Preparation method of boron carbide ceramic with rare earth silicon carbon compound as sintering aid

Abstract

The invention belongs to the technical field of boron carbide ceramics, and relates to a preparation method of boron carbide ceramics with a rare earth silicon carbon compound as a sintering aid. The invention discloses a preparation method of boron carbide ceramic taking a rare earth silicon carbon compound as a sintering aid, which comprises the following steps: mixing the sintering aid rare earth silicon carbon compound RExSiyCz and B4C according to the mass ratio of (0.1-10): (90-99.9), drying, sieving, pre-pressing and sintering to obtain the boron carbide ceramic taking the rare earth silicon carbon compound as the sintering aid. According to the invention, the rare earth silicon carbon compound is added into B4C as a sintering aid, and a liquid phase is formed by using the rare earth silicon carbon compound, so that the particle rearrangement and mass transfer process of the ceramic raw material can be promoted, the ceramic sintering temperature is reduced, and the sintering densification degree is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of boron carbide ceramics, and relates to a preparation method of boron carbide ceramics using rare earth silicon carbide compounds as sintering aids. Background Art

[0002] Boron carbide (B4C) is widely used in fields such as abrasives, lightweight bulletproof vests, and neutron shielding materials due to its excellent properties such as low theoretical density (TD = 2.52 g / cm 3 ), high melting point (about 2763 °C), high Young's modulus (440 GPa), and high Vickers hardness (30 GPa). However, since B4C ceramics are compounds mainly composed of strong covalent bonds, with the covalent bond proportion as high as 93.94%, this results in a relatively high melting point, low self-diffusion coefficient, and difficult grain boundary migration. Therefore, its sintering temperature is high and sintering densification is difficult, which limits its application in the engineering field. Under normal pressure, at a high sintering temperature of 2300 °C, B4C ceramics with a relative density lower than 80% can usually be obtained, and the mechanical properties of the prepared B4C ceramics are poor and cannot meet the requirements of engineering applications. Currently, in order to improve the sintering densification of B4C ceramics and reduce their sintering temperature, pressure-assisted sintering technology and the use of sintering additives are usually adopted.

[0003] Adding sintering aids to ceramics can react with the grain boundaries of ceramics during the sintering process to form solid solutions or secondary phases with microscopic sizes, thereby enhancing the binding force of the grain boundaries. At the same time, sintering aids can also inhibit the growth of ceramic particles and the migration of grain boundaries by changing the grain boundary energy, which is beneficial to the elimination of closed pores and the improvement of ceramic sintering densification. Rare earth silicon carbide compounds are a new type of layered ceramic material with a special structure similar to the MAX phase, and were first developed and applied by Wolfgang Jeitschko, Martin H. Gerdes, etc. from the Institute of Chemistry of the University of Stuttgart in Germany. According to relevant literature, rare earth compounds will form a liquid phase at high temperatures, which can promote the rearrangement between particles and accelerate their diffusion rate. Moreover, RE3Si2C has been applied as a sintering additive in the sintering of various ceramics such as SiC and Si3N4 and has shown good sintering effects.

[0004] Currently, the commonly used sintering additives for B4C are carbon, metallic elements, metal oxides, etc. Among them, carbon is used as a sintering additive because the eutectic temperature of B4C-C is about 2375 °C, which can form a eutectic liquid phase. However, due to the high temperature of the formed eutectic liquid phase, the sintering temperature is also high. In addition, the added carbon needs to be added in an active form, otherwise the effect of improving sintering densification cannot be achieved. Metallic elements as sintering aids have good sintering effects, but they are prone to react with B4C, and there is a possibility of generating compounds that are not conducive to the mechanical properties of B4C ceramics, resulting in their inability to meet the requirements of engineering applications; metal oxides as sintering aids may chemically react with boron carbide or the free carbon therein to generate CO gas, which is not conducive to the closure of pores inside the sample, resulting in an increase in the porosity of the sample and a decrease in the densification degree. Summary of the Invention

[0005] The object of the present invention is to address the above problems existing in the prior art and propose a preparation method of boron carbide ceramics using a rare earth silicon carbide compound as a sintering aid. During the sintering process, the rare earth silicon carbide compound can not only form a liquid phase at a lower temperature, effectively promoting the rearrangement and mass transfer process of ceramic raw material particles and promoting the sintering densification of boron carbide ceramics, but also the SiC generated by the decomposition of the rare earth compound at high temperature can both promote sintering and improve the properties of B4C ceramics.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A preparation method of boron carbide ceramics using a rare earth silicon carbide compound as a sintering aid, the preparation method comprising:

[0008] Mixing a sintering aid rare earth silicon carbide compound RE x Si y C z with B4C, drying, sieving, pre-pressing and then sintering to obtain boron carbide ceramics using the rare earth silicon carbide compound as a sintering aid;

[0009] In the sintering aid rare earth silicon carbide compound RE x Si y C z the rare earth element RE is at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; 1 ≤ x ≤ 5, 1 ≤ y ≤ 4, 1 ≤ z ≤ 4. Preferably, in the sintering aid rare earth silicon carbide compound RE x Si y C z x ≥ y, x ≥ z.

[0010] More preferably, the sintering aid rare earth silicon carbide compound RE x Si y C z is RE x Si2C2, where 2 < x ≤ 5.

[0011] Even more preferably, the rare earth silicon carbide compound includes one or more of Y3Si2C2, Gd3Si2C2, Pr3Si2C2, Er3Si2C2, Ce3Si2C2, Dy3Si2C2, La3Si2C2, Eu3Si2C2.

[0012] Preferably, the average particle size of B4C is 1.0 - 10 μm, and the average particle size of the rare earth silicon carbide compound is 2.5 - 200 μm.

[0013] Preferably, the mixing includes at least one of wet mixing and dry mixing, and the solvent used in wet mixing includes but is not limited to water and alcohols.

[0014] More preferably, the mixing is carried out by wet mixing, and the solvent is alcohol.

[0015] Preferably, the pre - pressing includes at least one of die pressing and cold isostatic pressing, and the pre - pressing pressure is 10 - 800 MPa.

[0016] Preferably, the sintering is carried out in a quartz tube furnace.

[0017] Preferably, the sintering temperature is 1000 - 2300 °C, the sintering time is 10 - 300 min, and the sintering heating rate is 5 - 100 °C / min.

[0018] Preferably, the sintering includes at least one of pressureless sintering and pressure sintering.

[0019] More preferably, the pressure of the pressure sintering is 10 - 100 MPa, the sintering temperature is 1000 - 1900 °C, the sintering time is 10 - 120 min, and the sintering heating rate is 30 - 100 °C / min.

[0020] More preferably, the pre - pressure of the pressureless sintering is 200 - 400 Mpa, the sintering temperature is 1800 - 2300 °C, the sintering time is 30 - 300 min, and the sintering heating rate is 5 - 50 °C / min.

[0021] Preferably, the sintering is pressure sintering, specifically spark plasma sintering (SPS) sintering.

[0022] Further preferably, in the spark plasma sintering (SPS), the applied pressure is 10 - 50 Mpa, the sintering temperature is 1000 - 1900 °C, and the sintering time is 10 - 30 min. The heating and cooling rate during sintering is 20 - 50 °C / min.

[0023] Preferably, the rare earth silicon carbide compound as the sintering aid is prepared by mixing rare earth hydride and silicon carbide powder, drying, sieving, pre-pressing, then calcining at high temperature and crushing.

[0024] Further preferably, the molar ratio of the rare earth hydride to silicon carbide is (1 - 10):1.

[0025] Further preferably, the high-temperature calcination is carried out in at least one of the high-temperature furnaces such as the molten salt furnace synthesized by the molten salt method, the vacuum graphite cracking furnace in solid-phase synthesis, and the quartz tube furnace.

[0026] Even more preferably, the high-temperature calcination is carried out in a vacuum graphite cracking furnace.

[0027] The vacuum graphite cracking furnace selected in the present invention for solid-phase synthesis has higher purity compared to the molten salt furnace.

[0028] Further preferably, the sintering temperature for the high-temperature calcination is 600 - 1600 °C, the sintering time is 120 - 420 min, and the heating rate during sintering is 2 - 10 °C / min.

[0029] Further preferably, the average particle size of the rare earth hydride is 50 - 200 μm, and the average particle size of silicon carbide is 0.1 - 1 μm.

[0030] Preferably, the preparation method of the rare earth silicon carbide compound as the sintering aid includes: mixing SiC and rare earth hydride REH2 with a molar ratio of 1:(1 - 5), ball-milling with ethanol, drying, sieving, and crushing to obtain a premixed powder; then pre-pressing under a pressure of 2 - 50 MPa, and subsequently placing it in a quartz tube furnace for sintering at a temperature of 1000 - 1600 °C for 120 - 300 min.

[0031] Preferably, the preparation method of the boron carbide ceramic using the rare earth silicon carbide compound as the sintering aid includes: mixing the sintering aid rare earth silicon carbide compound (RE3Si2C2) and boron carbide powder with a mass ratio of (0.1 - 10):(90 - 99.9), using ethanol as a solvent, mixing in a planetary ball mill, drying, sieving to obtain a premixed powder, placing the premixed powder in a graphite mold, pre-pressing under a pressure of 10 - 50 MPa, and then sintering under a pressure of 10 - 100 MPa and at a temperature of 1500 - 1900 °C for 10 - 30 min.

[0032] A boron carbide ceramic using rare earth silicon carbide compound as a sintering aid, with a density of ≥2.0 g / cm 3 , and an open porosity of ≤10%.

[0033] Preferably, the boron carbide ceramic using rare earth silicon carbide compound as a sintering aid has a density of 2.1 - 2.7 g / cm 3 , and an open porosity of 1.7 - 10%.

[0034] Application of a boron carbide ceramic using rare earth silicon carbide compound as a sintering aid in the fields of neutron shielding materials, neutron absorption materials, and bulletproof materials.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. In the present invention, rare earth silicon carbide compound is added to B4C as a sintering aid. The rare earth silicon carbide compound forms a liquid phase at 700 - 1600 °C, promoting the rearrangement of ceramic raw material particles and the mass transfer process, and reducing the ceramic sintering temperature.

[0037] 2. In the present invention, rare earth silicon carbide compound is used as a sintering aid. The rare earth silicon carbide compound decomposes at high temperature to generate silicon carbide compound, further promoting the sintering of boron carbide and improving the properties of boron carbide.

[0038] 3. The electrical conductivity, thermal conductivity, and hardness of the boron carbide ceramic using rare earth silicon carbide compound as a sintering aid in the present invention are simultaneously improved.

[0039] 4. The boron carbide ceramic using rare earth silicon carbide compound as a sintering aid in the present invention has good hardness, fracture toughness, and flexural strength at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a scanning electron microscope (SEM) image of the surface and cross-section of the boron carbide ceramic prepared in Example 1 of the present invention;

[0041] Figure 2 is a scanning electron microscope (SEM) image of the surface and cross-section of the boron carbide ceramic prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] The following are specific examples of the present invention, further describing the technical solutions of the present invention, but the present invention is not limited to these examples.

[0043] Unless otherwise specified, the materials used in the present invention are commercially available products, and the methods used are conventional technical means.

[0044] Example 1

[0045] In this embodiment, a method for preparing boron carbide ceramics using rare earth silicon carbide compound Y3Si2C2 as a sintering aid includes the following steps:

[0046] (1) Weigh the raw material components according to the molar ratio YH2:SiC = 3.02:2, place them in a zirconia-lined vacuum ball milling jar, add ethanol and milling beads to it according to the mass ratio of 1:3:6, evacuate the ball milling jar to prevent the oxidation of YH2, then place the ball milling jar in a planetary ball mill with a rotation speed of 300 r / min, after ball milling for 4 h, take out the slurry, place it in a rotary evaporator for drying to obtain the pre-treated powder of the sintering aid.

[0047] (2) After subjecting the pre-treated powder of the sintering aid in step (1) to a pre-pressing treatment of 4 MPa, place it in an Al2O3 crucible, heat it to 1300 °C at a rate of 10 °C / min in a vacuum graphite cracking furnace, and hold for 5 h; after sintering, grind the powder with an agate mortar and pass it through a 200-mesh sieve to obtain the sintering aid Y3Si2C2.

[0048] (3) Mix 4 wt% of Y3Si2C2 with B4C, add ethanol and SiC milling beads to it according to the mass ratio of 1:3:6, then place it on a horizontal drum mixer with a rotation speed of 200 r / min, after ball milling for 4 h, take out the slurry, and dry it using a rotary evaporator. After drying, grind the powder with an agate mortar and pass it through a 200-mesh sieve to obtain the pre-mixed powder.

[0049] (4) Put the pre-mixed powder in step (3) into a graphite mold, subject it to a pre-pressing treatment of 9 MPa, then put it into an SPS furnace, heat it to 1700 °C at a rate of 50 °C / min, hold for 30 min, apply 50 MPa, and then cool it to room temperature at a rate of 50 °C / min to obtain the rough boron carbide ceramic. Then, polish the surface of the rough boron carbide ceramic to remove the surface graphite paper to obtain a boron carbide ceramic with a thickness of about 4 mm.

[0050] Figure 1 This is the scanning electron microscope (SEM) image of the boron carbide ceramic in this embodiment. It can be seen that the boron carbide ceramic has small pores and a high degree of densification.

[0051] The density of the boron carbide ceramic in this embodiment is 2.34 g / cm 3 , and the open porosity is 6.21%.

[0052] The hardness of the boron carbide in this embodiment is 23 GPa, the fracture toughness is 2.37 MPa*m 1 / 2 , and the flexural strength is 204 MPa.

[0053] Example 2

[0054] In this embodiment, a method for preparing boron carbide ceramics using rare earth silicon carbide compound Gd3Si2C2 as a sintering aid includes the following steps:

[0055] (1) Weigh each component raw material according to the molar ratio GdH2:SiC = 3.02:2, place it in a zirconia-lined vacuum ball milling tank, add ethanol and ball milling beads to it according to the mass ratio of 1:3:6, perform vacuum treatment on the ball milling tank to prevent GdH2 from oxidizing, then place the ball milling tank in a planetary ball mill with a rotation speed of 300 r / min. After ball milling for 4 h, take out the slurry and dry it using a rotary evaporator to obtain a pre-treated powder of the sintering aid.

[0056] (2) After subjecting the pre-treated powder of the sintering aid in step (1) to a pre-pressing treatment of 4 MPa, place it in an Al2O3 crucible, heat it to 1400 °C at a rate of 10 °C / min in a vacuum graphite cracking furnace, and hold for 5 h; after sintering, grind the powder with an agate mortar and pass it through a 200-mesh sieve to obtain the sintering aid Gd3Si2C2.

[0057] (3) Mix 4 wt% of Gd3Si2C2 with B4C, add ethanol and SiC ball milling beads to it according to the mass ratio of 1:3:6, then place it on a ball stick mill with a rotation speed of 200 r / min. After ball milling for 4 h, take out the slurry and dry it using a rotary evaporator. After drying, grind the powder with an agate mortar and pass it through a 200-mesh sieve to obtain a pre-mixed powder.

[0058] (4) Put the pre-mixed powder in step (3) into a graphite mold, perform a pre-pressing treatment of 9 MPa on it, then put it into an SPS furnace, heat it to 1700 °C at a rate of 50 °C / min, hold for 30 min, apply 50 MPa, and then cool it to room temperature at a rate of 50 °C / min to obtain a crude boron carbide ceramic. Then, polish the surface of the crude boron carbide ceramic to remove the surface graphite paper to obtain the boron carbide ceramic.

[0059] In this embodiment, the density of the boron carbide ceramic is 2.48 g / cm 3 , and the open porosity is 5.43%.

[0060] Example 3

[0061] In this embodiment, a method for preparing boron carbide ceramics using rare earth silicon carbide compound Er3Si2C2 as a sintering aid includes the following steps:

[0062] (1) Weigh each component raw material according to the molar ratio of ErH2:SiC = 3.02:2, place it in a zirconia-lined vacuum ball milling jar, add ethanol and ball milling beads to it according to the mass ratio of 1:3:6, conduct a vacuum treatment on the ball milling jar to prevent the oxidation of ErH2, then place the ball milling jar in a planetary ball mill with a rotation speed of 300 r / min, after ball milling for 4 h, take out the slurry, and dry it using a rotary evaporator to obtain the sintering aid pretreated powder.

[0063] (2) After subjecting the sintering aid pretreated powder in step (1) to a pre-pressing treatment of 4 MPa, place it in an Al2O3 crucible, heat it to 1400 °C at a rate of 10 °C / min in a vacuum graphite cracking furnace, and hold for 5 h; after sintering, grind the powder with an agate mortar and pass it through a 200-mesh sieve to obtain the sintering aid Er3Si2C2.

[0064] (3) Mix 4 wt% of Er3Si2C2 with B4C, add ethanol and SiC ball milling beads to it according to the mass ratio of 1:3:6, then place it on a ball stick mill with a rotation speed of 200 r / min, after ball milling for 4 h, take out the slurry, and dry it using a rotary evaporator. After drying, grind the powder with an agate mortar and pass it through a 200-mesh sieve to obtain the premixed powder.

[0065] (4) Put the premixed powder in step (3) into a graphite mold, conduct a pre-pressing treatment of 9 MPa on it, then put it into an SPS furnace, heat it to 1700 °C at a rate of 50 °C / min, hold for 30 min, apply 50 MPa, and then cool it to room temperature at a rate of 50 °C / min to obtain the crude boron carbide ceramic. Then, polish the surface of the crude boron carbide ceramic to remove the surface graphite paper to obtain the boron carbide ceramic.

[0066] In this example, the density of the boron carbide ceramic is 2.47 g / cm 3 , and the open porosity is 6.46%.

[0067] Example 4

[0068] In this example, a preparation method of a boron carbide ceramic using rare earth silicon carbide compound Pr3Si2C2 as a sintering aid includes the following steps:

[0069] (1) Weigh each component raw material according to the molar ratio of PrH2:SiC = 3.02:2, place it in a zirconia-lined vacuum ball milling jar, add ethanol and ball milling beads to it according to the mass ratio of 1:3:6, conduct a vacuum treatment on the ball milling jar to prevent the oxidation of PrH2, then place the ball milling jar in a planetary ball mill with a rotation speed of 300 r / min, after ball milling for 4 h, take out the slurry, and dry it using a rotary evaporator to obtain the sintering aid pretreated powder.

[0070] (2) After subjecting the sintering aid pretreated powder in step (1) to a pre-pressing treatment at 4 MPa, it is placed in an Al2O3 crucible and heated to 1200 °C at a rate of 10 °C / min in a vacuum graphite cracking furnace and held for 5 h. After sintering, the powder is ground with an agate mortar and passed through a 200-mesh sieve to obtain the sintering aid Pr3Si2C2.

[0071] (3) Mix 4 wt% of Pr3Si2C2 with B4C, add ethanol and SiC milling beads to it in a ratio of 1:3:6 by mass, and then place it on a ball-stick ball mill with a rotational speed of 200 r / min. After ball milling for 4 h, the slurry is taken out and dried using a rotary evaporator. After drying, the powder is ground with an agate mortar and passed through a 200-mesh sieve to obtain the premixed powder.

[0072] (4) Put the premixed powder in step (3) into a graphite mold and subject it to a pre-pressing treatment at 9 MPa. Then place it in an SPS furnace, heat it to 1700 °C at a rate of 50 °C / min, hold for 30 min, apply 50 MPa, and then cool it to room temperature at a rate of 50 °C / min to obtain a crude boron carbide ceramic. Then, the surface of the crude boron carbide ceramic is polished to remove the surface graphite paper to obtain the boron carbide ceramic.

[0073] In this example, the density of the boron carbide ceramic is 2.38 g / cm 3 , and the open porosity is 4.23%.

[0074] Example 5

[0075] In this example, a method for preparing a boron carbide ceramic using rare earth silicon carbide compounds Y3Si2C2 + Pr3Si2C2 as sintering aids includes the following steps:

[0076] (1) Weigh the raw material components according to the molar ratio PrH2:SiC = 3.02:2, place them in a zirconia-lined vacuum ball mill tank, add ethanol and milling beads to it in a ratio of 1:3:6 by mass, evacuate the ball mill tank to prevent PrH2 from oxidizing, and then place the ball mill tank in a planetary ball mill with a rotational speed of 300 r / min. After ball milling for 4 h, the slurry is taken out and dried using a rotary evaporator to obtain the sintering aid Pr3Si2C2 pretreated powder.

[0077] Weigh the raw material components according to the molar ratio YH2:SiC = 3.47:1, place them in a zirconia-lined vacuum ball mill tank, add ethanol and milling beads to it in a ratio of 1:3:6 by mass, evacuate the ball mill tank to prevent YH2 from oxidizing, and then place the ball mill tank in a planetary ball mill with a rotational speed of 300 r / min. After ball milling for 4 h, the slurry is taken out and dried using a rotary evaporator to obtain the sintering aid Y3Si2C2 pretreated powder.

[0078] (2) After subjecting the pre-treated powder of the sintering aid Pr3Si2C2 in step (1) to a pre-pressing treatment at 4 MPa, it was respectively placed in an Al2O3 crucible and heated to 1200 °C at a rate of 10 °C / min in a vacuum graphite cracking furnace and held for 5 h; after sintering, the powder was ground with an agate mortar and passed through a 200-mesh sieve to obtain the sintering aid Pr3Si2C2; the above steps were repeated to obtain the sintering aid Y3Si2C2.

[0079] (3) 2 wt% of Y3Si2C2, 2 wt% of Pr3Si2C2 were mixed with B4C, ethanol and SiC milling beads were added thereto in a ratio of 1:3:6 by mass, and then it was placed on a ball stick mill with a rotation speed of 200 r / min. After ball milling for 4 h, the slurry was taken out and dried using a rotary evaporator. After drying, the powder was ground with an agate mortar and passed through a 200-mesh sieve to obtain the premixed powder.

[0080] (4) The premixed powder in step (3) was put into a graphite mold and subjected to a pre-pressing treatment at 9 MPa, and then it was put into an SPS furnace, heated to 1700 °C at a rate of 50 °C / min, held for 30 min, and a pressure of 50 MPa was applied, and then cooled to room temperature at a rate of 50 °C / min to obtain a crude boron carbide ceramic. Then, the surface of the crude boron carbide ceramic was polished to remove the surface graphite paper to obtain the boron carbide ceramic.

[0081] The density of the boron carbide ceramic in this example is 2.38 g / cm 3 , and the open porosity is 5.52%.

[0082] Example 6

[0083] Compared with Example 1, the difference is that the addition amount of the sintering aid Y3Si2C2 in step (3) is 2 wt%.

[0084] The density of the boron carbide ceramic in this example is 2.19 g / cm 3 , and the open porosity is 10.0%.

[0085] Example 7

[0086] Compared with Example 1, the difference is that the addition amount of the sintering aid Y3Si2C2 in step (3) is 10 wt%.

[0087] The density of the boron carbide ceramic in this example is 2.54 g / cm 3 , and the open porosity is 1.7%.

[0088] Comparative Example 1

[0089] Compared with Example 1, the difference is that the sintering aid Y3Si2C2 is not added in step (3).

[0090] Weigh B4C, add ethanol and SiC ball milling beads to it according to the mass ratio of 1:3:6, and then place it on a planetary ball mill with a rotation speed of 200 r / min. After ball milling for 4 h, take out the slurry, place it on a rotary evaporator for drying. After drying, grind the powder with an agate mortar and sieve it through a 200-mesh sieve to obtain the premixed powder.

[0091] Put the premixed powder into a graphite mold, and perform a pre-pressing treatment on it at 9 MPa. Then put it into an SPS furnace, heat it to 1700 °C at a rate of 50 °C / min, hold it for 30 min, apply 50 MPa, and then cool it to room temperature at a rate of 50 °C / min to obtain the rough boron carbide ceramic. Then polish the surface of the rough boron carbide ceramic to remove the surface graphite paper to obtain the boron carbide ceramic.

[0092] Figure 2 This is the scanning electron microscope (SEM) image of the boron carbide ceramic in this comparative example. It can be seen that at 1700 °C, the sintering of pure B4C is not dense and there are many pores.

[0093] The density of the boron carbide ceramic in this comparative example is 1.97 g / cm 3 , and the open porosity is 22.1%.

[0094] The hardness of the boron carbide ceramic in this comparative example is 11.74 GPa, the fracture toughness is 2.5 MPa·m 1 / 2 , and the flexural strength is 102 MPa.

[0095] Comparative Example 2

[0096] Compared with Example 1, the difference is that in step (4), the premixed powder is put into a graphite mold, and a pre-pressing treatment is performed on it at 50 MPa. Then put it into an SPS furnace, heat it to 1700 °C at a rate of 50 °C / min, hold it for 30 min, without applying pressure, and then cool it to room temperature at a rate of 50 °C / min to obtain the rough boron carbide ceramic. Then polish the surface of the rough boron carbide ceramic to remove the surface graphite paper to obtain the boron carbide ceramic.

[0097] The density of the boron carbide ceramic in this comparative example is 2.26 g / cm 3 , and the open porosity is 15.98%.

[0098] Comparative Example 3

[0099] Compared with Example 1, the difference lies in that in step (4), the premixed powder is put into a graphite mold and pre-pressed at 9 MPa, then put into an SPS furnace, heated to 1700 °C at a rate of 50 °C / min, held for 30 min, and 50 MPa is applied, and then cooled naturally to room temperature to obtain a crude boron carbide ceramic. Then, the surface of the crude boron carbide ceramic is polished to remove the surface graphite paper to obtain the boron carbide ceramic.

[0100] The density of the boron carbide ceramic in this comparative example is 2.38 g / cm 3 , and the open porosity is 7.83%.

[0101] According to the above content, it can be seen that the boron carbide ceramic prepared by the preparation method of the boron carbide ceramic using rare earth silicon carbide compound as a sintering aid of the present invention realizes sintering densification at a lower sintering temperature.

[0102] Comparing Examples 1, 6, and 7, it can be seen that within a certain range, as the addition amount of the sintering aid increases, the sintering densification of the boron carbide ceramic is gradually improved, and the relative density increases from 78.17% to 95.38%.

[0103] In summary, the present invention adds a rare earth silicon carbide compound as a sintering aid to B4C. By using the rare earth silicon carbide compound to form a liquid phase, it can promote the rearrangement of ceramic raw material particles and the mass transfer process, reduce the ceramic sintering temperature, and improve the degree of sintering densification.

[0104] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art of the present invention can make various modifications or supplements to the described specific embodiments or use similar methods to replace them, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for preparing boron carbide ceramics using rare earth silicon carbon compounds as sintering aids, characterized in that: The preparation method comprises: mixing a sintering aid rare earth silicon carbon compound RE with a mass ratio of (0.1-10): (90-99.9) x Si y C z Mixing with B4C, drying, sieving, pre-pressing and sintering to obtain boron carbide ceramics with rare earth silicon carbon compounds as sintering aids; The sintering aid rare earth silicon carbon compound RE x Si y C z The medium rare earth element RE is at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; 1≤x≤5, 1≤y≤4, and 1≤z≤4.

2. The preparation method according to claim 1, characterized in that: The sintering aid rare earth silicon carbon compound RE x Si y C z where x≥y, x≥z.

3. The preparation method according to claim 1, characterized in that: The sintering aid rare earth silicon carbon compound RE x Si y C z For RE x Si2C2,2<x≤5.

4. The preparation method according to claim 1, characterized in that: The average particle size of the B4C is 1.0-10 μm, and the average particle size of the rare earth silicon carbon compound is 2.5-200 μm.

5. The preparation method according to claim 1, characterized in that: The sintering temperature is 1000-2300° C., the sintering time is 10-300 min, and the sintering heating rate is 5-100° C. / min.

6. The preparation method according to claim 1, characterized in that: The sintering includes at least one of pressureless sintering and pressure sintering.

7. The preparation method according to claim 6, characterized in that: The pressure of the pressure sintering is 10-100 MPa, the sintering temperature is 1000-1900° C., the sintering time is 10-120 min, and the sintering heating rate is 30-100° C. / min.

8. The preparation method according to claim 6, characterized in that: The pre-pressure of the pressureless sintering is 200-400Mpa, the sintering temperature is 1800-2300°C, the sintering time is 30-300min, and the sintering heating rate is 5-50°C / min.

9. A boron carbide ceramic using a rare earth silicon carbon compound as a sintering aid obtained by the preparation method according to claim 1, characterized in that: Its density is ≥2.0g / cm 3 , open porosity is ≤10%.

10. Use of the boron carbide ceramics with rare earth silicon carbon compounds as sintering aids according to claim 9 in the fields of neutron shielding materials, neutron absorbing materials and bulletproof materials.

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