CN106830942B

CN106830942B - Porous B4C ceramic skeleton and its freezing injection moulding process

Info

Publication number: CN106830942B
Application number: CN201710044834.6A
Authority: CN
Inventors: 张中武; 马云涛; 张贺新; 王志伟; 唐小存; 蒋波; 壮新
Original assignee: Zhenjiang Niukeli Nuclear Energy New Material Technology Co Ltd; Harbin Engineering University
Current assignee: Zhenjiang Niukeli Nuclear Energy New Material Technology Co Ltd; Harbin Engineering University
Priority date: 2017-01-20
Filing date: 2017-01-20
Publication date: 2020-02-18
Anticipated expiration: 2037-01-20
Also published as: CN106830942A

Abstract

The invention relates to a porous B₄C ceramic skeleton and its freezing injection moulding process, porous B₄C is as neutron absorbing material B₄A ceramic skeleton of C/Al is prepared by impregnating B₄Al is infiltrated into C skeleton to increase B content₄B in C/Al structure₄The ceramic content is increased, and the neutron absorption capacity is increased; the B is₄C selecting different particles with the particle diameters of 5 mu m, 10 mu m, 20 mu m and 40 mu m respectively, taking water as a freezing injection molding solvent, mixing the particles according to mass percent, adding a proper amount of dispersing agent and binding agent, freezing and sublimating to obtain B₄C ceramic blank, sintering at 2000 ℃ to obtain B for impregnating Al₄C, a ceramic framework; b of the invention₄Moderate strength of C ceramic skeleton, B₄High content of C ceramic, good through-hole structure, resistance to pressure generated in Al infiltration process, simple preparation process, and good corrosion resistance₄The increase of C content can greatly increase B₄C/Al neutron absorption efficiency.

Description

Porous B4C ceramic skeleton and its freezing injection moulding process

Technical Field

The invention relates to a B used for neutron absorption of spent fuel₄Porous B of C/Al composite material₄A preparation process of a C ceramic framework, belonging to the field of ceramic materials.

Background

B₄The C/Al composite material contains the element B with good neutron absorption performance, so that the C/Al composite material can be used for preparing a neutron absorption storage structure material. Its advantages are high resistance to corrosion and radiation, long service life and high safety and economy of storage and transportation of spent fuel. B is₄Common preparation methods of the C/Al neutron absorbing material include a fusion casting method, a powder metallurgy method, an infiltration method and the like. The interface reaction of the composite material obtained by the fusion casting method is serious, the powder metallurgy method has complex process, B₄Low C content, B₄C distribution is not uniform, and the like. In recent years, impregnation method for preparing B₄The process of the C/Al composite material is rapidly developed in China, and the infiltration method is to melt aluminum metal and spontaneously infiltrate the aluminum metal into solid B₄C porous skeleton preform, but the preparation of this method requires B to be advanced₄And C, sintering to prepare the porous ceramic skeleton.

The porous ceramic skeleton may be prepared through various processes, such as soaking in foam, pressureless sintering, etc. The freeze-injection molding process has the advantages of simple method, uniform pore structure and the like, and has relatively rapid development in the aspect of preparing porous materials. Currently, in the production of boron carbide by sintering, mainly working on the production of boron carbide such as rubicun, etc. (see patent document 1), a gel injection molding production method of a reaction sintered boron carbide ceramic composite material has been developed, in which resorcinol, formaldehyde, sodium carbonate and deionized water are mixed, and B is added₄C powder of C to form B₄C, mixing the slurry; 2): vacuum degassing, injection molding and sealing the mixed slurry; carrying out sol gelation in a water bath, and aging for 4-50 h; drying under normal pressure and then carbonizing at high temperature to obtain B₄C/C biscuit; 3): in B₄And placing silicon on the C/C biscuit, carrying out high-temperature infiltration to obtain a sintered body, cooling to remove redundant silicon, and obtaining the reaction sintered boron carbide ceramic composite material. Great vanoh et al disclose a zirconium-containing boron carbide-aluminum alloy composite material and a method for preparing the same (see patent literature)Document 2), the method adopts a powder sintering method to prepare a porous boron carbide matrix, and then molten zirconium-containing aluminum alloy is infiltrated into the porous boron carbide matrix to prepare the compact composite material. The invention has reasonable element collocation, scientific structural design and simple preparation process, and the obtained product has low density, high hardness, good fracture toughness and good thermal shock resistance, is not limited by the shape and is suitable for being used as a light high-hardness impact-resistant structural material. The invention discloses a preparation method of a boron carbide composite material (see patent document 3), and the preparation method of the boron carbide composite material comprises the following steps: pretreating boron carbide powder; carrying out compression molding on the pretreated boron carbide powder; pre-sintering a boron carbide framework; carrying out pressureless infiltration treatment on the boron carbide skeleton after pre-sintering and the infiltration metal; and carrying out heat treatment on the pressureless infiltrated boron carbide composite material primary blank to obtain the high-purity boron carbide composite material. Although there are many reports on the preparation method of porous boron carbide, the preparation method of B in the freeze injection molding method using water as a solvent₄The aspect of C porous ceramic skeleton is not reported.

At present, although B is prepared by infiltration method or powder metallurgy method₄The C/Al performance is relatively excellent, but the B contained in the alloy₄The content of C is relatively low, the process cost is high, the operation is complex, the interface is not easy to control, and the material strength is low, so that the research on a better porous boron carbide ceramic forming method is to obtain high-quality B₄The invention provides a novel porous boron carbide ceramic framework forming process aiming at the important direction of a C/Al composite material.

Patent document 1: CN 105777130A;

patent document 2: CN 105483487A;

patent document 3: CN 105523764A.

Disclosure of Invention

The invention aims at a porous B₄C ceramic skeleton and its freeze injection molding process, B₄The C ceramic skeleton has high strength and can resist the melting and infiltration pressure of metal Al, and the B ceramic skeleton is also required to be₄The C ceramic framework has good through hole aperture, and can realize the complete infiltration of the metal aluminum.

The specific technical scheme is as follows:

porous B of the invention₄C ceramic skeleton and its freezing injection moulding process for ensuring B₄Density and mechanical strength of C skeleton, B₄C selecting four kinds of powder with different grain sizes of 5 μm, 10 μm, 20 μm and 40 μm respectively, mixing, and B₄The mole percentage of the C powder was 8:4:2: 1.

Porous B of the invention₄C ceramic skeleton and its freeze injection moulding process, using water as solvent, polyvinyl alcohol as adhesive, liquid nitrogen as freezing adjuvant and B₄The mass ratio of C to water is 1:4, and the mass percentage of polyvinyl alcohol in the ceramic slurry is 0.3%.

The porous B₄The C ceramic skeleton is prepared through proportioning, ball milling at constant temperature, freeze molding, sublimation drying and high-temp sintering₄The boron carbide ceramic skeleton is required by the technological background of C/Al composite infiltration technology.

The preparation method is realized by the following steps: 1) selecting raw materials according to the designed chemical component proportion of the boron carbide freeze injection mold; 2) putting the proportioned raw materials into a ball mill with a constant temperature system for ball milling and mixing for 10 hours to ensure that boron carbide particles are uniformly mixed in a water solvent; wherein the ball milling constant temperature is 60 ℃, and at the temperature, water can be in a good dispersion state with ceramic particles and a dispersant and can be well mixed with boron carbide; 3) performing freeze injection molding on the mixed slurry, adopting liquid nitrogen to quickly solidify and form the slurry in order to prevent the slurry from coagulating, scanning the solidified slurry as shown in figure 3, and forming a through hole channel by water under a directional freezing gradient, so that metal melting and infiltration and circulation can be facilitated; 4) demolding the slurry after freezing injection molding, wherein a polytetrafluoroethylene mold is adopted for demolding, and glycerol is coated inside the polytetrafluoroethylene mold to be used as a lubricant; 5) after demoulding treatment, the slurry is placed in a freezing chamber with a ventilation system for 20 days, so that water is fully sublimated and volatilized; 6) and sintering the obtained porous boron carbide green body at high temperature in a high-temperature sintering furnace, wherein the specific sintering process comprises the following steps: the heating speed is 1 ℃/min, the temperature is kept at 300 ℃ for 30min, the temperature is raised to 1800 ℃ at 5 ℃/min, the temperature is kept for 2h, then the temperature is raised to 2000 ℃ and the temperature is kept for 2h, and the mixture is taken out of the furnace and cooled.

The invention is based on the porous structure preparation scheme designed for the Al metal infiltration of the porous boron carbide material at high temperature, and carries out structural analysis and process optimization on the porous boron carbide obtained by the molding process, so as to obtain a boron carbide porous skeleton with through holes and certain mechanical strength, and ensure that the sintered porous ceramic has excellent mechanical properties. The compactness of framework sintering is ensured by the boron carbide particles with different particle sizes, a communicated pore diameter channel is obtained in the slurry forming process by water in the directional freezing and solidification process, and the rapid condensation of the boron carbide slurry is ensured by liquid nitrogen cooling, so that the boron carbide in the whole structure is uniformly dispersed, and the material has reliable mechanical strength.

The boron carbide ceramic skeleton material obtained by adopting the freeze injection molding process has a uniform through hole structure, and the compressive strength of the sintered material is about 23 MPa. Can ensure the completeness of Al infiltration and prevent structural deformation, and meets the requirement of preparing B by an infiltration method₄The use of the C/Al material in the substrate material of the wet ball mill is required.

Drawings

FIG. 1 is a process flow diagram of the present invention.

FIG. 2 is a view showing the structure of a refrigerating apparatus according to the present invention.

FIG. 3 shows the texture of the slurry after freezing in accordance with the present invention.

FIG. 4 shows a view of the present invention B₄And C, powder constant temperature nodular graphite drawing.

FIG. 5 shows a schematic view of the invention B₄And C, a ceramic skeleton.

Detailed Description

In order to make the technical scheme of the invention clearer and clearer, the invention is further described with reference to the accompanying drawings, and any scheme obtained by carrying out equivalent replacement and conventional reasoning on the technical characteristics of the technical scheme of the invention falls into the protection scope of the invention.

Reference numerals

The device comprises a freezing container 1, a metal bottom plate 2, heat-preservation foam 3, a polytetrafluoroethylene mold 4, a freezing auxiliary agent 5 and ceramic slurry 6.

The invention relates to a method for preparing a neutron absorption material B₄Porous B of C/Al₄C, a freezing injection molding process of a ceramic skeleton, which comprises the following steps: water as solvent, B₄C selecting four kinds of powder with different grain sizes of 5 μm, 10 μm, 20 μm and 40 μm respectively, mixing, and B₄The mol percentage of the C powder is 8:4:2:1, the polyvinyl alcohol is used as a dispersing agent, the liquid nitrogen is used as a freezing auxiliary agent, a polytetrafluoroethylene die with the inner wall coated with a lubricant is adopted, and the B powder₄The mass percentage of C and water is 1:4, and the mass percentage of polyvinyl alcohol is 0.3%.

The freeze injection molding process comprises the following specific steps:

(1) for B with different particle diameters₄Mixing the powder C according to the proportion, wherein the selected powder B₄The purity of the powder C is more than 99.9 percent, and the molar ratio of boron carbide with four different granularities of 5 mu m, 10 mu m, 20 mu m and 40 mu m is 8:4:2: 1; the specific components are shown in table 1:

TABLE 1B₄C, main technical indexes of the powder are as follows:

(2) preparation of porous B by Freeze injection Molding Process₄C ceramic skeleton, water as solvent, polyvinyl alcohol as disperser, and B₄Mixing the powders to obtain a ceramic slurry, B₄The mass ratio of the C powder to the water is 1:4, the polyvinyl alcohol accounts for 0.3 percent of the mass of the ceramic slurry, and the ceramic slurry is ball-milled in a ball mill with a constant temperature device for 10 hours; FIG. 4 shows a schematic diagram of a constant temperature ball mill;

(3) pouring the mixed ceramic slurry into a pre-prepared refrigerating device, wherein the refrigerating device comprises a refrigerating container 1, a metal bottom plate 2 is arranged at the center of the refrigerating container, a circle of heat-insulating foam 3 with a cylindrical sleeve structure is arranged on the metal bottom plate, a circle of polytetrafluoroethylene mold 4 is arranged in the heat-insulating foam, liquid nitrogen is used as a refrigerating auxiliary agent 5 and is arranged in the refrigerating container, and the ceramic slurry 6 is added into the polytetrafluoroethylene mold; in order to form more longitudinal frozen crystals so as to obtain directional pore canals after drying, a layer of glycerin is coated on the inner wall of the polytetrafluoroethylene mold to be used as a lubricant, and the periphery of the polytetrafluoroethylene mold is coated with a heat-insulating material; the purpose of the metal bottom plate is that under the action of a liquid nitrogen freezing auxiliary agent, a bottom water solvent rapidly grows upwards to generate crystals, so that longitudinal crystals from bottom to top are obtained; demolding after the slurry is completely solidified;

(4) placing the blank after injection molding in a freezing chamber with a ventilation device for sublimation treatment;

(5) sintering the dried boron carbide ceramic blank, wherein the process comprises the following steps: the temperature rise speed is 1 ℃/min, the temperature is kept at 300 ℃ for 30min, the residual solvent and dispersant in the boron carbide particles are completely decomposed, the temperature is raised to 1800 ℃ at 5 ℃/min and kept for 2h, the boron carbide framework is sintered to form a sintering neck, certain mechanical strength is generated, the temperature is raised to 2000 ℃ and kept for 2h, the framework is further densified, and then the boron carbide ceramic framework with the directional through holes is obtained after the boron carbide ceramic framework is taken out of the furnace and cooled.

And analyzing the mechanical property of the sintered boron carbide skeleton, and obtaining the compressive strength of 23MPa by taking 6-8 points for the compressive strength test and taking the average value of the points.

The pore structure of the boron carbide porous ceramic skeleton of the present invention was observed by using a philips FEI silicon scanning electron microscope, as shown in fig. 5. As can be seen from the figure, the boron carbide framework is compact, the porosity is uniform, the boron carbide framework has a good through hole structure, and the boron carbide framework plays a role in promoting the infiltration of Al metal to a certain extent.

Claims

1. Used for preparing neutron absorption material B₄Porous B of C/Al₄The freezing injection molding process of the C ceramic skeleton is characterized in that the process comprises the following steps: water as solvent, B₄C selecting four kinds of powder with different grain sizes of 5 μm, 10 μm, 20 μm and 40 μm respectively, mixing, and B₄The mol percentage of the C powder is 8:4:2:1, the polyvinyl alcohol is used as a dispersing agent, the liquid nitrogen is used as a freezing auxiliary agent, a polytetrafluoroethylene die with the inner wall coated with a lubricant is adopted, and the B powder₄The mass percentage of C and water is 1:4, the mass percentage of polyvinyl alcohol is0.3％；

The freeze injection molding process comprises the following specific steps:

TABLE 1B₄C, main technical indexes of the powder are as follows:

(2) preparation of porous B by Freeze injection Molding Process₄C ceramic skeleton, water as solvent, polyvinyl alcohol as disperser, and B₄Mixing the powders to obtain a ceramic slurry, B₄The mass ratio of the C powder to the water is 1:4, the polyvinyl alcohol accounts for 0.3 percent of the mass of the ceramic slurry, and the ceramic slurry is ball-milled in a ball mill with a constant temperature device for 10 hours;

(3) pouring the mixed ceramic slurry into a pre-prepared refrigerating device, wherein the refrigerating device comprises a refrigerating container, a metal bottom plate is arranged at the center of the refrigerating container, a circle of heat-insulating foam with a cylindrical sleeve structure is arranged on the metal bottom plate, a circle of polytetrafluoroethylene mold is arranged in the heat-insulating foam, liquid nitrogen is used as a refrigerating auxiliary agent and is arranged in the refrigerating container, and the ceramic slurry is added into the polytetrafluoroethylene mold; in order to form more longitudinal frozen crystals so as to obtain directional pore canals after drying, a layer of glycerin is coated on the inner wall of the polytetrafluoroethylene mold to be used as a lubricant, and the periphery of the polytetrafluoroethylene mold is coated with a heat-insulating material; the purpose of the metal bottom plate is that under the action of a liquid nitrogen freezing auxiliary agent, a bottom water solvent rapidly grows upwards to generate crystals, so that longitudinal crystals from bottom to top are obtained; demolding after the slurry is completely solidified;

(5) sintering the dried boron carbide ceramic blank, wherein the process comprises the following steps: heating up at a speed of 1 ℃/min, keeping the temperature at 300 ℃ for 30min to completely decompose the solvent and the dispersant remained in the boron carbide particles, heating up to 1800 ℃ at a speed of 5 ℃/min, keeping the temperature for 2h to sinter the boron carbide skeleton to form a sintering neck, generating a certain mechanical strength, heating up to 2000 ℃ and keeping the temperature for 2h to further densify the skeleton, then discharging and cooling to finally obtain the boron carbide ceramic skeleton with the directional through holes.