Method for preparing boron carbide porous ceramics based on stereolithography 3D printing process

Abstract

The present invention belongs to the technical field of the preparation of boron carbide porous ceramics, and particularly relates to a method for preparing boron carbide porous ceramics based on a photocuring 3D printing process. The boron carbide porous ceramics are prepared by using the photocuring 3D printing process and high-temperature carbothermal reduction. During the preparation process, on the one hand, the added boric acid decomposes into B2O3 during the vacuum debinding process and further acts as a sintering aid during the pressureless sintering process, effectively promoting the sintering of the boron carbide ceramic green body, thereby endowing the boron carbide porous ceramics with excellent mechanical properties; on the other hand, the added polymer dispersant and pore-forming agent decompose and carbonize during the vacuum debinding process to form pores; furthermore, the pore structure of the boron carbide porous ceramics can be regulated by controlling the process to achieve the ultra-lightweight of the boron carbide porous ceramics. In addition, the formed carbon element can act as a reducing agent to reduce boron oxide to B4C at high sintering temperatures, which is beneficial to improving the purity of the boron carbide porous ceramics.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of boron carbide porous ceramics, and particularly relates to a method for preparing boron carbide porous ceramics based on a photocuring 3D printing process. Background Art

[0002] Ceramic materials have characteristics such as high melting point, high modulus, high strength, high hardness, corrosion resistance, wear resistance, and radiation resistance. Therefore, many ceramic-based neutron shielding materials have been developed successively for use in the field of aviation nuclear power. Among them, boron-containing ceramics represented by boron carbide (B 4 C) have attracted much attention and research from materials scholars in recent years due to their large neutron capture cross-section, wide capture energy spectrum, strong absorption ability and other characteristics.

[0003] B 4 C is mainly composed of covalent bonds, and the proportion of its covalent bonds is as high as more than 93%, showing intrinsic brittleness. In addition, B 4 C ceramics have a high melting point, a low self-diffusion coefficient, and slow volume diffusion and grain boundary diffusion rates during sintering. A very high sintering temperature and a special sintering process are required to obtain dense B 4 C ceramic materials. On the other hand, when applying B 4 C ceramic materials to the field of nuclear power equipment, due to the limited shielding space, the volume and weight are restricted. Therefore, B 4 C ceramic materials need to have characteristics such as light weight and high strength to play a structural support role. However, it is difficult to prepare B 4 C porous ceramic materials with both excellent mechanical properties and neutron shielding properties in the prior art, which restricts their large-scale promotion and application in nuclear technology fields such as aerospace and military defense. Summary of the Invention

[0004] To solve the problems raised in the background art, the present invention provides a method for preparing boron carbide porous ceramics based on a photocuring 3D printing process.

[0005] The technical solution of the present invention is as follows:

[0006] The present invention provides a method for preparing boron carbide porous ceramics based on a photocuring 3D printing process, including the following steps:

[0007] (1) Mixing a resin monomer and a photoinitiator to obtain a liquid photosensitive resin;

[0008] (2) Adding boron carbide powder, boric acid, a dispersant and a pore former to the liquid photosensitive resin, and dispersing evenly to obtain a photosensitive resin-based boron carbide ceramic slurry;

[0009] (3) Subjecting the photosensitive resin-based boron carbide ceramic slurry to photocuring 3D printing to obtain a boron carbide ceramic green body;

[0010] (4) After the boron carbide ceramic green body is degummed under vacuum, it is sintered without pressure to obtain porous boron carbide ceramics;

[0011] In the photosensitive resin-based boron carbide ceramic slurry in step (2), the addition amount of the boron carbide powder is 45-70 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of the dispersant is 0.2-5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of boric acid is 0.5-5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the molar ratio of the boron element content in the added boric acid to the carbon element content in the added pore-forming agent is 3.3-5.5:1;

[0012] In the non-pressure sintering in step (4), the sintering atmosphere is a vacuum atmosphere or an inert atmosphere, the sintering temperature is 2050-2200 °C, the heat preservation time is 30-120 min, the heating rate is 5-20 °C / min, and the cooling rate is 2-10 °C / min;

[0013] For the porous boron carbide ceramics, the pore size is 2.6-22.3 μm, the porosity is 25-45%, and the density is 1.40-1.88 g / cm 3 , and the compressive strength is 116.8-145.5 MPa.

[0014] In step (2), the average particle size of the boron carbide powder is 1-20 μm.

[0015] In step (1), the resin monomer is one, two or a mixture of three of butyl acrylate, butyl acrylate, lauryl acrylate, ethoxyethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl methacrylate, isobornyl methacrylate, isobornyl methacrylate, isobornyl methacrylate, trimethylolpropane formal acrylate, acryloylmorpholine, dimethylolpropane tetraacrylate, 1,6-hexanediol diacrylate, 1,6-methyl diacrylate, tripropylene glycol diacrylate, polyethylene glycol 200 diacrylate, polyethylene glycol 400 diacrylate, polyethylene glycol 600 diacrylate, propoxylated neopentyl glycol diacrylate, tricyclodecane dimethanol diacrylate, trimethylolpropane triacrylate, (ethoxy)trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate;

[0016] The photoinitiator is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0017] In step (1), the photoinitiator is 1-10 wt% of the mass of the resin monomer.

[0018] In step (2), the dispersant is one of Solsperse 41000, KOS190, KOS110, DISPERBYK-111, and DISPERBYK-180; the pore former is one or a mixture of polyvinyl alcohol, dextrin, carbon powder, and starch.

[0019] In step (2), for uniform dispersion, ball milling is used. The ball milling time is 1 - 12 h, the ball-to-material ratio is 3:1 - 20:1, and the rotation speed is 150 - 600 r / min.

[0020] In step (3), for photocuring 3D printing, the exposure power is 35 - 100 mW / cm 2 , the exposure time is 5 - 60 s, and the slice thickness is 25 - 50 μm.

[0021] In step (4), for vacuum debinding, the heating rate is 3 - 15 °C / min, the debinding temperature is 400 - 800 °C, and the heat preservation time is 0.5 - 6 h.

[0022] Beneficial effects

[0023] The present invention uses a photocuring 3D printing process and high-temperature carbothermal reduction to prepare boron carbide porous ceramics. During the preparation process, on the one hand, the added boric acid decomposes into B 2 O 3 during the vacuum debinding process, and further acts as a sintering aid during the pressureless sintering process, effectively promoting the sintering of the boron carbide ceramic green body, thereby endowing the boron carbide porous ceramics with excellent mechanical properties; on the other hand, the added polymer dispersant and pore former decompose and carbonize during the vacuum debinding process to form pores; furthermore, the pore structure of the boron carbide porous ceramics can be regulated by controlling the process to achieve the ultra-lightweight of the boron carbide porous ceramics. In addition, the formed carbon element can act as a reducing agent to reduce boron oxide to B 4 C at high sintering temperatures, which is beneficial to improving the purity of the boron carbide porous ceramics.

[0024] The preparation method of the boron carbide porous ceramics of the present invention is simple and effective, can achieve the net shaping of products with complex shapes without secondary processing, reduces the material cost and process cost, and expands the application of 3D printing technology in the nuclear power field.

[0025] The boron carbide porous ceramics prepared by the method of the present invention have a pore size of 2.6 - 22.3 μm, a porosity of 25 - 45%, a density of 1.40 - 1.88 g / cm 3 , and a compressive strength of 116.8 - 145.5 MPa, and have the characteristics of light weight, high strength, and excellent neutron shielding performance. Description of the drawings

[0026] Figure 1XRD pattern of the boron carbide porous ceramic prepared in Example 1 of the present invention.

[0027] Figure 2 SEM photograph of the boron carbide porous ceramic prepared in Example 3 of the present invention.

[0028] Figure 3 Stress-strain curve of the boron carbide porous ceramic prepared in Example 2 of the present invention. Detailed implementation manners

[0029] The following examples are intended to illustrate the present invention rather than further limit the present invention.

[0030] The present invention provides a method for preparing boron carbide porous ceramics based on a photocuring 3D printing process, comprising the following steps:

[0031] (1) Mix a resin monomer and a photoinitiator to obtain a liquid photosensitive resin.

[0032] Preferably, in the step (1), the resin monomer is one, two or three of butyl acrylate, butyl acrylate, lauryl acrylate, ethoxyethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl methacrylate, isobornyl methacrylate, isobornyl methacrylate, isobornyl methacrylate, trimethylolpropane formal acrylate, acryloylmorpholine, diethylene glycol diacrylate, 1,6-hexanediol diacrylate, 1,6-methylenediacrylate, tripropylene glycol diacrylate, polyethylene glycol 200 diacrylate, polyethylene glycol 400 diacrylate, polyethylene glycol 600 diacrylate, neopentyl glycol diacrylate propoxylate, tricyclodecane dimethanol diacrylate, trimethylolpropane triacrylate, (ethoxy)trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate. For example, when three monomers are mixed, let the mass fractions of each monomer be a, b, c, where 0 wt% ≤ a ≤ 100 wt%, 0 wt% ≤ b ≤ 100 wt%, 0 wt% ≤ c ≤ 100 wt%, and a + b + c = 100%;

[0033] The photoinitiator is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0034] Furthermore, to ensure uniform mixing and complete fusion of each component, in the step (1), the photoinitiator is 1-10 wt% of the mass of the resin monomer.

[0035] (2) Add boron carbide powder, boric acid, a dispersant and a pore former to the liquid photosensitive resin, and disperse evenly to obtain a photosensitive resin-based boron carbide ceramic slurry.

[0036] Among them, the boron carbide powder is the boron carbide powder after drying to remove moisture and impurities in the raw materials. The drying method is vacuum drying or drying in an argon-protected atmosphere. When it is vacuum drying, the vacuum degree is 0.01 - 0.07 MPa, the drying temperature is 50 - 120 °C, and the drying time is 1 - 48 h; when it is drying in an argon-protected atmosphere, the argon pressure is 0.1 - 1 MPa, the drying temperature is 50 - 120 °C, and the drying time is 1 - 48 h.

[0037] Preferably, in the step (2), the average particle size of the boron carbide powder is 1 - 20 μm.

[0038] In addition, in the photosensitive resin-based boron carbide ceramic slurry in the step (2), the addition amount of the boron carbide powder is 45 - 70 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of the dispersant is 0.2 - 5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of boric acid is 0.5 - 5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the molar ratio of the boron element content in the added boric acid to the carbon element content in the added pore-forming agent is 3.3 - 5.5:1.

[0039] Among them, in the step (2), the dispersant is one of Solsperse 41000, KOS190, KOS110, DISPERBYK-111, DISPERBYK-180; the pore-forming agent is one or a mixture of polyvinyl alcohol, dextrin, carbon powder, starch.

[0040] In addition, to make the obtained slurry uniform and facilitate subsequent photocuring 3D printing, for uniform dispersion in the step (2), the ball milling method is adopted, the ball milling time is 1 - 12 h, the ball-to-material ratio is 3:1 - 20:1, and the rotation speed is 150 - 600 r / min.

[0041] (3) The photosensitive resin-based boron carbide ceramic slurry is subjected to photocuring 3D printing to obtain a boron carbide ceramic green body.

[0042] Preferably, in the photocuring 3D printing in the step (3), the exposure power is 35 - 100 mW / cm 2 , the exposure time is 5 - 60 s, and the slice thickness is 25 - 50 μm.

[0043] Applying the photocuring 3D printing process to the preparation of boron carbide porous ceramics further simplifies the preparation process, can realize the net forming of products with complex shapes, eliminates the need for secondary processing, reduces the material cost and process cost, and expands the application of 3D printing technology in the nuclear power field.

[0044] (4) After the boron carbide ceramic green body is subjected to vacuum debinding, it is sintered without pressure to obtain boron carbide porous ceramics.

[0045] Preferably, in the step (4) of vacuum debinding, the heating rate is 3 - 15 °C / min, the debinding temperature is 400 - 800 °C, and the heat preservation time is 0.5 - 6 h.

[0046] During the vacuum debinding process, the added boric acid decomposes into B 2 O 3 ; the added polymer dispersant and pore former decompose and carbonize to form pores; furthermore, the pore structure of boron carbide porous ceramics can be regulated by controlling the process to achieve the ultra-lightweight of boron carbide porous ceramics.

[0047] After the debinding is completed, during the pressureless sintering process, preferably, the sintering atmosphere is a vacuum atmosphere or an inert atmosphere, the sintering temperature is 2050 - 2200 °C, the heat preservation time is 30 - 120 min, the heating rate is 5 - 20 °C / min, and the cooling rate is 2 - 10 °C / min. If the cooling rate is too high, a large number of cracks will be formed in the product, reducing the strength of the material.

[0048] Among them, the B 2 O 3 generated during the vacuum debinding process plays the role of a sintering aid during the pressureless sintering process, effectively promoting the sintering of the boron carbide ceramic green body, thereby endowing the boron carbide porous ceramics with excellent mechanical properties; moreover, the carbon element formed by the carbonization of the added polymer dispersant and pore former can be used as a reducing agent to reduce boron oxide to B 4 C at high sintering temperatures, which is beneficial to improving the purity of boron carbide porous ceramics.

[0049] Regarding the method for preparing boron carbide porous ceramics based on the photocuring 3D printing process, most preferably, the average particle size of the boron carbide powder is 5 μm; in the liquid photosensitive resin, the photoinitiator is 3 wt% of the mass of the resin monomer; the resin monomer is a mixture of three monomers, namely acryloylmorpholine, 1,6 - hexanediol diacrylate, and trimethylolpropane triacrylate, and their monomer mass fractions are 25 wt%, 60 wt%, and 15 wt%; in the photosensitive resin - based boron carbide ceramic slurry, the addition amount of the boron carbide powder is 58 wt% of the photosensitive resin - based boron carbide ceramic slurry; the addition amount of the dispersant KOS190 is 3 wt% of the photosensitive resin - based boron carbide ceramic slurry; the addition amount of boric acid is 3 wt% of the photosensitive resin - based boron carbide ceramic slurry; the molar ratio of the boron element content in the added boric acid to the carbon element content in the added pore former is 4.5:1; in the photocuring 3D printing, the exposure power is 35 mW / cm 2 , the exposure time is 60 s, the slice thickness is 25 μm; during the vacuum debinding process, the heating rate is 8 °C / min, the debinding temperature is 650 °C, and the heat preservation time is 1.5 h; during the pressureless sintering process, the sintering atmosphere is an argon atmosphere, the sintering temperature is 2180 °C, the heat preservation time is 60 min, the heating rate is 12 °C / min, and the cooling rate is 6 °C / min.

[0050] The boron carbide porous ceramic prepared by the method of the present invention has a pore diameter of 2.6 - 22.3 μm, a porosity of 25 - 45%, and a density of 1.40 - 1.88 g / cm 3 , and a compressive strength of 116.8 - 145.5 MPa, and has characteristics such as light weight, high strength, and excellent neutron shielding performance.

[0051] The present invention uses a photocuring 3D printing process and high-temperature carbothermal reduction to prepare boron carbide porous ceramics. During the preparation process, on the one hand, the added boric acid decomposes into B 2 O 3 during the vacuum debinding process, and further acts as a sintering aid during the pressureless sintering process, effectively promoting the sintering of the boron carbide ceramic green body, thereby endowing the boron carbide porous ceramic with excellent mechanical properties; on the other hand, the added polymer dispersant and pore-forming agent decompose and carbonize during the vacuum debinding process to form voids; furthermore, the pore structure of the boron carbide porous ceramic can be regulated by controlling the process to achieve ultra-lightweight of the boron carbide porous ceramic. In addition, the formed carbon element can be used as a reducing agent to reduce B 2 O 3 to B 4 C at high sintering temperature to facilitate the improvement of the purity of the boron carbide porous ceramic.

[0052] The preparation method of the boron carbide porous ceramic of the present invention is simple and effective, can achieve net shaping of products with complex shapes, without secondary processing, reduces material costs and process costs, and expands the application of 3D printing technology in the nuclear power field.

[0053] Example 1

[0054] (1) The boron carbide powder is dried to remove moisture and impurities in the raw materials. The drying method is vacuum drying, the vacuum degree is 0.03 MPa, the drying temperature is 50 °C, and the drying time is 48 h; among them, the average particle size of the boron carbide powder is 20 μm.

[0055] (2) The resin monomer 1,6-hexanediol diacrylate and the photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide are mixed evenly until all components are completely fused to obtain a liquid photosensitive resin; among them, the photoinitiator is 5 wt% of the resin monomer mass.

[0056] (3) Add the boron carbide powder dried in step (1), boric acid, dispersant Solsperse 41000, and pore former starch to the liquid photosensitive resin. Then, place them in a ball milling tank with a ball-to-material ratio of 20:1 and conduct mechanical ball milling at a rotation speed of 600 r / min for 2 h to obtain a photosensitive resin-based boron carbide ceramic slurry. Among them, in the photosensitive resin-based boron carbide ceramic slurry, the addition amount of the boron carbide powder is 45 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of the dispersant Solsperse 41000 is 0.2 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of boric acid is 5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the molar ratio of the boron element content in the added boric acid to the carbon element content in the added pore former is 5.5:1.

[0057] (4) The photosensitive resin-based boron carbide ceramic slurry is subjected to photocuring 3D printing to obtain a boron carbide ceramic green body. Among them, the exposure power is 50 mW / cm 2 , the exposure time is 50 s, and the slice thickness is 25 μm.

[0058] (5) After the boron carbide ceramic green body is placed in a vacuum debinding furnace for vacuum debinding, take out the green body, load it into a pressureless sintering furnace, and conduct pressureless sintering to obtain a porous boron carbide ceramic. Among them, for vacuum debinding, the heating rate is 15 °C / min, the debinding temperature is 400 °C, and the holding time is 0.5 h; for pressureless sintering, the sintering atmosphere is an argon atmosphere, the sintering temperature is 2050 °C, the holding time is 30 min, the heating rate is 20 °C / min, and the cooling rate is 10 °C / min.

[0059] Example 2

[0060] (1) The boron carbide powder is dried to remove moisture and impurities in the raw materials. The drying method is drying under an argon protection atmosphere, the argon pressure is 0.1 MPa, the drying temperature is 120 °C, and the drying time is 1 h. Among them, the average particle size of the boron carbide powder is 13 μm.

[0061] (2) Mix the resin monomer and the photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide evenly until all components are completely fused to obtain a liquid photosensitive resin. Among them, the photoinitiator is 1 wt% of the resin monomer mass; the resin monomer is a mixture of three monomers, namely hydroxyethyl acrylate, 1,6-hexanediol diacrylate, and trimethylolpropane triacrylate, and their monomer mass fractions are 31 wt%, 58 wt%, and 11 wt%.

[0062] (3) Add the boron carbide powder, boric acid, dispersant DISPERBYK-111, and pore former dried in step (1) to the liquid photosensitive resin. Then, place them in a ball milling tank at a ball-to-material ratio of 10:1 for mechanical ball milling at a rotation speed of 450 r / min for 4 h to obtain a photosensitive resin-based boron carbide ceramic slurry. Among them, in the photosensitive resin-based boron carbide ceramic slurry, the addition amount of the boron carbide powder is 65 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of the dispersant DISPERBYK-111 is 2 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of boric acid is 2 wt% of the photosensitive resin-based boron carbide ceramic slurry; the pore former is a mixture of dextrin and carbon powder with a mixing ratio of 1:1; the molar ratio of the boron element content in the added boric acid to the carbon element content in the added pore former is 4:1.

[0063] (4) The photosensitive resin-based boron carbide ceramic slurry is subjected to photocuring 3D printing to obtain a boron carbide ceramic green body. Among them, the exposure power is 60 mW / cm 2 , the exposure time is 40 s, and the slice thickness is 50 μm.

[0064] (5) After the boron carbide ceramic green body is placed in a vacuum debinding furnace for vacuum debinding, take out the green body, load it into a pressureless sintering furnace, and perform pressureless sintering to obtain a porous boron carbide ceramic. Among them, for vacuum debinding, the heating rate is 3 °C / min, the debinding temperature is 600 °C, and the holding time is 2 h; for pressureless sintering, the sintering atmosphere is a vacuum atmosphere, the sintering temperature is 2100 °C, the holding time is 90 min, the heating rate is 10 °C / min, and the cooling rate is 2 °C / min.

[0065] Example 3

[0066] (1) The boron carbide powder is dried to remove moisture and impurities in the raw materials. The drying method is drying under an argon protection atmosphere with an argon pressure of 1 MPa, a drying temperature of 60 °C, and a drying time of 24 h. Among them, the average particle size of the boron carbide powder is 1 μm.

[0067] (2) The resin monomer and the photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide are mixed evenly until all components are completely fused to obtain a liquid photosensitive resin. Among them, the photoinitiator is 10 wt% of the resin monomer mass; the resin monomer is a mixture of two monomers, dimethylolpropane tetraacrylate and 1,6-hexanediol diacrylate, with mass contents of 50 wt% and 50 wt% respectively.

[0068] (3) Add the boron carbide powder, boric acid, dispersant KOS110, and pore former polyvinyl alcohol dried in step (1) to the liquid photosensitive resin. Subsequently, place them in a ball milling tank at a ball-to-material ratio of 15:1 for mechanical ball milling at a rotation speed of 300 r / min for 9 h to obtain a photosensitive resin-based boron carbide ceramic slurry. Among them, in the photosensitive resin-based boron carbide ceramic slurry, the addition amount of the boron carbide powder is 70 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of the dispersant KOS110 is 4 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of boric acid is 0.5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the molar ratio of the boron element content in the added boric acid to the carbon element content in the added pore former is 3.3:1.

[0069] (4) The photosensitive resin-based boron carbide ceramic slurry is subjected to photocuring 3D printing to obtain a boron carbide ceramic green body. Among them, the exposure power is 60 mW / cm 2 , the exposure time is 25 s, and the slice thickness is 50 μm.

[0070] (5) After the boron carbide ceramic green body is placed in a vacuum debinding furnace for vacuum debinding, take out the green body and load it into a pressureless sintering furnace for pressureless sintering to obtain porous boron carbide ceramics. Among them, for vacuum debinding, the heating rate is 5 °C / min, the debinding temperature is 800 °C, and the holding time is 2.5 h; for pressureless sintering, the sintering atmosphere is an argon atmosphere, the sintering temperature is 2200 °C, the holding time is 120 min, the heating rate is 5 °C / min, and the cooling rate is 5 °C / min.

[0071] Example 4

[0072] (1) The boron carbide powder is dried to remove moisture and impurities in the raw materials. The drying method is vacuum drying, the vacuum degree is 0.07 MPa, the drying temperature is 100 °C, and the drying time is 6 h. Among them, the average particle size of the boron carbide powder is 10 μm.

[0073] (2) Mix the resin monomer and the photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide evenly until all components are completely fused to obtain a liquid photosensitive resin. Among them, the photoinitiator is 8 wt% of the mass of the resin monomer; the resin monomer is 1,6-hexanediol diacrylate and trimethylolpropane triacrylate, and their mass contents are 75 wt% and 25 wt% respectively.

[0074] (3) Add the boron carbide powder dried in step (1), boric acid, dispersant DISPERBYK-180, and pore former to the liquid photosensitive resin. Then, place it in a ball mill jar with a ball-to-material ratio of 3:1 and conduct mechanical ball milling at a rotation speed of 150 r / min for 12 h to obtain a photosensitive resin-based boron carbide ceramic slurry. Among them, in the photosensitive resin-based boron carbide ceramic slurry, the addition amount of the boron carbide powder is 50 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of the dispersant DISPERBYK-180 is 5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of boric acid is 3.5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the pore former is a mixture of polyvinyl alcohol, carbon powder, and starch, and their mixing ratio is 1:1:1; the molar ratio of the boron element content in the added boric acid to the carbon element content in the added pore former is 5:1.

[0075] (4) The photosensitive resin-based boron carbide ceramic slurry is subjected to photocuring 3D printing to obtain a boron carbide ceramic green body. Among them, the exposure power is 100 mW / cm 2 , the exposure time is 5 s, and the slice thickness is 25 μm.

[0076] (5) After the boron carbide ceramic green body is placed in a vacuum debinding furnace for vacuum debinding, take out the green body, load it into a pressureless sintering furnace, and conduct pressureless sintering to obtain porous boron carbide ceramics. Among them, for vacuum debinding, the heating rate is 10 °C / min, the debinding temperature is 500 °C, and the holding time is 6 h; for pressureless sintering, the sintering atmosphere is a vacuum atmosphere, the sintering temperature is 2130 °C, the holding time is 45 min, the heating rate is 15 °C / min, and the cooling rate is 8 °C / min.

[0077] Example 5

[0078] (1) The boron carbide powder is dried to remove moisture and impurities in the raw materials. The drying method is vacuum drying, the vacuum degree is 0.01 MPa, the drying temperature is 80 °C, and the drying time is 24 h. Among them, the average particle size of the boron carbide powder is 5 μm.

[0079] (2) Mix the resin monomer and the photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide evenly until all components are completely fused to obtain a liquid photosensitive resin. Among them, the photoinitiator is 3 wt% of the resin monomer mass. The resin monomer is a mixture of three monomers, acryloylmorpholine, 1,6-hexanediol diacrylate, and trimethylolpropane triacrylate, and their monomer mass fractions are 25 wt%, 60 wt%, and 15 wt%.

[0080] (3) Add the boron carbide powder dried in step (1), boric acid, dispersant KOS190, and pore-forming agent dextrin to the liquid photosensitive resin. Then, place them in a ball mill tank at a ball-to-material ratio of 6:1 for mechanical ball milling at a rotation speed of 350 r / min for 6 h to obtain a photosensitive resin-based boron carbide ceramic slurry. Among them, in the photosensitive resin-based boron carbide ceramic slurry, the addition amount of the boron carbide powder is 58 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of the dispersant KOS190 is 3 wt% of the photosensitive resin-based boron carbide ceramic slurry; the addition amount of boric acid is 3 wt% of the photosensitive resin-based boron carbide ceramic slurry; the molar ratio of the boron element content in the added boric acid to the carbon element content in the added pore-forming agent is 4.5:1.

[0081] (4) The photosensitive resin-based boron carbide ceramic slurry is subjected to photocuring 3D printing to obtain a boron carbide ceramic green body. Among them, the exposure power is 35 mW / cm 2 , the exposure time is 60 s, and the slice thickness is 25 μm.

[0082] (5) After the boron carbide ceramic green body is placed in a vacuum debinding furnace for vacuum debinding, take out the green body, load it into a pressureless sintering furnace, and perform pressureless sintering to obtain a porous boron carbide ceramic. Among them, for vacuum debinding, the heating rate is 8 °C / min, the debinding temperature is 650 °C, and the holding time is 1.5 h; for pressureless sintering, the sintering atmosphere is an argon atmosphere, the sintering temperature is 2180 °C, the holding time is 60 min, the heating rate is 12 °C / min, and the cooling rate is 6 °C / min.

[0083] Experimental results

[0084] 1. Phase characterization

[0085] Perform X-ray diffraction (XRD) analysis on the porous boron carbide ceramic prepared in Example 1. As Figure 1 shown, the porous boron carbide ceramic is a high-purity B 4 C phase, and there are no other impurity phases. Moreover, the high B element content can greatly improve the neutron shielding efficiency of the material.

[0086] 2. Morphology analysis

[0087] Perform morphology analysis on the porous boron carbide ceramics prepared in Examples 1-5. Among them, the porous boron carbide ceramic prepared in Example 3 ( Figure 2 ) exhibits a porous structure, and the pore structure is evenly distributed, with an average pore diameter of 2.6 μm.

[0088] 3. Compressive strength analysis

[0089] Detect the stress-strain of the porous boron carbide ceramics prepared in Examples 1-5. Among them, the stress-strain curve of the porous boron carbide ceramic prepared in Example 2 is as Figure 3As shown, the compressive strength is 137.2 MPa.

[0090] The compressive strength, porosity, density and average pore diameter of the boron carbide porous ceramics in Test Examples 1-5 were measured. Four examples in the patent with publication number CN 116655383 A (Porous Boron Carbide Ceramic Material for Neutron Shielding Material and Its Preparation Method) were used as Comparative Examples 1-4 for comparison. See Table 1 for details.

[0091] Table 1 Performance Comparison of Boron Carbide Porous Ceramics Prepared in Examples 1-5

[0092]

[0093] As can be seen from Table 1, the porosity and density of the boron carbide porous ceramics prepared in Examples 1-5 are 25-45% and 1.40-1.88 g / cm 3 respectively, and the porosity and density of the boron carbide porous ceramics prepared in Comparative Examples 1-4 are 28-36% and 1.8-2.2 g / cm 3 respectively. It can be seen that the porosity range of the boron carbide porous ceramics prepared in Examples 1-5 is larger, indicating that the preparation method of the present invention can effectively adjust the porosity of the boron carbide porous ceramics by changing the content of the pore-forming agent and the solid content of the slurry, and has the advantage of controllable process. In addition, the boron carbide porous ceramics prepared in Examples 1-5 have a lower density than those prepared in Comparative Examples 1-4, and are obviously lighter. Moreover, the through-hole rate of the boron carbide porous ceramics prepared in Examples 1-5 is ≥80%, and they have a higher purity, which is more conducive to fully exerting the neutron shielding performance of the material.

[0094] The compressive strength of the boron carbide porous ceramics prepared in Examples 1-5 is in the range of 116.8-145.5 MPa. By comparing with Comparative Examples 1-4, it is found that under the same porosity condition, the boron carbide porous ceramics prepared by the present invention have a higher compressive strength. As shown in Table 1, the average pore diameter of the boron carbide porous ceramics prepared in Examples 1-5 is 2.6-22.3 μm. This means that the preparation method of the present invention can realize the regulation of the pore structure of the boron carbide porous ceramics by controlling the process, and thus can meet different application requirements.

Claims

1. A method for preparing porous boron carbide ceramics based on a photocuring 3D printing process, characterized in that: The following steps are involved: (1) Resin monomers and photoinitiators are mixed to obtain liquid photosensitive resin; (2) adding boron carbide powder, boric acid, a dispersant and a pore-forming agent into a liquid photosensitive resin and dispersing them uniformly to obtain a photosensitive resin-based boron carbide ceramic slurry; (3) The photosensitive resin-based boron carbide ceramic slurry is subjected to light-curing 3D printing to obtain a boron carbide ceramic body; (4) After vacuum debinding, the boron carbide ceramic body is subjected to pressureless sintering to obtain a porous boron carbide ceramic; In the photosensitive resin-based boron carbide ceramic slurry of step (2), the amount of boron carbide powder added is 45-70 wt% of the photosensitive resin-based boron carbide ceramic slurry; the amount of dispersant added is 0.2-5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the amount of boric acid added is 0.5-5 wt% of the photosensitive resin-based boron carbide ceramic slurry; the molar ratio of the boron content in the added boric acid to the carbon content in the added pore-forming agent is 3.3-5.5:1; In the step (3), the exposure power of the light-curing 3D printing is 35-100 mW / cm 2 , exposure time was 5-60 s, and slice thickness was 25-50 μm; In the step (4), the vacuum debinding is performed with a heating rate of 3 to 15 °C / min, a debinding temperature of 400 to 800 °C, and a holding time of 0.5 to 6 h; The step (4) is pressureless sintering, the sintering atmosphere is a vacuum atmosphere or an inert atmosphere, the sintering temperature is 2050-2200°C, the holding time is 30-120 min, the heating rate is 5-20°C / min, and the cooling rate is 2-10°C / min; The boron carbide porous ceramic is a high-purity B4C phase with a pore size of 2.6-22.3 μm, a porosity of 25-45%, and a density of 1.40-1.88 g / cm 3 , the compressive strength is 116.8~145.5 MPa.

2. The method for preparing porous boron carbide ceramics based on a photocuring 3D printing process according to claim 1, characterized in that: In the step (2), the average particle size of the boron carbide powder is 1-20 μm.

3. The method for preparing porous boron carbide ceramics based on a photocuring 3D printing process according to claim 1, characterized in that: In the step (1), the resin monomer is one of butyl acrylate, lauryl acrylate, ethoxyethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, isobornyl methacrylate, cyclotrimethylolpropane methylal acrylate, acryloyl morpholine, dimethylenepropane tetraacrylate, 1,6-hexanediol diacrylate, 1,6-methyl diacrylate, tripropylene glycol diacrylate, polyethylene glycol 200 diacrylate, polyethylene glycol 400 diacrylate, polyethylene glycol 600 diacrylate, propoxylated neopentyl glycol diacrylate, tricyclodecane dimethanol diacrylate, trimethylolpropane triacrylate, (ethoxy) trimethylolpropane triacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate, or a mixture of two or three thereof; The photoinitiator was bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

4. The method for preparing porous boron carbide ceramics based on a photocuring 3D printing process according to claim 1, characterized in that: In the step (1), the photoinitiator is 1-10 wt% of the mass of the resin monomer.

5. The method for preparing porous boron carbide ceramics based on photocuring 3D printing process according to claim 1, characterized in that: In the step (2), the dispersant is one of Solsperse 41000, KOS190, KOS110, DISPERBYK-111, and DISPERBYK-180; and the pore-forming agent is a mixture of one or more of polyvinyl alcohol, dextrin, carbon powder, and starch.

6. The method for preparing porous boron carbide ceramics based on a photocuring 3D printing process according to claim 1, characterized in that: The uniform dispersion in step (2) is achieved by ball milling, with a ball milling time of 1 to 12 h, a ball-to-material ratio of 3:1 to 20:1, and a rotation speed of 150 to 600 r / min.

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