阅读说明：本技术 致密化六方氮化硼陶瓷及其制备方法和装置 (Densified hexagonal boron nitride ceramic and preparation method and device thereof ) 是由 张洪波 旷峰华 任佳乐 任瑞康 崔鸽 于 2020-12-31 设计创作，主要内容包括：本发明是关于一种致密化六方氮化硼陶瓷及其制备方法和装置。所述方法包括以下步骤：将六方氮化硼陶瓷原料装入石墨模具中；所述石墨模具包括石墨容器和石墨压头；所述石墨容器和所述石墨压头配合将所述六方氮化硼陶瓷原料完全包覆；为所述石墨模具通电使其升温；沿所述石墨压头的移动方向施加压力；保温保压；降温,得到六方氮化硼陶瓷；其密度≥1.6g/cm～3,弯曲强度≥28MPa。所要解决的技术问题是如何制备一种致密化六方氮化硼陶瓷,使其既能快速烧结提高生产效率,所烧结的六方氮化硼陶瓷又具有较高的强度能够满足承载性的使用需求,同时所制备的产品尺寸不受限制,成本更经济,从而更加适于实用。(The invention relates to a densified hexagonal boron nitride ceramic and a preparation method and a device thereof. The method comprises the following steps: putting a hexagonal boron nitride ceramic raw material into a graphite mold; the graphite mold comprises a graphite container and a graphite pressure head; the above-mentionedThe graphite container is matched with the graphite pressure head to completely coat the hexagonal boron nitride ceramic raw material; electrifying the graphite mould to heat the graphite mould; applying pressure along the moving direction of the graphite pressure head; preserving heat and pressure; cooling to obtain hexagonal boron nitride ceramic; the density is more than or equal to 1.6g/cm 3 The bending strength is more than or equal to 28 MPa. The technical problem to be solved is how to prepare a densification hexagonal boron nitride ceramic, which can be rapidly sintered to improve the production efficiency, and the sintered hexagonal boron nitride ceramic has higher strength to meet the use requirement of bearing capacity, and meanwhile, the size of the prepared product is not limited, and the cost is more economic, thereby being more suitable for practicality.)

1. A preparation method of densified hexagonal boron nitride ceramic is characterized by comprising the following steps:

1) putting a hexagonal boron nitride ceramic raw material into a graphite mold; the graphite mold comprises a graphite container and a graphite pressure head; the graphite container and the graphite pressure head are matched to completely coat the hexagonal boron nitride ceramic raw material;

2) electrifying the graphite mould to heat the graphite mould; applying pressure along the moving direction of the graphite pressure head; preserving heat and pressure; and cooling to obtain the hexagonal boron nitride ceramic.

2. The preparation method according to claim 1, wherein the hexagonal boron nitride ceramic raw material comprises, in mass percent, not more than 5% of sintering aid and not less than 95% of hexagonal boron nitride ceramic; the hexagonal boron nitride ceramic raw material is powder or a preformed block.

3. The preparation method according to claim 1, wherein the step 2) of electrifying the graphite mold is to adopt a graphite electrode to be tightly attached to the graphite container and then electrifying the graphite electrode; the current of the graphite electrode and the current of the graphite mold are 1-10 KA.

4. The preparation method according to claim 3, wherein the graphite mold and the graphite electrode are made of high-purity graphite with a flexural strength of more than 60MPa and a resistivity of less than or equal to 20 μ Ω -m.

5. The method according to claim 1, wherein the temperature rise rate in step 2) is 50-100 ℃/min, and the temperature rise rate is 1750-1950 ℃.

6. The method according to claim 1, wherein the pressure applied in step 2) is a step pressure or a constant pressure, and the pressure is 10 to 60 MPa.

7. The method according to claim 1, wherein the heat-preserving and pressure-maintaining in step 2) is performed at 1750-1950 ℃ under 10-60 MPa for 1-10 min.

8. The preparation method according to claim 1, wherein the temperature reduction in the step 2) is water cooling, and the temperature reduction speed is 50 ℃/min to 100 ℃/min.

9. The preparation method according to claim 1, wherein the sum of the process time of the heating, the heat preservation and the cooling in the step 2) is less than or equal to 120 min.

10. A densified hexagonal boron nitride ceramic prepared by the production method according to any one of claims 1 to 9, characterized in that its density is 1.6g/cm or more³The bending strength is more than or equal to 28 MPa.

11. An apparatus for hexagonal boron nitride ceramic densification, comprising:

a graphite die comprising a graphite container and a graphite ram; the graphite container and the graphite pressure head are matched to form a cavity;

the graphite electrode is tightly attached to the graphite container and used for electrifying the graphite mold to heat the graphite mold;

an axial pressure unit for applying pressure to the graphite container and the graphite pressure head;

the water cooling unit is used for cooling the graphite container and the graphite pressure head;

the control system is respectively connected with the graphite electrode, the axial pressure unit and the water cooling unit; and the control system controls the graphite electrode, the axial pressure unit and the water cooling unit to be opened or closed according to a set sintering program.

12. The hexagonal boron nitride ceramic densification apparatus of claim 11, wherein the graphite mold and the graphite electrode both use high purity graphite with a flexural strength greater than 60Mpa and a resistivity less than or equal to 20 μ Ω -m.

13. The hexagonal boron nitride ceramic densification apparatus of claim 11 or 12, wherein the graphite vessel comprises:

the bottom plate is a flat plate made of graphite;

the die cavity is a block made of graphite; the block body is provided with a plurality of through holes; the block is placed on the bottom plate in a direction in which the open end of the through hole directly contacts the surface of the bottom plate.

14. The hexagonal boron nitride ceramic densification apparatus of claim 11, further comprising a thermal insulation layer and a stage; the heat insulation layer is arranged above the graphite pressure head and used for insulating and insulating the graphite pressure head; the stage is disposed below the graphite container to support the graphite container and insulate the graphite container.

15. The hexagonal boron nitride ceramic densification apparatus of claim 14, wherein the water cooling unit comprises an upper cooling layer and a lower cooling layer;

the upper cooling layer is arranged above the heat insulation layer; the upper cooling layer comprises a circulating water pipe; the circulating water pipe penetrates through the heat insulation layer to cool the graphite pressure head;

the lower cooling layer is arranged below the objective table; the lower cooling layer comprises a circulating water pipe; the circulating water pipe penetrates through the objective table to cool the graphite container.

Technical Field

The invention belongs to the technical field of ceramic manufacturing, and particularly relates to a densified hexagonal boron nitride ceramic and a preparation method and a device thereof.

Background

Hexagonal boron nitride (h-BN) is a ceramic material which is difficult to densify due to the characteristics of special lamellar structure, low self-diffusion coefficient and the like. At present, the commonly used preparation methods of the hexagonal boron nitride ceramics mainly include pressureless sintering (PLS), hot-pressing sintering (HP), Spark Plasma Sintering (SPS) and the like. However, the hexagonal boron nitride ceramics prepared by the above methods have defects.

The hexagonal boron nitride ceramic prepared by pressureless sintering has low density and poor mechanical property, and can only meet the use requirement of non-bearing property.

Although the hexagonal boron nitride ceramic prepared by hot-pressing sintering can be obtained, the hexagonal boron nitride ceramic with high density and high strength has the problems of long sintering period, limited specification and size of a sintered product and the like, so that the hexagonal boron nitride ceramic with large specification is difficult to prepare, and the hexagonal boron nitride ceramic has the problems of high production cost, low batch efficiency and the like.

Although the hexagonal boron nitride ceramic prepared by spark plasma sintering can obtain high-density and high-strength hexagonal boron nitride ceramic, the hexagonal boron nitride ceramic also has the technical problems of high equipment cost, limited product size and the like.

Disclosure of Invention

The invention mainly aims to provide a densified hexagonal boron nitride ceramic and a preparation method and a device thereof, and aims to solve the technical problem of how to prepare the densified hexagonal boron nitride ceramic, so that the densified hexagonal boron nitride ceramic can be rapidly sintered to improve the production efficiency, the sintered hexagonal boron nitride ceramic has higher strength and can meet the use requirement of bearing capacity, and meanwhile, the prepared product is not limited in size and is more economic in cost, so that the method is more suitable for practical use.

The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme. The preparation method of the densified hexagonal boron nitride ceramic provided by the invention comprises the following steps:

1) putting a hexagonal boron nitride ceramic raw material into a graphite mold; the graphite mold comprises a graphite container and a graphite pressure head; the graphite container and the graphite pressure head are matched to completely coat the hexagonal boron nitride ceramic raw material;

2) electrifying the graphite mould to heat the graphite mould; applying pressure along the moving direction of the graphite pressure head; preserving heat and pressure; and cooling to obtain the hexagonal boron nitride ceramic.

The object of the present invention and the technical problems solved thereby can be further achieved by the following technical measures.

Preferably, in the preparation method, the hexagonal boron nitride ceramic raw material comprises, by mass, not more than 5% of sintering aid and not less than 95% of hexagonal boron nitride ceramic; the hexagonal boron nitride ceramic raw material is powder or a preformed block.

Preferably, in the preparation method, the step 2) of electrifying the graphite mold refers to adopting a graphite electrode to be closely attached to the graphite container, and then electrifying the graphite electrode; the current of the graphite electrode and the current of the graphite mold are 1-10 KA.

Preferably, in the preparation method, the graphite mold and the graphite electrode are both made of high-purity graphite with the breaking strength of more than 60Mpa, and the resistivity of the high-purity graphite is less than or equal to 20 mu omega-m.

Preferably, in the preparation method, the temperature rising speed in the step 2) is 50-100 ℃/min, and the temperature rises to 1750-1950 ℃.

Preferably, in the preparation method, the pressure applied in the step 2) is a step pressure or a constant pressure, and the pressure is 10 to 60 Mpa.

Preferably, in the preparation method, the maintaining of the temperature and the pressure in the step 2) is performed at 1750-1950 ℃ and 10-60 Mpa for 1-10 min.

Preferably, in the preparation method, the temperature reduction in the step 2) is water cooling, and the temperature reduction speed is 50 ℃/min to 100 ℃/min.

Preferably, in the preparation method, the total time of the heating, heat preservation and cooling in the step 2) is less than or equal to 120 min.

The object of the present invention and the technical problem to be solved are also achieved by the following technical means. The density of the densified hexagonal boron nitride ceramic prepared according to the preparation method provided by the invention is more than or equal to 1.6g/cm³The bending strength is more than or equal to 28 MPa.

The object of the present invention and the technical problem to be solved are also achieved by the following technical means. According to the invention, the hexagonal boron nitride ceramic densification device comprises:

a graphite die comprising a graphite container and a graphite ram; the graphite container and the graphite pressure head are matched to form a cavity;

the graphite electrode is tightly attached to the graphite container and used for electrifying the graphite mold to heat the graphite mold;

an axial pressure unit for applying pressure to the graphite container and the graphite pressure head;

the water cooling unit is used for cooling the graphite container and the graphite pressure head;

the control system is respectively connected with the graphite electrode, the axial pressure unit and the water cooling unit; and the control system controls the graphite electrode, the axial pressure unit and the water cooling unit to be opened or closed according to a set sintering program.

Preferably, in the above hexagonal boron nitride ceramic densification apparatus, the graphite mold and the graphite electrode both use high-purity graphite with a flexural strength greater than 60Mpa, and the resistivity thereof is less than or equal to 20 μ Ω · m.

Preferably, the hexagonal boron nitride ceramic densification apparatus of the preceding, wherein the graphite vessel comprises:

the bottom plate is a flat plate made of graphite;

the die cavity is a block made of graphite; the block body is provided with a plurality of through holes; the block is placed on the bottom plate in a direction in which the open end of the through hole directly contacts the surface of the bottom plate.

Preferably, the hexagonal boron nitride ceramic densification device further comprises a heat insulation layer and a stage; the heat insulation layer is arranged above the graphite pressure head and used for insulating and insulating the graphite pressure head; the stage is disposed below the graphite container to support the graphite container and insulate the graphite container.

Preferably, the hexagonal boron nitride ceramic densification apparatus described above, wherein the water cooling unit comprises an upper cooling layer and a lower cooling layer;

the upper cooling layer is arranged above the heat insulation layer; the upper cooling layer comprises a circulating water pipe; the circulating water pipe penetrates through the heat insulation layer to cool the graphite pressure head;

the lower cooling layer is arranged below the objective table; the lower cooling layer comprises a circulating water pipe; the circulating water pipe penetrates through the objective table to cool the graphite container.

By means of the technical scheme, the densified hexagonal boron nitride ceramic and the preparation method and device thereof provided by the invention at least have the following advantages:

1. the densified hexagonal boron nitride ceramic and the preparation method and the device thereof have the advantages that the sintering speed is extremely high, direct current or alternating current is directly supplied to a graphite die through a graphite electrode to form large current, a heating assembly is formed by a graphite backing plate, a graphite die cavity and a graphite pressure head, the hexagonal boron nitride ceramic raw material is subjected to full-coating heating, the whole sintering process can be completed within 120 minutes from temperature rise to temperature reduction, and the sintering heat preservation time is less than 10 minutes;

2. the densified hexagonal boron nitride ceramic and the preparation method and the device thereof have simple structural design, do not need to be provided with a vacuum chamber, and also do not need to provide a vacuum environment and atmosphere protection, so that the device has small occupied area and low manufacturing cost;

3. according to the densified hexagonal boron nitride ceramic and the preparation method and device thereof, sintering of large-size products can be realized, on one hand, the processing environment of the device is not limited due to the fact that the device does not need a vacuum cavity, and on the other hand, the hexagonal boron nitride ceramic raw material is completely coated by the heating component and is directly heated, so that the hexagonal boron nitride ceramic is uniformly heated integrally, and the hexagonal boron nitride ceramic with the diameter not less than 600mm can be prepared;

4. according to the densified hexagonal boron nitride ceramic and the preparation method and device thereof, the graphite mold is designed to be a combined design of a graphite backing plate, a graphite mold cavity and a graphite pressure head, the graphite mold cavity can be a single cavity or a plurality of cavities, and different graphite mold cavities can be assembled, so that the requirement of simultaneous sintering of a plurality of groups of samples can be met, and high-throughput research and development and batch preparation of materials are realized.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.

Drawings

FIG. 1 is a schematic structural view of a hexagonal boron nitride ceramic densification apparatus in accordance with the present invention;

FIG. 2 is a schematic diagram of a graphite mold cavity configuration-a single chamber;

fig. 3 is a schematic diagram of a graphite mold cavity configuration-multi-cavity.

Detailed Description

To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description will be made on the specific implementation, structure, features and effects of a hexagonal boron nitride ceramic and a method and an apparatus for preparing the same according to the present invention with reference to the accompanying drawings and preferred embodiments.

The invention provides a preparation method of densified hexagonal boron nitride ceramic, which comprises the following steps: 1) putting a hexagonal boron nitride ceramic raw material into a graphite mold; the graphite mold comprises a graphite container and a graphite pressure head; the graphite container and the graphite pressure head are matched to completely coat the hexagonal boron nitride ceramic raw material; 2) electrifying the graphite mould to heat the graphite mould; applying pressure along the moving direction of the graphite pressure head; preserving heat and pressure; and cooling to obtain the hexagonal boron nitride ceramic.

The hexagonal boron nitride ceramic is also called h-BN ceramic.

Forming a coating layer of a hexagonal boron nitride ceramic raw material by using a graphite container and a graphite pressure head, and completely coating the hexagonal boron nitride ceramic raw material; and electrifying the graphite mould, heating the graphite mould, and sintering the hexagonal boron nitride ceramic raw material coated by the graphite mould. The hexagonal boron nitride ceramic raw material is sintered all the time in the temperature rising process, and the hexagonal boron nitride ceramic is not densified before pressure is not applied.

In the technical scheme, the hexagonal boron nitride ceramic raw material preferably comprises, by mass, not more than 5% of a sintering aid and not less than 95% of hexagonal boron nitride ceramic; the hexagonal boron nitride ceramic raw material is powder or a preformed block.

The hexagonal boron nitride ceramic raw material can be a pure-phase component, and can also contain a sintering aid with the mass percentage of less than or equal to 5% to assist the sintering of the hexagonal boron nitride ceramic raw material.

Preferably, the step 2) of electrifying the graphite mold refers to adopting a graphite electrode to be tightly attached to the graphite container and then electrifying the graphite electrode; the current of the graphite electrode and the current of the graphite mold are 1-10 KA.

The electrode adopts a graphite electrode, mainly considers that the graphite electrode is high-temperature resistant and has high conductivity, can work at the sintering temperature of the hexagonal boron nitride ceramic, and can rapidly heat up with large current, so that the rapid sintering and densification of the hexagonal boron nitride ceramic can be realized.

When the temperature rise rate is the same, the current value increases with the increase in temperature.

When the temperature is the same, the current value increases as the temperature increase rate increases.

Preferably, the graphite mold and the graphite electrode both adopt high-purity graphite with the breaking strength of more than 60Mpa, and the resistivity of the high-purity graphite is less than or equal to 20 mu omega m.

The graphite mold can bear the pressure applied by the axial pressure unit in the sintering process, so that the graphite mold has certain requirements on the breaking strength of a graphite material, the graphite is required to have the compression strength which is greater than or equal to 60Mpa so as to enable the graphite mold to work normally under the pressure condition, and the resistivity which is less than or equal to 20 mu omega-m so as to enable the graphite mold to realize large-current rapid temperature rise.

Preferably, the temperature rise speed in the step 2) is 50-100 ℃/min, and the temperature rises to 1750-1950 ℃.

The sintering temperature of the hexagonal boron nitride ceramic is 1750-1950 ℃. In order to save labor hour and realize rapid achievement of the sintering conditions, the graphite electrode is limited to be directly electrified for the graphite mold, and the material of the graphite and the hexagonal boron nitride ceramic raw material are limited to be fully coated by the graphite mold, so that the graphite mold can realize rapid temperature rise with large current, thereby improving the production efficiency and realizing cost economy.

Preferably, the pressure applied in the step 2) is a step pressure or a constant pressure, and the pressure is 10-60 Mpa.

The pressure can be applied in a stage during the temperature rising process, and the pressure can be changed according to the process requirement; or constant pressure can be kept in the processes of temperature rise and heat preservation. In the actual production process, the sintering procedure can be set according to the sintering process of the hexagonal boron nitride ceramic.

Preferably, the heat preservation and pressure maintaining in the step 2) is performed for 1-10 min at 1750-1950 ℃ and 10-60 Mpa.

Preferably, the temperature reduction in the step 2) is water cooling, and the temperature reduction speed is 50 ℃/min to 100 ℃/min.

Preferably, the sum of the process time of the heating, the heat preservation and the cooling in the step 2) is less than or equal to 120 min.

According to the preparation method of the densified hexagonal boron nitride ceramic, the graphite mold is completely coated with the hexagonal boron nitride ceramic raw material, the graphite mold is directly electrified to form a large current to rapidly heat the graphite mold, and pressure is applied to the graphite mold to sinter and densify the hexagonal boron nitride ceramic, so that the sintering speed of the hexagonal boron nitride ceramic is extremely high, the whole sintering process can be completed within 120 minutes from temperature rise to temperature reduction, and the sintering heat preservation time is less than 10 minutes.

The invention also provides the densified hexagonal boron nitride ceramic prepared by the preparation method, wherein the density of the densified hexagonal boron nitride ceramic is more than or equal to 1.6g/cm³The bending strength is more than or equal to 28 MPa.

The invention also provides a hexagonal boron nitride ceramic densification device, as shown in the accompanying fig. 1 to 3, comprising:

a graphite mold 7, which comprises a graphite container 4-3 and a graphite pressure head 4-1; the graphite container 4-3 and the graphite pressure head 4-1 are matched to form a cavity;

the graphite electrode 6 is tightly attached to the graphite container 4-3 and used for electrifying the graphite mold 7 to heat the graphite mold 7;

an axial pressure unit 1 for applying pressure to the graphite container 4-3 and the graphite head 4-1;

the water cooling unit is used for cooling the graphite container 4-3 and the graphite pressure head 4-1;

the control system is respectively connected with the graphite electrode 6, the axial pressure unit 1 and the water cooling unit; and the control system controls the graphite electrode 6, the axial pressure unit 1 and the water cooling unit to be opened or closed according to a set sintering program.

The cavity is used to accommodate hexagonal boron nitride ceramic feedstock 5 to be densified.

The control system comprises a power supply control system, a pressure control system, a temperature monitoring system and a circulating water control system; the power supply control system and the temperature monitoring system are used for controlling whether direct current or alternating current is supplied to the graphite electrode to heat the graphite mold; the pressure control system is used for controlling whether the axial pressure unit applies pressure to the graphite mold; the circulating water control system and the temperature monitoring system are used for controlling whether the water cooling unit enables the graphite container and the graphite pressure head to be cooled by water.

The temperature monitoring system adopts infrared temperature measurement.

The hexagonal boron nitride ceramic densification device does not need vacuum and atmosphere protection, does not need to design a vacuum chamber, and is small in occupied area and low in manufacturing cost.

The axial pressure unit 1 applies pressure to the graphite container 4-3 and the graphite pressure head 4-1 through mechanical transmission or hydraulic transmission.

The above hexagonal boron nitride ceramic densification apparatus further comprises a susceptor 10 for supporting the apparatus; a cavity is formed inside the base 10, and a mechanical transmission part, a hydraulic transmission part and a transformer part are arranged in the cavity; the material of the base 10 may be a high temperature resistant and high thermal conductivity material such as cast iron, 304 stainless steel, 316L stainless steel, etc.

Preferably, the graphite mold and the graphite electrode both adopt high-purity graphite with the breaking strength of more than 60Mpa, and the resistivity of the high-purity graphite is less than or equal to 20 mu omega m.

The graphite mold can bear the pressure applied by the axial pressure unit in the sintering process, so that the graphite mold has certain requirements on the breaking strength of a graphite material, the graphite is required to have the compression strength which is greater than or equal to 60Mpa so as to enable the graphite mold to work normally under the pressure condition, and the resistivity which is less than or equal to 20 mu omega-m so as to enable the graphite mold to realize large-current rapid temperature rise.

Preferably, the graphite container 4-3 includes:

the bottom plate 4-2 is a flat plate made of graphite;

the die cavity is a block made of graphite; the block body is provided with a plurality of through holes 4-4; the block is placed on the bottom plate 4-2 in a direction in which the open end of the through hole 4-4 directly contacts the surface of the bottom plate 4-2.

The graphite container 4-3 is set as the structure form that the bottom plate 4-2 and the die cavity can be movably assembled, and the purpose is that: firstly, the die cavity is easier to process; secondly, the sintered and molded densified hexagonal boron nitride ceramic product is easier to demould; thirdly, when the size and the shape structure of the product are changed, only the die cavity needs to be replaced, and the bottom plate can be shared, so that the processing technology is simpler.

Preferably, the mold cavity comprises a plurality of through holes 4-4, that is, the mold cavity can be in a single-cavity structure or a multi-cavity structure, so that high-throughput research and development and mass production can be realized.

Preferably, the mold cavities can be used in combination with each other, i.e., products with different shapes and specifications can be prepared in one processing process.

Preferably, the size of the die cavity can be adjusted at will; when the diameter of the die cavity is larger than 600mm, the graphite die, namely a heating component consisting of the bottom plate 4-2, the die cavity and the pressure head 4-1, completely coats the densified hexagonal boron nitride ceramic raw material, so that the hexagonal boron nitride ceramic raw material can be uniformly heated, and a large-size densified hexagonal boron nitride ceramic product is manufactured.

Preferably, the device does not need vacuum or atmosphere protection, is not designed with a vacuum chamber, so that the device is not restricted by the vacuum chamber, can realize the sintering of the large-size hexagonal boron nitride ceramic, and the diameter of the maximum sample is more than or equal to 600 mm.

Preferably, it further comprises a thermal insulation layer 3 and an object stage 8; the heat insulation layer 3 is arranged above the graphite pressure head 4-1 and is used for insulating and insulating the graphite pressure head 4-1; the stage 8 is disposed below the graphite container 4-3 to support the graphite container 4-3 and insulate the graphite container.

The stage 8 is made of the same material as the insulating and heat insulating layer 3, and functions as the insulating and heat insulating layer in addition to supporting the graphite mold. The material of the object stage and the heat insulation layer can be heat insulation materials such as alumina, zirconia, mullite, corundum, spinel and the like.

Preferably, the water cooling unit comprises an upper cooling layer 2 and a lower cooling layer 9;

the upper cooling layer 2 is arranged above the heat insulation layer 3; the upper cooling layer 2 comprises a circulating water pipe; the circulating water pipe penetrates through the heat insulation layer 3 to cool the graphite pressure head 4-1;

the lower cooling layer 9 is arranged below the objective table 8; the lower cooling layer 9 comprises a circulating water pipe; the circulating water pipe penetrates through the objective table 8 to cool the graphite container 4-3.

The material of the upper cooling layer 2 and the lower cooling layer 9 may be high temperature resistant and high thermal conductivity materials such as cast iron, 304 stainless steel, 316L stainless steel, and the like; furthermore, the upper cooling layer and the lower cooling layer are internally provided with circulating water channels so as to realize the water-cooling temperature reduction of the device.

The technical solution of the present invention is further illustrated by the following more specific examples. The density and flexural strength of the test items in the examples were measured by a test method customary in the art.

Example 1

The embodiment provides a preparation method of densified hexagonal boron nitride ceramic, which comprises the following steps:

putting a hexagonal boron nitride ceramic raw material into a graphite mold; the hexagonal boron nitride ceramic raw material is pure hexagonal boron nitride ceramic powder, and no sintering aid is added; the graphite mold comprises a graphite container and a graphite pressure head; the flexural strength of the graphite is 60MPa, and the resistivity of the graphite is 12.7 mu omega-m; the graphite container and the graphite pressure head are matched to completely coat the hexagonal boron nitride ceramic raw material; a graphite electrode is tightly attached to the graphite container, then the graphite electrode is electrified, the current is 1-10 KA, and the heating rate is controlled to be 100 ℃/min; the graphite pressure head applies downward pressure; the pressure regime was as follows: heating to 800 deg.C, applying pressure of 10MPa, continuously heating to 1950 deg.C under constant pressure of 10MPa, and applying pressure of 60 MPa; preserving heat and pressure for 10min at 1950 ℃ and 60 MPa; cooling to room temperature at a speed of 100 deg.C/min.

The density of the densified hexagonal boron nitride ceramic prepared in this example was 1.6g/cm³The flexural strength was 28 MPa.

Example 2

The embodiment provides a preparation method of densified hexagonal boron nitride ceramic, which comprises the following steps:

putting a hexagonal boron nitride ceramic raw material into a graphite mold; the hexagonal boron nitride ceramic raw material comprises 99% of hexagonal boron nitride ceramic powder and 1% of sintering aid; the graphite mold comprises a graphite container and a graphite pressure head; the flexural strength of the graphite is 60MPa, and the resistivity of the graphite is 12.7 mu omega-m; the graphite container and the graphite pressure head are matched to completely coat the hexagonal boron nitride ceramic raw material; a graphite electrode is tightly attached to the graphite container, then the graphite electrode is electrified, the current is 1-10 KA, and the heating rate is controlled to be 100 ℃/min; the graphite pressure head applies downward pressure; the pressure regime was as follows: when the temperature is increased to 800 ℃, the pressure is applied to 50MPa, and the temperature is increased to 1750 ℃ under the constant pressure of 50 MPa; maintaining the temperature and pressure at 1750 ℃ and 50MPa for 7 min; cooling to room temperature at a speed of 100 deg.C/min.

The density of the densified hexagonal boron nitride ceramic prepared in this example was 1.9g/cm³The bending strength was 30 MPa.

Example 3

The embodiment provides a preparation method of densified hexagonal boron nitride ceramic, which comprises the following steps:

putting a hexagonal boron nitride ceramic raw material into a graphite mold; the hexagonal boron nitride ceramic raw material comprises 97% of hexagonal boron nitride ceramic powder and 3% of sintering aid; the graphite mold comprises a graphite container and a graphite pressure head; the flexural strength of the graphite is 60MPa, and the resistivity of the graphite is 12.7 mu omega-m; the graphite container and the graphite pressure head are matched to completely coat the hexagonal boron nitride ceramic raw material; a graphite electrode is tightly attached to the graphite container, then the graphite electrode is electrified, the current is 1-10 KA, and the heating rate is controlled to be 50 ℃/min; the graphite pressure head applies downward pressure; the pressure regime was as follows: heating to 800 deg.C, applying pressure of 20MPa, heating to 1850 deg.C under constant pressure of 20MPa, and applying pressure of 40 MPa; maintaining the temperature and pressure at 1850 deg.C and 40MPa for 5 min; cooling to room temperature at a speed of 50 deg.C/min.

The density of the densified hexagonal boron nitride ceramic prepared in this example was 2g/cm³The bending strength was 35 MPa.

Example 4

The embodiment provides a preparation method of densified hexagonal boron nitride ceramic, which comprises the following steps:

putting a hexagonal boron nitride ceramic raw material into a graphite mold; the hexagonal boron nitride ceramic raw material is a pre-sintered block prepared from 95% of hexagonal boron nitride ceramic powder and 5% of sintering aid; the graphite mold comprises a graphite container and a graphite pressure head; the flexural strength of the graphite is 60MPa, and the resistivity of the graphite is 12.7 mu omega-m; the graphite container and the graphite pressure head are matched to completely coat the hexagonal boron nitride ceramic raw material; a graphite electrode is tightly attached to the graphite container, then the graphite electrode is electrified, the current is 1-10 KA, and the heating rate is controlled to be 50 ℃/min; the graphite pressure head applies downward pressure; the pressure regime was as follows: when the temperature is increased to 800 ℃, the pressure is applied to 30MPa, the temperature is increased to 1950 ℃ under the constant pressure of 30MPa, and the pressure is applied to 30 MPa; preserving heat and pressure for 5min at 1950 ℃ and 30 MPa; cooling to room temperature at a speed of 50 deg.C/min.

The density of the densified hexagonal boron nitride ceramic prepared in this example was 2.2g/cm³The flexural strength was 43 MPa.

The features of the invention claimed and/or described in the specification may be combined, and are not limited to the combinations set forth in the claims by the recitations therein. The technical solutions obtained by combining the technical features in the claims and/or the specification also belong to the scope of the present invention.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention are still within the scope of the technical solution of the present invention.