CN113620714A - Preparation method of boron carbide-graphite shielding body - Google Patents
Preparation method of boron carbide-graphite shielding body Download PDFInfo
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- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 66
- 239000010439 graphite Substances 0.000 title claims abstract description 66
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 title claims abstract description 35
- 229910052796 boron Inorganic materials 0.000 title claims abstract description 35
- 238000002360 preparation method Methods 0.000 title claims abstract description 14
- 229910052580 B4C Inorganic materials 0.000 claims abstract description 54
- INAHAJYZKVIDIZ-UHFFFAOYSA-N boron carbide Chemical compound B12B3B4C32B41 INAHAJYZKVIDIZ-UHFFFAOYSA-N 0.000 claims abstract description 54
- 238000000034 method Methods 0.000 claims abstract description 49
- 238000005245 sintering Methods 0.000 claims abstract description 47
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 44
- 239000000843 powder Substances 0.000 claims abstract description 41
- 230000008569 process Effects 0.000 claims abstract description 34
- 238000005469 granulation Methods 0.000 claims abstract description 23
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- 235000015895 biscuits Nutrition 0.000 claims description 29
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- 239000002994 raw material Substances 0.000 claims description 18
- 239000000839 emulsion Substances 0.000 claims description 15
- 239000002245 particle Substances 0.000 claims description 15
- 238000001816 cooling Methods 0.000 claims description 13
- 239000007921 spray Substances 0.000 claims description 11
- 238000002156 mixing Methods 0.000 claims description 10
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 8
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 8
- 238000001272 pressureless sintering Methods 0.000 claims description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 238000000748 compression moulding Methods 0.000 claims description 5
- 238000004321 preservation Methods 0.000 claims description 5
- 239000007864 aqueous solution Substances 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 4
- 238000003825 pressing Methods 0.000 claims description 4
- 238000003756 stirring Methods 0.000 claims description 4
- 229910052786 argon Inorganic materials 0.000 claims description 3
- 238000009694 cold isostatic pressing Methods 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims description 3
- 239000007787 solid Substances 0.000 claims description 3
- 238000000465 moulding Methods 0.000 claims description 2
- 238000001694 spray drying Methods 0.000 claims description 2
- 238000005303 weighing Methods 0.000 claims description 2
- 239000000919 ceramic Substances 0.000 abstract description 20
- 238000004519 manufacturing process Methods 0.000 abstract description 5
- 238000010923 batch production Methods 0.000 abstract description 2
- 238000007792 addition Methods 0.000 description 18
- 239000003292 glue Substances 0.000 description 13
- 239000008187 granular material Substances 0.000 description 10
- 238000007599 discharging Methods 0.000 description 5
- 229910010293 ceramic material Inorganic materials 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 239000011358 absorbing material Substances 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
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- 238000002844 melting Methods 0.000 description 2
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- 229910052582 BN Inorganic materials 0.000 description 1
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 description 1
- 229910052688 Gadolinium Inorganic materials 0.000 description 1
- 229910052772 Samarium Inorganic materials 0.000 description 1
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- 238000000429 assembly Methods 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 229910052793 cadmium Inorganic materials 0.000 description 1
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
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- 239000010432 diamond Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- UIWYJDYFSGRHKR-UHFFFAOYSA-N gadolinium atom Chemical compound [Gd] UIWYJDYFSGRHKR-UHFFFAOYSA-N 0.000 description 1
- 230000005251 gamma ray Effects 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
- C04B35/563—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on boron carbide
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
- C04B35/62605—Treating the starting powders individually or as mixtures
- C04B35/62695—Granulation or pelletising
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- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/64—Burning or sintering processes
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F1/00—Shielding characterised by the composition of the materials
- G21F1/02—Selection of uniform shielding materials
- G21F1/06—Ceramics; Glasses; Refractories
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
- C04B2235/30—Constituents and secondary phases not being of a fibrous nature
- C04B2235/42—Non metallic elements added as constituents or additives, e.g. sulfur, phosphor, selenium or tellurium
- C04B2235/422—Carbon
- C04B2235/425—Graphite
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- C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
- C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
- C04B2235/74—Physical characteristics
- C04B2235/77—Density
Abstract
The invention discloses a preparation method of a boron carbide-graphite shield, which belongs to the technical field of shield production, wherein graphite powder is added into boron carbide powder, the boron carbide-graphite ceramic shield is obtained through the processes of granulation, blank preparation and sintering after the boron carbide powder is mechanically and uniformly mixed, and the relative density of the shield can be adjusted by selecting proper graphite addition and proper sintering temperature, so that a boron carbide-graphite shield material with higher density can be obtained, the density can reach more than 70%, the shield with high density has excellent performance and better service performance. The preparation method has simple process and low cost, and is suitable for batch production.
Description
Technical Field
The invention belongs to the technical field of shield production, and particularly relates to a preparation method of a boron carbide-graphite shield.
Background
In nuclear reactor core assemblies, neutron absorbing materials (control rods, conditioning rods, accident rods, safety rods, shielding rods) are next to the fuel elements important functional components. Because the neutron absorption cross section of the boron carbide is high, the absorption energy spectrum is wide,10the thermal cross section of B is up to 347 x 10～24cm2Second only to a few elements such as gadolinium, samarium, cadmium, etc. While B is present in relation to the pure elements B and Gd4The price of C is low, the raw material source is rich, strong gamma-ray secondary radiation is not generated after neutrons are absorbed, and the corrosion resistance and the thermal stability are good, so that the waste material treatment is easy. Boron carbide is therefore an important neutron absorbing material and is becoming increasingly favored as a material for nuclear reactors.
The hardness of boron carbide is second to that of diamond and cubic boron nitride, and the boron carbide also has the advantages of high elastic modulus, wear resistance, corrosion resistance and the like, but the boron carbide belongs to a ceramic material and has poor mechanical property and thermal property. The boron carbide ceramic has the advantages of extremely strong covalent bond in the structure, over 90 percent of covalent bond fraction, extremely low self-diffusion coefficient, extremely high temperature for eliminating internal air holes, grain boundary and volume diffusion, extremely difficult sintering of pure boron carbide ceramic and difficult densification. Graphite is a two-dimensional nano material, has a large specific surface and excellent mechanical properties, and is an ideal ceramic reinforcement.
Since boron carbide ceramics are difficult to sinter, densification is difficult. Thus, the relative density can be improved by adding other auxiliary materials and sintering at different temperatures.
Disclosure of Invention
The invention aims to solve the technical problems that in the prior art, the boron carbide ceramic is difficult to sinter in the sintering process, and the finally obtained boron carbide ceramic has low density and the like.
In order to solve the technical problem, the invention discloses a preparation method of a boron carbide-graphite shield, which comprises the following steps:
(1) mixing materials: weighing raw materials, wherein the raw materials comprise boron carbide powder and graphite powder, and adding the raw materials into a mixer to be uniformly mixed to obtain composite powder;
(2) and (3) granulation: performing a granulation process of spray drying on the composite powder to obtain composite powder particles;
(3) blank preparation: preparing biscuit from the composite powder particles by adopting a compression molding process;
(4) and (3) sintering: sending the biscuit into a degumming furnace for draining water and degumming, then sending the biscuit into a sintering furnace for sintering, and cooling to obtain a boron carbide-graphite shielding body;
in the raw material, the mass percent of boron carbide powder is X, the mass percent of graphite powder is Y, wherein 94% is less than or equal to X < 100%, and 0 < X < 6%; purity of boron carbide powder is not less than 98%, and size is D50＝5.4-7.0μm。
Further, the granulation process comprises the following steps:
(1) preparing an emulsion: firstly, preparing a polyvinyl alcohol aqueous solution with the concentration of 5-10 wt%, then adding the composite powder, and stirring and mixing uniformly to obtain an emulsion; the weight of polyvinyl alcohol in the emulsion accounts for 1-5 wt% of the weight of the composite powder, and the solid content in the emulsion is 40-70 wt%;
(2) and (3) granulation: and (3) carrying out spray granulation on the emulsion by adopting a centrifugal spray granulator to obtain composite powder particles with the particle size of 60-100 meshes.
Further, in the drainage degumming process, the vacuum degree in the degumming furnace is 10-500Pa, the temperature is 120-700 ℃, the heating rate is 1-5 ℃/min, and the heat preservation time is 2-6 h.
Furthermore, in the drainage degumming process, the temperature is respectively kept for 4 hours at 120 ℃ and 400 ℃, and then kept for 10 hours at 700 ℃; and cooling to 200 ℃ along with the furnace after the heat preservation is finished.
Further, in the sintering process, vacuum sintering is carried out at room temperature to 1700 ℃ at first, and the vacuum degree is 10-300 Pa; then argon is introduced into the mixture at the stage of 1700-2175 ℃ for atmosphere sintering; then carrying out pressureless sintering at the temperature of 2175 ℃ and 2275 ℃; and finally, cooling along with the furnace to obtain the boron carbide shield.
Further, pressureless sintering is performed at 2200 ℃, 2225 ℃, or 2250 ℃.
Further, the mixer is a V-shaped mixer, the ball-to-material ratio in the V-shaped mixer is 2:1, and the mixing time is 3-5 hours.
Further, the purity of the graphite powder is not less than 99.5%, and the size of the graphite powder is D50≦3.5μm。
Further, the compression molding process is a dry pressing method or a cold isostatic pressing process.
Furthermore, the molding pressure in the compression molding process is 150-250 MPa.
The invention mainly aims at boron carbide ceramic materials, and obtains the most excellent relative density of the boron carbide ceramic materials by adding a proper amount of graphite, mechanically mixing and at a certain sintering temperature. A method is provided for directly doping graphite into boron carbide powder and preparing a boron carbide-graphite shield by vacuum pressureless sintering. The method has the advantages of simple process, high productivity, low cost, capability of preparing boron carbide shields with different graphite contents according to requirements and the like, and realizes an industrial production technology for preparing boron carbide-graphite shields with low cost and stability in batches.
Compared with the existing product, the preparation method of the boron carbide-graphite shield has the following advantages:
(1) the preparation process is simple, the productivity is high, the cost is low, and the prepared biscuit has the characteristics of certain strength, capability of being processed into different shapes, small shrinkage after the biscuit body is sintered, suitability for batch production and the like; compared with a hot isostatic pressing process, the method has the advantages of simple production process, low manufacturing cost and mass production.
(2) The invention verifies the influence of different graphite addition amounts and sintering temperatures on the relative density of the prepared boron carbide ceramic. The relative density of the boron carbide ceramic shield can be adjusted by changing the addition amount of graphite and the sintering temperature; the use cost and the safety performance of the nuclear power unit are greatly reduced.
(3) The invention breaks through the limitation that the traditional pressureless sintering process must adopt 1 micron boron carbide as the raw material; the process adopts boron carbide with different particle sizes to prepare a series of boron carbide block materials with different densities; according to a similar compatibility principle, graphite powder with a certain mass fraction is added, and an oxidation film on the surface of boron carbide is removed by utilizing the deoxidation effect of the graphite powder, so that the sintering activity is improved.
(4) The density of the boron carbide prepared by the method can reach more than 70 percent, and the boron carbide has good mechanical property and thermal shock property, corrosion resistance, no density change in a high-temperature process and the like.
Drawings
FIG. 1: influence curves of different graphite addition amounts and different sintering temperatures on the relative density of the boron carbide-graphite shield.
Detailed Description
The technical solution of the present invention will be described in detail by the following specific examples.
The raw materials used in the following examples of the invention are commercially available products, and the equipment is conventional equipment in the industry, including electronic balances, electronic platform scales, common mixers, glue melting machines, high-speed mixers, centrifugal granulators, cold isostatic presses or hydraulic presses, cutting machines, milling machines and high-temperature vacuum sintering furnaces. The examples are given solely for the purpose of illustrating the invention and are not to be construed as limiting the invention to the examples set forth below.
A preparation method of a boron carbide-graphite shield comprises the following steps:
(1) mixing materials: adding the raw materials into V-shaped mixture according to the proportionIn the material machine, the ball-material ratio is 2:1, and the material mixing time is 3.5h, so that the uniformly mixed composite powder is obtained. Wherein the raw materials comprise: boron carbide powder with the mass percentage of X and graphite powder with the mass percentage of Y, wherein 94% is less than or equal to X < 100%, and 0 < X < 6%; purity of boron carbide powder is not less than 98%, and size is D505.4-7.0 μm; the purity of the graphite powder is not less than 99.5 percent, and the size is D50≦3.5μm。
(2) Preparing an emulsion: adding PVA with a certain mass into deionized water, heating in a glue melting machine in a water bath to 90-100 ℃, and continuously stirring to prepare a PVA aqueous solution with the mass fraction of 5-10 wt%; then adding the composite powder into the PVA aqueous solution, and stirring and mixing uniformly to obtain emulsion; wherein the mass of PVA in the emulsion accounts for 1-5% of the mass of the composite powder, and the solid content in the emulsion is 40-70 wt%.
(3) And (3) granulation: and (3) carrying out spray granulation on the emulsion by adopting a centrifugal spray granulator to obtain composite powder particles with the particle size of 60-100 meshes, and then carrying out 60-100-mesh sieve treatment on the particles to obtain the composite powder particles with more uniform particle size.
(4) Blank preparation: and (3) forming the granulated composite powder particles into a biscuit by adopting a cold isostatic pressing process, wherein the pressing pressure is 240MPa, and the size of the obtained biscuit is 127 multiplied by 84.8 multiplied by 36.6 (unit: mm, and the size tolerance is +/-0.2 mm).
(5) Draining water and degumming: placing the biscuit into a degumming furnace for draining and degumming, wherein in the draining and degumming process, the biscuit is respectively kept at 120 ℃ and 400 ℃ for 4 hours, and then kept at 700 ℃ for 10 hours; and cooling to 200 ℃ along with the furnace after the heat preservation is finished. Water and organic substances in the biscuit are removed, thereby ensuring full glue removal.
(6) And (3) sintering: placing the biscuit subjected to binder removal into a vacuum sintering furnace for sintering, wherein in the sintering process, vacuum sintering is firstly carried out at the room temperature of-1700 ℃ and the vacuum degree is 10-300 Pa; then argon is introduced into the mixture at the stage of 1700-2175 ℃ for atmosphere sintering; then carrying out pressureless sintering at the temperature of 2175 ℃ and 2275 ℃; and finally, cooling along with the furnace to obtain the boron carbide shield.
Example 1
In the embodiment, the raw material is 98.5 wt% of boron carbide micro powder, the addition amount of graphite is 1.5 wt%, the boron carbide micro powder and the graphite are uniformly mixed in a V-shaped ball mill, and then granulation is carried out through a spray granulation process to obtain granules; making a blank of the granulated material; degumming the biscuit in a degumming furnace, keeping the temperature of the degumming furnace at 120 ℃ and 400 ℃ for 4h respectively, keeping the temperature at 700 ℃ for 10h, fully discharging the glue from the biscuit, sintering the biscuit in a vacuum sintering furnace at 2200 ℃, 2225 ℃ or 2250 ℃ respectively after the glue discharge is finished, keeping the temperature for 1.5h, and obtaining a boron carbide-graphite ceramic block which is the boron carbide-graphite shielding body after the cooling is finished.
Example 2
In the embodiment, the raw material is 97 wt% of boron carbide micro powder, the addition amount of graphite is 3 wt%, the boron carbide micro powder and the graphite are uniformly mixed in a V-shaped ball mill, and then granulation is carried out through a spray granulation process to obtain granules; making a blank of the granulated material; degumming the biscuit in a degumming furnace, keeping the temperature of the degumming furnace at 120 ℃ and 400 ℃ for 4h respectively, keeping the temperature at 700 ℃ for 10h, fully discharging the glue from the biscuit, sintering the biscuit in a vacuum sintering furnace at 2200 ℃, 2225 ℃ or 2250 ℃ respectively after the glue discharge is finished, keeping the temperature for 1.5h, and obtaining a boron carbide-graphite ceramic block which is the boron carbide-graphite shielding body after the cooling is finished.
Example 3
In the embodiment, the raw material is 95.5 wt% of boron carbide micro powder, the addition amount of graphite is 4.5 wt%, the boron carbide micro powder and the graphite are uniformly mixed in a V-shaped ball mill, and then granulation is carried out through a spray granulation process to obtain granules; making a blank of the granulated material; degumming the biscuit in a degumming furnace, keeping the temperature of the degumming furnace at 120 ℃ and 400 ℃ for 4h respectively, keeping the temperature at 700 ℃ for 10h, fully discharging the glue from the biscuit, sintering the biscuit in a vacuum sintering furnace at 2200 ℃, 2225 ℃ or 2250 ℃ respectively after the glue discharge is finished, keeping the temperature for 1.5h, and obtaining a boron carbide-graphite ceramic block which is the boron carbide-graphite shielding body after the cooling is finished.
Example 4
In the embodiment, the raw material is 94 wt% of boron carbide micro powder, the addition amount of graphite is 6 wt%, the boron carbide micro powder and the graphite are uniformly mixed in a V-shaped ball mill, and then granulation is carried out through a spray granulation process to obtain granules; making a blank of the granulated material; degumming the biscuit in a degumming furnace, keeping the temperature of the degumming furnace at 120 ℃ and 400 ℃ for 4h respectively, keeping the temperature at 700 ℃ for 10h, fully discharging the glue from the biscuit, sintering the biscuit in a vacuum sintering furnace at 2200 ℃, 2225 ℃ or 2250 ℃ respectively after the glue discharge is finished, keeping the temperature for 1.5h, and obtaining a boron carbide-graphite ceramic block which is the boron carbide-graphite shielding body after the cooling is finished.
Comparative example 1
In the embodiment, the raw material is 100 wt% of boron carbide micro powder, the addition amount of graphite is 0, the boron carbide micro powder and the graphite are uniformly mixed in a V-shaped ball mill, and then granulation is carried out through a spray granulation process to obtain granules; making a blank of the granulated material; degumming the biscuit in a degumming furnace, keeping the temperature of the degumming furnace at 120 ℃ and 400 ℃ for 4h respectively, keeping the temperature at 700 ℃ for 10h, fully discharging the glue from the biscuit, sintering the biscuit in a vacuum sintering furnace at 2200 ℃, 2225 ℃ or 2250 ℃ respectively after the glue discharge is finished, keeping the temperature for 1.5h, and obtaining a boron carbide ceramic block which is the boron carbide shield after the cooling is finished.
The densities of the materials prepared in each of examples and comparative example 1 were measured by the Archimede drainage method, and the relative densities thereof were calculated, and the test results are shown in tables 1, 2, and 3.
TABLE 1 Density and relative Density of boron carbide-graphite shields sintered at 2200 ℃ with different graphite additions
TABLE 2 Density and relative Density of boron carbide-graphite shields with different graphite additions at 2225 ℃ sintering
TABLE 3 Density and relative Density of boron carbide-graphite shields sintered at 2250 ℃ with different graphite additions
With reference to fig. 1, tables 1, 2 and 3 are analyzed, respectively, and the addition amount of graphite has a large influence on the relative density of the boron carbide ceramic at the same sintering temperature; at the sintering temperature of 2200 ℃, the relative density of the boron carbide ceramic block increases along with the addition of graphite and tends to increase and decrease, and when the addition of graphite is 3.0 wt%, the maximum is 69.45%; at the sintering temperature of 2225 ℃, the relative density of the boron carbide ceramic body gradually increases along with the increase of the addition amount of graphite, and when the addition amount of the graphite is 6.0 wt%, the relative density of the boron carbide ceramic body is 71.14%; at the sintering temperature of 2250 ℃, the relative density of the boron carbide ceramic body tended to increase first and then decrease slightly as the graphite addition amount increased, and reached a maximum of 75.98% when the graphite addition amount was 4.5 wt%. When the amount of graphite added is the same, the relative density of the boron carbide ceramic body gradually increases as the sintering temperature increases, indicating that increasing the sintering temperature is effective in increasing the relative density. In conclusion, the relative density of the boron carbide shield can be effectively improved by adding a certain amount of graphite; and the amount of graphite added to reach the maximum relative density at different sintering temperatures is also different.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like made within the design concept of the present invention should be included in the scope of the present invention.
Claims (10)
1. A preparation method of a boron carbide-graphite shield is characterized by comprising the following steps: the method comprises the following steps:
(1) mixing materials: weighing raw materials, wherein the raw materials comprise boron carbide powder and graphite powder, and adding the raw materials into a mixer to be uniformly mixed to obtain composite powder;
(2) and (3) granulation: performing a granulation process of spray drying on the composite powder to obtain composite powder particles;
(3) blank preparation: preparing biscuit from the composite powder particles by adopting a compression molding process;
(4) and (3) sintering: sending the biscuit into a degumming furnace for draining water and degumming, then sending the biscuit into a sintering furnace for sintering, and cooling to obtain a boron carbide-graphite shielding body;
in the raw material, the mass percent of boron carbide powder is X, the mass percent of graphite powder is Y, wherein 94% is less than or equal to X < 100%, and 0 < X < 6%; purity of boron carbide powder is not less than 98%, and size is D50＝5.4-7.0μm。
2. The method of preparing a boron carbide-graphite shield according to claim 1, wherein: the granulation process comprises the following steps:
(1) preparing an emulsion: firstly, preparing a polyvinyl alcohol aqueous solution with the concentration of 5-10 wt%, then adding the composite powder, and stirring and mixing uniformly to obtain an emulsion; the weight of polyvinyl alcohol in the emulsion accounts for 1-5 wt% of the weight of the composite powder, and the solid content in the emulsion is 40-70 wt%;
(2) and (3) granulation: and (3) carrying out spray granulation on the emulsion by adopting a centrifugal spray granulator to obtain composite powder particles with the particle size of 60-100 meshes.
3. The method of preparing a boron carbide-graphite shield according to claim 1, wherein: in the drainage degumming process, the vacuum degree in the degumming furnace is 10-500Pa, the temperature is 120-700 ℃, the heating rate is 1-5 ℃/min, and the heat preservation time is 2-6 h.
4. The method of preparing a boron carbide-graphite shield according to claim 3, wherein: respectively preserving heat for 4 hours at 120 ℃ and 400 ℃ in the drainage degumming process, and then preserving heat for 10 hours at 700 ℃; and cooling to 200 ℃ along with the furnace after the heat preservation is finished.
5. The method of preparing a boron carbide-graphite shield according to claim 1, wherein: in the sintering process, firstly, vacuum sintering is carried out at the room temperature of 1700 ℃ below zero, and the vacuum degree is 10-300 Pa; then argon is introduced into the mixture at the stage of 1700-2175 ℃ for atmosphere sintering; then carrying out pressureless sintering at the temperature of 2175 ℃ and 2275 ℃; and finally, cooling along with the furnace to obtain the boron carbide shield.
6. The method of preparing a boron carbide-graphite shield according to claim 5, wherein: pressureless sintering is carried out at 2200 ℃, 2225 ℃ or 2250 ℃.
7. The method of preparing a boron carbide-graphite shield according to claim 1, wherein: the mixer is a V-shaped mixer, the ball-to-material ratio in the V-shaped mixer is 2:1, and the mixing time is 3-5 h.
8. The method of preparing a boron carbide-graphite shield according to claim 1, wherein: the purity of the graphite powder is not less than 99.5 percent, and the graphite powder has the size of D50≦3.5μm。
9. The method of preparing a boron carbide-graphite shield according to claim 1, wherein: the pressing forming process is a dry pressing method or a cold isostatic pressing forming process.
10. The method of preparing a boron carbide-graphite shield according to claim 9, wherein: the molding pressure in the compression molding process is 150-250 MPa.
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