature.

[0082] In step A, the silicon carbide material with an aluminum content of 0.1% is mixed with 9.46g of alumina powder, 3.5kg of silicon powder and 1.5kg of carbon powder, and kept at a constant temperature of 2220℃ for 10h, then cooled to room temperature, and taken out and processed to obtain a volume of 50mm 3 Aluminum-containing silicon carbide material;

[0083] Silicon carbide material with an aluminum content of 0.2% is made by mixing 18.96g of alumina powder with 3.6kg of silicon powder and 1.4kg of carbon powder. The mixture is kept at a constant temperature of 2250℃ for 30h, then cooled to room temperature. After being taken out and processed, a volume of 200mm is obtained. 3 Aluminum-containing silicon carbide material;

[0084] Silicon carbide material with an aluminum content of 0.4% is made by mixing 47.69g of alumina powder with 3.7kg of silicon powder and 1.3kg of carbon powder. The mixture is kept at a constant temperature of 2300℃ for 50h, then cooled to room temperature. After being taken out and processed, a volume of 500mm is obtained. 3 Aluminum-containing silicon carbide material.

[0085] See also Figure 9 The blue silicon carbide gemstone prepared in this embodiment was sliced ​​and observed to have uniform color.

[0086] Example 2

[0087] This embodiment provides a method for preparing a blue silicon carbide gemstone, comprising the following steps:

[0088] Step 1: synthesize silicon carbide with an aluminum content of 0.1%, silicon carbide with an aluminum content of 0.2%, and silicon carbide with an aluminum content of 0.4%, respectively, and then divide and sieve the silicon carbide with an aluminum content of 0.1% to obtain 60mm 3 Silicon carbide particles, the silicon carbide material with an aluminum content of 0.2% is divided and sieved to obtain 300mm 3 Silicon carbide particles, the silicon carbide material with an aluminum content of 0.4% is divided and sieved to obtain 600mm 3 of silicon carbide particles;

[0089] Step 2: Prepare the pellets with aluminum content of 0.4% and a volume of 500 mm 3 The silicon carbide material is placed at the bottom of the crucible, and a 10mm thick layer of activated carbon and a 10mm thick layer of graphite felt are placed on the silicon carbide material;

[0090] Step 3: Prepare the pellets with aluminum content of 0.2% and particle size of 200 mm 3 The silicon carbide material is placed in the middle, and a layer of activated carbon with a thickness of 5mm and a layer of graphite soft felt with a thickness of 5mm are placed on it;

[0091] Step 4: Prepare the pellets with an aluminum content of 0.1% and a volume of 50 mm 3 Place it on the upper part, and place a porous graphite plate with a pore size of 0.2mm and tungsten particles on the material; among them, the weight ratio of silicon carbide materials with aluminum contents of 0.4%, 0.2% and 0.1% is 1.5:2:2.5; then install the graphite ring 200 and the seed crystal cover 100 in the crucible body 300, and the loading is completed.

[0092] Step 5. Place the loaded crucible in a crystal furnace and use the physical vapor transport method to grow crystals: first, in an argon atmosphere, quickly raise the temperature in the furnace to 2000°C at a rate of 10°C, and then slowly raise the temperature to 2300°C at a rate of 5°C. During this process, the pressure drops from 300mbar to the growth pressure of 3mbar. Then, stably grow under this condition for 150 hours. After the crystal growth is completed, cool to room temperature to obtain a blue silicon carbide gemstone.

[0093] The method for synthesizing silicon carbide materials with different aluminum contents in step 1 comprises the following steps:

[0094] A. Mix alumina, carbon powder and silicon powder in a certain proportion;

[0095] B. Place the mixed material in a graphite crucible, and place the graphite crucible in a synthesis furnace;

[0096] C. Raise the temperature to 2200-2350°C in an argon atmosphere, keep constant temperature for 10-50 hours, and then cool to room temperature.

[0097] In step A, 6.68 g of aluminum carbide (Al4C3) was mixed with 3.5 kg of silicon powder and 1.5 kg of carbon powder, and the mixture was kept at 2230 ° C for 20 hours, then cooled to room temperature, and taken out and processed to obtain a volume of 60 mm 3 Aluminum-containing silicon carbide material;

[0098] Silicon carbide material with an aluminum content of 0.2% is made by mixing 13.37g of aluminum carbide with 3.6kg of silicon powder and 1.4kg of carbon powder. The mixture is kept at a constant temperature of 2260℃ for 40h, then cooled to room temperature. After being taken out and processed, a volume of 300mm is obtained. 3 Aluminum-containing silicon carbide material;

[0099] Silicon carbide material with an aluminum content of 0.4% is made by mixing 26.81g of aluminum carbide with 3.7kg of silicon powder and 1.3kg of carbon powder. The mixture is kept at a constant temperature of 2320℃ for 50h, then cooled to room temperature. After being taken out and processed, a volume of 600mm is obtained. 3 Aluminum-containing silicon carbide material.

[0100] See also Figure 10 The blue silicon carbide gemstone prepared in this embodiment is sliced ​​and observed to have uniform color.

[0101] Comparative Example 1

[0102] The difference between this comparative example and Example 1 is that in step 1, only silicon carbide material with an aluminum content of 0.4% is synthesized, and when charging, only silicon carbide material with an aluminum content of 0.4% is charged, and silicon carbide materials with different aluminum contents are not placed in layers.

[0103] See also Figure 11 The blue silicon carbide gemstone prepared in Comparative Example 1 was sliced ​​and observed to find that the color of the blue silicon carbide gemstone was first dark and then light, and the color was uneven.

[0104] By comparing Examples 1-2 and Comparative Example 1, it can be found that the examples use silicon carbide materials with different aluminum contents and sizes, and then load them in order from high to low aluminum content to form a gradient hierarchical structure, thereby controlling the release of aluminum elements during the crystal growth stage. Large particles release slowly and are resistant to high temperatures, and can provide materials for crystal growth in the later stages of growth. Small particles decompose into blocks and can provide materials for crystal growth in the early stages of growth. Therefore, the blue silicon carbide gemstones obtained in Examples 1-2 have uniform colors. Comparative Example 1, on the other hand, uses silicon carbide materials with a single aluminum content, and is unable to control the release of aluminum elements during the crystal growth stage, resulting in dark colors in the early stages of growth and light colors in the later stages of growth. The resulting blue silicon carbide gemstones have uneven colors and exhibit stratification.

[0105] In summary, the present invention provides a blue silicon carbide gemstone and a preparation method thereof. By synthesizing aluminum-containing silicon carbide materials with different aluminum contents and different sizes as gradient materials, and then laying buffering and absorption materials - activated carbon and soft felt - between different materials to form a hierarchical release structure, the release of aluminum elements can be controlled to obtain a blue silicon carbide gemstone with uniform color.

[0106] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing blue silicon carbide gemstone, characterized in that: The following steps are involved: synthesizing multiple groups of silicon carbide materials with different aluminum contents, and dividing and screening the silicon carbide materials with different aluminum contents to obtain multiple groups of silicon carbide materials with different aluminum contents and different sizes, wherein the aluminum content of the silicon carbide material is positively correlated with the particle size of the silicon carbide material; Placing the silicon carbide materials in a crucible in descending order of aluminum content, and placing a slow-release layer between two adjacent layers of the silicon carbide materials; The physical vapor transport method was used for crystal growth to obtain blue silicon carbide gemstones.

2. The method for preparing blue silicon carbide gemstone according to claim 1, wherein: The steps of synthesizing multiple groups of silicon carbide materials with different aluminum contents include: The aluminum-containing material is mixed with carbon powder and silicon powder in different proportions to prepare multiple groups of mixed materials; Placing multiple groups of the mixed materials in graphite crucibles respectively, and placing multiple groups of graphite crucibles containing the mixed materials in a furnace respectively; The temperature is raised to 2200-2350° C. in an argon atmosphere, and after constant temperature growth for 10-50 hours, the material is cooled to room temperature to obtain multiple groups of silicon carbide materials with different aluminum contents.

3. The method for preparing blue silicon carbide gemstone according to claim 2, wherein: The molar ratio of the carbon powder to the silicon powder is 1:(1-1.2), and the aluminum-containing substance accounts for 0.01%-20% of the total weight of the silicon powder and the carbon powder.

4. The method for preparing blue silicon carbide gemstone according to claim 2, wherein: The aluminum-containing substance includes one or more of aluminum oxide, aluminum nitride, aluminum carbide, mullite, yttrium aluminum garnet, aluminum boride, and aluminum-based high-temperature alloy.

5. The method for preparing blue silicon carbide gemstone according to claim 1, characterized in that: Multiple groups of silicon carbide materials with different aluminum contents include a first silicon carbide material, a second silicon carbide material, and a third silicon carbide material. The aluminum content of the first silicon carbide material is greater than the aluminum content of the second silicon carbide material, the aluminum content of the second silicon carbide material is greater than the aluminum content of the third silicon carbide material, the particle size of the first silicon carbide material is greater than the particle size of the second silicon carbide material, and the particle size of the second silicon carbide material is greater than the particle size of the third silicon carbide material.

6. The method for preparing blue silicon carbide gemstone according to claim 5, characterized in that: The particle volume of the first silicon carbide material is 500-1000mm 3 The particle size of the second silicon carbide material is 100 to 500 mm 3 The particle volume of the third silicon carbide material is 0 to 100 mm 3 .

7. The method for preparing blue silicon carbide gemstone according to claim 5, characterized in that: The step of placing the silicon carbide materials in a crucible in order from high to low aluminum content, and placing a slow-release layer between two adjacent layers of the silicon carbide materials comprises: placing the first silicon carbide material at the bottom of a crucible, and placing a first slow-release layer on the first silicon carbide material; placing the second silicon carbide material on the first slow-release layer, and placing a second slow-release layer on the second silicon carbide material; The third silicon carbide material is placed on the second slow-release layer, and a third slow-release layer and metal particles are placed on the third silicon carbide material.

8. The method for preparing blue silicon carbide gemstone according to claim 7, characterized in that: The first slow-release layer includes a first activated carbon and a first graphite soft felt, the second slow-release layer includes a second activated carbon and a second graphite soft felt, the thickness of the first activated carbon is 10 to 20 mm, the thickness of the first graphite soft felt is 10 to 20 mm, the thickness of the second activated carbon is 5 to 15 mm, and the thickness of the second graphite soft felt is 5 to 15 mm; the third slow-release layer includes a porous graphite plate, the thickness of the porous graphite plate is 5 to 10 mm, and the pore size is 0.2 to 2 mm; the metal particles include one or more of tantalum, tungsten, molybdenum, niobium, zirconium, tantalum carbide, and tungsten carbide.

9. The method for preparing blue silicon carbide gemstone according to claim 7, characterized in that: The weight ratio of the first silicon carbide material, the second silicon carbide material and the third silicon carbide material is (1-2): (1.5-2.5): (2-3).

10. A blue silicon carbide gemstone, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 9.

Images