Nano boron nitride / magnesium aluminum spinel composite powder additive and preparation method thereof

Abstract

The present invention belongs to the technical field of refractory materials and discloses a nano-boron nitride / magnesium aluminum spinel composite powder additive. The present invention also discloses a preparation method of the composite powder additive, comprising: step 1, placing boron oxide, magnesium oxide, and ammonium chloride in a ball mill, adding deionized water, and ball-milling and mixing, then adding aluminum oxide and ferrocene and continuing to ball-mill and mix, mixing evenly, removing and drying to obtain a mixed powder; step 2, placing the mixed powder obtained in step 1 in a microwave induction heating device, performing a microwave high-temperature reaction, and cooling after the reaction to obtain a nano-boron nitride / magnesium aluminum spinel composite powder. Adding the composite powder additive of the present invention to low-carbon magnesium-carbon refractory materials can improve the antioxidant properties of magnesium-carbon bricks, thereby extending the service life of the magnesium-carbon bricks.

Description

Technical Field

[0001] The invention belongs to the technical field of refractory materials, and relates to a nano boron nitride / magnesium aluminum spinel composite powder additive. The invention also relates to a preparation method of the composite powder additive. Background Art

[0002] Magnesium-carbon refractories are widely used in the linings of metallurgical equipment such as converters, electric arc furnaces, and RH vacuum furnaces. Graphite, as the primary carbon source, significantly improves the material's thermal shock and slag resistance due to its high thermal conductivity, low elastic modulus, and non-wetting properties with molten slag. However, oxidation of high graphite content at high temperatures severely limits its service life. On the one hand, oxidation results in a loose structure and reduced strength; on the other hand, oxidation products (CO / CO₂) increase carbon in the molten steel, affecting the quality of low-carbon steelmaking. Therefore, driven by the urgent need for clean steelmaking and energy conservation and consumption reduction, the development of magnesium-carbon refractories must prioritize low-carbon and even ultra-low-carbon materials. However, simply reducing the graphite content inevitably degrades the material's thermal shock and slag resistance, making it unsuitable for demanding service environments. Therefore, there is an urgent need to improve the oxidation resistance of low-carbon and ultra-low-carbon magnesium-carbon refractories.

[0003] Nano-boron nitride has a large specific surface area and high reactivity. When added as an additive to low-carbon magnesium-carbon refractory materials, it is beneficial to improve the oxidation resistance of the refractory materials and meet the development requirements of low-carbon magnesium-carbon refractory materials. However, currently, nano-boron nitride (BNNSs) is mainly prepared by high-temperature and high-pressure methods or chemical vapor deposition methods, which have three major bottlenecks: (1) harsh reaction conditions lead to increased energy consumption costs; (2) the product easily agglomerates to form micron-sized particles; (3) the batch yield is extremely low, which is difficult to meet industrial needs. These process defects directly increase the cost of material application and restrict its large-scale application in refractory materials. Therefore, if a process method for efficiently preparing nano-boron nitride powder can be developed and added to magnesium-carbon refractory materials, it will help improve the oxidation resistance of refractory materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a nano boron nitride / magnesia alumina spinel composite powder additive with a high boron nitride content. Adding the nano boron nitride / magnesia alumina spinel composite powder additive to a low-carbon magnesium-carbon refractory material can improve the oxidation resistance of the magnesium-carbon brick.

[0005] Another object of the present invention is to provide a method for preparing the composite powder additive, which has the characteristics of a wide range of raw material sources, simple operation, a green and environmentally friendly process, and can realize large-scale industrial production.

[0006] The technical solution adopted by the present invention is a method for preparing a nano boron nitride / magnesium aluminum spinel composite powder additive, which is specifically implemented according to the following steps:

[0007] Step 1: Place boron oxide, magnesium oxide, and ammonium chloride in a ball mill, add deionized water, and perform ball milling, then add aluminum oxide and ferrocene and continue to perform ball milling, mix thoroughly, and then take out and dry to obtain a mixed powder;

[0008] Step 2: placing the mixed powder obtained in step 1 in a microwave induction heating device to perform a microwave high-temperature reaction, and cooling after the reaction to obtain nano boron nitride / magnesium aluminum spinel composite powder.

[0009] The present invention is also characterized in that:

[0010] In step 1, the molar ratio of magnesium oxide, boron oxide and aluminum oxide is 1:1~1.8:1.6~2.6.

[0011] In step 1, the amount of ammonium chloride added is 30% to 60% by weight of the total weight of the mixed powder, and the amount of ferrocene added is 0.25% to 0.5% by weight of the total weight of the mixed powder.

[0012] In step 1, the ratio of the mass of the added deionized water to the total mass of the mixed powder is 5 to 7:1.

[0013] In step 1, the time for ball milling the boron oxide, magnesium oxide and ammonium chloride is 15 to 25 minutes. After adding aluminum oxide and ferrocene, the ball milling is continued for 15 to 25 minutes.

[0014] In step 1, the particle size of magnesium oxide is 100-200 mesh, the particle size of boron oxide powder is 100-200 mesh, and the particle size of aluminum oxide is 100-200 mesh.

[0015] In the microwave high-temperature reaction of step 2, the heating power is 2000-4000W, the reaction temperature is 1500-1700°C, and the insulation time is 30-60min.

[0016] Another technical solution adopted by the present invention is a nano boron nitride / magnesium aluminum spinel composite powder additive, which is prepared by the above method. In the composite powder additive, boron nitride nanosheets are wrapped on the surface of the magnesium aluminum spinel crystals, the boron nitride nanosheet grain diameter is 2μm~6μm, the sheet thickness is 5nm~10nm, the particle size of the magnesium aluminum spinel is 2μm~12μm; the content of the boron nitride nanosheets is 5wt.%~6wt.%.

[0017] The beneficial effects of the present invention are:

[0018] (1) The main raw materials used in the method of the present invention are widely available and inexpensive. The raw materials are non-toxic, harmless, non-flammable and non-explosive. The nano-boron nitride / magnesium aluminum spinel composite powder will not produce toxic or harmful substances during use, and will not pollute the environment or endanger human health.

[0019] (2) The composite powder of the present invention is synthesized by microwave high-temperature reaction method, which reduces energy consumption and environmental pollution compared with conventional energy methods such as electricity, coal and oil. The process is simple and easy to scale up for industrial production.

[0020] (3) The method of the present invention adds ammonium chloride, which forms ammonia during the microwave high-temperature reaction process. Ammonia reacts with boron oxide to form nano-boron nitride. The existing conventional method is to introduce nitrogen. The method of the present invention uses ammonium chloride instead of nitrogen to provide a nitrogen source for the formation of nano-boron nitride, reducing nitrogen waste.

[0021] (4) Ferrocene in the method of the present invention undergoes pyrolysis during the heating process, releasing highly dispersed iron nanoparticles, which are evenly dispersed in the reaction system as catalytic active sites. The iron particles adsorb nitrogen sources (NH4Cl) and boron sources (B2O3), reducing the energy barrier for BN bond formation and promoting low-temperature nitridation reaction. In addition, ferrocene pyrolyzes iron or iron boride particles in the reaction system to form liquid catalyst droplets, which adsorb gaseous B / N precursors (such as B2O2, NH x ), after reaching supersaturation, h-BN lattice is epitaxially precipitated, which helps to form a nanosheet layered structure;

[0022] (5) Deionized water is added during the mixing process of the present invention, which can promote the reaction of boron oxide and magnesium oxide with water to form boric acid and magnesium hydroxide. During the microwave high-temperature reaction stage, boric acid and magnesium hydroxide are highly active and can promote the formation of nano-boron nitride / magnesium aluminum spinel composite powder. In addition, the water vapor generated after the decomposition of boric acid and magnesium hydroxide can make the mixed powder loose, promoting the high-temperature reaction;

[0023] (6) Through XRD semi-quantitative determination and comparative test, the content of boron nitride nanosheets in the composite powder additive of the present invention is as high as 5wt.% to 6wt.%. Adding the composite powder additive to low-carbon magnesium carbon bricks can significantly improve their antioxidant properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a process flow chart of the method of the present invention;

[0025] Figure 2 This is the XRD pattern of the nano-boron nitride / magnesium aluminum spinel composite powder prepared in Example 1 of the present invention;

[0026] Figure 3 This is an SEM image of the nano-boron nitride / magnesium aluminum spinel composite powder prepared in Example 1 of the present invention;

[0027] Figure 4 This is a cross-sectional view of a magnesia carbon brick with composite powder added and a magnesia carbon brick without composite powder added after oxidation at 1400° C. for 1 hour in Example 1 of the present invention;

[0028] Figure 5 This is the XRD pattern of the nano-boron nitride / magnesium aluminum spinel composite powder prepared in Example 2 of the present invention;

[0029] Figure 6 This is a cross-sectional view of a magnesia carbon brick with composite powder added and a magnesia carbon brick without composite powder added after oxidation at 1400° C. for 1 hour in Example 2 of the present invention;

[0030] Figure 7 This is the XRD pattern of the nano-boron nitride / magnesium aluminum spinel composite powder prepared in Example 3 of the present invention;

[0031] Figure 8 This is a cross-sectional view of a magnesia-carbon brick with composite powder added and a magnesia-carbon brick without composite powder added after oxidation at 1400° C. for 1 hour in Example 3 of the present invention;

[0032] Figure 9 This is the XRD pattern of the composite powder prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] The preparation method of the nano boron nitride / magnesium aluminum spinel composite powder additive of the present invention is as follows: Figure 1 As shown, boron oxide, magnesium oxide, aluminum oxide, and ammonium chloride are used as raw materials and ferrocene is used as a catalyst to synthesize nano boron nitride / magnesium aluminum spinel composite powder through microwave high temperature reaction. The specific implementation is as follows:

[0035] Step 1: ball milling to obtain mixed powder:

[0036] Place boron oxide, magnesium oxide, and ammonium chloride in a ball mill, add deionized water, and ball-mill for 15 to 25 minutes. Then add aluminum oxide and ferrocene and continue ball-milling for 15 to 25 minutes. After mixing, take out and dry to obtain a mixed powder.

[0037] The molar ratio of magnesium oxide, boron oxide and aluminum oxide is 1:1~1.8:1.6~2.6; the particle size of magnesium oxide is 100~200 mesh, the particle size of boron oxide powder is 100~200 mesh, and the particle size of aluminum oxide is 100~200 mesh.

[0038] The amount of ammonium chloride added is 30% to 60% of the total weight of the mixed powder in weight percentage, and the amount of ferrocene added is 0.25% to 0.5% of the total weight of the mixed powder in weight percentage.

[0039] The ratio of the mass of the added deionized water to the total mass of the mixed powder is 5 to 7:1.

[0040] Step 2: Microwave high temperature reaction to obtain nano boron nitride / magnesium aluminum spinel composite powder:

[0041] The mixed powder obtained in step 1 is placed in a microwave induction heating device for microwave high-temperature reaction with a heating power of 2000-4000W, a reaction temperature of 1500-1700°C, and a holding time of 30-60min. After the reaction is completed, the mixture is cooled to obtain nano-boron nitride / magnesium aluminum spinel composite powder.

[0042] The prepared nano-boron nitride / magnesium aluminum spinel composite powder is boron nitride nanosheets wrapped on the surface of magnesium aluminum spinel crystals. The diameter of the boron nitride nanosheet grains is 2μm to 6μm, the thickness of the sheet is 5nm to 10nm, and the particle size of the magnesium aluminum spinel is 2μm to 12μm; the content of boron nitride nanosheets in the boron nitride nanosheet / magnesium aluminum spinel composite powder is 5wt.% to 6wt.%.

[0043] Example 1:

[0044] In this embodiment, boron oxide, magnesium oxide, aluminum oxide, and ammonium chloride are used as raw materials and ferrocene is used as catalyst to synthesize nano boron nitride / magnesium aluminum spinel composite powder by microwave high temperature reaction. Figure 1 The process shown in FIG. 1 is as follows:

[0045] Step 1, mixing and drying:

[0046] The raw materials boron oxide, magnesium oxide, and ammonium chloride were weighed according to weights of 28g, 12g, and 50g, and added to a ball mill together with 910g of deionized water and mixed for 20 minutes; then 61g of aluminum oxide and 0.6g of ferrocene were added and mixed for a further 20 minutes; after mixing evenly, the mixture was taken out and placed in a drying oven for drying.

[0047] Step 2, microwave-induced high temperature reaction:

[0048] The dried powder was placed in a microwave induction heating device and the microwave induction heating power was adjusted to 2000W. The high temperature reaction temperature reached 1500℃ and was kept warm for 35 minutes. After the reaction was completed, nano boron nitride / magnesium aluminum spinel composite powder was obtained. The phase analysis diagram is shown in FIG. Figure 2 As shown in the figure, it can be seen that the synthesized product is mainly composed of nano boron nitride (h-BN) and magnesium aluminum spinel (MgAl2O4), among which the dominant growth surface of h-BN is the (002) crystal plane. The microstructure of the synthesized product is shown in the figure. Figure 3 As shown in a, it can be clearly observed that the diameter of the covered flake is about 2 μm and the thickness is about 10 nm. The element analysis results of point 1 are as follows Figure 3 As shown in b, the thin slice is composed of B and N elements. The diameter of the covered block is about 3μm. The element analysis results of point 2 are as follows Figure 3As shown in c, the block is composed of Mg, Al and O elements, combined with Figure 2 From the XRD results, it can be determined that the thin sheets are boron nitride nanosheets and the coated blocks are magnesia alumina spinel.

[0049] The nano boron nitride / magnesium aluminum spinel composite powder obtained in this example was added to a magnesia carbon brick with a carbon content of 3% at a weight ratio of 5%, and the magnesia carbon brick and the magnesia carbon brick without the composite powder were oxidized at 1400 ° C for 1 hour. After oxidation, the magnesia carbon brick was cut open and the oxidized area of ​​the cross section was compared. The results are as follows: Figure 4 As shown in the figure, Figure a is a sample without adding composite powder, and Figure b is a sample with adding composite powder. It can be seen that the oxidation area of ​​the magnesia carbon brick with added composite powder is significantly smaller than that of the magnesia carbon brick without adding composite powder. This shows that the nano boron nitride / magnesia aluminum spinel composite powder synthesized by the method of the present invention can effectively improve the antioxidant properties of magnesia carbon bricks.

[0050] Example 2:

[0051] In this embodiment, boron oxide, magnesium oxide, aluminum oxide, and ammonium chloride are used as raw materials and ferrocene is used as catalyst to synthesize nano boron nitride / magnesium aluminum spinel composite powder by microwave high temperature reaction. Figure 1 The process shown in FIG. 1 is as follows:

[0052] Step 1, mixing and drying:

[0053] The raw materials boron oxide, magnesium oxide, and ammonium chloride were weighed according to weights of 28 g, 12 g, and 50 g, and added to a ball mill together with 910 g of deionized water and mixed for 15 minutes; then 61 g of aluminum oxide and 0.6 g of ferrocene were added and mixed for a further 25 minutes; after mixing evenly, the mixture was taken out and placed in a drying oven for drying.

[0054] Step 2, microwave-induced high temperature reaction:

[0055] The dried powder was placed in a microwave induction heating device and the microwave induction heating power was adjusted to 3000W. The high temperature reaction temperature reached 1600℃ and was kept warm for 50 minutes. After the reaction was completed, nano-boron nitride / magnesium aluminum spinel composite powder was obtained. The phase analysis diagram is shown in FIG. Figure 5 As shown, it can be seen that the synthesized product is mainly composed of nano-boron nitride (h-BN) and magnesium aluminum spinel (MgAl2O4), among which the dominant growth plane of h-BN is the (002) crystal plane. In addition, the diffraction peak intensity of BN is significantly enhanced, indicating that increasing the reaction temperature and increasing the holding time are beneficial to the formation of BN.

[0056] The nano boron nitride / magnesium aluminum spinel composite powder obtained in this example was added to a magnesia carbon brick with a carbon content of 3% at a weight ratio of 5%, and the magnesia carbon brick and the magnesia carbon brick without the composite powder were oxidized at 1400 ° C for 1 hour. After oxidation, the magnesia carbon brick was cut open and the oxidized area of ​​the cross section was compared. The results are as follows: Figure 6 As shown in the figure, Figure a is a sample without adding composite powder, and Figure b is a sample with adding composite powder. It can be seen that the oxidation area of ​​the magnesia carbon brick with added composite powder is significantly smaller than that of the magnesia carbon brick without adding composite powder. This shows that the nano boron nitride / magnesia aluminum spinel composite powder synthesized by the method of the present invention can effectively improve the antioxidant properties of magnesia carbon bricks.

[0057] Example 3:

[0058] In this embodiment, boron oxide, magnesium oxide, aluminum oxide, and ammonium chloride are used as raw materials and ferrocene is used as catalyst to synthesize nano boron nitride / magnesium aluminum spinel composite powder by microwave high temperature reaction. Figure 1 The process shown in FIG. 1 is as follows:

[0059] Step 1, mixing and drying:

[0060] The raw materials boron oxide, magnesium oxide, and ammonium chloride were weighed according to weights of 28 g, 12 g, and 50 g, and added to a ball mill together with 910 g of deionized water and mixed for 15 minutes; then 61 g of aluminum oxide and 0.6 g of ferrocene were added and mixed for a further 15 minutes; after mixing evenly, the mixture was taken out and placed in a drying oven for drying.

[0061] Step 2, microwave-induced high temperature reaction:

[0062] The dried powder was placed in a microwave induction heating device and the microwave induction heating power was adjusted to 4000W. The high temperature reaction temperature reached 1700℃ and was kept warm for 60 minutes. After the reaction was completed, nano-boron nitride / magnesium aluminum spinel composite powder was obtained. The phase analysis diagram is shown in FIG. Figure 7 As shown in the figure, it can be seen that the synthesized product is mainly composed of nano-boron nitride (h-BN) and magnesium aluminum spinel (MgAl2O4), among which the dominant growth plane of h-BN is the (002) crystal plane. In addition, when the reaction temperature continues to rise to 1700℃, the intensity of the BN diffraction peak weakens, indicating that BN can be obtained within the appropriate reaction temperature range. When the reaction temperature is too high (≥1700℃), it is not conducive to the formation of BN.

[0063] The nano boron nitride / magnesium aluminum spinel composite powder obtained in this example was added to a magnesia carbon brick with a carbon content of 3% at a weight ratio of 5%, and the magnesia carbon brick and the magnesia carbon brick without the composite powder were oxidized at 1400 ° C for 1 hour. After oxidation, the magnesia carbon brick was cut open and the oxidized area of ​​the cross section was compared. The results are as follows: Figure 8As shown in the figure, Figure a is a sample without adding composite powder, and Figure b is a sample with adding composite powder. It can be seen that the oxidation area of ​​the magnesia carbon brick with added composite powder is significantly smaller than that of the magnesia carbon brick without adding composite powder. This shows that the nano boron nitride / magnesia aluminum spinel composite powder synthesized by the method of the present invention can effectively improve the antioxidant properties of magnesia carbon bricks.

[0064] Example 4:

[0065] In this embodiment, boron oxide, magnesium oxide, aluminum oxide, and ammonium chloride are used as raw materials and ferrocene is used as catalyst to synthesize nano boron nitride / magnesium aluminum spinel composite powder by microwave high temperature reaction. Figure 1 The process shown in FIG. 1 is as follows:

[0066] Step 1, mixing and drying:

[0067] The raw materials boron oxide, magnesium oxide, and ammonium chloride were weighed according to weights of 21g, 12g, and 75g, and added to a ball mill together with 1222g of deionized water and mixed for 15 minutes; then 66g of aluminum oxide and 0.5g of ferrocene were added and mixed for a further 15 minutes; after mixing evenly, the mixture was taken out and placed in a drying oven for drying.

[0068] Step 2, microwave-induced high temperature reaction:

[0069] The dried powder is placed in a microwave induction heating device, and the microwave induction heating power is adjusted to 3500W. At this time, the high-temperature reaction temperature reaches 1700°C and is kept warm for 40 minutes. After the reaction is completed, nano-boron nitride / magnesium aluminum spinel composite powder can be obtained.

[0070] The nano boron nitride / magnesium aluminum spinel composite powder obtained in this example was added to a magnesia carbon brick with a carbon content of 3% at a weight ratio of 5%, and the composite powder was oxidized at 1400°C for 1 hour together with the magnesia carbon brick without the composite powder. After oxidation, the magnesia carbon brick was cut open and the oxidized area of ​​the cross section was compared. It can be seen that the oxidized area of ​​the magnesia carbon brick with the composite powder added was significantly smaller than that of the magnesia carbon brick without the composite powder. This shows that the nano boron nitride / magnesium aluminum spinel composite powder synthesized by the method of the present invention can effectively improve the oxidation resistance of the magnesia carbon brick.

[0071] Example 5:

[0072] In this embodiment, boron oxide, magnesium oxide, aluminum oxide, and ammonium chloride are used as raw materials and ferrocene is used as catalyst to synthesize nano boron nitride / magnesium aluminum spinel composite powder by microwave high temperature reaction. Figure 1 The process shown in FIG. 1 is as follows:

[0073] Step 1, mixing and drying:

[0074] The raw materials boron oxide, magnesium oxide, and ammonium chloride were weighed according to weights of 38 g, 12 g, and 140 g, and added to a ball mill together with 1251 g of deionized water and mixed for 20 minutes; then 49 g of aluminum oxide and 1.2 g of ferrocene were added and mixed for a further 20 minutes; after mixing evenly, the mixture was taken out and placed in a drying oven for drying.

[0075] Step 2, microwave-induced high temperature reaction:

[0076] The dried powder is placed in a microwave induction heating device, and the microwave induction heating power is adjusted to 4000W. At this time, the high-temperature reaction temperature reaches 1600°C and is kept warm for 50 minutes. After the reaction is completed, nano-boron nitride / magnesium aluminum spinel composite powder can be obtained.

[0077] The nano boron nitride / magnesium aluminum spinel composite powder obtained in this example was added to a magnesia carbon brick with a carbon content of 3% at a weight ratio of 5%, and the composite powder was oxidized at 1400°C for 1 hour together with the magnesia carbon brick without the composite powder. After oxidation, the magnesia carbon brick was cut open and the oxidized area of ​​the cross section was compared. It can be seen that the oxidized area of ​​the magnesia carbon brick with the composite powder added was significantly smaller than that of the magnesia carbon brick without the composite powder. This shows that the nano boron nitride / magnesium aluminum spinel composite powder synthesized by the method of the present invention can effectively improve the oxidation resistance of the magnesia carbon brick.

[0078] Example 6:

[0079] In this embodiment, boron oxide, magnesium oxide, aluminum oxide, and ammonium chloride are used as raw materials and ferrocene is used as catalyst to synthesize nano boron nitride / magnesium aluminum spinel composite powder by microwave high temperature reaction. Figure 1 The process shown in FIG. 1 is as follows:

[0080] Step 1, mixing and drying:

[0081] The raw materials boron oxide, magnesium oxide, and ammonium chloride were weighed according to weights of 28 g, 12 g, and 150 g, and added to a ball mill together with 1413 g of deionized water and mixed for 20 minutes; then 61 g of aluminum oxide and 0.8 g of ferrocene were added and mixed for a further 25 minutes; after mixing evenly, the mixture was taken out and placed in a drying oven for drying.

[0082] Step 2, microwave-induced high temperature reaction:

[0083] The dried powder is placed in a microwave induction heating device, and the microwave induction heating power is adjusted to 4000W. At this time, the high-temperature reaction temperature reaches 1700°C and is kept warm for 30 minutes. After the reaction is completed, nano-boron nitride / magnesium aluminum spinel composite powder can be obtained.

[0084] The nano boron nitride / magnesium aluminum spinel composite powder obtained in this example was added to a magnesia carbon brick with a carbon content of 3% at a weight ratio of 5%, and the composite powder was oxidized at 1400°C for 1 hour together with the magnesia carbon brick without the composite powder. After oxidation, the magnesia carbon brick was cut open and the oxidized area of ​​the cross section was compared. It can be seen that the oxidized area of ​​the magnesia carbon brick with the composite powder added was significantly smaller than that of the magnesia carbon brick without the composite powder. This shows that the nano boron nitride / magnesium aluminum spinel composite powder synthesized by the method of the present invention can effectively improve the oxidation resistance of the magnesia carbon brick.

[0085] Comparative Example 1:

[0086] This comparative example is substantially the same as Example 1, except that the catalyst ferrocene is not added.

[0087] The composite powder obtained in this comparative example was subjected to XRD test, and the obtained phase analysis diagram is as follows: Figure 9 As shown, it can be seen that the main phases in the final synthetic product are magnesium aluminum spinel and aluminum borate, and a trace amount of boron nitride is generated. Compared with Example 1, the content of boron nitride nanosheets in the product is very small, and a low-melting-point phase aluminum borate is generated as a by-product.

Claims

1. A method for preparing a nano boron nitride / magnesium aluminum spinel composite powder additive, characterized in that: Please follow the steps below to implement it: Step 1: Place boron oxide, magnesium oxide, and ammonium chloride in a ball mill, add deionized water, and perform ball milling, then add aluminum oxide and ferrocene and continue to perform ball milling, mix thoroughly, and then take out and dry to obtain a mixed powder; Step 2: placing the mixed powder obtained in step 1 in a microwave induction heating device for microwave high-temperature reaction, and cooling after the reaction to obtain a nano boron nitride / magnesium aluminum spinel composite powder additive; In the microwave high-temperature reaction of step 2, the heating power is 2000-4000W, the reaction temperature is 1500-1700°C, and the insulation time is 30-60min.

2. The method for preparing the nano boron nitride / magnesium aluminum spinel composite powder additive according to claim 1, characterized in that: In step 1, the molar ratio of magnesium oxide, boron oxide and aluminum oxide is 1:1~1.8:1.6~2.

6.

3. The method for preparing the nano boron nitride / magnesium aluminum spinel composite powder additive according to claim 1, characterized in that: In step 1, the amount of ammonium chloride added is 30% to 60% by weight of the total weight of the mixed powder, and the amount of ferrocene added is 0.25% to 0.5% by weight of the total weight of the mixed powder.

4. The method for preparing the nano boron nitride / magnesium aluminum spinel composite powder additive according to claim 1, characterized in that: In step 1, the ratio of the mass of the added deionized water to the total mass of the mixed powder is 5 to 7:

1.

5. The method for preparing the nano boron nitride / magnesium aluminum spinel composite powder additive according to claim 1, characterized in that: In step 1, the time for ball milling the boron oxide, magnesium oxide and ammonium chloride is 15 to 25 minutes. After adding aluminum oxide and ferrocene, the ball milling is continued for 15 to 25 minutes.

6. The method for preparing the nano boron nitride / magnesium aluminum spinel composite powder additive according to claim 1, characterized in that: In step 1, the particle size of magnesium oxide is 100-200 mesh, the particle size of boron oxide powder is 100-200 mesh, and the particle size of aluminum oxide is 100-200 mesh.

7. Nano boron nitride / magnesium aluminum spinel composite powder additive, characterized in that: It is prepared by the method described in any one of claims 1 to 6. In the composite powder additive, boron nitride nanosheets are wrapped on the surface of magnesium aluminum spinel crystals, the diameter of the boron nitride nanosheet grains is 2μm to 6μm, the thickness of the sheet is 5nm to 10nm, the particle size of magnesium aluminum spinel is 2μm to 12μm; the content of boron nitride nanosheets is 5wt.% to 6wt.%.

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