Crucible for producing colorless moissanite and method for producing colorless moissanite

Abstract

The present invention relates to the technical field of moissanite production, and in particular to a crucible for producing colorless moissanite and a method for producing colorless moissanite, wherein the crucible comprises a crucible body and a crucible cover, wherein a cavity is arranged inside the crucible body, wherein the cavity comprises, from bottom to top, a powder source area for placing a silicon carbide powder source and a free flow area for conveying silicon carbide gas, wherein a filter layer is arranged above the powder source area, wherein the filter layer is filled with an adsorbent for adsorbing impurity gas in silicon carbide sublimation gas flowing out of the powder source area, wherein a heat preservation component surrounding the inner wall of the crucible body is arranged inside the free flow area, and a seed crystal graphite group for bonding seed crystals is arranged below the crucible cover. The present application can effectively remove small particle impurities and impurity gases in silicon carbide sublimation gas by arranging a filter layer filled with an adsorbent inside the crucible body, thereby effectively preventing the problem of moissanite having variegated colors.

Description

Technical Field

[0001] The invention relates to the technical field of moissanite production, and in particular to a crucible for producing colorless moissanite and a method for producing colorless moissanite. Background Art

[0002] Moissanite, also known as synthetic moissanite and synthetic carbon silicon stone, is a synthetic gemstone with the chemical composition of silicon carbide (SiC). Since the Mohs hardness of moissanite is 9.25, slightly lower than the Mohs hardness of diamond (the Mohs hardness of diamond is 10), moissanite has high wear resistance and is not easily scratched during daily wear. At the same time, its dispersion value is 0.104, which is also higher than the 0.044 of diamond, further enhancing its fire effect, making it more dazzling under light. However, as a very rare natural mineral, natural moissanite usually only appears in the form of small particles in the soil, which limits their use in jewelry making.

[0003] The artificial cultivation methods of moissanite mainly include high temperature and high pressure method, physical vapor deposition method, chemical vapor deposition method (CVD), cold crucible method, etc. These methods can greatly improve the preparation efficiency of moissanite. However, the moissanite cultivated by these artificial methods currently has certain differences in color, ranging from colorless to green, yellow, and gray in the same batch of products. At the same time, low-quality moissanite will also have tiny needle-shaped impurities, which may make the moissanite look hazy and opaque, and will also affect the refraction effect of the fire, making the overall color feel yellowish.

[0004] The authorization announcement number is CN109911899B, which discloses a method for preparing colorless moissanite, including: placing a high-purity semi-insulating silicon carbide wafer into a crucible, loading a furnace and setting growth parameters, heating the crucible, sublimating the high-purity semi-insulating wafer and recrystallizing it at the top of the crucible, cooling it out of the furnace to obtain colorless moissanite. The growth parameters are: temperature at 2000~2300℃, and pressure at 1~700 Torr. This method requires synthesizing colorless moissanite using high-purity semi-insulating silicon carbide wafers as raw materials, thereby successfully solving the problems of raw material nitrogen content doping, moissanite gray-yellow color, and reuse of unqualified silicon carbide wafers. However, this method still has the problems of small raw material application range and high cost. Summary of the invention

[0005] The present invention aims to overcome the problem that the method for artificially cultivating moissanite in the prior art cannot synthesize colorless and pure moissanite, and provides a crucible for producing colorless moissanite and a method for producing colorless moissanite.

[0006] To achieve the above-mentioned purpose, the present invention is implemented by the following technical solutions:

[0007] In a first aspect, the present invention first provides a crucible for producing colorless moissanite.

[0008] It comprises a crucible body and a crucible cover, wherein a cavity is arranged inside the crucible body, and the cavity comprises, from bottom to top, a powder source area for placing a silicon carbide powder source and a free flow area for conveying silicon carbide gas, a filter layer is arranged above the powder source area, the filter layer is filled with an adsorbent for adsorbing impurity gases in the silicon carbide sublimation gas flowing out of the powder source area, a heat preservation component surrounding the inner wall of the crucible body is also arranged inside the free flow area, and a seed crystal graphite group for bonding seed crystals is arranged below the crucible cover.

[0009] The inventors of the present application have found in experiments that the factors that can affect the purity and color of moissanite during the physical vapor deposition process include solid particle impurities and gaseous impurities in the silicon carbide sublimation gas. Among them, solid particle impurities can produce tiny needle-shaped impurities in moissanite, which will affect the propagation and scattering of light, making the moissanite look hazy and opaque, thereby affecting the refraction effect of the fire. Gaseous impurities can be deposited inside the moissanite along with the silicon carbide gas, causing lattice defects and dislocations inside the crystal, resulting in the crystal itself having a certain yellow hue.

[0010] Compared with the crucible used for depositing moissanite in the prior art, the crucible used for producing colorless moissanite in the present application has a filter layer arranged above the powder source area. Therefore, when the silicon carbide powder source in the powder source area is heated and sublimated, the sublimation gas generated will first be filtered by the filter layer, so that the solid particles mixed in the sublimation gas can be effectively filtered and removed, effectively preventing these small solid particles, impurities or inclusions from entering the interior of the moissanite, thereby improving the clarity of the prepared moissanite.

[0011] In addition, since the filter layer is filled with adsorbent, the impurity gas originally doped in the sublimation gas will be adsorbed by the adsorbent through physical or chemical means, thereby reducing the content of impurity gas in the sublimation gas, and avoiding these impurity gases from participating in the crystallization process of moissanite during the condensation and crystallization stage, thereby avoiding problems such as lattice defects and dislocations, and effectively preventing the problem of moissanite appearing discolored due to crystal defects.

[0012] Finally, another important difference between the present application and the prior art is that the insulation component in the prior art is usually arranged outside the crucible body to achieve the insulation of the crucible. In the present application, the insulation component is arranged around the inner wall of the free flow zone. The inventor found that after the insulation component is arranged inside the free flow zone, it can introduce the following unexpected technical effects: First, it can prevent the mutual diffusion of heat inside and outside the free flow zone in a targeted manner, so that the temperature in the free flow zone is more uniform. At the same time, since the insulation component is arranged around the inner wall of the free flow zone, there is a certain temperature difference between the free flow zone and the powder source zone, thereby improving the deposition efficiency of moissanite. Finally, since the insulation component is arranged inside the free flow zone, the inner diameter of the free flow zone is reduced, so that the silicon carbide sublimation gas can be guided to flow in the direction of the seed crystal, thereby further improving the deposition efficiency of the silicon carbide sublimation gas on the surface of the seed crystal.

[0013] Preferably, the filter layer comprises a filter container made of porous graphite, and a receiving cavity for filling an adsorbent is arranged inside the filter container.

[0014] The porous graphite can effectively filter small impurity particles in the silicon carbide sublimation gas, and at the same time has good permeability to the silicon carbide sublimation gas.

[0015] Preferably, the adsorbent is a combination of one or more of titanium carbide powder, high-purity titanium powder and metal vanadium powder.

[0016] Preferably, the thermal insulation component comprises a thermal insulation felt surrounding the inner wall of the crucible body, and an L-shaped isolation layer for isolating and protecting the thermal insulation felt is arranged on the outer side of the thermal insulation felt.

[0017] Preferably, the L-shaped isolation layer is erected above the filter layer.

[0018] Preferably, the seed crystal graphite group includes a hard graphite substrate and a flexible substrate bonded to the graphite substrate, and the seed crystal is bonded to the bottom of the flexible substrate.

[0019] In the production process of moissanite in the prior art, the seed crystals used are usually small in size, and the stresses at various positions of the small-sized seed crystals during the growth of the moissanite are basically the same, so the quality of the moissanite formed by the small-sized seed crystals during the crystallization process is relatively uniform, and the processing loss is relatively small. However, since the large-sized seed crystals are bonded under the crucible cover, the heating conditions and stress conditions at various positions are different, so in the process of growing large-sized moissanite, the obtained moissanite will have lattice defects and dislocations and other undesirable defects, which ultimately leads to an increase in the loss rate of the moissanite.

[0020] In order to overcome the above technical problems, the inventors of the present application have found that if the large-sized seed crystals are first bonded to the surface of a flexible substrate, and then the flexible substrate with the large-sized seed crystals is bonded to the crucible cover for physical vapor deposition, the above defects can be effectively avoided. The reason is that the flexible substrate can effectively buffer the thermal expansion and contraction and stress concentration of various parts of the large-sized seed crystals, thereby effectively eliminating stress, avoiding lattice defects and dislocations that may occur in the moissanite during the deposition process, and improving the effective utilization rate of the moissanite.

[0021] Preferably, the seed crystal graphite group further comprises a seed crystal holder fixedly connected to the bottom of the crucible cover for supporting the seed crystal.

[0022] The quality of the moissanite formed in the process of growing moissanite using large-sized seed crystals is usually large. Therefore, if the bonding strength between the seed crystal and the crucible cover is not enough, the defect of the moissanite falling may occur. Therefore, in addition to using the bonding method to bond the seed crystal to the crucible cover, the present application also designs a seed crystal holder to support the seed crystal, thereby effectively maintaining the stability of the seed crystal bonding.

[0023] In a second aspect, the present invention also provides a method for producing colorless moissanite, which is based on the crucible as described in any one of the above, and comprises the following steps:

[0024] (S.1) bonding the seed crystal to the bottom of the seed crystal graphite group;

[0025] (S.2) adding silicon carbide powder source and adsorbent to the powder source area and the filter layer respectively, heating and evacuating the interior of the crucible body to remove impurity gases in the crucible body;

[0026] (S.3) Argon gas is introduced into the crucible body for thermal field protection, and then colorless moissanite is deposited on the surface of the seed crystal by physical vapor deposition.

[0027] Preferably, in the step (S.2), the pressure inside the crucible body is evacuated to 1-50 mbar.

[0028] Preferably, in the step (S.2), the physical vapor deposition temperature is controlled at 2000-2400° C., and the physical vapor deposition time is 100-500 h.

[0029] Therefore, the present invention has the following beneficial effects:

[0030] The present application can effectively remove small particle impurities and impurity gases in the silicon carbide sublimation gas by arranging a filter layer filled with an adsorbent inside the crucible body, thereby preventing these impurities from participating in the crystallization process of moissanite during the condensation and crystallization stage, thereby avoiding problems such as lattice defects and dislocations, and effectively preventing the problem of moissanite having variegated colors due to crystal defects. At the same time, the present application effectively improves the deposition efficiency of moissanite by arranging the heat preservation component inside the free flow zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic structural diagram of a crucible for producing colorless moissanite provided in Example 1 of the present invention.

[0032] Figure 2 This is a schematic diagram of the structure of the filter layer provided in Example 1 of the present invention.

[0033] Figure 3 This is a schematic diagram of the structure of the seed crystal holder provided in Example 1 of the present invention.

[0034] Figure 4 This is a photo of the colorless moissanite ingot prepared in Example 1 of the present invention.

[0035] Figure 5 This is a photo of the colorless moissanite particles obtained after cutting.

[0036] Figure 6 This is a schematic structural diagram of a crucible for producing colorless moissanite provided in Comparative Example 2 of the present invention.

[0037] Wherein: crucible body 1, crucible cover 2, cavity 3, powder source area 4, free flow area 5, filter layer 6, adsorbent 7, insulation component 8, seed crystal 9, seed crystal graphite group 10, filter container 11, accommodating cavity 12, insulation soft felt 13, L-shaped isolation layer 14, graphite substrate 15, flexible substrate 16, seed crystal holder 17, annular groove 18. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0039] Example 1

[0040] like Figure 1 , Figure 2 as well as Figure 3 As shown, the present invention first provides a crucible for producing colorless moissanite, and its structure includes a crucible body 1 and a crucible cover 2 matched therewith. The crucible body 1 is provided with a cavity 3 inside, and the cavity 3 can be divided into a powder source area 4 for placing silicon carbide powder source and a free flow area 5 for conveying silicon carbide gas from bottom to top. A seed crystal 9 for depositing colorless moissanite is bonded to the bottom of the crucible cover 2. The silicon carbide powder source inside the powder source area 4 is sublimated after being heated to form silicon carbide sublimation gas. The silicon carbide sublimation gas flows upward along the inner wall of the crucible body 1 to the free flow area 5, and gradually cools and crystallizes on the surface of the seed crystal 9, thereby forming moissanite.

[0041] In order to ensure that the formed moissanite is colorless moissanite with high clarity, in this embodiment, the inventors set a filter layer 6 above the powder source area 4, and the filter layer 6 includes a filter container 11 composed of porous graphite, and a receiving cavity 12 for filling the adsorbent 7 is arranged inside the filter container 11. Among them, the filter container 11 composed of porous graphite has a porous structure, so it can allow the silicon carbide sublimation gas to pass through, and the tiny impurity particles mixed in the silicon carbide sublimation gas can be effectively filtered and removed, thereby preventing these small solid particle impurities or inclusions from entering the interior of the moissanite, thereby improving the clarity of the prepared moissanite. When the silicon carbide sublimation gas enters the accommodating chamber 12, the silicon carbide sublimation gas can fully contact with the adsorbent 7, so that the impurity gas originally doped in the sublimation gas will be adsorbed by the adsorbent through physical or chemical means, thereby reducing the content of the impurity gas in the sublimation gas, avoiding these impurity gases from participating in the crystallization process of moissanite during the condensation and crystallization stage, thereby avoiding problems such as lattice defects and dislocations, and effectively preventing the problem of moissanite appearing in color due to crystal defects.

[0042] Generally speaking, the typical impurity gas that can affect the color of moissanite is nitrogen. When nitrogen is doped into moissanite, the color of moissanite will turn yellow. Therefore, the adsorbent 7 is preferably a substance that can adsorb nitrogen. After screening, the inventors found that any one or a combination of titanium carbide powder, high-purity titanium powder, and metal vanadium powder can achieve selective adsorption of nitrogen in silicon carbide sublimation gas.

[0043] In addition, the present application further provides an insulation component 8 surrounding the inner wall of the crucible body 1 inside the free flow zone 5, which mainly includes an insulation soft felt 13 surrounding the inner wall of the crucible body 1. In order to protect the insulation soft felt 13 from damage by external forces, in this embodiment, an L-shaped isolation layer 14 is further provided on the outside of the insulation soft felt 13, thereby achieving isolation and protection of the insulation soft felt 13.

[0044] Compared with the prior art, the present application transfers the heat preservation component 8 usually arranged outside the crucible body 1 to the inside of the free flow zone 5, so that it can prevent the heat inside and outside the free flow zone 5 from diffusing each other in a targeted manner, thereby ensuring the independence and uniformity of the temperature inside the free flow zone 5, so that there is a certain temperature difference between the free flow zone 5 and the powder source zone 4, which ensures the deposition efficiency of moissanite. In addition, in this embodiment, since the heat preservation component 8 is arranged inside the free flow zone 5, the inner diameter of the free flow zone 5 is reduced, so that the silicon carbide sublimation gas can be guided to flow in the direction of the seed crystal 9, thereby further improving the deposition efficiency of the silicon carbide sublimation gas on the surface of the seed crystal 9.

[0045] In order to make the crucible in this embodiment suitable for the production of large-sized colorless moissanite, a seed crystal graphite group 10 for bonding seed crystals 9 is arranged under the crucible cover 2 in this embodiment. The seed crystal graphite group 10 specifically includes a hard graphite substrate 15 connected to the bottom of the crucible cover 2 and a flexible substrate 16 bonded to the graphite substrate 15. After bonding the large-sized seed crystal 9 to the flexible substrate 16, the flexibility of the flexible substrate 16 can effectively buffer the thermal expansion and contraction and stress concentration of various parts of the large-sized seed crystal 9, thereby effectively eliminating stress, avoiding lattice defects and dislocations that may occur in the deposition process of moissanite, and improving the effective utilization rate of moissanite. The flexible substrate 16 can be selected from a combination of one or more of graphite paper, polyimide film, polysiloxane film, and ultra-thin glass.

[0046] At the same time, in order to improve the structural stability of the large-sized seed crystal 9 after being bonded to the flexible substrate 16, the seed crystal graphite group 10 in this embodiment further includes a seed crystal holder 17 fixedly connected to the bottom of the crucible cover 2 for supporting the seed crystal 9. The seed crystal holder 17 includes an annular groove 18 at the center thereof, and the seed crystal 9 is embedded in the annular groove 18.

[0047] In order to verify the actual effect of the crucible, this embodiment also uses the crucible to carry out a deposition test of colorless moissanite, which includes the following steps:

[0048] S.1 Use a glue spreader to spin-coat a layer of polyamide glue with a viscosity of 1200 cp and a film thickness of 50 μm on the surface of an 8-inch seed crystal 9, and then bond the seed crystal 9 with the glue on the surface to the surface of the flexible substrate 16 at the bottom of the seed crystal graphite group 10;

[0049] S.2 Pour 5N purity silicon carbide powder source evenly into the powder source area 4, and fill the metal vanadium powder into the filter layer 6, heat the inside of the crucible body 1 to 1500°C, and then evacuate the inside to a pressure of 20 mbar. This process is repeated 4 times to remove the impurity gas in the crucible body 1;

[0050] S.3 Argon gas is introduced into the graphite crucible and the temperature is raised to 2200°C for physical vapor deposition. The process is stopped after continuous deposition for 300 hours and the temperature is lowered until it is taken out of the furnace, thereby forming colorless moissanite.

[0051] The actual photo of the prepared colorless moissanite single crystal ingot is as follows Figure 4 As shown, Figure 4 The colorless moissanite particles obtained after cutting the colorless moissanite in Figure 5 shown.

[0052] Comparative Example 1

[0053] The difference between Comparative Example 1 and Example 1 is that the filter layer 6 inside the crucible body 1 is removed, and the rest of the structure remains unchanged.

[0054] Comparative Example 2

[0055] The difference between Comparative Example 2 and Example 1 is that: Figure 6 As shown, the filter layer 6 originally arranged inside the crucible body 1 is arranged outside the crucible body 1, and the rest of the structure remains unchanged.

[0056] Comparative Example 3

[0057] The difference between Comparative Example 3 and Example 1 is that the heat preservation component 8 inside the free flow area 5 is removed, and the rest of the structure remains unchanged.

[0058] Comparative Example 4

[0059] The difference between Comparative Example 4 and Example 1 is that the flexible substrate 16 in the seed crystal graphite group 10 is removed, and the seed crystal 9 is directly bonded to the surface of the graphite substrate 15, and the rest of the structure remains unchanged.

[0060] The colorless moissanite prepared in Example 1 and Comparative Examples 1 to 4 (the preparation methods are the same except for the crucibles used) was observed, weighed, and color comparison was performed using a color card. It was then cut to remove the defective parts on the surface and edge of the moissanite, and the loss rate of the moissanite was calculated. The results are shown in Table 1 below:

[0061] Table 1

[0062] project Moissanite Quality Loss rate Color (clarity) Example 1 3.75Kg 10.3% White / 95% Comparative Example 1 3.82Kg 10.8% Slightly yellow / 97% Comparative Example 2 3.31 Kg 12.5% White / 95% Comparative Example 3 3.18Kg 13.2% White / 95% Comparative Example 4 3.55Kg 16.3% White / 97%

[0063] From the above test results, we can see that the method of the present invention can effectively improve the clarity and preparation efficiency of colorless moissanite. At the same time, by introducing a flexible substrate during the deposition process, the probability of adverse phenomena in colorless moissanite is effectively reduced, thereby significantly reducing the loss rate of colorless moissanite.

[0064] The specific embodiments described herein are merely examples of the spirit of the present invention. A person skilled in the art of the present invention may make various modifications or additions to the specific embodiments described or replace them in a similar manner, but this will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A crucible for producing colorless moissanite, characterized in that: The invention comprises a crucible body (1) and a crucible cover (2), wherein a cavity (3) is arranged inside the crucible body (1), wherein the cavity (3) comprises, from bottom to top, a powder source area (4) for placing a silicon carbide powder source and a free flow area (5) for conveying silicon carbide gas, wherein a filter layer (6) is arranged above the powder source area (4), wherein the filter layer (6) is filled with an adsorbent (7) for adsorbing impurity gases in silicon carbide sublimation gas flowing out of the powder source area (4), and wherein the free flow area (5) is also provided with a filter layer (6) surrounding the crucible body. (1) a heat-insulating assembly (8) around the inner wall, the heat-insulating assembly (8) being mounted above the filter layer (6), a seed crystal graphite group (10) for bonding a seed crystal (9) being arranged below the crucible cover (2), the seed crystal graphite group (10) comprising a hard graphite substrate (15) and a flexible substrate (16) bonded to the graphite substrate (15), the seed crystal (9) being bonded to the bottom of the flexible substrate (16), the flexible substrate being selected from a combination of one or more of a polyimide film, a polysiloxane film, and ultra-thin glass.

2. A crucible for producing colorless moissanite according to claim 1, characterized in that: The filter layer (6) comprises a filter container (11) made of porous graphite, and a receiving cavity (12) for filling an adsorbent (7) is arranged inside the filter container (11).

3. A crucible for producing colorless moissanite according to claim 1 or 2, characterized in that: The adsorbent (7) is a combination of one or more of titanium carbide powder, high-purity titanium powder, and metal vanadium powder.

4. A crucible for producing colorless moissanite according to claim 1, characterized in that: The heat-insulating component (8) comprises a heat-insulating soft felt (13) surrounding the inner wall of the crucible body (1), and an L-shaped isolation layer (14) for isolating and protecting the heat-insulating soft felt (13) is arranged on the outer side of the heat-insulating soft felt (13).

5. A crucible for producing colorless moissanite according to claim 4, characterized in that: The L-shaped isolation layer (14) is mounted above the filter layer (6).

6. A crucible for producing colorless moissanite according to claim 1, characterized in that: The seed crystal graphite group (10) further comprises a seed crystal holder (17) fixedly connected to the bottom of the crucible cover (2) and used for supporting the seed crystal (9).

7. A method for producing colorless moissanite, characterized in that: It is based on the crucible according to any one of claims 1 to 6, and comprises the following steps: (S.1) bonding the seed crystal (9) to the bottom of the seed crystal graphite group (10); (S.2) adding a silicon carbide powder source and an adsorbent (7) to the powder source area (4) and the filter layer (6) respectively, heating and evacuating the interior of the crucible body (1) to remove impurity gases in the crucible body (1); (S.3) Argon gas is introduced into the crucible body (1) for thermal field protection, and then colorless moissanite is deposited on the surface of the seed crystal (9) by physical vapor deposition.

8. The method according to claim 7, characterized in that In the step (S.2), the crucible body (1) is evacuated to a pressure of 1-50 mbar.

9. The method according to claim 7, characterized in that: In the step (S.2), the physical vapor deposition temperature is controlled at 2000-2400° C., and the physical vapor deposition time is 100-500 hours.

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