Modified aluminum-lithium alloy powder stably existing in hydroxyl-terminated polybutadiene and preparation method of modified aluminum-lithium alloy powder

Abstract

The invention relates to modified aluminum-lithium alloy powder stably existing in HTPB and a preparation method of the modified aluminum-lithium alloy powder, and the preparation method comprises the following steps: adding aluminum-lithium alloy powder into normal hexane and carrying out ultrasonic oscillation to obtain aluminum-lithium alloy powder dispersion liquid; the preparation method comprises the following steps: sequentially adding isocyanate and polyol into an aluminum-lithium alloy powder dispersion liquid, uniformly stirring and mixing, then adding a catalyst, carrying out a condensation reaction while stirring, and sequentially carrying out suction filtration, washing and vacuum drying treatment after the reaction is finished, so as to obtain a final product. A compact polyurethane coating layer is formed on the surface of the aluminum-lithium alloy powder, so that the stability of the aluminum-lithium alloy powder is improved, and meanwhile, the combustion performance of the aluminum-lithium alloy powder in the composite solid propellant is further improved; technical guarantee is provided for practical application of the aluminum-lithium alloy powder in energetic materials such as composite solid propellants, and in addition, the aluminum-lithium alloy powder has the advantages of being simple in process, easy to prepare on a large scale, low in cost and the like.

Description

Technical Field

[0001] The present invention relates to a method for modifying aluminum-lithium alloy powder, and particularly to a modified aluminum-lithium alloy powder stably present in hydroxyl-terminated polybutadiene and a preparation method thereof. Background Art

[0002] Metal alloys play the role of high-energy fuels in propellants due to their high combustion enthalpy, greatly enhancing the specific impulse and energy of composite propellants. Aluminum has become the focus of research due to its economic affordability, abundant earth reserves, and high combustion heat release value. However, aluminum powder faces challenges such as the compactness of the alumina layer, high ignition temperature, and incomplete combustion in practical applications. These problems increase the loss of two-phase flow and reduce the proportion during the combustion process of the propellant.

[0003] Lithium metal is known for its high combustion heat (43.1 kJ / g) and low melting point (460 K), which improves the combustion efficiency and solves the significant two-phase flow loss problem of aluminum powder-containing fuel propellants during combustion. Aluminum-lithium alloys have always been regarded as one of the most promising high-energy fuels in propellants. However, due to the extremely high reactivity of lithium and the precipitation of lithium-rich phases in grain boundaries, the storage and handling of aluminum-lithium alloy powder become complicated. Specifically, if the powder is stored under non-vacuum conditions, the lithium-rich phase easily reacts with air and water to form LiOH and Li 2 O / Li 2 CO 3 , which seriously damages the surface structure of the aluminum-lithium powder, leading to a decrease in stability and overall performance. In addition, the precipitation of lithium-rich phases may also react with oxidants (such as ammonium perchlorate) and binders in the propellant, resulting in the failure of the propellant grain. Therefore, ensuring the stability of aluminum-lithium powder is the key to the preparation, storage, and transportation of propellants. At the same time, it is necessary to improve the combustion performance and stability of aluminum-lithium powder to enhance its application potential in propellants.

[0004] Surface coating is one of the simplest methods to enhance the stability of aluminum-lithium powder, maintaining its activity while improving the combustion performance of active metal powder. Metals (such as nickel and iron) and organic substances (such as fluorides, tannic acid, and polydopamine) are coated on the surface of aluminum powder in multiple layers to improve the combustion and stability performance. Chinese invention patent CN110550990A discloses a preparation method for polymerized tannic acid-coated aluminum powder / silicon powder, which effectively protects the activity of aluminum powder or silicon powder, can provide additional combustion heat, and promotes the rapid combustion reaction of aluminum powder or silicon powder, thereby improving the combustion performance of solid propellants. Chinese invention patent CN11500091A discloses a preparation method for polyphenol compound / nitrogen-containing polymer-coated micro-nano aluminum powder, which not only improves the stability of aluminum powder in hot liquids but also increases the active sites and oxidation efficiency of the oxidation reaction of aluminum powder, improves the burning rate of aluminum powder, and can improve the detonation performance of explosives.

[0005] Chinese invention patent CN114539009A discloses a method for preparing modified aluminum-lithium alloy powder with high stability and high compatibility, obtaining modified aluminum-lithium alloy powder that can stably exist in high-temperature and high-humidity environments, and improving the activity and compatibility of aluminum-lithium alloy powder. Chinese invention patent CN116422878A discloses a method for stabilizing aluminum-lithium alloy powder through organic coating, forming a layer of aluminum carboxylate (or lithium carboxylate film) or a waxy coating layer on the surface of the alloy powder. The formed film layer is relatively dense, which can effectively block the contact between the aluminum-lithium alloy powder and water vapor, reduce the hygroscopicity of the aluminum-lithium alloy powder, and reduce the corrosion rate of internal aluminum-lithium by water vapor, thereby extending the storage time of the aluminum-lithium alloy powder. However, this method cannot solve the problem of mutual incompatibility between the aluminum-lithium alloy powder and hydroxyl-terminated polybutadiene (hereinafter referred to as HTPB).

[0006] However, the above coating materials have problems in reducing the energy of the aluminum-lithium alloy powder with high lithium content or showing stability problems, or both, and cannot resist the oxidation or hydroxide corrosion of the modified aluminum-lithium alloy powder in a high-temperature and high-concentration HTPB environment during the assembly and molding process of aluminized explosives, thus unable to meet the actual assembly and molding process requirements of composite solid propellants. Summary of the Invention

[0007] In view of the defect that the aluminum-lithium alloy powder with high lithium content is extremely easy to be corroded or oxidized in HTPB, the present invention provides a method for preparing modified aluminum-lithium alloy powder that stably exists in HTPB, including the following steps:

[0008] (1) Add the aluminum-lithium alloy powder to n-hexane and ultrasonically oscillate to uniformly disperse the aluminum-lithium alloy powder in n-hexane, obtaining an aluminum-lithium alloy powder dispersion;

[0009] (2) Sequentially add isocyanate and polyol to the aluminum-lithium alloy powder dispersion obtained in step (1), stir and mix evenly, and then add a catalyst and carry out a condensation reaction while stirring to form a dense polyurethane coating layer on the surface of the aluminum-lithium alloy powder; after the reaction is completed, carry out suction filtration, washing, and vacuum drying treatments in sequence to obtain the modified aluminum-lithium alloy powder.

[0010] As a preference of the present invention, the mass ratio of the aluminum-lithium alloy powder to n-hexane in step (1) is 1:13, which not only ensures that the aluminum-lithium alloy powder can be uniformly dispersed in n-hexane but also prevents the excessive addition of n-hexane from affecting the rate of the subsequent condensation reaction.

[0011] As a preference of the present invention, the mass of lithium in the aluminum-lithium alloy powder in step (1) accounts for 5-10% of the total mass of the lithium alloy powder. The mass of lithium in the aluminum-lithium alloy powder within this range can further improve its combustion performance.

[0012] As a preference of the present invention, the ultrasonic oscillation time in the step (1) is 5 to 10 min. Controlling the duration of ultrasonic oscillation within this range can further remove the oxide layer on the surface of the aluminum-lithium alloy powder and fully mix the reagents, which is beneficial to the subsequent condensation reaction on the surface of the aluminum-lithium alloy powder.

[0013] As a preference of the present invention, the isocyanate in the step (2) is one or a mixture of more than one of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI) or lysine diisocyanate (LDI).

[0014] As a preference of the present invention, the polyol in the step (2) is one or a mixture of more than one of pentaerythritol, ethylene glycol (EG), 1,3-propanediol (1,3-PG), 1,4-butanediol (BDO), 1,6-hexanediol (HD), neopentyl glycol (NPG), diethylene glycol (EG·), dipropylene glycol (I)(PG), trimethylolpropane (TMP) or glycerol. Combining the polyol with the isocyanate to generate a polyurethane with a long-chain structure can better coat the surface of the aluminum-lithium alloy.

[0015] As a preference of the present invention, the catalyst in the step (2) is one or a mixture of more than one of triethylamine (TEA), dimethylcyclohexylamine (DMCHA), dibutyltin dilaurate (DBTDL), tributyltin oxide (TBTO), zirconium tetrabutoxide (Zr(OBu) 4 ) or lead naphthenate (Pb(OAc) 2 ).

[0016] As a preference of the present invention, the solvent used for suction filtration and / or washing in the step (2) is one of ethanol, ethyl acetate or tetrahydrofuran. Using this type of solvent for suction filtration and / or washing can remove the impurities remaining from the reaction and further improve the purity of the product.

[0017] As a preference of the present invention, the stirring and mixing time in the step (2) is 50 to 70 min; the reaction time is 3 to 6 h, the reaction temperature is 20 to 25 °C; the vacuum drying time is 16 to 24 h, and the drying temperature is 40 °C to 70 °C.

[0018] As a preference of the present invention, the mass ratio of the aluminum-lithium alloy powder, isocyanate, polyol and catalyst is controlled at 1:0.04:0.04 - 0.06:0.001 - 0.02. When the mass ratio of the four raw materials is within this range, the polyurethane coating layer formed by the condensation reaction can completely cover the surface of the aluminum-lithium alloy powder, while avoiding excessive polyurethane coating layer from affecting the performance of the final product.

[0019] Another object of the present invention is to provide a modified aluminum-lithium alloy powder prepared by the above preparation method.

[0020] The present invention has the following beneficial effects compared with the prior art:

[0021] (1) Due to the presence of highly active lithium inside and on the surface of the aluminum-lithium alloy, it is extremely easy to react with substances such as water, oxygen and carbon dioxide in the air, resulting in partial inactivation. Therefore, the present invention uses polyurethane to coat and stabilize the aluminum-lithium alloy powder, forming a dense polyurethane film on the surface of the alloy powder. This coating film will effectively prevent the aluminum-lithium alloy from reacting with substances such as water, oxygen and carbon dioxide in the air, resulting in partial inactivation, improve the stability of the aluminum-lithium alloy, and further extend the storage time of the aluminum-lithium alloy.

[0022] (2) The modified aluminum-lithium alloy powder prepared by the present invention effectively isolates the erosion of HTPB, avoids the overall inactivation of the propellant caused by the corrosion inside the propellant grain, and at the same time further improves the combustion performance of the aluminum-lithium alloy powder.

[0023] (3) The preparation method of the modified aluminum-lithium alloy powder of the present invention is relatively simple, only requiring four steps and can be completed at normal temperature and pressure. The raw materials are cheap and easy to obtain, facilitating mass production, and playing an important role in the field of engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the infrared spectrogram of the modified aluminum-lithium alloy powder before and after modification in Example 1 of the present invention.

[0025] Figure 2 It is the scanning electron microscope image of the modified aluminum-lithium alloy powder before and after modification in Example 1 of the present invention.

[0026] Figure 3 It is the combustion heat image of the modified aluminum-lithium alloy powder before and after modification in Example 1 of the present invention.

[0027] Figure 4 It is the stability test image of the unmodified aluminum-lithium alloy powder.

[0028] Figure 5 It is the stability test image of the modified aluminum-lithium alloy powder in Example 1 of the present invention.

[0029] Figure 6 This is the stability test image of the aluminum-lithium alloy modified powder in Example 2 of the present invention.

[0030] Figure 7 This is the stability test image of the aluminum-lithium alloy modified powder in Example 3 of the present invention.

[0031] Figure 8 This is the stability test image of the aluminum-lithium alloy modified powder in Example 4 of the present invention. Detailed implementation manners

[0032] The preparation method and performance of the highly stable modified aluminum-lithium alloy powder of the present invention will be further described below through specific examples.

[0033] Example 1

[0034] At room temperature (25 °C), 5 g of aluminum-lithium alloy powder (the mass content of lithium is 5%) was added to 100 mL of n-hexane, and ultrasonic oscillation was carried out for 5 min to obtain an aluminum-lithium alloy dispersion liquid. Subsequently, 0.2 g of isophorone diisocyanate and 0.21 g of ethylene glycol were added to the dispersion liquid, and stirring was carried out for 50 min to mix evenly. Then, 0.005 g of dibutyltin dilaurate was added as a catalyst, and sufficient stirring was carried out for 4 h to form a dense polyurethane film on the surface of the aluminum-lithium alloy powder; then, filtration and washing were carried out with ethyl acetate, and vacuum drying was carried out at 60 °C for 16 h to obtain the modified aluminum-lithium alloy powder.

[0035] As Figure 1 shown, the black curve represents the unmodified aluminum-lithium alloy powder, and the red curve represents the modified aluminum-lithium alloy powder; compared with before modification, the absorption peak of the modified aluminum-lithium alloy powder also appears at about 2900 - 2800 cm -1 −1, representing the C-H stretching vibration in the -CH 3 3 and -CH 2 2 groups; in addition, due to the C=O stretching vibration in the ester group contained in polyurethane, the absorption peak appears at 1750 cm -1 −1 and around 700 cm -1 −1; the C-N stretching vibration, and the absorption peak appears at around 1250 cm -1 −1; these characteristics indicate that the surface of the aluminum-lithium alloy is covered by polyurethane, proving the success of coating.

[0036] As Figure 2 shown, the left figure is the unmodified aluminum-lithium alloy, and the right figure is the modified aluminum-lithium alloy powder. Polyurethane forms a dense film on the surface of the aluminum-lithium alloy powder, and the structure is synaptic. The coating material changes the surface morphology of the aluminum-lithium alloy powder, and this film can effectively prevent the powder from contacting with HTPB and maintain the high stability of the aluminum-lithium alloy powder.

[0037] As Figure 3As shown, the combustion heats of the unmodified aluminum-lithium alloy powder and the modified aluminum-lithium alloy powder were measured by an oxygen bomb calorimeter in a 3 MPa oxygen atmosphere. The combustion heats of the unmodified aluminum-lithium alloy powder and the modified aluminum-lithium alloy powder were 27399 J / g and 28486 J / g respectively, indicating that the coating modification not only did not inhibit the combustion of the aluminum-lithium alloy powder, but further improved the combustion performance of the aluminum-lithium alloy powder.

[0038] Example 2

[0039] At room temperature (20 °C), 5 g of aluminum-lithium alloy powder (lithium mass content is 7%) was added to 100 mL of n-hexane, and ultrasonically oscillated for 7 min to obtain an aluminum-lithium alloy dispersion. Then, 0.2 g of diphenylmethane diisocyanate and 0.22 g of 1,3-propanediol were added to the dispersion and stirred for 60 min to mix evenly. Then, 0.006 g of tributyltin oxide was added as a catalyst and stirred thoroughly for 3 h to form a dense polyurethane film on the surface of the aluminum-lithium alloy powder; then, it was filtered and washed with ethanol, and vacuum dried at 70 °C for 18 h to obtain the modified aluminum-lithium alloy powder.

[0040] Example 3

[0041] At room temperature (22 °C), 5 g of aluminum-lithium alloy powder (lithium mass content is 10%) was added to 100 mL of n-hexane, and ultrasonically oscillated for 10 min to obtain an aluminum-lithium alloy dispersion. Then, 0.2 g of toluene diisocyanate and 0.25 g of 1,4-butanediol were added to the dispersion and stirred for 60 min to mix evenly. Then, 0.01 g of triethylamine was added as a catalyst and stirred thoroughly for 5 h to form a dense polyurethane film on the surface of the aluminum-lithium alloy powder; then, it was filtered and washed with tetrahydrofuran, and vacuum dried at 40 °C for 20 h to obtain the modified aluminum-lithium alloy powder.

[0042] Example 4

[0043] At room temperature (24 °C), 5 g of aluminum-lithium alloy powder (lithium mass content is 10%) was added to 100 mL of n-hexane, and ultrasonically oscillated for 10 min to obtain an aluminum-lithium alloy dispersion. Then, 0.2 g of toluene diisocyanate and 0.3 g of 1,6-hexanediol were added to the dispersion and stirred for 70 min to mix evenly. Then, 0.008 g of lead naphthenate was added as a catalyst and stirred thoroughly for 6 h to form a dense polyurethane film on the surface of the aluminum-lithium alloy powder; then, it was filtered and washed with tetrahydrofuran, and vacuum dried at 40 °C for 24 h to obtain the modified aluminum-lithium alloy powder.

[0044] Stability test

[0045] In order to confirm that the modified aluminum-lithium alloy powder prepared by the present invention has excellent stability under heating conditions and in an HTPB environment, the modified aluminum-lithium alloy powders prepared in Examples 1 to 4 of the present invention were compared with the unmodified aluminum-lithium alloy powder, and the results are shown in Figures 4 to 8 .

[0046] According to Figures 4 to 8 The results show that when the unmodified aluminum-lithium alloy powder exists for 10 minutes under the condition of pure HTPB at a heating temperature of 50 °C, part of it is oxidized or corroded. By 20 minutes, the degree of oxidation or corrosion of the unmodified aluminum-lithium alloy powder becomes more obvious; while the modified aluminum-lithium alloy powders in Examples 1 to 4 can all stably exist for at least 10 hours without being oxidized or corroded under the same conditions. Therefore, the modified aluminum-lithium alloy powder of the present invention can effectively improve the stability of the aluminum-lithium alloy powder in an HTPB environment.

[0047] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, various changes, modifications, substitutions, and variations can be made to these embodiments, and these changes, modifications, substitutions, and variations should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a modified aluminum-lithium alloy powder stably existing in terminal hydroxyl polybutadiene, characterized in that: The preparation method steps are as follows: (1) adding aluminum-lithium alloy powder to n-hexane and ultrasonically oscillating to obtain an aluminum-lithium alloy powder dispersion; (2) adding isocyanate and polyol to the aluminum-lithium alloy powder dispersion obtained in step (1) in sequence and stirring to mix well, then adding a catalyst to carry out a condensation reaction while stirring, and after the reaction is completed, filtering, washing, and vacuum drying are carried out in sequence to obtain a modified aluminum-lithium alloy powder.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of aluminum-lithium alloy powder to n-hexane is 1:13; the mass of lithium in the aluminum-lithium alloy powder accounts for 5-10% of the total mass of the lithium alloy powder.

3. The preparation method according to claim 1, characterized in that: The ultrasonic oscillation time in step (1) is 5 to 10 minutes.

4. The preparation method according to claim 1, characterized in that: In step (2), the isocyanate is a mixture of one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate or lysine diisocyanate.

5. The preparation method according to claim 1, characterized in that: In step (2), the polyol is a mixture of one or more of pentaerythritol, ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, trimethylolpropane or glycerol.

6. The preparation method according to claim 1, characterized in that: The catalyst in step (2) is a mixture of one or more of triethylamine, dimethylcyclohexylamine, dibutyltin dilaurate, tributyltin oxide, tetrabutoxyzirconium or lead naphthenate.

7. The preparation method according to claim 1, characterized in that: The solvent used for filtration and / or washing in step (2) is one of ethanol, ethyl acetate or tetrahydrofuran.

8. The preparation method according to claim 1, characterized in that: In step (2), the stirring and mixing time is 50 to 70 minutes; the reaction time is 3 to 6 hours, and the reaction temperature is 20 to 25° C.; the vacuum drying time is 16 to 24 hours, and the drying temperature is 40 to 70° C.

9. The preparation method according to claim 1, characterized in that: The mass ratio of the aluminum-lithium alloy powder to isocyanate, polyol and catalyst is 1:0.04:0.04-0.06:0.001-0.

02.

10. The modified aluminum-lithium alloy powder prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The modified aluminum-lithium alloy powder is an aluminum-lithium alloy powder having a polyurethane coating layer on the surface.

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