MAB-phase ceramic powder as well as preparation method and application thereof

Abstract

The invention provides MAB-phase ceramic powder as well as a preparation method and application thereof, and belongs to the technical field of ceramic materials. Firstly, elementary substance M powder and boron powder serve as raw materials, and MB powder is prepared through ball milling treatment, tabletting, heat treatment and grinding; the simple substance M powder is selected from transition metal powder; the preparation method comprises the following steps: by taking MB powder and aluminum powder as raw materials, carrying out wet ball-milling treatment, compression molding, packaging and sintering treatment to prepare MAB-phase ceramic powder; the packaging is carried out by adopting potassium bromide powder. According to the invention, an MS3-fused salt shielding synthesis / sintering method is adopted, salt is used as a reaction medium and a salt bed, the exterior of a sample is packaged with salt, so that a synthetic product is prevented from being oxidized during high-temperature synthesis in the air, and the preparation method has the characteristics of rapidness, high efficiency, energy conservation, environmental protection, low cost and the like, and is simple, convenient and feasible in the aspect of promotion of large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic materials, and in particular to a MAB phase ceramic powder and a preparation method and application thereof. Background Art

[0002] MAB phase materials are a type of layered ternary transition metal boride, where M is a transition metal element (Cr, Mn, Fe, Mo, W, etc.), A is a IIIA and IVA group element (only Al has been discovered), and B is a boron element. The crystal structure of MAB phase materials is composed of alternating stacking of MB layers and Al atomic layers, and is similar to MAX phase materials in structure and performance. For binary transition metal borides, a unique ternary transition metal boride layered structure is constructed by cleverly introducing IIIA and IVA group elements, showing great potential to reduce the intrinsic brittleness of the material and improve toughness and oxidation resistance. In view of this, an innovative ternary layered transition metal boride material - MAB phase material, has become a hot topic for domestic and foreign researchers in recent years.

[0003] Although MAB phase materials have great application prospects and potential, there are still great deficiencies in the research on MAB phase powder synthesis technology. Mn2AlB2 is a 212 type MAB phase material. The only synthesis method is to load the mixed powder into a graphite mold lined with graphite foil and put it into a vacuum hot press (HP). The sample is heated to 1323K at a rate of 500K / h under mechanical vacuum (<20Pa), and a load of 36MPa stress is pressed simultaneously during the last hour of heating to 1323K. Keep at this temperature and pressure for 2h, and then the furnace is passively cooled to RT. The bonded graphite is ground with a diamond pad, and then the sample is prepared. The reaction time is long, the process flow is complicated, the production efficiency is low, and the cost is high, which greatly limits the promotion and application of ceramic powder materials and is difficult to form industrialization and industrialization. Therefore, it is of great significance to study a MAB phase ceramic powder and its preparation method and application, reduce costs and shorten reaction time. Summary of the invention

[0004] The object of the present invention is to provide a MAB phase ceramic powder and a preparation method and application thereof, so as to solve the problems of high cost and low efficiency in the preparation of MAB phase ceramic powder in the prior art.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing MAB phase ceramic powder, comprising the following steps:

[0007] S1: Using elemental M powder and boron powder as raw materials, MB powder is obtained by ball milling, tableting, heat treatment and grinding;

[0008] The single substance M powder is selected from transition metal powder;

[0009] S2: MB powder and aluminum powder are used as raw materials, and MAB phase ceramic powder is prepared by wet ball milling, pressing, packaging and sintering.

[0010] The packaging is performed using potassium bromide powder.

[0011] Preferably, in step S1, the mass ratio of elemental M powder to boron powder is 4-6:1; the heat treatment temperature is 1200-1400°C, and the holding time is 2-15 min.

[0012] Preferably, in step S2, the molar ratio of MB powder to aluminum powder is 2:1.6-2.0.

[0013] Preferably, in step S2, the medium for wet ball milling is anhydrous ethanol, the mass ratio of the total mass of MB powder and aluminum powder to anhydrous ethanol is 1:2-3, the rotation speed of wet ball milling is 100-200 rpm, and the time is 4-8 hours.

[0014] Preferably, in step S2, the packaging includes a first packaging and a second packaging.

[0015] Preferably, the first packaging step is: wrapping the pressed green body with potassium bromide powder and then performing secondary pressing to obtain secondary pressed tablets; the thickness of the potassium bromide powder wrapped around the green body is 20 to 30 mm.

[0016] Preferably, the second packaging step is: placing the secondary pressed tablet on a potassium bromide powder salt bed, and then completely covering and sealing the secondary pressed tablet with potassium bromide.

[0017] Preferably, in step S2, the heating rate during sintering is 6-10°C / min, the sintering temperature is 1000-1100°C, and the sintering time is 0.5-2h; and the sintering process also includes alkali washing and drying.

[0018] The present invention also provides a MAB phase ceramic powder obtained by the above-mentioned method for preparing the MAB phase ceramic powder, wherein the MAB phase ceramic powder has a layered structure.

[0019] The present invention also provides an application of the above-mentioned MAB phase ceramic powder in a wave absorbing material.

[0020] Beneficial effects of the present invention:

[0021] (1) The present invention can prepare low-cost, high-purity boride ceramic powders using low-cost single transition metal elements and boron powder as raw materials. No complicated process flow is required and the synthesis can be performed mainly through vacuum heat treatment. This can save a lot of energy, reduce energy consumption, and has high production efficiency and low process cost.

[0022] (2) In the prior art, the preparation of non-oxide ceramic powders has always been carried out in an argon atmosphere to protect the material from oxidation, but this method is costly and not suitable for large-scale production. 3 -Molten salt shielding synthesis / sintering method, using salt as the reaction medium and salt bed, the sample is encapsulated with salt to protect the synthesized product from oxidation during high-temperature synthesis in air. The molten salt shielding method is not only low-cost, simple to operate, and has a low synthesis temperature, but also can directly synthesize the product in an air atmosphere, and the final product is a high-purity, fine and loose powder without the need for additional grinding steps.

[0023] (3) In the molten salt shielding process, potassium bromide powder is used as the reaction medium. It has good chemical stability and is not easy to react chemically with the shielded material or other components in the process. It can ensure the stability of its own properties during the molten salt shielding process. Utilizing this characteristic of potassium bromide, the sample can be hermetically sealed around the sample before further heating in potassium bromide.

[0024] (4) The MAB phase ceramic powder prepared by the molten salt shielding method of the present invention has the advantages of high purity, simple process, cost saving, low energy consumption, etc., and can be used for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the packaging process in the present invention;

[0026] Figure 2 is the XRD pattern of the MnB powder obtained in Example 1;

[0027] Figure 3 XRD diagrams of Mn2AlB2 powders prepared in Examples 1 to 3 and Comparative Example 2, wherein 1100°C corresponds to Example 1, 1050°C corresponds to Example 2, 1000°C corresponds to Example 3, and 900°C corresponds to Comparative Example 2;

[0028] Figure 4 This is the SEM image of the Mn2AlB2 powder obtained in Example 1;

[0029] Figure 5 This is the SEM image of the Mn2AlB2 powder prepared in Comparative Example 1;

[0030] Figure 6 This is a diagram of the microwave absorption performance of the Mn2AlB2 powder prepared in Comparative Example 2;

[0031] Figure 7 This is a diagram showing the microwave absorption performance of the Mn2AlB2 powder prepared in Example 2. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing MAB phase ceramic powder, comprising the following steps:

[0033] S1: Using elemental M powder and boron powder as raw materials, MB powder is obtained by ball milling, tableting, heat treatment and grinding;

[0034] The single substance M powder is selected from transition metal powder;

[0035] S2: MB powder and aluminum powder are used as raw materials, and MAB phase ceramic powder is prepared by wet ball milling, pressing, packaging and sintering.

[0036] The packaging is performed using potassium bromide powder.

[0037] In the present invention, the transition metal powder is selected from Cr, Mn, Fe, Mo or W, preferably Mn.

[0038] In the present invention, in the step S1, the mass ratio of the elemental M powder and the boron powder is 4 to 6:1, preferably 5.06:1; the temperature of the heat treatment is 1200 to 1400°C, preferably 1200 to 1300°C, and more preferably 1200°C, and the insulation time is 2 to 15 min, preferably 2 to 10 min, and more preferably 2 to 5 min.

[0039] In the present invention, the tabletting pressure is 4-6 MPa, preferably 5 MPa, and the pressure holding time is 1-3 min, preferably 2 min.

[0040] In the present invention, in step S2, the molar ratio of MB powder to aluminum powder is 2:1.6-2.0, preferably 2:1.62-1.95. Aluminum powder has a low melting point (660°C), and adding excess aluminum powder can promote the transformation of MB powder into MAB phase ceramic powder.

[0041] In the present invention, in step S2, the medium for wet ball milling is anhydrous ethanol, the mass ratio of the total mass of MB powder and aluminum powder to anhydrous ethanol is 1:2-3, preferably 1:2, the rotation speed of wet ball milling is 100-200 rpm, preferably 150 rpm, the time is 4-8 h, preferably 5-7 h, and more preferably 6 h.

[0042] In the present invention, in step S2, the pressure of the pressing molding is 4-6 MPa, preferably 5 MPa, and the holding time is 1-3 min, preferably 2 min.

[0043] In the present invention, in step S2, packaging includes a first packaging and a second packaging.

[0044] The present invention adopts double packaging to better isolate oxygen in the air and generate pure MAB phase ceramic powder.

[0045] In the present invention, the first packaging step is: wrapping the pressed green body with potassium bromide powder and then performing secondary pressing to obtain a secondary pressed tablet; the secondary pressing pressure is 4-6MPa, preferably 5MPa, and the holding time is 1-3min, preferably 2min; the thickness of the potassium bromide powder wrapped in the green body is 20-30mm, preferably 20mm.

[0046] In the present invention, the second packaging step is: placing the secondary pressed tablet on a potassium bromide powder salt bed, and then completely covering and sealing the secondary pressed tablet with potassium bromide.

[0047] In the present invention, in step S2, the heating rate during sintering is 6-10°C / min, preferably 6°C / min, 8°C / min, 10°C / min, the sintering temperature is 1000-1100°C, preferably 1000°C, 1050°C, 1100°C; the sintering time is 0.5-2h, preferably 1h; and the sintering process also includes alkali washing and drying. The sintering process can be carried out in an air atmosphere, and potassium bromide powder is used as a reaction medium to ensure that the sample is not oxidized.

[0048] In the present invention, the alkali washing is performed using a sodium hydroxide solution with a mass concentration of 10%, and the number of alkali washings is 3 times; the drying temperature is 60-70° C., preferably 65° C., and the drying time is 8-12 hours, preferably 10 hours.

[0049] The present invention also provides a MAB phase ceramic powder obtained by the above-mentioned method for preparing the MAB phase ceramic powder, wherein the MAB phase ceramic powder has a layered structure.

[0050] The present invention also provides an application of the above-mentioned MAB phase ceramic powder in a wave absorbing material.

[0051] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0052] Example 1

[0053] 8.35 g of Mn powder and 1.65 g of B powder were poured into a polytetrafluoroethylene ball pot, and zirconium oxide balls were added as grinding media. The powder was ball-milled in a QM-3SP2 ball mill (ball-to-material ratio was 5:1, rotation speed was 150 rpm, and time was 1 h). Then, the evenly mixed powder was poured into a circular mold with an inner diameter of 30 mm, placed on a tablet press, pressurized to 5 MPa, maintained at pressure for 2 min, and pressed into a green body; the green body was placed in a graphite crucible, placed in a hot press furnace, and maintained at 1200°C for 2 min under vacuum conditions, naturally cooled to room temperature, and the block was ground into powder with a mortar, and passed through a 200-mesh stainless steel sieve to obtain MnB powder.

[0054] 1.5 g of MnB powder and 0.5 g of Al powder were mixed and placed in a ball mill, and anhydrous ethanol was added (the mass ratio of the total mass of MnB powder and Al powder to anhydrous ethanol was 1:2), and the amount of anhydrous ethanol was ensured not to exceed two-thirds of the volume of the ball mill, and wet ball milling was performed at a speed of 150 rpm for 6 h. The obtained slurry was dried to obtain a powder, and the powder was poured into a circular mold with an inner diameter of 30 mm, and pressed at a pressure of 6 MPa to obtain a primary tablet, and then a layer of potassium bromide powder was first spread in a circular mold with an inner diameter of 50 mm, and then the primary tablet was placed in a 50 mm circular mold, and potassium bromide powder was continued to be added until the potassium bromide powder was The potassium powder completely covers the tablet and performs secondary pressing to obtain a secondary tablet, ensuring that the thickness of the wrapped potassium bromide powder is 20 mm; a layer of potassium bromide powder is spread on the bottom of the alumina crucible as a salt bed, the secondary tablet is placed on the salt bed, and potassium bromide powder is continued to be added until the secondary tablet is completely covered, the crucible is covered and sealed, and then transferred to a muffle furnace for sintering, and the temperature is increased to 1100°C at a heating rate of 10°C / min, and kept at 1100°C for 1h. After sintering, it is cooled to room temperature with the furnace, and after being taken out, it is washed 3 times with a sodium hydroxide solution with a mass concentration of 10% to remove residual molten salt, and then dried at 60°C for 10h to obtain Mn2AlB2 powder.

[0055] Example 2

[0056] The preparation process of MnB powder is the same as that of Example 1;

[0057] 1.5 g of MnB powder and 0.56 g of Al powder were mixed and placed in a ball mill. Anhydrous ethanol was added (the mass ratio of the total mass of MnB powder and Al powder to anhydrous ethanol was 1:2), and the amount of anhydrous ethanol was ensured not to exceed two-thirds of the volume of the ball mill. The mixture was wet-milled at a speed of 150 rpm for 6 h. The obtained slurry was dried to obtain a powder. The powder was poured into a circular mold with an inner diameter of 30 mm, and pressed at a pressure of 5 MPa to obtain a primary tablet. Then, a layer of potassium bromide powder was first spread in a circular mold with an inner diameter of 50 mm. The primary tablet was then placed in a 50 mm circular mold, and potassium bromide powder was continued to be added until the bromide was 100%. The potassium bromide powder completely covers the tablet and performs secondary pressing to obtain a secondary tablet, ensuring that the thickness of the wrapped potassium bromide powder is 20 mm; a layer of potassium bromide powder is spread on the bottom of the alumina crucible as a salt bed, the secondary tablet is placed on the salt bed, and potassium bromide powder is continued to be added until the secondary tablet is completely covered, the crucible is covered and sealed, and then transferred to a muffle furnace for sintering, and the temperature is increased to 1050°C at a heating rate of 8°C / min, and kept at 1050°C for 1h. After sintering, it is cooled to room temperature with the furnace, and after being taken out, it is alkaline washed three times with a sodium hydroxide solution with a mass concentration of 10% to remove residual molten salt, and then dried at 60°C for 10h to obtain Mn2AlB2 powder.

[0058] Example 3

[0059] The preparation process of MnB powder is the same as that of Example 1;

[0060] 1.5 g of MnB powder and 0.6 g of Al powder were mixed and placed in a ball mill, and anhydrous ethanol was added (the mass ratio of the total mass of MnB powder and Al powder to anhydrous ethanol was 1:2), and the amount of anhydrous ethanol was ensured not to exceed two-thirds of the volume of the ball mill, and wet ball milling was performed at a speed of 150 rpm for 6 h. The obtained slurry was dried to obtain a powder, and the powder was poured into a circular mold with an inner diameter of 30 mm, and pressed at a pressure of 4 MPa to obtain a primary tablet, and then a layer of potassium bromide powder was first spread in a circular mold with an inner diameter of 50 mm, and then the primary tablet was placed in a 50 mm circular mold, and potassium bromide powder was continued to be added until the potassium bromide powder was The potassium powder completely covers the tablet and performs secondary pressing to obtain a secondary tablet, ensuring that the thickness of the wrapped potassium bromide powder is 20 mm; a layer of potassium bromide powder is spread on the bottom of the alumina crucible as a salt bed, the secondary tablet is placed on the salt bed, and potassium bromide powder is continued to be added until the secondary tablet is completely covered, the crucible is covered and sealed, and then transferred to a muffle furnace for sintering, and the temperature is increased to 1000°C at a heating rate of 6°C / min, and kept at 1000°C for 1h. After sintering, it is cooled to room temperature with the furnace, and after being taken out, it is washed 3 times with a sodium hydroxide solution with a mass concentration of 10% to remove residual molten salt, and then dried at 60°C for 10h to obtain Mn2AlB2 powder.

[0061] Comparative Example 1

[0062] 10.2gMn powder, 1.65gB powder and 2.7gAl powder were directly poured into a ball mill, zirconia balls were added as grinding media, the ball-to-material ratio was set to 5:1, the rotation speed was 150rpm, and ball milling was performed for 3h. The mixed powder was then poured into a circular mold with an inner diameter of 30mm and pressed into a green body under a pressure of 5MPa. The green body was placed in a graphite crucible and placed in a high-temperature furnace. Under vacuum conditions, the temperature was raised to 1600℃ at a heating rate of 15℃ / min, and kept at this temperature for 3h, and then naturally cooled to room temperature with the furnace. The obtained block was not subjected to alkali washing treatment, but was directly ground into powder and passed through a 200-mesh stainless steel sieve to obtain Mn2AlB2 powder.

[0063] The SEM spectrum of Comparative Example 1 is as follows Figure 5 The conventional mixing, pressing and sintering method is used to prepare Mn2AlB2 powder. Due to the high reaction temperature and long reaction time, the raw materials are prone to react with impurities in the air. At the same time, the high temperature will also cause the crystal to grow too fast and produce crystal defects.

[0064] Comparative Example 2

[0065] The difference from Example 2 is that the sintering temperature is 900° C., and other conditions are the same.

[0066] Figure 1 This is a schematic diagram of the packaging process before material sintering. Figure 2 It can be determined that the prepared powder is MnB powder. Figure 3 It can be determined that the prepared powder is Mn2AlB2 powder. Figure 4 It can be seen that the Mn2AlB2 powder prepared in Example 1 of the present invention is lath-shaped particles with obvious layered structure. Figure 5 This is the SEM image of the Mn2AlB2 powder prepared in Comparative Example 1. It can be seen that the morphology of the Mn2AlB2 powder is completely different from that of the Mn2AlB2 powder prepared in Example 1 and does not have an obvious layered structure.

[0067] Performance Verification:

[0068] The absorption performance of the Mn2AlB2 powders obtained in Example 2 and Comparative Example 2 was tested: the reflection loss of Mn2AlB2 samples with different thicknesses (1.5 mm to 5 mm) was tested in the frequency range of 2 to 18 GHz using the coaxial method. The test results are shown in Figure 2. Figure 7 and Figure 6 shown.

[0069] from Figure 6It can be seen that the reflection loss curves of the Mn2AlB2 powder prepared at a sintering temperature of 900°C are complex, with no obvious single increasing or decreasing trend, indicating that at 900°C, the wave absorption performance of Mn2AlB2 varies with frequency in a complex manner and is significantly affected by frequency. From the reflection loss value, the reflection loss of curves with different thicknesses is mostly close to 0dB, which means that at this temperature, the absorption capacity of Mn2AlB2 of different thicknesses for electromagnetic waves is generally weak, and a large amount of electromagnetic waves are reflected. This shows that the sintering temperature of 900°C is not suitable for the preparation of MAB phase ceramic powder with wave absorption performance.

[0070] from Figure 7 It can be seen that Mn2AlB2 exhibits different absorbing properties at different thicknesses. The entire test frequency band (2-18GHz) covers the S, C, X and Ku bands. As the thickness of the sample increases, the reflection loss curve shows different trends. When the sample thickness is 4.85mm, the minimum reflection loss of -41.5dB can be achieved at a specific frequency, indicating that it has a strong absorption capacity for electromagnetic waves at this time. At the same time, when the reflection loss is lower than -10dB, it means that the material has a good absorption effect on electromagnetic waves and can effectively reduce the reflection of electromagnetic waves. From Figure 7 It can be observed that samples of different thicknesses can meet this criterion in multiple frequency bands and exhibit good wave absorption properties.

[0071] Compared with the common absorbing materials on the market, Mn2AlB2 has obvious advantages in terms of absorbing frequency band width, absorption intensity and thickness adaptability. For example, although silicon carbide fiber has a certain absorbing ability in a certain frequency band, it is far inferior to Mn2AlB2 in frequency band width and absorption intensity; and although metal nanoparticle composite materials can absorb waves in a wider frequency band, they have more stringent requirements on material thickness. In contrast, Mn2AlB2 can maintain good absorbing performance at different thicknesses. This makes Mn2AlB2 have broader application prospects and potential market competitiveness in the fields of radar stealth and electromagnetic shielding.

[0072] The preparation process of ternary layered ceramic powder has the problems of complicated process and equipment, high synthesis temperature, long time consumption and high cost. The preparation method of MAB phase ceramic powder of the present invention has the characteristics of fastness, high efficiency, energy saving, environmental protection, low cost, etc., and is simple and easy to promote large-scale production.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing MAB phase ceramic powder, characterized in that: The steps include: S1: MB powder is prepared by ball milling, tableting, heat treatment and grinding with single substance M powder and boron powder as raw materials; The single substance M powder is selected from transition metal powders; S2: MB powder and aluminum powder are used as raw materials, and MAB phase ceramic powder is prepared by wet ball milling, pressing, packaging and sintering. The packaging is performed using potassium bromide powder.

2. The method for preparing the MAB phase ceramic powder according to claim 1, characterized in that: In the step S1, the mass ratio of the elemental M powder to the boron powder is 4-6:1; the temperature of the heat treatment is 1200-1400° C., and the insulation time is 2-15 min.

3. The method for preparing the MAB phase ceramic powder according to claim 1 or 2, characterized in that: In the step S2, the molar ratio of MB powder to aluminum powder is 2:1.6-2.

0.

4. The method for preparing the MAB phase ceramic powder according to claim 3, characterized in that: In step S2, the medium for wet ball milling is anhydrous ethanol, the mass ratio of the total mass of MB powder and aluminum powder to anhydrous ethanol is 1:2-3, the rotation speed of wet ball milling is 100-200 rpm, and the time is 4-8 hours.

5. The method for preparing the MAB phase ceramic powder according to claim 1, 2 or 4, characterized in that: In the step S2, packaging includes a first packaging and a second packaging.

6. The method for preparing the MAB phase ceramic powder according to claim 5, characterized in that: The first packaging step is: wrapping the pressed green body with potassium bromide powder and then performing secondary pressing to obtain secondary pressed tablets; the thickness of the potassium bromide powder wrapped on the green body is 20-30 mm.

7. The method for preparing the MAB phase ceramic powder according to claim 6, characterized in that: The second packaging step is: placing the secondary pressed tablet on a potassium bromide powder salt bed, and then completely covering and sealing the secondary pressed tablet with potassium bromide.

8. The method for preparing MAB phase ceramic powder according to claim 2, 4 or 7, characterized in that: In the step S2, the heating rate during sintering is 6-10°C / min, the sintering temperature is 1000-1100°C, and the sintering time is 0.5-2h; and the sintering process also includes alkali washing and drying.

9. The MAB phase ceramic powder obtained by the method for preparing the MAB phase ceramic powder according to any one of claims 1 to 8, characterized in that: The MAB phase ceramic powder has a layered structure.

10. Use of the MAB phase ceramic powder according to claim 9 in wave absorbing materials.

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