CN107500768A - A kind of preparation method of boron carbide ceramics, boron carbide ceramics and application thereof - Google Patents

Abstract

The application discloses a preparation method of boron carbide ceramic, the boron carbide ceramic and application thereof. The preparation method of the boron carbide ceramic comprises the steps of (1) uniformly mixing boron carbide powder and silicate glass powder to prepare a mixture; (2) adding a binder solution into the mixture, and granulating; (3) pouring the granulated particles into a mould, and pressing a biscuit at 5-30 MPa; (4) and drying the biscuit, and sintering the biscuit at a temperature lower than 1000 ℃ in an inert atmosphere, a reducing atmosphere or vacuum to prepare the boron carbide ceramic. The method realizes the low-temperature normal-pressure sintering of the boron carbide ceramic, and has the advantages of low energy consumption, simple and easy operation and low cost; the silicate glass powder has rich raw materials, low price and easy obtainment, thereby further reducing the cost; the prepared boron carbide ceramic contains no hydrogen, can greatly reduce neutron scattering background, and is particularly suitable for manufacturing neutron absorption and shielding devices around detectors. The method lays a foundation for the mass and large-scale production of the boron carbide ceramic material with good neutron shielding effect.

Description

A kind of preparation method of boron carbide ceramics, boron carbide ceramics and application thereof

technical field

The present application relates to the field of boron carbide ceramics, in particular to a method for preparing boron carbide ceramics, the prepared boron carbide ceramics, and applications thereof.

Background technique

Boron carbide, also known as black diamond, is usually gray-black micropowder. It is a substance whose hardness is second only to diamond and cubic boron nitride. The Mohs hardness is 9.3 and the microhardness is 55-67Gpa. Boron carbide has good chemical stability. It does not react with acids, alkalis and most compounds at room temperature. It only corrodes slowly in the mixture of hydrofluoric acid-sulfuric acid and hydrofluoric acid-nitric acid. It is one of the most stable chemical compounds. . At the same time, boron carbide has a low density of only 2.52g/cm ³ , high temperature hardness, and excellent slow neutron absorption capacity. Therefore, boron carbide has important applications in the fields of wear-resistant and corrosion-resistant devices, bullet-proof materials, engine nozzles, sandblasting nozzles, ceramic bearings, grinding media, nuclear energy, and neutron shielding materials.

Boron carbide has an extremely important position in the nuclear industry because of its excellent neutron absorption capacity. Boron carbide is the most commonly used neutron absorbing material in the traditional nuclear industry at present. In the announced reactors in the world, quite a few of them often use boron carbide as the adjustment rods, control rods, shielding rods and neutron shielding of nuclear reactors. materials, the importance of shielding rods is second only to fuel elements.

The atomic radii of C and B in boron carbide are very close, and the difference in electronegativity between the two is very small, forming a strong covalent bond with a covalent bond ratio as high as 93.94%, which makes the densification and sintering of pure boron carbide extremely difficult. Ordinary B ₄ C powder is sintered at 2250-2300°C under normal pressure to obtain a relative density of the finished product that can only reach 80%-87%. Usually, it is necessary to use boron carbide ultrafine powder and adopt hot pressing sintering, hot isostatic pressing sintering or recent The spark plasma sintering (abbreviated as SPS) technology developed in 2009 is sintered at above 2000°C; even with the addition of sintering aids, the sintering temperature is above 1600°C. For example, the patent CN1541981A prepares lightweight boron carbide armored ceramics by hot pressing and sintering at 2200 ° C to 2300 ° C; Al ₂ O ₃ was used as a sintering aid to prepare boron carbide ceramics under the conditions of 1750℃ and 35MPa hot pressing. Due to the complex sintering process, high energy consumption and high cost of the existing boron carbide ceramics, its use is limited, and it is not suitable for large-scale industrial production.

Neutrons are a powerful means for human beings to explore the microscopic world of matter. Neutrons are uncharged, have magnetic moments, strong penetrating power, can distinguish light elements, isotopes and neighboring elements, and are non-destructive to samples. Therefore, neutron scattering technology is widely used in biology, Research fields such as life, national energy, environment and new materials play an important role. In order to meet the application requirements in different fields, it is necessary to build various types of neutron scattering spectrometers for different purposes. In the design and construction of neutron scattering spectrometers, the signal-to-noise ratio is a common and important index to measure the performance of various spectrometers. In order to reduce the background of the spectrometer caused by stray neutrons, it is necessary to use a large number of neutron-absorbing materials around the beamline of the spectrometer. Especially around the beamline of the neutron detector, it is required that the neutron absorbing material used should contain as few active elements as possible to generate stray signals, such as Ni, Co, Cu, etc. Elements such as typical H elements. However, most of the existing boron carbide-based neutron absorbing materials contain more H elements in order to enhance the moderation effect on high-energy neutrons, such as boron-containing polyethylene. Patent CN 104310400A uses colloidal bonding and solidification to prepare a shaped boron carbide-based neutron absorber. Although the hydrogen content is reduced, the material still contains a certain amount of hydrogen, which is not suitable for use as neutron absorbing materials around the detector. .

Contents of the invention

The purpose of this application is to provide a new preparation method of boron carbide ceramics, the prepared hydrogen-free boron carbide ceramics and its application.

The application adopts the following technical solutions:

One aspect of the present application discloses a method for preparing boron carbide ceramics, comprising the following steps,

(1) Boron carbide powder and silicate glass powder are uniformly dispersed and mixed by ball milling or ultrasonic to make a mixture;

(2) Add binder solution in the compound of step (1), granulate;

(3) Pour the granules prepared in step (2) into a mould, and press it into a green body under a pressure of 5-30MPa;

(4) Drying the green body in step (3), and then sintering in an inert atmosphere, a reducing atmosphere or a vacuum condition to produce boron carbide ceramics, and the sintering temperature is lower than 1000°C.

Wherein, the green body is usually dried to a constant weight; the binder solution can use a conventional binder.

It should be noted that in the preparation method of this application, silicate glass powder is added to boron carbide powder. Due to the introduction of silicate glass powder, the sintering temperature is reduced, and the low temperature and normal pressure below 1000 ° C are realized for the first time. Boron carbide ceramics were prepared by sintering. Moreover, in the preparation method of the present application, the green body is first dried to remove most of the distilled water and evaporable materials, and finally sintered in an inert atmosphere, a reducing atmosphere or a vacuum condition, which overcomes the oxidation problem of boron carbide during the sintering process , so as to successfully solve the problem of water absorption and pulverization of the sintered body, so that the prepared boron carbide ceramics have excellent waterproof performance. In addition, the boron carbide ceramics prepared in the present application do not contain hydrogen elements, and are especially suitable for making neutron absorbing and shielding devices around detectors.

Preferably, boron carbide powder accounts for 50-90% of the total weight of the mixture in step (1), silicate glass powder accounts for 10-50% of the total weight of the mixture in step (1), and the consumption of the binder solution is the step (1) 1) 1.5-22% of the total weight of the mixture.

It should be noted that the addition of silicate glass powder will reduce the sintering temperature, thereby achieving low-temperature sintering. The low temperature in this application refers to a temperature lower than 1000°C, which is a low temperature compared to the existing sintering methods; it can be understood that, The amount of silicate glass powder added will directly affect the temperature of low-temperature sintering, but the larger the amount added, it will also affect the material properties of boron carbide itself. Therefore, in the preferred solution of this application, boron carbide and silicate glass The amount of powder used is limited, while achieving low-temperature sintering, the performance of boron carbide materials can be effectively guaranteed. It should be added that this application is to ensure that boron carbide ceramic materials are used as neutron-absorbing shielding materials. If it is used for other purposes, such as wear-resistant and corrosion-resistant devices, bullet-proof materials, For engine nozzles, sandblasting nozzles, ceramic bearings, grinding media, etc., the amount of boron carbide and silicate glass powder can be adjusted by yourself, as long as it can be sintered at low temperature to prepare boron carbide ceramics.

Preferably, the purity of the boron carbide powder is greater than 95wt.%, the purity of the silicate glass powder is greater than 95wt.%, and the particle size of the boron carbide powder is less than 250 microns.

Preferably, the silicate glass powder does not contain hydrogen.

It should be noted that the preparation method of the present application or the prepared boron carbide ceramics may also contain other additives to improve the performance of boron carbide ceramics, as long as it does not contain hydrogen, easily activated elements and non-elastic neutron scattering Elements with larger cross-sections are sufficient, and other doping elements or additives can refer to existing preparation methods and boron carbide ceramics, and are not specifically limited here.

Preferably, the binder is at least one of polyvinyl alcohol, phenolic resin, starch, sugar, cellulose and dextrin.

Preferably, the green body includes but not limited to a cylindrical shape, a strip shape or a long plate shape.

It should be noted that the green body can be prepared into various shapes according to the needs of use, among which the more common ones are cylindrical, long strip or long plate.

Preferably, the drying temperature in step (4) is lower than 100°C.

Preferably, in step (4), the sintering temperature is 500°C-765°C, and the sintering time is 0.5h-4h.

Another aspect of the present application discloses the boron carbide ceramic prepared by the preparation method of the present application.

It should be noted that, compared with the existing boron carbide materials, the boron carbide ceramics obtained by the preparation method of the present application do not contain hydrogen elements, and are especially suitable for neutron absorption shielding around detectors.

Another aspect of the present application discloses the application of the boron carbide ceramic of the present application in neutron absorption or neutron shielding.

It should be noted that the boron carbide ceramics of the present application do not contain hydrogen elements, and are especially suitable for neutron absorption around detectors, so they can be applied to the preparation of various neutron absorption or neutron shielding equipment, parts, etc. Similarly, the boron carbide ceramics of the present application are also applicable to the application fields of general boron carbide materials, such as wear-resistant and corrosion-resistant devices, bullet-proof materials, engine nozzles, sandblasting nozzles, ceramic bearings, grinding media, etc.

The beneficial effect of this application is:

The preparation method of boron carbide ceramics of the present application realizes sintering of boron carbide ceramics at low temperature and normal pressure for the first time, with low energy consumption, simple preparation process and easy operation, which greatly saves the preparation cost; the silicate glass powder used as an additive material is rich in raw materials , low price, very easy to obtain, further reducing the raw material cost of boron carbide ceramics; moreover, the prepared boron carbide ceramics do not contain hydrogen, and are especially suitable for neutron shielding absorbing materials and devices around detectors. The preparation method of the present application lays the foundation for mass production of boron carbide ceramic materials with good neutron shielding effects.

Description of drawings

Fig. 1 is the X-ray diffraction analysis spectrum of the boron carbide ceramics prepared in the embodiment of the present application;

Fig. 2 is the differential scanning calorimetry (abbreviation DSC) and thermogravimetry (abbreviation TG) analysis collection of boron carbide ceramics prepared in the embodiment of the present application;

Fig. 3 is the scanning electron microscope picture of the boron carbide ceramics prepared in the embodiment of the present application;

Fig. 4 is the EDS energy spectrum analysis figure and composition list of the boron carbide ceramics prepared in the embodiment of the present application;

Fig. 5 is an EDS energy spectrum analysis diagram and a composition list of boron carbide ceramics prepared in the examples of the present application.

detailed description

The existing neutron absorbing material is mainly boron carbide, but the boron carbide sintering process conditions are complicated and the cost is high; moreover, the existing boron carbide composite material still contains a certain amount of hydrogen, and its strong inelastic scattering effect Adds scattering background when used with neutron absorbing materials. Therefore, the present application has found through a lot of research and experiments that adding silicate glass powder to boron carbide powder can effectively reduce the sintering temperature, realize low temperature and normal pressure sintering, greatly reduce the sintering temperature and reduce production energy consumption. Moreover, the boron carbide ceramics obtained by the preparation method of the application do not contain hydrogen, and are especially suitable for neutron shielding and absorption around detectors.

The present application will be described in further detail below through specific examples. The following examples only further illustrate the present application, and should not be construed as limiting the present application.

Embodiment one

In this example, 70% by weight of boron carbide powder and 30% by weight of silicate glass powder are used to prepare boron carbide ceramics. The binder solution is a polyvinyl alcohol solution with a concentration of 5 wt%. The specific preparation method is as follows:

(1) 70g boron carbide powder and 30g silicate glass powder are mixed uniformly by ball milling to make a mixture;

(2) Add 2g concentration of 5wt% PVA solution and an appropriate amount of distilled water in the mixture of step (1), manually stir and granulate into particles of about 400 microns;

(3) Pour the granules prepared in step (2) into a metal mold, and press under a pressure of 10 MPa to form a cylindrical green body with a diameter of 19.05 mm and a height of about 4.8 mm;

(4) Dry the biscuit in step (3) to constant weight at 60°C, then put it into a vacuum sintering furnace, evacuate it and fill it with nitrogen, and in a nitrogen atmosphere, wait until the vacuum degree drops to 1×10 ⁰ Pa After that, raise the temperature to 500°C at a heating rate of 2°C/min and hold for 30 minutes to completely remove the organic binder, then raise the temperature to 765°C at a heating rate of 4°C/min, hold for 90 minutes, and then cool with the furnace Obtain the boron carbide ceramics of this example, the shape is basically consistent with the green body.

Embodiment two

In this example, 60% by weight boron carbide powder and 40% by weight silicate glass powder are used to prepare boron carbide ceramics, and the binder solution is polyvinyl alcohol solution with a concentration of 5 wt%. Specifically, 60g of boron carbide powder and 40g of silicate glass powder are mixed uniformly by ball milling to make a mixture; the rest are the same as in Example 1, and finally sintered in a vacuum sintering furnace and cooled with the furnace to obtain the boron carbide of this example ceramics.

Embodiment Three

In this example, 70% by weight of boron carbide powder and 30% by weight of silicate glass powder are used to prepare boron carbide ceramics. The binder solution is a polyvinyl alcohol solution with a concentration of 5 wt%. The specific preparation method is as follows:

(1) 70g boron carbide powder and 30g silicate glass powder are mixed uniformly by ball milling to make a mixture;

(2) Add 2g concentration of 5wt% PVA solution and appropriate amount of distilled water in the mixture of step (1), granulate;

(3) Pour the granules prepared in step (2) into a metal mold, and press under a pressure of 10 MPa to form a cylindrical green body with a diameter of 19.05 mm and a height of about 4.8 mm;

(4) Dry the biscuit in step (3) at 60°C to constant weight, then put it into a nitrogen atmosphere sintering furnace, pass nitrogen gas for 10 minutes in advance, set the nitrogen flow rate to 30mL/min, and then increase the temperature at 2°C/min Raise the temperature to 500°C, hold for 30 minutes, then raise the temperature to 765°C at a heating rate of 4°C/min, hold for 90 minutes, and then cool with the furnace to obtain the boron carbide ceramic of this example, whose shape is basically consistent with the green body.

Embodiment Four

In this example, 80% by weight of boron carbide powder and 20% by weight of silicate glass powder are used to prepare boron carbide ceramics, and the binder solution is a polyvinyl alcohol solution with a concentration of 5wt%. Specifically, 80g of boron carbide powder and 20g of silicate glass powder are uniformly mixed by ball milling to make a mixture; the rest are the same as in Example 3, and finally sintered in a nitrogen atmosphere sintering furnace and cooled with the furnace to obtain the carbonization of this example. boron ceramics.

With reference to GB/T 6569-2006 and GB/T 3808-2002, three-point bending experiments were used to measure the bending front of the boron carbide ceramics prepared in the four examples of the application; The impact toughness of the boron carbide ceramics prepared in the examples; the test results are shown in Table 1.

The density and apparent porosity of the boron carbide ceramics prepared in the four examples were measured by the Archimede drainage method, and the test results are shown in Table 1.

Table 1 Performance test of boron carbide ceramics

Example Density (g/cm ³ ) Apparent porosity(%) Impact toughness (kJ/m ² ) Bending strength (MPa) 1 1.622 22.93 2.36 28.89 2 1.701 19.19 2.84 36.28 3 1.560 25.93 2.73 24.65 4 1.531 28.07 1.76 15.81

The results in Table 1 show that as the composition of silicate glass increases, the mechanical properties of boron carbide ceramics, namely, the bending strength and impact toughness, as well as the density increase, and the porosity decreases; while in nitrogen atmosphere and vacuum Compared with sintering, vacuum sintering has higher sintering density and bending strength, while sintering in nitrogen atmosphere has relatively higher apparent porosity and impact toughness.

The internationally used MCNPX software is used to calculate the transmittance of boron carbide ceramic materials with different thicknesses to neutrons of different wavelengths under different ratios, and neutrons of different wavelengths are neutrons of different energies. Among them, the different proportions refer to the parts by weight of boron carbide powder. For example, if boron carbide is 90wt.%, the silicate glass powder is 10wt.%, and boron carbide is 80wt.%, then the silicate glass powder is 20wt.%. %, boron carbide is 70wt.%, then silicate glass powder is 30wt.%, boron carbide is 60wt.%, then silicate glass powder is 40wt.%. For the calculation of different thicknesses, specifically, this example calculates the transmittance of boron carbide ceramics with a thickness of 1mm, 2mm, 3mm, 4mm and 5mm to neutrons of different energies under each ratio. In this example, a wavelength of 1 Angstrom (abbreviation ), 2 Angstrom and 3 Angstrom neutron transmittance. The calculation results are shown in Table 2.

Table 2 Neutron transmittance of boron carbide ceramics

The results in Table 2 show that for the same thickness, the transmittance of neutrons of a certain wavelength or energy decreases with the increase of boron carbide in the material ratio; and when the boron carbide content is 60% and the thickness is 5mm, for the wavelength The neutron transmittance is only 4.62E-05, while the wavelength neutrons are completely absorbed.

The boron carbide ceramics prepared in the three examples were detected by an X-ray diffractometer, and the diffraction patterns were obtained. Part of the results are shown in Figure 1, and Figure 1 is an analysis result diagram of the boron carbide ceramics prepared in Example 1. The results of X-ray diffraction analysis show that the intensity of the diffraction peak of boron carbide is obvious, and because it contains 30% silicate glass, a "steamed bread peak" appears at 10° to 30°; and no diffraction peaks of boron oxide, boric acid, etc. appear, As shown in Figure 1, it shows that the boron carbide ceramic prepared by this method successfully solves the oxidation problem of boron carbide.

The boron carbide ceramics prepared in the four examples were detected respectively using a differential scanning calorimetry synchronous thermogravimetric analyzer, and a thermogram was obtained. Part of the results are shown in Figure 2, and Figure 2 is the biscuit prepared in Example 3 under nitrogen Diagram of analysis results in atmosphere. The results of differential simultaneous thermal analysis show that there is an obvious exothermic peak below 100°C, which is the evaporation of water; between 100°C and 550°C, it is the volatilization process of organic matter; between 550°C and 765°C, it is the liquid phase sintering process. And there is no obvious mass increase at 25°C-1000°C, indicating that boron carbide has not been oxidized, as shown in Figure 2.

The microstructures of the cross-sections of the boron carbide ceramics prepared in the three examples were respectively observed using a scanning electron microscope. Part of the results are shown in FIG. 3 . The scanning electron microscope observation results show that the material is brittle fracture, and the molten silicate glass forms a network structure and tightly bonds the boron carbide particles, as shown in Figure 3.

The boron carbide ceramics prepared by the four examples were detected respectively using an EDS energy spectrum analyzer, and the analysis spectrum was obtained. Part of the results are shown in Figure 4 and Figure 5, and Figure 4 and Figure 5 are the results of the boron carbide ceramics prepared in Example 3 Analysis spectrum, that is, the analysis diagram corresponding to spectrum 1 and spectrum 2 in Fig. 3 respectively. Four regions were selected, and each region was replicated at least 5 times, where the neglected peaks were background peaks. The EDS spectrum shows that the boron carbide ceramic materials prepared in the four examples of the present application do not contain hydrogen, as shown in Fig. 4 and Fig. 5 .

The above content is a further detailed description of the present application in conjunction with specific implementation modes, and it cannot be considered that the specific implementation of the present application is limited to these descriptions. For those of ordinary skill in the technical field to which this application belongs, some simple deduction or substitutions can be made without departing from the concept of this application, which should be deemed to belong to the protection scope of this application.

Claims (10)

1. A kind of 1. preparation method of boron carbide ceramics, it is characterised in that：Comprise the following steps,

   (1) boron carbide powder and silicate glass powder are well mixed by ball milling or ultrasonic disperse, compound is made；

   (2) binder solution is added in the compound of step (1), is granulated；

   (3) particle prepared by step (2) is poured into mould, biscuit is pressed under 5-30MPa pressure；

   (4) biscuit of step (3) is dried, is then sintered under inert atmosphere, reducing atmosphere or vacuum condition, carbonization is made Boron ceramics, the temperature of the sintering are less than 1000 DEG C.
2. 2. preparation method according to claim 1, it is characterised in that：The boron carbide powder accounts for step (1) compound gross weight The 50-90% of amount, the silicate glass powder account for the 10-50% of step (1) compound gross weight, the use of the binder solution Measure as the 1.5-22% of step (1) compound gross weight.
3. 3. preparation method according to claim 1, it is characterised in that：The purity of the boron carbide powder is more than 95wt.%, institute The purity for stating silicate glass powder is more than 95wt.%, also, the particle diameter of the boron carbide powder is less than 250 microns.
4. 4. preparation method according to claim 1, it is characterised in that：Protium is not contained in the silicate glass powder.
5. 5. preparation method according to claim 1, it is characterised in that：The binding agent is polyvinyl alcohol, phenolic resin, shallow lake At least one of powder, carbohydrate, cellulose and dextrin.
6. 6. preparation method according to claim 1, it is characterised in that：The biscuit includes but are not limited to cylinder, length Bar shaped or long plate shape.
7. 7. according to the preparation method described in claim any one of 1-6, it is characterised in that：The temperature of drying in the step (4) Less than 100 DEG C.
8. 8. according to the preparation method described in claim any one of 1-6, it is characterised in that：In the step (4), the temperature of sintering For 500 DEG C -765 DEG C, sintering time 0.5h-4h.
9. 9. boron carbide ceramics prepared by the preparation method according to claim any one of 1-8.
10. 10. application of the boron carbide ceramics according to claim 9 in neutron-absorbing or neutron shield.