Induction heating furnace crucible for preparing boron nitride nanosheets on a kilogram scale

Abstract

This invention discloses a high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram level. The crucible includes a crucible body and a crucible lid. A nickel substrate layer and a nickel lining layer are respectively provided on the bottom and inner walls of both sides of the crucible body. The space formed by the bottom nickel substrate layer and the inner walls of both sides is used to hold the material to be heated. A first positioning brick is provided between the nickel substrate layer and the inner walls of both sides of the crucible body. A boron nitride powder filling layer is provided between the inner walls of both sides of the crucible body and the nickel lining layer. A second positioning brick is placed on top of the boron nitride powder filling layer, located between the inner walls of both sides of the crucible body and the nickel lining layer. The first positioning brick is located below the boron nitride powder filling layer. The crucible provided by this invention can significantly reduce the pulverization and shedding of graphite crucibles, significantly extend the crucible life, reduce the amount of foreign impurities in the product, and improve the purity of the product.

Description

Technical Field

[0001] This invention relates to the field of high-temperature furnace crucible technology for preparing boron nitride nanosheets, and specifically provides an induction heating furnace crucible for preparing boron nitride nanosheets at the kilogram level. Background Technology

[0002] The kilogram-scale preparation method of boron nitride nanosheets involves reacting boron and nitrogen sources in a liquid flux environment to obtain amorphous boron nitride agglomerates. These agglomerates then undergo crystallization at high temperatures to form monodisperse boron nitride nanosheets. The high-temperature furnace requires two key performance conditions: firstly, a sufficiently rapid heating rate exceeding 600 °C / h; and secondly, a heating temperature sufficient for the crystallization of the boron nitride nanosheets, meaning the furnace heating element should be able to reach 1300 °C. These two requirements dictate that graphite crucibles, capable of withstanding both rapid heating and high temperatures, are an ideal material. Furthermore, graphite crucibles can self-heat within induction heating systems, making them highly suitable for induction heating furnaces.

[0003] However, in the preparation environment of boron nitride nanosheets, the graphite crucible is subject to erosion from the penetration and fumigation of the liquid flux, leading to surface pulverization and peeling. The bottom surface of the graphite material is also stripped of a layer of graphite powder due to the shrinkage effect during the solidification of the liquid flux, and this graphite powder becomes trapped in the product and cannot be separated. Furthermore, the degree of erosion is related to the amount of material in the crucible. In larger crucibles weighing kilograms or even tens of kilograms, the pulverization and detachment of graphite are more pronounced, especially in the graphite crucible lid. Under continuous fumigation with flux vapor, a large amount of graphite particles detach after only two or three uses, drastically shortening its lifespan. Utility Model Content

[0004] Therefore, the purpose of this invention is to provide an induction heating furnace crucible for preparing boron nitride nanosheets at the kilogram level; The technical solution provided by this utility model is: a high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram level, wherein the crucible is a graphite crucible and is placed inside an induction heating coil as an induction heating element; the crucible includes a crucible body and a crucible lid; The crucible body has a nickel substrate layer and a nickel lining layer on its bottom and two inner walls, respectively. The space formed by the nickel substrate layer at the bottom and the nickel lining layers on both sides is used to hold the material to be heated. A first positioning brick is provided between the nickel substrate layer and the inner walls on both sides of the crucible body. A boron nitride powder filling layer is provided between the inner walls on both sides of the crucible body and the nickel lining layer. A second positioning brick is placed on top of the boron nitride powder filling layer. The second positioning brick is located between the inner walls on both sides of the crucible body and the nickel lining layer. The first positioning brick is located below the boron nitride powder filling layer. A flue component is installed in the center of the crucible cover. Two protective gas inlets are symmetrically arranged on the crucible cover and on both sides of the flue component. A protective gas tube is inserted into the protective gas inlet and extends into the crucible body. An opening is provided on the side of the bottom of the protective gas tube body. The openings of the two protective gas tubes are arranged in opposite directions. A temperature measuring port is located in the middle of the line connecting the two protective gas inlets along the circumference of the crucible lid; an infrared temperature measuring tube is installed in the temperature measuring port.

[0005] Preferably, a nickel substrate layer and a nickel lining layer are respectively provided on the bottom surface and the inner walls on both sides of the crucible body. Specifically, a nickel substrate layer is laid on the bottom surface of the crucible body, and a nickel lining layer is provided on both sides of the nickel substrate layer. The nickel lining layer is perpendicular to the nickel substrate layer and extends to the upper edge of the crucible body, with its height lower than the inner wall of the crucible body.

[0006] Preferably, a boron nitride receiving tray is placed in the center of the material to be heated, and the boron nitride receiving tray is located below the flue opening.

[0007] Preferably, a gap is left between the nickel substrate layer and the first positioning brick.

[0008] Preferably, the crucible body is a split or integrated structure.

[0009] Preferably, an insulation layer is provided between the outer walls of the induction heating coil and the outer surface of the crucible, and the insulation layer covers the outer surface of the crucible.

[0010] Preferably, the flue component includes a flue base and a flue, the flue base being a graphite structure and in direct contact with the crucible lid, and the flue being placed on the flue base.

[0011] The present invention provides an induction heating furnace crucible for preparing boron nitride nanosheets at the kilogram level. Using this crucible, several kilograms to tens of kilograms of crude boron nitride nanosheets can be obtained in one sintering process. At the same time, it significantly reduces the pulverization and shedding of graphite crucibles, significantly extends the crucible life, reduces the amount of foreign impurities in the product, and improves the purity of the product. Attached Figure Description

[0012] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments: Figure 1 A schematic diagram of the overall structure of the high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram level provided by this utility model; Figure 2 This is a top view schematic diagram of the high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram level according to this utility model. Detailed Implementation

[0013] The present invention will be further explained below with reference to specific implementation schemes, but it is not limited to the present invention.

[0014] To address the problems of pulverization and short lifespan of existing induction heating furnace crucibles used for kilogram-scale preparation of boron nitride nanosheets, such as... Figure 1-2 As shown, this embodiment provides a high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram level, using induction heating as the heating method and a graphite crucible as the induction heating element. The crucible includes a crucible body and a crucible lid. The bottom of the graphite crucible is covered with a nickel substrate – nickel substrate layer 4. The nickel substrate protects the bottom of the graphite crucible 3, preventing the liquid flux during the boron nitride nanosheet synthesis process from flowing and settling at high temperatures and directly contacting the bottom of the graphite crucible 3. This prevents the liquid flux from condensing and peeling off the graphite powder from the bottom of the graphite crucible 3, which then adheres to the boron nitride nanosheet product and cannot be separated. The liquid flux cannot penetrate into metallic nickel, nor can it peel off the surface layer of metallic nickel. The nickel material does not participate in the reaction in the boron nitride nanosheet synthesis system; the overall reducing nature of the reaction system prevents nickel from forming nickel oxide and entering the product.

[0015] The distance between the edge of the nickel substrate 4 and the inner wall of the graphite crucible 3 is about a few centimeters, in order to allow space for thermal expansion of the substrate. The coefficient of thermal expansion of nickel is approximately 2 centimeters per meter at 1000 degrees Celsius. Therefore, a few centimeters of expansion space should be reserved.

[0016] A nickel liner layer 5 is formed around the edge of the nickel substrate layer 4 using nickel material, extending to near the upper edge of the graphite crucible. The nickel liner can be a single nickel tube or a rolled nickel sheet. When rolled from a nickel sheet, as long as the material does not leak along the seams, welding or other connection methods are not required at the ends. The liner is positioned a certain distance from the upper edge of the graphite crucible to provide space for longitudinal expansion and facilitate atmosphere flow.

[0017] A first positioning brick 6 is placed between the nickel substrate layer 4 and the graphite crucible 3 wall for positioning, leaving a small gap for thermal expansion and contraction of the nickel substrate layer 4. A second positioning brick is placed above the boron nitride powder filling layer 7 for positioning the upper part of the nickel lining layer 5. Positioning bricks are placed between the substrate, lining, and graphite crucible wall for positioning. The positioning bricks prevent the nickel substrate and lining from accidentally shifting too close to the graphite crucible during crucible movement, loading, or unloading. Because the electromagnetic field penetration depth of the induction heating furnace is greater than the thickness of the graphite crucible, the metal plate may still be subjected to eddy current heating effects within a few centimeters inside the graphite crucible; at the same time, the graphite crucible, as a heating element, has a temperature higher than the required temperature of the material due to the temperature gradient, and the maximum temperature may exceed the melting point of metallic nickel. Therefore, positioning bricks are used to prevent the substrate and lining from accidentally approaching the graphite crucible wall, which could lead to overheating and melting. Positioning bricks should be evenly distributed in the gap between the substrate and the graphite crucible wall, and should have a certain height and width to play a positioning role. At the same time, the thickness should be slightly smaller than the gap between the substrate and the graphite crucible wall.

[0018] Since the positioning bricks will be directly attached to the graphite crucible, the materials used for the positioning bricks must not melt at at least 1400℃. Optional materials include, but are not limited to, high-purity alumina refractory bricks, high-temperature resistant magnesia-carbon bricks, magnesia-chrome bricks, and magnesia-alumina spinel bricks.

[0019] A high thermal conductivity boron nitride powder filler layer 7 is formed between the nickel lining layer 5 and the graphite crucible wall 3. Since air is a poor conductor of heat and convection is difficult in the gaps between the lining and the graphite crucible wall, using high thermal conductivity boron nitride increases the rate at which heat is conducted inward from the graphite heating element. The high thermal conductivity boron nitride powder is very stable at 1400℃ under a protective atmosphere, does not melt, and does not react with graphite and nickel. It also occupies some of the gap space, reducing the internal air content and minimizing oxidation of the graphite crucible. Positioning bricks are evenly distributed above the filler layer to position the upper part of the lining and guide its directional expansion. The space formed by the lining and substrate is not covered. Due to the condensation of reaction volatiles and high-temperature flux at the joint between the cover and the lining, a metal cover would easily stick to the lining and be difficult to open.

[0020] The graphite crucible is equipped with a lid, and a large flue 9 is located in the center of the lid. This allows for the rapid discharge of gases generated during the reaction and fumes from the evaporation of high-temperature flux, while also preventing the flue from becoming clogged with deposits after repeated use. A boron nitride receiving tray 12 is located directly below the flue 9. This tray is placed on top of the material after the crucible is filled. Boron nitride is used because this area is most susceptible to oxidation. The oxides formed from the oxidation of nickel can be dissolved by the liquid high-temperature flux and may enter the material. Boron nitride is resistant to high temperatures, oxidation, liquid flux, and reactive atmospheres, making it a more ideal material when used in small quantities.

[0021] The size requirement for receiving plate 12 is that it can catch the vast majority of objects falling from the flue.

[0022] The crucible lid has two symmetrical protective gas inlets, which protect the graphite crucible lid while providing airflow guidance.

[0023] A protective gas pipe 10 enters the graphite crucible through the protective gas inlet. The protective gas pipe 10 opens from the side, perpendicular to the diameter of the crucible lid, and has two protective gas outlets facing different directions from the lid. Both protective gas pipes 10 simultaneously blow out tangential airflow, which, combined with the large central flue, allows the airflow during the boron nitride generation stage and flux vapors to be quickly discharged from the flue, reducing the chance of fumigating the graphite crucible lid and extending its lifespan. A temperature measuring port is located on the crucible lid, perpendicular to the line connecting the protective gas inlets, and an infrared thermometer passes through this port. Before use, the surface of the crucible lid is covered with insulating filler.

[0024] The flue is assembled using flue component 9, which includes a flue base and a flue. The flue base is made of graphite and extends through the insulation filler layer that wraps the crucible, making direct contact with the crucible lid. The flue is placed on the flue base.

[0025] like Figure 2 As shown. There is a temperature measuring port on the crucible lid, perpendicular to the line connecting the protective gas inlet, and an infrared thermometer passes through the temperature measuring port.

[0026] The container space consisting of the lining and the substrate is uncovered. When the lining is filled with the material to be heated, a boron nitride receiving tray 12 is placed in the center of the material to receive the flue gas drips.

[0027] Preferably, the graphite crucible is covered with insulating filler on all sides and bottom to form an insulating layer 2. The graphite crucible can be a split type, with the bottom and side walls being independent and replaceable separately; or it can be a one-piece type, with no gaps between the bottom and side walls.

[0028] This invention uses nickel as the substrate 4 and lining 5 of the graphite crucible. The dense surface of the nickel material can effectively prevent the penetration of a large amount of liquid flux during kilogram-scale reactions and has good resistance to flux fumigation. The graphite crucible only serves as a heating element and is no longer directly subjected to the penetration and fumigation of liquid flux, which greatly extends the life of the graphite crucible. The nickel material is resistant to high temperatures and can also withstand carburization, and it does not bear mechanical force. It can be used for a long time in boron nitride synthesis systems containing carbon elements, and has a very long life.

[0029] This invention uses refractory bricks to limit the substrate and lining, which can prevent the substrate and lining from accidentally shifting and directly contacting the graphite crucible during crucible movement, loading and unloading, etc., so as to absorb or induce excessive heat and cause melting; at the same time, the gap between the substrate, lining and graphite crucible is filled with high thermal conductivity boron nitride to provide space for thermal expansion.

[0030] This invention uses dual protective gas inlets to blow out tangential airflow, which, together with the large central flue, allows the airflow during the boron nitride generation stage to be quickly discharged from the flue, reducing the chance of fumigating the graphite crucible lid and extending its lifespan. A small amount of graphite particles that fall off near the flue are received by the boron nitride receiving plate, which has better high-temperature oxidation resistance, and do not contaminate the reaction products.

[0031] Example 1 A graphite crucible with an inner diameter of 700 mm and a height of 600 mm is placed inside the induction coil of the induction heating furnace, and its sides and bottom are covered with insulating filler. A circular nickel plate with a diameter of 600 mm is placed in the center of the bottom of the graphite crucible as a substrate. Four arc-shaped refractory bricks, each 240 mm long, 120 mm high, and 40 mm wide, are evenly distributed along the four edges of the substrate as positioning bricks. A 10 mm space is reserved in each of the four directions for substrate expansion.

[0032] A nickel tube with an outer diameter of 600 mm, a length of 500 mm, and a thickness of 4 mm, or a nickel plate with a length of 1890 mm, a width of 500 mm, and a thickness of 4 mm, rolled into a tube, is used as a liner along the edge of the substrate. The liner is placed at the edge of the substrate without any fixing means. High thermal conductivity boron nitride powder is used as a filler between the liner and the graphite crucible wall. Four other positioning bricks of the same size are placed at the positions corresponding to the four positioning bricks at the top and bottom of the filler.

[0033] Fill the lining with the raw materials to be reacted until the lining volume is nearly full. Place a boron nitride receiving plate with a diameter of 300 mm and a thickness of 10 mm in the center to catch the debris falling from the flue.

[0034] The crucible lid has two symmetrical protective gas inlets pre-drilled at half its radius, and a temperature measuring hole perpendicular to the line connecting the protective gas inlets at half its radius. A 150 mm diameter flue hole is located in the center of the lid. After placing the lid on, insert the two protective gas tubes symmetrically into the protective gas inlets. Rotate the tubes so that the gas outlets are perpendicular to the radius of the graphite crucible lid, and the two outlets face opposite sides of the lid. Insert the temperature measuring tube into the measuring hole, connect the protective gas path and an infrared thermometer, and assemble the flue using the flue components. Finally, fill the graphite crucible lid with insulating filler to a certain thickness, turn on the protective gas, and then power on to heat the crucible.

[0035] After the synthesis and cooling of boron nitride nanosheets are completed, the insulating filler is removed, and the temperature measuring tube, protective gas tube, and flue components are disassembled. The graphite crucible lid is opened, and the boron nitride receiving tray is removed, allowing for material discharge. The internal lining, positioning bricks, and boron nitride powder filler can remain in place for an extended period. This completes one operation cycle.

[0036] The specific embodiments of this utility model are written in a progressive manner, emphasizing the differences between each implementation scheme, and the similar parts can be referred to each other.

[0037] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram-scale, characterized in that, The crucible is a graphite crucible, which serves as an induction heating element and is placed inside the induction heating coil (1); the crucible includes a crucible body and a crucible lid; The crucible body has a nickel substrate layer (4) and a nickel lining layer (5) on the bottom and the inner walls on both sides respectively. The space formed by the nickel substrate layer (4) at the bottom and the nickel lining layers (5) on both sides is used to hold the material to be heated. A first positioning brick (6) is provided between the nickel substrate layer (4) and the inner walls on both sides of the crucible body. A boron nitride powder filling layer (7) is provided between the inner walls on both sides of the crucible body and the nickel lining layer (5). A second positioning brick is placed on top of the boron nitride powder filling layer (7). The second positioning brick is located between the inner walls on both sides of the crucible body and the nickel lining layer (5). The first positioning brick (6) is located below the boron nitride powder filling layer (7). A flue component (9) is installed in the center of the crucible cover. Two protective gas inlets are symmetrically provided on the crucible cover and on both sides of the flue component (9). A protective gas tube (10) is inserted into the protective gas inlet. The protective gas tube (10) extends into the crucible body. An opening is provided on the side of the bottom of the protective gas tube (10). The openings of the two protective gas tubes (10) are set in opposite directions. A temperature measuring port is provided in the middle of the line connecting the two protective gas inlets along the circumference of the crucible lid; an infrared temperature measuring tube (11) is provided in the temperature measuring port.

2. The high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram scale according to claim 1, characterized in that, The crucible body has a nickel substrate layer (4) and a nickel lining layer (5) on the bottom surface and the inner walls on both sides, respectively. Specifically, a nickel substrate layer (4) is laid on the bottom surface of the crucible body, and a nickel lining layer (5) is provided on the two sides of the nickel substrate layer (4). The nickel lining layer (5) is set perpendicular to the nickel substrate layer (4) and extends to the upper edge of the crucible body. Its height is lower than the inner wall of the crucible body.

3. The high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram scale according to claim 1, characterized in that, A boron nitride receiving plate (12) is placed in the center of the material to be heated, and the boron nitride receiving plate (12) is located below the flue opening.

4. The high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram scale according to claim 1, characterized in that, A gap is left between the nickel substrate layer (4) and the first positioning brick (6).

5. The high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram scale according to claim 1, characterized in that, The crucible body can be either a split type or a one-piece structure.

6. The high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram scale according to claim 1, characterized in that, The induction heating coil (1) has an insulation layer (2) between its outer wall and the outer wall of the crucible, and the insulation layer (2) covers the outside of the crucible.

7. The high-temperature furnace crucible for preparing boron nitride nanosheets at the kilogram scale according to claim 1, characterized in that, The flue component (9) includes a flue seat and a flue. The flue seat is a graphite structure and is in direct contact with the crucible lid. The flue is placed on the flue seat.

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