High-hardness neutron absorption boron ball and preparation method thereof

Abstract

The invention belongs to the field of neutron absorption materials, and particularly relates to a high-hardness neutron absorption boron ball and a preparation method thereof. Polyvinyl alcohol and paraffin are added into boron powder for granulation, and a spherical boron ball prefabricated blank is obtained; in a vacuum environment or an argon environment, raising the temperature from normal temperature to 620-680 DEG C through a vacuum sintering furnace, pre-sintering at the temperature, carrying out self-propagating reaction on the blank, cooling along with the furnace, and then carrying out ball milling and scattering treatment to obtain preformed boron ball particles; and heating to 1200-1300 DEG C in a vacuum sintering furnace in an argon atmosphere or a vacuum environment, sintering at the temperature, cooling along with the furnace, and carrying out autogenous grinding and spheroidizing to obtain the spherical boron balls. The spherical boron ball is high in forming rate and sphericity degree, large in hardness, uniform in size, high in internal density, free of pores and not prone to breakage, and neutron absorption of nuclear reactor control rods, nuclear waste storage and shielding layer filling boron balls through a guide rail or a slide way remotely is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of neutron absorption materials, and particularly relates to a high-hardness neutron-absorbing boron ball and a preparation method thereof. Background Art

[0002] Boron (especially isotope boron-10, with a natural abundance of about 20%) is widely used in neutron absorption materials due to its high neutron absorption cross-section. After neutrons are absorbed by boron-10, the following nuclear reaction occurs:

[0003] 10 B + n → 7 Li + α + γ

[0004] This reaction can effectively consume neutrons and inhibit nuclear chain reactions. Therefore, boron is indispensable in the nuclear energy field, especially playing a core role in reactor control and radiation protection, and is widely used in nuclear reactor control, radiation shielding, nuclear waste treatment, neutron detection, medical treatment, and nuclear fuel management, and is an important material in the nuclear energy field.

[0005] In the early 20th century, boron was mostly used in military and high-end medical equipment in the fields of neutron absorption and deceleration, resulting in a small market for boron profiles. In the processing of spherical boron materials, domestic equipment and processes were almost blank, mainly relying on foreign imports. However, due to the poor fluidity, easy dusting, and inconvenient operation of boron powder itself, boron composite materials are mostly used in fields such as shielding materials, composite materials, and coolant additives due to their limited absorption performance. With social progress and the development of technology, the marketization degree of the nuclear industry has expanded in some fields, the demand for spherical boron materials has increased day by day, and due to the severe international situation and the market restrictions on the export of boron balls to China by foreign countries, the domestic demand for boron balls has become more prominent.

[0006] In high-radiation scenarios, since various operations cannot be carried out too close, it can be considered to use guide rails or chutes to fill boron powder in nuclear reactor control rods, nuclear waste storage, and shielding layers as neutron absorption materials. However, due to the poor roundness, poor fluidity, low density, easy breakage, easy dusting, and inconvenient operation of boron powder itself, when filling boron powder through guide rails or chutes, due to its lack of roundness and low regularity, uneven powder discharge and blockage are likely to occur, and the hardness is insufficient, and it is easy to collide and break during the filling of boron powder, resulting in the inability to fill, the inability to smoothly carry out filling and absorption, and the precise control of the addition amount of boron raw materials. Summary of the Invention

[0007] In order to overcome the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a high-hardness neutron-absorbing boron ball and a preparation method thereof. The prepared spherical boron ball has a very high forming rate and sphericity, uniform size, high fluidity, high density and hardness, no pores, and no adhesion problems. While improving the neutron absorption performance, it realizes remotely controlling the control rods of nuclear reactors, storing nuclear waste, and filling boron balls in the shielding layer through rails or chutes to absorb neutrons, is not prone to uneven discharging and blockage phenomena, and is not easily broken during high-speed transmission in the track or slide rail, solving the problems of the prior art that remote feeding and quantitative feeding cannot be carried out.

[0008] The present invention provides a preparation method for a high-hardness neutron-absorbing boron ball, comprising the following steps:

[0009] (1) Adding polyvinyl alcohol and paraffin wax as binders to boron powder, and granulating in a granulator to obtain a spherical boron ball preform;

[0010] (2) Under a vacuum environment or an argon environment, heating the spherical boron ball preform from room temperature to 620°C - 680°C in a vacuum sintering furnace, then pre-sintering at this temperature to cause a self-propagating reaction of the preform, cooling with the furnace, and then performing ball milling and dispersion treatment to obtain preformed boron ball particles;

[0011] (3) Under an argon atmosphere or a vacuum environment, heating the preformed boron ball particles from room temperature to 1200°C - 1300°C in a vacuum sintering furnace, then sintering at this temperature, cooling with the furnace, and then performing self-grinding and spheroidization to obtain spherical boron balls.

[0012] The present invention has found through research that due to the non-uniform particle size of the raw material boron powder and differences in different batches, the present invention adds polyvinyl alcohol (PVA) and paraffin wax as binders to the boron powder. Polyvinyl alcohol (PVA) and paraffin wax synergistically enhance the bonding performance, applying both the high adhesion of the hydroxyl group (-OH) of polyvinyl alcohol and the alkane chain of paraffin wax to improve the compatibility of the raw materials, expand the bonding range, have better bonding to boron powders with different particle sizes, contribute to forming spherical boron ball preforms after granulation, facilitate the forming of boron balls, improve the forming rate and sphericity, and improve the hardness and density of the formed boron balls, making them not easily broken. Preferably, in step (1), 0.8% - 1.2% by mass of polyvinyl alcohol and 0.5% - 1.0% by mass of paraffin wax with a particle size of 1um - 3um are added to the boron powder as binders, and the effect is the best.

[0013] If direct high-temperature sintering is carried out, it is impossible to avoid the deformation and adhesion of boron balls. Through a large number of experimental studies, the present invention conducts sintering in two steps. The first step is low-temperature pre-sintering, and the second step is high-temperature sintering. While improving the hardness, it avoids the deformation and adhesion of boron balls and improves the sphericity and uniformity. By first carrying out pre-sintering, boron ball particles that are relatively independent, have relatively high strength, good sphericity retention, certain hardness, and less adhesion and deformation can be obtained. Then, after ball milling and dispersion, high-temperature sintering is carried out. Finally, through self-grinding and spheroidization, the non-round parts and the powder adhered to the surface of the boron balls are knocked off. The finally obtained spherical boron balls have a very high forming rate and sphericity, with a sphericity greater than 91%, which helps to evenly distribute the neutron absorber, improve the shielding effect, have high strength, large hardness, uniform size, no adhesion problem, and realize the precise control of quantitative feeding for fixed scenarios by remotely absorbing neutrons through the control rods of nuclear reactors, storing nuclear waste, and filling boron balls in the shielding layer by counting or flow statistics through rails or chutes.

[0014] Preferably, in step (1), the boron powder is crystalline boron powder with a purity of more than 99.6%. Boron powder is mainly divided into amorphous boron powder and crystalline boron powder. Amorphous boron powder has an amorphous structure, disordered atomic arrangement, and lack of long-range order. Crystalline boron powder has a clear lattice structure, ordered atomic arrangement, stable crystal structure, high purity, and few metal impurities. The present invention selects crystalline boron powder as the raw material.

[0015] The present invention has found through research that by adjusting the tilt angle of the pressure plate in the granulator, the residence time of the material can be controlled, thereby affecting the particle size, forming rate, and sphericity. It has been found through research that in step (1), the conditions for granulation in the granulator are: the rotation speed parameter is 150 r / min - 170 r / min, the tilt angle of the pressure plate is 45° - 50°, and the granulation time is 28 - 30 minutes. Under these conditions, the forming rate and sphericity can be improved, and the problem of difficult forming of boron balls can be solved. The granulation particle size is between 0.2 - 5 mm, with relatively high strength and easy to take out.

[0016] In step (2), the vacuum environment is 1×10-3 Pa. Pre-sintering is carried out in a vacuum environment and an argon environment. In particular, the boron ball blanks sintered in an argon atmosphere have a higher density than those sintered in a vacuum environment.

[0017] Preferably, in step (2), the temperature is raised from room temperature to 620°C - 680°C at a heating rate of 4.5 - 5.5°C / min in a vacuum sintering furnace, and then pre-sintered at this temperature for 3 - 4 hours. The preformed boron ball particles obtained by pre-sintering under these conditions have the least adhesion, relatively high strength, and the best sphericity retention. If the pre-sintering temperature is too low, the boron balls obtained by sintering have low hardness and are not easily dispersed for treatment; if the pre-sintering temperature is too high, the sintered boron balls are severely bonded, resulting in deformation of the boron balls and inability to be dispersed; at a heating rate of 4.5 - 5.5°C / min, the effect is the best.

[0018] In step (2), the ball milling and dispersion treatment is as follows: for the material obtained by furnace cooling, agate balls with a diameter of 1 - 3 mm are mixed with the material in a ratio of 3.0 - 3.1:1 and dispersed at a rotation speed of 90 - 110 r / min in an argon atmosphere environment for the partially bonded boron ball blanks to obtain preformed boron ball particles. Solving the above pre-sintering process and ball milling and dispersion treatment enables the obtained preformed boron ball particles to solve the bonding problem caused by direct high-temperature sintering and obtain preliminarily formed boron balls.

[0019] In step (3), the vacuum environment is 1×10-3 Pa, and the spherical boron ball preform blanks are sintered in a vacuum environment and an argon atmosphere. In particular, the boron ball blanks sintered in an argon atmosphere have a higher density than those sintered in a vacuum environment.

[0020] Forming and adhesion problems: Since boron balls need to flow at high speed in a fixed track during later applications, in order to prevent the boron balls from cracking during high-speed movement, causing blockage of the track, uneven discharging, etc., the Mohs hardness of the boron balls is generally required to be above 5.0. Hardness and purity problems: For the pre-sintered boron ball blanks, due to their low hardness, they are easily broken, and there is still residual polyvinyl alcohol after pre-sintering. To solve the above problems, the present invention performs secondary sintering on the pre-sintered boron balls. In step (3), in a vacuum sintering furnace, the preformed boron ball particles are heated from room temperature to 1200°C - 1300°C at a heating rate of 8 - 10°C / min in an argon atmosphere, and then sintered at this temperature for 4.5 - 5.5 hours. Using this technical means can improve the hardness of the boron ball particles, and the obtained boron balls have a Mohs hardness above 5.0, and basically no adhesion occurs. The sintered boron balls have high hardness, high internal density, no pores, are not easily broken, and are easily dispersed for treatment. If the sintering temperature is too low, the obtained boron balls have low hardness, low internal density, many pores, are very fragile and easily contaminated by external media, and are not easily dispersed for treatment; if the sintering temperature is too high, the bonding of the boron ball blanks becomes more serious. The more serious the bonding, the more serious the deformation of the boron balls, the fewer boron balls that can be dispersed, the greater the difficulty, and the extremely low sphericity of the dispersed boron balls.

[0021] In the present invention, polyvinyl alcohol (PVA) and paraffin are added to boron powder as binders. During the pre-sintering process, when the temperature is 400 - 500 °C, polyvinyl alcohol completely decomposes into gas, and the polyvinyl alcohol in the boron balls can be removed during the pre-sintering process of the present invention. During the two sintering processes, when the temperature reaches 600 - 800 °C, paraffin is oxidized to CO2 and H2O. Most of the paraffin components in the boron balls can be basically removed during the pre-sintering process of the present invention, and the paraffin components can be completely removed during the second sintering process.

[0022] There will be some defects affecting the sphericity on the surface of the boron balls obtained by secondary sintering. To reduce the pollution of external media, the present invention adopts self-grinding spheroidization treatment. The boron balls after secondary sintering are subjected to self-grinding spheroidization for 22 - 25 hours in an argon atmosphere, thereby improving the sphericity. The grinding residue obtained after 12 hours of self-grinding spheroidization is 1.1%, and the grinding residues obtained after 24 hours and 36 hours of self-grinding spheroidization are both 1.5%. During the self-grinding process of the boron balls, the non-round parts and the debris adhered to the surface of the boron balls will be knocked off. Most of the non-round and adhered debris on the surface of the boron balls can be removed through self-grinding. The fewer the amount of grinding residue, the higher the sphericity of the boron balls themselves and the fewer the adhesion defects. Therefore, the present invention preferably adopts the more energy-saving scheme of 24 hours.

[0023] Preferably, in step (3), a vibrating screen with a slope angle of 5 degrees is used for flow classification to screen the self-ground balls, and finally spherical boron balls with a larger sphericity are obtained.

[0024] According to actual needs, after self-grinding spheroidization in step (3), flow classification is carried out to screen boron balls with the target particle size.

[0025] The present invention also provides a high-hardness neutron-absorbing boron ball prepared by the above preparation method.

[0026] The present invention also provides a neutron shielding layer, the composition of which includes boron balls combined with other shielding materials (such as polyethylene) and is used to manufacture a neutron shielding layer. Its spherical structure is more conducive to uniform distribution and diffusion in a medium environment such as polyethylene compared with the existing boron powder, and a composite material with uniform distribution is obtained to improve the shielding effect.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The spherical boron balls prepared by the present invention have a high forming rate, the forming rate is greater than 90%, the sphericity is greater than 90%, high strength, high hardness, uniform size, high internal density, no pores, are not easy to break and are not easily polluted by external media, are easy to disperse and process, do not have adhesion problems, can be evenly filled in control rods or absorbers. Due to the large sphericity, it helps to evenly distribute the neutron absorber, improve the shielding effect, provide stable neutron absorption performance, and is used in nuclear waste storage facilities to absorb neutrons in the waste and prevent accidental chain reactions.

[0029] 2. The present invention prepares spherical boron balls from boron powder which has poor roundness, poor fluidity, low density, is easy to break, easy to generate dust, and is inconvenient to operate, and realizes remotely absorbing neutrons by filling boron balls into control rods of nuclear reactors, nuclear waste storage, and shielding layers through guide rails or chutes. First, the boron balls provided by the present invention have high roundness, uniform size, high fluidity, high density and hardness. When filling boron powder through guide rails or chutes, due to high roundness, uniform size, and high fluidity, collisions and blockages are not likely to occur. Second, due to the high density and hardness of the boron balls of the present invention, they are not easy to break after collision. Third, the boron balls provided by the present invention have uniform size and high uniformity, and can realize remote and precise control of the addition amount of boron raw materials. By adopting the method of counting or flow statistics, precise control of quantitative feeding in a fixed scenario is achieved. The present invention effectively solves the problems that the prior art cannot perform remote feeding and quantitative feeding, solves the blockage problem in the process of high-density feeding, and the problems of inability to quantify and low density, etc.

[0030] 3. The spherical boron balls prepared by the present invention have a compact structure, high density, a relatively high boron content per unit volume, high uniformity, high hardness, are not easy to break, and are not easy to generate dust, and are suitable for environments with high requirements for cleanliness.

[0031] 4. The present invention also provides a neutron shielding layer, the composition of which includes the combination of boron balls and other shielding materials (such as polyethylene) and is used for manufacturing a neutron shielding layer. Its spherical structure is more conducive to uniform distribution and diffusion in a medium environment such as polyethylene compared with the existing boron powder, and a composite material with uniform distribution is obtained to improve the shielding effect. Description of the Drawings

[0032] Figure 1 is the SEM image of the spherical boron balls prepared in Example 1;

[0033] Figure 2 is the SEM image of the surface of the spherical boron balls prepared in Example 1;

[0034] Figure 3 is the particle image of the spherical boron balls prepared in Example 1;

[0035] Figure 4 is the SEM image of the spherical boron balls prepared in Example 2;

[0036] Figure 5 is the SEM image of the spherical boron balls prepared in Example 4;

[0037] Figure 6 is the SEM image of the spherical boron balls prepared in Example 5;

[0038] Figure 7 is the SEM image of the boron balls prepared in Comparative Example 1;

[0039] Figure 8 It is the SEM image of the surface of the boron spheres prepared in Comparative Example 2;

[0040] Figure 9 It is the particle image of the spherical boron spheres prepared in Comparative Example 2;

[0041] Figure 10 It is the particle image of the spherical boron spheres prepared in Comparative Example 3;

[0042] Figure 11 It is the SEM image of the boron spheres prepared in Comparative Example 3;

[0043] Figure 12 It is the SEM image of the boron spheres prepared in Comparative Example 4;

[0044] Figure 13 It is the SEM image of the boron spheres prepared in Comparative Example 5;

[0045] Figure 14 It is the SEM image of the surface of the boron spheres prepared in Comparative Example 5;

[0046] Figure 15 It is the SEM image of the boron spheres prepared in Comparative Example 6;

[0047] Figure 16 It is the SEM image of the surface of the boron spheres prepared in Comparative Example 6;

[0048] Figure 17 It is the image of the spherical boron spheres prepared in Comparative Example 7;

[0049] Figure 18 It is the SEM image of the boron spheres prepared in Comparative Example 7. Detailed Embodiments

[0050] The present invention will be further described below through specific examples. The examples described in the present invention are only for the illustration of the present invention and do not limit the scope of the present invention.

[0051] The granulator used in the detailed embodiments is a conventional commercially available granulator.

[0052] Example 1

[0053] A method for preparing high-hardness neutron-absorbing boron spheres, comprising the following steps:

[0054] (1) Select crystalline boron powder with a purity above 99.6%, add polyvinyl alcohol with a mass fraction of 1.0% and paraffin with a mass fraction of 0.8% and a particle size between 0.5 um and 0.8 um as a binder, and granulate in a granulator. The rotation speed parameter of the granulator is 160 r / min, the inclined angle of the pressure plate is 48°, and the granulation time is 28 minutes to obtain a spherical boron ball preform;

[0055] (2) Under an argon atmosphere, heat the spherical boron ball preform in a vacuum sintering furnace from room temperature to 650 °C at a heating rate of 5 °C / min, then pre-sinter at this temperature for 3.5 hours, heat and sinter to cause a self-propagating reaction of the preform, cool with the furnace, and then use 2 mm agate balls to mix according to a ball-to-material ratio of 3.0:1 and disperse the partially bonded boron ball preform at a rotation speed of 100 r / min in an argon atmosphere to obtain preformed boron ball particles;

[0056] (3) Under an argon atmosphere, heat the preformed boron ball particles in a vacuum sintering furnace from room temperature to 1250 °C at a heating rate of 9 °C / min, then sinter at this temperature for 5 hours, cool with the furnace, and then perform self-grinding spheroidization for 24 hours in an argon atmosphere. For flow classification, use a vibrating screen with a slope angle of 5 degrees to screen the self-ground balls, and finally obtain spherical boron balls. The forming rate is 95%, and the sphericity is greater than 95%. The SEM image of the spherical boron balls prepared in Example 1 is shown in Figure 1 , the SEM image of the surface of the boron balls is shown in Figure 2 , the image of the obtained spherical boron ball particles is shown in Figure 3 , it can be seen that the prepared spherical boron balls have high roundness, very high sphericity, high forming rate, no bonding, uniform size, and no obvious pores on the surface.

[0057] Example 2

[0058] A preparation method of high-hardness neutron-absorbing boron balls, comprising the following steps:

[0059] (1) Select crystalline boron powder with a purity above 99.6%, add polyvinyl alcohol with a mass fraction of 0.8% and paraffin with a mass fraction of 1% and a particle size between 0.5 um and 0.8 um as a binder, and granulate in a granulator. The rotation speed parameter of the granulator is 150 r / min, the inclined angle of the pressure plate is 45, and the granulation time is 30 minutes to obtain a spherical boron ball preform;

[0060] (2) The spherical boron ball preform is placed in a vacuum environment of 1×10-3 Pa, and in a vacuum sintering furnace, it is heated from room temperature to 620 °C at a heating rate of 4.5 °C / min, then pre-sintered at this temperature for 4 hours. Heating and sintering cause the preform to undergo a self-propagating reaction, and it is cooled with the furnace. Then, 2-mm agate balls are used to mix with the ball material ratio of 3.1:1 and rotate at a speed of 90 r / min in an argon gas atmosphere environment to break up the partially bonded boron ball preform, obtaining preformed boron ball particles;

[0061] (3) The preformed boron ball particles are placed in a vacuum environment of 1×10-3 Pa, and in a vacuum sintering furnace, they are heated from room temperature to 1200 °C at a heating rate of 8 °C / min, then sintered at this temperature for 5.5 hours, and cooled with the furnace. Then, self-grinding spheroidization is carried out for 25 hours in an argon gas atmosphere. Flow classification is performed, and a vibrating screen with a slope angle of 5 degrees is used to screen the self-ground balls. Finally, spherical boron balls are obtained. The forming rate is 93.5%, and the sphericity is greater than 93%. The SEM image of the spherical boron balls finally prepared in Example 2 is shown in Figure 4 , with high roundness, high sphericity, high forming rate, no bonding, uniform size, and no obvious pores on the surface.

[0062] Example 3

[0063] A preparation method of high-hardness neutron-absorbing boron balls, comprising the following steps:

[0064] (1) Select crystalline boron powder with a purity of more than 99.6%, add polyvinyl alcohol with a mass fraction of 1.2% and paraffin with a particle size between 0.5 um and 0.8 um and a mass fraction of 0.5% as a binder, and granulate in a granulator. The rotation speed parameter of the granulator is 170 r / min, the inclination angle of the pressure plate is 50°, and the granulation time is 28 minutes to obtain a spherical boron ball preform;

[0065] (2) The spherical boron ball preform is placed in an argon gas environment, and in a vacuum sintering furnace, it is heated from room temperature to 680 °C at a heating rate of 5.5 °C / min, then pre-sintered at this temperature for 3 hours. Heating and sintering cause the preform to undergo a self-propagating reaction, and it is cooled with the furnace. Then, 2-mm agate balls are used to mix with the ball material ratio of 3.0:1 and rotate at a speed of 110 r / min in an argon gas atmosphere environment to break up the partially bonded boron ball preform, obtaining preformed boron ball particles;

[0066] (3) The preformed boron ball particles were heated from room temperature to 1300 °C at a heating rate of 10 °C / min in a vacuum sintering furnace under an argon atmosphere, sintered at this temperature for 4.5 hours, cooled with the furnace, and then subjected to self-grinding spheroidization for 22 hours under an argon atmosphere. Flow classification was carried out using a vibrating screen with a slope angle of 5 degrees to screen the self-ground balls, and finally spherical boron balls were obtained. The forming rate was 94%, and the sphericity was greater than 93%. The prepared spherical boron balls have high roundness, very high sphericity, high forming rate, no adhesion, uniform size, and no obvious pores on the surface.

[0067] Example 4

[0068] A preparation method of high-hardness neutron-absorbing boron balls is basically the same as that of Example 1, and the only difference is that: in step (2), the heating rate is 10 °C.

[0069] The forming rate of the spherical boron balls prepared in Example 4 was 90.5%, and the sphericity was greater than 90.5%. The SEM image is shown in Figure 5 , it can be seen that the prepared spherical boron balls have relatively high sphericity, and the density is slightly worse than that of Example 1.

[0070] Example 5

[0071] A preparation method of high-hardness neutron-absorbing boron balls is basically the same as that of Example 1, and the only difference is that: in step (3), the heating rate is 5 °C.

[0072] The forming rate of the spherical boron balls prepared in Example 4 was 91%, and the sphericity was greater than 90%. The SEM image is shown in Figure 6 , it can be seen that the prepared spherical boron balls have relatively high sphericity.

[0073] Comparative Example 1

[0074] A preparation method of high-hardness neutron-absorbing boron balls is basically the same as that of Example 1, and the only difference is that: in step (3), the sintering temperature is 1500 °C.

[0075] Result: After high-temperature sintering, bonding occurred between the boron balls, the boron balls deformed, there were few boron balls that could be dispersed, and it was difficult. During the dispersion process, the sphericity of the boron balls was damaged, and the sphericity of the dispersed boron balls was low. The forming rate of the prepared spherical boron balls was less than half, the sphericity was low, and most of them were not spherical. The SEM image of the boron balls with better forming is shown in Figure 7 .

[0076] Comparative Example 2

[0077] A preparation method of high-hardness neutron-absorbing boron balls is basically the same as that of Example 1, and the only difference is that: in step (3), the sintering temperature is 1000 °C.

[0078] Result: The forming rate of the prepared spherical boron balls is about 70%. The hardness of the prepared spherical boron ball particles is not good, the internal density is not high, there are many and deep pores, and they are very fragile. The SEM image of the surface of the boron balls with better forming is shown in Figure 8 , and the image of the prepared spherical boron ball particles is shown in Figure 9 .

[0079] Comparative Example 3

[0080] A preparation method of high-hardness neutron-absorbing boron balls is basically the same as that of Example 1, and the only difference is that: the pre-sintering step in step (2) is removed, and the temperature is directly raised to 1250 °C for sintering. After sintering, ball milling and dispersion treatment are carried out.

[0081] Result: The boron balls are severely deformed and bonded, broken after being dispersed, and there are almost no formed boron balls, and the hardness is low and they cannot be used. The image of the prepared spherical boron ball particles is shown in Figure 10 , and the SEM image of the boron balls with better forming is shown in Figure 11 .

[0082] Comparative Example 4

[0083] A preparation method of high-hardness neutron-absorbing boron balls is basically the same as that of Example 1, and the only difference is that: the sintering temperature in step (2) is 850 °C.

[0084] Result: The sintered boron balls are severely bonded, resulting in deformation and inability to disperse of the boron balls, and there are almost no formed boron balls. The SEM image of the boron balls with better forming is shown in Figure 12 .

[0085] Comparative Example 5

[0086] A preparation method of high-hardness neutron-absorbing boron balls is basically the same as that of Example 1, and the only difference is that: the sintering temperature in step (2) is 480 °C.

[0087] Result: The hardness of the sintered boron balls is not high, the internal density is not high, there are many pores, and they are very fragile and not easy to disperse and process, and there are almost no formed boron balls. The SEM image of the boron balls with better forming is shown in Figure 13 , and the SEM image of the surface of the boron balls is shown in Figure 14 .

[0088] Comparative Example 6

[0089] A preparation method of high-hardness neutron-absorbing boron balls is basically the same as that of Example 1, and the only difference is that: polyvinyl alcohol is replaced by boric acid in step (1).

[0090] Result: The forming rate is 40%, and the sintered boron balls are easy to disperse, with not high hardness, not high internal density, many pores, very fragile, not easy to disperse and process. The SEM image of the boron balls with better forming is shown inFigure 15 , the SEM image of the boron ball surface is shown in Figure 16 .

[0091] Comparative Example 7

[0092] A preparation method of a high-hardness neutron-absorbing boron ball is basically the same as that of Example 1, except that: in step (1), granulation is carried out in a granulator, the rotation speed parameter is 100 r / min, and the inclination angle of the pressure plate is 35°.

[0093] Result: The spherical boron ball diagram obtained by preparation is shown in Figure 17 , the particle size of the obtained boron balls is uneven, the forming rate is 65%, and the SEM image of the boron balls with better forming is shown in Figure 18 .

Claims

1. A method for preparing a high-hardness neutron-absorbing boron ball, characterized in that: The following steps are involved: (1) adding polyvinyl alcohol and paraffin as a binder to boron powder, granulating in a granulator to obtain a spherical boron ball prefabricated blank; (2) The spherical boron ball preform blank is heated from room temperature to 620°C-680°C in a vacuum sintering furnace in a vacuum environment or an argon environment, and then pre-sintered at this temperature to cause a self-propagating reaction of the blank, cooled with the furnace, and then ball-milled and scattered to obtain preformed boron ball particles; (3) The preformed boron sphere particles are heated from room temperature to 1200°C-1300°C in a vacuum sintering furnace in an argon atmosphere or a vacuum environment, sintered at this temperature, cooled in the furnace, and then self-grinded to obtain spherical boron spheres.

2. The method for preparing high-hardness neutron-absorbing boron balls according to claim 1, characterized in that: In step (1), 0.8%-1.2% by mass of polyvinyl alcohol and 0.5%-1.0% by mass of paraffin wax with a particle size of 1um-3um are added to the boron powder as a binder.

3. The method for preparing high-hardness neutron-absorbing boron balls according to claim 1, characterized in that: In step (1), the conditions for granulation in the granulator are: the granulator speed parameter is 150r / min-170r / min, the granulator platen inclination angle is 45°-50°, and the granulation time is 28-30 minutes.

4. The method for preparing high-hardness neutron-absorbing boron balls according to claim 1, characterized in that: In step (1), the boron powder is crystalline boron powder with a purity of more than 99.6%.

5. The method for preparing high-hardness neutron-absorbing boron balls according to claim 1, characterized in that: In step (2), the temperature is raised from room temperature to 620°C-680°C in a vacuum sintering furnace at a heating rate of 4.5-5.5°C / min, and then pre-sintered at this temperature for 3-4 hours.

6. The method for preparing high-hardness neutron-absorbing boron balls according to claim 1, characterized in that: In step (2), the ball milling and scattering treatment is as follows: for the material obtained by furnace cooling, 1-3 mm agate balls are used to mix at a ball-to-material ratio of 3.0-3.1:1 and the partially bonded boron ball blanks are scattered at a speed of 90-110 r / min in an argon atmosphere to obtain preformed boron ball particles.

7. The method for preparing high-hardness neutron-absorbing boron balls according to claim 1, characterized in that: In step (3), the temperature is raised from room temperature to 1200°C-1300°C in a vacuum sintering furnace at a heating rate of 8-10°C / min, and then sintered at this temperature for 4.5-5.5 hours.

8. The method for preparing high-hardness neutron-absorbing boron balls according to claim 1, characterized in that: In step (3), the self-grinding spheroidization is performed under an argon atmosphere for 22-25 hours.

9. The method for preparing high-hardness neutron-absorbing boron balls according to claim 1, characterized in that: In step (2) and step (3), the vacuum environment is 1×10- 3 Pa vacuum environment.

10. A high-hardness neutron-absorbing boron sphere prepared by the preparation method according to any one of claims 1 to 9.

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