Preparation method of a functionalized compact core-shell high-energy boron powder composite

Abstract

The application discloses a preparation method of a regulatable functionalized compact core-shell high-energy boron powder composite material. The method combines surface acidification and coating to improve the ignition and combustion performance of boron powder, and meanwhile, the surface oxide layer of the boron powder and the binder system are isolated to a certain extent to solve the incompatibility problem of the boron powder in the application and preparation process. The ignition and combustion performance of the boron powder can be controlled by controlling the reaction conditions of the surface acidification, so as to meet the requirements of different fuel-rich propellants.

Description

Technical Field

[0001] This invention relates to powder surface modification technology, specifically to a method for preparing a high-energy boron powder composite material. Background Technology

[0002] Boron (B) possesses high energy density and high volumetric calorific value, and its combustion products are clean. The gaseous products can effectively improve the thermal energy conversion efficiency in engine nozzles and reduce two-phase flow losses, making it one of the most promising fuels among fuel-rich propellants. However, the presence of impurities such as boron oxide (B₂O₃) and boric acid (H₃BO₃) on the surface of boron leads to several problems in practical applications. For example, the significant difference in melting and boiling points of B₂O₃ on the surface limits the ignition and combustion of boron to the range of 450℃-1860℃. Within this range, the evaporation rate of the liquid oxide layer is lower than the oxidation reaction rate, resulting in the formation of a molten layer that causes particle adhesion and accumulation, preventing the combustion of a large number of boron particles and hindering actual ignition and combustion efficiency. Furthermore, during the preparation of fuel-rich propellants, boron particles cross-link with hydroxyl prepolymers in the propellant, increasing the interfacial bonding strength between the boron particles and the hydroxyl prepolymers. This makes it difficult to mix the boron-based fuel-rich propellants evenly during preparation, resulting in the generation and retention of a large number of internal bubbles and deterioration of the production process.

[0003] To address the major challenges of boron powder in ignition and practical applications, numerous solutions have been published in domestic and international research, primarily categorized as follows: 1. Preparing boron powder fuels with different particle sizes and morphologies, blending fine-particle-size nano-boron with spherical boron to increase the specific surface area for practical applications. This significantly improves fuel efficiency and system energy without affecting system compatibility and stability. However, while increasing the specific surface area, it also increases the contact area between active boron and external oxygen, accelerating the slow oxidation of boron powder and hindering propellant storage. Furthermore, this method does not address the issues related to propellant preparation processes; 2. Energizing the surface of boron powder through pretreatment to generate active sites on the boron surface and grafting energy-rich groups, thereby improving... While improving the rheological properties of boron in the binder system, the high energy release rate also improves the processability to some extent, but it does not completely solve the problem of cross-linking deterioration between the surface oxide layer and the binder in the propellant; 3. Functional coating modification of boron powder, using oxidants, binders, flammable metals, etc. as coating agents, shortens the contact distance between the fuel and the coating agent, increases the effective active boron content, and improves the mass transfer and heat transfer rate and ignition performance. However, current research shows that the shell density and thickness of the prepared core-shell structure are still difficult to control, resulting in uneven coating and a large number of exposed boron particles. The processing technology of the propellant has not been effectively improved, and it cannot be applied to the production practice of propellants in large quantities. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a tunable functionalized compact core-shell high-energy boron powder composite material.

[0005] The technical solution for achieving this invention is as follows: a method for preparing a functionalized compact core-shell high-energy boron powder composite material, the specific steps of which are as follows:

[0006] The first step is to add the raw boron powder and dispersant into a reaction vessel according to a certain mass ratio, and stir magnetically at a certain temperature to obtain a boron powder suspension with good dispersion performance.

[0007] The second step is to add concentrated nitric acid to the boron powder suspension and stir it magnetically at a certain temperature until the suspension solution forms a homogeneous and stable state.

[0008] The third step involves washing and filtering the sample while it is still hot using a solvent that is miscible with concentrated nitric acid, and then drying it under vacuum at a certain temperature to obtain acidified modified hydroxy boron.

[0009] The fourth step involves adding the modified hydroxy boron and the dispersant to a reaction vessel in a certain mass ratio, and then magnetically stirring the mixture in a low-temperature water bath below 0°C for a certain period of time to obtain a boron powder suspension, which is then kept at the same temperature.

[0010] Fifth step: Prepare a saturated solution of AP-dimethylformamide in a constant temperature water bath at 80±5℃;

[0011] Step 6: A saturated solution of AP-dimethylformamide is added dropwise at a constant rate to the boron powder suspension from step 4. AP rapidly crystallizes to form a compact core-shell structure with hydroxy boron as the crystal nucleus. After standing for a period of time, the supernatant is removed. After vacuum drying at a certain temperature, the dried composite material, namely B-OH@AP composite material, is obtained.

[0012] Preferably, in the first step, the dispersant is a solvent that does not react with boron powder, such as acetone, ethyl acetate, cyclohexane, acetonitrile, or ethanol.

[0013] Preferably, in the first step, the mass ratio of boron powder to dispersant is 1g:10ml.

[0014] Preferably, in the second step, magnetic stirring is performed at 25°C.

[0015] Preferably, in the second step, the mass ratio of boron powder to concentrated nitric acid is 10g:(1~3)ml.

[0016] Preferably, in the third step, the solvent that is miscible with concentrated nitric acid is any one of alcohol, ether, benzene, etc.

[0017] Preferably, in the third step, vacuum drying is carried out at 55~60℃ for 24 hours.

[0018] Preferably, in the fourth step, the mass ratio of modified hydroxyboron to dispersant is 1g:10ml.

[0019] Preferably, in the fourth step, the dispersant is a solvent that does not react with boron powder, such as acetone, ethyl acetate, cyclohexane, acetonitrile, or ethanol.

[0020] Ideally, in step six, the drip rate is 2 ml / min.

[0021] Preferably, in step six, vacuum drying is performed at 55~60℃ for 24 hours.

[0022] Compared with the prior art, the significant advantages of this invention are: 1. This invention uses a combination of surface acidification and coating to improve the ignition and combustion performance of boron powder, while isolating the oxide layer on the surface of boron powder and the binder system to a certain extent, thus solving the problem of incompatibility in the application and preparation process; 2. By controlling the reaction conditions of surface acidification, this invention can controllably change the ignition and combustion performance of boron powder, which can meet the needs of different fuel-rich propellants. Attached Figure Description

[0023] Figure 1 This is a SEM image of the functionalized compact core-shell high-energy boron powder prepared according to Example 3 of the present invention.

[0024] Figure 2 This is a SEM-EDS image of the functionalized compact core-shell high-energy boron powder prepared according to Example 1 of the present invention.

[0025] Figure 3 This is a SEM-EDS image of the functionalized compact core-shell high-energy boron powder prepared according to Example 2 of the present invention.

[0026] Figure 4 This is a SEM-EDS image of the functionalized compact core-shell high-energy boron powder prepared according to Example 3 of the present invention.

[0027] Figure 5 This is a comparison of the ignition light intensity signals of the functionalized compact core-shell high-energy boron powders prepared according to Examples 1, 2, and 3 of this invention.

[0028] Table 1 shows... Figure 2 , 3 The percentage mass ratio of specific elements in 4, and the calculated ratio of boron to ammonium perchlorate coating. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] This invention addresses the shortcomings and defects of existing modification technologies by analyzing the basic physicochemical properties of boron powder. Utilizing the chemical properties of the boron powder surface, a simple acidification process is used to convert the oxide layer on the surface into hydroxyl groups. Simultaneously, this conversion improves the interaction between the oxide layer and the hydroxyl groups in the coating agent, resulting in a core-shell composite boron powder with controllable shell integrity and structural strength. Generally, the successful application of boron powder in composite materials depends on the formation of a good interface between the boron powder and the coating material. Current modifications to boron-based materials primarily focus on improving ignition performance or compatibility, without truly eliminating the disadvantages of using boron powder in solid propellant components. This invention addresses the issue from multiple perspectives. During combustion, the decomposition of the shell layer ammonium perchlorate generates heat and oxidizing components, accelerating the vaporization of the oxide layer while reacting with the core hydroxy boron powder. This effectively solves the problem of low combustion efficiency in boron-containing propellants due to incomplete combustion of boron powder, thus improving the overall performance of solid ramjet tactical missiles. Hydroxy boron differs from raw materials and silane-modified boron in that its surface-grafted hydroxyl groups have extremely strong intermolecular forces with the oxygen-containing groups in ammonium perchlorate. This promotes the growth rate and extent of ammonium perchlorate on the crystal nucleus surface, resulting in good and close contact between the fuel boron powder and the oxidizer. This effectively isolates the exposed internal oxide layer and prevents external oxygen penetration, improving the propellant processing technology while giving it superior storage performance.

[0031] Example 1

[0032] 1. Weigh 10g of amorphous boron powder and mix it with acetone at a mass ratio of 1:10 at 1000rpm at room temperature (25°C) to prepare a clean boron suspension.

[0033] 2. After stirring for 24 hours, the suspension was filtered and vacuum dried at 25°C for 24 hours to obtain the activated boron sample;

[0034] 3. Place 5g of activated boron powder and 100ml of cyclohexane in a reaction vessel, turn on the magnetic stirrer, and stir at 800rpm for 30min to obtain an activated boron suspension;

[0035] 4. Weigh 25g of ammonium perchlorate and add it to 70ml of dimethylformamide. Dissolve the solution in an 80℃ constant temperature water bath for 20min to prepare a saturated ammonium perchlorate solution.

[0036] 5. Adjust the rotation speed of the activated boron suspension to 500 rpm, and set the temperature of the low-temperature bath to -5℃ for circulating cooling;

[0037] 6. Adjust the drip rate to 2 ml / min;

[0038] 7. Start the metering peristaltic pump and drip the saturated ammonium perchlorate solution into the activated boron suspension while keeping it at a constant temperature;

[0039] 8. After the addition is complete, continue stirring at 500 rpm for 10 minutes;

[0040] 9. After stirring, allow the mixture to stand, filter, and vacuum dry at 60℃ for 24 hours to obtain the core-shell composite sample. SEM-EDS images are shown below. Figure 2 As shown in Table 1, the percentage of element content is as follows.

[0041] Example 2

[0042] 1. Weigh 10g of amorphous boron powder and mix it with acetone at a mass ratio of 1:10 at 1000rpm at room temperature (25°C) to prepare a clean boron suspension.

[0043] 2. Add 1 ml of nitric acid, stir for 24 h, filter the suspension, and vacuum dry at 25 °C for 24 h to obtain the modified hydroxy boron sample;

[0044] 3. Place 5g of modified hydroxy boron powder and 100ml of cyclohexane in a reaction vessel, turn on the magnetic stirrer, and stir at 800rpm for 30min to obtain an activated boron suspension;

[0045] 4. Weigh 15g of ammonium perchlorate and add it to 40ml of dimethylformamide. Dissolve the solution in an 80℃ constant temperature water bath for 20min to prepare a saturated ammonium perchlorate solution.

[0046] 5. Adjust the rotation speed of the activated boron suspension to 500 rpm, and set the temperature of the low-temperature bath to -5℃ for circulating cooling;

[0047] 6. Adjust the drip rate to 2 ml / min;

[0048] 7. Start the metering peristaltic pump and drip the saturated ammonium perchlorate solution into the modified hydroxyboron suspension while keeping it at a constant temperature;

[0049] 8. After the addition is complete, continue stirring at 500 rpm for 10 minutes;

[0050] 9. After stirring, allow the mixture to stand, filter, and vacuum dry at 60℃ for 24 hours to obtain the core-shell composite sample. SEM-EDS images are shown below. Figure 3 As shown in Table 1, the percentage of element content is as follows.

[0051] Example 3

[0052] 1. Weigh 10g of amorphous boron powder and mix it with acetone at a mass ratio of 1:10 at 1000rpm at room temperature (25°C) to prepare a clean boron suspension.

[0053] 2. Add 3 ml of nitric acid, stir for 24 h, filter the suspension, and vacuum dry at 25 °C for 24 h to obtain the modified hydroxy boron sample;

[0054] 3. Place 5g of modified hydroxy boron powder and 100ml of cyclohexane in a reaction vessel, turn on the magnetic stirrer, and stir at 800rpm for 30min to obtain an activated boron suspension;

[0055] 4. Weigh 15g of ammonium perchlorate and add it to 40ml of dimethylformamide. Dissolve the solution in an 80℃ constant temperature water bath for 20min to prepare a saturated ammonium perchlorate solution.

[0056] 5. Adjust the rotation speed of the activated boron suspension to 500 rpm, and set the temperature of the low-temperature bath to -5℃ for circulating cooling;

[0057] 6. Adjust the drip rate to 2 ml / min;

[0058] 7. Start the metering peristaltic pump and drip the saturated ammonium perchlorate solution into the modified hydroxyboron suspension while keeping it at a constant temperature;

[0059] 8. After the addition is complete, continue stirring at 500 rpm for 10 minutes;

[0060] 9. After stirring, let stand, filter, and vacuum dry at 60℃ for 24h to obtain a core-shell composite sample.

[0061] Its appearance is like Figure 1 As shown, the structure is regular and the surface is relatively smooth; the SEM-EDS image is as follows. Figure 4 As shown, the surface O element distribution is more dense than in the other two embodiments; the element content percentage is shown in Table 1. With the increase of concentrated nitric acid, the hydroxyl content on the B surface increases, and the proportion of surface AP calculated based on O wt% continuously increases, resulting in a better coating effect.

[0062] Table 1

[0063] sample O wt% B wt% AP:B Example 1 63.45 8.09 1.30:1 Example 2 74.04 4.06 2.68:1 Example 3 69.78 3.34 2.84:1

[0064] The ignition performance of the samples obtained in Examples 1 to 3 is compared. Figure 5 As shown, compared with other examples 1 and 2, the ignition delay time of the sample obtained in example 3 is significantly earlier, and the intensity of the flame light is about twice that of other examples.

[0065] In summary, this invention prepares a coating layer with adjustable shell density, effectively solving the cross-linking compatibility problem between the oxide layer on the surface of boron powder and the binder system, slowing down the slow oxidation of boron powder, and greatly promoting ignition and combustion performance. It can be effectively applied in the production of propellant systems.

Claims

1. A method for preparing a functionalized compact core-shell high-energy boron powder composite material, characterized in that, The specific steps are as follows: The first step is to add the raw boron powder and dispersant into a reaction vessel according to a certain mass ratio, and stir magnetically at a certain temperature to obtain a boron powder suspension with good dispersion performance. The second step is to add concentrated nitric acid to the boron powder suspension and stir it magnetically at a certain temperature until the suspension solution forms a homogeneous and stable state. The third step involves washing and filtering the sample while it is still hot using a solvent that is miscible with concentrated nitric acid, and then drying it under vacuum at a certain temperature to obtain acidified modified hydroxy boron. The fourth step involves adding the modified hydroxy boron and the dispersant to a reaction vessel in a certain mass ratio, and then magnetically stirring the mixture in a low-temperature water bath below 0°C for a certain period of time to obtain a boron powder suspension, which is then kept at the same temperature. Fifth step: Prepare a saturated solution of AP-dimethylformamide in a constant temperature water bath at 80±5℃; Step 6: Add the saturated AP-dimethylformamide solution to the boron powder suspension from step 4 at a constant dropping rate. After standing for a period of time, remove the supernatant. After vacuum drying at a certain temperature, the dried composite material, namely B-OH@AP composite material, is obtained.

2. The method as described in claim 1, characterized in that, In steps one and four, the dispersant is any one of acetone, ethyl acetate, cyclohexane, acetonitrile, or ethanol.

3. The method as described in claim 1, characterized in that, In the first step, the mass-to-volume ratio of boron powder to dispersant is 1g:10mL.

4. The method as described in claim 1, characterized in that, In the second step, the mixture is magnetically stirred at 25°C.

5. The method as described in claim 1, characterized in that, In the second step, the mass-to-volume ratio of boron powder to concentrated nitric acid is 10g:(1~3)mL.

6. The method as described in claim 1, characterized in that, In the third step, the solvent that is miscible with concentrated nitric acid is any one of alcohol, ether, or benzene.

7. The method as described in claim 1, characterized in that, In steps three and six, vacuum drying is carried out at 55~60℃ for 24 hours.

8. The method as described in claim 1, characterized in that, In the fourth step, the mass-to-volume ratio of modified hydroxyboron to dispersant is 1g:10mL.

9. The method as described in claim 1, characterized in that, In step six, the dropping rate is 2 mL / min.

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