A large-size self-heating graphite core for diamond preparation and its preparation method

Abstract

This application belongs to the field of superhard material production and preparation technology, specifically relating to a large-size self-heating graphite core for diamond preparation and its preparation method. The large-size self-heating graphite core has an overall structure that can be divided into three layers from the outside to the inside: an outer cylinder, a heat-conducting layer, and an inner cylinder; the heat-conducting layer is a tin foil uniformly coated with aluminum oxide powder; the outer and inner cylinders are interlocking graphite catalyst cores. In this application, based on dividing a conventional graphite core into a ring and a cylinder structure, a heat-conducting layer is embedded in the middle to achieve bidirectional radiation heating during the synthesis and preparation of diamond, thus overcoming the technical defects of insufficiently rapid and uniform heat conduction when indirectly heating the graphite core. This structural design can effectively overcome the technical problem of unbalanced temperature field within the cavity under the trend of large cavity in current synthetic diamond production and preparation.

Description

Technical Field

[0001] This application belongs to the field of superhard material production and preparation technology, specifically relating to a large-size self-heating graphite core for diamond preparation and its preparation method. Background Technology

[0002] Diamond is a major representative product of superhard materials. Due to the significant cost advantage of synthetic diamonds and their wide range of industrial applications, there is a strong industrial demand for synthetic diamonds.

[0003] The principle behind the production of synthetic diamonds involves transforming a graphite (carbon) core into diamond under high temperature and pressure conditions within a specific device (a press). Therefore, the structure of the graphite core has a significant impact on the quality of synthetic diamonds.

[0004] In existing graphite core structures, indirect heating is often used. This involves encasing the graphite core in a heat-conducting element (heater), with heat then radiating inwards from the outer periphery during diamond production. However, due to factors such as production volume, large-cavity growth is currently the primary technological trend for diamond fabrication. Therefore, conventional graphite core structures face challenges when used in large-cavity equipment, including temperature field imbalance (uniformity) and slow heat conduction. Furthermore, assembly of these structures is not always convenient, significantly impacting production efficiency. Therefore, exploring improvements to graphite core structures to meet the needs of large-cavity synthetic diamond production is of paramount technical significance. Summary of the Invention

[0005] Based on the trend of synthetic diamond preparation and production technology with a large cavity (diameter of not less than 60mm) in the top press, the purpose of this application is to provide a new self-heating graphite core structure, thereby laying a certain technical foundation for the preparation and production of synthetic diamond.

[0006] The technical solution adopted in this application is described in detail below.

[0007] A large-size self-heating graphite core for diamond preparation solves technical problems such as temperature field imbalance by dividing the existing graphite core into two parts: an inner core and an outer core, and by adding a thermally conductive material between the two parts.

[0008] Specifically, the large-size self-heating graphite core column has an overall structure that can be divided into three layers from the outside to the inside; the three layers from the outside to the inside are: an outer column, a heat-conducting layer, and an inner column;

[0009] The heat-conducting layer is a tin foil uniformly coated with aluminum oxide powder; the particle size of the aluminum oxide powder is 100 mesh, the thickness of the tin foil is generally no more than 0.2 mm, and the thickness of the tin foil after coating with aluminum oxide powder should not exceed 1 mm;

[0010] The outer and inner pillars are both graphite catalyst core pillars prepared with reference to existing technologies;

[0011] The large-size self-heating graphite core column is prepared through the following steps:

[0012] (a) Material preparation

[0013] Tin foil, inner pillar, and outer pillar for the thermally conductive layer were prepared separately.

[0014] The thermally conductive layer is made of tin foil. During preparation, aluminum oxide powder with a particle size of 100 mesh is uniformly coated on the surface of the sheet-like tin foil (single-sided coating; during coating, the aluminum oxide powder can be mixed evenly with an urethane-based water-based adhesive and then directly sprayed onto the surface of the tin foil). The thickness of the aluminum foil after coating with aluminum oxide is no more than 1 mm; the thickness of the tin foil is generally no more than 0.2 mm.

[0015] The inner column is prepared as a solid cylindrical graphite catalyst core column according to existing technology;

[0016] According to existing technology, the outer column is prepared as a hollow annular graphite catalyst core column (ring column), the diameter of which is equivalent to the outer diameter of the inner ring (i.e., the diameter of the hollow inner ring is equal to or only slightly larger than the outer diameter of the inner column, that is, it is necessary to ensure that the inner column can be well nested into the inner ring of the outer column); in a preferred design, the height of the outer column is slightly lower than that of the inner column (e.g., slightly lower by 0.5 mm), so as to facilitate the maintenance of consistent height after subsequent assembly and processing into finished products;

[0017] The graphite catalyst core column, by mass ratio, has the following specific formulation composition reference: graphite: metal catalyst = 7.5-8.5: 2.5-1.5;

[0018] The graphite has a purity of not less than 99.9% and a particle size of ≥300 mesh;

[0019] The metal catalyst is a mixture of iron, nickel, cobalt, and manganese powders, with a mass ratio of iron:nickel:cobalt and manganese powder = 6:3:1; all types of metals are powders with a purity of not less than 99.9% and a particle size of ≥300 mesh;

[0020] The inner column has a diameter of 35~40mm.

[0021] The outer column has an outer diameter of 70-85mm and an inner diameter of 35.5-40.8mm.

[0022] (ii) Assembling the finished graphite core column

[0023] First, the inner and outer columns are sealed and wrapped with tin foil using a heat-conducting layer (the tin foil surface without aluminum oxide coating is in direct contact with the column surface); after wrapping, carbon powder heating material is evenly adhered to both ends of the outer column and carbon powder heating material is evenly adhered to the side surface of the inner column.

[0024] Then, the inner cylinder, after being wrapped, is embedded into the inner ring of the outer cylinder. After the nesting is completed, the inner cylinder and the outer cylinder are at the same height, and the carbon powder heating material attached to both ends of the outer cylinder and the carbon powder heating material attached to the side of the inner cylinder are fully in contact as a whole.

[0025] After assembly, circular thermally conductive tin foil is evenly adhered to both ends of the assembled composite column; the diameter of the circle is slightly smaller than the inner diameter of the assembled composite column (for example, the diameter of the circle is 1mm smaller than the inner diameter of the composite column).

[0026] After attaching the thermally conductive layer with tin foil, carbon powder heating material is finally attached to both ends of the composite column after the interlocking is completed.

[0027] The carbon powder heating material is specifically graphite powder (particle size ≤ 800 mesh, purity not less than 90%), with an adhesion thickness not exceeding 0.5 mm (during adhesion, water glass can be sprayed onto the corresponding surface before direct adhesion).

[0028] (III) Preparation of finished products

[0029] The graphite core column assembled in step (II) is pressed into shape (for example, using a four-column two-sided top press, with specific specifications as follows: height 40~50mm, outer diameter 60~75mm). After molding, it is calcined at 550~650℃ for 1.5~3h (preferably at 600℃ for 2h) under a reducing atmosphere (for example, hydrogen atmosphere).

[0030] It should be explained that the "self-heating" mentioned in this application means that, since there is an aluminum foil layer coated with aluminum oxide and a carbon powder heating material layer between the inner and outer columns, the relevant materials can form an electrical circuit under current conditions during the preparation of artificial diamond. However, due to the high resistance of the relevant materials, the effect of bidirectional heating of the graphite core column by the heat-conducting layer is achieved.

[0031] In this application, a conventional graphite core is divided into a ring and a cylindrical structure. A heat-conducting layer is embedded in the middle of these components to achieve bidirectional radiative heating during the synthesis and processing of diamond. This overcomes the shortcomings of existing indirect heating methods where heat conduction is not rapid or uniform. Preliminary experimental results show that this structural design effectively addresses the problem of unbalanced temperature fields within large cavities in current synthetic diamond production, and effectively solves the technical challenge of heat conduction within the graphite core, thereby improving heating efficiency and effect. Furthermore, it overcomes the inconvenience of assembling and using existing graphite cores. Therefore, it has significant practical value for ensuring and stabilizing the quality of synthetic diamond manufacturing. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the graphite core column structure provided in this application;

[0033] Figure 2 A schematic diagram of the inner column (left) and outer column (right) structure of the graphite core provided in this application;

[0034] Figure 3 This is a schematic diagram illustrating the "self-heating" principle during the processing of the graphite core provided in this application. Detailed Implementation

[0035] The present application will be further explained below with reference to the embodiments. Example

[0036] like Figure 1 , Figure 2 As shown, the large-size self-heating graphite core for diamond preparation provided in this application solves technical problems such as temperature field imbalance by dividing the existing graphite core into two parts: an inner core and an outer core, and by adding a thermally conductive material between the two parts. Its overall structure is a cylinder with three layers from the outside to the inside: an outer core, a thermally conductive layer, and an inner core.

[0037] The specific preparation method of the large-size self-heating graphite core is as follows.

[0038] (a) Material preparation

[0039] Tin foil, inner pillar, and outer pillar for the thermally conductive layer were prepared separately.

[0040] The thermal conductive layer is made of tin foil. During preparation, aluminum oxide powder with a particle size of 100 mesh is uniformly coated on the surface of the sheet tin foil, and the thickness of the aluminum foil after coating with aluminum oxide is not greater than 1 mm; the thickness of the tin foil is generally not more than 0.2 mm.

[0041] When coating, a single-sided coating method is adopted. The coating method is as follows: after mixing the aluminum oxide powder with urethane-based water-based adhesive evenly, it can be directly sprayed onto the surface of the tin foil.

[0042] The inner column is prepared as a solid cylindrical graphite catalyst core column according to existing technology;

[0043] The outer column is prepared by means of a hollow, annular graphite catalyst core column (ring column) according to existing technology, wherein the diameter of the inner ring is equivalent to the outer diameter of the inner column;

[0044] The graphite catalyst core column, by mass ratio, has the following specific formulation: graphite: metal catalyst = 7.5-8.5: 2.5-1.5;

[0045] The graphite has a purity of not less than 99.9% and a particle size of ≥300 mesh;

[0046] The metal catalyst is a mixture of iron, nickel, cobalt, and manganese powders, with a mass ratio of iron:nickel:cobalt and manganese powder = 6:3:1; all types of metals are powders with a purity of not less than 99.9% and a particle size of ≥300 mesh;

[0047] The inner column has a diameter of 35~40mm.

[0048] The outer column has an outer diameter of 70-85mm and an inner diameter of 35.5-40.8mm.

[0049] (ii) Assembling the finished graphite core column

[0050] First, the inner and outer columns are sealed and wrapped with tin foil using a heat-conducting layer. After wrapping, carbon powder heating material is evenly adhered to both ends of the outer column and carbon powder heating material is evenly adhered to the side surface of the inner column.

[0051] Then, the inner cylinder, after being wrapped, is embedded into the inner ring of the outer cylinder. After the nesting is completed, the inner cylinder and the outer cylinder are at the same height, and the carbon powder heating material attached to both ends of the outer cylinder and the carbon powder heating material attached to the side of the inner cylinder are fully in contact as a whole.

[0052] After assembly, circular thermally conductive tin foil is evenly adhered to both ends of the assembled composite column; the diameter of the circle is slightly smaller than the inner diameter of the assembled composite column (for example, the diameter of the circle is 1mm smaller than the inner diameter of the composite column).

[0053] After attaching the thermally conductive layer with tin foil, carbon powder heating material is finally attached to both ends of the composite column after the interlocking is completed.

[0054] The carbon powder heating material is graphite powder (particle size ≤ 800 mesh, purity not less than 90%), and the adhesion thickness is not more than 0.5 mm (during adhesion, water glass is sprayed onto the corresponding surface and then directly adhered; the aforementioned adhesion is also done in this way).

[0055] (III) Preparation of finished products

[0056] The graphite core column assembled in step (II) is pressed into shape (specifically, the height is 40mm and the outer diameter is 60mm). After molding, it is kept at 600℃ for 2 hours under a reducing atmosphere (hydrogen atmosphere).

[0057] When the graphite core is specifically used to prepare synthetic diamond, after it is placed into the large cavity of the press, because there is an aluminum foil layer coated with aluminum oxide and a carbon powder heating material layer between the inner and outer cores, the relevant materials can form an electrically connected circuit (e.g., ...) under current conditions. Figure 3 As shown in the figure, due to the high resistance of the relevant materials, the effect of bidirectional heating of the graphite core column by the heat-conducting layer is achieved.

[0058] Taking the self-heating graphite core prepared in this embodiment and the graphite core prepared by existing technology (i.e., referring to the aforementioned material formulation, but without specifically distinguishing between the inner and outer cylinders, only a single cylindrical structure) as examples, the actual preparation results show that:

[0059] Compared to existing graphite cores, in terms of the uniformity of diamond growth in the cross-section of the core, the diamond growth distribution uniformity during the synthesis process of the self-heating graphite core prepared in this application is about 97.6%, while the diamond growth uniformity in the cross-section of existing conventional graphite cores is only about 72%. This result shows that the uniformity of diamond growth can be greatly improved by adjusting the heating method.

[0060] Regarding the particle size of the synthesized diamond, statistical results show that the proportion of the main peak particle size of diamond prepared using the self-heating graphite core column of this application exceeds 45%, while the proportion of the main peak particle size of diamond prepared using existing conventional graphite core columns is only between 30% and 40%. In particular, the proportion of high-quality material of grade 60 and above can be increased by more than 12 percentage points compared with existing methods. Further statistical results on the proportion of related crystal forms show that the proportion of isothermal crystal forms of diamond prepared using the self-heating graphite core column of this application can reach 92%, while the proportion of isothermal crystal forms of diamond prepared using existing conventional graphite core columns is only 66% at most.

[0061] The above results all indicate that adjusting the graphite core structure and heating method can significantly improve the diamond preparation effect and has good production application value.

Claims

1. A large-size self-heating graphite core for diamond preparation, characterized in that, The large-size self-heating graphite core column has an overall structure that can be divided into three layers from the outside to the inside: an outer column, a heat-conducting layer, and an inner column. The heat-conducting layer is a tin foil uniformly coated with aluminum oxide powder; The outer and inner pillars are graphite catalyst core pillars that can be interlocked and matched. The large-size self-heating graphite core column is prepared through the following steps: (a) Material preparation Tin foil, inner pillar, and outer pillar for the thermally conductive layer were prepared separately. The thermally conductive layer is made of tin foil, which is prepared by uniformly coating the surface of the sheet-like tin foil with aluminum oxide powder. The inner column is a solid cylindrical graphite catalyst core column; The outer column is a hollow, annular graphite catalyst core column, and the diameter of its inner ring is approximately equal to the outer diameter of the inner column. (ii) Assembling the finished graphite core column First, the inner and outer columns are sealed and wrapped with tin foil using a heat-conducting layer. After wrapping, carbon powder heating material is evenly adhered to both ends of the outer column and carbon powder heating material is evenly adhered to the side surface of the inner column. Then, the inner cylinder, after being wrapped, is embedded into the inner ring of the outer cylinder. After the nesting is completed, the inner cylinder and the outer cylinder are at the same height, and the carbon powder heating material attached to both ends of the outer cylinder and the carbon powder heating material attached to the side of the inner cylinder are fully in contact as a whole. After assembly, circular thermally conductive tin foil is evenly adhered to both ends of the assembled composite column; after adhering the thermally conductive tin foil, carbon powder heating material is finally adhered to both ends of the assembled composite column. (III) Preparation of finished products The graphite core column assembled in step (II) is pressed into shape, and then calcined under a reducing atmosphere.

2. The large-size self-heating graphite core for diamond preparation as described in claim 1, characterized in that, The aluminum oxide powder has a particle size of 100 mesh, the tin foil thickness does not exceed 0.2 mm, and the tin foil thickness after coating with aluminum oxide powder does not exceed 1 mm.

3. The large-size self-heating graphite core for diamond preparation as described in claim 2, characterized in that, When coating tin foil, coat only one side.

4. The large-size self-heating graphite core for diamond preparation as described in claim 1, characterized in that, In step (one), The inner column has a diameter of 35~40mm; The outer column has an outer diameter of 70~85mm and an inner diameter of 35.5~40.8mm.

5. The large-size self-heating graphite core for diamond preparation as described in claim 1, characterized in that, After assembly, the circular heat-conducting layer is made of tin foil that is 1 mm smaller than the inner diameter of the composite column after assembly.

6. The large-size self-heating graphite core for diamond preparation as described in claim 1, characterized in that, The graphite catalyst core column, by mass ratio, has the following specific formulation: graphite: metal catalyst = 7.5-8.5: 2.5-1.5; The graphite has a purity of not less than 99.9% and a particle size of ≥300 mesh; The metal catalyst is a mixture of iron, nickel, cobalt and manganese powders, with a mass ratio of iron:nickel:cobalt and manganese powder = 6:3:1; all types of metals are powders with a purity of not less than 99.9% and a particle size of ≥300 mesh.

7. The large-size self-heating graphite core for diamond preparation as described in claim 1, characterized in that, In step (3), keep warm at 600℃ for 2 hours.

8. The method for preparing a large-size self-heating graphite core for diamond preparation as described in claim 1, characterized in that, Specifically, the steps include the following: (a) Material preparation Tin foil, inner pillar, and outer pillar for the thermally conductive layer were prepared separately. The thermally conductive layer is made of tin foil, which is prepared by uniformly coating the surface of the sheet-like tin foil with aluminum oxide powder. The inner column is a solid cylindrical graphite catalyst core column; The outer column is a hollow, annular graphite catalyst core column, and the diameter of its inner ring is approximately equal to the outer diameter of the inner column. (ii) Assembling the finished graphite core column First, the inner and outer columns are sealed and wrapped with tin foil using a heat-conducting layer. After wrapping, carbon powder heating material is evenly adhered to both ends of the outer column and carbon powder heating material is evenly adhered to the side surface of the inner column. Then, the inner cylinder, after being wrapped, is embedded into the inner ring of the outer cylinder. After the nesting is completed, the inner cylinder and the outer cylinder are at the same height, and the carbon powder heating material attached to both ends of the outer cylinder and the carbon powder heating material attached to the side of the inner cylinder are fully in contact as a whole. After assembly, circular thermally conductive tin foil is evenly adhered to both ends of the assembled composite column; after adhering the thermally conductive tin foil, carbon powder heating material is finally adhered to both ends of the assembled composite column. (III) Preparation of finished products The graphite core column assembled in step (II) is pressed into shape, and then calcined under a reducing atmosphere.

9. The method for preparing a large-size self-heating graphite core for diamond preparation as described in claim 8, characterized in that, In step (3), keep warm at 600℃ for 2 hours.

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